General

Having been involved for more than 30 years in rotating equipment and fluid separation technology, I have just as long been concerned about the many misapplications and misuse of centrifuges, especially in the so-called purification of oil.

Properly used, in some cases, they allow us to separate substances to a considerable degree and do so quickly, although not inexpensively. However, misuse has become more common as centrifuge manufacturers seek to expand their markets where perceived applications seem suitable. Sadly, these practices often result is users acquiring centrifuges for applications that are actually detrimental to the oil and often produce inferior separation at great expense to the end-user. Economic justification and application must therefore be considered and knowledge of the rheological behavior of the fluid in a centrifuge is essential.

Why Not a Centrifuge for Solids Removal?

A centrifuge separates the liquid charge into two phases; the overflow consisting mostly of the lighter fluids and the fine solids and the underflow consisting of coarser, heavier solids and some of the interstitially retained liquid. Solids in a liquid such as rotating equipment lubrication and seal oil exist in a range of particle sizes from gross solids like corrosion products down to fine and ultra fine colloidal particles.

Consider the behavior of solids in a liquid that is being centrifuged.

With the centrifuge rotating at a constant speed the solid particles, which are of many different densities and shapes, respond to gravitational forces in accordance to Stokes’ Law. The oil viscosity provides an opposing force on the solid particle.

When the tow opposing forces balance one another, the particle in question stops moving. It has reached its terminal velocity. This illustrates the main disadvantage of a centrifuge. You have little control over the size and types of solids that are separated. Ultra-fine and colloidal solids will remain the overflow and are returned to the oil reservoir, where they accumulate and agglomerate.

What about separating water from oil?

Water exists in oil in three phases; free, emulsified and dissolved water, each with different densities.

Free water readily settles out, while in an emulsion of water-in-oil the water particles are kept in a matrix of oil or vice versa. Emulsions are created by turbulent mixing of water and oil. An emulsion is a stable layer of tightly-held water particles and a centrifuge cannot separate an emulsion.

As a matter of fact, the turbulence that normally exists in a centrifuge often creates an extremely tight emulsion that cannot be separated and is thus carried over to the oil reservoir.

Mineral oil is essentially non-polar, while water is highly polar. Up to a certain limit, a small amount of water will dissolve in oil, depending on the temperature. The solubility of water in oil increases exponentially with the temperature. The water content directly affects the quality of the oil.

In the separation of free, emulsified and dissolved water, a centrifuge is onlu capable of removing free water. It will not remove an emulsion nor will it remove dissolved water.

The Maintenance will kill your budget

1. Centrifuges have high power consumption.
2. Experienced operators are required to operate and optimize performance as well as execute repairs.
3. Performance is difficult to monitor because the operator’s view of centrate and feed is obstructed
4. Maintenance is intensive as with all high-speed rotating equipment,
5. Special structural considerations must be taken into account. As with any piece of high speed rotary equipment, the base must be stationary and level due to dynamic loading,
6. High noise levels while running,
7. Spare parts are expensive and internal parts are subject to abrasive wear,
8. Start-up and shut down may take an hour to gradually bring the centrifuge up to speed and slow it down for clean out prior to shut down,
9. Power consumption is high,
10. Electrical installation is expensive,
11. Frequent starts and stops are not possible,
12. Continuous vibration monitoring is essential,
13. A large capital investment is required.

Conclusion

There are better, more economical and more effective systems for the purification of oil. These are based on proven solid chemical engineering principles and consistently produce clean separations of contaminants from oil. These systems are fully automatic, PLC-controlled and do not require operators to be in attendance.

The Load Tap Changer (LTC) is a mechanical switching device and is the most expensive and vulnerable accessory of a power transformer. Tap changers cause more failures and outages than any other component of the transformer. They easily account for 40% of all transformer fires and 40-50% of maintenance cost.

The function of an LTC is to change the turns ratio without interrupting the load current. LTC failures are categorized as electrical, mechanical and thermal but most are mechanical in the beginning and develop into electrical faults. This occurs due to problems with the contacts, transition resistors and insulation fluid breakdowns due to contamination. The curious fact is that for maintenance, the tap changer is no more than an afterthought.

Failures and Protective Devices

Failures can generally be grouped as: 1) Mechanical, 2) Erosion of contacts) and 3) Contact coking leading to high resistance and overheating. Most serious faults inside the switching compartment generate large amounts of gas, powerful pressure pulses and a subsequent low oil flow to the conservator tank and trigger a rapid power switch trip of the transformer. In order to minimize the risk of fire or explosion from an internal failure of the diverter or selector switch compartment, several standards protective devices have been installed.

Protection Systems

There are four major protection systems used for on-load tap changers.

The current international standard, IEC 602114-1 states that in order to minimize the risk of fire or explosion resulting from an internal failure, the diverter or selector switch compartment shall be fitted with the following protective devices:

• Over-pressure relay
• Pressure relief device
• Liquid-flow controlled relay

The over-pressure relay responds in the event pressure in the oil exceeds a pre-set value, causing the transformer to be tripped. This is the first option in many transformers.

The pressure relief device opens when a pre-set pressure is exceeded. This system is secondary because it is slower to trip than the over-pressure relay.

The liquid-flow relay is installed in the pipe between the top of the tap changer and the conservator tank. It responds to a predetermined oil flow to trip the transformer.

A fifth protective device is an on-line, continuous oil filtration system, which will be described further below.

Anatomy of a Spark

The mechanical drive mechanism physically moves the position of the electrical contacts to select he appropriate ratio taps of the regulated winding. Differences in voltage between the tap positions cause arcing to take place as the electrical contacts connect and part.

Arc Gas Composition

Note: The most dangerous gas generated is Hydrogen. It is created in the largest quantity with every arc and it is the least soluble in oil and the most explosive of all gases created in an arc.

Continuous On-line Filtration

The Allen Tap Changer Filter System (ATF) is a completely self-contained single or multiple element filtration unit that can be designed to remove solids, adsorb gases as well as absorb small quantities of water on a continuous or timed basis, to keep the oil in the tap changer clean. Mechanical abrasion of the moving parts of the diverter switch is also reduced. Consequently, maintenance cost is minimized.

An electric motor-driven positive displacement gear pump forces contaminated oil through a filter element (or several elements) and returns clean oil to the Tap Changer compartment. The low capacity pump produces little or no turbulence in the OLTC oil compartment.

The Allen ATF’s are designed to operate unattended. They are enclosed in a steel weather-proof (NEMA 4) cabinet and the individual components are positioned for easy access and maintenance. Lifting lugs are provided for ease of installation.

Allen ATF’s are used on Power Transformers for the following applications:

• For applications with a very high number of switching operations (> 40,000) per year at high service currents;
• For applications at high insulation levels e.g. for line-end applications;
• For selector switches in transformers > or = 60 kV in delta connections.

Filtering the diverter tank oil improves the dielectric strength for a long period and reduces mechanical abrasion of the moving diverter switch parts thus prolonging the life of the actual tap changer.

A Typical Allen Tap Changer Filter System (ATF) in operation at CFE, Mexico

General

De conservas de pescado y la fabricación de subproductos se produce en casi todos los países que las fronteras en el mar. La industria experimentó un aumento del 20% en la cantidad de pescado procesado y de aumentos adicionales que se espera también. Las exportaciones de conservas de pescado y de harina de pescado también están aumentando debido a la disminución de los suministros en otros países. Allen Filtros, el Departamento de Ingeniería Inc tiene muchos años de experiencia en la elaboración de planes de tratamiento integral de agua fábrica de conservas y de transformación de las aguas residuales y el control de la contaminación. Esto es parte de una serie destacan varios estudios de casos de gestión de residuos en corriente de una variedad de industrias. La siguiente es una historia de un caso de una fábrica de conservas típicas con un grave problema de contaminación de las aguas residuales, lo que es varias multas significativas.

Agua de Descongelación

Esta fábrica de conservas de transformación del pescado se inicia con la congelación de las capturas tan pronto como se trae a partir de 125 de la compañía barcos de pesca. Los barcos tienen congeladores a bordo inicialmente congelación de las capturas frescas. Las capturas se mueven entonces a varios congeladores muy grandes a la espera de procesamiento.

Cuando el pescado se descongela posteriormente, un importante flujo de agua con hielo con las piezas de pescado se genera todo el día. Esta es la corriente de residuos se compone de agua fría y algunas partes de pescado. Esto constituye flujo de residuos no. 1.

Aceite para freír

Además de las conservas de pescado para el consumo humano de la compañía también produce frito, camarones empanizados y palitos de pescado, listo para el embalaje y la exportación. El aceite usado es sobre todo de soja y aceite de cártamo.

La compañía quería volver a utilizar el aceite tantas veces como podía hacerse con seguridad.

Este fue el problema de que no. 2.

Combustible de Calderas

Las calderas de la empresa son la quema de combustible pesado (HFO) del petróleo, que estaba causando problemas con los inyectores del quemador de conectar y causando la contaminación del aire. El calor se utiliza en varias operaciones diferentes, tales como cocinar, la salazón y secado de cabezas de pescado y espinas dorsales para la venta a África.

El pre tratamiento requeridas de HFO.

Este fue el problema de que no. 3.

Tratamiento de aguas residuales

El agua más contaminadas es generado por la principal zona de procesamiento de pescado.Las aguas residuales contienen grandes cantidades de piezas de pescado y de sangre, resultando el de la carga orgánica elevada.

La pre cocción también genera un poco de agua de residuos, que se combina con el flujo de residuos de procesamiento de pescado. Este fue el problema de que no. 4.

Ingenieros de Allen ideó una solución global para todos los problemas como se muestra a continuación. Puso de relieve no sólo tratamiento de líquidos, sino también la reutilización de aguas depuradas.

FIGURA 1 - TRATAMIENTO DE AGUA FRIA Y REUTILIZACIÓN

Soluciones

Los sistemas instalados se muestran en la Figura 1.

Tratamiento de Agua Descongelación y Reutilización

El agua generada por la operación de deshielo es la menos contaminada. Tiene una pequeña cantidad de piezas de pescado, pero de lo contrario, es sólo frío en cerca de 8-10? C. El agua fría es bombeada a través de una serie de coladores de acero inoxidable reutilizables. Cada filtro tiene un sistema de retrolavado, que se activa automáticamente por cada uno de interruptores de presión diferencial. Después de cada lavado, los filtros están listos para ser utilizados de nuevo. El lavado se dirige a la operación de la harina de pescado se convierta en fertilizante o alimento animal.

El agua limpia y fresca se dirige a los intercambiadores de calor para funcionar como agua de enfriamiento.

Tratamiento de combustible pesado.

La compañía tiene varios grandes calderas que utilizan aceite combustible pesado (HFO). El combustible pesado es un aceite de alta viscosidad con una importante concentración de azufre y rica en asfáltenos. Los asfáltenos son de cadena larga, las moléculas de alto peso molecular que se polimeriza y crear problemas de obstrucción de boquillas de los quemadores y provocando un alto nivel de contaminación del aire.

La solución a este problema es un aditivo que las fracturas de los polímeros de los asfáltenos, homogeneíza el combustible, lo que hace menos viscoso. El aditivo es también un catalizador de la combustión, lo que mejora la combustión más limpia con menos humo y hollín. El mantenimiento de la caldera se reduce considerablemente también.

El aditivo es inyectado en el combustible, antes de ser sometidos a un proceso de destilación al vacío en un acondicionador de aceite Allen, para eliminar el agua, los contaminantes volátiles y reducir el contenido de azufre. El combustible homogeneizado resultante se bombea a las calderas. Significativamente menos humos emitidos por la caldera de pila señaló inmediatamente. De muestreo de la contaminación del aire se creen en el futuro.

Tratamiento y reutilización de Aceite para freír

Aceite para freír al calentamiento continuo durante un período de tiempo pueden polimerizar y formar radicales libres, que son peligrosas para la salud humana. También tiene una tendencia a volverse rancio y oloroso. Los restos de harina y las partículas tienden a acelerar el deterioro del aceite.

El proceso de fritura de aceite Allen tratamiento consiste en filtración de sólidos del aceite caliente en forma de bucle-renal, a través de tamices de acero inoxidable recleanable para quitar los sólidos como las partículas de harina y pan rallado. El sistema está diseñado o soportar hasta 1500° C. El aceite es bombeado a través de filtros de adsorción de carbón activado. El carbón activo absorbe los radicales libres y los polímeros, lo que permite la reutilización del aceite limpio varias veces más.

Auto-oxidación es una reacción de los radicales libres de oxígeno que la participación conduce a un deterioro de las grasas y aceites que afectan a los sabores y olores.

Para detectar el límite de la reutilización, el índice de peróxido se determina mediante el uso de un kit de prueba de campo. Se trata de una determinación volumétrico.

El índice de peróxidos es la concentración de peróxido en forma de aceite o grasa. Es útil para evaluar la medida en que el deterioro ha avanzado. El índice de peróxidos se define como la cantidad de peróxido de oxígeno por 1 kilogramo de grasa o aceite. Esto se expresa en unidades de mili equivalentes. El límite para la reutilización es de 10 mili equivalentes.

El aceite de buena calidad se reutiliza, mientras que el aceite malo se mezcla con el combustible de la caldera y quemados, realizando así un ahorro adicional en el costo del combustible.

Procesamiento de aguas de pescado residuales

Estas aguas residuales se caracterizan por una carga orgánica muy alta, compuesta de piezas de pescado y de sangre.

Para tratar este tipo de residuos, un extendido proceso de lodos activados de aireación se utiliza para reducir la materia orgánica mediante tratamiento biológico en un paquete de tratamiento de residuos. Después del tratamiento biológico, el efluente es desinfectado por la radiación ultravioleta, seguido por la filtración fina y adsorción con carbón activado.

Después de este tratamiento, el agua puede ser reutilizada en diversas formas, tales como el maquillaje de agua, agua de alimentación de calderas o dado de alta. Criterios de efluentes han sido sistemáticamente inferiores a 5 mg / l BOD5, sólidos suspendidos totales (SST), DQO y carbono total (TC).

Conclusión

A pesar de fábricas de conservas han sido a menudo implicados en las aguas superficiales y la contaminación del océano, incurrir en multas considerables, existe la tecnología para evitar esto. Los sistemas de tratamiento individuales, pueden aplicarse en los módulos, durante un período de tiempo.

General

Fish canning and byproduct manufacturing occurs in almost every country that borders on the ocean. The industry experienced a 20% increase in the quantity of fish processed and additional increases are expected as well. Exports of canned fish and fish meal are also increasing because of diminishing supplies in other countries. Allen Filters, Inc’s Engineering Department has many years of experience in devising comprehensive treatment plans for cannery water and waste water processing and pollution control.

This is part of a series highlighting several case histories of waste stream management in a variety of industries.

The following is a case history of a typical cannery with a severe waste water pollution problem, resulting is several significant fines.

Fish Processing

Defrost water

This cannery’s fish processing begins with freezing the catch as soon as it is brought in from the company’s 125 fishing ships. The ships have freezers on board to initially freeze the fresh catch. The catch is then moved to several very large freezers to await processing.

When the fish is subsequently defrosted, a significant flow of ice water with fish parts is generated around the clock. This is waste stream consists of cold water and some fish parts. This constitutes waste stream no. 1

Frying Oil

In addition to fish canning for human consumption the company also produces fried, breaded shrimp and fish sticks, ready for packing and exporting. The oil used is mostly soy and safflower oil.

The company wanted to reuse the oil as many times as could be safely done.

This was problem no. 2.

Boiler Fuel

The company’s boilers are burning heavy fuel (HFO) oil, which was causing problems with burner nozzles plugging and causing air pollution. The heat is used in several different operations such as cooking, salting and drying of fish heads and backbones for sale to Africa.

The HFO required pretreatment.

This was problem no. 3.

Fish Processing Waste Water

The most heavily polluted water is generated by the main fish processing area. The waste water contained large quantities of fish parts and blood, resulting a in high organic loading.

The precooking also generates some waste water, which is combined with the fish processing waste stream.

This was problem no. 4

Allen’s Engineers devised a comprehensive solution for all problems as is shown below. It emphasized not only treatment of fluids but also the reuse of purified water.

FIGURE 1 – COLD WATER TREATMENT AND REUSE

Solutions

The systems installed are shown in Figure 1.

Defrost Water Treatment and Reuse

The water generated by the defrosting operation is the least polluted. It has a minor amount of fish parts, but otherwise it is just cold at about 8-10 ? C. The cold water is pumped through a series of stainless steel reusable strainers. Each strainer has a backwash system, which is activated automatically by individual differential pressure switches. After each backwash, the strainers are ready to be used again. The backwash is directed to the fish meal operation to be turned into fertilizer or animal feed.

The clean cold water is directed to the heat exchangers to function as cooling water.

Heavy Fuel Treatment.

The company has several large boilers that use Heavy Fuel Oil (HFO).

Heavy Fuel Oil is a high-viscosity oil with a significant concentration of sulfur and rich in asphaltenes. Asphaltenes are long-chain, high molecular weight molecules that polymerize and create problems clogging burner nozzles and causing a high level of air pollution.

The solution to this problem was an additive that fractures the asphaltenes polymers, homogenizes the fuel, making it less viscous. The additive is also a combustion catalyst, which improves cleaner burning with less smoke and soot. Boiler maintenance is greatly reduced also.

The additive is injected into the fuel, prior to being subjected to a vacuum distillation process in an Allen Oil Conditioner, to eliminate water, volatile contaminants and reduce the sulfur content. The resulting homogenized fuel is pumped to the boilers. Significantly less smoke emitted by the boiler stack was immediately noted. Air pollution sampling will be instituted in the future.

Frying Oil Treatment and Reuse

Frying oil when continuously heated over a period of time may polymerize and form free radicals, which are hazardous to human health. It also has a tendency to become rancid and odorous. The remnants of flour and particles also tend to accelerate the deterioration of the oil.

The Allen Frying Oil treatment process consists of solids filtration of the hot oil in a kidney-loop fashion, through stainless steel recleanable strainers to remove solids such as flour particles and bread crumbs. The system is designed o withstand up to 1500 ?C. The oil is then pumped through activated carbon adsorption filters. The activated carbon absorbs any free radicals and polymers, thereby allowing the reuse of the clean oil several more times.

Auto-oxidation is a free radical reaction involving oxygen that leads to deterioration of fats and oils which affect flavors and odors.

To detect the limit of reuse, the peroxide value is determined by using a field test kit. It is a titrimetric determination.

The peroxide value is the concentration of peroxide in an oil or fat. It is useful for assessing the extent to which spoilage has advanced. The peroxide value is defined as the amount of peroxide oxygen per 1 kilogram of fat or oil. This is expressed in units of milliequivalents. The limit for reuse is 10 milliequivalents

The good quality oil is reused, while the bad oil is mixed with the boiler fuel and burned, thereby realizing an additional savings in fuel cost.

Fish Processing Waste Water

This waste water is characterized by an extremely high organic loading, consisting of fish parts and blood.

To treat this waste, an Extended Aeration Activated Sludge Process was used to reduce the organics by biological treatment in a packaged waste treatment plant. After the biological treatment, the effluent is disinfected by Ultra Violet Radiation, followed by fine filtration and activated carbon adsorption.

After this treatment, the water can be reused in various ways, such as make-up water, boiler feed water or discharged. Effluent criteria have been consistently below 5 mg/l BOD5 , Total Suspended Solids (TSS), COD and Total Carbon (TC).

Conclusion

Although canneries have often been implicated in surface water and ocean pollution, incurring considerable fines, the technology exists to prevent this. The individual treatment systems can be implemented in modules, over a period of time.

Waste oil pits like suppurating pustules are scattered throughout the United States.

These open pits are filled with a mixture of tar, oil, water, dirt and debris. They are the product of an industry without conscience, irresponsible, motivated purely by greed. This type of greed and neglect continues to cause casualties and death, long after the oil derricks have gone and its owners have gone on to continue the practice.

The waste oil is collected in production overflow pits, waste storage pits and flare pits which continue kill birds and other wildlife and pollute groundwater aquifers by slow and steady infiltration of their toxic soup.

An Abandoned Facility With A Lasting Heritage _{Courtesy US Fish & Wildlife Service}

Note the flags that are suppose to scare the birds.

Currently an estimated 500,000 to 1 million birds are lost every year in oilfield skim pits and centralized oilfield wastewater disposal facilities. These ponds and pits present a deadly attraction because they resemble water.

An Abandoned Flare Pit

One that did not get away.

A Solution

The picture below shows a solution to the waste oil open pit problem. It is an Allen Filters, Inc. mobile Vacuum Distillation Oil Purifier.

It uses the waste oil, filters the solids out and subjects the oil to a high vacuum and a temperature of 180? F. This separates any hydrocarbon light ends that remain and purifies the waste oil to the point that it becomes again, reusable lubrication oil or burner fuel.

The volatile condensable gases can be condensed while the oil-free water phase is evaporated into the atmosphere. The vacuum distillation systems have been manufactured by Allen Filters, Inc. since 1960. They are used worldwide in refineries, Oil & Gas Plants and anywhere if oil needs to be purified and reused. They have been proven in over 50 countries like Saudi Arabia, the Far and Near East, Latin America and the USA

A Typical mobile explosion-proof vacuum distillaction system (AOC) for oil purification.

Statistics and Photos courtesy of the US Fish & Wildlife Service

Quench oil serves two primary functions:

1. It facilitates hardening of steel during quenching
2. It enhances wetting of steel during quenching to minimize the formation of undesirable thermal and transformational gradients, which may lead to distortion or cracking

When hot metal is quenched, a vapor envelope is initially formed around the hot metal as it is immersed in the oil. The stability of this vapor envelope—and thus the ability of the oil to harden steel—is dependent on the metal surface irregularities, the presence of oxides, surface wetting agents (which accelerate the wetting process and destabilize the vapor envelope), and the presence of other oil degradation by-products.

Upon further cooling, the vapor envelope collapses, resulting in so-called nucleate boiling, which is the fastest heat transfer.

Nucleate boiling is a type of boiling that can take place under certain conditions. It is the process of forming steam bubbles within liquid in micro cavities adjacent to the wall if the wall temperature at the heat transfer surface rises above the saturation temperature while the bulk of the liquid is sub-cooled. The bubbles grow until they reach some critical size at which point they separate from the wall and are carried into the main fluid stream. There the bubbles collapse because the temperature of bulk fluid is not as high as at the heat transfer surface where the bubbles were created. Heat and mass transfer during nucleate boiling has a significant effect on the heat transfer rate. This heat transfer process helps to quickly and efficiently carry away the energy created at the heat transfer surface. When the temperature of the hot steel interface is less than the oil’s boiling point, nucleate boiling will stop and convective cooling will begin.

Oil degradation is often accompanied by sludge and varnish formation. These by-products do not adsorb uniformly on the steel surface as it is being quenched, resulting in cooling rate variations and thermal gradients.

Another source of non-uniform heat transfer is water contamination of the quench oil. Water causes thermal gradients and lower viscosity.

Effects of Contaminants

Viscosity

Of all the variables that can affect the maximum cooling rate during nucleate boiling, temperature has the most significant effect on the maximum cooling rate. Increasing the temperature increases the maximum cooling rate due to the change in viscosity. At room temperature, the oil is viscous and does not wet the surface of the part well. As the viscosity decreases with increased temperature, the result is better wetting of the part and consequently better heat transfer.

Soot

Soot has the second largest impact on maximum cooling rate. The maximum cooling rate increases as the amount of soot in the oil increases. This is due to the soot particles functioning as nucleation sites for bubble formation during nucleate boiling. Soot also causes the temperature of maximum cooling to increase.

Salt

Salt crystals have an effect similar to soot particles since they do not dissolve in oil and form nucleation sites for bubble formation during nucleate boiling.

Water

Water increases the maximum cooling rate and substantially decreases the temperature of maximum cooling. This increases the chances of distortion of the part by increasing the thermal gradients within the part.

Hydraulic Fluid

Contamination with hydraulic fluid increases the maximum cooling rate and the temperature at which maximum cooling occurs. Because hydraulic fluids are miscible in quench oil, the properties of the quench oil change. The boiling point of the mixture will likely increase, causing an increase in maximum cooling rate and the temperature at which maximum cooling rate occurs.

Oxidation

Oxidation causes the maximum cooling rate and the temperature of maximum cooling to decrease, which is caused by increases in viscosity of the quench oil. This in turn causes a decrease in wetting. Increase in viscosity also causes bubble formation to become more difficult while the maximum cooling rate and the temperature of maximum cooling is reduced.

Precautions

Percent Water

This contaminant in amounts as low as 1,000 parts per million (ppm) can cause foaming, fires, and explosions.

Flash Point

This value should be as high as possible. Changes usually indicate contamination or degradation. Low flash points increase the chance of fires.

Percent Sludge

This is the result of oxidation and polymerization.

Percent Ash

Increased inorganic ash content indicates degradation.

Kinematic Viscosity

As oil degrades, viscosity usually increases. Some contaminants reduce viscosity and flash point.

Neutralization Number

Increased oxidation causes the oil to become more acidic.

Quenching Speed

Either a GM Quenchometer test or a cooling rate curve should be used to evaluate the cooling/quenching characteristics of the oil.

Reclamation

The effects of contamination can cause significant changes in the maximum cooling rate and the temperature of maximum cooling. This can result in distortion, cracking, and non-uniformity of properties. A control program to monitor and track quench oil performance is necessary to ensure high quality parts.

Quench oil can be reclaimed even when it is severely contaminated. Today’s disposal problems and the eventual cycling of oil economics make the reclamation and revitalization processes extremely attractive. Reclamation of contaminated quench oil can be performed by using an Allen Oil Conditioner equipped with a water-cooled heat exchanger. We use a strainer to collect the solid particles and then cool the oil before it goes into the vacuum dehydration technology, which removes the water and gases and restores the quench oil to a like-new condition.

References

1. Herring, D. H. “Oil Quenching Part 1: How to Interpret Cooling Curves.” Industrial Heating, Aug 2007.
2. MacKensie, D.S. et al. “Effects of Contamination on Quench-oil Cooling Rate.” Houghton International, Inc. 2002.
3. Wachter, D.A. et al. “Quenchant Fundamentals-Quench Oil Bath Maintenance.”

• High dielectric strength
• Low viscosity
• Freedom from inorganic acids, alkali, and corrosive sulfur
• Resistant to emulsification
• Freedom from sludging under normal operation
• Rapid settling of arc products
• Low pour point
• High flash point

Enemies of insulating oil are:

• Oxidation Oxidation is the most common cause of oil deterioration. Careful and routine vacuum dehydration to remove air and water is essential to maintaining good oil.
• Contamination Moisture is the main source of contamination. It tends to lower the dielectric strength of the oil and promote acid formation when combined with air and sulfur.
• Excessive Temperature Excessive heat breaks down the oil and will increase the rate of oxidation. Avoid overloading the transformer.
• Corona Discharges Sparking and local overheating can also break down the oil and produce gases and water.

The following table lists the physical properties for insulating oil.

A more recent measure being used to evaluate oil is the particle count distribution (PCB). This provides information on the size and number of particles in the oil. Additionally in some countries the presence of PCBs is still prevalent. The quality of insulating oil and the routine purification by vacuum distillation is most important in assuring that the high quality of insulating oil is maintained.

References

1.    Pearce, H.A. “Significance of Transformer Oil Properties.”  Electric Insulating Oils. STP 988 H.G. Erdman Ed. ASTM, 1988.

 

Metal working fluids (MWF) are fluids used during machining and grinding to prolong the life of the tool and protect the working surfaces of the work pieces. Workers are exposed to MWFs by inhaling mists and by skin contact with the fluid. Skin contact occurs by dipping the hands in the fluid, splashing, or handling the work pieces coated in the fluid. A substantial amount of scientific evidence indicates that workers routinely exposed to MWF mists have an increased risk of respiratory and skin diseases.

Types of Metal Working Fluids

There are four different classes of MWFs:

Straight Oil

These are solvent-refined petroleum oils or other animal, vegetable, or synthetic oils often used with additives.

Soluble Oil

These are combinations of 30% to 85% refined lubricant-based oils and emulsifiers with other performance additives. Soluble oils are diluted with water.

Semi-Synthetic

These contain a lower amount of lubricant-based oil and a higher proportion of emulsifiers and water.

Synthetic

These contain no petroleum oils and may be water soluble and water dispersible. The synthetic concentrate is diluted with water.

Exposure hazards

Exposure to hazardous contaminants in MWFs presents a health risk to workers. Contamination may occur from process chemicals, metals, and alloys from parts, water, cleaning agents, and chemicals introduced to control biological growth. Water-based MWFs are an excellent growth medium for many kinds of bacteria and fungi. Research has suggested that microorganisms and their by-products such as endo-toxins can cause respiratory effects seen in exposed workers.

Biocides

Biocides are chemicals used to limit bacterial growth, however, adaptation quickly causes bacteria to become used to the biocides and begin using it for nutrients. Some constituents in biocides are toxic to humans.

Health Risks

Dermatological Conditions

Workers exposed to MWFs suffer a high rate of skin diseases. Straight MWFs are linked to folliculitis, oil acne, and keratosis. Soluble semi-synthetic and synthetic MWFs have been linked to contact dermatitis and, in some cases, allergic contact dermatitis. The prognosis for dermatitis is poor. Some workers eventually have become disabled as a result of their skin disorders.

Cancer

Substantial evidence indicates some MWFs are associated with increased risk of larynx, pancreas, skin, scrotum, and bladder cancer. The time between initial exposure and appearance of most types of cancer is often 20 years or more.

Lung Disease

Exposure to MWF mists can cause a variety of respiratory conditions such as lipid pneumonia, hyper-sensitivity pneumonites, asthma, acute airways irritation, chronic bronchitis, and impaired lung function. While cases of deep lung-lipid pneumonia, hard metal disease, and legionellosis appear relatively unusual, hyper-sensitivity pneumonites, asthma, and other airway disorders have recently emerged as an important risk factor for workers exposed to MWF mists.

Prevention

Mist Inhalation

A breathing face mask must be mandatory. Mist collectors and exhausts should be installed over every machine that uses MWFs to prevent general inhaling of uncontrolled MWF mists.

Filtration

Continuous filtration of MWFs will remove microorganisms without having to add toxic biocides. A 0.5-micron fine solids filter will trap most bacteria as well as metal solids and debris.

The Allen Continuous Filter System extends fluid life by removing metal solids, dirt, and debris as well as bacterial solids and odors from metal working fluid. The system consists of a self-contained filter vessel suitable for one stacked-disc type filter element, and includes a differential pressure gauge that automatically shuts the motor down if the filter element clogs and needs to be changed. The vessel is provided with an automatic air vent. The Allen Continuous Filter System is available in larger capacities for large volumes of metal working fluid purification.
 

Terminology

Hyper-Sensitivity Pneumonites

Sometimes called “machine operator’s lung,” it is an allergic reaction caused by bacteria and chemicals found in machine working fluids. Symptoms include chills, fever, shortness of breath, and a deep cough.

Biocides

Biocides kill bacteria but are also highly toxic to humans if adsorbed through the skin or inhaled with mists.

Dermatitis

Dermatitis is a skin disease caused by contact with metal working fluids. Outbreaks involve dry, scaly, and cracked skin; pimples on the arms and hands; and raw sores.

EHC fluid is expensive, so it makes sense to keep the fluid in the best possible condition. This does not always work out to be the case. EHC fluid is used in steam turbine control systems that govern, among other things, the operation of a trip-throttle valve. This valve shuts of the steam supply to the turbine in case of a threat of over speed.

Figure 1: Gimple Trip-Throttle Valve

What happens to EHC fluid with normal use?

When you read the many engineering and lubrication forums on the Internet, you will find that the following problems occur most often:

• High solids contamination
• High acidity
• High phosphorus content
• High values of magnesium (Mg), calcium (Ca), sodium (Na), aluminum (Al), tin (Sn), and potassium (K)
• Sludge and gel formation
• Filter clogging
• High moisture content
• At or close to relative saturation point
• Free water is dropping out
• Discoloration

That is where the “sharks” who have been circling move in. The sharks are the equipment manufacturers who have been trolling these forums, waiting for a chance to give you “unbiased” advice to use their equipment to solve all the above mentioned problems. They offer “bandages” while ignoring the advancing disease. What is the root cause of the disease? It is neglect; nothing more, nothing less.

As with all oil types, phosphate esters—in the operating environment of a steam turbine—are a discrete system like blood in the human body. That means one problem can affect or create several other problems in the same system. That is why you must consider the entire phosphate ester system as a homogeneous system at equilibrium. The presence of one contaminant will disturb this equilibrium. It boils down to carefully maintaining the equilibrium between all the variables. For instance, moisture is the most prevalent contaminant. Its presence can progressively lead to the following contaminants:

• Hydrolysis—an autocatalytic hydrolytic degradation—generates phosphoric acid (autocatalytic means the products of hydrolysis further catalyze the hydrolytic process)
• This increases the total acid number (TAN)
• This causes increased corrosion of metal surfaces
• Corrosion creates rust particles, increasing the particulate content
• Increased particulate content and sludge creates more sludge, varnish, and gel
• This will clog the filter

There are documented cases where a trip-throttle valve was rusted in an open position causing the turbine to over-speed and self-destruct. The replacement cost in one particular case was US$13 million for a new turbine and US$100 million in lost production. The sad part is that a US$50,000 purification system could have prevented this incident that was created by neglect and exacerbated by management indecision to purchase the purification system. The general manager of the refinery was re-assigned and never heard from again.

What was this system that could have prevented a US$113 million incident? It was not a fuller's earth adsorption system. It was not an ion-exchange system. Nor was it like any other bandage solution currently on the market. It was an Allen Minivac, a portable skid-mounted vacuum distillation/filtration system specifically designed for small- to medium-sized turbine control systems containing EHC fluid.

Figure 2: Allen Minivac Flow Diagram

This fully automatic programmable-logic-controlled system operates continuously to remove the following contaminants:

• 100% of free and emulsified water
• moisture down to 2-6 wppm
• solids to less than 0.5 microns
• all varnish particles by adsorption on treated cellulose fibers
• 100% of entrained and dissolved air and other gases
• an optional fuller's earth adsorption filter can be added

If you are lucky enough to have an Allen Minivac, how do you make it work for you?

How the Allen Minivac System will keep your EHC fluid clean and long-lasting

• By removing the free, emulsified, and dissolved water the major contaminant is removed and kept to a minimum
• No more moisture means no more hydrolysis
• No more hydrolysis means no more acid creation
• Solids and sludge are removed and no longer accumulate
• Corrosion particles are removed and no longer pose a danger
• Varnish particles are adsorbed onto the treated cellulose filter fibers

Figure 3: An Allen Minivac

Of course this will occur if your EHC fluid has not deteriorated beyond salvation. What you do before you hook up the Allen Minivac is you take a sample of your EHC fluid and have a laboratory analysis done.

Figure 4: The Levels at Which EHC Fluid is Beyond Recovery

Fluid water content must be maintained at less than 10 wppm total water. This can only be done consistently by a vaccum distillation system.

The table shown above indicates at what level the EHC fluid is beyond recovery. The control system will then need to be flushed with new EHC fluid and the Allen Minivac must be connected and put in operation to keep contaminants at the level of new fluid.

Conclusion

The major drawback of using ion exchange, activated alumina, or fuller's earth cartridges by themselves is that the acidity can reach uncontrolled levels very quickly and—in all cases of ion exchange, activated alumina, or fuller's earth—metal salts will leach out into the fluid, thereby forever destroying any chance of recovery. In general, operators will not be vigilant enough to prevent run-away acidity. When faced with these conditions, the Allen Minivac quickly becomes the most cost-effective solution for maintaining in good condition.

The Biodiesel Opportunity

Among the bio-fuels that have been invented, biodiesel seems the most promising. It is a clean-burning fuel; just follow a city bus in traffic and smell the French fries. Within its evolution the number of biodiesel producers has steadily grown and three distinct segments of producers have emerged:

1. large producers that are well-capitalized and have engineered processing facilities,
2. intermediate producers who are less well-capitalized and are using equipment from various sources, and
3. the low-cost “do-it-your-selvers” operating with equipment they make themselves and do not have the capital, nor the desire to expand production beyond that for their own use.

Allen Filters, Inc. has for over 60 years of its manufacturing history produced equipment that purifies mineral and synthetic oils and proves that they can be reused almost indefinitely. As such, we have made those oils a “renewable resource."

With the advent of diesel production, we have received many requests for the application of our oil purification equipment to the biodiesel process. Allen Filters, Inc. equipment applies the same proven principles of mineral oil purification to the various components of the biodiesel process:

• separation by distillation (vacuum or non-vacuum) in accordance to the boiling points of the individual components and
• recovery by refrigerated condensing of those components that need to be collected and reused.

As such, our equipment performs as follows:

• It removes moisture and solids from the waste vegetable oil, improving the efficiency of the esterification reaction
• It removes moisture and color from crude biodiesel, creating a more valuable fuel
• It removes moisture and color from glycerol and purifies it to pharmaceutical grade, adding the sale of this product to the revenue stream
• It recovers the excess methanol by thermal vaporization and subsequent refrigerate condensation to liquid methanol of a high purity, reducing the overall cost of production

The two types of Allen equipment used in the biodiesel process are the Allen Bioscav and the Allen Biovac. Part one of this series describes the use of the Allen Bioscav in the biodiesel process. These two systems are primarily used by intermediate producers who want to optimize their batch process and produce higher quality, more valuable products.

Figure 1: The Allen Bioscav for Biodiesel

1. Chiller Unit, 2. Refrigerated Condenser, 3. Separator Vessel, 4. Control Box, 5. Duplex Positive Displacement Pump & Motor, 6. Filter, 7. Heater

Waste Vegetable Oil Purification

One of the readily available sources for biodiesel is waste vegetable oil. This type of base material has been reheated several times during the course of its usage and therefore must be treated before it can be used for the biodiesel process. The reheating will cause some of the fatty acids bonded to the glycerol to break away and float freely in the oil. These are the free fatty acids which have to be esterified before transesterification. As the presence of water favors the cleavage of fatty acids in vegetable oil, standard DIN V 51 605 limits the water content to 750 ppm. However, the lower the water content the better the quality of the end product. The actual water content can be determined by Karl Fischer titration.

The Allen Bioscav can be used to filter out the solids and remove free, emulsified, and dissolved water down to 50 ppm total water by circulating the oil through the system multiple times.

Figure 2: Removal of Water and Solids from Waste Vegetable Oil

Methanol Recovery From Biodiesel

The recovery of methanol vapor is accomplished by the refrigerated condensing of the methanol vapor. When the Allen Bioscav is connected to the biodiesel tank—which contains the decanted biodiesel, water, and methanol mixture—the same process of components separation by boiling point is used. The boiling points of the components are:

• Methanol: 148.5 °F (64.7 °C) (evaporates first)
• Water: 212 °F (100 °C) (evaporates next)
• Biodiesel: 955-662 °F (512-350 °C)¹

For methanol separation, the valve at the Separator Vessel manifold is opened to the refrigerated condenser, while the valve to the atmosphere is closed. The PLC's accurate ( ± 0.01 °C) temperature control of the Bioscav is set at slightly above the boiling point of methanol to account for the latent heat of evaporation (the amount of energy required to overcome the cohesive forces between the molecules and expand the gas to a vapor). The biodiesel and the water are not affected since the temperature is lower than either boiling point. The methanol begins to evaporate and is condensed in the refrigerated condenser. Since this is a distillation process, the liquid methanol has a high degree of purity.

Once all the methanol has been evaporated and condensed, the PLC temperature controller can be set to slightly over 212 °F (100 °C) to begin to evaporate the water. The valve to the chiller will be closed while the valve to the atmosphere will be opened. The water vapor will escape from the Separator Vessel to the atmosphere. The vapor is free of contamination by methanol or biodiesel. The final water content of the biodiesel can be verified by Karl Fischer Titration.

Figure 3: Methanol Recovery

Refining of Crude Glycerol

For the subsequent separation of water, residual fatty acids (soap), and salt from crude glycerol, the process temperature is first set at 212 °F (100 °C) or slightly higher and the valve on the Separator Vessel manifold is opened to the atmosphere to allow the water to evaporate. To separate and condense the glycerol, the process temperature is increased to between 554 and 572 °F (290 and 300 °C) and the vapor is routed to the refrigerate condenser. The pH of the glycerol must be kept at 4-5. Foaming will occur at values above pH 5.

Bleaching of Biodiesel

Crude biodiesel will have an orange tint, which can be bleached with activated carbon or fuller's earth adsorption filters. Glycerol can be similarly bleached to a ligther color. The activated carbon or fuller's earth filters can be an optional and integral part of the Bioscav.

Notes

1. Biodiesel has a very high latent heat of evaporation and will not be affected by the removal boiling points of methanol and water.

References

1. Cecil, Steve, Kathy Kiefer, and Jim Walbridge. "New Biodiesel Standards for EN 14105 and ASTM D6584." Analytix: Advances in Analytical Chemistry 4, (2005) 4-5.
2. Kojima, Seiji, Dongning Du, Masayasu Sato, and Enoch Y. Park. "Efficient Production of Fatty Acid Methyl Ester from Waste Activated Bleaching Earth Using Diesel Oil as Organic Solvent." Journal of Bioscience & Bioengineering 98, no. 6 (2004): 420-424.
3. Methanex Corp. Technical Information & Safe Handling Guide for Methanol. Methanex Corp, 2002. http://methanex.com/products/documents/TISH_english.pdf.
4. Sigma-Aldrich. "Standards for Biodiesel Analysis." Analytix: Advances in Analytical Chemistry 4, (2005).
5. Simon, R. "Microorganism Growth in Petrodiesel and Biodiesel." Chemcical Engineering Department, Rice University, 2000.
6. Van Gerpen, J. H., Earl G. Hammond, Lawrence A. Johnson, Stephen J. Marley, Liangping Yu, Inmok Lee, Abdul Monyem. "Determining the Influence of Contaminants on Biodiesel Properties." Final report prepared for The Iowa Soybean Promotion Board, Iowa State University, July 31 1996.
7. Yong, K. C., T. L. Ooi, K. Dzulkefly, W. M. Z. Wan Yunus, and A. H. Hazimah. "Refining of Crude Glycerine Recovered from Glycerol Residue by Simple Vacuum Distillation." Journal of Oil Palm Research 13, no. 2 (2001) 39-44.

Many developing countries experience either a lack of dependable power or suffer through countless periods of blackouts. The reasons vary from vandalism to theft of insulating oil, but stem most often from poor or non-existent maintenance and security of the existing power grid. The consequence is often the complete destruction of transformers. A comprehensive maintenance and security program for transformers can prevent this.

The availability of dependable electric power is necessary for economic development. The Allen Group devised a plan for a country in Africa that would allow the National Electric Authority to improve their maintenance procedures. It includes the design of a comprehensive, centrally-monitored security and data transmission system. The objective was to clearly show the cost-effectiveness and return on investment (ROI), a direct consequence of implementation of the plan.

This article is the first in a series that will outline the approach any power provider can take to maximize transformer useful service life. Sustainable power is now changing lives and changing countries in Africa.

The Plan

The master plan covers the following subjects:

• Diagnostic Methods
• Transformer Maintenance
• Security
• Remote Data Monitoring

Diagnostic Methods

Diagnostic methods are either reactive or preventive. In practice, transformer maintenance procedures involve a combination of both.

The diagnostic part of this master plan has three elements:

1. Obtaining the basic diagnostic equipment and acquiring the skills to operate it
2. Obtaining baseline operating characteristics (signature) of every transformer in the grid
3. Determining the schedule for periodic re-testing and monitoring

The Basic Equipment Defined

Infrared Thermography

A comprehensive infrared thermography scan shows areas of unusually high temperature, which could present a danger of fire or explosions. A scan should be performed at least once a year for every transformer. A typical scan is shown below. The bright yellow indicates a hot spot that requires attention.

Image courtesy of Fluke

Dielectric Tester

A dielectric tester indicates the insulating strength of the transformer oil. A low dielectric reading indicates a decrease in insulating strength and an accumulation of contaminants such as moisture. A typical portable tester is shown below.

Image courtesy of Hipotronics

Moisture Detection with a Moisture Analyzer

Moisture is one of the most harmful contaminants in transformer insulating oil. If the oil is sampled for moisture at all, the resulting value is often meaningless because it does not reflect the relative saturation of the moisture in the oil at the time the sample was taken. The relative saturation must be recorded along with the oil temperature.

Typical moisture meters are shown below. The instrument measures the ppm of the water in the oil, relative saturation, and temperature of the oil or the dew point and temperature of the gas. It takes only 2 to 3 minutes to attach the adapters and just a few more minutes to obtain a stable reading once oil or gas is flowing.

Images courtesy Doble Engineering

Fault Gas Detection with Dissolved Gas Analyzers

Several organic gases are generated in transformer insulating oil. The types, quantities, and distribution of the gases are indicative of the internal faults. A valuable tool to detect these gases is the dissolved gas analyzer. Depending on results, readings should be taken at least twice a year. More frequent analysis is needed if the results indicate it. A typical permanently installed dissolved gas analyzer is shown below.

Image courtesy of Serveron Co.

The Serveron Transformer Monitor offers accurate and repeatable measurements of eight critical fault gases and other key parameters.

Acidity Detection with a Test Kit

Moisture reacts with the sulfur in oil and creates sulfuric acid. The indication is a rise in the total acid number (TAN). Acid will promote sludge formation and will ultimately destroy the cellulose insulation.

A simple test will yield the level of acidity.

Image courtesy of Dexsil Co.

A Transformer’s Signature

Any diagnostic program must begin by establishing the current state of the transformers in the grid. Data collected on each transformer will provide a baseline reference from which future trends can be determined. Such data includes:

• Dissolved gas analysis
• Oil power factor
• Insulation resistance
• Insulation power factor
• FRA
• Winding resistance
• Turns ratio

Preventive measures can then be taken before major damage occurs.

Determining the Schedule of Diagnostic Testing

From the results of the baseline data, a schedule can be put together for repeat testing. The transformers that indicated borderline problems in any of the measured parameters must be tested more frequently until the problem has been corrected by any of the maintenance procedures.

In my next article, I will describe transformer maintenance methods that will extend a transformer’s useful service life to between 40 to 50 years.

Further Reading

Water Activity in Oil white paper

The Aging of Cellulose white paper

The Allen AOC Series Oil Conditioner is a vacuum distillation system that is used by several major manufacturers during the last phase of the building or repair of large power transformers, the testing phase.

In this part of the process, the Allen Oil Conditioner fulfills the multiple tasks that consist of moving large quantities of test oil from the test oil tank to the new transformer and, after completion of the test, return the oil to the test oil tank. This allows the same batch of oil to be used almost indefinitely because the Allen Oil Conditioner keeps purifying the oil throughout this process.

New or Repaired Transformer Testing

The working fluid in transformer manufacture is insulating oil. It is used to immerse the newly manufactured transformer winding and core assembly in the tank which is then filled with oil. The oil is used for insulating purposes and for the dissipation of generated heat from the windings. The assembly of the windings on the core allows gaps to improve the oil circulation around the windings. The tank is constructed with fins to allow better circulation of the oil and to provide a greater surface area for contact with the cooling air. Very large transformers have banks of cooling fans to provide forced-air cooling which are coupled to thermostats. Some transformers have a pumped oil circulation system and an oil cooling circuit as well.

Prior to final testing, the assembled core and windings are heated to between 850 and 1200 °C for a certain length of time. This sometimes takes a few weeks for large transformers. The windings are considered dry when the values of power factor drop to a minimum and the insulation resistance increases rapidly. Before the final tests, the transformer is left to stand for several days to let any remaining air bubbles dissipate into the oil. The final tests usually include ratio, polarity, resistance, and tap changer operation tests. The test oil is then pumped out of the transformer tank, returned to the test oil storage tank, and stored for future use.

Process Optimization with an Allen Transformer Oil Conditioner

Filling the new transformer: Using the Allen Oil Conditioner's inlet pump, the test oil is first purified and, using the outlet pump of the oil conditioner, is pumped into the new transformer. This insures that clean, dry, and uncontaminated oil enters the new transformer.

Emptying the new transformer: Using the Allen Oil Conditioner’s inlet pump, the oil is once again pumped through the system and purified before the oil is returned to the test oil storage tank by the system discharge pump. If desired, the oil conditioner can be bypassed and the oil can be returned directly to the test oil tank via the Allen Oil Conditioner suction and discharge pump.

The manifold and valves for this process are incorporated in the oil conditioner design. The entire operation can be fully automated by the on-board programmable logic controller (PLC), which can control electrically-actuated valves in a programmed sequence.

The optional Allen Remote Monitoring System (ARMS) designed by our Allen IT specialists can facilitate monitoring from a central control room with one computer screen and a tie-in via the Internet. ARMS also allows monitoring of the entire process via a cellular telephone.

Problems in the EHC Fluid

The servo and  directional valves of a steam turbine control system, such as the trip-throttle valve, are extremely sensitive to the presence of particulate matter because of their tight clearances. For instance typical servo valve clearances are between 1µ and 4µ, while directional valve tolerances are between 2- and 8-micron. Sludge and silt particles with typical sizes between 1- to 5-micron enter the valve clearances and degrade performance through wear and sticking of valve components. Field samples have indicated that over 80% of the solid particles measured were in the range of 2- to 5-micron. This indicates that solids filtration to an ISO 14/11 should be maintained. We have found that a 5-micron filter element will suffice because it is only 5-micron for a short time. Very quickly the layer of solids that accumulates on the membrane will make it filter finer.

Phosphate esters are hygroscopic, i.e. they attract water. This causes a hydrolytic reaction that creates phosphoric acid. This reaction is self-perpetuating, i.e. it creates more acid as time passes. Obviously this corrodes the control system internals severely, sometimes with disastrous consequences.

The manufacturer recommends the following EHC fluid parameters:

• Viscosity at 40 °C to be between 37.8 and 46.2 cSt
• The resistivity to be a minimum of 4 Gohm.cm
• The TAN to be 0.3 mg KOH.gm of fluid maximum
• Water content to be between 1500 and 2000 ppm
• Particulate count to be ISO 14/10 to 16/13 maximum
• Chlorine content to be 150 p pm maximum

If you believe these parameters you will be buying a lot of new EHC fluid and the manufacturer will like you very much. Your manager will probably fire you.

Why?

Consider, for instance, resistivity. Below 4 or even below 5 or 6, electro-kinetic etching of the valve internals begins. We found in our refineries that we had to keep resistivity at a safe level of 20 with frequent sampling.

Secondly, consider a TAN of 0.3 mg KOH/gm of fluid. Again our practice has been to keep the TAN at or below 0.05 mg KOH/gm of fluid. At 0.3 the fluid is beginning to reach the point of no return even when using fuller's earth or ion exchange.

Thirdly, consider a water content of 1500 to 2000 ppm. This is absolutely insane. First of all it neglects to consider the saturation value of the fluid at the operating temperature. That water level could be very close to the saturation point and could be on the verge of dropping out as free water. We found that we had to keep the water level no higher than 10 ppm with at least a 30% safety margin between the water concentration and the saturation point.

A high chlorine content indicates internal corrosion and any value higher than 10 mg/l is a danger sign.

The Solution

There are two ways to keep your EHC fluid in good condition. One way is complicated, expensive, and messy and may backfire on you by making the fluid more contaminated. The other is economical in the long run: neat, clean, and proven to be highly effective.

Method 1: The Expensive, Messy, and Dangerous One

It consists of absorbing water with water adsorbing filter cartridges.

These cartridges hold a relatively small amount of water and simultaneously filter out solids to about 2-micron. They are expensive and usually have to be replaced quite often. Subsequent filtration consists of fuller's earth, activated alumina, or ion exchange cartridges. These are supposed to absorb the acid in the EHC fluid. However, if the acidity rises above a TAN of 0.2, all these media will start leaching various metal salts into the fluid, thereby further degrading it. Eventually the fluid will have to be discarded if the acidity has progressed beyond 0.5 mg KOH/gram of oil. A rigorous sampling and testing program in this case is vital.

Method 2: The Proven Effective Method of Filtration and Vacuum Distillation

An Allen Vacuum Distillation System such as the Allen AOC Series Oil Conditioner; will eliminate solids by filtration, evaporate moisture and gases by the process of vacuum distillation, and will continue to do so reliably for a very long time. This makes the system much more cost-effective in the long run when compared to the continued cost of expensive elements.

The Vacuum Distillation System is a compact, skid-mounted system consisting of a pre- and post-filter, a heater, and a vacuum vessel. The vacuum vessel is filled with randomly packed Raschig Rings™ which provide a large surface area for the oil to flow over in a thin film. The vacuum and the heat provide the necessary mass transfer to remove the moisture and other contaminants as a vapor, which is trapped in a condensate collection tank before it can reach the vacuum pump.

It purifies the EHC oil to the following parameters:

• Moisture down to 5 to 10 ppm total water
• Viscosity to as-new condition or better
• Solids down to 0.5-microns or less
• TAN at or below 0.05 mg KOH/gm of fluid
• Zero concentration of dissolved or entrained gases
• Resistivity > 20 Gohm.cm

Case History

In a large overseas oil refinery a steam turbine driver had not had its control oil sampled for at least one year. One fine day, the turbine experienced a variance in load. The servo valve system did not function and the trip-throttle valve did not shut off the steam supply. The turbine sped up uncontrolled and went into overspeed. Pieces of the turbine casing were found up to one mile from the refinery. Fortunately no one was hurt.

Upon examination it was found that the entire servo system including the trip-throttle valve stem was corroded to the point of immobility. A rigorous sampling program was instituted and a trailer-mounted Allen Oil Conditioner was purchased specifically to purify the control oil in ten large steam turbines. Later the Oil Conditioner was used to purify all lubrication oil throughout the refinery.

Cellulose is the common material of plant cell walls. It occurs in almost pure form in cotton fiber and in combination with other materials such as lignin and hemi-cellulose, wood, and plant leaves and stalks. Cellulose is a long-chain molecule (polymer) made up of recurring units of glucose, a simple sugar. The structural unit is shown below in Figure 1.

Because of the strong hydrogen bonds that exist between cellulose chains, cellulose does not dissolve in common solvents. The positions of the hydroxyl (-OH) groups protrude laterally along the molecule chain. Those positions make them readily available for hydrogen bonding. As a consequence, cellulose can adsorb large quantities of polar compounds such as water and other contaminants. Bundles of cellulose molecules are aggregated together in the form of micro-fibrils in which highly ordered (crystalline) regions exist with less ordered amorphous regions. When the fibers adsorb water or other polar contaminants both intra-crystalline and inter-crystalline swelling occurs. As the fiber swells, inter-molecular bonds are broken as a result of internal stresses produced by swelling. With very strong swelling agents, it is possible to reach a critical point where the entire crystalline structure is disrupted and the fiber structure is lost. Some binary mixtures of liquids can produce more swelling than either compound alone. This effect is particularly true when water is one of the liquids.

When used in bulk filter cartridges, the bulk density of the compressed fibers has to be around 1.00 grams per cubic centimeter. At this density, the swelling is very rapid. The swelling power of water reaches in excess of 90%, while that of diesel or fuel oil only reaches 2%. This is what makes cellulose such a good adsorbing material when it is used to remove water from fuel.

A lesser known application of cellulose adsorbing filter elements is the removal of varnish and sludge from lubrication oil.

What is Varnish?

It is that thin film that deposits itself on servo valves and bearings. It is a high-molecular weight substance that is insoluble in oil. When suspended in oil it is made up of 75% soft contaminants that are less than 1-micron in size. They cannot be measured by traditional particle count nor can they be filtered out. However, these insoluble compounds have polar affinities and as such they migrate from the oil to machine surfaces under the influence of environmental factors such as temperature and pressure. The presence of other contaminants such as water and wear metal particles further enhances varnish and sludge production.

Why Solids Filters Don't Work

In an effort to remove the varnish and sludge precursors, operators are using finer filtration. While this is totally ineffective, it has the undesirable effect of creating static charge buildup in the oil system. The discharge of the static charge creates arcs with extremely high temperatures. This auto-degradation effect further damages the oil.

What to Do

Remember cellulose? Remember the hydroxyls (-OH) sticking out all over the millions of square feet of crystals? AHA!! Varnish and sludge particles are polar compounds that will be attracted to these hydroxyl spikes. They will bond with them in a process called adsorption, which is the chemical bonding of particles to a surface called the adsorbent. Adsorption is dependent on temperature, flow rate, concentration, etc. that solids filters are less sensitive to.

Cellulose fiber filter elements can sustain higher flow rates than normal solids filter elements and are used in a “kidney-loop” continuous filtration on an oil tank. They are inexpensive and dependably remove moisture, acids, varnish, and sludge.

Activated Carbonized Cellulosic Fibers

Cellulose fibers, such as cotton, are hollow as is shown in the photomicrograph below.

Cotton fiber also has a hollow structure that helps increase surface area and porosity. Use of ACF for non-woven production will greatly enhance non-woven performance and to expand end-use applications including military protective clothing, solvent recovery, wastewater treatment, water purification, air cleaning, and acoustic insulation. A photo-micrograph of a cotton fiber is shown below.

Studies have shown that activated carbon fiber with high adsorption capacity and micro-porosity can be prepared from rayon and cotton non-woven fabrics by heating at 800 °C for four hours. A photo-micrograph of carbonized cotton fiber is shown below.

The Allen Cellulose Adsorbent Filter Cartridges

Standard filters are manufactured using a cellulose filtration medium. A protective polypropylene netting is applied to the exterior of the cartridge. Plate end caps that engage most standard industrial filter housings. Nominal particulate rating (20 _m) is for >85% of a given size as determined from single-pass particle counting results.*

Standard Allen filter cartridge dimensions are 7” x 18” and 11” x 18”. They are sold in cases of four (4) elements per case. Common applications are to remove moisture from diesel, kerosene, and jet fuel as well as transformer and breaker insulating oil.

* Nominal Filter Rating: Filter rating indicating the approximate size particle, the majority of which will not pass through the filter. It is generally interpreted as meaning that 85% of the particles of the size equal to the nominal micron rating will be retained by the filter.

References

1. Nan Jiang Doctor's Thesis. Louisiana State University, December 2008.
2. Mantanis, G.I. et al. “Swelling of Compressed Cellulose Fiber Webs in Organic Liquids, Cellulose.” 1995, vol. 2, 1-22.
3. Magats, S. “Varnish in Turbine Oils: Causes, Effects, and Solutions.”
4. Buddy Atherton, United Air Specialists, Inc./kleentek, “Discovering the Root Cause of Varnish Formation.” Practicing Oil Analysis Magazine. March 2007
5. Justin Stover, C.C. Jensen, Inc., “Adsorption: A Simple and Cost-effective Solution to Remove Varnish.” Practicing Oil Analysis Magazine. March 2008

Deep fat frying is a processing procedure used world-wide for the preparation and production of foods. During the deep frying process, oil is subjected to high temperatures, air, and moisture. These conditions cause a variety of degradation reactions to occur such as thermal polymerization, auto-oxidation isomer cyclization, and hydrolysis.

The overuse of frying oil will noticeably affect the flavor stability, color, and texture of fried food. The oil itself undergoes chemical and physical changes resulting in increased smoking, foaming, and changes in viscosity and color. Filtering systems such as the Allen Fry Life System can significantly extend the life of frying oil by using adsorbent material to reduce the level of free fatty acids and colored compounds as well as the polar compounds, the peroxides, and saturated carbonyls.

The Allen Fry Life System consists of a solids filter vessel with two 5-micron filter elements and an activated carbon filter vessel with two cartridges of treated activated carbon, which adsorbs the contaminants from the used frying oil. A reversible oil pump pumps the hot oil via the inlet hose through the filters into the insulated tank for temporary storage while the fryer is being cleaned. The hot oil is then returned to the clean fryer via the reversible pump and the outlet hose. For the best results, the solids and carbon filter elements should be changed between filtration jobs to prevent cross-contamination.

Experimental data concluded the following decrease in contaminants of the filtered frying oil:

These values were reached after nine treatments. More details can be obtained from the following references:

McNeill, J. et al. “Improving the Quality of Used Frying Oils by Treatment with Activated Carbon and Silica.” JAOS vol. 63, no. 12, December 1986.

Orthoefer, F.T. “Care of Food Service Frying Oils.” JAOCS vol. 65, no. 9, September 1988.

How Fresh Are Your Fries?

French fries are one of our favorite foods. We consume billions of pounds of them. They are good, they are salty, and they can be dangerous. Dangerous because of the widespread practice in many restaurants and fast food places to reuse frying oil. The business of “filtering” and reusing frying oil is big because frying oil is one of the largest expenses in the restaurant business. So why exactly can reusing frying oil be dangerous to your health. If there is anything we at Allen Filters, Inc. know it is oil, from cooking oil to lubrication oil; from phosphate esters to soybean oil and so on and so forth. So let me explain.

What is Cooking Oil?

Cooking oil consists of glycerol esters of fatty acids. It may be derived from plants or animals and the more common frying oils are peanut, safflower, canola oils, or animal fat or lard. Deep fat frying is a traditional and age-old method used for cooking and it is popular throughout the world. In third-world countries the use of animal lard is still prevalent.

What Happens to Oil When it is Repeatedly Heated?

In frying the oil, it is usually heated to 170-220 °C (338-428 °F). When heated to these temperatures in the presence of oxygen (air), the oil undergoes chemical reactions such as hydrolysis, oxidation, and polymerization. In other words it changes its character. Degradation products can include free fatty acids, hydro-peroxides, and polymerized triglycerides. The oil viscosity increases, its color will grow darker, and rancidity begins to develop.

What is Rancidity?

Rancidity is the decomposition of fats, oils, and other lipids through oxidation. Oxidation of fats result in the replacement of an oxygen ion with a hydrogen ion in the fatty acid molecule. This substation destabilizes the molecule and makes it possible for other odd chemical fragments to find a place along the chain. Factors which accelerate fat oxidation are trace metals (iron, zinc, copper, etc.), salt, light, water, bacteria, and molds. Oxidation occurs primarily in unsaturated fats by a free-radical-mediated process. These chemical reactions generate highly reactive molecules in rancid food which also may destroy nutrients in the food. Free radicals formed by fatty acids react with oxygen to generate peroxides that enter into a multitude of reactions, producing numerous compounds such as aldehydes, ketones, acids, esters, and polymerized fats.

Hazards of Prolonged Heating

The amounts of degradation products increase with the duration of heating at high temperatures. The toxicity of these degradation products present a health concern. Other contaminants such as polycyclic aromatic hydrocarbons may be concentrated by prolonged heating. Some of these have been found to be potential carcinogens. Certain types of plant oils such as peanut oil are sometimes contaminated by naturally occurring aflatoxin which is a human carcinogen. Peroxides and other by-products are also formed, indicating a change in the oil on a molecular level. Secondary breakdown products of peroxides and hydro-peroxides are rapidly formed by prolonged heating. Trans-fatty acids and a substance called acrylamide are also produced.

Health Effects

Thermal oxidation forms volatile and non-volatile decomposition products. The latter present the most risk to our health since they remain in the oil, are absorbed into fried foods, and are then ingested. Diets high in lipid oxidation and polymerization products (found in used frying oils) are associated with cellular alteration, reduced endothelial function, as well as LDL oxidation. Endothelial function is the normal biochemical processes carried out by the cells that line the inner surface of all blood vessels including arteries and veins as well as the internal lining of the heart and lymphatics. A diet high in frying oil content has been shown to induce glucose intolerance in rats. The presence of excess polar compounds and polymers in the frying oils were positively associated with the risk of hypertension.

In 2002, Swedish scientists discovered acrylamide formation in some starchy foods fried at high temperatures. This has since become a major concern in the food industry. Consistent evidence has shown that acrylamide is formed in foods with a high content of the free amino acid aspargine and of reducing sugars. The optimum condition for such formation is in potato chips since potatoes contain a very high concentration of aspargine. Once formed, the acrylamide can easily be absorbed by inhalation, ingestion, or skin absorption and reacts with proteins to form its metabolite glycidamide, an epoxide which can react with DNA. The effect of these reactions is the formation of hemoglobin adducts and neurotoxins. These adducts and toxins have led to serious health effects such as protein malfunction and muscle control problems.

Ingesting deep-fried oils has an effect on allergic reactions of the digestive tract, growth retardation, increased weight of the liver and kidneys and other biochemical reactions. Necrosis, dark red patches, and bleeding were found in rats fed a diet of food fried in used oil and concern has been raised that frying oil contained in many ready-made foods and snacks such as potato chips can change human serum levels and damage liver and kidneys.

The Used Oil Filtration Business

Several franchises have sprung up that use portable filtration devices to filter the hot frying oil, temporarily storing it in an insulated tank while the fryers are being cleaned out. They subsequently return the “filtered” hot oil to the fryer, saving the restaurant owner the cost of replacing the oil. Of course this will remove crumbs, etc. but does not really clean the oil which is heated over and over as many times as possible without regard to thermal deterioration byproducts.

What to look out for:

• Clear golden yellow color and a good smell are good
• Brown edges and dark colors are bad

Put your nose in it; go ahead, you’ll smell the difference.
 

Characteristics of Diesel

Diesel is a hydrocarbon by-product with a boiling point between 150 °C and 400 °C. It has carbon chain lengths of C15-C22 and a molecular weight of between 212 and 294. A variety of additives such as aliphatic amines, chelating agents, detergents, and corrosion inhibitors are usually added by the refiners, but some of these eventually become a nutrient source for microorganisms. Diesel is the fuel that suffers most from microbial contamination.

Contamination in Storage Tanks

Even in the best maintained tanks, microbial contamination can be a problem. Tanks that hold strategic reserves are particularly vulnerable and large quantities of microbial growth have been reported. One of the essential substances for microbiological growth is water:

• Water that is dissolved in the fuel will condense on tank walls
• Moisture in the air that enters through vents or floating tank lids
• Poorly designed tanks that do not drain properly allow water to remain in the bottom
• High water content of “new” diesel fuel that is delivered

Even the allowable amount of moisture in new diesel is enough to start a microbiological colony growing. The resulting cell metabolism then produces more water and the cycle continues. Since oxygen is usually present, all ingredients needed for rapid microbiological growth are present including the carbon source from diesel.

The equation of life and evolution is:

Bacteria + Water + Oxygen --> More Bacteria + Carbon Dioxide + More water

Even if oxygen were not present, such facultative organisms such as Bacillus and anaerobes such as sulfur-reducing bacteria (SRB) continue to thrive and corrode tank material. It is best to keep the water content of diesel below 50 wppm.

Problems Caused by Microbial Growth

In diesel, microbial contamination will contribute to aging instability of the fuel, but by far the most serious damage is done by microbially induced corrosion of the storage tanks and pipe work as well as the formation of thick microbial mats that will block filters and pipelines and wear out pumps.

The following microorganisms have been isolated from petrodiesel and biodiesel:

• Thirty (30) types of bacteria
• Twelve (12) types of yeasts
• Eighty-three (83) types of filamentous fungi (mat forming)

During a recent hurricane in Florida, emergency generators in five hospitals did not start when they were needed. Their fuel tanks, pipes, and filters were clogged with microorganisms.

Some Uninvited Guests

	Pseudomonas aeruginosa
	Cladosporium
	Candida tropicalis
	Hormoconis resinae

Counter Measures

Magnetism

When microorganisms are subjected to a strong magnetic flux field, the ability of the protein channels that maintain the electrical and chemical potential across the cell membrane is torn apart and the microorganism is destroyed. The resulting debris settles to the bottom of the tank or can be filtered out. This is an expensive and often impractical method.

Biocides

Biocides are expensive and highly toxic chemicals that have potential for serious environmental contamination. The fallout of dead cells creates sludge in the bottom of the tank, clogging fuel lines and filters alike. Over time, the microorganisms develop a resistance to any biocide through the process of evolution and other toxins must be brought to bear.

Filtration

Continuous filtration of petrodiesel or biodiesel with filter elements that remove water as well as bio-solids will maintain the fuel at a high degree of cleanliness. One such system is the Allen Continuous Filtration System (ACF).

The Allen ACF system is designed to operate continuously to remove moisture and solids from diesel fuel. It ensures that the fuel is continuously cleaned and that the generator is ready to start when needed.

A special inexpensive filter element removes water and solids from the fuel. The system will have paid for itself the first time the emergency generator starts without a problem.

The same thing that turns a good doctor into a great doctor: experience.

Greatness first manifests itself in an uncanny diagnostic capability. A great engineer can look at a piece of equipment, listen to it, smell it, feel it, and can arrive unfailingly at the identification of the problem. Similarly, a great engineer can always find a better way to do what others have accepted as impossible to improve upon. The same holds for the age-old process of distillation. One of the most popular books ever written was Rules of Thumb for Chemical Engineers. Not that these rules take the place of rigorous calculations, but when memorized can save many hours of analysis and design.

Case in point is distillation and in particular vacuum distillation as it is used at Allen Filters for the purification of fluids.

Distillation is the process used for separating multi-component fluids into high purity products. A designer is required to have a thorough understanding of mass transfer, phase change, and pressure-drop fundamentals before he or she can successfully optimize the process design. Most engineers rely heavily on vendor recommendations, thereby absolving themselves of the fundamental function of the creative application of the basic principles of chemical engineering.

The purification of fluids contaminated by multi-component mixtures with different solubilities and partial pressures, involves the separation of these contaminants from the base fluid.

Allen Filters technology originally applied by founder Albert Allen is based on the design of distillation columns similar to those used in refineries. A distillation column can use either trays or packing. The mechanisms of mass transfer differ but both are based on achieving a steady-state equilibrium by using large amounts of interfacial area. This interfacial area is the result of the passage of vapor through the open spaces in the trays or between the packing and the spreading of the liquid in a very thin layer on the surface of the packing. While at first we used interlocking trays in our vacuum vessels, after several years of research using pilot systems and computer modeling, verified by countless tests, we found that for the optimum mass transfer a certain combination of packing type, heat, and vacuum produced the best separation efficiency. Serious consideration was given to the influence of the shape of the packing on the liquid flow behavior as a result of fluid dynamics studies in our pilot systems.

The variety of shapes and types of packing and the variations in geometry that are available tend to empiricize the design of packed columns and we had to limit the choices for our research into the optimum performance to just a few packing types. We concentrated on obtaining an even distribution of liquid in the packed bed, in addition to providing the shortest diffusion pathway between vapor and liquid flow

Packing can be divided in two groups, depending on the type of packing used: random (dumped) or structured (ordered). Each type of packing is also available in a variety of sizes. This means they are geometrically similar but vary only by a characteristic dimension.

Mass transfer in the distillation column occurs at the interface between the liquid film on the surface of the packing and the vapor. The efficiency of mass transfer depends on the specific area of the packing, which is controlled by the packing's nominal size. We found after many experiments that random packing provided the best results. Packing installed in a random fashion orients itself in an irregular fashion and this influences the relationship between the characteristic dimension and the specific area of the packing. The vertical height of the packing column also has an influence on the mass transfer efficiency.

Mass transfer in a packed column is typically described in terms of HETP, the height equivalent of a theoretical plate—that is the height of packing required for a theoretical stage of separation.

Performance remains relatively constant and stable, except for at high or low rates. At low liquid throughput, sheets of liquid are not stable and rivulets do not spread evenly to wet the entire surface of the packing, so mass transfer is poor. As the column throughput increases, there is a large stable area of the curve where packing is properly wetted and the HETP is relatively stable.

At the higher rate portion of the stable region, mass transfer improves. This improvement is caused by an increase in interfacial area due to liquid turbulence and entrainment. At higher rates, performance decreases rapidly due to increased liquid entrainment in the vapor that is being carried upwards through the column. This entrainment degrades the composition of the vapor and can result in liquid carryover and vapor redistribution.

Poor Wetting of Packing

In the distillation column, liquid flows from the distributor onto the packed column in fine streams. Good wetting requires that the packing elements distribute these streams evenly throughout the column's cross-section. The liquid flow rate controls the hydrodynamic behavior of the liquid film.

Thus for continuous distillation, the downward flowing liquid phase is in contact with the upward flowing vapor phase.

A significant amount of data was also generated on behavior of pressure drop in the column. Liquid as it flows down the packed column raises pressure drop by occupying space, increasing turbulence related eddies and providing liquid droplet entrained in the vapor phase.

Flooding

As the column throughput increases beyond the stable region, the pressure drop rises more quickly due to more liquid entrainment in the vapor and greater vapor velocity due to the reduced area of escape. Substantial quantities of liquid flow upwards through sections of the column and because the packing is relatively open, liquid and vapor tend to redistribute themselves, resulting in a sharp drop-off of mass transfer. Ultimately the column will flood and in the case of vacuum distillation, liquid and vapor will carry over into the condensate tank.

Optimization Rules

1. Allen Filters uses random packing elements with a small characteristic dimension.
2. We run the column near the upper range of the stable region.
3. We use packing with large specific area which tend to be more efficient.
4. Because pressure drop tends to improve mass transfer, we use packing types with a relatively higher pressure drop, although this may sometimes require a larger column diameter.
5. The operating range of internals, especially the liquid distributor is more often than not the controlling factor. Allen Filters uses a proprietary (patent pending) fluid distributor on our vacuum distillation columns.
6. Allen Filters process design always places a solids filter before the vacuum distillation column to prevent fouling of the packing. For that reason, under normal operation, the vacuum vessel never needs to be opened for cleaning.
7. Packed columns can be designed with great accuracy, using the empirical equations generated by research.

Vacuum Distillation

Vacuum lowers the boiling points of individual components in a multi-component mixture by reducing the vapor pressure, causing evaporation beginning with the compounds with the highest boiling points. As such it facilitates mass transfer at relatively lower temperatures. Numerous pilot plant tests have shown that between vacuum and heat, the latter is the more important variable. These tests in addition to extensive proprietary computer modeling have allowed us to optimize the combination of the right amount of heat and vacuum to achieve the most efficient mass transfer at the highest capacity and at the lowest pressure drop.

Raschig Super-Rings

Raschig Super-Rings are a fourth generation random packing made by Raschig GmbH. They were first introduced in 1995 and have since been widely used in the refinery and chemical process industry. The distinct characteristic of Raschig Rings is that the emphasis was on producing liquid films as much as possible and avoid droplet formation. The rings have no droplet promoting edges in their geometry and as a consequence achieve a very even distribution of liquid over the packed bed. This leads to a highly homogeneous distribution and optimal mass transfer.

References

1. Pd Dr. –Ing. M Schultes. “Raschig Super-rings-A New Fourth Generation Random Packing.” February 2001.
2. American Institute of Chemical Engineers. “Optimize Distillation Columns.” 2000.
3. Koshy, T. D. and Rukovena, F. “Distillation Pilot Plant Design, Operating Parameters, and Scale-up Considerations.” The Chemical Engineers Resource Page.
4. Seader, J.D. and Henley, E. J. “Separation Process Principles.” John Wiley & Sons, Inc., 1998.
5. Perry, R.H. “Chemical Engineers’ Handbook.” McGraw-Hill.
6. Simon, R.J. “Computational Hydrodynamics and Distillation Column Design.” Allen Filters, Inc. Internal Publication, 2006.

The reason is that a marvel of creation—the hydrological cycle—has been savagely and callously interrupted. Nature often operates in cycles and water is a prime example of this. Water is not just a combination of hydrogen and oxygen. It has unique properties that allow it to exist simultaneously as a liquid, solid, or gas under the earth's atmospheric conditions.

These conditions are an integral part of the hydrological cycle. The hydrological cycle takes place in the earth's hydrosphere, which is the area where all the water on earth is contained. The cycle begins with condensation, the vaporization of water that forms clouds. When the clouds become saturated the water returns to earth as rain, which in turn creates run-off, infiltration into aquifers, and provides a considerable part that is absorbed by vegetation. This is followed by evaporation from the lakes, rivers, and oceans, which then completes the cycle, returning as condensation.

The problem facing humanity now is the so called "shortage" of water. As we said before, there is no shortage of water, it is just not always where we want it to be. There are many ways to bring water where it is needed, most of them expensive and labor intensive and the situation will get worse not better. The reason is that the cycle has been interrupted by human ignorance of the laws of nature. Numerous civilizations have tried to ignore those laws and most have disappeared ignominiously into the fog of history, leaving behind a desiccated tree-less wasteland and a legacy of brutal abuse of their habitat. It is the cycle, stupid.

So in spite of our best efforts to bring water where it is needed—to purify it and make it safe when we return it to the cycle—we return it corrupted and polluted with our waste.

Eventually, the cycle cannot keep up with the rate of pollution. The ocean areas now the size of Texas covered with plastic waste will cover the entire oceans; they will interrupt currents and change the weather. And so our "civilization" does not have to wait for the sun to immolate itself as a white dwarf. We will die and disappear into the fog of history as many did before us. And history will die with us. Are we that stupid and arrogant to believe that we can pollute our habitat with impunity?

Unfortunately most of us are indeed that stupid and arrogant to think the laws of nature do not apply to us. So the latest best thing is to design and manufacture systems to provide clean water to those who do not have it. This water is gratefully used and discarded in a polluted state, because the technocrats of the industrial world are forgetting that clean water is returned polluted. So much for philanthropy according to the United Nations, NGOs, charitable organizations, and industrial conglomerates that provide these clean water systems and forget to add treatment systems to make the resource sustainable.

At Allen Filters, we plan to provide solar-powered water purification systems together with solar-powered waste water purification systems to close the cycle. We will do this free of charge to those who need it.

Are we tilling at windmills? I am from Holland and we tamed the windmills back during the Middle Ages to do our bidding and provide us with land from the sea. It is not that difficult because once you obey the laws of nature, they can serve you well.

Fuller's earth is a general term for industrially used smectite or polygorskite-sepiolite clays with a large surface area and strong absorptive, binding, gelling, thickening, and decolorizing ability. Fuller's earths are composed of several combinations of absorptive clay minerals, often with varying amounts of impurities such as silica, kaolinite, zeolites, and carbonate minerals. Mineralogy, crystalline property and shape, particle size and crushability, and specific gravity all are critical to the absorptive and cation exchange capacity and decolorizing capability. Therefore it is important to obtain only refined products. The adsorptive properties of the crystals are determined by the removal of bound water by thermal treatment.

The American Geological Institute's definition of fuller's earth is that it is a fine-grained, earthy substance with high water absorptive capacity and the ability to refine and decolorize edible, synthetic, and mineral oils.

Industrial Uses of Fuller's Earth

Attapulgite (AT) or polygorskite is a family of fibrous, hydrous magnesium silicates. AT clay has numerous other components besides AT such as quartz and carbonate. These chemicals exist in the form of relatively large particles, which will deteriorate the crystal matrix unless removed by purification.

In the areas of environmental technology, fuller's earth is used mainly to treat lubrication and transformer oils, waxes, resins, polymers, diesel fuel, jet fuel, etc. AT crystals have an extremely large surface area; one pound of AT crystals has an approximate surface area of 13 acres.

The capability of AT to adsorb contaminants is used in two ways:

Contact Method: The oil to be treated is pumped through cartridges filled with fuller's earth at a flow rate designed to provide sufficient contact time between the oil and the AT crystals. The surface loading of the cartridges depends on the particle size of AT used.

Percolation Method: Here the oil is spread over the surface of a column of AT. Again the surface loading of the column must take into account the required contact time between oil and AT.

Adsorbent Handling and Regeneration

The purpose of the thermal pre-treatment of AT is to drive off the bound moisture adsorbed during shipping and storage. Optimum activity is achieved by driving off a pre-determined amount of residual moisture from the composition. For AT, the "tempering" temperatures are 500 °F to 800 °F.

The regeneration has as its objective the restoration of the adsorptive efficiency of the adsorbent to as close as possible to its initial level. Even under the best of conditions, the adsorbent loses some of its adsorptive capacity with each repetition of the regenerative process.

This degradation of efficiency is due mainly to increasing losses of bound water, which results in the alteration of the crystal structure, pore volume, and surface area. It is also due to the fusible materials precipitated and thermo-fused on the adsorbent by the oil being refined. Bound water losses increase rapidly at temperatures above 1,100 °F. Therefore, the regeneration temperature must be carefully controlled between 1,000 °F and 1,100 °F with the lower temperature preferable.

Degradation of Efficiency

The degradation of adsorbent efficiency can be expressed as a fraction of that of the newly tempered adsorbent. The rate of efficiency degradation conforms to the equation:

EW = a / (n + k)b

Where EW equals the weight efficiency fraction of the adsorbent which has been through n number of cycles of adsorption and regeneration.

EW is further defined as Yn / Y1 in which Yn is the yield from a weight unit of adsorbent at the nth cycle and Y1 is the yield from the same weight unit of adsorbent on the first cycle.

a & b are constants for a particular system. n equals the last of a sequence of adsorption and regeneration cycles.

k equals a constant which appears related to the control of the vessel in which the adsorbent is regenerated. This is always a number between 0 and 5.

This equation can be plotted as is shown in Figure 2. The various curves illustrate clearly the effect of regeneration vessel temperature control on the rate of adsorption degradation. These curves also indicate the point at which the adsorbent should be discarded. The usual criterion for discard is economic and depends on many factors such as the cost of power required to regenerate, the cost of new AT, the amount of air pollution released during regeneration, cost of manpower, etc. The economic conditions usually dictate three to six cycles prior to discard.

Figure 2: Efficiency Decline with Repeated Regeneration (Static Bed Percolation)

Figure 3: Mixture of Activated Alumina and AT (Static Bed Percolation)

Adsorption Characteristics of a Mixture of Adsorbents

The rate of adsorptive degeneration for a mixture of activated aluminum and AT is less than that of only AT. The equilibrium efficiency method with make-up and no discard is normally used. The make-up normally amounts to 1% to 2% by weight per regeneration cycle. Degradation rates and equilibrium efficiency curves are shown in Figure 3.

It is evident that the equilibrium efficiency rises with increased rates of make-up, making this method ultimately economically disadvantageous. Another interesting point shown in Figure 3 is that the efficiency for producing a light-colored product decreases faster that that for a darker color product.

The Environmental Effects of Adsorbent Regeneration

When the filtrate has reached its specification level, the feed to the adsorption column is discontinued. This leaves the head space above the adsorbent and the voids and pores of the adsorbent itself full of oil. This amount is about 70% of the bulk volume of the adsorbent. This oil is recovered by washing with a solvent such as naphtha. The washing step is followed by steaming the column to displace the final portion of the wash. The steam functions to vaporize the remaining naphtha. The effect on the environment and attending personnel consist mainly of release of a considerable amount of toxic hydrocarbon vapors into the atmosphere. This must be weighed against the unfavorable economics of constructing an elaborate system and controls to regenerate an adsorbent that is available throughout the world at relatively low cost.

The conclusion is invariably that it does not make economic and environmental sense to regenerate a universally available and cheap adsorbent.