Patent Publication Number: US-2006000787-A1

Title: Purification of impure oil by centrifugation

Description:
BACKGROUND OF THE INVENTION  
      The oil industry refines crude oil into several types of products, such as gasoline, diesel fuel and home heating oil. Crude oil contains a number of impurities that are removed during the refinement process. Also, certain refinement processes can produce byproducts that contaminate the oil. Some of these byproducts include inorganic materials such as ash, catfines or fines. The presence of such impurities in the oil causes damage to equipment that uses the oil (e.g., engines, furnaces, etc.). Unfortunately, the end user bears the cost in having to repair or replace this equipment.  
      As such, a need exists to develop a refinement or purification process that reduces the amount of impurities in oil. In particular, a need exists to reduce such impurities while refining large amounts of crude oil quickly and efficiently.  
     SUMMARY OF THE INVENTION  
      The present invention pertains to methods for purifying large quantities of oil in an efficient manner. The methods of the present invention allow for the removal of impurities or inorganic material including ash, catfines, and/or fines. The removal of such material results in better quality end products such as gasoline, diesel fuel and home heating oil, which, in turn, advantageously reduces the damage done to equipment associated with these end products. The present invention provides for improved combustion with less impurities.  
      In particular, the present invention relates to methods for purifying an impure oil, or removing impurities, inorganic material or ash from an impure oil, at a rate of about 80 Gallons Per Minute (GPM) (303 Liters Per Minute (LPM)) or greater by subjecting the impure oil to a centrifuge referred to as a “disk stack centrifuge” to thereby obtain a purified oil. The rate of oil passing through the centrifuge generally can range from about 80 GPM (303 LPM) to about 350 GPM (1324.9 LPM). The bowl speed of the centrifuge, in one aspect of the invention, is greater than about 1000 Revolutions Per Minute (RPM), or preferably between about 1000 RPM and about 4000 RPM. In one embodiment, the impure oil prior to centrifugation has an impurity content, an inorganic material content and/or ash content of about 0.1% by weight or greater (e.g., in a range between about 0.1% by weight and about 2.1% by weight, preferably between about 0.5% and about 0.7% by weight, or more preferably about 0.6% by weight). After centrifugation, the purified oil has an impurity content, an inorganic material content or ash content less than that prior to centrifugation. One embodiment relates to having a purified oil with an impurity content, an inorganic material content or ash content greater than about 2 fold less (e.g.,about 3× less, about 4× less, about 5× less, about 6× less, or about 7× less), or between about 2 fold less and about 7.5 fold less, than that of the impure oil. Another aspect of the invention includes purifying the impure oil so that the purified oil has impurity content, inorganic material content, and/or ash content of less than about 0.3% by weight (e.g., in a range between about 0.01% and about 0.3% by weight, and preferably between about 0.15% and about 0.05% by weight). One aspect of the invention includes having a purified oil that has an aluminum content of less than about 0.03% by weight (or less than about 300 parts per million (PPM), e.g., between about 50 and about 300 PPM), and/or a silicon content of less than about 0.04% by weight (or less than about 400 PPM), e.g., between about 50 and about 400 PPM. Note that 1% by weight equals 10,000 PPM. In one embodiment, the invention includes heating the impure oil to a temperature between about 79° C. (about 175° F.) and about 135° C. (about 275° F.), prior to subjecting the impure oil to the disk stack centrifuge. Also, an aspect of the invention includes filtering the impure oil e.g., to remove particles that are greater than about 80 microns (e.g., 90 microns, 100 microns, 110 microns, or 120 microns), prior to subjecting the impure oil to the disk stack centrifuge. One embodiment of the invention includes using a particular type of disk stack centrifuge referred to as a “disk type nozzle centrifuge” or a “nozzle centrifuge.” 
      Another embodiment of the invention relates to methods for purifying an impure oil having an impurity content, inorganic material content and/or ash content of greater than about 0.1%, as described herein, by subjecting the impure oil to a disk stack centrifuge at a rate greater than about 80 GPM, to thereby obtain a two products, a purified oil and a slurry. The purified oil has an impurity content, inorganic materials content or ash content of less than that of the impure oil, and the slurry has an impurity content, inorganic materials content or ash content greater than that of the impure oil. In particular, the purified oil has an impurity content, an inorganic material or ash content greater than about 2 fold less (e.g.,about 3× less, about 4× less, about 5× less, about 6× less, about 7× less), or between about 2 fold less and about 7.5 fold less, than that of the impure oil. The invention, in another aspect, includes purifying the impure oil so that the purified oil has impurity content, inorganic material content and/or ash content of less than about 0.3% by weight (e.g., in a range between about 0.01% and about 0.3% by weight, preferably between about 0.15% and 0.05% by weight). The invention results, in another embodinfent, with a slurry that has an impurity content, inorganic materials content and/or ash content in a range between about 1.0% and about 6.0% by weight. An advantage of this embodiment is that the slurry, even with its high impurity content, is recycled into purified oil having an impurity content and/or ash content of less than about 0.3% by weight. Recycling the slurry, in one embodiment, involves subjecting the slurry to a second centrifuge at a rate of between about 10 GPM (38 LPM) and about 150 GPM (568 LPM). Several types of centrifuges can be used in the recycling process as the second centrifuge. An example of a second centrifuge includes, but is not limited to, a decanter centrifuge. The second centrifuge produces a petroleum product having an impurity content, inorganic materials content and/or ash content of less than about 2.5% by weight (e.g., between about 2.5% and about 0.05% by weight, preferably about 0.8% by weight). In an embodiment, the slurry is mixed by one or more mixers prior to entering the second centrifuge. After being subjected to the second centrifuge, the recycling process further includes subjecting the petroleum product, one or more times, to a disk stack centrifuge, as described above, at a rate greater than about 80 GPM, to thereby obtain a purified oil having an impurity content, inorganic materials content and/or ash content of less than about 0.3% by weight. Additionally, the present invention relates to the purified oil, as obtained by the methods described herein.  
      Furthermore, the present invention pertains to an apparatus or system for purifying impure oil. The apparatus includes a combination of one or more of the following: a first tank for providing impure oil, a pump, a disk stack centrifuge that excretes a centrate and a slurry; a heat exchanger that heats the oil to a temperature in a range between about 79° C. and about 135° C.; and a second tank for receiving the centrate. The impure oil is processed in the centrifuge at a rate greater than about 80 GPM, as further described herein. The apparatus can further comprise a filter that removes particles that are greater than about 80 microns, and also a second heat exchanger that chills the centrate to a temperature less than about 93° C. (about 200° F.), or between about 93° C. (about 200° F.) and about 66° C. (about 150° F.), and preferably to about 82 ° C. (about 1 80° F.).  
      In another aspect; the invention relates to apparatus or system for purifying impure oil that comprises one or more of the following: a first tank for providing oil, a pump, a first centrifuge (e.g., a disk stack centrifuge that excretes a centrate and a slurry), a second centrifuge that receives the slurry from the first centrifuge, a recirulation means for moving the centrate from the second centrifuge to the first centrifuge, and a second tank, connected to the first centrifuge, for receiving the centrate for the first centrifuge. The impure oil is processed in the centrifuge at a rate greater than about 80 GPM, as further described herein. The second centrifuge can be e.g., a decanter centrifuge.  
      Advantages of the present invention include the ability to produce a cleaner oil which reduces wear on engines components, burners, etc. This advantage reduces cost to the end users since such equipment will generally need less repair and/or replacement. The present invention advantageously also reduces the cost and quantity of the hazardous waste generated by the end user due to the use of such products. Since the process allows for efficient purification of oil in large quantities, a further advantage of the present invention is the ability to increase profit by selling oil with less impurities at a higher price. The present invention advantageously further reduces costs associated with storage and maintenance of crude oil because the present invention allows the oil to be processed quickly and efficiently, rather than being stored for prolonged periods of time (e.g., for a month). As a result, processing the oil with the present invention also reduces the risk of environmental leakage associated with oil storage tanks.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
       FIG. 1  is a schematic representation showing one embodiment of an oil purification process.  
       FIG. 2  is a cross-sectional view of a nozzle centrifuge.  
       FIG. 3  is a schematic representation showing another embodiment of the oil purification process of the present invention.  
       FIG. 4  is a schematic representation showing sample maximum flow conditions for feed, centrate, recycled oil, wash liquid (e.g., cutter stock) and concentrate (e.g., slurry) from the disk stack centrifuge for one embodiment of the purification process of the present invention. Abbreviations: gpm—gallons per minute; bb/hr—barrels per hour; bb/24hr—barrels per 24 hours; wt. %—amount in percent weight; lbs/hr—pounds per hour; rpm—revolutions per minute; G&#39;s—Gravitational force; deg F—degrees Fahrenheit; Hp—house power; API—specific gravity; CP—viscosity.  
       FIG. 5  is a schematic representation showing another embodiment of the oil purification process.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention relates to methods for refining and/or purifying an impure oil (e.g., crude oil or clarified oil) so that better quality end products, such as gasoline and heating oil, can be made. The present invention involves removing certain impurities that can cause damage to equipment that uses the oil. The methods described herein allow for quick and efficient purification of large quantities of oil, and include subjecting oil in need of purification (e.g., oil having certain impurities) to a disk stack centrifuge at high flow rates to result in a purified oil.  
      Purifying oil or refining oil refers to a process of decreasing, removing or separating away one or more impurities from the oil. The phrases, “purifying oil” or “refining oil” are used interchangeably herein. The process of the present invention purifies the oil so that the impurity content, inorganic materials content or ash content is decreased or lessened, as compared to the respective content prior to centrifugation, as described herein. In particular, purifying oil or removing impurities, inorganic material or ash from the oil is used herein to mean to take away, partially or completely, one or more impurities, inorganic materials (e.g., inorganic elements), or ash, respectively.  
      The impure oil that is purified by the methods described herein can be a crude oil or a clarified oil. Examples of impure oil include Cat Bottoms, Bayway—Cat cracked clarified oil, Bayway—Cat Cracker Bottoms, Bayway—Cat Tar, Bayway—Clarified oil, Bayway—Cycle Gas oil, Bayway—Slurry oil, Cat, Cat Crack Clarified oil (East Coast), Trainer Decanted oil, and wood river Cat Crk Clarified oil. Crude oil is a mixture of several types of chemicals and compounds, primarily hydrocarbons. Crude oil can be obtained in any number of ways, such as drilling or from a well. One or more pre-purification steps can be conducted prior to subjecting impure oil to the stack centrifuge. For example, crude oil can be clarified by a process referred to catalytic cracking in which crude oil is broken down or “cracked” into simpler hydrocarbon compounds at the molecular level by means of extreme heat, pressure, and/or exposure to a chemical catalyst. Essentially, the process changes the long-chain hydrocarbon molecules into shorter-chain compounds.  
      The present invention purifies impure oil, including crude oil or clarified oil, having an impurity content, inorganic material content and/or ash content of greater than about 0.1% by weight or greater (e.g., in a range between about 0.1% and about 2.1% by weight, and preferably between about 0.5% by weight and about 0.7% by weight). Percent by weight is determined by dividing the weight of the impurity with the overall weight of the oil multiplied by 100%. Impurity content, inorganic material content or ash content can also be measured in Parts Per Million (PPM). Impurity content, inorganic materials content or ash content can be measured using methods known in the art, or those later developed. PPM can be converted to a percent by weight, and viscera, with the following formula: 1% by weight=10,000 PPM.  
      Consequently, the impurity content refers to a combination of one or more elements, chemical compounds that include such elements, or particles that are not wanted in the impure oil (e.g., sulfur, sodium, silicon, aluminum, vanadium, ash, catfines, fines, and used lubricating or cutter oils), as measured by a percent by weight or in parts per million (PPM). Inorganic material content, measured as a percent by weight or PPM, pertains to one or more non-carbon elements or materials that are not wanted in the impure oil, and includes e.g., sulfur, sodium, silicon, aluminum, vanadium, ash, catfines, or fines. Ash is defined as a certain type of inorganic material or impurity found in oil which cannot burn at the combustion temperature, or can be seen as the residue after all the combustible components have been burned. Essentially, ash, catfines and fines are unwanted inorganic material found in oil, and the three terms are sometimes used interchangeably. More specifically, ash which is generally also measured as a percent by weight, can include, but is not limited to, a combination of one or more of the following, for example: vanadium, aluminum, silicon, sodium, iron oxides, sand, dirt, and used lubricating or cutter oils. Fines (e.g., catalyst fines or iron ore fines) are defined as small particles or powder resulting from the refining process. Catfines are a type of fines derived from spent catalysts from the catalytic cracking process.  
      The following table is an example of a breakdown of its impurity content, as measured by a percent by weight or PPM, of an impure oil prior to being subjected to centrifugation, as described herein:  
                           TABLE 1                                   Impurity   Amount                          Ash   0.46% weight*           Aluminum,   858 PPM (.0858% weight*)           MDL = 1           Silicon,   1304 PPM (.1304% weight*)           MDL = 1                         *Percent by weight = weight of impurity/weight of total volume of oil × 100%             
 
      After being subjected to the steps of the present invention, one or more of the elements that comprise the impurity content decreases. The following is an example of the impurity content of a purified oil after being subjected to centrifugation with a nozzle centrifuge.  
                   TABLE 2                       Impurity   Amount                  Ash   0.09% weight*       Aluminum,   165 PPM (.0165% weight*)       MDL = 1       Silicon,   248 PPM (.0248% weight*)       MDL = 1                 *Percent by weight = weight of impurity/weight of total volume of oil × 100%             
 
      In one embodiment, the method of the invention is conducted in apparatus g(system) 100, shown in  FIG. 1 . Apparatus  100  includes tanks  10  and  26  (one for storing the impure oil, and another for receiving the purified oil), pumps  20  and  22  (one for supplying oil to centrifuge and another for supplying the oil to tank  26 ), heat exchangers  14  and  24  (one for heating the oil and another for chilling the oil), filter  16  and disk stack centrifuge  12 .  
      Tanks  10  and  26  are storage tanks. Tank  10  is used for holding crude petroleum or clarified (e.g., impure oil), and tank  26  is used for storing the purified oil. Tanks  10  and  26  can be constructed, for example, from steel or another suitable material. Generally, the capacity of Tank  10  should be sufficient to supply the apparatus or oil purification system at the proper rate, as further described herein. In other embodiments, a continuous method can be employed, whereby petroleum product is generated from an oil well and employed in the method of the invention continuously, without being held in a storage tank such as tank  10 . Similarly, a continuous method can be used to bypass the use of tank  26 , wherein the purified oil is deposited directly into a pipeline or the like.  
      From tank  10 , impure oil is directed by pump  20  to heat exchanger  14 , where it is heated. The impure oil is pumped by pump  20  at a rate of about 80 GPM (302.8 LPM) or greater. Flow rates that can be employed in the methods of the invention are in the range of between about 80 GPM and about 350 GPM (1324.9 LPM), preferably in the range of between about 180 (681.4 LPM) and about 255 GPM (965.3 LPM). A specific example of a flow rate is about 200 GPM (757.1 LPM). A number of pumps can be used throughout the purification system. Pumps for delivering oil at the specified rate are known in the art and are commercially available. In one embodiment, to supply the centrifuge at above rate, one can use a 4″ valve and a discflow pump (e.g., a Discflow SP Series disc pump, Disc Flo Corporation, Santee, Calif.). This pump has the following characteristics: Hydraulic flow—2-10,000 GPM (0.5-2250 m 3 /h); pump speeds—up to 3600 RPM; Viscosities—up to 300,000 cPs; temperature—up to 1000° F. (523° C.). Another example of a pump that can be used in the oil purification system of the present invention is a Blackmere paddle pump model No: NP4F, E.I. by DuPont (Wilmington, Del.).  
      The oil is heated such that it enters the disk stack centrifuge  12  at a temperature in a range about between about 79° C. (about 175° F.) and about 135° C. (about 275° F.) (e.g., between about 90° C. and about 120° C., and preferably between about I 00° C. and 110° C.). Proper oil temperature contributes to efficient centrifugation of the impure oil, and to achieve the desired impurity, inorganic material or ash content. Several methods for heating oil can be used. Methods that are known in the art or later developed can be used for heating the oil in a manner as described herein. Heating the oil involves the following variables: starting temperature of the oil, the rate of oil passing through the heating device, the size of the heating device, and the amount heat emitted by the heating device.  
      Referring to  FIG. 1 , the impure oil is heated by directing it, via pump  20 , to a heat exchanger. A heat exchanger is a device used to transfer heat to oil passing through it. Examples of heat exchangers that can be used to carry out the present invention include: an air heat exchanger, a fin tube heat exchanger, a block type heat exchanger, a plate heat exchanger, a shell &amp; tube heat exchanger, a spiral heat exchanger, a U-tube heat exchanger, a fin fan heat exchanger, a tube in tube heat exchanger, and others. Suitable heat exchangers are commercially available through several vendors such as Canzler, L. L. C. (Columbia, Md.), Alfa Laval Thermal, Inc.(Richmond, Va.) and Kinetic Engineering Corp. (Houston, Tex.). A specific example of a heat exchanger is the Alfa Laval spiral heat exchanger (Alfa Laval Thermal, Inc.(Richmond, Va.)), and its use is demonstrated in the Exemplification Section. In this section, this spiral heat exchanger, in conjunction with a steam boiler  13 , was used to process oil at a rate of about 200 GPM with a starting temperature of about 82.2° C. (180° F.) to heat the oil to a temperature of 104.4° C. (220° F.), suitable for entry into the centrifuge. One can manipulate the variables (e.g., flow rate, input, starting temperature, ending temperature) described herein to achieve the desired temperature. Put another way, these variables can be captured by “Delta T,” the number of BTUs needed to raise the temperature of a known fluid from one temperature to another temperature at a set flow rate. A heat exchanger can have valves, temperature gauges and pressure gauges, or a combination thereof.  
      Temperature gauges, pressure gauges, sample points, and flow meters are known in the art and can be installed at various points in the purification system. In one embodiment, shown in  FIGS. 1 and 3 , the Alfa laval spiral heat exchanger has a 4″ valve, temperature gauge and pressure gauge on its suction and discharge. In another embodiment, a sample point was installed at a pressure gauge (not shown in  FIG. 1 ) located between heat exchanger  14  and filter  16 . In yet another embodiment, a 4″ turbine style flow meter mounted on the top of a valve is utilized between heat exchanger  14  and filter  16 . A suitable flow meter is a EZ-IN® Series BF flowmeter from NuFlo Measurements Systems (Houston, Tex.), and has the following characteristics: flowmeter size—2 inch; linear flow range 40-400 GPM (9.09-90.85 m 3 /h); Nom. Calibration factor—55 pulses/gallon (14.5 pulses×1000/m 3 ) ; maximum output frequence—365 pulses/sec.  
      Referring to  FIG. 1 , from heat exchanger  14 , impure oil is directed to filter  16  and is filtered before entering the disk stack centrifuge  12 . The oil can be heated before or after filtration. In another embodiment, impure oil is directed to a filter that is located before heat exchanger  14 . Thus when filtering is conducted, it takes place before impure oil enters the centrifuge.  
      In general, a filter that can be used with the present invention is one that can remove particles having a size of about 80 microns or greater (e.g., about 90 microns, about 100 microns, 110 microns). The filter to be used with the present invention removes particles in a range preferably between about 60 microns and about 100 microns. In one application of the invention, an 80 micron filter was used. Types of filters that can be used with the present invention include, but are not limited to, Basket filters, or Pot filters. Such filters should have a sturdy screen that separates particles about 80 microns or greater. Companies from which one can obtain filters include, e.g., puraDYN Filter Technologies Inc. (Boynton Beach, Fla.), and Grotto Filters (Mumbai, INDIA). Filters now known or developed in the future can be used with the present invention so long as they filter particles of the range described herein.  
      From filter  16 , filtered petroleum is directed to disk stack centrifuge  12 . A disk stack centrifuge is used in the present invention to purify oil at high rates of speed. An impure oil, having an impurity content, inorganic material content, ash content of greater than 0.1% is subjected to a disk stack centrifuge (e.g., one or more disk stack centrifuges). Subjecting the impure oil to a disk stack centrifuge refers to allowing the oil to entering the centrifuge, e.g., providing piping and pumps to allow the oil to supply the centrifuge from the tank at the proper rate.  
      Generally, a disk stack centrifuge separates solids from one or more liquid phases using high centrifugal forces. When subject to centrifugal forces, the denser solid particles are pressed outwards against the rotating bowl wall, while the less dense liquid phases form concentric inner layers. The disk stack plates provide additional surface settling area which contributes to the separation process.  
      A disk stack centrifuge is a centrifuge that has a set of conical disks that spin in a circular motion to separate solids and liquid in the feed (e.g., influent), the product entering the centrifuge. As the conical disks spin, the less dense oil moves upwards and out of the centrifuge through an inlet pipe at the conical tip. This less dense oil that moves through the conical tip is referred to as the “centrate” or as the “purified oil.” The phrase, “purified oil,” is used herein to refer to an oil that has less of one or more impurities (e.g., ash), as compared to the respective impurity prior to centrifugation. Put in another way, purified oil is an oil that is cleaner or purer (i.e., having been separated from one or more impurities) than it was prior to being subjected to the steps of the present invention. In particular, purified oil has an impurity content, an inorganic materials content and/or ash content of less than about 0.3% by weight (e.g., in a range between about 0.01% and about 0.3% by weight, and preferably between about 0.05% and about 0.15% by weight). The purified oil, in another embodiment, can have an impurity content, an inorganic materials content or ash content greater than or equal to about 2 fold less (e.g., greater than about 3 fold less, about 4 fold less, about 5 fold less, about 6 fold less, about 7 fold less, etc.) than the respective content of the impure oil. The content of the purified oil is preferably in a range of between about 2 fold and about 7.5 fold less than that of the impure oil. The feed, in the Exemplification Section, had an ash content of about 0.46%, and after centrifugation with a nozzle centrifuge, the purified oil had an ash content of about 0.09%.  
      One factor that can impact the impurity content of the purified oil is the impurity content of the impure oil, or the feed oil. A feed oil having a greater amount of impurities can result in a purified oil having more impurities, than one that resulted from a feed oil having an impurity content in lower in the range described herein. For example, an impure oil having an impurity content of about 0.6% by weight could result in a purified oil having an impurity content of about 0.25% by weight, whereas subjecting an impure oil having an impurity content of about 0.2% by weight to the present invention can result in a purified oil having an impurity content, for example, of about 0.08% by weight.  
      Several types of disk stack centrifuges can be used with the present invention. A preferred disk stack centrifuge used with the present invention is referred to as a “nozzle centrifuge” or “disk type nozzle centrifuge”, and these phrases are used herein interchangeably. A disk type nozzle centrifuge is a disk stack centrifuge with a nozzle attached for the excretion of the slurry, the denser excreted product, as described with reference to  FIG. 2 , which shows a cross-sectional view of the nozzle centrifuge.  
      As shown in  FIG. 2 , the feed containing the liquid and the solids are introduced to the rotating centrifuge bowl from the top via a stationary inlet pipe  50 , and is accelerated in the distributor  52  before entering the disc stack  54 . It is between the discs that the separation takes place. The liquid phase moves through the disc stack  54  towards the center of the bowl, from where it is discharged over a power-ring  56 . The heavier solids phase is collected at the bowl periphery, from where it is continuously discharged through the nozzles  58 . Filler pieces  60  can be used to help avoid build-up of the sludge between the nozzles  58 . A portion of the concentrated solids discharged through the nozzles  58 , can be recirculated into the bowl again through the recirculation inlet pipe  62 , a separate distributor  64  and recirculation tubes  66 . The bowl can be mounted on a vertical spindle  68 , driven by a vertically mounted motor, via a flat belt.  
      Other examples of disk stack centrifuges that can be used with the present invention include a high speed self ejecting centrifuge, and a high speed solid bowl centrifuge. Disk stack centrifuges that are known in the art, or later developed, can be used to carry out the present invention. One can obtain disk stack centrifuges from various manufacturers such as Alfa Laval (Richmond, Va.), Centrifuge Solutions, Inc (LaPorte, Tex.), or Wesfailia (Ann Arbor, Mich.). One or more disk stack centrifuge can be used alone or in combination, and if used in combination, the same or different types of disk stack centrifuges can be used in parallel or series to increase production and/or efficiency.  
      Disk type centrifuges have traditionally been used by the dairy industry for skimming, standardization and clarification of milk and whey, by the beverage industry for the clarification of wine and juices, and by other industries for other low rate clarifications. Nozzle type disk centrifuges have been generally used for classification and dewatering of industrial clays, such as kaolin. The present invention is the first application of crude oil refinement at high rates of purification for large quantities of oil.  
      When used to carry out the steps of the present invention, in one embodiment, the disk stack centrifuge (e.g., the nozzle type centrifuge) processes an impure oil having an impurity content (e.g., an inorganic materials content or ash content) of 0.1% or greater by weight (e.g., between about 0.5% and about 0.7% by weight). The oil enters the centrifuge at a high rate, for example, between about 80 GPM to about 350 GPM (e.g., about 200 GPM). The disks or the bowl speed are moving between about 1000 RPM to about 4000 RPM, for example at about 3500 RPM, to achieve this rate and impurity content of the purified oil. In the Exemplification Section, the nozzle centrifuge had a bowl speed of about 3500 RPM, and the oil entered the centrifuge at a rate of about 200 GPM.  
      With respect to  FIG. 1 , the purified oil (e.g., the centrate) is pumped by pump  22  and cooled with heat exchanger  24  prior to entering tank  26 . The purified oil is chilled to a temperature that is suitable for storage. The oil is cooled to a temperature less than about 93° C. (less than about 200° F.), e.g., preferably to about 82° C. (about 180° F.). Cooling or chilling the purified oil involves similar variables as for heating the oil: starting temperature of the oil, the rate of oil passing through the cooling device, the size of the cooling device, and the rate of cooling released by the device. One can manipulate the variables (e.g., flow rate, starting temperature) described herein to achieve the desired temperature. Any number of cooling systems, that are known in the art or later developed, can be used to cool the oil, as described herein. Examples of heat exchangers for cooling liquid include cooling water heat exchanger, fixed tubesheet exchanger, floating head removable tubular heat exchanger, spiral heat exchanger, and plate heat exchangers. In particular, the oil, in one embodiment, is cooled with a propeller fin fan used in conjunction with a spiral cooling exchanger (Alfa Laval heat exchanger (Alfa Laval Thermal, Inc.(Richmond, Va.))) to cool the oil to about 82° C. so that it is suitable for being deposited into tank  26 . Chilling the oil can be bypassed if the oil is not going to be stored in a tank, e.g., when it is deposited directly into a pipeline. A spiral cooling exchanger is commercially available from a number of manufacturers such as API Heat transfer (Buffalo, N.Y.), Alfa Laval Thermal, Inc.(Richmond, Va.) and Calorplast Wärmetechnik GmbH (Krefeld, Germany).  
      In one aspect, heat exchanger  24  is provided with an air chiller. The chiller is a large  2  propeller fin fan setup. Water is circulated through the fins and then through the 1065 sq. ft heat exchanger  24  and back to the fins. This enables the apparatus to cool the hot disk centrate to a temperature suitable for pumping into tank  26 . The air chiller includes a fin cooler, a circulating pump, a 3″ steel pipe and 3″ tanker hoses.  
      In another embodiment, during centrifugation, the less dense oil moves through the top of the conical disks, while the more dense oil moves to the bottom of the disk centrifuge and out through the nozzle  58 . This more dense oil that exits from the centrifuge (e.g., that moves through the nozzle of a Nozzle type centrifuge) is referred to herein as the “slurry.” An embodiment of the present invention includes subjecting the slurry to a second centrifuge  28 . The slurry has an impurity content, inorganic materials content and/or ash content of greater than about 1.0% (e.g., between about 1.0% and about 6.0%). The slurry enters second centrifuge  28  at a flow rate in a range between about 10 GPM and about 150 GPM. (Shown in  FIG. 3 ) The second centrifuge is a centrifuge that separates oil having the above impurity, inorganic material and/or ash contents, and results in a centrate having about 2.5% by weight or less impurity content, inorganic materials content and/or ash content (e.g., between about 0.05% by weight and about 2.5% by weight). The oil can enter the second centrifuge at a temperature in a range between about 75° F. (24° C.) and about 275° F. (135° C.). Several types of centrifuges that are known in the art can be used to carry out this step, and can be obtained from a number manufacturers, such as Centrysis Corp. (Chicago, Ill.), H&amp;H manufacturing (Houston, Tex.), and Flottweg (Germany). One example of such a centrifuge includes the decanter centrifuge. Centrifuges that are known or later developed can also be used to carry out this step so long as the second centrifuge can separate oil having the impurity content, inorganic materials content or ash content described above, and result in a centrate having about 2.5% by weight or less (e.g., about 2.1% by weight less) impurity content, inorganic materials content, and/or ash content. In a particular embodiment, a decanter centrifuge was used to carry out this step, as further described herein. In an example, the influent of the decanter centrifuge had an ash content of about 1.5% by weight, and a centrate of about 0.6% by weight.  
      Table 3 is one example of an impurity breakdown of oil after being processed by a decanter centrifuge:  
                           TABLE 3                                   Impurity   Amount                          Ash   0.12% weight*           Aluminum,   215 PPM (.0215% weight*)           MDL = 1           Silicon,   328 PPM (.0328% weight*)           MDL = 1                         *Percent by weight = weight of impurity/weight of total volume of oil × 100%             
 
      The centrate (e.g., petroleum product) is then circulated or recycled so that it is subjected to disk stack centrifuge  12 . Piping, pumps and/or tanks are arranged to get the oil to disk stack centrifuge  12 . See  FIGS. 3 and 5 , further discussed below, for examples of this arrangement. This process can be repeated several times until the desired impurity content, inorganic materials content or ash content is achieved.  
      In particular,  FIG. 3  shows another embodiment of the present invention that involves recycling the slurry from disk stack centrifuge  12 . In this embodiment, the feed (e.g., the impure oil) comes from the side of tank  10  at the 4′ level (4′ off the ground). The conduits (piping) for directing the feed from tank  10  to other elements of the system shown in  FIG. 3  are provided with valves and gauges (e.g., pressure or temperature gauges) as known in the art. For simplicity, theses valves and gauges are not specifically shown in the figures. For example, the conduit connecting tank  10  with pump  20  is provided with a 6″ shell valve and then a 4″ line valve (4″ diameter). After the 4″ valve there is a pressure 1″ blow down and temperature gauge (not shown) before the line drops to pump  20 . Feed then flows through a 4″ valve on the discharge of pump  20 , past a temperature gauge and into heat exchanger  14 . From heat exchanger  14 , the feed goes through filter  16 , past another pressure gauge, and is fed to disk stack centrifuge  12  through a ¼ turn 4″ valve. If the feed needs to bypass disk stack centrifuge  12  then it flows through a 4″¼ turn valve mounted in the bypass system to a point between pump  22  and a 4″ block valve on second holding tank  18  suction.  
      Sample maximum flow conditions for the system set-up shown in  FIG. 3  can be found in  FIG. 4 . The flow conditions from the figure include those for the feed, centrate, recycled oil, wash liquid (e.g., cutter stock) and concentrate (e.g., slurry) from the disk stack centrifuge for one embodiment of the invention.  
      The feed is separated in disk stack centrifuge  12  into 2 phases: purified oil (centrate) and solids laden oil (slurry). The centrate is discharged to second holding tank  18  via an 8″ dump line from disk stack centrifuge  12 &#39;s housing. The centrate leaves holding second holding tank  18  passes a temperature gauge (not shown), through a 4″ valve to pump  22  (e.g., a 4″ Blackmere paddle variable drive pump). The centrate then passes a temperature gauge (not shown), 4″ block valve, another temperature gauge (not shown), a sample point (not shown in  FIG. 3 ) and is pumped through a heat exchanger  24  preferably coupled with an air chiller, as known in the art. The centrate then flows past a 4″ block valve, sample point (not shown in  FIG. 3 ), a 4″ valve at the bypass header, two more 4″ block valves, additional pressure and temperature gauge (not shown) prior to the 4″ block valve and 4″ check valve at tank  26 . If the material is off specification (e.g., has an impurity content, inorganic materials content or ash content more than desired amount), then it can be diverted into the bypass and flow back to tank  10  past a pressure and temperature gauge, a 4″ valve and a 6″ valve at tank  10 .  
      In one aspect, the piping used for the present invention can be 4″ schedule  40  steel, welded flanges,at all connections, steam traced with ½″ copper, Watson McDaniel steam traps, and rock wool insulation that is metal wrapped.  
      The slurry from disk stack centrifuge  12  can optionally be recirculated back to disk stack centrifuge  12 , to second centrifuge  28 , as described herein, and/or to fractionation (FRAC) tank  32  or  33 , if necessary. The direction of the slurry depends on a number of factors, and can be determined by an operator, automated system, or computerized system. These factors include the temperature of the slurry, the impurity content, inorganic content or ash content of the slurry, the rate of the slurry, the rate of processing of the a centrifuge, etc.  
      In one aspect, and with respect to  FIG. 3 , slurry in first holding tank  17  passes out through a 4″ valve, temperature gauge (not shown) and into pump  48 , a variable drive mono pump. Pump  48  pushes the slurry down a 4″ insulated steel line to either the mix tank  34 , first FRAC tank  32  or second FRAC tank  33 . The distinction is made by the operator, or by an automated or computerized system, and is facilitated by to 4″ valves on the discharge manifold of the mono pump. The disk centrate can be by-passed to tank  10 . Injection point at tank  10  is 12″ from the floor and is considered a sump line. Centrate can also be pumped by pump  22  to first cutter tank  37  via a 2″ line from P 2  to the top of-first cutter tank  37 .  
      Prior to entering second centrifuge  28 , the slurry can optionally be mixed by one or more mixers. Mix tank  34  can be insulated and equipped with heating coils. In one example, the slurry was mixed by three vertical mixers prior to entering second centrifuge  28 . A variety of mixers can be used, are commercially available and are known in the art.  FIG. 3  shows a system where slurry in mix tank  34  is mixed with 3 vertical mixers and held for solids removal in a second centrifuge, a horizontal decanter centrifuge  28 . The mix tank  34  is e.g., a 400 bbl. insulated tank with 3 mixers and a dual set of heating coils.  
      In an embodiment, slurry is pulled from mix tank  34  through a 4″ insulated and steam traced line, past a 4″ block valve and into a variable speed mono pump, pump  44 . Slurry is pumped through a 2″ line past a ball style block valve to the feed tube in second centrifuge  28 . Slurry that is stored in FRAC tank  32  or  33  is pulled through 4″ insulated and steam traced lines pump  46 , a mono pump, into the mix tank  34  for processing.  
      Second centrifuge  28 , in one example, is a horizontal decanter centrifuge. The machine separates the solids from the oil. The oil (centrate) gravity flows to a 4000 gallon receiver tank mounted below the centrifuge stand. The centrate then travels through a 4″ tar hose to a 4″ pump  42 . The fluid then passes through 4″ block valve, blow down, temperature and pressure gauge and continues down a 4″ insulated and steam traced line to the bypass line and into Tank  10 . There is a 4″ block and 6″ block valve at the base of Tank  10 . In one example, using the decanter centrifuge, the influent had an ash content of about 1.5% by weight, and the centrate had an ash content of about 0.6% by weight. Solids are gravity dropped into a roll off container, solids box  30 , and disposed of at an approved location.  
      Lubricant oil, commonly referred to as cutter stock, generally is a light end oil. Cutter stock is added, in some embodiments, where necessary to thin out the feed entering the centrifuge or recirculating line to prevent clogging. This is an optional step. In one example, the cutter stock is stored in cutter tanks  37  and  38  that are connected to the feed line, as shown in  FIG. 3 .  
      In one example, cutter and flush oil is pumped from the front of first cutter tank  37  by a 3×2 pump past a pressure gauge, through 1½″ duplex strainer, through a 2″ insulated line, through a 2″¼ turn ball valve and into the disk feed line after the 4″¼ turn valve. This line has a 2″ turbine flow meter. Flush oil, also referred to as “heavy cycle oil,” “PGO” or “light cycle oil,” and is generally used to clean or “flush” out debris after use. Whereas, cutter oil, referred to as “diesel oil” or “heating oil,” is used to thin out the oil or feed. Cutter oil can be used herein to dilute the oil so that the impurity content is in the described range.  
      In one embodiment shown in  FIG. 5 , the oil present in the tank  10  is pumped by pump  20  to a heat exchanger  14  where the oil is heated with steam from steam boiler  13 . The oil then moves to filter  16  and then to disk stack centrifuge  12 . Once processed by the centrifuge  12 , the oil can take at least two different paths. It can go to second holding tank  18 , and then pump  22  directs the oil to heat exchanger  24  where it is chilled with air chiller  23  before entering tank  10 . Alternatively, the oil can move to FRAC Tank  32 , where it can then be recirculated. Specifically, oil is directed from FRAC Tank  32  to disk stack centrifuge  12  and then follows the pathway described above. The vapor phase is exhausted from FRAC Tank  32  as known in the art.  
      A description of preferred embodiments of the invention follows.  
      Exemplification  
      Purification of Crude Oil  
      The apparatus for purifying oil, as depicted in  FIG. 3 , was used to purify impure oil. The impure oil, after being clarified by a catalyst-cracked process, was pumped from tank  10  at a rate of about 200 GPM (between about 180 and 250 GPM) with pump  20 . Pump  20  is a SP Series Disc Pump from Discflow (Disc Flo Corporation, Santee, Calif.). The impure oil having an initial temperature in tank  10  of about 180° F. (82.2° C.) was heated with heat exchanger  14  (Alfa Laval Type I, II or III heat exchanger (Alfa Laval Thermal, Inc.(Richmond, Va.))) to about 220° F. (104.4° C.) and filtered with filter  16 , an 80 micron filter (model #: Velcon Model VC 4854003). The heat was generated with a steam boiler. The oil was then subjected to a nozzle centrifuge (Nozzle centrifuge, Alfa Laval Thermal, Inc.(Richmond, Va.), type CHQX 320B-31CGR). The bowl speed of the nozzle centrifuge was about 3500 RPM (between 3000 and about 3700 RPM). The centrate from the nozzle centrifuge was pumped with pump  22  (Blackmere paddle pump model No: NP4F, E.I. by DuPont Wilmington, Del.) and then chilled to temperature in a range between about 180° F. and about 200° F. with heat exchanger  24  (Alfa Laval Type I, II or III heat exchanger (Alfa Laval Thermal, Inc.(Richmond, Va.))), and then deposited into tank  26 .  
      Table 4 below shows the impurity content of the impure oil prior to being subjected to the above process, and the impurity content of the purified oil after undergoing the above process.  
                       TABLE 4                       Impurity   Amount of Impure Oil   Amount of Purified Oil                  Ash   0.46% weight*   0.09% weight*       Aluminum,   858 PPM** (.0858%   165 PPM** (.0165%       MDL = 1   weight*)   weight*)       Silicon,   1304 PPM** (.1304%   248 PPM** (.0248%       MDL = 1   weight*)   weight*)                 *Percent by weight = weight of impurity/weight of total volume of oil × 100%            **1% by weight = 10,000 PPM.             
 
      At certain points, as determined by the operator, the slurry was directed to mix tank  34 , Frac Tanks  32  or  33 , and/or to second centrifuge  30 . The second centrifuge used in this instance was a horizontal decanter centrifuge. Once processed, the centrate from the decanter centrifuge was recirculated back to tank  10 . The impurity content and ash content of the centrate from the decanter centrifuge can be seen in Table 3 infra. At other times, the centrate from disk stack centrifuge  12  was directly recirculated back to centrifuge  12  for further processing before being moved to tank  26 .  
      Specifications of the Nozzle Centrifuge:  
      All liquid-welded parts are made in high-grade stainless steel except the nozzles  58  (tungsten carbide), rubber gaskets (nitrite), O rings, PTFE coated Viton, and filler pieces (polyamide  12 , filled). A special controlled-torque motor eliminates the need for a clutch between the motor and the centrifuge  12 . The spindle  68  is mounted in a cartridge which contains bearings, a lubrication oil bath, an integrated oil pump and an oil clarifier. Disk centrifuge  12  is equipped with sensors for monitoring of bowl speed, vibration level and lubrication oil pressure. The  18  nozzles  58  are tangentially placed in the periphery in order to recover energy from the discharged nozzle flow. The power-rings  56  for the liquid phase discharge are also designed for maximum recovery of energy.  
      Technical Specification:  
                                                          Max. throughput capacity   200   m 3 /h 1)             Max. solids-handling capacity   72   m 3 /h 2)             Feed temperature range   0-100°   C.           Feed inlet pressure required   240   kPa 3)             Installed motor power   135   kW           Noise level (ISO 3744 or 3746)   79   dB(A)                      
          1) Actual throughput capacity depends on particle sizes, densities, viscosity and required degree of separation.     2) Wet solids.     3) Actual pressure depends on throughput, density and viscosity. The above refers to 200 m 3 /h of water. 
 
 Due to the process running at 250° F., and water will boil off at 220° F., all flush and safety fluids are of a light oil consistency (e.g., motor oil or hydraulic oil). 
       

      Utilities Consumption &amp; Dimension  
                                                  Utilities consumption &amp; dimension                                 Electric power   70-130   kW 1)             Sealing water   90   dm 3 /h           Safety water   22-80   m 3 /h 2)             Centrifuge with bowl and motor           Net weight:   4100   kg           Gross weight:   4400   kg           Volume:   8   m 3                        
          1) Actual consumption depends on throughput, nozzle flow and back pressure.        

      The above refers to throughput from 100-200 m 3 /h including a nozzle flow of 20-72 m 3 /h. 
          2) The bowl should be filled with liquid at start, stop and normal operation. In case process liquid is not available, safety water should be used. Minimum flow shall be above nozzle flow. The above refers to nozzle sizes from 1.6 to 3.00 mm.        

      The relevant teachings of all references, journal articles, patents and/or patent applications cited herein are incorporated herein by reference in their entirety.  
      While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.