PATENT ABSTRACT
A modular apparatus having certain processing equipment mounted on portable skids that are adaptable and versatile to permit customized arrangement for oil-recovery processing of a wide range of oil-base sludge compositions in a cost-efficient manner. In one aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a high concentration of low density solids, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a chemical skid, a phase separator skid, a gas purification skid, a decanter skid, and an oil purification skid. In another aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a high concentration of high density solids, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a first chemical skid, a decanter skid, a second chemical skid, a phase separator skid, a gas purification skid, and an oil purification skid. In still another aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a very low solids content, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a chemical skid, a phase separator skid, a gas purification skid, and an oil purification skid.

PATENT DESCRIPTION
BACKGROUND OF INVENTION 
       [0001]    Oil-based sludges of various types and consistencies are commonly generated as waste streams during oil or other hydrocarbon production processes. These sludges arise during well tests and initial production, as a by-product waste stream of hydrocarbon production, and as tank bottom sediments. The basic components of sludges are hydrocarbon oils of various consistencies, water, and solids of an inorganic and organic nature. Oil-based sludge typically refers to a complex water-in-oil emulsion stabilized by salts of organic compounds and fine solids. The oil phase contains a complex mixture of hydrocarbons of various consistencies including waxes and asphaltenes which may be solid or semi-solid at ambient temperature. 
         [0002]    The chemistries of oil-based sludges and the relative proportions of the oil, water, and solid phases of sludges vary greatly and can change over time. To dispose of the waste, sludge is often stored in open pits where it may be left for considerable time before being treated. During such aging periods, the sludge or “pit sludge” undergoes overall chemical composition changes due to the effects of weathering, including: volatilization of lighter hydrocarbons; temperature induced crosslinking of hydrocarbons; addition of rain water; and, invariably, the introduction of a variety of other contaminants, particulates, and debris. In addition to a variable complex chemistry, oil-based sludge typically has a high solids content. Sludge solids normally include both high density and low density solids. High density solids, i.e., high gravity solids, may be large solids introduced into the drilling fluid during the drilling of a formation (e.g. formation solids, drill bits, etc.) or other solids that are relatively dense such as barite or hermatite. While low density solids, i.e., low gravity solids, are those solids within the sludge that have a lower density or are relatively small fine solids (e.g., entrained solids such as sand). 
         [0003]    Currently, treatment of sludge is a major operational cost for producers. Sludge is collected, stored, and then disposed of in tanks or delivered to a sludge pit. One challenge of sludge treating systems is that the recovery of marketable oil from the sludge is generally not cost-effective and thus not commercially viable. Due to wide variability in sludge composition, different sludge processing systems may be needed to optimize the processing of sludge for recovering oil of sufficient quality in a cost efficient manner. The quality of oil is frequently characterized by its Basic Sediment and Water (BS&amp;W) content, in vol. %. The current marketable BS&amp;W of recovered oil is less than about 2 vol. %. Furthermore, it is desirable to treat pit sludge to reduce the risk of contamination of the surrounding pit area, in accordance with increasingly strict environmental regulations, as well as decrease the overall waste volume, and ultimately to permit pit closure. 
       SUMMARY 
       [0004]    The present invention is generally directed to a modular oil-based sludge separation and treatment apparatus that is easily adapted to provide processing flexibility in order to ensure quality oil recovery from oil-based sludge in an efficient and cost-effective manner. The modular approach allows the configuration of processing equipment to be adapted to the oil-recovery processing requirements of the particular oil-based sludge composition. Providing a customizable apparatus maximizes the quantity and quality of the recovered oil while minimizing the processing time and cost to the operator. 
         [0005]    It is an objective of the present invention to provide a modular apparatus having certain processing equipment mounted on portable skids that are adaptable and versatile to permit customized arrangement for oil-recovery processing of a wide range of oil-base sludge compositions in a cost-efficient manner. 
         [0006]    In one aspect, the invention is directed to a modular apparatus for recovering oil from oil-based sludge having a high concentration of low density solids. The modular apparatus includes: a pumping skid having a pump operable to homogenize an oil-based sludge; a shaker skid having a screen that removes particulates from the oil-based sludge as the sludge traverses the screen to form a debris-free sludge; a heating skid shaving a heat exchanger operable to heat the debris-free sludge as: the debris-free sludge flows through the heat exchanger to form a heated sludge; a chemical skid having at least one chemical injection mixer operable to inject a chemical into the heated sludge and mix the chemical with the heated sludge to form a chemically-treated sludge; a phase separator skid having a three-phase separator operable to separate the phases of the chemically-treated sludge to form a first solids component stream, a first water component stream, a first oil component stream, and a first gas component stream; a decanter skid having a decanter centrifuge operable to remove solids from the first oil component stream to form a second solids component stream and a second oil component stream; and an oil purification skid having a disk stack centrifuge operable to remove water and solids from the second oil component stream to form a third solids component stream, a second water component stream, and a third oil component stream. 
         [0007]    In another aspect, the invention is directed to a modular apparatus for recovering oil from oil-based sludge having a high concentration of high density solids. The modular apparatus includes: a pumping skid: having a pump operable to homogenize an oil-based sludge; a shaker skid having a screen that removes particulates from the oil-based sludge as the sludge traverses the screen to form a debris-free sludge, a heating skid having a heat exchanger operable to heat the debris-free sludge as the debris-free sludge flows through the heat exchanger to form a heated sludge; a first chemical skid having at least one chemical injection mixer operable to inject a chemical into the heated sludge and mix the chemical with the heated sludge to form a first chemically-treated sludge: a decanter skid having a decanter centrifuge operable to remove solids from the first chemically-treated sludge to form a first solids component stream and a decanter-processed sludge; a second chemical skid having at least one chemical injection mixer operable to inject a chemical into the decanter-processed sludge and mix the chemical with the decanter-processed sludge to form a second chemically-treated sludge; a phase separator skid having a three-phase separator operable to separate the phases of the second chemically-treated sludge to form a second solids component stream, a first water component stream, a first oil component stream, and a first gas component stream; and an oil purification skid having a disk stack centrifuge operable to remove water and solids from the first oil component stream to form a third solids component stream, a second water component stream, and a second oil component stream. 
         [0008]    In still another aspect, the invention is directed to a modular apparatus for recovering oil from oil-based sludge having very low solids content. The modular apparatus includes: a pumping skid having a pump operable to homogenize an oil-based sludge; a shaker skid having a screen that removes particulates from the oil-based sludge as the sludge traverses the screen to form a debris-free sludge; a heating skid having a heat exchanger operable to heat the debris-free sludge as the debris-fee sludge flows through the heat exchanger to form a heated sludge; a chemical skid having at least one chemical injection mixer operable to inject a chemical into the heated sludge and mix the chemical with the heated sludge to form a chemically-treated sludge; a phase separator skid having a three-phase separator operable to separate the phases of the chemically-treated sludge to form a first solids component stream, a first water component stream, a first oil component stream, and a first gas component stream; and an oil purification skid having a disk stack centrifuge operable to remove water and solids from the first oil component stream to form a second solids component stream, a second water component stream, and a second oil component stream. 
         [0009]    These and other features are more fully set forth in the following description of preferred or illustrative embodiments of the disclosed and claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1  is a flow chart depicting a modular skid arrangement optimized for recovering the valuable hydrocarbon component of pit sludge having a high concentration of low density solids, according to an embodiment of the invention; 
           [0012]      FIG. 2  is a flow chart depicting another modular skid arrangement optimized for recovering the valuable hydrocarbon component of pit sludge having a high concentration of high density solids, according to another embodiment of the invention; 
           [0013]      FIG. 3  is a flow chart depicting still another modular skid arrangement optimized for recovering the valuable hydrocarbon component of pit sludge having very low solids content, according to still another embodiment of the invention; 
           [0014]      FIGS. 4 and 5  are schematics of an exemplary modular apparatus for separating and treating an oil-base sludge having a high concentration of low density solids to recover the valuable hydrocarbon component, in accordance with the skid arrangement shown in  FIG. 1 ; 
           [0015]      FIGS. 4 and 6  are schematics of an exemplary modular apparatus for separating and treating an oil-base sludge having a high concentration of high density solids to recover the valuable hydrocarbon component, in accordance with the skid arrangement shown in  FIG. 2 ; and 
           [0016]      FIGS. 4 and 7  are schematics of an exemplary modular apparatus for separating and treating an oil-base sludge having very low solids content to recover the valuable hydrocarbon component, in accordance with the skid arrangement shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The claimed subject matter relates to a modular apparatus having one of several skid arrangements depicted in  FIGS. 1-3  for recovering the valuable hydrocarbon component of oil-based sludges having a wide variability in sludge composition. Depending upon the particular sludge composition and its solids content, the skid arrangements of the modular apparatus of the present invention may be easily configured, and re-configured, in order to optimize the separation and purification of the recovered oil while minimizing the time and cost to an operator. 
         [0018]    According to an embodiment of the invention,  FIG. 1  depicts the skid arrangement: of a modular apparatus  100  optimally configured for recovering the valuable hydrocarbon component of sludge  14  initially having a high concentration of low density solids, Modular apparatus  100  comprises a pumping skid  102 , a shaker skid  104 , a heating skid  106 , a chemical skid  108 , a phase separator skid  110 , a gas purification skid  112 , a decanter skid  114 , and an oil purification skid  116 . Each of the skids  102 - 116  are described in more detail in the description that follows with respect to the modular apparatus  100  schematically illustrated in  FIGS. 4 and 5 . 
         [0019]    As illustrated in  FIGS. 4 and 5S  modular apparatus  100  processes pit sludge through the pumping skid  102 , the shaker skid  104 , the heating skid  106 , the chemical skid  108 , the phase separator skid  110 , the gas purification skid  112  the decanter skid  114 , and the oil purification skid  116 . Referring to  FIG. 4 , the pumping skid  102  includes a hydraulic submersible sludge pump  122  that homogenizes a pit sludge  10  contained in a pit  12  and then pumps a homogenized sludge  14  to the shaker skid  104 . The pump  122  may be mounted on a hydraulic arm in order to reach inner areas of the pit  12 . During ageing, the pit sludge  10  separates into basically three layers or phases, wherein the top layer of the pit is an oil-rich phase, the middle layer of the pit sludge  10  is a water-rich phase, and the bottom layer of the pit sludge  10  is a solids-rich phase. The pump  122  forms a homogeneous mixture or slurry of the three phases contained within the pit in order to provide a generally constant feed composition to the remainder of the apparatus  100  for processing. 
         [0020]    The shaker skid  104  includes a shaker screen  124  and a holding tank  126  mounted thereon and within the confines of the area in the skid  104  so as to maintain portability of the skid  104 . The shaker screen  124  physically separates and removes large particulates such as stones or debris from the sludge  14 . A debris-free sludge  16  exiting the shaker screen  124  collects in the holding tank  126 . Holding tank  126  may be essentially any type of tank that can contain a sufficient amount of sludge to supply and maintain a constant sludge flow rate to a heat exchanger  130 . A first transfer pump  128  in fluid communication with the holding tank  126  transfers the sludge  16  from the holding tank  126  to the heating skid  106 . In a preferred embodiment, the holding tank  126  is an augured V-Tank coupled to the pump  128  which is VFD (variable frequency driver) controlled in order to automatically provide a steady state flow rate of the sludge  16  to the heat exchanger  130 . 
         [0021]    The heating skid  106  has the heat exchanger  130 , a steam boiler  132 , and a fuel tank  134  mounted thereon and within the confines of the area of the skid  106  so as to maintain the portability of the skid  106 . Sludge  16  is heated to a desired temperature as it travels through the heat exchanger  130 . Because oil-based sludges often include waxy hydrocarbons, heating advantageously melts the waxy hydrocarbons into liquid form and lowers the viscosity of the sludge  16 . Also, heating advantageously aids in breaking the emulsion (secondary phase) and promotes phase separation within the sludge  16 . Providing heat to the heat exchanger  130  is accomplished by use of the steam boiler  132 . The steam boiler  132  generates steam and circulates the steam to the heat exchanger  130  via a first steam line  136  and a second steam line  138 . The flow rate, pressure, and temperature of the steam entering the heat exchanger  130  via line  136  are controlled so as to provide adequate heat transfer to the sludge  16  as it flows through the heat exchanger  130 . A heated sludge  18 , having the desired temperature and viscosity, exits the heat exchanger  130  and is subsequently transferred to the chemical skid  108 . In one example, the type of heat exchanger  130  used is a spiral type heat exchanger, wherein sludge  16  flows through the heat exchanger  130  in a path separate from that of the steam, but adjacent to it such that heat from the steam is transferred to the sludge  16 . It is understood that other types of heat exchangers can be used without departing from the scope of this invention. 
         [0022]    Depending upon the particular sludge composition, the sludge  16  is heated to essentially any temperature sufficient to liquefy the sludge  16  and lower its viscosity. When the viscosity is lower, treatment chemicals may be more easily blended with the heated sludge  18  in downstream processing. Furthermore, when the sludge viscosity is lower, entrained solids are more easily released in downstream processing. The desired temperature of the heated sludge  18  and its corresponding rheological profile can be predetermined and optimized using a viscometer, such as an oilfield Fann  35  viscometer available from Fann Instrument Co. In one example, sludge  18  is heated to a temperature in the range from about 65° C. to about 85° C. to sufficiently liquefy the sludge  18  and reduce its viscosity for downstream processing. More preferably, sludge  18  is heated to a temperature in the range from about 70° C. to about 80° C. Although it is desirable to heat the sludge  16 , care should be taken to ensure that the temperature of the heated sludge  18  is lower than the flash point temperature of the sludge  16 . The flash point is that minimum temperature at which there is enough evaporated fuel in the air to start combustion. The flash point of the sludge  16  can be determined by the use of a flash-point measuring device such as the Pensky Martens Closed Cup according to method ASTM D93B. 
         [0023]    Preferably, the fuel tank  134  is co-located on the skid  106  to provide fuel to the steam boiler  132  for heating the steam. Optionally, a power supply (not shown) is provided on the skid  106  to actuate valves (not shown) that regulate the flow rate of the steam through the first and second steam lines  136 ,  138 , and also regulate the flow rates of the water supply and the fuel provided to the steam boiler  132 . A control panel (not shown) may be co-located on the skid  106  to monitor and automatically control the valves in order to automate the heating process at the heat exchanger  130 . In addition, the boiler  132 , flow lines  136 ,  138 , and heat exchanger  130  are preferably thermally insulated to better maintain temperature uniformity and control. 
         [0024]    Once heated, the sludge  18  is transferred to a chemical skid  108  for chemically altering the sludge  18  to break up the emulsion and promote phase separation. The chemical skid  108  includes a plurality of chemical injection mixers  140   a - d  and chemical supply tanks  142   a - d  mounted thereon and within the confines of the area of the skid  108  so as to maintain the portability of the skid  108 . Chemical addition is typically required to destabilize the emulsion and change such properties to enhance separation of the water and solids from the sludge  18 , as well as decrease the separation: time required. Each of the chemical injection mixers  140   a - d  includes a static shear mixer having an injection point. The injection point introduces a chemical into the sludge  18  while the mixer simultaneously blends the chemical and the sludge  18  under the shearing action of the mixer. The chemical injection mixer advantageously provides a homogeneous distribution of the chemical within the sludge  18  to aid in its complete and efficient chemical reaction therein. As depicted in  FIG. 5 , four chemicals are added to the heated sludge  18  as the sludge is directed through the chemical injection mixers  140   a - d . Each of the chemical injection mixers  140   a - d  has a corresponding chemical supply tank  142   a - d  for storing the chemicals until they are transferred via chemical lines  144   a - d  to the mixers  140   a - d  for injection into the sludge  18 . Once all the chemicals are introduced and blended into the heated sludge  18 , a chemically-treated sludge  20  exits the last chemical injection mixer  140   d  and is subsequently transferred to the phase separator skid  110  for further processing. 
         [0025]    Depending upon the particular initial sludge  14  composition, a wide variety of chemicals, may be introduced and blended into the sludge  18  in order facilitate subsequent processing to separate the solid, water, and oil phases of the chemically treated sludge  20 . Suitable chemicals include acids, demulsifiers, wetting agents, surfactants, flocculants, and defoamers. Demulsifiers modify the interfacial tension of the emulsion film to release the water and assist in separating out the water from the oil. Wetting agents alter the wetability of solid particles thereby causing the solid particles to become hydrophilic which increases the solids affinity for water and causes further breakup of the interfacial emulsion film. Flocculants induce the solids to aggregate and form larger solids to facilitate separation of the solids in the sludge. In one example, as the heated sludge  18  travels through the first injection mixer  140   a , the mixer  140   a  injects an acid and blends the acid with the sludge  18  therein in order to neutralize adsorbed ions present at the interfacial emulsion film of the sludge  18  and chemically prepare the sludge  18  for chemical treatment with a demulsifier. Subsequently, the sludge  18  is directed through the second injection mixer  140   b  wherein a demulsifier is injected and blended into the sludge  18  to break the interfacial emulsion film for release of the secondary water phase. The sludge  18  then passes through the third injection mixer  140   c  wherein a wetting agent is injected and blended into the sludge to alter the affinity of the solids towards the water phase. Afterwards, the sludge  18  passes through the fourth injection mixer  140   d  wherein a defoamer is injected and blended into the sludge for the purpose of counteracting surfactants (detergents) present in the sludge that may otherwise undesirably cause foaming. After chemical treatment in injection mixers  140   a - d , a chemically-treated sludge  20  exits the chemical skid  108  and is ready for subsequent processing. It should be noted that the present invention is not intended to be limited to the use of any particular chemicals, and other chemicals may be substituted for any of the aforementioned chemicals. 
         [0026]    Furthermore, additional chemicals may be incorporated into the sludge  18  by providing additional injection mixers (e.g.,  140   e - n ) on the skid  108  such that all the desired chemicals may be introduced into the sludge. For example, a fifth injection mixer (not shown) may be included on skid  108  to introduce a pour point suppressant into the sludge  18  in order to extend the fluidity of the sludge to lower temperatures. Because wax in the sludge can cause issues for pumping and phase separation in terms of the high viscosity it imparts and coating of entrained solids, pour point suppressants can be added to depress the temperature at which wax molecules in the oil phase of the sludge  18  solidify, Conversely, in another example, fewer chemicals may be incorporated into the sludge  18  by bypassing one or more of the injection mixers  140   a - d  or, alternatively, removing one of more of the mixers  140   a - d  from the skid  108 . 
         [0027]    Preferably at least one dosing pump (not shown) in fluid communication with each of the chemical injection mixers  140   a - d  is used to provide a predetermined quantity of chemical to the injection point of the mixer for introduction into the sludge  18 . The quantity of each of the chemicals introduced into the sludge  18  depends upon the particular initial sludge composition  14 . For example, a dosing pump in fluid communication with the second injection mixer  140   b  provides demulsifier in the predetermined amount of 2-3% by volume of sludge  18 . Although essentially any type of dosing pump may be used, in one example each of the dosing pumps is a gear pump with a VFD control panel. In addition, preferably, the chemical injection mixers  140   a - d  are thermally insulated to better maintain the sludge temperature and fluidity. 
         [0028]    After chemical treatment, the sludge  20  is directed to the phase separator skid  110  for separating the solid, water, oil, and gas phases of the sludge  20 . The phase separator skid  110  includes a surge tank  146  and a three-phase separator  148  mounted thereon and within the confines of the area of the skid  110  so as to maintain the portability of the skid  110 . The sludge  20  is fed into the vertically-oriented surge tank  146  which separates heavier solids from the sludge  20  and provides a continuous flow of a liquid portion of the sludge  22  to the three-phase separator  148 . The surge tank  146  contains an interior plate that facilitates the small solids (e.g., solids in suspension) within the sludge  20  to aggregate and form larger solids such that gravity is sufficient to separate these heavier solids out of the sludge  20 . Separated solids  24  that settle and accumulate in a bottom region of the surge tank  146  are discharged and directed to a solids receiving tank  150 . The liquid portion of the sludge  22 , which comprises oil, water, gas, and fine solids, is directed to the three-phase separator  148 . 
         [0029]    The liquid portion of the sludge  22  flows into the three-phase separator  148  through an inlet located at one end of the separator  148 . The separator  148  is designed to separate the phases and flow the separated phases to their respective outlets. Within the retention section of the three-phase separator  148 , the liquid portion of the sludge  22  separates into a water-rich phase  28 , an oil-rich phase  30 , and a gas phase  44 . Furthermore, additional solids  26  that may settle out of the sludge  22  and accumulate in a bottom region of the separator  148 , primarily as a result of the re-distribution or separation of the phases, are discharged and directed to the solids receiving tank  150 . The water-rich phase  28  is discharged to a water tank  152 . The oil-rich phase  30  is transferred to the decanter skid  114  for fine solids removal. The gas phase  44  is directed to the gas purification skid  112  to clean the gas for release into the atmosphere. One exemplary three-phase separator  148  is the Horizontal Longitudinal Flow Separator commercially available from NATCO Group Inc., Houston, Tex. However, the present invention is not limited to a particular type of surge tank or three-phase separator. In addition, the surge tank  146  and three-phase separator  148  are both preferably insulated to better maintain the sludge temperature and fluidity. 
         [0030]    The oil-rich phase  30  is transferred to the decanter skid  114  to separate the fine solids out of the oil-rich phase  30 . The decanter skid  114  includes a decanter centrifuge  154  and a heating tank  156  mounted thereon and within the confines of the area of the skid  114  so as to maintain the portability of the skid  114 . For the removal of solids, the decanter centrifuge  154  is particularly useful in reducing the solids content in liquids having a solids concentration in excess of about 3 vol. % to a solids concentration less than about 2 vol. %. Once the oil-rich phase  30  is fed into the decanter centrifuge  154 , centrifugal force causes suspended solids to separate out of the oil-rich phase  30  and coalesce for subsequent removal from the decanter, Solids  32  are discharged through a solids outlet located in the bottom of the decanter centrifuge  154 . At this point in the processing, a decanter-processed oil-rich phase  34  that exits the decanter  154  has a BS&amp;W of less than about 2 vol. %. Suitable decanter centrifuges include decanter centrifuges having a rotational speed of 3000 rpm or greater. Exemplary decanter centrifuges include Model 500 (3000 rpm) and Model 518 (5000 rpm) commercially available from M-I L.L.C., Houston, Tex. 
         [0031]    After the fine solids removal, the decanter-processed oil-rich phase  34  is transferred to the heating tank  156  and optionally heated therein. Because a significant amount of cooling can occur during the various prior processing steps, since being previously heated in the heat exchanger  130 , the oil-rich phase  34  is optionally heated to a desired temperature in the heating tank  156  in order to enhance its final phase separation and purification during the next processing step at the oil purification skid  116 . The heating tank  156  includes a heating element (e.g., a steam coil) capable of heating the contents of the tank  156 . After heating, a heated oil-rich phase  36  is pumped via a second transfer pump  158  to the oil purification skid  116  for final purification. In one example, the heated oil-rich phase  36  is heated to a temperature in the range from about 65° C. to about 85° C. 
         [0032]    The heated oil-rich phase  36  is transferred to the oil purification skid  116  for its final purification and recovery of oil therefrom having a BS&amp;W of less than about 1 vol. %. The oil purification skid  116  includes a disk stack centrifuge  160 . As depicted in  FIG. 5 , the heated oil-rich phase  36  is fed into the disk stack centrifuge  160  to further purify the oil. The disk stack centrifuge uses a combination of plates (i.e., the disk stack) and extremely high centrifugal forces to separate the very fine water emulsion and the ultra-fine solids out of the oil-rich phase  36 . After separation, a water stream  38 , a recovered oil stream  40 , and an ultra-fine solids phase  42  are discharged from the centrifuge  160 . After final processing in the disk stack centrifuge  160 , the recovered oil stream  40  has a BS&amp;W less than about 1 vol. % and is commercially marketable. Exemplary disk stack centrifuges are commercially available from Alfa Lavel Inc., Richmond, Va. 
         [0033]    The gas phase  44  is transferred to the gas purification skid  112  where the gas phase  44  is treated to remove volatile organic compounds (VOCs) prior to discharge into the environment. The gas purification skid  112  preferably includes a free water knockout pot  162 , at least one mist impinger  166 , and at least one activated carbon filter  168  mounted thereon and within the confines of the area of the skid  112  so as to maintain the portability of the skid  112 . A VFD-controlled vacuum blower  164  attached to the knockout pot  162  is used to draw the gas phase  44  from a gas vent located in an upper side of the three-phase separator  148  through the knockout pot  162  filled with water. The gas phase  44  enters a gas inlet located near the bottom of the knockout pot  162 , and hydrocarbons in the gas phase  44  adhere to the water as the gas travels upwardly through the pot  162 . Water in the knockout pot  162  is periodically emptied into a liquid waste disposal and replaced with fresh water. Because the exiting gas is saturated with water, a wet-gas  46  that exits a gas outlet near the top of the knockout pot  162  is directed through at least one mist impinger  166  to remove water from the gas  46  and provide a dry gas  48 . The dry gas  48  that exits the at least one mist impinger  166  is then transferred to an activated carbon filter  168  to remove contaminants (e.g., remaining VOCs) therefrom in order to ensure a gas  50  that meets the environmental regulatory standards for release to the atmosphere. In one example, as depicted in  FIG. 5 , the knockout pot  162  removes hydrocarbons from the gas phase  44 , and afterwards the exiting wet-gas  46  is directed through two mist impingers  166  to adequately dry the gas prior to directing the dry gas  48  through one or more activated carbon filters  168 . When the activated carbon filter  168  becomes exhausted, it may be treated to reactivate the carbon or, alternatively, may be disposed of according to appropriate regulatory procedures. 
         [0034]    According to another embodiment of the invention,  FIG. 2  depicts the skid arrangement of a modular apparatus  200  optimally configured for recovering the valuable hydrocarbon component of sludge  14  initially having a high concentration of high density solids. In  FIG. 2  the same reference numerals are used to indicate the same skids as those previously described with respect to the apparatus  100  depicted in  FIG. 1 . Modular apparatus  200  comprises the pumping skid  1025  the shaker skid  104 , the heating skid  106 , a first chemical skid  118 , the decanter skid  114 , a second chemical skid  120 , the phase separator skid  110 , the gas purification skid  112 , and the oil purification skid  116 . In this embodiment, two chemical skids  118 ,  120  are utilized with the decanter skid  114  positioned between the chemical skids  118 ,  120 . For sludge  14  initially having a high concentration of high density solids, it is preferable to remove solids from the sludge using a decanter centrifuge prior to delivery of all the chemicals during the chemical treatment of the sludge. Skids  118  and  120  are described in more detail in the description that follows with respect to the modular apparatus  200  schematically illustrated in  FIGS. 4 and 6 . 
         [0035]    Illustrated in  FIGS. 4 and 6 , modular apparatus  200  processes pit sludge through the pumping skid  102 , the shaker skid  104 , the heating skid  106 , the first chemical skid  118 , the decanter skid  114 , the second chemical skid  120 , the phase separator skid  110 , the gas purification skid  112 , and the oil purification skid  116 . As previously described with respect to  FIG. 4  the modular apparatus  200  processes pit sludge  10  through the pumping skid  102 , the shaker skid  104 , and the heating skid  106  to provide a heated sludge  18 . 
         [0036]    Referring now to  FIG. 6 , the heated sludge  18  is transferred to the first chemical skid  118  for chemically altering the sludge  18  to break up the emulsion and promote solids separation. In  FIG. 6  the same reference numerals are used to indicate the same features as those previously described with respect to apparatus  100  depicted in  FIG. 5 . The chemical skid  118  includes a plurality of chemical injection mixers  140   a ,  140   b  and chemical supply tanks  142   a ,  142   b  mounted thereon and within the confines of the area of the skid  118  so as to maintain the portability of the skid  118 . Chemical addition is typically required to destabilize the emulsion and change such properties to facilitate separation of the solids from the sludge  18  and decrease the separation time required. Each of the chemical injection mixers  140   a ,  140   b  includes a static shear mixer having an injection point for introducing a chemical into the sludge  18  while the mixer simultaneously blends the chemical and the sludge  18  under the shearing action of the mixer. As illustrated in  FIG. 6 , two chemicals are added to the heated sludge  18  as the sludge is directed through the chemical injection mixers  140   a ,  140   b . Chemical supply tanks  142   a ,  142   b  store the chemicals until they are transferred via chemical lines  144   a ,  144   b  to the mixers  140   a ,  140   b  for injection into the sludge  18 . Preferably at least one dosing pump (not shown) in fluid communication with each of the chemical injection mixers  140   a ,  140   b  is used to provide a predetermined quantity of chemical to the injection point of the mixer for introduction into the sludge  18 . In addition the chemical injection mixers  140   a ,  140   b  are preferably insulated to better maintain the sludge temperature and fluidity. Once the chemicals are introduced and blended into the heated sludge  18 , a first chemically-treated sludge  202  exits the last chemical injection mixer  140   b  and is subsequently transferred to the decanter skid  114  to separate the high density solids out of the first chemically-treated sludge  202 . It should be noted that additional chemical injection mixers may be added to the first chemical skid  118  for the introduction of additional chemicals into the sludge  18 . 
         [0037]    Depending upon the particular initial sludge  14  composition, a wide variety of chemicals may be introduced and blended into the sludge  18  in order facilitate subsequent processing to separate the solids out of the first chemically-treated sludge  202 . Suitable chemicals include acids, demulsifiers, wetting agents, surfactants, flocculants, and defoamers. In one example, as the heated sludge  18  travels through the first injection mixer  140   a , the mixer  140   a  injects an acid and blends the acid with the sludge  18  therein in order to neutralize adsorbed ions present at the interfacial emulsion film of the sludge  18 . Subsequently, the sludge  18  is directed through the second injection mixer  140   b  wherein a wetting agent is injected and blended into the sludge to alter the affinity of the solids towards the water phase. It should be noted that the present invention is not intended to be limited to the use of any particular chemicals, and other chemicals may be substituted for any of the aforementioned chemicals. 
         [0038]    The first chemically-treated sludge  202  is directed to the decanter skid  114  for solids removal. The chemically-treated sludge  202  entering the decanter skid  114  can have a solids content as high as in the range of 6 vol. % to 15 vol. %. As previously described, the decanter skid  114  includes a decanter centrifuge  154  and a heating tank  156  mounted thereon and within the confines of the area of the skid  114 . The decanter centrifuge  154  is used to reduce the solids content in the sludge  202  to a solids concentration less than about 2 vol. %. In the decanter centrifuge  154 , centrifugal force causes solids  204  to separate out of the sludge  202  and coalesce for subsequent removal from the decanter through a solids outlet located in the bottom of the decanter centrifuge  154 . A decanter-processed sludge  206  that exits the decanter centrifuge  154  has a solids content of less than about 2 vol. %. As previously described, suitable decanter centrifuges include decanter centrifuges having a rotational speed of 3000 rpm or greater. 
         [0039]    After reducing the solids in the sludge  206 , the decanter-processed sludge  206  is transferred to the heating tank  156  and optionally heated therein. Because a significant amount of cooling can occur during the previous processing steps since being heated in the heat exchanger  1301  the decanter processed sludge  206  may be heated to a desired temperature in the heating tank  156  in order to lower its viscosity and facilitate blending of additional chemicals into the sludge  206  during the next processing step at the second chemical skid  120 . After heating, a heated decanter-processed sludge  208  is pumped via the second transfer pump  158  to the second chemical skid  120 . In one example, the heated decanter-processed sludge  208  is heated to a temperature in the range from about 65° C. to about 85° C. 
         [0040]    The heated decanter-processed sludge  208  is transferred to the second chemical skid  120  for chemically altering the sludge  208  to further break up the emulsion and promote phase separation. The chemical skid  120  includes a plurality of chemical injection mixers  140   c ,  140   d  and chemical supply tanks  142   c ,  142   d  mounted thereon and within the confines of the area of the skid  120  so as to maintain the portability of the skid  120 , Chemical addition is typically required to further destabilize the emulsion and change such properties to enhance oil-water-solids phase separation during the next processing steps at the phase separator skid  110 . Each of the chemical injection mixers  140   c ,  140   d  includes a static shear mixer having an injection point for introducing a chemical into the sludge  208 . As illustrated in  FIG. 6 , two chemicals are added to the sludge  208  as the sludge travels through mixers  140   c ,  140   d . Chemical supply tanks  142   c ,  142   d  store the chemicals until they are transferred via chemical lines  144   c ,  144   d  to the mixers  140   c ,  140   d . Preferably at least one dosing pump (not shown) in fluid communication with each of the chemical injection mixers  140   c ,  140   d  is used to provide a predetermined quantity of chemical to the injection point of the mixer for introduction into the sludge  208 . In addition, the chemical injection mixers  140   c ,  140   d  are preferably insulated to better maintain the sludge temperature and fluidity. Once the chemicals are introduced and blended into the sludge  208 , a second chemically-treated sludge  210  exits the last chemical injection mixer  140   d  and is subsequently transferred to the phase separator skid  110 . It should be noted that additional chemical injection mixers may be added to the second chemical skid  120  for the introduction of additional chemicals into the sludge  208 . 
         [0041]    Depending upon the particular sludge  208  composition, a wide variety of chemicals may be introduced and blended into the sludge to promote separation of the water, oil, and solid phases of the second chemically-treated sludge  210 . Suitable chemicals include acids, demulsifiers, wetting agents, surfactants, flocculants, and defoamers. In one example, as the sludge  208  travels through the third injection mixer  140   c , the mixer  140   c  injects a demulsifier into the sludge  208  to break the interfacial emulsion film to release the secondary water phase. Afterwards, the sludge  208  is directed through the fourth injection mixer  140   d  wherein a defoamer is injected and blended into the sludge for the purpose of preventing foaming. Again, it should be noted that the present invention is not intended to be limited to the use of any particular chemicals, and other chemicals may be substituted for any of the aforementioned chemicals. Furthermore, additional chemical injection mixers may be added to the second chemical skid  120  for the introduction of additional chemicals into the sludge  208 . 
         [0042]    After the second chemical treatment, the sludge  210  is directed to the phase separator skid  11  for separating water and solids from the oil phase of the sludge  210 . As previously described, the phase separator skid  110  includes a surge tank  146  and a three-phase separator  148  mounted thereon. The sludge  210  is fed into the vertically-oriented surge tank  146  which separates solids from the sludge  210  and provides a continuous flow of a liquid portion of the sludge  212  to the three-phase separator  148 . Separated solids  214  that settle and accumulate in a bottom region of the surge tank  146  are discharged to the solids receiving tank  150 . The liquid portion of the sludge  212  which comprises oil, water, gas, and fine solids is directed to the three-phase separator  148 . 
         [0043]    The liquid portion of the sludge  212  flows into the three-phase separator  148  through an inlet located at one end of the separator  148 . After phase separation within the retention section of the three-phase separator  148 , a water-rich phase  218  is discharged to a water tank  152 , an oil-rich phase  220  is transferred to the oil purification skid  116 , and a gas phase  228  is directed to the gas purification skid  112 . Any solids  216  that may settle out of the sludge  212  and accumulate in a bottom region of the separator  148  during separation of the phases are discharged to the solids receiving tank  150 . 
         [0044]    The oil-rich phase  220  is transferred to the oil purification skid  116  for final purification and recovery of oil therefrom having a BS&amp;W of less than about 1 vol. %. As previously described, the oil purification skid  116  includes a disk stack centrifuge  160  mounted thereon. The oil-rich phase  220  is fed into the disk stack centrifuge  160  wherein extremely high centrifugal forces separate the very fine water emulsion and the ultra-fine solids out of the oil-rich phase  220 . After phase separation, a water stream  222 , a recovered oil stream  224 , and an ultra-fine solids phase  226  are discharged from the centrifuge  160 . The recovered oil stream  224  has a BS&amp;W less than about 1 vol. % and is commercially marketable. 
         [0045]    The gas phase  228  is transferred to the gas purification skid  112  where the gas phase  228  is treated to remove VOCs prior to discharge into the environment. As previously described, the gas purification skid  112  preferably includes a free water knockout pot  162 , at least one mist impinger  166 , and at least one activated carbon filter  168  mounted thereon. A VFD-controlled vacuum blower  164  attached to the knockout pot  162  is used to draw the gas phase  228  from a gas vent located in an upper side of the three-phase separator  148  through the knockout pot  162  filled with water. Hydrocarbons in the gas phase  228  adhere to the water as the gas travels upwardly through the pot  162 . A wet-gas  230  that exits a gas outlet near the top of the knockout pot  162  is directed through at least one mist impinger  166  to remove water from the gas  230  and provide a dry gas  232 . The dry gas  232  is transferred to an activated carbon filter  168  to remove contaminants (e.g., remaining VOCs) therefrom in order to ensure a gas  234  that meets the regulatory standards for release to the atmosphere. 
         [0046]    According to still another embodiment of the invention,  FIG. 3  depicts the skid arrangement of a modular apparatus  300  optimally configured for recovering the valuable hydrocarbon component of sludge  14  initially having a low concentration of solids. In  FIG. 3  the same reference numerals are used to indicate the same skids as those previously described with respect to the apparatus  100  depicted in  FIG. 1 . Modular apparatus  300  comprises the pumping skid  102 , the shaker skid  104 , the heating skid  106 , the chemical skid  108 , the phase separator skid  110 , the gas purification skid  112 , and the oil purification skid  116 . This embodiment excludes the use of the decanter skid  114 . For sludge  14  initially having a low concentration of solids, it may be unnecessary to include a decanter centrifuge for the removal of solids. 
         [0047]    Illustrated in  FIGS. 4 and 7 , modular apparatus  300  processes pit sludge through the pumping skid  102 , the shaker skid  104 , the heating skid  106 , the chemical skid  108 , the phase separator skid  110  the gas purification skid  112 , and the oil purification skid  116 . As previously described with respect to  FIG. 4 , the modular apparatus  300  processes pit sludge  10  through the pumping skid  102 , the shaker skid  104 , and the heating skid  106  to provide a heated sludge  18 . 
         [0048]    Referring now to  FIG. 7 , the heated sludge  18  is transferred to the chemical skid  108  for chemically altering the sludge  18  to break up the emulsion and promote phase separation. In  FIG. 7  the same reference numerals are used to indicate the same features as those previously described with respect to apparatus  100  depicted in  FIG. 5 . As previously described, the chemical skid  108  includes a plurality of chemical injection mixers  140   a - d  and chemical supply tanks  142   a - d  mounted thereon. Chemical addition is typically required to destabilize the emulsion and change such properties of the sludge  18  to enhance the its phase separation during the next processing step at the phase separator skid  110 . As previously described, each of the chemical injection mixers  140   a - d  includes a static shear mixer having an injection point for introducing a chemical into the sludge  18  while the mixer simultaneously blends the chemical and the sludge  18  under the shearing action of the mixer. As illustrated in  FIG. 7 , four chemicals are added to the heated sludge  18  as the sludge is directed through the chemical injection mixers  140   a - d . Chemical supply tanks  142   a - d  store the chemicals until they are transferred via chemical lines  144   a - d  to the mixers  140   a - d  for injection into the sludge  18 . Preferably at least one dosing pump (not shown) in fluid communication with each of the chemical injection mixers  140   a - d  is used to provide a predetermined quantity of chemical to the injection point of the mixer for introduction into the sludge  18 . Preferably, chemical injection mixers  140   a - d  are thermally insulated to better maintain the sludge temperature and fluidity. Once the chemicals are introduced and blended into the heated sludge  18 , a chemically-treated sludge  302  exits the last chemical injection mixer  140   d  and is subsequently transferred to the phase separator skid  110  for separating the water, oil and solid phases of the sludge  302 . Again, it should be noted that additional chemical injection mixers may be added to the chemical skid  108  for the introduction of additional chemicals into the sludge  18 . 
         [0049]    After chemical treatment, the sludge  302  is directed to the phase separator skid  110  for separating water and solids from the oil phase of the sludge  302 . As previously described, the phase separator skid  110  includes a surge tank  146  and a three-phase separator  148  mounted thereon. The sludge  302  is fed into the vertically-oriented surge tank  146  which contains an interior plate that facilitates the small solids within the sludge to aggregate and form larger solids that settle out of the sludge  302  and accumulate in a bottom region of the surge tank  146 . Separated solids  306  that accumulate in the surge tank  146  are discharged to the solids receiving tank  150 . The surge tank  146  also provides a continuous flow of a liquid portion of the sludge  304  to the three-phase separator  148  for oil, water, gas, and solid phase separation. 
         [0050]    The liquid portion of the sludge  304  flows into the three-phase separator  148  through an inlet located at one end of the separator  148 . After phase separation within the retention section of the three-phase separator  148 , a water-rich phase  310  is discharged to a water tank  152 , an oil-rich phase  312  is transferred to the oil purification skid  116 , and a gas phase  320  is directed to the gas purification skid  112 . Any solids  308  that may settle out of the sludge  304  and accumulated in a bottom region of the separator  148  during separation of the phases are discharged to the solids receiving tank  150 . 
         [0051]    The oil-rich phase  312  is transferred to the oil purification skid  116  for final purification and recovery of oil therefrom having a BS&amp;W of less than about 1 vol. %. As previously described, the oil purification skid  116  includes a disk stack centrifuge  160  mounted thereon. The oil-rich phase  312  is fed into the disk stack centrifuge  160  wherein extremely high centrifugal forces separate the very fine water emulsion and the ultra-fine solids out of the oil rich phase  312 . After phase separation, a water stream  314 , a recovered oil stream  316 , and an ultra-fine solids phase  318  are discharged from the centrifuge  160 . The recovered oil stream  316  has a BS&amp;W less than about 1 vol. % and is commercially marketable. 
         [0052]    The gas phase  320  is transferred to the gas purification skid  112  where the gas phase  320  is treated to remove VOCs prior to discharge into the environment. As previously described, the gas purification skid  112  preferably includes a free water knockout pot  162 , at least one mist impinger  166 , and at least one activated carbon filter  168  mounted thereon. A VFD-controlled vacuum blower  164  attached to the knockout pot  162  is used to draw the gas phase  320  from a gas vent located in an upper side of the three-phase separator  148  through the knockout pot  162  filled with water. Hydrocarbons in the gas phase  320  adhere to the water as the gas travels upwardly through the pot  162 . A wet-gas  322  that exits a gas outlet near the top of the knockout pot  162  is directed through at least one mist impinger  166  to remove water from the gas  322  and provide a dry gas  324 . The dry gas  324  is transferred to an activated carbon filter  168  to remove contaminants (e.g., remaining VOCs) therefrom in order to ensure a gas  326  that meets the regulatory standards for release to the atmosphere. 
         [0053]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.