Abstract:
An apparatus for treating oil-based sludge includes a boiler, a heat exchanger having a circulatory steam path in fluid communication with the boiler and a sludge path receiving sludge, a plurality of serially-aligned mixers in fluid communication with the sludge path of the heat exchanger, a separation tank in fluid communication with the plurality of mixers, and wherein the separation tank includes a tank having a plurality of walls, a hydrocyclone mounted within the tank receiving sludge from the plurality of mixers, wherein the hydrocyclone includes a solids outlet directing a solids component towards a bottom portion of the tank and a fluid outlet directing a fluid component into the tank, a means for conveying separated solids along the bottom portion of the tank to a solids outlet, and a plurality of fluid outlets vertically located along a tank wall, wherein each outlet includes a valve providing selective fluid communication from the tank.

Description:
This application claim priority to U.S. Provisional Patent Application Ser. No. 60/682,472 filed on May 19, 2005 entitled, “Oil-Based Sludge Separation and Treatment System” incorporated herein by reference for all purposes. 
    
    
     BACKGROUND OF INVENTION 
     The term “sludge” is a generic description of an oily waste stream that typically has a high solids content and varying quantities of hydrocarbons and water. Certain sludges, such as those generated in the production of various hydrocarbon products, includes vessel sludges, tank bottom sediments and emulsions from water treatment systems. Waste sludge resulting from producing oil and gas wells, for example, is often stored in open pits where it may be left for considerable time before being treated. During such aging periods, the sludge undergoes chemical changes including the effects of weathering and volatilization. It is desirable to treat the sludge to reduce the risk of contamination of the surrounding area and to recover the valuable hydrocarbon component in the sludge. 
     Traditionally, disk stack centrifuges have been used to condition slope oil or sludge, but they are only effective for non-emulsified water and oil blends. However, due to the existence of the in-situ natural emulsifiers, production sludges are characterized by strong water-in-oil emulsions. For such blends, a disk stack centrifuge is ineffective. It would be an improvement in the art to have a method and apparatus that thermally and chemically treats the sludge. 
     SUMMARY 
     In one aspect, the invention is generally directed to an apparatus for treating oil-based sludge includes a boiler, a heat exchanger having a circulatory steam path in fluid communication with the boiler and a sludge path receiving sludge, a plurality of serially-aligned mixers in fluid communication with the sludge path of the heat exchanger, a separation tank in fluid communication with the plurality of mixers, and wherein the separation tank includes a tank having a plurality of walls, a hydrocyclone mounted within the tank receiving sludge from the plurality of mixers, wherein the hydrocyclone includes a solids outlet directing a solids component towards a bottom portion of the tank and a fluid outlet directing a fluid component into the tank, a means for conveying separated solids along the bottom portion of the tank to a solids outlet, and a plurality of fluid outlets vertically located along a tank wall, wherein each outlet includes a valve providing selective fluid communication from the tank. 
     In another aspect the invention is directed to an apparatus for treating oil-based sludge including a boiler producing steam, a heat exchanger having a circulatory steam path in fluid communication with the boiler and a sludge path receiving sludge, a plurality of mixers in fluid communication with the sludge path of the heat exchanger, wherein the mixers are aligned in series, a separation tank in fluid communication with the mixers, including a plurality of walls defining a tank, a selectively closable hood mounted to an upper edge of at least one wall of the tank, a hydrocyclone retained within a portion of the tank, wherein the hydrocyclone receives treated sludge from the mixers and removes a solid component from a fluid component in the sludge, directing the solids to a bottom portion of the tank and directing fluid to another portion of the tank, a plurality of fluid outlets each including a valve selectively communicating fluid from the tank, a solids outlet including a valve selectively communicating solids from the tank, and a means for conveying solids located along a bottom portion of the tank to the solids outlet. 
     In another aspect, the invention is directed to a method for treating oil-based sludge including warming sludge in a heat exchanger, injecting a demulsifying chemical into the sludge, shearing the sludge and the demulsifying chemical, separating a solid component from the sludge fluid in a hydrocyclone, discharging the separated solid component to a tank floor of a tank, conveying the separated solid component along the tank floor to a solids outlet, and feeding the sludge fluid to the tank, discharging the fluid from the tank to a fluids collection area. 
     Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a heating section of a modular sludge treatment apparatus. 
         FIG. 2  is a perspective view of a separation and settling section of the modular sludge treatment apparatus. 
         FIG. 3  is a perspective view of the modular sludge treatment apparatus. 
         FIG. 4  is a diagram of a sludge treatment process. 
         FIG. 5  is a top view of the heating section of the modular sludge treatment apparatus. 
         FIG. 6  is a schematic of the mixing section of the modular sludge treatment apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     The claimed subject matter relates to a modular apparatus  100 , shown in  FIG. 3 , for treating oil-based sludge and a method for using the apparatus. The apparatus includes three primary sections, a heating section, a mixing section, and a separation and settling section. The heating section, shown in  FIGS. 1 ,  3 , and  5 , includes a boiler  102  and a heat exchanger  104 . The mixing section, shown in  FIG. 3  and schematically in  FIG. 6 , includes mixers  106 ,  108 . The separation and settling section, shown in  FIGS. 2 and 3 , includes a tank  110  within which a hydrocyclone  112  is located. As depicted in  FIG. 3 , in one embodiment, all three sections are co-located on a skid  114 , making the entire apparatus  100  easily transportable. 
     Referring to  FIGS. 1 and 5 , the heating section includes the boiler  102  and the heat exchanger  104 . The boiler  102  is used to provide steam to the heat exchanger  104 . Steam, heated in the boiler  102  is directed from a first steam outlet  116  to a first steam inlet  118  of the heat exchanger  104 . After flowing through the heat exchanger  104 , the cooled steam exits through a second steam outlet  120  and returns to the boiler  102  through a second steam inlet  122  to be reheated. 
     Sludge from a sludge holding area or tank (not shown) is directed into the heat exchanger  104  through a first sludge inlet  124 . The sludge flows through the heat exchanger  104  in a path separate from that of the steam, but adjacent to it such that heat from the steam is transferred to the sludge. The pressure and temperature of the steam entering the heat exchanger  104  are preferably controlled so that the thermal properties of the sludge being warmed in the heat exchanger are within predetermined parameters. The sludge is warmed to a temperature sufficient to dissolve waxy hydrocarbons and lower the viscosity of the sludge so that it can flow through the apparatus  100 . The temperature at which the sludge becomes liquid, and the corresponding rheological profile, can be determined using a viscometer, such as an oilfield Fann 35 viscometer available from Fann Instrument Co. As sludge will often be heated to melt wax components and aid phase separation, the flash point of the sludge is important. 
     As the temperature increases, vapor pressure increases and therefore the concentration of evaporated flammable liquid in the air increases. 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 can be determined. An example of a device for measuring the flash point of a liquid is the Pensky Martens Closed Cup according to method ASTM D93B. 
     The sludge, warmed by the steam in the heat exchanger  104 , exits through a first sludge outlet  126 . The heat exchanger  104  should fit within the confines of the area in the skid  114  to maintain portability of the entire sludge treatment apparatus  100 . In one embodiment, the type of heat exchanger  104  used is a spiral type heat exchanger. It is understood that other types of heat exchangers can be used without departing from the scope of this invention. Some oil-based sludges include waxy hydrocarbons, which are preferably dissolved into liquid form in the heat exchanger  104  to lower the viscosity of the sludge. Treatment chemicals may be more easily blended with the sludge when the viscosity of the sludge is lower. Further, when the viscosity is lower, entrained solids are more easily released in downstream processing. 
     A fuel tank  128  may be co-located on the skid  114  to provide fuel to the boiler  102  for heating the dry steam. A control panel  129  may also be co-located on the skid  114  to monitor and control the treatment process. 
     In one embodiment, a first heat panel  130  is mounted to the skid  114  between the boiler  102  and the heat exchanger  104 . The heat panel  130  isolates the boiler  102  from the heat exchanger  104 . By insulating the boiler  102  from the heat exchanger  104 , the predetermined parameters of the sludge may be better maintained than if the heat from the boiler unit  102  adds heat to the heat exchanger  104  outer surface. 
     In one embodiment, a second heat panel  132  is mounted to the skid  114  between the fuel tank  128  and the boiler  102  and heat exchanger  104 . The second heat panel  132  insulates the fuel tank  128  from both the boiler  102  and heat exchanger  104 . 
     In one embodiment, the boiler  102  is located within an insulating chamber  134 , as shown in  FIG. 3 . 
     In certain sludge, where there is no emulsion or only a weak emulsion present, heat and gravity is sufficient to promote separation. Referring to  FIGS. 3 and 6 , for other sludge types, chemical addition may be required to weaken the emulsion and change such properties as wettability to decrease the separation time required. Such chemicals may include flocculant to induce the formation of flocs to which solids may coagulate and form larger solids. Demulsifiers may also be used to break any emulsion between water and oil in the sludge. Each chemical may be added to the sludge as the sludge is directed through the mixing section of the modular apparatus  100 . The mixing section includes a plurality of mixers  106 ,  108 . The chemicals are stored in tanks  136 ,  138  until they are injected into the sludge. One or more dosing pumps  140 ,  142  may be used to direct predetermined quantities of chemicals into the sludge. In one embodiment the predetermined amount of demulsifier is 2-3% by volume of sludge. The quantity of 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 sludge to prevent insoluble wax molecules in the oil phase from building a lattice at colder temperatures and results in the sludge maintaining its fluidity even at lower temperatures. In one embodiment, each treatment chemical is introduced to the sludge within a corresponding inline mixer  106 ,  144 . In this embodiment, mixer  108  is a static shear mixer used to further blend the chemicals and the sludge. When it is desired to add more chemicals, each may be added through a corresponding mixer before the mixture is introduced to the static shear mixer  108 . The static shear mixer  108  enhances blending of the treatment claims and sludge by inducing shear such that the flow is turbulent. 
     The sludge mixture is directed to the separation and settling section depicted in  FIGS. 2 and 3 . The separation and settling section includes a tank  110  and a hydrocyclone separator  112 . The hydrocyclone separator  112  is preferably housed within the tank  110 , near one end  133 . The sludge and chemical mixture is fed directly to the hydrocyclone separator  112 , which separates heavier solids from the mixture. The separated solids are released through a solids outlet  148  in the bottom portion  150  of the hydrocyclone separator  112 . The liquid portion of the sludge mixture is fed through a fluid outlet  152  of the hydrocyclone separator  112  into the tank  110 . 
     The tank  110  includes a plurality of walls, preferably two opposing end walls  154 ,  156  and two opposing side walls  158 ,  160 , interconnected to form the tank  110 . A bottom portion  164  of the tank  110 , together with a top portion  162  form a basin for receiving material therein. The bottom portion  164  preferably includes a pair of opposed inclined walls  166 ,  168 , which direct the sludge to a solids accumulation area  170  along a tank floor  172 . Solids from the hydrocyclone separator  112  are directed to the tank floor  172  beneath the solids outlet  148 . Finer solids remaining in the liquid portion of the separated sludge after exiting the hydrocyclone separator  112  can settle out of the fluid to the tank floor  172  while the sludge is in the tank  110 . 
     A means for conveying settled solids  174  is located along the solids accumulation area  170  of the tank floor  172 . The means for conveying settled solids  174  transfers solids in the accumulation area  170  to a solids outlet  176 . In one embodiment, an auger is used for conveying solids. It will be appreciated by those of skill in the art that other means for conveying settled solids  174  may also be used. 
     A hood  178 , shown in  FIG. 3 , may be mounted to the tank  110  to enclose the basin formed by the top portion  162  and the bottom portion  164 . The hood  178  is preferably mounted in such a way that it may be selectively opened to provide access to the tank  110 . An air outlet  180  may be provided through the hood  178  for the evacuation of gases that may collect in the tank  110 . A vacuum pump (not shown) may be used to evacuate air from the tank and a charcoal filter (not shown) may be provided within the air conduit (not shown) to deodorize air before it is released to the atmosphere. Further filters may be used to clean air prior to its release. 
     Referring again to  FIGS. 2 and 3 , in one embodiment, steam coils  182  are incorporated into the side walls  158 ,  160  and bottom portion  164  of the tank  110  The steam coils  182  include a steam inlet  184  for receiving steam from the boiler  102 . Steam is returned to the boiler  102  through a steam outlet  186  from the steam coils  182 . The steam coils  182  direct steam along the sides and bottom of tank  110 . The circulation of steam through the side walls  158 ,  160  and bottom portion  164  of the tank  110  provide heat to the separated sludge fluid as well as solids along the tank floor  172 . In one embodiment, a single steam coil  182  is incorporated into the side walls  158 ,  160  and bottom portion  164  of the tank  110 . 
     In one embodiment, steam coils  182  are constructed immediately adjacent to the outer surface of the side walls  158  and  160  and bottom portion  164 . In one embodiment, a single steam coil  182  is constructed immediately adjacent to the outer surface of the sidewalls  158  and  160  and bottom portion  164 . The hood  178 , shown in  FIG. 3 , insulates the tank  110  to reduce heat loss from the top of the tank  110 . The heat keeps the fluid at a lower viscosity, which improves the settling of solids from the fluid. The heat also helps soften the solids, making them easier to convey. 
     Referring to  FIG. 2 , the tank  110  may include a plurality of vertically arranged valves  188  along one wall  158  and one of the inclined walls  166  in the bottom portion  164  of the tank  110 . One or more of the valves  188  may be opened to direct the fluid to a separate treatment area or collection area (not shown). If demulsifiers have been used to help separate the oil component of the fluid from the water component of the fluid, valves  188  along or closer to the bottom portion  164  of the tank may be opened to remove the water component from the tank  110 . Alternatively, valves  188  closer to the top of the tank  110  may be opened to remove the oil component from the tank  110 . The valves  188  may be manually actuated or remotely actuated. 
     A plate  190  may be located within the tank  110  to separate the portion of the tank  110  in which the hydrocyclone separator  112  is located from the remainder of the tank  110 . The plate  190  is may be placed at an angle within the tank  110  such that it is closer to one end wall  156  of the tank  110  at a top edge  192  and closer to the opposing end wall  154  of the tank  110  at a bottom edge  194  of the plate  190 . The plate  190  is shaped to provide an opening between the bottom edge  194  and the tank floor  172  through which the means for conveying  174  directs the solids from the hydrocyclone separator  112 . The plate  190  may be selectively located within the tank  110  to vary the volume of the portion of the tank in which the hydrocyclone  112  is located and the remaining portion of the tank. 
     Referring to  FIG. 4 , a process for treating oil-based sludge including the modular apparatus  100  is shown. Oil-based sludge  202  from a collection area  200  is transferred to the modular apparatus  100 . The transfer from the collection area to the modular apparatus  100  may be made directly through use of a viscous fluid transfer apparatus  210 . Alternatively, the transfer may be by utilizing a mobile discharge and feed system including a truck trailer  204 . Sludge from the collection area  200  is transferred to the trailer  204 . The truck then drives the sludge to a treatment area. The treatment area includes the modular apparatus  100 , previously described. The treatment area may further include another treatment apparatus  206 , such as a frac tank. In the modular apparatus  100 , solids are removed and collected. The oil and water may be separated within the modular apparatus  100 , as previously described and removed for further processing. 
     While the claimed subject matter has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the claimed subject matter as disclosed herein. Accordingly, the scope of the claimed subject matter should be limited only by the attached claims.