Abstract:
A system and method are disclosed for processing grease trap waste to produce brown grease oil. Heat to promote waste grease stratification is provided by combustion of brown grease itself. A portion of the brown grease, which would normally be transported to an end user, is retained in a separate holding vessel at the grease processing site. The brown grease within the holding vessel is thermally conditioned to adjust viscosity so that it may be drawn through one or more pumps to increase pressure for atomization in a boiler. The heat of the brown grease combustion is applied to grease trap waste in the containment vessel by heating tubes immersed in the grease trap waste in which a heat transfer medium circulates and gives up its heat to the grease trap waste to thereby promote stratification of the grease trap waste and production of the brown grease oil.

Description:
The present invention relates to fuel oil production, and more particularly to a system and method for processing grease trap waste to produce a rich brown grease that can be used as an industrial fuel. 
     BACKGROUND OF THE INVENTION 
     In the processing of grease trap waste, the waste is typically loaded into a containment vessel configured to provide even heating of the waste so as to promote stratification of the waste into different layers. Heating of the waste is typically accomplished through the combustion of a petroleum based fuel, such as natural gas or light heating oil. The proper time and temperature relationship promotes stratification to form a bottom layer of mostly water. Directly above the layer of water will be a region containing food scrap residue. The top layer will consist of rich brown grease with viscosity, combustion, and heating value characteristics similar to the petroleum based product commonly known as Bunker 5, Bunker 6 or Heavy Fuel Oil. Typically, the brown grease layer is extracted to a separate storage vessel for transport to the end user. 
     BRIEF DESCRIPTION OF THE INVENTION 
     One object of the present invention is the processing of grease trap waste to attain water that would have lower levels of FOG (fats, oil and grease). This water could then easily be treated, and thus be disposable to local sewage plants. 
     Another object of the present invention is to produce a marketable, rich brown grease oil 
     A further object of the present invention is to use the renewable rich brown grease as the only fuel source for the grease trap waste processing. 
     In the present method and apparatus for processing grease trap waste to produce rich brown grease oil, the heat to promote waste grease stratification is provided by combustion of the brown grease oil itself. A portion of the heavy brown grease, which would normally be transported to the end user, is instead retained in a separate holding vessel at the processing site and combusted by a boiler. The brown grease within the holding vessel is thermally conditioned to adjust viscosity so that it may be drawn through a pump or series of pumps to increase pressure for atomization through a small nozzle. The nozzle atomizes, meters and creates a spray pattern to maintain the combustion of the brown grease with the aid of a spark generating mechanism and the appropriate combustion air flow. Combustion byproduct gases are vented from the area. The heat of brown grease combustion is applied to the grease trap waste containment vessel in close proximity to the combustion process itself by a heat transfer medium transferred between the boiler and the grease trap waste containment vessel. The grease trap waste containment vessel contains at least one set of heating tubes in which the heat transfer medium circulates and which run through the containment vessel, so as to be immersed in the grease trap waste stored in the containment vessel. The grease trap waste in the containment vessel is heated by the heat transfer medium circulating in the heating tubes giving up its heat to the grease trap waste. The present system and method allow the production of rich brown grease without the direct combustion of a petroleum based product to promote waste grease stratification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of a tank used to separate brown grease. 
         FIG. 2A  is a left side elevational view of the brown grease separator tank. 
         FIG. 2B  is a left side cross-sectional view of the brown grease separator tank. 
         FIG. 3  is a front elevational view of heat and fuel equipment that is part of the brown grease separator system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a system and method for processing grease trap waste to produce rich brown grease oil. For this purpose, the grease trap waste is placed in a holding tank or other vessel  10  that also serves as a separator tank or vessel in which the grease trap waste is separated into rich brown grease  12 , food scrap  14  and residual water  16 .  FIGS. 1 and 2A  are front and side elevational views, respectively, of the tank  10  used to separate brown grease, while FIG.  2 B is a left side cross-sectional view of the brown grease separator tank  10 . Tank  10  is preferably an insulated tank capable of holding a large volume of waste. In the embodiment of holding tank  10  shown in  FIGS. 2A and 2B , three inch perlite insulation  11  is used to insulate tank  10 , which has the ability to hold 10,000 gallons. Preferably, holding tank  10  is generally cylindrical in shape and resting on at least two supports  15 . The tank  10  can be a commercially available tank that can be purchased “off the shelf”. However, this “off the shelf” tank will typically require modification to add at least tubes  56 , manifolds  58  and an inspection trough  60  discussed below. It should be noted that, besides a cylindrical shape, other shapes can be used for tank  10 . 
     The system of the present invention preferably includes a hydronic steam boiler  18  and a fuel system  20  for pumping the brown grease oil. A hydronic steam boiler typically uses circulating hot water or steam as the heat-transfer medium in heating. It should be noted that, other suitable heat-transfer media could be used.  FIG. 3  is a front elevational view of the hydronic steam boiler  18  and the fuel system  20  that form the heat and fuel equipment that is used by the brown grease separator system. The hydronic steam boiler  18  can be a commercially available boiler that can be purchased “off the shelf”. 
     The fuel system  20  includes an insulated fuel tank  22  in which is stored brown grease fuel. Preferably, the fuel tank  22  is made of Stainless Steel. Within the fuel tank  22  is an immersion pipe or loop  24  that functions to transfer heat to the brown grease to thermally condition the grease. The immersion pipe or loop  24  is mounted inside and near the bottom of the fuel tank  22 . A second, smaller tank  26 , which is a hot water reservoir, is mounted on top of the fuel tank  22 . Preferably, the hot water reservoir  26  is insulated. 
     The hot water reservoir  26  has a fill opening  30 , a lower outlet  32 , an inlet fitting  34  and a sight gauge  36 . The lower outlet  32  of the hot water reservoir is connected to the inlet of a commercial electric water heater  38 . The water heater outlet is connected to the inlet of a hot water circulation pump (not shown). The outlet of the hot water circulation pump is connected to the inlet  40  of the immersion pipe or loop  24  in the fuel tank  22 . The outlet of the immersion pipe or loop  24  is connected to an inlet fitting (not shown) on the hot water reservoir  26 . This arrangement forms a heat cycle for heating the brown grease oil stored in the fuel tank  22  so that it can be thermally conditioned. 
     The fuel system  20  also includes two sets of two manifold fuel filter units  42  and  44  constituting a total of four filters  46  and a heavy duty gear drive hot oil fuel pump  28  that will deliver a continuous oil flow of five gallons per minute (“GPM”). 
     The grease stored in the fuel tank  22  is thermally conditioned by hot water circulating through the immersion pipe or loop  24  to thereby adjust its viscosity so that it may be drawn through the hot oil fuel pump  28  or series of pumps to increase pressure for atomization of the hot brown grease oil through a small nozzle  48  located in the hydronic steam boiler  18 . The hot brown grease oil flows from the oil fuel tank  22  to one set  42  or  44  of the fuel filters  46 , and then on to an inlet (not shown) of the hot oil fuel pump  28 . The outlet (not shown) of the pump  28  then sends the hot oil to a second set  42  or  44  of the fuel filters  46 , and then on to the burner assembly  50  within the hydronic steam boiler  18 . Installed at the connection to the burner  50  is a return line (not shown) with a gauge and needle flow valve (not shown). This allows a constant regulated hot oil flow returning to the fuel tank  22  and supplies fuel on demand to the burner assembly  50  of the boiler  18 . Constant return of the oil to the fuel tank  22  allows a true thermal conditioning of the brown grease. If the boiler were to cycle off at high temperature, the fuel would stop and cool, reverting to a gel/lard consistency, and would not re-establish flow, when the boiler was cycled back on by the boiler controls. 
     The operation of the hydronic steam boiler  18  and the fuel system  22  is controlled by a control panel  52  preferably located in the vicinity of the boiler  18  and fuel system  22 . The control panel typically includes controls for emergency shut down, “on/off” of the boiler power, “on/off” of the fuel pump, and “on/off” of the fuel heat. Preferably, the hydronic steam boiler  18 , the fuel system  22  and the control panel  52  are located on a support base  51 . 
     The hydronic steam boiler  18  and fuel system  22  are preferably operated “continuously” by control panel  52 , that is, 24 hours a day, 7 days a week. Preferably, the fuel tank  22  is operated at a temperature of approximately 105 to 115 degrees Fahrenheit. This temperature is measured at the outlet of fuel tank  22 . Preferably, the grease waste holding tank  10  is operated at a temperature of approximately 140 degrees to 180 degrees Fahrenheit. This temperature is important to achieving stratification of the grease trap waste in the holding tank  10 , which starts at about 100 degrees Fahrenheit. The temperature of holding tank  10  is monitored at control panel  52 . The temperature controls to maintain the noted temperatures in the fuel tank  22  and the holding tank  10  are standard system controls that can be purchased “off the shelf”. 
     The hydronic steam boiler  18  and fuel system  20 , together, form a highly dependable boiler system that can operate completely on brown grease and be used to produce additional brown grease that can be used as a fuel oil. Thus, the boiler system formed by the hydronic steam boiler  18  and fuel system  20  is used to separate grease trap waste and provide a marketable, rich brown grease. 
     The heat of the brown grease being combusted in the hydronic steam boiler  18  is applied to the grease trap waste stored in the holding tank  10 , in close proximity to the combustion process itself, by a heat transfer medium that is heated in the hydronic steam boiler  18  and then transferred from the boiler  18  to the holding tank  10  by an appropriate conduit arrangement, which is preferably a piping system  19  running between the boiler  18  and the tank  10  for moving a heat-transfer medium between the boiler  18  and the tank  10 . 
     Hydronic steam boiler  18  preferably uses circulating hot water or steam as the heat-transfer medium for heating the grease trap waste stored in the holding tank  10 . For this purpose, as shown in  FIGS. 2A AND 2B , holding tank  10  preferably contains at least one set  54  of heating tubes  56  that run through the process holding tank  10 , so as to be immersed in the grease trap waste stored in holding tank  10 . The tubes are all connected to corresponding manifolds  58 , which, in turn, are connected to the piping system running between the hydronic steam boiler  18  and the storage tank  10 . Preferably, heated water or steam is transferred from hydronic steam boiler  18  to a first manifold  58 , which then distributes the heated water or steam to the tubes  56  which are connected to it, and which are immersed in the grease trap waste stored in tank  10 . The heated water or steam that is circulating in the tubes  56  serves to heat the grease trap waste by giving up its heat to the grease trap waste. Thereafter, the cooled water or condensed steam in the tubes  56  resulting from the heated water or steam giving up its heat to the grease trap waste passes to a second manifold  58 , through which the cooled water or condensed steam then returns to the hydronic steam boiler  18  for further heating. Where heated water is used, the water is circulated between the boiler  18  and the tank  10  preferably by means of a circulator pump  21 . Where steam is used, the steam is circulated from the boiler  18  to the tank  10  preferably by means of the pressure of the steam, and the condensed steam is returned from the tank  10  to the boiler  18  preferably by means of pitched pipes that allow gravity to eventually take the condensed steam back to the boiler  18 . 
     Preferably, holding tank  10  includes at least one set  54  of four immersion tubes  56 , more preferably, two sets  54  of four immersion tubes  56 , and most preferably, two sets  54  of five immersion tubes  56  running through it, providing a total of ten immersion tubes. Where there is one set  54  of immersion tubes  56 , preferably, the immersion tubes  56  are positioned generally in the center of tank  10 , although it should be noted that the tubes  56  could be located in other positions within tank  10 . Where there are two sets  54  of immersion tubes  56 , preferably, the immersion tubes  56  are positioned, such that one set  54  is generally located on one side of the tank  10  in the lower part of the tank  10 , while the second set  54  of tubes  56  is generally located on the other side of the tank  10  in the upper part of the tank  10 . The “five high/five low” arrangement of the tubes  56  in tank  10  allows all layers in tank  10  to heat more evenly. It has been found that the tubes  56  should be immersed in the grease layer  12  because grease will not heat well above hot water. The grease almost acts like an insulator, so the tubes  56  are kept to the side of inspection trough  60 , out of the way. 
     The one set of four immersion tubes has been found to be very effective in sufficiently heating the grease trap waste stored in holding tank  10 . Two sets of four immersion tubes provide a more satisfactory result in heating the grease trap waste in holding tank  10 . The most satisfactory result in heating the grease trap waste is provided by the two sets of five immersion tubes. Preferably, each of the tubes  56  in the sets  54  of immersion tubes is four inches in diameter and 21 feet long and connected to the other tubes in the set by a six inch manifold  58 . The four inch diameter, 21 foot long tubes  56 , and the number of such tubes  56 , are sized and numbered to provide “sufficient” heating of the amount of grease trap waste capable of being stored in a 10,000 gallon tank, such as storage tank  10 . The dimensions and/or number of the tubes  56  in tank  10  could be reduced where the size of the storage tank  10  is reduced. The boiler  18  shown in  FIG. 3  is about an 800,000 BTU per hour boiler; so it is of a size that can practically heat the ten tube  56  arrangement shown in  FIGS. 1 ,  2 A and  2 B. 
     The holding tank  10  also includes an inspection trough  60 , which is also used to inspect, filter and/or harvest the rich brown grease  12 . The inspection trough  60  is located on top of the storage tank  10 . Preferably, for the 10,000 gallon tank shown in  FIGS. 2A and 2B , the inspection trough  60  is two feet tall, four feet wide, and eight feet long, and welded into top of the tank  10 . The inspection trough  60  includes a lid  62  to cover, and thereby close, the trough  60 . 
     By heating the grease trap waste in the separator tank  10  to a temperature between 140-180 degrees Fahrenheit and then allowing it to rest for a period of 6 to 12 hours, stratification or separation is accomplished. Three distinct layers are formed, i.e., the bottom layer of residual water  16 , the upper mid layer of food debris  14  and the top layer of rich brown grease  12 . 
     Adjacent to the inspection trough  60 , also on top of the tank  10 , is an observation deck  64  by which an operator can inspect the contents of tank  10  to determine whether the grease trap waste heated in the separator tank  10  has stratified into the layers of residual water  16 , food debris  14  and brown grease  12 . To allow an operator to reach the observation deck  64 , an access stairs  66  is provided. Also provided for safety reasons is a guard rail  68  that extends around the observation deck  64  and along side the access stairs  66 . 
     The rich brown grease layer  12  in tank  10  is harvested after separation as a hot, brown grease oil. The hot grease oil has a viscosity similar to that of a 20W motor oil. This “grease oil” has viscosity, combustion, and heating value characteristics similar to the petroleum based Bunker 5, Bunker 6 or Heavy Fuel Oil discussed in the background section above. However, the grease oil is fat based, not petroleum based. After removal from tank  10 , the hot grease oil is filtered and then pumped either to the brown grease separator fuel equipment for refilling either the fuel tank  22  of the boiler  18  and/or a nearby insulated holding tank, which could be a road transport trailer ready for market. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.