Abstract:
A process for producing saleable liquids from organic material comprising the following steps. Providing organic material and separating it into solids, liquids and vapor. Reacting the liquids, combining it with water vapor and producing a volatized gas stream. Removing nitrogen dioxide from the gas stream to produce a scrubbed volatized gas stream. Reacting the scrubbed volatized gas stream with water vapor to produce a combined volatized gas stream. Removing carbon dioxide from the combined volatized gas stream to produce a subtracted volatized gas stream. Reacting the subtracted volatized gas stream with methanol to produce an enhanced volatized gas stream. Distilling the enhanced volatized gas stream to produce ethanol.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
     This patent application relates to U.S. Provisional Patent Application Ser. No. 60/381,710 filed on May 20, 2002 entitled Process for producing ethanol from sewage sludge which is Incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the production of ethanol from the processing of dewatered sewage sludge. 
     BACKGROUND OF THE INVENTION 
     Sewage sludge is typically processed by municipalities into a product called “cake”. This is the result of incubation with specialized bacteria for a prescribed length of time, then processing with a polymer prior to squeezing as much water out of the mixture as possible. The cake so formed is then disposed of in a variety of ways, all of which have problems. The most common means of disposal has been incineration, but studies are revealing that the metals, some of which are toxic, present in the sewage are accumulating in the soils around incinerators. 
     The second most prevalent means of disposal is the spreading of the partially processed sewage on agricultural, park, and other land. The sewage still has a significant number of pathogens present, however, which limits the type of crop grown and the time in which the harvest can safely be made. Sewage which is processed more than that used directly on the land is sometimes used for other types of fertilizer. The extent to which this can be done depends on the thoroughness of the processing, and the survival of some of the pathogens. 
     Some sewage sludge, (the cake), is sometimes landfilled. The persistent bacterial activity causes more methane to form than other waste. The problem of pathogen- and metal-leaching into the groundwater remains a concern. 
     All in all, the sewage remains a problem which has not resulted in a good solution. Sewage is a good source of organic feedstock for selected processes, and is underutilized. 
     SUMMARY OF THE INVENTION 
     According to the invention a process for producing saleable liquids from organic material comprises the following steps. Providing organic material and separating it into solids, liquids and vapour. Reacting the liquids, combining it with water vapour and producing a volatized gas stream. Removing nitrogen dioxide from the gas stream to produce a scrubbed volatized gas stream. Reacting the scrubbed volatized gas stream with water vapour to produce a combined volatized gas stream. Removing carbon dioxide from the combined volatized gas stream to produce a subtracted volatized gas stream. Reacting the subtracted volatized gas stream with methanol to produce an enhanced volatized gas stream. Distilling the enhanced volatized gas stream to produce ethanol. 
     In another aspect of the invention dewatered sewage sludge is dried continuously in a vessel at temperatures sufficient to volatize the water, leaving behind the organic components of the sludge. The steam produced by drying the sludge is used in another part of the process. The dried solids are then volatized in an oxygen-free vessel. The gas stream emerging is cleaned by conventional methods and scrubbed to remove chlorine and sulfur. The gases are then compressed and reacted in a heated vessel with steam and a catalyst to form a synthesis gas. 
     A calculated amount of biomass, typically wood waste, is steam-gasified in a separate vessel. The gases evolved are cleaned and compressed. Any carbon removed from the gas stream is processed with the sludge gases in the same reactor to form a synthesis gas. The compressed gases are reacted in a pressurized heated vessel to form methanol. The methanol is then processed in a separate heated vessel with a catalyst, and the synthesis gases from the sludge, to form ethyl alcohol (ethanol). 
     The vaporous mixture of alcohol and steam is cooled. Any unrecombined gases present are recycled through the burner used to heat the retorts used for drying the sewage or gasifying the biomass. The liquids from the cooler are then distilled to separate the ethanol and the water. Some water is recycled into the system, but there is excess which is removed from the process. 
     Both the retorts for the biomass gasification and the sludge volatizing are heated indirectly by the partial combustion of methane or a suitable mixture of combustible gases. The spent gases are blended in with the biomass gases to enhance the process yields and decrease air emissions. 
     Further features of the invention will be described or will become apparent in the course of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a flow chart of a process for converting organic material into saleable liquids; and 
         FIG. 2  is a schematic representation of an apparatus in accordance with the present invention for producing ethanol from sewage sludge. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  the process is shown generally at  10 . A mixture  12  of organic material mixed with water is pumped into a separator  14  wherein generally in the absence of oxygen (air) the mixture is separated into solids  16 , liquids  18  and gases or vapour  20 . The mixture  12  can be from 5-99% moisture (water). The process is particularly useful for the processing of sewage sludge. The pump is selected according to mixture consistency. 
     The separator  14  is heated at least to 115° C. However the temperature depends on the percentage of solids in mixture  12 . The separator  14  is slightly sub-atmospheric resulting from the gases being withdrawn. The solids  16  are removed from the process. The amount of moisture in the organic material and the temperature selected will determine the dwell time in the separator  14 . 
     Sulfur and chlorine are removed from the liquid as shown at  22 . These may be removed by passing the liquid  18  through an iron sponge. The liquids are then passed into a reactor  24  where they are heated to between 225 and 300° C. at 7400-7600 kpa. A catalyst  26  is added to the reactor  24 . The catalyst is cobalt (Co) on a ceramic or the like. In addition a portion of the vapour  20  which is generally water vapour is added. In reactor  24  generally a gas stream containing CO+H 2 +NO 2  is formed. 
     Gas stream is then cleaned or scrubbed  28  wherein NaOH is sprayed on the gas stream so that the NO 2  in the gas stream combines to form NaNO 2  which is removed thereafter. The gas also has particulate removed  30 . The gas is the remaining gas which is generally CO and H 2  is split into two streams in splitter  32 . 
     One portion of the gas stream is processed by a second reactor  34  wherein the gas stream is heated to 225-300° C. at 7400-7600 kpa. A catalyst  36  is introduced which is iron (Fe) and cobalt (Co) on a silica base or the like. As well a portion of the vapour  20  is introduced into reactor  34 . The gas is then separated  38  into CO 2 +H 2 +H 2 O. The CO 2  is removed from the gas stream. 
     The gas stream is then passed into a third reactor  40  wherein H 2  and H 2 O are combined with methanol. Third reactor  40  combines gases from four gas streams described in more detail below. Third reactor is at a range of 350-380° C. and a pressure of 19,443 to 21,490 kpa in the presence of catalyst such as iron and cobalt on a silica base. The gas stream is distilled  42  into three components, specifically H 2 , H 2 O and ethanol. The H 2  is passed to a combustor  44  wherein it is combusted with oxygen and the combustor is used as a heat source. The water  46  is removed. 
     The water vapour  20  discussed above is divided into three streams. One stream is added to reactor  24 , another stream is added to second reactor  34  and the third stream is passed fourth reactor  48 . In the fourth reactor the gas stream is reacted with natural gas at a temperature of 225-300° C.; 7400-7600 kpa in the presence of a catalyst Fe and CO on silica. 
     If necessary sulfur and chlorine are removed from the liquid with an iron sponge. Similarly the gas may be scrubbed wherein NaOH is sprayed on the gas stream so that the NO 2  in the gas stream combines to form NaNO 2  which is removed. This gas stream is then passed to third reactor  40 . 
     A separate stream may be used to produce methanol that is added to the gas stream. For example the input may be biomass  50 . The biomass is gasified  52  in for example a fluid bed gasifier. The handling of the biomass is determined by the particular gasification method chosen and the moisture content of the particular biomass chosen. It may be that predrying is included. The heat for gasification may be provided by combustor  44 . The gasification is provided at 650-900° C., and preferably at 650 C. Gasification generally takes place in the absence of oxygen. The gas stream is cleaned  54  to remove carbon particles. The gas stream is passed to a fifth reactor  56 . The carbon particles are processed via a water/gas shift  58  to produce syngas. This takes place at a temperature of 225-300° C. and pressure 7400-7600 kpa in the presence of a catalyst which is a Fe and Co on silica base. The resulting syngas are then passed to fifth reactor. Natural Gas is combusted  60  using sub-stoichiometric oxygen (O 2 ) (ratio 2:1) to produce heat and syngas. The heat is used for gasification or other reactors where heat is required. The syngas is directed to fifth reactor  56 . 
     In reactor  56  the three gas streams are heated to a temperature of 200-300° C. and pressure of 50-150 atm in the presence of a catalyst Copper-zinc oxide-aluminium oxide, or selected from the group of state-of-the-art catalysts. 
     As discussed above preferably heat for the process is provided by the combustor  44  and partial oxidation of the natural gas  60 . 
     Referring to  FIG. 2  an apparatus for producing ethanol for sewage sludge is shown generally at  100 . Dewatered sewage sludge  102  containing on average 80% moisture is fed continuously into an air-free drying vessel  104 . However it will be appreciated that sludge with a higher water content could also be processed. The temperature is controlled to volatize the water, leaving the organic components without breaking the chemical bonds. Nonvolatized material is continuously removed from the vessel  104  and sent to a gasifier or volatizer  106 . Volatizer  106  is also generally air-free, and is heated to a temperature which volatizes the organic compounds without breaking chemical bonds. Inorganic components remain in the vessel and are removed at intervals  108 . The volatized gases exit from the gasifier  106  and are scrubbed  110  to remove chlorine and any other elements such as arsenic. The gases are then compressed  112 , then fed into a pressurized catalytic reactor  114  where they are converted into a synthesis gas containing a preponderance of carbon monoxide and hydrogen. 
     While sewage sludge is being dried and processed, dry biomass  116  with about 20% moisture is fed into a gasifier  118 . It will be appreciated by those skilled in the art that biomass with a higher moisture content could also be used but then it would be predried. The gasifier  118  is heated indirectly by the combustion of gases in a burner  138  in the presence of sub-stoichiometic oxygen. The oxygen is produced by an oxygen generator  122 , which is set to supply enough oxygen to combust the gases to form maximum carbon monoxide and hydrogen. The gasifier is fed with steam exiting from the sewage dryer  104  to steam-gasify the biomass. The gases emerge from the gasifier  118  and are cleaned  124  by the removal of particulate matter  125 . The particulate matter  125  which is typically carbon is collected and sent to the synthesis gas reactor  114 . The gases from the gas cleaner  124  are first compressed  126  then sent to a heated reactor with a catalyst selected to form methyl alcohol (methanol)  130 . 
     The products from the methanol reactor  130  are sent to a heated pressure vessel or ethanol reactor  134  which has a catalyst selected to form ethyl alcohol (ethanol). The vapor stream emerging from the ethanol reactor  134  is cooled in a chiller  136 , and the liquids sent on to a distillation column  142 . If there are gases present in the chiller  136 , they are sent to the burner at  138  and mixed with the combustion gases  140 . 
     The distillation column  142  separates the ethanol  144  from water  146 . The ethanol  144  is removed from the process for sale. Some of the water  146  is used to supply internal processes such as the reactor  148 . This reactor  148  supplies additional synthesis gas to the methanol reactor  130  by the processing of methane with water. The water  146  not needed in the system is removed from the process. 
     Combustion gases are needed for heating at several stages in the process. They are supplied to burner  138  and are burned in the presence of sub-stoichiometic oxygen supplied by the oxygen generator  122 . The resulting spent gases are high in carbon monoxide and hydrogen and merge with the stream from the gas cleaner  124  where they are compressed  126  prior to entering the methanol reactor  130 . The burner  138  also supplies hot gases to indirectly heat the dryer for the sewage sludge  104 . The spent gases are then compressed  126  and sent to the methanol reactor  130 . 
     As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and opened rather than exclusive. Specifically, when used in this specification including the claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or components are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
     It will be appreciated that the above description related to the invention by way of example only. Many variations on the invention will be obvious to those skilled in the art and such obvious variations are within the scope of the invention as described herein whether or not expressly described.