Abstract:
A zero-pollution wastes disposal and clean-energy generation system is improved by introducing to it a catalyst to lower down the gasification temperature and to prolong the life of the gasification reactor, a simultaneous direct and indirect heat transfer to supply the heat required for carbon-steam reaction and a means for extracting clean water from raw sewage sludge to supply the steam required by carbon-steam reaction. These improvements increase the efficiency and economy of the system and promote the smoothness of its operation.

Description:
REFERENCES CITED  
       U.S. PATENT DOCUMENTS  
         [0001]    U.S. No. Pat. 4,353,713 10/1982 Cheng . . . 48/202  
           [0002]    U.S. No. Pat. 4,448,588 5/1984 Cheng . . . 48/99  
           [0003]    U.S. No. Pat. 4,597,771 7/1986 Cheng . . . 48/77  
           [0004]    U.S. No. Pat. 4,594,140 6/1986 Cheng . . . 208/414  
         STATEMENT REGARDING FEDERALLY SPONSORED AND DEVELOPMENT  
         [0005]    Not applicable.  
         REFERENCE TO A “MICROFICHE APPENDIX” 
         [0006]    Not applicable.  
         FIELD OF INVENTION  
         [0007]    This present invention relates to processes and equipment for the integrated gasification of coal, municipal solid wastes, sewage sludge and hazardous wastes. It also relates to the generation of clear energy from various wastes and coal.  
         BACKGROUND OF THE INVENTION  
         [0008]    With the declining of cheap energy sources and increasing concern for environmental contamination by various wastes, I made a number of proposals in form of U.S. patents. These include: 1. a process which can gasify municipal solid wastes, coal, sewage sludge and hazardous wastes at the same time (U.S. Pat. No. 4,353,713), 2. an apparatus to accommodate the said process (U.S. Pat No. 4,448, 588), 3. a fluidized reactor system for the integrated gasification of coal and various wastes (U.S. Pat. No. 4,597,771), and 4. an integrated gasification system for carrying out coal liquefaction and electricity generation simultaneously. (U.S. Pat. No. 4,594,140). All of these processes or apparatus have three common features: 1. All of them have an integrated gasifier, which is operated at temperatures above 800° C. At such high temperatures, the reactor life may be shortened, 2. in all of them, the reaction heat for the C—H 2 reaction comes from CO 2 —CaO reaction only. It is designed to use the latter reaction to supply all the heat required by the gasification, the feed to the gasifier will be too bulky and the gasifying reactor will be oversized, 3. for economical as well as environmental reasons, all the prior arts prefer to use sewage sludge as source of steam to support the integrated gasification. However, even sewage sludge contain only 3 to 4% of solids, the colloid nature of the suspension renders the conventional separation methods ineffective. Therefore, without improvement in the separation of the solid contents from the sludge before it is converted into steam, pipe lines in the steam generation system tend to be plugged by solid deposits. Due to these mentioned technical difficulties, the mentioned prior art processes or apparatus must be improved to make them more effective and less troublesome.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    It is therefore an object of the present invention to provide a catalytic reaction lowering the gasification temperature by about 100° C., prolonging the gasifier&#39;s life and improving the quality of product fuel gas. It is another object of this invention to provide a flexible method of supplying the heat required for gasification and a smoother operation. The third object of this invention is to provide the system of zero-pollution wastes disposal and clean energy generation with a process of producing clean steam from raw sewage sludge. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0010]    The above mentioned objects, features and advantages of the present invention will become more readily apparent from the attached drawing. There is only one view for the drawing. However, this drawing serves as a flow sheet for the preferred embodiment of an apparatus complex for implementing the method of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    Reference will now be made in detail to the present preferred embodiment of the method of the invention.  
       Mixing the Feeds Into The Pyrolyzer  
       [0012]    As can be seen from the attached drawing, coal is fed into co storage  2  via line  101 . From the storage, the coal is sent into a crusher  3  via line  102 . The coal may be ground to a finer size if necessary. The catalyst comes from feed line  113 . The ground municipal solid wastes (WSW) pass through MSW feed line  115 , then the MSW grinder  10 , via the MSW feed line,  114 , into pyrolyzer  5 . Finally, the solid contents from sludge solids removers,  17  and  18 , together with the solids from the filter  19  via line  119  are also fed into pyrolyzer  5  through line  120 .  
       Pyrolysis of Coal, MSW and Solid Contents of Municipal Sewage Sludge (MSS)  
       [0013]    Coal, ground MSW, sludge solid contents and the catalyst are all pyrolyzed in  5 . Alternatively, the catalyst can be fed into the integrated gasifier  9  directly instead of feeding into the pyrolyzer  5  indirectly. The heat required by pyrolysis is supplied by burning pyrolyzed gases from the storage  1  via line  152 , or by burning a part of the product gas coming from gas storage  6  through lines  107  and  104  . The pyrolyzer is a part of a kiln or a furnace (not shown).  
       The Integrated Gasification  
       [0014]    The pyrolyzed residues are continuously or intermittently flow into the feed mixture bin  4 . From which, the pyrolyzed residues are fed into the integrated gasifier  9  via lines  106  and  111  by means of a screw conveyor  4 a. Compressed CO 2  from line  155  which leads from the CO 2  compressor  23  is fed into the gasifier. The carbon dioxide reacts with lime (or calcined dolomite) which is recycled into the gasifier via stream  154  from the air preheater  8 . From time to time the system is replenished with fresh lime (or calcined dolomite) through line  110 . The required steam comes from the waste heat boiler  15  via lines  129  and  130 . And the pressure of the steam is bolstered by the compressor  14 . To decrease the gasification temperature by about 100° C. and improve the quality of the product gas, a catalyst is added directly into the gasifier or indirectly into the system through the pyrolyzer. Without the catalyst, the carbon-steam reaction carries out at temperatures around 850 to 900° C. These high temperatures would shorten the life of the gasifier. Since these temperature are above the decomposition temperatures of limestone and dolomite, in order to drive the recombination of carbon dioxide and lime or calcined dolomite, a high pressure in the gasifier is necessary for carrying out the exothermic reaction to provide the reaction-heat for carbon-steam reaction. The use-of catalyst can lower the optimum temperature of carbon-steam reaction down to around 777° C. The catalysts employed are various combinations of alkaline metal salts-and salts of iron and chromium. Alkaline metal salts consist of NaCl, KCl, Na 2 CO 3 , K 2 CO 3 , LiCl, Li 2 CO 3  and sulfates of sodium, potassium and lithium. The second part of the catalyst consists of chlorides, sulfates and carbonates of iron and chromium. The atomic ratio between alkaline metal and iron or chromium varies between 5 to 95 to 95 to 5. The quantity of catalyst used is in the range from 0.01 to 5%. If the gasification-heat is solely coming from the recombination of carbon dioxide and lime (or calcined dolomite), the feed mixture to the gasifier will be too bulky. Therefore, a part of the heat required for the gasification should come from indirect-heat-transfer from burning a part of the pyrolyzed gas generated. The ratio between these two heat sources(heat from indirect-heat-transfer to the chemical reaction heat) varies from 1:4 to 4:1. To lower the cost of carbon dioxide, the supply of carbon dioxide to the gasifier should adopt a counter-current principle to keep the partial pressure of carbon dioxide in the product stream leaving the gasifier as low as possible.  
       Generation of Clean Steam From Municipal Sewage Sludge (MSS)  
       [0015]    Municipal sewage sludge is pumped from the MSS storage  13 , via line  151 , and mixed with 0.05 to 4.0% of electrolytes choosing from soluble salts of sodium, potassium and iron, into a series of sludge solids removers  17  and  18 . They are screw-conveyor type heat-exchangers. The water content of the sludge flows into a filter  19 . The solid contents of the MSS are removed from the liquid phase by a combined influence of mechanical shears, heat, electrolytes and filtration. The soluble contents and the hardness of the MSS are removed by chromatograph and ion exchangers (not shown in the drawing). The purified water is pumping to waste-heat-boiler  15  via line  131 . The heat supplied to the boiler is coming from the flue gas leaving the combustor  7  via line  128 . The steam from boiler  15  is fed into steam compressor  14 . High pressure steam from  14  is fed into the integrated gasifier to support the carbon-steam reaction.  
       Combustion of Gasification Residues  
       [0016]    The gasification residues leave the gasifier via lines  118 ,  125  and move into combustor  7 . They are burnt with the preheated air from air preheater  8 . Air comes into preheater  8  via line  109 . The air is preheated by the outgoing calcined lime (or dolomite) and the ashes from the burning of gasification residues. The air should be preheated to 700-800° C. or above before entering combustor  7 . The preheater and the combustor can be two zones of one piece of equipment. In the combustor, the preheated air meets with the hot (around 777° C.) gasification residues from the gasifier counter-currently. A combustion temperature above 1600° C. can be achieved. Under such condition, the limestone (or dolomite) formed in the gasifier decomposes to carbon dioxide and calcined lime (or calcined dolomite). A part of the heat from the combustion is stored endothermically in the mixture of carbon At dioxide and calcined lime (calcined dolomite) as chemical energy. This energy will later release exothermically when carbon dioxide and lime (or calcined dolomite) recombine in the gasifier to support the carbon-steam reaction (which is endothermic). Hazardous materials present originally in the feed stocks or in the raw hazardous wastes introduced into the combustor, or formed in the pyrolysis or gasification, such as PCBS, dioxins, pesticides, etc. are destroyed at such high temperatures. Hydrochloric acid and chlorine formed are neutralized by the lime or calcined dolomite present. In both the preheater and the combustor, high turbulence is produced in the air and solids streams by rotary stirrers in case of small scale operation and by means of rotary type kiln in case of large scale operation. Extremely efficient heat-transfer is maintained between the media, the lime (or dolomite) mixed with ashes and the air. The lime (or calcined dolomite) and ashes, after serving as heat transfer agents, are returned to the gasifier to recombine with carbon dioxide to generate heat required for carbon-steam reaction. The flue gas which contains considerable quantity of carbon dioxide is first sent to a waste heat boiler  15  vis line  128 , then into a carbon dioxide recovery system through lines  132  and  141 . The walls of the combustor and the preheater are subjected to high temperatures, they should be made of tantalum or its alloys. The combustor and preheater pair is optimally designed to achieve a combustion with a highly preheated air, thermal field averaging, highly efficient heat transfer, maximum heat recovery and minimum NOX formation. Additional heat transfer agent such as ceramic balls may be introduced into the system to increase the temperature of the preheated air. In a extreme case, pure oxygen may be admitted to enrich the oxygen content of the incoming air.  
       The Treatment of Lime (or Calcined Dolomite)-Ash Mixture  
       [0017]    After recycling many times between the gasifier and the combustor, the lime (or calcined dolomite) will lose its ability to recombine with carbon dioxide. Therefore, part of the lime (or calcined dolomite)-ash mixture must be purged, and fresh lime (or limestone) or dolomite must be added into the system through line  110 . The purged stream is leached with water. The heavy metals content of the leachate is recovered fractionally with hydrogen sulfide or other agents. The remaining solution is evaporated to recover its soluble salt contents which is recycled back to the system to served as catalyst.  
         [0018]    Purification, Disposal and Utilization of Carbon Dioxide There are three reasons for the recovery of carbon dioxide from both the product gas and the flue gas: 1. The removal of carbon dioxide from the product gas will increase its heating value of combustion, which will in turn increase the efficient of power generation when the product gas is used as the energy source. 2. The removal of carbon dioxide from the flue gases will prevent the releasing of this global warming gas into the atmosphere. 3. This process requires that a part of recovered carbon dioxide be recycled to the gasifier to promote the recombination of carbon dioxide and lime (or calcined dolomite) to supply the heat required by the carbon-steam reaction. In this system, there are two absorber-stripper pairs. One for the product gas, another for flue gases. The raw product gas comes from cyclone  12  attaching to gasifier  9 . Then it passes through line  127  into waste-heat-boiler  16 , then via line  140  into the CO 2  absorber  24 . In  24 , carbon dioxide is absorbed by one of the solutions of alkali, methyl and ethyl amine or other absorbing agents. In stripper  25 , carbon dioxide is stripped from the absorbing agent by a low pressure steam. The absorbing liquid is recycled between the two towers via line  142 . A part of the recovered carbon dioxide is compressed as a gas by compressor  23  and it is recycled into the gasifier via line  155 . And the rest carbon dioxide is further liquefied, and discharged through lines  146  and  148 , to beneficial disposal, such as ocean dumping, replacing methane from methane-hydrate, tertiary oil recovery or-other industrial utilization. Equipment E 1  is another similar carbon dioxide recovery system for the flue gases. Flue gases come from waste-heat-boilers  16  and  20  and via lines  132  and  140 . The clean flue gas is discharged into atmosphere through line  153 .  
       Dual Cycle Power Generation  
       [0019]    A part of the carbon-dioxide-free product gas from the absorber  24 , passing through lines  138  and  135 , is burned in a gas turbine  22 . Electricity is delivered via line  144 . The combustion exhaust from  22  is sent to a steam turbine to generate additional electricity, which is delivered via line  143 . The exhaust steam from the steam turbine, passing through line  145  and entering tower  25 , is used as process steam, mainly to recover pure carbon dioxide in the carbon dioxide stripping tower  25 . The balance of the product gas is sent to the product gas storage  6  via line  123  for the propose of process heating.