US20010039760A1

US20010039760A1 - Zero-pollution wastes disposal and energy generation

Info

Publication number: US20010039760A1
Application number: US09/802,399
Authority: US
Inventors: Shang-I Cheng
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-17
Filing date: 2000-12-11
Publication date: 2001-11-15

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

U.S. No. Pat. 4,353,713 10/1982 Cheng . . . 48/202

U.S. No. Pat. 4,448,588 5/1984 Cheng . . . 48/99

U.S. No. Pat. 4,597,771 7/1986 Cheng . . . 48/77

U.S. No. Pat. 4,594,140 6/1986 Cheng . . . 208/414

STATEMENT REGARDING FEDERALLY SPONSORED AND DEVELOPMENT

Not applicable.

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable.

FIELD OF INVENTION

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

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 ₂reaction comes from CO₂—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

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'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

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.[0010]

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the present preferred embodiment of the method of the invention. [0011]

Mixing the Feeds Into The Pyrolyzer

As can be seen from the attached drawing, coal is fed into co storage [0012] 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)

Coal, ground MSW, sludge solid contents and the catalyst are all pyrolyzed in [0013] 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

The pyrolyzed residues are continuously or intermittently flow into the feed mixture bin [0014] 4. From which, the pyrolyzed residues are fed into the integrated gasifier 9 via lines 106 and 111 by means of a screw conveyor 4a. Compressed CO₂from line 155 which leads from the CO₂compressor 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, Na₂CO₃, K₂CO₃, LiCl, Li₂CO₃and 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)

Municipal sewage sludge is pumped from the [0015] 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

The gasification residues leave the gasifier via [0016] 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

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 [0017] 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.
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 [0018] cyclone 12 attaching to gasifier 9. Then it passes through line 127 into waste-heat-boiler 16, then via line 140 into the CO₂absorber 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 E1 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

A part of the carbon-dioxide-free product gas from the [0019] 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.

Claims

I claim:

1. A method for improving the economy, efficiency and promoting a smoother operation of the system of zero-pollution wastes disposal and clean energy generation by introducing a catalyst into the integrated process of gasification of coal municipal solid wastes and sewage sludge.

(a) The said catalyst mentioned in

claim 1

consists of salts of two metals to lower the optimal temperature of the carbon-steam reaction by about 100° C. and to prolong the life of the reactor.

(b) The catalyst defined in

claim 1

(a) consists of two parts.

The first part I is selected from one of the salts of chlorides, sulphates, carbonates of sodium or potassium:

Part II is taken from one of salts of the chlorides, sulfates, or carbonates of iron or chromium.

(c) In the said catalyst defined in

claim 1

(a) and 1(b), the atomic ratio of metal I (sodium or potassium) to metal II (iron or chromium) lies between 1:50 to 50:1.

(d) The quantity of the said catalyst defined in claims 1(a) to 1(c) recycling in the system between the gasifier and preheater-combustor, back and forth, is between 0.05 to 5% of the total weight of feed to the gasifier.

(e) The said catalyst defined in claims 1(a) to 1(c) is depleted continuously in the system by various losses. The depletion is made up continuously or intermittently by adding fresh catalyst into the gasifier. Alternative, it is added into the system through the pyrolyzer. In the latter case, the quality of the pyrolyzed gas is improved.

2. A method of improving the system of zero-pollution wastes disposal and clean energy generation by supplying the heat required by carbon-steam reaction in the gasifier through using both the direct and indirect heat transfer simultaneously.

(a) The said indirect method of supplying heat in

claim 2

consists of burning a fuel gas outside the walls of the gasifer in a kiln or a furnace designed for this purpose. The said direct method of heat transfer defined in

claim 2

is to utilize the heat from the reaction between carbon dioxide and the calcined lime in the gasifier.

(b) In the simultaneous heat transfer as defined in

claim 2

, the amount of heat transferred by direct means to that by indirect transfer through the walls of the gasifier varies from 1:4 to 4:1.

3. A method of improving the economy, efficiency and promoting a smoother operation of the system of zero-pllution wastes disposal and clean energy generation by extracting clean steam from raw sewage sludge to support carbon-steam reaction, which comprises of:

(a) passing the raw sludge into a series of steam jacketed screw-conveyor type sludge-solid-content removers. The separation of the solids and water components of the sludge is carried out under the combined influence of mechanical shears, electrolytes and heating.

(b) Removing the remaining solid contents of the water coming out of sludge-solids-removers further by a filter.

(c) Feeding the water passing through the filter and one or series of ion-exchanger to a boiler to generate clean steam which is utilized for supporting carbon-steam reaction.