CA1082921A

CA1082921A - Method and apparatus for producing synthetic fuels from solid waste

Info

Publication number: CA1082921A
Application number: CA246,522A
Authority: CA
Inventors: Michael J. Antal, Jr.
Original assignee: US Department of Energy
Current assignee: US Department of Energy
Priority date: 1975-03-28
Filing date: 1976-02-25
Publication date: 1980-08-05
Also published as: DE2612040A1; JPS51138704A; FR2305489B1; GB1534759A; CH610594A5; FR2305489A1; BE839896A; US3993458A

Abstract

Abstract of the Disclosure Organic solid wastes represented by the general chemical formula CXHYOZ are reacted with steam at elevated temperatures to produce H2 and CO2. The overall process is represented by the re-action CXHYOZ + 2(X-Z/2)H2O ? XCO2 +
(1) [(Y/2) + 2(2X-Z/2)] H2 .

Reaction (1) is endothermic and requires heat. This heat is sup-plied by a tower top solar furnace; alternatively, some of the solid wastes can be burned to supply heat for the reaction. The hydrogen produced by reaction (1) can be used as a fuel or a chem-ical feedstock. Alternatively, methanol can be produced by the commercial process CO2 + 3H2 ? CH3OH + H2O . (2) Since reaction (1) is endothermic, the system represents a method for storing heat energy from an external source in a chemical fuel produced from solid wastes.

Description

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METHOD AND APPARATUS FOR PRODUCING SYNTHETIC

' FUELS FROM SOLID WASTES
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; Background of the Invention 1. Field of the Invention ~; Past research has suggested that only a small fraction of our nation's energy demand can be met with fuel produced from , solid wastes. However, research presently being conducted suggests that hydrogen produced from solid wastes could econom-ically meet the nation's entire natural gas demand. Alter-natively, large quantities of methanol could be produced by this system for use as a motor fuel.
Organic solid wastes represented by the general chemical ; formula CXHyOz are reacted with steam at elevated temperatures to produce H2 and CO2. The overall process is represented by ~,` the reaction CXHyOz + 2(X-Z/2)H2O ~ XCO2 + ~(Y/2) + 2(X-Z/2)]H2 . (1) ; ., ~
, Reaction (1) is endothermic and requires heat. This heat is supplied by a tower top solar furnace; alternatively, some of ~,.;-~il 20 the solid wastes can be burned to supply heat for the reaction.
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The hydrogen produced by reaction (1) can be used as a fuel or a chemical feedstock. Alternatively, methanol can be produced by the commercial process C2 + 3H2~ CH30H ~ H20 . (2) Since reaction (1) is endothermic, the system represents a method for storing heat energy from an external source in a chemical fuel produced from solid wastes.
The system of this invention uses solar energy to provide heat for the pyrolysis of solid wastes and the gasification of the remaining char. Pyrolysis of solid wastes results in the evolution of C02, C0, H2, CH4 and various other gases, tars, oils, and char. The gaseous and liquid by products are catalytically converted to H2, C0, CH4, and C02 in a steam atmosphere using a commercial nickel catalyst. The remaining char, C0, C02, and CH4 are catalytically reacted according to the following formulae:
:
!;, CH4 + 2H20 ~ C02 + 4H2 C2 + C ~ 2C0 (4) ; CO + H20 ~ C2 + H2 ; 20 C + H20---~ C0 + H2 (6) ; Thus pyrolysis of solid wastes in a steam atmosphere has been used to manufacture a producer gas containing H2, C0, and C02.
The C0 can be shifted to hydrogen, or reacted with the hydrogen already present to produce methanol using the commercial reaction CO + 2H2----t CH30 (2) Alternatively, if a producer gas rich in C0 is desired, some C02 can be added to the steam reactant to produce excess C0 via re-action (4).
Reactions (4) and (6) are normally observed at temperatures above 800C and such temperatures impose severe engineering prob-lems. Catalysts have been used to lower the temperature range .

~82921 for the practice of reaction (6), however, catalysts have not been discovered for reaction (4) using pyrolytic char from solid wastes as a source of carbon. The catalysts cobalt molybdate, NaHCO3, and other alkali metal catalysts have been successfully employed to facilitate reaction (4). The catalysts were dissolved in water and deposited on the char by soaking the char in the catalyst-water solution and subsequently vaporizing the water. Since reactions (3), (5), and ~6) require water (steam) this method of catalyst deposition is well suited to the system of interest. The catalyst is recovered by soaking the ash residue remaining after the gasi-fication of the solid wastes in water. Tables 1 and 2 illustrate the effect of the catalysts on reaction (4) for representative space velocities and temperatures.

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' BLANK RUNS

Description: CO2 was reacted with char produced by the ' Monsanto Process containing no catalyst Temperature Space Velocity % Conversion 700C 59.3 cm31min trace 750C 59.3 cm3/min 4%
' 750C 10.8 cm /min 9%
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CATALYST RUNS

; Description: CO2 was reacted with char produced by the Monsanto Process. The cata-lyst was deposited on the char by the method described in the text Temp. Space Velocity Catalyst % Conver.

700C 59.3 cm ~min NaHCO3 5%
750C 59.3 cm3/min NaHCO3 12%
750C 59.3 cm3Jmin Cobalt 8%
Molybdate ~ 750C 10.8 cm3~min Cobalt 16%
;~ Molybdate ` - 3 -.:
''' 10829Zl ; 2. Prior Art The PURO ~ System (covered by U. S. Patent No. 3,729,298) was developed by Union Carbide Corporation in response to the need for advanced solutions to the problems of solid waste dis-posal and resource recovery. The PUROX System utilizes oxygen, instead of air, to produce high-temperature incineration and pyrolysis of all types of refuse. The only products formed are a compact, sterile residue and a fuel gas valuable as a clean-burning source of energy. The basic PUROX System consists of a vertical shaft furnace into which refuse is fed through a charg-ing lock at the top. Oxygen is injected into the combustion zone at the bottom of the furnace where it reacts with carbon ; char residue from the pyrolysis zone. The temperature generated in the hearth is sufficiently high to melt and fuse all noncom-bustible materials. The molten material continuously overflows from the hearth into a water quench tank where it forms a hard, sterile granular product. The hot gases formed by the reaction of oxygen and carbon char rise through the descending waste. In the middle portion of the vertical shaft furnace, organic mate-rials are pyrolyzed under an essentially reducing atmosphere to yield a gaseous mixture high in carbon monoxide and hydrogen (typically about 50~ CO and 30% H2 by volume on a dry basis). As ; the hot gaseous products continue to flow upward, they dry the ; entering refuse in the upper zone of the furnace. The high ther-mal efficiency of PUROX System is indicated by the relatively low temperature (about 200F) of the by-product gas exiting through a duct to the gas cleaning section of the system. As it leaves the furnace, the gas mixture contains water vapor, some oil mist formed by the condensation of high-boiling organics, and minor ~, :'~

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~V82921 amounts of fly ash. ~he oil mist and fly ash solids are re-moved by a gas cleaning system~ After cleaning, the product gas is passed through a condenser. The resultant dry gas is a clean-, burning fuel, comparable to natural yas in combustion character-istics. Its heating value is approximately 300 BTU/cu.ft.
This recovered gas can be used effectively as a supplementary i fuel in an existing utility boiler or other fuel-consuming oper-ations without downrating of the boiler or making extensive and costly boiler modifications. Because the gas produced by the 10 PUROX System is essentially sulfur-free and contains only about one-tenth the amount of fly ash allowable under federal air ~uality standards, it is an ideal fuel for all types of existing gas-fired furnaces.
The system produces four times as much energy as it consumes.
Only 20~ of the total energy recovered by the system is needed to ` meet all of its internal energy requirements, including that con-sumed to produce oxygen used in the furnace. The remaining 80%
` is available for other fuel applications. This is an important recovered resource, particularly in view of the growing shortage of clean fuels. The granular solid residue produced from the noncombustible portions of the refuse is free of any biologically active material. The volume of solid by product is only about

2 to 3 percent of the volume of incoming refuse, depending upon the amount of noncombustible materials in the mixed wastes. By , contrast, a well-designed and efficiently-operated conventional incinerator produces a solid residue volume of 10% or more of the ~olume o~ refuse burned. Importantly, the dense granular residue produced by the PUROX System is considered suitable as a construc-tion fill material or for other potentially valuable uses. The .... .

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PuRox System is notaDle in another xespect. It is designed to use only a small fraction of the oxidant gas required in conven-tional incineration. The PUROX System requires only one-fifth of a ton of oxygen per ton of refuse, while a conventional inciner-ator requires approximately seven tons of air per ton of solid waste burned. This 3~-fold difference in oxidant gas flow means that the PUROX System will produce only one-twentieth as much gas-volume to be cleaned. This factor, in turn, makes it possible to reduce fly ash content in the ~aseous emissions to less than one-tenth of that attainable with a conventional incinerator.
Combustion of the fuel gas from the PUROX System produces emis- ~-sions far below the allowable maximum specified by federal air quality standards. The use of oxygen enables the PUROX System to process effectively solid waste of widely varying composition.
This flexibility is especially advantageous in adapting to operat-ing variations which commonly result from seasonal, regional, and socio-economic factors. Another important feature of this System is its compatibility with other solid waste disposal facilities either new or existing. It can readily handle refuse in "as re-ceived" condition, or it can be used to treat refuse which hasbeen preprocessed by shredding, separation, or resource recovery ~ operations in existing equipment.
i~ 3. Comparison of Prior Art and the Method and Device of This Invention ' Similarities:
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~ Both produce a clean~urning gas, eliminate pollution admis--- sions to the atmosphere, are flexible enough to handle a variety of solid wastes, and appear to be economically attractive.

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Dissimilarities:
The prior art (PU~OX) uses combustion, pyrolysis, and requires a source of pure oxygen which results in a granular residue. The method and device of this invention is a pure pyrolysis process which produces 190% more clean, usable energy per ton of refuse than the prior art. This invention does not leave a granular residue but does require an organic feedstock (separation and classification of the solid wastes) and a high temperature heat source and catalyst. The prior art method does not require a pure organic feedstock, external heat source nor catalyst.
Advantages:
The method and device of this invention produces much more -- energy per ton of solid waste than the PUROX method. It produces hydrogen, which can be used to replace natural gas in a hydrogen .
economy, to make fertilizer, or as a chemical feedstock.
Alternatively, the hydrogen can be reacted with either CO2 or CO
using commercial processes to produce methanol for use as a .....
gasoline additive. It does not produce a granular residue requiring disposal. It does not require a source of pure oxygen (although such a source may prove useful). It provides an attractive method for putting solar energy to use.
Summary of the Invention According to the invention, a method for employing an external moderately high temperature heat source in the pyrolysis ,~ and gasification of organic material comprises: A. heating by '~ means of solar energy using a tower top solar furnace either steam, carbon dioxide, or a mixture of steam and carbon dioxide ~- to a temperature of 600-700C in a reactor; B. mixing the organic material with either cobalt molybdate, sodium bicarbonate, or a mixture of cobalt molybdate and sodium bicarbonate;

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-~ 1082921 C. injecting the heated steam or carbon dioxide or mixture thereof under pressure into a porous reactant bed on which the mixture of organic material and catalyst is located, thus fluidizing the mixture; and D. allowing the organic material to pyrolyze, thus producing a solid char residue and H2, CO2, CO, ~ .
CH4, or any mixture thereof.
Also according to the invention, an apparatus suitable for carrying out the above-recited method of the invention is given.
Also, according to the invention, any suitable heating means to achieve a temperature of 600-700C is used in a method : of pyrolyzing and gasifying organic material, the method compris-ing:
A. heating steam, carbon dioxide, or a mixture of steam - -and carbon dioxide to a temperature of 600-700C in a reactor;
B. mixing the organic material with cobalt molybdate;
C. injecting heated steam or carbon dioxide or mixture thereof under pressure into a porous reactant bed on which the mixture of organic material and cobalt molybdate is located, thus fluidizing the organic material; and D. allowing the organic material to pyrolyze, thus producing a solid char residue and H2, CO2, CO, CH4, or any mixture thereof.
. Further, according to the invention, a method for reducing to 600-700C the temperature required for gasifying char accord-ing to the reaction C02 ~ C --~ 2CO comprises using as a catalyst cobalt molybdate.
8rief De~scription of the Drawing , .
The FIGURE shows a flow sheet and schematic of this invention for the production of hydrogen by employing a tower top solar furnace for the pyrolysis and gasification of solid waste or other organic materials.

-7a--- Description of the Preferred Embodiment A method for employing an external moderately high temper- -ature heat source in the pyrolysis and gasification of solid wastes, coal, or other organic materials is described as follows:
As shown in the FIGURE, steam, CO2, or some mixture of these two gases is heated to a temperature of 600C or more in a chemical reactor located at the focus of a tower top solar furnace.
This working fluid (steam, CO2, or a mixture thereof) is used to fluidize the reactant bed of char and organic material. For our purposes we assume the material to be solid wastes; however, the - process is also suitable for any other type of organic material (coal, manure, food waste, etc.). As further shown in the FIGURE, solid wastes, shredded or unshredded, depending on the economics of the system, are introduced into the top of the reactor through a feed hopper and an airlock system. At this time they are mixed with a steam-carbon catalyst. The wastes ,....
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~ 082921 the intense heat of the working fluid, producing char and a gas-eous product containing tars, oils, liquors, and gases (CO2, CO, CH4, and H2). The higher hydrocarbons may be "cracked" catalytic-ally so that the pyrolysis gas contains only H2, CO2, CO, and CH4. The solid char migrates to the bottom of the reactor where it is catalytically gasified by the working fluid using the re-actions C + H2O ~ CO + H2 (7) CO + H2O ~ CO2 + H2 (8) -C + CO2 ~ 2CO (9) H + CO ~ 1 CH + 1 CO (10) h 3 H + 1 CO ~ 1 CH + 1 H O (11) The temperatures, catalysts, working fluid, and composition of the solid wastes will determine which of these reactions play -a primary role in the gasification process. These gases exit the reactor together with the pyrolysis gases. This producer gas is rich in CH4, CO, and H2 and may be manipulated to produce methane using reactions (10) and (11), hydrogen using the reverse of reactions (10) and (11) and reaction (8), or methanol using 20 reaction (2). These reactions may be practiced using standard commercial catalysts. The final product or products of the pro-cess is to be determined by economic considerations.
The process just described may be adapted to many special situations. For example, if it is desirable to introduce the working fluid into the reactor at an elevated temperature, part of the producer gas may be recycled and mixed into the working fluid, and a regulated amount of oxygen injected into the work-ing fluid gas stream. The oxygen mixes with the producer gas , _9_ ... . . . .

-^` 1082921 and burns according to the reactions H2 + 2 2 H2~ (12) CO + 12 2 ' C2 (13) CH4 + 2O2 ~ CO2 + 2H2O (14) thereby heating the incoming gas stream. Since the by products of reactions (12), (13), and (14) are the constituents of the ~, ~; working fluid (or may be chosen to be by introducing only the . ., H2 or CO portions of the producer gas) they do not contaminate ; the gas stream in any way. Moreover, this provides an extremely 10 efficient method of heating the gas stream, since heat is lost only through conduction out the containing pipe. This same method can be used to heat the gas leaving the reactor, which , may prove desirable if the methane reforming reaction is prac-ticed.
It is also clear that the process just described can be readily adapted to the changing character of the solid waste ~., input. For example, should the wastes contain substances that might poison the catalysts used to produce a particular product, the process described here would readily adapt to the production of some other product using a different catalyst. Moreover, by varying the composition of the working fluid and catalysts al-most any desired mixture of the product gas can be produced. For example, a product gas rich in CO may be produced by using CO2 as the working fluid. As opposed to many other pyrolysis systems, this process primarily has only gaseous products which are read-ily salable. Any ash residue produced is readily disposed of.
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Since the steam or CO2 reactant can be heated by burning some of ;~ the stored producer gas, the process readily combines with a solar furnace and would not have to "shut down" on a cloudy day.
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~08Z921 Moreover, current technology is sufficient for the design and construction of a solar furnace with an output temperature of 600C-700C. The process described here is also unique due to its ability to store heat energy supplied from an external source in the producer gas. If desired, the process can produce elec-tricity by burning the producer gas in a turbine generator. If - not burned to produce electricity, the hot gases evolved by the process may be cooled in a heat exchanger and used to provide " steam or hot C02 to the solar furnace. Thus the process is able 10 to efficiently use all the heat produced by the solar furnace in a temperature range of 600C-700C.
~A A tower top solar furnace appears to be well suited to meet 'J the needs for the system of this invention. This type of furnace uses many flat individually guided mirrors (heliostats) to re-flect and focus solar light to the top of a tower where it is .- converted to heat. G. Francia, Solar Energy 12, 51 (1968) des-cribes the use of such a furnace for the continuous daylight generation of 150 kg/h of steam at 150 atm and 500-700C.
The chemical reactor described in the FIGURE is ideally 20 suited for use with a tower top solar furnace. Focused sunlight -passing through the two quartz windows is absorbed on the surface of the char present in the fluidized bed and converted to heat.
The excellent thermal transfer properties of the fluidized bed distributes the heat throughout the bed. Steam or hot CO2 flow-ing through perforations in the inner quartz window fluidize the bed. Finely ground organic solids are admitted through the air-lock on the top of the reactor~ Upon contact with the fluidized bed these solids undergo rapid pyrolysis resulting in char and gases. The gases are recirculated under pressure as shown.
30 Thermal losses from the reactor are limited by the insulation .:
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-- 10829Zl properties of the CO2 and steam present between the reactor and the jacket. The primary advantage of this reactor is that it simplifies heat exchange problems by converting radiant light energy to thermal energy on the surface of the reactants where the endothermic reactions are occurring.
This scheme could also be used as a heat exchanger to super-heat steam for the production of electricity. For this appli-cation, only steam would be pumped into the reactor and the fluidized bed would contain some unreactive, black, finely ground solid (black quartz) to absorb the radiant energy.
The major obstacle confronting the use of solar thermal ener-gy is its intermittent nature. Utilities have to generate elec-tricity all day long; not just when the sun shines. Using solar furnaces to produce a synthetic fuel circumvents this problem since the fuel serves as a means of storing the sun's energy for use at any time. Thus the production of synthetic fuels from solid wastes represents an ideal use of a solar furnace.
, The inventor has discovered catalysts which are useful in ; lowering the temperature range for the practice of reaction (4):

CO + C catalYst~ 2CO

The catalysts are cobalt molybdate and NaHCO3. Using pyrolytic char from solid wastes as a source of carbon, the catalysts are dissolved in water and deposited on the char by soaking the char in the catalyst-water solution and subsequently vapor-izing the water. The catalyst is recovered by soaking the ash residue remaining after the gasification of the solid waste and water. Table II shows the effect of this catalyst on reaction ~ (4).

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Claims

WHAT I CLAIM IS:

1. A method for employing an external moderately high temper-ature heat source in the pyrolysis and gasification of organic material, said method comprising:
a. heating by means of solar energy using a tower top solar furnace at least one first gas selected from the class consisting of steam, carbon dioxide, and a mixture of steam and carbon dioxide to a temperature of 600-700°C
in a reactor, thus producing a heated first gas;
b. mixing said organic material with at least one catalyst selected from the class consisting of cobalt molybdate and sodium bicarbonate, thus producing catalyst-mixed organic material;
c. injecting under pressure said heated first gas into a porous reactant bed on which is located said catalyst-mixed organic material, thus fluidizing said catalyst-mixed organic material;
d. allowing said catalyst-mixed organic material to pyrolyze and to produce a solid char residue and at least one second gas selected from the class consisting of H2, CO2, CO, CH4, and mixtures thereof.

2. The method of claim 1 in which said at least one first gas is steam and in which said organic material is organic wastes.

3. The method of claim 1 in which said at least one first gas is CO2 and in which said organic material is organic wastes.

4. The method of claim 1 in which said catalyst is cobalt molybdate and in which said organic material is organic wastes.

5. The method of claim 1 in which said catalyst is NaHCO3 and in which said organic material is organic wastes.

6. An apparatus comprising in operable communication:
a. a tower top solar furnace; and b. a reactor comprising:
1. a chamber having a bottom end and a top end, said bottom end and said top end comprising means for sealing said chamber, said top end comprising an inlet means for introducing a waste material into said chamber, and said bottom end being formed by a first quartz window and containing perforations through which a hot gas can be passed into said chamber so as to fluidize and pyrolyze said waste material and so as to produce a resulting gas;
2. a second quartz window through which light is passed into said chamber, said second quartz window being located adjacent to and below said first quartz window;
3. an extracting means for extracting said resulting gas from said chamber, said extracting means including a heat exchanger; and 4. a recirculating means for recirculating a portion of said resulting gas from said extracting means back into said chamber, said recirculating means including a compressor.

7. A method for the pyrolysis and gasification of organic material, said method comprising:
a. heating at least one first gas selected from the class consisting of steam, carbon dioxide, and a mixture of steam and carbon dioxide to a temperature of 600-700°C
in a reactor, thus producing a heated first gas;
b. mixing said organic material with cobalt molybdate, thus producing cobalt molybdate-mixed organic material;

c. injecting under pressure said heated first gas into a porous reactant bed on which is located said cobalt molybdate-mixed organic material, thus fluidizing said cobalt molybdate-mixed organic material;
d. allowing said cobalt molybdate-mixed organic material to pyrolyze and to produce a solid char residue and at least one second gas selected from the class consisting of H2, CO2, CO, CH4, and mixtures thereof.

8. The method of claim 7 in which said organic material is organic wastes.

9. The method of claim 8 in which said at least one first gas is steam.

10. The method of claim 8 in which said at least one first gas is CO2.

11. A method for lowering to 600-700°C the temperature required to gasify char comprising carbon according to the reaction C + CO2 ? 2CO , said method comprising:
a. mixing CO2, said char, and a catalyst comprising cobalt molybdate together to form a mixture; and b. allowing said mixture to react at a temperature of 600-700°C, thus forming CO.

12. A method of producing gases such as CO2, CO, CH4, and H2 from the pyrolysis and gasification of solid organic waste contained within a reactor comprising:
a. solar heating by means of a solar top furnace to a temperature of 600°- 700°C a working fluid selected from the class consisting of steam, CO2, or a mixture of these gases, said working fluid contained in the lower section of said reactor situate at the focus of the said solar top furnace, b. mixing at least one catalyst selected from the class consisting of NaHCO3 and cobalt molybdate with the solid organic waste, c. injecting under pressure the heated working fluid into a porous reactant bed on which is situate the catalyst-mixed organic waste, d. pyrolyzing the catalyst-mixed organic waste causing the formation of CO2, CO, CH4, and H2 gases, and a char residue, e. extracting the gases and char from the reactor, and f. recovering the said catalyst by soaking the char with water.

13. The method of claim 1 in which said gas is steam.

14. The method of claim 1 in which said gas is CO2.

15. The method of claim 1 in which the said gas is a mixture of CO2 and steam.

16. The method of claim 1 in which said catalyst is cobalt molybdate.

17. The method of claim 1 in which said catalyst is NaHCO3.