|Publication number||US3820964 A|
|Publication date||Jun 28, 1974|
|Filing date||May 30, 1972|
|Priority date||May 30, 1972|
|Publication number||US 3820964 A, US 3820964A, US-A-3820964, US3820964 A, US3820964A|
|Original Assignee||Cons Natural Gas Svc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (14), Classifications (28)|
|External Links: USPTO, USPTO Assignment, Espacenet|
[ REFUSE GASIFICATION PROCESS AND APPARATUS  Inventor: John C. Janka, Chicago, 111.
 Assignee: Consolidated Natural Gas Service Company, Cleveland, Ohio 22 Filed: May 30,1972  Appl. No.: 257,633
 US. Cl 48/113, 48/209, 48/215  Int. Cl. Cl0j 3/16  Field of Search 48/197 A, 209, 215, 202, 48/210, 113
 References Cited UNITED STATES PATENTS 2,238,367 4/1941 Mohr et a1. 48/197 R 2,840,462 6/1958 Gorin 48/202 X 3,194,644 7/1965 Gorin et al 48/202 X 3,471,275 10/1969 Borggreen 48/197 X 3,503,724 3/1970 Benson 48/202 X 3,511,194 5/1970 Stookey 48/209 UX June 28, 1974 3,671,209 6/1972 Teichmann et a1. 48/215 3,687,646 8/1972 Brent et a1. 48/209 3,702,039 1 1/1972 Stookey et al. 48/209 X Primary Examiner-R. E. Serwin Attorney, Agent, or Firm-Dominik, Knechtel, Godula & Demeur ABSTRACT A refuse gasification process and apparatus for producing high-BTU pipeline gas which is interchangeable with natural gas. The gasification process is a relatively low pressure process, and utilizes a gasifier with a slagging bed rather than a fluidized bed as in many existing process. The raw refuse is gasified with steam and oxygen to produce a raw synthesis gas, and the H /CO ratio is controlled, by proper adjustment of the steam supply to the gasifier, in such a way as to yield a raw synthesis gas from the gasifier having sufficient H, for methanation. In this fashion, recourse to a water-gas shift reaction is completely eliminated.
12 Claims, 5 Drawing Figures POWER GENERAUON STEAM PRODUCTION GAS PURIFICATION SECTION RECYCLE OUENCH METHANATION PRODUCTION PATENTEDJUH28 I974 SHEET 2 BF 3 0.303 mqw wojOm REFUSE GASIFICATION PROCESS AND APPARATUS This invention relates to a refuse gasification process and apparatus for producing high-BTU pipeline gas which is interchangeable with natural gas.
With the gasification process and apparatus of the invention, the refuse which is basically carbonaceous and organic matter is gasified, with yields of approximately 6.5 X BTU/ton of refuse gasified. Volume reduction is essentially 100 percent, since the process does not produceany solid material which cannotbe sold. The metal fraction of the refuse is recovered as slag, and the glass and ash parts thereof are recovered as frit which is suitable for use in road construction.
The gasification process is a relatively low pressure process, and utilizes a gasifier with a slagging bed rather than a fluidized bed as in many existing processes. Also, in most existing systems or processes, the synthesis gas produced contains an insufficient quantity of H and the H /CO ratio thereof must be adjusted via the water-gas shift reaction:
to provide a synthesis gas containing sufficient H for methanation. In the present process, theraw refuse is gasified with steam and oxygen to produce a raw synthesis gas, and the H /CO ratio is controlled, by proper adjustment of the steam supply to the gasifier, in such a way as to yield a H /CO ratio of approximately 3 to In addition to the above generally discussed unique feature of the gasification process, a controlled cooling process is used to separate water soluble oils produced in the gasifier. During devolatilization of the refuse, a
significant amount of liquid hydrocarbons, typically 15 to 30 percent by weight of the total refuse fed, is produced. These liquid hydrocarbons are mostly of a water-soluble nature and are separated in a fractional quench system by passing the synthesis gas stream first through an oil quenching tower wherein the components with boiling points in excess of the dew point of the water in the synthesis gas stream are condensed and separated therefrom. The synthesis gas stream then is passed through a water quenching tower wherein the water is condensed and separated from it. In this fashion, most of the oil and the water are condensed separately.
These oils are of a very refractory nature and cannot be gasified by normal techniques. In the present gasification process, the oils are recycled to the base of the gasifier, where combustion of fixed carbon in the refuse and recycle oil produces temperatures in excess of 3,000F, causing the oils to react by thermal cracking and partial oxidation. Thus, the oils are completely gasified, and the efficiency of the gasifier is increased by about 20%. The need for supplementary heat supply for slagging, as in other processes, is also eliminated. The recycle oil to the base of the gasifier also helps to supply the heat of fusion of the metal and glass parts of the refuse.
Accordingly, it is an'object of the present invention to provide an improved refuse gasification process and apparatus for producing high-BTU pipeline gas which is interchangeable with natural gas.
Another object is to provide an improved refuse gasification process and apparatus wherein recourse to a water-gas shift reaction to adjust the H /CO ratio of the synthesis gas such that the latter contains sufficient hydrogen for methanation is completely eliminated.
A further object is to provide an improved refuse gasification process and apparatus wherein the raw refuse is gasified with steam and oxygen to produce a synthe sis gas containing sufficient hydrogen for methanation, the H /CO ratio being controlled by proper adjustment of the steam supplied to the gasifier.
A still further object is to provide an improved gasifcation process and apparatus in which a fractional quenching system can be used to separate water soluble oils produced in the gasifier.
Still another object is to provide an improved gasification process and apparatus wherein the oils produced in the gasifier are separated from the synthesis gas stream, recycled to the gasifier and gasified, to thereby increase the efficiency of the gasifier and supply part of the heat requirements for slagging.
Other objects of the invention will in and will in part appear hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the apparatus embodying features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the followpart be obvious ing detailed description taken in connection with the accompanying drawings'in which:
7 FIG. 1 is a flowsheet of a refuse gasification system exemplary of the invention;
FIG. 2 is a sectional view of a typical gasifier which can be used in the system of FIG. 1;
FIG. 3 is a block diagram representation of the various zones within the gasifier;
FIG. 4 is a graph generally representative of the temperature profiles of the gas and solids in the various zones in the gasifier; and
FIG. 5 is a graph generally illustrating the effect of the steam feed to the gasifier on the H /CO ratio in the synthesis or product gas.
Similar reference characters refer to similar parts throughout the several views of the drawings.
Referring now to the drawings, in FIG. 1 there is shown a flowsheet of a refuse gasification system exemplary of the invention, for a typical system in which 3,000 ton/day of refuse having a heating value of 5,500 BTU/lb. can be gasified to yield 19.4 X 10 BTU/day of pipeline-quality gas along with metal and glass frit as by-products; The system also requires L800 ton/day of refuse as fuel, or its equivalent in heating value from some other source. The total refuse processed in the system therefore amounts to 3,000 to 4,800 ton/day.
As can be seen, the system includes as its principal components a main reactor or gasifier 10; oil quenching apparatus 11; water quenching apparatus 12; gas
compression apparatus I3; gas purification apparatus l4; methanation apparatus 15; final gas drying apparatus l6; and offsites including an oxygen production plant 17, a steam generating plant 18, a power generating plant 19, boiler and cooling water treatment facili- 4 (l,700'l ,90()F) reaction. referred to as gasification". The latter reaction is uite similar to that ofcoal.
The effect of devolatilization on the solid phase appears, from various tests, to be independent of the gaseltzesliand a coolmg tower, all as more fully descr1bed be ous atmosphelre below 6000B T o ing general AS can be best Seen in FIG 2, the gasifier 10 can be types of reachons may occur dunng devolat1l1zat1on:
characterized as a countercurrent shaft furnace, genir- CHHZ H 2 CnHz" 2 all resembling a conventional blast furnace. lts heig t, y
mi. typical 3,000 ton/day system, would be approxi- 10 2 UH:
mately 80 feet. The raw refuse, stream 1 in FIG. 1, en- C0 H O CO H ters the gasifier 10 through a refuse charging bell or loading hopper 21 at its top. As the refuse passes 2C0 T CO2 +C through the gasifier 10, it enters various zones th i Thermobalance tests show that the devolatilization recountercurrent to the flow of hot gases which are genaction is initiated at 55001: and is completed y 9000!:-
erated. These different zones within the gasifier are nal gas temperature is governed by the quantity of generally characterized as a preheat zone; a devolatilyg n p ye In t partial Oxidation stage, stream ization zone; a partial oxidation zone; a heat transfer 15 in The r bution Of Carbon among the zone; a gasification zone; and a combustion and slag- Product Components C0, 2 hydrocarbons. Oil
ging zone. The different zones within the gasifier 10 are and Solid residue is determined y temperature and generally illustrated in block diagram in FIG. 3, and a ydr gen p r ial pressure.
temperature profile 0f the solids and gases in these vari- The carbon in the refuse SOliClS entering the devolatilous zones is generally illustrated in FIG. 4. Approxiization zone distributes itself among the compounds mate physical locations of these zones are indicated in Show in Table as a result Of th e olatilization re- FIG. 2. The zones can be generally characterized as fol- 25 actions.
TABLE l-MATERIAL AND ENERGY BALANCE FOR GASIFIER Gas, lb.-mol.
Temp. Enthalpy. Stream NO co co2 H. 11.0 01-1. cm. 0.11. c.1-1. ms 1 1. 011 F 1310 TABLE 2 MATERIAL AND ENERGY BALANCE FOR GASIFIER Stream Solid s, lb- Temp. Enthalpy, No. Moisture C H O N S Ash Metal F Btu la 17.1847 31.3482 4.1645 29.4567 0.4202 0.1336 10.6221 6.6700 60.0 544,716 20 0.0 31.3482 4.1645 29.4567 0.4202 0.1336 10.6221 6.6700 550.0 568,713 311 00 13.2309 0.6010 0.8837 0.3361 0.0732 10.6221 6.6700 900.0 241,960 4a 0.0 13.2309 0.6010 0.8837 0.336] 0.0732 10.6221 6.6700 900.0 241,960 0.0 132309 0.6010 0.8837 0.3361 0.0732 10.6221 6.6700 1800.0 257,254 60 0.0 3.5385 0.0 0.0 0.0 0.0 106221 6.6700 1800.0 81,755 7a 0.0 0.0 0.0 0.0 0.0 0.0 10.6221 6.6700 3270.9 105,022
lows, and the material and energy balances associated TABLE 3 w1th them are shown 1n Tables 1 and 2 below. d 'b'Z 'R 'ON. 7 Preheat Zone AMOEQBBQDLJQISQE.
In this zone, the refuse is heated and dr1ed to 550F gEng REE C by contact with hot synthesis gas. As the synthesis gas cools, the water-gas shift reaction ceases at the equilib- C0 '1 15 1 100F w m f 11 CO2 r1um va ues at a out ater 1n ere use 15 a Hydmqurbmb. I vaponzed at 212F. The preheat zone termmates when S M 11 U t ll the sollds reach 550F, where devolat1l1zat1on reactlons W e begun to occur. 2. Dcvolatilization Zone Refuse gasificatlon, like coal gasificatlon, may con ve- The general category denoted hydrocarbons in Table niently be viewed as consisting of two distinct operations: a low-temperature (550900F) reaction, called fdevolatilization, and a high-temperature 3 above includes CH and higher molecular weight gaseous hydrocarbons, both saturated and unsaturated, under the generic term hydrocarbons, as shown in Table 4 below. For design purposes, these compounds may be represented by CH C H C3Hg and C H in the indicated proportions.
TABLE 4 4 2 6 II H 2 4 40.0 18.0 20.0 22.0
H/C 04133-005408 In T S/C 0.0I0495.5046 10"1 Overall oxygen conversion exhibits regular behavior, and an overall conversion of 97% may be used for design purposes.
The process also generates a large quantity of liquid hydrocarbon productswhich are of a water-soluble nature. The oil fractions can be characterized as low and high temperature fractions, and an average yield ratio of 79.32 percent for the low temperature and 20.68 percent for the high temperatures is observed. The aggregate oil formula determined experimentally for these oil fractions is: I
5.000 6.2239 2.2943 IHHHI) 0.0056
As indicated above, the synthesis gas stream is subjected to a controlled cooling or fraction quench, first with oil at an intermediate temperature and then with water at a low temperature, to separately condense these oil fractions and water from it. The oil fractions then are recycled to the base of the gasifier 10, to both increase the overall conversion of the feed refuse and to increase the efficiency of the gasifier. 3. Partial Oxidation Zone In the devolatilization zone of the gasifier 10, the devolatilization reaction is induced by passing over the solids the high-temperature synthesis gas which is produced by partial oxidation of the gas from the gasiflcation zone. In the partial oxidation zone, it is assumed that methane remains unburned because hydrogen exhibits a higher flame speed or combustion rate corresponding to the oxygen-deficient case, and that the water-gas shift reaction is in equilibrium. Because of the rapidity ofthe devolatilization reaction, solids temperatures remain unchanged all the way through this zone in the gasifier. 4. Heat Transfer Zone Countercurrent heat transfer between gas and solids occurs in this zone. Gasification reactions are not assumed to occur until the solids temperature reaches I,800F. Water gas shift reaction freezes at l,I00F-. The gas temperature prior to oxygen injection is determined by heat balance. 5. Gasification Zone when solids temperature reaches I,800F, bon and residual hydrogen aod oxygen are gasitied with hydrogen and steam in a 1:1.43 mole ratio. The watergas shift reaction is in equilibrium as in the reaction C+ 2H CH burned to CO This hot gas supplies the heat required to operate the gasification zone above it, which is basically endothermic. Recycle oil is also introduced into this zone. 7. Slagging Zone In the slagging zone, metal and ash are liquefied to form a complex aggregate with the estimated composition shown in Table 5 below. The metal objects in the refuse are not oxidized as in various other slagging gasifiers operating on coal where all of the oxygen required for reaction has been supplied at one location. As can be seen in FIGS. 1 and 2, in the present process, steam and oxygen are supplied for gasification through water-cooled steel ports in the side of the refractory at the base of the gasifier l0, and oxygen for devolatilization is supplied through water-cooled ports at a higher elevation. The slagging process therefore consists merely of liquefaction of the metal parts of the refuse, rather than actual oxidation. This does not imply that the process would be thermally unbalanced. as in a blast furnace where reduction is actually occurring, because the iron and aluminum in the metal" part of the refuse are already reduced. It is only necessary to see that they do not become oxidized. The slag shown in Table 5 has a silica ratio of 34.8, which guarantees adequate fluidity (5 poise or less) at temperatures above 2,800F. The softening temperature of this composite is estimated at 2,000F. Metal and slag are tapped at separate notches in the hearth. Separation of these two components of refuse slag has been observed to occur by gravity at temperatures in excess of 3,000F. The shape and size of the hearth or slagging section of the gasifier follow standard blast furnace practice.
TABLE 5 ESTIMATED COMPOSITION OF SLAG METAL. COMPONENT Wt'/( Fe 79.36 AI 20.63
ASH AND GLASS COMPONENT Si0 49.38 AI O 25.82 I1 0 7.86 (:10 I044 Mg() 280 Nn O 3.70
AGGRI-LGA'IE COMPOSITION WWI Ft: 30.61 Al 7.96 SiO 30.33 AI O I586 Fe O 4.83 CiiO 6.41 MgO L72 N320 2.28
7 8 cess in FIG. 1, for a typical 3,000 ton/day system, are as stream 2 which, in Table 61), 1S termed the gasifier shown in Tables 6a, 6b and 60 below. effluent.
[ABLE 6a MATERIAL BALANCE Single Component Streams Pressure, Stream No. Component Quantity/Hr Temp, "F psig 1 Garbage 125 tons 60 30 10 Oil 306 moles 60 50 11 Water 103,201 lb 200 13 Steam 69,1261b 550 50 14 Oxygen 76,541 lb 60 50 15 Oxygen 6,291 lb 60 50 16 Oxygen 41.5 ton 60 50 17 Slag 43,279 lb 3271 50 18 Garbage 75 ton 60 30 19 Steam A. 181,2731b 338 100 B. 328,410 lb 550 400 20 Steam 207,882 lb 338 100 22 Steam 26,609 lb 338 100 23 Steam 69,1261h 550 50 24 Steam 86,330 lb 550 400 25 Steam 153,970 lb 550 400 26 Steam 88,1101b 550 400 3 Gas Same as in 2 16,373 moles 550 25 21 Water 21 L328 lb 100 75 TABLE 6b MAT ERlAL BALANCE Stream No. 2 4 5 6 Stream Name Gasifier Effluent 1st Quench Effluent 2nd Quench Effluent Feed to CO +H S Removal Temperature. "F 894 260 100 240 Pressure, psig 30 20 15 100 7 Component M01 71 Moles/hr Mol Moles/hr M01 Moles/hr Mol M l /h CO 6.92 1.133 7.05 1,133 10.95 L133 19.21 1,133 CO 27.09 4,435 27.60 4,435 42.85 4,435 0.97 H: 21.88 3,583 22.30 3,583 34.62 3,583 60.75 3,583 H O 36.69 6,006 37.39 6,006 2.78 288 3.82 288 CH 4.65 762 4.74 762 7.36 762 12.92 762 C- H, 0.35 58 0.36 58 0.56 58 0.98 58 C -,H 0.02 3 0.02 3 0.03 3 0.05 3 C H 0.24 39 0.24 39 0.38 39 0.66 39 H 8 006 10 0.06 10 0.10 10 N 0.23 38 0.24 38 0.37 38 0.64 38 Oil 1.87 306 TABLE 66 MATERIAL BALANCE Stream No. 7 8 9 l2 Stream Name Methanation Feed Methanation Effluent Methanation Recycle Pipeline Gas Temperature, "F 100 706.2 100 100 Pressure, psig 90 84 75 75 Component Mol Moles/hr M01 Moles/hr M01 Moles/hr M01 70 M l /h CO 19.79 1,133 0.07 15 0.08 13 0.09 2 C0 1.00 57 2.58 522 2.73 460 2.74 62 H 62.59 3,583 2.83 574 3.00 506 3.05 69 H O 0.91 52 6.58 1,335 0.96 162 CH 13.31 762 86.37 17,520 91.57 15.429 92.44 2,091 H, 1.01 58 0.05 3 C61 1 0.68 39 N2 0.66 38 I57 318 1.66 280 1.68 38 Total 100.00 5.725 w 100.00 20284 100.00 16,850 100.00 2,262 A The raw refuse, stream l, as indicated above, enters A temperature recording controller (TliC) 26 is couthe gasifier 10 through a charging bell or loading hoppled to the stream 2 and controls a flow recording conper 21 at its top. In charging the gasifier 10, bulky items troller (PRC) 27 which, in turn, controls the supply of such as refrigerators, automobile bodies and the like oxygen, stream 15, into the partial oxidation zone of should be manually removed and the charging rate of the gasifier 10. The TRC 26 detects the temperature of the same controlled so as to maintain a relatively stan- 5 the stream 2 and controls the PRC 27 to supply Sllffidard or typical composition of refuse supplied to the cient oxygen for partial oxidation of the gas from the gasifler. As this stream 1 of raw refuse passes through g asification zone, to thereby provide a highthe gasifier 10, a raw synthesis gas is produced and exits temperature synthesis gas to induce th dilblatllizatbn reaction. The TRC 26 and the PRC 27 are set-up such that the gas stream 2 is maintained at a temperature of approximately 894F, and to maintain the latter at this temperature, approximately 6,291 lb. per hour of oxygen is supplied to the gasifier 10. This oxygen, as can be seen in Table 6a, is supplied at a temperature of 60F and at a pressure of 50 psig.
The stream 2 of synthesis gas or gasifier effluent as it leaves the gasifier 10 is subject to a fractional quenching, by first passing it through a waste heat boiler 22 of conventional design. When the dew point of the oil fractions in the stream 2 is reached, at approximately 550F, the stream 2 passes, as stream 3, into an oil quenching tower 23 where direct contact oil cooling is used to condense those oil components with boiling points in excess of the dew point of the water in the stream. ()ils leaving the bottom of the quenching tower 23 are separated in a separator drum 24, into light and heavy fractions. Part of the heavy fraction, as illustrated, is pumped through a heat exchange 25 wherein it is cooled, and fed to the top of the quenching tower 23 to serve as the cooling medium. The light and excess heavy fractions are pumped, as stream 10, to the base of the gasifier 10. Approximately 306 moles per hour of oil are recycled to the gasifier and, as more fully discussed above, recycling the oil in this fashion increases by approximately percent the efficiency of the gasifier. Also, by recycling the oil to the base of the gasifier where combustion of the fixed carton in the refuse produces temperatures in excess of 3,000F, the oil is caused to react by thermal cracking and partial oxidation, thus gasifying it completely. The addition of the recycle oil to the base of the gasifier also helps to supply the heat of fusion of the metal and glass parts of the refuse.
The first quench effluent, stream 4, from the quench-- ing tower 23 is at a temperature where water can condense, approximately 260F for a system operated at psig. The stream 4 next is subjected to a water quench in a water quench tower 28, where its temperature is reduced to l00F and water is condensed. Part of the water leaving the bottom of the quenching tower is pumped through a heat exchanger 29 wherein it is cooled, and then fed to the top of the quenching tower to serve as the cooling medium. The remaining water, stream 11, passes through a waste treatment system 30, and is disposed of in an appropriate fashion. Approximately l03,02l lb/hour of water is condensed and disposed of in this fashion.
The second quench effluent, stream 5, is at a temperature of approximately 100F and its pressure is regulated by a pressure register controller 31 at approximately 15 psig, as it leaves the water quench tower 28 and preferably is delivered to the gas compression system 13. The stream is compressed within the latter, to approximately 100 psig for more efficient methanation, and then delivered as stream 6, to the gas purification system 14. Compressing the stream to 100 psig also permits the use of hot carbonate scrubbing of acid gases under economical conditions. The pressure of the stream 6 is controlled by the feed-back system including a pressure recording controller 32. The gas compression system 13 utilizes approximately 88,110 lb/hour of steam, and the latter is delivered thereto, as stream 26.
The acid gas portion of the stream 6 is formed of CO and H S, and these are removed in the gas purification apparatus 14, by scrubbing with a 30 percent K CQ,
solution in an absorber operated at 100 psig and 240F.
The rich K CO solution containing CO and H 8 is regenerated in a stripper operating at 25 psig where acid gases are removed by steam stripping and a lean hot carbonate solution recirculated to the absorber. The final traces of H 8 are removed by passing the stream over a bed of zinc oxide. The H S removal is essential to avoid sulfur poisoning of the methanation catalyst. The gas purification apparatus 14 utilizes approximately 207,882 lb/hour of steam, and the latter is delivered to it as stream 20.
The scrubbed gas stream or methanation feed, stream 7, is fed to the methanation system 15, and contains a Hg/CO ratio of slightly over 3 and essentially no H 8. The CO in the stream 7 is reacted with H in the presence of the methanation catalyst to form methane. The CO content in the final gas is limited to less than 0.1 percent. Themethanation system 15 can be comprised of, for example, four reactors with a recycle stream from the methanation effluent mixing with the feed to each reactor to maintain the bed temperature between 550 and 900F. The methanation effluent, stream 8, is delivered to a heat exchanger 33 wherein it is cooled to approximately 100F, and fed to a dryer 34 which can be an ethylene glycol dryer, to meet the moisture requirement in pipeline gas specifications. Approximately 88 percent of the stream 8 fed to the dryer 34 is recycled, as the methanation recycle stream 8, to provide a methanation recycle-to-feed ratio of approximately 2.96.
The pipeline gas, stream 12, is at approximately lO0F and at a pressure of psig, and is delivered to a storage tank 35 or the like, for storage.
As indicated above, in order to carry out the methanation reaction:
H and CO must be present in the gas, in the illustrated example, stream 7, in the proper proportions, that is, approximately 3.2 to l H /CO mole ratio. In the present process, the proper H /CO ratio is maintained by proper adjustment of the steam feed to the gasifier 10. By using an appropriate quantity of steam with the oil recycle, the need for the normally required water-gas shift reactor is eliminated. In the illustrated embodiment, the quantity of steam feed to the gasifier 10 is controlled by the H /CO ratio in the gas, stream 7, fed to the methanation system or apparatus 15. For this purpose, a H sensitive analytical indicator controller (AIC) 38 and a CO sensitive analytical indicator controller (AIC) 39 are coupled to the stream 7 for determining respectively the H and CO content of the gas in stream 7. The outputs of the AIC 38 and the AIC 39 are coupled to a ratio determining instrument 40 which is operative to compare the outputs and to, in turn, control the operation of a feed recording controller 41. The latter, in turn, controls the steam feed to the base of the gasifier 10. The effect of the steam feed to the gasifier 10 on the H /CO ratio in the product gas is shown in FIG. 5, and it can be seen that approximately 28-29 pounds of steam per pound of refuse is required to establish and maintain a 3.2 to 1 ratio. Accordingly, in a typical 3,000 ton/day system, the steam required by the gasifier, stream 13, approximates 69,126
lb/hour. In addition, in order to gasify the raw refuse to produce the raw synthesis gas, approximately 76,541 lb/hour of oxygen is required, and the latter is delivered to the gasifier as stream 14. The oxygen feed to the gasifier is controlled by a feed recording controller (F RC) 42 which is, in turn, controlled by a temperature recording controller (TRC) 43 coupled to the slag output stream 17. An optical pyrometer or similar device may be used. As indicated above, the oxygen feed to the gasifier 10 is such that the metal parts of the refuse are merely liquefied, and not oxidized. Also, the supply of oxygen is controlled to maintain the temperature of the molten slag to assume adequate fluidity for the gravity separation of the glass and metal materials from the slag.
The oxygen required in the refuse gasification process is produced from air onsite, by means of the oxygen system or plant 17 which may be a conventional oxygen producing plant. Oxygen requirements for the process approximate 41.5 ton/hour, stream 16, and to produce this oxygen approximately 153,970 lb/hour of steam is required, as represented by stream 25. The oxygen is produced at low pressure, and compressed to 50 psig for use in the gasifier 10.
A portion of the steam required by the gasifier 10 can be generated by waste heat recovery and the remaining steam for process requirements, power generation and for oxygen plant 17 can be generated in the steam generating plant 18 having, for example, three refuse fired boilers, each of which would require and use approximately 600 ton/day of refuse, stream 18. The steam generated, stream 19, is at 550F and 400 psig for power generation (stream 24) and for the oxygen plant 17 (stream 25), whereas the reaction steam for the gasifier l0 (stream 13) is at 550F and 50 psig. The steam for hot K CO regeneration (stream is at 338F and 100 psig. Therefore, including the refuse used as fuel to produce the required quantities of steam, the total refuse processed by the system is 4,800 ton/day. In addition, the process requires approximately 48,924 gpm of cooling water and approximately 37,000 hp. in power requirements.
From the above description, it can be seen that the refuse gasification process provides numerous advantages and improvements over presently existing systems, in that yields of pipeline gas of approximately 6.5 X 10 BTU/ton of refuse gasified can be produced. In addition, all of the solid materials resulting from the process can be sold, thus further reducing both the cost of producing the pipeline gas and the cost of refuse disposal per se. The process is economically attractive in comparison to similar systems, in that the need for the apparatus normally required to provide a water-gas shift reaction is completely eliminated. The use of oil recycle to the base of the gasifier 10, together with the use of a fractional quenching system to separate water soluble oils produced in the gasifier also are improved features of the system which contribue to the overall improved operation. Conventional apparatus and techniques are generally employed within the system, so that known data presently is available for use, in designing various capacity systems, to establish the most economical and efficient system.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and certain changes may be made in carrying out the above method and in 12 the construction set forth. Accordingly, it is intended that'all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Now that the invention has been described, what is claimed as new and desired to be secured by Letters Patent is:
l. A refuse gasification process for gasifying raw untreated refuse material including as a portion thereof carbonaceous material, metal and ash to produce pipeline-quality gas which is interchangeable with natural gas comprising the steps of:
a. passing ina continuous manner, raw untreated refuse material downwardly within a substantially vertical shaft furnace countercurrent to the flow of hot gases therein;
b. injecting steam and oxygen into the base of said shaft furnace to liquefy the metal and ash portion of said refuse material to form a molten slag and to gasify part of said carbonaceous material in said refuse material to produce a raw reducing gas containing H and CO at the base, said reducing gas upon being partially oxidized within said shaft furnace producing methane and a raw synthesis gas by devolatilizing the refuse material;
0. injecting oxygen into said shaft furnace at a higher vertical elevation to partially combust the H and CO in said reducing gas to supply heat for the devolatilization reaction, whereby the amount of carbonaceous-material in said refuse which is available for the devolatilization reaction to produce methane directly is increased and thus permitting more methane to be formed by direct reaction in said shaft furnace;
d. controlling the supply of steam injected into the base of said shaft furnace to establish a H /CO ratio in said synthesis gas suitable for methanation, whereby the need for a water-gas shift reactor is eliminated; and
e. reacting the H and CO in said synthesis gas in the presence of a methanation catalyst to form additional methane.
2. The refuse gasification of claim I, further including compressing said synthesis gas to a higher pressure for more efficient methanation thereof.
3. The refuse gasification process of claim 1, further including the step of controlling the supply of oxygen injected into the base of said shaft furnace to control the temperature of the molten slag to assure adequate fluidity for the gravity separation of glass and metal materials of said slag.
4. The refuse gasification process of claim 1, further including the step of subjecting said raw synthesis gas from said shaft furnace to a controlled cooling process to separate water soluble oils produced in said shaft furnacefrom said raw synthesis gas.
5. The refuse gasification process of claim 4, wherein the controlled cooling process is by fractional quenching of said raw synthesis gas by first quenching said raw synthesis gas with oil at an intermediate temperature and then with water at a low temperature so that oil and water from said raw synthesis gas are condensed separately therefrom.
6. The refuse gasification process of claim 1, further including the steps of separating oils from said raw synthesis gas; and recycling a portion of said oils separated from said synthesis gas into the base of said shaft furnace, said oil upon being injected into said base of said shaft furnace being completely gasified by thermal cracking and partial oxidation.
7. The refuse gasification process of claim 1, further including the step of removing the acid gas portion of said raw synthesis gas before said raw synthesis gas is methanated.
8. The refuse gasification process of claim 1, wherein the supply of steam injected into the base of said combustion chamber to establish the H /CO ratio in said synthesis gas is controlled by the H /CO ratio in the gas fed to methanation.
9. Apparatus for gasifying raw untreated refuse material including as a portion thereof carbonaceous material, metal and ash to produce pipeline-quality gas which is interchangeable with natural gas comprising:
ane and a raw synthesis gas by devolatilizing the refuse material;
c. means for injecting oxygen into said shaft furnace at a higher vertical elevation to partially combust the H and CO in said reducing gas to supply heat for the devolatilization reaction, whereby the amount of carbonaceous material in said refuse which is available for the devolatilization reaction to produce methane directly is increased and thus permitting more methane to be formed by direct reaction in said shaft furnace;
d. means for controlling the supply of steam injected into the base of said combustion chamber to establish a H /CO ratio in said synthesis gas suitable for methanation; and
e. means for reacting the CO and the H in said synthesis gas in the presence of a methanation catalyst to form additional methane.
10. The apparatus of claim 9, further including means for compressing said synthesis gas to a higher pressure for more efficient methanation thereof.
11. The apparatus of claim 9, further including a means for separating oils from said raw synthesis gas.
the base of said shaft furnace.
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|U.S. Classification||48/113, 518/705, 48/215, 518/703, 48/209, 48/111|
|International Classification||C10L3/08, C10J3/08|
|Cooperative Classification||C10L3/08, C10J2300/0909, C10K1/005, C10J2300/1884, C10K1/004, C10J2300/1662, C10J2300/1687, C10J3/08, C10J2300/0946, C10K1/101, C10J2300/0973, C10J2300/1678, C10J2300/1671, C10K1/122, C10K1/16, C10J2300/0959, C10K1/32, C10J3/723|
|European Classification||C10L3/08, C10J3/08|