CA1113380A - Method for the recovery of power from lhv gas - Google Patents
Method for the recovery of power from lhv gasInfo
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- CA1113380A CA1113380A CA332,095A CA332095A CA1113380A CA 1113380 A CA1113380 A CA 1113380A CA 332095 A CA332095 A CA 332095A CA 1113380 A CA1113380 A CA 1113380A
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Abstract
METHOD FOR THE RECOVERY OF POWER FROM LHV GAS
Abstract of the Disclosure A method is disclosed for the utilization of energy in gas of low heating value discharged from a production well of an in-situ combustion process for the production of oil.
The low heating value gas is mixed with an amount of air that will provide oxygen in an amount that will limit the maximum temperature rise in a catalytic combustion chamber to avoid excessive temperatures regardless of changes in composi-tion of the low heating value gas. The mixture is preheated and delivered into the catalytic combustion chamber at a temperature exceeding about 400° F. that will cause ignition of the combustibles on contact with the catalyst. In a preferred embodiment, combustion is accomplished in two combustion chambers connected in series with a heat exchanger between the combustion chambers for cooling the combustion products discharged from the first combustion chamber before they are delivered to the next combustion chamber. Approximately fifty percent of the total combustion air is mixed with the combustible gas before delivery into each of the combustion chambers. Effluent from the second combustion chamber is used to drive a gas turbine for generation of power or direct driving of air compressors.
Abstract of the Disclosure A method is disclosed for the utilization of energy in gas of low heating value discharged from a production well of an in-situ combustion process for the production of oil.
The low heating value gas is mixed with an amount of air that will provide oxygen in an amount that will limit the maximum temperature rise in a catalytic combustion chamber to avoid excessive temperatures regardless of changes in composi-tion of the low heating value gas. The mixture is preheated and delivered into the catalytic combustion chamber at a temperature exceeding about 400° F. that will cause ignition of the combustibles on contact with the catalyst. In a preferred embodiment, combustion is accomplished in two combustion chambers connected in series with a heat exchanger between the combustion chambers for cooling the combustion products discharged from the first combustion chamber before they are delivered to the next combustion chamber. Approximately fifty percent of the total combustion air is mixed with the combustible gas before delivery into each of the combustion chambers. Effluent from the second combustion chamber is used to drive a gas turbine for generation of power or direct driving of air compressors.
Description
This invention relates to the recovery of the energy in gases produced in an in-situ combustion process for the pro-duction of oil from underground carbonaceous deposit~ and more particularly from underground deposits of oil and oil shale.
One method for increasing the production of heavy crude oils of high viscosity from underground formations is the in-situ combustion prQceSS. In that proces~, air is injected at a high pressure throu~h an injection well into the underground formation containing the heavy oil. The oil in the formation adjacent the injection well is ignited by any of several known procedures such as the procedure disclosed in U. S. Patent No. 3,172,472 of F. M. Smith. Injection of air is continued after ignition to burn part of the oil in the formation and to increase the pressure in the formation adjacent the injection well and thereby drive oil in the formation toward a production well spaced from the injection well. A typical in-si~u combustion process is described in U. S. Patent No.
One method for increasing the production of heavy crude oils of high viscosity from underground formations is the in-situ combustion prQceSS. In that proces~, air is injected at a high pressure throu~h an injection well into the underground formation containing the heavy oil. The oil in the formation adjacent the injection well is ignited by any of several known procedures such as the procedure disclosed in U. S. Patent No. 3,172,472 of F. M. Smith. Injection of air is continued after ignition to burn part of the oil in the formation and to increase the pressure in the formation adjacent the injection well and thereby drive oil in the formation toward a production well spaced from the injection well. A typical in-si~u combustion process is described in U. S. Patent No.
2,771,951 of Simm. The heat released by combustion of some of the oil in the formation heats the formation and oil whereby the viscosity of the oil i~ greatly reduced by the high tempera-ture, cracking of the oil, and by solution in the oil of low molecular weight hydrocarbons formed by the cracking. The reduced viscosity and the pressure of the injected gases cause the oil to flow throuyh the underground reservoir to a production well.
During in-situ combustion processes, the combustion front at which oil in the formation is hurned does not move radially outward at a uniform rate in all directions.
Usually the oil reservoir will vary in permeability and oil saturation from one location to another between the injection and production wells. Some of the injected air fingers through the formation toward a production well and combustion oc~urs at the boundaries of the fingers. There may be a breakthrough of combustion products in the nature of a flue ~as long before the production of oil by the in-situ process is completed.
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Volatile constituents in the oil, or formed by cracking o th~ oil, are entrained in the injected air or flue gases and carried by them ts:~ the production well~ All o~ these factors contribute toward variations in the composition of the gas 5 produced from time to time during an in-situ combustion for the production of oil ~rom a reservoir. Such variations may re~ult in periodic increases of 100 percent or more in the heating value of the gas producedf The fluids produced at the production well are separated into liquid petroleum products which are delivered to storage or a delivery line and gaseous products. The gaseous products customarily have been vented ~o the atmosphere.
The gaseous products, hereina~ter referred to as LHV gas, from in-situ combustion contain low concentrations of methane and C2-C6 hydrocarbons, as well as nitrogen, carbon dioxide, sulfur compounds such as hydrogen sulide, mercaptans and carbonyl sulfide, and in 50me instances a small amount of carbon monoxida and traces of oxygen. Those gaseous products constitute low heating value fuel capabIe of supplying a subst~ntial part of the en rgy required to compress the air for in~ection into the su~surace formation at the injection well. The shortage of natural gas make~ it important that the energy in the products from an in-sltu combustion process be ~ully utllized. Moreover, tightening of l~w9 relating to pollution of the atmosphere has place~ stringent limitations on the amount of carbon monoxide, the sulfur compounds most freguently present in the gaseous products, and hydrocarbon~ other than methane that may be dis-charged into the atmosphere.
U. S. Patent No. 3,113,620 of Hemminger describes a single well in-situ combustion process in which a cavity filled
During in-situ combustion processes, the combustion front at which oil in the formation is hurned does not move radially outward at a uniform rate in all directions.
Usually the oil reservoir will vary in permeability and oil saturation from one location to another between the injection and production wells. Some of the injected air fingers through the formation toward a production well and combustion oc~urs at the boundaries of the fingers. There may be a breakthrough of combustion products in the nature of a flue ~as long before the production of oil by the in-situ process is completed.
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Volatile constituents in the oil, or formed by cracking o th~ oil, are entrained in the injected air or flue gases and carried by them ts:~ the production well~ All o~ these factors contribute toward variations in the composition of the gas 5 produced from time to time during an in-situ combustion for the production of oil ~rom a reservoir. Such variations may re~ult in periodic increases of 100 percent or more in the heating value of the gas producedf The fluids produced at the production well are separated into liquid petroleum products which are delivered to storage or a delivery line and gaseous products. The gaseous products customarily have been vented ~o the atmosphere.
The gaseous products, hereina~ter referred to as LHV gas, from in-situ combustion contain low concentrations of methane and C2-C6 hydrocarbons, as well as nitrogen, carbon dioxide, sulfur compounds such as hydrogen sulide, mercaptans and carbonyl sulfide, and in 50me instances a small amount of carbon monoxida and traces of oxygen. Those gaseous products constitute low heating value fuel capabIe of supplying a subst~ntial part of the en rgy required to compress the air for in~ection into the su~surace formation at the injection well. The shortage of natural gas make~ it important that the energy in the products from an in-sltu combustion process be ~ully utllized. Moreover, tightening of l~w9 relating to pollution of the atmosphere has place~ stringent limitations on the amount of carbon monoxide, the sulfur compounds most freguently present in the gaseous products, and hydrocarbon~ other than methane that may be dis-charged into the atmosphere.
U. S. Patent No. 3,113,620 of Hemminger describes a single well in-situ combustion process in which a cavity filled
3--with rubble is formed in a subsurface oil shale deposit b~
means of a nuclear explosion. An in-situ combustion process in the cavity is then conducted to remove oil from the rock, aid in draining the oil into a pool in the bottom of the cavity, and force the oil up th~ well to th~ surface. The composition of the gases produced with the oil difers from the composition of gas produced in a conventional in-situ combustion process in an oil reservoir. Because o the diferent composition of the gas, Hemminger is able to burn the off-gas directly in a flame combustor of a gas turbine used to drive an air compressor.
U. S. Patent No. 2,44~,096 of Wheeler, ~r. describes a process for the recovery of power from gas discharged from a regenerator in a fluidized catalytic cracking process. The hot gases from the regenerator are first passed countercurrently to a nonvolatile oil in a scrubber whereby a small amount of hydro~
carbons is entrained in the gas. The gas with entrained hydrocarbons is passed through a catalytic oxidizer for burn ing ~he hydrocarbons and the ~ombustion products are delivered either to a turbine or direGt power recovery or to a steam generator.
U. S. Patent No. 2, 8591~54 of Grey describes a power recovery system for a blast furnace in which blast urnace gas is compressed, burned, and then expanded in a turbine to provide energy ~for compressing air used in the blast furnaceO The com-bustible material in the blast furnace gas is largely carbonmonoxide and hydrogen. Those gases are more readily ignited and burned in dilute mixtures with inert gases than is methane.
The blast furnace gas, which typically has a heating value above 90 btu/scf, is burned by Grey in flame-type combustors for release of the thermal energy.
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U. S. Patent No. 3~g28,9~1 of Pfeferle describes the catalytic combustion o fuels to drive gas turbines. rrhe method of Pfefferle conducts catalytic oxidations at a temperature in the range of 1700 F. to 3~00~ F., preferably in the range of 2000 P. to 3000 F., described by Pfe~ferle a~
the autoignition range. That temperature is high enough to initiate thermal combustion, but not high enou~h to c~use subs~antial formation of nitrogen oxides. Combustion in the P~eferle method is primarily thermal combustion. Air at least stoichiometrically e~uivalent to the fuel is used to complete the oxidation. When the combustion is used for gas turbine operations, the weight ratio of air to ~uel is far above the stoichlometric ratio and ranges ~om about 30:1 to 200 or .
more to 1. Because the composition o the ~uel is constant, thP
excess of oxygen in the air-fuel mixture does not cause wide variations in the temperature of the combustion products.
Because oil shale is impermeable, in-situ combustion processes for the recuvery of oil from oil shale require that permeability of the shale be established befoxe the in-situ combustion is begun~ It is pref~rred that the permeability be established by rubbli2ing shale in a selected portion of the shale deposit to form an underground retort. Combustion of shale in the retort to release shalP oil is preferably accom-plished at low pressures to avoid leakage of gas to adjacent retorts that are being rubblize~. Gases discharged from retorts for in-siku combu~tion processes for shale oil pro-duction are usually, there~ore~ at pressuxes too low for delivery directly into gas turbines or power recovery.
Typical in-situ combustion processes for the recovery of oil from oil shale are descri~ed in U. S. Patent No. 2,780,449 o Fisher et al and U. S. Patent No. 3,0~1,776 of Van Poollen.
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Summary of the Invention This invention resides in a system for the recovery of power from and reduction of pollutants in LHV gas discharged from production wells of in-situ combustion processes for the production of oil. The LHV gas, after separating rom liquid products produced from the well, i~ mixed with a limited quantity of air~ preheate~ to a tempexature exceeding approxi~
mately 400 F., and delivered into a cata]ytic combustion chamber in which combustibles in the LHV gas are burned.
The amount of air mixed with the L~V ga~ is less than the stoichiometric equivalent of the combustibles in the L~V ga~
and thereby limits the amo~nt of combustion and the maximum temperature that may occur in the combustion chamber. In a preferred embodiment, the I.HV gas is burned in a primary and a secondary catalytic combustion chamber with approximately fifty percent of the total air introduced into each combustion chamber. Hot gases discharged frvm khe primary ca$alytic combustion chamber~are mixed with the air for the sacondary combustion and~then cooled to a temperature suitable for introduction into the secondary catalytic combustion chamber~
; The cooled ga~es are delivered into the secondary catalytic combustion chamber for combustion of combustible material remaining in the gas. Preferably, the combustion products discharged from the second combustion chamb~r are expanded in 2S a turbine to generate power ~or compression of air used in the in-situ combustion process.
Brief Description o~ the Drawin~s Figure 1 of the drawings is a diagrammatic flow sheet of a preferred embodiment of this invention as used for the recovery of power rom LHV gas discharged from an in-situ combustion system ~or the reco~ery of oil from an underground oil reservoir.
Figure 2 of the drawing~ i~ a diagrammatic 10w sheet of an embodiment of this invention in which the combusti~n products generate steam that is used to drive a turbine.
Fi~ure 3 is a chart showing tne varia~ion in ~he S heating value of c3ases produced in an in-situ combustion process for the recovery of oil from an oil reservoix over a two and one-half year period.
Description o~ Preferred Embodiment Referring to Figure 1 of the drawing~, a subsurface formation 10 containing crude oil, u~ually of hiyh density and viscosity, is penetrated by a production well 12 and an injection well 14 spaced from the production well. Flu~ds produced from the production well 12 are delivered through a line 16 into a separator 18 in which the produced LHV gas is separated from liquids produced through well 12. The liquids are discharged from the lower end of the separator 18 into a delivery line 20 and the ~HV gas is discharged from the top of separator 18 into a feed line 22. It will usually be desirable to pass the gas from the separator 18 through a suitable gas clean-up, not shown, to remove solid particulates, catalyt poisons, or other undesirable constituente before delivery into line 22. A 10w controller 23 maintains a constant flow rate of the LHV gas to the turbine as hereinafter described.
Typical hydrocarbon concentrations in the LHV gas range fxom about 1 to 8 per cent by volume. The hydrocarbons are principally methane; the concentration of C2-C~ hydrocarbons usually belng less than 2 percent. In the concentrations present in the LHV gas, stable combustion of methane and the other low molecular weiyht hydrocarbons produced in in situ production is obtained only in the presence of a catalyst.
The heating value of the LHV yas produced from in-situ combustion in oil reservoirs may range from S to 80 BTU/scf, and ordinarily will be in the range of 40 to 70 BTU/scf, a range in which the process is particularly useful. On some occasions, usually fox short periods, the heating value may rise to 100 BTU/scE. LEIV gas having a heating value above lS BTU/scf can be burned in a catalytic combustor without an external source of heat. If other sources of heat are available to provide additional preheat, LHV gas having a heating value as low as 5 BTU/scf can be oxidized in catalytic combustion chambers.
For most affective use in driving a gas turbine to compress air used in the in-situ combustion process, for example, the gases dischaxged from the sepaxator 18 should be at a pres-sure of at least 75 psig. I~ the gas is at lower pressure, i part of the energy is used in compressing the LHV gas to a pres-sure high enough to drive a turbine, however, LHV gas at lower pressures may contain substantial energy which can be useful in supplying heat for heater-treaters and other oil field equipment or for developing power by supplying heat to generate steam at :
a pressure high enough to drive a turbine. The pressure in the production wells of an in-situ combustion process usually range from slightly above atmospheric pressuxe to 800 psig. The pressure is dependent, at Jeast in part on the depth of the formation in which the combustion occurs. Pressures higher than 800 psig in the production wells can be used but such high pressures suffer the disadvantage of high costs for compressing the air injected into the underground formation; however, much - of the energy used in compressing the air can be recovered.
The gas in line 2~ is mixed with air from a line 24 and, during startup, passed through a heater 26. A fuel, such ..
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as LPG, supplied through line 28 is burned in heater 26 to raise the temperature of the mixkure of LHV gas and air to a tempera-ture at which oxidation will occur on contact with the oxidation catalyst hereinafter described. The heater 26 is used only during S startup, and after oxidation of the LHV gas commences, heat~r 26 is bypassed by flowing the air from line ~ through bypa.ss 30.
The mixture o~ air and LHV gas discharged from heater 26 is delivered through line 32 into a heat exchanger 34. No hea* kransfer to the mixture of air and ~HV gas occurs in heat exchanger 34 until after combustion has begun in khe catalytic combustion chamber as hereinafter descri~ed.
After pa~sing through h~at exchanger 34, the mixture o air and LHV gas is delivered through line 36 into a primary catalytic combustion chamber 38. The temperature of the gas delivered to the combustion chamber 38 should be in the range of approximately 400 to 800 F. whereby oxidation will be i~ltiated on contact of the LHV gas with the catalyst.
Usually, the~inlet temperature will be in the upper part of that:temperature range.
In a preferred catalytic oxidation chamber, platinum is deposited on the surfaces of a commercially available ceramic honeycomb-type catalyst suppoxt arranged in primary combustion chamber 38 in a series of transverse slabs 39 sepa.rated from one another by ~ree spaces 40. The free spaces between the slabs are designed:to allow equalization o~ the temperature of the gases between the slabs and thereby minimize development of hot spots; however, satisfactory operation has been obtained wikh adjacent slabs touching. The honeycomh-type of catalyst support .
~is advantageous in allowing high throughputs with a low pressure drop through the catalyst. ~n a typical combustion chamber there may be 10 to 20 or even more slabs 39. ~ catalyst that can be used is described in U. S. Patent No~ 3,870,455 of Hindin~
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The arrangement a~d catalyst shown are preferred for use in this invention; however, this invention is not restricted to the use of a particular catalyst. Other oxida~ion catalysts supported on other supports can be used. For example, catalysts containing cobalt or lanthanum as the cata]ytically active ingredients s~pported on honeycomb or on sponge type supports can be used. Other catalysts that can be used are described in U. S. Patent No. 3,565,830 of Keith et al. Oxidation catalysts used at temperatures higher than ~000 Fo are described in U. S.
Patent No. 3,928,961 of Pfefferle.
The gases are discharged from combustion chamber 38 at a maxim~m temperature preferably of approximately 1600 F.
through line 41 and mixed with additional air supplied through line 42. The maximum temperature is limited by the highest temperature that the catalyst can withstand over long operating periods without deterioration. Preferred oxidation catalysts for this invention in which combustion products are passed through a gas turbine that consist of platinum on a ceramic support can withstand higher temperatures than 1600 F. for short periods ~0 but their life lS shortened by continued use at the higher tem-peratures. As previously indicated, the amount of air supplied through line 42 preferably is approximately one-half of the total amount o~ air supplied ~or oxiclation of the LHV gas.
Addltion of air through line 42 will ordinarily result in a temperature drop of approximately 200 F. in the gases in line 41. The gases are deli~ered throuyh line 41 into heat exchanger 34 and passed therein in indirect heat exchange with the initial mixture of air and LHV gas delivered to the hea~
exchanger through line 32. ~he mixture o air and partially oxidized LHV gas i~ discharged from heat exchanger 34 at a temperature preferably o~ 600 F. to 300 Fo and delivered via line 44 into a secondary catalytic combustion chamber 46.
Secondary catalytic combustion chamber 46 may be identical to -10~
3~ g primary c~talytic combustion chamber 38. Oxidation of combus-tibles in the partially oxidized LHV gas delivered ~rom heat exchanger 34 occurs in secondary combustion chamber 46. By limiting -the total air flow into the primary and secondary catalytic combustion chambers to an amount slightly ~e.g. 5 .
percent) less than the s$oichiometric equivalent of an LHV
gas heating value that would cause the maximum permissible temperature rise,excessive temperatures in the catalytic combustion chambers are. avoi-led even though the composition of the L~IV may vary widely.
Heat released in the secondary combustion chamber may increase the temperature o~ the gases to, ~or example, approximately 1600 F. at the outlet line 48 rom the secondary combustion chamber. Usually, it will be desirable to cool the gases in line 48 to reduce the temperature of the gases to a temperature that provides a margin of safety below the maximum operating temperature o~ a gas turbine 52 into which the gas is delivered. Some turbines are capable of withstandiny tem-peratures up to about ~000 ~.; however, it is preferred to ~ reduce the temperature of the gas~s to 1400 F. to 1600 F.
by dilution with air before delivery into the turbine. The desired cooling may be accomplished by introducing cooling air into line ~8 from line 50. The temperature at which the com-bustion products leave the secondary combustion chamber is far below the temperature required to ignite those partially burned gases o low heating value in the absence of a catalyst;
consequently, there is no danger of further combustion with resultant development of excessive temperatures occurxing on mixing air from line 50 with the hot gases in line 48 even though the hot gases usually include unburned combustibles.
The air introduced through line 50 is, therefore, cooling air rather than combustion air.
Referring to Figure 3 of the drawings, it will be noted that the heating value of the LHV gas produced during a typical in-situ combustion process varies substantially.
Most of the time during the 2-l/2 year operation shown in Figure 3, the LHV gas produced by the in-situ process had a heating value above about 55 BTUJsc~; however, the heating value was frequently in the range of 70 BTV/scf and on one occasion increased to over lO0 B~U/scf. At other times, the heating value dropped below 50 BTU/scf. The wide swings in LHV
gas composition introduce problems of controlli.ng the temperature to prevent excessive temperatures that would damage the catalyst or the gas turbine and still operate ~he gas turbine under opti-mum conditions. To control the maximum temperature that may be attained and also maintain a uniform temperature~ the catalyt.ic comhustion chambers are operated with less alr than the stoich-iome$ric equivalent of the combustibles in the LHV gas. In this manner r the amount of air supplied to the catalytic combustion chambers establishes the maximum temperature rise in the catalytic combustion cha~bers and r consequently, the maximum ; 20 ~emperature that is attained. If the maximum permissible tem-perature in the catalytic combustion chamber i.s 1600 F., the amount of air mixed with the cold LHV gas entering the heat exchanger 34 will be such that when the oxygen in that air is completely consumed in burning combustibles in the LHV gas, the temperature in the combustion chamber will not exceed 160~ F.
If oxidation catalysts having an acceptabl~ life when used at higher temperatures to burn LHV gas should be used, and ~he ~eating value of the LHV gas should be high enough to raise the temperature of the:combustion products abo~e the maximum operating temperature of the catalyst, the amount of air delivered tc the combustion chambers could be increased and thereby raise d3 the maximum temperakure that might be reached in the com-bustion chambers. The amount of air would be less than the stoichiometric equivalent of the LHV ~as to maintain the desired temperature control.
Assuming that the mixture of LHV gas and air in line 32 to the preheater 34 is at a temperature of 175 F. and the maximum permissible catalyst temperature is 1600 F., the maximum total amount of air mixed with the I.HV gas entering the primary combustion chamber 38 and with the hot combustion products discharged from that combustion chamber can contain oxygen stoichiometrically equivalent to the combustibles in LHV
gas having a heating value of approximately 50 BTU/scf. If the heating value of the LHV gas should be as shown in Figure 3, that amount of air would be less than stoichiometrically equiva lent dur1ng approximately 90 percent of the time. Preferably, approximately fifty per~cent of the total amount of combustion air is introduced into the system by mixing with the LHV gas before delivery into the primary:combustion chamber and the remainder is mixed with the products of combustion from the primary combustion chamber before delivery to the secondary combustion chamber.
While controlling the rate of air a~mixture with the LHV gas introduced into the primary and into the secondary catalytic combustion chambers at a rate that is less than the 2S stoichiometric equivalent of the normal LHV gas composition limits the maximum temperature rise in the combustion chambers and is effective in protecti.ng the catalyst from temperature rises that might:~otherwise result ~rom increases in the heating value of the LHV~gas, precise con~rol to maintai.n a constant mass flow rat and temperature of the gas delivered to the turbine is desirable for most efi.cient operation of the turbine.
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Flow controllex ~3 in line 22 from separator 18 maintains the desired rate of ~low of LHV gas into the system. Since the rate of flow of air to the combustion chambers is constant, a drop in the temperature of gases discharg~d Erom the secondary catalytic combustion chamber indicates that the combustible materials in the LHV gas are less than the stoichiometric equivalent o~ the combustion air delivered into the systemO
The desired temperature can be obtained with li-ttle change in the mass 10w rate by introducing an auxiliary uel into the system. A temperature sensor 53 in line 48 adjacent the outlet end of secondary combustion chamber 46 can bs connected to actuate a flow control valve 55 in an auxiliary fuel line 57.
If the temperature in line 48 should drop, the temperature sensor 53 would actuate flow control valve 55 to enrich the mixture delivered to the secondary combustion chamber 460 To provide stable operation, the controls will inject sufficient auxiliary fuel to increase the heating value of the LHV gas delivered to the co~bustion chambers an amount such that the air is slightly less than the stoichiomet.ric equivalent of the total combustibles in the LHV gas and auxi.liary fuel. Alterna-tively, a hydrocarbon analyzer can be installed to withdraw a sample from line 22 and determine the hydrocarbon content, and, hence, the heating value, of the LHV gas. A signal generated by the hydrocarbon analyzer can be used to contxol valve 55.
Clearly, the auxiliary fuel can be introduced into the system at any point upstream of the secondary catalyti.c combustion chamber, such a~ into line 22 Usually, the auxiliary fuel will be natural gas or LPG. The heating values of natural gas and LPG are high and the concentration of inerts is low;
consequently, a desired increase in the temperature of the combustion products can be o~kaine~ with a negligible change in the mas.s 10w rate to the turbine.
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The hot gases are expanded in the turbine to sub-stantially atmospheric pressure~ and the gases from the turbine are diseharged to the atmosphere. I necessary, gases discharged from the turbine can be passed through a suitable scrubber to remove contaminants before being discharged into the atmosph~re.
The gases discharged from turbine 52 will be hot and could be passed through a heat exchanger to supply heat for process or other use, i desired.
Energy produced by turbine 52 is used to compress air used in the combustion of the LMV gas and in the in-situ combustion process. In ths embodiment illustrated, the turbine is shown as directly connected to drive a low pressure compressor 54 which compresses air to a pressure exceeding the operating pressure of the catalytic combustion chamber 38 sufficiently ~or easy control of air flow into the system. That air is delivered in~o a header 56 to which line.s 24, 42 and 50 are connected or delivery of aix as needed for the combustion of th~ LH~ gas and subsequent cooling of the combustion products from the secondary con~ustion chamber~
Turbine 5~ also drives a high-pressure compressor 58 that compresses air for use in the in-situ combustion process.
Air compressed in compressor 54 in excess of the air required for combustion o~ the LHV gas and cooling is bled from compressor 54 and delivered to compressor 58 through a line 59.
~5 Line 59 is provided with flow control means indicated by valve 61 to control the flow of bleed air to compressor 58. In a preferred arrangement, ~he turbine-type compressor 58 compresses air to an intermediate pressure of ~he order of 250-300 psig, and that air is d~livered through line 60 to a cen rifugal or reciprocating compressor 62 for ~urther compression to a pressure typically in the range of 2,000 psig to 3~000 psig.
~15-The pressure to which the air is compressed by compressor 62 will depend upon the parti.cular in situ combustion process and will vary with several parameters of ~he in-si~u combus~ion process such as the depth oE the subsurface formation into which the air is to be injected, the viscosity of the oil, ~he permeability of the subsur~ace formation, the rate of in~ection of air into the formation, and the desired pres~ure at the production well. Air from compressor 62 is delivered through line 64 into injection well 14. In an alternative arrangement, air compressor 58 is constructed to allow withdrawal of air from an intermediate stage of the compressor at a low pressure for use in combustion of the LHV gas. With that arrangement, low pressure compressor 54 will not be necessary.
Whil~ supplying air at a rate that is less than the stoichiometric equivalent of the combustibles in the LHV gas causes some loss of the potential enexgy available in the com-bustibles in the LHV gas, the importance of such loss is minimized by the gain in the compressed air that is made available for use in the in-situ combustlon process. If air were delivered to the ca~alytic combustion chambers at a rate equivalent to the stoich-iometric equi~alent of an LHV gas having a heating value of 70 BTU/scf, for example, and the maximum permissibla temperature in the gas turblne remained at 1~00 F., it would be necessary to cool the gas discharged from the secondary combustion chamber before delivery to the turbine. I~ air from compressor 54 should be used to dilute the combustion products and thereby cool them to the desired *emperature for delivery *o the gas turbine, such air would reduce the amount of air delivered from compressor 54 to compressor 58 for use in the in-situ combustion process.
It is an important advantage of this invention that the desired safeguards against temperature and flow rate ~3~ 3 variations and excessive temperatures can be obtained while complying with the usual antipollu~ion regulations.
Hydrogen sulfide and the higher molecular weight hydrocarbons are preferentially, as compared to methane, oxidized in the catalytic combust:ion chambers. The unoxiaized combustible material discharged from the secondary combustion chamber because of the deficiency in air i.s almost entirely methane, a gas that usually is nok subject to antipollution regulations.
As an example of the preferential oxidation of the hydrocarbons having a higher molecular weight than methane, a hydrocarbon gas-air mixture was passed in contact with a platinum catalyst deposited on a ceramic support at an inlet temperature of 840 F. and a maximum temperature of 1430 F.
The hydro~arbons were mixed with about 50 percent oF the stoichiometric air, thereby giving a mixture with a severe - deflciency in air.~ The composition of the hydrocarbons, the outlet composition, and the percent conversion of each : of the hydrocarbons are set forth below:
TABLE I
H~drocarbon Conversion Inlet Composition Outlet Compositlon % Converslon Methane 1.09% 0.97% 11.00 Ethane 0.22% 0.15% 31.8 Propane 0-34% 0.19% 44.1 i Butane 0.06~ 0.03% 50~0 n Butane 0.22% 0.10~ 54,5 i Pentane 0.06% 0% 100.0 n Pentane 0.08~ 0% 100.0 Similar tests were made with larger equivalence ratios (ratio of amount of air supplied to the amount of air stoichiometrically equivalent to the comhustibles in the gas). The results are presented in Tables II and II:
TABLE II
ydrocarbon Conversion Inlet Composition Outlet Composition % Conversion Methane 3.54% 0~47% 87 ~thane 0.39% 0% 100 Propane 0.32% 0% 100 i-Butane 0.11~ 0~ 100 n-Butane Q.24~ 0% 100 i-Pentane 0O14% 0% 100 n-Pentane 0.16% 0% 100 Equivalence Ratio = 0.96 TABLE III
Hydrocarbon Conversion Inlet Composition Outlet Composition ~ Conversion Methane ~ 3.62% 2.23% 38~
Ethane 0.40% ; ~ 0.16% 60%
Propane 0.28% 0.06% 79~
i-Butane 0.09% 0~ 100%
n-Butane 0.18% 0~ 100%
i-Pentane 0.08% 0~ 100~
n-Pentane 0.07% o% 100%
~ Equlvalence Ratio = 0.60 It is apparent from the results shown in Ta~les I, II
:
and III that even with a deficiency of air more severe than would normally be caused by a surge in combusti~les in the LHV gas, preferential removal of the heaviest hydrocarbons from the LHV
gas was accomplished in the catalytic combustion chamber.
Combustion of methane lagged far behind the combustion of other hydrocarbons. ~s the equivalence ratio increased to the 3~
range normall~ used, the hydrocarbons other than methane are virtually completely consumed. This invention is/ therefore, particularly advantageous when the fuel available varies in heating value and con~ists of a mixture o~ combustibles that includes methane as one of the combus~ible constituents.
An important ad~antage of the process of this inven-tion in utilizing LHV gas from in-situ combustion processes from which the LHV gas is produced at pressures, preferably exceeding 75 psig, high enough to drive a gas turbine, is that the utilization of energy in the LHV gas is more efficient than in gas of higher heating value. If fuels of high heating value such as natural gas are used in gas turbines, the air to fuel ratio is high, such as 40 to 1 or higher, to dilute the combustion products and thereby avoid temperatures higher than the turbine blades can withstand. A substantial portion of the energy produced by the turbine is used to compress the diluent air for mixture with the hot gases before delivery into the turbine. In contrast, the LHV gas contains inert gases that will serve as a diluent to help avoid excessive temperatures in the turbine, and it is necessary to compress only very little dilution air above that required for burning the combustibles in the LHV gas.
The temperature rise that occurs on burning a 50 BTU/scf ~HV gas with s-tolchiometric air is approximately 1425 F. Because it is necessary that the temperature of the LHV~air mixture delivered to the ca~alyst be at least 40G F., and preferably in the range of 600 F. to 800 F., burning a 50 BTU gas in a single stage would cause catalyst -temperatures exceeding 1600 F~ Thereforel a single-stage, self-supporting LHV catalytic combustion process in which the combustibles in a 50 BTU/scf LHV gas are consumed is possible only if the 33~;v ~
catalyst can withstand prolonged exposure to temperatures of 1825 F. and higher, and preferably higher than 2025 F. ~he term self-supporting is used to designate a process in which the hot combustio~ products from the catalytic combustion chamber heat the LHV gas-air mixture to 400 F. or higher.
Single-stage catalytic combustion with a catalyst limited to a maximum temperature of 1600 F. is limited to burning combustibles to liberats about 33 BTU/scf of the L~V gas.
Such an operation would suffer a disadvantage, as contrasted to ~he pre~erred two-stage operation, of lower turbine efficiency resulting from the lower temperature of the gases delivered to the turbine if the hot gases from the combustion chamber are used to heat the L~V gas-air mixture to 400 F. or higher.
In a single stage operation uti~izing a catalyst limited tv a maximum temperature of 1600 F., the amount o air mi~ed with the LHV gas would be limited to the stoichiometric equivalent of 33 BTU/scf L~ gas to protect the catalyst from excessive temperatures resulting from periodic increases in he heating value of the LHV gas composition such a~ occur in in-situ combustion processes. The concept of protection against varia tions in fuel composition by limiting the oxygen supplied to the combustion chamber can, therefore, be used in a single-stage operation. A two-stage catalytic combustion process is preferred for L~IV gas having a heating value of 40-80 BTU/scf, however to recover a larger part of the energy available in the LHV gas and to operate the tuxbine more efficiently.
If two-stage catalytic combustion of the type described with respect to Figure 1 is used to burn gases consistently having heating values higher than about 80 BTU/scf, it will be necessary to discard a substantial amount of the heating value of the gas in the form of unburned hydrocarbons leaving the secondary combustion chamber.
~ ~ ~ 3 3~D
If the normal heating value of the gas from the in-situ combustion process should be consist~ntly above approximately 70 BTU/scf, for example ranging upwardly from 70 to 80 BTU/scf, and the maximum permissible catalyst and turbine temperatures are appxoximately 1600 F., it is desirable to use a third catalytic combustion chamber to reduce the loss of energy in the unburned hydrocarbons. It will then be necessary to cool the gases discharged from the secondary catalytic combustion chamber before delivering the gases to the third combustion chamber. Such cooling can be obtained by passing gases discharged from the second combustion chamber, preferably after mixing with air for the third combustion stage, through a boiler in heat exchange with water to generate steam.
Steam generated in the boiler can be used as process steam or to drive a turbine. A preferred method for recovering additional energy from LHV gas having a heating value normally exeeding about 70 BTU is to poSitiQn a tertiary catalytic combustion ~hamber 66 downstream of the gas turbine 52. The gases dis-~ charged from the turbine are delivered to the third stage combustion chamber at a temperature in the range of 400 to 800 F.
Air is dellvered to the tertiary ombustion chamber 66 through a line 67 from the compressor 54 and the mixture passed in contact with an oxidation catalyst in the combustion chamber to oxidize hydrocarbons xemaining in the gas discharged from the turbine.
Valves in lines 67 and 59 allow control of the amount of air delivered to each of tertiary catalytic combustion chamber 66 and compressor 58. The hot gases from tertiary combustion chamber 66 are delivered to a boiler 68 for the generation of steam. In the event three combustion chambers are used, the delivery of air to the fixst two combustion stages is controlled to operate the 3~
turbine at optimum conditions. The third combustion stage could operate at stoichiometric conditions or with an excess of air if the heating value of the gas i8 such that excessiv~
catalyst temperaturess are not developed ln the third sta~e.
The gas turbine 52 operates with le~s than sto:ichiom~tric air at all times.
The embodiment o~ the invention illustrated in Figure 2 is or use in those situations where the LHV gas discharged from the in-situ process is not at a high enough pressure for efficient use in driving a gas turbine. The low pressure LHV gas may, for example, be produced in an in-situ com~ustion process for recovery of oil fxom a shallow under-ground reservoir at a low pressure or in the in situ combustion of oil shale. The LHV gas is delivered through a pipe line 70 to a suitable gas cleanup unit 7~ for xemoval of solid particles or other components that may interfere with the subsequent catalytic oxidation of the gas. The gas cleanllp unit 72 may be in the form of a suitable separator or screening or washing apparatus. LHV ga~ from the gas cleanup unit 72 is delivered to a preheater 74 similar to preheater 34 in the embodiment illus-trated in Figure 1, for preheating to a temperature of 400 F. to 800 F. Preheated LHV gas discharged from the preheater 74 is mixed with combustion air supplied by a suitable blower or com-pressor 76 and delivered into a primary catalytic combustion chamber at a temperature o 400 F. to 800 F. Catalytic com-bustion chamber 78 is preferably similar to catalytic COmbU~tiGII
chamber 38 illustrated in Figure 1.
The hot combustion products from the primary catalytic combustion chamber 78 are deli~ered into preheater 74 for indirect heat transfer with the LHV gas. The combustion products from preheater 74 are mixed with additional combustion air from blower 80, which results in a temperature in the range of 400 F.
to 800 F., and delivered into a secondary catalytic combustion chamber 82. As in the embodiment illustrated in Figure l, air for oxidation in the secondary chamber also can be mixed with S the partially burned gases rom the primary combustion chamber before those gases are delivered to preheater 74.
Instead of delivering the combustion products from secondary catalytic combustion chamber 82 to a gas turbine, as in ~he embodiment illustrated in Figure 1, the combustion I0 products are delivered to a boilex 84 fo~ generating steam.
Because the combustion products from the secondary catalytic combustion chamber 82 are not delivered to a turbine, they are not cooled hefore delivery to the boiler 84. The high tem-perature of the combu~tion products discharged rom the secondary catalytic co~bustion chamber allows generation of steam at a high pressure suitable for driving a steam turbine.
Steam from the boilsr 84 is delivered through line 86 to a steam tyrbine 88 which lS preferably connected to a generator 90 to generate electricity~to drive air compressors for the in-situ combustion process. The steam turbine may, alternati~ely, be directly connected to compressors. Steam discharged from turbine 88 Ls delivered to a condenser 92 and the condensed steam passed through suitable water treatment 94 which includes a pump for returning the condensed water to boiler 84. ~s an alternative to the generation of steam as illustrated in Figure 2, low pressure off gases rom in-situ combustion of oil shale, for example, could be used in the system o E'igure l modi-fied to utiliæe a portion of the energy generated by turbine 52 to compress the LHV gas to a pressure high enough to drive the turbine.
3~i~3 The temperatures to which the LHV gas is preheated and combustion products from the primary catalytic combustion chamber are cooled in preheater 74 are designed to avoid excessively high temperatures which could damage the catalyst in combu~tion chambers 78 and 82. As in the embodiment illustrated in Figure 1, control of the maximum temperatures is obtained by control of the amount of air mixed with the LHV gas before delivery into the catalytic combustion chambers to prevent overheating of the catalytic combustion chambers even though there should be a substantial i~crease in the concentration of combustibles in the LHV gas delivered through pipe 70.
The amount of air supplied by blower 76 is preferably approxi-mately one-half the stoichiometric equivalent o the quantity of combustibles that will give tha maximum permissible tem-perature use; and an equal amount of air is supplied by blower 80for the oxidation in the secondary combustion chamber 82.
The method and apparatus herein described are highly advan~ageous or the recovery of power from LHV gas from in-situ combustion process~s for the recovery of oi~ because of the variations from time to time in the heating value of the gas.
While the method is most useful for the recovery of power from the gas produced at elevaked pressures in in-situ combustion processes for the recovery of oil from oil or tar sand reservoirs, it is also useful;in reco~ery of power from low-pressure off-gases from the in-situ combustion of oil shale in those instances when such off-gases cannot be burned in a flame co~ustor because of its low heating value. The limitation of ~he amount of air mixed with the LHV gas tG the stoi~hiometric equivalent of the normal LHV gas provides protection for both the catalyst and the turbine against wide variations that occur in the composition o the LHV
gas. This invention is particularly valuable when methane is one of the combustible constituents of the LHV gas.
-~4-
means of a nuclear explosion. An in-situ combustion process in the cavity is then conducted to remove oil from the rock, aid in draining the oil into a pool in the bottom of the cavity, and force the oil up th~ well to th~ surface. The composition of the gases produced with the oil difers from the composition of gas produced in a conventional in-situ combustion process in an oil reservoir. Because o the diferent composition of the gas, Hemminger is able to burn the off-gas directly in a flame combustor of a gas turbine used to drive an air compressor.
U. S. Patent No. 2,44~,096 of Wheeler, ~r. describes a process for the recovery of power from gas discharged from a regenerator in a fluidized catalytic cracking process. The hot gases from the regenerator are first passed countercurrently to a nonvolatile oil in a scrubber whereby a small amount of hydro~
carbons is entrained in the gas. The gas with entrained hydrocarbons is passed through a catalytic oxidizer for burn ing ~he hydrocarbons and the ~ombustion products are delivered either to a turbine or direGt power recovery or to a steam generator.
U. S. Patent No. 2, 8591~54 of Grey describes a power recovery system for a blast furnace in which blast urnace gas is compressed, burned, and then expanded in a turbine to provide energy ~for compressing air used in the blast furnaceO The com-bustible material in the blast furnace gas is largely carbonmonoxide and hydrogen. Those gases are more readily ignited and burned in dilute mixtures with inert gases than is methane.
The blast furnace gas, which typically has a heating value above 90 btu/scf, is burned by Grey in flame-type combustors for release of the thermal energy.
' .. .. .
3~P~
U. S. Patent No. 3~g28,9~1 of Pfeferle describes the catalytic combustion o fuels to drive gas turbines. rrhe method of Pfefferle conducts catalytic oxidations at a temperature in the range of 1700 F. to 3~00~ F., preferably in the range of 2000 P. to 3000 F., described by Pfe~ferle a~
the autoignition range. That temperature is high enough to initiate thermal combustion, but not high enou~h to c~use subs~antial formation of nitrogen oxides. Combustion in the P~eferle method is primarily thermal combustion. Air at least stoichiometrically e~uivalent to the fuel is used to complete the oxidation. When the combustion is used for gas turbine operations, the weight ratio of air to ~uel is far above the stoichlometric ratio and ranges ~om about 30:1 to 200 or .
more to 1. Because the composition o the ~uel is constant, thP
excess of oxygen in the air-fuel mixture does not cause wide variations in the temperature of the combustion products.
Because oil shale is impermeable, in-situ combustion processes for the recuvery of oil from oil shale require that permeability of the shale be established befoxe the in-situ combustion is begun~ It is pref~rred that the permeability be established by rubbli2ing shale in a selected portion of the shale deposit to form an underground retort. Combustion of shale in the retort to release shalP oil is preferably accom-plished at low pressures to avoid leakage of gas to adjacent retorts that are being rubblize~. Gases discharged from retorts for in-siku combu~tion processes for shale oil pro-duction are usually, there~ore~ at pressuxes too low for delivery directly into gas turbines or power recovery.
Typical in-situ combustion processes for the recovery of oil from oil shale are descri~ed in U. S. Patent No. 2,780,449 o Fisher et al and U. S. Patent No. 3,0~1,776 of Van Poollen.
--5~
Summary of the Invention This invention resides in a system for the recovery of power from and reduction of pollutants in LHV gas discharged from production wells of in-situ combustion processes for the production of oil. The LHV gas, after separating rom liquid products produced from the well, i~ mixed with a limited quantity of air~ preheate~ to a tempexature exceeding approxi~
mately 400 F., and delivered into a cata]ytic combustion chamber in which combustibles in the LHV gas are burned.
The amount of air mixed with the L~V ga~ is less than the stoichiometric equivalent of the combustibles in the L~V ga~
and thereby limits the amo~nt of combustion and the maximum temperature that may occur in the combustion chamber. In a preferred embodiment, the I.HV gas is burned in a primary and a secondary catalytic combustion chamber with approximately fifty percent of the total air introduced into each combustion chamber. Hot gases discharged frvm khe primary ca$alytic combustion chamber~are mixed with the air for the sacondary combustion and~then cooled to a temperature suitable for introduction into the secondary catalytic combustion chamber~
; The cooled ga~es are delivered into the secondary catalytic combustion chamber for combustion of combustible material remaining in the gas. Preferably, the combustion products discharged from the second combustion chamb~r are expanded in 2S a turbine to generate power ~or compression of air used in the in-situ combustion process.
Brief Description o~ the Drawin~s Figure 1 of the drawings is a diagrammatic flow sheet of a preferred embodiment of this invention as used for the recovery of power rom LHV gas discharged from an in-situ combustion system ~or the reco~ery of oil from an underground oil reservoir.
Figure 2 of the drawing~ i~ a diagrammatic 10w sheet of an embodiment of this invention in which the combusti~n products generate steam that is used to drive a turbine.
Fi~ure 3 is a chart showing tne varia~ion in ~he S heating value of c3ases produced in an in-situ combustion process for the recovery of oil from an oil reservoix over a two and one-half year period.
Description o~ Preferred Embodiment Referring to Figure 1 of the drawing~, a subsurface formation 10 containing crude oil, u~ually of hiyh density and viscosity, is penetrated by a production well 12 and an injection well 14 spaced from the production well. Flu~ds produced from the production well 12 are delivered through a line 16 into a separator 18 in which the produced LHV gas is separated from liquids produced through well 12. The liquids are discharged from the lower end of the separator 18 into a delivery line 20 and the ~HV gas is discharged from the top of separator 18 into a feed line 22. It will usually be desirable to pass the gas from the separator 18 through a suitable gas clean-up, not shown, to remove solid particulates, catalyt poisons, or other undesirable constituente before delivery into line 22. A 10w controller 23 maintains a constant flow rate of the LHV gas to the turbine as hereinafter described.
Typical hydrocarbon concentrations in the LHV gas range fxom about 1 to 8 per cent by volume. The hydrocarbons are principally methane; the concentration of C2-C~ hydrocarbons usually belng less than 2 percent. In the concentrations present in the LHV gas, stable combustion of methane and the other low molecular weiyht hydrocarbons produced in in situ production is obtained only in the presence of a catalyst.
The heating value of the LHV yas produced from in-situ combustion in oil reservoirs may range from S to 80 BTU/scf, and ordinarily will be in the range of 40 to 70 BTU/scf, a range in which the process is particularly useful. On some occasions, usually fox short periods, the heating value may rise to 100 BTU/scE. LEIV gas having a heating value above lS BTU/scf can be burned in a catalytic combustor without an external source of heat. If other sources of heat are available to provide additional preheat, LHV gas having a heating value as low as 5 BTU/scf can be oxidized in catalytic combustion chambers.
For most affective use in driving a gas turbine to compress air used in the in-situ combustion process, for example, the gases dischaxged from the sepaxator 18 should be at a pres-sure of at least 75 psig. I~ the gas is at lower pressure, i part of the energy is used in compressing the LHV gas to a pres-sure high enough to drive a turbine, however, LHV gas at lower pressures may contain substantial energy which can be useful in supplying heat for heater-treaters and other oil field equipment or for developing power by supplying heat to generate steam at :
a pressure high enough to drive a turbine. The pressure in the production wells of an in-situ combustion process usually range from slightly above atmospheric pressuxe to 800 psig. The pressure is dependent, at Jeast in part on the depth of the formation in which the combustion occurs. Pressures higher than 800 psig in the production wells can be used but such high pressures suffer the disadvantage of high costs for compressing the air injected into the underground formation; however, much - of the energy used in compressing the air can be recovered.
The gas in line 2~ is mixed with air from a line 24 and, during startup, passed through a heater 26. A fuel, such ..
3~
as LPG, supplied through line 28 is burned in heater 26 to raise the temperature of the mixkure of LHV gas and air to a tempera-ture at which oxidation will occur on contact with the oxidation catalyst hereinafter described. The heater 26 is used only during S startup, and after oxidation of the LHV gas commences, heat~r 26 is bypassed by flowing the air from line ~ through bypa.ss 30.
The mixture o~ air and LHV gas discharged from heater 26 is delivered through line 32 into a heat exchanger 34. No hea* kransfer to the mixture of air and ~HV gas occurs in heat exchanger 34 until after combustion has begun in khe catalytic combustion chamber as hereinafter descri~ed.
After pa~sing through h~at exchanger 34, the mixture o air and LHV gas is delivered through line 36 into a primary catalytic combustion chamber 38. The temperature of the gas delivered to the combustion chamber 38 should be in the range of approximately 400 to 800 F. whereby oxidation will be i~ltiated on contact of the LHV gas with the catalyst.
Usually, the~inlet temperature will be in the upper part of that:temperature range.
In a preferred catalytic oxidation chamber, platinum is deposited on the surfaces of a commercially available ceramic honeycomb-type catalyst suppoxt arranged in primary combustion chamber 38 in a series of transverse slabs 39 sepa.rated from one another by ~ree spaces 40. The free spaces between the slabs are designed:to allow equalization o~ the temperature of the gases between the slabs and thereby minimize development of hot spots; however, satisfactory operation has been obtained wikh adjacent slabs touching. The honeycomh-type of catalyst support .
~is advantageous in allowing high throughputs with a low pressure drop through the catalyst. ~n a typical combustion chamber there may be 10 to 20 or even more slabs 39. ~ catalyst that can be used is described in U. S. Patent No~ 3,870,455 of Hindin~
~h~3~J~
The arrangement a~d catalyst shown are preferred for use in this invention; however, this invention is not restricted to the use of a particular catalyst. Other oxida~ion catalysts supported on other supports can be used. For example, catalysts containing cobalt or lanthanum as the cata]ytically active ingredients s~pported on honeycomb or on sponge type supports can be used. Other catalysts that can be used are described in U. S. Patent No. 3,565,830 of Keith et al. Oxidation catalysts used at temperatures higher than ~000 Fo are described in U. S.
Patent No. 3,928,961 of Pfefferle.
The gases are discharged from combustion chamber 38 at a maxim~m temperature preferably of approximately 1600 F.
through line 41 and mixed with additional air supplied through line 42. The maximum temperature is limited by the highest temperature that the catalyst can withstand over long operating periods without deterioration. Preferred oxidation catalysts for this invention in which combustion products are passed through a gas turbine that consist of platinum on a ceramic support can withstand higher temperatures than 1600 F. for short periods ~0 but their life lS shortened by continued use at the higher tem-peratures. As previously indicated, the amount of air supplied through line 42 preferably is approximately one-half of the total amount o~ air supplied ~or oxiclation of the LHV gas.
Addltion of air through line 42 will ordinarily result in a temperature drop of approximately 200 F. in the gases in line 41. The gases are deli~ered throuyh line 41 into heat exchanger 34 and passed therein in indirect heat exchange with the initial mixture of air and LHV gas delivered to the hea~
exchanger through line 32. ~he mixture o air and partially oxidized LHV gas i~ discharged from heat exchanger 34 at a temperature preferably o~ 600 F. to 300 Fo and delivered via line 44 into a secondary catalytic combustion chamber 46.
Secondary catalytic combustion chamber 46 may be identical to -10~
3~ g primary c~talytic combustion chamber 38. Oxidation of combus-tibles in the partially oxidized LHV gas delivered ~rom heat exchanger 34 occurs in secondary combustion chamber 46. By limiting -the total air flow into the primary and secondary catalytic combustion chambers to an amount slightly ~e.g. 5 .
percent) less than the s$oichiometric equivalent of an LHV
gas heating value that would cause the maximum permissible temperature rise,excessive temperatures in the catalytic combustion chambers are. avoi-led even though the composition of the L~IV may vary widely.
Heat released in the secondary combustion chamber may increase the temperature o~ the gases to, ~or example, approximately 1600 F. at the outlet line 48 rom the secondary combustion chamber. Usually, it will be desirable to cool the gases in line 48 to reduce the temperature of the gases to a temperature that provides a margin of safety below the maximum operating temperature o~ a gas turbine 52 into which the gas is delivered. Some turbines are capable of withstandiny tem-peratures up to about ~000 ~.; however, it is preferred to ~ reduce the temperature of the gas~s to 1400 F. to 1600 F.
by dilution with air before delivery into the turbine. The desired cooling may be accomplished by introducing cooling air into line ~8 from line 50. The temperature at which the com-bustion products leave the secondary combustion chamber is far below the temperature required to ignite those partially burned gases o low heating value in the absence of a catalyst;
consequently, there is no danger of further combustion with resultant development of excessive temperatures occurxing on mixing air from line 50 with the hot gases in line 48 even though the hot gases usually include unburned combustibles.
The air introduced through line 50 is, therefore, cooling air rather than combustion air.
Referring to Figure 3 of the drawings, it will be noted that the heating value of the LHV gas produced during a typical in-situ combustion process varies substantially.
Most of the time during the 2-l/2 year operation shown in Figure 3, the LHV gas produced by the in-situ process had a heating value above about 55 BTUJsc~; however, the heating value was frequently in the range of 70 BTV/scf and on one occasion increased to over lO0 B~U/scf. At other times, the heating value dropped below 50 BTU/scf. The wide swings in LHV
gas composition introduce problems of controlli.ng the temperature to prevent excessive temperatures that would damage the catalyst or the gas turbine and still operate ~he gas turbine under opti-mum conditions. To control the maximum temperature that may be attained and also maintain a uniform temperature~ the catalyt.ic comhustion chambers are operated with less alr than the stoich-iome$ric equivalent of the combustibles in the LHV gas. In this manner r the amount of air supplied to the catalytic combustion chambers establishes the maximum temperature rise in the catalytic combustion cha~bers and r consequently, the maximum ; 20 ~emperature that is attained. If the maximum permissible tem-perature in the catalytic combustion chamber i.s 1600 F., the amount of air mixed with the cold LHV gas entering the heat exchanger 34 will be such that when the oxygen in that air is completely consumed in burning combustibles in the LHV gas, the temperature in the combustion chamber will not exceed 160~ F.
If oxidation catalysts having an acceptabl~ life when used at higher temperatures to burn LHV gas should be used, and ~he ~eating value of the LHV gas should be high enough to raise the temperature of the:combustion products abo~e the maximum operating temperature of the catalyst, the amount of air delivered tc the combustion chambers could be increased and thereby raise d3 the maximum temperakure that might be reached in the com-bustion chambers. The amount of air would be less than the stoichiometric equivalent of the LHV ~as to maintain the desired temperature control.
Assuming that the mixture of LHV gas and air in line 32 to the preheater 34 is at a temperature of 175 F. and the maximum permissible catalyst temperature is 1600 F., the maximum total amount of air mixed with the I.HV gas entering the primary combustion chamber 38 and with the hot combustion products discharged from that combustion chamber can contain oxygen stoichiometrically equivalent to the combustibles in LHV
gas having a heating value of approximately 50 BTU/scf. If the heating value of the LHV gas should be as shown in Figure 3, that amount of air would be less than stoichiometrically equiva lent dur1ng approximately 90 percent of the time. Preferably, approximately fifty per~cent of the total amount of combustion air is introduced into the system by mixing with the LHV gas before delivery into the primary:combustion chamber and the remainder is mixed with the products of combustion from the primary combustion chamber before delivery to the secondary combustion chamber.
While controlling the rate of air a~mixture with the LHV gas introduced into the primary and into the secondary catalytic combustion chambers at a rate that is less than the 2S stoichiometric equivalent of the normal LHV gas composition limits the maximum temperature rise in the combustion chambers and is effective in protecti.ng the catalyst from temperature rises that might:~otherwise result ~rom increases in the heating value of the LHV~gas, precise con~rol to maintai.n a constant mass flow rat and temperature of the gas delivered to the turbine is desirable for most efi.cient operation of the turbine.
3r~
Flow controllex ~3 in line 22 from separator 18 maintains the desired rate of ~low of LHV gas into the system. Since the rate of flow of air to the combustion chambers is constant, a drop in the temperature of gases discharg~d Erom the secondary catalytic combustion chamber indicates that the combustible materials in the LHV gas are less than the stoichiometric equivalent o~ the combustion air delivered into the systemO
The desired temperature can be obtained with li-ttle change in the mass 10w rate by introducing an auxiliary uel into the system. A temperature sensor 53 in line 48 adjacent the outlet end of secondary combustion chamber 46 can bs connected to actuate a flow control valve 55 in an auxiliary fuel line 57.
If the temperature in line 48 should drop, the temperature sensor 53 would actuate flow control valve 55 to enrich the mixture delivered to the secondary combustion chamber 460 To provide stable operation, the controls will inject sufficient auxiliary fuel to increase the heating value of the LHV gas delivered to the co~bustion chambers an amount such that the air is slightly less than the stoichiomet.ric equivalent of the total combustibles in the LHV gas and auxi.liary fuel. Alterna-tively, a hydrocarbon analyzer can be installed to withdraw a sample from line 22 and determine the hydrocarbon content, and, hence, the heating value, of the LHV gas. A signal generated by the hydrocarbon analyzer can be used to contxol valve 55.
Clearly, the auxiliary fuel can be introduced into the system at any point upstream of the secondary catalyti.c combustion chamber, such a~ into line 22 Usually, the auxiliary fuel will be natural gas or LPG. The heating values of natural gas and LPG are high and the concentration of inerts is low;
consequently, a desired increase in the temperature of the combustion products can be o~kaine~ with a negligible change in the mas.s 10w rate to the turbine.
~33~
The hot gases are expanded in the turbine to sub-stantially atmospheric pressure~ and the gases from the turbine are diseharged to the atmosphere. I necessary, gases discharged from the turbine can be passed through a suitable scrubber to remove contaminants before being discharged into the atmosph~re.
The gases discharged from turbine 52 will be hot and could be passed through a heat exchanger to supply heat for process or other use, i desired.
Energy produced by turbine 52 is used to compress air used in the combustion of the LMV gas and in the in-situ combustion process. In ths embodiment illustrated, the turbine is shown as directly connected to drive a low pressure compressor 54 which compresses air to a pressure exceeding the operating pressure of the catalytic combustion chamber 38 sufficiently ~or easy control of air flow into the system. That air is delivered in~o a header 56 to which line.s 24, 42 and 50 are connected or delivery of aix as needed for the combustion of th~ LH~ gas and subsequent cooling of the combustion products from the secondary con~ustion chamber~
Turbine 5~ also drives a high-pressure compressor 58 that compresses air for use in the in-situ combustion process.
Air compressed in compressor 54 in excess of the air required for combustion o~ the LHV gas and cooling is bled from compressor 54 and delivered to compressor 58 through a line 59.
~5 Line 59 is provided with flow control means indicated by valve 61 to control the flow of bleed air to compressor 58. In a preferred arrangement, ~he turbine-type compressor 58 compresses air to an intermediate pressure of ~he order of 250-300 psig, and that air is d~livered through line 60 to a cen rifugal or reciprocating compressor 62 for ~urther compression to a pressure typically in the range of 2,000 psig to 3~000 psig.
~15-The pressure to which the air is compressed by compressor 62 will depend upon the parti.cular in situ combustion process and will vary with several parameters of ~he in-si~u combus~ion process such as the depth oE the subsurface formation into which the air is to be injected, the viscosity of the oil, ~he permeability of the subsur~ace formation, the rate of in~ection of air into the formation, and the desired pres~ure at the production well. Air from compressor 62 is delivered through line 64 into injection well 14. In an alternative arrangement, air compressor 58 is constructed to allow withdrawal of air from an intermediate stage of the compressor at a low pressure for use in combustion of the LHV gas. With that arrangement, low pressure compressor 54 will not be necessary.
Whil~ supplying air at a rate that is less than the stoichiometric equivalent of the combustibles in the LHV gas causes some loss of the potential enexgy available in the com-bustibles in the LHV gas, the importance of such loss is minimized by the gain in the compressed air that is made available for use in the in-situ combustlon process. If air were delivered to the ca~alytic combustion chambers at a rate equivalent to the stoich-iometric equi~alent of an LHV gas having a heating value of 70 BTU/scf, for example, and the maximum permissibla temperature in the gas turblne remained at 1~00 F., it would be necessary to cool the gas discharged from the secondary combustion chamber before delivery to the turbine. I~ air from compressor 54 should be used to dilute the combustion products and thereby cool them to the desired *emperature for delivery *o the gas turbine, such air would reduce the amount of air delivered from compressor 54 to compressor 58 for use in the in-situ combustion process.
It is an important advantage of this invention that the desired safeguards against temperature and flow rate ~3~ 3 variations and excessive temperatures can be obtained while complying with the usual antipollu~ion regulations.
Hydrogen sulfide and the higher molecular weight hydrocarbons are preferentially, as compared to methane, oxidized in the catalytic combust:ion chambers. The unoxiaized combustible material discharged from the secondary combustion chamber because of the deficiency in air i.s almost entirely methane, a gas that usually is nok subject to antipollution regulations.
As an example of the preferential oxidation of the hydrocarbons having a higher molecular weight than methane, a hydrocarbon gas-air mixture was passed in contact with a platinum catalyst deposited on a ceramic support at an inlet temperature of 840 F. and a maximum temperature of 1430 F.
The hydro~arbons were mixed with about 50 percent oF the stoichiometric air, thereby giving a mixture with a severe - deflciency in air.~ The composition of the hydrocarbons, the outlet composition, and the percent conversion of each : of the hydrocarbons are set forth below:
TABLE I
H~drocarbon Conversion Inlet Composition Outlet Compositlon % Converslon Methane 1.09% 0.97% 11.00 Ethane 0.22% 0.15% 31.8 Propane 0-34% 0.19% 44.1 i Butane 0.06~ 0.03% 50~0 n Butane 0.22% 0.10~ 54,5 i Pentane 0.06% 0% 100.0 n Pentane 0.08~ 0% 100.0 Similar tests were made with larger equivalence ratios (ratio of amount of air supplied to the amount of air stoichiometrically equivalent to the comhustibles in the gas). The results are presented in Tables II and II:
TABLE II
ydrocarbon Conversion Inlet Composition Outlet Composition % Conversion Methane 3.54% 0~47% 87 ~thane 0.39% 0% 100 Propane 0.32% 0% 100 i-Butane 0.11~ 0~ 100 n-Butane Q.24~ 0% 100 i-Pentane 0O14% 0% 100 n-Pentane 0.16% 0% 100 Equivalence Ratio = 0.96 TABLE III
Hydrocarbon Conversion Inlet Composition Outlet Composition ~ Conversion Methane ~ 3.62% 2.23% 38~
Ethane 0.40% ; ~ 0.16% 60%
Propane 0.28% 0.06% 79~
i-Butane 0.09% 0~ 100%
n-Butane 0.18% 0~ 100%
i-Pentane 0.08% 0~ 100~
n-Pentane 0.07% o% 100%
~ Equlvalence Ratio = 0.60 It is apparent from the results shown in Ta~les I, II
:
and III that even with a deficiency of air more severe than would normally be caused by a surge in combusti~les in the LHV gas, preferential removal of the heaviest hydrocarbons from the LHV
gas was accomplished in the catalytic combustion chamber.
Combustion of methane lagged far behind the combustion of other hydrocarbons. ~s the equivalence ratio increased to the 3~
range normall~ used, the hydrocarbons other than methane are virtually completely consumed. This invention is/ therefore, particularly advantageous when the fuel available varies in heating value and con~ists of a mixture o~ combustibles that includes methane as one of the combus~ible constituents.
An important ad~antage of the process of this inven-tion in utilizing LHV gas from in-situ combustion processes from which the LHV gas is produced at pressures, preferably exceeding 75 psig, high enough to drive a gas turbine, is that the utilization of energy in the LHV gas is more efficient than in gas of higher heating value. If fuels of high heating value such as natural gas are used in gas turbines, the air to fuel ratio is high, such as 40 to 1 or higher, to dilute the combustion products and thereby avoid temperatures higher than the turbine blades can withstand. A substantial portion of the energy produced by the turbine is used to compress the diluent air for mixture with the hot gases before delivery into the turbine. In contrast, the LHV gas contains inert gases that will serve as a diluent to help avoid excessive temperatures in the turbine, and it is necessary to compress only very little dilution air above that required for burning the combustibles in the LHV gas.
The temperature rise that occurs on burning a 50 BTU/scf ~HV gas with s-tolchiometric air is approximately 1425 F. Because it is necessary that the temperature of the LHV~air mixture delivered to the ca~alyst be at least 40G F., and preferably in the range of 600 F. to 800 F., burning a 50 BTU gas in a single stage would cause catalyst -temperatures exceeding 1600 F~ Thereforel a single-stage, self-supporting LHV catalytic combustion process in which the combustibles in a 50 BTU/scf LHV gas are consumed is possible only if the 33~;v ~
catalyst can withstand prolonged exposure to temperatures of 1825 F. and higher, and preferably higher than 2025 F. ~he term self-supporting is used to designate a process in which the hot combustio~ products from the catalytic combustion chamber heat the LHV gas-air mixture to 400 F. or higher.
Single-stage catalytic combustion with a catalyst limited to a maximum temperature of 1600 F. is limited to burning combustibles to liberats about 33 BTU/scf of the L~V gas.
Such an operation would suffer a disadvantage, as contrasted to ~he pre~erred two-stage operation, of lower turbine efficiency resulting from the lower temperature of the gases delivered to the turbine if the hot gases from the combustion chamber are used to heat the L~V gas-air mixture to 400 F. or higher.
In a single stage operation uti~izing a catalyst limited tv a maximum temperature of 1600 F., the amount o air mi~ed with the LHV gas would be limited to the stoichiometric equivalent of 33 BTU/scf L~ gas to protect the catalyst from excessive temperatures resulting from periodic increases in he heating value of the LHV gas composition such a~ occur in in-situ combustion processes. The concept of protection against varia tions in fuel composition by limiting the oxygen supplied to the combustion chamber can, therefore, be used in a single-stage operation. A two-stage catalytic combustion process is preferred for L~IV gas having a heating value of 40-80 BTU/scf, however to recover a larger part of the energy available in the LHV gas and to operate the tuxbine more efficiently.
If two-stage catalytic combustion of the type described with respect to Figure 1 is used to burn gases consistently having heating values higher than about 80 BTU/scf, it will be necessary to discard a substantial amount of the heating value of the gas in the form of unburned hydrocarbons leaving the secondary combustion chamber.
~ ~ ~ 3 3~D
If the normal heating value of the gas from the in-situ combustion process should be consist~ntly above approximately 70 BTU/scf, for example ranging upwardly from 70 to 80 BTU/scf, and the maximum permissible catalyst and turbine temperatures are appxoximately 1600 F., it is desirable to use a third catalytic combustion chamber to reduce the loss of energy in the unburned hydrocarbons. It will then be necessary to cool the gases discharged from the secondary catalytic combustion chamber before delivering the gases to the third combustion chamber. Such cooling can be obtained by passing gases discharged from the second combustion chamber, preferably after mixing with air for the third combustion stage, through a boiler in heat exchange with water to generate steam.
Steam generated in the boiler can be used as process steam or to drive a turbine. A preferred method for recovering additional energy from LHV gas having a heating value normally exeeding about 70 BTU is to poSitiQn a tertiary catalytic combustion ~hamber 66 downstream of the gas turbine 52. The gases dis-~ charged from the turbine are delivered to the third stage combustion chamber at a temperature in the range of 400 to 800 F.
Air is dellvered to the tertiary ombustion chamber 66 through a line 67 from the compressor 54 and the mixture passed in contact with an oxidation catalyst in the combustion chamber to oxidize hydrocarbons xemaining in the gas discharged from the turbine.
Valves in lines 67 and 59 allow control of the amount of air delivered to each of tertiary catalytic combustion chamber 66 and compressor 58. The hot gases from tertiary combustion chamber 66 are delivered to a boiler 68 for the generation of steam. In the event three combustion chambers are used, the delivery of air to the fixst two combustion stages is controlled to operate the 3~
turbine at optimum conditions. The third combustion stage could operate at stoichiometric conditions or with an excess of air if the heating value of the gas i8 such that excessiv~
catalyst temperaturess are not developed ln the third sta~e.
The gas turbine 52 operates with le~s than sto:ichiom~tric air at all times.
The embodiment o~ the invention illustrated in Figure 2 is or use in those situations where the LHV gas discharged from the in-situ process is not at a high enough pressure for efficient use in driving a gas turbine. The low pressure LHV gas may, for example, be produced in an in-situ com~ustion process for recovery of oil fxom a shallow under-ground reservoir at a low pressure or in the in situ combustion of oil shale. The LHV gas is delivered through a pipe line 70 to a suitable gas cleanup unit 7~ for xemoval of solid particles or other components that may interfere with the subsequent catalytic oxidation of the gas. The gas cleanllp unit 72 may be in the form of a suitable separator or screening or washing apparatus. LHV ga~ from the gas cleanup unit 72 is delivered to a preheater 74 similar to preheater 34 in the embodiment illus-trated in Figure 1, for preheating to a temperature of 400 F. to 800 F. Preheated LHV gas discharged from the preheater 74 is mixed with combustion air supplied by a suitable blower or com-pressor 76 and delivered into a primary catalytic combustion chamber at a temperature o 400 F. to 800 F. Catalytic com-bustion chamber 78 is preferably similar to catalytic COmbU~tiGII
chamber 38 illustrated in Figure 1.
The hot combustion products from the primary catalytic combustion chamber 78 are deli~ered into preheater 74 for indirect heat transfer with the LHV gas. The combustion products from preheater 74 are mixed with additional combustion air from blower 80, which results in a temperature in the range of 400 F.
to 800 F., and delivered into a secondary catalytic combustion chamber 82. As in the embodiment illustrated in Figure l, air for oxidation in the secondary chamber also can be mixed with S the partially burned gases rom the primary combustion chamber before those gases are delivered to preheater 74.
Instead of delivering the combustion products from secondary catalytic combustion chamber 82 to a gas turbine, as in ~he embodiment illustrated in Figure 1, the combustion I0 products are delivered to a boilex 84 fo~ generating steam.
Because the combustion products from the secondary catalytic combustion chamber 82 are not delivered to a turbine, they are not cooled hefore delivery to the boiler 84. The high tem-perature of the combu~tion products discharged rom the secondary catalytic co~bustion chamber allows generation of steam at a high pressure suitable for driving a steam turbine.
Steam from the boilsr 84 is delivered through line 86 to a steam tyrbine 88 which lS preferably connected to a generator 90 to generate electricity~to drive air compressors for the in-situ combustion process. The steam turbine may, alternati~ely, be directly connected to compressors. Steam discharged from turbine 88 Ls delivered to a condenser 92 and the condensed steam passed through suitable water treatment 94 which includes a pump for returning the condensed water to boiler 84. ~s an alternative to the generation of steam as illustrated in Figure 2, low pressure off gases rom in-situ combustion of oil shale, for example, could be used in the system o E'igure l modi-fied to utiliæe a portion of the energy generated by turbine 52 to compress the LHV gas to a pressure high enough to drive the turbine.
3~i~3 The temperatures to which the LHV gas is preheated and combustion products from the primary catalytic combustion chamber are cooled in preheater 74 are designed to avoid excessively high temperatures which could damage the catalyst in combu~tion chambers 78 and 82. As in the embodiment illustrated in Figure 1, control of the maximum temperatures is obtained by control of the amount of air mixed with the LHV gas before delivery into the catalytic combustion chambers to prevent overheating of the catalytic combustion chambers even though there should be a substantial i~crease in the concentration of combustibles in the LHV gas delivered through pipe 70.
The amount of air supplied by blower 76 is preferably approxi-mately one-half the stoichiometric equivalent o the quantity of combustibles that will give tha maximum permissible tem-perature use; and an equal amount of air is supplied by blower 80for the oxidation in the secondary combustion chamber 82.
The method and apparatus herein described are highly advan~ageous or the recovery of power from LHV gas from in-situ combustion process~s for the recovery of oi~ because of the variations from time to time in the heating value of the gas.
While the method is most useful for the recovery of power from the gas produced at elevaked pressures in in-situ combustion processes for the recovery of oil from oil or tar sand reservoirs, it is also useful;in reco~ery of power from low-pressure off-gases from the in-situ combustion of oil shale in those instances when such off-gases cannot be burned in a flame co~ustor because of its low heating value. The limitation of ~he amount of air mixed with the LHV gas tG the stoi~hiometric equivalent of the normal LHV gas provides protection for both the catalyst and the turbine against wide variations that occur in the composition o the LHV
gas. This invention is particularly valuable when methane is one of the combustible constituents of the LHV gas.
-~4-
Claims (24)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for the in-situ recovery of oil from a subsurface carbonaceous deposit comprising igniting the carbonaceous deposit to form a combustion front, delivering air into the carbonaceous deposit under pressure and displacing it through the combustion front to burn a portion of the carbonaceous deposit and drive oil and LHV gas ahead of the combustion front, delivering produced oil and LHV as to the surface, mixing air with the LHV gas and passing the mixture in contact with an oxidation catalyst to oxidize combustibles in the LHV gas to produce hot combustion products, the amount of air mixed with the LHV gas being less than the stoichiometric equivalent of the combustibles in the LHV gas and limiting the maximum temperature reached on oxidation to the maximum operating temperature of the catalyst, generating power with the hot combustion products from the oxidation, and driving a compressor with power generated to compress the air delivered into the carbonaceous deposit.
2. A method as set forth in claim 1 in which the generation of power with the hot combustion products is accomplished by expansion in a gas turbine and the gas turbine driving the compressor.
3. A method as set forth in claim 1 in which the subsurface carbonaceous deposit is a petroleum reservoir and the oil produced is a petroleum oil.
4. A method as set for in claim 1 in which the subsurface carbonaceous deposit is oil shale and the oil produced is shale oil.
5. A method as set forth in claim 2 in which the carbonaceous deposit is a petroleum reservoir, the oil and LHV
gas are separated at the surface, the pressure of the LHV gas is at least 75 psig, the air is mixed with the LHV gas in two substantially equal increments and the oxidation of the combustibles is accomplished in a primary stage and a secondary stage, the first increment of air is mixed with the LHV gas before delivery to the primary oxidation stage to form a primary oxidation mixture, the second increment of air is mixed with the effluent from the first oxidation stage to form a secondary oxidation mixture, the primary oxidation mixture is passed in heat exchange with the secondary oxidation mixture to raise the temperature of the primary oxidation mixture to a temperature at which oxidation occurs on contact with an oxidation catalyst, after said heat exchange the primary oxidation mixture is delivered to the primary oxidation stage and the secondary oxidation mixture is delivered to the secondary oxidation stage, and the effluent from the secondary combustion state is the hot combustion products delivered to the gas turbine.
gas are separated at the surface, the pressure of the LHV gas is at least 75 psig, the air is mixed with the LHV gas in two substantially equal increments and the oxidation of the combustibles is accomplished in a primary stage and a secondary stage, the first increment of air is mixed with the LHV gas before delivery to the primary oxidation stage to form a primary oxidation mixture, the second increment of air is mixed with the effluent from the first oxidation stage to form a secondary oxidation mixture, the primary oxidation mixture is passed in heat exchange with the secondary oxidation mixture to raise the temperature of the primary oxidation mixture to a temperature at which oxidation occurs on contact with an oxidation catalyst, after said heat exchange the primary oxidation mixture is delivered to the primary oxidation stage and the secondary oxidation mixture is delivered to the secondary oxidation stage, and the effluent from the secondary combustion state is the hot combustion products delivered to the gas turbine.
6. A method for the recovery of energy from LHV gas of variable heating value produced in an in-situ combustion process for the production of oil comprising:
(a) mixing with the LHV gas air in an amount less than the stoichiometric equivalent of the combustibles in the LHV gas, the amount of air limiting the temperature reached on oxidation in step (c) to a temperature lower than the maximum operating temperature of the catalyst;
(b) heating the mixture from step (a) to a temperature higher than 400°F. at which combustion is initiated on contact of the mixture with an oxidation catalyst;
(c) oxidizing combustibles in the LHV gas by passing the hot mixture from step (b) in contact with an oxidation catalyst to produce hot combustion gas;
and (d) passing the hot combustion gas from step (c) through a gas turbine to generate power.
(a) mixing with the LHV gas air in an amount less than the stoichiometric equivalent of the combustibles in the LHV gas, the amount of air limiting the temperature reached on oxidation in step (c) to a temperature lower than the maximum operating temperature of the catalyst;
(b) heating the mixture from step (a) to a temperature higher than 400°F. at which combustion is initiated on contact of the mixture with an oxidation catalyst;
(c) oxidizing combustibles in the LHV gas by passing the hot mixture from step (b) in contact with an oxidation catalyst to produce hot combustion gas;
and (d) passing the hot combustion gas from step (c) through a gas turbine to generate power.
7. A method as set forth in claim 6 in which the LHV gas containing methane and hydrocarbons of higher boiling point and the unburned hydrocarbons in the hot combustion gas from step (c) is principally methane.
8. A method as set forth in claim 6 in which the LHV gas with which the air is mixed is at a pressure of at least 75 psig.
9. A method as set forth in claim 7 in which the oxidation of the combustibles in the LHV gas is accomplished in a primary stage and a secondary stage with intercooling between the primary stage and secondary stage and air being mixed with the LHV gas delivered to each stage, and the amount of air mixed with the LHV gas for each stage is less than the stoichiometric equivalent of the combustibles in the LHV gas delivered to the stage.
10. A method as set forth in claim 7 in which the oxidation of the combustibles is accomplished in a primary stage and a secondary stage with intercooling between the two stages and approximately one-half of the total amount of air mixed with the LHV gas is mixed with the gas before delivery into each stage.
11. A method as set forth in claim 6 in which the hot combustion gas from step (c) is cooled by dilution with air to a temperaure below the maximum operating temperature of the gas turbine before being passed through the gas turbine.
12. A method as set forth in claim 9 which includes:
(1) mixing air for the primary stage of oxidation with the LHV gas;
(2) passing the mixture from step (1) in heat exchange with combustion products from the primary stage of oxidation for the intercooling of such combustion products;
(3) passing the mixture of air and LHV gas from step (1) in contact with an oxidation catalyst in the primary stage of combustion oxidation;
(4) mixing air for the secondary stage of oxidation with combustion products discharged from the primary oxidation stage before passing such combustion products in heat exchange with the mixture from step (1); and (5) passing the intercooled combustion products from step (2) in contact with an oxidation catalyst in the secondary stage of oxidation.
(1) mixing air for the primary stage of oxidation with the LHV gas;
(2) passing the mixture from step (1) in heat exchange with combustion products from the primary stage of oxidation for the intercooling of such combustion products;
(3) passing the mixture of air and LHV gas from step (1) in contact with an oxidation catalyst in the primary stage of combustion oxidation;
(4) mixing air for the secondary stage of oxidation with combustion products discharged from the primary oxidation stage before passing such combustion products in heat exchange with the mixture from step (1); and (5) passing the intercooled combustion products from step (2) in contact with an oxidation catalyst in the secondary stage of oxidation.
13. A method as set forth in claim 13 in which the amount of air mixed with LHV gas before delivery into the primary stage of oxidation and secondary stage of oxidation is controlled to limit the maximum temperature in each stage to 2,000°F.
14. A method as set forth in claim 12 in which the amount of air mixed with the LHV gas before delivery into the primary stage and the secondary stage of oxidation is controlled to limit the maximum temperature of oxidation in each stage to 1600°F.
15. A method as set forth in claim 12 in which the total amount of air mixed with the LHV gas is approximately stoichiometrically equivalent to the combustibles in LHV gas having a heating value of 50 BTU/SCF.
16. A method as set forth in claim 13 which includes diluting hot combustion gas discharged from the secondary stage of oxidation with air to produce a mixture having a temperature not exceeding the maximum operating temperature of the gas turbine.
17. A method as set forth in claim 6 in which the LHV gas is from the in-situ combustion of petroleum.
18. A method as set forth in claim 6 in which the LHV gas is from the in-situ combustion of oil shale.
19. A method as set forth in claim 18 in which the LHV gas produced by in-situ combustion of oil shale is compressed to a pressure of at least 75 psig before oxidation.
20. A method as set forth in claim 6 in which the oxidation of the combustibles is accomplished in a primary, secondary and tertiary oxidation stage with intercooling between the primary and secondary stages and between the secondary and tertiary stages, and air in an amount less than the stoichiometric equivalent of the combustibles in the mixture delivered to each stage is mixed with the gas delivered to each stage.
21. A method as set forth in claim 20 in which the intervening cooling between the secondary and tertiary stages is accomplished by passing the hot combustion gas fom the secondary stage through the gas turbine and the gas discharged from the gas turbine is delivered to the tertiary stage.
22. A method as set forth in claim 6 in which the hot combustion gas from step (c) is delivered to a boiler.
23. A method as set forth in claim 1 wherein the power is generated by delivering the hot combustion products from the oxidation to a boiler.
24. A method for the in-situ recovery of oil from a subsurface carbonaceous deposit comprising igniting the carbonaceous deposit to form a combustion front, delivering air into the carbonaceous deposit under pressure and displacing it through the combustion front to burn a portion of the carbonaceous deposit and drive oil and LHV gas ahead of the combustion front, delivering produced oil and LHV gas to the surface, mixing air with the LHV gas and passing the mixture in contact with an oxidation catalyst to oxidize combustibles in the LHV gas to produce hot combustion products, the amount of air mixed with the LHV gas being less than the stoichiometric equivalent of the combustibles in the LHV gas and limiting the maximum temperature reached on oxidation to the maximum temperature reached on oxidation to the maximum operating temperature of the catalyst, delivering the hot combustion products to a boiler to generate steam, and driving a turbine with the steam to generate electric power.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA332,095A CA1113380A (en) | 1979-07-18 | 1979-07-18 | Method for the recovery of power from lhv gas |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA332,095A CA1113380A (en) | 1979-07-18 | 1979-07-18 | Method for the recovery of power from lhv gas |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1113380A true CA1113380A (en) | 1981-12-01 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA332,095A Expired CA1113380A (en) | 1979-07-18 | 1979-07-18 | Method for the recovery of power from lhv gas |
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| Country | Link |
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| CA (1) | CA1113380A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8210259B2 (en) | 2008-04-29 | 2012-07-03 | American Air Liquide, Inc. | Zero emission liquid fuel production by oxygen injection |
-
1979
- 1979-07-18 CA CA332,095A patent/CA1113380A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8210259B2 (en) | 2008-04-29 | 2012-07-03 | American Air Liquide, Inc. | Zero emission liquid fuel production by oxygen injection |
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