CA1188516A - Fuel admixture for a catalytic combustor - Google Patents

Abstract

FUEL ADMIXTURE FOR A CATALYTIC COMBUSTOR

Abstract of the Disclosure Disclosed is a catalytic combustor and systems for the boilerless stoichiometric production of a working fluid such as steam from a fuel-mixture comprised of a carbonaceous fuel and a diluent such as water mixed in a thermally self-extinguishing mass ratio. Production of the steam is by a controlled substantially stoichiometric process utilizing a combustor to provide steam over a wide range of heat release rates, temperatures and pressures for steam flooding an oil bearing formation. Even though formation characteristics change during a steam flooding operation, output steam of the combustor may be kept at a constant heat release rate by dividing the total amount of water passing through combustor between a first portion which is included in the fuel-mixture and a second portion which is injected into the heated products of combustion.
In this way, the space velocity of the fluid stream passing through the combustor catalyst may be kept within operational limits of the catalyst while maintaining stoichiometric combustion. When necessary, preheating of at least one of the components of the mixture burned in the catalyst is provided by a portion of the heat of combustion.

Description

FUEL ADMIXTURE FOR A CATALYTIC COMBUSTOR
Technical Field The present invention relates to a system, apparatus, fuel and method utilized in producing a heated working fluid such as steam.

One prior art patent disclosing a catalytic combustor such as may be used in the production of steam or enhanced oil recovery is Uni.ted States patent 4,237,973.
~nokher combustor which may be used to produce steam downhole includes United States patent 3,456,721. One method of start-up for a downhole combustor ls disclosed in United States patent 4,053,015 relating to the use of a start fuel plug. Some characteristics of fuels used in combustor~ are mentioned in United States pa-tent 3,420,300 and the injection of water to cool products of combustion are disclosed in United States Patent 3,980,137. Another United States patent which may be of interest is 3,223,166.
De~initions - Unless indicated otherwise, the following definitions apply to their respective terms wherever used herein:
adiabatic fl.ame temperature - the highest possible combustion temperature obtained under the conditions that the burning occurs in an adiabatic vessel, that it is complete, and that dissociation does not occur. .-~
admixture - the formulated product of mixing two ~8~
or more discrete substances.
air - any gas mixture which includes ox~gen~
combustion - the burning of gas, liquid, or solid in which the fuel is oxidizing, evolviny heat and often light.
combustion temperature ~ the temperature at which burning occurs under a yiven set of conditions, and which may not be necessarily stoichiometric or adiabatic.
instantaneous ignition temperature - that temperature at which, under standard pressure and with stoichiometric quantities of air, combustion of a fuel will occur substantially instantaneously.
spontaneous ignition temperature - the lowest possible temperature at which combustion of a fuel will occur given sufficient time in an adiabatic vessel at standard pressure and with oxygen present.
theoretical adiabatic flame temperature - the adi.ahatic flame temperature o.f a mixture containing fuel when combusted with a stoichiometric ~uantity of oxygen a~nospheric air when the mixture and atmospheric air are . supplied at standard temperature and pressureO
Di _ osure of Invention According to an aspect of the invention there is provided a fluid admixture for burning in a catal.ytic combustor, the admixture comprising a non-combustible diluent and a carbon-

2-cb/ ~ ~

aceous fuel mixed in a thermally self--extinyuishing mass ratio.
The present invention contemplates a new and improved boilerless steam ~enerating process and a system including a combustor for carrying out the process whereby carbonaceous fuel, water and substantially stoichiometric quantities of air form a burn-mixture which may he combusted catalytically to produce steam by utilizing the heat of combustion to heat the water directly. Generallyl invention herein lies not only in the aforementioned process and system but also in the proportional combination of water and carbonaceous fuel together to form a ~uel mixture which is fed into the combustor for comhustion~ Specifically, -2a-", . ..
cb/ ~

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herein, the Euel mixture is mixed in a thermally self~extinguishing mass ratio~ in that, the ratio of water to fuel is such that the theoretical adiabatic flame temperature for the mixture is below that temperature necessary to support a stable flame in a conventional thermal combustor.
Water is of course well known as a useful working fluid due at least in part to its high heat capacity and the fact that it passes through a phase change from a liquid to a gas at relatively normal temperatures. The present invention in its broadest sense, however, should not be considered as being limited to the production of steam as a working fluid. Virtually any non-combustable diluent having a high heat capacity may be mi~ed with the fuel to produce a suitable working fluid. For example, carbon dioxide may be used as a diluent under some circumstances instead of water while still practicing the present invention.
More particularly, the present invention resides in the use of a catalyst as the primary combustion means in a combustor for low temperature, stoichiometric combustion of a carbonaceous fuel to direct].y heat a quantity of water proportionally divided in f;.rst and second amounts which are adde.d select.i.vely (1) to the fuel prior to catalytic combustion to form a controlled fuel-mixture to control combu9~ion temperature in the catalyst and ~he space veloci.-ty of the fluids passing over the catalyst for combust.ion purposes, and (2) to the highly heated fluid exiting the catalyst to cool such fluid prior to exiting the combustor and thereby control the temperature of the heated working fluid produced by the combustor.
In addition to the foregoing, invention also resides in the novel manner of controlling th0 combustor for the burn-mixture to combust stably at temperatures considerably below the normal combustion temperature for the fuel even though the burn~mixture inc].udes substantially stoichiometric quantities of carbonaceous fuel and air.
Several advantages result from ~uch low temperature, 53~

stoichiometric combustion particularly in that, the products of combustion are not highly chemically active, the formati.on of oxi.de~ of nitrogen is avo.ided, v.irtually all the oxygen in the air is u~ed and soot formation is kept remarkably low.
S-till further invention resides in the novel manner in which the combustor is started and shut down, particularly during start~up, in the control and mixing of fuel to assure that a light-off tempera-ture is attained for the catalyst in the combustor before introducing the steam-generating burn-mixture, and during shu~ down to keep the catalyst from becoming wetted.
: Another novel aspect of the present invention lies in the construction of the combustor so as to catalytically combust the thermally self-extinguishing fuel-mixture and, perhaps more generally, in the discovery that a fuel-mixture comprisiny diluent to fuel mass ratios generally in the range of 1.6:1 to 11:1 may be combusted with ~ubstantially ~toichiometric quantities of oxidant to produce a useful working fluid. Advantageously, the exemplary combustor pro~ides for simple, efficient clean combustion of heavy hydrocarbon fuels.
Another important aim of the present invention is to provide a combustor and operating system therefore and a method of operating the same to enable the production of steam at different pressures, temperatures and rates of flow, which are somewhat independent of each other within l.imits, so that a single combustor can be used for example in enhanced oil recovery to treat oil bearing formations having widely different flow characteristics, the combustor being usable on each such formation to maximize the production of oil from the formation wh.ile minimizing the consumption of energy during such production~
The present invention also contemplates a unique system for preheating either the air or the fuel-mixture prior to entry into the combustor with heat generated by the combustion of fuel-mixture in the combustor.

5~6 .5.
Novel controls also are provided for regulating the temperature of the steam produced by the combustor to be within a specified low range of ternperatures within which the catalyst is capable of functioning to produce steam, S that is, for example between the light~off temperature of the catalyst and the temperature for its upper limit of stability. Additionally, controls and mean~ are provided for injec-ting water into the steam produced by combustion over the catalyst to cool the steam and convert further amounts of water into steam.
More particularly, the present invention contemplates a novel manner of controlling the ca~alytic combustor to produce. steam over a wide range of different temperatures, pressures and heat release rates such as may be desired to match the combustor output to the end use contemplated. Thus, for example, a desired change in the heat release rate of the combustor may be achieved by changing the rate of flow of carbonaceous fuel through the combustor and ma]cing corresponding proportional changes in, the flow rate of the oxidant or air necessary for substantially stoichiometric combustion, and the total quantity of water passing through the combustor to produce the steam. Advantageously, extension of the operating range of the combustor may be achieved by making use of the range of operating temperatures of the catalyst and space velocities at which the burn-mixture. may be passed -through the catalyst while still maintaining suhstantially complete combustion of the burn-mixture. This may be accomplished by adjusting the proportion of the water in the fuel-mixture (the combustion water) and making a complimentary change in the proportion of injection water so as to operate the catalyst within an acceptable range of space velocities with the discharge temperature of the steam e~iting the cornbustor being kept at sub~tantially the same level as before the 3S adjustment. In this way, the heat release rate may be changed without a corresponding change in the discharye temperature all the while keeping the space velocity of -the burn-mixture through the catalyst within an acceptable range .6.
for stable operation of the combustor.
The~e and o-ther features and advantages of the presen-t invention will become more apparent from the following description of the best modes o carrying out the invention when considered in conjunc-tion with -the accompanying drawings.
Br.ief Description of Drawings -Fig. 1 is a schematic diagram of one embodiment of a 5 team generating system embodying the novel features of the present invention.
Fig. 2 is a cross-sectional view of the combustor utilized in the exemplary sytem shown in Fig. 1.
Fig. 3 is an alternative embodiment of a steam generating system embodying the novel features of the present invention.
Figs. 4 and 5 comprise a combined cross-sectional view of the combustor utilized in the alternative system shown in Fig. 3.
Figs. 6 and 7 are cross-sectional views taken substantially along lines 6-6, and 7-7 of Fig. 4.
Fig. 8 i~ a schematic diagram oE the controls utilized in the exemplary systems.
Figs. 9, 10 ll~and~lb are flow diagrams of steps 2S performed in the operation of the exemplary steam generating systems.
Figs. 12 and ]3 are graphs useul in understanding the operation and control o the exemplary systems.
Fig. 14 is a representative injectivity curve for pressurized injection of nitrogen gas into a formation bearing heavy oil.
Figs. 15 and 16 are maximum burn rate curves for different fuel-mixtures for a combustor equipped with catalysts of two different sizes; with the curve of Fig. 15 matched with the injectivity c~rve of FigO 14.
Fig. 17 is an enlarged sec-tion of the curve shown in Fig. 15 illustrating the overlapping operative ranges of the combustor for fuel-mixtures having different water.fuel .7.
mas~ ratios.
Best Modes of Carrying Out the Invention As shown in the drawings for purpose~ of illustration, the present invention is embodied in a boilerless steam generator such as may be used in the petroleum industry for enhanced oil recovery. It will be appreciated, however, the present invention is not limited to use in the production of steam for enhanced oil recovery, but may be utilized in virtually any set of circumstances wherein when it may be desirable to heat a fluid by combustion of a fuel such as in making a heated working fluid or in the processing of a fluid for other purposes.
In the production of steam or any other heated working fluid; it is desirable to be both mechanically and thermally efficient to enable the greatest amount of work to be recovered at the least cost. It also is desirable that in the process of producing the working fluid damage to -the environment be avoided.
The present invention contemplates a unique fuel-mixture and a novel combustion system 10 including a new combustor 11, all providing for more efficient pollution-ree production of a heated working fluid at relatively low combustion temperatures. For these purposes, ~5 the ~uel-mixture is catalytically combusted in a novelly controlled manner in the combustor to produce the working 1uid. Speciically, the fuel-mixture contemplated herein is an admixture comprised of a diluent, such as water, and a carbonaceous fuel mixed in a thermally self-extinguishing mass ratio. The amount of water in this mixture is dependent, at least in part, upon the heat content of the fuel portion of the fuel-mixture to regulate ~he temperature of combustion of the fuel-mixture when burnt in a catalytic combustion zone 13 (see FigO 2) in the combustor 11.
Specifically, the combustion temperature is kept within a pre~esignated low temperature range. Control also is provided to assure the delivery of substantially stoichiometric quantities of oxidant to the catalyst for 5~Çi mixing with -the fuel-mixture to form a burn-mixture which passes over a catalyst 12 in the combustion zone 13.
Advantageously, the high ratio of di]uent -to fuel in the fuel-mixture keeps the theoretical adiabatic flame 5 temperature of the mixture low so that the combustion temperature also is low thereby avoiding the formation of thermal nitrous oxides and catalyst stability problems otherwise associated with high temperature combustion.
Additionally, catalytic combustion of the fuel-mixture avoids soot and carbon monoxide problems normally associated with thermal combustion and, by combusting substantially stoichiometrically, lower power is required to deliver oxidant to the combustor. Moreover the working fluid produced in this manner is virtually oxygen free and thus is le~s corrosive than thermal combustion products.
Two exemplary embodiments of the present invention are disclosed herein and both are related to the use of steam for enhanced oil recovery. The first embodiment (Figs. 1 and 2) to be described contemplates location of the combustor 10 on the earth's surface such as at the head of a well to be treated. Although the system of this first embodiment illustrates treatment of only one well the system could be adapted easily to a centralized system connected to treat multiple wells simultaneously. A second embodiment contemplated for downhole use is shown in Figs. 3 and 4 with pa~ts corresponding to those described in the first embodiment identified by the same but primed reference numbers. The fueL-mixture and controls for the two di~ferent embodiments are virtually identical. Accordingly, the description which follows will be limi~ed primarily to only one version for purposes of brevity with differences between the two systems identifed as may be appropriate, it being appreciated that the basic description relating to similar components in the two systems is the same.
As shown in Fig. 1, the first embodiment of the system contemplated by the present invention includes a mixer 14 wherein water from a source lS and fuel oil from a source 16 are mechanically mixed in a calculated mass ratio for delivery to a homogenizer 17. The homogenizer forms the fuel-mixture as an emulsi.on for delivery t.hrough a line 19 to the combustor 11 for cornbustion. Air containing stoichiometric quan-tities of oxygen is delivered ~hrough another line 20 ~o the combus-tor 11 by means of a compres~or 21 driven by a prime mover 23. Within the combustor (see Fig. 2), the emulsified fuel~mixture and air are mixed intimately together in an inlet chamber 24 to form the burn-mixture befQre flowing into the combustion zone 13 o the combustorO In the presence of the catalyst 12, the carbonaceous fuel contained within the burn-mixture is combusted directly heating the water therein to form a heated fluid comprised of super heated steam ancl the products of such combustion. Upon passing from the catalyst ; lS the heated fluid flows into a discharge chamber 25 wherein additional water from the source 15 is injected into the fluid to cool it prior to exiting the combustor. From the discharge chambex, the hea-ted working fluid (s-team) exits the combustor through an outlet 26 connected with tubing 35 leading into the well. Downhole, a packer 34 seals between the tubi.ng and the interior oE the well casing 33 and the tubing extends through the packer to a nozzle 32 particularly designed for directing the steam outwardly into an oil bearing formation through perforations in the casing.
Herein, -the nozzle comprises a series of stacked frusto conical sections 32a held together by angularly spaced ribs 32b~ Preferably, the space hetween the walls of adjacent sections are shaped as diffuser areas to recover at least some of the dynamic pressure in the steam so a~ to help in overcoming the natural formation pressure which resists the flow of steam in~o the formation. In the embodiment illustrated in Fig. 1 in order to recover some of the heat that might otherwise be lost by radiation ~rom the tubing string 35 toward the well casing 33, inlet air to the compressor 21 through -the line 20 is circulated through the annulus 18 surrounding the tubing striny above the packer 34 to preheat the air somewhat before entering -the compressor.

s~
.10 .
At the top of the casing, an outlet line 22 from the compressor extends into the well through the well head with an open lower end 37 of the line located ju~t above the packer 34. Air from the compressor exi-ts the lower end 37 of the line and flows upwardly within the annulus 18 to exit the well through an upper outlet opening 39 at the well head connecting with the inlet line 20 to the combustor. In the downhole version of the present invention, the combustor 11' (see Figs. 3 and 4) the compressor outlet line 20' connects at the well head to the uppex end of tubing string ~5' with the combustor 11' being connected to the lower end of the tubing string just above the packer 34'.
For controlling both the ratio of water to fuel in the fuel-mixture and the ratio of fuel-mixture and air relative to stoichiometric, control sensors ~Fig. 2) including temperature ~ensors TSl~ TS2, and TS3 and an oxygen sensors OS are provided in the combustor 11.
Temperature sensor TSl, TS2 and TS3 are located in the inlet chamber 24, in the discharge chamber 25 ahead of the post injection water, and in the discharge chamber 25 beneath the post injection water, respectively, while the oxygen sensor OS is located in -the discharge chamber. A schematic of this arrangement is shown in Fig~ 8 wherein signals from the c~ntrol sensors are processed in a computer 27 and latter is 2$ UQed to control the amount of air delivered by the compressor 21 to the combustor, pumps 29 and 30 in delivering relative quantities of water and fuel to the hornogenizer 17 and the amount of water delivered by the post injection water pump 31.
As previously mentioned, several significant advantages are attained by combusting in accordance with t~e pre~ent invention. High thermal efficiency is attained, mechanical efficiency of system components is increased and virtually pollution free production of steam is accomplished at low combustion temperatures all with a fuel-mixture which does not combust thermally under normal conditions.
Moreover, use of the fuel-mix-ture results in a boilerless production of steam by directly heating the water in the 5~;
.11 .
mixture with the heat generated by the combustion of the fuel in the mixture. Herein, one fuel-mixture contemplated com~rises a mass ratio of water to fuel of 5.2:1 for deioniæed water and number two fuel oil and, wlth stoichiome~ric quantities of air of about 2430 scfm passirlg over the catalyst 12, catalytic combustion of the fuel will produce an adiabatic flame temperature of approximately 1700F without an application of preheat from some external source. O~her carbonaceous fuels which may be used in producing an acceptable fuel~mi~ture advantageously include those highly viscous oils which otherwise have only limited use as combustion fuels. In one early test, a topped crude oil, specifically Kern River heavy fuel oil, of approximately 13API was formed as an emulsion with water and was combusted catalytically to directly heat ~he water in the emulsion ultimately to produce steam at a temperature of 1690F with a carbon conversion efficiency of 99.~ . In that test, the mass ratio of water produced in the form of steam, including the products of combustion, to fuel combusted was 14:1.
Although perhaps steam may be the most desi.rable working fluid produced by combustion in accordance with the present invention, it will be appreciated that the invent.ive concept herein extends to the direct hea-ti.ng of a diluent as ~5 a result of combustion of a carbonaceous fuel mixed i.ntimately with the diluent. ~he characteristics of the diluent -that are important are, that the di.luent have a high heat capacity, that it be a non-combustible, that it be useful in performing work, and that it give the fuel-mixture a theoretical adiabatic flame temperature which is below the upper temperature stability limi-t of the catalyst. The latter is of course important to keep the catalyst or its support from being sintered, melted or vaporiæed as a result of the heat gen~rated duriny combustion of the fuel portion of the mixture. Having a hiyh heat capacity is im~ortant from the standpoint of thermal efficiency in that relatively more heat is required to raise the temperature of the diluent one degree over other substances of equal mass.

.120 Here.in, any heat capacity generally like that of water or above may be considered as being a "high heat capacity".
Additionally, it is desirable that the diluent be able to utilize the heat of combustion ~o go through a phase change. With most of these characteristics in mind, other chemical moieties that may be acceptable diluents include carbon dioxide.
In selecting the mass ratio of diluent to fuel in the fuel-mixture, both the heat of combustion of the fuel and the upper and lower temperature stability limits of the catalyst 12 are taken into consideration. The lower : stability limit of the catalyst, herein is that low temperature at which the catalyst still efficiently causes the fuel to combust. Accordingly, for each type of catalyst that may be suitable for use in the exemplary combustor 11, some acceptable range of temperatures exis~s for efficient combustion of the fuel wit'hout causing damage to the catalyst. A selected temperature within this range then respresents the theoretical adiabatic 1ame temperature for the fuel-mixture~ Specifically, the ratio of the diluent, or water as is contemplated in the preferred embodiment, to fuel is set by the heat of combustion (that amount of he~t which theoretically is released by combustiny the fuel) and is such that the amount of heat released i5 ' 25 t'hat which i~ necessary to heat up both the diluent and the ; products of combus-tion to the aforementioned selected temperature. This temperature, of course, is se].ected to maximi~e the performance of useful work by ~he working fluid : produced from the combustor 11 given the conditions under which the working fluid must operate. Stated more hriefly, . the ratio of the diluent to the fuel is the same as the ratio of the heat capacity of the diluent plus the heat capacities of the products of combustion relative to the ; heat of combustion o the fuel utilized in the combustor.
The system for providing the fuel-mixture to the combustor 11 is shown schematically in Fig. 1 with a schematic :representation of the controls util.ized in regulating the mass ratio of the fuel-mixture shown in Fig.

':

. .

s~
.13.
8. While the .system shown in Figs. 1 and 8 illustrates the various components thereof as being connected directly to each other, it ~hould be recognized that the functions performed by some of the componen~s may be performed at a site remote from the combustor 11u More particularly, the water sour~e 15 of the exemplary system 10 is connected by a line 40 to a deionizer 41 for removing impurities from the water which may otherwise foul or blind the catalyst 12. From the deionizer, the line 40 connects with a storage tank 43 from which the deionized water may be drawn by pumps 29 and 31 for delivery ultimately to ~he combustor llo The p~mp 29 connects directly with the mixer 14 through the line 40 and a branch line 44 connects the mixer with the fuel pump 30 for the mixer to receive fuel from the fuel source 16. The deionized water and fuel are delivered to the mixer 14 in relative quantities forming an admixture whose proportions are equal to the aforementioned thermally self-extin~uishing mass rat.io. At the mixer, the two liquids are stirred together for delivery through an outlet line 45 to the homogenizer 17 where the two liquias are mixed intimately together as an emulsion to complete the mixing processl From the homogenizer, the admixture emulsion is tran~ferred to an intermediate storage tank 48 through a line 46 and a pump 47 connecting with the latter tank provides the means by which the e~ulsion or fuel-mixture may be delivered in controlled volume through the line 19 connecting with the combuætor 11~
While the preferred embodiment of the present invention contemplates a system 10 in which the fuel-mixture is ormed as an emulsion which is fed without ~ubstantial delay to the combustor 11 for combusting the fuel in the mixture, in instances where greater 3tabillty in the emulsion may be desired, various chemi~al stabilizing AgentS
including one or more nonionic sur~actants and a linking agerlt, if desired, may be used to keep the emulsion from separating. In the aforementioned Kern River hea~ fue].
oil, the ~urfactants "NEODOL*91 2.5" and "NEODOL 23-6~5"

*trade mark 5~
.14.
manufactured by Shell Oil Company were utili~ed with butylcarbitol. In other instances, with suitable nozzles in the inlet chamber 24 of the combustor 11, the water and fuel may be sprayed from the nozzles in a manner sufEicient to provide for adequate mixing of the water, fuel and air for proper operation of the catalyst 12. With this latter type of arrangemen~, the need for the homogenizer 17 may be avoided .
For combustion of the fuel-mixture in the combustor 11, oxyg~n is provided by air delivered by the compressor 21 to the combustor 11 through the line 20.
Specifically, the compressor draws in air from the atmosphere through an inlet 49 and pumps higher pressure air to the combustor through the line 22, the annulus 18 and the line 20 to the combustorO At the combustor the line 20 connects to the inlet chamber 24 through the housing 51 and the fuel-mixture is delivered through line 19. The latter connects with the housing through an intake manifold 42 (see Fiy. 2) which in turn communicates with the inlet chamber 24 through openings S0 in the combustor housing 51. Upstream O e the manifold 42 within the line 19, a pressure check valve 66 is utilized to keep emulsion from draining into the catalyst before opera-tional pressure levels are achieved.
Simi].arly, a check valve 64 is located in the line 20 to ~5 keep air rom flowing into the inlet chamber 24 before ; operational pre~sure levels are achievecl. Within the inlet chamber 24, a fuel mixture spray noz71e 65 is fixed to the inside of housing around each of the openings 50 arld, through these nozzles, the emulsion is sprayed into the inlet chamber 24 for the fuel mixture to be mixed thoroughly with the air to form the burn-mixture. The burn-mixture then flows through a ceramic heat shield 52. Following the heat shield is a nichrome heatiny element 58 for initiating combustion of a start-fuel mixture in the well head system.
In the downhole version, the burn mixture also flows past an ; electrical starter element 95 (see Figs. 40 and 41) before f]owing through the catalyst 12 for combustion of the fuel.
In both the surface generator and the downhole yenerator, .15.
the catalyst 12 is a graded cell monolith comprised of palladium with platinum on alumina supported on material such as cordierite and operates at a temperature below the thermal combustion temperature for number two die~el fuel.
As shown more par-ticularly in Fig. 2, the catalyst 12 in the combustor 11 is generally cylindrical in shape and .is supported within the combustor housing 51 by means of a series of concentric cylindrical members including a thermal insulating fiberous mat sleeve 53 surrounding the catalyst to support the ca~alyst against subs-tantial movement in a radial direction while still allowing for thermal expansion and contraction. Outside of the sleeve is a monolith support tube 54 whose lower end 55 abuts a support ring 56 which is held longitudinally in the housing by means of radial support projections 57 integrally formed with and extending inwardly from the combustor housing. Inwardly extending suppor~ flanges 59 integrally formed with the inside surface of the support tube abut the lower end of the bottom cell 60 of the catalyst to support the latter upwardly in the housing 51. At the upper end of the support tube 54, a bellville snap ring 63 seats within a groove to allow -the monolith to expand and contract while still provid.ing vertical support.
In catalytically combusting the fuel, the temperature o~ the burn-mixture as it enter~ the catalyst 12 must be high enough for at least some of the fuel in the rnixture to have vaporized so the oxidation reaction can take place. This i9 assuming that the temperature of the catalyst is close to its operating temperature so that the vaporized Euel will burn thsreby causing the remaining fuel in the burn-mixture -to vaporize and burn. Thus i-t is desirable to preheat either the fuel-mixture or the air or the catalyst to achieve the temperature levels at which it is desirable for catalytic combustion to take place.
In accordance with one advantageous feature of the present invention, p.reheating is achieved by utilizing some oE the heat generated during combustion. For this purpose, a device is provided in the combustor between the .:L6.
inlet and discharcJe c~ambers 24 and 25 or conducting some of the heat from combustion of the uel to at least one of the components of the burn-mixture so as -to preheat the fluids entering the catalyst 12. Advantageously, this construction provides adequate preheating for vaporization of enough of the fuel to sustain normal catalytic combustion of the burn-mixture without need of heat from some external source. Moreover, this allows for use of heavier fuels in the burn-mixture as the viscosity of such uels lowers and their vapor pressures increase with increasing temperature.
In the present instance, the device for delivering preheat to the burn-mixture prior to its entering the catalyst 12, includes our angularly spaced tubes 67 communicating between the combustor inlet and discharge chambers 2~ and 25 (see Fig.2 ). The tubes are located within the combustor housing 51 between the inside wall of the housing and the outside of the catalyst suppor-t tube 54. Opposite end portions 69 and 70 of each o the tubes 67 are bent to extend generally radially inward with the lower end portions 69 being also 1a.red upwardly so that hot combustion gases from the discharge chamber 25 may first flow downwardly and then radially outward through the tubes. Thereafter, the hot combustion gases, including some steam flow upwardly through the tubes and at the upper end portions 70 thereof 10w radially inward to mix with the uel-mixture and air within the inlet chamber 24. The heat in this discharge fluid thus provides the heat necessary or raising the temperature o the 1uids in the inlet chamber preferably to the catalytic instantaneous ignition temperature of the resulting burn-mixture. The number of, the internal diameter of, and the inlet design of, the flow tubes at least to some e~tent determines the rate at which heat may be transerred from the discharge chamber back to the inlet chamber~
This uni~ue preheat construction relies upon what is believed to be the natural increase in pressure of the products o combustion (steam and hot gases) over the pressure of the 1uid stream passing through the ca-talyst 12 35~6 .17.
in order to drive heat back to the inlet chamber 24. This may be explained more fully by considering the temperature profile (see Fig. 12) of the combustor ll. Because the temperature profile for a constant volume of gas can be translated directly into a dynamic pressure profile, it may be seen that the temperature of the fluid stream passing through the catalyst rises as combustion occurs. As shown in the profile, the temperature, T~s, of the fluid stream rises slightly and then decreases as the emulsion pas~es through the spray nozzles 65 which are located at the point A in the temperature profile. Feedback h~at F enters at the point B on the profile tc keep the temperature Erom falling further due to the sudden drop in pressure as the fuel-mixture is sprayed from the no~zles. The point C on the profile indicates the beginning of catalytic combustion which is cornpleted just prior to the point D. Throughout the catalyst 12 the temperature of the fluid stream flowing therethrough first increases sharply and then le~els off as combustion of the fuel in the fluid stream is completed. At point E, additional water is injected in-to the heated products of combustion and the super heated steam exiting the catalyst to bring down the temperature of this fluid mixture before performing woxk. Although the foregoing arrangement for direct preheating the burn-mixture prior to entering the catalyst is thought to be particularly useful in the exemplary combustor, other methcds of preheating such as by indirect contact of the burn-mixture with the exhaust gases (such as through a heat exchanger) or by electrical preheater~ also may be acceptable methods of preheating.
Additionally, it will be recognized herein that some of the radiant heat absorbed by the heat shield 52 will be absorbed by the burn mixture as it passes through the shield to also help in preheating the burn-mixture.
For the post combustion injection of water into the heated fluid stream produced by the combustor ll, a water supply line 71 (see Figs. l and 2) is connected through an end 73 of the housing 51 and extends into the discharge chamber 25 . r r ozzle end 74 of the line direc ts ' 8~
.18.
water into the flow path of the heated fluid stream e~iting the catalyst 12. To deliver the injection water to the combustor, the pump 31 communica~es with the storage tank 43 of the deionized water and circulates this cooler water through loops 74 and 75 connecting ~rith heat e~changers 76 and 77 in the prime mover and compressor, respecti~ely, to absorb heat that otherwise would be lost from the system by operation of these two devices. This water then is delivered through line 71 ~o the combustor ll for post injection cooling of the super heated steam exiting the catalyst.
In accordance with another important feature of the present invention, the relative mass ~low of diluent or water to fuel is regulated to obtain a fuel-mixture which herein is an admixture whose theoretical adiabatic flame temperature for catalytic combustion is above the the light-off temperature of the catalyst 12 and below the upper stability limit temperature of the catalyst and its support. For these purposes, the exemplary system .include~
sensor means including the temperature ~ensor TS2 for determininy the temperature T~ of the heated fluid stream exiting the catalyst 12 and control means responsive to ~uch sensor. The control means regulate the proportions of diluent and fuel in the burn-mixture so that, if combusted with theoretical quantities of oxidant, the temperature of the resulting fluid stream theoretically i5 the aforesaid specified temperature. Advantageou~ly, with this arrangement the thermal efficiency of the combustor is maximized and losses in mechanical efficiency resulting from otherwise excessive pumping are minimized.
In the present instance, a schematic illustration of the exemplary system controls is shown in Fig. 8 and includes the thermocouples TSl, TS2 and TS3 for detecting the ternperature Tl within the catalyst inle~ chamber 24, the temperature T2 at the outlet end of the catalyst 12 prior to post combusti.on water injection and the temperature T3 of the stearn discharged from the combustor 11. Additionally, the oxygen sensor OS disposed within the discharge chamber .19.
2S serves to detect the presence of oxygen in the heated fluid stream to provide a control signal to aid the computer 27 in controlling combustion relative to stoichiometric.
More specificallyt signals representing ~he temperatures T1, T2, T3 and oxygen content are processed throuyh suitable amplifiers 79 and a controller 80 before entering the computer. The temperature signals are proces~ed relative to a reference temperature provided by a thermistor 81 to obtain absolute temperatures. Thereafter, both the temperature and oxygen content signals are fed to an analog to digital converter 83 for delivexy to the computer 27 to be at least temporarily stored within the computer as data.
This information along with other information stored in t~e computer is then processed to provide ou~put signals which are fed through a digital to analog converter 84 to provide appropriate control signals for controlling flow regulating devices 85, 86, 87, 88 for the air compressor 21, the emulsion water pump 29 and the fuel pump 30,and the injection water pump 31, respectivelyO As the temperatures Tl, T2 and T3 and oxygen content of the heated fluid stream may vary during the course of operation of the combustor ll, the data fed into the computer 27 changes resulting in the changes being made in the output signals of the computer and in turn the control signals controlling the proportions of Elow i.n the components of the fuel and the air forming the burn mixture.
As 4hown in Figs. 2 and 4, the thermocouples TSl, TS2, and TS3 and the oxygen sensor OS are connected by leads through the housing 51 of the combustor ll and to box 89 containing the controller 80. In the well head system shown in Figs. l and 2, the box 89 is mounted adjacent the combustor housing 51. In the downhole system shown in Figs. 34a and 46, the insulated box 89' is hermetically sealed to the tubing string 35' which connects with the top 73' of the combustor housing 51. Heat conducting fin~ 90 mounted within the box 89' are connected with the tubing 35' so that the air flowing through the tubing may be utilized to maintain a standard temperature within the box for proper 85~
.20.
operation of the thermistor 81'.
Part of the information providing a data base for the computer ~7, is illustrated graphically in Fig. 13 which shows general combustor temperature curves at varying air~fuel ratios for three different fuel admixtures~ For example, curve I represents the temperature of the fluid stream produced by combustion of an emulsion having a water to fuel ratio of 502 with different air~fuel ratios and curve II represents the temperature of heated fluid stream producec~ by combination of an emulsion having a mass ratio of water to fuel of 6.2. The water to fuel ratio associated with curve III is even higher. The peak temperature for each curve occurs theoretically when the air to fuel-admixture ra~io is stoichiometric. The vertical line "S" in the graph represents generally the ~toichiometric ratio o air to fuel-admixture. As may be seen from the curves, when there is excessive fuel for ~he amount of air (a rich mixture) the tempera~ure oE combustion is lower than the peak temperature for the particular mass ratio being combusted. Similarly, if there is excessive air, the temperature also drops. Moreover, it is seen that as the water content of the fuel-admixture increases, the peak temperature decreases, the water serving to absorb some of the heat of combustion. While the curves illustrated in E'ig. 13 show different fuel-admixtures, the heating valve of the fuel portion of each of the admi~tures is the same. For fuels having different heating valve~, the temperatures of combustion for equal mass ratios of admixture utilizing such difEerent fuels will vary from one fuel to next.
Accordingly, the data base of the computer is prcvided with comparable information for each fuel to be used.
In addition to the foregoing information, the data base of the computer 27 is provided with specific information including that resulting from performing preliminary processing steps performed to obtain information unique to each end use contemplated for the combustorls heated output fluid. An example of such is shown in outline Eorm in Fig. 9 such as when preparing the combustor for use 8~
.21.
in steam flooding an oil bearing formationO
Generally speaking, the physical characteristics of each oil bearing formation are unique and such characteris~ics as permeability, porosity, strength, pressure and temperature affect the ability of the formation to accept steam and release oil. Accordingly, oil from different oil bearing formations may be produced most efficiently by injection of steam at different flow rates~
pressures and temperatures dependent upon the formation's ability to accept flow and withstand hea~ and pressure without being damaged.
In accordance with one of the more important aspects of the presenk inventionl the exemplary combustor 11 may be used -to produce oil from oil bearing formations which have substantially different physical characteristics by providing a heated working fluid over a wide range of heat release rates, pressures and temperatures so as to best match the needs of a formation for efficent production of oil from that formation. Briefly, this is deri~ed by firs-t ~0 testing the formation to be produced to determine the desired producticn parameters such as pressure, heat release rate and temperature and then matching the combustor output to these parameters by operating the combustor in a particularly novel manner to provide a heated working fluid output matching these conditions. Inititally, this is done by selection of the combustor catalyst size which provides the widest combustor operating envelope within desired production parameters Eor the formation. Then, during combustor operation, the flow of air, fuel and diluent advantageously may be adjusted to precisely achieve the output characteristics desired even if these characteristics may change because of changes in the formation characteristics due -to the induced flow of fluids -through the formation. Thus, for example, the heat release rate of the combustor may be adjusted by changing the rate of flow of the carbonaceous fuel through the catalyst without affecting the temperature of the working fluid by making corresponding changes in the diluent and air flowing through L8~5~
the combustor. Advantageously, this may be ef~ected over a substantially wide range of heat release rates by selectively proportioning the total water flowing through the combustor between that water which is added to the fuel to make the fuel-mixtuxe and that which is injected subsequent to combustion so as to maintain a flow of the burn-mixture over ~he catalyst within a range of space velocities at which efficient combustion of ~he fuel ta~es place.
When using the exemplary system in a steam flooding operation, the amount of air to be pumped into the combustor 11 ~or oxidizing the fuel may be established theoretically by conducting a permeability study of the well which is to receive the steam. Preferably, this is done utilizing nitrogen gas which may be provided from a high pressure source (not shown) to generate empirically a reservoir injectivity curve unique to the formation to be flooded. The use of nitrogen gas is preferred over air so as to avoid forcing oxygen into the formation and ri.sking the possibility of fire in the formation. Available calculational techniques employed by petrolum engineers enable conversion of the flow and pressure data obtained usiny nitrogen into similar data fox the heated fluid stream produced by the combustor. With this latter data, a theoretical injectivity curve (See Fig. 14) for the ~ormation may be generated for selecting the dimensions of the catalyst 12 used in the combustor 11 in order to obtain a maximum heat release rate and steam flow for the combustor.
As shown in Figs. 15 and 16, different sizes of catalyst 12 perform most efficiently at different heat release rates and pressures. Fig. 15 illustrates a representative maximum burn rate curve for combustor A
having one size of catalyst while Fig. 16 illustrates a 3S second representative maximum burn rate curve for combustor B having another size of catalyst. The physical dimensions, largely diameter and length, of the catalysts determine the slopes o~ these maximum burn rate curves for each s~
.23~
stoichiometric burn-mi~ture whi]e the rates of cornbustion are functions of the mass flow of the burn-mixture and the pressure at which the burn-mixture is passed over the catalyst. The area above ~he curves in these two ~igures represents a flame out zone within which the rate of flame propogation for the burn-mixture being combusted is less than the space velocity of the burn-mixture through the catalyst. The family of curves represented by the dashed lines in each graph illustrates fuel mixtures having ]0 different mass ratios of water to carbonaceous fuel with the curve of Fig. 15 illustrating representative mass ratios ranging from 9:1 to 4:1. In actuality, the dash lines of the maximum burn rate curves represent the center of ~he combustion envelope within which the particular fuel-mixture may be combusted at a given pressure over a range of heat release rates and space ~elocities. A representative section of a maximum burn rate curve is shown in Fig. 17 for fuel-mixtures having mass ratios of 5:1 and 6:1 with the shaded cross-hatching representing the areas at w~lich combu~tion of the mixtures may occur. As may be seen from this enlargement, the areas of combustion for these different mass r~tios of water to fuel overlap each other.
To select the proper comhustor for efficient thermal cornbustion under the operating conditions expected, the combustor chosen is the one whose combustor maximum burn curve most closely matches the injectivity curve of the formation. Matching is done to provide the combustor with the widest range of operating envelope for the desired flow and pressure at which the steam is to be injected into the formation. Advantageously then, as forma~ion conditions change during operation the combustor can be adjusted to compensate for the changes and still provide the output desired.
Once the proper size of catalyst 12 has been chosen ancl the catalyst is installed in the cornbustor housing 51, then the combustor 11 may be connected with the well for delivery of steam to the formation for steam Elooding purposes. But, before steam flooding a test is .24.
made of the fuel ~o be combus~ed to determine its actual heating valve, and calcula-tions performed to determine if the heat and materials balance for the burn-mix~ure selected using this Euel check theoretically across the combustor within the range of operating temperatur~s (T2min~ T2max) for the combustor utilizing the selected size of catalyst~
Assuming the fuel test is satisfactory, the information as to desired heat release rate, maximum combustor outlet temperature T3 of the steam, maximum combustion temperature, T2maX~ and steam pressure is fed as imput data into the computer 27 for use in controlling operation of the combustor during start-up, shut down and steady state operations. Also, calculations are performed to obtain estimated values for the mass ratio of the fuel-mixture, the fuel/air ra~io, the ratio of injection water to fuel, and the steady-state flow rates for the fuel-mixture air and injection water. From these figures, the flow regulating devices 85, 87, 86 and 88 associated with pumps 29, 30, and 31, respectively, may be set to provide the desired flow rates of fuel, water and air to the combustor. The flow rates for all of these fluids are first determined as estimated functions of the empirically established flow of nitrogen gas into the formation. Given -the temperature data ~or the burn-mixture being combusted in accordance with the curves as illustrated in Fig. 13, these flow values may be established so as to have a theore-tical stoichiometric combustion temperature within the aforesaid temperature range represented by the stability limits of the catalyst.
12.
With the emulsion prepared at the proper mass ratio of water to carboneacous fuel and the fuel, air and water supply lines 19, 20 and 71 leading to the combustor 11 charged to checked pressure, the combustor is ready to begin operation. The ~low chart representing operation of the combustor is shown generally in Fig. 10 with a closed looped control for steady state combustion (step 20 Fig 10) being shown in Figs. lla and llb. The closed loop control for start-up of combustion (step lS Fig. 10) is substantially .25.
the same a~ that for steady state operation except that the data base information to the computer 27 is characterized particularly as to the s~art fuel utilized. Accord.ingly, the specific descr.iption of the start-up control loop is omitted with the understanding that such would be substantially the same as the subsequently described st2ady ; state operation.
Upon entering operation (s~ep 12), preignition flow rates are established in the fuel, air and water supply 10 lines 19, 20, and 71, respectively opening ~he check valves 66 and 64 to cause ignition fuel and air to be delivered to the combustor 11 (step 13). In the surface ~ersion of ~he exemplary system, ignition (step 14) o:E the fuel .is accomplished through the use of an electrical resistance igniter 58 located above the upper end of the catalyst 12 ~see Fig. 2) while in the downhole version, the use of a glow plug 9S also is contemplated as an electrical starting means. Once the ignition fuel begins to burn, closed loop control (steps 15-17) of the ignition cycle continues until the combustion becomes stable. If the ignition burn is unstable after allowing for sufficient time to a~hieve stability, a restart attempt is made automatically (see Fig. 10 steps 12-16). Once stability i9 achieved in the .ignition cycle, the steady state fuel for the fuel-mixture \25 i~ phased in (step 18) with the system being brought gradually up to a steady state burning mode. As steady state burning con-tinues, control of the combustor is maintained as is set forth in the closed loop control system illustrated .in Figs. lla and llbo In the closed loop control, the thermalcouples TSl, TS2, and TS3 detect the temperatures within the inlet chamber 24, the discharge chamber 25, and the combustor outlet 26 and this information is fed to and stored in the computer 27 (see Fig. lla sub-step A). Additionally, information as to the flow rates of the fuel-mixture, air and injection water are stored in the computer and heat and materials balances for the combustor system are calculated (sub-step B) using actual temperature data. Two heat and materials balances are 8~
.26.
computed/ one for the overall system utilizing the actual output temperature 'r3a and one internal balance utili~ing the ca-talyst discharge temperature or combus-tion temperature T2. 1~is information is utilized to assure proper functioning (sub step C) of the various sensors in the system. If the sensors are determined to be functioning properly, then the system variables (water flow, fuel flow, and air flow) are checked to make sure that they are within limits (sub-step F) to assure proper functioning of the combustor without damage being caused by inadvertently exceeding the stability limits of the catalyst 12 and the maximum temperature and heat release rates at which steam may be injected into the formation. If the variables outside of the safety limits or the system, then the system is shut down. If the variables are within their limits, the computer analyzes the inputed temperature and fluid flow data to calculate the actual heat release rate of the combustor and compare it to the desired level to be fed into the formation being treated (sub-step G). If the actual h~at release rate requires changing to obtain the heat re1ease rate desired, the flow rates of the fuel-mixture, air and injection water are ad~usted proportionally hlgher or lower as may be necessary to arrive at the desired heat release rate. Once the heat release rate is as desired, a comparison oE the actual temperature (T3a) of the heated working fluid discharged by the combustor to the set point -temperature (T3sp) for such fluid is made. Depending upon the results o this comparison, the amount of injection water sprayed into the heated fluid is either increased or decreased to cause the actual temperature IT3a) thereof to either decrease or increase so as to equal the discharge set point temperature. After reaching the desired set point temperature, the actual combustion temperature i8 checked by the computer to determine if the temperature T~a is within the stability limits of the catalyst. If so, the computer then checks the combustor to determine if the combustor is operating substantially at stoichiometry. If the temperature T2a requires correction, then an adjustment is .27.
made in the mass ratio of the water to fuel in the fuel mixture. As the response time for making this type of correc~ion may be fairly lony, information as to prior similar corrections is stored in the computer data bank and is taken into consideration in making subsequent changes in the fuel-mixture ma~s ratios so as to avoid over compensation in making changes in the mixing of water and fuel to produce the emulsified fuel-mixture. Assuming that some form of correction is needed, the percentage of water in the fuel-mixture is either increased or decreased as may be appropriate to either decrease or increase the actual combustion temperature T2a to bring this temperature within the stability limits of the combustion system~
Advantageously, in making a change in the amount lS of fuel in the fuel-mixture, an equal but opposite r-hange is made in the amount of injection water so -that the total quantity of water passing through the combustor 11 remains the same (~ub-steps K-N). As a result, the outlet fluid temperature T3a remains the same while allowing for adjustment in the cornbustion temperature ~o arrive at a temperature and space velocity of fluids passing over the catalyst 12 at which combustion occurs most efficiently for the amount o fuel being combustedO
For example, if the actual combustion temperature 2S T2a is found to be too low, and any previously corrected fuel-mixture has had time to reach the combustor, then by decreasing the amount o~ water in the fuel-mixture and making a corresponding increase in the amount of water in the injection water, the temperature T2a should increase without any corresponding change in the temperature T3a of the fluids exhausted from the combustor. If the combustion temperature T2a where too high, the reverse follows with the combustion temperature T2a being lowered by increasing the quantity of water in the fuel-mixture and decreasing the amount of injection water by a like quan~ity.
To assure combustion in stoichiometric quantities, the oxygen sensor OS is utilized to detect the oxygen content (presence or absence) of oxygen in the heated fluids s~q~
~ 2~.
in the discharge c~amber 25 of the combustor 11. If oxygen is present in these heated fluids, the fuel-mixture is being combusted lean and coversely, if no oxygen is present, the : fuel-mixture i9 being combusted e.ither stoichiometrically or as a rich mixture. To obtain stoichiometric combustion herein, the amount of fuel is increased or decreased relative to ~he amount of oxygen beiny supplied to the combustor until the change in the amount of fuel is negligible in changing from an indication of oxygen presence to an indication that oxygen is not present in the heated discharge fluid of the combustor. I~us, for example in Fig. llb substeps O-S of step 20, if oxygen is determined to be present, the fuel flow is increased relative to the : oxygen flow to provide additional fuel in a small incremental. amount for combusting with the amount of air being supplied to the combustor. After a suitable period of time has passed allowi.ng the combustor to respond to the change in the bu.rn-mixture, data from the oxygen sensors is again considered by the computer to determine whether oxygen is present or absent. If oxygen i8 present, this sub-cycle repeats to again increase the fuel suppled to the combustor. However, if no oxygen is detected as being present, then stoichiometry has been crossed and the : burn-mixture will be beiny supplied to the combustor in substantially stoichiometric quantities. If oxygen is found to be present in the first instance, the fuel supply is decrea~ed incrementally relative to the oxy~en supply in a similar manner unt:il stoichiometry is crossed. While the forego.ing description establishing stoichiometric dcombustion by controlling the relative amounts of fuel and oxygen, this may be accomplished either by adjusting the flow of fuel relative to a fixed amount air as shown in E'ig. llb or by adjusting the flow of air relative to a fi~ed amount of fuel.
Once the combustor 11 is burning stiochio-metrically, the control process recycl~s con-tinuously computing through the closed loop control cycle (step 20) to maintain stoichiometric combustion at the desired heat 5~
.29.
release rate and output temperature T3sp until the steam flooding operation is completed. At the end of each cycle, if the operation has not received a shut-down signal (step 21) the loop repeats, otherwise, the system is shut down.
As an alternative method of establishing stoichiometric combustion of the fuel-mixture without the use of an oxygen sensor, the actual combustion temperature T2a for a particular fuel may be used as a secondary indication of stoichiometric combustion. In this connection, the information disclosed in Fig. 13 and previously described herein is utilized to vary the flow volume of the emulsion relative to the volume of air in order to obtain stoichiometric quantities of air and fuel for combustion in the combustor 11~ In considering the graph of Fig. 13, it will be appreciated that iXl attempting to reach the peak temperature of a curve it is nece6sary to know whether combustion is taking place with a burn-mixture which is either rich or lean. If the burn-mixture is rich the proportional flow of emulsion should be decreased relative to the flow of air in order to increase the combustion temperature to a peak temperature. But if the combustion mixture i9 leant it is necessary to increase the proportion oE emulsion relative to air in order to increase the combustion temperature to a peak temperature.
Accordingly, the first determination made is whether the temperature T2a for the existing emulsion has increased or decrea~ed over the temperature previously read into the computer data base in response to a change in the emulsion flow rate. IE the temperature T2a has increased, then the the flow of emulsion should be increased again if the flow of emulsion was increased previously. I~is would occur when burniny lean. If the temperature has increased in respon~e to relative decrease in the flow volume of the emulsion to air, then the flow volume of emulsion should be decreased again and this would occur when burning rich. If, on the other hand, the temperature T2a has decreased and the flow oE emulsion was also decreased previously, the flow of emulsion should be adjusted upwardly because this set of .30.
conditions would indicate lean burning. ~lternatively, if the temperature has decreased and the flow of emulsion was increased previously, the flow of emulsion should be decreased because this set of conditions would indicate rich burning. Continued checking of the temperature and the making of corresponding subsequent adjustments in the relative flow of emulsion to air are made in finer and finer increments to obtain stoichiometric flow rates of the air and emulsion for a particular fuel.
Advantageous:Ly, with the combustor system as described thus far, it will be appreciated that as formation conditions change, the combustor operation can be adjusted automatically within limits to provide the desired heat release rate to the formation at the desired temperature T3 while still combusting efficiently. For example, assuming that as the steam flooding proceeds over a period o time the injectivity of the formation increases, then the working fluid produced by the combustor will flow into the format.ion more easily and because of this, flow past the catalyst 12 will increase thereby tending to increase the heat release rate into the formation. With the exemplary combu.stor however, adjustment may be made in the heat realease rate by reducing the relative flow of fuel mixture as in sub-steps &
and H. This may be done to certain degree Eor any particular mass ratio of watex to fuel because of ~he width of the combustion envèlope for the combustor using this particular fuel-mixture (see Figs. lS-17~. If, however, the injectivity decrease is substantial, a change also may be required in the mass ratio of the fuel-mixture in order to combust within the operable space velocities for the combustor at the new injectivity pressure requirements. In thi.s instance, a lower mass ratio of wa-ter to fuel in the fuel-mixture would be expected in order to maintain substantially the same heat release rate into to formation 3S at a lower pressure and, as a result, a greater relative arnount of injection water may be needed in order to maintain the exhaust temperature T3a at the desired set point temperature ~3sp ~ ~3~
In accordance with the more detailed aspect of the present invention, a novel procedure i5 followed in starting the combustor 11 to bring the catalys-t 12 up to a temperture at which catalytic combustion of the burn-mixture may take place. For this purpose, while applying electrical energy to heat the nichrome heating element 58, a thermally combustible start fuel is ~upplied to the inlet chamber 24 of the combustor and is ignited to bring the catalyst temperature up to its light-of temperature. Herein, the start fuel is a graded fuel including a first portion which has a low auto ignition temperature (steps 14 through 18) followed by an int.ermediate portion (step 19) having a higher combustion temperature and finally by the burn-mixture (steps 19 and 20) to be combusted normally in the combustor~
Specifically methanol is contemplated as comprising the first portion of the start fuel. Methanol has an auto-ignition temperature of 878F. Other suitable low auto-ignition temperature fuels that may be used in the first portion of the start fuel include diethyl ether which has an auto-igniting temperature of 366~F; normal octane, auto-ignition temperature of 464F; l-tetradecene, auto-ignition temperature of 463F; 2-methyl-octane auto-ignition temperature of 440; or 2-methyl-nonane which has an auto--ignition temperature of 418E'. The intermediate portion O:e the start fuel is contemplated as heing a diesel fuel or other heavy hydrocarbon liquid and a mi~ture of the start fuel and the fuel-mixture to be combusted. During start up, the first portion of the graded start up fuel may be burnt thermally to both heat the catalyst 12 and to provide some recirculating heat for preheating the subsequent fuel. As the outlet temperature T2 of the catalyst reaches the lower limit of the combustion range for the catalyst, the light-off temperature of th~ catalyst will be surpassed and the burn-mi~ture may be phased into the combustor for normal steady state combustion.
Ag shown in Fig. 1, a start uel pump 9l is connected by a branch line 93 to the inlet line 19 of the .32.
combuster 11 to deliver the start fuel to the combustor upon start up. A valve 94 in the branch line is selectively closed and opened to regulate the flow of start fuel into the branch line as may be desired during the s~ar-t up and shu~ down of the system. Preferably, operation of the heating element 58 is controlled ~hrough the computer 27 so as to be lit during start up as long as the temperature, Tl, in the inlet chamber 24, is below the auto-ignition temperature of methanolO
In shutting down the exemplary combustion system 10, a speci.al sequence of steps is followed to protect the catalyst 12 against thermal shock and to keep it dry for restartin~ (see Fig. 10 steps 22 through 24). Accordingly, when shutting down the system khe flow volumes of fuel and a.ir are main~ained in stoichiometric quantities while a higher concentration of water to fuel is fed into the emulsion ultimate].y reducing the temperature Tl in the inlet chamber 24 to appro~imately the light-off temperature for the catalyst. Upon reaching this light-off temperature, the flow of emulsion is reduced along wi~h a proportional reduction in air so as to maintain stoichiometry. As the alr is reduced in volume, a like volume of nitrogen from a source 96 is introduced int.o the line 20 through a valve 92 until the pressure in the fuel mixture line 19 drops below the check val.ve pressure cau~sing the ch~ck valve 66 to close. At this point nitrogen is substituted completely for the air and pressure in the line 20 is mai.ntained so as to drive all of the burn-mixture in the inlet chamber 24 past the catalyst 12. As the burn-mixture is expelled, the outlet temperature of the catalyst T2 will begin to drop and, as it drops, the amount of injection water is reduced proportionally. Ultimately, the injection water is shut-off when T2 equals the desired combustor discharge temperature T3sp~ Preferably, in the downhole version, pre.ssure downstream of the combustor is maintained by a check valve 98 (see Fig. 5) above the nozzle 32 so as to pervent well fluids from entering the combustor 11 after ~hutdown.

.33.
Advantageously, for restarting purposes, a start plug of diethyl ether or methanol may be injected into the fuel line 19 at an appropria-te stage in the shut down procedure so that a portion of this s~art plug passes the check valve 66 5 at the inlet to the combustor 11. If this latter step is followed, the inlet temperature Tl may increase sucldenly as a portion of the start plug en-ters the inlet chamber 24. By stopping flow of the fluid in the fuel line 19 with this sudden increase in temperature, the catalyst may be easily restarted with the portion of the plug remaining above the check valve.
In view of the foregoing, it will be appreciated that the present invention brings to -the art a new and particularly useful combustion system 10 including a novel combustor 11 adapted for operation in a unique fashion to produce a heated workiny fluido Advantageously, the working fluid may be produced to efficiently over a wide range of heat release rates, temperatures, and pressures so that the same combustor may be used for a wide range of applications ~0 such as i.n the steam flooding of oil bearing formations having widely different reservoir cha~acteristics. ~o these ends, boilerless production of the working fluid is achieved by con~truction of the combustor with the catalyst 12 being used as the primary combustor. Advantageously, in using this combustor the diluent i5 mixed in a controlled amount intimately with the fuel prior to combustion and thus serves to keep the combustor temperature at a selectively regulated low temperature for efficient combustion. An additional selected quantity of diluent is injected into the heated fluid exiting the catalyst to cool the fluid to its useful temperature. From one use to the next or as changes in output requirements develop, the flow of diluent, fuel and air may be regulated so as to produce the cnaracteristics desired in the discharge fluid of the combustor.

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fluid admixture for burning in a catalytic combustor, said admixture comprising a non-combustible diluent and a carbonaceous fuel mixed in a thermally self-extinguishing mass ratio.

2. A fluid admixture as defined by claim 1 wherein said diluent is a fluid having a heat capacity generally close to or within the range defined by the mean molal heat capacities of H2O and CO2.

3. A fluid admixture as defined by claim 2 wherein said diluent is H2O or CO2.

4. A fluid admixtue as defined by claim 2 wherein the theoretical adiabatic flame temperature thereof is below an upper temperature stability limit for said catalytic combustor.

5. A fluid admixture as defined by claim 1, 3 or 4 wherein said admixture is a liquid.

6. A fluid admixture as defined by claim 1, 3 or 4 wherein said admixture is an emulsion.

7. A fluid admixture as defined by claim 1, 3 or 4 wherein said admixture includes liquid particles dispersed in gas.

8. A fluid admixture as defined by claim 4 wherein said admixture is gaseous.

9. A fluid admixture as defined by claim 4 having a low-catalytic spontaneous ignition temperature and a low adiabatic flame temperature.

10. A fluid admixture as defined by claim 4 having a high non-catalytic spontaneous ignition temperature and a low adiabatic flame temperature.

11. A fluid admixture as defined by claim 4 wherein said adiabatic flame temperature is no lower than by a light-off temperature of the catalyst used in said combustor.

12. A fluid admixture for burning in a catalytic combustor to directly produce steam, said admixture comprising a liquid water portion and a liquid carbonaceous fuel portion mixed together in a thermally self-extinguishing mass ratio.

13. A fluid admixture as defined by claim 12 wherein said admixture is an emulsion.

14. A fluid admixture as defined by claim 13 including an agent for stablizing said emulsion against separation of said water and fuel.

15. A fluid admixture as defined by claim 14 wherein said agent is a hydrophilic surfactant and said admixture further includes a lyophilic surfactant and a linking agent.