Steam generating system

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.

TECHNICAL FIELD 
The present invention relates to a system, apparatus, fuel and method 
utilized in producing a heated working fluid such as steam. 
BACKGROUND ART 
One prior art patent disclosing a catalytic combustor such as may be used 
in the production of steam for enhanced oil recovery is U.S. Pat. No. 
4,237,973. Another combustor which may be used to produce steam downhole 
includes U.S. Pat. No. 3,456,721. One method of start-up for a downhole 
combustor is disclosed in U.S. Pat. No. 4,053,015 relating to the use of a 
start fuel plug. Some characteristics of fuels used in combustors are 
mentioned in U.S. Pat. No. 3,420,300 and the injection of water to cool 
products of combustion are disclosed in U.S. Pat. No. 3,980,137. Another 
United States patent which may be of interest is 3,223,166. 
Definitions 
Unless indicated otherwise, the following definitions apply to their 
respective terms wherever used herein: 
adiabatiq flame 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 or more discrete 
substances. 
air: any gas mixture which includes oxygen. 
combustion: the burning of gas, liquid, or solid in which the fuel is 
oxidizing, evolving heat and often light. 
combustion temperature: the temperature at which burning occurs under a 
given 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 adiabatic flame temperature of 
a mixture containing fuel when combusted with a stoichiometric quantity of 
oxygen atmospheric air when the mixture and atmospheric air are supplied 
at standard temperature and pressure. 
DISCLOSURE OF INVENTION 
The present invention contemplates a new and improved boilerless steam 
generating 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 be combusted catalytically 
to produce steam by utilizing the heat of combustion to heat the water 
directly. Generally, 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 fuel mixture which is fed into the 
combustor for combustion. Specifically, herein, the fuel 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 mixed 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 directly heat a 
quantity of water proportionally divided in first and second amounts which 
are added selectively (1) to the fuel prior to catalytic combustion to 
form a controlled fuel-mixture to control combustion temperature in the 
catalyst and the space velocity of the fluids passing over the catalyst 
for combustion 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 the combustor for the burn-mixture to combust stably at 
temperatures considerably below the normal combustion temperature for the 
fuel even though the burn-mixture includes substantially stoichiometric 
quantities of carbonaceous fuel and air. Several advantages result from 
such low temperature, stoichiometric combustion particularly in that, the 
products of combustion are not highly chemically active, the formation of 
oxides of nitrogen is avoided, virtually all the oxygen in the air is used 
and soot formation is kept remarkably low. 
Still 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 temperature is attained for the 
catalyst in the combustor before introducing the steam-generating 
burn-mixture, and during shut 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 comprising diluent to fuel mass ratios 
generally in the range of 1.6:1 to 11:1 may be combusted with 
substantially stoichiometric quantities of oxidant to produce a useful 
working fluid. Advantageously, the exemplary combustor provides 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 limits, 
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 while 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. 
Novel controls also are provided for regulating the temperature of the 
steam produced by the combustor to be within a specified low range of 
temperatures within which the catalyst is capable of functioning to 
produce steam, that is, for example between the light-off temperature of 
the catalyst and the temperature for its upper limit of stability. 
Additionally, controls and means are provided for injecting 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 catalytic 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 making 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 
substantially 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 
exiting the combustor being kept at substantially the same level as before 
the adjustment. In this way, the heat release rate may be changed without 
a corresponding change in the discharge temperature all the while keeping 
the space velocity of the burn-mixture through the catalyst within an 
acceptable range for stable operation of the combustor. 
These and other features and advantages of the present invention will 
become more apparent from the following description of the best modes of 
carrying out the invention when considered in conjunction with the 
accompanying drawings.

BEST MODES OF CARRYING OUT THE INVENTION 
As shown in the drawings for purposes 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-free production of a heated working fluid at 
relatively low combustion temperatures. For these purposes, the 
fuel-mixture is catalytically combusted in a novelly controlled manner in 
the combustor to produce the working fluid. Specifically, 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 
the temperature of combustion of the fuel-mixture when burnt in a 
catalytic combustion zone 13 (see FIG. 2) in the combustor 11. 
Specifically, the combustion temperature is kept within a predesignated 
low temperature range. Control also is provided to assure the delivery of 
substantially stoichiometric quantities of oxidant to the catalyst for 
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 
diluent to fuel in the fuel-mixture keeps the theoretical adiabatic flame 
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 less 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 parts corresponding to those described in the first embodiment 
identified by the same but primed reference numbers. The fuel-mixture and 
controls for the two different embodiments are virtually identical. 
Accordingly, the description which follows will be limited 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 15 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 emulsion for delivery through a line 19 to the 
combustor 11 for combustion. Air containing stoichiometric quantities of 
oxygen is delivered through another line 20 to the combustor 11 by means 
of a compressor 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 before flowing into the 
combustion zone 13 of the combustor. 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 and the products of such combustion. Upon passing from 
the catalyst 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 chamber, the heated 
working fluid (steam) exits the combustor through an outlet 26 connected 
with tubing 35 leading into the well. Downhole, a packer 34 seals between 
the tubing and the interior of 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 
between the walls of adjacent sections are shaped as diffuser areas to 
recover at least some of the dynamic pressure in the steam so as to help 
in overcoming the natural formation pressure which resists the flow of 
steam into the formation. In the embodiment illustrated in FIG. 1 in order 
to recover some of the heat that might otherwise be lost by radiation from 
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 string above the packer 34 to preheat the air 
somewhat before entering the compressor. 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 just above the packer 
34. Air from the compressor exits 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 upper end of tubing string 35' 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 sensors TS1, TS2, and TS3 and an oxygen 
sensors OS are provided in the combustor 11. Temperature sensor TS1, 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 control sensors are processed in a 
computer 27 and latter is used 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 homogenizer 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 the present 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-mixture results in a boilerless production of steam by directly 
heating the water in the mixture with the heat generated by the combustion 
of the fuel in the mixture. Herein, one fuel-mixture contemplated 
comprises a mass ratio of water to fuel of 5.2:1 for deionized water and 
number two fuel oil and, with stoichiometric quantities of air of about 
2430 scfm passing over the catalyst 12, catalytic combustion of the fuel 
will produce an adiabatic flame temperature of approximately 1700.degree. 
F. without an application of preheat from some external source. Other 
carbonaceous fuels which may be used in producing an acceptable 
fuel-mixture 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 
13.degree. API was formed as an emulsion with water and was combusted 
catalytically to directly heat the water in the emulsion ultimately to 
produce steam at a temperature of 1690.degree. F. with a carbon conversion 
efficiency of 99.7%. 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 desirable working fluid produced by 
combustion in accordance with the present invention, it will be 
appreciated that the inventive concept herein extends to the direct 
heating of a diluent as a result of combustion of a carbonaceous fuel 
mixed intimately with the diluent. The characteristics of the diluent that 
are important are, that the diluent 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 limit of the catalyst. The latter is of 
course important to keep the catalyst or its support from being sintered, 
melted or vaporized as a result of the heat generated during combustion of 
the fuel portion of the mixture. Having a high heat capacity is important 
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. Herein, 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 to 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 exists for 
efficient combustion of the fuel without causing damage to the catalyst. A 
selected temperature within this range then respresents the theoretical 
adiabatic flame 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 heat which 
theoretically is released by combusting the fuel) and is such that the 
amount of heat released is that which is necessary to heat up both the 
diluent and the products of combustion to the aforementioned selected 
temperature. This temperature, of course, is selected to maximize the 
performance of useful work by the working fluid produced from the 
combustor 11 given the conditions under which the working fluid must 
operate. Stated more briefly, 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 of 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 
utilized in regulating the mass ratio of the fuel-mixture shown in FIG. 8. 
While the system shown in FIGS. 1 and 8 illustrates the various components 
thereof as being connected directly to each other, it should be recognized 
that the functions performed by some of the components may be performed at 
a site remote from the combustor 11. 
More particularly, the water source 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 
the combustor 11. The pump 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-extinguishing mass ratio. At the mixer, the two liquids are stirred 
together for delivery through an outlet line 45 to the homogenizer 17 
where the two liquids are mixed intimately together as an emulsion to 
complete the mixing process. From the homogenizer, the admixture emulsion 
is transferred 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 
emulsion or fuel-mixture may be delivered in controlled volume through the 
line 19 connecting with the combustor 11. 
While the preferred embodiment of the present invention contemplates a 
system 10 in which the fuel-mixture is formed as an emulsion which is fed 
without substantial delay to the combustor 11 for combusting the fuel in 
the mixture, in instances where greater stability in the emulsion may be 
desired, various chemical stabilizing agents including one or more 
nonionic surfactants and a linking agent, if desired, may be used to keep 
the emulsion from separating. In the aforementioned Kern River heavy fuel 
oil, the surfactants "NEODOL 91-2.5" and "NEODOL 23-6.5" manufactured by 
Shell Oil Company were utilized 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 sufficient to 
provide for adequate mixing of the water, fuel and air for proper 
operation of the catalyst 12. With this latter type of arrangement, the 
need for the homogenizer 17 may be avoided. 
For combustion of the fuel-mixture in the combustor 11, oxygen 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 combustor. 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 FIG. 2) which in turn 
communicates with the inlet chamber 24 through openings 50 in the 
combustor housing 51. Upstream of the manifold 42 within the line 19, a 
pressure check valve 66 is utilized to keep emulsion from draining into 
the catalyst before operational pressure levels are achieved. Similarly, a 
check valve 64 is located in the line 20 to keep air from flowing into the 
inlet chamber 24 before operational pressure levels are achieved. Within 
the inlet chamber 24, a fuel-mixture spray nozzle 65 is fixed to the 
inside of housing around each of the openings 50 and, 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 heating 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 before 
flowing through the catalyst 12 for combustion of the fuel. In both the 
surface generator and the downhole generator, 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 diesel fuel. 
As shown more particularly 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 catalyst against substantial 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 support 
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 providing vertical support. 
In catalytically combusting the fuel, the temperature of the burn-mixture 
as it enters the catalyst 12 must be high enough for at least some of the 
fuel in the mixture to have vaporized so the oxidation reaction can take 
place. This is assuming that the temperature of the catalyst is close to 
its operating temperature so that the vaporized fuel will burn thereby 
causing the remaining fuel in the burn-mixture to vaporize and burn. Thus 
it 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, 
preheating is achieved by utilizing some of the heat generated during 
combustion. For this purpose, a device is provided in the combustor 
between the inlet and discharge chambers 24 and 25 for conducting some of 
the heat from combustion of the fuel 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 fuels 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 four 
angularly spaced tubes 67 communicating between the combustor inlet and 
discharge chambers 24 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 support tube 54. Opposite end portions 69 and 70 
of each of the tubes 67 are bent to extend generally radially inward with 
the lower end portions 69 being also flared 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 flow radially inward to mix with the 
fuel-mixture and air within the inlet chamber 24. The heat in this 
discharge fluid thus provides the heat necessary for raising the 
temperature of the fluids 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 extent determines the rate at which heat may be 
transferred from the discharge chamber back to the inlet chamber. 
This unique preheat construction relies upon what is believed to be the 
natural increase in pressure of the products of combustion (steam and hot 
gases) over the pressure of the fluid stream passing through the catalyst 
12 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 11. 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.sub.fs, of the fluid stream rises slightly and then 
decreases as the emulsion passes through the spray nozzles 65 which are 
located at the point A in the temperature profile. Feedback heat F enters 
at the point B on the profile to keep the temperature from falling further 
due to the sudden drop in pressure as the fuel-mixture is sprayed from the 
nozzles. The point C on the profile indicates the beginning of catalytic 
combustion which is completed just prior to the point D. Throughout the 
catalyst 12 the temperature of the fluid stream flowing therethrough first 
increases sharply and then levels off as combustion of the fuel in the 
fluid stream is completed. At point E, additional water is injected into 
the heated products of combustion and the super heated steam exiting the 
catalyst to bring down the temperature of this fluid mixture before 
performing work. 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 methods of 
preheating such as by indirect contact of the burn-mixture with the 
exhaust gases (such as through a heat exchanger) or by electrical 
preheaters 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 11, a water supply line 71 (see FIGS. 1 and 2) 
is connected through an end 73 of the housing 51 and extends into the 
discharge chamber 25. A nozzle end 74 of the line directs water into the 
flow path of the heated fluid stream exiting the catalyst 12. To deliver 
the injection water to the combustor, the pump 31 communicates with the 
storage tank 43 of the deionized water and circulates this cooler water 
through loops 74 and 75 connecting with heat exchangers 76 and 77 in the 
prime mover and compressor, respectively, 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 to the combustor 11 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 flow 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 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 includes sensor means including the temperature sensor 
TS2 for determining the temperature T.sub.2 of the heated fluid stream 
exiting the catalyst 12 and control means responsive to such 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 is the 
aforesaid specified temperature. Advantageously, 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 TS1, TS2 and 
TS3 for detecting the temperature T.sub.1 within the catalyst inlet 
chamber 24, the temperature T.sub.2 at the outlet end of the catalyst 12 
prior to post combustion water injection and the temperature T.sub.3 of 
the steam discharged from the combustor 11. Additionally, the oxygen 
sensor OS disposed within the discharge chamber 25 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 specifically, signals representing the temperatures 
T.sub.1, T.sub.2, T.sub.3 and oxygen content are processed through 
suitable amplifiers 79 and a controller 80 before entering the computer. 
The temperature signals are processed 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 delivery to the computer 27 to be at least 
temporarily stored within the computer as data. This information along 
with other information stored in the computer is then processed to provide 
output 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, respectively. As 
the temperatures T.sub.1, T.sub.2 and T.sub.3 and oxygen content of the 
heated fluid stream may vary during the course of operation of the 
combustor 11, 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 flow in the components of 
the fuel and the air forming the burn-mixture. 
As shown in FIGS. 2 and 4, the thermocouples TS1, TS2, and TS3 and the 
oxygen sensor OS are connected by leads through the housing 51 of the 
combustor 11 and to box 89 containing the controller 80. In the well head 
system shown in FIGS. 1 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 fins 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 operation of the 
thermistor 81'. 
Part of the information providing a data base for the computer 27, 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 5.2 with different air-fuel ratios and curve II represents the 
temperature of heated fluid stream produced 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 ratio is 
stoichiometric. The vertical line "S" in the graph represents generally 
the stoichiometric ratio of air to fuel-admixture. As may be seen from the 
curves, when there is excessive fuel for the amount of air (a rich 
mixture) the temperature of 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 FIG. 13 show different fuel-admixtures, 
the heating valve of the fuel portion of each of the admixtures is the 
same. For fuels having different heating valves, the temperatures of 
combustion for equal mass ratios of admixture utilizing such different 
fuels will vary from one fuel to next. Accordingly, the data base of the 
computer is provided 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 combustor's heated output 
fluid. An example of such is shown in outline form in FIG. 9 such as when 
preparing the combustor for use in steam flooding an oil bearing 
formation. 
Generally speaking, the physical characteristics of each oil bearing 
formation are unique and such characteristics 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 heat and pressure without 
being damaged. 
In accordance with one of the more important aspects of the present 
invention, 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 derived by first testing the formation to be produced to 
determine the desired production 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 for 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 the combustor. Advantageously, this may be 
effected 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-mixture and 
that which is injected subsequent to combustion so as to maintain a flow 
of the burn-mixture over the catalyst within a range of space velocities 
at which efficient combustion of the fuel takes place. 
When using the exemplary system in a steam flooding operation, the amount 
of air to be pumped into the combustor 11 for 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 risking the possibility of 
fire in the formation. Available calculational techniques employed by 
petrolum engineers enable conversion of the flow and pressure data 
obtained using nitrogen into similar data for the heated fluid stream 
produced by the combustor. With this latter data, a theoretical 
injectivity curve (See FIG. 14) for the formation 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 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 lopes of these maximum burn rate curves for each 
stoichiometric burn-mixture while the rates of combustion 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 the curves in 
these two figures 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 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 the combustion envelope within which the 
particular fuel-mixture may be combusted at a given pressure over a range 
of heat release rates and space velocities. 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 which combustion of the mixtures may occur. As may be seen from 
this enlargement, the areas of combustion for these different mass ratios 
of water to fuel overlap each other. 
To select the proper combustor for efficient thermal combustion 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 
formation 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 and the catalyst is 
installed in the combustor housing 51, then the combustor 11 may be 
connected with the well for delivery of steam to the formation for steam 
flooding purposes. But, before steam flooding a test is made of the fuel 
to be combusted to determine its actual heating valve, and calculations 
performed to determine if the heat and materials balance for the 
burn-mixture selected using this fuel check theoretically across the 
combustor within the range of operating temperatures (T.sub.2min, 
T.sub.2max) 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 T.sub.3 of the steam, 
maximum combustion temperature, T.sub.2max, 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 ratio, 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 for 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 theoretical 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 flow 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. 11a and 
11b. The closed loop control for start-up of combustion (step 15 FIG. 10) 
is substantially the same as that for steady state operation except that 
the data base information to the computer 27 is characterized particularly 
as to the start fuel utilized. Accordingly, the specific description of 
the start-up control loop is omitted with the understanding that such 
would be substantially the same as the subsequently described steady state 
operation. 
Upon entering operation (step 12), preignition flow rates are established 
in the fuel, air and water supply lines 19, 20, and 71, respectively 
opening the check valves 66 and 64 to cause ignition fuel and air to be 
delivered to the combustor 11 (step 13). In the surface version of the 
exemplary system, ignition (step 14) of 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 95 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 achieve 
stability, a restart attempt is made automatically (see FIG. 10 steps 
12-16). Once stability is achieved in the ignition cycle, the steady state 
fuel for the fuel-mixture is phased in (step 18) with the system being 
brought gradually up to a steady state burning mode. As steady state 
burning continues, control of the combustor is maintained as is set forth 
in the closed loop control system illustrated in FIGS. 11a and 11b. In the 
closed loop control, the thermalcouples TS1, 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. 11a 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 computed, one for the overall system utilizing the 
actual output temperature T.sub.3a and one internal balance utilizing the 
catalyst discharge temperature or combustion temperature T.sub.2. This 
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 for 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 heat release rate 
requires changing to obtain the heat release rate desired, the flow rates 
of the fuel-mixture, air and injection water are adjusted proportionally 
higher or lower as may be necessary to arrive at the desired heat release 
rate. Once the heat release rate is as desired, a comparison of the actual 
temperature (T.sub.3a) of the heated working fluid discharged by the 
combustor to the set point temperature (T.sub.3sp) for such fluid is made. 
Depending upon the results of this comparison, the amount of injection 
water sprayed into the heated fluid is either increased or decreased to 
cause the actual temperature (T.sub.3a) 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 is checked by the computer to determine if the temperature 
T.sub.2a 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 T.sub.2a 
requires correction, then an adjustment is made in the mass ratio of the 
water to fuel in the fuel-mixture. As the response time for making this 
type of correction may be fairly long, 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 mass 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 T.sub.2a to bring this 
temperature within the stability limits of the combustion system. 
Advantageously, in making a change in the amount of fuel in the 
fuel-mixture, an equal but opposite change is made in the amount of 
injection water so that the total quantity of water passing through the 
combustor 11 remains the same (sub-steps K-N). As a result, the outlet 
fluid temperature T.sub.3a remains the same while allowing for adjustment 
in the combustion temperature to arrive at a temperature and space 
velocity of fluids passing over the catalyst 12 at which combustion occurs 
most efficiently for the amount of fuel being combusted. 
For example, if the actual combustion temperature T.sub.2a is found to be 
too low, and any previously corrected fuel-mixture has had time to reach 
the combustor, then by decreasing the amount of water in the fuel-mixture 
and making a corresponding increase in the amount of water in the 
injection water, the temperature T.sub.2a should increase without any 
corresponding change in the temperature T.sub.3a of the fluids exhausted 
from the combustor. If the combustion temperature T.sub.2a where too high, 
the reverse follows with the combustion temperature T.sub.2a being lowered 
by increasing the quantity of water in the fuel-mixture and decreasing the 
amount of injection water by a like quantity. 
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 in the discharge chamber 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 is 
being combusted either stoichiometrically or as a rich mixture. To obtain 
stoichiometric combustion herein, the amount of fuel is increased or 
decreased relative to the amount of oxygen being 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. Thus, for example in FIG. 
11b 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 allowing the combustor to respond to the change in the 
burn-mixture, data from the oxygen sensors is again considered by the 
computer to determine whether oxygen is present or absent. If oxygen is 
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 being supplied 
to the combustor in substantially stoichiometric quantities. If oxygen is 
found to be present in the first instance, the fuel supply is decreased 
incrementally relative to the oxygen supply in a similar manner until 
stoichiometry is crossed. While the foregoing 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 FIG. 11b or by adjusting the 
flow of air relative to a fixed amount of fuel. 
Once the combustor 11 is burning stiochiometrically, the control process 
recycles continuously computing through the closed loop control cycle 
(step 20) to maintain stoichiometric combustion at the desired heat 
release rate and output temperature T.sub.3sp 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 T.sub.2a 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 in attempting to reach the peak temperature of a 
curve it is necessary 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 is lean, it is necessary to 
increase the proportion of emulsion relative to air in order to increase 
the combustion temperature to a peak temperature. Accordingly, the first 
determination made is whether the temperature T.sub.2a for the existing 
emulsion has increased or decreased over the temperature previously read 
into the computer data base in response to a change in the emulsion flow 
rate. If the temperature T.sub.2a has increased, then the flow of emulsion 
should be increased again if the flow of emulsion was increased 
previously. This would occur when burning lean. If the temperature has 
increased in response 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 T.sub.2a has decreased and the flow of emulsion was also 
decreased previously, the flow of emulsion should be adjusted upwardly 
because this set of conditions would indicate lean burning. Alternatively, 
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. 
Advantageously, 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 T.sub.3 while 
still combusting efficiently. For example, assuming that as the steam 
flooding proceeds over a period of time the injectivity of the formation 
increases, then the working fluid produced by the combustor will flow into 
the formation 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 combustor however, adjustment may be made in 
the heat realease rate by reducing the relative flow of fuel-mixture as in 
sub-steps G and H. This may be done to certain degree for any particular 
mass ratio of water to fuel because of the width of the combustion 
envelope for the combustor using this particular fuel-mixture (see FIGS. 
15-17). 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 this instance, a lower mass ratio of 
water to fuel in the fuel-mixture would be expected in order to maintain 
substantially the same heat release rate into to formation at a lower 
pressure and, as a result, a greater relative amount of injection water 
may be needed in order to maintain the exhaust temperature T.sub.3a at the 
desired set point temperature T.sub.3sp. 
In accordance with the more detailed aspect of the present invention, a 
novel procedure is followed in starting the combustor 11 to bring the 
catalyst 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 supplied to the inlet chamber 24 of the combustor and is 
ignited to bring the catalyst temperature up to its light-off 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 
intermediate 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 878.degree. 
F. 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.degree. F.; normal octane, auto-ignition 
temperature of 464.degree. F.; 1-tetradecene, auto-ignition temperature of 
463.degree. F.; 2-methyl-octane auto-ignition temperature of 440.degree. ; 
or 2-methyl-nonane which has an auto-ignition temperature of 418.degree. 
F. The intermediate portion of the start fuel is contemplated as being a 
diesel fuel or other heavy hydrocarbon liquid and a mixture 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 T.sub.2 of the catalyst reaches 
the lower limit of the combustion range for the catalyst, the light-off 
temperature of the catalyst will be surpassed and the burn-mixture may be 
phased into the combustor for normal steady state combustion. 
As shown in FIG. 1, a start fuel pump 91 is connected by a branch line 93 
to the inlet line 19 of the 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 start up and shut down of the system. 
Preferably, operation of the heating element 58 is controlled through the 
computer 27 so as to be lit during start up as long as the temperature, 
T.sub.1, in the inlet chamber 24, is below the auto-ignition temperature 
of methanol. 
In shutting down the exemplary combustion system 10, a special sequence of 
steps is followed to protect the catalyst 12 against thermal shock and to 
keep it dry for restarting (see FIG. 10 steps 22 through 24). Accordingly, 
when shutting down the system the flow volumes of fuel and air are 
maintained in stoichiometric quantities while a higher concentration of 
water to fuel is fed into the emulsion ultimately reducing the temperature 
T.sub.1 in the inlet chamber 24 to approximately the light-off temperature 
for the catalyst. Upon reaching this light-off temperature, the flow of 
emulsion is reduced along with a proportional reduction in air so as to 
maintain stoichiometry. As the air is reduced in volume, a like volume of 
nitrogen from a source 96 is introduced into the line 20 through a valve 
92 until the pressure in the fuel mixture line 19 drops below the check 
valve pressure causing the check valve 66 to close. At this point nitrogen 
is substituted completely for the air and pressure in the line 20 is 
maintained 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 T.sub.2 will begin to drop and, as it drops, 
the amount of injection water is reduced proportionally. Ultimately, the 
injection water is shut-off when T.sub.2 equals the desired combustor 
discharge temperature T.sub.3sp. Preferably, in the downhole version, 
pressure 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 shutdown. 
Advantageously, for restarting purposes, a start plug of diethyl ether or 
methanol may be injected into the fuel line 19 at an appropriate stage in 
the shut down procedure so that a portion of this start plug passes the 
check valve 66 at the inlet to the combustor 11. If this latter step is 
followed, the inlet temperature T.sub.1 may increase suddenly as a portion 
of the start plug enters 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 working fluid. 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 such as in the steam flooding of oil bearing 
formations having widely different reservoir characteristics. To these 
ends, boilerless production of the working fluid is achieved by 
construction of the combustor with the catalyst 12 being used as the 
primary combustor. Advantageously, in using this combustor the diluent is 
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 characteristics desired in the 
discharge fluid of the combustor.