Note: Descriptions are shown in the official language in which they were submitted.
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/ ~
.3.
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.
