Programmed combustion steam generator

The present invention provides a steam generator which comprises rocket-type multielement injector head and a small diameter, highly elongated, cylindrical combustion chamber whose walls are formed from a plurality of longitudinally adjoined water tubes. The multielement injector head injects an array of associating streams of fuel and oxidizer into the combustion chamber under sufficient pressure to maintain a combustion pressure in the range of 25-150 psia whereupon the narrowness of the combustion chamber serves to constrict the resultant combustion gases to thereby promote radiant and convective heat transfer from the flame of combustion through the walls of the combustion chamber into the water passing through the water tubes. By such arrangement the production of nitrogen oxides in the combustion chamber is avoided.

FIELD OF THE INVENTION 
The present invention relates generally to combustors for boilers and steam 
generators and more particularly, to combustors for steam generators which 
include means for controlling nitrogen oxide emissions. 
BACKGROUND AND DESCRIPTION OF THE PRIOR ART 
It would take the likes of a Carl Sagan to utter a number large enough to 
represent the amount of steam generated each day for industrial and other 
commercial purposes throughout the world. All this sounds heartening at 
first, until it is realized that a good part, if not all of this steam is 
generated in boilers or steam generators which create large volumes of air 
pollutants, particularly, carbon monoxide, unburnt hydrocarbons and 
nitrogen oxides. The generation of these pollutants and the existence of 
stringent air quality standards, especially with respect to the nitrogen 
oxides, have required operators of steam generators to take measures for 
cleansing these pollutants from their systems' exhaust. These measures 
often require quite costly and complicated machinery. 
The taking of such post-combustion measures ignores the real source of the 
problem--the combustor. The normal combustor or furnace device operates at 
low static pressure (1 psig) and uses a relatively large chamber to 
maintain therein one or more ball-shaped flames in steady state condition. 
Because the flame is not allowed any significant degree of convection from 
one spatial location to another, thermal striations develop in the flame 
wherein there exists a high temperature central core surrounded by a 
cooler exterior envelope of combusting gas. The hot core most often 
exceeds the critical temperature required for the production of nitrogen 
oxides (approximately 2800.degree. F.). Also, the temperatures of the 
gases surrounding the core are too low for complete combustion. These 
peripheral cooler gases cause the flame to emit carbon monoxide and 
incompletely combusted hydrocarbons in addition to the nitrogen oxides 
generated at the hot core of the flame. 
There is the downhole steam generator described in U.S. Pat. No. 4,243,098 
to Meeks et al. which seems to depart from the usual design for steam 
generators, but which nonetheless exhibits the same shortcomings. In Meeks 
et al, a combustor comprising a combustion chamber and a single nozzle is 
used as a source of heated gas for purposes of generating steam at the 
base of a petroleum well hole. However, there is shown in FIG. 1 a single, 
elongated ball-flame and it is stated therein that the heated gases 
initially attain a temperature of approximately 3200.degree. F., a 
temperature well above the critical temperature where nitrogen oxides 
being forming. 
OBJECTS OF THE PRESENT INVENTION 
It is therefore an immediate object of the present invention to provide a 
combustor suitable for use in a steam generator which burns fuel more 
completely without producing nitrogen oxides. 
It is another object of the present invention to provide a steam generator 
which does not require treatment of its exhaust gases for purposes of 
controlling nitrogen oxides and other pollutants. 
SUMMARY OF THE INVENTION 
The present invention achieves these and other objects by providing a steam 
generator which comprises rocket-type multielement injector head and a 
small diameter, highly elongated, cylindrical combustion chamber whose 
walls are formed from a plurality of longitudinally adjoined water tubes. 
The multielement injector head injects an array of associating streams of 
fuel and oxidizer into the combustion chamber under sufficient pressure to 
maintain a combustion pressure in the range of 25-150 psia whereupon the 
narrowness of the combustion chamber serves to constrict the resultant 
combustion gases to thereby promote radiant and convective heat transfer 
from the flame of combustion through the walls of the combustion chamber 
into the water passing through the water tubes. The array of associating 
streams of fuel and oxidizer is patterned to create a burning-rate profile 
which results in the progression of combustion in discrete stages along 
the entire length of the combustion chamber. The graduated release of 
combustion heat is taken up by the flow of water at a rate which balances 
the rate of heat generated in the combustion chamber so that the 
combusting gases therein remain at a low enough temperature to avoid 
production of substantial quantities of nitrogen oxides. The invention 
also provides longitudinally oriented fins at the inlet of the combustion 
chamber for increasing the rate of heat transfer where heat generation and 
temperature would be expected to peak.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawing. 
Referring to FIG. 1, 1a., 1b. and 1c. the preferred embodiment of the 
present invention provides a steam generator generally designated 1 and 
comprising a rocket-type multielement injector assembly 2 situated at 
inlet end 4 of a narrow, extremely elongated cylindrical combustion 
chamber 6. Walls 8 of combustion chamber 6 are preferably constructed from 
a plurality of longitudinally adjoined tubes 10 constructed of thermally 
conductive material. Combustion chamber 6 preferably has a length of at 
least 25 times greater than its width, and a typical operational version 
might have a diameter of approximately six inches and length of thirty 
feet or more. A flow of water from tank 12 and pump 14 travels down line 
16 to header 18 from whence it enters tubes 10 at the inlet end 4 of 
combustion chamber 6. As the flow of water travels through tubes 10 to 
manifold 20 at outlet end 22 of the combustion chamber 6, the water 
absorbs the heat transferred from combustion chamber 6 through walls 8 and 
turns into useable steam. 
Referring to FIG. 1, 1c., 2a. and 2b., multielement injector assembly 2 
comprises a circular injector plate 24 for housing a plurality of 
individual injector elements 26 in an arrayed-pattern typically found in 
rocket-type injector plates. Each individual injector element 26 comprises 
at least one fuel orifice 28 and at least one oxidizer orifice 30 which 
emit associating streams of fuel and oxidizer, respectively. It is to be 
understood that the term "associating streams" herein refers to both the 
fuel jetlet(s) 32 and oxidizer jetlet(s) 34 that are emitted from a single 
individual injector element 26 as well as to the stream of resultant 
combustion products created by chemical interaction of the jetlets 32 and 
34. Injector plate 24 also comprises an oxidizer manifold 36 and a fuel 
manifold 38 which are constructed in a manner well known to the art and 
which supply oxidizer and fuel to the respective orifices of each 
individual injector element 26. A supply of oxidizer is supplied via line 
40 to oxidizer manifold 36 from an external tank 42 and pump 44 and fuel 
is supplied to fuel manifold 38 via line 16 from external tank 42 and pump 
44. Preferably, the oxidizer is compressed air and the fuel is fuel oil 
although other fuels such as diesel fuel, natural gas or a rocket-type 
fuel might be used instead. The present invention prefers, however, that 
the selected fuel and oxidizer be injected under sufficient pressure to 
create a combustion pressure of the range of 25-150 psia so that the 
narrowness of combustion chamber 6 serves to constrict the combusting 
gases as they travel from inlet end 4 to outlet end 22 of the combustion 
chamber. The constrictive effect of combustor walls 8 causes the 
combustion gases to be in contacting relationship therewith so that heat 
transfer can be effected through both convection and radiation into walls 
8. The narrowness of combustion chamber 6 also serves to substantially 
increase the intensity of heat radiation from the combusting gases by 
reason that the radiation beam length of the gases at the central regions 
of the combustion chamber is shortened so that there is less interference 
from the surrounding gases. 
Besides the constrictive and cooling effects provided by walls 8 to the 
gases in combustion chamber 6, another important feature of the present 
invention is the creation of a burning-rate profile across the width of 
combustion chamber 6 which profile is achieved by the particular 
arrangement of the individual injector elements 26 on injector plate 24. 
As is shown in FIG. 1c., face 52 of injector plate 24 comprises an inner 
circular region 54 which houses individual injector elements 26' which are 
larger and of a different type than those elements 26" housed at the 
peripheral region 56 of face 52. These differences in size and type cause 
an array of associating streams of fuel and oxidizer to be emitted from 
injector plate 24 wherein a core of relatively slow combusting gases are 
surrounded by a sleeve of more rapidly combusting gases. This situation 
results in a burning-rate profile as depicted in FIG. 3 wherein the 
vertical line C--C corresponds to line C--C in FIG. 1 to represent radial 
displacement above and below the axial centerline of combustion chamber 6. 
The centerline of combustion chamber 6 is represented by the line labled 
C/L and lines 58 and 60 represents the boundaries of walls 8 of combustion 
chamber 6. The line labled C/L also serves to represent increasing burning 
rate in the direction of the arrowhead and the curved line gives 
indication of the preferred burning-rate profile to be achieved by 
injector plate 24. In accordance with the preferred burning-rate profile, 
associating streams of fuel and oxidizer from peripheral region 56 of 
injector plate 24 are to burn at a more rapid rate than those from inner 
circular region 54. As a result, the combustion process progresses in 
indiscrete stages along the entire length of combustion chamber 6 as more 
and more of the core region of the combusting gas begins to burn. This 
delayed effect causes the heat released from the combustion process to be 
similarly smeared-out or graduated, which situation in turn allows for the 
rate of heat generation from the combusting gases at any given length 
segment of combustion chamber 6 to be matched by the rate of heat 
transferred to the flow of water passing through tubes 10 so that the 
combusting gases never attain a temperature where substantial quantities 
of nitrogen oxides are produced. This avoidance of nitrogen oxide 
producing temperatures can be further understood by reference to FIG. 4 
wherein line 64 represents a temperature line along the length of a 
typical combustion chamber of the prior art wherein a ball-flame is 
introduced into a combustion chamber which does not confine the flame. As 
is shown line 64 peaks at a temperature above that where nitrogen oxides 
being to form (approximately 2800.degree. F.). However, the temperature 
line 66 of the present invention peaks below the threshold temperature. 
It is also to be understood the heat extraction by the water flow through 
tubes 10 helps achieve these favorable results in two ways: by removing 
heat from combustion chamber 6 at a rate which avoids local overheating 
within the combusting gases; and by removing heat at a rate which prolongs 
the delayed combustion process initiated by the burning-rate profile. The 
ultimate result is that steam is generated in tubes 10 while fuel is 
combusted completely in combustion chamber 6, but without the production 
of significant quantities of nitrogen oxides. 
Referring to FIGS. 1 and 5, the practice of the present invention might 
require the additional of longitudinally oriented fins 68 be added to 
walls 8 along segments of combustion chamber 6 where the temperature of 
combusting gases would be expected to be highest. These fins serve to 
increase thermal transfer to walls 8 so that the undesired threshold 
temperature is avoided. A shown in FIG. 1, fins 68 are likely needed at 
the inlet end 4 and might also prove necessary at the beginning of a 
constriction 70 in combustion chamber 6. Such constrictions serve to 
increase mixing of the combusting gases at selected down-range locations 
along combustion chamber 6 and are therefore locations where temperatures 
can be expected to jump. It is to be noted that fins 68 have notches 72 at 
points along their length to intermittently upset boundary layers which 
might otherwise form thereon and lessen their thermal conductivity. 
Referring back to FIGS. 1c. 2a. and 2b., it is preferred that the 
individual injector elements 26' situated at inner circular region 54 of 
injector face 52 serve to emit a core of associating streams of fuel and 
oxidizer which combusts at rate slower than those streams emitted from 
injectors 26' at peripheral region 56. As previously mentioned, this 
result can be achieved by making individual injector elements 26' larger 
and of a different type from elements 26". In terms of type, it is 
preferred that injector elements 26' be of the coaxial type as is shown in 
FIG. 2b. wherein central jetlets 34 of oxidizer are encased with 
associating jetlets 32 of fuel. Impinging-type injector elements 76 as 
shown in FIG. 2a. could also be used, but with an angle of impingement (B) 
which is smaller than that of similar types to be used as injector 
elements in peripheral region 56 of injector face 52. The small angle of 
impingement delays mixing of the associating streams and thus their 
combustion. 
Other means can be employed in order to arrive at the desired pattern-array 
of associating streams of fuel and oxidizer. For instance, injector 
elements 26' of inner circular region 54 might be less closely packed both 
in the radial or circumferential manner across injector face 52 than 
elements 26". Also, the velocity ratios between oxidizer jetlet 34 and 
fuel jetlet 32 might be made to impede rapid mixing for injector elements 
26' than for elements 26" at peripiheral region 56, or the fuel/air ratios 
might be similarly differentiated or any combination of these means for 
producing the desired burning-rate profile. 
FIG. 1d. is provided to show an injector face wherein the bounds of inner 
circular region 54 is less well defined than that of injector face shown 
in FIG. 1c. However, FIG. 1d. is more representative of a rocket-type 
injector plate 24 which might be used in accordance with the present 
invention. Injector plate 24 comprises 5 to 10' circumferential bands 78 
of individual injector elements 26"', the outer band 80 containing 
approximately 20 of injector elements 26"' for an injector of 
approximately 6 inches diameter. 
It is to be understood that multielement injector assembly 2 is sealingly 
affixed to walls 8 at input end 4 of combustion chamber 6. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. For instance, another cooling 
medium other than water might be applied through tubes 10. It is therefore 
to be understood that, within the scope of the appended claims, the 
invention may be practiced otherwise than as specifically described.