US3915124A

US3915124A - Compact high-pressure steam generator

Info

Publication number: US3915124A
Application number: US495350A
Authority: US
Inventors: Jr Ralph F Kuhn; James O Bates; Jr John Campbell; Larry H Russell
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1974-08-07
Filing date: 1974-08-07
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

A fast start-up compact high-pressure high-temperature steam generator is comprised of a multiplicity of individual fire tube boiler combustion devices housed in an enclosure. Each boiler assembly is supported by tube sheets and consists primarily of concentric inner and outer tubes. The inner tubes serve as a combustion chamber wherein a near stoichiometric mixture of fuel and oxidizer are burned. An annular chamber is formed between the inner and outer tubes and serves as a vehicle for water that is directed helically therethrough. Heat transfer through the walls of the inner tube convert said water from a liquid to a superheated steam for use with conventional steam turbine power plants or the like.

Description

States Pate [1 1 Kuhn, Jr. et al..

COMPACT HIGH-PRESSURE STEAM GENERATOR Inventors: Ralph F. Kuhn, Jr., Calabassas;

James O. Bates, Northridge; John Campbell, Jr., Woodland Hills; Larry H. Russell, Agoura, all of Calif.

Assignee: Rockwell International Corporation,

El Segundo, Calif.

Filed: Aug. 7, 1974 Appl. No.: 495,350

US. Cl 122/115; 122/271; 122/367 R; 122/501 Int. Cl. F22b 7/00; F22b 25/00 Field of Search 122/114, 115, 136 R, 149, 122/271, 367 R, 367 C, 501

References Cited UNITED STATES PATENTS 5/1929 Vincent 122/271 10/1951 Denker et al. 122/271 X PROPANE Rossi.... 122/271 X Bliss 122/149 Primary Examiner-Kenneth W. Sprague Attorney, Agent, or FirmL. Lee Humphries; Robert G. Upton [57] ABSTRACT A fast start-up compact high-pressure hightemperature steam generator is comprised of a multiplicity of individual fire tube boiler combustion de vices housed in an enclosure. Each boiler assembly is supported by tube sheets and consists primarily of concentric inner and outer tubes. The inner tubes serve as a combustion chamber wherein a near stoichiometric mixture of fuel and oxidizer are burned. An annular chamber is formed between the inner and outer tubes and serves as a vehicle for water that is directed helically therethrough. Heat transfer through the walls of the inner tube convert said water from a liquid to a superheated steam for use with conventional steam turbine power plants or the like.

25 Claims, 9 Drawing Figures U... Patent 0a. 28, 1975 Sheet 1 of 5 3,915,124

PROPANE U.S. Patent 0m. 28, 1975 Sheet 2 of5 3,915,124

FIG.'2

US. Patent Oct.28, 1975 Sheet40f5 3,915,124

COMPACT HIGH-PRESSURE STEAM GENERATOR CROSS REFERENCE TO RELATED APPLICATIONS This disclosure is related to a copending patent application entitled, Ignition System for a Compact High- Pressure Steam Generator.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is related to the field of fuel fired steam generators. More particularly this invention is related to a compact high-pressure high-temperature steam generator wherein water is superheated in a single unit, of relatively small surface area and volume, thus enabling the physical size of the steam generator to be far less than a conventional fuel fed steam generator while providing peaking power on short notice during maximum consumer power usages.

2. Description of the Prior Art Generally, prior art superheaters operate in a temperature range of lllllW-ZQUWF, the maximum gas temperature in the boiler operating in the 350040lllll region. The temperature does not get above MNMVF because of the flame quenching effect of the nitrogen in the atmosphere since the boiler uses atmospheric air to provide oxygen for combustion. Additionally, a substantial temperature drop is usually taken in the furnace before the gas enters the steam superheater.

The fire tube concept of the present invention is capable of high heat fluxes which range in the neighborhood of ll-2 BTU/sq.in./sec. Normal state-of-the'art steam boilers run at 1/10 to 1/ 100 the foregoing ratio.

The present invention utilizes fuels and oxidizers that are relatively free of pollutants (little nitrogen and sulfur). A near stoichiometric mixture ratio assures clean burning of the foregoing propellants at a pressure that runs as high as 70 psi. Since most conventional boilers operate at 3700F in ambient pressure (14 psi) it is clearly apparent that the present invention goes well beyond the state-of-the-art of conventional steam boilers.

In the nuclear field a liquid moderated vapor reactor, US. Pat. No. 3,085,959, generates steam in the following manner. A series of individual fuel rod elements are suspended between tube sheets, the elements being surrounded by a cooling liquid such as water. Each fuel element is additionally surrounded by a cooling jacket wherein water is directed between the outer casing of the fuel element and the inner wall of the outer jacket. The cooling water surrounding each of the elements is directed in a spiral path, the helix of which is varied in pitch. The helix angle depends upon the heat pattern along the length of the fissionable fuel element. The water contained within the outer jackets of each of the elements is converted to steam for use to driveturbines and the like.

The instant invention differs from the nuclear steam heat device in that the inner tube is hollow and is utilized as a fire tube. At one end of the fire tube is a rocket engine-like injector which feeds a near stoichiometric mixture of a fuel and an oxidizer that is ignited and burned at a high temperature. The heat generated by the combustion zone downstream of the injector is transferred through the walls of the inner combustion tube to water entering the annular chamber between the outside wall of the inner fire tube and the inside wall of the surrounding outer tube. The water is directed spirally, the helix being varied in pitch so that a maximum heat transfer is imparted to the surrounding water as it traverses down the annular chamber surrounding the frre tube. The multiplicity of concentric tube boiler assemblies of the present invention are not immersed in a liquid coolant such as that which is described in US. Pat. No. 3,085,959, nor is the center heat generating element a solid mass fuel rod comprised of fissionable material as disclosed in the foregoing patent.

The present invention relates to a multiplicity of boiler assemblies in a housing, each boiler assembly being comprised of an inner fire tube that utilizes oxidizers and fuels as propellants. The compact steam generator is designed primarily to supplement or replace current conventionally fueled boiler plants.

SUMMARY OF THE INVENTION The compact steam generator of the instant inven' tion for example is approximately 3 ft. in diameter and 25 ft. in length. The device is capable of replacing a conventional fuel fed boiler that is normally housed in a five-story building. Obviously the present invention lends itself to any size range and is not limited to the foregoing example. The compact steam generator has a start-up time of approximately one-half hour as compared to a twelve hour start-up for conventional boilers.

The compact steam generator is essentially a Rankine-cycle device that can be used as a supplemental power source during peak power usage periods that features a steam generator in which a fuel and oxygen are burned at high temperatures and high pressures, the resulting heat being transferred to water producing superheated steam. The steam is expanded in a turbine, condensed and recycled in the fashion of a typical Rankine cycle. Feed water is regenerated with the residual heat of combustion products for higher thermal efficiency. In a typical application, the conventional turbine condenser and other auxiliaries are utilized at the site of a conventional boiler plant, the compact steam generator being installed adjacent thereto. Typically, a turbine driven by the compact steam generator of the present invention will provide the power to drive an electrical generator having a name plate rating of, for example, 10,000 kw. Pollutants are essentially eliminated or controlled with the use of relatively clean burning fuels such as natural gas and an oxidizer that are reacted in stoichiometric porportions.

The design of the steam generator is based upon rocket engine technology rather than power plant boiler practices; a light hydrocarbon fuel such as natural gas and a liquefied oxygen (L0 are stored in cryogenic low-pressure tanks. The propellants prior to use by the steam generator, are pumped to high pressures and metered through flow control throttle valves before they are directed to the steam generator. To fire the steam generator a source of ignition in the form of acombustion wave (described in detail in the here tofore mentioned copending application) is supplied to each of the multiplicity of boiler assemblies to ignite a pilot flame. A source of fuel such as, for example, propane is bled into the inner fire tube adjacent the injector to act as a pilot flame for the injected fuel and oxidizer. Each fire tube is provided with an oxygen rich atmosphere downstream of the injector face so that the combustion wave directed to each of the injectors to ignite each pilot flame will not propagate down the fire tubes. Fuel is provided through the system of conduits that directs the combustion wave to each of the inner individual fire tubes of the boiler assemblies while oxygen is supplied via a separate manifold, thereby providing the bi-propellant system to effectuate clean combustion at near stoichiometric mixture ratios.

The whole start-up process is a tightly controlled sequence of events starting with directing preheated water through the passage surrounding the inner fire tube boilers prior to initiation of the combustion wave to ignite the pilot in each of the boiler assemblies followed by a sequencing of fuel and an oxidizer to each of the inner fire tubes for subsequent main steady-state combustion.

Each inner fire tube is surrounded by an outer coaxial tube in which the high pressure feed water is directed. The flow of water is started prior to the ignition sequence so as to prevent damage to the combustion chambers due to excessive heat. In addition, the water is preheated to raise the temperature above ambient in each of the fire tubes to reduce the temperature differential prior to ignition. The annular chamber formed by the outer wall of the inner fire tube and the inner wall of the outer concentric tube making up the boiler assembly is provided with a spirally wrapped support structure to direct the feed water in a spiral direction down the tube. The helix angle of the support structure is varied, to provide higher steam and water velocities in different portions of the tube.

The helix is very tight at the injector end of the fire tube to effect maximum cooling and heat transfer at a point where the combustion gases are the hottest. As the water traverses down the annulus formed by the tubes, the spiral becomes less tight and allows the water/steam to be directed in a more axial direction at lesser velocities near the exit end of the annulus. Heat energy from the very hot combustion products is transferred through the inner fire tube to the water down the length of the tube to produce the desired dry superheated steam.

The combustion products, by the time they exit the fire tube, are cooled to approximately 1000F. The exhaust gas is directed through a pressure recovery nozzle system attached to each of the tubes.

The exhaust gas pressure recovery nozzle system acts primarily to meter the flow of the exhaust gases and provide the same quantity of gas through each fire boiler assembly. Successful operation of this kind of compact steam generator requires that the ratio of the gas quantity through each inner fire tube to the water and steam flow through each boiler assembly, be very accurately, constantly maintained. The control of the gas flow is affected through having an accurate metering orifice in the fuel supply to each burner, as well as an accurate metering orifice in the oxygen supply to each burner, and the so-called pressure-recovery nozzle at the exit of each inner fire tube associated with each boiler assembly. In addition, the fuel supply ducting the oxygen supply manifolding is carefully arranged to provide essentially constant fuel and oxygen supply pressures to each of the metering orifices mentioned. On the water and steam sides the water supply to each annulus between the concentric tubes of the boiler assembly is carefully metered through ann accurate orifice at the inlet to the annulus of each boiler assembly, the water supply manifolding is carefully arranged to provide essentially constant upstream pressure at each orifice, and the steam gathering ducting at the exit of each annulus between boiler tubes is carefully arranged to minimize differences in pressure imposed at each exit. Furthermore, great care is exercised in assuring that the spiral structure separating the multiplicity of concentric tubes is the same in each and every boiler assembly and the tubes are carefully selected for uniform O.D.s of the inner fire tubes, uniform I.D.s of the outer tubes and in addition the tubes are carefully arranged in matching pairs so that the annulus space between each concentric tube is as uniform as possible. The pressure recovery system acts to assure that the pressures in each of the tubes remains relatively constant during steam generator operation so that the axial growth of each of the fire tubes remains approximately the same during thermal expansion and contraction of the device. The nozzles at the downstream end of each of the fire tubes provide a means to recover some of the pressure which acts to expel the exhaust products from each of the fire tubes out of the compact steam generator exhaust system. The superheated dry steam of course, is directed through a separate conduit system to drive steam turbines or the like.

Means are provided in the surrounding steam generator housing to compensate for thermal expansion, growth, and contraction, of the individual fire tubes, the housing being cooler than the boiler assemblies during operation.

Therefore, it is an object of this invention to provide a fast start-up compact steam generator to primarily act as an additional power source during peak hours to supplement a conventional boiler plant.

More specifically, it is an object of this invention to provide a multiple fire tube compact steam generator that utilizes a fuel and an oxidizer that is cleanly burned at near stoichiometric mixture ratios, thus providing heat to quickly convert circulating water to superheated dry steam in a relatively small device.

An advantage over the prior art conventionally fueled boiler plants is the ability to provide superheated steam in a single compact unit.

Another advantage over the prior art is the ability to provide a fire tube steam generator that provides heat in the range of 6000F, thus enabling the circulating water to be converted to superheated dry steam in a relatively short period of time.

Yet another advantage is portability of the compact generator and its movement from one location to another where it may be more needed.

Still another advantage is the use of oxygen, which contains so little nitrogen that the nitrogen-oxide pollutants are not formed in significant quantities.

Yet another advantage is rapid starting and stopping of the compact steam generator and rapid response to load changes.

Still another advantage over the prior art is the rapid response to load changes inherent in the compact steam generator of the present invention.

The above noted objects and advantages of the present invention will be more fully understood upon a study of the following detailed description in conjunction with the detailed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a semi-schematic view of the overall compact steam generating system;

FIG. 2 is a cross-sectional view of the combustion end of the main body of the compact steam generator;

FIG. 3 is a partial cross-sectional view of the exhaust end of the main body of the compact steam generator;

FIG. 4 is an enlarged cross-sectional view of the combustor end of the individual fire tubes within the body of the steam generator;

FIG. 5 is a cross-sectional view taken through lines 5-5 of FIG. 4;

FIG. 6 is an enlarged cross-sectional view of the exhaust end of each of the fire tubes within the body of the compact steam generator;

FIG. 7 is a partial cross-sectional view of one of six removable fire tubes, the six tubes being equidistantly spaced one from the other around the outer periphery of the multiplicity of tubes within the compact steam generator;

FIG. 8 is a view taken through lines 8-8 of FIG. 2 illustrating the various water passages through the water manifold tube sheet, the passages communicating with an annular water jacket surrounding the tube sheet; and

FIG. 9 is a view taken through lines 9-9 of FIG. 8 illustrating the means by which the water is metered and directed to the space between the inner and outer fire tubes within the compact steam generator.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, the compact steam generator system generally designated as 10 is comprised of a housing member 12. The housing 12 supports a combustion end generally designated as 8 and an exhaust and steam collection end generally designated as 11. The main body 12 of the steam generator is normally positioned vertically with the combustion end 8 positioned at the bottom with the exhaust and steam collection end 11, at the opposite end.

Housing 12 supports and contains, for example 162 individual boiler assemblies generally designated as 1110. The boiler assemblies are comprised of concentric tubes, one tube within another, the outer wall of the inner fire tube and the inner wall of the outer tube providing a passageway for water. Each boiler assembly is a separate combustion device that utilizes, for example, a light hydrocarbon fuel and a gaseous oxygen. A fuel under pressure such as, for example, methane gas is directed through a conduit 64 into a combustion wave plenum chamber generally designated as 18. A gaseous oxygen under pressure is pumped through conduit 60 into an oxygen inlet maniford 16 which directs gaseous oxygen into each of the concentric boiler assemblies generally designated as 110. A portion of the gaseous oxygen is directed through conduit or line 62 into the combustion wave plenum chamber 18. A source of ignition (not shown) such as, for example, a spark plug communicates with the interior of the plenum chamber 18. A fuel-rich combustible mixture is directed to the combustion wave plenum chamber 18 and ignited by the ignition source. The combustion wave then propagates through conduit 66 to each of the individual combustors in each of the boiler assemblies 110. A pilot gas supply 68 such as, for example, propane is directed through conduit into each of the individual 162 combustors to provide a source of gas for a pilot flame for subsequent main stage or steady-state combustion.

After the pilot is lit in each fire tube, the plenum chamber 18 then serves as a gaseous fuel reservoir for supplying fuel under pressure through conduits 66 to each of the individual combustors.

Prior to ignition of each of the boiler assemblies a source of water is circulated through the annulus 122 (FIG. 2) in each of the boiler assemblies. To prevent damage to the tubes during main-stage combustion, the water is preheated by a heater generally designated as 40 as it exits steam separator 52. Water is initially directed through pipe 32 into branches 34. Water preheater 40 heats the water to a temperature in the neighborhood of 180F which lessens the shock and diminishes the heat differential between the fire tubes and the cooling water that is converted to steam. The water temperature may vary from to 250F. After mainstage combustion is achieved in each of the boiler assemblies, the water is heated by an economizer section generally designated as 28. The economizer 28 utilizes the exhaust gas heat to preheat the water passing through the economizer to a temperature of approximately 180F. The heater 40 is then subsequently shutdown. Pump 38 serves to circulate water through the water circulation system. The preheated water lessens the shock and diminishes the heat differential between the steam which is generated immediately after ignition and the assorted tube sheets, flanges, housings or shells, heads or manifolds and other relatively thick pressure components of the steam generator.

At the top end of housing 12 is positioned a steam plenum chamber generally designated as 20. Water passing through the annulus of each of the boiler assemblies 110 is converted to dry steam and is directed into plenum 20 and out through connecting pipe 50 which communicateswith a. steam separator device generally designated as.52. At the top of the steam separator is a safety valve 58 which vents steam overpressures overboard without damage to the overall steam generating plant .10. A water drain 56 is provided to drain off and recirculate pre-ignition water and condensed water from the steam separator device. Conduit 54 communicating with the steam separator delivers dry steam to conventional steam turbines and the like.

Above the steam plenum chamber 20 is an exhaust collection or plenum chamber 22. The exhaust chamber serves to direct the exhaust gases from each of the individual fire tubes out of the steam generator through pipe 26 into the economizer section 28. An exhaust pipe 30 is provided to expel exhaust gases to the atmosphere.

The entire compact steam generator start-up and shutdown sequence is automatically controlled (not shown) to insure safe and stable operation of the water and steam circuits as well as the fuel burning system. Toward this end the following equipment and procedures are employed.

A minimum fuel burning rate is established at startup of approximately 25 percent of full propellant flow during steady-state operation to insure gas side stability. Prior to ignition the steam spaces partially filled with water are prepressurized by, for example, an inert gas such as nitrogen to start steam production to above ambient pressure (approximately 50 psi) to obtain steam and system flow stability. The nitrogen under pressure is directed into steam plenum chamber through conduit 23. The pressure in the steam passages (annulus 122 and plenum 20) and temperature of the flowing water/steam are automatically ramped up, i.e., a gradual increase in pressure and temperature from an initial starting condition of approximately 50 psi and 280F to the final steady-state operating conditions, of approximately 500 psi and 750F, and at a rate that avoids excessive thermal strains in the steam pressure parts. The steam pressure is controlled by valve 58. During the initial period of low-steam pressure Operation, steam flow is 78 lbs. per second. The water flow is maintained substantially higher (approximately 14-15 lbs. per second) than the steam flow. The foregoing sequence of events maintains sufficiently high pressure drop across a water metering orifice assembly 316 (FIGS. 8 and 9) at the entrance to each steam generating tube boiler assembly 110 to insure stability of water and steam flow. The excess water is drained and recirculated from conduit 56. At steady-state operation water and steam flow are equal and range between 9 and .36 lbs. per second based on steam turbine load demand. The ignition sequence is started after the water circulating system is initiated. A source of gas and a small amount of oxidizer is ignited in plenum 18 by an ignition source (not shown). The combustion wave then propagates to each of the boiler assemblies 110 which ignites the pilot flame in each tube. After ignition of the pilot flame, the plenum 18 then becomes a fuel distribution chamber to supply fuel through pipes 66 to each of the combustion devices 110. Gaseous oxygen is subsequently supplied under pressure to the interior of each of the boiler assemblies 110. The pilot flame ignites the near stoichiometric mixture of fuel and oxygen in the combustion chamber to provide a steady-state clean combustion which results in the production of both water and carbon dioxide which are both non-noxious exhaust products.

An ignition detection system generally designated as 24 is supplied at the very top end of the housing 12. The detection device (not shown) is essentially comprised of individual detetors which detect ignition and steady-state operation of each of the boiler assemblies 110. When ignition is achieved in each of the boiler assemblies and a steady-state combustion is confirmed, the circulating water is heated by economizer 28 and heater 40 is shut down. An expansion joint 13 in housing 12 is provided as a transition member between the housing and member 15. As the individual boiler assemblies heat up, the surrounding cooler shell or housing expands and contracts at a different rate than the boiler housed therein. Additionally a vent opening 19 is provided in housing 12 to equalize the pressure between the inside of the housing 12 and the outside atmosphere. After steady-state combustion is achieved, the water is quickly converted to dry steam in each of the boiler assemblies. The steam is directed into the steam plenum chamber 20, out through conduit 50, into steam separator 52, and out through conduit 54 to the steam turbines, or the like. The exhaust gases from each of the boiler assemblies are directed into exhaust plenum 22 which directs gases out conduit 26 into the economizer section 28 and out through the exhaust pipe 30 to the atmosphere.

Turning now to FIG. 2, each of the combustion wavefuel tube feed pipes 66 from plenum chamber 18 (not shown) communicate with each of the inner fire tubes 114 of boiler assembly 110. The propane pilot light feed tube likewise joins tubes 66 adjacent the injector of each fire tube. Each of the combustion wave-fuel feed pipes extends through a fuel tube retaining coupling or nut 144, the nut being secured in the oxygen manifold tube sheet 128. The conduit 66 transitions into inner combustion wave-fuel inlet post 138 which extends into an oxygen injection post 132. The oxygen injection post is sealed to a removable retaining nut 126 that is an integral part of inner fire tube 114. The retaining nut is connected to the water manifold tube sheet 124. Tube sheet 124 has a series of axially aligned openings 125 to accommodate each of the 162 boiler assemblies 110. Six of the fire tubes generally (designated as 170) have inner combustor tubes 1 14' that are connected to retaining nut 126 and are removable for inspection. The six tubes are equidistantly spaced around the outer periphery of the oxygen and

water manifolds

128 and 124. Oxygen in chamber 130 enters annulus 136 in injection posts 132 through orifices 134. The annulus is defined by the outer surface of fuel combustion wave post 138 and the inner wall of the oxygen injection post 132. Pilot tube 140 extends through annulus 136 and terminates adjacent face 139 at the base of injection post 138, thus directing propane through opening 142 from source 68 to an area adjacent the point of impingement of fuel and oxidizer to assure ignition of the propellants.

Each of the fire tubes is comprised of an inner combustion tube 114--1l4' and an outer tube 112-112' with an annular space 122 therebetween. An infinitely variable spiral wrap structure 120 separates the inner and outer tubes (FIG. 7). Structure 120 may be a wire metallurgically bonded between

tubes

114 and 112.

Water from manifold 14 is routed into a series of radially extending passages 330 within the water tube sheet 124 to the annular space 122 formed by the concentric tubes.

A recessed chamber 118 is formed by terminating end 139 of inlet pipe 138 upstream of end 145 of oxygen injection post 132. The chamber 118 serves as a sort of propellant premixing chamber wherein fuel and oxidizer are premixed prior to main-stage combustion. Better propellant mixing and cleaner burning upon subsequent main-stage ignition is thereby achieved. A near stoichiometric mixture is substantially completely combusted in combustion chamber 116. Main-stage combustion results in temperatures in the range of 5500 to 6000F. Heat is transferred from the inside of the combustion chamber 116 through the walls of tubes 114-114 of the combustion chamber into the spirally directed water in annulus 122. The extremely high temperature quickly converts water to steam, the steam being directed down the rapidly diminishing angle of the spiral wrap structure 120, finally exiting past end 1 15 to tubes 112112' (FIG. 3). Each of the boiler assemblies 110 must obtain steady-state combustion before the compact steam generator becomes fully operational. As heretofore stated, the heat combustion detection mechanism at the top end 11 of the steam generator, assures that each of the fire tubes are in a steady-state condition.

Turning now to FIG. 3, the top end 11 of housing 12 is comprised of a steam plenum chamber generally designated as 20. Flange 216 peripherally extending from the plenum chamber 20 mates with flange 214 connected to housing 12. Each of the boiler assemblies 1 10 pass through and is supported by a tube sheet plate 210 that is positioned approximately midway between ends 11 and 11. Tube sheet 210 assures that each of the tire tubes are maintained in a spatial relationship, one from the other, thus assuring that the tubes do not contact each other within housing 12. Each of the outer tubes 112-112' terminates and are welded in tube sheet support plate 212. The inner tubes terminate in tube sheet 2211, with 156 of the tubes 114 being welded into the tube sheet and the six removable tubes 11 1' sliding in and being sealed against inner wall 176 of an annular sleeve 174 which is, in turn, welded to tube sheet 220. The inner combustion tubes 11 1 of the six special removable tubes generally designated as 170 terminate within exhaust nozzles 172. Nozzles 172 are housed within annular sleeves 174- that are welded to yet another tube sheet 221). Each of the six tubes 1711 has the inner combustion tube 114' removable from its companion outer concentric tube 112. The end 178 of tube 114. slides over surface 173 which is the upstream end of nozzle 172. The outer peripherial surface of inner tube 114' supports a pair of sealing rings 181) which seal the inner tube 114' with the outer sleeve 17 1 of nozzle assembly 172. Thus it can be seen that inner fire tube 114 connected to nut 126 may slide out through the ignition end of each of the six removable combustion boiler assembly devices 170. The ends 115 of outer tubes 112-112 terminate flush with the face 215 of tube sheet 212. The steam exits the annulus 122 past ends 115 into the interior of the steam plenum chamber 2h. The dry steam 236 passes out through opening 1 19 into the steam plenum chamber and is separated from the combustion exhaust gases by a bellows assembly generally designated as 218. The bellows assembly 218 is suspended axially between the exhaust tube sheet assembly 221) and flange 2211 connected to the upper end of plenum chamber 21). The bellows as sembly separates the exhaust gases from the dry steam collected in chamber 20. An annular heat sheild 232 is connected to the exhaust plenum 22 and extends past the length of the bellows assembly, thus protecting the bellows from the extremely hot exhaust gases 234 exiting into the exhaust plenum chamber 22. A similar axially extending heat shied 222 is intended to cause the dry steam to flow over the surface of bellows 218, thus cooling the bellows.

The nozzle assembly attached to each of the tubes is designed to maintain an equal pressure internally of each of the boiler assemblies 1111. Throat 163 defined by each of the nozzles function to assure an equal pressure within each of the fire tubes. Additionally, the restriction at throat 1153 enables the gases exiting through the exhaust nozzles 1611 to recover some of the pressure lost through the nozzle, thus aiding the ejection exhaust products 23 1 out through the exhaust plenum 22 into the exhaust duct 26 through economizer 28 and out exhaust pipe 311, as indicated in FIG. 1. A pair of expansion domes 22 1 and 226 are provided to accommodate for any radial expansion of the tube sheets 212 and 2211, respectively.

The ignition detection system 2 1 is comprised of several individual rods 238 that are directed through a perforated tube sheet 2 12, each detector having a sensor 2 1 1 to detect main-stage ignition of each of the fire tubes. Tube sheet 242 has several perforations 2 13, therethrough to pass exhaust gases 2341 through exhaust plenum chamber 22.

The exhaust nozzles generally indicated as 162 associated with concentric tubes 112-11 1 differ from the removable fire tubes 1'71) as follows.

The end 1 1 of inner tube 1141 is flared as it exits face 215 of tube sheet 212 and slides into a larger opening in and is welded to a tube sheet 22h. A transition mem her 164 fits within the inside wall 117 of end and tapers down to circumferentially fit snug with the outer surface of nozzle piece 162, thereby connecting the nozzle 162 to the end of outer tube 112. Inner tube 114, transition member 16 1 and nozzle portion 162 are welded together to form a solid mount for the end of fire tube 114. With the exception of the six removable boiler tube assemblies 176 heretofore described, all of the rest of the 156 boiler assemblies 1111 are fixed as heretofore described to tube sheet 2211.

Referring now to FIGS. 1, 5,. 6, and 7, the various views are enlargements of the individual boiler assemblies which comprise the heart of the compact steam generator 111. P11 4 depicts one of the 156 fixed concentric tubes suspended between

tube sheets

128, 124, 210, 212, and 2211. A fuel metering orifice 1511 is positioned within retainer 144 to properly meter the right amount of pressurized fuel into the inner fuelcombustion wave tube 1311. The fuel concentric tube 138 transitions into a thin wall section 143 just before terminating at opening 139. The pilot flame propane tube 711 enters through retainer 114 and is placed adjacent to the outer wall of inner tube 138. The pilot tube is flattened at section 141 and transitions into oxygen injection post 132 at section 1 111.. Flattened section 1 111 terminates at opening 112 and is flush with opening 139 of tube 13511. A. pair of spacer bars 1 1% is positioned 12111 from the position of the pilot tube 1411 so as to maintain the end 1319 of the fiiel injection post 138 concentrically within the chamber 13111 defined by the outside wall of post 138 and the inside wall of the oxygen injection post 132. This feature is clearly seen in F111. 5. At least a pair of openings 139 1 is provided in the oxygen injection post to direct gaseous oxygen under pressure within chamber 1311 into the annulus 136.

The variable pitch spiral support structure 1211 maintains the inner tube 1 1 1- concentrically within the outer tube 112, while providing a means to vary the velocity of water/steam through annulus. 122 so as to achieve maximum heat transfer. As the combustion gases cool down the length of the fire tubes, the pitch angle of the spirally wrap support structure 1211 is lessened so that the pitch more parallels the axis of the concentric tubes. The pitch angle of the spiral wrap is lessened as it nears the exit of the concentric tubes because the heat flux is not as great as it is closer to the burner, and therefore the velocity is not as high to maintain the tube wall temperature within acceptable limits. The pitch angle is reduced so that the flow more nearly parallels the axis of the concentric tubes so that the velocity is reduced, all to the purpose that the pressure drop required to force the water and steam through the tubes is not greater than that which is needed to ensure adequate cooling.

All of the outside tubes 112 and 112' are welded to the water manifold tube sheet 12 1, thereby providing a permanent insulation of the tubes to the tube sheet.

NOS. 6 and 7 more clearly define the individual fire tubes, both the fixed version and the removable version. FIG. 7 illustrates one of the six removable boiler assemblies 1711. The inner combustion tube 114' is removed from the compact steam generator by removing retaining nut 144 in the oxygen manifold 128 (FIG. 2) and by removing retaining nut 126 in the water manifold 124. The inner fire tube 114 can then be pulled out from the combustion end 8 of the compact steam generator 10. At the opposite end 178 of combustion 114' is a pair of sealing-type rings 180 which are designed to seal the space between the end of tube 114 and sleeve 174 (FIG. 6) which is welded to tube sheet 220. As the combustion tube 114' is removed axially from its retaining outer tube 112, the rings slip past the interface between the sleeve 174 and the end 178 of tube 114'. Thus it can be seen that the six fire tubes 114 of boiler assembly 170 can easily be removed from the steam generator for inspection purposes. As indicated before, the spirally wrapped structure 120 varies in pitch from a very tight pitch at the hot or combustion end of boiler assembly 170 to a lesser pitch as indicated at 120 towards the exhaust end 1 1. All of the tubes 1 12 and 112' terminate and are metallurgically bonded adjacent face 213 of tube sheet 212. The dry steam 236 exits the end 115 of tubes 112 and 112' into the steam plenum chamber 20. Throat 163 in nozzle portion 172 provides a means to regulate the internal pressure within the inner

concentric fire tubes

114 and 114 in all 162 fire tubes. The expanded portion 166 of inner fire tube 114 terminates around an inner sleeve 164 which tapers down to circumvent the outer periphery of nozzle 162. Weldments 182 connect nozzle portion 162, transition piece 164, and the expanded portion 166 of inner fire tube 114. The nozzles assure a relatively constant pressure internally of each of the boiler assemblies, so that during steady-state operation the tubes expand and contract an equal distance, thereby minimizing an equal force between tubes. The bellows (FIG. 3) 218 serves to take up any axial expansion or contraction of the tubes affixed to tube sheet 220 that supports all of the nozzles connected thereto.

As heretofore stated the

domes

224 and 226 connected to

tube sheets

212 and 220, respectively, take care of any radial expansion of

tube sheets

212 and 220.

Turning now to FIGS. 8 and 9, a series of water conducting holes or passages 330 are drilled parallel with the face 127 of water manifold 124 to provide a source of water to each of the individual boiler assemblies 1 10. Each of the passages 330 communicate with the water manifold 14 (FIG. 1). A series of holes 314 are drilled partially through tube sheet 124 and aligned traverse to passages 330. The holes 314 are aligned parallel with each of the fire tubes. Holes 314 extend a distance deeper than the intersecting passages 330 and step down to a smaller size as indicated as 320 (FIG. 9). A slanted hole 322 is drilled between orifice 125 in tube sheet 124 and the water passageway 320. A metering orifice assembly generally designated as 316 is positioned within the axially aligned hole 314 below the water passage 330. A precise orifice 318 is drilled through the orifice assembly to closely control the flow of water into passageway 122 defined by the concentric tubes, thereby providing the proper water pressure flow rate and flow stability into annulus 122. After performing the foregoing drilling operations, interconnecting all of the water passages in tube sheet 124, holes 314 are closed off by plug 328.

The various components associated with the compact steam generator may be fabricated from the following materials. The concentric tubes 112-112 and 114114' may be fabricated from nickel-ironchromium alloy such as ASME specifications SB408, SB407 and SB409. The

tube sheets

124, 128, 210, 212 and 220 may be fabricated from nickel-iron-chromium alloy as above or low alloy carbon steels, or low carbon steels, according to service temperatures and pressures. The housing 12 is normally constructed of low carbon steel and the expansion joint 13 of austenitic stainless steel. The bellows 218 is fabricated from nickel-ironchromium alloy SB408, SB or S8409 as above.

Different fuels and oxidizers may be utilized by adjusting the various parameters of the steam generator to suit, such as burner configuration, fuel and oxidizer supply pressures, ignition system, and ratio of oxidizer to fuel flow rates.

It will of course be realized that various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principle, preferred construction, and mode of operation of the invention have been explained and what is now considered to represent its best embodiment has been illustrated and described, vit should be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. A compact high-pressure high-temperature steam generator to produce superheated steam comprising:

an elongated housing having at least one manifold means connected to one end and steam collection and exhaust expulsion means positioned adjacent the opposite end of said housing, at least one elongated boiler tube assembly having a first and second end positioned within and connected to opposite ends of said housing, said boiler tube assembly having an inner combustion containing fire tube concentrically positioned within an outer tube, the outside wall of said inner fire tube and the inside wall of said outer tube forming an annular chamber thereby,

a source of water in said at least one manifold means in communication with said annular space at said first end of said boiler tube assembly,

an injector means connected to a first end of said inner fire tube of said at least one elongated boiler tube assembly, said injector means being in communication with and connected to said at least one manifold means, i

a source of fuel under pressure and a source of an oxidizer under pressure in said manifold means in communication with said injector means,

ignition means to ignite said fuel and said oxidizer in a combustion zone positioned adjacent to and downstream of said injector means in said first end of said boiler tube assembly,

a variable spiral structure means positioned in said annular chamber defined by said inner and outer tubes, the pitch of said variable spiral being closely spaced adjacent said combustion zone, thereby providing a means to vary the velocity of the flow of water and steam in said annular space, and pitch of the spirally oriented structure gradually opening up becoming more axially aligned with said elongated boiler tube assembly towards said second end of said tube, and

means to compensate for expansion and contraction of said concentric inner fire tube and said outer tube of said at least one boiler tube assembly relative to said housing means.

2. The invention as set forth in claim 1 wherein a multiplicity of individual boiler tube assemblies are contained within said housing.

3. The invention as set forth in claim 2 further comprising a boiler tube assembly equalization means affixed to said second end of said boiler tube assembly to equalize gas flow through each inner fire tube and to equalize water and steam flow through said annulus between said concentric tubes of said multiplicity of boiler tube assemblies to assure that each tube expands and contracts an equal amount.

The invention as set forth in claim 3 wherein said equalization means is a nozzle, said nozzle being affixed to a nozzle tube sheet attached to said housing.

5. The invention as set forth in claim 4 wherein said nozzle additionally serves to recover a portion of said pressure within said multiplicity of boiler tube assemblies to aid in the expulsion of exhaust products from said ignited fuel and oxidizer.

6. The invention as set forth in claim 5 wherein means are provided to remove said inner fire tube from said at least one elongated boiler tube assembly to facilitate replacement and repair of said inner tube.

7. The invention as set forth in claim 6 wherein said means to remove said inner fire tube includes fastening means at said first end of said inner fire tube that is threadably engaged with at least one manifold means, said inner fire tube having at least one ring positioned within a groove in the outside wall of a second end of said fire tube, said ring being sealably and slidably engaged with an inner wall of said nozzle.

The invention as set forth in claim 7 further comprising a dome shaped structure centrally positioned and connected to said nozzle tube sheet to accommodate for any radial expansion of said tube sheet during operation of said steam generator.

9. The invention as set forth in claim 8 wherein said means to separate said combustion exhaust products from said superheated steam is a bellows assembly, said bellows being connected at one end to said nozzle tube sheet, the opposite end of said bellows being connected to said housing, said bellows serving to accommodate for expansion and contraction of said multiplicity of boiler tube assemblies during operation of said steam generator. lid. The invention as set forth in claim 1 wherein said housing and said at least one elongated boiler tube as sembly contained therein is oriented substantially vertically, said first end containing said injector means is positioned at the bottom of said vertically oriented housing and boiler tube assembly.

ll ll. The invention as set forth in claim l wherein said fuel is a methane gas under pressure.

112. The invention as set forth in claim 1 wherein said oxidizer is gaseous oxygen under pressure.

13. The invention as set forth in claim 11 wherein said boiler tube assembly injector is comprised of an open ended inner tube that terminates within an open ended outer oxidizer body positioned thereover, the outside wall of said inner tube and said inside wall of said outer oxidizer body forming an annular space thereby, said ltd inner tube having fuel metered therethrough under pressure in a chamber upstream of said injector, said oxidizer being directed through at least one orifice defined by the outer oxidizer body, into said annular chamber, said orifice being positioned in an upstream portion of said oxidizer body, said fuel mixing with said oxidizer where said fuel exits said open ended inner tube.

114. The invention as set forth in claim ll wherein the end of said open ended inner tube is recessed upstream of the end of said open ended outer oxidizer body thereby forming a fuel and oxidizer mixing chamber to premix said fuel and oxidizer prior to main-stage combustion in saidcombustion zone.

15. The invention as set forth in claim Ml further comprising an individual source of fuel for a pilot flame, said fuel being directed to said open end of said inner tube of said injector means by a pipe positioned in said annulus between said inner fuel tube and said outer oxidizer body.

16. The invention as set forth in claim 15 wherein said pilot flame is supplied by a source of propane fuel.

17. The invention as set forth in claim 1 wherein said oxidizer under pressure is introduced into each of said inner combustion fire tubes prior to introduction of said fuel' through said injector means so as to provide an oxygen rich atmosphere in said inner fire tube to prevent propagation down said inner fire tube upon said ignition of said fuel and oxidizer.

18. The invention as set forth in claim T wherein the temperatures within said combustion zone within said inner fire tube range from 500(1 to 600tlF 19. The invention as set forth in claim 1 wherein said source of water is preheated to a temperature between l5tlF and 250F and the flow of said water is directed into a water manifold, and from there through said annular chamber defined by said inner and outer tubes making up said at least one boiler tube assembly prior to start-up of said steam generator to narrow the temperature differential in said boiler tube assembly as well as downstream steam pressure components after initiation of said ignition sequence.

20. The invention as set forth in claim i9 wherein said preheated water communicating with said injector means is introduced upstream of said combustion zone to prevent burn up of said boiler tube assemblies upon initiation of said steam generator.

211. The invention as set forth in claim 2@ wherein said preheated water is metered through a metering orifice assembly positioned in said water manifold thereby closely controlling the flow of water into said annular chamber to assure flow stability.

22. The invention as set forth in claim 21 wherein said water is preheated by a separate heater source prior to start-up of said steam generator, said separate heater is subsequently shut down after steady-state operation is achieved, the water then is rerouted in a conduit that passes through an economizer section, the

water in said conduit is then heated by the exhaust products as they pass over said conduit prior to expulsion of said exhaust products from said economizer section.

23. The invention as set forth in claim ll further comprising an expansion joint in said housing surrounding said at least one elongated boiler tube assembly to compensate for the difference in the rate of expansion between said at least one boiler tube assembly and said elongated housing.

24. The invention as set forth in claim 1 wherein the 25. A method of operating a compact high-pressure high-temperature steam generator to produce superheated steam comprising the steps of:

preheating a source of water by a first heater means,

circulating and metering said preheated water through at least one elongated boiler tube assembly prior to main-stage ignition of said steam generator, said boiler tube assembly having a first and a second end positioned within and connected to opposite ends of a housing, said boiler tube assembly having an inner combustion-containing fire tube concentrically positioned within an outer tube, the outside wall of said inner fire tube and the inside wall of said outer tube forming an annular chamber thereby, said preheated water being metered into and directed through said chamber,

injecting a gaseous oxygen through an injector at said first end of said at least one boiler tube assembly into said combustion-containing fire tube prior to main-stage ignition of said steam generator,

injecting a source of pilot fuel into said combustioncontaining fire tube through said injector prior to ignition of said steam generator,

igniting said pilot fuel by directing a combustion wave through at least one conduit leading from a combustion wave plenum chamber into said first end of said at least one boiler tube assembly, after ignition of said pilot fuel, said combustion wave plenum chamber subsequently becomes a main fuel supply plenum that directs said main fuel through said conduit into said first end of said boiler tube assembly containing said injector,

mixing said main fuel with said oxidizer in stoichiometric proportions within said combustioncontaining inner tube,

igniting said mixture by said burning pilot fuel thus providing main-stage combustion in said combustion-containing inner fire tube of said at least one boiler tube assembly,

equalizing the gas flow through said inner fire tube by directing said gas flow through a nozzle assembly means at said second end of said boiler tube assemy.

controlling the flow rate of said preheated water metered into said chamber by providing a variable spiral structure in said chamber between the outer wall of said combustion-containing inner tube and the inner wall of said outer tube to transfer heat from the combusted oxidizer and fuel, the pitch of said variable pitch structure gradually opening up becoming more axially aligned with said boiler tube assembly towards said second end of said assembly,

separating means at said second end of said boiler tube assembly to separate the exhaust products from the superheated steam, said separating means being a bellows assembly,

heating said circulating water after main-stage combustion by bypassing said first heater means and directing said water into an economizer means, said economizer means serves to transfer exhaust gas heat into said circulating water thus, preheating the water prior to metering said water into said chamber defined between said inner and outer tubes of said boiler tube assembly, and

collecting means to collect said superheated steam for use to drive a steam turbine or the like.

Claims

1. A compact high-pressure high-temperature steam generator to produce superheated steam comprising: an elongated housing having at least one manifold means connected to one end and steam collection and exhaust expulsion means positioned adjacent the opposite end of said housing, at least one elongated boiler tube assembly having a first and second end positioned within and connected to opposite ends of said housing, said boiler tube assembly having an inner combustion containing fire tube concentrically positioned within an outer tube, the outside wall of said inner fire tube and the inside wall of said outer tube forming an annular chamber thereby, a source of water in said at least one manifold means in communication with said annular space at said first end of said boiler tube assembly, an injector means connected to a first end of said inner fire tube of said at least one elongated boiler tube assembly, said injector means being in communication with and connected to said at least one manifold means, a source of fuel under pressure and a source of an oxidizer under pressure in said manifold means in communication with said injector means, ignition means to ignite said fuel and said oxidizer in a combustion zone positioned adjacent to and downstream of said injector means in said first end of said boiler tube assembly, a variable spiral structure means positioned in said annular chamber defined by said inner and outer tubes, the pitch of said variable spiral being closely spaced adjacent said combustion zone, thereby providing a means to vary the velocity of the flow of water and steam in said annular space, the pitch of the spirally oriented structure gradually opening up becoming more axially aligned with said elongated boiler tube assembly towards said second end of said tube, and means to compensate for expansion and contraction of said concentric inner fire tube and said outer tube of said at least one boiler tube assembly relative to said housing means.

4. The invention as set forth in claim 3 wherein said equalization means is a nozzle, said nozzle being affixed to a nozzle tube sheet attached to said housing.

8. The invention as set forth in claim 7 further comprising a dome shaped structure centrally positioned and connected to said nozzle tube sheet to accommodate for any radial expansion of said tube sheet during operation of said steam generator.

9. The invention as set forth in claim 8 wherein said means to separate said combustion exhaust products from said superheated steam is a bellows assembly, said bellows being connected at one end to said nozzle tube sheet, the opposite end of said bellows being connected to said housing, said bellows serving to accommodate for expansion and contraction of said multiplicity of boiler tube assemblies during operation of said steam generator.

10. The invention as set forth in claim 1 wherein said housing and said at least one elongated boiler tube assembly contained therein is oriented substantially vertically, said first end containing said injector means is positioned at the bottom of said vertically oriented housing and boiler tube assembly.

11. The invention as set forth in claim 1 wherein said fuel is a methane gas under pressure.

12. The invention as set forth in claim 1 wherein said oxidizer is gaseous oxygen under pressure.

13. The invention as set forth in claim 1 wherein said boiler tube assembly injector is comprised of an open ended inner tube that terminates within an open ended outer oxidizer body positioned thereover, the outside wall of said inner tube and said inside wall of said outer oxidizer body forming an annular space thereby, said inner tube having fuel metered therethrough under pressure in a chamber upstream of said injector, said oxidizer being directed through at least one orifice defined by the outer oxidizer body, into said annular chamber, said orifice being positioned in an upstream portion of said oxidizer body, said fuel mixing with said oxidizer where said fuel exits said open ended inner tube.

14. The invention as set forth in claim 11 wherein the end of said open ended inner tube is recessed upstream of the end of said open ended outer oxidizer body thereby forming a fuel and oxidizer mixing chamber to premix said fuel and oxidizer prior to main-stage combustion in said combustion zone.

15. The invention as set forth in claim 14 further comprising an individual source of fuel for a pilot flame, said fuel being directed to said open end of said inner tube of said injector means by a pipe positioned in said annulus between said inner fuel tube and said outer oxidizer body.

17. The invention as set forth in claim 1 wherein said oxidizer under pressure is introduced into each of said inner combustion fire tubes prior to introduction of said fuel through said injector means so as to provide an oxygen rich atmosphere in said inner fire tube to prevent propagation down said inner fire tube upon said ignition of said fuel and oxidizer.

18. The invention as set forth in claim 1 wherein the temperatures within said combustion zone within said inner fire tube range from 5000*F to 6000*F.

19. The invention as set forth in claim 1 wherein said source of water is Preheated to a temperature between 150*F and 250*F and the flow of said water is directed into a water manifold, and from there through said annular chamber defined by said inner and outer tubes making up said at least one boiler tube assembly prior to start-up of said steam generator to narrow the temperature differential in said boiler tube assembly as well as downstream steam pressure components after initiation of said ignition sequence.

20. The invention as set forth in claim 19 wherein said preheated water communicating with said injector means is introduced upstream of said combustion zone to prevent burn up of said boiler tube assemblies upon initiation of said steam generator.

21. The invention as set forth in claim 20 wherein said preheated water is metered through a metering orifice assembly positioned in said water manifold thereby closely controlling the flow of water into said annular chamber to assure flow stability.

22. The invention as set forth in claim 21 wherein said water is preheated by a separate heater source prior to start-up of said steam generator, said separate heater is subsequently shut down after steady-state operation is achieved, the water then is rerouted in a conduit that passes through an economizer section, the water in said conduit is then heated by the exhaust products as they pass over said conduit prior to expulsion of said exhaust products from said economizer section.

23. The invention as set forth in claim 1 further comprising an expansion joint in said housing surrounding said at least one elongated boiler tube assembly to compensate for the difference in the rate of expansion between said at least one boiler tube assembly and said elongated housing.

24. The invention as set forth in claim 1 wherein the temperature of the superheated steam exiting said steam collection end of said housing is between 500*F and 1000*F.

25. A method of operating a compact high-pressure high-temperature steam generator to produce superheated steam comprising the steps of: preheating a source of water by a first heater means, circulating and metering said preheated water through at least one elongated boiler tube assembly prior to main-stage ignition of said steam generator, said boiler tube assembly having a first and a second end positioned within and connected to opposite ends of a housing, said boiler tube assembly having an inner combustion-containing fire tube concentrically positioned within an outer tube, the outside wall of said inner fire tube and the inside wall of said outer tube forming an annular chamber thereby, said preheated water being metered into and directed through said chamber, injecting a gaseous oxygen through an injector at said first end of said at least one boiler tube assembly into said combustion-containing fire tube prior to main-stage ignition of said steam generator, injecting a source of pilot fuel into said combustion-containing fire tube through said injector prior to ignition of said steam generator, igniting said pilot fuel by directing a combustion wave through at least one conduit leading from a combustion wave plenum chamber into said first end of said at least one boiler tube assembly, after ignition of said pilot fuel, said combustion wave plenum chamber subsequently becomes a main fuel supply plenum that directs said main fuel through said conduit into said first end of said boiler tube assembly containing said injector, mixing said main fuel with said oxidizer in stoichiometric proportions within said combustion-containing inner tube, igniting said mixture by said burning pilot fuel thus providing main-stage combustion in said combustion-containing inner fire tube of said at least one boiler tube assembly, equalizing the gas flow through said inner fire tube by directing said gas flow through a nozzle assembly means at said second end of said boiler tube assembly, controlling the flow rate of said preheated wateR metered into said chamber by providing a variable spiral structure in said chamber between the outer wall of said combustion-containing inner tube and the inner wall of said outer tube to transfer heat from the combusted oxidizer and fuel, the pitch of said variable pitch structure gradually opening up becoming more axially aligned with said boiler tube assembly towards said second end of said assembly, separating means at said second end of said boiler tube assembly to separate the exhaust products from the superheated steam, said separating means being a bellows assembly, heating said circulating water after main-stage combustion by bypassing said first heater means and directing said water into an economizer means, said economizer means serves to transfer exhaust gas heat into said circulating water thus, preheating the water prior to metering said water into said chamber defined between said inner and outer tubes of said boiler tube assembly, and collecting means to collect said superheated steam for use to drive a steam turbine or the like.