WO1986000387A1

WO1986000387A1 - Pressurized cyclonic combustion method and burner for particulate solid fuels

Info

Publication number: WO1986000387A1
Application number: PCT/US1985/001190
Authority: WO
Inventors: Franklin D. Hoffert; J. David Milligan; James A. Morrison
Original assignee: Power Generating, Inc.
Priority date: 1984-06-29
Filing date: 1985-06-24
Publication date: 1986-01-16
Also published as: EP0188525A1

Abstract

A pressurized cyclonic combustion method and a cylindrical burner apparatus (10) for pressurized combustion of particulate solid fuels to produce a pressurized clean effluent product gas. In the burner, the particulate solids such as wood chips are fed tangentially into a primary combustion chamber (15) at its inlet end (16) and flow at high tangential velocity in a helical path through the burner. Oxygen-containing combustion gas such as air is supplied tangentially at high velocity through multiple ports (18a, 18b, 18c) spaced apart longitudinally along the burner length to maintain and/or increase the high tangential velocity and produce high centrifugal forces on the particulate solids and provide for prolonged combustion and produce high burner volumetric heat release rates exceeding about 400,000 Btu/hr ft3. A choke opening (20a) is provided centrally located at the combustion chamber outlet end for promoting prolonged combustion of solid fuel particles upstream of a quench zone. A secondary combustion chamber (25) is provided downstream of the choke opening (20a). Also, a quench gas stream (30) is introduced into the choke zone preferably in a tangential flow direction opposite to the helical flow. In the burner primary combustion chamber (15), so as to effectively mixt the quench gas with the hot effluent gas and/reduce its temperature, usually to about 1400-2000oF as determined by downstream metallurgy considerations. The resulting pressurized effluent gas can be further processed to remove any existing fine solids, and the clean pressurized gas can be expanded in a gas turbine to produce useful power.

Description

PRESSURIZED CYCLONIC COMBUSTION METHOD AND BURNER FOR PARTICULATE SOLID FUELS

BACKGROUND OF INVENTION

This invention pertains to a pressurized cyclonic combustion method and burner apparatus for effective com¬ bustion of particulate solid fuels to produce clean pres¬ surized hot effluent gases. It pertains ^"particularly to_ a cylindrical pressurized burner which utilizes helical flow patterns to provide prolonged combustion of the fuel solids and uses an intermediate choke zone and an air quench step to improve combustion and control temperature of the effluent gases produced.

Various types of burners for particulate solid fuels have been previously proposed such as disclosed by U.S. Patent 2,614,573 to Miller et al; U.S. Patent 2,769,411 to Simmons; and U.S. Patent 2,881,720 to Lotz which utilize tangential swirling flow patterns and a restricted exit opening intended to retain solids in the burner longer for more complete combustion. U.S. 3,199,476 to Nettel discloses a similar burner for coal having dual tangential inlet for the small and coarser coal particles, a restricted throat exit for combustion gases and a lower drain port for slag removal. Other similar burners have been disclosed by U.S. 3,244,220 to Kloecher; U.S. 3,453,976 and U.S. 3,472,185 to Burden et al, but they do not have restricted outlets and are not intended for pressurized operations. U.S. 3,777,678 and U.S. 4,053,505 to Lutes et al disclose a horizontal cyclonic type burner for combustible solid materials in which the fuel is introduced tangentially into the combustion chamber at its inlet and combustion air is introduced tangen¬ tially along the length of the burner, which has a restricted choke outlet. Also, U.S 4,422,388 to Raskin discloses a horizontal cylindrical burner for solid fuel introduced tangentially at one end, but maintains a fluidized bed of fuel in its lower portion. In addition, scroll or dual register horizontal fired type burners such as the Coen DAZ burner have been used for the combustion of the air conveyed solid fines. Such burners have dual registers with concen¬ tric louvers which in effect divide the air stream into two counter-rotating concentric streams which scrub against each other and provide turbulent mixing action for the fuel introduced into the annular space between the dual air streams.

It is noted that these prior art burners are useful for burning particulate solids at essentially atmospheric pressure for incineration and also for the recovery of heat energy. However, further improvements are needed in combus¬ tion of particulate solid fuels at above atmospheric pressure and in burner design for achieving higher throughputs for the fuels and higher heat release rates in the burner to produce relatively solids-free pressurized hot effluent gases suitable for power recovery applications.

Burning solid fuels, unlike burning vaporous and volatile liquid fuels, require increased reaction time constants which are orders of magnitude longer for complete combustion, i.e., mass diffusivity is rate controlling in the rapid oxi¬ dation of solid fuels. Historically, this longer combustion time requirement has been minimized by solids size reduction, as in firing pulverized coal instead of chunk or briquette coal. While such size reduction is beneficial, it still does not permit the firing of solid fuel materials at combustion rates which approximate those attained for non- solid fuels. This difference is most apparent when volume¬ tric energy releases for various heat generators are compared.

In order to increase the fuel particle retention time in a burner, which time varies inversely with combustor size for a given heat release, a new method for achieving in¬ creased dual phase residence time for the solid fuel par¬ ticles has now been developed. In this method, the solid

,γπ"yτE s πεε fuel particles having higher mass are retained for very long periods of time relative to the lower mass combustible volatiles and gaseous materials in a cylindrical combustion chamber having an aspect ratio of longitudinal length more than about twice that of the chamber inside diameter. Into this combustion chamber the particulate solid fuel is intro¬ duced tangentially in lean phase transport near the inlet end. The fuel tangential velocities in the burner are sufficient so that very high centrifugal forces are imposed on the fuel particles which are swirled around the inner periphery of the burner, while the gaseous material not as subject to such centrifugal forces and moving by molecular motion is free to move along the burner longitudinal axis while rapidly combusting, and then escape through a modula¬ ting restriction opening at the burner exit end.

The solid fuel particles are maintained in this helical flow pattern, trapped by their relatively high mass and high rotational velocity, slowly moving helically and at high Reynolds number condition toward the outlet end of the combustion chamber. This extended combustion path is signi¬ ficantly prolonged by the tangential injection of combustion air along the longitudinal axis of the burner at a high velocity. This combustion air is introduced under conditions of high tangential velocity and associated high Reynolds number, so as to impart an additional tangential acceleration to the fuel particles sufficient to overcome any reduction in velocity due to flowing resistance of the orbiting parti¬ cles. Accordingly, this combustion process is continued under high Reynolds number conditions until the fuel particles are sufficiently destructed to produce gaseous products which escape the centrifugal forces in the combustion chamber and pass out at the burner exit end.

The gas residence time in the combustion chamber is a function of the volumetric throughput only, however, the fuel solids residence time is pathway dependent and is determined by the combustion chamber circumference and the number of revolutions divided by the velocity of the parti¬ cles. Therefore, a particle can be retained in the burner to destruction for a much longer time than can volatile fuels and products of combustion which accompany the particle.

This improved combustion method also promotes more rapid combustion of solid fuels by forcing the circulating particles closely adjacent to the hot radiating interior surfaces of the combustion chamber. This radiating surface is quite large relative to the particle and served to sustain the reaction by constantly providing the threshold energy needed for combustion. The addition of the acceleration air along the helical, path, of the fuel particle promotes rapid oxidation by continually supplying fresh oxygen very near the particulate fuel solids undergoing reaction.

The addition of combustion air tangentially along the length of the combustion chamber also provides an additional benefit to the mechanical integrity of the burner by buffer¬ ing and tempering the surface of the heat resistant refrac¬ tory insulation material lining the interior of the burner chamber from the very hot products of combustion. This air addition prevents the insulation surface from reaching reaction temperatures which would be deleterious to the insulation. This air-sweep is enhanced by the design and installation of the air inlet tuyeres.

Accordingly, it is an object of the present invention to provide a pressurized cyclonic combustion method and burner apparatus for particulate solid fuels which provides for prolonged combustion of the fuel particles at conditions of high tangential velocities, high centrifugal forces, and high Reynolds numbers. Another object is to provide such a burner which operates at highly turbulent conditions and high Reynolds numbers and provides very high volumetric heat release rates approaching those for liquid and gaseous fuels. Another object is to provide a burner for solid

-•T ? particulate fuels such as wood chips which produces a clean hot pressurized effluent gas stream suitable for use in power producing processes.

SUMMARY OF INVENTION

The present invention provides an improved combustion method and burner apparatus for the pressurized combustion of particulate solid materials to produce hot pressurized effluent gases having low solids content. In the method of the invention, a particulate solid fuel having particle size smaller than about 0.70 inch major dimension is pressurized and pneumatically fed tangentially into the burner primary combustion chamber operated at a pressure at least about 3 atm. absolute and usually not exceeding about 20 at . pressure. The superficial gas velocity for fuel transport into the burner primary combustion chamber should be at least about 80 ft/sec and preferably about 90-120 ft/sec. An oxygen-containing combustion gas is also supplied into the combustion chamber tangentially through multiple tuyeres at a high tangential velocity exceeding about 100 ft/sec and at a Reynolds number relative to the tuyere openings exceed¬ ing about 900,000. The fuel particles and combustion gas in the combustion chamber flow in a swirling helical motion or flow pattern at high tangential velocity exceeding about 100 ft/sec, so as to provide high centrifugal forces on the particles exceeding about 140 gravitational or 'g' units. Because of the rotational motion and the high centrifugal forces generated on the fuel particles, the burner according to the present invention retains the fuel particles in the burner combustion chamber near the hot wall for a substan¬ tially longer time than occurs for conventional prior art burners, so that the fuel solids are more rapidly and com¬ pletely combusted. Also, this high rotational velocity and high centrifugal force flow pattern not only retains the particulate solids in the burner longer for more complete

SUBSTITUTE SHEET combustion, but additionally achieves flows at very high

Reynolds numbers exceeding about 150,000 and provides for very high volumetric heat release rates in the burner ex-

3 ceeding about 400,000 Btu/hr ft chamber volume, which substantially exceed the heat release rates provided by conventional solid fuel burners. Furthermore, the present burner advantageously provides heat release rates for burning particulate solid fuels comparable to those for burning liquid or gaseous fuels in gas turbine an -internal combus¬ tion engines.

Accordingly, it is an important feature of the present invention that the fuel particles remain near the hot radiant wall of the combustion chamber until all volatile matter is continually evolved from the fuel particles, which steadily diminish in size until the particles are substan¬ tially completely combusted into gas. Also, because the burner inside length to diameter ratio is at least about 2.5 and can advantageously be up to about 10, this cylindrical configuration contributes to the fuel particles remaining in the burner primary combustion zone significantly longer for more complete combustion than for prior burner configurations.

The hot pressurized effluent gas produced in the primary combustion zone is usually at temperature of about 2100- 2800° F and is cooled by mixing it with a quench gas such as additional air or steam in a quench zone to reduce the gas temperature to a lower temperature as desired, such as limited only by the characteristics of a power recovery turbine, and usually to about 1400-2000° F. Any remaining solids in the effluent gas can be removed in a gas-solids separation step prior to expansion in a gas turbine for producing useful power.

The present invention also provides a burner apparatus for pressurized combustion of particulate solid fuels to produce a hot pressurized effluent or product gas. The burner includes an elongated cylindrical shaped pressurizable

- outer metal casing, an inner refractory lining located adjacent the casing inner wall to provide an elongated cylindrical shaped primary combustion chamber, a tangential opening located near the burner inlet end for feeding a particulate fuel tangentially into the primary combustion chamber, a plurality of tangentially oriented openings each having an aspect ratio at least about 2:1 and spaced apart longitudinally along the length of the burner for intro¬ ducing a combustion gas tangentially into the combustion chamber, a choke opening located at the combustion chamber exit end, and at least one aperture located tangentially in the choke opening, the aperature being preferably oriented opposite to the tangential opening in the combustion chamber inlet end, whereby the particulate fuel is combusted rapidly at high rotational velocity and high volumetric heat release rate and the resulting hot effluent gas is quenched and cooled to provide a lower temperature pressurized product gas. Downstream from the choke, a secondary cylindrical combustion chamber is connected pressure-tightly to the outer casing of the primary combustion chamber. The choke zone between the two chambers is tapered outwardly into the secondary chamber, so as to minimize irrecoverable pressure differential for the product gas flowing therethrough.

The burner of the present invention is useful for burning various combustible particulate solid materials, such as sawdust, wood chips, trim and shavings, petroleur. coke, and mixtures thereof. The burner is particularly useful for combusting wood chips smaller than about 0.70 inch and preferably smaller than about 0.130 major dimension.

It is an advantage of the present pressurized combustion method and burner apparatus that because of the greater length/diameter ratio provided in the burner- and the high rotational velocities and centrifugal forces achieved for the fuel particles, the particulate solids are retained in the burner for a significantly longer time for achieving more complete combustion, thereby producing higher volume¬ tric heat release rates and a cleaner product gas. Because of the high rotational velocity of the combustible particles in the burner and the resulting high centrifugal forces developed, the burner is substantially unaffected by gravity and can be operated while oriented in any direction. Also because the resulting hot effluent gas is effectively quenched with air, steam or mixtures thereof, the effluent gas is provided at a controlled lower temperature which is advantageous for subsequent power recovery from the gas in an engine or turbine.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be further described with reference to the accompanying drawings, in whichr

Fig. 1. shows a longitudinal cross-sectional view of a cyclonic burner assembly according to the present invention, including the primary and secondary combus¬ tion chambers;

Fig. 2 shows a cross-sectional view of the burner feed inlet taken along lines 2-2 of Fig. 1;

Fig. 3 shows a cross-sectional view taken through the burner choke section along lines 3-3 of Fig. 1;

Fig. 4 is a graph showing the centrifugal forces plotted vs. tangential velocity for fuel particles in the burner, compared to similar conventional burners; and

Fig. 5 is a graph showing volumetric heat release rate plotted vs. internal pressure for the burner of the present invention compared to similar conventional burners.

SUBSTITUTE SHEET DETAILED DESCRIPTION OF INVENTION

A pressurized cyclonic burner for providing prolonged pressurized combustion of particulate solid fuels and constructed and operated in accordance with the present invention is shown in Fig. 1. In the illustrated preferred embodiment, the burner asse bley 10 has a cylindrical shaped pressurizable outer metal casing 12 and a head 13, which are retained together by bolted flange 12a. -A refractory lining material 14 is located adjacent the inner wall of casing 12 and within head 13 and defines a primary combustion chamber 15, with the lining material being suitable for withstanding temperatures up to about 3000° F.

The particulate solids combustible fuel material, such as wood chips preferably smaller than about 0.130 inch major dimension, is uniformly fed by suitable means (not shown) into the burner primary combustion chamber 15 at tangential inlet connection 16 located near the inlet end head 13 of the burner. In the chamber, the solids are air entrained at tangential velocity at least about SO ft/sec and preferably 100-200 ft/sec. If desired, to improve ignition of the particulate solids feed entering the combustion chamber, the end wall 14a of refractory lining 14 can be made convex shaped and extend axially into the combustion chamber to a location not more than about 0.5 the burner internal diair.eter past the plane of the fuel inlet 16, as shown in dotted lines in Fig. 1. This arrangement results in the solids feed material moving closer to the hot refractory surface 14a to provide for more effective radiant heating of the feed.

Multiple tangential inlet openings or tuyeres 18a, 18b, 18c, etc., are provided through casing 12 and lining 14 and spaced apart along the length of the burner for supplying combustion air into the combustion chamber. The tuyere openings 18, 18a, etc., are preferably provided as double rows, as shown in Fig. 2 sectional drawing, with at least 3

^SUBST and usually not more than 20 such tuyere openings in each row. The tuyere openings 18, 18a, etc., are made elongated in shape in a direction parallel to the longitudinal axis of the burner. The tuyere openings preferably should have a length/width aspect ratio exceeding about 2:1 and preferably in a range of 3:1 to 5:1.

The combustion air is supplied through the tuyere openings at a velocity exceeding about 100 ft/sec and at a Reynolds number relative to the tuyere openings exceeding about 900,000. The combustion air is preferably supplied through the tuyeres at tangential velocity of 110-150 ft/sec and at Reynolds number of 1,000,000-3,000,000. A flanged clean-out opening 17 is provided through the lower portion of head 13 and includes a removable refractory plug 17a. Also, a sight tube 19 is provided through the upper portion of head 13 for viewing the combustion process within chamber 15.

The combustion chamber 15 is operated at internal . pressure of about 3-20 atm. absolute and preferably 4-10 atm. The useful weight ratio of combustion air to the particulate fuel feed ranges from about 1.0 to 4.0 times the stoichiometric value.

At the exit end of the burner combustion chamber 15, a centrally-located choke element 20 is provided which has a generally cylindrical opening 20a therethrough, and has. a cross-sectional area appreciably smaller than that for the combustion chamber 15. The opening 20a in choke 20 should be made small enough to help retain the circulating combust¬ ing solids in the primary combustion chamber, so as to prolong the solids residence time for substantially complete combustion therein, but the opening is not made so small that undesired differential pressure for the effluent gases flowing through the choke is appreciably increased. The cross-sectional area of the choke 20 should be at least about 30% that of the combustion chamber 15, and usually is 40-50% the cross-sectional area of the combustion chamber. Also, if desired to facilitate the passage of ash from the primary combustion chamber, the choke opening 20a can be located near the lower portion of the chamber, or alter¬ natively, the opening can be made non-circular shaped with a portion of the opening extending downwardly towards the - lower wall of the chamber. This choke 20 is usually made annular shaped and is preferably formed as a castable re¬ fractory material that is more abrasion-resistant than the refractory lining 14. The choke 20 preferably has a curved inlet surface 20b and a tapered outer surface 20c to assist in retaining it in place in the surrounding refractory material 24. Also, if desired, a refractory cement material 21 can be used between the choke element 20 and the surround¬ ing refractory material 24 to help hold the choke in place.

For the burner of the present invention, visual obser¬ vations made of the solid fuel particles in the burner during combustion operation indicate that the particles move in a helical flow path which is nearly perpendicular to the longitudinal axis of the burner, thus indicating that the helix angle of the particle path relative to the burner axis is only slightly less than 90°. This flow pattern indicates that the fuel particles make a great number of revolutions in the burner primary combustion chamber until they are completely devolatized and consu.ec. Also, because of the particle rotational velocity, the particulate solids respond to high centrifugal forces produced in the burner and the gaseous products of combustion respond to Reynolds numbers which are very high. By using the burner configu¬ ration of this invention, the volumetric heat release rates for pressurized burning of particulate solid fuels are significantly higher than for conventional type burners, and approach heat release rates which occur for burning liquid or gaseous fuels in internal combustion engines.

Because of the high tangential velocity and high centri¬ fugal forces generated on the solid fuel particles in the burner primary combustion zone 15, the particulate solids make very many revolutions therein and are thus retained in the combustion zone adjacent the hot refractory lining 14 for e substantially longer residence time until all the solids have been devolatized and combusted, thereby achiev¬ ing the very high volumetric heat release rates. The centri¬ fugal force produced on the particulate solids being burned exceeds about 140 times earth gravity 'g' and is preferably about 150-300 g, and Reynolds number for the hot effluent gases is at least about 150,000 and preferably 200,000- 500,000. The volumetric heat release rates in the burner primary combustion chamber is at least about 400,000 Btu/hr

3 ft primary combustion chamber volume, and is preferably

500,000 to 3,000.000 Btu/hr ft³.

A secondary cylindrical shaped combustion chamber 25 is preferably provided downstream from the primary chamber 15 and choke 20, and about 25% of the total combustion may occur in the secondary chamber. Secondary combustion chamber 25 has a cylindrical shaped metal casing 22 surround¬ ing a refractory lining 24. The casing 22 is connected pressure-tightly to the casing 12 of primary combustion chamber 15 by bolted flange 26, and can be connected pressure- tightly to downstream ducting as desired by flange 27. Also, refractory lining 24 abuts against the refractory lining 14 at a location radially outwardly from choke 20. A reduced diameter intermediate zone 28 is provided immediately downstream from choke 20 and usually has a length: diameter ratio of about 1:1 to 1.5:1. The intermediate zone 28 is followed by outwardly tapered zone 29 connecting to a full diameter zone of secondary chamber 25 having an inside diameter approximately the same as for the primary combustion chamber 15.

A quench gas such as additional pressurized air or steam is provided into secondary chamber 25 through at least one opening 30 through refractory 24 located immediately downstream from choke 20 for quenching and cooling the hot __{χ 3}_

effluent gas flowing from the choke. Usually two openings 30 are provided and are preferably oriented in a tangential direction opposite to that for the fuel inlet 16 and multiple openings 18 for the combustion air in the primary combustion chamber 15. Thus, the counter or oppositely flowing quench gas stream flowing tangentially from conduit 32 through openings 30 provides a high velocity shear type mixing flow pattern for the quench gas and the hot effluent gas upstream from secondary combustion chamber 24, thereby advantageously achieves highly effective mixing of the hot effluent gas and the quench gas so as to lower the hot effluent gas temp¬ erature from about 2700° F to a lower temperature, such as 1500-1800° F suitable for passing to a gas turbine. The preferred quench gas is pressurized air because of its general availability. The useful weight ratio of the quench air to the combustion gas upstream of choke 20 is from about 0.8 to about 1.5. If steam is used as the quench gas, the steam conditions and amount used should be such that no condensate is provided in the gas turbine exhaust. Also, to facilitate transfer of ash from the lower portion of the primary combustion chamber 15 into the secondary combustion chamber 25, a passageway 33 is provided which bypasses the choke 20.

The pressurized cyclonic combustion method and burner apparatus of this invention will be further described with reference to the following example, which should not be construed as limiting the scope of the invention.

EXAMPLE

A cylindrical shaped cyclonic type pressurizable test burner was constructed to have structural features and performance characteristics according to the present inven¬ tion, as listed below in Table I, which provides a compari¬ son with two similar conventional horizontal burners and a prototype cylindrical shaped cyclonic-burner used for burning

TUTE SHEET particulate solid fuels and having similar nominal or total heat release ratings. This new test burner was operated by burning wood chips having particle size smaller than about 0.125 inch, which were fed tangentially into the burner under pressurized operating conditions as listed in Table I. For this burner comparison, the particulate fuel is intro¬ duced into each burner at essentially ambient temperature. Numerous observations of the burner operation by viewing through ports indicated that the solid particles in the primary combustion chamber swirled around in a helical flow path about the periphery of the burner until consumed. Table I also shows the test burner operating results achieved as compared to performance characteristics of the other similar conventional non-pressurized burners.

TABLE I_ Burner Construction and Comparative Performance Characteristics

Type of Burner Dual Register* Commerical Cyclonic Burner Per Invention Test Unit Prototype

Combustion Chamber Inside Diameter, in. 48 48 20 27

Primary Combustion Chamber Volume, ft 226 24.6 10 28

Burner Aspect Ratio, 4 Internal Length/Diameter 2 3 > 3

Restriction Ratio, Choke dia. /Burner I.D. None 0.2 0.3 0.3

Solid Fuel Burned Dried Particulate : π Internal Pressure, atm. abs. 1+.01 4.5 >6.5

Fuel Solids Tangential Velocity into Burner, fps Nil 75-80 80-100 80-100

Combustion Air Inlet Aspect Ratio Non Applicable 2

Reynolds Number for Combustion Air At Tuyeres Not Applicable 806,000 1,060,000 >2, 000,000

Type of Burner Dual Register* Commercial Cyclonic Burner Per Invention

Test Unit Prototype

Centrifugal Force on

Fuel Solids in Burner, g 1 130 200 >150

Nominal Heat Release,

10⁶ Btu/hr 15 23.4 18.6 50

Volumetric Heat Release ^■Rate, 10⁶Btu/hr f 3 0.07 0.23 1.86 >1.9

Reynolds Number in

Combustion Chamber 40,000 103,000 279,000 400,000

Auxiliary Air Inlet

Reynolds Number None None 4,040,000 >4,000,000

Secondary Combustion

Chamber length, in. None Undefine d 60 78

5-10% supplemental fuel required for flame stability in burner

From the above comparison of the burner structural features and performance characteristics, it is seen that the primary combustion chamber for the improved pressurized cyclonic burner of the present invention has a greater aspect ratio and larger choke restriction ratio than for the similar known cyclonic type solid fuel burners. Also, it is noted that the present burner provides a significantly higher Reynolds number for the combustion air entering the primary combustion chamber, and also provides greater tangential flow velocities and significantly greater centri¬ fugal forces on the helical flowing solid fuel particles being combusted, as is additionally shown by Fig. 4. In addition, it is seen that the present burner provides substantially higher volumetric heat release rates and higher Reynolds numbers for the hot effluent gas material flowing from the pressurized burner primary and secondary combustion chambers than do the similar conventional burners, A comparison of the volumetric heat release ratings is also shown graphically in Fig. 5. Such improved burner perfor¬ mance at pressurized operating conditions was unexpected and the present invention advantageously provides the combustion industry with a significant and unobvious improvement in burner design and performance for pressurized burning of solid particulate fuels, such as for use in power producing processes.

Although the present invention has been described broadly and also in terms of certain preferred embodiments, it will be understood that various modifications can be made within the spirit and scope of the invention, which is defined by the following claims.

Claims

WE CLAIM I

1. A method for pressurized combustion of particulate solid fuel materials to produce a pressurized hot combustion gas, said method comprising:

(a) pressurizing a particulate solid fuel having size smaller than about 0.70 inch major dimension to at least about 3 atm. pressure, and feeding the fuel solids tangentially into the inlet end of a burner cylindrical shaped primary combustion chamber;

(b) introducing an oxygen-containing combustion gas tangentially into said combustion chamber through a plurality of tuyere openings spaced apart along the burner length, said tuyeres having an aspect ratio of at least about 2:1, said combustion gas having a Reynolds number at the tuyere opening exceeding about 900,000, so as to provide a swirling helical flow pattern for the solids therein at a high tangential velocity and at centrifugal force exceeding about 140 gravitational units, thereby producing a volumetric heat release

3 rate exceeding about 400,000 Btu/hr ft ; and

(c) passing the resulting hot effluent gas through a choke zone located at the combustion chamber exit end, the choke zone containing an opening having a cross-sectional area about 20-50% that of the combustion chamber, thereby producing a hot pressurized effluent gas product.

2. A pressurized combustion method according to Claim 1, wherein the particulate fuel is wood chips having a major dimension not exceeding about 0.130 inch.

3. A pressurized combustion method according to Claim 1, wherein the combustion chamber internal pressure is 3-20 atm.abs. and the superficial gas velocity for combustion air introduced into the primary combustion chamber exceeds about 100 ft/sec.

4. A pressurized combustion method according to Claim 1, wherein the combustion gas is air and the weight ratio of the combustion air to the particulate fuel is from 1.0 to about 4.0 times the stoichiometric value.

5. A pressurized combustion method according to Claim 1, wherein the combustion gas is introduced into said primary combustion chamber at a Reynolds number between about 1,000,000 and 3,000,000.

6. A pressurized combustion method according to Claim 1, wherein the particulate solids in the primary combustion chamber are subjected to centrifugal forces of about 150-200 gravitational units.

7. A pressurized combustion method according to Claim 1-, wherein the effluent gas in the combustion chamber has a Reynolds number of 150,000-500,000.

δ. A pressurized combustion method according to Claim 1, wherein the vclur.etric heat release rate in the cor.bustior. chamber is about 500,000 to 3,000,000 Btu/hr ft^J.

9. A pressurized combustion method according to Claim 1, wherein a quench gas stream is introduced into said choke zone with a rotational direction opposite to that of the solids in the primary combustion chamber, so as to limit the effluent gas temperature to not exceeding about 2000° F.

10. A pressurized combustion method according to Claim 1, including passing the combustion gas from said choke section into a secondary combusiton chamber for further combustion and cooling the gas to 1400-2000° F temperature.

11. A method for pressurized combustion of particulate solid wood materials to produce a pressurized hot combustion gas, said method comprising:

(a) pressurizing wood chips having size smaller than about 0.130 inch major dimension to 3-20 atm. pressure, and feeding the wood solids tangentially into the inlet end of a burner cylindrical shaped primary combustion chamber;

(b) introducing combustion air tangentially into said combustion chamber through a plurality of tuyere openings spaced apart along the burner length and at a Reynolds number range of 900,000 to 3,000,000, so as to provide a swirling helical flow pattern for the fuel solids therein at tangential velocity of 80-120 ft/sec, so as to produce a volumetric heat release rate in the combustion chamber

3 exceeding about 400,000 Btu/hr ft ,

(c) passing the resulting hot effluent gas through a choke .located at the combustion chamber exit end, the choke zone containing an opening having a cross-sectional area about 20-40% that of the combustion chamber and thereby producing a hot pressurized effluent gas; and

(d) introducing a quench air stream into said choke zone to limit the hot effluent gas temperature to not exceeding about 2000° F, said quench air being introduced with a rotational direction opposite to that for the solids in the primary combustion chamber to provide a shear type mixing pattern, thereby producing a hot pressurized effluent gas product at controlled temperature.

12. A burner apparatus for burning particulate combustible fuel to produce a pressurized effluent gas, said burner comprising: (a) a pressurizable cylindrical shaped outer metal casing;

(b) an inner refractory lining located adjacent said casing inner wall, said refractory lining providing therein an elongated cylindrical shaped primary combustion chamber;

(c) a tangential opening located tangentially in said combustion chamber inlet end for introducing a fuel tangentially into the combustion chamber;

(d) a plurality of tangentially oriented tuyere openings for introducing a combustion gas tangen¬ tially into said combution chamber, said tuyere openings each having an aspect ratio at least about 2:1, and being spaced apart longitudinally along the length of the chamber;

(e) a choke opening located at the exit end of said primary combustion chamber; and

(f) at least one aperature located in the choke opening, said aperture oriented for flow of a quench gas relative to the helical flow of a hot effluent gas, whereby the particulate fuel is combusted rapidly at high rotational velocity and high heat release rates and the resulting hot product gas is quenched to provide a lower temper¬ ature pressurized product gas.

13. A burner apparatus according to Claim 12, wherein the primary combustion chamber internal length to diameter ratio is between about 2:1 and 10:1.

14. A burner apparatus according to Claim 12, wherein said tuyere openings each have an aspect ratio between about 3:1 and 5:1.

15. A burner apparatus according to Claim 12 wherein, the inlet and refractory lining 12 is made convex-shaped and extends into the combustion chamber to a cross-sectional plane past said tangential opening for introducing a fuel.

16. A burner apparatus according to Claim 12, wherein said choke opening has a cross-sectional area about 30-50% the cross-sectional area of the primary combustion chamber.

17. A burner according to Claim 12, wherein the refractory lining for the primary combustion chamber is selected so as to provide, sufficient heat outflow to the environment to avoid fuel slagging conditions on the refractory surface in the primary combustion chamber.

18. A burner apparatus according to Claim 12, wherein a secondary cylindrical combustion chamber is provided joined pressure-tightly to the burner downstream from said choke opening.

19. A burner apparatus according to Claim 12, wherein said choke opening is tapered outwardly into the secondary combustion zone to minimize irrecoverable pressure differen¬ tial for effluent gas flowing therethrough.

20. A burner apparatus according to Claim 12, wherein the choke opening is provided by an annular shaped removable element of abrasion-resistant refractory material.

21. A burner apparatus according to Claim 12, wherein said aperture located in the choke opening is oriented tangentially opposite to said tangential opening at the primary combustion chamber inlet end to provide turbulent shear type mixing of the gas streams.

22. A burner apparatus according to Claim 12, wherein a passageway extends from the primary combustion chamber lower portion into the secondary combustion zone downstream from the choke.

23. A burner apparatus for burning particulate combustible fuel to produce a pressurized effluent gas, said burner comprising:

(a) a pressurizable cylindrical shaped outer metal casing;

(b) an inner- refractory lining located adjacent said casing inner wall, said refractory lining shaped to provide an elongated cylindrical shaped primary combustion chamber;

(c) an opening located tangentially in the burner cylindrical wall near the burner inlet end for introducing a fuel tangentially into said combustion chamber;

(d) a plurality of tangential oriented tuyere openings spaced apart along the length of the burner for introducing a combustion gas tangentially into the combustion chamber;

(e) a choke opening located at the exit end of said primary combustion zone;

(f) a secondary combustion chamber joined pressure- tightly to the exit end of the burner outer casing; and

(g) dual apertures located tangentially in the choke opening, said apertures oriented opposite to the tangential opening at the combustion chamber inlet end for tangential flow of a quench gas in direction opposite to the helical flow of a hot effluent gas, whereby the particulate fuel is combusted rapidly at high velocity and high heat release rate and the resulting hot effluent gas is effec¬ tively quenched to provide a lower temperature pressurized product gas.