This Application is a continuation of U.S. Patent Application Serial Nos. 06/625,707 and 06/626,417 filed on June 29, 1984.

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 diffuεivity is rate controlling in the rapid oxi¬ dation of solid fuels. Historically, this longer combustion time requirement has been minimized by solids size reduction, aε 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

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 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 particle 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 reactior 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-sveep 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

particulate fuels εuch aε 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 iε pressurized and pneumatically fed tangentially into the burner primary combustion chamber operated at a pressure et least about 3 atm. absolute and usually not exceeding about 20 atπ.. 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 gaε is also supplied into the combustion chamber tangentially through multiple tuyeres at a high tangential velocity exceeding about 100 ft/εec 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/εec, 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, εo that the fuel εolidε are more rapidly and com¬ pletely combusted. Also, this high rotational velocity and high centrifugal force flow pattern' ot only retains the particulate εolidε in the burner longer for more complete

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 and 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.

In the embodiment disclosed any remaining particulate solids in the effluent gas leaving the burner are mechanically separated from the gas in a cyclone separator, after which the clean gas is then expanded to a lower pressure through a gas turbine for driving a compressor to provide the pres¬ surized combustion air required in the burner. The gas

turbine provides net shaft power output for driving a load, which is usually an electric power generator.

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 tangetially 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, petroleum 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 mixture 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 which:

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 alongs 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;

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; and

Fig. 6 is a schematic diagram of a system incor¬ porating the burner of Fig. 1.

DETAILED DESCRIPTION OF INVENTION

A preεεurized cyclonic burner for providing prolonged preεεurized combuεtion of particulate solid fυelε and conεtructed and operated in accordance w th the present invention iε shown in Fig. 1. In the illustrated preferred embodiment, the burner aεεembley 10 haε 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 iε located adjacent the inner wall of caεing 12 and within head 13 and defines a primary combuεtion chamber 15, with the lining material being εuitable for withεtanding temper tureε up to about 3000° F.

The particulate εolidε combuεtible fuel material, εuch aε wood chipε preferably εmaller than about 0.130 inch major dimension, is uniformly fed by εuitable eanε (not shown) into the burner primary combuεtion chamber 15 at tangential inlet connection 16 located near the inlet end head 13 of the burner. In the chamber, the εolids ere air entrained at tangential velocity at least about 80 ft/εec and preferably 100-200 ft/εec. If desired, to improve ignition of the particulate εolidε feed entering the combustion chamber, the end wall 14a of refractory lining 14 can be made convex shaped and extend exially into the combustion chamber to a location not more than about 0.5 the burner internal diamete past the plane of the fuel inlet 16, as shown in dotted lines in Fig. 1. This arrangement results in the εolidε feed material moving cloεer to the hot refractory surface 14a to provide for more effective radiant heating of the feed.

Multiple tangential inlet openingε or tυyereε 18a, 18b, 18c, etc., are provided through caεing 12 and lining 14 and spaced apart along the length of the burner for εupplying combuεtion air into the combuεtion chamber. The tuyere openingε 18, 18a,• etc., are preferably provided as double rows, as εhown in Fig. 2 εectional drawing, with at leaεt 3

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 combuεtion air is preferably supplied through the tuyeres at tangential velocity of 110-150 ft/εec and at Reynolds number of 1,000,000-3,000,000. A flanged clean-out opening 17 iε provided through the lower portion of head 13 and includeε a removable refractory plug 17a. Alεo, a sight tube 19 iε provided through the upper portion of head 13 for viewing the combuεtion process within chamber 15.

The combustion chamber 15 iε operated at internal presεure of about 3-20 at . ebεolute and preferably 4-10 atm. The uεeful weight ratio of combuεtion air to the particulate fuel feed rangeε from about 1.0 to 4.0 ti eε the εtoichio etric value.

At the exit end of the burner combuεtion chamber 15, a centrally-located choke element 20 iε provided which has a generally cylindrical opening 20a therethrough, and haε a croεε-εectional area appreciably εmaller than that for the combuεtion chamber 15. The opening 20a in choke 20 should be made small enough to help retain the circulating combust¬ ing εolidε in the primary combuεtion chamber, εo aε to prolong the solids residence time for substantially complete combuεtion therein, but the opening iε not made εo small that undeεired differential preεεure for the effluent gaεeε flowing through the choke iε appreciably increaεed. The crosε-sectional area of the choke 20 should be at least about 307. that of the combustion chamber 15, and uεually iε 40-50% the croεε-sectional area of the combustion chamber.

- 1 3 -

Alεo, if deεired to facilitate the paεεage of aεh from the primary combuεtion 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 towardε the lower wall of the chamber. This choke 20 is usually made annular shaped and iε preferably formed aε a caεtable re¬ fractory material that iε more abraεion-resistant than the refractory lining 14. The choke 20 preferably has a curved inlet εurface 20b and a tapered outer εurface 20c to aεεiεt in retaining it in place in the surrounding refractory material 24. Also, if deεired, a refractory cement material 21 can be uεed 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 obεer- vationε made of the εolid fuel particleε in the burner during combustion operation indicate that the particleε move in a helical flow path which iε nearly perpendicular to the longitudinal axis of the burner, thus indicating that the helix angle of the particle path relative to the burner axiε iε only slightly less than 90 ^e . This flow pattern indicates that the fuel particleε make a great number of revolutions in the burner primary combuεtion chamber until they are completely devolatized and consumed. Also, because of the particle rotational velocity, the particulate εolidε respond to high centrifugal forces produced in the burner and the gaεeouε products of combustion respond to Reynolds numbers which are very high. By uεing the burner configu¬ ration of thiε invention, the volumetric heat releaεe rateε for preεεurized burning of particulate εolid fuels are εignificantly higher than for conventional type burners, and approach heat releaεe rateε which occur for burning liquid or gaεeouε fuelε -in internal combuεtion engineε.

Becauεe of the high tangential velocity and high centri¬ fugal forceε generated on the εolid fuel particleε in the burner primary combuεtion zone 15, the particulate εolidε

©ske very many revolutions therein and are thus retained in the combustion tone adjacent the hot refractory lining 14 for a 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 gaseε iε at least about 150,000 and preferably 200,000- 500,000. The volumetric heat release rateε in the burner primary combustion chamber iε at least about 400,000 Btu/hr ft primary combustion chamber volume, and iε preferably 500,000 to 3,000.000 Btu/hr ft ³ .

A secondary cylindrical shaped combuεtion chamber 25 iε 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 combuεtion chamber 25 haε a cylindrical shaped metal caεing 22 εurroun - ing a refractory lining 24. The casing 22 is connected pressure-tightly to the casing 12 of primary combuεtion chamber 15 by bolted flange 26, and can be connected pressure tightly to downstream ducting aε desired by flange 27. Alεo, refractory lining 24 abutε againεt the refractory lining 14 at a location radially outwardly from choke 20. A reduced diameter intermediate zone 28 iε provided immediately downεtream from choke 20 and υεually haε a length: diameter ratio of about 1:1 to 1.5:1. The intermediate zone 28 iε followed by outwardly tapered zone 29 connecting to a full diameter zone of secondary chamber 25 having an inside diameter approximately the same aε for the primary combustion chamber 15.

A quench gas such as additional preεεurized air or steam is provided into secondary chamber 25 through at least one opening 30 through refractory 24 located immediately

effluent gaε flowing from the choke. Uεually two openingε 30 are provided and are preferably oriented in a tangential direction oppoεite to that for the fuel inlet 16 and multiple openingε 18 for the combuεtion air in the primary combuεtion chamber 15. Thuε, the counter or oppoεitely flowing quench gas stream flowing tangentially from conduit 32 through openingε 30 provideε a high velocity εhear type mixing flow pattern for the quench gaε and the hot effluent gas upstream from εecondary combustion chamber 24, thereby advantageously achieves highly effective mixing of the hot effluent gas and the quench gas εo aε to lower the hot effluent gaε temp¬ erature from about 2700° F to a lower temperature, εuch as 1500-1800° F suitable for passing to a gas turbine. The preferred quench gas is pressurized air because of itε 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 iε used as the quench gas, the steam conditions and amount used εhould be εuch 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 εecondary combustion chamber 25, a passageway is provided which bypasseε 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 εhould 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 characteristicε according to the preεent inven¬ tion, aε liεted below in Table I, which provides a compari¬ son with two εimilar conventional horizontal burnerε and a rotot e c lindrical εha ed c clonic burner used for burnin

particulate εolid fuelε and having εimilar nominal or total heat releaεe ratingε. Thiε new teεt burner was operated by burning wood chipε having particle εize smaller than about 0.125 inch, which were fed tangentially into the burner under preεεurized operating conditionε aε liεted in Table I. For thiε burner comparison, the particulate fuel iε intro¬ duced into each burner at essentially ambient temperature. Numerous obεervationε of the burner operation by viewing through portε indicated that the εolid particleε in the primary combustion chamber εwirled 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 εimilar conventional non-preεsurized burners.

TABLE I Burner Construction and Comparative Performance Characteristics

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

Combustion Chamber

Inside Diameter, in. 8 48 20 27

Primary Combus ion3

Chamber Volume, ft 226 24.6 10 28

Burner Aspect Ratio, Internal Length/Diameter 4.3 2 3 > 3

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

Solid Fuel Burned Dried Parti<culate

Internal Pressure, atm. abs. 1+.01 4.5 >6.5

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

Combustion Air Inlet Aspect Ratio Mon Applicable 2

Reynolds Number for Combustion Air At Tuveres 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,

8 1 130 200 >150

Nominal Heat Release,

10 ⁶ Btu/hr 15 23.4 18.6 50

Volumetric Heat Release

Rate, 10 ⁶ Btu/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 > ,000,000

Secondary Combustion

Chamber length, in. None Undefined 60 78 5-107„ supplemental fuel required for flame stability in burner.

From the above comparison of the burner structural features and performance characteristics, it is seen thβt the primary combustion chamber for the improved pressurized cyclonic burner of the present invention haε a greater aspect ratio and larger choke restriction ratio than for th εimilar known cyclonic type εolid fuel burners. Also, it i noted that the present burner provides a significantly higher Reynolds number for the combustion air entering the primary combuεtion chamber, and alεo provides greater tangential flow velocities end εignificantly greater centri fugal forces on the helical flowing εolid fuel particleε being co buεted, aε iε additionally εhown by Fig. 4. In addition, it iε εeen that the present burner provides εubεtantially higher volumetric heat releaεe rateε and higher Reynolds numbers for the hot effluent gaε material flowing from the preεεurized burner primary and εecondary combuεtion chambers than do the εimilar conventional burner A compariεon of the volumetric heat releaεe ratings iε also shown graphically in Fig. 5. Such improved burner perfor¬ mance at pressurized operating conditions was unexpected an the present invention advantageously provides the combustio industry with a significant end unobviouε improvement in burner design end performance for pressurized burning- of solid particulate fuels, ευch as for use in power producing processes.

Referring now to Fig. 6, there will be described the system incorporating the burner 10 of Fig. 1.

A source 110 provides wood chips having size smaller than about 0.70 inch major dimension, and preferably smaller than about 0.130 inch, which chips are collected at 111 in the hopper 112 maintained at substantially atmospheric pressure. The chips 111 are fed from the hopper 112 by a variable speed screw conveyor 114 driven by motor 114a into a vertically oriented chute 115, and are then passed to a suitable feeder means 116 for delivering the wood particu¬ late solids material into pressurized conveying conduit 118. Feeder 116 preferably consists of two rotary valves 116a and 116b connected in series and arranged for transferring the particulate solids material by gravity flow from the chute 115 into the conduit 118 at a pressure of about 3-20 atm. absolute, and preferably at 4-15 atm. pressure. The pres¬ surized transport air from conduit 117 flows in conduit 118 at 40-120 ft/sec superficial velocity and preferably at 60- 100 ft/sec velocity and pneumatically conveys the particulate solids material tangentially to the pressurized burner 10.

The particulate solids fuel material is fed pnuemati- cally into burner 10 at near its inlet end through tangential inlet port 16 at superficial gas velocity exceeding about 80 ft/sec and preferably at 90-150 ft/sec into primary combustion chamber 15. Additional combustion air is introduced tangen¬ tially into the primary combustion chamber 15 at superficial velocity exceeding about 100 ft/sec, and preferably 110-150 ft/sec, through multiple spaced-apart openings or tuyeres 18a, 18b, 18c, etc., located axially along the length of chamber 15. If preheating or drying the solids in conduit 118 is desired, such preheating can be provided in heat exchanger 119 using any convenient source of heat such as turbine exhaust gas flowing through a jacket surrounding an elongated heat exchanger.

In the combustion chamber 15, the fuel solids are made to swirl around at high rotational velocity exceeding about 80 ft/sec and preferably at 100-150 ft/sec and produce high

'g', while the particles are rapidly heated by the hot chamber walls and progressively devolatized and burned to produce a hot pressurized effluent gas at a temperature of about 2100-2800° F. The particles are also advantageously retained in the primary chamber 15 for prolonged combustion therein, not only by the high centrifugal forces but also by the effect of choke opening 20a, located at the exit end of the primary chamber 15. The choke opening 20a has a smaller cross-sectional opening area than the combustion zone 15 so as to prolong the particle solids combustion time therein and thereby provide for more complete combustion of the particulate fuel solids and produce very high volumetric

3 heat release rates exceeding about 400,000 Btu/hr ft of primary chamber volume and preferably 500,000-3,000,000

Btu/hr ft ³ .

It has been found advantageous that the primary com¬ bustion chamber 15 should have a length/diameter aspect ratio for the chamber at least about 2.5:1 and usually need not exceed about 10:1 to provide for adequate combustion time for the solids. The combustion chamber inside diameter should be at least about 1.5 ft. for achieving a reasonable throughput rate for the combustible solids material and usually should not exceed about 3 ft. diameter to achieve adequate rotational velocity for the solid particles therein.

In the choke section 20 of chamber 15, the hot effluent gas is mixed with additional combustion air provided through conduit 32, to quench and cool the hot effluent gas to lower temperature such as 1500-1800° F suitable for extended use in a gas turbine.

The secondary or quench air is introduced in the choke zone through dual openings 30 oriented in a tangential di¬ rection opposite to that for tuyeres 18 in the primary com¬ bustion chamber 15, thereby producing highly turbulent shear type mixing of the two streams in the choke zone leading to secondary combustion zone 25. The flow of supplementary air at conduit 32 is controlled relative to combustion air

in conduits 123a, 123b, 123c, etc. to the tuyeres 18a, 18b, 18c, etc. by controller 132, which monitors the air flows at flow meters 131a, 131b, and operates control valve 129 in condiut 32.

The resulting cooled effluent gas in the secondary com¬ bustion chamber 25, which may still contain a very small concentration of incombustible particulate solids, is passed through a cyclone type separator device 34 for substantially complete removal of such fine solids. The cyclone separator 34 preferably uses an axial flow type element 35 to provide for a more compact separator overall arrangement. From separator 34, a clean hot effluent gas stream at 1500-1800° F temperature is removed at 36, while the particulate solids removed are withdrawn through valve 37 for suitable disposal.

The cleaned effluent gas at 36 at 3-10 atm. pressure is then passed through conduit 38 to the inlet of gas turbine 40, which is connected to drive air compressor 42 for supplying pressurized air source at 44 for the combustion air at tuyers 18 and the quench air at 32. Also, a portion of the compressed air stream at 44 is cooled at 45 against stream 45a sufficient to avoid combustion of the particulate solids such as to about 200° F, usually by heat exchange with ambient air. The air at 47 is further compressed at 46, preferably by a positive displacement type compressor, to a differential pressure such as 2-10 psi and preferably 4-8 psi to provide the pressurized air at 117 required in conduit 118 for pneumatically conveying the wood chips into the burner 10.

Turbine 40 also rotatively drives a load device 50, which is usually an electric generator for generating electric power. From turbine 40, exhaust stream 41 at near atmospheric pressure and at 900-1000° F temperature can be passed to a heat recovery step at 52 and used as a heat source for generating steam, for heating another fluid used for heating purposes, or as a hot gas for preheating and/or drying the particulate feed material in heat exchanger 119.

The gas turbine unit 40 can be divided into two sepa¬ rate turbines each operating at different rotational shaft speeds, with the first turbine 40a used for driving the compressor 42 at a high rotational speed, and the inter¬ mediate exhaust gas stream at 41a from the first turbine 40a being passed to second turbine 40b which is gear-connected to an electric generator 50 for driving the generator at a lower rotational speed. Alternatively, a single shaft type turbine-compressor unit can be used in which both the com¬ pressor and electric generator are driven by a single turbine.

During start-up of the process, an auxiliary burner (not shown) using a hydrocarbon fuel source such as propane is used to initially heat the refractory walls of primary combustion chamber 10 to a temperature sufficient to ignite the particulate solid fuel introduced at 16. Also, an auxiliary drive motor 54 is used to drive compressor 42 to provide the hot air source initially needed for combustion. Also, air further compressed by compressor 46 is used for initially pneumatically conveying the particulate fuel solids through conduit 118 into the burner 10.

The solid fuel pressurized combustion and power gene¬ ration process of this invention will be further described with reference to the following example of operations, which should not be construed as limiting the scope of the in¬ vention.

EXAMPLE

Wood chips and shavings, such as produced from a wood processing mill source and having nominal size of about 1/8 inch, were transferred from an atmospheric pressure col¬ lection hopper through tandem rotary feeder valves into a pressurized transfer pipe operating at about 5 atm. pressure. The wood chips were pneumatically conveyed at superficial gas velocity of about 80 ft/sec and fed tangentially into the inlet end of a horizontally oriented cylindrical cy¬ clonic burner primary combustion chamber having dimensions

as shown in Table II below. Pressurized combustion air was also supplied tangentially into the combustion chamber through 6 sets of dual tuyeres spaced-apart axially along the chamber length and at superficial gas velocity of about

100 ft/sec. Numerous observations of burner operation made through viewing ports indicated that the particulate solids were circulated in a swirling helical flow path in the combustion chamber at calculated tangential velocity of about 100 ft/sec until consumed.

In the primary combustion chamber, the wood particles being circulated at the high rotational velocity developed high centrifugal forces of about 200 'g ¹ , which provided for prolonged total combustion of the particles at high Reynolds number and produced high volumetric heat release rates of

3 about 1,800,000 Btu/hr ft . Thus, the solid fuel particles were rapidly devolatized and combusted to produce a hot effluent gas at 2700-2800° F temperature, which passed through a restricted choke opening at the exit end of the combustion chamber.

The resulting hot effluent gas at about 2700-2800° F temperature was quenched by additional pressurized secondary air injected tangentially into the throat portion of the choke opening. The quench air was injected tangentially in a direction opposite to that of the swirling effluent gas from the primary combustion chamber, thus producing highly turbulent shear type mixing of the two gas streams so that the hot effluent gas was effectively cooled to about 1700° F and then passed into a secondary combustion chamber located immediately downstream from the choke.

From the secondary combustion chamber, a portion of the cleaned effluent gas containing about 250 ppm (wt.) fine particulate solids was then passed through a centrifugal typ ^e gas-solids separator in which the fine particulate solids in the gas were substantially all centrifugally separated and removed.

The resulting cooled and cleaned gas at about 1600° F

temperature is then expanded through a gas turbine driving a rotary air compressor to provide the pressurized transport and combustion air, and also driving an electric generator to produce net electric power. Based on burner operating data and related experience, the projected continuous oper¬ ating period for this process is in excess of 30,000 hours. Performance data obtained for the pressurized combus¬ tion step and typical performance for the power-producing process of this invention are provided in Table II below:

TABLE II Solid Fuel Pressurized Combustion and Process Characteristics

Test Unit Prototype

Primary combustion chamber:

Inside diameter, in. 20 27

Length/diameter, ratio 3 >3

Choke diameter, in. 6 6.5

Wood Chip feed rate, Ib/hr 2020 6100

Transport and combustion air flow rate, lb/hr 26,300 85,500

Combustor pressure, pεia 66 95

Combustor pressure, atm. abs. 4.5 6.5

Volumetric heat release rate,

Btu/hr ft3 1,866,000 1,900,000

Quench air flow rate, lb/hr 9,000 85,000

Secondary combustion chamber ^" effluent:

Gas Temperature, ^C F 1780 1780

Solids concentration, pp . (wt . ) 250 250

Solids concentration of separator effluent, ppm (w . ) 3£ 30

Gas turbine:

Inlet temperature, ^C F 1700

Inlet pressure, pεia 90

Exhaust temperature, ^C F 900

Exhaust pressure, pεia 15

Gas flow rate, lb/hr 176,600

Net power produced, kv 3000

From the above data, is is seen that the present process utilizes improved pressurized combustion of wood chips or other particulate solid combustible material to provide high volumetric heat release rates in the burner. The process also utilizes effective quenching and cooling of the hot effluent gas together with gas-solids separation to provide a clean pressurized effluent gas suitable for extended use in a gas turbine to produce electrical power.

Although the present invention has been described broadly and also in terms of certain preferred embodiments, it will be understood that various modification and varia¬ tions can be made within the spirit and scope of the inven¬ tion, which is defined by the following claims: