US2866697A - Combustion chambers - Google Patents

Description

Dec. 30, 1958 D. E. ELLIOTT COMBQSTION CHAMBERS 2 Sheets-Sheet 2 Filed Feb. 14, 1955 Inv: ntqr I 11:1 a Jul.

4L4 ttorney;

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2,866,697 COMBUfiTlGN CHAMBERS Douglas Ernest Elliott, Weybridge, England, assignor to Power Jets (Research and Development) Limited, London, England, a British company Application February t, 1955, Serial No. 488,910

Claims priority, application Great Britain February 25, 1954 p 7 Claims. (Cl. 48-203) ried out at high temperatures, and with apparatus therefor.-

To save time (by speeding up reactions), to save capital cost, to improve the nature of the process and for other purposes it is often desirable to operate at a temperature above 1200 C. and possibly above 2000 C. Thus for the efiicient combustion of certain fuels and more particularly for promoting the weakly exothermic reactions of gasification of solid andv liquid fuels with steam and oxygen-bearing gases it is extremely important to maintain temperatures above 1200 C. and there is usually a continual gain in rate of reaction with increase oftemperature up to at least I800" C.

The invention aims at permitting these high temperatures while avoiding considerable transfer of heat to the combustion chamber wall. The smaller thecomb'u'stion chamber, the more serious is the loss due to this transfer. To reduce transfer, a metal wall may be lined with a heatinsulating refractory but if the reaction produces hot slag this will attack and erode the refractory. No refractory is yet known which will long withstand very high temperatures combined with the attack for example of hot liquid slag from coal. Uninsulated metal walls must be externally coolede. g. water-cooled to avoid over-heating and the heat loss is then a considerable proportion of the total heat released. Any slag formed from the fuel will build up a layer on such a metal wall which is solid adjacent to the wall but is molten ontits inner surface. This slag layer is a good heat insulator,

high rate of transfer of heat to the walls.

The invention consists broadly in centrifugally main taining a thick layer of partly molt-en heat-insulating ma terial as a lining on combustion-chamber walls. More particularly, according to the invention the combustion chamber enveloping the space wherein a high-temperature reaction occurs is rotary, its walls are shaped to retain a thick molten layer, and it has driving means for rotating the chamber around its axis at such a speed as to provide the centrifugal force necessary for building and maintaining the desired thickness of this layer. Hitherto the slag layer thickness has been a fraction of an inch whereas in apparatus according to the present invention the thickness will be several inches-usuallyof the order of one foot. Thus it is possible to operate at Patented Dec, 30,1958

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temperatures above 1200 C. or 1"500 C. in a chamber lined with fused coal ash of a thickness of: the order of onefoot, which will, at its inner surface, be molten. and at a temperature not much below the reaction tempera; ture-but at its outer surface. will be solid and at. a com.-: paratively. low temperature.

The invention furthermore, consists in carrying, out. a high temperature reaction in a, space. enclosedby a thick rotating and centrifugally retained layer of heat-insulate ing material which is molten at leastonits inner. surface.

The term combustion chamber has been used, inv defining the invention, to meanthe vessel wherein. the heat: evolvingchemical reactione.. g, combustion or partial. combustiontakes place. The slag may be fused ashv evolved by the combustion of fuel, butvwhere. the re-- action will produce nothing to form'an insulatingdayer. on the walls, ash or refractory pebbles may be introduced into the chamber where they will be, fused by theheat- Certain processes -especially metallurgical processes which do not produce ash may nevertheless provide a layer which will buildup on the wall andpartiallysolidify, to serve as heat insulation. For lack of a more. com; prehensive name, the term slagfis used, in definingthe invention, to include any substances evolvedby the reaction to form a heat-insulating layer on' the walls, as well as slag or the equivalent separately introduced into. the chamber. 7

One particular construction, according tosthe inven-. tion, of rotary cyclone combustion chamber forthe combustion or gasification of pulverisedcoaL'is shown. in. the. accompanying drawings, of which Figure 1 is a vertical half section,

to the thickness desired at the top (which maybeseveral inches), an axially extending flange lbaround the...

.inside of the rim 1a, and a lower and centrally-apertured.

part. 10 (which could be paraboloidal but is. shown as conical) tapering towards its lower end. This partly cylindrical and partly tapered chamber is rotatable about its axis; accordingly the cylinder is supported 'by a radial,-

thrust bearing arrangement around its outside wall, as.

hereinafter described. Enveloping the cylinder I is an outer casing 2 which supports the bearings. The top.- of easing 2 is partly closed, except for the necessary air and fuel inlets and gas outlet, by the circular stationary top cover 3, and the circular stationary centrally-aper:

tured top plate 4. Welded to cylinder 1. at intervalsaround its periphery are the outwardly projectingbearing brackets 5 which are of built-up plate construction.-

These carry the outer ring 6 serving as a'bearing race; Ball bearings 7 between ring 6 andthe inner race 8.- centralise and support the Weight of the combustion chamber. Race 8 stands on support ring 9 mounted on. brackets 10 in casing 2. To rotate the chamber, the. electric or other motor 11 drives, through coupling,12,

the shaft 13 which passes into the casing 2 through the of the combustion chamber is the outlet tube 16 for.

egress of the gaseous products. The space around tube,

16 serves asan annular inlet passage for combustion air.

enteringby inlet 411 (Fig. 2,). Vanes 22 secured t t-and;

Figure 2 is .a half plan section on II'II"of,I Figure disposed in a ring around tube 16 are inclined so as to impart swirl to the incoming air, as shown in the part development view Fig. 3. Also secured to and disposed around the tube 16 is at least one and preferably two ducts 23 for incoming fuelwith carrier air. Each duct 23 is also inclined as shewn in Fig. 3 to constitute an inclined port admitting the fuel with swirl. A labyrinth seal is formed by a cylindrical baffle 4a onplate 4 and a similar batfie 1a on the top of chamber 1. An inlet 3a admits cooling air to flow through the outer casing 2 to the air outlet 2c; the air pressure in the casing may be sufficient to oppose any appreciable leakage into the casing past the labyrinth seal.

The lower part 2a of casing 2 is of tapered form around the corresponding part 1c of the chamber 1. A slag-outlet tube 17 depending from the bottom of part and a corresponding enveloping tube 18 depending from the bottom of part 20 form a seal by dipping into water in the stationary slag-collector 19 on base 20. It is assumed that the pressure in the combustion chamber is low enough for the collector 19 to be open to atmospheric pressure and that there is no need for a closed collector and means for pumping away the collected slag. The casing 2 and motor 11 are carried by the uprightcolumns of a support structure 21 standing up from the base 20. A tube 24 extending down beside the outlet tube 16 allows means to be inserted on occasion to ignite the fuel in chamber 1. V

In operation, powdered or crushed coal or other fuel, carried by air under pressure, enters the chamber 1 by ducts 23 and will swirl about the vertical'axis of the chamber. The main supply of combustion air enters the chamber, with similar swirl in the same direction, from inlet 4b and mixes with the fuel. The mixture is ignited in the chamber. The air and burning fuel therein travel inwardly in a spiral vortex within the chamber to the central outlet formed by tube16; the fused ash par ticles evolved are thrown centrifugally outwards to build up a layer S on the walls of cylinder 1. This may be solid in contact with the wall, but the inner surface S of the layer will remain molten. If the cylinder 1 were stationary, according to former practice, all the molten slag would run down to the bottom and drop into the collector 19. With rotation of the cylinder 1 by motor 11, according to the invention, the liquid slag will spread out centrifugally in the well-known manner of liquid in a vessel rotating about a vertical axis, to form a layer and the cylinder dimensions, are chosen to give the de sired thickness of layer, according to the heat insulation desired. To aid in quickly forming the necessary internal diameter of combustion space, prepared molten slag may be poured in. Preferably, the chamber 1 is given an initial lining of cement or other heat resistant material to a thickness less than the total desired. The slag layer which forms may attack this material and gradually replace it until the whole thickness of lining is of slag. When the desired layer thickness has built up, surplus slag in liquid form runs down into the water in the collector 19;steam thereby produced enters the chamber 1. If no appreciable slag is formed by the combustion in the chamber, then some slag-forming materiale. g. ash or refractory pebbles-may be introduced either through the inlet 4b or with the fuel, and fused by burning some of the fuel; the resulting slag particles which collect are built up centrifugally to complete the thick layer S by rotation of the chamber. Or alternatively the chamber maybe lined with cement or other material,

as aforesaid, which fuses at the combustion temperature. The cooling air entering the outer casing by inlet 3a and swirling around the combustion chamber cools the outer surface of the chamber wall and so keeps the bearings cool. The air passes between the chamber wall and the enveloping wall 22 and thence to the outlet 20. Some slag will probably collect inside outlet tube 16, to a comparatively small thickness, but in any case this tube 16 will get very hot inside and serve to transfer heat to the comparatively cool incoming air around its outside surface.

The invention is not limited to the construction shown. Thus the arrangement may be such that surplus slag may be centrifuged out of the top of the combustion chamber, instead of discharged from the bottom. The slag may spray over the top rim either continuously, or intermittently during temporary speeding-up of the rotary cylinder, and preferably such that the slag sprayed over solidifies in small lumps; this slag falls into acollector on the top of the outer casing 2. With slag spraying from the top, the bottom of the combustion chamber may be completely closed; there is then a thick heat-insulating layer between the combustion space and the bottom of the chamber.

The invention is not limited to a cyclone or vortex chamber but may be applied to a chamber with a straight-through flow. In one such construction the rotary vertical cylinder is open at both ends but has at each end an inturned rim such as In of sufficient width to retain the desired thickness of layer of slag. The cylinder is supported by a hearing as described. Air and fuel are introduced into the chamber through inlets in a stationary bottom plate around which the lower end of the cylinder revolves. Gases discharge through the open upper end of the cylinder. Slag deposits on the inner wall of the cylinder, as already described; surplus slag from the thick layer may fall from the bottom of the cylinder or be centrifugally sprayed over the top of the cylinder into the outer casing for collection and removal as already described. The combustion air may be swirled and this will tend to throw ash outwards on to the wall of the chamber. Alternatively the air and fuel inlets may be at the top and the gas outlet at the bottom.

It will be understood how the latter construction may be modified so that the combustion chamber is horizontal and rotates about a horizontal axis. For the slag layer to have an internal diameter of 2 feet the speed need only be 60 R. P. M. and need be only 35 R. P. M. for 6 feet internal diameter.

In any of the above-described constructions the motor 11 and pinion 15 may be omitted and the combustion chamber rotated by the action of the incoming air-or possibly of the outgoing gason vanes, turbine-blading or the equivalent attached to the rotary chamber.

From the foregoing it will be understood how the described constructions can be adapted for use'as the chamber for any of various different heat-evolving high-temperature reactions. Thus the invention may be applied to a high-temperature process wherein a chemical process has one product at leastwhich may be the desired prodnet for which the process is carried outwhich is heat insulating and molten at the reaction temperature, the enclosing layer being then of this product; excess over the desired thickness of layer issues from the chamber for utilisation. A typical process is one for making calcium carbide.

I claim:

1. A very high temperature combustion reaction process which comprises establishing a reaction zone in a chamber at temperatures high enough to melt a heat insulating material, continuously supplying reactants to said zone, establishing a thick partly molten layer of said heat insulating material against the chamber wall around an axis through said zone to circumferentially enclose & ,said zone, and continuously rotating the chamber and hence said layer about said axis at a speed sufiicient to centrifugally retain said layer, and continuously withdrawing from said reaction zone molten heat insulating material in excess of that required to form the heat insulating layer.

2. A very high temperature chemical reaction process wherein a chemical product-of the process is molten at the reaction temperature which comprises establishing a reaction zone in a chamber at temperatures high enough to melt said product, continuously supplying reactants to said zone, establishing a thick layer of said molten reaction product against the chamber wall around an axis through said zone to circumferentially enclose said zone, and continuously rotating the chamber and hence said layer about said axis at a speed sufiicient to centrifugally retain said layer, and withdrawing continuously from said reaction zone a proportion of molten reaction product in excess of that required to form the heat insulating layer.

3. The process of gasifying a slag-forming fuel to yield hot gaseous products which comprises establishing a reaction zone in a chamber, continuously supplying said slag forming fuel and at least one other reactant to said zone to maintain the temperature of reaction therein at not less than 1200 C., establishing by the deposition of molten slag against the chamber wall from the reaction a thick layer of slag around an axis through said zone to circumferentially enclose said zone, and con-- tinuously rotating the chamber and hence said layer about said axis at a speed sufilcient to centrifugally retain said layer and withdrawing continuously from said reaction zone molten slag deposited on said thick layer in excess of that required for said layer.

4. The process of gasifying fuel to yield hot gaseous products, the fuel being such that the reaction produces no appreciable slag, which comprises establishing a reaction zone in a chamber, continuously supplying said fuel and at least one other reactant to said zone to maintain. the temperature of reaction therein at not less than 1200 C., supplying to said zone a heat insulating or slag forming material such as ash which is molten at said temperatureof reaction, establishing a thick layer of said material against the chamber wall around an axis through said zone to circumferentially enclose said zone, and continuously rotating the chamber and hence said layer about said axis at a speed sufficient to centrifugally retain said layer and continuously withdrawing molten heat insulating material in excess of that required to form the layer.

5. The process of continuously gasifying a slag-forming fuel which comprises establishing a reaction zone in a chamber at a temperature sufi'icient to melt the slag, continuously supplying said slag-forming fuel to said reaction zone, establishing a thick layer of molten slag around said zone by centrifugal force on the chamber wall by continuously rotating the chamber and hence said layer at a speed suflicient to centrifugally retain said layer against the chamber wall so as to provide heat insulation for said zone and continuously replacing that part of, the said layer nearest to said zone by withdrawing the said part in a molten state and supplying additional slag-forming fuel into the reaction zone and causing the molten slag content of said additional fuel to be applied to said layer by centrifugal force to continuously replace the withdrawn slag. I

6. The process of gasifying fuel to yield hot gaseous products, the fuel being such that the reaction produces no appreciable slag, which comprises establishing a reaction zone in a chamber, continuously supplying said fuel and at least" one other'reactant to said zone to maintain the temperature of the reaction at not less than 1200 C. supplying to said zone a heat insulating slagforming material which is molten at said temperature of the reaction, establishing a thick layer of said material around an axis through said zone against the chamber wall to circumferentially enclose said zone, continuously rotating said chamber and hence said layer about said axis at a speed sufficient to centrifugally retain said layer and continuously withdrawing that part of the layer Which is nearest to said axis in a molten condition at reaction temperature and replacing continuously the withdrawn layer by the supply of additional slag-forming material.

7. A very high temperature combustion reaction process Which comprises establishing a reaction zone in a chamber at a temperature high enough to produce slag, supplying to said reaction zone reactants along with slagforming material, forming a thick layer of slag against the chamber wall to enclose circumferentially said zone about a vertical axis so as to provide heat insulation therefor, retaining said layer by centrifugal force by continuously rotating'the chamber and hence said layer at a speed sufiicient to centrifugally retain said layer against the chamber Wall, the retained layer including a molten portion nearest to said reaction zone superimposed on a partially solid portion more remote from said zone and continuously replacing said molten portion as it runs down the partially solid portion by the introduction of additional slag forming material into said reaction zone.

References Cited in the file of this patent

Claims (1)

1. 5. THE PROCESS OF CONTINUOUSLY GASIFYING A SLAG-FORMING FUEL WHICH COMPRISES ESTABLISHING A REACTION ZONE IN A CHAMBER AT A TEMPERATURE SUFFICIENT TO MELT THE SLAG, CONTINUOUSLY SUPPLYING SAID SLAG-FORMING FUEL TO SAID REACTION ZONE, ESTABLISHING A THICK LAYER OF MOLTEN SLAG AROUND SAID ZONE BY CENTRIFUGAL FORCE ON THE CHAMBER WALL BY CONTINUOUSLY ROTATING THE CHAMBER AND HENCE SAID LAYER AT A SPEED SUFFICIENT TO CENTRIFUGALLY RETAIN SAID LAYER AGAINST THE CHAMBER WALL SO AS TO PROVIDE HEAT-INSULATION FOR SAID ZONE AND CONTINUOUSLY REPLACING THAT PART OF THE SAID LAYER NEAREST TO SAID ZONE BY WITHDRAWING THE SAID PART IN A MOLTEN STATE AND SUPPLYING ADDITIONAL SLAG-FORMING FUEL INTO THE REACTION ZONE AND CAUSING THE MOLTEN SLAG CONTENT OF SAID ADDITIONAL FUEL TO BE APPLIED TO SAID LAYER BY CENTRIFUGAL FORCE TO CONTINUOUSLY REPLACE THE WITHDRAWN SLAG.

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