FR2468836A1 - Pulverised fuel combustion furnace - has air pre-heater and feed chute with blower to convey heated air and fuel to furnace - Google Patents

Abstract

The furnace consists of a cylindrical combustion chamber, mounted horizontally. The chamber connects with an ash container (2) located below the cylinder. The ends of the cylinder are closed, and a smaller cylinder (3) is fitted inside the first. This cylinder is opened at one end (17). Fuel is supplied from a side chute into the furnace through an opening (9), mixed with pre heated air. Circulating air is admitted through the opening (12). The furnace is lined with refractory material (5), and air is supplied from a separate blower.

Description

 The present invention relates to methods and apparatuses for burning solid fuels in the divided state and of small particle size.

The technical sector of the invention is that of the construction of combustion appliances of the hearth-cyclone type or combustion chambers with a horizontal axis.

The expression divided solid fuels designates any ground or chopped solid combustible material having a small or medium particle size, the particle size of which is neither too large nor too fine, for example vegetable waste of the type chopped straw, bales of cereals, coffee or peanut shells, leaves and shavings of canes or reeds, marc and resin seeds, crushed household waste, coal or ground charcoal, crushed but not pulverized, chippings or sawdust, etc. meration not being limiting.

 Are already known cylindrical combustion chambers, with a horizontal or substantially horizontal axis, in which the gases move helically with a cyclonic movement. These combustion chambers are also called cyclone hearths.

The technique of cyclone hearths with horizontal axis has been widely used in different applications, for example as a combustion chamber on boilers with water tubes, with walls in tubes and / or in refractory materials, intended for the combustion of pulverized coal or certain vegetable fuels or the mixed combustion of pulverized coal and liquid or gaseous fuels.

 The objective of the present invention is to provide various improvements to combustion devices comprising a cyclonic combustion chamber, with a horizontal or substantially horizontal axis, in particular improvements in the combustion air, fuel and ash circuits in order to make this a more competitive and reliable technique which makes it possible to widen the field of use thereof to many divided fuels and also to widen the possible applications of this type of apparatus.

The objectives of the invention are achieved by means of a method for burning divided solid fuels, of small particle size, in a cylindrical combustion chamber with a substantially horizontal axis, which method comprises the following steps
- Combustion air is preheated by circulating it in an annular space which surrounds said combustion chamber;
- Said solid fuels are entrained by preheated air;
- And injected tangentially at high speed near one end of said combustion chamber said solid fuels ......

mixed with preheated combustion air.

According to a preferred method, the preheated combustion air is injected into a converging-diverging nozzle which is extended by a conduit which opens tangentially into said combustion chamber and said divided solid fuels are introduced into the neck of said nozzle where a pressure prevails. close to atmospheric pressure.

An apparatus according to the invention for burning divided solid fuels of small particle size comprises, in combination
- A cylindrical combustion chamber, with a substantially horizontal axis, comprising two coaxial cylindrical walls which delimit between them an annular space which communicates at its two ends before a free space intermediate between end flanges;
- a fan which circulates combustion air through said spaces, so that this air is preheated and cools the walls of the combustion chamber;
- A convergent-divergent nozzle through which circulates the preheated combustion air, which nozzle is extended by a conduit which opens tangentially into the combustion chamber;
- And a device for loading solid fuel located above said nozzle and connected to the neck thereof.

 According to a preferred embodiment, the internal wall of the combustion chamber is made of sheet steel and has an internal lining composed of several rows of silicon carbide plates, each row being composed of several curved plates, in the form of sectors. circular, which are juxtaposed and assembled end to end.

 Preferably, one or more layers of a thermal insulating product, resistant to high temperatures, is interposed between said linings and the internal wall to allow the free expansion of the parts of said lining.

An apparatus according to the invention further comprises an ash receptacle disposed below an opening which extends over a part of the lower generator of said combustion chamber, which receptacle comprises means for extracting the ash and said silicon carbide packing has cutouts in the part located above said opening.

 The invention results in improved apparatuses for burning solid fuels in the divided state with a small particle size, but greater than the particle size of the pulverized materials which can be fluidized.

An advantage of the devices according to the invention is that they make it possible to use as fuels all kinds of plant, mineral or industrial waste after having crushed or chopped them to divide them into fragments of relatively small size, for example of the order of a few millimeters to a few centimeters.

The fact that the combustion air is preheated by circulating it around the combustion chamber has several advantages.

First, part of the calories that would be lost to the outside of the hearth are recovered, then the walls of the hearth are cooled, which prevents damage to the lining linings of the combustion chamber. Finally, the combustion air which mixes with the fuel is already preheated. a higher temperature is obtained in the flame which facilitates the combustion in the same appliance of different fuels having a calorific value and a water content which can vary greatly from one fuel to another. The high temperature cyclonic combustion which is carried out in an apparatus according to the invention extends the residence time of the particles in the combustion chamber, so that the quantity of unburnt substances contained in the ashes and in the gases leaving the hearth is low.

The silicon carbide plates which line the cylindrical walls of the combustion chamber are resistant to abrasion wear due to the abrasive and inflamed solid particles which are projected against this wall as a result of the helical displacement of the hot gases. Because these linings are made up of curved juxtaposed plates, it is easy to replace one or more of them in the event of deterioration without having to redo the entire coating.

 The passage of preheated air through a diverging convergent nozzle ensures the entrainment of solid fuel by the depression due to the passage of air and to obtain a mixture of air and solid fuel in proportions which remain substantially constant in that the quantity of solid fuel entrained varies in the same direction as the air flow.

 Of course, a combustion chamber according to the invention can be connected to a heat generator or to any user device, for example on an oven, a dryer, an oven, a boiler, an exchanger, etc., by means of connecting parts adapted to each particular case, parts which can be separated from the combustion chamber or form an integral part thereof.

 The following description refers to the appended drawings which represent, without any limiting character, exemplary embodiments of apparatus according to the invention.

 Figure i is an axial section of an apparatus.

 Figure 2 is a half cross section of Figure i along II-II.

 FIG. 3 represents a diagram of the operation of an apparatus according to FIGS. 1 and 2.

FIG. 4 represents an alternative operating mode of an apparatus according to FIGS. I and 2.

Figures I and 2 show a combustion apparatus for burning solid fuels in the divided state. This appliance comprises a cylindrical combustion chamber having a horizontal axis x xl. Of course, the word horizontal must be understood as designating a horizontal or substantially horizontal line, because in certain applications, it is advantageous to tilt the axis x xl slightly to facilitate, for example, the removal of the ashes.

The combustion chamber comprises a cylinder 1, made of sheet metal, which has at its lower part, an opening 2a which communicates with a receptacle 2 of any shape which is located below the opening 2a and which is intended to collect the ashes and other solid combustion wastes.

The two axial ends of the cylinder 1 are closed by side walls or flanges IA and IB perpendicular to the axis x xl. The combustion chamber comprises a second sheet metal cylinder 3, coaxial with the cylinder 1 and situated inside the latter with which it delimits an annular space 15 and the two axial ends of the cylinder 3 are closed by side walls 3A and 3B which respectively define with the side walls IA and IB intermediate spaces 16A and 16B.

The side wall 3a is pierced with an orifice 17, preferably axial, which communicates with a cylindrical conduit 18, through which the hot gases leave the combustion chamber. The cylinder 18 passes through the wall 1A and is connected to a user device - for calories, for example a dryer, an oven, a generator of heat transfer fluid, an exchanger, etc. The interior of the cylinder 3 and of the side walls 3A and 3B are coated with refractory and / or thermal insulating materials.

 The cylindrical wall 3 is coated internally with n rows, for example four rows in the case of the figure, of linings 4 of silicon carbide. Each row is formed by several sections in the form of curved plates according to circular sectors, the number of which depends on the diameter, which are juxtaposed to cover the entire periphery and which are assembled together during assembly, for example by stud assemblies. and mortises or any other equivalent means of assembly.

 Between the lining 4 and the sheet metal wall 3, one or more layers of a flexible and insulating material 5 of very high quality are inserted intended to allow the free expansion of the curved plates 4 and to reduce the loss of calories to the outside of the foyer.

 The material 5 can be, for example, thermal insulating cardboard or any other equivalent material, of high quality, resistant to high temperatures.

The vertical walls 3A and 3B as well as the walls of the cylindrical duct 18 and the walls of the receptacle 2 are coated internally with a refractory lining 19, for example of shaped parts, whether or not baked, in refractory concrete or in ceramic or in material flexible insulating, in one or more layers.

 The linings 4 located above the opening 2a have openings 4a. These openings are cut for example at the junction between two rows of fittings and symmetrically on either side of this junction, each opening is composed for example of two half squares, two half diamonds or two half circles which come together end to end to form a square, diamond-shaped or circular opening.

 The covering 19 of the cylindrical conduit 18 preferably comprises inclined cutouts 20 in the form of a slot.

 The end wall A1 is fixed on flanges 6 which make the device removable. Manholes 7 and 8 provide access to the interior of the combustion chamber and the receptacle 2.

 An orifice 9 is cut through the two cylindrical walls I and 3 and through the lining 4 for the passage of a conduit 9a, having a section of any shape, for example rectangular, which is connected to a converging-diverging nozzle 10 visible in Figure 2. The nozzle 10 has an opening 10a, to which is connected a supply of preheated air, as will be explained below. Above the nozzle 10 is arranged a device for loading the solid fuel divided. The loading device can comprise, for example, a hopper 14 and a rotary airlock 14a, the outlet of which is connected to the nozzle. The loading device can be reconstituted according to other equivalent variants, for example of an endless screw, of a sole dispenser, or a simple chute into which the divided fuel falls.

 The nozzle 10 comprises a converging part upstream of the arrival of the solid fuel and a diverging part downstream, so that the combustible product falls in the intermediate part between the converging and the diverging, where a lower pressure prevails, close to atmospheric pressure. This pressure may be slightly higher than atmospheric pressure in some cases. It is lower than the atmospheric pressure in all cases where the nature or the particle size of the solid fuel does not allow the use of an isolation lock 14a, such as a rotary lock or a worm.

The duct 9a opens tangentially into the combustion chamber in the vicinity of the end opposite to the outlet duct 18, so that the gases and fumes progress inside the combustion chamber along a helical path.

 A second passage is cut through the cylindrical walls I and 3 and through the linings 4 near the orifice 9 for the passage of an auxiliary burner there. The burner 11 is supplied with liquid or gaseous fuel and is used to preheat the combustion chamber at the time of ignition.

 The free space 16A located between the bottoms 1A and 3A communicates with an air inlet duct 12. Likewise, the free space 16B intermediate between the bottoms 1B and 3B communicates with an air outlet duct 13. These conduits 12 and 13 can be located at any point of the volumes 16A and 16B. The volumes 16A and 16B communicate respectively with the two axial ends of the annular space 15.

 FIG. 3 represents a first example of embodiment of the connections of the combustion air preheating circuit.

The discharge of a fan 21, which draws in outside combustion air, is connected to the duct 12. The combustion air is distributed in the volume 16A, circulates in the annular space 15 where it is preheated, while cooling the walls of the combustion chamber. it is then collected in the space 16B and leaves via the conduit 13 which is connected to the inlet 10a of the nozzle 10.

A possible branch connection, shown in dotted lines in FIG. 3, supplies preheated combustion air to the auxiliary burner 11.

 FIG. 4 represents an alternative embodiment in which the fan 21 is placed between the duct 13 and the inlet 10a of the nozzle 10. In this variant, the suction of the fan is connected to the duct 13 and sucks in air combustion through orifice 12 and volumes 16A, 15 and 16B.

 Figures 3 and 4 are simplified diagrams on which we have not shown all known accessories such as registers or flaps for adjusting the air flow, flow rate measuring devices, temperatures and pressures, valves and other sectioning devices etc ..., which can be arranged in any way and well known on the two variants of circuits shown in FIGS. 3 and 4, variants which differ from one another only by the location of the fan 21.

 The device shown in Figures 1 and 2 can be placed on legs or on a frame or be suspended.

The operation is as follows.

 Upon ignition, the auxiliary burner 11 is started to pre-heat the combustion chamber. The combustion air which circulates in the annular space 15 is preheated. it passes through the nozzle 10 and causes the solid fuel to entrain which penetrates at high speed and tangentially into the combustion chamber while being mixed with preheated air. The combustion of solid fuel starts and takes place in a cyclonic fashion at very high temperature. The cyclonic effect prolongs the residence time of the solid particles in the combustion chamber and makes it possible to obtain a complete combustion of these.

 The linings 4 made of silicon carbide are isolated from the hot wall 3 by the insulating layer 5. These linings can be brought to a high temperature which depends on the calorific value and on the moisture content of the solid fuel and can, in certain cases, reach and exceed 15000C. The linings 4 are resistant to such temperatures as well as abrasion and ash.

 Depending on the setting of the appliance and in particular the excess combustion air, the internal operating temperature can be adjusted. Depending on the type of fuel used and its ash melting curve, an effort will be made to adjust the temperature to avoid the risk of ash deposition, detrimental to the operation of the device. In general, the appliance will work so that the ash is in the state of molten slag and that it flows along the linings 4. In some cases where the ash melts only at very high temperature, the appliance can be adjusted so that the powdered ash remains in solid form and is evacuated with the smoke.

 The inclined slot 20 which is provided in the refractory lining 19 of the conduit 18 allows the flow of liquid slag which could be deposited in the bottom of the conduit 18. Incandescent fly ash remain in the hot gases which exit through the conduit 18. The temperature of these ashes is between 12000C and 17000C, depending on the fuel and the settings.

 It will be noted that the diverging portion of the nozzle 10 is situated in a horizontal plane where it is produced by widening the width of the nozzle. This widening does not appear in Figure 2.

 Of course, without departing from the scope of the invention, the various constituent elements of the apparatus which has just been described by way of example, may be replaced by equivalent elements fulfilling the same functions.

Claims (6)

mixed with preheated combustion air.  end of said combustion chamber, said solid fuels  - And we inject tangentially, at high speed, in the vicinity of a - Said solid fuels are entrained by preheated air;  annular space which surrounds said combustion chamber  - combustion air is preheated by circulating it in a  horizontal, characterized in that  lometry, in a cylindrical combustion chamber with substantially axis I - Process for burning divided solid fuels, of small grain 2 - Method according to claim 1, characterized in that the com air  preheated bustion is injected into a convergent-divergent nozzle  which is extended by a conduit which opens tangentially into the  said combustion chamber and said solid fuels are introduced  divided in the neck of said nozzle where there is a pressure close to atmospheric pressure. 3 - Apparatus for burning divided solid fuels, of small granulo metrics, characterized in that it comprises, in combination  - a cylindrical combustion chamber with a substantially horizontal axis  comprising two coaxial cylindrical walls (1, 3) which delimit  between them an annular space (15) which communicates at its two ends mites before a free space (16A, 16B) intermediate between flanges  end (1A, 3A and 1B, 3B);  - a fan (21) which circulates combustion air through said spaces (16A, 15 and 16B), so that this air is preheated  and cools the walls of the combustion chamber;  - a converging-diverging nozzle (10) through which the air circulates of preheated combustion, which nozzle is extended by a duct (9a) which opens tangentially into the combustion chamber;  - And a device (14) for loading solid fuel located at  above said nozzle and connected to the neck thereof. 4 - Apparatus according to claim 3, characterized in that the wall in dull (3) combustion chamber is made of sheet steel and has  an internal lining 4 composed of several rows of plates of silicon carbide, each row being composed of several plates curved, in the form of circular sectors, which are juxtaposed and assembled end to end. 5 - Apparatus according to claim 4, characterized in that one or more  layers (5) of a thermal insulating product resistant to temperatures  high is interposed between said linings (4) and the inner wall (3) to allow free expansion of the parts of said lining. 6 - Apparatus according to any one of claims 4 and 5, characterized  in that it has an ash receptacle (2) arranged below an opening (2a) which extends over part of the lower generator  of said combustion chamber, which receptacle includes  means (8) for extracting the ashes and said carbide packing (4)  of silicon has cutouts (4a) in the part located above of said opening (2a).