AU8338587A

AU8338587A - Assembly for burning solid fuels

Info

Publication number: AU8338587A
Application number: AU83385/87A
Authority: AU
Inventors: Bengt Bengtsson
Original assignee: BENGTSSON BIOVARME AB
Current assignee: Bengtsson Biovarme AB
Priority date: 1986-11-26
Filing date: 1987-11-17
Publication date: 1988-06-16
Also published as: SE8605060L; SE8605060D0; WO1988004009A1; SE455640B

Description

ASSEMBLY FOR BURNING SOLID FUELS Field of the invention

The present invention relates to an assembly for burning solid fuels, comprising a combustion chamber through which a strand of fuel is supplied to a burning or glowing fire contiguous to the fuel strand, the burning fire being supplied with combustion air in a direction countercurrent to the fuel supply. An assembly this type is previously known from SE patent- application 8304228-3.

Background of the invention

In many types of solid fuel burning assemblies, i.e. such as comprise a grate of some type or other, combustion occurs wholly or mainly on a grate beneath an overlying fuel bed. In actual practice, the com- bustion directly exposed to the primary air current from below and protected by superadjacent unburned fuel shows a pronounced tendency to form slag which seriously interferes with the combustion process in that it blocks the grate so that the air supply is gradually reduced and ceases.

The difficulties and shortcomings encountered in combustion assemblies equipped with grates do not occur in a combustion assembly of the type referred to in the introduction since the combustion air is not supplied to the fuel bed from below via a grate, but from the end of the fuel bed or strand in a direc¬ tion countercurrent to the fuel supply direction. However, it frequently happens during operation of the combustion assembly mentioned in the introduction that the burning fire at least partly collapses and is reduced in height so that there is formed, between the upper side of the burning fire and the upper part or ceiling of the combustion chamber in question, a free space through which the combustion air can pass without penetrating properly into the fire. In consequence of the air thus leaking past the burning fire without coming into contact with the fuel, a low combustion efficiency is obtained, as well as a large ash percentage and large contents of solid combustion residues in the exhaust.

Summary of the invention The present invention aims at obviating the above- mentioned shortcomings of prior art solid fuel burning assemblies of the type mentioned in the introduction, and at providing an assembly of superior combustion efficiency. This and other objects are achieved, in accordance with the main characteristic features of the invention, in that at least one movable and/or flexible, preferably flap-shaped shielding member is arranged to engage the upper and/or front side of the burning fire in order to delimit, independently of the varying height of the fire, the space between the fire and the ceiling of the combustion chamber, thereby to constantly force the combustion air to pass through and not above the burning fire.

in a preferred embodiment of the invention, the shielding member is a flap or door which is pivot- ably movable, more particularly about a substantially horizontal shaft mounted in the area of the ceiling, of the combustion chamber.

Brief description of the accompanying drawings

In the drawings. Figs. 1-3 are simplified longi¬ tudinal sections of three different alternative embodi¬ ments of the assembly according to the invention. Detailed description of preferred emobdi ents of the invention

The assembly shown in Fig. 1 comprises a combustion chamber 1 defined by a ceiling 2, a bottom 3 and two preferably vertical side walls, one 4 of which is shown in the drawing. The ceiling, the bottom and the side walls may be provided, in actual practice, with linings 5 of refractory material. A duct 6 for evacuating exhaust gases from the combustion chamber 1 passes through the upper part or ceiling 2. At its front end, the combustion chamber is defined by an end wall 7 which, in the embodiment illustrated, com¬ prises at least one pipe 8 for supplying primary air to the combustion chamber and the fire burning therein. At the end of the assembly opposite to the front end wall 7, there is provided a feeder device 9 illustrated schematically in the form of a ram for feeding fuel 10 into the combustion chamber. The feeder device is preferably designed in the manner disclosed by SE patent application 8304229-1. In actual opera¬ tion, the feeder device operates in such a manner that it introduces, very slowly and intermittently, a strand or bed of fuel which may consist of, for example, pellets, chips, pieces of wood, briquettes or the like. At the front end of the fuel strand 10 is the burning or glowing fire 11 in which the co - bustion proper occurs. Finally, it should be mentioned that there is provided, at the front end of the assembly and on a level below the bottom 3, a pocket 12 adapted to receive ash, slag or other combustion residues 13 from the fire 11.

The illustrated assembly as described above is previously known in every essential respect from SE 8304228-3. The novel matter of the invention resides in the flap or door 14 serving as a shielding member. In the embodiment illustrated, the flap 14 is pivot- ably movable, more particularly about an essentially horizontal shaft 15 mounted in the area of the com¬ bustion chamber ceiling. It should also be noted that the flap 14 is mounted in the area between the ash pocket 12 and the duct 6 through which the exhaust gases from the fire 11 are evacuated. If a single flap or panel is used, it must have an axial extent substantially equal to the width of the combustion chamber 1 so that the flap will cover the entire with of the chamber, and the length, i.e. the distance from the shaft 15 to the free end 16 of the flap, should be approximately equal to the headroom of the combustion chamber in the zone within which the fire is located.

, As will appear from Fig. 1, the flap 14, because of its pivotal mounting, will constantly be in contact with the upper and/or front side of the fire 11 and, independently of any variations in the vertical extent of the fire and the fuel strand 10 (due to, for example, variations in the fuel structure and fuel properties and any ensuing variations in the fuel feed) , will delimit the space between the fire and the ceiling of the combustion chamber. In this manner, the primary air introduced via the pipe 8 is forced to pass through the fire, not over it. In other words, the flap 14 guarantees an intense and homogeneous admixture of the combustion air to the fuel, while providing an extremely high combustion efficiency. Practical tests have shown that the assembly according to the invention has an efficiency which is 100-200 % higher than that of similar prior art assemblies. Fig. 2 illustrates an assembly of the burner type, which is especially suitable for burning pellets, for example peat pellets. In the embodiment shown in Fig. 2, the fuel strand 10 is fed to the combustion zone within the area of the flap 14' by means of a per se known feeder screw 17 instead of by the ram feeder 9 according to Fig. 1. Moreover, there is pro¬ vided, in connection the ash pocket 12' , a second conveyor screw 18 by which the solid combustion resi- dues sliding down into the pocket 12' can be mechanical¬ ly removed from the assembly. In other respects, the assembly operates essentially in the same manner as the embodiment shown in Fig. 1, i.e. the pivotably mounted flap 14' ensures that primary air introduced via the pipe 8 ' in a direction countercurrent to the direction of the fuel feed is forced to pass through the fire, not over it.

Fig. 3, fi'nally, illustrates an embodiment in which a boiler 19 is mounted on top of the assembly according to the invention or the furnace. In the embodiment illustrated, the bottom 3" is sloping in a direction obliquely downwardly from the point of fuel introduction to the ash pocket 12". The fuel is supplied by means of a screw feeder 17', and a scraper 20 of per se known type is arranged to supply, or contribute to supplying, the fuel to the fire after the fuel has entered the combustion chamber via the screw feeder 17'. Between the bottom 3" and the ceiling or upper part 2" of the combustion chamber 1", there is provided, in accordance with the principle of the invention, a flap 14" which, in the embodiment illustrated, is hollow in that it .comprises double walls and has a multiplicity of holes 21 for blowing air towards the burning fire 11". The air thus supplied sustains, together with the primary air from the pipe 8", the combustion of the fuel in the fire, and above all the air cools the flap in contact with the burning fire, whereby the life of the flap can be increased considerably. In this connection, it is pointed out that it is possible in and per se to supply all com- bustion primary air via the holes 21 in the flap and to dispense with the separate primary air pipe 8", especially if the holes at the free end of the flap are made larger than the holes adjacent the pivot shaft of the flap so that the major part of the requi- site combustion air is supplied to the fire at the lower or free end of the flap.

Possible modif cations of the invention

It will be appreciated that the invention is not restricted to the embodiments described above and illustrated in the drawings. For example, it is possible to use, instead of a single whole flap or panel as shielding member, two or more panels which are individually pivotable in relation to the shaft in question and thus mutually movable and which, op¬ tionally, can overlap one another. It is also possible to use, instead of rigid members in the form of flaps, doors or panels, shielding members of flexible re¬ fractory material depending in the form of a cloth or curtain from the area of the upper part the com¬ bustion chamber down to the upper and/or front side of the fire.

Claims

1. An assembly for burning solid fuels, comprising a combustion chamber (1) through which a strand of fuel (10) is supplied to a burning or glowing fire (11) con¬ tiguous to the fuel strand, the burning fire being sup- plied with combustion air in a direction countercurrent to the fuel supply, c h a r a c t e r i s e d in that at least one movable and/or flexible, preferably flap- shaped shielding member (14) is arranged to engage the upper and/or front side of the burning fire (11) in order to delimit, independently of the varying height of the fire, the space between the fire and the ceiling (2) of the combustion chamber (1), thereby to constantly force the combustion air to pass through and not above the burning fire.

2. An assembly as claimed in claim 1, c a r¬ a c t e r i s e d in that the shielding member (14) is pivotably movable, more particularly about a substanti¬ ally horizontal shaft (15) mounted in the area of the ceiling of the combustion chamber.

3. An assembly as claimed in claim 1 or 2, c h a r a c t e r i s e d in that said shielding member (14) is mounted in the area between a pocket (12) adap- ted to receive ash and/or slag and a duct (6) for eva¬ cuating exhaust gases from the fire.

4. An assembly as claimed in any one of the pre¬ ceding claims, c h a r a c t e r i s e d in that the shielding member (14") is hollow and has a multiplicity of holes (21) for blowing air against the fire.