WO1998037363A1

WO1998037363A1 - Combustion device for solid fuel

Info

Publication number: WO1998037363A1
Application number: PCT/SE1998/000314
Authority: WO
Inventors: Göran Hultmark
Original assignee: Bentone Ab
Priority date: 1997-02-21
Filing date: 1998-02-20
Publication date: 1998-08-27
Also published as: CA2282460A1; EP0968390A1; NO994010D0; SE9700609L; AU6129098A; NO994010L; SE9700609D0

Abstract

Combustion device for solid fuel in particular granular material. The device comprises a fuel dosing device (12) with one in a cylinder formed house (19) rotatable dosing chamber (18). The dosing chamber is so formed that during rotation it successively supplies fuel through the dosing device (12) in such a way that its intake port (10) and the outlet port (17) of the dosing means cannot at any occasion communicate. The dosing device (12) is axially connected to a fuel conveyor (14), which supplies fuel to a combustion chamber (15). The dosing chamber (18) and the fuel conveyor (14) have a power transmission connection and are arranged to be run by a common driving device (27). The invention also concerns the combustion chamber of the combustion device. The fuel conveyor is arranged essentially axially in relation to the longitudinal direction of the combustion chamber. On the inner wall (43b) of the combustion chamber is arranged in level with and in the extension of the centre axis (42) of the fuel conveyor at least one guide rail (43) which directs an air stream diagonally against the opposite inner wall of the combustion chamber. The invention also concerns a method for combustion of solid fuel.

Description

COMBUSTION DEVICE FOR SOLID FUEL

TECHNICAL FIELD

The present invention concerns a combustion device for solid fuel and a method for combustion of solid fuel, in particular granulate material and comprising a fuel dosing device with one in a cylinder formed house rotatable dosing means, which is arranged to successively supply fuel through the dosing device during rotation in such a way that the intake port to the dosing device and the outlet port of the dosing means cannot at any occasion communicate.

BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEM

Combustion devices of the above mentioned types are earlier known in a lot of different forms of execution. When stoking different types of bio fuel, such as pellets of different qualities (wood pellets, peat pellets, bark pellets etc.), wood chip, peat, straw, grain and others a limitation is that the combustion chamber normally is designed for one type of fuel and that the efficiancy falls when stoking with another fuel or that one gets problems with formation of slag and with the discharge of ashes.

An other problem is that it can be difficult to fulfil the fire security demand that the fire in the combustion chamber must not spread to the fuel store. One has tried to solve this by letting the fuel fall freely from the fuel store to the feeding screw. An air bridge between said units should prevent flash back, but hot air from the combustion chamber can pass through the feeding screw to the fuel store, which especially can occur at stoppage or other disturbancies. The rise for fire is therefor not eliminated.

Another problem is the feeding of the solid fuel to the combustion chamber. If the supply of fuel varies too much the fuel can be compressed in the feeding screw, which lead to that too much fuel from time to time is supplied so that the hearth is overfilled and a poor combustion is achieved. The fuel evaporates too slow and causes discharge of gases harmful for the environment. If on the other hand the combustion is too fast the melting temperature for the ask is reached which causes formation of slag. From DE 3427043 C2 is known a device for supplying a stoking device with fuel or waste, which should be disintegrated at the same time. This device comprises a rotatable lock between two screw conveyors, which lock has two functions, to prevent a fire to flush back and to cut the fuel into pieces. One drawback is that this known device demands either two engines for driving the rotatable lock and one of the screw conveyors or an engine and a worm gear. This device is therefor expensive and a lot of space is needed for the arrangement.

THE PURPOSE WITH THE INVENTION AND THE SOLUTION OF THE PROBLEM

The purpose with the present invention is to make a combustion device: a) which can be used with different kinds of fuel, also fuels which are moisted and keep a high efficiancy, b) which fulfils the safaty demands against flash back, i.e. that the fire cannot spread to the fuel store, c) which gives a controlled dosing and trouble-free feeding in of the fuel to the combustion chamber, d) which gives an air distribution above and below the fuel, which gives in view of fuel economy an effective use of the thermal value of the fuel, e) which have such a high degree of combustion that it reduces fumes harmful for the environment f) which is of a simple construction, has few movable parts, is easy to maintain, can be installed in existing heating boiler and can be controlled automatically mainly in the same way as an oil burner, g) which facilitate the removal of ashes, and h) which only demands one single driving device and is space saving

These purposes have been solved with the device and method defined in the patent claims. DESCRIPTION OF THE DRAWINGS

The invention will in the following be more closely described in connection with a few embodiments and with reference to the attached drawings.

Figure 1 shows a longitudinal section along the line I-I in figure 2 of a first embodiment of the combustion device in accordance with the invention.

Figure 2 shows the combustion device in accordance with figure 1 seen in rear view, i.e. from the combustion chamber side.

Figure 3 shows in an enlarged scale a longitudinal section of the fuel dosing device in a position for feeding out fuel. Figure 4 shows a cross section along the line IV-IV in figure 1.

Figure 5 shows a longitudinal section of a second embodiment of the combustion device.

Figure 6 shows a longitudinal section of an embodiment of a combustion chamber with a grid. Figure 7 shows a section along the line NII-VII in figure 1.

Figure 8 shows a section along the line NIII-NIII in figure 1.

Figure 9 shows in view from above and partly in section the embodiment in accordance with figure 5.

Figure 10 shows in perspective the combustion chamber in accordance with the invention.

Figure 11 shows a section of a modified fuel dosing device.

DESCRIPTION OF EMBODIMENTS

In the figures 1-4 11 represents a first embodiment of a combustion device in accordance with the invention, which device has a fuel dosing device 12. The fuel dosing device is via a vertical feeder funnel 13 connected with a not shown fuel store and to one end of a mainly horisontel fuel conveyor 14. The opposite end of the fuel conveyor is connected with a combustion chamber 15.

The dosing device 12 includes a dosing means 18 in form of a cylindrical dosing chamber 18 which is rotatably mounted in a cylindrical house 19. The dosing means 18 has one common intake and outlet opening 16, which when the dosing means rotates can be placed to communicate with an intake opening 10 at the upper part of the house and with an outlet opening 28 at the lower part. The intake opening 10 coincides with said feeder funnel 13. One sidewall 20 of the house delimit the dosing device from the fuel conveyor 14. The intake and outlet opening 16 is arranged in the cylindrical mantle 21. In connection to this opening 16 is arranged a further outlet opening 17 in the end wall 22 of the dosing chamber 18, which outlet opening 17 is located just opposite the outlet opening 28. The intake and outlet opening 16 of the dosing means and the intake opening 10 and outlet opening 28 of the house are so arranged and formed that the fuel during the rotation of the dosing means is supplied through the dosing device 12 in such a way, that the intake opening 10 of the house 19 and the outlet opening 16 from the dosing means cannot a any occasion communicate, i.e. a direct connection between the feeder funnel 13 and the fuel conveyor cannot be established. Both of the end walls 22 and 23 of the dosing chamber has an axle bar 24 and 25. The lastmentioned axle bar is the axle shaft for the dosing means, which axle shaft via a gear 26 is run by an electric motor 27, while the axle bar 24 is connected to the screw conveyor 35 of the fuel conveyor 14.

When the dosing chamber 18 is rotated by the electric motor 27, the intake port 16 will during a short time be located just opposite the intake opening 10 and a part of the fuel in the feeder funnel 13 will fall down into the dosing chamber.

When the dosing chamber has turned 180° the outlet port 16, 17 is in its totally open lower position just opposite the outlet opening 28 and the contents in the dosing chamber can be discharged.

Insted of a cylindrical dosing chamber the dosing device 18 can be in the form of a blade wheel (not shown) rotatably mounted in the house 19, which together with the cylindrical mantle wall 21 form a number of blade wheel cells, which also are arranged in such a way that a direct communication cannot be established between the feeder funnel 13 and the fuel conveyor. The fuel conveyor 14 comprises an outer and an inner tube 29 and 30, which are arranged concentrically in each other for forming an annular duct 31. The duct 31 is closed in the end at the dosing device and at its open end provided with steering means 32 in form of a short helical spring, which gives the air streaming through the duct a tangential exhaust direction and a turbulent flow. The combustion air is generated by a fan 33, which is connected to an air admission opening 34 in the outer tube 29 and which blows air into the duct 31 just opposite the dosing chamber 12. During its passage through the air duct 31 the air works as cooling air, which cools the inner tube, and at the same the combustion air is preheated.

In the inner tube is arranged a screw conveyor 35, which suitably consists of a helical spring. The helical spring is via an agitator device 36 connected to the axle bar 24 of the dosing chamber 18. The electrical motor 27 thus brings the dosing chamber 18 as well as the screw conveyor 35 in rotation and transfer the fuel in direction towards the combustion chamber 15 arranged at the opposite end of the fuel conveyor.

The combustion chamber 15, which suitably is a ceramic tube 37, preferably has a pear- shaped cross section, see figures 7,8 and 10, with a wider upper part 38 located in the extension of the fuel conveyor 14 and in direct connection to its opening 39, and with a lower converging part 40, which forms a conduit 41, where the combustion occur. One end of the fuel conveyor 14 is connected to the combustion chamber 15. In the upper internal part of the combustion chamber and in level with the centre axis 42 of the fuel conveyor and along at least one of the inner side, is arranged a guide rail 43 of heavy plate or similar, which with its upper radial surface 43a directs the combustion air diametrically towards the opposite inside of the combustion chamber. The guide rail 43 has its largest heights measured from the wall 43b of the combustion chamber, closest to the opening 39 of the fuel conveyor and decreases successively in direction towards the opposite end of the combustion chamber. The extension of the guide rail towards the wall of the combustion chamber increases in the same direction. This has the effect that closest to the opening of the air duct in the first third of the combustion chamber a circulating air stream is achieved, which mainly is limited to the upper part of the combustion chamber (figure 7), where the air is heated and where a combustion of the gases occur. In the second third of the combustion chamber the height of the guide rail from the wall 43b of the combustion chamber has decreased to such a degree that the circulating air stream also reach the fuel bed 45. The combustion of gases then continues but also the carbonization phase has started. In the last third the height of the fuel bed decreases as ashes and slag successively is fed through the opening 50, and the circulating air is spread out over the total cross section of the combustion chamber. In this last phase essentially only carbonization occurs.

The guide rail 43, shown in the embodiment may have other forms than the above described. The important thing is that the combustion is as totally as possible and that the air circulation described above is undisturbed.

In stead of directing the air with guide rail arranged on the inside wall of the combustion chamber, the air can be directed out from the air duct 31 with one in connection with the duct arranged tube, which with the aid of nozzles or similar directs the air towards the opposite wall of the combustion chamber.

The end of the combustion chamber opposite the fuel conveyor is partly closed by an end wall 49, which at the bottom leaves an opening for fumes and ashes.

Two perforated air distribution tubes are arranged to supply secondary combustion air to the fuel bed 45, which distribution tubes are connected to the air duct 31. Primary air delivered by the fan 33 is directed by the screw-formed steering means 32 in the end of the air duct 31 tangentially against the upper part 38 of the wall of the combustion chamber, which wall part directs the air stream against the upper surface 43a of the guide rail 43. The upper surface 43 a directs the air stream diametrically to the opposite wall of the combustion chamber, where the air mainly streams upwards and back to the upper part 38. The circular movement of the air is supported by the subpressure, created when the air around the opening 57 of the air duct is ejected together with the air from the duct 31. A smaller part of the supplied air is directed downwards and passes over the fuel, where it is heated, and is then directed upwards towards the underside 43c of the guide rail 43. From the underside 43c the hot air is directed against the opposite side and is at the same time mixed with the incomming cool air which thereby is preheated. The air distribution tubes 44 blows air into the fuel bed 45, whereby the amount of air can be regulated with a check valve (not shown) or similar. A scraping device 46 can be arranged for removal of ashes and slag from the combustion chamber and for cleaning of the conduit 41. The scraping device 46 can consist of a plate, which is formed similar to the conduit. The scraping device can for example be fastened to the lower border of the opening 39 of the fuel conveyor 14 and starts to function when the fuel conveyor 14 and the dosing device 12 is moved into the combustion chamber

15. The scraping device pushes all the material in the conduit out through the opening 50. Removal of ashes can possibly be performed automatically with the aid of a driving device (not shown).

The combustion device in accordance with figure 5, differs from the above described embodiment in that the primary air and the secondary air is supplied separately. The primary air is supplied through the air duct 31 and the secondary air through a conduit 59 connected to the distribution chamber, which conduit 59 in its turn is connected with at least one perforated air distribution tube 44. The manufacturing and assembling are simplified with this construction. The lead of the screw conveyor 35, i.e. the helical spring, and the diameter is so chosen that the fuel is supplied intermittently in the inner tube. A continous fuel bed, which could spread a fire from the combustion chamber, is thereby avoided.

The cleaning of the combustion conduit 41 is in the embodiment made without touching the combustion device. The cleaning is performed with the aid of a shaft 51 fastened to the scraping device 46. It is therefor possible to remove remnants from the combustion during ongoing operation. The shaft 51 is led through holes in the front wall 53 of the combustion chamber and the front wall of the stoking device 52. The shaft can be operated manually or automatically. The combustion chamber in accordance with figures 6 and 9 differs from the above described in that it is provided with one in direction towards the back part of the combustion chamber inclined grid 47. Secondary air is connected through tubes 48 to the underside of the grid. The guide rail is in this embodiment integrated with the wall of the combustion chamber and is formed in one piece with the combustion chamber, preferably of a ceramic material. The back end of the combustion chamber is partly covered by the end wall 49, which at the bottom has an opening 50 for the fumes and for the removal of ashes and slag.

Figure 11 shows a modification of the fuel dosing device 12 described above with reference to figures 1-3. If one wishes to supply large amount of fuel without increasing the rotation velocity or take the step to bigger dimensions of the conduits 29,30, the dosing chamber can be axially elongated and the intake port 16 can be placed on the side of the outlet port in the cylindrical mantle 21.

The control automatic (not shown) for controlling of the combustion device includes means:

- for controlling of the fuel supply from a store to the feeder funnel 13,

- for activating an electric ignitor, - for operation of the fan 33 in dependence of the temperature of the combustion,

- for controlling the velocity of rotation of the dosing chamber and the screw conveyor.

The invention is not limited to the above described embodiments but a lot of variations and combinations of the different details shown in the embodiments are possible.

Claims

1. Combustion device for solid, in particular gramular material and comprising a fuel dosing device (12) with one in a cylinder formed house (19) rotatable dosing means (18), which is so formed that it under rotation successively supplies fuel through the dosing device (12) in such a way that its intake port (10) and the outlet port (16) of the dosing means (18) cannot at any occasion communicate, characterized in that the dosing device (12) is axially connected to a screw conveyor (35), which supplies fuel to a combustion chamber (15), and that the dosing means (18) and the fuel conveyor (35) have a power transmission connection and are arranged to be run by a common driving device (27).

2. Combustion device according to claim 1, characterized in that the dosing means (18) is a dosing chamber in the form of a cylinder, which has an opening (16, 17) in its mantle (21), which opening serves as intake as well as outlet of the dosing chamber.

3.Combustion device in accordance with claim 1 , characterized in that the dosing means (18) is a blade wheel, which together with the cylinder formed house (19) is arranged to form a number of blade wheel cells.

4.Combustion device in accordance with claim 2, characterized in that the dosing chamber (18) is in the form of a cylinder , that in the mantle (21) of said cylinder is arranged said intake and outlet opening (16), and that adjacent said intake and outlet opening is arranged in one end wall (22) of the dosing chamber a sector formed outlet opening (17) , which is arranged to cooperate with one in a similar way formed cavity (28) in the lower part of one side wall (20) of the fuel conveyor.

5. Combustion device according to claim 1, characterized in that the rotatable dosing chamber (18) is mounted in axle bars (24,25), one of which is driven by an engine and the other (24) is connected with the screw conveyor (35).

╧î.Combustion device in accordance with figure 1, characterized in that the fuel conveyor (14) comprises an inner and outer tube (29), between which tubes is formed an annular duct (31) and that a fan (33) is connected to the end of the duct (31), which end is located adjacent the dosing device (12).

7. Combustion chamber for solid fuel, in particular granular material and comprising a fuel conveyon (14), which supplies fuel to the combustion chamber (15), characterized in that the fuel conveyor is arranged essentially axially in relation to the longitudinal direction of the combustion chamber, that at the inner wall (43b) of the combustion chamber is arranged essentially in level with and in the extension of the centre axis (42) of the fuel conveyor at least one guide rail (43) which directs an air stream diagonally against the opposite innerwall of the combustion chamber.

8. Combustion device according to claim 7, characterized in that a fuel dosing device (12) is connected to that end of the of the fuel conveyor (14) which is opposite the combustion chamber , that the fuel dosing device (12) has a rotatable dosing means (18), which is so arranged that it during rotation successively supplies fuel through the dosing device (12) in such a way that the intake (10) to the dosing device and the outlet from the doing means (18) cannot at any occasion communicate.

9.Combustion device according to claim 7, characterized in that the fuel conveyor (14) comprises an inner (30) and an outer tube (29) , between which is formed an annular duct (31), that a steering means (32) is arranged in the opening (39) of the annular duct (31), which steering means gives an tangential airstream from the opening, which airstream is directed against the upper part (38) on that side of the inner wall (43b) which is provided with said guide rail (43).

10. Combustion device in accordance with claim 7, characterized in that the combustion chamber (15) consists of one in cross section preferably pear- shaped tube (37), that one end of the fuel conveyor (14) is connected to the upper wider part of the tube and that the converging lower part of the tube serves as combustion conduit (41) and as conduit for ashes.

11. Combustion device in accordance with claim 7, characterized in that the guide rail (43) along one inner side wall of the combustion chamber (15) is formed with from the front end to the back end of the combustion chamber decreasing heights and increasing width , and that the guide rail is provided with upper and lower guiding surfaces (43a, 43c) for direction of the air stream against the opposite inner side wall.

12. Combustion device in accordance with claim 7, characterized in that along or at the combustion conduit (41) is arranged at least one perforated air spreading tube on at least one opening (44, 48) connected to a fan.(33).

13. Combustion device in accordance with claim 7, characterized in that an inclined grid (47), and below it at least one air spreading tube (44) or opening are arranged in the combustion chamber (15).

14. Combustion device in accordance with claim 7, characterized in that the combustion chamber (15) has an end wall (49), which is arranged to cover at least the upper part of that end of the combustion chamber which is located opposite the fuel conveyon (14).

15. Combustion device in accordance with claim 7, characterized in that the screw conveyor (35) consists of a helical spring, which is arranged with such a lead and diameter that the fuel is supplied intermittently along an essential part of its length.

16. Combustion chamber in accordance with claim 7, characterized in that a scraping device (46) is arranged moveable along the combustion and ash conduct (41) and has the same form as the conduit.

17. Combustion device in accordance with claim 15, characterized in that the scraping device is connected with that end of the fuel conveyor (14) which is directed towards the combustion chamber or alternatively is provided with one outside the combustion chamber manouverable shaft (51).

18. Method for combustion of solid fuel, in particular granular material, in a combustion chamber characterized in that the combustion air, which is supplied axially to the combustion chamber (15), when entering the combustion chamber is directed essentially radially outwards, which air thereafter is so effected by the wall of the combustion chamber and possible guide rails (43) that a circulating air stream is achieved in mainly the upper part of the combustion chamber in a first part of said combustion chamber, that in a second part of the combustion chamber the airstream is directed in the upper part of the combustion chamber as well as down over the fuel bed (45) and that in the last part of the combustion chamber the air stream is spread mainly over the total cross section of the combustion chamber.