EP0058658B1

EP0058658B1 - Arrangement for firing solid fuels

Info

Publication number: EP0058658B1
Application number: EP80900738A
Authority: EP
Inventors: Johan Thorsten Hellzen
Original assignee: HELLZEN Johan Thorsten
Current assignee: HELLZEN Johan Thorsten
Priority date: 1980-04-16
Filing date: 1980-04-16
Publication date: 1985-12-18
Also published as: EP0058658A1; DE3071296D1; WO1981003057A1; AU5987580A; ATE17036T1

Abstract

Arrangement for firing solid fuels, comprising a fuel space with a fire-place, to which combustion air is supplied in a controlled manner and from which fuel gases are lead off via a duct to a chimney. At this type of arrangement for firing solid fuels, for example wood, coke, coal, peat, chips and the like, the combustion normally is incomplete as soon as the air supply is throttled. For eliminating this problem, the invention suggests the arrangement of an additional fire-place (11) in the draught direction after the fire-place (14) of the fuel-space for combusting gases coming from said last mentioned space.

Description

This invention relates to an arrangement for firing solid fuels, comprising a fuel space with an upwardly located, preferably sealable opening for fuel filling-up, the bottom of said space consisting of a grate for supporting fuel to the fuel space and for leading off ash to an ash-space located beneath the grate, at least one intake for adjustable supply of combustion air and a duct connected to a chimney or the like for carrying away the flue gases from the arrangement to said chimney, and that the lead-off duct connected to a fire-place in the lower portion of the fuel space is throttled in the draught direction after said connection and includes in the throttled area a nozzle opening with an area smaller than the duct in general on both sides of said opening, and means are provided to pass combustion air from the intake both to the fire-place of the fuel space and to the nozzle opening in order therein to effect combustion of gases coming from the fuel-hearth in the fire-place of the fuel space.
From the art is known GB-A-1 151 741 disclosing a solid fuel heating appliance where the primary air is fed to an ashpot under firebars carrying solid fuel. The primary air then passes up between the firebars to the solid fuel, without no special control of the primary air.
Concerning the secondary air GB-A-1 151 741 discloses that such air is fed through an inlet port, then transported upwards in a duct and then transported downwards through a duct. This arrangement is not satisfactory in the respect that the incoming secondary air is heated during its transportation in the ducts. The downward transportation in the duct will then be counteracted by the heating of the secondary air since heated air tends to rise upwards.
The object of the present invention, therefore is to produce an arrangement for the firing of solid fuels which does not show the aforesaid disadvantages, but renders possible a combustion as complete as possible due to a complete distribution of the primary air and due to the special design of the secondary air intake.
This object is achieved in that the arrangement according to the present invention has been given the characterizing features defined in the attached claims.
The invention is explained in greater detail in the following, with reference to the accompanying drawing, in which

Fig. 1 is a schematic section through a firing arrangement according to the present invention,
Fig. 2 is a partial section substantially along the line II-II in Fig. 1,
Fig. 3 is a partial section substantially along the line III-III in Fig. 1 through a pair of air supply ducts, and
Fig. 4 shows a mechanism for opening and closing two doors comprised in the arrangement.

In the drawing, 1 designates a fuel space, which at its upper portion is provided with an opening 3 for filling-in fuel. Said opening preferably can be sealed by means of a door 2 and has a bottom in the form of a grate 4 for supporting the fuel in the fuel space 1 and for passing ash formed at the combustion to an ash-space 5, which is located beneath said grate 4 and said fuel space 1 and includes a preferably sealable door 6 for removing ash from the ash space.
To the lower portion of the fuel space which can be said to constitute a part of the fire-place of the present invention, a relatively wide duct 8 is connected which extends to a chimney 7 for conducting away flue gases from the combustion. Said duct 8 is in other respects separated entirely from the fuel space 1 by means of a partition wall 9, which should be provided with incombustible insulation 10 for restricting the heat transfer from the duct 8 to the fuel space 1.
In said duct 8, in close connection to the fire-place of the fuel space, a throttling 11 is provided, for example in the form of a perforated plate 12, which has at least one through hole 13, the cross- sectional area of which is smaller than the duct 8 in general on both sides of the throttling. The said throttling acts as a combustion nozzle and is intended to bring about an effective combustion of combustible gases, which come from the fire-place of the fuel space and must pass through the throttling 11, because this is located, seen in the draught direction, after the fire-place of the fuel space which generally is designated by 14.
At the embodiment shown in the drawing, the primary combustion air required for the combustion is supplied both to the fire-place 14 of the fuel space and to the combustion nozzle 11 through a common piping system 15, which by an adjustable damper or draught valve 17 is connected to an intake 16 with adjustable damper or draught valve 17. Although not shown in the drawing, it is possible, within the scope of the principles on which the present invention is based, to arrange separate piping systems for the supply of the primary combustion air to the fire-place of the fuel space and to the combustion nozzle 11.
The piping system shown in the drawing comprises a plurality of pipes 18, which extend from the air distribution chamber 19 provided in the connection to said intake 16 inward beneath the fuel space 1, and which at least in their portion facing toward the fuel space 1 are provided with air holes 20, which are arranged in at least two rows and are directed obliquely upward-outward at a relative angle of e.g. 80 to 90°. Through these air holes 20 in the pipes 18 necessary combustion air is supplied to the fire-place 14 of the fuel space in a way distributed over the surface of the fire-place, in order to maintain the combustion in said fire-place, which per se need not be complete, but may take place with a certain air deficit. The combustion, however, shall be such that in the fire-place 14 of the fuel space a more or less glowing or burning fuel-hearth, depending on the amount of supplied air, is maintained, to which hearth new fuel is fed continuously from above as long as fuel is available in the fuel space.
In order to prevent this continuous feed of fuel to the fuel-hearth from being stopped, particularly when the fuel is in the form of wood, the fuel space 1 widens downward to the grate 4 as shown in the drawing.
At the embodiment shown in the drawing, the pipe of said pipes 18 which is located beneath the throttling 11 is provided with an upward pipe neck 21, the end of which located at some distance from the nozzle opening 13 is closed but provided with a number of air holes 22 both at the end and in adjacent wall portions for the supply of necessary primary combustion air to the nozzle opening formed by the throttling 11, which opening thus constitutes the remaining portion of the fire-place of the present arrangement, in which fire-place the combustible gases coming from the fuel-hearth are mixed with the combustion air, which flows out of the air holes 22 of said pipe neck and is preheated by the heat from the fuel-hearth, and thereby are combusted at a high combustion temperature, not the least due to the increase in speed caused by the throttling and the short distance to the fuel-hearth.
For adjusting the primary combustion air, the intake to the air distribution chamber 19, in which the combustion air is distributed to the different pipes 18, is formed as an exchangeable high-efficiency nozzle 16 and controlled in known manner by means of the draught-valve 17, which is located in front of the intake or nozzle 16 and can be controlled automatically in response to the temperature in or outside the fire-place for obtaining continuous or intermittent draught control, though it is shown in the drawing to be manually adjustable in different draught positions between fully open and fully closed position. The high-efficiency nozzle is shown in the drawing in the form of an exchangeable plate 23 with one or several holes 24 having a total flow area ensuring the supply of an air amount required for high-efficiency combustion at fully open draught valve.
In order to be able to maintain the fuel-hearth even at fully closed draught valve 17 so as to prevent the hearth from going out, an exchangeable idling nozzle in the form of an exchangeable plate 25 is provided in the draught valve, which plate has a small flow hole 26, which permits the passage only of the amount of air required for keeping the fuel hearth alive and in the nozzle opening 13 to effect the combustion of gases coming from the fuel-hearth. When the combustion air flowing out through the pipe neck21 is not sufficient for effecting a complete combustion of said gases, preferably pre-heated secondary air can be supplied through an adjustable secondary air damper, which in the drawing is shown to consist of a slide 38 movable in the holder and provided with a plurality of holes 36 located to the side of each other at a predetermined distance. In open position of the damper shown in Fig. 1, said holes are located directly in front of corresponding holes 37 in the wall to the duct 8, and by moving the slide 38 in its longitudinal direction the damper, thus, can be adjusted by covering the holes 37 entirely or partially, whereby a control of the secondary air is obtained. The secondary air damper can be used for supplying extra combustion air whenever required and also at fully open draught valve 17.
The combustion air flowing in through the intake or nozzle 16, thus, is distributed, independently of the position of the draught valve in the distribution chamber 19, to the different pipes 18 and then, in proportions defined by the air holes 20 and, respectively, 22, to the two fireplaces. Owing to the increase in speed and the resulting higher turbulence brought about by the throttling 11 in the duct 8, the combustion air supplied to the nozzle opening 13 is mixed intimately with the gases coming from the fuel hearth whereby an efficient and substantially complete combustion is obtained which substantially is independent of whether the combustion speed is high or low. The flue gases leaving the arrangement according to the present invention are thereby clean and protective to the environment.
In order to prevent smoke flowing out when the door 3 is opened for filling-in fuel, the fuel space 1 can be connected to the chimney 7 through a door 29 which, thus, must be opened about simultaneously with the door 2. For this reason, the filling-in door 3 is locked in closed position by a locking arm 32, which is attached to an axle 31 connected to the door 29. For being able to open the door 3, the locking arm 32 must be pivoted upward, whereafter by said locking arm the door 29 can be displaced and the fuel space 1 connected to the chimney 7. Before the filling-in door 3 again can be locked, the door 29 must first be moved back to the position shown in Fig. 1 by means of the locking arm 32, which first thereafter can be pivoted downward for locking the filling-in door 3. Said arm is arranged to co-operate by a clamp nose 33 with guide groove 34 in order to be drawn in to the door 3 by a pressure nose 35 to press on the door 3 and hold it closed in locked position.
The partition wall 9 between the fuel space 1 and the duct 8 is at its lower portion and beneath the throttling 11 in the duct 8 formed as fingers 27, along which the fuel can slide and which partly prevent the fuel from gushing in and clogging the space beneath the throttling 11. For this reason, the grate 4 also is bent upward and by its upward bent portion rests against the pipe neck 21 and against support brackets on the other pipes 18, which brackets however are not shown in the drawing.
As shown in Fig. 3, also a grate 28 can be provided beneath the pipes 18, which grate should have a finer mesh than the grate 4. In certain cases it may be sufficient with a grate located beneath the pipe 18.

Claims

1. An arrangement for firing solid fuels, comprising a fuel space (1) with an upwardly located, preferably sealable opening (3) for fuel filling-up, the bottom of said space consisting of a grate (4) for supporting fuel to the fuel space and for leading off ash to an ash-space (5) located beneath the grate, at least one intake (16) for adjustable supply of combustion air and a duct (8) connected to a chimney (7) or the like for carrying away the flue gases from the arrangement to said chimney, and that the lead-off duct (8) connected to a fire-place (14) in the lower portion of the fuel space is throttled in the draught direction after said connection and includes in the throttled area (11) a nozzle opening (13) with an area smaller than the duct (18) in general on both sides of said opening, and means (18, 21) are provided to pass combustion air from the intake (16) both to the fire-place (14) of the fuel space and to the nozzle opening (13) in order to therein to effect combustion of the gases coming from the fuel-hearth in the fire-place of the fuel space, characterized in that said means for passing primary air from the intake to the fire-place (14) and to the nozzle opening (13) consist of pipes (18), which are provided with air holes and extend from the intake and are located beneath the nozzle opening (13) and fuel space (1), the main portion of the air holes of said pipes being directed upward and outward, and that at least one of said pipes (18) is provided with secondary air diversion (21) being arranged adjacent to the combustion air inlet.

2. An arrangement as defined in claim 1, characterized in that at least one of said pipes (18) is provided with a pipe neck (21), which extends . to the nozzle opening (13_') and is provided with air holes (22) for guiding combustion air directly to the nozzle opening.

3. An arrangement as defined in any one of the preceding claims, characterized in that the intake (16) is provided with a high-efficiency nozzle and adjustable by means of a draught-valve (17).

4. An arrangement as defined in claim 3, characterized in that the draught-valve (17) is provided with an exchangeable idling nozzle for the supply of a predetermined smaller amount of combustion air at completely closed draught-valve.

5. An arrangement as defined in any one of the preceding claims, characterized in that the fuel- space (1) widens toward its lower portion for effecting self-feed of fuel to the fuel hearth.

6. An arrangement as defined in any one of the preceding claims, characterized in that an adjustable secondary air damper (36-38) is provided for passing in secondary combustion air to the nozzle opening (13.