System for Controlling Combustion Air

Abstract

The object of the invention is to provide a system for controlling combustion air supply, in which the air supply to the primary and secondary air supply can be infinitely variable. The object is also to enable said system to be retrofitted in furnaces having a primary and a secondary air supply. To achieve this, a housing (1) having an internal, pot-shaped insert (5) provided with radial openings (9; 10) associated with either the primary air supply (7) or the secondary air supply (8) of the furnace is located between the furnace and the supply line for the combustion air, the cross-sections of said openings being infinitely variable via a pivotally mounted (17) motion link, the rotary angle of which is restricted by one or more stops (19). The motion link (17) is actuated by means of a drive unit (13) which in turn can be controlled by a control unit (23).

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a system for controlling the combustion air supply in a solid fuel furnace with a primary air supply and a secondary air supply according to the preamble to claim 1.

PRIOR ART

In wood or coal-burning solid fuel furnaces the air required for combustion is usually supplied by a primary air supply and a secondary air supply. In such a case, the primary air required for heating up and for the combustion of coal is supplied to the furnace's combustion chamber in the lower area, i.e. through the grate. On the other hand, during the combustion of wood the combustion air is supplied into the upper area of the combustion chamber only via the secondary air supply following the heating up phase in which the combustion air is supplied via the primary air supply and secondary air supply.

Usually, the primary air supply and secondary air supply are set manually. The disadvantage of this control method, however, is that settings can only be made by trial and error and by making estimates. In addition, making settings in this way is very time-consuming as corrections have to be repeatedly made depending on the state of combustion.

Optimum combustion cannot therefore be achieved. Very many different types of systems for controlling the air supply have therefore since been developed to optimize the combustion of solid fuels such as wood or coal.

For example, a solid fuel furnace is known from DE 20 2010 003 329 U1 which has a regulating device for the primary air supply and a regulating device for the secondary air supply, both of which can be activated by a linkage which is coupled to an adjusting device.

The disadvantage of this solution is that the regulating device, and therefore the solid fuel furnace as well, is costly and complicated to construct.

A chimney furnace is described in EP 2 221 534 A2 with a control device for the air supply. To set the volume of the primary air supply and secondary air supply the respective air ducts leading into the combustion chamber are closed to a greater or lesser extent by means of a rotatable control disk in which geometrically different openings are arranged.

Apart from the fact that this embodiment too is very costly and complicated to construct, it has the further disadvantage that the volumes of air flowing through it can be set only in steps over the cross section created by the geometrically different openings in the control disc.

A further means of controlling the combustion air supply into the combustion chamber of a furnace via the primary or secondary air supply is presented in EP 2 096 356 A2. This solution requires only one control mechanism, comprising a temperature sensor and a flow regulator. However, the embodiment requires its own valve mechanism for the primary air supply and its own valve mechanism for the secondary air supply. In addition, the embodiment also has separate shut-off elements which must be activated independently of the control mechanism in order to close the air supply that is not required.

Despite the inherent simplicity of its design made possible because only one control mechanism is required, the embodiment is still very costly to construct.

The principal reason why all these systems listed above for controlling the air supply are costly and complicated to manufacture is that they are combined with the furnace. An associated additional disadvantage of all the embodiments previously referred to is that they cannot be retrofitted.

STATEMENT OF THE INVENTION

The present invention addresses the problem of developing a system for controlling the combustion air supply to a solid fuel furnace with a primary air supply and a secondary air supply in which the supply of air to the primary or secondary air supply is to be controlled in an infinitely variable manner. Its structure and manufacture are to be as simple as possible and the system is to be capable of being retrofitted in furnaces with a primary and secondary air supply.

The problem is solved according to the invention in that a housing is arranged between furnace and combustion air supply line, said housing having an internal, pot-shaped insert which is provided with radial openings which are assigned either to the furnace's primary air supply or secondary air supply, and whose cross sections are infinitely variable by means of a pivotally mounted motion link whose rotary angle is restricted by one or a plurality of stops, wherein the motion link can be actuated by means of a drive unit which can in turn be controlled by a control unit.

A solution has therefore been found which overcomes the disadvantages of the prior art referred to above. The use of a motion link provides a very simple solution which does not require additional mechanical adjusting devices such as valves, rods and the like.

The structure of the furnace is simplified and, at the same time, the need for an additional large installation space in the furnace is eliminated because it no longer has to accommodate complicated control components

A possible advantageous embodiment of the invention is set out in the other claim. The openings located in the housing which are normally closed and which can function as a bypass enable additional air to be supplied, if required, into the primary air supply and/or secondary air supply, by bypassing the system for controlling the combustion air supply. This ensures that there is always a minimum chimney draft to avoid the danger of the accumulation of dangerous gases.

EXECUTION EXAMPLE

An exemplary embodiment of a system for controlling the combustion air supply according to the invention is described in detail below by means of an execution example. The diagrams show the following details:

FIG. 1 a perspective view of the inlet side of a system according to the invention for controlling the combustion air supply,

FIG. 2 a perspective view of the outlet side of a system according to the invention for controlling the combustion air supply,

FIG. 3 a view of a system according to the invention for controlling the combustion air supply,

FIG. 4 a section A-A from FIG. 3 in the closed position of the system for controlling the combustion air supply,

FIG. 5 a section B-B from FIG. 3 in the open position of the system for controlling the combustion air supply,

FIG. 6 a section A-A from FIG. 3 during the control of the combustion air supply of the primary air supply

FIG. 7 a section A-A from FIG. 3 during the control of the combustion air supply of the secondary air supply.

As can be seen in FIGS. 1 and 3, the system according to the invention for controlling the combustion air supply comprises a housing 1 fitted on the inlet side with a collar 2 which provides a means of accommodating a flexible air hose (not illustrated) for supplying the air required for combustion, if this is not to be removed from the installation space. A basket-shaped attachment 11 fastened in a fixed position, for example by means of a bayonet lock 12, is located on the inlet side of the housing 1. A drive unit 13, described in detail below, is arranged in the interior of the attachment 11 (FIG. 5). The air required for combustion can flow through slit 14 through the housing 1 in the direction indicated by a directional arrow.

On its outlet side the housing 1 has a flange 4 by means of which the system for controlling the combustion air supply can be connected to a furnace which is also not illustrated and which is suitable for the combustion of solid fuels such as wood and/or coal and which has for this purpose a divided inlet for the combustion air supply, in this execution example an inlet divided into a primary air supply on one side and a secondary air supply on the other side.

In the housing 1 there is a pot-shaped insert 5 which is opened to the inlet side of the housing 1 and, in addition, separates the inlet side from the outlet side (FIG. 2). In manufacturing this as a plastic component it has proved to be advantageous, as shown in this execution example, to construct housing 1 and insert 5 as a single piece. The inner wall of the housing 1 is connected to the outer wall of the insert 5 by intermediate webs 6, thereby continuing in the housing 1 the division of the combustion air supply existing at the inlet of the furnace into a primary air supply 7 on one side and a secondary air supply 8 on the other side. The inlet side of the housing 1 is fluidically connected to the primary air supply 7 on the outlet side by means of an opening 9 located in the circumferential area of the insert 5 and is fluidically connected to the secondary air supply 8 on the outlet side by means of an opening 10, also located in the circumferential area of the insert.

The base of the pot-shaped insert 5 has in its center a bore which has been designed as a bearing 15 for an axle which serves as a fulcrum for a motion link 17 attached to it. As can be clearly seen from FIGS. 4 and 5 the radius of the motion link 17 has been determined such that the exterior circumferential area of the motion link 17 slides on the inner wall of the insert 5.

At the same time the arc length of the circumferential area of the motion link 17 is dimensioned such that the two openings 9 and 10 can be completely covered on the one hand (FIG. 4), but also almost completely opened on the other hand (FIG. 5). The pivoting range of the motion link 17 required for this operation is defined by a rib 18 located on the internal side of the motion link 17 and a stop 19 located on the attachment 11,

The drive unit 13, which has already been referred to above and which is attached in the interior of the attachment 11, serves to bring the motion link 17 into the required position. A rotary motion is generated in the drive unit and transmitted to a driver 20 which is arranged centrally to the axle 16 and which incorporates a counterpart 21 located on the axle 16 to enable the motion link 17 to be pivoted into the required position.

An electronic control unit 23, which in this execution example is attached by means of a holder 22 to the housing 1, controls the drive unit 13 by means of a cable which has not been depicted for the sake of clarity, with control effected on the basis of data determined by sensors and processed in the electronic control unit 23. In this case the sensors comprise, for example, a door contact switch, a sensor for recording the temperature of the furnace body and a flue gas temperature sensor.

In addition, in this execution example the system according to the invention for controlling the combustion air supply enables additional air to be supplied to the primary air supply and/or the secondary air supply by bypassing the controlled air supply. To that end the flange 4, as can be seen in FIG. 5, has a plurality of closed openings 24 in the area of the primary air supply 7 and the secondary air supply 8 which must be opened in varying numbers and assignments dependent on the design of the furnace to which the flange is connected. Where plastic is used as a material, this component can be conveniently manufactured, as described above, in the form of a thin plastic layer with re-closable predetermined breaking points. If necessary, the openings 24 can, for example, be re-closed by stoppers that are not illustrated.

The system according to the invention for controlling the combustion air supply described in this execution example has the following mode of operation:

In FIG. 4 the system for controlling the combustion air supply is shown in the closed position, i.e. in standby mode. The heating up phase begins as soon as the furnace is filled with the selected fuel, an operation signaled by the door contact switch. The motion link 17 is pivoted so far that both openings 9 and 10 are opened by the electronic control unit 23 by means of the drive unit 13 as shown in FIG. 5.

The control phase begins on completion of the heating-up phase, usually defined as a minimum as the attainment of a specific flue gas temperature and furnace body temperature.

If coal is used as a fuel, the combustion air supply of the primary air supply 7 is controlled. The motion link 17 is pivoted so far that the opening cross section of the opening 9 for the primary air supply 7 is opened and the opening 10 for the secondary air supply 9 is closed (FIG. 6). This ensures that the opening 10 for the secondary air supply 8 remains closed by the motion link 17, even when the opening cross section of the primary air supply 7 changes when the positions of the motion link 17 change during the control process.

By contrast, if wood is used as a fuel, the combustion air supply of the secondary air supply 8 is controlled. The motion link 17 is pivoted so far that the opening cross section of the opening 10 for the secondary air supply 8 is opened and the opening 9 for the primary air supply 7 is closed (FIG. 7). It goes without saying that the system ensures in this case too that the opening 9 for the primary air supply 7 remains closed by the motion link 17 when the opening cross section of the secondary air supply 8 changes because of the changing positions of the motion link 17 during the control process.

On completion of the control phase the system for controlling the combustion air supply assumes the standby mode shown in FIG. 4. Both openings 9 and 10 are closed by the motion link 17.

LIST OF REFERENCE NUMERALS

• 1 Housing
• 2 Collar
• 3 Directional arrow
• 4 Flange
• 5 Insert
• 6 Intermediate web
• 7 Primary air supply
• 8 Secondary air supply
• 9 Opening (primary air)
• 10 Opening (secondary air)
• 11 Attachment
• 12 Bayonet lock
• 13 Drive unit
• 14 Slot
• 15 Bearing
• 16 Axle
• 17 Motion link
• 18 Rib
• 19 Stop
• 20 Driver
• 21 Counterpart
• 22 Holder
• 23 Control unit
• 24 Opening

Claims

1. System for controlling the combustion air supply in a solid fuel furnace which has a primary air supply and a secondary air supply which are connected to an air supply line characterized in that a housing (1) is arranged between said furnace and said air supply line that has an internal pot-shaped insert (5) that is provided with radial openings (9;

10) which are assigned either to the primary air supply (7) or the secondary air supply (8) of the furnace and whose cross sections are infinitely variable by means of a pivotally mounted motion link (17), whose rotary angle is restricted by one or a plurality of stops (19), wherein the motion link (17) can be actuated by means of a drive unit (13) which can in turn be controlled by a control unit (23).

2. System for controlling the combustion air supply according to claim 1, characterized in that closable openings (24) are located in the housing (1) for a defined addition of additional air into the primary air supply (7) and/or the secondary air supply (8).

3. A controller for combustion air supply in a solid fuel furnace having a primary air supply and a secondary air supply connected to an air supply line, comprising:

a housing disposed between said furnace and said air supply line, including an internal insert provided with openings assigned to said primary air supply and openings assigned to said secondary air supply;

a control unit;

a drive unit controlled by said control unit and connected to a motion link disposed to infinitely vary the cross-sections of said openings; and

a plurality of stops disposed to restrict the rotary angle of said motion link.

4. A claim in accordance with claim 3, further comprising that said openings are radial openings provided in said housing.

5. A claim in accordance with claim 3, wherein said internal insert is pot-shaped (5).

6. A claim in accordance with claim 3, wherein the radial openings (9; 10) which are assigned either to the primary air supply (7) or the secondary air supply (8) of the furnace and whose cross sections are infinitely variable.