Gas/air ratio controller for pre-mixing valve of combustion device

Description of the invention

The present invention relates to a gas / air ratio control device for a pre-mixing combustion device.

In order to minimize the emission of harmful substances and to optimize the efficiency of the combustion device, efforts are made to keep this gas / air ratio at the optimum point.

So far, systems with pneumatic coupling and with electronic coupling are known.

In the case of air-coupled systems (known from US patent 4,385,887), the size of the gas flow is kept constant in relation to the size of the air flow. This is done by a pressure controlled regulator in the gas path. The pressure difference is used as the control pressure to control the gas flow rate, that is to say in direct relation to the amount of air flow sucked in. The control pressure of the regulator is generated either in the mixing device or on the diaphragm, in the air path.

Pneumatic coupling systems do not require electrical or electronic components. Their mechanical structure is very simple and they work very quickly. Only a few moving parts are required. The preparation of the mixture by means of a pneumatic combination has the advantage that it allows a very rapid response to pressure fluctuations and flux sizes in the combustion plant and allows the gas / air ratio to be kept constant over a wide modulation range. As a result, these systems have proven successful in many installations.

However, the influencing factors such as gas quality, air pressure and combustion air temperature cannot be regulated in these systems and require final adjustment in the installation. Due to the liberalization on the gas market, one must take into account greater fluctuations in gas quality, which in these systems require constant adjustment.

In addition, air-coupled systems, in the case of a large modulation range, become inaccurate in the lower operating range, especially after extended periods of operation. In order to guarantee a long-term, high-quality combustion, the minimum capacity, depending on the version, must therefore not be set below 15 to 20%. In electronically coupled systems, the exhaust gas composition in or after flame or the flame temperature is measured using a sensor. The sensor produces a signal that is evaluated by an electronic regulator. The controller controls an actuator which determines the amount of gas. These electronically coupled systems are slower in adjusting variations in air volume. The sensors used are sensitive and of limited durability. A reliable sensor signal is essential for the safe functioning of the combustion system. However, fluctuations in gas quality, air pressure and combustion air temperature can be adjusted.

The object of the invention is to realize the advantages of the electronic coupling systems in a pneumatic coupling system without losing the advantages achieved therein.

To accomplish this task, a device for regulating the gas / air ratio for a pre-mixing combustion device was constructed, comprising a pneumatic regulator that maintains a constant ratio between the pressure in the gas line and the pressure in the air line, and a mixing device arranged downstream of the regulator in the flow. characterized by the fact that it has:

- a mixing chamber that enlarges from its outlet opening in the direction of the stream's movement as in a Venturi nozzle,

- a nozzle connected to the air tube that enters the inlet of the mixing chamber,

- an annular gap connected to the gas conduit, which is formed between the edge of the inlet opening of the mixing chamber and the nozzle connected to the air conduit, the device according to the essential features of the invention, characterized in that it comprises a cone arranged in the air conduit, which in depending on the sensor signal, it is adjustable in the axial direction in relation to the nozzle connected to the air conduit, and a blower with a controllable number of revolutions, which supplies the mixture from the mixing chamber to the combustion device. The device is also characterized in that the cone is actuated by a linear motor and in that the cross-section of the orifice connected to the air duct of the nozzle is adapted to the cross-section of the cone, so that the nozzle with the cone is completely closed. Moreover, the device is characterized in that the cone angle is less than 30 °.

The regulator is a pneumatic association of the system, and the sensor provides a signal that allows you to adjust fluctuations in gas quality, air pressure and combustion air temperature. Depending on this signal, it is reset, which is preferably actuated by a motor

The cone is linear and travels more or less deeply into the interior of the connection nozzle for the air line. This makes it extremely easy to ensure that the combustion device always works with the optimum gas / air ratio.

The sensor can reveal the composition and / or temperature of the exhaust gases, and the electronics can from the obtained data determine the corresponding values ​​of the gas quality, air pressure and temperature of the combustion air, which enables the corresponding adjustment by shifting the cone. By thus varying the pressure ratios and the flow rates in the mixing chamber that is expanding - like a venturi nozzle, it is possible to vary the gas / air ratio over a wide range, without sacrificing the advantages of the pneumatic combination. By introducing the cone into the connection nozzle into the air line, the air velocity increases at the entrance to the mixing chamber. As a result, a greater pressure is built up in the annular gap connected to the gas line, which allows the gas input into the mixing chamber to be increased. At the same time, by reducing the cross-section of the nozzle connected to the air duct, the size of the inlet air stream is reduced. As a result - using less air, more gas is delivered to the mixing chamber.

Moreover, according to the essence of the invention, the degree of modulation increases, whereby, with reduced efficiencies, the resulting inaccuracies can be adjusted.

If the combustion device is shut down, the cone in the nozzle connected to the air conduit may close it completely. Thus, if the combustion appliance is connected to a waste gas installation to which other combustion appliances operating with the exhaust gas overpressure may be connected, then a backflow of the waste gas into the air duct of the disconnected combustion appliance is prevented in this way.

In case of damage to the sensor, the cone is completely removed from the nozzle connecting to the air conduit. The lowest efficiency of the combustion device is so increased that combustion is kept within the operating range and no absolute sensor interaction is required. For example, the lowest efficiency will be raised to about 20%. The basic setting of the pneumatic regulator here ensures that a sufficiently high excess air is maintained with the desired gas types, air temperatures and altitudes. In this position of the cone, the adjustment corresponds to a conventional pneumatic pairing. The combustion plant does not need to be shut down and the emissions of harmful substances remain below the prescribed limits. Previously known systems with electronic association must be set aside when selecting a sensor. In summary, the following advantages can be achieved by using the invention.

Fluctuations in gas quality, air pressure, and combustion air temperature can be adjusted without sacrificing the benefits of pneumatic combination, i.e. the ability to react quickly to changes in capacity and pressure fluctuations.

The combustion device also works in the event of a sensor failure, since the pneumatic linkage on which the control is based remains operational.

The pneumatic linkage control, which has a mixing chamber that expands like the Venturi nozzle, can also be sensor-controlled supplementary with a cone.

The degree of efficiency increases as the combustion is regulated closer to the stoichiometric value. As a result, at a higher dew point, more condensate is formed and less air is heated for combustion. In the case of pneumatic control without sensor control, a high excess of air must be maintained so that in the event of fluctuations in gas quality, the air pressure and temperature of the combustion air are kept at a sufficient distance from the stoichiometric value. Only in this way can the formation of poisonous carbon monoxide be reliably prevented in these systems.

The degree of regulation is increased in that a lower minimum capacity can be set. In the case of pure pneumatic coupling, with such low capacities, it is difficult to ensure a sufficient efficiency of the gas / air ratio.

The start / stop emissions are thus minimized, since fewer switching operations are required with a lower minimum capacity.

The combustion device can be connected to other installations with a common exhaust gas extraction system operating with overpressure, without causing any danger, in the event of failure of the combustion device - that the exhaust gas will flow back into the room in which the device is operated, because the cone can completely close the pipe air.

PL 202 022 B1

Advantageously, the opening angle t of the nozzle connected to the air conduit corresponds substantially to the angle of the cone. This contributes to the fact that the nozzle connected to the air line is completely closable by the cone, as provided for in the further development of the invention.

It has proved very advantageous to make a cone with an angle of less than 30 [deg.]. This angle allows a more sensitive adjustment of the cone and thus a very precise adjustment. However, in case of difficulties, cones with an angle greater than 30 ° are also possible.

The invention is explained in more detail below on the basis of a preferred example and the attached drawing.

The figure shows on:

- fig. 1 is a schematic diagram of the device according to the invention

- fig. 2 - an axial section through one diagrammatic representation in fig. 1 - a structural element,

The device according to Fig. 1 has a gas line 1 and an air line 2. A pneumatic regulator 3 operates between these two lines, which controls the pressure in the gas line 1 as a function of the pressure in the air line 2. The gas line 1 and the gas line. with the air 2 fall together into the mixing device 4. Downstream of the mixing device 4 there is a fan 5 with a controllable speed, which transports the mixture to a combustion device (not shown).

Fig. 2 shows in detail the structure of the mixing device 4 to which the blower 5 is directly connected. The latter is driven by a motor 6 with a controllable number of revolutions. The mixing device 4 has a mixing chamber 7 which, from its inlet opening in the direction of flow of the stream, enlarges similarly to a venturi nozzle. A nozzle 8 enters the inlet opening to the mixing chamber 7, which is connected to the air duct 2. The nozzle 8 forms an annular gap 10 with the edge 9 of the inlet opening of the mixing chamber 7, which is connected to the gas line 1. In the air line 2 there is a cone 11 which is adjustable by the linear motor 12 in the axial direction of the nozzle 8. Cone 11 is controlled by a sensor not shown, which in the presented case reveals (measures) the composition of the combustion exhaust gas. It signals the quality of the gas that is present.

In the position according to Fig. 2, a cone 11, the angle of which, in this embodiment, is less than 30 ° and coincides with the opening angle of the nozzle 8 and enters the nozzle. If the gas quality changes towards lower calorific values, the linear motor 12 moves the cone 11 to the left, deeper, into the nozzle 8. This increases the speed at which air enters the mixing chamber 7. Accordingly, the mixing chamber 7 is supplied with more gas. At the same time, the amount of air entering the mixing chamber 7 is reduced. As a result, less air and more gas are supplied to the mixing chamber 7. This compensates for the falling calorific value.

The control works in the opposite direction when the calorific value increases. Fluctuations in air pressure and temperature of the combustion air can be compensated by shifting the cone 7.

This invention combines the benefits of pneumatic association with the benefits of electronic matching while increasing the degree of modulation. The minimum efficiency of the combustion device can be lowered without loss of stability.

If the combustion device is stopped, the cone 11 can be inserted so deep into the nozzle 8 that it will close it. This prevents the formation of a backflow of waste gas into the air duct 2 if the combustion device is connected to the exhaust gas discharge system which is loaded by downstream combustion devices operating at positive pressure.

If the sensor controlling the linear motor 12 of the cone 11 fails, the cone 11 will move so far to the right that it fully exposes the cross-section of the nozzle 8. The combustion device is then controlled solely and exclusively by the pneumatic regulator 3, i.e. in a conventional pneumatic combination. In this case, it is recommended not to increase the minimum capacity of the connecting device.

Of course, it is possible to modify the system within the scope of the invention. And so - it is possible for the pneumatic regulator 3 to receive the control pressure controlling the pressure in the gas line 1 in a different place than in the air line 2; for example in a mixing chamber 7. Also the sensor controlling the linear motor 12 can, for example, evaluate (measure) only the combustion air temperature and / or the air pressure or the gas quality.