EP0644377B1 - Control device for gas burners - Google Patents

Description

The invention relates to a control device for the supply of gas and combustion air to a burner controlled by the heat requirement of a consumer, as described in the preamble of claim 1. In a control device of this type known from EP-A 0 390 964, the reinforcing pneumatic control module has a large-area control membrane, which is acted upon by the differential pressure on both sides, and a control membrane of smaller area, which is supported on the control membrane by a spring, carries the closing body of the blow-off valve. Another servo valve is connected between the drive chamber for the diaphragm of the main valve and a connecting line to the outlet of the gas control valve, the closing body of which is under the pretension of a compression spring which limits the maximum gas pressure. The control diaphragm is supported on an adjustable stop by a compression spring.

In a similar control device known from EP-A 0 326 880, one membrane chamber of the control module is connected to a venturi nozzle provided in the combustion air duct and the other membrane chamber is connected to the bottom of the combustion chamber. The membrane of the control module acts directly on the main gas valve via a valve rod.

Furthermore, from DE-U 83 00 157 a device for the simultaneous control of the gas and air supply to a burner is known, whereby an air control valve provided with a diaphragm actuator has a temperature sensor controlled servo pressure regulator is attached and a gas control valve also provided with a diaphragm actuator receives its control pressure from the same servo pressure regulator. A pressure regulator is placed on the gas control unit and a pneumatic pressure or power amplifier is placed on top of it.

The invention characterized in claim 1 greatly simplifies the construction of a gas control device of the type described in the introduction. It also enables simple adjustment of the control device when using different fuel gases. The differential pressure signal, which is proportional to the combustion air flow rate, is here pneumatically compared directly with the gas pressure at the outlet of the gas control valve, and a pneumatic control variable for the diaphragm drive of the main gas valve is obtained therefrom. Advantageous refinements of the invention result from the subclaims. An additional adjustment device in the gas supply line to the burner allows the gas / air mixture to be fine-tuned to the value required for optimal combustion.

The invention is explained below with reference to an embodiment shown schematically in the drawing.

A heat exchanger 2 and a burner 3 are arranged in the combustion chamber 1 of a gas-fired heating device. The heat exchanger is connected via a flow line 4 and a return line 5 to a consumer, not shown. A temperature sensor 6 measures the flow temperature of the hot water supplied to the consumer and delivers a corresponding signal to the actual value input 7 of the temperature controller 8. This receives at its setpoint input 9, for example from one Manual adjuster a setpoint signal corresponding to the desired temperature. For example, it controls the energy supply to the motor 10 of the blower 11 via a converter, which feeds combustion air to the burner 3 via the supply air duct 12. The exhaust gases leave the otherwise closed combustion chamber 1 through the flue gas discharge 13. The gas to be burned is fed to a gas nozzle 14 in the feed line 12 to the burner 3 from a gas control valve 15. Air supply, gas supply and mixing chamber can also be designed and / or arranged differently. For example, the fan 11 can be provided in the trigger 13.

The gas control valve 15 serving as the main gas valve is connected between the gas inlet 16 and the gas outlet 17. It comprises a closing body 19 which is biased in the closing direction by a spring 18 and which cooperates with a valve seat 21 inserted into the partition 20. The closing body 19 is actuated via a valve rod 22 by a membrane 23 which closes the control chamber 24. The control chamber 24 of the main gas valve 15 is connected on the one hand via a first throttle 25 to the gas inlet 16 and on the other hand to a blow-off valve provided in a control module 26, the closing body 27 of which is carried by the membrane 28 of the control module 26. The seat 29 of the blow-off valve 27, 29 is connected to the control chamber 24 via a line 30. A spring 31 acts on the closing body 27 in the opening direction, while an opposing spring 32 is supported on an adjusting screw 33 and is effective in the opposite direction.

The combustion air throughput generated by the blower 11 is measured with the aid of a differential pressure measuring device which is inserted into the supply air duct 12 and which has an orifice 34 and an upstream, that is to say on the high pressure side of the fan in the supply air duct 12 opening first measuring line 35 and a downstream of the panel in the supply air duct 12 opening second measuring line 36. The line 35 is connected to the control chamber 36 of the control module. The blow-off chamber 37 of the control module 26 is connected on the one hand via a second throttle 38 to the outlet 39 of the main gas valve 15 and on the other hand via a third throttle 40 to the low pressure line 36 of the differential pressure measuring device 34, 35, 45. Both chokes 38 and 40 are preferably adjustable. An adjustable fourth throttle 43 is arranged in the gas feed line 17 between the branch 41 to the second throttle 38 and the mouth 14 into the gas / air feed duct 42 to the burner 3. The throttle 25 can also be adjustable.

The speed of the fan 11 and thus the combustion air throughput is controlled as a function of the heat requirement by the controller 8. If the air throughput increases, the pressure in the measuring line 35 also increases, as a result of which the pressure prevailing in the control chamber 45 of the control module 26 increases and the membrane 28 is thus moved downward. The blow-off valve 27, 29 is moved in the direction of the closed position, as a result of which the pressure in the control chamber 24 increases and the main valve 19, 21 opens further. The increased air throughput is thus followed by an increased gas throughput.

In this respect, it is a sequential control with which the gas throughput is tracked to the air throughput. By switching on the two chokes 38 and 40, this control becomes a closed control loop. The line 41 with the throttle 38 namely couples the blow-off chamber 37 of the control module at the same time to the outlet side 39 of the gas control valve. If the pressure at the outlet 39 of the gas control valve increases for any reason, it increases via the line 41 and the throttle 38 also the pressure in the connecting line 44 between the blow-off chamber 37 of the control module 26 and throttle point 40. This means that the control diaphragm 28 of the control module 26 counteracts a greater pressure from below and thus the control pressure generated by the air throughput in the high-pressure measuring line 35 the control chamber 45, the membrane 28 and with it the closing body 27 cannot move as far down as without the increased pressure in the line 44. The blow-off valve 27, 29 is closed less, the pressure in the control chamber 24 decreases, and the Spring 18 can move the closing body 19 of the main gas valve in the closing direction and thus throttle the gas throughput. In this way, air throughput and gas throughput are pneumatically linked to one another in the same sense. The throttle 40 between the blow-off chamber 37 and the low-pressure measuring line 36 ensures, on the one hand, that pressure can build up in the connecting line 44 and, on the other hand, the pressure in the chamber 37 can be reduced when the blow-off valve 27, 29 is closed.

The combination of the gas pressure P _g in the gas nozzle 14 with the combustion air pressure P _a generated by the blower 11 results from the throttle 43 being neglected $${\text{P}}_{\text{G}}\text{=}\frac{{\text{<figure-callout id="38" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{38}}{\text{+ R}}_{\text{40}}}{{\text{<figure-callout id="40" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{40}}}{\text{· P}}_{\text{a}}$$

R ₃₈ and R _{40 are} the flow resistances of the two restrictors 38 and 40, respectively. The pneumatic gain factor of the control module 26 is set at 1: 1. The following is obtained for the pressure P ₃₇ in the blow-off chamber 37: $${\text{<figure-callout id="37" label="P" filenames="imgf0001.png" state="{{state}}">P</figure-callout>}}_{\text{37}}\text{=}\frac{{\text{R}}_{\text{40}}}{{\text{<figure-callout id="38" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{38}}{\text{+ R}}_{\text{40}}}{\text{· P}}_{\text{G}}$$

$${\text{dP}}_{\text{a}}{\text{= P}}_{\text{a}}{\text{- P}}_{\text{42}}$$

$${\text{dP}}_{\text{37}}{\text{= P}}_{\text{37}}{\text{- P}}_{\text{42}}\text{.}$$

If the pressure in the mixture feed line 42 is designated P ₄₂ , the following pressure differences result: $${\text{dP}}_{\text{G}}{\text{= P}}_{\text{G}}{\text{- <figure-callout id="42" label="P" filenames="imgf0001.png" state="{{state}}">P</figure-callout>}}_{\text{42}}$$

$${\text{dP}}_{\text{a}}{\text{= P}}_{\text{a}}{\text{- <figure-callout id="42" label="P" filenames="imgf0001.png" state="{{state}}">P</figure-callout>}}_{\text{42}}$$

$${\text{<figure-callout id="37" label="dP" filenames="imgf0001.png" state="{{state}}">dP</figure-callout>}}_{\text{37}}{\text{= P}}_{\text{37}}{\text{- <figure-callout id="42" label="P" filenames="imgf0001.png" state="{{state}}">P</figure-callout>}}_{\text{42}}\text{.}$$

$${\text{dP}}_{\text{37}}\text{=}\frac{{\text{R}}_{\text{40}}}{{\text{R}}_{\text{38}}{\text{+ R}}_{\text{40}}}{\text{· dP}}_{\text{g}}$$

Follow from this: $${\text{dP}}_{\text{G}}\text{=}\frac{{\text{R}}_{\text{38}}{\text{+ R}}_{\text{40}}}{{\text{R}}_{\text{40}}}{\text{· DP}}_{\text{a}}$$

$${\text{<figure-callout id="37" label="dP" filenames="imgf0001.png" state="{{state}}">dP</figure-callout>}}_{\text{37}}\text{=}\frac{{\text{R}}_{\text{40}}}{{\text{<figure-callout id="38" label="R" filenames="imgf0001.png" state="{{state}}">R</figure-callout>}}_{\text{38}}{\text{+ R}}_{\text{40}}}{\text{· DP}}_{\text{G}}$$

The gain or proportionality factor with which the change in the gas pressure dP _{g is} linked to that of the air pressure dP _a can thus be set in the desired manner by adjusting the restrictors 38 and 40. By adjusting the stop 33 for the spring 32, the offset of the controller can be set. The throttle 43 can be used to fine-tune the gas / air ratio. If in the exemplary embodiment shown the combustion air throughput is adjusted by changing the speed of the blower 11 to the heat requirement, it can be seen that for the present invention the type of control of the combustion air throughput is of subordinate importance and can also be carried out, for example, by an air flap or by an air valve.

Claims (6)

1. Control apparatus for controlling the supply of gas and combustion air to a burner dependent on the demand for heat of a load, whereat

   a) an output signal of a heat demand controller controls the supply of combustion air;

   b) a differential pressure measuring device (34, 35, 45) generates a differential pressure signal which is proportional to the air flow rate and feeds this signal to the diaphragm chambers (45, 37) of a pneumatic control module (26);

   c) the pneumatic output signal of the control module (26) acts upon the diaphragm (23) of diaphragm operated main gas valve (15) provided within the gas supply passage (16, 17, 39);

   d) the control chamber (24) of the main gas valve (15) on the one side is connected to the gas inlet side (16) of the main valve via a first throttle (25) and on the other side is connected to a bleed valve (27, 28, 29) within control module (26) with the closure member (27) of said bleed valve being carried by the diaphragm (28) of the control module; and

   e) the pressure chamber (45) of the control module (26) is connected to the high pressure side (35) ofthe differential pressure measuring device (34, 35, 45);

      characterized in that
   f) the bleed chamber (37) ofthe control module (26) on the one side is connected to the outlet (39) of the main valve (15) via a second throttle (38) and at the other side is connected to the low pressure side (36) of the differential pressure measuring device (34, 35, 45) via a third throttle (40).
2. Control apparatus of claim 1, characterized in that the diaphragm (28) of the control module abuts via a spring (32) against an abutment (33) which is adjustable within the housing of the control module (26).
3. Control apparatus of claim 1 or 2, characterized in that the first, second and/or third throttle (25, 38, 40) is adjustable.
4. Control apparatus of claim 1, 2 or 3, characterized in that a fourth adjustable throttle (43) is provided within the gas supply pipe (39, 17, 14) between the branch (39) to the second throttle (38) and the port (14) into the gas/air passage (42) for the burner (3).
5. Control apparatus according to one of the claims 1 to 4, characterized by such a dimension or adjustment of the second (38) and third (40) throttles that: $${\text{P}}_{\text{g}}\text{=}\frac{{\text{R}}_{\text{38}}{\text{+ R}}_{\text{40}}}{{\text{R}}_{\text{40}}}{\text{· P}}_{\text{a}}\text{,}$$

   

   wherein

   P_g =   gas pressure at the port (14) of the gas supply line (17) into the mixture passage (42);

   P_a =   air pressure at the high pressure side of the differential pressure measuring device (34, 35, 45);

   R₃₈ =   flow resistance of the second throttle (38);

   R₄₀ =   flow resistance of the third throttle (40).
6. Control apparatus according to one of the claims 1 to 5, characterized in that the pneumatic gain factor ofthe control module (26) is chosen 1:1.

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