Method and apparatus for monitoring and controlling combustion in combustible gas burner apparatus

Abstract

The apparatus and method according to the present invention are adapted to adjust, in a combustible gas burner, a mixture of gas formed by a first gas and a second combustible gas, wherein the gas mixture is provided through the appropriate mixing of an amount of said first gas by means of a first adjustment element and an amount of said combustible gas by means of a second adjustment element. Said first or second adjustment elements are managed, during operation, by a controller, which processes the data coming from at least two sensors.

1 . A method for controlling the composition of a gas mixture for a burner, said mixture comprising a first gas, regulated by a fan of which the number of revs per minute, n, is controlled and a second combustible gas, regulated by a valve of which the degree of opening, s, is controlled; wherein a first sensor is adapted to provide a signal proportionate to the number of revs per minute of the fan and a second flame sensor is adapted to provide a signal proportionate to an electrical feature of the flame of the burner, and wherein said method comprises three control loops for adjusting the thermal power, W, supplied by the burner: a first quick adjustment control loop adapted to set the number of revs n of said fan and the position, s, of the actuator of said valve based on values of reference contained in a table, T 1 , T 2 , and associated with the thermal power value, W, required for the burner, a second slow adjustment control loop adapted to monitor the combustion through the detections of said first flame sensor and a third slow adjustment control loop adapted to monitor the combustion through the calculation of the ratio between the variation of the detection of said first flame sensor and the variation of the position, s, of the actuator of said valve, which caused it. 
     
     
         2 . The method according to  claim 1  wherein the values of reference contained in said table T, are selected so as to set a combustion having a preset air number, λ. 
     
     
         3 . The A method according to  claim 1  comprising an initial calibration procedure, wherein the following steps are performed: setting a number of revs per minute, n, of the fan and a position, s, of the actuator of the valve and starting the burner, said number of revs per minute, n, and said position s being contained in a table, T 1 , of values of reference measured in the laboratory; starting the burner;
 modifying the composition of said gas mixture, acting on the position s of the actuator of the valve, and the corresponding reading of said at least one electrical parameter of the flame of the burner, R, until a value s 1  is identified, which corresponds to a minimum of said electrical parameter of the flame of the burner, Rmin, corresponding, in turn, to an excess air value, λ, equal to 1; 
 further modifying the composition of said gas mixture, acting on the position s of the actuator of the valve, until a value s* is reached, which corresponds to the desired excess air, λ*; 
 detecting the value of said electrical parameter of the flame of the burner, R*, corresponding to the required excess air value, λ*; 
 updating said table, T 1 , with the s* value; 
 repeating the previous steps for different values of number of revs per minute, n, and position s of the actuator of the valve. 
 
     
     
         4 . The A method according to  claim 3  comprising the following steps:
 measuring, by means of a third pressure sensor associated with said fan, the atmospheric pressure, P 0 , with the fan at a standstill; 
 starting the fan at a number of revs per minute n 1 ; 
 measuring, by means of said third pressure sensor, the pressure of said first gas, Pn 1 ; 
 calculating the pressure variation ΔP=P n1 −P 0 ; 
 updating said table T 1 , with the value Pn 1  and ΔP=P n1 −P 0 . 
 
     
     
         5 . The A method according to  claim 1  comprising an adjustment step, wherein the following steps are performed:
 reading the thermal power value, W 1 , required for the burner; 
 reading the value of the number of revs, n, of the fan; 
 reading, from a table, T 1 , T 2 , of a number of revs, n 1 , of the fan and a degree of opening, s 1 , of the adjustment valve corresponding to the thermal power value, W 1 , required for the burner; 
 if n is different from n 1 , setting the fan motor at a number of revs equal to n 1 ; 
 setting the actuator of the adjustment valve to obtain a degree of opening, s 1 . 
 
     
     
         6 . The A method according to  claim 1  comprising an adjustment step, wherein the following steps are performed:
 reading the detection of the flame sensor, R; 
 comparison between R and the value, R 1 , present in the table, T 1 , T 2  corresponding to W 1 , n 1  and s 1 ; 
 if |R−R 1 | is less than a certain predetermined tolerance n 1  and s 1  are maintained; 
 otherwise, the actuator of the adjustment valve is acted upon until a value s 1   n  is reached, whereby there is correspondence between the measured R and the R 1  value provided for the power W 1 ; 
 the actuator of the adjustment valve is set so as to obtain a degree of opening, s 1   n . 
 
     
     
         7 . The A method according to  claim 1  comprising an adjustment step, wherein the following steps are performed:
 varying the position, s, of the actuator of said valve by an amount Δs; 
 reading the detection of the flame sensor, R 2 ; 
 calculating ΔR=R 2 −R and ΔR/Δs; 
 calculating the difference between the measured ΔR/Δs and the value present in the table T; 
 if the difference is less than a certain predetermined tolerance and the sign is the same, n 1  and s 1  are maintained; 
 otherwise an alarm signal is produced or a new calibration procedure is made. 
 
     
     
         8 . An apparatus for monitoring and controlling the composition of a gas mixture comprising a first gas and a second combustible gas, said apparatus comprising: a fan for adjusting the flow of a first gas, a valve adapted to adjust the composition of said gas mixture, a burner adapted to burn said gas mixture, a first sensor adapted to measure the number of revs of the fan, at least one second sensor arranged close to the flame of the burner and adapted to measure at least one electrical parameter of the flame of the burner, a controller adapted to pilot said fan and said valve based on the processing of the signals coming from said first sensor and from said at least one second sensor. 
     
     
         9 . The apparatus according to  the preceding claim 1 , wherein said controller comprises at least one memory unit configured to store tables, T 1 , T 2 , comprising values of number of revs per minute, n, of the fan and values of opening, s, the adjustment valve ( 6 ), corresponding to thermal power values, W, of the burner and adapted to allow the combustion to proceed with a desired air number value λ. 
     
     
         10 . The An apparatus according to  the preceding claim 1 , wherein said tables, T 1 , T 2 , comprise values of at least one electrical parameter of the flame of the burner corresponding to said values of number of revs per minute, n, of the fan and to said values of opening, s, of the adjustment valve. 
     
     
         11 . The An apparatus according to  claim 8  wherein said controller is adapted to update the contents of said tables, T 1 , T 2 . 
     
     
         12 . The An apparatus according to  claim 8  comprising a further absolute pressure sensor associated with said fan and adapted to measure the pressure of said gas mixture. 
     
     
         13 . The An apparatus according to  claim 8  to comprising a further temperature and absolute pressure sensor associated with said fan and adapted to measure the temperature and pressure of said gas mixture.