Apparatus for controlling and adjusting the combustion in a fuel gas burner

Abstract

An apparatus for adjusting and controlling the combustion in a fuel gas burner. The apparatus comprises the following mutually integrated components: a comburent gas/fuel gas mixing pipe provided with a Venturi mixer in correspondence of which a fuel gas supply duct opens; means for adjusting the flow rate of fuel gas; a fan, at least partially housed in said mixing pipe; a burner arranged downstream of said fan; a safety system based upon the detection of the flame present in said burner; and an electronic control unit of devices belonging to the apparatus. The apparatus is characterized in that it further comprises: a temperature probe arranged on the inner surface of the burner; a valve for adjusting the fuel gas flow rate in the duct; said valve belonging to said control means and being mechanically controlled by an actuator; and an electronic card, electronically connected to said probe, to said fan and to said actuator.

Claims

1. An apparatus for adjusting and controlling the combustion in a fuel gas burner comprising the following mutually integrated components: a comburent gas/fuel gas mixing pipe provided with a Venturi mixer in correspondence of which a fuel gas supply duct opens; a pneumatic gas valve feeding gas in an amount corresponding to the depression generated downstream of the valve by the Venturi mixer and, therefore, corresponding to the amount of air passing through it; ventilation means, at least partially housed in said mixing pipe; combustion means arranged downstream of said ventilation means; a safety system based upon the detection of the flame present in said combustion means; and an electronic control unit for controlling the pneumatic gas valve and the ventilation means; said apparatus being characterized in that it further comprises: a temperature probe arranged on the inner surface of combustion means; a throttle valve for adjusting the fuel gas flow rate in the duct; an interchangeable calibrated diaphragm arranged along said fuel gas supply duct to said combustion means; wherein a size of said calibrated diaphragm is selected in accordance with the fuel gas and prevents said combustion means from working with an excess gas also in case of failure of other components; and an electronic card, separate from the electronic control unit that monitors a temperature sensed by the temperature probe and a working parameter associated with the ventilation means and adjusts the throttle valve to maintain a temperature at the inner surface at a predetermined value.

2. The apparatus according to claim 1, characterized in that said electronic card is electronically connected to said electronic control unit.

3. The apparatus according to claim 1, wherein the ventilation means is a fan and the working parameter is a rotational speed of the fan.

4. The apparatus according to claim 2, characterized in that said electronic control unit comprises electronic means performing safety functions by means of a flame detection device; said electronic control unit further comprising electronic means to control the operation of said ventilation means through said electronic card.

5. The apparatus according to claim 1, wherein said temperature probe is advantageously arranged on the inner surface of a perforated duct belonging to said combustion means from which the flame propagates, and in such a position that it can detect increasingly high temperatures by decreasing the power supplied by said combustion means and by decreasing the air/gas ratio.

6. The apparatus according to claim 1, characterized in that the temperature probe, the electronic card, the throttle valve and said calibrated diaphragm comprise a retrofit kit.

7. The apparatus according to claim 1, characterized in that said throttle valve and said actuating means are physically integrated in a gas valve.

8. The apparatus according to claim 1, characterized in that said electronic card is physically integrated, but functionally separated, in said electronic control unit, thus leaving unaltered the control function of the flame presence performed by said electronic control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention it is now described a preferred embodiment, purely by way of non limitative example and with a reference to the accompanying drawings, wherein:

(2) FIG. 1 shows a prior art embodiment of an apparatus for adjusting and controlling combustion;

(3) FIG. 2 shows an apparatus for adjusting and controlling the combustion, manufactured according to the principles of the present invention;

(4) FIG. 3 shows some graphs showing how the values of the flame temperature vary depending on the value in the apparatus schematically shown in FIG. 3; the curves are parameterized depending on the burner operating power;

(5) FIG. 4 shows some graphs showing how the temperature values detected by the probe 60 vary depending on the burner operating power; the curves are parameterized depending on the values;

(6) FIG. 5 shows some graphs to which reference will be made in order to explain the general operation of the apparatus of FIG. 3;

(7) FIG. 6 shows some graphs to which reference will be made in order to explain the operation at full capacity of the apparatus of FIG. 3 by varying the kind of gas used; and

(8) FIG. 7 shows some graphs to which reference will be made in order to explain the operation of the apparatus of FIG. 3 by varying the power supplied by the burner.

BEST MODE FOR CARRYING OUT THE INVENTION

(9) In FIG. 2, reference 1000 indicates in its whole an apparatus for adjusting and controlling the combustion made according to the teaching of the present invention.

(10) The same references have been used in FIG. 2 for elements which were identical or similar to those illustrated in FIG. 1.

(11) It is evident that most of the components are the same, and therefore they will not be described again.

(12) The following structural elements were, however, added or changed in the apparatus 1000 illustrated in FIG. 2: a temperature probe 60 (typically, a thermocouple) arranged on the inner surface (SUP) of the perforated metal wall of burner 40, from which the flame propagates outwards; the temperature probe 60 is advantageously arranged in an area of the perforated duct around which the flame (FLM) propagates, and it is in such a position that it can detect increasingly high temperatures by decreasing the Pot power supplied by burner 40; the duct 22 is provided with a throttle valve 24 mechanically controlled by an actuator 25 which is in turn controlled by a special electronic card 70, physically separated from the electronic control unit (CE); and an interchangeable calibrated diaphragm 80, selected according to the gas family, which is indifferently arranged at the beginning, at the end or along the path of duct 22 for purposes which will be better explained below; the calibrated diaphragm 80 must be sized so that it operates the system under safe conditions even in case of failure of other components.

(13) Possibly; the valve 24 and the related actuator 25 can be physically integrated in the gas valve 20 without affecting the adjustment and safety functions inherent to the gas valve 20.

(14) As also shown in FIG. 3, the electronic control unit (CE) is electronically connected to the gas valve 20, to the fan 30, to the safety spark plug 50 and to the electronic card 70.

(15) In other words, the apparatus 1000 illustrated in FIG. 3 is based upon the use of traditional components, previously seen in FIG. 1, for a premix burner 40; namely the burner 40, on whose surface the combustion of the previously formed air/gas mixture is carried out; the fan 30, which determines the amount of air required for the perfect and complete gas combustion and, therefore, also determines the Pot power of the burner 40; a traditional pneumatic gas valve, in which the opening for the gas passage and the gas amount required from the valve derives from the depression generated by the Venturi mixer and, therefore, from the amount of air ventilated by the fan; and a throttle valve 24 controlled by an actuator 25 (preferably, but not necessarily, an electric actuator) which operates as described hereinafter.

(16) In the present invention, and as shown in FIG. 3, the temperature values T measured in the burner 40, parameterized for each value of Pot power, are related to the values of the air/gas ratio .

(17) In such a case, by decreasing the values, the detected temperature values T increase.

(18) However, by decreasing the parameterized values of Pot power, the detected temperature values T increase though the values are the same (FIG. 3).

(19) Furthermore, by varying the Pot power, the trend of the curves remains perfectly analogous.

(20) In particular, FIG. 3 also shows that with values1.0, temperature values T, measured with a particular parameterized Pot power, remain constant.

(21) For each of the curves illustrated in FIG. 3, and therefore for each Pot power value, it is never possible to obtain two identical temperature values when is more than or equal to 1.

(22) This means that the electronic controller does not have to perform complex control operations to check whether, for a given fan speed (and therefore for a corresponding power), the burner is operating in excess or in defect of air.

(23) Since (as already stated in the introduction) the optimal value of has been experimentally confirmed to be suitable to any kind of gas belonging to the same family, it must be noted that these temperature trends are not related to the kind of gas used, but only to the value of the power supplied by the burner.

(24) Therefore, it has been experimentally verified that, as shown in FIG. 4, the temperature T, measured on the inner surface of the burner 40 in the immediate flame (FLM) area, maintains the same trend as the power values varies, translating downwards when the value increases and upwards when the decreases; but always with an upper limit curve corresponding to the value =1.0.

(25) The fact that the temperature T of the flame (FLM) decreases by increasing the Pot power of burner 40 is due to the fact that for increasing the Pot thermal power of the burner, the flow rate of fan 30 and therefore of the air/gas mixture coming out of burner 40 must be increased; and this causes a removal of the flame front (FLM) from the outer cylindrical surface of burner 40 and its subsequent cooling.

(26) Therefore, the following choices have been made in order to obtain an intrinsically safe system: the aforesaid calibrated diaphragm has been inserted on the gas line (either in the gas valve, at its output or at the input of the throttle; or even downstream of the throttle itself) so that, even with a completely open throttle and with gases having a higher Wi within the same group (the so called incomplete combustion gases), the excess air values are always sufficient to ensure CO emissions below the limit allowed by the rules; it has been used a traditional pneumatic gas valve, in which the opening for the gas passage and the gas amount required from the valve derives from the depression generated by the Venturi mixer and, therefore, from the amount of air sucked by the fan; the check on the presence of a flame is entrusted to the traditional detection system based on the detection of the passage of current occurring between the detection spark plug and the mass only in the presence of a flame; in case of a partially closed throttle, whatever the gas used, the values of excess air are so high that they cause the detachment of flame, thus activating the safety system seen in the preceding paragraph.

(27) The safety of the system is therefore entrusted to safety devices traditionally present in premix burners (pneumatic gas valve and flame detection system) and to the size of the nozzle regulating the maximum gas flow.

(28) With a reference to FIG. 5, let us explain now the operating logic of the system.

(29) For each of the two reference gas families, the second and the third one, an optimal reference curve of the temperature detected inside the burner has been set according to the supplied power.

(30) As previously shown, each curve corresponds to a defined value which is optimal to obtain the best possible combustion with the reference gases of the two families.

(31) In our case, the same values have been obtained: for the second family: G20 and G25: =1.35; for the third family: G30 and G31: =1.35.

(32) In any case, it is possible to choose values different from the one indicated in the example reported in FIG. 6, or even values which are slightly different in the passage between the maximum and the minimum Pot power depending on specific needs such as, for instance, the production of a smaller mass of fumes or a further reduction of pollutants or a better ignition.

(33) It has therefore been designed the aforesaid electronic card 70 shown in FIG. 2, which: measures the speed of the rotor of the fan, thus indirectly measuring the power supplied by the burner; measures the temperature of the burner inner wall; and acts on the actuator of the gas throttle valve in the supply duct so that the burner temperature reaches the predetermined value as quickly as possible, thus reaching the predetermined optimal value.

(34) The speed and accuracy with which this value is reached are entrusted to a special control algorithm that allows, in a few seconds, to reach the stable desired value.

(35) Operation at Full Capacity Varying the Kind of Gas Used (FIG. 6)

(36) The burner 40 works, for instance, at the intermediate power of 18 kW with natural gas G20.

(37) The fan 30 works at the intermediate air flow rate.

(38) The Venturi mixer 15 generates an intermediate depression causing the opening of the shutter of the gas valve 20 in the intermediate position.

(39) Under these conditions, the temperature detected by the temperature probe 60 within the burner 40 is 370 C. and the valve 24 is partially closed in such a position that it has the predetermined value of =1.35.

(40) In fact, the electronic controller has measured the rotation speed of the rotor of the fan 30 and has actuated the valve 24 closing it enough to obtain the temperature corresponding to that speed.

(41) By feeding gas G25 into the burner (gas having a 18% lower Wi than G20), in the absence of the apparatus 1000 object of the present invention, there would be an increase of the excess air, which would then become =1.45, with a subsequent temperature decrease to 340 C.

(42) Vice versa, when the temperature probe 60 detects a temperature decrease, the electronic controller activates the opening throttle, thus decreasing the air/gas ratio until it obtains again a temperature of 370 C. within the burner 40.

(43) In this way, automatically and consequently, the value is restored to the predetermined value of =1.35.

(44) A perfectly analogous operation, but in the opposite direction, is obtained by introducing gas G21 having a 9% higher Wi than G20 instead of natural gas G20.

(45) The calibrated diaphragm 80 arranged between the gas valve 20 and the valve 24 is sized so that values higher than 1.0 (therefore always with a suitable amount of excess air) are obtained with a completely open throttle and with flame return limit gas G21, in order to produce CO emissions below the limit allowed by the rules.

(46) If, for any reason, the valve 24 were blocked in a completely open position, the maximum emissions would therefore always be within the limit allowed by the rules.

(47) If, on the other hand, the valve 24 were blocked in a completely closed position, the gas would not reach the Venturi mixer; therefore no combustion would occur and the electronic controller, detecting no flame, would close the safety shutter of the gas valve.

(48) Variation of the Power Supplied by the Burner (FIG. 7)

(49) The burner 40, for instance, works at the intermediate power of 18 kW with natural gas G20.

(50) The starting reference conditions are therefore the same as previously seen.

(51) They correspond to a speed of the fan 30 equal to, for instance, 3500 rpm.

(52) By decreasing the speed of the fan 30, for instance, to 2500 rpm in order to decrease the Pot power, in the absence of the apparatus 1000 object of the present invention, there would be a proportional decrease of the amount of gas sucked by the Venturi mixer 15 without any variation in the air/gas ratio.

(53) At the same time there would be an increase of the temperature within the burner 40 from 370 C. to 390 C.

(54) Vice versa, with the apparatus 1000 there is a reduction of the speed of the fan 30, the system identifies the aforesaid reference temperature value of 390 C. and actuates, if necessary, the valve 24 by slightly opening the gas passage in order to reach more quickly that value; then it comes back to the previous position behaving to all effects like a diaphragm having a constant section.

(55) In such a way, after a transitional period of a few seconds, the value comes back to the predetermined =1.35.

(56) There is a perfectly analogous operation, but in the opposite direction, by increasing the speed of the fan 30, for example, from 3500 rpm to 4500 rpm.

(57) In this specific case, the electronic card 70 detects this speed increase, identifies the predetermined reference temperature value of 360 C., and actuates, if necessary, the valve 24, slightly closing the gas passage in order to reach more quickly that value; then it comes back to the previous position behaving to all effects like a diaphragm having a constant section.

(58) In this way, after a transitional period of a few seconds, the value comes back to the predetermined =1.35.

(59) In short, the present invention concerns an apparatus, a kit and a method relating to the combustion of a fuel gas.

(60) The first object of the present invention is an apparatus for adjusting and controlling the combustion in a fuel gas burner comprising the following mutually integrated components: a comburent gas/fuel gas mixing pipe provided with a Venturi mixer in correspondence of which a fuel gas supply duct opens; means for adjusting the flow rate of fuel gas; ventilation means, at least partially housed in said mixing pipe; combustion means arranged downstream of said ventilation means; a safety system based upon the detection of the flame present in said combustion means; and an electronic control unit of devices belonging to the apparatus; the apparatus is characterized in that it further comprises: a temperature probe arranged on the inner surface of combustion means; a valve for adjusting the fuel gas flow rate in the duct; said valve belonging to said control means and being mechanically controlled by an actuator; and an electronic card, electronically connected to said probe, to said ventilation means and to actuating means for adjusting the opening of said valve.

(61) The second object of the present invention is an auxiliary kit of an apparatus for adjusting and controlling the combustion in a fuel gas burner; said kit being characterized in that it comprises the following components: a temperature probe which can be arranged on the inner surface of a perforated metal wall of the burner, wall from which a flame propagates outwards; and a valve mechanically controlled by an actuator which is, in turn, controlled by a relating electronic card.

(62) The third object of the present invention is a method for adjusting and controlling the combustion in a fuel gas burner; method comprising the following steps:

(63) (f1) measuring the speed of ventilation means suitable to send a comburent gas to said combustion means;

(64) (f2) measuring the temperature of said combustion means; and

(65) (f3) acting on the opening of fuel gas supply means to said combustion means; said method being characterized in that it adjusts the combustion in order to maintain the temperature of said combustion means to predetermined values, experimentally defined, usually increasing with decreasing speed of said ventilation means; the predetermined temperature values of said combustion means being independent of the kind of gas used and being optimal for the combustion for each speed value of said ventilation means.

(66) The main advantage of the apparatus object of the present invention consists in that it operates premix burners with the same air/gas ratio which is optimal for any kind of gas belonging to the same family and at any power comprised in its working range, thus obtaining an optimal combustion (namely with a minimal emission of pollutants and with a maximum guarantee of burner ignition) and maintaining the safety and the reliability resulting from the use of traditional safety systems used in the prior art (pneumatic gas valve, air/gas Venturi mixer and flame ionization detector).