BURNER

PURPOSE:To protect a combustion furnace from troubles caused by an abnormal state on the side of air by comparing the air-fuel ratio that is calculated and the air-fuel ratio that is set and shutting off the combustion in the combustion burner in case of the judgement that the air-fuel ratio is low. CONSTITUTION:The output of an air flow rate detector 1 and the output of a fuel flow rate detector 2 are calculated by a ratio calculator 3, and its ratio signal is compared with the signal of an air-fuel ratio setting device 4 by an air-fuel ratio judgement device 5, and it gives a judgement. When the air-fuel ratio is lower than a set value, a signal that the air ratio is low is outputted from a relay 7 as a contact point output. An interlock circuit starts its operation by receiving the ON of the contact point 7 of air-fuel-ratio low, and when the operation is continued for a certain time, a timer 8 outputs, and since, if any one of the burner main valves is open 9, it indicates that it is in operation, a master fuel trip relay 10 totally closes a fuel shut-off valve 11 by the operation of a MFT trip 10 in which a master fuel trip relay 10 operates. Namely, by continuing the operation in the state of air-fuel ratio low unburned gases generated by an abnormal condition are ignited, and dangerous states such as explosion, etc., of combustion furnace are prevented before they occur.