| 摘要 |
PURPOSE:To prevent lowering of the efficiency of a boiler caused by an increase in CO concentration even during a change in a load irrespective of a kind of fuel, by a method wherein, based on a signal obtained from unburnt content concentration in exhaust gas, a lower limit value is set for control of an air excessive rate. CONSTITUTION:A deviation of a momentary subtracter 21 during a period of times T1 to T2, which had a negative value T1 minute before, will have a positive value due to a rapid increase in CO concentration, and with a monitor relay 25 actuated, its output 35 has logic '1', and thereby an output 33 of logical product also has logic '1'. The mode of a PI device 22 is transferred from tie back operation to proportional integral control operation. Simultaneously, an output signal 30 begins to increase, and when the output signal 30 is increased to exceed an output from a PI device 3a, through the working of a high value selector 28, an air-fuel ratio correcting signal 32 is switched from an output from the PI device 3a to the output 30 from a PI device 22. In this case, an air-fuel ratio correcting signal 32, having been decreased, is rapidly increased since the PI device 22 is in proportional integral control operation, an excessive air rate mu is increased, O2 concentration is increased, and this causes decrease in CO concentration. |
