AIR FLOW RATE CONTROL DEVICE FOR BOILER

摘要

PURPOSE:To improve a controlling characteristic of an air flow rate under a low load of a boiler by a method wherein a rotational speed of a forced draft fan is adjusted in such a way as a degree of opening of an inlet vane of the forced draft fan becomes the most appropriate degree (x) of vane which is convenient in controlling an air flow rate. CONSTITUTION:Under an automatic operation of a boiler, automatic-manual change-over devices 3 and 8 are changed over to its 'automatic' state and a boiler master command VS is given to a proportional integration adjuster 2 and a function generator 6. From the proportional integration adjuster 2 is outputted the most suitable degree of opening of vane (x) of an inlet vane 5 of the forced draft fan corresponding to an air flow rate Q0 determined by the boiler master command VS as an operating signal Z1. This operation signal Z1 is given to a control device 4 for adjusting a degree of opening of the inlet vane of the forced draft fan through an automatic-manual changing-over device 3, and a degree of opening X2 of the inlet vane 5 of the forced draft fan is adjusted to the most suitable degree of opening (x) of the vane corresponding to a boiler load by the control device 4. With such an arrangement, the air flow rate Q0 can be accurately controlled even in case of the low boiler load.