6. Furnace Draft Control
The boiler control system consists of this very important control loop named furnace draft control. As discussed in previous chapters, the boiler has two distinct zones of functional operation. The first one is the firing zone; the other is, in general, the heat exchanger zone. The firing zone consists mainly of various types of burners suitable for a variety of fuel types and appropriate types of flame scanners for monitoring the health of the firing through these burners. The firing zone along with waterwalls (to insulate the heat contents from around the side and top walls) is normally described as the furnace.
The pressure of the top portion of such a furnace is generally maintained at below atmospheric ...