1 TT

Temperature flue gas output BWT

2 TT

Temperature flue gas input BWT

3 TSAH

Temperature MAX output feed water BWT

4 PSAH

Feed water pressure MAX output feed water BWT

5 TIC

Temperature feed water return line BWT; control(s) adjust this temperature.

6 TT

Temperature feed water supply line BWT

7

Feed water pump

8

Control damper for flue gas flow BWT

9

Control damper for flue gas flow bypass

10

Servomotor for positioning the dampers (8) and (9).

Flow

The flue gases are directed by two dampers, which are moved in opposite directions by a motor, either by the BWT or via the bypass.

Purge

The purge behavior before the burner start would be ideal if initially only the bypass (checked with limit position) was to be purged and thereafter only the BWT (checked with limit position). However, se@vis and the safety control do not offer this type of two-stage purge sequence including monitoring of the limit positions.

The purge process with se@vis must be performed with both dampers in the center position (checked with limit position).

Control of the feed water temperature TIC

The goal is to keep the temperature of the water at a constant level. For this purpose, the speed of an additional feed water pump serves as an actuator for the controller. The flow rate of the water is regulated for as long as the temperature can be reached as a result. If the temperature of the water increases even though the pump is already running at fully capacity, an additional control must intervene to regulate the flow rate of flue gas between the BWT and bypass.