10 Drains systems
10.1 Function and system layout
During the start-up period of a turbine, the steam coming into contact with cooler metals results in the formation of condensate within the turbine cylinders, the steam piping and the valve chests. This condensate must be removed before the turbine can be run-up fully, to prevent a loss of efficiency and possible damage to the turbine.
Condensation occurs mostly during a cold start, but also forms during normal operation when a change in load or steam conditions results in a difference between steam and metal temperatures. The drains system provides an outlet for the condensate, whilst minimising leakage of steam from the turbine processes. A typical drains system is shown diagram-matically in Fig 2.80.
Each drain line is taken from the lowest point of the associated pipe system, where condensate is likely to collect, and the clean drains are led into the drains receivers where the water is eventually routed to the condenser.
To prevent loose pipe-scale and other foreign matter from blocking the drains, each drain is provided with a dirt trap. Dirty water drains are led to the station drains. Drains are classified as being either start-up or continuous.