Steam System


Click to enlarge

From the steam drum, steam passes through the superheater and into the turbine, which converts the heat into mechanical energy. The conversion is done in three stages to use as much heat energy as possible. After steam leaves the turbine, it is condensed back to water and recirculated to the boiler.

Steam is drawn from the steam drum and sent to the superheater where pressure, temperature and flow must be monitored. Steam comes out dry and superheated, ready for the turbine. A dripleg is used on superheated steam lines to collect particles of moisture still present in the dry steam which can cause severe damage to the turbine. A level switch senses the liquid level and opens a dump valve.

The reheater takes spent steam from the high pressure (HP) turbine and superheats it again before it goes to the intermediate pressure (IP) turbine. Steam passes directly from the IP turbine to the low pressure (LP) turbine. The turbine, the most expensive and critical component of a power plant, converts heat in the steam to mechanical energy. The turbine shaft turns a generator at high speed to generate electricity.

Spent steam exits the LP end of the turbine and enters the hotwell condenser, where it is cooled and condensed into water. Make-up water is added at the hotwell when required. Cooling systems are typically circulating water, refrigerant or some combination of the two, and require temperature, level and sometimes pressure instrumentation.

print