Reheat Attemperation is used as a final control of steam temperature into the IP section (sometimes LP section depending upon plant design) of the Steam Turbine. The steam extracted from the HP section of the turbine is passed back through the boiler, through the reheater, prior to entering the next stage of the turbine. A reheat attemperator is used here to spray water into either the reheat line to control the steam temperature. Like superheat attemperators, reheat attemperators are subject to the changes that are made in controlling main flue gas temperature in combustion. The reheat steam pressures exiting the HP section of the turbine; however, are much less than superheat steam pressures entering them, which means that the pressure drop across reheat temperature control valves is much greater. This dynamic can cause a cavitating process condition when these attemperators need to be operated close to the seat, which may be frequently in a cycling plant. These difficult service conditions typically make for rapid and excessive trim wear in these valves. Operationally, trim erosion in the reheat attemperators makes accurate reheat temperature difficult to impossible to control
in cycling operation, costing the plant inefficiency.
The use of REXA Linear and Rotary Actuators in reheat temperature control applications gives cycling power plants the ability to make substantial gains in efficiency, allowing for minimal valve throttling capabilities, tight shutoff, and maximum trim life, for virtually any manufacturers control valve.