Reduction in turbine/boiler thermal stress during bypass operation

Abstract

A method of reducing turbine inlet temperature excursions during sudden load demand reductions on a steam turbine, the turbine being coupled to a controllable source of high pressure, high temperature steam, incorporates throttling of steam within the steam source in conjunction with steam throttling at the turbine so as to apportion temperature drops between the source and turbine. In one form, the method includes the steps of sensing a sudden drop in load demand on the steam turbine, operating the steam source to reduce exit pressure of the steam at the steam source and bypassing sufficient steam around the steam turbine to reduce steam flow through the turbine by an amount commensurate with the drop in load demand. The steam source may be controlled by adjusting division valves between primary and secondary superheaters in the steam source to throttle steam pressure at the secondary superheater and then heating the steam in the secondary superheater to a temperature which compensates for the temperature drop across the division valves caused by throttling.