M/s Larsen & Toubro Limited, India, (L&T) is executing gas based combined cycle power plants at Konaseema near Rajahmundhry in the state of Andhra Pradesh in India on a turnkey basis.  L&T is engineering, procuring for and
constructing the power plants, which include Heat Recovery Steam Generators (HRSGs).

L&T’s scope of work at the 445 MW power plant for M/s Konaseema Gas Power Ltd (KGPL) is valued at $180 M.  The power block includes two 140 MW gas turbine generators (GTG), two triple-pressure HRSGs connected with bypass
arrangement for flue gas, and a steam turbine generator (STG) in a 2-2-1 configuration.  The project involved several firsts for L&T in terms of GTG size (previous projects were built with GTGs of 110 MW or smaller), number of steam pressure levels, and building two mirror-image HRSGs.

The following pertains to the HRSGs, which are a critical component of the power plant and are designed and built by L&T.  Order value for the two HRSGs was $14 M.

Each HRSG generates steam at three pressure levels, the high pressure (HP) steam being at 123 bar and 525°C.  Intermediate pressure (IP) steam & LP steam are generated at 26.2 bar and 330 deg C & LP Steam is generated at
6.8 bar and 231 deg C.  Turbine exhaust gases leave through a stack atop each HRSG at a height of 60 M from grade.

Heat input to HRSG varies as GTG load is changed to suit demand, and steam pressures slide at low loads.  This situation would arise even when one of the GTGs is out of operation. Hence the HRSGs have to be designed for sliding pressure operation.

Each HRSG weighs over 2500 MT, and includes 1110 MT of heat exchange modules supported from 800 MT of
steel structure.  350 MT of piping connects the exchangers to feedwater pumps, to water-steam separator drums, and
to other systems beyond HRSG battery limit (B/L).

The HRSG includes instruments to monitor process variables such as temperature, pressure and level in drums or tanks.  Based on analog and digital inputs from field sensors, a Distributed Control System (DCS) provides control signals to actuated valves (gate and globe valves) which are installed for isolation of circuits or for modulating fluid flows within the boiler.