A METHOD FOR ISOLATION OF EXTERNAL HEAT TRANSFER SURFACES OF SUPERHEATER AND REHEATER CONSTITUTING TUBE-BUNDLES IMMERSED INSIDE FLUIDISED BED HEAT EXCHANGER (FBHE) IN A CIRCULATING FLUIDISED BED COMBUSTION (CFBC) BOILER

摘要

A method for isolation of external heat transfer surfaces of Superheater and Reheater constituting tube-bundles immersed inside Fluidised Bed Heat Exchanger (FBHE) in a Circulating Fluidised bed Combustion (CFBC) boiler, the method comprising the steps of introducing a first bypass line (19) for isolating FBHE Intermediate SH bundles (4,5) which branches between a first De-superheater-1 (12) and a first intermediate SH-I (4), the bypass line (19) being connected between a second Intermediate SH-II (5), and a second DE-superheater-II (13); introducing a first gate valve (15) in the main line for closing the main line, and a second gate valve (16) provided in the bypass line for opening and diverting the steam flow through the bypass line (19) and vice versa during restoration; providing a first non-return valve (17) in the main line, and a second non-return valve (18) in the bypass line (19) for avoiding a reverse flow; providing a FBHE RH bypass line (20) for isolating the FBHE Reheater (6) which branches from a Cold reheat line before said Reheater-I (6) and connected between said Reheater-I (6) and a RH De-superheater (14); introducing a third gate valve (21) in the main line for closing the main line, and a fourth gate valve (22) provided in the bypass line (20) for opening and diverting the steam flow through the bypass line (20) and vice versa during restoration; providing for the reheater circuit, a first Non-return valve (23) in the main line and a second non-return valve (24) in the bypass line (20) for avoiding a reverse flow; and providing a first safety valve (25) before said FBHE SH bypass line (19) and a second safety valve (26) before the FBHE RH bypass line (20).