Standard Technical Features of BTG System for Supercritical 660 ...

Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsb) Minimum transverse tube pitching in the direction of gas flow path:1. 600 mm for banks/ sections placed in areas where gastemperature exceeds the FEGT (MHVT) value.2. For bank/sections placed in areas where gas temperature exceedsIDT of ash for the range of coals specified, the minimumtransverse pitching shall be under:• For tower type boiler - 1000 mm• For two pass boiler - 762 mmc) Maximum depth of tube banks/sections in the direction of gas flowshall be 2.5 meters or maximum soot blowing radius, whichever islower.d) Supporting arrangementAll horizontal heat transfer surfaces shall be supported by steam orwater cooled hanger tubes designed for a minimum of 2 times thecalculated load so as not to cause any dislocation/ damage to the tubebanks/sections. The stress in the hanger tubes under such conditionalso shall not exceed the maximum permissible limits as per IBR.Erosion allowance of one (1) mm shall be provided over and abovethe calculated thickness of hanger tubes.e) Arrangement of headersHeaders shall be located out side the gas path and shall be fullydrainable. Wherever, locating the headers in the gas path becomesunavoidable these shall be suitably protected with erosion shields/protectors. Further, the nipples and studs of the header shall also beprovided with wear resistance stainless steel shields of minimum 2.5mm or higher thickness. The arrangement of headers shall be suchthat it does not cause the high localised flue gas velocity on tubesdown stream side of the header.f) Attemperators1. Location : At inlet or between the two SH/ RH stages.2. Construction : Made from corrosion/ erosion resistant steeland fitted with removable liners.g) Minimum tube thickness1. For leading tubes of the bank: Erosion allowance of 1.0 mm(minimum) over and above the calculated thickness as per IBRshall be provided.39