Standard Technical Features of BTG System for Supercritical 660 ...
Standard Technical Features of BTG System for Supercritical 660 ...
Standard Technical Features of BTG System for Supercritical 660 ...
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<strong>Standard</strong> <strong>Technical</strong> <strong>Features</strong> <strong>of</strong> <strong>BTG</strong> <strong>System</strong> <strong>for</strong> <strong>Supercritical</strong> <strong>660</strong>/800 MW Thermal Unitsd) Maximum permissible spray attemperation flow (as percentage <strong>of</strong>main steam flow at superheater/ reheater outlet)1. Superheater attemperation 8% <strong>of</strong> main steam flow atsuperheater outlet.2. Reheater attemperation 3% <strong>of</strong> steam flow at reheateroutlet (0% under normaloperating conditions).Above permissible limits shall be applicable to all boiler loads withany combination <strong>of</strong> mills in service and shall be guaranteed. TheSH/ RH attemperation system shall, however, be sized <strong>for</strong> 12% <strong>of</strong>the rated main steam flow requirement <strong>for</strong> superheater and 8% <strong>of</strong>the spray flow rated reheat flow <strong>for</strong> reheater, both at 100% BMCRload. The steam temperature downstream <strong>of</strong> desuperheater shallhave at least 10 0 C superheat to ensure proper evaporation.e) Spray water carryover Nilf) Maximum steam side header pressure unbalance 6%g) Ash bridging between the tubes NilNote: The steam generator design shall ensure that no damage is causedto the reheaters with sudden closure <strong>of</strong> turbine interceptor valve.iv) For continuous monitoring <strong>of</strong> tube metal temperatures <strong>of</strong> SH and RHelements, adequate number <strong>of</strong> thermocouples shall be provided as perstandard and proven practice <strong>of</strong> the OEM. A suggested criterion <strong>for</strong>provision <strong>of</strong> thermocouples is indicated as below:a) For supherheaters and reheaters elements placed be<strong>for</strong>e furnace exitplane (in the direction <strong>of</strong> gas flow), chromel-alumel thermocoupleson at least two elements <strong>of</strong> every fifth assembly between the twoheaders shall be provided.b) In addition to the above, adequate number <strong>of</strong> chromel-alumelthermocouples <strong>for</strong> measurement <strong>of</strong> tube metal temperatures outsidethe gas path shall also be provided. Total number <strong>of</strong> thermocouplesincluding those at (a) above shall, however, not be less than 2 (two)thermocouples per RH/SH assembly between the two headers.v) For maintenance/inspection <strong>of</strong> SH/RH:a) 1.5 m clear cavity height shall be provided between two sections/banks <strong>of</strong> horizontal heat transfer surfaces <strong>for</strong> personnel access. Forvertical surfaces, minimum clearance between the two banks shallbe 600 mm.41
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