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

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Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsd) Maximum permissible spray attemperation flow (as percentage ofmain steam flow at superheater/ reheater outlet)1. Superheater attemperation 8% of main steam flow atsuperheater outlet.2. Reheater attemperation 3% of steam flow at reheateroutlet (0% under normaloperating conditions).Above permissible limits shall be applicable to all boiler loads withany combination of mills in service and shall be guaranteed. TheSH/ RH attemperation system shall, however, be sized for 12% ofthe rated main steam flow requirement for superheater and 8% ofthe spray flow rated reheat flow for reheater, both at 100% BMCRload. The steam temperature downstream of 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 of turbine interceptor valve.iv) For continuous monitoring of tube metal temperatures of SH and RHelements, adequate number of thermocouples shall be provided as perstandard and proven practice of the OEM. A suggested criterion forprovision of thermocouples is indicated as below:a) For supherheaters and reheaters elements placed before furnace exitplane (in the direction of gas flow), chromel-alumel thermocoupleson at least two elements of every fifth assembly between the twoheaders shall be provided.b) In addition to the above, adequate number of chromel-alumelthermocouples for measurement of tube metal temperatures outsidethe gas path shall also be provided. Total number of 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 of SH/RH:a) 1.5 m clear cavity height shall be provided between two sections/banks of horizontal heat transfer surfaces for personnel access. Forvertical surfaces, minimum clearance between the two banks shallbe 600 mm.41
Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsb) Access openings alongwith air/ gas tight hinged doors shall beprovided for approach to above maintenance spaces without anyhindrance from hanger tubes.1. All access door shall be of 450mm x 450mm size (minimum).2. Access doors 800 mm above the nominal floor level shall haveaccess platform.3. Hanger tubes of horizontal banks shall have access opening forcrossing over.c) Stainless steel erosion shields shall be provided for all bends ofoutermost tube/ coil of all SH/ RH sections and hanger tubes inareas where flue gas temperature is below FEGT. For the pendanttube sections, the erosion shield shall be provided on the leadingtubes and wherever else considered necessary as per the provendesign.d) Suitable arrangement for internal inspection of attemperators/headers shall be provided.vi) Headers and pipes, if made using X-20 Cr MO V 121 to DIN 17175material, shall have provisions to ensure that no site welding of thismaterial with similar or dissimilar material is needed.6.5.7 Economisersi) Economizer design shall conform to the following criteria/requirementsunder all condition of operation and for the complete range of specifiedfuels.a) Economizer type Non-steaming type with parallel crossflow or counter flow arrangement.b) Approach temperature 17°C (minimum).within control rangec) Maximum average flue 10 m/sec (maximum localized velocitygas velocity through theeconomizer tube banks,across the cross-section not to exceed 12m/sec).with 25% excess air ateconomizer outlet. For high GCV low ash (say 10% andbelow) coals:12 m/sec (maximum localized velocityacross the cross-section not to exceed 14d) Economizer tubethicknessm/sec).i) Erosion allowance of 1mm (minimum)shall be provided in addition tothickness calculated as per IBRformulae.42
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