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

Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units10.10.2 A minimum rapping acceleration of 75 g measured normal to the plane of theplate shall be imparted on all parts of all the collecting plates.10.10.3 The perforated plates and/or guide vanes furnished for gas distributionsystem shall also be provided with rapping systems. The rapping mechanismshall produce sufficient force to keep the perforated plates/guide vanes clean.10.11 Dust Hoppers10.11.1 Dust hoppers shall be of pyramidal type or conical. Each having a storagecapacity of minimum of eight (8) hours corresponding to the maximum ashcollection rate of the field under which the hopper is being provided whentwo preceding fields are de-energised. The hopper capacity shall be based onthe inlet dust burden, gas flow rate and gas temperature specified for thedesign point condition while firing the maximum ash coal. Storage shall beupto a level that will not reduce the overall efficiency of the precipitator dueto re-entrainment. Ash storage capacity shall be at least 10% higher than theash storage capacity theoretically required for each dust hopper. Specificweight of ash shall be assumed as 650 kg/m³ for calculating storage capacityand 1350 kg/m³ for structural design. Further, for hopper strength and ESPstructural calculations, the level of ash in ESP shall be considered atleastupto the top of hopper partition plane or the bottom of plates (whichever ismore). The number and arrangement of dust hoppers shall be such that thereis at least one dust hopper per TR set. The hoppers for all fields shall beidentical in shape and size.10.11.2 Hoppers shall be in welded steel plate construction. The lower 1.5 meters ofeach hopper shall be lined with 16 gauge or heavier stainless steel 304 sheet/plate. All hopper internal sloping corners shall have 100 mm radius. Hoppervalley angle to the horizontal shall not be less than sixty (60) degrees.Hopper outlet flanges shall be terminated at a height of 3.5 meters above theground level to facilitate installation of fly ash removal system.10.11.3 The dust hoppers shall be electrically heated upto a minimum of lower onethird (1/3) of the dust hopper height but not less than 1.5 meter in height bythermostatically controlled panel type heating elements to prevent ash bridgeformation. The heaters shall be capable of maintaining internal hopperstemperature of 140 0 C or the gas temperature whichever is lower. Maximumexcursion of flue gas temperature upto 300°C, while the air heaters are out,shall also be considered for heater mechanical design.10.11.4 Each hopper shall be provided with two (2) nos. of 100 mm dia poke hole inopposite directions, with threaded caps. The caps shall have flat iron barssuitable for striking with a hammer, to assist in breaking free any seizedthreads. The hoppers shall also be provided with suitably designed andlocated rapping anvils for loosening the fly ash by striking with sledgehammer.84