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

Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units10.11.5 Each dust hopper shall be provided with a high level and a low-level dustlevel monitor operating on proven radio frequency measurement principle.The level monitoring system shall incorporate all the necessary accessoriesincluding two nos. level switches per hopper (one for high and other for lowlevel), each with 2 NO + 2 NC contacts, local and remote signaling lampsand high and low level alarms. The logic shall also have provisions to deenergisethe TR set of the particular field of the affected ash hopper, ifcorrective action is not taken. The level control device shall be unaffected byash build up, due to moisture or charged ash on either the hopper walls or onthe probe itself.10.11.6 Each hopper shall be provided with a quick opening access door of not lessthan 600 mm dia, if round or not less than 450 mm x 600 mm, if rectangular.Access doors shall be hinged vertically and provided with a safety chain andgrounding strap. Suitable access ladders shall be provided from the walkwaybeneath the hoppers to facilitate approach to the access doors.10.11.7 The hopper outlet shall not be less than 350 mm x 350 mm.10.12 Casing10.12.1 Each of the ESP streams shall be housed in its own separate casing. Thespace provision shall be kept for installation of one additional field in allstreams of the ESP in future, if required.10.12.2 The precipitator elements shall be enclosed in gas tight, weather proof, andall welded reinforced steel plates. Sway bracing, stiffener and other localmembers shall be incorporated into the shell construction. The precipitatorcasing shall be fabricated from all welded reinforced, 5 mm minimumthickness, carbon steel plates conforming to ASTM A36/ IS-2062. Theexposed surfaces shall be self-draining and seal welded to prevent ingress ofmoisture during monsoon.10.12.3 The precipitator casing and its elements shall be designed to withstand apressure of ± 660 mmwc at 67% of yield strength and a temperature of200°C. The casing shall also be able to withstand excursion temperature upto300°C that may persist for upto thirty (30) minutes on account of air preheater failure. Adequate provision shall be made to accommodate thermalexpansion and movements as required by the arrangement and operatingconditions. In order to prevent distortions, the structural design shall takecare of unequal expansions.10.12.4 The precipitator casing and hoppers shall form a common structurereinforced to withstand the wind load (in accordance with IS: 875) and loaddue to dust storage in the hoppers etc.10.12.5 Access door of quick opening type, shall be provided to allow entry to allsections of the precipitators for maintenance and access. The design shall besuch as to eliminate air-in leakage through the doors.85