Standard Technical Features of BTG System for Supercritical 660 ...
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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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Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal UnitsCHAPTER 14FEED WATER HEATING PLANT AND FLASH TANKS14.1 General Requirements14.1.1 The plant shall be designed as per IS 2825 or ASME Boiler and pressurevessel code, section VIII, Division-I (Latest) and Heat Exchange InstituteStandards (USA). In addition the requirements of latest edition of ASME-TDP-1 code for turbine damage prevention shall also be taken care of. Plantshall be designed for all operating conditions including transients like suddenload throw-off, HP-LP bypass coming in operation, preceding one or twoheaters going out of service etc.14.1.2 The HP heater drains shall normally be cascaded to successively lowerpressure HP heaters and lowest pressure HP heater drain shall be led to thedeaerator. The LP heater drains shall be cascaded to successively lower LPheaters and lowest LP heater drain shall be led to the condenser. AlternativeHP heater drains shall be directly led to deaerator and condenser andalternative LP heater drains shall be directly led to condenser in case ofincreasing level in the heaters. The drains to the condenser shall be ledthrough flash tanks.14.1.3 The plant shall be suitable for operation in conjunction with steam turbineoffered. It shall be capable of raising the temperature of feed water from thatin the condenser to design temperature at the outlet of top heater at ratedoutput with zero percent make-up and design back pressure. TTDs and DCAsof heaters shall correspond to the heat rate guarantee conditions.14.1.4 The Feed regulating station (FRS) shall be located at upstream of HP heaterswith no isolating valve provided at upstream of economiser. Each heatershall be designed for removal from service individually without shutdown ofunit, using hydraulically operated or motorised bypass & isolating valves orfail safe type media operated three-way valve as per proven standard practiceof OEM and as per approval of IBR. In case HP heaters are provided in twostrings, these shall be isolated as a string and not individually.In case HP heaters are provided with isolating & bypass valves,spring loaded relief valve(s) shall be provided in the bypass of each HPheater(s) so as to prevent BFP shut off pressure from being communicated todownstream piping system and HP heaters. Further, in case HP heaters areprovided in two strings, 2x50% capacity spring loaded relief valves shall beprovided in the bypass of HP heaters with each valve capable of bypassing50% BMCR feed flow.14.1.5 Heaters shall be designed with minimum pressure drop on tube side. Velocityof water through the tubes shall be restricted to 3.05 m/sec under normaloperating conditions.107

Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units14.1.6 Each of the HP heaters, LP heaters and drain cooler shall be capable ofhandling 110% of the design flows from BFPs, CEPs as the case may bewithout undue vibrations and deleterious effects.14.1.7 Heaters shall be provided with start-up and operating vents with orifices andrelief valves. Provision shall be made for removing non condensable gasescollecting on shell side individually to the condenser. Vent orifices shall besized to pass 0.5% of rated steam flow to respective heater under TMCRconditions.14.1.8 Tube material shall be stainless steel as per ASTM A 213 Gr TP304 forseamless tubes without circumferential joints, or ASTMA 688 Gr. TP304 forwelded tubes.14.1.9 Tube sheet material shall be carbon steel as per ASTM. A516 Grade 70 orSA 266 Gr- 2 or SA 350 LF-2 and it shall be welded to shell and water box.Tube support plates shall be of common quality steel of 16mm (min)thickness.14.1.10 Tube size shall be minimum 15.875 mm OD and minimum wall thicknessshall be as per HEI.14.1.11 Corrosion allowance of minimum 3.2mm shall be considered for shell andwater box of each heater.14.1.12 Sentinel relief valve shall be provided on tube side. Relief valve on shell sideshall be sized to pass flow from clean rupture of one tube (two open ends) or10% of water flow corresponding to VWO condition with 1% make up anddesign condenser pressure at 10% accumulation whichever is higher and setto open at heater shell design pressure.14.1.13 Arrangement shall be provided for preservation by nitrogen blanketingduring shut down period.14.1.14 Proper drainage of bled steam lines shall be ensured. Each bled steam lineshall have ordinary and power assisted NRVs and motorized isolation valvesexcept for heater mounted in condenser neck and extraction to heater fromCRH line.14.1.15 No copper or brass shall be used in the internal construction of heaters toavoid copper pick up through condensate/ drips.14.1.16 Provision shall be made for differential expansion between shell and tubes.14.2 Low Pressure Heaters and Drain Cooler14.2.1 The LP heaters shall be horizontal and U-tube type with integral drain cooler.However, heater(s) in condenser neck may be of U- tube or straight type andmay or may not be provided with drain cooler as per standard practice of theOEM.108

<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 UnitsCHAPTER 14FEED WATER HEATING PLANT AND FLASH TANKS14.1 General Requirements14.1.1 The plant shall be designed as per IS 2825 or ASME Boiler and pressurevessel code, section VIII, Division-I (Latest) and Heat Exchange Institute<strong>Standard</strong>s (USA). In addition the requirements <strong>of</strong> latest edition <strong>of</strong> ASME-TDP-1 code <strong>for</strong> turbine damage prevention shall also be taken care <strong>of</strong>. Plantshall be designed <strong>for</strong> all operating conditions including transients like suddenload throw-<strong>of</strong>f, HP-LP bypass coming in operation, preceding one or twoheaters going out <strong>of</strong> service etc.14.1.2 The HP heater drains shall normally be cascaded to successively lowerpressure HP heaters and lowest pressure HP heater drain shall be led to thedeaerator. The LP heater drains shall be cascaded to successively lower LPheaters and lowest LP heater drain shall be led to the condenser. AlternativeHP heater drains shall be directly led to deaerator and condenser andalternative LP heater drains shall be directly led to condenser in case <strong>of</strong>increasing level in the heaters. The drains to the condenser shall be ledthrough flash tanks.14.1.3 The plant shall be suitable <strong>for</strong> operation in conjunction with steam turbine<strong>of</strong>fered. It shall be capable <strong>of</strong> raising the temperature <strong>of</strong> feed water from thatin the condenser to design temperature at the outlet <strong>of</strong> top heater at ratedoutput with zero percent make-up and design back pressure. TTDs and DCAs<strong>of</strong> heaters shall correspond to the heat rate guarantee conditions.14.1.4 The Feed regulating station (FRS) shall be located at upstream <strong>of</strong> HP heaterswith no isolating valve provided at upstream <strong>of</strong> economiser. Each heatershall be designed <strong>for</strong> removal from service individually without shutdown <strong>of</strong>unit, using hydraulically operated or motorised bypass & isolating valves orfail safe type media operated three-way valve as per proven standard practice<strong>of</strong> OEM and as per approval <strong>of</strong> IBR. In case HP heaters are provided in twostrings, these shall be isolated as a string and not individually.In case HP heaters are provided with isolating & bypass valves,spring loaded relief valve(s) shall be provided in the bypass <strong>of</strong> each HPheater(s) so as to prevent BFP shut <strong>of</strong>f pressure from being communicated todownstream piping system and HP heaters. Further, in case HP heaters areprovided in two strings, 2x50% capacity spring loaded relief valves shall beprovided in the bypass <strong>of</strong> HP heaters with each valve capable <strong>of</strong> bypassing50% BMCR feed flow.14.1.5 Heaters shall be designed with minimum pressure drop on tube side. Velocity<strong>of</strong> water through the tubes shall be restricted to 3.05 m/sec under normaloperating conditions.107

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