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- 18POWER CYCLE PIPING, VALVES AND THERMALINSULATION18.1 Power Cycle Piping18.1.1 Generali) All the piping systems and equipments supplied shall be designed tooperate without replacement and with normal maintenance for a plantservice life of 25 years and shall withstand the operating parameterfluctuations and cycling which can be normally expected during thisperiod.ii)The design, engineering, erection, testing, etc. of the complete pipingsystems shall be to the requirements of power piping code ANSI B31.1. In addition to this, requirements as laid down in Indian BoilerRegulations (latest edition) shall also be met completely.18.1.2 Pipe sizingi) Inside diameters of piping shall first be calculated for the flowrequirement of various systems based on velocity limits listed below:a) Main steam, CRH & HRH : 76m/sb) Auxiliary steam : 50 m/sc) Feed water suction : 2.0-3.0 m/sd) Feed water discharge : 4.0-6.0 m/se) HP/LP bypass upstream : 100 m/sf) HP/LP bypass downstream : 125 m/sg) Extraction steam (superheated) : 60 m/sh) Extraction steam (saturated) : 30 m/si) Condensate suction : 1.5 m/sj) Condensate discharge : 3.0-5.0 m/sk) Other pipings : As per good engg.practice171
Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsii)iii)iv)Pressure drop in reheat steam circuit (cold reheat, hot reheat line &reheater) should not exceed 10 % of HP turbine exhaust pressure.Pipes shall be sized for the worst operating conditions (i.e. maximumflow, temperature and pressure values). In case of BFP suction piping,transient analysis shall be carried out for optimum sizing of the systemin order to establish the pipe inside diameter for minimum pressuredrop in system to match with the pump NPSH requirement under worstoperating conditions.The design pressure for BFP discharge piping up to and includingdownstream valve at feed regulating station (FRS) shall be selectedsuch that the minimum calculated thickness for various pipes at designtemperature is sufficient for the following conditions, consideringallowable stresses as per ASME B31.1:a) Discharge pressure corresponding to turbine driven BFP tripspeed at shut off head condition, if TDBFP characteristics isgoverning for calculation of boiler feed discharge piping designpressure.b) Discharge pressure corresponding to motor driven BFP trip speed(frequency 51.5Hz) at shut off head condition if MDBFPcharacteristics is governing for calculation of boiler feeddischarge piping design pressure.v) With feed regulating station (FRS) located at upstream of HP heatersand no isolating valve provided at inlet of economiser, the designpressure of boiler feed discharge piping at downstream of FRS shall beworked out corresponding to design pressure of the boiler. This shallbe for HP heaters provided with spring loaded relief valve(s) or havingprovision of media operated three way valves at inlet/ outlet of HPheater(s) as per approval of IBR so as to prevent BFP shut off pressurefrom being communicated to downstream piping system and HPheaters.vi)The design pressure and temperature, down-stream of any pressurereducing valve upto and including the first block valve shall be thesame as that at up-stream of pressure reducing valve. If a pressurerelief valve is provided in the down stream of PRV, the downstreampiping shall be designed to a lower pressure as per set pressure of therelief valve.The piping at down stream of de-superheater shall be designed forspray failure condition. The length of piping system considered forspray failure condition shall not be less than the length required forproper spray mixing as recommended by de-superheater supplier.172
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