HP LP BYPASS SYSTEM IN THERMAL POWER PLANTS

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HP LP BYPASS SYSTEM IN THERMAL POWER PLANTS: 

HP LP BYPASS SYSTEM IN THERMAL POWER PLANTS SHIVAJI CHOUDHURY

OBJECTIVE: 

OBJECTIVE The most important feature of this system is to allow operation of the boiler independent of the availability of the turbine. In the event of turbine trip, the boiler can be kept in operation and the bypass system provides an alternative path for flow of steam from boiler to condenser. Thus the boiler need not be relighted during restarting of the unit and a considerable time & oil is saved.

PURPOSE: 

PURPOSE Initial warming up of steam pipe line etc. during cold start-up. Keeps the boiler on fire even during large load throw-off. Minimizes safety valve operation during sudden load throw-off thereby reducing D. M. water loss from the cycle. Control main steam and reheat steam pressure.

HP BYPASS: 

HP BYPASS The HP Bypass valve can handle a maximum of 60 %of the full load turbine steam flow.. This system controls the steam pressure at HP turbine inlet before and during turbine start-up as well as during turbine trip and shut-down conditions by the pressure control valves.

HPLP BYPASS SYSTEM: 

HPLP BYPASS SYSTEM

HP BYPASS SYSTEM: 

HP BYPASS SYSTEM The system consists of two parallel paths that direct steam from main steam line to cold reheat line. The steam passes through these branches and is regulated by hydraulically actuated control valves on each branch. These valves maintain upsteam pressure at desired set level. The steam at outlet of the pressure reducing valves is desuperheated in order to keep steam temperature within limits.

HP BYPASS: 

HP BYPASS For this purpose two (2) nos. spray water temperature control valves – one for each branch – are provided. One (1) no. spray water pressure control valve has been provided for adjusting pressure to achieve favourable conditions for spray injection. The HP bypass valves and spray water valves are provided with hydraulic actuators to provide adequate forces for quick action of the final control elements. The hydraulic fluid is supplied from the oil supply unit.

INTERLOCKS –FAST OPENING: 

INTERLOCKS –FAST OPENING The following will activate the ‘Fast Opening’ Signal :- Generator breaker open. Turbine load shedding relay operated Pressure controller deviation more (+) 10 %. Depressing of the ‘FAST OPEN’ push button from UCB.

HP BYPASS SYSTEM: 

HP BYPASS SYSTEM

LP BYPASS SYSTEM : 

LP BYPASS SYSTEM The LP bypass controller is designed to control the pressure in the reheat system under specified operating condition. The steam which cannot be accepted by the intermediate and low pressure turbines, must be bypassed to the condenser during start-up and shutdown of the turbine, on partial load below the boiler minimum load and in occurrence of faults i. e. load rejection, turbine trip etc.

LP BYPASS : 

LP BYPASS The LP bypass controller operates the bypass stop valve and control valve by means of the electrohydraulic converter and various intermediate linkage elements in the hydraulic section. The protective and safety elements for the condenser are integrated in the LP bypass controller. In the event of the injection water pressure being insufficient or the condenser pressure being excessive, the bypass stop valves are closed. The opening of the LP bypass control valves is limited on excessive LP bypass steam flow.

LP BYPASS SYSTEM: 

LP BYPASS SYSTEM

HP LP BYPASS VALVES: 

HP LP BYPASS VALVES

Startup Curve: 

Startup Curve Cut in HPLP Bypass

HP TURBINE BYPASS VALVE (500 MW): 

HP TURBINE BYPASS VALVE (500 MW) Design press – 189.5/55 kg/sq cm Design temp--- 545/500 deg c Body material- SA 182 F22 CL 3 Nozzle material- SA 182 F22 CL3 Code - TRD Flow max -647 t/hr Leakage class -MSS SP 61 Actuator -hydraulic OPERATING PARAMETERS (normal) Press before valve-170 kg/sq cm Press after valve - 45 kg/sq cm Temp before valve- 535 deq c Temp after valve- 326 deg c Flow per valve 575 t/hr

HP BYPASS: ELECTRO HYDRAULIC SYSTEM: 

HP BYPASS: ELECTRO HYDRAULIC SYSTEM

ELECTRO HYDRAULIC SYSTEM: 

ELECTRO HYDRAULIC SYSTEM Performance requirements for turbine bypass valves quick opening and closing and precise plug positioning. For demanding applications ,valves are driven by hydraulic piston actuators . The electro hydraulic system ,which includes fluid reservoir ,redundant oil supply pumps and motors, fluid filtering system.

STANDARD: 

STANDARD ANSI/ISA -77.13.01 :Fossil fuel power plant steam turbine bypass system. (www. isa. org)

THANKING YOU : 

THANKING YOU