26-04-2012, 12:12 PM
LP bypass system
[attachment=20864]
INTRODUCTION:
This bypass system has been providing to allow the steam generator to build up during start up, matching steam parameters with the turbine. The steam generated is dumping into condenser. Thus avoiding the loss of boiler water. This system enable starting of the unit of sliding parameters & also facilitates hot restarting of the unit in the event of losses of load on turbine, the bypass system disposes the steam produce by the boiler automatically to the condenser without affecting the boiler operation.
The bypass has two sections: HP & LP:
The HP Bypass system diverted the steam before main steam valve (MSV) to cold reheat line CRH. HP bypass system also reduces the rated steam parameters of the incoming steam from the super heater. SH) to the steam condition expected in the CRH line.
The LP bypass system divert the incoming steam from Hot reheat line(HRH ) line before intercepting valve(IV) to the condenser After reducing HRH steam parameters to the condition approximately LP steam turbine Exhaust steam
The purpose of HP bypass system is to allow the steam pressure at the HP turbine inlet controlled before & during turbine start-up, as well as during trip & shut down conditions the HP bypass (BP) valves. In addition the dump steam is attemperater (de-superheated) by spray water via temperature control valves (BPE valves) to the temperature in accordance with the cold reheat inlet the design capacity of HP bypass is 70 %.
OPERATION OF HP LP BYPASS SYSTEM:
When ever short trip outs takes place, the steam supply to turbine is totally out off from the main steam (high) pressure line. Now certain quantity of the high pressure & high temperature is passed through HP by pass system where the pressure of the steam is reduced & then de-superheated to the down stream conditions The comparatively cold steam at blow pressure ( cold reheat steam ) is passed through the re-heater to cool the re-heater coils.
The hot but blow pressure steam (hot reheat steam ) is once again isolated from the turbine and bypassed through the low pressure system to the condenser after pressure reduction & de-superheating: Therefore with HP & LP bypass system, a minimum circulation is maintained in the boiler tubes ,super-heaters & re-heaters with low firing rate during short trip out .When the short trip outs are over, the bypass system can be closed & high temperature, high pressure steam in main steam line & low pressure high temperature steam in re-heater outlet are readily available with a matching temperature of turbine for quick restart & subsequent reloading.
Pre-start conditions for charging of HP-LP Bypass:
• Turbine oil system is started & turbine is running on barring gear.
• Condensate extraction pumps are started & condensate discharge header pressure is normal.
• CW system is established.
• Vacuum in the condenser is greater than 0.85 kg/cm2
• Boiler feed pump is started & supplying adequate discharge header pressure.
Warming of main steam line & HP Bypass valves;
• During cold startup the warming up of main steam line can be started after boiler blow down at 10 kg/cm2 pressure
• Ensure that drain valves of main steam lines ,CRH & HRH line are open
• Charge the main steam line by opening integral bypass valves (MS 301A,302A)
• Open the warm up valves of HP bypass valves locally
• The warming up operation of MS line is completed when steam temperature before HP bypass is more than the mid-wall temperature of ESVs.
• Open the main boiler outlet valves (MS301 &302 & close their integral bypass valves)
[attachment=20864]
INTRODUCTION:
This bypass system has been providing to allow the steam generator to build up during start up, matching steam parameters with the turbine. The steam generated is dumping into condenser. Thus avoiding the loss of boiler water. This system enable starting of the unit of sliding parameters & also facilitates hot restarting of the unit in the event of losses of load on turbine, the bypass system disposes the steam produce by the boiler automatically to the condenser without affecting the boiler operation.
The bypass has two sections: HP & LP:
The HP Bypass system diverted the steam before main steam valve (MSV) to cold reheat line CRH. HP bypass system also reduces the rated steam parameters of the incoming steam from the super heater. SH) to the steam condition expected in the CRH line.
The LP bypass system divert the incoming steam from Hot reheat line(HRH ) line before intercepting valve(IV) to the condenser After reducing HRH steam parameters to the condition approximately LP steam turbine Exhaust steam
The purpose of HP bypass system is to allow the steam pressure at the HP turbine inlet controlled before & during turbine start-up, as well as during trip & shut down conditions the HP bypass (BP) valves. In addition the dump steam is attemperater (de-superheated) by spray water via temperature control valves (BPE valves) to the temperature in accordance with the cold reheat inlet the design capacity of HP bypass is 70 %.
OPERATION OF HP LP BYPASS SYSTEM:
When ever short trip outs takes place, the steam supply to turbine is totally out off from the main steam (high) pressure line. Now certain quantity of the high pressure & high temperature is passed through HP by pass system where the pressure of the steam is reduced & then de-superheated to the down stream conditions The comparatively cold steam at blow pressure ( cold reheat steam ) is passed through the re-heater to cool the re-heater coils.
The hot but blow pressure steam (hot reheat steam ) is once again isolated from the turbine and bypassed through the low pressure system to the condenser after pressure reduction & de-superheating: Therefore with HP & LP bypass system, a minimum circulation is maintained in the boiler tubes ,super-heaters & re-heaters with low firing rate during short trip out .When the short trip outs are over, the bypass system can be closed & high temperature, high pressure steam in main steam line & low pressure high temperature steam in re-heater outlet are readily available with a matching temperature of turbine for quick restart & subsequent reloading.
Pre-start conditions for charging of HP-LP Bypass:
• Turbine oil system is started & turbine is running on barring gear.
• Condensate extraction pumps are started & condensate discharge header pressure is normal.
• CW system is established.
• Vacuum in the condenser is greater than 0.85 kg/cm2
• Boiler feed pump is started & supplying adequate discharge header pressure.
Warming of main steam line & HP Bypass valves;
• During cold startup the warming up of main steam line can be started after boiler blow down at 10 kg/cm2 pressure
• Ensure that drain valves of main steam lines ,CRH & HRH line are open
• Charge the main steam line by opening integral bypass valves (MS 301A,302A)
• Open the warm up valves of HP bypass valves locally
• The warming up operation of MS line is completed when steam temperature before HP bypass is more than the mid-wall temperature of ESVs.
• Open the main boiler outlet valves (MS301 &302 & close their integral bypass valves)