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Hi everybody,

I have a question about thermal power plant. Is HP bypass flow necessary to control in power plant? If we don't use it, how do we measure the flow?

>I have a question about thermal power
>plant. Is HP bypass flow necessary to
>control in power plant? If we don't use
>it, how do we measure the flow?

Your question is not specific enough to give a useful answer. HP bypass is usually found on combined cycle plants.

I have yet to see a "boiler plant" with a HP or any type of bypass system in a purely electrical (utility) plant.

I suggest reading training information regarding the type of plant you are operating. There are many different designs out there depending on the needs of the customer. Some plants only make electricity, some make electricity and give heat to buildings, some make steam for a chemical process and use extra energy to make electricity, etc.

hi
you cannot measure / control the flow of HP feed water or steam using the bypass. it is commonly to measure the flow before the main and bypass. i hope the i understood your question.

If I understood your question correctly HP bypass flow is not necessary to control it is the pressure.

HP Bypass is used in the combined cycle or Cogen Plants (at least in my knowledge) and we try to control the pressure (back pressure) to control the steam pressure to main steam line.

Do we need back pressure control yes so that we maintain certain pressure and temperature of steam to supply steam to ST.

I hope i didn't confuse you any more.

Hi,

It is not necessary to measure flow of HP B/P because Pressure is the one to be controlled. However if u want to measure by knowing the valve opening ie. stroke and pr. of the steam we can calculate. Also there should be a MS flow measurement in Turbine and Boiler side that will help u know the flow.

Paval.

Bypass system is generally used in Combined Cycle Power Plants.
Purpose of keeping HP bypass OPEN is to achieve the flow of steam and control the steam pressure for Steam Turbine rolling.

If you don't open the HP bypass valve and you achieve the pressure, Temp for roll-up, steam flow will be very little. and on achieving Pressure and Temp only, if you start to roll steam turbine your HRSG drum level will get very disturb. it will tend to positive level as pressure decrease causing false level raise in drum ,and then steam will utilize for steam turbine flow will increase your drum level will get decreasing.

So this operation will be very difficult. As some parameters for ST rolling are very important and try to keep that very near or match
Nature of Startup (Cold, warm or hot)

GT load, ST metal temp, HP/LP main steam Temp/press/flow, Turbine Supervisory parameters etc.

Hope this will be helping for you