Steam turbine Condenser vacuum transfer condensate without pump?

[silebi66]

Dear Sir

I am a process engineer in HRSG combined cycle power plant project. The P&ID is attached in the post. The process description is following :

Makeup water to be demineralized and supplied through condensate water transfer pump or vacuum drag line for deaeration from the condensate storage tank to steam turbine condenser to make heat exchange.

The elevation of the condensate tank shall be enough extension upwards to supply make up water by vacuum drag without assistance from pumps or with assistance from pumps. Maximum quantity of makeup during Full Load operation shall be 4 percent of maximum expected turbine throttle steam flow

My question is how the vacuum drag line real function (be supplied from the condensate storage tank to the condenser). And, how do we measure or calculated that the elevation of the condensate storage tank is enough extended upwards to make up water by vacuum drag without assistance from pumps to the condenser or not?

I warmly appreciate for your kindly help and instruction.
Thank you very much.

 

[crshears]

Just for starters...

Based on a condenser back pressure of not more than 10 kPa, a condensate tank internal pressure only slightly above atmospheric, and no condesate pre-heating, I would not expect to be able to lift the make-up water into the condenser a vertical distance exceeding 4 metres, assuming adequate pipe size, of course.

The warmer the condensate is, the higher the likelihood that it will flash to steam as it is lifted, at which point unassisted lift could no longer take place due to vapour lock.

The make-up flow control valve should be immediately adjacent to the condenser and designed to handle any flashing to vapour that may occur as the pressure of the condensate drops in its transit through the valve.