Condenser Vacuum System in PowerPlant

Condenser Vacuum System in Power Plant

In Power Plants, wherever Steam Turbine is used for Power Generation, Condenser is employed for cooling of the steam exhausted from steam Turbine. 

Turbine converts steam heat energy (mass x enthalpy) in to shaft power which rotates Electric Generator to produce electricity. As the exhaust pressure reduce, exhaust enthalpy will be lower which will increase turbine output. Hence, Condenser is operated in vacuum condition to get the maximum power output from steam turbine.

Condensate formed by cooling of the steam is extracted by Condensate Extraction Pump (CEP) and forwarded to Deaerator/HRSG/Boiler as per System Design. 

Refer fig.1 for Understanding.  

Due to condenser is operating in vacuum condition air may leak from the joints with the condenser or cooling water may leak from the condenser tube joints. As this is a continuous process, over the time non-condensable gases/air may accumulate in the condenser which will increase the condenser operating pressure and results in reduction in turbine output.  

Hence, to remove non-condensable gases and air from the condenser, vacuum system is provided. Vacuum system operation during normal plant running condition called Holding operation.

Vacuum System is also used to create the vacuum in the condenser during plant startup before admitting steam in to the condenser. This process to create vacuum called the Hogging Operation.

Widely used Vacuum System in power plants are Liquid Ring Vacuum pumps or steam jet air ejectors. As most of the power plants utilize Liquid Ring Vacuum Pumps, this article focused on Liquid Ring Vacuum Pump system.

Why It’s called Liquid Ring Vacuum Pumps?

Pumps works on the principle of positive volume displacement where Closed volumes are created by Impeller and Liquid Ring. Refer below sketch for functional understanding of liquid Ring Vacuum Pump parts:

Liquid Ring Vacuum pumps capacity Selection:

Vacuum pumps Hogging and Holding capacity selection criteria is provided in HEI for surface condenser based on steam flow and number of turbine opening.

 For Hogging operation capacity selection, standby pumps are considered in operation.

 Liquid Ring Vacuum Pumps Configuration:

Liquid Ring Vacuum pumps configuration can be selected by supplier for the provided process condition based supplier (OEM) technology. It can be two stage vacuum pumps or single stage vacuum pump with air ejector. With seal water pump or without seal water pump subjected to OEM guarantee for performance.

Refer below sketch for vacuum pump skid basic arrangement.  

Cooling water for seal water cooling:

Cooling water is taken from either condensate system or condenser cooling water (if river water is available for condenser cooling). Incase of sea water cooling heat exchanger may get corroded earlier than condensate water or fresh water which may increase the maintenance cycle.

Separator:

Separator is used to separate the moisture from the non condensable gases. moisture separated will be collected in separator. It is also used as seal water storage vessel.

Vent Pipe:

Non-condensable gases will be discharged to atmosphere via vent pipe which needs to be routed to safe location outside the building.