Maintaining Vacuum in the Steam Turbines?

Lines 4-10 answer the question in line 2.

The answer to line 3 is "the presence of non-condensibles in the steam"; air is the main culprit. Stopping the air getting in is the solution.

The second culprit is insufficient cooling. As the temperature in the condenser rises, the vacuum drops, being an inevitable consequence of the change in boiling/condensing temperature of H₂O with pressure. For surther details, refer to a set of Steam Tables: Mayhew & Rogers' "Thermodynamic Properites of Process Fluids" is a prime example; there are many others.

The following link may be of use...

http://cr4.globalspec.com/thread/74205#newcomments

Ron

PWSlack pretty much gave you the good answers as to why you need it for performance but you should also remember that shipboard use and some other applications most often requires you to maintain that vacuum while in port or while on standby. It also applies to electrical generation systems where units are kept warmed up and rolling over for fast starts to add capacity at times of high usage.

Main drive units engage a jacking gear drive to slowly roll the turbine while on standby as well as when cooling down for shutdown. Vacuum must be maintained to prevent leakage into the condenser since regaining vacuum can take considerable time and since you want to keep the turbine warm. The sealing steam is often a source of keeping the turbine warm.

It also serves to keep oxygen out of the BFW-condensate systems although as I understand it there are some recent changes in thinking about complete O2 removal as was the old philosophy.