Page 117 - Boiler_Operators_Handbook,_Second_Edition

102 Boiler Operator’s Handbook

drain about five to ten minutes after you closed it; you make a real difference in the overall operating cost of a
should get nothing but steam. boiler plant. Wise operators know that and operate them
Stop any electric driven oil pump and observe oil wisely.
pressures to ensure the turbine’s pump is satisfactorily
providing proper lubrication pressures. Some electric
pumps will automatically stop as the turbine’s oil pump POWER TURBINE OPERATION
generates a higher pressure.
What if you have to bring one up in a hurry? I hope Power turbines can operate similar to auxiliary
you never do have to because the potential for damage turbines in that their exhaust consists of steam under
to an auxiliary turbine by rapid starting is very high. If pressure that is used for other purposes than simply
you are in an operation that must be able to bring a tur- powering the turbine. These are referred to most com-
bine up quickly then you should have condensate traps monly as back-pressure turbines with the only limita-
on the casing and steam supply drains, an automatic tion on their exhaust pressure being the capability of
air vent at the top of the casing, and means to rotate the the turbine casing to withstand the pressure. A common
turbine regularly, either automatic or prescribed manual exhaust pressure for back-pressure turbines is 150 psig.
means, so it’s always ready. When starting one of these These turbines are commonly used to generate electric
units always check by opening a free blow drain to en- power from superheated steam produced by the boil-
sure the casing is dry before starting the turbine. They ers and their exhaust used to service the facility. The
make a lot of racket and exhaust steam piping and the amount of steam generated and passing through the
deaerator can get pretty rattled if you start that turbine turbines is typically controlled to maintain the facility
with any accumulation of water in the casing. service pressure by throttling the steam to the turbines.
When shutting down and the turbine has an elec- Unlike auxiliary turbines that may have simple
tric oil pump make certain it is running. Begin to shut ring lubricated bearings or a startup lubricating oil
down the turbine by slowly closing down on the trip pump that is supplanted by a shaft driven oil pump
valve. The steam supply shut-off should be open or power turbines normally have a complete lubricating
shut, not throttled, so there’s no erosion or wire draw- oil system that includes pumps to pump the oil to the
ing to cause it to leak. Make certain that the load served bearings and gears of the turbine and the equipment it
by the driven equipment is handled by another turbine powers. We never shut the main lubricating oil system
or motor driven device as the turbine you’re shutting down on the ship other than for maintenance of that
down starts slowing noticeably. system. It has gravity tanks, a large reserve of oil in
When the turbine has slowed a little more close the tanks installed much higher than the turbine that use
discharge valve of any pump powered by the turbine to the static head to produce the pressure for feeding the
ensure a hung up check valve doesn’t allow reverse flow oil to the turbine, and oil pumps that lift the oil from
to start driving everything backwards. Throttle down on the sump of the turbine and gear casing back up to the
the trip valve until the turbine is gently rolling over and gravity tanks. The pumps always deliver more oil than
allow it to continue rolling for twenty minutes to one the turbine and gear require so there is an overflow
half hour. This slow rolling allows the turbine parts to line from the tanks that drops oil back to the sump. The
cool from operating conditions to exhaust temperatures piping has an illuminated observation window at the
and slow cooling is desirable for the heavy metal parts. operating level and it is always a comforting thing to
After that cool down period close the trip valve see that oil flowing through that port back to the sump.
and high pressure steam supply valve then immediately It means we have a reserve of oil that would keep the
open all the drains a couple of turns. If you’re going turbine and main gears lubricated for a period of time
to start it back up again in a few hours leave it under even if electric power is lost. Shore-side turbines may
exhaust pressure. Otherwise, after the turbine stops rely on emergency generators to operate the lubricating
rolling, close the exhaust valve, open the vent and drain oil pumps but some may have a similar arrangement to
valves completely and once the rotor stops turning, stop provide enough lubrication to allow the main turbine to
any electric oil pump. come to a stop without losing lubrication in the event of
It’s a little complicated, it takes time, you have to loss of power.
handle small handwheels in tight spaces around the tur- On the ships, to prevent distortion of the rotor
bine because the guy that piped it never thought about shafts we always engage a “jacking gear” driven by a
operating. Proper operation of auxiliary turbines can small electric motor that powers one of the turbine ro-