Page 116 - Boiler_Operators_Handbook,_Second_Edition

Boiler Plant Operations 101

still be colder than design operating temperature when normal operating range and you’re absolutely certain
you start rolling the turbine over and you may have in- you don’t hear any screeching, bumping, or grinding
sufficient lubrication because the oil is too cold. By using in the whole assembly. It doesn’t hurt to use the screw-
the casing heating to warm up the oil you ensure it’s at driver at the casing with handle in your ear trick to
the right temperature for operation before you start roll- listen for any unusual sounds while a turbine is slowly
ing the turbine. It’s the kind of consideration you need rolling over. Open valves for cooling water to any reduc-
to include in your SOPs but I’ve never run into a turbine tion gear or oil coolers on the driven equipment.
that overheated oil while warming up the casing. The final step before bringing the turbine up to
Once you’re certain the casing and the steam supply speed is checking the trip. Normally there is some link-
piping is warm and dry and the oil is up to operating tem- age between the turbine and the trip valve and all you
perature it’s time to start rolling the turbine. Sometimes have to do is push gently on the lever closest to the
you have to run the trip valve down (turn it as if closing turbine shaft to trip the valve. Some turbines will have a
it) because someone tripped it earlier and didn’t reset it. If means to manually operate the trip. Make sure it works
the valve doesn’t seem to be opening try that first; there’s then reset and open it again to restore normal rolling.
a spring loaded trip mechanism that shuts the valve by When you’re satisfied that the turbine is rolling
releasing the yoke screw and you have to turn the valve as over without problems and the overspeed trip should
if to close it until the trip mechanism is reset. work you can start bringing it up to speed. First make
Open the supply shut-off valve. Crack the trip certain that you and anyone around you are not in line
valve and continue slowly opening it until the turbine with the rotor. If it flies apart and pieces penetrate the
starts to turn over. The minute you see the shaft start casing you don’t want to be in the way.
moving stop opening the valve and close it back down You want to open that trip valve real slow. A fair
to maintain a slow rotation of the turbine. amount of energy is required to overcome the inertia of
If your ears suddenly hurt because of a loud the rotor, driven equipment, and any gears to get them
screeching noise shut the trip immediately and back up moving but once they’re moving it doesn’t take much to
in the start-up process because you forgot to open the keep the speed up. If you bring the turbine up to speed
exhaust valve or there’s another valve in the exhaust too fast it will overspeed and sometimes that trip just
piping that’s closed or throttled. Auxiliary turbines are doesn’t act fast enough. If the turbine has a tachometer
equipped with what we call a sentinel valve. It’s expen- you should watch it and slow the opening of the trip
sive to put a full capacity relief valve on every turbine valve as normal speed is approached.
casing in case someone forgets to open the exhaust The turbine speed controls should eventually take
valves so sentinel valves are used. They’re like a relief over control of the steam flow. Once that happens you
valve but they don’t have much capacity; they just let can run the trip valve the rest of the way open. If the tur-
enough steam out to make one loud squeal that’s de- bine is equipped with a process control (like feedwater
signed to shake up any operator that forgot to open all header pressure or feedwater to steam pressure differ-
the exhaust valves. ential) that valve or controller should take over. Resist
This is prior to the most critical stage of auxiliary the temptation to bring a turbine up on one of those
turbine operation and where things can go very wrong controllers, especially if they’re in automatic. Neither
so it’s important to take your time and allow the turbine the controller nor the manual signal output can control
to gently roll over for a while. You’ve just started steam the steam flow as well as you can with your hands on
flowing in the exhaust piping and any pockets of con- that trip valve.
densate should be slowly flushed out during this time. If you were starting a centrifugal pump it’s time to
If there are known areas where the piping may have open the pump discharge valve. Open it slowly so the
pockets of condensate and they’re equipped with drain turbine controller has an opportunity to respond to the
valves those valves should still be open. increased load.
If there’s a reduction gear between the turbine and Once the turbine is up to speed and carrying load
driven equipment you want to give it time to warm up you can close the vent and drain valves, provided you
and get the oil properly distributed over the gears and don’t see any condensate coming out. If the exhaust line
bearings. Some will have heaters to keep the oil hot from the turbine is routed up from the casing connection
enough while the turbine is down, some will have cool- then the casing should have a steam trap to continuous-
ers, and some have nothing but a sump full of oil. Let the ly remove condensate. Make certain that such traps are
turbine roll slowly until all the temperatures are in the really working by temporarily opening a manual casing