Page 119 - Boiler_Operators_Handbook,_Second_Edition

104 Boiler Operator’s Handbook

ter has to be established which requires starting at least admitting steam to the nozzles. Then, after the jacking
one main condensate pump and to ensure continuous gear is disengaged steam can be admitted to either type
flow a recirculating valve is opened so some condensate of turbine to start rotation.
runs back to the main condenser. Then the steam jets It isn’t necessary to establish a complete vacuum
can be placed in service by opening their steam valves. before starting operation of the turbine. As long as
When I was sailing that recirculating valve was manu- there’s cooling water flow and evidence that the vacuum
ally controlled and for reasons I’ll never understand, systems are working the turbine can be started. Before
so oversized that it was an absolute pain, requiring starting that turbine always disengage the jacking gear.
frequent adjustments. Most of them were too far open at Admitting steam to the nozzles may automatically force
one quarter turn which represents about five percent of the jacking gear to disengage but I would rather do it
the disc travel manually. Admitting steam with the gearing engaged
While the casing is pressurizing on a back-pressure won’t turn the turbine but increasing steam in an effort
turbine or vacuum is building on a condensing turbine to get turning can result in damage to the jacking gear.
steam piping upstream of the throttle valves can be As with auxiliary turbines you should admit
pressurized. Drains in that piping must be opened to enough steam to achieve rotation and allow the turbine
remove condensate. Once the turbine is up and running to slowly rotate and come up to operating temperature.
the superheated steam will not produce any condensate The higher the temperature of supply steam the longer it
in the piping so there are no steam traps attached to that will take to bring the turbine up. As with many other el-
supply piping. The drain valves are always operated ements of operation always read the instruction manual
manually. Ensuring there is no water collected over any for the turbine before you operate it and pay special at-
one of the control valves or in the piping is necessary to tention to this part of the operation. We actually rotated
prevent a slug of water banging on the turbine blades. I the turbine (and the propeller) forward and backward
only screwed this up once and will never do it again. I initially to evenly warm up both ahead and astern tur-
was bringing up a boiler at the same time that I was pre- bine components.
paring the main turbine for operation and didn’t open An over-speed trip is provided on power turbines
the isolating valve from the boiler until we suddenly got and it should be tested during startup similar to aux-
a bell indicating a need for full astern operation. What iliary turbines. I’ve know these to fail with disastrous
we referred to as a “bell” was the ringing of a bell on a results so be very careful in testing the trip to be certain
large circular dial marked in different pie shaped sec- it will work when it’s needed. Regardless, always bring
tions with “Finished with Engines, Stop, Slow Ahead, the turbine up to speed slowly so you don’t over-speed
Slow Astern, Full Ahead and Full Astern” providing because there is no load on the turbine to prevent it. At
instruction from the bridge as to how they wanted the some point the controls for the turbine should automati-
engine (the main turbine) operated. The First Assistant cally take over to control the speed and you can spin the
Engineer (the one that normally operates the engine dur- trip valve the rest of the way open.
ing maneuvers) spun open the astern throttle valve and Once an electric generator turbine is up to speed it
things went awry. Sensing a drop in pressure in the main must be electrically connected to pick up a load. On the
header the controls increased the firing rate on the two older ships I operated we had all direct current power
boilers but, since I forgot to open the stop valve from and it was rather easy to raise the speed until the voltage
one, only one provided steam. The pressure in the boiler on the generator was above the main line and throw the
with the closed valve climbed as the one connected to breaker to engage the generator I just started. It’s an-
the header dropped and its water level dropped as the other story with alternating current generators because
one serving the header went up. I rushed up and opened you have to match the alternating current frequency.
that stop valve but there was some water laying on top There are panel mounted devices that inform you when
of it and I’ll never forget the clatter as it raced toward the the generator is synchronous with the line but you re-
turbine. Luckily there was no damage to the turbine or I ally want the generator you just started to be running
might have lost my license. So, make damn sure all those just a little faster so it picks up some load as soon as it’s
drains are clear of condensate and all the right valves are engaged. Then, you have to throw that breaker at the
open well in advance of turbine operation. precise instant when the generator and line are in synch.
The main exhaust valve of a back-pressure turbine This is one more place where reading and understand-
can be opened as soon as the casing pressure matches ing all the instructions are very important. Your plant’s
the main exhaust pressure but it must be opened before SOPs should always address a turbine startup.