Page 155 - Boiler_Operators_Handbook,_Second_Edition

140 Boiler Operator’s Handbook

stabilize before leaving the engine. Frequently engines associated equipment so PCI was not responsible for the
are started with compressed air or hydraulic fluid pres- design. On an extremely cold winter night the year after
surized by compressed air and restoration of the pressure the installation, when temperatures drop below 11° F, the
should be checked before leaving the engine. utility called but the engines would not start. We were
During normal operation of an engine you should called to resolve the problem and discovered there were
check for proper lubricating oil level, pressure drop no heaters for the fuel oil or the lubricating oil. It took
through air filters and fuel filters, then log cooling and lu- a combination of halogen lights and welding machines
bricating oil pressures and temperatures every shift. I’m to heat the oil and get the engines running. So, even if
reminded that there are engines that don’t permit check- you don’t have that agreement to deal with you should
ing oil level while they’re operating, like your car, they consider the potential for an extremely cold start of your
have to be shut down to check the oil level. Regardless, emergency generator and be assured that it will start and
this puts you next to the engine where your ears and your run and carry a load.
brain are put to work to detect any abnormal sounds and
their meaning.
Remember that the air used for combustion must GAS TURBINES
come from outdoors. I’ve always questioned the applica-
tion of air filter sensors (these usually provide a green or One type of gas turbine, that I’m used to and would
red indication) that are simply connected to the air piping be installed in a boiler plant, is referred to as aeroderiva-
between the filter and engine. On large engines I would tive. The turbine assembly consists of a typical jet airplane
specify the sensor detect the difference between outside engine with its exhaust discharging into a few stages of
air and the piping so failure of automatic louvers and the gas turbine blading connected to the power output shaft.
like to operate properly would produce a red indication. All other GTs (gas turbines) consist of a combination of
It is always a good idea when shutting down an en- compressor, burners, then turbine mounted on the same
gine to remove the load, if that’s possible, and allow the shaft as the compressor and connected to a generator or
engine to cool down from load conditions. Alternatively other piece of driven equipment. I have only seen a few
reduce load to cool the engine. Stopping it immediately dozen and, for all practical purposes, they were all differ-
could result in carburization of oil in areas where the oil ent so, once again, the instruction manual becomes very
is trapped instead of flowing through. When the engine is important.
equipped with an auxiliary oil pump it should be started Unlike an engine most gas turbines are cooled by
before shutting down the engine and stopped only after air flow and the lubricating oil. The lubricating oil is, in
the oil temperatures entering and leaving the engine dif- turn, cooled by air or water. Many of the aeroderivative
fer by less than 5°F. Then, treat the cooling system simi- plants have staged oil cooling where the airplane engine’s
larly but don’t shut it down until after the auxiliary oil oil is cooled by another lubricating oil system. For air
pump is shut down. cooling some of the air compressed by the compressor
Like boilers, idle engines deserve to be checked flows around the combustion chamber(s) for cooling then
regularly. Potential problems include loss of starting mixes with the burner exhaust to reduce the tempera-
power, freezing cooling water, and moisture condensing tures entering the turbine section. More modern engines
and accumulating in the crankcase to name a few. have cooling air from the compressor diverted through
It isn’t unusual for emergency generators to be treat- the turbine blades to cool them. The air leaves the blades
ed as peaking generators. In other words the owner of the through multiple orifices at the tip of the blade to flow
emergency generator has a contract with the local electric over the external surface of the blade to help protect the
utility that pays the owner to operate the generators dur- blade from the hot flue gases.
ing periods of peak electric load. This arrangement is It isn’t uncommon to require fuel gas compressors
beneficial to both parties. The agreement does normally for natural gas-fired turbines. Despite the large supply
include provisions for penalty should the owner fail to of natural gas at the time of preparing this edition many
operate the equipment when it’s requested by the utility. gas turbines exist that are designed to fire fuel oil as well
While someone could imagine that peak electric loads as natural gas. The oil nozzle may look a little Strange
occur in the summertime it’s also possible in the winter. (Figure 4-10) but you should be used to enough varia-
PCI installed a couple of large emergency generators for tions now that you won’t appear to be confused when
a customer under those circumstances a number of years confronted with something like this.
ago. Luckily the owner had purchased the generators and Gas turbines, like engines, need to be started. At