Page 121 - Handbook of Energy Engineering Calculations

The gas turbine “came on the scene” at one of the most opportune times in

engineering history. Just as the world began to worry about greenhouse gases
(GHGs), global warming, and the air pollution coal-fired plants caused, the
aero-derivative gas turbine showed up. The advantages of this new prime
mover were many:

• It had already been proven in aircraft service to be reliable, relatively low

cost, efficient, lightweight, and compact. Further, gas turbines can be
started rapidly (as compared to hours for a steam plant), can be operated
remotely, can be started and stopped unattended, and easily handle wide-

load swings. Maintenance is simple; most gas turbines operate for long
periods between overhauls. Coolants are usually not required for a gas
turbine.

• The gas turbine’s footprint for land service is small—few utilities wanting
to install gas turbines for topping, standby, or combined cycles even have

to expand existing structures, let alone put up a new building.

• Permit requirements are simple compared to getting a new coal-fired station
approved.

• Heat-recovery steam generators (HRSG) hooked to the exhaust of a gas
turbine provide additional steam in a cogeneration mode while recovering

heat that would otherwise be wasted. The additional steam can be used to
generate electric power in a steam turbine, or it can be used for space
heating, industrial processes, district heating, and so on.

• Natural gas, a popular fuel for gas turbines, has concurrently become more
readily available, and at lower prices. Further, additional sources of natural

gas are being found using a new technique called “fracking.” Light
distillate oils are also used for gas turbines. Heavy residual oil can be used
as well, but its corrosive nature must be allowed for in the manufacture of

the combustor and turbine.

• When introduced into steam plants in a combined cycle, the gas turbine
raises the overall thermal efficiency of the plant to a new level, without