A Turbine Close to Home – Part 1

by Carter Palmer, Power Systems SpecialistForecast International.

GE’s 7HA high efficiency, air cooled gas turbine. Source: GE

In the power generation game, gas turbines have long cemented their position.  What is the norm now and what might lie in the future?

Gas turbines can be used in two ways for power generation.  Depending on the requirements of a specific installation, a simple-cycle or combined-cycle design is preferred.  Cogeneration and trigeneration setups are also possible with these machines.

Simple-cycle power plants run a gas turbine strictly by itself.  Air goes into the compressor, fuel is mixed and burned, the turbine extracts mechanical energy to turn the generator, and finally the heated exhaust is expelled from the machine.  Aviation turbines work in a similar way.  However, simple-cycle design is not the most efficient way to generate power with gas turbines.

Instead of letting the heated exhaust go unused, a combined-cycle design utilizes that heat to create steam and, in turn, power a steam turbine.  The design consists of one or two gas turbines with one steam turbine; each turbine has a generator.  A combined-cycle power plant can obtain greater efficiencies compared to a simple-cycle plant, thus saving the operator money.

Heat can also be used in cogeneration, where the gas turbine’s exhaust is used for district (community) heating or, on a smaller scale, for some industrial processes.  Trigeneration includes heat and also cooling through an absorption chiller.  The utilization of heat, albeit not to power a steam turbine, also means these designs are efficient.

Efficiency, the magic word in the gas turbine world, has been improving over time.  Not too long ago, the target for gas turbine manufacturers was 60 percent efficiency in a combined-cycle design.  That level was surpassed early this decade, and now turbines are performing well above that mark.  One such turbine to best this efficiency milestone is the GE 7HA.

Although not the largest turbine that GE produces, the 7HA represents technology that has only been available recently.  The advertised efficiency of the 7HA is 63.5 percent, an impressive achievement.  Again, efficiency is key: More efficient machines save on operating costs, effectively giving more bang for the buck.  A more efficient turbine is also cleaner for the environment, a positive factor in this day and age.  And now manufacturers are gearing up to do even better: 65 percent efficiency is the new target.

Forecast International’s team of industrial and marine turbine specialists were given the opportunity to see a GE 7HA up close.  Be sure to check out Part Two.

Be sure to visit Forecast International power systems analysts Carter Palmer and Stu Slade at Power-Gen International on December 4th through 6th, Booth 1360


As an analyst for Forecast International’s Industrial & Marine Turbine Forecast, author Carter Palmer specializes in examining key gas turbine programs for electrical power generation, mechanical drive, and marine propulsion applications.