Page 70 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Power Equipment and Systems 49

use chilled water from absorption chillers driven by recovered steam from the steam
turbine generator exhaust. Still other turbine inlet air cooling systems cool the inlet air use
chilled water from ice storage with the ice produced by electric power at night when other
facility electrical loads are lower. The advantage of ice is that ice can produce lower inlet
air temperatures than can be produced with absorption produced chilled water.
Types and Sizes
Combustion turbines are either single-shaft or two-shaft designs and are classified as
either aero-derivative or industrial type. Aero-derivative gas turbines for stationary
power are adapted from their jet, helicopter, and turboshaft aircraft engine counter-
parts. This type of combustion turbine is essentially a jet engine that is anchored to a
fixed frame. While these turbines are lightweight and thermally efficient, aero-derivative
turbines can be more expensive than products designed and built exclusively for
stationary applications. Aero-derivative combustion turbines are available from many
manufacturers in electrical capacities ranging from about 1 MW up to about 15 MW
(although some manufacturers have much larger units) and up to 40 percent simple
cycle efficiency (based upon LHV with recuperated turbine and no heat recovery). As
previously discussed, the fuel-to-electrical efficiency can be increased by use of waste
heat steam to produce more power (combined cycle). Steam generated in a waste heat
recovery steam generator (HRSG) located at the turbine discharge can produce more
electrical power in a steam turbine generator (STG) or it can be injected into the CTG
combustor after the compressor to increase the flow of gases through the turbine, cooling
the gases to reduce NO , and increasing the CTG power produced.
x
Industrial, or frame, combustion turbines are built for stationary electrical genera-
tion and are available in much higher capacities (up to around 500 MW). Industrial
combustion turbines are heavier than their aero-derivative cousins as well as typically
less efficient. Industrial combustion turbines have maximum simple cycle efficiencies
of approximately 36 percent (based upon HHV). As shown in Fig. 3-3 and as discussed

1.2

Heat rate
Relative turbine capacity, Heat rate 1.0 Capacity
1.1

0.9

0.8

Rating point 59°F
0.7
40 50 60 70 80 90 100 110 120
Compressor inlet air temperature (°F)
FIGURE 3-3 Relative turbine power output and heat rate versus inlet air temperature. [Source:
2008 ASHRAE Handbook: HVAC Systems and Equipment (Ref. 1).]