emissions can be controlled to very low levels using dry combustion techniques,
water or steam injection, or exhaust treatment. Maintenance costs per unit of power
output are about a third to a half of those of reciprocating engine generators. Low
maintenance and high-quality waste heat render gas turbines a preferred choice for
industrial or commercial CHP applications greater than 3 MW.
Gas turbines can be used in a variety of configurations: (1) simple cycle operation, in which a single gas turbine produces power only; (2) CHP operation, in which
a simple cycle gas turbine operates with a heat recovery heat exchanger that recovers
heat from the turbine exhaust and converts it to useful thermal energy, usually in the
form of steam or hot water; and (3) combined cycle operation in which high pressure
steam is generated from recovered exhaust heat and used to create additional power
using a steam turbine. Some combined CHP cycle systems extract steam at an
intermediate pressure for use in industrial processes.
The most efficient commercial technology for central station power-only generation is the gas turbine-steam turbine combined-cycle plant, with efficiencies
approaching 60% lower heating value (LHV). Simple-cycle gas turbines for
power-only generation are available with efficiencies approaching 40% LHV. Gas
turbines have long been used by utilities to provide peaking capacity. However, with
changes in the power industry and advancements in technology, the gas turbine is
increasingly being used for base load power.
Gas turbines produce high-quality exhaust heat that can be used in CHP configurations to reach overall system efficiencies (electricity and useful thermal energy)
of 70–80%. By the early 1980s, the efficiency and reliability of smaller gas turbines
(1–40 MW) had progressed sufficiently to be an attractive choice for industrial and
large institutional users for CHP applications.
5.3.2 Steam Turbine
Steam turbines are one of the most versatile, and oldest, prime mover technologies
still in general production. They are used to drive a generator or mechanical
machinery. Power has been generated using steam turbines for approximately
100 years, since reciprocating steam engines were replaced due to higher efficiencies
and lower costs. The capacity of steam turbines can range from 50 kW to several
hundred MW for large utility power plants. Steam turbines are widely used for CHP
applications in the United States and Europe.
Unlike gas turbine and reciprocating engine CHP systems, where heat is a
by-product of power generation, steam turbines normally generate electricity as a
by-product of heat (steam) generation. A steam turbine is captive to a separate heat
source and does not directly convert fuel to electrical energy. Energy is transferred
from a boiler to the turbine through high pressure steam that in turn powers the
turbine and generator. This separation of functions enables steam turbines to operate
with an enormous variety of fuels, varying from clean natural gas to solid waste,
including all types of coal, wood, wood waste, and agricultural by-products (e.g.,
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water or steam injection, or exhaust treatment. Maintenance costs per unit of power
output are about a third to a half of those of reciprocating engine generators. Low
maintenance and high-quality waste heat render gas turbines a preferred choice for
industrial or commercial CHP applications greater than 3 MW.
Gas turbines can be used in a variety of configurations: (1) simple cycle operation, in which a single gas turbine produces power only; (2) CHP operation, in which
a simple cycle gas turbine operates with a heat recovery heat exchanger that recovers
heat from the turbine exhaust and converts it to useful thermal energy, usually in the
form of steam or hot water; and (3) combined cycle operation in which high pressure
steam is generated from recovered exhaust heat and used to create additional power
using a steam turbine. Some combined CHP cycle systems extract steam at an
intermediate pressure for use in industrial processes.
The most efficient commercial technology for central station power-only generation is the gas turbine-steam turbine combined-cycle plant, with efficiencies
approaching 60% lower heating value (LHV). Simple-cycle gas turbines for
power-only generation are available with efficiencies approaching 40% LHV. Gas
turbines have long been used by utilities to provide peaking capacity. However, with
changes in the power industry and advancements in technology, the gas turbine is
increasingly being used for base load power.
Gas turbines produce high-quality exhaust heat that can be used in CHP configurations to reach overall system efficiencies (electricity and useful thermal energy)
of 70–80%. By the early 1980s, the efficiency and reliability of smaller gas turbines
(1–40 MW) had progressed sufficiently to be an attractive choice for industrial and
large institutional users for CHP applications.
5.3.2 Steam Turbine
Steam turbines are one of the most versatile, and oldest, prime mover technologies
still in general production. They are used to drive a generator or mechanical
machinery. Power has been generated using steam turbines for approximately
100 years, since reciprocating steam engines were replaced due to higher efficiencies
and lower costs. The capacity of steam turbines can range from 50 kW to several
hundred MW for large utility power plants. Steam turbines are widely used for CHP
applications in the United States and Europe.
Unlike gas turbine and reciprocating engine CHP systems, where heat is a
by-product of power generation, steam turbines normally generate electricity as a
by-product of heat (steam) generation. A steam turbine is captive to a separate heat
source and does not directly convert fuel to electrical energy. Energy is transferred
from a boiler to the turbine through high pressure steam that in turn powers the
turbine and generator. This separation of functions enables steam turbines to operate
with an enormous variety of fuels, varying from clean natural gas to solid waste,
including all types of coal, wood, wood waste, and agricultural by-products (e.g.,
5 Realizing a Local Low-Carbon Society Through Urban-Rural Linkage
113