Full resolution (JPEG) - On this page / på denna sida - 1958, H. 10 - Power Generation by Large Gas Turbine Units, by Lars E Lingstrand and Jan R Schnittger
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nomy. When new water power projects are
developed under such conditions a supplementary
production by thermal power plants is concurrently
required which power plants may be used for peak
power production during the occurrence of
maximum demands and for base power production during
periods of scanty water supply.
Investigations, based on current production costs
of conventional thermal power as well as of water
power in Sweden, show that the most favorable
economy is obtained if about 20 or 25 per cent of the
power projects are developed as thermal power
plants. The load factor of the thermal power
increments varies widely dependant on the water
supply and averages about 0.1 or 0.2. At this low
load factor a low capital cost becomes more
important than a favorable rate of efficiency and low fuel
costs. In the matter of introducing gas turbines,
judged financially sound according to Swedish
conditions, it is therefore most essential that a reduction
of the capital costs should be strived at, even at the
expense of a slower rate of improvement of the plant
efficiency.
The peak power stations should be capable of
making quick starts and of accounting for an
inexpensive starting-up and shutting-down. Furthermore the
personnel requirement should be small and a low
cost of emergency service in off-operations should
prevail. The experience already gathered shows that
the gas turbine complies with these requirements
to a greater extent than achieved by any other
machine type.
End-of-line Generating Plants
Several factors determine the selection of the site
of a thermal power station. The most important are
the costs of fuel transportation and storing as well
as the influence of the production upon the
aggregate transmission costs in the power system. In the
selection of a construction alternative it is safe to
assume that gas turbine plants may be placed just
as favorably as the condensing power plants, or else
the same site may be considered to be utilized. The
gas turbine plants are of a lesser magnitude as
compared with those using condensing power.
Moreover, they are in a lesser degree dependent upon
supply of cooling water for which reason great
possibilities crop up to place them in localities that
are more favorable in an overall economic sense.
As end-of-line generating plants the gas turbine
power plants will yield savings and gains in the
matter of transmission costs, due partly to deferred
investments and partly to diminished transmission
losses. These savings may also warrant the
designation of sites in localities where the increase of fuel
costs will be relatively great.
The opportunity of using the gas turbine as an
end-of-line generating plant is more ore less
restricted within the different kinds of power systems;
generalizing estimates or evaluations would not do.
Construction is now in progress of a 40 MW plant
in Västervik, a city on the Swedish East coast. In
principle this plant furnishes an example of an
end-of-line generating plant. It has led to the
postponement for some years of the construction of a 130
kV line and the saving of an investment in capa-
citor banks, amounting to about one million Swedish
crowns (kronor).
In order to attain the greatest possible reduction
of transmission losses synchronous operations must
be resorted to during such hours of maximum
demands when power production is not going on. The
units should therefore be designed in such a way
that the generator may be put in synchronous
running having the turbine disconnected. Shunting
between active power production and synchronous
running should be a matter of speed, which requires
an automatic coupling between the generator and
the turbine to be employed at the full number of
revolutions in the process of disconnection as well
as of switching in.
Design of a Large Gas Turbine Plant
The Swedish Turbine Company Ljungström, STAL,
has been charged with designing a 40 MW gas
turbine plant with emphasis on low fixed charges and
convenience for peak load and power factor
correction service. Less stress has been put on the outmost
possible thermal efficiency.
Working with an open thermal cycle one may
establish the following with regard to the general
influence on fixed charges and thermal efficiency
of components, added to the simplest cycle
comprising a compressor, a combustion chamber and a
turbine:
a) Addition of a heat exchanger alone may increase
thermal efficiency but hardly raises the specific
power in kW per pound airflow per second, that
is the size of the unit is increased by the heat
exchanger without a corresponding increase in output.
Further it may be shown, that with high efficiency
compressor and turbine components it is necessary
to employ heat exchanges of more than about 60 %
heat transfer effectiveness before any gain at all in
Fig. 1. Principal arrangement of the STAL AO MW gas
turbine power plant. A Alternator, Cpl Detachable power
operated spline coupling, PT Dual flow power
turbine, IT Intermediate pressure turbine, HT High
pressure turbine, CC Combustion chambers, HC
High pressure compressor, IK Intercooler, LC Low
pressure compressor.
1 138 ELTEKN I K 1958
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