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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Fig. 5. Possible power capacity during varying air (ta)
and cooling water (tw) temperatures in reference
to a 40 MW gas turbine.
the peak power running may be accomplished at
an average capacity and peak power efficiency that
is higher than 40 MW and 27 % respectively. The
increase of capacity obtained during the peak loads
has a value and may justify a cut of a few per cent
in the specific construction cost, since this cost was
based on the rated capacity of the design, or 40 MW.
In starting-up and in shutting-down during peak
power running effected by a condensing power
plant, the heat losses will be potent in affecting the
efficiency, ranging a few per cent. Assuming a 10
minutes starting-up time reckoned from standstill to
full load, the corresponding losses in the gas turbine
plant will turn out relatively small, whereby the
difference in the efficiency of both classes of power
tends to be equalized. The yearly efficiency of the
gas turbine at a load factor of 0.1 or 0.2 is estimated
at 25 % and the yearly efficiency of the condensing
power plant at 31 % under the assumed operative
conditions. According to the current prices of
Bunker C oil cif Swedish port the corresponding fuel
costs will be 4.1 ore per kWh and 3.4 ore per kWh
respectively.
Thus the cost of operations relative the gas turbine
power plant would amount to 10 crowns per kW
per year plus 4.5 ore per kWh as against 18 crowns
per kW per year plus 3.8 ore per kWh relative the
condensing power plant. The total production costs
of the same plants would be 56 crowns per kW per
year plus 4.5 ore per kWh and 74 crowns per kW
and year plus 3.8 ore per kWh (exclusive of the
costs of harbour and oil storing facilities)
respectively.
Conclusions and Future Trends
The economic comparison shows that in a gas
turbine power plant, rated at 40 MW, production costs
are brought down to a lower level than that
prevalent in a big condensing power plant having brief
utilization periods, mainly because of lower capital
costs and a reduced working force. As the utilization
period is expanded the inferior efficiency of the gas
turbines and the ensuing higher fuel costs will bring
down the gain. Production costs on an equal level
are obtained at approximately 2 500 hours of
utilization time per year, corresponding to a load factor
of 0.3. In view of the Swedish load balancing
conditions, where the load factor of thermal power ranks
around 0.1 or 0.2, it is evident that the entire
requirement of peak power may be gainfully supplied by
gas turbine power plants. However, in using smaller
sized gas turbines of 10 or 25 MW the remunerative
utilization time will be considerably reduced and
consequently the opportunities for their utilization
in the great power systems will be curtailed, except
on a limited scale.
When the Västervik plant is put in actual operation
and is shown to come up to expectations there is
the occasion offered the Swedish power concerns
to let big-sized gas turbines far and wide supply
their need for peak power.
The great merits of the gas turbines are their low
capital cost and their simple starting and operation
facilities. The main reasons for the low capital cost
are the slight material and space requirement per
installed kW. In view of the trend towards
bigger-sized turbine units there are still further gains to
be gathered in the way of saving materials and
space.
Even at present opportunities are offered to
improve efficiency by conventional methods. However,
these appear to imply too steep a rise of the capital
cost, bringing down the overall economic result and
therefore prohibiting such measures. The trend
towards higher efficiencies has progressed rapidly
during the last years and there are good reasons to
presume that it also will point to successful results
in the future. Under any circumstances a more
substantial rise of the rate of efficiency may be
expected in the gas turbine field rather than in the
condensing power field.
The use of gas turbines in running peak power is
generally acknowledged. Continued hydro-power
developments demand thermal power supplements
for peak power production and this situation paves
the way for an enlargement of the gas turbine
capacity. In case the hydro-power countries turn to
nuclear power this will not change the situation very
much, because the need will remain for a gradual
construction of new gas turbine power plants.
Other needs and uses may be in store for sizeable
gas turbines. The use of gas turbines in the
processes of nuclear power production appears to be
feasible. Hence, the development of sizeable gas
turbines may be considered a very urgent pursuit.
Summary
Within power system where the development of
peak power plants may progress by large strides
the gas turbines must be capable of competing with
large condensing units. In order to attain a necessary
improvement of the economic return, a trend
towards larger-sized gas turbine units is desirable. A
large gas turbine power plant is under
construction in Sweden. Cost accounting shows that the
increase in unit size renders the gas turbine power
plants so favorable from the point of view of
economic returns that condensing power plants should
no longer be considered to function as peak power
stations.
1 42 ELTEKN I K 1958
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