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Basic Calculations for a Power Plant- Calculating the Coal
Quantity
written by: johnzactruba edited by: Lamar Stonecypher updated:
10/15/2009
How to make quick estimate of the coal required for running a
power plant? Thisarticle describes a simple method.
Very often, the Power engineer is required to perform some basic
calculationsregarding the key parameters of a power plant. Most
important is the quantity andcost of fuel that is required.This
article gives the simple calculation method. (Adetailed calculation
required in the context of a contract, tender, performancerepor,t
or a legal document may require more accurate input data.)
We take the example of a 100 MWCoal Fired Power Plant.
Energy Content in Coal
The basic function of the power plant is to convert energy in
coal to electricity.Therefore, the first thing we should know is
how much energy there is in coal.Energy content of coal is given in
terms of KiloJoules (kJ) per Kilogram (kg) of coalas theGross
calorific value (GCV) or the Higher Heating value (HHV) of coal.
Thisvalue can vary from 10500 kJ/kg to 25000 kJ/kg depending on the
quality and typeof the coal.
You should have an idea of the type of coal, or the source or
mine from where the
the plant gets the coal. Published data about the sources,
mines, regions or theprocurement data gives an idea about the HHV
of coal. For this example we use aHHV of 20,000 kJ/kg.
EfficiencyEnergy conversion takes place in two stages.
The first part of the conversion is efficiency of the boiler and
combustion. For this
example we take 88 % on an HHV basis that is the normal range
for a well-
optimized power plant. Second part is the steam cycle
efficiency. Modern Rankine cycle, adopted in coal
fired power plants, have efficiencies that vary from 32 % to 42
%. This dependsmainly on the steam parameters. Higher steam
perssure and temperatures in therange of 600 C and 230 bar have
efficiencies around 42 %. We assume a valueof 38 % for our
case.
Theoverall conversion efficiency then is (38% x 88%) 33.44
%.
http://www.brighthubengineering.com/power-plants/18082-coal-fired-thermal-power-plant-the-basic-steps-and-facts/http://www.brighthubengineering.com/power-plants/22202-burning-coal-in-power-plants-calorific-value-and-moisture/http://www.brighthubengineering.com/power-plants/19182-how-efficient-is-energy-conversion-in-a-thermal-power-plant/http://www.brighthubengineering.com/power-plants/19182-how-efficient-is-energy-conversion-in-a-thermal-power-plant/http://www.brighthubengineering.com/power-plants/22202-burning-coal-in-power-plants-calorific-value-and-moisture/http://www.brighthubengineering.com/power-plants/18082-coal-fired-thermal-power-plant-the-basic-steps-and-facts/
7/27/2019 Coal Requirement Calculation (2)
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Heat Rate
Heat rate is the heat input required to produce one unit of
electricity. (1 kw hr)
One Kw is 3600 kJ/hr. If the energy conversion is 100 %
efficient then to produceone unit of electricity we require 3600
kJ.
After considering the conversion efficiency in a power plant we
require an heatinput of (3600 / 33.44% ) 10765 kJ/ kw hr.
Coal Quantity
Since coal has a heat value of 20,000 kJ/kg, for producing one
kw.hr we require(10765 / 20000) 0.538 kg of coal. This translates
to (0.538 x 100 x 1,000) 53800kg/hr (53.8 T/hr) of coal for an
output of 100 MW.
