Coal-fired Power Plant: World Overview

Introduction

• Coal-fired power plants, also known as power stations, provide over 42% of global electricity supply. 
• At the same time, these plants account for over 28% of global carbon dioxide (CO2) emissions.
• Coal is the world’s most abundant and widely distributed fossil fuel with reserves for all types of coal estimated to be about 990 billion tonnes, enough for 150 years at current consumption.

Energy in Coal

• For fuels, the difference between gross calorific value (GCV) and net calorific value (NCV) stems from the assumptions made about the availability of the energy present in the moisture in the combustion products.
• The GCV measures all the heat released from fuel combustion, with the products being cooled back to the temperature of the original sample. In the NCV assessment, it is assumed that water in the combustion products is not condensed, so latent heat is not recovered.
• Using the NCV basis is questionable: a modern condensing boiler could potentially achieve a heating efficiency in excess of 100%, in violation of the first law of thermodynamics.

Coal-Fired Power Plant Efficiency

• A typical 500 MW subcritical pulverized coal-fired boiler, where the electrical output is 39% of the heat input and the heat rejected by the condenser to the cooling water is 52.5%.
• power generation efficiency = output power energy/total energy input
• heat generation efficiency = output heat energy/total energy input

The overall energy efficiency of the plant can then take account of power and heat export, as applicable:

• plant efficiency = (output power energy + output heat energy)/total energy input

For example, consider a plant with a fuel energy input of 500 GJ producing power with an energy equivalent of 200 GJ (56 MWh). The overall plant efficiency equals power generation efficiency because there is no heat output:

power generation efficiency = 200/500 = 40.0%

If 150 GJ of the waste heat is used, then the overall plant efficiency increases:

overall plant efficiency = (200 + 150)500 = 70.0%

The apparent electrical or power generation efficiency is now:

power generation efficiency = 200/(500 – 150) = 57.1%

Similar analysis can be used to calculate the efficiency of heat production:

heat generation efficiency = 150/(500 – 200) = 50.0%

A  plant with a heat rate (i.e. heat consumption rate) of 9 000 kJ/kWh of output would have an energy efficiency of 40%. A 1% change in heat rate would change heat consumed by 1% but would only change the efficiency value by 0.4 percentage points.