Coal is a flammable black or a brown sedimentary rock made of organic carbon, hydrogen, oxygen, sulfur, and nitrogen.
It is also the most used fossil fuels for producing electricity. 40% of the world’s electricity is from coal.
The production of cement is from coals as well as industrial purposes such as refining metals.
Types of Coal
There are four main types of coal. They are:
It’s hard coal, which contains 86-97% carbon and mainly used by the metals industry, space heating in addition to generating electricity.
It’s dark, hard coal, which contains 45-86% carbon and it’s an important fuel for generating electricity and as a raw material for making iron and steel.
It’s dull black coal which typically contains 35-45% carbon, and it’s used for generating electricity and space heating.
It’s brownish-black coal which contains 25-35% carbon, it’s crumbly and has high moisture content so it’s mostly used for generating electricity.
And we can also classify coal into:
Thermal coal: it’s mostly used for power generation because it’s more abundant, has lower carbon content and higher moisture than the metallurgical coal.
Metallurgical coal: it’s mostly used for steel production.
How does a coal power plant work?
The coal power plant has a simple and straightforward working principle which follows the Rankine cycle.
The coal is initially milled to a fine powder to be pulverized and then burnt in a furnace (combustion chamber of a boiler).
Then the heat energy released is used to heat water into super-hot steam. This under high pressure and temperature is used to turn the turbines connected to electrical generators by a shaft. It then drives the generators to produce electricity.
After this process, electricity is transported by transmission and distribution lines to homes, industries, hospitals, workplaces, and so on.
And we also cool and condense back the steam into the water to reuse in the boiler.
It’s important to know that to produce a 1000 MWe in a coal-fired power plant we use 9000 tonnes of coal.
Coal-fired power plant diagram
The coal power plant diagram shows the components of the plant and the different stages of transforming the chemical energy (coal) into electrical energy.
We start with the boiler or the steam generation system; we supply the coal from coal bunkers via coal conveyors to be crushed into coal mills. And in the air heater, the air is preheated from flue gas via the air circulation sub-system.
Then we supply this pulverized coal with preheated air in a boiler furnace for firing.
And the hot gases are re-circulated through boiler tubes and boiler drum for exchanging the heat to water to convert it into dry and superheated steam.
Then under high pressure, this steam turns the blades of a turbine.
And as the turbine is connected to an electrical generator by a shaft, the generator also spins to produce electrical energy.
Then the separated saturated water and water vapors from the turbine passes through the condenser and the heater to be converted into saturated water.
It is then injected via feed pumps into the boiler to complete the cycle.
Coal power plant efficiency
The coal power plant is the most used around the world with about 33% efficiency.
The following are efforts to deploy high efficiency up to 40% and low emission of this plant.
- Deploying advanced off-the-shelf technology could cut 2 Gt of Co2 emissions and allows affordable energy for economic development and poverty.
- It’s great to know that the reduction in Co2 emission implies a reduction in coal usage; which will cause a reduction in running costs plus reduction of overall use of coal and extension of the lifetime of coal reserves.
- Also, using modern high-efficiency plants will reduce the emission of nitrogen oxides; sulfur dioxide; and particulate matter.
- Minimizing the heat losses; equipment refurbishment; plant upgrades; and improved operation maintenance schedules also affect plant efficiency.
- Also upgrading some existing coal plant system to super or ultra-supercritical operation results in an improvement in efficiency and hence justify the extension of the life of the plant.
- And of course; improving the efficiency of the coal-fired power plant will make us use less coal per unit of energy.
Coal-fired power plant environmental impact:
There are several environmental and public health issues associated with coal power plants.
For instance, asthma, cancer, acid rain, global warming, heart and lung ailments, and neurological problems.
Yes coal power plants may be an important factor in damaging the environment as:
- Burning coal releases many pollutants like oxides of nitrogen, sulfur, mercury, particulate matter, and heavy metals; which lead to smog, acid rain, toxins in the environment, cardiovascular and cerebrovascular effects.
- Also, burning coal emits greenhouse gases like carbon dioxide and methane, which contributes to global warming and climate change. This is something to worry about, as just from 1980 to 2005, the overall change in co2 emissions for electricity generation was 0.9 billion metric tons.
- We can reduce this air pollution by coal washing; in which we use large quantities of water to remove impurities from coal. It will result in less sulfur dioxide and less carbon dioxide.
- Also, mining can destroy the land and pollute water, which would affect fish and aquatic life.
Advantages of a coal-fired power plant
Here are some advantages;
- It’s abundant and easy to burn.
- It doesn’t depend on the weather or existing climatic conditions for mining coal.
- Coal is cheap unlike other sources like oil, gas, and nuclear energy.
- It’s safer than other plants like the nuclear power plant.
- It has low investment costs compared to power plants in the same capacity.
- It’s a reliable energy source that is capable to supply electricity during peak power demand either as base power.
- It also provides a high load factor as it gives access to an efficient level of energy through combustion.
- We can use coal with renewable energy to help to reduce the amount of carbon dioxide, and ash produced from the burning process.
- Coal transportation is also easy and cheap.
Disadvantages of a coal-fired power plant
In spite of all those advantages, coal-fired power plants have significant disadvantages as:
- It’s a non-renewable energy source.
- Miner’s life in underground mining is under risk most of the time.
- Coal combustion isn’t environmentally friendly because it produces harmful waste like carbon dioxide; sulfuric acid; sulfur dioxide; nitrogen oxide….etc.
- It may also lead to global warming and climate change.
- Coal mining leads to land sliding, deforestation, climatic change, etc.
- Burning coal by large-scale factories to the power industry may lead to acid rain in some regions.
- Coal transportation may be a problem because it requires an extensive transportation system.
- Coal open cast mining also results in the destruction of the habitat of the scenery; as it leads to the removal of trees and pollution of air and water surrounding the mines.
- Also, coal mining leads many people to displace; as a result of the pitting of the earth brought about by underground mining.