Coal-fired power plant (Principle, Diagram and environmental impact)
What is coal energy?
Coal-fired power plant … Coal is a flammable black or a brown sedimentary rock made of organic carbon in addition to hydrogen, oxygen, sulfur, and nitrogen.
Coal also is the most used fossil fuels for producing electricity as we use coal power plant for producing around 40% of the world’s electricity, and we commonly use it in cement manufacturing and industrial purposes such as refining metals.
There are four main types of coal, which are formed in a similar manner both formed from decomposed vegetation composed at high temperatures over millions of years beneath layers of sand, rock, and sediment. There are:
- Anthracite coal: it’s a hard coal, which contains 86_97% carbon and mainly used by the metals industry, space heating in addition to generating electricity.
- Bituminous coal: it’s a 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.
- Subbituminous coal: it’s a dull black coal which typically contains 35_45% carbon, and it’s used for generating electricity and space heating.
- Lignite coal: it’s a 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.
As the coal is initially milled to a fine powder to be pulverized and then burnt in a furnace (combustion chamber of a boiler); and we use the heat energy released to heat water into super hot steam which under high pressure and temperature used to turn the turbines connected to electrical generators by a shaft which then drive the generators to produce electricity.
After this process, electricity 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 as:
We started with the boiler or the steam generation system; as we supply the coal from coal bunkers via coal conveyors to be crushed into coal mills. And in the air heater, air is preheating from flue gas via 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 connected to an electrical generator by a shaft the generator also spins to produce the electrical energy.
Then the separated saturated water and water vapors from the turbine passes through the condenser and the heater to be converted into a saturated water which 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 so there are many efforts to deploy high efficiency up to 40% and low emission of this plant as:
- 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 all also affect the plant efficiency.
- Also upgrading some existing coal plant system to super or ultra_super critical operation results in 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:
I will surprise you when I say that; coal power plant is linked with several environmental and public health impacts like 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 as 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 as carbon dioxide and methane; which contribute to global warming and climate changing.
We can reduce this air pollution by coal washing; in which we use large quantities of water to remove impurities from coal.
And that resulted 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 coal-fired power plant:
It’s known that coal is the most widely used fuels for generating power and electricity around the world which means that the coal_fired power plant has many advantages as:
- 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.
- The capital investment costs are fairly low compared to power plants in the same capacity.
- It’s a reliable energy source which 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 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 at most of the time.
- Coal combustion isn’t environmental 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 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 resulted in the destruction of the habitat of the scenery; as it leads to removal of trees and pollution of air and water in 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.