Pulverised coal-fired (PCF) power plants.
In these plants, coal is ground into a fine powder and blown into a boiler. It burns at between 1,300°C and 1,700°C, creating steam which drives a generator and turbine. This method is by far the most established and common of the three. PCF plants account for over 90 percent of the electricity produced from coal, and about 38 percent of the power generated from any source around the world.
The bad news is that PCF plants are also horribly inefficient. Even the most efficient ones still waste half of their energy and the worldwide average thermal efficiency of PCF plants is less than 32 percent meaning that almost 70 per cent of the energy is wasted . The lower the efficiency level, the more coal needs to be burnt to generate electricity, spewing out even more CO2 emissions.
Ninety percent of the coal fired power stations in the world use this type of technology.
Fluidised bed combustion (FBC) plants
Here, coal is burned with air in a fluid bed mixing gas and solids. This is done either at ambient ("normal" atmospheric) pressure (called Atmospheric FBC) or under pressure (called Pressurised FBC), and at temperatures lower than those in PCF plants.
The lower combustion temperatures in FBC systems cut the amount of NOx produced.[iv] Finally, because more than 95 percent of sulphur pollutants from the coal can be captured inside the boiler, FBC plants produce less SO2 .
However FBC technology is often used with low quality coal. This together with lower thermal efficiencies means that CO2 pollution increases.
Integrated gasification combined cycle (IGCC) plants
IGCC plants are the newest of the three, with average thermal efficiencies between 40 and 50 percent. At present, the use of IGCC for coal-based electricity production is limited with only four coal-based IGCC demonstration plants in operation globally.
The process they use involves two separate steps: First, coal is turned into gas through a controlled ‘shortage’ of air in an enclosed pressurized reactor. The resulting gas – a mixture of carbon monoxide (CO) and Hydrogen (H2) called Syngas – is then burnt to drive a gas turbine. In the second step, the exhaust gas from step one is used to create steam, which drives a separate steam turbine.
Typically, the gas turbine in step one generates 60 – 70 percent of the power, with the steam turbine generating the rest.
No "right way" to burn coal
Although some plants are better than others, coal is an inherently dirty fuel. Along with the harm caused by coal mining, global warming CO2 and other pollutants are always produced when it's burnt.
The coal industry is pushing plans to bury their CO2 underground or pump it into the sea. Read more about carbon capture and storage.
There are better energy alternatives than burning coal. Our blueprint for an energy revolution shows the way.