Air Pollution Countermeasures
The main air pollutants emitted from thermal power plants include sulfur oxide (SOx), nitrogen oxide (NOx), and soot and dust.
In an effort to reduce these emissions, we have implemented countermeasures that take into account "fuel", "facility" and "operational" measures, helping us maintain some of the lowest emission levels in the world.
International Comparison of SOx/NOx Emissions Intensity
An fluee gas desulfurization facility is used to remove SOx in exhaust gas by having it react with limestone.
The Company employs this method of desulphurization at the Hitachinaka Thermal Power Station and Units No. 5 and 6 at the Hirono Thermal Power Station, two coal-fired thermal power plants.
With flue gas desulfurization facility, ammonia is injected into the exhaust gas containing NOx from the boiler, the chemical reaction is accelerated by the action of the catalyst, NOx is reduced and decomposed into N2 and H2O.
With the exception of gas-fired power plants which do not emit soot and dust, all thermal power plants are equipped with advanced electrostatic precipitators.
These work by electrifying the soot and dust for collection by applying an electric force in the direction of the collector electrode when the soot and dust is passed through electrodes discharging at high voltages.
Reducing combustion temperatures in boilers and gas turbine combustion devices helps curtail NOx emissions. Specifically, we strive to reduce NOx emissions through a combination of the following methods.
Boiler-side Combustion Improvements
- Partially mixing exhaust gases with the combustion air reduces the concentration of oxygen in the combustion air and induces slow combustion (exhaust gas mixing method)
- Leading combustion air into the boiler in two stages induces slow combustion (two-step combustion method)
- The use of burners that curtail high temperature combustion zones (low NOx burners)
Gas turbine-side Combustion Improvements
- Mixing fuel and air prior to combustion to use fuel in an even and stable manner (premix combustion method)