Our Business / Thermal Power StationsTreatment of Coal Ash
When coal is combusted, about 10% of coal ash is generated, and effective use of large amounts of coal ash becomes an issue. For example, units 1 to 5 of the Hekinan Thermal Power Station at our company use about 10 million tons of coal every year, so that 1 million tons of coal ash generated every year is calculated.
Coal ash has superb material characteristics such as (1) fine particles, (2) light, and (3) increasing strength. In order to effectively use limited resources, our company uses a variety of recycling methods.
Coal Ash Development Process
Coal ash can be classified largely into “fly ash” and “clinker ash”.D> Let us look at how “fly ash” and “clinker ash” are generated at the coal thermal power station.
- (1) At the coal thermal power station, coal broken down into powder form is combusted in the boiler and that energy is converted into electricity. The coal ash particles melted by this combustion float in hot combustion gases; the particles become the vitreous round shape when dropping the temperature out of the boiler to be collected by the electric precipitators. This is generally called “fly ash”.
- (2) The quality of this fly ash is managed online by the “quality management system” that analyzes the characteristics of the coal ash, sifts according to the usage, and aligns the size of the particles to store in each silo.
- (3) Also, particles of the coal ash in the boiler, adhere each other, form a lump with many holes and drop to a water tank (clinker hopper) on the bottom of the boiler. These lumps, dropping to and accumulating on the water tank (clinker hopper), crushed into sand like form particles are called “clinker ash”. Normally clinker ash, after letting it dry out in the hydrating tank, is stored as is in this sand form.
What is Fly Ash?
The main components of fly ash are “silica” and “alumina”, the same components as soil. When mixed with cement, it reacts with the “calcium hydroxide” generated by hydration of cement (formation of a new compound by reaction of water and cement) and works to improve durability and water impermeability. Also because fly ash are small circular particles, when mixed in concrete, it has excellent features in improvement of the fluidity of the concrete.
What is Clinker Ash (Bottom Ash)?
Clinker ash, formed from ash melted red hot in a high temperature boiler and dropped to the bottom of the water tank and immediately cooled and crushed with a crusher, has the particle size adjusted to a sand form. The main components of clinker ash are “silica” and “alumina”, the same components as fly ash. Because the surface of the clinker ash has many small holes, it has excellent features in water retention, water drainage and breathability.
Effective Use of Coal Ash
Among our thermal power stations, coal thermal power stations use the coal ash effectively.
- Coal ash is transported by sea or land to cement factories and effectively used as an ingredient for cement.
- Coal ash is used effectively as landscape building material.