What is fly ash

  • we use coal in most of the thermal power plants in India. To generate electricity, coal is first grounded into the fine powders, so that it can be fired into the boiler furnace. after this, the combustion of coal takes place, and it changes into coal ash.
  • Based on their particle size, this coal ash can further be subcategories into bottom ash and Fly ash. As a matter of fact, fly ash is the lightest spherical shape particle of size ranges 1 micron to 0.3 mm. Coal, when subjected to the high temperature, the clay minerals present in it, changes into the fused fine particles of aluminum and silicate. As a result of such fine particles, fly ash possesses both pozzolanic and ceramic characteristics. Further, when we mix, this finely divided pozzolanic material with water, it will react with calcium hydroxide to form (Portland cement) cementitious compounds. therefore, Fly-ash can partially replace the cement, used to produce concrete, bricks, etc.
what is fly ash

How is it harmful

  • In fact, fly ash is a finer particle, of the size range of 1 micron to 300 microns, therefore it shows weightlessness. As a result of this, it tends to travel far in the air and causes respiratory problems when inhaled. Therefore, proper disposal of fly ash is a big concern. If we don’t dispose of, fly ash properly, it can cause air, water, and Fsoil pollution, and disrupt our ecological cycle. When it settles on the leaves and crops, near the power plant, It lowers the production of crops. Currently, 180 million tons of fly ash produced in India and its disposal requires a large quantity of land.
  • Secondly, Coal is a type of dirty fuel that contains a variety of heavy metals, uranium, and thorium, etc. The amount of uranium elements in the coal is in the range of 1 to 5 ppm. Sometimes it may be as high as 600 ppm which is dangerous. When we burn 1 kg of coal, it produces 250 grams of ashes as a result of this, the concentration of uranium in fly ash maybe 4 times that coal. Hence 1 kg of fly ash may contain an amount up to 20 mg/kg of uranium. however, damage starts to appear after taking the uranium more than 25 mg.

Reason to use fly ash

  • In developing countries, like India, the construction of Infrastructure with the economy is the utmost requirement. Recently Government of India announced, “Housing for All” under Pradhan Mantri Awas Yojna and facilitating the construction of 150 lakh additional housing units (50 lakh in Rural Areas and 100 lakh in Urban Areas). As a result of this, the use of economical and eco-friendly material is only the solution.
  • As was previously stated, we can replace up to 30 percent cement with fly-ash. Thus we can reduce the production of cement from 28 crore tones to 20 tonnes annually, subsequently, a reduction of 10 crore tonnes CO2 gas per year. A reduction in one ton of carbon dioxide gas is equal to 1 carbon credit. therefore we can earn 10 crores of carbon credit every year. Such credit can be sold in the international market at a prevailing market rate. According to the past transaction,  the average price of a carbon credit is Rs. 182.00/carbon credit and this trading can take place in the open market. In short, with our partial replacement of cement with fly-ash, Our cement industry can sell or hold the 10 crores of carbon credit annually, amounting to Rs. 1820 crore.

Properties of Fly Ash

Engineering Properties of Fly-Ash
Specific Gravity:- 1.90- 2.55
Plasticity:- Non-Plastic
Proctor Compaction Test Data
Maximum dry density (gm/cc):- 0.90-1.60
Optimum Moisture Content:- 18 to 38 percent
Angle of internal fraction:- 30 to 40 Degree
Cohesion (kg/cm):- (Negligible)
Compression Index:- 0.05-0.4
Permeability(Cm/Sec):- 10^5 to 10^3
Particle Size Distribution
Clay Size Fraction:- 1 to 10 percent
Silt size fraction:- up to 85 percent
Sand size fraction:- 7 to 90 percent
Gravel size fraction:- 0 to 10 percent
Coefficient of Uniformity:- 3.1 to 10.7