Fly ash is the result of coal combustion in large boilers (mainly for generation of electricity). Coal combustion produces two types of ash residues, namely Pulverized Fuel Ash (PFA = 80 % of the total ash production) and 20 % Furnace Bottom ash (FBA). To avoid that PFA is emitted in to the atmosphere it is trapped in electrostatic precipitators from where it is collected for beneficial use or disposal.
There is a number of applications for PFA as shown in the following graph. In India nearly 180 million MT of PFA was generated in 2017. PFA generation in India is even bound to increase up to 400 million MT/year in the next decade.
The application in cement and concrete had reached 48.50 % already in 2015. In the meantime this beneficial application of PFA has crossed 60 %. The use in concrete and cement (for later use in concrete) can replace up to 70 % of the cement which is for concrete production.
Cement production, even with the latest emission technologies emits approximately 0.8 MT of CO2 per MT of cement produced. By replacing the cement with PFA, cement production is reduced and by that CO2 emissions are reduced as well.
The application of PFA as cement replacement was introduced by Georg Dirk in India in the year 2000. Some year later, the use of PFA in concrete became a standard practise in India. Since 2000 only the DIRK India Nashik plant has saved more than 1.5 million MT of CO2. In the totality of India around 120 million MT of CO2 emissions were avoided in 2017.
Besides saving CO2 emissions the power generator is saving vast amounts of water which is required to transport the PFA in a slurry form from the boiler to the disposal site (150 gram of ash need 1 cbm to form the slurry), the water which is scarce and required for irrigation and human consumption.
The slurry water seeps into the ground water contaminating the wells in the neighbourhood of any wet disposal site (ash ponds /lagoons). A typical ash lagoon is shown in the picture.
Ash lagoons can dry up in the hot season. The fine dry PFA gets air-born. PFA contains a cocktail of heavy metals and humans and animals are exposed to this dust which affects negatively their health.