Pulverised ash brick (PAB) technology is a process of converting industrial waste materials into quality building materials. At present, the technology is well established in converting thermal power plant waste into quality bricks.
PAB technology uses dry ash (fly ash collected from ESP or silos of thermal power plants); filler materials (usually coarse sand or stone crusher dust); and additives (lime, gypsum or cement). The strength of the bricks can be engineered by varying compositions. Equipment used can be manual or mechanised. Mechanised machines deploy hydraulic compaction to produce a variety of bricks and can be operated through electric or diesel power.
What is ash?
Scale of problem
Pulverised coal ash (PCA) is one of the major residues generated
during the combustion of coal in thermal power plants. Though PCA is a waste product for the power sector, it's used as a raw material, primarily, in construction. PCA is generally
classified into three types depending upon its particle size and zone of collection.
‘FLY ASH’ is the extremely fine ash ‘flying’ along with flue gases is trapped in electro-static precipitators (ESP) and is collected. The relatively coarser ash generated at the bottom of the boilers is mixed with water, made into slurry and pumped into fill sites called ‘ash ponds’.
This ash forms the bulk of the ash generated and is termed as ‘POND ASH’.
Depending upon the boiler design and efficiency, the ratio of fly ash to pond ash varies between 70:30 and 80:20. In some older and relatively inefficient thermal power plants, a coarser variety of ash is generated called ‘BOTTOM ASH’.
This has appreciable carbon content but cannot be collected separately. This is also mixed with pond ash and pumped to ash fill sites.
India generated 145,000 MW of power in 2008. 63% of it was from coal-based thermal power plants. During generation of the above, approximately 150 million tonne of pulverized ash was generated in 2008 alone. In India, low-ash high-grade coal is reserved for the metallurgical industry. Thermal power plants, therefore, are compelled to use high-ash low-grade coal with ash content that is often as high as 40% or more. This is the major source of generation of vast amounts of PCA. As the power requirement goes up in coming years and more power plants are built, the amount of PCA generated will increase and create more problems for safe disposal. It is estimated that by 2012, India will generate around 175 million tonnes of PCA every year.
Flyash bricks production
The Ministry of Environment and Forests (through its notification published in the Gazette of India, Part II, Section 3, sub section (ii), vide S.O. 763(E) dated 14th September, 1999) issued directives for proper utilisation
of fly ash discharged from coal or lignite-based thermal power plants. The importance for restricting the excavation of top soil for manufacture of bricks and promoting the utilisation of fly ash in the manufacture of building materials and in construction activity was recognised. It was notified that within a radius of 100 km from a coal or lignite-based thermal power plant, all brick making units must compulsorily utilise 25% of fly ash (by weight) This notification was supported by the High Court of Delhi in its order dated 25th August, 1999 in Centre for Public Interest Litigation, Delhi v/s Union of India (CWP No. 2145/99).
The highlights of the notification was
1. Use of fly ash, bottom ash or pond ash in the manufacture of bricks and other
a) Within a radius of 100 km from coal or lignite based thermal power plants, no person shall manufacture clay bricks,
tiles or blocks (for use in construction activities) without mixing at least 25% of ash with soil on weight basis.
b) The authority for ensuring the use of specified quantity of ash shall be the concerned Regional Officer of the State Pollution
In case of non-compliance, the authority (in addition to cancellation of consent order issued to establish the
brick kiln) shall move the district administration for cancellation of the mining lease. To enable the authority to verify the
actual use of ash, the thermal power plant shall maintain monthly records of ash made available to each brick kiln.
2. Availability of fly ash for brick making
a) Every thermal power plant shall make available ash, for at least ten years without any payment or any other consideration
for the purpose of manufacturing ash-based products.
b) Central and State Government Agencies, State Electricity Boards, NTPC
and the management of the thermal power plants
shall facilitate in making available land, electricity and water for manufacturing activities and also provide access to the
ash lifting area. This will promote and encourage setting up of ash-based production units proximate to the area where
ash is generated by the power plant.
3. Specifications for use of ash based products
a) Every construction agency engaged in the construction of buildings within a radius of 100 km from thermal power plants
shall use fly ash bricks in construction projects. It shall be the responsibility of the construction agencies (either
undertaking the construction or approving the design or both) to ensure compliance.