Power plants using less-polluting washed coal— with ash content not exceeding 34% and gross calorific value not less than 4,000 Kcal/kg on a daily average basis — may get faster environment clearances from 2014.
The move, which will benefit power projects of more than 100 MW, comes in the wake of the recent nationwide power outages for which the ministry of environment and forests (MoEF) was also blamed, given its failure to give timely green clearances for projects. Although the immediate reason for the recent collapse of power grids could be reckless overdrawal of power by states, what lies beneath the flouting of grid code is a widening demand-supply gap for power.
In a bid to speed up the clearance process, the MoEF recently agreed that thermal power projects, with firm coal-linkage indicating the quality of coal and basket of mines of Coal India Singareni Collieries Company, will be considered for early environmental clearance.
“It is essential to have detailed information regarding quality of coal to assess the environmental impacts of a thermal power project.
The various important parameters of coal quality include calorific value, sulphur content and ash content,”
At present, decisions on projects are taken within 105 days of the receipt of complete information, as provided for in the environmental impact assessment (EIA) notification, 2006. Of these, 60 days are for appraisal by the ministry’s expert appraisal committee (EAC) and 45 days for processing and communicating the decision.
The calorific value of coal would determine the quantity of coal requirement per unit of power generation
Ash content would determine the land requirement for the ash pond as also the water consumption for its disposal in slurry mode.
Sulphur content would impact on the sulphur dioxide emissions, which, in turn, would affect the air quality.
“Accordingly, the quality of coal to be used in the project is taken into consideration while preparing the EIA report and carrying out the environmental appraisal.
Under the new norms, thermal power plants located beyond 500 km from the mine should use only treated coal that has gross calorific value below 4000 Kcal/kg. The same applies for captive thermal power plant of more than 100 MW capacity and located beyond 500 km from pit head, along with any captive power plant above 100 MW or independent power plant located in an urban area or an ecologically sensitive area.
Coal arriving at a power plant contains mineral content that needs to be removed before it is burnt. A number of processes are available to remove unwanted matter and make the coal burn more efficiently.
Coal washing involves grinding the coal into smaller pieces and passing it through a process called gravity separation.
One technique involves feeding the coal into barrels containing a fluid that has a density which causes the coal to float, while unwanted material sinks and is removed from the fuel mix. The coal is then pulverised and prepared for burning.
Coal gasification plants are favoured by some because they are flexible and have high levels of efficiency. The gas can be used to power electricity generators, or it can be used elsewhere, i.e. in transportation or the chemical industry.
In Integrated Gasification Combined Cycle (IGCC) systems, coal is not combusted directly but reacts with oxygen and steam to form a “syngas” (primarily hydrogen). After being cleaned, it is burned in a gas turbine to generate electricity and to produce steam to power a steam turbine.
Coal gasification plants are seen as a primary component of a zero-emissions system. However, the technology remains unproven on a widespread commercial scale.
Burning coal produces a range of pollutants that harm the environment: Sulphur dioxide (acid rain); nitrogen oxides (ground-level ozone) and particulates (affects people’s respiratory systems).
There are a number of options to reduce these emissions:
Sulphur dioxide (SO2)
Flue gas desulphursation (FGD) systems are used to remove sulphur dioxide. “Wet scrubbers” are the most widespread method and can be up to 99% effective.
A mixture of limestone and water is sprayed over the flue gas and this mixture reacts with the SO2 to form gypsum (a calcium sulphate), which is removed and used in the construction industry.
Nitrogen oxides (NOx)
NOx reduction methods include the use of “low NOx burners”. These specially designed burners restrict the amount of oxygen available in the hottest part of the combustion chamber where the coal is burned. This minimises the formation of the gas and requires less post-combustion treatment.
Electrostatic precipitators can remove more than 99% of particulates from the flue gas. The system works by creating an electrical field to create a charge on particles which are then attracted by collection plates. Other removal methods include fabric filters and wet particulate scrubbers.