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FGD Technology: the next frontier of air pollution control in India?

With increasingly stringent norms for gaseous emissions, FGD technology is emerging as a clear choice with plant operators to reduce emissions.

by Ecomak Systems

Introduction – What is FGD?

Flue Gas Desulphurization or FGD is a set of technologies used to remove SO2 from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulphur oxide-emitting processes. Sulphur dioxide is released in the combustion of coal, gas and oil. In this system, equipment such as absorber towers, demister supports, gas outlets, recycle and process piping, process tanks, and agitators are highly exposed to corrosive and abrasive environments [2].  Flue gas is highly corrosive and contains high levels of sulphur and usually moisture. 

Power facilities are the largest generators of SO2, which may cause acid rain. Sulphur is one common element found in coal. When burned, the sulphur in coal turns into sulphur dioxide, an acidic compound that can pollute the air. For example, in England SO2 has been responsible for causing acid rain which has damaged the country’s lakes and forests.

Types of FGD Technologies

TechnologyDry ScrubberSemi-Dry ScrubberWet Scrubber
DescriptionHeat up the incoming flue gas to vaporize the liquid in the lime slurry used to scrub the SO2 from the gas, resulting in a dry waste stream.Employs a circulating fluidized bed, dry spray, or duct dry spray to produce powdered mixtures of calcium compounds.Uses an excess of slurry and produces a wet waste stream. All internal surfaces as subjected to a saturated environment or are in immersion. This type of system is the most common.
USPEasily retrofitted onto existing combustion facilitiesDry processes injects lime or sodium bicarbonate into the furnace of the boiler to absorb the SO2. The sorbent is then extracted, together with the fly ash, as a mixture of ash and calcium/sodium components. Bi-products are then sold as additional revenue.Tend to utilize sorbent more efficiently than dry processes and typically can reduce SO2 emissions by more than 90%.

Current Policy Scenario in India:

  1. Government Norms, amended from 21st Feb 2019 [2]:

The notification from Ministry of Environment, Forest and Climate Change (MoEF&CC) dated 07-Dec-2015 amended the permissible limits of particulate emissions, SO2, NOx and Mercury from Thermal Power Plants (TPP).

Date of InstallationPM (mg/Nm3)SO2NOXMercury (Hg)
Before 31-12-2003100600 mg/Nm3 for < 500 MW

200 mg/Nm3 for >= 500 MW
600 mg/Nm30.03 mg/Nm3 for >= 500 MW
After 01-01-2004 & Upto 31-12-201650600 mg/Nm3 for < 500 MW

200 mg/Nm3 for >= 500 MW
300 mg/Nm30.03 mg/Nm3
On or after 01-01-201730100 mg/Nm3

100 mg/Nm30.03 mg/Nm3
Table 1: New Regulations on Emissions

Selection of FGD Technology

The So2 reduction technology shall be done considering following factors:

  1. Sulphur Content in Coal.
  2. So2 removal Efficiency requirement of particular plant.
  3. Availability of Reagent (if Any).
  4. Disposal and handling of By-product.
  5. Locational/Geographical factors of the plant.
  6. Plant life.
  7. Space requirement for FGD facility

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Sources:

[1] Anticorrosive Rubber Lining, Rubber Lining for a Sulfur Dioxide Scrubbing System, ISBN 978-0-323-44371-5

[2] https://cea.nic.in/old/reports/others/thermal/umpp/fgd_new_rules.pdf

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