Flue Gas

Flue Gas Latest News

A high-powered committee of experts, chaired by Principal Scientific Adviser (PSA) Ajay Sood, recently recommended that India do away with a decade-long policy of mandating equipment, called Flue Gas Desulphurisation (FGD) units, in all coal-fired thermal power plants (TPP).

About Flue Gas

• Flue gas (sometimes called exhaust gas or stack gas) refers to the gas that is released from combustion plants. It is a by-product of burning fossil fuels.
• Flue gas actually contains a mixture of gases, such as carbon monoxide (CO), carbon dioxide (CO2), water vapor, nitrogen oxides (NO & NO2), sulfur dioxide (SO2), other trace pollutants, and often some particulate matter. 
• This mixture can escape through long pipes, chimneys, and ducts traditionally called ‘flues’, hence the term ‘flue gas’. 
• The exact composition of flue gas will vary depending on the type of fuel used and the combustion conditions.
• It often contains pollutants that must be removed before being released into the atmosphere.
• Flue gas analysis is critical for evaluating combustion conditions. Not only may it be required for compliance with environmental regulations, it also enables efficiency and safety, providing valuable insights into the following:
  • Air-to-fuel ratios: Achieving the optimal air-to-fuel mix is essential to maximizing energy output and reducing emissions & particulate matter.
  • Burner efficiency: Regular flue gas analysis helps regulate burner performance in boilers and furnaces, leading to lower fuel consumption and operating costs.
  • Pollutant levels:  Monitoring concentrations of harmful gases like NOx and SO2 is essential to meeting environmental standards and reducing the risk of corrosion or damage to industrial equipment.

What is Flue Gas Desulphurisation (FGD)?

• It is a technology to eliminate sulphur compounds from exhaust emissions.
• FGD Process:
  • FGD is done through the addition of absorbents, which can remove up to 95% of the sulphur dioxide from the flue gas.
  • Substances such as ammonia or sodium sulphite are used as absorbents; however, the use of lime or limestone slurry (wet limestone scrubbing) is also widespread. 
  • The uncleaned flue gas is sprayed in a scrubber tower (absorber tower) with a mixture of water and limestone (scrubbing slurry), whereby most of the sulphur dioxide is bonded by chemical reaction.

Flue Gas FAQs

Q1: What is flue gas?

Ans: Gas released from combustion plants during fossil fuel burning.

Q2: What is the primary purpose of flue gas analysis in industrial settings?

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Ans: To evaluate combustion conditions, efficiency, and emissions.

Q3: Why is the gas emitted during combustion called ‘flue gas’?

Ans: Because it escapes through chimneys or ducts called ‘flues’.

Source: TH