Stack Emission Testing

The advent of Industrial revolution brought many changes in lifestyle and environment. One thing it also brought was air pollution.

In the beginning of the industrial revolution, the waste products from manufacturing industries were directly released into the environment. But, soon enough the adverse effects of the waste products (pollutants) were experienced and thus, it lead to the evolution of chimneys.

Chimneys also known as stacks were constructed to disperse flue gases of industries into atmosphere.

What is Stack?

A stack is a vertical pipe structure through which flue gases (combustion product gases) are exhausted out in the atmosphere.

Today, just as the tall stacks/chimneys, air pollution levels are also touching the sky.  To keep the pollution levels low, stack emission monitoring is carried. In India, the guidelines for stack emission monitoring and testing are provided by CPCB (Central Pollution Control Board).

Stack Emission Monitoring or Stack Emission Testing

Stack emission testing is a procedure for sampling of gas stream from an emission point. It measures emission of industrial waste or pollutants entering the atmosphere.

Stack Emission monitoring is performed using

  • Sampling and
  • Analytical procedures

Sampling procedure

In this procedure, the selection of sampling point is very critical. A sample taken should be representative and in order to achieve representative data, selection of sampling point or traverse point is very critical.

Usually, the location of traverse points is decided by pollution control board.

To obtain a sample for analytical procedures, a sampling device is inserted into traverse point to collect a sample of flue gas.

Analytical procedures

The sample collected from stack is sent to laboratories to test for pollutants. Common pollutants encountered in the stack emissions are;

  • Sulphur Dioxide (SO2)
  • Oxides of Nitrogen (NOX)
  • Particulate Matter (PM)

Along with this physical parameters are to be measured;

  • Humidity of gas
  • Temperature of gas

Depending upon the type of industry the following compounds should be measured;

  • Ammonia (NH3)
  • Mist and Vapours of Hydrochloric acid (HCl)
  • Mist and Vapours of Sulphuric acid (H2SO4)
  • Mercury (Hg)
  • Lead (Pb)
  • Hydrogen fluoride (Hf)
  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)

Importance of Stack Emission Monitoring

The pollutants released into the environment have detrimental effect on human health and environment.

Pollutants like NOX, SO2 and PM are responsible for disorders like Asthma, airway inflammation, pulmonary oedema, circulatory collapse, eye irritation, corneal haze, etc. These pollutants also have detrimental effect on environment, like; acid rain, depletion of nutrients in soils, damage to sensitive forest and farm crops, affect diversity of ecosystems etc. To avoid these detrimental effects on human health and environment, stack emission monitoring is carried out.

With the help of Stack emission monitoring,

  • We can measure different pollutants present in stack emissions
  • We can keep a check on the pollutant levels exhausted out from stack are in the permissible limits prescribed CPCB (Central Pollution Control Board).
  • We can study efficiency of pollution control equipments.
  • Stack emission monitoring helps to device new pollution control strategies.

Stack Emission levels

During, Stack emission monitoring/Stack testing, if it is found that emission levels are exceeding the permissible limits prescribed by CPCB, it is to be considered as an indication for adoption of new pollution control strategies.

The pollution control equipments or techniques one can install to bring down the emission levels are Scrubbers, Cyclones, Electrostatic precipitators, Incineration, Condensation, etc.

Every manufacturing industry should carry Stack emission monitoring. They should bring their emissions levels to the minimum or in the range prescribed by CPCB so as to have pollution free, clean and fresh air.

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