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In-situ technology for Continous Emission Montioring : Week 7/18/2012

In our last article, we discussed about care to be taken at ESP & how to avoid formation of CO. We also discussed about monitoring of CO. In this article, we will discuss about benefits of monitoring O2 & CO. We’ll also discuss about the need for on-line measurement of stack gas emissions & why ‘In-Situ’ technology is gaining importance today

Benefits of monitoring Oxygen & CO

Having seen the need of having O2 & CO monitoring, let’s also see what are the benefits of measuring these gases on-line

  • It would be possible to achieve proper combustion
  • There could be energy saving due to increased combustion efficiency, which may amount to 3 to 4 % of fuel costs
  • NOx reduction would be possible, because the thermal oxidising of nitrogen would be lower
  • Total CO2 emission would be reduced, because less fuel would be burned
  • Lifetime of the combustion area / heat exchanger walls would be increased and therefore CO corrosion would be at a minimum
  • Prevention against explosion risk, where there is possibility of explosion by unburned, inside the ESP

However, only O2 & CO monitoring may not be enough. Let’s see why.

Online monitoring of Stack gas emission

During the combustion process, Nitrogen in Air (air used for burning coal) oxidizes with Oxygen and forms Oxides of Nitrogen i.e NOx. Sulphur in coal after oxidation forms SO2. Similarly coal after burning becomes ash i.e dust. CO,SO2,NOx gases are highly toxic and are harmful to the environment. Hence the pollution control board has to govern the industrial emissions, and thus it becomes necessary to have online monitoring of CO, SO2, NOx & dust emission

To continuously monitor the stack gas emission, earlier the only available technique was Extractive gas analyser. Later in the 90’s, up gradation in design and construction with a direct ‘On Stack’ mounted analyser (i.e In Situ analyser) became popular and resulted in the demand for this technology in the market for Continuous emission monitoring.

There are many advantages of going In-Situ

    Firstly it avoids the need for sampling system. It means one can do away with lots of issues related to a sampling systems.

    These issues include:

    Maintenance of an air conditioned room or a shelter,

    Clogging of pipelines,

    Elaborate procedures for extracting, transporting & conditioning of the gases,

    Need for heat tracing to avoid condensation,

    Need for pressure regulation & so on.

Technological benefits of In Situ gas analyser

  • These type of analyzers are very rugged and reliable
  • These are field mounted (No Air Conditioning room / shelter required)
  • These work on Infrared (IR) measurement technique for measuring gases like CO, SO2, NOx, CO2, H2O, HCL, CH4.
  • Measurement of CO, SO2, NOx, HCL, CH4 gases is possible in ppm range, with an accuracy of 2 to 5 ppm.
  • As the analyzers work on IR gas filter correlation technique , no moisture interference is possible
  • The analyzer works on Gas diffusion technique, hence no filter choking
  • There is no need for sampling/conditioning of gases
  • There is built in measurement of CO2,H2O,Temperature & Pressure for On-line Normalization. No need of separate Oxygen analyser for online normalization, when CO2 measurement can do a similar job
  • On line calibration is possible using audit gases
  • Bulk Measurement – no straight run required
  • Negligible maintenance - No need of AMC
  • Low power consumption. There are analyzers that consume upto only 400 watt
  • These analyzers usually come with a heated probe option, This is meant for flue gas temperature application below dew point

In our next article, we will discuss some good things about pressure reducing and desuperheating