Overview of Flue Gas Analysers and Infrared Sensors

Industrial infrared sensor in housing used as a process control device and for general measuring functions. These units are in operation worldwide in fermentation and other industries where precise monitoring of gas concentrations is necessary. The infrared sensor is available for CH₄ (also known as methane or natural gas) and for CO₂ (carbon dioxide or fermentation gas). The measurement of methane is essential in biogas generation systems, also referred to as cogeneration plant. These use a diesel engine converted to run on biogas generated by decomposition of waste. The level of carbon dioxide will show how far advanced the decomposition is and the level of methane will allow the injection system to be optimised.

Here is a different type of infrared sensor, used here typically for home climate control amongst other uses. It will measure in a low range and be used for control of the ventilation system in a building. These infrared sensors use single channel technology and are a low cost answer to the problem of optimum ventilation in indoor climate. This type of device is becoming increasingly important now that home climate control and ventilation regulation are regulated in some countries now. It is no longer necessary to open and close windows to renew the air in a building, the ventilation fan is automatically regulated to keep the level of carbon dioxide below a preset level. The ambient gas analyser is becoming very popular.

A typical continuous emissions monitor system, known in the trade as CEMS for short. These system are used on larger combustion systems such as power stations and incinerators for checking the pollution control device. These can be seen as the big brother of the portable flue gas analyser. These systems may contain many sensors, typical applications being 5 gas analysers. They are mandatory in many countries for EPA compliance testing and are required to be checked regularly. They may be fitted with analogue or digital outputs for control of the combustion system. A combustion gas monitor allows permanent checking of the burner system. it is important to realise that these instruments serve a very necessary role. The output signals can be used to change the burner parameters and optimise the process on a continuous basis.

This is a portable flue gas analyser, here fitted with a sample conditioning system. These instruments are used for EPA compliance testing and general burner testing. They range from simple oxygen analysers to 9 gas analysers with sample conditioning. The combustion gas analyser has been with us for some time now, and general requirements include carbon monoxide and nitric oxide testing. In some countries the emphasis is more on sulphur dioxide due to the quality of the fuel used, especially with the effect of sulphur dioxide on the dewpoint of the flue gases. The American model favours the 3 or 4 gas analyser due to the accurate measurement of NO_x allowed. A pressure sensor is generally also fitted to allow measurement of draught in the chimney. Whichever instrument is chosen, the basic idea is gas measurement for pollution control or compliance testing for this purpose. The measurement of hydrocarbons or just methane is now essential due to the greenhouse effects.

This is a handheld combustion gas analyser used for basic checking and burner optimisation. Although it may share many of the features of the bigger portable flue gas analysers, it is naturally more limited in the options and will not usually be used for compliance testing. For basic testing of stack gas,this kind of instrument is very popular due to a low price and rugged design. It would be generally fitted with sensors for carbon monoxide and nitric oxide which allows the NOx to be calculated. The hand-held flue gas analyser is part of the standard equipment for every self-respecting boiler service man. With this instrument it is possible to follow the changes in efficiency and lambda that occur when changes are made to the burner settings and to accurately measure the carbon monoxide emissions produced. The stack draft will also be measured at this point. Many of these instruments are in use by the companies operating burners, allowing them to ensure that no unnecessary toxic gases are produced and that they are within the legal limits at all times.

As can be seen, the combustion analyzer comes in many shapes and sizes, depending on what is to be measured. Basic units will measure oxygen concentration, the flue gas and the ambient temperatures. With these factors the combustion efficiency, excess air number and carbon dioxide concentration can be calculated, together with the stack loss. A sensor for carbon monoxide is fairly standard these days on even the simplest instrument. This enables the loss by incomplete combustion to be calculated as well. Even the smaller instruments in certain countries are fitted with sensors for sulfur dioxide, since this is one of the big problems in many areas.

Here we can see a portable flue gas analyzer in use for boiler optimisation and compliance testing. A combustion gas analyzer is far superior to other chemical means used in earlier times. The carbon monoxide and nitric oxide values are seen instantly for every change made to the burner allowing full optimisation. For certain applications it is also necesary to measure the nitrogen dioxide level to attain a true measure of NO_x. These instruments have been in use for about 25 years now, but the present lower prices and especially simpler instruments have made their use much more common in the last five years. Combustion monitoring naturally also saves money in the medium to long run, especially with today's high fuel costs. The combustion gas analyzers from madur electronics are an ideal way to carry out stack testing due to the ease of operation and accuracy of the gas measurement. This may on larger equipment include an infrared sensor to measure carbon dioxide to fulfil all obligations under the Kyoto Protocol. Here the stack testing becomes a means of earning money since the carbon dioxide emissions can now be traded if combustion gas monitoring allows accurate gas measurement.

Click on the link for a short and illustrated description of flue gas analyser construction.

The greenhouse effects have prompted interest in a number of other gases other than just carbon dioxide. In particular, nitrous oxide and methane have been eyed critically for their part in the process of global warming. Not just methane, but total hydrocarbons have been investigated. Normal combustion processes only really have methane detectable in the residual gases, but the internal combustion engine has conditions of high temperature and pressure, which can form longer hydrocarbon chains.

When we extend the gas analysis field to include the modern topic of biogas, we come up with different compositions of gases and have to place the priorities elsewhere. Here, we have mostly methane and carbon dioxide, both of which have been discussed above, but also increased amounts of hydrogen sulphide and even ammonia.