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Five Uses for Portable Flue Gas Analysers

Monday, November 1, 2021 | Derek Stuart
Categories : Products

Fixed flue gas analysers measure emissions of gaseous pollutants from large combustion sources such as power plants and industrial boilers. They continuously provide data 24 hours per day for extended periods, but they are bulky and expensive.

Lancom 4 inc. Sample Probes

Portable analysers such as the AMETEK Land Lancom 4 can measure the same gases, and they offer a flexible and inexpensive option for many smaller combustion sources. Their size and portability also allow some measurements that are impractical with fixed systems. Here are a few of the most frequently used uses for such instruments.

Setting the fuel-air ratio
Setting the correct ratio of fuel to air is essential for any combustion source to maximise efficiency and minimise emissions of pollutants. Measurements of oxygen and carbon monoxide in flue gas give the essential information for these adjustments. As shown in the diagram below, too much residual oxygen indicates that heat is being lost through too much hot air leaving the stack, whereas a high level of carbon monoxide is indicative of incomplete combustion and wasted fuel.

Minimising NOx formation
Oxides of nitrogen are formed in combustion sources through two principal mechanisms. Nitrogen compounds in the fuel react with oxygen in the air (fuel NOx), and nitrogen molecules in the air react with oxygen in a high-temperature reaction that takes place above 1330 °C (thermal NOx). Fuel NOx is difficult to avoid, other than by changing fuels, but thermal NOx can be controlled by reducing the amount of excess oxygen in the combustion process and by reducing the peak temperature of the flame. Measuring the concentrations of oxygen, nitric oxide, and nitrogen dioxide in the flue gas allows the operator to tune the combustion parameters to minimise NOx formation whilst maintaining good combustion efficiency.
Flue Gas Diagram

Compliance with emissions regulations

Many small combustion processes such as reciprocating engines can demonstrate compliance with emissions rules by periodic measurements using a portable flue gas analyser. In most cases, the measurements must be made in accordance with a recognised standard such as ASTM D6522 or SCAQMD 1110.2. These standards typically cover oxygen, carbon monoxide, nitric oxide, and nitrogen dioxide measurements and include detailed requirements for calibration and quality assurance.

Checking a CEMS
Although a well-designed and -maintained continuous emissions monitoring system (CEMS) is reliable, it can malfunction and give anomalous results. A quick way to check an unusual CEMS measurement is to connect a portable analyser to the sample system. If the two measurements give similar readings, the CEMS is likely correct, and there is a process upset. If the portable instrument disagrees with the CEMS, the next step is to investigate whether the CEMS has a malfunction.

Validate a combustion efficiency monitor
Many small combustion processes such as process heaters and thermal oxidisers control their burners by measuring oxygen and “CO equivalent” (sometimes called “combustibles”) using an instrument such as the AMETEK Thermox WDG-VC. Although these instruments are rugged and reliable, they use a thermal sensor that does not truly measure carbon monoxide concentration. In addition, they do not generally measure NOx emissions. Periodic measurements of oxygen, carbon monoxide and nitric oxide with a portable flue gas analyser allow for a better understanding of the combustion conditions and enable a more efficient and cleaner process.

Click here for more information on the AMETEK Land Lancom 4 Portable Gas Analyser


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