Nov-2021

Role of gas analysis in clean air strategies to reduce emissions

Gas analysis plays an essential role in cleaner plant and refinery operations, and will also be crucial to the production of current and future cleaner energy sources.

Matt Halsey
Servomex

Article Summary

Reducing carbon emissions to the atmosphere is an area of growing importance for industrial plant operators. The raised sensitivity towards this issue has been led in part by the introduction of increasingly stringent environmental regulations. International action to reduce the impact on climate, including the 2016 Paris Agreement, has intensified awareness of the effect of greenhouse gases, driving operators to reduce emissions and find more ecologically responsible ways of operating.

Gas analysis provides an effective solution for these efforts, not only by supporting measurement of harmful emissions, but also by improving efficiency to ensure fewer emissions are generated in the first place.

Servomex, the global expert in gas analysis, has developed a strategy for clean air that is based around three main process areas: combustion efficiency, gas clean-up (including carbon capture processes), and emissions monitoring.

Combining solutions for these three areas supports operator goals to deliver cleaner processes, also optimising these processes to reduce fuel consumption and deliver higher production yields.

Combustion control solutions
Combustion reactions mix fuel with oxygen (from air) in a fired heater to generate heat energy for a process. They typically need a significant amount of fuel, create potential safety hazards, and generate harmful emissions including carbon dioxide (CO2).

Running fired heaters with high excess air — which was the case prior to gas analyser technology — avoids creating unsafe conditions that could lead to an explosion, but is highly inefficient, increasing fuel consumption.

Excess oxygen (O2) also combines with nitrogen and sulphur in the fuel to produce unwanted emissions such as oxides of nitrogen (NOx) and sulphur (SOx). Accurate gas analysis of O2 and combustibles such as carbon monoxide (CO) helps to optimise the ratio between the air and fuel and creates a more efficient reaction.

Controlling combustion in this way benefits plants looking to meet environmental standards requirements. Fuel consumption is reduced, resulting in fewer emissions, a reduction in NOx, SOx and CO, and a decrease in CO2.

Zirconia-based sensing technology is long established as a solution for O2 monitoring in combustion, with reliable, accurate results and a fast response to changing conditions. A combustibles sensor can be added easily at modest cost to provide an all-in-one combustion control solution, such as in Servomex’s ServoTough FluegasExact 2700 combustion analyser.

Tunable diode laser (TDL) technology provides an even faster measurement, particularly for CO, and gives an average measurement across the measurement path, rather than the result at a single point. However, since TDL sensing is highly specific to the gas being measured, separate analysers are required for O2 and CO.

Servomex’s ServoTough Laser 3 Plus Combustion TDL analyser provides a solution for this application, and this can be configured to measure either O2 or CO. It can also be configured for a joint measurement of CO and CH4, providing a rapid-response measurement for safety in natural gas fired heaters and boilers.

Gas analysis also supports greater process efficiency in many other applications. An efficient process reaction reduces the amount of harmful emissions likely to be generated.

Gas clean-up and carbon capture
Gas analysis plays an important role in gas cleaning, the removal of harmful substances from process gases that might otherwise be emitted by the plant.

Typical examples of gas clean-up processes include DeNOx (ammonia slip) treatment, flue gas desulphurisation, and carbon capture and storage (CCS).

By capturing and storing CO2, the operator ensures it is not released into the atmosphere. This results in a cleaner environment, and allows the CO2 to be used in other processes.

Three different methods exist for CCS: pre-combustion, oxyfuel, and post-combustion CCS.

Post-combustion CCS takes place when CO2 is removed from the flue gas after fossil fuels have been burned. Oxyfuel CCS produces a flue gas consisting almost entirely of CO2 and steam by reacting the fuel source with almost pure O2 — this means flue gas can be stored/sequestered without significant pretreatment. Both these methods can be used in new plants, or retrofitted to existing ones.

A third method, pre-combustion CCS, is performed before burning the fuel, and converts the fuel into a mixture of hydrogen and CO2. This is difficult to retrofit, so is better for newly built facilities.
Whichever method is used, the captured CO2 is then compressed into a liquid and transported for storage.

As countries look to meet their responsibilities under Paris Agreement carbon reduction targets, the use of industrial-level CCS is likely to grow significantly, as is the requirement for accurate gas analysis to support the processes.

Servomex’s ServoTough SpectraExact 2500 photometric analyser is ideally suited to this application. It is capable of single or multi-component gas monitoring in corrosive, toxic or flammable streams, using infrared and gas filter correlation technologies to measure CO2 at percentage and parts-per-million levels.

This means it can be used to measure the flue gas to ensure most CO2 has been removed, and to assess the purity of the removed CO2 before it is sent to storage.

Monitoring flue gas emissions
Carbon emissions reduction has been a key issue for many countries in recent years, with legislation limiting the amounts of greenhouse gases — CO2, CH4 and nitrous oxide (N2O) — that can be emitted. NOx, SOx, and CO are also seen as key pollutants.

Monitoring flue gas emissions helps determine the process efficiency and protect the environment, and demonstrates that plant operators are complying with the necessary regulations.