Putting a lid on pollution with CEMS

The latest generation of CEMS equipment can help to achieve a cleaner environment

Stephen Gibbons
ABB Measurement & Analytics

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Article Summary

Pollution has been a growing problem for many years. As well as the headline pollutants of CO2 and methane that form the major greenhouse gases, there are also many other toxic gases and particulate matter that affect human health, wildlife, water and the general environment. These include carbon monoxide, ammonia and hydrogen chloride, all of which need monitoring and controlling to avoid harm to people and the environment.

Combatting these emissions requires stricter regulations and many countries are demanding that companies responsible for pollution install Continuous Emission Monitoring Systems or CEMS, systems that provide continual monitoring and analysis of the effluent gas streams that result from combustion in industrial processes. A CEMS operates constantly, even when the process it is monitoring is not operational. 

The global ambition to cut emissions is fuelling an increase in the market for CEMS, with projections from the ARC1 projecting a CAGR of 4.8% between 2018 and 2023. Much of this growth will be driven by Asia, as India, China and Southeast Asia increase their levels of industrial activity, as well as demand from operators involved in electric power generation, incineration and chemicals manufacture, which collectively represent the world’s largest markets for emissions monitoring systems.

Cleaning up our act
One of the major drivers behind the adoption of CEMS is the determination to cut CO2 emissions. The EU has adopted ambitious new targets in this area, determined to cut carbon emissions by at least 55% by 2030 compared with 1990 levels.2

The new US administration has also committed to reaching net zero emissions by 2050, while the UK has drawn up radical plans to cut carbon emissions by 78% by 2035.3

As part of its fight against pollution, the EU has published its IED waste incineration plant BREF notes. The broadened legislation demands that companies measure extra chemical species – the legislation also lowers the emission limits for others. The regulations stipulate that companies must adopt the best available technologies by 2024. A new requirement is that CEMS will be required for ammonia. 

The EU is also tightening up the rules on combustion plant, closing the loophole between large combustion plants and smaller appliances like boilers. The EU’s Medium Combustion Plant Directive (MCPD) applies to the 143,000 plants in the EU with a rated thermal input equal to or greater than 1 Megawatt thermal (MWth) and less than 50 MWth. Its principal aim is to control emissions of sulphur dioxide, nitrogen oxides and dust.

In the large combustion plant area, the EU is demanding additional species must be continuously monitored on EU large combustion plants for most solid fuels, such as power stations burning biomass. The additional CEMS requirements include analysis mercury, hydrogen chloride, hydrogen fluoride, carbon monoxide, ammonia and total VOCs.

These new rules will bring the CEMS requirements for large combustion plants in Europe to the same level as waste incineration plants. 

With Asia being a strongly developing industrial area, it’s no surprise that highly populous countries like India are bringing in stricter legislation on monitoring. 2018 saw India legislate for the installation of new CEMS in plants in 17 categories of polluting industries. These include many sectors of the metal industry, such as aluminium, cement, copper and iron and steel, food and beverage industries such as distilleries and sugar and many chemical sectors such as dying, chlor-alkali, fertilisers, oil refineries, petrochemical plants, pesticides and pharmaceuticals, as well as power plants and pulp and paper mills. 

The Indian rules stipulate that CEMS parameters to measure include particulates, fluoride, ammonia, sulphur dioxide, oxides of nitrogen, chlorine, hydrogen chloride, carbon dioxide, carbon monoxide and oxygen.

China’s recent industrial growth has been phenomenal. The resultant increase in pollution has been similarly spectacular, and the world become familiar with images of the persistent smog and poor air quality in cities like Beijing. In 2018, the region of Sichuan reported an economic loss of over 34 billion yuan caused by natural disasters that were the direct result of environmental pollution.4

In an effort to combat this, the 2018 environmental legislation in China introduced the ability for provinces to implement taxation on 44 gaseous atmospheric pollutants. This ‘Blue Sky’ legislation covers particulate matter, carbon monoxide, chlorine, oxides of nitrogen, sulphur dioxide, hydrogen chloride, ammonia, the BTEX group, formaldehyde and chloro-benzene. This should have the effect of stimulating companies to mitigate the risk if these extra taxes by controlling pollutants through the installation of CEMS.

The country has seen some successes over the last decade, for example reducing sulphur dioxide emissions from a high of over 24.6 million tonnes in 2007 to only 8.75 million tonnes in 2017.5

Achieving emissions goals aids production
Depending on legislation and the type of information companies require, many industries need to use CEMS equipment to monitor their emissions, including power generation, waste incineration, oil and gas, chemicals and petrochemicals, pulp and paper, metals and minerals, landfills and biogas, marine and cement production.

CEMS solutions can range from simple systems monitoring natural gas fired boilers, measuring gases such as carbon monoxide, carbon dioxide and oxides of nitrogen, to more complex systems set up to monitor large waste incinerators. In this case, the system would be measuring rarer pollutants such as hydrogen fluoride and ammonia. 

Gas analysers can be used to achieve a number of goals. As well as continuously gathering emissions data for process monitoring or for compliance purposes, solutions are also available for combustion control applications, measuring flue gas for oxygen, carbon monoxide and carbon dioxide and optimising combustion temperature to reduce fuel use and lower emissions.

Another use is to increase plant efficiency to extend the lifetime of equipment. In turn, this can help decrease the plant’s operating and maintenance costs and improve productivity. 

Other typical applications of gas analysers include safety measurement and protection against explosions, monitoring leaks and checking on the status of filters. 
In terms of the actual sites where gas analysers are used, these can include stack emission monitoring, flue gas desulfurisation, dust filter monitoring, and boiler control, turbo generators, coal mills and coal bins.

For example, in cement production, gas analysers are used in a kiln gas outlet. Monitoring gases such as carbon monoxide, oxygen, methane and nitric oxide, the analysers are used to optimise primary firing, reduce fuel consumption and maintain clinker quality. 

In the coal mill of a cement plant, the analysers would be used in safety measurement, preventing smouldering and monitoring the air entrance for the presence of carbon monoxide and oxygen. 

Practical application 
There are essentially two types of measurements in use with gas analysis – extractive and in-situ. 

Commonly used for gases, extractive techniques can be divided into two main methods. 

The first is heated extraction, which involves taking a sample of gas from the stack using a sample probe, a heated line, gas conditioning equipment and a heated sample pump. Before analysing the gas sample, any condensate is usually removed - the temperature is also reduced to protect the analysers. This is known as “cold/dry” measurement. 

By contrast, the “hot/wet” technique keeps the gas hot all the way through the system. This ensures that the gas gets to the analyser inlet in the same condition it was in in the stack - it’s important to protect against any sample loss or degradation. With this method, a number of single component and multi-gas analysers can be used.

Extractive techniques also mean that only the probe is in contact with the gas, avoiding the risk of damage to sensitive optical components. 

Because the analyser system is installed in a clean and accessible environment, usually at ground level, maintenance is much more convenient. Components are easy to work on and remove and test gas cylinders can be stored nearby to allow easy calibration of the devices. 

The other main method is in-situ analysers. 

In-situ analysers have the advantage that no sample extraction is needed, as they are installed directly in the gas stream. Despite this, many plants across the globe use extractive techniques, which tend to have a lower cost of ownership. 

Also, whereas in-situ devices are usually limited to one or two gas components, an extractive system can measure multiple components using a sequence of sensors. This offers the added advantage of requiring fewer holes in the stack.

Another popular technique is cross-duct analysers, which project IR or UV (ultraviolet) energy across the stack. These analysers then detect the change in energy state of the gas molecules as they absorb this energy at characteristic wavelengths. For example, NDIR (non-dispersive infrared) gas analysers can be configured to detect the characteristics of a range of IR-active gases, such as carbon monoxide, carbon dioxide, nitrogen monoxide and nitric oxide.

Most cross-duct systems measure one to two gases over a range of wavelengths. They often need less maintenance and operator involvement as they don’t come into contact with the target gases.

Although cross-duct systems can be more complicated to calibrate, an automatic calibration system can get round this and deliver the accuracy needed. 

Other types of detectors include FID (flame ionisation detector) analysers for total hydrocarbons, paramagnetic analysers for percentage level oxygen analysis and electrochemical oxygen detectors that can offer a lower cost alternative. 

Overall, CEMS are a vital tool in the fight against air pollution – modern systems based on highly accurate and capable detectors are helping companies from many industries keep their emissions in check and meet the increasingly strict legislative demands of countries across the globe. 

1 ARC – Emission Monitoring Systems Global Market 2018-2023 - https://www.arcweb.com/market-studies/emission-monitoring-systems 
2 https://www.bbc.co.uk/news/world-europe-56828383#:~:text=The%20EU%20has%20adopted%20ambitious,2030%2C%20compared%20with%201990%20levels.
3 https://www.bbc.co.uk/news/uk-politics-56807520 
4 https://www.statista.com/statistics/300303/china-direct-economic-loss-due-to-natural-disasters-by-region/ 
5 https://www.statista.com/statistics/282680/china--sulphur-dioxide-emissions/

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