PREDICTIVE OR CONTINUOUS – A GUIDE TO CHOOSING THE RIGHT EMISSIONS MONITORING SOLUTION
Predictive Emissions Monitoring Systems (PEMS) are emerging as a viable alternative to Continuous Emissions Monitoring Systems (CEMS), but they should not be considered a like for like swap in all applications. Gregorio Ciarlo, Product Manager for Predictive Emission Monitoring Systems for ABB Measurement & Analytics, explains this new technology, and examines how it fi ts alongside established continuous emission monitoring systems
Today’s industrial plant owners and operators face a wide range of challenges that affect the operations and productivity of their facilities. One example is the tightening environmental regulations and emission limits that require the continuous acquisition of emission data to monitor and control a variety of pollutants and greenhouse gases released into the atmosphere, which are putting the onus on companies to put sustainability at the heart of their processes.
Failing to provide emission data to authorities can lead to fi nancial penalties, and even forced plant shutdowns. Accurate emissions monitoring is therefore crucial to managing and mitigating the impact that a company’s operations have on the environment. For this reason, emissions monitoring is an area where it is increasingly important to ensure that the best possible systems are in place to capture and report data.
Introducing PEMS
Traditionally emissions monitoring is achieved using Continuous Emissions Monitoring equipment (CEMS), whereby a small sample of gas is extracted and measured by a gas analyzer. A wide range of solutions are available to measure different gases, either individually, or using equipment such as ABB’s ACF5000, across multiple gases.
These established solutions are now being joined by a new breed of emission monitoring system. Utilizing advanced mathematical modelling techniques, software-based predictive emission monitoring systems (PEMS) are increasingly providing an alternative for monitoring and recording air pollutant emissions.
In gas measuring applications, PEMS can be used either alone or alongside CEMS to improve effi ciency and accuracy. PEMS involves dedicated software which provides a reliable real-time estimation of emission properties by means of a mathematical model (e.g. neural networks), using process values such as temperature, fl ow and pressure as input variables. The software is used to estimate pollutant concentrations, with predictive models exploiting the inherent correlations between process variables, ambient conditions, and emission properties (NOx, SO2, CO, CO2). From this, the system uses AI to provide emission estimations with an accuracy comparable to conventional hardware analyzers. Crucially, PEMS improves system uptime. A typical CEMS can generally be expected to achieve 95 percent availability, while the use of PEMS increases this to 99.5 percent.
As a means of measurement, model-based emission monitoring provides several key advantages, including:
• Recognition as an accepted measurement technique by IET JANUARY / FEBRUARY 2022
international environmental regulations and standards.
• Ability to offer increased emission data availability up to 99.5%
• Lower capital investments and reduced ownership costs, with minimal maintenance needs and not requiring consumables and spare parts.
• Easy integration at plant – no measurement hardware or sample handling system is required in a PEMS, freeing up space and minimizing disturbance to plant operations while reducing physical requirements for maintenance to zero, with no compromise on accuracy.
• As a back-up for CEMS systems, PEMS can help identify possible malfunctions and provide an alternative measurement when the analyzers are in maintenance
Predictive emission monitoring systems (PEMS) are increasingly being used for monitoring and recording air pollutant emissions.
• They can provide an overview on the process, highlighting anomalies and providing a preliminary evaluation of excess emissions
Crucially, the suitability of PEMS for emission measurement has been recognized by various regulatory authorities around the world, and recent changes to permit their use is opening new possibilities for the effective measurement and control of emissions.
These advantages are seeing PEMS playing a widespread role in the future monitoring of emissions from industrial plants, with a corresponding growth in take up as its benefi ts are realized. According to the ARC’s 2019 report ‘Emissions Monitoring Systems Global Market 2018 to 2023’[1], shipments of PEMS solutions are projected to grow at a CAGR of around 6.8 percent, from USD 29.5 million in 2018 to USD 41.1 million in 2023, with growth driven by a combination of increased environmental awareness and stringent environmental regulations to achieve targets such as those set by the 2016 Paris Agreement.
How to choose between PEMS and CEMS
The choice of whether to use PEMS or CEMS will depend on a vareity of factors including process layout, equipment and operative conditions. Ideally, an effective solution portfolio should include both software and hardware-based emission monitoring strategies, providing the ability to cover the whole range of possible applications. For example, the model-based nature of PEMS means it may have an edge when applied to boilers, gas turbines or furnaces where conditions are relatively stable, while conventional CEMS are to be preferred in applications with more changeable conditions such as waste incinerators or the most complex industrial processes such as those in the chemical industry.
Whilst a PEMS can be used as a standalone solution, or as a back- up for CEMS, it should not be considered as a direct replacement. To that end, CEMS still very much have their place in the modern plant.
Many companies offer either CEMS or PEMS solutions, but very few can do both. ABB is an example of a company that has
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