Condensed from an OPSIS AB article by Bengt Löfstedt, first published 2023-05-05.
In an ideal world combustion would emit only water and carbon dioxide. Water is not a problem, and carbon dioxide is now closely watched for its role in climate change, but the emission question does not end there. Thermal processes also produce nitrogen oxides, mainly NO, and depending on the fuel, the type of combustion process and in some cases the flue gas cleaning, other gaseous pollutants appear as well: carbon monoxide, sulphur dioxide, ammonia, hydrogen chloride, hydrogen fluoride, mercury and dioxins. Each has its own effect on health and the environment and its own threshold concentration. Almost every region now controls emissions from large combustion sources through laws, permits and other regulations, whether the source is a power plant, a hazardous waste incinerator, a refinery or a cement works. A typical framework is the EU Industrial Emissions Directive, which points to best available techniques and their reference documents and conclusions — about thirty BREFs, one per industrial sector, each discussing measures and proposing emission limit values for a range of pollutants, with national authorities then setting the actual limits. Legislation therefore decides which pollutants an industry may emit and how much, and to prove compliance the operator has to meet detailed monitoring requirements. In some cases periodic sampling of the flue gas is enough, or even occasional fuel analysis with calculation from fuel flow, but where fuel composition or the process is expected to vary over time, continuous monitoring is usually necessary — which in turn imposes requirements on the equipment itself: type approval, maintenance and calibration.
In China the equivalent structure is familiar: emission standards by industry set the limits, the HJ 75 and HJ 76 series set how a CEMS must be designed, installed, accepted and operated, and HJ 212 governs how the data reach the regulator's platform. Three points we would add for anyone planning a system. First, the pollutant list follows the standard for the specific industry, not a generic list — cement, incineration, non-ferrous smelting and power each have their own set, and the oxygen reference level differs with them. Second, the acceptance procedure is a project in its own right: a period of stable operation, calibration and comparison with the reference method, and documentation, all before the data count. Third, continuous monitoring brings an obligation that periodic sampling does not: availability. A system that is well specified but poorly maintained produces gaps, and gaps are treated as missing or invalid data, not as zero. That is why the design of the sampling or optical path, the shelter and the maintenance plan deserve as much attention as the analyser itself.
Continuous Emissions Monitoring: What, Why and How — read the original at opsis.se ↗
Written by Bengt Löfstedt, OPSIS AB, first published 2023-05-05. The summary and the A.Johnson note above are our own text; the OPSIS article remains the authoritative version. Chinese reader? See the full Chinese article.
Send the gases, ranges, duct or path dimensions and required certification — we will respond with a technical proposal.