Condensed from an OPSIS AB article by Bengt Löfstedt, first published 2025-09-19.
Cement production is a large global industry with a simple basic principle: limestone is ground and calcined at close to 1,500 °C, where calcium carbonate reacts with siliceous minerals to form calcium silicates, and additives are then used to set properties such as setting time. Mixed with water, sand and gravel it becomes concrete, used throughout construction. The environmental side is demanding. Raw material handling produces large amounts of dust, and the fuels and the raw material itself produce gaseous pollutants such as NOx, SO2 and sometimes HCl and HF. The very high temperatures also make cement plants a place for waste co-processing, so kilns often burn waste, some of it classified as hazardous. Most harmful gases decompose at those temperatures, but some can pass through or react to form new harmful substances, leading to dioxin and PCB emissions, and both the clinker reaction and fuel combustion release large amounts of CO2. Regulations in many countries limit air pollutant emissions from cement plants and require continuous monitoring: process parameters such as temperature, oxygen, pressure and flow, together with dust, NOx, SO2 and CO. Where SNCR is used to reduce NOx, ammonia slip has to be monitored, and HCl, HF and TOC are usually measured continuously or periodically, with periodic dioxin and metal monitoring. In emission terms the duty resembles a waste-to-energy plant, except that dust concentrations are usually higher — which is where the OPSIS approach suits, since an open-path DOAS measurement is relatively insensitive to the dust that forces frequent maintenance on extractive systems, and a single system covers the many gases a cement plant needs.
Chinese cement plants work to GB 4915 for emissions, and a CEMS there follows HJ 75 and HJ 76 like any other stationary source, with the oxygen reference and the pollutant list set by that standard; co-processing of waste brings additional requirements from the hazardous waste rules. Three field points from our cement work. First, dust: the kiln and the raw mill produce dust loads that foul extractive probes and optical windows alike, so purge air design and window access decide availability more than the analyser does. Second, ammonia slip where SNCR is used — the reagent dosing is often tuned by hand, and a tunable diode laser measurement at the outlet turns that into a control loop. Third, mercury: cement kilns recirculate mercury in the raw mill and the preheater, so concentrations can be higher and more variable than the raw material content suggests, and a total mercury measurement needs a converter that is maintained, not just installed. Where the same system already reports NO, SO2, CO, HCl and HF, adding the mercury channel is a modest step rather than a new project.
Cemented Success — read the original at opsis.se ↗
Written by Bengt Löfstedt, OPSIS AB, first published 2025-09-19. 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.
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