CEMS (CEMS)

A Continuous Emission Monitoring System (CEMS) is a permanently installed instrument suite that measures the concentrations of regulated pollutants in industrial stack gas in real time and transmits the data to the State Pollution Control Board's online portal. CEMS is mandatory under CPCB directions issued in 2014 and progressively expanded — for 17 categories of highly polluting industries (HPI) including cement, fertiliser, refinery, pulp & paper, sponge iron, distillery, and waste-to-energy plants, and for all CTO holders above prescribed scale thresholds.

A typical CEMS measures: particulate matter (by triboelectric, light scattering or beta-attenuation), SO2 (NDIR or DOAS), NOx (chemiluminescence or NDIR), CO (NDIR), O2 (paramagnetic or zirconia), and process variables stack temperature, pressure, moisture and flow. Specialised configurations add HCl, HF, mercury, total hydrocarbons and dioxin/furan surrogates for hazardous-waste incinerators. The full system includes a sampling probe inside the stack, a heated sample transport line, a sample conditioning unit (water removal, particulate filtration), the analyser cabinet, a data acquisition and handling system (DAHS), and a one-way data link to the CPCB's Online Continuous Effluent and Emission Monitoring System (OCEMS) server.

Calibration discipline is strict. Daily zero/span checks, fortnightly cylinder-gas calibrations, quarterly preventive maintenance, and annual third-party comparative emission monitoring (CEM-AS) against a manual reference method (isokinetic stack survey under IS 11255). Data availability above 85% of operational hours is the SPCB acceptance threshold; gaps trigger compliance review.

For recycling plants, CEMS becomes mandatory at scale — a tyre pyrolysis unit above 100 TPD, a plastic pyrolysis line above 50 TPD, a battery smelter at any scale, a hazardous-waste co-processing kiln. Capital cost runs Rs 30-90 lakh per stack depending on parameter count and stack accessibility; annual operating cost (calibration gases, spare consumables, AMC, electricity, internet) sits at Rs 4-9 lakh. The compliance trade-off is real: CEMS eliminates the option of "on-paper" compliance during regulator visits — every hour of every day of operation is on the SPCB's dashboard. Plants that have not internalised process control improvements before installing CEMS often face notices within weeks of commissioning, because steady-state averages that looked acceptable in monthly spot-checks reveal frequent excursions when monitored continuously.