A continuous emission monitoring system (CEMS) continuously measures dust, CO, SO₂, NOx, HCl, O₂ and stack temperature, pressure and flow, calibrates automatically and transmits data online to the environmental authority. ISE advises on, supplies and integrates CEMS to Vietnamese requirements (Circular 10/2021/TT-BTNMT, QCVN 19:2024/BTNMT) and European practice (EN 14181, EN 15267) – for accurate, stable data accepted by regulators.
Who needs a continuous emission monitoring system?
Facilities with large flue-gas flows or high-pollution activities (power, cement, steel, chemicals, large boilers, waste incinerators…) must install continuous emission monitoring under the 2020 Law on Environmental Protection and implementing decrees. Thresholds and parameter lists should be checked against each facility’s environmental permit.
Monitored parameters
| Parameter | Common technology | Note |
|---|---|---|
| Dust (PM) | Scattered light, opacity, triboelectric | Mounted on the stack |
| SO₂, CO, CO₂, NO | Non-dispersive infrared (NDIR), NDUV | Extractive or in-situ |
| NO₂, NOx | Chemiluminescence, NDUV | Extractive |
| HCl, NH₃, H₂O, multi-gas | FTIR, tunable diode laser | Hot-wet extractive |
| O₂ | Zirconia, paramagnetic | For reference-O₂ correction |
| Temperature, pressure | Pt100/thermocouple, pressure transmitter | Mounted on the stack |
| Flue-gas flow | Ultrasonic, DP pitot | For mass emission (kg/h) |
CEMS configuration
- Sample probe and heated sample line (extractive): stainless steel, heated to prevent condensation, no sharp bends.
- Analyser cabinet: sample conditioning (filtering, chilling/drying or hot-wet), gas analysers, O₂ analyser.
- In-situ devices: dust, temperature, pressure and flow on the stack.
- Calibration system: zero/span gases with scheduled automatic calibration.
- Datalogger & software: acquisition, correction to mg/Nm³ at reference O₂, mass emissions, storage, reporting and data transmission.
- CCTV: stack outlet and station monitoring, day and night.
- Shelter: air-conditioning, lightning protection, UPS for analyser stability.
Extractive or in-situ?
| Method | Advantages | Considerations |
|---|---|---|
| Cold-dry extractive | Stable, easy to calibrate; common for SO₂, NOx, CO, O₂ | Water-soluble gases (HCl, NH₃) lost with condensate |
| Hot-wet extractive (FTIR) | Measures HCl, NH₃, H₂O and many gases simultaneously | Higher cost; fully heated sample path |
| In-situ | No sample line, fast response | Affected by dust and vibration; more complex calibration |
European standards for CEMS
In Europe, CEMS at plants under the Industrial Emissions Directive 2010/75/EU (IED) are quality-assured to EN 14181 at four levels (Gasmet):
| EN 14181 level | Content | Frequency |
|---|---|---|
| QAL1 | Certification of instrument suitability to EN 15267 (TÜV, MCERTS…) | Once, before selection |
| QAL2 | Installation check and calibration against a standard reference method (SRM) by an ISO/IEC 17025 accredited laboratory | At installation, typically every 5 years or after major changes |
| QAL3 | Ongoing zero/span drift control during operation | Continuous, by the operator |
| AST | Annual surveillance test – a “mini-QAL2” | Annually |
Common SRMs: EN 14789 (O₂), EN 15058 (CO), EN 14792 (NOx), EN 14791 (SO₂), EN 1911 (HCl), EN 14790 (water vapour), EN 13284-1 (dust), EN 16911 (flow).
Requirements in Vietnam
- Circular 10/2021/TT-BTNMT: internationally certified instruments encouraged (US EPA, MCERTS, TÜV); range at least 3× the regulatory limit; monthly checks with reference materials, recalibration if deviation ≥ 10 %; annual independent quality control with relative accuracy RA ≤ 20 %; manual monitoring if the system is down for 48 h or more.
- QCVN 19:2024/BTNMT: industrial emission limits, corrected to reference O₂ by sector.
- Continuous data transmission to the provincial environment department; technical files, SOPs, logs and calibration records kept on site.
Benefits of an EU-standard CEMS
- Accurate, stable data – lower risk of violations, data gaps and penalties.
- QAL1/TÜV/MCERTS certified instruments – easier annual quality control.
- Automatic calibration and diagnostics – less maintenance.
- O₂ and CO data also support combustion optimisation and fuel savings.
ISE turnkey service
- Stack and sampling-point survey; parameters per environmental permit.
- CEMS design and selection of certified instruments.
- Supply and installation of shelter, analysers, datalogger and cameras.
- Data-link set-up, technical documentation and initial quality control support.
- Maintenance, periodic calibration, calibration gases and spares.
FAQ
How does a CEMS differ from a combustion gas analyser?
A combustion analyser (such as the IECOAL4000 flue gas analyzer) supports process control. A CEMS supports environmental reporting and requires certification, QA and regulated data transmission.
Which certification should the instruments have?
Prefer QAL1 certification to EN 15267 (TÜV) or MCERTS / US EPA, as encouraged by Circular 10/2021.
Related
- Flue gas analyzer CO, NO, NO₂, SO₂, O₂
- SST flue-gas oxygen sensor
- Cement kiln oxygen measurement
- Boiler oxygen trim control
Contact ISE about emission monitoring
EQUIPMENT INDUSTRIAL SOLUTION CO., LTD (ISE) – Ho Chi Minh City, Vietnam – advises on, supplies and integrates EU-standard continuous emission monitoring systems.
Contact us: Sales +84 909 617 185 – Technical +84 979 117 185 – Email: [email protected]
Regulatory information is for reference; check the original documents and your environmental permit.
