QAL Stack 181 WS


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The PCME STACK 181 WS is able to monitor saturated flue gas which is critical for the application of monitoring emissions from a coal fired power plant fitted with a wet FGD system and meets the requirements of EN 14181.

Product Description


The extractive instrument takes a representative continuous sample from the stack, heats this well above dew point to evaporate water droplets and then measures the particulate concentration under dry conditions.

The PCME STACK 181 WS is suitable for measuring particulate emissions from wet scrubbers and other processes where the flue gas falls below dew point (cold stack conditions) or water droplets are present.

This extractive approach with heating overcomes the problems of interference from condensation and water droplets associated with using in-situ particulate monitors after wet collectors.

The PCME STACK 181 WS uses an advanced ProScatter™ Forward Scatter sensor (PCME QAL 181) which is certified by TUV and MCERTS as QAL1 compliant.

With certification ranges covering both 0-15mg/m3 and 0-100mg/m3, the sensor is suitable for monitoring the highly abated emissions found after Flue Gas Desulphurisation plant (FGD).

The instrument is able to monitor saturated flue gas which is critical for the application of monitoring emissions from a coal fired power plant fitted with a wet FGD system and meets the requirements of PS-11 and EN 14181.

Resolution and Sensitivity

The PCME QAL 181 sensor within the PCME STACK 181 WS uses a low-angle forward light scattering measurement principle unique to PCME (see ProScatter Forward Scatter). The measured ‘cone’ of scattered light is larger than in typical light scatter instruments, which provides:

  • Excellent sensing resolution and sensitivity, due to an increased signal-to-noise ratio
  • Reduced cross-sensitivity to changing particle size, allowing a greater range of applications for which the instrument is suitable

System Self Checks

Flow rates and heater temperatures are continually monitored in the extractive flow line, to ensure any sample line blockages or problems with insufficient heating are automatically detected and avoided. The system automatically indicates when valid measurements are occurring, hence avoiding any measurement errors during any system warm up. In addition, trace heaters may be added to the intake air to ensure there is no risk of condensation in the pipes.

Modular Design and Ease of Maintenance

The system has been designed to facilitate ease of maintenance and cleaning of all major components, and the central control system records all critical measurements for rapid diagnosis of problems. The system can be isolated from the stack with a safety shut off valve and the vaporising chamber is easily accessed and cleaned by opening the hinged heater cover. The PCME STACK 181 WS is designed in a truly modular format for safety and ease of installation and maintenance, allowing parts to be replaced while still mounted on the stack.

Audit Tools & QAL3 Reporting

As an approved Particulate Measurement System for compliance monitoring, the PCME QAL 181 sensor within the PCME STACK 181 WS has fully automated self checks (Zero and Span) with a dedicated audit channel for QA data logging. This enables a simplified process for operators to meet QAL3 standards, with the option of PCME’s QAL Reporter PC software for automated QAL3 reporting in full compliance with EN 13284-2.

In addition to automatic self checks, the PCME STACK 181 WS has been designed for easy and safe operator access to the measurement volume for external auditing as required for the AST linearity test for EN 14181 compliance and absolute correlation audit for PS-11 compliance. The ProScatter™ 5-point Filter audit unit facilitates a comprehensive instrument check via a 5 point linearity check.

The PCME STACK 181 WS is suitable for:

  • Stacks below dew point / with water droplets
  • After wet scrubber arrestment plant
  • After Flue Gas Desulphurisation (FGD) plant
  • Flue gas velocity range 1-20m/s
  • Corrosive flue gases (corrosion protection option)
  • Variable particulate size  

Typical Applications

The PCME STACK 181 WS is used to monitor emissions from the following types of processes:

  • Coal and Oil fired power plant with FGD
  • Waste incineration plant with wet scrubbers
  • Pulp and paper recovery boilers
  • Metallurgical and chemical processes with wet scrubbers
  • Sugar beat dryers/boilers with high moisture in flue gas
  • Particle board and fibre drying


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