Stack Dust and Opacity Monitor

What is the Stack Dust and Opacity Monitor?

An optical instrument that continuously measures particulate emissions in a stack by light scattering or transmission, reporting relative dust concentration or opacity. It is the right choice for bag filter and electrostatic precipitator performance monitoring and for regulatory dust reporting after site-specific calibration.

Overview

Dust monitors fall into two main types. Forward or backward scattering sensors measure light scattered by particles at a small angle and are sensitive from about 0.1 to 500 mg/m³, suited to bag filter stacks. Transmissometers send light across the duct to a retroreflector and measure attenuation, reporting opacity or extinction for higher dust loads, as in older precipitators and boilers. Both are calibrated against manual isokinetic gravimetric measurement under EN 13284-1 to build a site-specific function relating signal to mg/m³. Air purge keeps windows clean, and automatic contamination checks correct for deposits. Triboelectric probes are an additional technology that detect charge transfer from moving particles. Instruments should be selected to suit moisture, droplet presence and stack diameter, because wet stacks can cause false signals.

How does it work?

Emission monitors determine pollutants in hot, wet and dusty flue gas. Extractive systems withdraw a sample through a heated probe and line at 180 °C, remove particles with a filter, and either keep the gas hot for analysis or dry it in a chiller before measurement. Analyzers use non-dispersive infrared for CO, CO2 and SO2, chemiluminescence or UV for NOx, paramagnetic or zirconia cells for O2, and FTIR for multi-component measurement. In-situ systems measure across the stack using tunable diode laser absorption or UV. Particulate monitors use light scattering, transmissometry for opacity, or triboelectric signals, and flow is measured by differential pressure pitot tubes or ultrasonic transit time. A data acquisition system normalizes values to reference oxygen, dry basis and standard conditions, applies calibration and reports averages.

What are the key features?

• Forward scatter sensing resolves low dust levels below 1 mg/m³ in filtered stacks.
• Transmissometer option covers high opacity ranges in boilers and precipitators.
• Automatic contamination compensation maintains accuracy between window cleanings.
• Air purge system protects optics from dust deposition and heat.
• Calibration function entry supports site-specific mg/m³ correlation per EN 13284-2.
• 4–20 mA and relay outputs signal filter failure and exceedance events.

What are the technical specifications?

A typical stack dust and opacity monitor configuration offers measurement principle of Forward scatter or transmissometer, dust range (scatter) of 0–50 / 0–500 mg/m³, opacity range (transmission) of 0–100%, detection limit of ≤ 0.1 mg/m³ (scatter), wavelength of Visible LED or laser, 550–680 nm and duct diameter of 0.3–15 m (transmission). Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Stack Dust and Opacity Monitor is used in bag filter leak detection, electrostatic precipitator performance, cement and lime plant dust emissions and biomass and waste boiler stacks. Across the wider Emission Monitoring class, laboratories also deploy it for coal and gas power plant stacks, cement and lime kiln emissions and waste incineration monitoring.

Which standards and certifications apply?

Relevant standards and methods include EN 14181, EN 15267-3, EN 15259, ISO 12039, US EPA 40 CFR Part 60, US EPA 40 CFR Part 75, HJ 75 and HJ 76. Certification candidates for this model are CE, EN 15267-3 QAL1 and China CEMS certification; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Choose sampling locations that meet EN 15259 or HJ/T 397 requirements for straight duct length and port access, because flow profile affects representativeness. Keep heated lines above the acid dew point to prevent condensation and corrosion, and replace probe filters and pump heads regularly. Perform daily automatic zero and span checks, quarterly or annual linearity checks, and an annual surveillance test against a standard reference method under EN 14181 QAL3 and AST. Protect cabinets from dust and temperature extremes, and provide calibration gas cylinders with certified uncertainties. Keep records of maintenance, calibration and data substitution, since regulators audit these, and train operators in safe work on platforms.

How do I select the right Stack Dust and Opacity Monitor?

Select scatter sensors for low-level dust after fabric filters and transmissometers for high-dust or opacity limits. Neither measures mass without calibration against gravimetric samples. In an RFQ, specify dust range, duct diameter, temperature, moisture and droplet presence, purge air and certification requirements.

How does it compare with other Emission Monitoring variants?

Start with the regulated pollutants, emission limits and the standard your permit cites, such as EN 14181 or HJ 75. Decide between extractive and in-situ systems according to stack temperature, moisture, acid gas content and the number of species: extractive suits multi-component and low-level measurements, while in-situ suits single gases and fast response. Check that measurement ranges are suitable for the limits, with limits in the lower third of the range where possible. Consider reporting requirements for averaging, data validation and certified instrument status under schemes such as EN 15267 or China CEMS certification. Include sample conditioning maintenance, calibration gas logistics, shelter size and the ability to cope with wet scrubber stacks.