Stack Dust Emission Measurement: Isokinetic Sampling and Dust Monitors
Measurement of dust and particulate emissions from stacks: isokinetic sampling devices and continuous laser dust monitors, pitot and hand-held control units.
Measurement methods: Gravimetric Particulate Sampling, Optical Scattering (Laser Photometer)
What is stack dust and why is it measured?
Dust or particulate emission in flue gas is the solid particle load discharged from the stack after gas cleaning in combustion and production processes. The performance of equipment such as bag filters, electrostatic precipitators and cyclones is monitored directly through stack dust concentration. In Türkiye, legislation on industrial air pollution requires dust emissions to be measured periodically according to plant type and monitored continuously at certain plants. There are therefore two complementary approaches to dust: periodic isokinetic sampling, which serves as a reference, and continuous dust monitors.
Where are dust emissions measured?
- Stacks of cement, lime, metal and energy plants
- Post-filter ducts: Bag filter and electrostatic precipitator outlets
- Waste incineration and biomass boilers
Methods for measuring stack dust
Isokinetic sampling is sampling in which the gas velocity at the nozzle is matched to the gas velocity in the stack. The sample is collected on a filter and weighed gravimetrically in the laboratory; the result is given in mg/Nm³. The method is defined by standards such as EN 13284-1 and provides the reference for calibrating continuous monitors. In this process, a probe with pitot tube, a thermocouple and a hand-held control unit maintain the isokinetic condition by adjusting pump flow according to velocity.
Continuous dust monitors measure dust concentration on the duct through the scattering or transmission of laser light; the transmitter and receiver sit on either side of the duct, and measurement is direct and real time.
Choosing a dust measuring system
- A sampling device for periodic measurement or a monitor for continuous monitoring
- Duct diameter, dust load, temperature and dew point
- Reference measurement plan for monitor calibration
Stack dust measurement with Tetra
Tetra supplies Mega System X1 APIS and Lifetek XP-R isokinetic sampling systems, the Isocheck hand-held control unit, S-Probe probe sets and the NEO Monitors LaserDust laser dust monitor. Installation, commissioning, calibration and service are carried out in Türkiye by Tetra.
Frequently asked questions
How is a continuous dust monitor calibrated?
Optical dust monitors do not measure mg/Nm³ directly; their signal is calibrated by correlating it with parallel isokinetic gravimetric measurements at the same stack. In continuous emission monitoring systems, this is done in the QAL2 process under EN 14181, and zero and span drift during operation is tracked with QAL3. The calibration curve may need renewing when the process or fuel changes.
How is dust measurement affected if the isokinetic condition is lost?
If the velocity at the nozzle is lower than the stack gas velocity, too many coarse particles enter the nozzle and the concentration is measured too high. If the nozzle velocity is higher, coarse particles cannot follow the flow and the result is too low. Velocity and temperature are therefore monitored throughout sampling, and pump flow is adjusted continuously.
Can a laser dust monitor be used in wet flue gas?
In gases containing water droplets, such as after a wet scrubber, optical monitors can detect droplets as particles. For such applications, extractive measurement systems that heat the sample to evaporate the droplets are considered. The gas dew point and temperature must be determined before selection.
How is the measurement point for dust measurement selected?
The measurement section should be in a straight stretch of duct where the flow is uniform, sufficiently far from disturbances such as bends, fans and contractions. In periodic measurements, samples are taken at several points across the section, so suitable measurement ports and a working platform are required. Rules for the measurement plane are defined in EN 15259.
Products measuring this parameter
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