Model DCEM2000 - Dual Pass Opacity / Dust Monitor (Integrated Version)
From Dust Monitors
The DCEM2000 is a dual-pass transmissometer configured for the continuous measurement of opacity and dust in flue gases. Opacity, Dust mg/m2, Normalised Dust mg/Nm2. The DCEM2100 provides a continuous measurement of opacity or dust concentration in flue gases by continuously measuring the transmissivity of visible light across a process duct or stack. Its dual-pass optical arrangement is based on twin transmissometers measuring in opposing directions through the same section of the gas stream, providing not only an accurate average of the dust loading, but also providing a unique dynamic assessment of any misalignment errors due to stack movement.
- % opacity or dust density in mg/Nm3
- TUV & MCERT Approved
- Dual-pass, open-path transmissometer
- Integral auto zero and span check
- Full contamination check on all active optical surfaces
- Dynamic misalignment check
- Integral high efficiency air curtains for maximum uninterrupted service
The DCEM2000 and DCEM2100 provide a continuous measurement of opacity or dust concentration in flue gases by continuously measuring the transmissivity of visible light across a process duct or stack.
Its dual-pass optical arrangement is based on twin transmissometers measuring in opposing directions through the same section of the gas stream, providing not only an accurate average of the dust loading, but also providing a unique dynamic assessment of any misalignment errors due to stack movement.
The measurement of opacity or particulate (dust) emissions from a process stack by measuring changes in optical transmission is simple in concept, the monitor must be insensitive to any other factors that degrade the optical transmission such as contamination of optical surfaces or gross misalignment.
- Large Combustion Plants
- Small Combustion Plants
- Dust Collectors
Purge air failure
Power or purge air failure can allow hot, corrosive gases to flow back to the instrument and vent through the purge blower. This can result in catastrophic failure of the system.
An integral ball valve mounted between each transceiver and its air purge acts as an automatic shut off valve which closes on loss of power or purge air.
Many devices only measure optical contamination at the transceiver. They cannot measure contamination on the reflecting mirror on the opposite side of the stack. Many factors ensure that these surfaces often have different levels of contamination.
A retro mirror mounted on the ball of each auto shut off valve can be automatically rotated into and out of the optical path of each transceiver. This enables the individual window contamination to be measured and corrected for each transceiver and individual compensation applied.
Although some systems provide the facility to manually detect misalignment, they cannot detect misalignment automatically. If there is duct movement, or the instrument is inadvertently misaligned, it may result in significant errors over an undefined period.
Optical transmissivity is measured simultaneously in opposite directions over the same gas path using identical transceivers. When optical alignment is correct these measurements are identical. Any optical misalignment produces different transmissivities. The analyser automatically detects this and raises an alarm.
Many instruments only provide a simple measurement of opacity. Opacity is not proportional to dust density.
The outputs can be expressed in % opacity and dust density in mg/m3 or mg/Nm3 (corrected to Standard O2, temperature, pressure and H2O).
The DCEM2000/2100 incorporates unique features that resolve each of these problem issues, resulting in an instrument that surpasses the performance of all previous opacity monitors.
Particles emitted from industrial processes include smoke, soot, ash and carried-over process materials. All of these particles are visible and they can be measured by looking at how much they absorb and scatter visible light.
The CODEL DCEM2100 utilises two separate transceivers – each measuring across the same path. The LED light sources are turned on sequentially such that each transceiver measures either the transmitted light from its own source (Io) or the received light from the opposing source (Ir).
This provides the basic measurement of Transmittance where: Transmittance (T) = Received light (Ir) / Transmitted light (Io)
(Any difference between the 2 measurements of Transmittance indicates misalignment)
% Opacity (Smoke Density) = (1-Transmittance (T)) x 100
Dust density can also be measured if the physical and chemical nature of the particles are constant. It is directly proportional to another function of Transmittance called Extinction where: Extinction = loge (1 / Transmittance (T))
It is vital that an empirical ratio between the measured Extinction and actual dust density is established for each application by collecting a sample of the dust under controlled conditions. The DCEM2000/2100 can then use a Dust Factor where: Dust Factor = Sampled mg/m3 / Average Extinction during the collection. This Dust Factor is then used in normal operation to provide an output directly in mg/m3 where: mg/m3 = Dust Factor x Measured Extinction
(In the absence of actual data, assume (250/x)mg/m3 of dust will typically generate 10% opacity across a one metre path.
This is only a general rule. It is not reliable above 20% opacity and must be verified by sampling.)
Where other measurements are available, the DCEM2000/2100 can provide normalised measurements in mg/Nm3
Contamination correction is necessary because transmissometers cannot differentiate between solids held in suspension in the gas stream (emissions) and solids deposited on the optical surfaces (contamination). An inegral retro mirror is automatically presented to each transceiver enabling full contamination correction.
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