Measuring dust emissions – can this also be done easily?

In order to be able to reliably and exactly measure dust and particle concentrations, the following criteria must be considered:

Depending on the boundary conditions, scattered light or transmittance measurement can be more suitable for detecting dust concentrations. With the transmittance measurement principle, the measurement is based on the attenuation of a light beam by the light absorption of the particles. In scattered light measurement, the radiated light is scattered by the particles in the gas mixture and detected by a sensitive receiver.

Transmittance measurement technology: measurement at high dust concentration and inhomogeneous media

Transmittance measurement technology detects light attenuation by dust particles. Transmittance dust measuring devices are well suited for medium to high dust concentrations and large gas duct diameters. Fields of application are emission and process monitoring as well as room air monitoring. The measuring devices measure over the entire gas duct diameter, which partially compensates for inhomogeneities in the particle distribution. This leads to a very representative measurement result. The devices do not protrude into the gas duct and thus have no direct contact with aggressive process gases.

Scattered light measurement: The right choice for small concentration of dust

Due to its high sensitivity, the scattered light principle is well-suited for low dust concentrations in particular, even those under 1 mg/m Depending on the system-specific requirements and particle properties, either forward or backward scattering can be used.

In some processes, exhaust gases are cleaned in scrubber units before they are released. Recording a reliable measurement for dust concentration is particularly difficult when the dust is damp. Conventional dust measuring devices cannot differentiate between specks of dust and drops of water, leading to distorted measurement readings. only one thing can help here: using a bypass system to extract the medium from the stack, dry it, and then measure it. This is the approach applied by the extractive scattered light dust measuring device, the FWE200DH. It extracts flue gas from the stack on a permanent basis, dries it within a few seconds using a thermo cyclone, and records particularly low concentrations of dust accurately using forward light scattering.

In some areas of application, such as the fertilizer industry, the condensate that forms in the sample gas often contains high levels of lime or salt and would clog the hoses and sample gas probe after a certain period of operation. Variants of the FWE200DH with backwash devices clean the circuit at regular intervals with air or water, thus ensuring high availability under difficult measuring conditions.

In addition to the selection of the best available technologies, a whole string of influences and requirements must be taken into account when creating a successful measuring task:

Emission measurements in dry and wet exhaust gases

Incinerators play an important role in many industrial processes. Continuous measuring devices are used in dedusting plants. These applications place very high demands on the measuring devices including, for example, in relation to the composition, temperature, and moisture content of the exhaust gases. Depending on the medium and the operating  mode of the plant, the water or acid dew point might be undershot, causing corrosion of the parts of the measuring device that come into contact with the exhaust gas. Therefore, both dry and wet exhaust gases must be measured highly accurately – with maximum possible availability and low maintenance overheads.

Safe filter monitoring

For efficient control of filter performance and function monitoring, dust concentration is measured continuously directly downstream of the filter. The more sensitively and quickly a measuring device is able to react to a change in dust concentration, the better equipped the plant will be to operate without dust penetration. The DUSTHUNTER SP100 is ideal for this type of application, because it can be installed very easily from one side. The probe design renders mechanical adjustment and alignment with a particlefree measuring distance unnecessary.

Filter monitoring synchronized with dedusting

It is important to identify a filter defect at an early stage so that permissible emission limit values are not exceeded. If only the defective bag or group of bags is to be replaced, the exact location of the defect must be located. To do this, dust concentration must be measured synchronized with the dedusting of the bags, so that filter defects can be detected through the occurrence of emission peaks. The DUSTHUNTER SP30 has a proven track record in rising to this particular challenge.

In machining and processing areas of production facilities, more and more effort is being put into increasing efficiencies, which is why the dust measuring devices from Endress+Hauser are not only performing traditional emission measurement, but are also increasingly being installed in closed systems, containers, tanks and rooms. Shavings, lint, powders or dust particles can form an explosive atmosphere, whether it be in the food industry, in pharmaceutical manufacturing, in the dye industry, or when processing wood or metal. 

To ensure there are no ignition sources present when measuring process gases, only explosion proof measurement devices can be used. The DUSTHUNTER SP100 is also approved in variants for Ex zones 2/22 or 1/21.