Bulk solids measurements in the chemical industry A firm grip on material flow - cpp - chemical plants & processes

Bulk solids measurements in the chemical industry

A firm grip on material flow

A flexible measuring technology package has been compiled by SWR Engineering for bulk solids. The spectrum covers everything from microwave to radar measuring devices and is suitable for achieving sustainable improvements in bulk solids handling. The Flowjam flow/no-flow detector, the Progap limit level meter and the M-Sens 2 humidity sensor are just three examples.

The author: Marcus Bronner Sales Manager, SWR Engineering

The Flowjam microwave motion detector works contactlessly and can be used to monitor the flow of a variety of bulk solids. The dielectric constant of the material is not important. The sensor monitors material flow rates of 10 cm/s or more. Detection is based on the Doppler effect and is independent of the direction of flow. Material flow in pipes, shafts and free-fall sections or at transfer points is indicated by two switching states of the output relay. Other applications include conveyor belts, material feeding and volumetric dosing systems. The device has been continuously adapted to different processes presenting a wide range of requirements. It was this ongoing optimisation that led to the development of the extremely sensitive Flowjam-high.
All members of the product family can be equipped with an optional process adapter that allows operation at temperatures up to 200 °C and pressures up to 20 bar. The adapter is also approved for installation in Ex Zones 20/22. A ceramic fitting even permits insulation against very hot areas such as cyclones. The key advantage of the Flowjam is its complete insensitivity to dirt. It detects through material aggregations, which are very common in bulk transport processes, without any problems. Monitoring the solids flow through non-metallic materials such as glass, PVC, ceramics, etc. is a further option.
Maximum or minimum?
It is often surprisingly difficult to find a reliable answer to this simple question where heavy-duty processes are concerned. Radar has proven valuable under these conditions. The limit level of nearly all types of bulk solids can be detected with the Progap II. The danger of clogged equipment if the container is overfilled or quality variations if it is run empty can be prevented by timely alarms. Measurements are possible in all containers up to a diameter of 18 m as standard. The Progap system scans the material level across the whole cross-section of the container. There is no longer any risk of clogging or of free vibration without contact, which is inevitable with measuring devices based on vibration technology.
Damage from the material is ruled out, as the equipment is installed flush with the wall. The transmitter and receiver, which have an identical design, are normally mounted using 1½” screw necks. However, any other method of attachment that ensures that they are correctly aligned with one another is also allowed. Like the Flowjam, the Progap II can be equipped with a process adapter for temperatures up to 200 °C, pressures up to 20 bar and Ex Zone 20/22 separation as well as with a flange connection for high-temperature applications. The Progap II likewise detects through non-metallic materials.
Measuring bulk solids flow rates online
Belt scales and baffle plates are not the only ways to monitor bulk solids flow rates online. The number of applications in which these flow rates are measured electronically is steadily increasing. The advantages for the user are obvious: retrofitting the systems is easy, no additional installation height is required, no internals protrude into the flow of materials, spontaneous test measurements can be carried out simply and hazardous areas or temperatures up to approximately 400 °C are not a problem. In combination with a patented signal evaluation device, the Solidflow microwave sensor provides a direct indication of the mass flow up to a rate of 20 t/hour. This system is capable of measuring all powders, dusts and pellets up to this amount in free fall as well as in pneumatic pipes.
Solids are often dosed using volumetric methods. The only reference point for setting the desired flow rate is the speed of the mechanical transport devices, usually rotary feeders or screw conveyors. However, the compressibility of the material and the filling level of the conveyor are not always constant, leading to frequent differences between the target and actual discharge rates. Quality variations and unnecessary material consumption are the outcome. Radar technology can be used to upgrade from speed controlled metering to controlled dosing without having to install a weighing unit. The Maxxflow HTC works without any mechanical systems and requires no expensive, additional installation height, irrespective of the material to be measured in large mass flows (. 20 t/h). This device is suitable whenever large quantities of bulk solids have to be measured downstream of mechanical conveyor systems. There is no upper limit to the flow rate.
Any material flow rate can be measured. The sensor element has an installation height of 300 mm. It can be easily retrofitted in existing equipment because any orientation is allowed. The system is designed for material temperatures up to 120 °C. The sensor can be installed immediately downstream of the conveyor discharge. An outlet section is not normally required.
Online moisture measurement
Online moisture measurement, i. e. without interrupting the process, is possible using microwave technology. The moisture measurement device developed by SWR Engineering is based on the principle of an open resonator. Measurements take place in the high-frequency range. Surface and capillary moisture are detected. The attenuation of the microwave in the measured material is converted to a moisture value. The change in attenuation is proportional to the water content. The measuring window of the sensor, which is mounted in a flanged, stainless steel housing, is protected by a wear-resistant ceramic disc.
The most important requirement for accurate measurements of the residual moisture in bulk solids is the choice of an optimal installation position for the sensor. If the bulk solid is transported on a chute or a conveyor belt, care must be taken to ensure that the bed thickness is as constant as possible when it passes the sensor. Good results have been achieved when the M-Sens 2 is installed in a screw conveyor. The user is provided with a 4 to 20 mA signal as well as two alarm contacts. The sensor is approved for the highest Ex categories (gas and dust) and temperatures up to 120 °C.
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