THE LATEST TECHNOLOGIES OF FLOW MEASUREMENT OF BULK MATERIALS AND DUST
When we talk about flow measurement, we assume that the working fluid is liquid or gas. However, there is another large class of materials, which possesses fluidity, which is transported through different channels and pipelines, and which flow shall also be measured. These are so-called bulk substances in different fractions from fine dust to coarse granules. The sensors for bulk materials are uncommon for the market, so the products of SWR engineering Messtechnik GmbH (Germany), which interests in Ukraine are exclusively represented by CSC-AUTOMATION, will be interesting for the professionals, working in the field of industrial automation.
Measurement of mass flow of bulk materials.
As you know, there is no single flexible way to measure fluid and gas flow rates.
Based on the medium properties, such as pressure, temperature, density, viscosity, conductivity, etc., different types of flow meters are used. Same for the bulk materials, depending on the medium parameters, different types of instruments are used. The main parameters of bulk material, influencing the instrument type, are the flow density and speed of the material flow. For the cases of the low-density flow at the relatively high speed SolidFlow instrument has been developed.
This flush type device, which is mounted with the welded sleeve into the metal channels is used to measure the flow of dust, powders, granules with fraction of 1 nm to 1 cm. The principle of action of the instrument is based on the interaction of the high frequency electromagnetic field with the particles of material. The probe signal is reflected from the flying particles, is received by sensor and measured by frequency and amplitude. The instrument in fact operates in the particle counter mode. Due to the selective receiving by frequency, only the signals from the moving particles are processed, i.e. having the Doppler shift, and the signals from the stationary buildups, deposits, sediments, etc. are suppressed. The instrument consists of a sensor mounted into the channel and a processing module (transmitter) set at the distance to 1000 m from the mounting point. For the pipes up to 200 mm, one sensor shall be set, for the pipes over 200 mm — two or three sensors connected to the same transmitter. Maximal diameter of the channel for setting SolidFlow instrument is 600 mm.
SolidFlow instrument has various forms of application. It is used in elevators, at the feed-milling plants, mills and other food production sectors. SolidFlow allows to measure and control even product feeding through various pipelines, which results in correct account and compliance with the technology. The instrument is also used for batching various products, such as additives in the feed industry. When set at the screw feeder output, for example, SolidFlow allows to adjust screw rotation and maintain constant proportion. As a result, the stable product quality is achieved and expensive additives are saved. Also, it is typical to apply SolidFlow in various proportional mixing systems, when several components are loaded into a mixer. Complicated and expensive weighing systems are often too inaccurate for small amounts. SolidFlow solves the problem of batching components more efficiently.
Practical examples of application
Salt powder batching
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Customer: white salt producers
Material: salt
Flow rate: 3 t/h
Feed: transported by screw through the rotary gate
Setting: channel before the tank gate
Previous form of measurement: not measured, the flow rate was determined by the rotor wheel rotation speed
Client comment:
compared to the previous methods has the following advantages:
- continuous flow rate measurement
- previously, it was impossible to precisely determine the flow rate by drum rotations (not precisely enough)
Corn meal flow rate measurement
Customer: corn product producer
Product: corn meal
Flow rate: n/a
Feed: rotary valve
Setting: pipe before the gate bucket
Previous form of measurement: based on the valve rotation speed
Client comment:
The SolidFlow system has the following advantages:
- easy and simple maintenance,
- reliable, calibrated when installed
Benefits for Clients:
following the recipe when mixing, identification of the flow rate
Grain flow rate measurement
Customer: crops treatment, company (Germany)
Product: cereal
Flow rate: 10 .. 12 t/h
Feed: rotary valve
Setting: pipe before the gate bucket
Previous form of measurement: based on the rotary valve rotation speed
Client comment:
it provides bulk material feeding system, compared to the previous methods has the following advantages:
- reliable flow rate measurement
- simple service
- simple calibration
- simple installation
Benefits for the customers:
- recording of actual material flow rate
For the pipes over 125 mm and higher material flows, MaxxFlow instrument has been developed, which is produced for rated diameters DN 150, 200 and 250. This device only works in vertical sections of piping and takes measurements only under the free fall of the material. Vertical sections at the silo output, where the material is discharged, are typical for the instrument installation, e.g. by means of the butterfly gate. Also, the material free fall sections next to the belt conveyor, screw feeder, elevators and other similar devices can fit for setting.
Customer: food producers (Germany)
Example. Measurement of the potato starch flow rate
Product: potato starch
Flow rate: 60 .. 80 t/h
Feed: feed chain
Setting: free fall to the feed chain bin
Client comment:
The MaxxFlow system has the following advantages:
- easy re-equipment/setting
- not high compared to the volumetric batchers
- no wear and tear, no mechanical parts (no contact)
Benefits for the customers:
- continuous measurement
- quality ensured in the process of production
Due to the variety of the materials and their properties (particle size, permittivity, humidity, etc.), SolidFlow and MaxxFlow meters cannot be subject to the factory calibration. They are calibrated in place of setting, comparing measured amount with some previously known (weighed, measured) batch of material. After such in-place calibration SolidFlow and DensFlow meters ensure relative measurement error of 2...5%, аnd for MaxxFlow meters the values can be 1...3%. The relaxation piping requirements shall be followed in the process of installation. For the SolidFlow they are about 5DN at the input and 3DN at the output. MaxxFlow meter needs a free fall area of 200 mm only, and in some cases it is not required at all. All the flow meters have the analogue output signal 4...20 mA and digital interface RS-485. SWR engineering since its establishment in 1994, has been professing philosophy of maximal proximity to the needs of the real sector of industry and expertise in a small segment of the market of instruments. Often, the measurement targets when working with bulk materials and dust are not as clear as for the liquids and gases transported through the pipelines. However, the experience has proved high economic efficiency of their application in various technological processes.