Bulk material measurements in Cement Plants

In the permanently continued development of cement manufacturing processes, measuring technologies now assume a firm position along with new chemical procedures and mechanical optimization.

In the permanently continued development of cement manufacturing processes, measuring technologies now assume a firm position along with new chemical procedures and mechanical optimization. Different measuring procedures improve the handling of bulk material in a sustainable way, whether it is to determine if defined levels are reached or in-line material is still flowing at all; which moisture content is present or which volume is being put through.

Monitoring material flow

To monitor the material flow, the non-contact microwave-motion detector FlowJam can be used for all bulk materials; the DK-value of the material plays no role in this. Even with small volumes of silicic acid, FlowJam can still detect material flow. The envea™-SWR sensor makes material flow monitoring, from a flow rate of 10 cm/s, possible. The detection takes place, independently of the direction of movement, through the analysis of the Doppler Effect. Material movement in metallic piping, shafts, freefall sections or transfer points is shown through two switching states on the output relay. Additional operating areas can be found on conveyor belts, material infeeds or volumetric dosing systems.

The FlowJam Plus offers the rapid detection of material movement (Flow/No Flow), as well as the additional function “Detection of blockage” or “Material flow interruption”. In the case of a material flow interruption it is now possible to quickly detect whether there is a problem, because the lower screw no longer removes any material or the feed screw no longer supplies material.

All members of the FlowJam family can be equipped with the optionally available process adapter, which allows operation at temperatures of up to 200°C and pressures up to 20 bar. At the same time, the process adapter makes operations with FlowJam S in Ex-Zone 20/22 possible. With ceramic mounting parts, a decoupling from very hot areas, such as cyclones, is possible.

The decisive advantage of the FlowJam over other methods of material flow monitoring, is its absolute lack of sensitivity regarding any soiling. The FlowJam can effortlessly detect through caked material, which always occurs in bulk material processes.

The monitoring of material flow through non-metallic materials, such as glass, PVC, ceramics and similar materials, expands the range of possibilities.

(Figure: FlowJam - Material flow monitoring)

Fill level in raw process?

Maximum or minimum? – Obtaining a reliable answer to this simple question often proves to be unexpectedly difficult in reality. The utilization of radar has proven useful here as well. Almost all kinds of bulk material can be detected with regards to their level with the ProGap. The risk of aggregates gathering due to container overflow, or of quality fluctuations through idling, can be avoided through a timely alarm. As a standard, measurements can be taken in all containers that size up to a diameter of 18 meters. Even designs that are capable of displaying levels over significantly greater distances are available from envea™-SWR on request.

Especially in raw process areas such as fluff dosages, stone-crushers or waste chutes, the advantages of the ProGap system compared to other technologies are clear. Damages through the material are excluded, since the installation takes place flush to the wall. The installation of the two parts that are identical in construction, transmitter and receiver, is generally carried out using a 1½’ threaded connector. But it is also possible to perform the installation with any other type of fitting that ensures that both the transmitter and receiver are correctly aligned with one another other.

Just as with material flow monitoring using FlowJam, the ProGap can also be equipped with the process adapter for temperatures up to 200 °C, pressures up to 20 bar and Ex-zone separation 20/22, as well as with the flange mounting for high-temperature areas. The ProGap can detect through all non-metallic materials (e.g. PVC, quartz glass, Plexiglas, and fireclay). Monitoring processes can thus be completely decoupled from the container interior.

(Figure: ProGap – Level detection)

Online recording of bulk material volumes

To carry out an online recording of bulk material volumes, the use of only belt weighers and impact plates is no longer feasible. The number of applications in which bulk material measurements are carried out electronically rises continually. The advantages for the user are obvious: simple retrofitting of the systems; additional installation heights is not required; delivery flow path has no process flow restrictions; test measurements are possible in the short term without great time and effort; Ex-areas and temperatures up to approx. 400 °C are no obstacle.

In combination with a patented measurement signal analysis, the

SolidFlow 2.0 microwave sensor from envea™-SWR, for instance, supplies a direct measure for a mass flow of up to approx. 20 t/h. With this system, all powders, dusts and granulated material, up to the previously indicated volume, can be measured in freefall and in pneumatic lines. In the cement industry, the SolidFlow 2.0 has proven itself with the collection of aggregates, such as iron (II) sulfate and other additives, as well as in the measurement of carbon dust to the oven.

(Figure: SolidFlow 2.0 – Mass flow measurement)

The menu-led operation of the SolidFlow 2.0 analysis electronics allows the user a simple commissioning that can be carried out in just a few steps. The operator guidance optionally takes place in 3 languages (German/English/French) and can be carried out either via touchscreen or with a laptop computer. In addition, the evaluation electronics are equipped with a unit counter; also a 4 – 20 mA output and 2 relay outputs are available as output signals.

Today, the dosage of solid materials is often carried out volumetrically. The only indication for the setting of a desired volume is the rotational speed of mechanical delivery elements, usually rotary feeders or screw conveyors. However, since the material compressibility and fill level of the conveyor are demonstrably not always constant, there are often strong deviations between the target and actual discharge volumes. This results in quality fluctuations and unnecessary material waste, and thus increased costs.

Using radar technology, dosage controlled by rotary speed can be upgraded to regulated dosage, and without integrating a weighing installation that requires more effort and expense.

The SolidFlow 2.0 has an active roping compensation. Based on latest microprocessor-technology, the measuring signal is being dismantled in its frequency spectrum, which enables the sensor to compensate influences of roping.

Raw mix, cement, plaster, salt, gravel ... – it does not matter which material needs to be measured in great mass flows (>20t/h). Mechanical procedures and the creation of more expensive installation heights can be avoided with the MaxxFlow HTC.

The MaxxFlow HTC is used in areas where large volumes of bulk material have to be measured after mechanical conveyor organs, such as spiral conveyors, pneumatic conveyor systems, rotary conveyors or similar mechanical discharge elements. The fact that here, too, no fittings of any kind have to be installed in the path of the delivery flow, the advantages of this technology are clearly recognizable. An upper limit for the throughput does not exist; any material volume can be measured – regardless of the hourly performance (50, 180, 290 t/h or more); the installation height of the sensor element amounts to 300 mm, which is why retrofitting in existing systems is easy. This is also due to the fact that the installation position is completely arbitrary. MaxxFlow HTC has an extremely abrasion-resistant, ceramic interior; the system can be used up to a material temperature of 120 °C. If used in new systems, its small dimensions can often result in a reduction in installation height, which previously had to be planned for mechanical measuring devices. In case of continuous extraction, the transmitter can be installed immediately after the discharge of the conveyor organ, even though discharge sections are generally not required. The measurement is equally independent of the flow rate as it is of the flow pattern of the conveyed material in the line.

Among other places, the MaxxFlow HTC is used in several cement plants in which the measurement of cement volume is used as a reference input variable for the iron (II) sulfate addition. In additional applications, also in the cement area, the raw mix volume is recorded. This makes it possible to ensure the required mix ratios are respected and thus providing an output of constant quality.

Determination of material moisture

Determination of material moisture can take place through sample extraction and analysis in the lab. This requires great time and effort, however, often much time is needed until the production process can be adjusted on the basis of the obtained values. Quality and process reliability are reduced, this results in increased costs and necessary time. A possibility of recording material moisture online, during the ongoing process, is also offered by the microwave. The moisture measurement via microwave provided by envea™-SWR is based on the principle of an open resonator. It is measured in the high-frequency wave range, and is used to record the surface and capillary moisture. The current moisture value is allocated to the damping, the microwave is coupled into the object to be measured; changes in the damping are proportional to the moisture content. The measuring window of the probe that is located in a stainless steel flange housing is protected through a non-wearing ceramic disk. The measurement can also be carried out through plastic without a problem.

The most important prerequisite for a correct measurement of the residual moisture in bulk material is the correct selection of the installation location for the sensor. For bulk material slides or conveyor belts, care must be taken that the material is guided above the probe at a layer thickness that is as even as possible. The installation of the M-Sens 2 in spiral conveyors has proven to be especially advantageous. As output, the user receives a 4 – 20 mA signal, as well as 2 alarm contacts. The sensor may be installed in all Ex-zones (gas & dust) and up to a temperature of 120 °C.

(Figure: M-Sens – Online moisture measurement)

Dust monitoring

The Dusty was specially developed in order to reliably monitor clean sides after filters for any filter breaks without delay. Process steps like grinding, crushing or storing of cement entail an increased dust development. That is why these processes are typical applications of the Dusty.

The Dusty is a filter monitor that works on a triboelectric basis. This means that as soon as there is movement, electrically charged dust particles impact the sensor or fly past it, then an electric charge of the particles is transferred to the sensor rod. These very small signals are reinforced with the electronics and thus made visible. The Dusty can be used in metal channels in which dust particles are to be detected in flowing gas. Its operational range starts at dust volumes of 0.1 mg/m3. In systems with explosion hazard area zone 22, the "Dusty DustEx 22” type can be applied. Due to its speed and reliability, the Dusty can also be used optimally as an alternative and/or expansion to the "police filter” as well as an alternative to the differential pressure measurement.