MechChem Africa September-October 2023

Radiometric mass flow measurement in lime works When rock leaves a crusher with different particle-size fractions, there is no place for sensitive, easily damageable processing equipment or sensors. That’s why the operator of a major lime works decided to use a radiometric system from VEGA for precise mass flow measurement.

T he Lhoist Group is a world lead ing company that specialises in burnt and unburnt lime products. Headquartered in Belgium, the com pany is present in 25 countries with more than 100 subsidiaries around the globe. Rheinkalk is a Lhoist Group company in Germany that operates the Flandersbach plant in Wülfrath, the largest plant of the Lhoist Group and the largest lime works in Europe. Around 7.5 mil

lion tonnes of limestone are mined there every year. The production of unburnt limestone products in Wülfrath amounts to approxi mately 4.0-million tonnes. The raw limestone is either used as grit for road construction or it is ground and further processed. A special hallmark of the Flandersbach plant is the very high quality of its burnt lime. Some of this material is further processed there, but approximately 2.0-million tonnes

of it leaves the plant every year as an end product. Lime is known mainly for its use as a flux in

steelmaking process es. However, lime and limestone products are also an indispens able raw material in drinking water and sewage treatment, in construction and agriculture, and in flue gas cleaning.

The complete system consists of a WEIGHTRAC sensor, a frame, and a protective container with the radiation source. It operates contactlessly and is thus wear and maintenance free.

The quality demands placed on these prod ucts have grown steadily over the years. For example, the grain size specified by the customer must be strictly adhered to. At the same time, delivery periods are getting shorter and shorter. These factors, as well as many others, make it necessary to measure the material quantities much more accurately than ever before. Precision feeding Lime processing begins with the extraction of limestone from the quarry. The material is transported on large haul trucks to a process ing plant where it is pre-crushed, washed, pre-sorted according to size, and distributed to various storage areas. From there, the pre pared material is further refined or fed into burners. With the help of rotary and shaft kilns, the raw minerals are converted into lime products. At the end of the production process, the fired products are ready for a wide variety of applications. Numerous conveyor belts with different lengths ranging from a few metres to one kilometre ensure that the limestone, which can be in a wide variety of different process ing states, is transported to the right place for further processing. Ambient conditions are harsh. Operating at speeds of up to 4.0 m/s, the belts transport rock with diameters from 1.0 to 250 mm at delivery rates up to 4 000 t/h. Moisture, dust and dirt are the order of the day here. Nevertheless, exact measure ment of this mass flow is required to ensure that downstream processes are fed with the right amount of material. To measure the quantities passing through, mechanical belt scales are installed at strate gic points in the conveyor belt systems. These

Since it is a non-contact measuring instrument, wear is not a problem when using the WEIGHTRAC 31 system from VEGA.

22 ¦ MechChem Africa • September-October 2023