Using Activated Carbon For Precise Feeding Of Difficult Bulk Material

Carbon – well-measured and actively used for the environment and for consumption

Activated carbon is used in industrial and commercial cleaning processes due to its characteristic properties. It is used to remove and filter out unwanted substances from liquid and gaseous mixtures. A precise feeding of the activated carbon is indispensable – both to properly control the cleaning process and to use the expensive raw material activated carbon (well over 1,500 € / t) in a cost-efficient manner.

Activated carbon in wastewater treatment

With the increasing demands from environmental legislation, operators of wastewater treatment plants need to add additional cleaning steps to the established wastewater treatment process. They must ensure that substances which previously passed through the cleaning process are removed as fully as possible from the waste water.

Toxic residues of pharmaceutical materials, hormones and other organic components were being removed here. These enter the water cycle from the manufacturing industry, by their use on humans or animals, for example, and are therefore present in the wastewater found in communal and industrial sewage treatment plants.

The use of activated carbon allows such toxic materials or those which have poor biodegradability, to be removed from the waste water. To do this, activated carbon is added to the wastewater as a cleaning step and, after the materials have been adsorbed, it is removed again. The contaminated activated carbon is then sent for thermal disposal along with the sewage sludge. The extended cleaning stage using powdered activated carbon is also known as the process of Ulm.

There are proven systems marketed under the AK-DOS® brand for safe storage, highly-accurate feeding and efficient suspension creation using powdered activated carbon. They have already been implemented in several large plant systems. Together with Sülzle Kopf Anlagenbau (Plant Technology ¦ Engineering and Construction), Gericke has developed a system with a high level of operational reliability. The AK-DOS® system offers you safe storage of powdered activated carbon with demand-controlled feeding and dispersion as well as system control. The tailored interaction of all the modules results in higher dosing accuracy.

After the highly-accurate and secure feeding, the powdered activated charcoal is thoroughly wetted with water to create a suspension with a high elimination rate. When adding activated carbon, both the quantity of the activated carbon to the wastewater volume and possibly the contamination level of the waste water with pollutants need to be taken into account. If the amount added is too low, there is an inadequate cleaning effect, overdosing should be avoided for economic reasons. Quick adjustment of the amount being added to cope with changing wastewater volumes (e.g. when there is an increase during rainfall) with accurate feeding over a large performance range is therefore essential.

The figure shows a mechanical tare-compensated gravimetric feeding system using two Gericke DIW50 loss in weight feeders for waste water treatment. They continuously feed according to NAMUR 40 over a performance range of 2 to 40 kg/h, to generate an efficient suspension which is then mixed with the wastewater flow in a contact basin. In the contact basin, the materials to be eliminated are adsorbed. Finally, the contaminated powdered activated carbon is drawn off with the sewage sludge or separated using a filter system.

A hopper to refill the feeders is also included in the feeding plant. Refilling is done from a storage silo using a rotary valve and a reversible conveying screw to the hopper and from there into the feeders. The EasyDos Pro, which was developed by Gericke, is used to control the continuous feeding process. This communicates with the superior process control system from Sülzle Kopf Anlagenbau (Plant Technology ¦ Engineering and Construction).

The feeding system shown has been used successfully and without any faults in a communal waste water operation since October 2011.

Activated carbon in wine production

When producing wine, activated carbon is used as part of the fining process, along with other materials such as minerals or organic compounds. The fining is used to clarify the wine and for biochemical stabilisation. Any turbidity, discolouring and unwanted substances are removed from the wine. Activated carbon is particularly useful in removing undesired tastes and also for reducing coloured substances in white wine.

Activated carbon is usually added to the unfermented grape juice or to the wine. After a certain period of time to act, the wine is poured off, or the activated carbon is filtered out. The activated carbon must be used in a controlled way and exactly dosed so that all the desired substances remain in the wine. If this is not done, there could be a loss of quality with regards to the flavours and colours of the finished wine as the activated carbon does not work selectively against the unwanted substances in wine, rather it adsorbs numerous organic compounds.

This means that, along with the experience of the master vintner, precise and reliable feeding equipment is needed. Gericke is a specialist for continuous and exact feeding and has already delivered numerous feeding devices to well-known wine producers. The Gericke GLD 77 volumetric feeder used, covers a performance range of 2 to 40 l/h based on the volume of the activated carbon. With typical amounts used being from a few grammes to the maximum legally permitted in Germany of 100 grammes per hectolitre of grape juice or wine, the required quantities can be added to the wine being fined in a short time.

Expertise in activated carbon feeding

Gericke is a specialist in highly-precise, continuous feeding of bulk materials and, with its modular product range, a successful partner for leading system suppliers in the environmental and food sectors. The modularity allows tailored volumetric or gravimetric feeding equipment to be provided to meet the special requirements of the plant (loss in weight feeders / LIW feeders). These are used to provide the activated carbon metered to the required quantity accurately as well as securely and continuously in the follow-up process.

Bulk materials which are difficult to convey – like activated carbon (low bulk-density, different grain sizes with a variable fine-dust proportion, formation of agglomerates) – present no problem to Gericke feeders, where accuracies of below 1 % and better can be achieved when feeding. Along with activated carbon feeding systems for water treatment, Gericke has also supplied systems for flue gas cleaning using activated carbon which are used in steel plants and waste incineration plants, for example.

Dr. Andreas Husmann, Gericke GmbH