In order to guarantee full drying performance continuously, the proven intelligent, fully automatic HUBER throughput control system is also used in Kassel. Despite fluctuations in the input DR, it ensures constant water evaporation and constantly maximum plant capacity. The throughput control system has been further extended especially for this project. The control system now also reacts to the fluctuating inlet temperatures in the district heating network, to which the dryers are directly connected without hydraulic separation.
The direct connection to the district heating network gives the power plant operator the option of using the dryer as a heat sink. In the future, in conjunction with an extraction condensing turbine, this will enable the previously seasonal operation of the power plant to be converted to year-round operation. The possibility of partial load operation of the individual lines independently of each other further increases the usefulness of the plant.
A sewage sludge acceptance system was already installed at the site a few years ago. Via this system, the sewage sludge is now delivered with a piston pump both directly into the fluidised bed boiler and to the drying plant. The quantity is regulated via two control valves. In normal operation (total throughput 30 t/h) the quantity ratio of combustion to drying is 2:1.
HUBER scope of supply completely fills new building
In autumn 2019, Städtische Werke Energie + Wärme GmbH erected a hall in concrete frame construction especially for the drying plant. The challenge for HUBER here was to fit the entire plant periphery into the specified dimensions of the hall. This was achieved by arranging the aggregates as compactly as possible, some on several levels above each other.
In addition to the two HUBER Belt Dryers BT 30 and the associated ventilation system, HUBER also planned and supplied the entire wet and dry sludge conveying system as well as the exhaust air treatment in close cooperation with the customer.
Integrated in the wet sludge conveying system is a contaminant separator that removes foreign matter contained in the sludge and thus protects the downstream equipment and instruments from damage. After the contaminant separator, the sludge is conveyed via a distribution screw to two pump sumps from where the pelletizer of the respective belt dryer is fed by eccentric screw pumps.
After drying, the granular sludge is conveyed to an intermediate storage by various conveying units. By means of dosing into a pneumatic conveyor, it is then transported directly to the incinerator.
In case of maintenance, the dried sludge can be conveyed from the two belt dryers into a container with a capacity of approx. 20 m³. This container can be transported away directly afterwards with a hook lift vehicle.