Heat recovery (e.g. for heating buildings or digesters) is optionally possible, actively contributes to climate protection and also saves costs. Flow temperatures of up to 70 °C are possible (depending on dryer size and heat supply).
Energy-efficient use of waste heat for drying sewage sludge
The sludge is dried either with cold air (HPS®) or with hot air (BT) in a belt dryer. The dried product has a solid concentration ranging from 70% DS up to 95% DS.
The HUBER Cold Air Dryer HPS® is designed for small sewage treatment plants while the HUBER Belt Dryer BT is designed for medium to large treatment plants.
The HUBER Belt Dryer BT is used for the belt drying process, which operates according to the convection drying principle. The dewatered sewage sludge is fed onto a drying belt with an extruder.
Air heated by heat exchangers is passed through the dryer by means of fans and dries the sludge. As a medium-temperature dryer, the HUBER Belt Dryer operates with air temperatures ranging from 70 to 150°C.
The experts at HUBER develop a tailor-made plant for the drying of sewage sludge, based on the respective framework conditions and the available energy source. This opens up all options for economical disposal or recycling of the sludge.
HUBER Belt Dryer BT
HUBER Belt Dryer BT 20 at the site of a sewage sludge mono-incineration plant
Heat supply and fans of the HUBER Belt Dryer BT
Condensation stage with heat extraction and fully automatic heat exchanger cleaning
HUBER Belt Dryer BT 16 with integrated maintenance platform
Processing dewatered sludge
The Belt Drying Process
The entire belt drying process steps consist of the following main components and process steps:
Intermediate storage and feeding
To ensure continuous drying operation, the dewatered sewage sludge to be dried must be temporarily stored in a sludge bunker. The sludge is then fed from the sludge bunker to the dryer by means of a pump. To ensure continuous drying operation, independent of the operating time of the dewatering system, the dewatered sewage sludge is temporarily stored in a bunker. Special sludge pumps convey the sewage sludge to the belt dryer.
Belt dryer
The sewage sludge is fed onto the drying belt with an extruder, a feeding system specially developed for this application. This creates a defined, easily flowable layer of sludge, which is the basic prerequisite for efficient, uniform and low-dust drying. The sludge is slowly conveyed through the dryer and dried to a dry matter content of up to 95% TDR by means of hot air.
Provision of heat
The use of sustainable energy sources is clearly the focus when drying sludge with a belt dryer. The intelligent heat utilisation system of the HUBER Belt Dryer BT allows the use of any kind of waste heat for the drying process.
The most common examples are waste heat from combined heat and power units (CHP), process waste heat or the use of saturated steam downstream of a steam turbine for electricity production. Heat pumps can also be used to supply heat. For example, the wastewater treatment plant effluent can be used as an energy source using the HUBER Heat Exchanger RoWin.
Conveying and storing dried sludge
After drying, the sewage sludge is transported to a silo or containers or is loaded directly onto trucks, depending on the degree of drying. The necessary conveying units are optimally matched to the degree of dryness of the sludge. Generally, the is used. However, other conveyors, such as bucket elevators or tube chain conveyors, are also possible.
![[Translate to English (GB):] Design sketch: HUBER offers customised plant solutions for belt drying of sewage sludge.](/fileadmin/user_upload/huber-technology/application/02-sludge-treatment/02-thermal/img-application-belt-drying-sketch-en.png "[Translate to English (GB):] Design sketch: HUBER offers customised plant solutions for belt drying of sewage sludge.")
Media
Videos and Animations
FAQ
Frequently Asked Questions
For internal heat recovery, the residual heat of the dryer exhaust air is transferred to the dryer supply air by a heat exchanger, thus drastically reducing thermal energy consumption.
Storage volumes for the sludge bunker vary between 5 and 1,000 cubic metres, depending on the application. The storage size depends on several project-specific factors. For example, the running time of the dewatering units or the common delivery times for external sludge can be mentioned as influencing factors. But the planned running time of the drying plant also has an influence on the size of the intermediate storage tank. The aim is to dimension the sludge storage tank so as to ensure a continuous drying process.
The HUBER Belt Dryer BT, with its special extruder feed, has been designed for drying municipal sewage sludge with a DR content of approx. 16-35%. If other types of sludge are to be dried, for example industrial sludge, a precise laboratory analysis must be carried out beforehand.
The water vapour produced during drying is precipitated by the vapour condenser. There are various ways to process the vapour condensate so that it can be disposed of safely afterwards. Part of the heat used for drying can be recovered and fed into a district heating network, for example.
