The BTS is a low-temperature belt dryer from STELA that was specifically developed for drying sludges. As a 2-belt dryer with reheating, it achieves high drying performance on a compact footprint. The main area of application is the drying of sewage sludges from municipal and industrial wastewater treatment plants; in principle, the BTS is suitable for a wide range of pumpable, moldable, and lumpy sludges.

BT and BTL each operate with a single drying belt that is continuously ventilated from top to bottom. The BTS, on the other hand, is a 2-belt dryer: both belts are flowed through from below by the same air stream, which is reheated between the belts. As a result, the BTS achieves a high evaporation capacity with a more compact design; furthermore, material input and output are on the same side of the system – an advantage for the integration of back-mixing systems. While BT and BTL are available in different belt widths (2,000 to 8,400 mm), the BTS operates with a fixed, actively ventilated belt width of 3 m and is instead scaled to the desired throughput via the overall length.

A single BTS machine covers water evaporation capacities from 500 to 5,000 kg of water per hour. The specific design is determined by the overall length: standardized modules are lined up for the desired evaporation capacity.

The drying air flows first through the lower, then the upper of the two belts. Between the two dryer levels, the air is reheated in an additional heating coil before it flows through the second belt. This intermediate heating increases the evaporation capacity without the system having to grow in width – the design remains compact, which particularly facilitates integration into existing buildings. In combination with recirculating air management, energy efficiency can be further increased.

The BTS is modularly adaptable to different sludge consistencies: liquid sludges can be processed from a DS content of approx. 10% via back-mixing, pumpable and moldable sludges from approx. 20% via a pump with a die (see “STELA Matrix Feed”), and solid and lumpy sludges from approx. 40% via a double distribution screw. 

The STELA Matrix Feed is the BTS feeding system for pumpable and moldable sludges from a DS content of approx. 20%. The sludge is applied to the drying belt via a pump through a die, thus bringing it into a form suitable for drying. 

The thermal energy consumption of the BTS is – depending on equipment and temperature level – between 0.8 and 1.2 kWh per kg of evaporated water. Through intermediate heating and optional recirculating air management, energy efficiency can be further increased.

Yes. Via a condenser, the BTS can be operated without exhaust air or with significantly reduced exhaust air volumes. Optionally, an additional exhaust air cooler or scrubber is available, which lowers the exhaust air temperature – this also enables the use of temperature-sensitive, downstream exhaust gas cleaning systems.

The optional cooling screw cools the dried sludge while it is being transported out of the dryer. This is relevant, for example, when the dried sludge is to be stored safely in silo systems.

The BTS is heated indirectly via a heat exchanger, which ensures high operational reliability and efficiency. All common media are suitable as heat transfer media: hot water, steam, or thermal oil.

The BTS is designed as a modular system: for the desired water evaporation or the desired throughput, standardized modules are lined up in length, while the actively ventilated belt width remains constant at 3 m. This allows the system to be precisely designed for medium and large drying projects – from 500 to 5,000 kg of water evaporation per hour with a single machine.

With the BTS, the heat exchangers can be pulled out of the side of the system for maintenance. The following generally applies to STELA belt dryers: They are designed for continuous operation of 2,000 to 2,500 hours, the drying belt has a service life of up to 40,000 operating hours and can be replaced by operating personnel in 4 to 6 hours, and annual maintenance costs are around 1% of the purchase price.

Yes. The BTS is fundamentally designed for a wide spectrum of sludges – from liquid to solid and lumpy. In addition to municipal sewage sludge, it is therefore also suitable for industrial sludges, for example from dairies, breweries, the paper and pulp industry, or the chemical industry. The specific design is carried out project-specifically via the appropriate feeding system.