KREVOX European Environmental Centre
00-680 Warsaw, Żurawia 45n str.
tel. +48 22 756 52 20,
fax. +48 22 756 50 33

BDS Belt Dryer

BDS sludge belt dryer (BDS)

The Andritz SYS belt dryer is offered on the Polish market by Krevox Europejskie Centrum Ekologiczne, the company's sole representative. It's a unique technology that found its way mainly in drying communal waste sludge. During the last 6 years, the BDS drying technology has gained over 20 reference sites. It was chosen by such companies as: Degremont or OTV(Veolia).

Process description

The sludge for drying is being kept in a tank and supplied in a continuous manner to the feeding and mixing screw with a help from speed-controlling feeders. Part of the dried up granulate is recirculated via a feeding screw to the mixer and mixed with dehydrated sludge. The feeding screw carries a product with approx. 60-65% d.m. content to the distribution screw, supplying and evenly dozing the product to the dryer's belt. The distribution screw and roller will ensure even sludge mixture layer distribution on the entire width of the belt. Sludge layer on the belt, depending on the process parameters can be adjusted from 4 to 20 cm. As the product moves through the dryer, it is heated by hot air and dried. After passing through the drying zone, the product is chilled in the chilling zone, so the temperature of the granulate after leaving the dryer does not exceed 50 °C. At the end of the belt, the product is unloaded and part of the granulate is recirculated in order to mix it with dehydrated sludge, and the rest is drained outside of the system

Heat creation

The dryer is adapted to performing the continuous drying process, while omitting heat and indirect exchanger. In case of direct drying, the drying heat is produced during the fuel/biomass (natural gas, biogas, heating oil) burning process. The high-temperature fumes mix with air circulating inside the drying system in order to create an air mixture with 100-150°C temperature
An extremely important advantage of the BDS dryer is the ease of linking it with the available waste heat sources, such as heat plant/cement plant chimney fumes, technological steam.

The belt dryer has three sections: two heating sections (red arrows) and one cooling station (blue arrows). The heated air with a temperature of approx. 130oC is inserted into the dryer via top-blowers, visible on the picture below. The dryer has two independent drying sections, in which the drying temperature is regulated automatically.

Control and automation

The system is controlled and operated by a PLC controller (programmable). Turning the system on and off is done almost automatically, via previously programmed sequences. Besides the normal turning on and off modes, there are additional sequences: Quick Start and Quick Stop. The quick mode is used for turning the system on and off in a very short period of time, i.e. 5 and 15 min. accordingly.
During operation, the programmable controllers control and monitor proper data. The system is equipped with 4 cameras, allowing constant view of the system's strategic points.
Besides occasional supervision, the system does not require the presence of personnel, at night this can be done automatically (service-free mode). In case of a failure in the power system, changing sludge parameters or dehydration exceeding the acceptable range, the controller will automatically and safely turn the system off. End product dry mass is monitored via constant measurements. Besides the usual controlling and monitoring functions, the display also shows the characteristic operation curves, error messages, regulator settings and limit values (current or archive); all the data can be printed. The data can also be transferred to the main controlling system via an interface or to the third-party user via modem.

Safety technique

The system's safety is very important. The drying system, based on risk analysis (HAZOP and ATEX) functions as part of the newest EU requirements (in force since the second half of 2003). Basically, one has to remember that the drying method selected and the temperature parameters guarantee a high level of safety, since critical temperatures or dust concentrations do not occur. However, we equipped the system with additional security devices. A high level of automation and constant monitoring of the safety parameters result in the system being cut-off in case of a mistake by the operator or exceeding limit values. The system performs constant CO, CO2 and dust concentration measures in the drying air. In case of exceeding any of the norms, the system will shut off automatically and a sprinkler in the drying/burner section will be activated automatically.

BDS belt drying system advantages.

Belt dryers have been used for a couple of years now. Their reliability and simple use work great in every-day situations. Amongst many BDS dryer system's advantages, the main ones are:

• process flexibility – thanks to the recirculation of part of the granulate, the change in hydration of the sludge after mechanical dehydration does not impact the process and the end product quality

• dust-free granulate production with very good fertilizer and fuel qualities

• module construction of the installation allows its extension through a dried granulate burning module

• maximum sludge volume reduction thanks to achieving a granulate with a high bank density, which drastically reduces the storage or transportation costs

• low energy consumption – in case of using granulate in the burning process, additional energy is usually not required

• no odor emissions to the inside

• safety – temperature during any part of the process does not exceed 150oC, constant CO, CO2 and dust concentration measures, sprinkler system, four CCTV video cameras.

• closed drying air circulation, which, as a result, minimizes heat losses

• the heating chamber has a slight underpressure, which prevents drying air or dust from flying outside of the device

• automatic start and stop in a very short period of time, dozens of hours of downtime without delaying the installation, e.g. for the weekend

• the ability to dry partially and produce a 60%³granulate with dry mass content

• in case of indirect drying, only one heat exchanger – low operational costs and high reliability

• simple design – little peripheral equipment

• all elements having contact with the sludge outside of the belt are made of 1.4301 stainless steel

• more than 20 reference sites for 5 years

• technology based on 35 years of experiences drying sludge

• technology fully compatible with proper Directives' requirements EU (ATEX, HAZOP and others).


Below is a list of basic largest belt drying plant data, regarding the biggest belt sludge drying station in Karlstadt, Germany.

Belt dryer - Karlstadt / Germany


8000 kg/h

Sludge from over 20 plants

Heat source

Waste heat from the cement plant


24 h/d, 7 days a week

Financial product

dry granulate > 90% d.m.



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