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| 32 OVER YEARS INDUSTRY EXPERIENCE | |
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| 32 OVER YEARS INDUSTRY EXPERIENCE | |
Belt dryer for sawdust, pellets, wood chips and other biomasses
Low-temperature belt dryer
The low-temperature belt dryer is a highly-efficient system for drying sawdust, wood chips, bark, wood shavings and other biomasses with low-caloric heat. Low emissions as well as a high-quality final product with low consumption values are the striking advantages of the STELA belt dryer technology.
1. Process description:
The wet product is fed continuously into the dryer. Two conveyor screws distribute at first the wet product constantly across the belt width and level it. The suitable bed depth is variably adjustable and can thus be optimally adapted to the respective requirements fast and easily.
After distribution, the product is conveyed into the drying zone by means of the belt feed. Within the dryer tunnel, the generated hot air flows through the product. The hot air is generated by means of a heat exchanger from the available heating medium. During the hot air flows through the product layer, the moisture is dried off convectively and passed on to the air flow, which cools down by the necessary withdrawal of heat.
While air can be measured out exactly along the total length and thus adapted optimally to the respective drying section. Several radial fans (multivent system) provide an exact air measuring along the total length of the dryer. Much more air is required in the feeding zone (wet zone) than in the discharge zone. An adaption to these requirements utilizes the drying air very effectively and increases the efficiency.
The product layer is ventilated from top to bottom. Fines are separated by the product layer itself, like a filter mat. Additionally, the conveyor belt filters the exhaust air a second time.
In order to achieve a dry product as homogeneous as possible, the product layer is shifted and mixed in a controlled manner after half the length of the dryer by means of a proven turning device. Thus there is a balance between the dry upper layer and the somewhat moister bottom layer. This guarantees a very homogeneous dry product at the dryer outlet for the production of a high-quality final product.
Having passed the drying zone, the product is discharged. It falls from the conveyor belt into a conveyour screw and is removed for further processing.
The drying zone is sealed off from the feed and discharge zone; consequently there are only very few leakages. Additionally, the whole drying and hot air zone is operated in slight low-pressure so that no emission of leakage air is possible.
2. Control of the product moisture:
For pelletizing, a constant moisture of the dry product is required. As the initial moisture content of the product is subject to variations, an automatic moisture control is installed.
The product moisture at the dryer outlet is controlled and monitored by continuous measuring. The belt speed is infinitely variable via a frequency controlled gear motor and adapted to different initial moistures. The belt speed and consequently the throughput decreases with high moisture contents, whereas the belt speed rises with increasing throughput with lower initial moistures.
This control guarantees a constant moisture of the dry product and optimum utilization of the supplied heat energy.
The throughput can be controlled by throttling the heat energy supplied by customer, so that the evaporative capacity and consequently the output of dry product can be adjusted without any problems.
3. Cleaning:
The drying belt is cleaned by means of a continuous dry cleaning as well as a discontinuous wet cleaning.
The dry cleaning is carried out by a belt blowing system, which removes fine dust particles from the perforated drying belt at discharge side. The cleaning rests are fed to the discharged product.
For further cleaning of the belt, a high-pressure wet cleaning system is used. A rotating ring nozzle is charged with approx. 180 bar by means of a high-pressure pump. The generated water jet cleans the belt reliably from sticking deposits (like resing, lignins, grease). The rotating nozzle moves across the belt width by a pneumatic linear drive and can thus clean the whole belt. The dirty water is collected by a collecting tray and discharged by customer via a drain pipe.
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