Février 2012
Screening Technology for Biomass

The company Backers has 2 variations available for processing biomass.
1.Biomass made of root wood and cleared timber:
Root wood, cleared timber (and old wood) is roughly broken up and stored for 1-3 weeks so that the sand and soil sticking to the wood is pre-dried. At the IFAT- VDMA demonstration days, the company Backers Maschinenbau GmbH showed a starscreen 3-mtb processing this material. With the three-fraction starscreen, the material is roughly screened at 150 x 250/300mm to start. With the screening process, the fraction 0- 150 x 250/300 is thoroughly pre-cleaned and then the product fraction is freed of sand, soil and other fine particles at 14 mm on a 6.8 m long fine screen.

The advantage of this procedure is, on one hand, in braking the product with large pre-crushers. The rate is very good, the energy consumption very low and a large, rough pre-crusher is robust against stones and other impurities thanks to the large rotor rollers. Furthermore, the starscreen also displays a very good screening performance with optimum cleaning effect on the roughly broken material. In order for the performance to be right, it is important that the screen can work on binding soils and that the transport of the material from the machine works well.
The starscreen is mobile with the wheel crawler, making it particularly suitable for this application because is it driven by articulated lorry to the place of use and moved with the crawler chassis.
Compared with the production of logs, wood chips and pellets, the cost for fire wood is much more cost-effective after the described process.


2. Biomass made of wood chips:
Incinerators work best when the wood chips are free of dust and fine materials as well as excessive lengths. It is also an advantage for the storage of wood chips (development of mould, drying and spontaneous combustion) that fine dust particles are separated. The 3-fraction starscreen from Backers meets these requirements with its new starscreens.

The rough screening process takes place first whereby the rough screen sorts out excess lengths up to approx. 200 mm. At the same time, the wood chips are loosened in the first screen section and given a fine screen coat in the second. With the premium starscreen, they are screened at 5 mm and material parts that are somewhat longer, even if they are finer than 5 mm, remain in the chip material. This means that the burnable wood chips remain at big as possible, which reflects positively on the energy balance! For the production of wood chips, the important thing is to achieve a high screening performance with good cleaning of the energy fraction. With a three fraction starscreen from Backers, 150-200m³/h wood chips can be freed of excess lengths and fine materials. Because the fine materials are screened three-dimensionally at around 5 mm, they can be used for the production of pellets.