Sustainable solid fuel can be obtained from biomass using a thermal process. In this technology, wood waste, e.g. from packaging companies, is used to produce reusable coal. The wood is treated during torrefaction, i.e. a charring process in the absence of air and at high temperatures. This thermal treatment increases the mass and volume-related energy density and therefore the calorific value of the raw material.
Mills and classifier systems from NEUMAN & ESSER are used in the grinding process. The wood waste is turned into high-quality coal powder. To produce coal powder, the wood waste is first sieved and coarse pieces and impurities are removed. They are then pre-shredded using a hammer mill. After torrefaction, a conveyor belt transports the wood to the feed container of the grinding system. From there, it is continuously fed via a dosing screw and a magnetic separator to the feed lock of an impact classifier mill, which reduces the wood to the desired particle size in order to increase the specific surface area and thus ensure efficient combustion and energy generation. The powder is then separated from the process air in a cyclone filter.
Impact classifier mills are ideally suited for the size reduction of brittle solids to a defined particle size limitation. Our patented ICM impact classifier mill combines efficient impact comminution with sharp separation in a single unit. The desired fineness of the final product is infinitely adjustable via the classifier wheel speed.
As torrefied wood often contains impurities such as sand, the high-speed ICM classifier mill requires special wear protection measures. The grinding speed, which has a disproportionately high influence on wear, has therefore been reduced by a third and the replaceable linings in the grinding chamber as well as the grinding and classifying tools have been designed to be extremely wear-resistant.
A cyclone filter is installed downstream of the impact classifier mill. It combines the principle of separation in a cyclone with inlet spiral, cylindrical housing and discharge cone with the advantages of a cartridge filter. The compact and pressure shock-resistant filter saves costs and installation space. The integrated radial fan eliminates the suction line from the filter to the fan, the sound insulation of the fan housing and the explosion.
A company produces coal from biomass, for which the biomass is torrefied at temperatures of 250 to 300 °C in the absence of air. To ensure that the wood can be used as an efficient fuel in furnaces, the "biochar" must be milled. For its production plant, the customer decided to make use of our grinding and classifying expertise and extensive experience in grinding a wide variety of materials. The scale-up was based on grinding tests on the demonstration plant at our Test Center in Übach-Palenberg. We then received an order for an ICM 240 grinding system for an input mass flow of 5,000 kg/h. In the production of its coal powder, the customer uses a hammer mill for comminution after screening its wood. In the grinding system, it is continuously fed via a dosing screw and a magnetic separator to the feed sluice of the classifier mill. The classifier mill reduces the wood to the average particle size of d50 = 150 μm required by the customer.
After the grinding and classifying process, the powder is suctioned out of the mill into a cyclone filter where it is separated from the carrier air flow. A rotary valve transports the finished coal powder out of the filter. By means of pneumatic conveying, it finally reaches a finished product silo with a loading station for silo vehicles. The grinding plant with the ICM 240 impact classifier mill effortlessly achieves throughputs of up to 5,000 kg/h.
