Ligno-cellulosic biomasses may be converted to biochemical products and fuels by means of different conversion processes.
Before entering a conversion process, the harvested ligno-cellulosic biomass is usually subjected to an initial processing for rendering the ligno-cellulosic biomass compatible with the conversion process and equipments.
It is desirable to remove inorganic components of the ligno-cellulosic biomass, such as silicates, salts and mineral elements, which are detrimental for the conversion process or equipment.
There is also the need to raise the water content of the raw ligno-cellulosic biomass, which in some cases are received in the conversion plant very dry.
Another problem arising in handling ligno-cellulosic biomasses received in the conversion plant is the presence of external contaminants, such as stones, gravel, sands, sand, dust, clay, metal objects which are present together with the ligno-cellulosic biomasses.
Different equipments and processes have been developed so far for preparing the raw ligno-cellulosic biomass to be further processed.
One approach is to carry out the preparation steps sequentially. As an example, the external contaminants may be first removed from the raw ligno-cellulosic biomass, for instance by means of air floatation equipments, and metallic objects are removed by means of magnetic separation devices. Thereafter, the raw ligno-cellulosic biomass may be treated with water and optionally additives, thereby washing the biomass and increasing its water content. Different methods for washing and/or soaking the biomass are used, typically providing mechanical agitation of the ligno-cellulosic biomass. In this case, an extended biomass handling section is present in the conversion plant, said biomass handling section containing many equipments, usually connected with conveyor belts, to convey the biomass. The distributed approach increases the capital and operative costs, as well as the risk of failure.
A different approach is to integrate the preparation steps into a unique equipment. As an example, in U.S. Pat. No. 8,771,472 an apparatus and a related methods for treating material by cutting, soaking and/or washing of the material are disclosed. The apparatus comprises a receptacle, a discharge element with a vortex generator and pumping means arranged to pump fluid and material from the receptacle towards the vortex generator, wherein the vortex generator and pumping means in combination are adapted to generate a vortex in the form of a conic helix in the fluid extending into the receptacle.
In US2008054108 a pulper having a tank for receiving materials to be shredded and a drive having a rotating hub within the tank id disclosed. A rotor is fixed to the rotating output of the drive, the rotor comprising an annular rotatable hub and a plurality of vanes projecting generally axially from the hub. Each of the vanes has a contour that is swept back from the direction of rotation, at least adjacent the radially outermost portion thereof. The vanes have a side edge facing an axial direction and a plurality of teeth are provided on the side edge of the vanes adjacent the radially outermost portion thereof for providing rapid shredding of material with a reduced energy requirement.
It is desirable that a low amount of water is used for processing of the raw ligno-cellulosic feedstock before entering the conversion process, as the water in excess has to be treated in a waste water facility. Thereby, a trade-off between amount of water used in the treatment and effectiveness of the treatment is desirable.
It is also desirable that the process uses a low amount of energy, which is both thermal energy from heating the process water and electrical energy for supplying mechanical agitation means.