Lohse Systems

Premises

PROMECO has been representing for years in Italy the German company Lohse, one of the most reputed suppliers of systems for the treatment of biowaste for use in the anaerobic digestion wet.

The cooperation with Lohse allowed to the supply the system of the German company pre-treatment to some of the most important Italian industries in the field - both public and private.

The pretreatment systems engineered and produced entirely by Lohse have many advantages:

• Flexibility: they are suitable for many different materials, such as the organic fraction of municipal solid waste; green and garden waste and agricultural biomass; organic fraction of MSW; food waste from households; food waste reject from food industries and packaged food waste and in general. 
  In particular:
• The dry portion of the input material can vary from 15% in case of food waste, to the 50% of some pre-selected organic waste from households.
• The continuous process in batches allows, by increasing the residence time in the pulper of the material to be treated, even the dissolution or the shredding of the most difficult materials.
• Improvement in yields of the anaerobic digestion: the vigorous mechanical action exerted on the material to be treated determines its complete disintegration. The small size of the material sent to digestion, increasing the contact surface available for the bacterial action, make possible a significant increase in efficiency and yields of the process.
• The possibility to treat input material with average size of around 150 mm allows to avoid the preliminary reduction in size (through shredders), thus lowering cost of plant and operations.
• Pulping and removal of impurities are stages of the process implemented in two distinct phases, with machines optimized for the specific task: the hydropulper and the Multisorter
• Heavy contaminants/impurities (rocks, gravel, metal, ceramics, batteries, etc..) are eliminated in the Hydropulper, which acts as a flotation tank. This protects downstream equipment and pumps.
• Light materials (laminates, plastic film, textile, etc..), are usually not affected by the Hydropulper action. Maintaining the same size they had when entering into the system, their capture by the system Multisorter is facilitated. This reduces the percentage of impurities/contamination in the digester, and allows to avoid the formation of floating impurities layers.

Description of the process

Following the separation of the waste as it is, obtained by means of the lines of separation between organic and inorganic fraction, the screen “unders” is collected by a system of conveying belts positioned below the sieve. Passing through a magnetic separator, the conveyors send the material to the hydropulper loading system. Hydropulper separates the different fractions present in the waste; as a result, a “clean” organic suspension will be sent to anaerobic digestion.

The hydropulper is an equipment dedicated to the selection of waste, or of heterogeneous mixtures of two or more different wastes. The selection made in a “wet” status, taking advantage of the dilution of the input material with water. It is accomplished in two stages and is implemented by two distinct machines:

• Hydropulper:  allows for the dispersion and dissolution of the organic fractions in water, by mechanical stirring. This mechanism leads to:
• disintegration and dispersion, in an aqueous solution, of the organic fractions.
• Gravimetric separation of the various materials by difference in specific weight. The heavy materials, with higher specific weight than water, will sink and are separated by sedimentation. The organic suspension and the light fraction is sent continuously to the multiple separator (MS).
• Multisorter: the light fraction is removed by flotation, and conveyed away by augers, while the inert fraction is decanted through the mesh of the sieve and extracted by a screw. The organic substance, dissolved in water, flows by gravity.

Materials treatable

• Screen “unders” from mechanical sorting of municipal waste
• Separation of heterogeneous plastics (PVC and PET interception or PE)
• Agro-food food waste in box, tin or glass
• Packaged food waste (ice cream, yogurt, dairy products, etc..)
• Paper pulper waste
• Wood waste mixed with plastic
• Heterogeneous waste materials consisting of heavy, light and organic materials.

Treatment capacity

Treatment capacity depends on the model of hydropulper, whose volume can vary from 6 up to 26 cubic meters, and according to the type of the material fed, which requires different times of permanence in the hydropulper, thus determining its volume.

System components

The system is composed by:

• Hydropulper
• Multisorter (separating multiple)

HYDROPULPER

The hydropulper for organic waste is formed by:

• Tank
• Mixing rotor
• Control unit
• Heavy fraction discharge system
• Screw conveyor for heavy fraction
• Drain pipe

Tank
The tank is cylindrical with conical shaped cover. The base of the tank is bound to the edge of the cylinder by highly resistant welding. The lid is flanged on the edge of the cylinder and is made of high strength material. The tank is supported by four legs,  welded to the base and to the sides of the cone and supported by a concrete foundation. The tank is entirely manufactured in stainless steel. The heavy fraction discharge outlet is flanged at the center of the cone base. The hub connected to the rotor is flanged to the center of the conical cover, which has an inspection opening with fanlight openers, an opening for the feeding of waste by means of the conveyor and other openings for the introduction of process water and various metering probes. After welding, the inner and outer walls of the tank are sandblasted, pickled and subsequently coated with a special resin. The suspension of material is removed by a pipe of stainless steel provided with exhaust damper, positioned at the base of the tank.

Mixing rotor 
The pre-treatment of organic waste, in particular waste containing impurities/contaminants, can cause problems in moving. For this reason the rotor, whose rotation axis coincides with the axis of the tank, is flanged to the hydropulper top part. The rotor has three different speeds of rotation and rotates around a tube that represents the axis of the rotor. A disc for mixing, equipped with teeth, is bolted in the terminal part of the rotation shaft. The rotor is designed in such a way that the organic waste are dissolved and dispersed in an aqueous solution. The ability to dissolve the organic waste in water is increased by the presence of baffles, bolted to the inner wall of the tank. The rotor blades are subject to wear, and for this reason the  teeth bolted on the blades are replaceable. The spiral is moved via a drive belt connected to a three phase electric motor. The motor is bound by means of terminals to a support bracket. The drive belt is protected by a guard for safety reasons.

Control unit 
The control panel is designed to be connected to PLC controlling the entire plant.

Heavy fraction discharge
The materials with a higher specific weight (such as stones, glass, metal and bone fragments) fall to the bottom of the tank during the mixing process. To remove these materials, an accumulation sump is specially welded to the bottom of the tank. The sump has a rectangular section: the flow in it may be interrupted by two valves, one positioned on top, one on the bottom. The opening and closing of the valves is controlled by two pneumatic cylinders, independently from the operation of the ongoing process. The sump can be washed automatically, before the opening, using water introduced from the bottom of the tank through a special pipe. The washing process can be observed by means of two inspection windows incorporated in the sump itself.

Screw conveyor for heavy fraction 
The screw conveyor moves the heavy fraction into a collecting bin: it is provided with recessed guides to prevent the water backflow. A container for the excess water is communicating with the auger. Excess water extracted from the process is filtered through a grid at the bottom of the container and subsequently recirculated.

Drain pipe 
The discharge pipe, made of stainless steel, is welded at the bottom of the tank and connects hydropulper to multisorter. A drain valve is used to regulate the outflow of the aqueous suspension, at the end of the operations of mixing and after the discharge of the inert fraction. The exhaust damper is composed of three telescopic overlapping plates, which move vertically through two elements driven by a pinion gear, connected to the engine and regulated by means of the frequency converter. The opening speed of the damper can adjust the volume of suspension contained in the pulper, according to the type of waste treated.

MULTISORTER

The multisorter is composed of:

• Casing structure
• System of separation of light fractions by means of sieve.
• Screw conveyors for sand and sieved.

Casing structure 
The casing structure is made of welded steel resistant to water and mounted on four feet, welded to a base structure, which is embedded in a concrete foundation. It hosts the selection system, consisting of a worm screw and a fixed sieve. Sieve is supported by four compression springs, kept into motion by a motor connected to an eccentric shaft and mounted on cross beams.

Separation of light fraction by screening 
The suspension coming from the hydropulper is fed into the separator, and distributed on the surface the screening sieve as uniformly as possible. The separation of the light fraction takes place by means of the friction exerted by a worm screw against a circular perforated plate, which allows the passage of the organic fraction and the finer fractions, retaining the coarser fractions. Material of coarse size is made to advance, by the worm screw, up to the discharge outlet, positioned at the rear closure wall of the multisorter. 
The screening panel is partially immersed in the suspension. The movement of the screen creates a cushion of air beneath the screening surface. The air trapped under the screen is dissipated through the mesh, allowing the removal of materials. This air cushion and the oscillating movement of the sieve carry the foreign material towards the point of discharge. 
The protruding part of the sieve has a pipe for spraying water to flush the material separated from the fibers or suspension still present. The water sprayed on the emerged surface of the screen allows for a further wash of foreign material. A builkhead integrated in the structure is used to adjust the level of suspension outgoing from the system. The suspension slumping away from the bulkhead goes to digestion.

Screw conveyors for sand and screened 
Two screw conveyors (one horizontal and one inclined) are installed on the bottom of the settling zone of the aqueous suspension to remove the sand. Heavy particles contained in the suspension decant in correspondence of the horizontal screw conveyor, which conveys the material to an inclined screw conveyor and therefore to a container, provided by the customer. The discharge of the light material is done by a conveying auger, which collects plastic, textiles and anything material contaminating the organic suspension from the extraction section of the multisorter to a squeezing press, removing the excess water.