The Organic Cellulose Fibre or Biomass
The organic fibre from processing MSW using a Seerdrum is extracted via an integrated trommel screen at the discharge end of the Seerdrum. The analysis of this raw pulp is dependent on the incoming MSW in terms of analysis, density and moisture content. Also, the trommel screen hole opening is important. It is generally assumed MSW is 25% moisture content, has a bulk density of a maximum of 250kg/m3 and contains a maximum of 50% organics comprising food, card and paper. In reality, MSW varies greatly in its analysis but with adjustments to the Seerdrum process a high organic fraction raw fibre can be produced.
Up to 240 litres water, hot or cold, is added to the Seerdrum inlet with the waste inflow to achieve the necessary pulping and extraction of the organics. This water can be low grade water or process waste water from food and beverage manufacturing, so, a useful method of disposal of these waters. The water addition is dependent on the waste moisture content.
The raw pulp is shown below and will have a percentage contaminants of inert material that also fall through the trommel screen openings. To improve the quality of the organic fraction recovered from the waste, it will need refining.
Generally, refining is required before the material is used for conversion to energy and this will be subject to local approvals.The refining can be undertaken in two ways. Using a MRF or by a washing system.
Vickers Seerdrum do not manufacture or supply MRFs or washing systems but can recommend partner companies to work with. For information, the two methods are described here.
MRF Refining of the Organic Fraction
This is the method used at Yellowstone Composting Facility where the Seerdrum produced organics are mixed with shredded green waste and dung before In Vessel composting. After the composting phase the product is not only matured but dried to around 25% moisture content. It is then passed over a MRF using 10mm screen, grit removal air classifier for lights to deliver the final compost product is shown below. Alternatively, this would make a good biomass fuel for renewable energy generation.
The In Vessel composting step can be omitted and replaced by low temperature drying. The dried biomass is then sent to the MRF for refining as described above.
West Yellowstone Composting Facility:
Seerdrum supplied by Vickers Seerdrum Ltd, UK
Composting technology supplied by Engineered Compost Systems ECS, USA.
Email : firstname.lastname@example.org
The MRF typically may include plastic film vacuum or air knife, overband magnet, eddy current separator, shaker screen an optical plastics sorter and air classifier. The quality of the final product is dependent upon the input material analysis and the trommel size screen opening specified in the Seerdrum.
The refined biomass using this process delivers a product of with approx 25 percent moisture content and a calorific value of approx 13 GJ per tonne.
Refining the Organics by Washing
This method produces a cleaner organic end product and of a finer composition when compared with the MRF. The Seerdrum would be operated as normal but instead of sending the recovered organic fraction to a MRF, it is sent to a washing system. This delivers three products:
Washed clean organic material in the 1 - 10 mm range.
An organic rich wash water.
The organic solid are de watered to 60% moisture using a screen and dewatering screw press making them ready for use as a biomass fuel.
The organically loaded wash water is sent to a high rate Anerobic Digester for biogas production. This AD doubles as the water treatment system and sends the treated water back to the washing system.
Both biogas and the biomass can be used for renewable energy production.
The gross calorific value of the refined biomass dry content is around 12 GJ/tonne.