Valorga Anaerobic Digestion Plants
Valorga report that they can provide AD Plants for mixed MSW. across a wide range of throughputs, in the range 52,000-300,000 Tonnes per annum (Tpa) of mixed waste. For source segregated wastes the range supplied is from 10,000 to 52,000 Tpa.
The development status for their plant type is advanced according to DEFRA (UK), and is considered to be a proven process, for source segregated bio-waste and mixed household waste/ MSW.
The Valorga Process System is designed to accept the organic fraction from mixed household waste/MSW, source segregated household bio-waste.
The process stages are described as follows:-
The main processing stages:
- waste reception and preparation;
- anaerobic digestion;
- biogas utilisation;
- aerobic post-treatment/refining;
- air treatment (windrowing).
Waste Reception and Preparation
In common with almost all AD plants the waste is delivered to an enclosed reception hall. Bag-opening and shredding systems, are provided as appropriate for the waste types accepted.
A pre-digestion stage is applied to all mixed wastes which separates the organic and non-organic material.
All recoverable material which is recoverable is carried out on the separated material, for glass, metals, plastic and some types of paper.
The remaining non-digestible high calorific fraction (mainly non-recycled paper and plastics) may or may not then be used as a Refuse Derived Fuel (RDF), and this depends upon the availability of suitable market outlet(s), if no markets are available, the non-digestible fraction is necessarily landfilled.
Anaerobic Digestion Stage
Recycled water is mixed with the organic fraction of the waste from the pre-digestion stage, to form a thick sludge. This sludge is pumped into the digester.
The Valorga Digester is a large free standing vertical cylindrical design. All important heating is provided to the digester by steam injection. The plant configuration is designed to give a waste retention time of 3 weeks.
Gas is recycled into the base of the digester to provide induced mixing. The liquors removed from the digester pass into screw presses and/or centrifuges to separate the solids from the liquid digestate. The solid fraction produced is transferred to the aerobic post-treatment unit.
Biogas Utilisation
The biogas produced from the Valorga AD Process can be used for electricity and heat production, or after purification, as a substitute transport fuel in vehicle fleets etc.
Aerobic Post-Treatment and Refining
After the Anaerobic Digestion stage the fibrous material produced by the digestion is sent for maturation and drying. This is achieved by placing the material in enclosed windrows where compost is stored for a minimum of 2 weeks. Further refining of the compost is provided before windrowing, to remove “foreign articles” (usually screening), is carried out before it is put into temporary storage. If bagging is needed for an order, it is bagged whenever time is available, and after bagging checks, the final compost product is stored again, ready for dispatch (and possibly also packaging) to comply with the EU Landfill Directive and the demand from the public for sustainable land filling practices.
Valorga AD has stated that buildings will be operated under negative pressure and all process air is passed through bio-filters.
The Waste Technology Data Centre on the official Environment Agency (EA’s) web site contains data about the Valorga System, where they state that the Valorga System is a proven process, and provide other information.
Further thoughts on the Valorga Anaerobic Digestion Process advantages suggest that the AD Plants are :
- Not reliant on source segregation;
- Capable of treating a variety of organic wastes;
- Net energy production with end-use flexibility;
- Produces compost as well as a renewable energy
- Small footprint.
For more information visit the EA’s web site here.
For Valorga’s web site go here.
|
