A waste autoclave is a form of solid waste treatment that utilises heat, steam and pressure of an industrial autoclave in the processing of waste. Waste autoclaves process waste in batches. Saturated steam is pumped into the autoclave at temperatures around 160°C [1]. The pressure in the vessel is maintained at 5 bar gauge for a period of up to 45 minutes to allow the process to fully 'cook' the waste. The autoclave process gives a very high pathogen and virus kill rate.
Modern autoclaves, also referred to as converters, can operate in the atmospheric pressure range to achieve full sterilization of pathogenic waste. Super heating conditions and steam generation are achieved by variable pressure control, which cycles between ambient and negative pressure within the sterilization vessel. The advantage of this new approach is the elimination of complexities and dangers associated with operating pressure vessels.
Contents |
Process results
The 'cooking' process causes plastics to soften and flatten, paper and other fibrous material to disintegrate into a fibrous mass, bottles and metal objects to be cleaned, and labels etc. to be removed. The process reduces the volume of the waste by ~60%. After 'cooking', the steam flow is stopped and the pressure vented via a condenser. When depressurised, the autoclave door is opened, and by rotating the drum the 'cooked' material can be discharged and separated by a series of screens and recovery systems.
In early systems, the primary product was cellulose fibres. This comprises the putrescible, cellulose and lignin elements of the waste stream. The biodegradability of the waste has not been affected by the autoclave and so must undergo further treatment to reduce its reactivity prior to landfilling. The fibres can be fed into anaerobic digesters to reduce the biodegradability of the waste and to produce biogas. Alternatively the fibre could be used as biofuel.
Newer technology systems wash out hydrolysed hemicellulose sugars and most of the protein as water-solubles. The remaining materials, after simple physical separation (trommel screen) has several valuable uses. One newer system is able to dry the cellulose during processing using heat, and another newer system is able to dry the cellulose (much more economically) using pressure and steam kinetics.
After fibre separation, the secondary streams comprise of mixed plastics, which have normally been softened and deformed which eases separation, a glass and aggregate stream, which can be exceptionally clean of both plastic and paper, and separate ferrous and non ferrous metals. The heat, steam and rotating action of the autoclave vessel strip off labels and glues from food cans leaving a very high quality ferrous/non-ferrous stream for recycling.
With the removal of water, fibre, metals, and much of the plastics, the residual waste stream for disposal may be less than 10% by weight of the original stream, and is essentially devoid of materials that decompose to produce methane. Systems in Europe meet and exceed all of the European waste treatment and recycling requirements.
The full process of loading, treatment and sorting is normally completed within 90 minutes in earlier models, and with the advent of newer technology, the cycle time has been decreased to one hour. In a typical "new" configuration, 2 10-ton units operating side by side would treat over 400 tons per day with time for preventative maintenance.
The size of the vessel varies between vendors. Experience shows that "small" vessels are not productive enough; while if the vessel is too large, the pressures in the vessel and the heavy weight of the vessel can cause equipment failures.
Commercial Application
Sterecycle and Re3 (www.re3group.com) currently operate industrial scale autoclave plants.
The Sterecycle plant has been operational in Yorkshire since June 2008 and is operating 24/7. This plant can process 100,000 tonnes per annum of waste, treating waste from Rotherham council under a long term contract. Sterecycle builds, owns and operates waste recycling plants, processing residual waste as a substitute for landfill.
Re3 has developed and constructed a new multi-million dollar dual autoclave facility in Limerick, Ireland. It is transforming tonnes of household and commercial waste into valuable biomass fibre - a clean, green alternative to fossil fuels. It also recovers valuable recyclables such as metals and plastics. A film showing and demonstrating the Re3 autoclave process in action may be viewed at www.re3group.com. Re3 is now preparing to introduce plants in the United States, Canada, South Africa and the Far East. The Re3 Process is a viable economic alternative to landfill and incineration. It's ideal for municipalities and businesses that want to reduce waste and re-use it for heat and power. The Chief Executive Officer of Re3, Professor Deborarh Boyd, was recently awarded the 2009 Sustainable Ireland Environmental Leader of the Year Award for her development of Re3 and autoclaving technology.
External links
- Re3 Limerick, Ireland. Autoclave Recycling Solutions - See Video
- FISSORE Agency - Screening & Recycling Solutions
References
- ^ Fibrecycle Process Environment Agency Waste Technology Data Centre Evaluation of Estech Fibrecycle Process
|
||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
