Solid waste with high calorific value can be processed to produce alternative fuels that replace primary energy sources in cement and power stations. A new plant in Germany exemplifies this technology and is able to accept both mixed and pre-treated waste.
The shortage of landfill space throughout Europe and the recognition that landfilling is not a sustainable long-term solution for waste management have prompted many countries to adopt landfill bans, at least for biodegradable waste. In addition, waste is increasingly being recognized as a resource in terms of both material and energy. This has resulted in a huge increase in processing capacity for alternative fuels.
Although the volumes processed are increasing dramatically, the sale and use of alternative fuels are dragging well behind. Disposal companies are having trouble finding a market, particularly for lower-quality alternative fuels.
Generating fuel from waste
Waste for alternative fuel production usually arises from one of two sources. Mono-fractions are processed from separated waste and partial fractions from mixed waste. The source type determines, to a large extent, the form of the plant used for processing the material.
While mono-fractions can be processed into alternative fuel without further pre-treatment, mixed waste has to be first separated by preliminary mechanical processing into fractions that are suitable (or not) for alternative fuel processing. Examples of ‘suitable’ fractions include paper, cardboard, textiles and plastic films.
Flexible handling of the material stream and the use of the best possible processing technology enable production of quality-assured alternative fuel, with a corresponding increase in the opportunity to secure sustainable sales. Quality assurance is central to the success of this technology.
The SITA plant in Olpe, Germany
In November 2005, SITA Umwelt Service GmbH, a subsidiary company belonging to the SITA Group, commissioned a new plant for preparation of alternative fuels in Olpe, Germany. With a total capacity of approximately 80,000 tonnes per year, the plant began full operation in February 2006.
 SITA’s waste treatment plant in Olpe, Germany produces alternative fuels from solid waste with high calorific value |
The design of the plant takes into account the varying characteristics of the waste to be processed. It is divided into two separate halls, located alongside each other.
Hall one: direct processing
Direct processing of highly calorific mono-fractions of known composition takes place in the first hall. This waste, originating from trading and industrial companies, is usually delivered by lorry in bulk containers. The material emptied from the containers is conveyed by means of feeding wheels along a conveyor belt into the hopper of a WEIMA WFC 2500 ‘FineCut’ granulator (see textbox on p. 80).
The waste is introduced to the granulator in a controlled way with the aid of a vibrating post-pressure device and is subsequently granulated between the rotor and stator blades. It is then delivered via free-fall through the perforations (diameter = 30 mm) of a sieve located underneath the rotor. In this way, a material fraction is obtained with a particle size of approximately 20 mm. Residual polyvinylchloride (PVC) and other heavy constituents are then removed from this material fraction, leaving the lighter materials (higher calorific fractions) to be used as refuse-derived fuel (RDF).
RDF is ideally characterized by:
• high and consistent energy content
• chlorine content of less than 0.3% by weight
• a particle size of approximately 20 mm.
Different types of RDF are distinguished primarily by granulate size. A predictable, more uniform end product is achieved by mixing RDF from mono-fractions as appropriate with the RDF from other mono-fractions and/or mixed-fractions.
Hall two: mechanical pre-treatment
The second hall in the Olpe plant is used for separating mixed waste into two main fractions - one that is suitable for the production of alternative fuel and one that is not. The suitable fraction is processed through preliminary granulation into a particle size of 200-300 mm, deposited into containers, and transported by lorry to the first hall (approximately 50 metres away). This refined fraction can then be mixed with the RDF from mono-fractions as appropriate. The fraction that is not suitable - the mid-calorific fraction - is usually disposed of by incineration.
The rationale behind this approach
The main advantage of this approach is that treated waste can be fed directly into the system (without requiring further pre-treatment) in addition to standard mixed waste. The plant therefore offers flexibility in treating waste from different sources. It can also offer capacity to other sites that may be full or unable to process a certain type of waste.
In addition, it is possible to optimize the energy content of the final product; low-energy fractions can be enriched with high-energy fractions and an overall optimum energy content set. The energy content of processed alternative fuel lies in the range of 19,000-25,000 kJ/kg.
Market outlook
Germany is playing a pioneering role in Europe - and perhaps worldwide - with its ban on the landfilling of untreated waste. As a consequence, its capacities for the production of RDF are increasing. However, some producers are finding a problem obtaining a market for their product. As time goes by the market may consolidate and the market indicators may change, for example, as a result of the ever-increasing price of fossil fuels. (To read more about the demand for RDF in Germany, see two articles in the May-June 2006 issue of Waste Management World .)
The primary markets for these alternative fuels are the power and cement industries. The European Cement Association (CEMBUREAU) recently released position papers on when a waste ceases to be a waste, the European Commission’s Thematic Strategy on the Prevention and Recycling of Waste, and the revision of the Waste Framework Directive.
CEMBUREAU comments that the use of waste in the production of clinker is undoubtedly a recovery operation of both the energy and material content. However, it believes that neither the thematic strategy nor the revised Waste Framework Directive should lead to a wholesale declassification from the waste status, thus enabling operators to bypass relevant waste legislation.
For wastes to be considered as alternative fuels, CEMBUREAU states that they should:
• be processed in a recovery operation for use as substitutes for raw virgin materials and fuels
• be intended for use in a specific, well defined installation or process
• meet technical specifications and requirements
• be processed under environment and health standards at least equivalent to those achieved under the current waste legislation
• be subject to quality control
• perform well as alternative fuels - demonstrating a long-term positive record in technical, environmental and health terms
This position sets a challenge for the waste industry, which must show it can deliver reliable alternative fuel. Both the cement industry and power plants will not purchase the fuel if they think that their business will be compromised. By working more closely with these industries, there is greater scope for developing this market, as well as offering much-needed treatment capacity for diverted waste.
Harald Hoffmann is Sales Director at WEIMA Maschinenbau GmbH, Isfled, Germany.
e-mail: Harald.Hoffmann@weima.com
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The WEIMA granulator
At the heart of the Olpe treatment plant is the WFC 2500 FineCut granulator. Its rotor has a diameter of 800 mm, with a working width of 2500 mm. This large surface area offers a mechanism for dissipating the heat generated by friction, thus preventing processed plastics (and other materials) from melting.
 The granulator used at the plant |
The electromechanical drive has a power rating of 250 kW at a rotation speed of 160-320 revolutions per minute (rpm). The machine runs continuously and has an output of approximately 6-8 tonnes per hour. Constant operation is vital, according to Heiner Biermann, the manager of the Olpe facility: ‘Our production runs practically around the clock. This requires robust engineering and good technical support’.
The life of the blades is approximately 150 hours when using conventional blade steel. Extensive trials have confirmed that blade life can be increased to 500 hours with the use of a hardened metal. The blades can be reversed and adjusted precisely to maximize efficiency. Central lubrication prevents damage to the rotor’s bearings.
 The rotor with blades |
Maintenance of the entire plant takes place on a weekly basis (each Saturday). Heiner Biermann adds: ‘several maintenance operations, such as setting the cutting gaps and changing the blades, can be performed very quickly due to the good access via hydraulically operated contamination and inspection flaps’. The sieve, which is segmented and made of Hardox metal, only needs changing once a year.
