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Efficient alternative fuel production with flexible plant concept |
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SITA Umwelt Service GmbH on a
successful path with WEIMA granulators
Alternative fuels are produced from industrial and trade waste with high
calorific value and meanwhile substitute, to an increasing extent, primary
energy sources in cement and power stations. SITA Umwelt Service GmbH, a
subsidiary company belonging to the SITA group, operates a highly modern plant
for preparation of alternative fuels in Olpe, Germany. A WFC 2500 (“FineCut”)
granulator from WEIMA Maschinenbau GmbH is integrated within the core this plant
and reduces waste suitable for alternative fuels down to a particle size of
around 20 mm, a size that is optimum for incineration. Important criteria
leading to the efficient use of the machine are its low energy consumption and
ability to be integrated within the entire plant. |
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Limited sales
capacities require top alternative fuel quality
The shortage of waste tip space throughout Europe and changing legislation have
resulted in a huge increase in processing capacity for alternative fuels.
Utilisation of the alternative fuels produced, and therefore their sales, is
however dragging well behind, i.e. the disposal companies can often no longer
sell the material, especially lower quality alternative fuel material.
Alternative fuel material is ideally characterised by high and consistent energy
content, by chlorine content of less than 0.5 weight % and by particle size of
approx. 20mm together with the corresponding particle size distribution for
consistent blowing capability.
Plant concept oriented to the material stream
Waste for alternative fuel production arise usually from one of two sources. On
one hand, mono fractions are processed from separated waste, and on the other
partial fractions from mixed waste. This type of this potential source
determines to a significant extent the form of the plant for production of
alternative fuels.
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 respectively suitable and not suitable for
alternative fuel processing. Suitable fractions consist generally of paper,
cardboard, textiles, plastic films, etc. Ideally, only those fractions from
deliveries of mixed waste reaching alternative fuel production, and thereby also
the users of the fuel, are those that also comply with the given criteria of the
processing technology used – such as, for example, compliance with permissible
heavy metal content, compliance of the chlorine content through prior
elimination of PVC, etc.
Flexible handling of the material stream and the use of best possible processing
technology enable here production of quality-assured alternative fuel, with a
corresponding increase in its opportunities for sustainable sales. The concept
behind the SITA plant in Olpe takes the different compositions of the waste
fractions to be processed into account. The entire plant is divided into two
halls in locations separated from each other, that are however located
immediately alongside each other.
Direct processing of mono fractions
Direct processing of highly calorific mono fractions of known composition takes
place via the part of the plant located in the first hall. This waste,
originating from trading and industrial companies, is usually delivered by lorry
in bulk containers by lorry. The material emptied from the containers is thrown
by means of feeding wheels via a conveyor belt into the hopper of the WEIMA WFC
2500 (“FineCut”) granulator. It is introduced in a controlled way with the aid
of a vibrating post-pressure device to the rotating rotor and subsequently
granulated between the rotor and stator blades. It is then delivered via free
fall through the perforations (d=30mm) of a sieve located underneath the rotor.
This way a material fraction is obtained with the ideal approx. 20mm particle
size that can be blown, as required by customers in the cement and power
generating industries. Residual PVC and other heavy constituents are separated
in a subsequent classification of heavy materials. Alternatively, lightweight
materials are passed on to for material recycling.
Mechanical pre-treatment of only mixed waste
Collected mixed waste is brought into the second hall. It is separated there by
mechanical pre-treatment into fractions respectively suitable and unsuitable for
production of alternative fuel. The suitable fraction is prepared through
preliminary granulation into a particle size of 200-300mm, deposited into
containers and transported by lorry to the first hall that is approx. 50 m away.
This plant concept enables efficient handling of material fractions that only
have to be granulated directly in one stage to the final particle size. In
addition, optimum setting of the energy content is possible here: 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
order of approx. 19-25,000 kJ/kg.
Local separation of the fractions to be processed guarantees high flexibility of
the entire plant. This plant concept has also corresponded in an ideal way with
the local situation in Olpe, as it enabled optimum use of two existing buildings.
In addition, optimum handling of material streams from other SITA locations is
also possible, this flexible combination resulting in maximum utilisation of the
plant’s capacity of approx. 80,000 t/a.
FineCut – technology for alternative fuel processing
The diameter of the special highly abrasion resistant rotor of the WFC 2500
FineCut granulator amounts to 800 mm, with working width of 2,500mm. The large
surface area of the rotor absorbs the naturally occurring friction heat very
well and conducts it away. This prevents possible plastification of the
processed plastics. Fast material delivery is enable by the large sieve area,
resulting from the mounting of the sieve around the rotor, and thereby the
granulator’s high output performance of approx. 68 t/h.
The electromechanical drive has a power rating of 250 kW at a rotation speed of
160-320 min-1, with step-less speed setting by a frequency converter. The
machine is characterised by very quite running of the rotor, also when under
full load. The offset, closed rotor bearings are provided with central
lubrication, eliminating laborious maintenance work and preventing damage to the
bearings.
High availability enables efficient operation
The blade life of the blades used on rotor and stators is approx. 150 hours with
use of conventional blade steel. The blade life can be increased however to 500
hours, simultaneously with sufficiently high safety against breakage, by the use
of a hardened metal, as extensive trials have confirmed. This enables a
significant reduction of wear costs for the cutting blades, which can also be
reversed several times. The counter blade has step-less adjustment, enabling
high precision cutting and therefore granulation with a high degree of energy
efficiency.
The plant works in three-shift operation, whereby maintenance of the entire
plant takes place on Saturdays, in the case of the granulator with correction of
the cutting gap and, when needed, any required change of the blades. Changing of
the sieve, which is segmented and made in Hardox metal, is only necessary once a
year.
SITA Umwelt Service GmbH in Lennestadt is a subsidiary of the disposal company
SITA Deutschland GmbH (www.sita-deutschland.de) and is therefore an integral
part of SITA S.A., a company in France that operates throughout Europe. The
services of the SITA group includes, apart from the development of waste
management and disposal concepts, in particular the collection, re-use and
disposal of waste. The SIT group sees itself as one of the leading alternative
fuel suppliers in Europe.
Entsorga-Enteco 2006, Cologne/Germany, 24.-27.10.2006, Hall 6, Stand C020/D025
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| © WEIMA Maschinenbau GmbH · September 2008 |
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