rapport 1129 Potentialbedömning av flygaskor ...

VÄRMEFORSK
dredged material but also up to 300 kg/m 3 can occur. With traditional commercial binders
such as cement and Merit 5000, with a market value of approximately 800 Swedish
krona/tonne, the cost of 100–200 kg/m 3 binders are around 80–160 Swedish krona/m 3
dredged material. The cost of binders represents about 80% of the total cost of
stabilising and may vary depending on the price of cement and Merit 5000. The cost of
fly ash has been estimated at 100–200 Swedish krona/tonne. Additional factors
affecting the cost are transportation, storage, etc. If a portion of the binder consists of
fly ash a significant cost reduction can be obtained. A binder amount of 150 kg/m 3 ,
which comprises 30% fly ash, creates a cost reduction of the binders by 25%. It is
possible that an optimization of the binder recipe may cause the proportion of fly ash to
be > 30%. Large cost reductions are therefore possible.
Use of multi-component binders requires logistical competence. The need for good
logistics is large, since several manufacturers of fly ash are needed to deliver sufficient
quantities during a limited time period. Since several fly ashes may be relevant for use,
the complexity of the project increases, which may lead to increased costs. Transport of
dry fly ash and the dry storage of fly ash, have corresponding requirements, as for
cement and Merit 5000. The cost of transport depends primarily on the distance
between the fly ash supplier and the current port. Transport of wetted fly ash (5–20%)
can be done in the “bulk” and can be stored on site, which means a lower cost than for a
completely dry fly ash. The storage period is limited by the fly ash’s reactivity, i.e. how
quickly the fly ash hardens and the amount of water added. If there is a sufficiently low
water ratio, all the “free” lime will not react with the added water. The need for quality
assurance increases if the fly ash is stored wet compared to dry.
Market – Needs and Acceptance
The method of stabilising / solidified contaminated dredged materials has been used for
a long time internationally, Holm et al. (2009) and, in recent years, even in the Nordic
countries. In Sweden, there are several examples of planned projects in the ports that
have been authorized to use the s / s method for the disposal and recycling of material,
including the Port of Gävle AB and Oxelösunds Port AB. The Port of Gävle AB received
permission in 2008 after only making one application to the Environmental
Court. Oxelösunds Port AB's permission to use s / s method was later upheld after an
appeal and finally established at the Environmental Supreme Court. Since the method
has been accepted by the Supreme Court, a praxis has been established to use the
method in future permit application processes. Another important aspect is that s / s
treatment of dredged material, and the use of the stabilised / solidified masses in geotechnical
structures, means that the masses are reused, which is supported by the new
Framework Directive (2008/98/EC) on waste where great emphasis is placed on recycling.
The Framework states that disposal should only be accepted in cases where
other options are impossible.
When selecting the method for taking care of contaminated dredged materials, a holistic
approach should be applied, i.e. technological, economical, environmental and social
aspects should be considered. A decision tool based on this approach (Multi-Criteria
Decision-tool) has indicated that s / s method is the most suitable methodology. s / s
method can be said to be the best available technology (BAT). Many ports have shown
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