de - Beste verfügbare Techniken (BVT) - Umweltbundesamt

6 EMERGING TECHNIQUES
6.1 Mixing improvement
Description
Chapter 6
Most OFCs are manufactured in batch stirred vessels, which are used for blending, reaction and
separation (e.g. crystallisation, liquid-liquid extraction). A very wide range of vessel and stirrer
designs is available, each having advantages and disadvantages depending on the process
requirements. Mixing conditions in a full scale stirred tank are likely to be significantly different
to those in a laboratory or pilot vessel, which may have a substantial effect on process
performance. The use of inappropriate mixing conditions on a plant may result in:
• a lower than expected yield (leading to more raw material use and more waste)
• a need to use excess reagents
• excess use of solvents (to counteract poor mixing in a vessel)
• excessive energy use (due to over-stirring, inefficient agitator design or excessive batch
times
• poor incorporation of solids into the process, leading to a waste of solid reagents or
excessive batch times
• poor transfer of gaseous reagents, leading to excessive gas use
• rejected batches due to product variability.
Achieved environmental benefits
These will vary from application to application, but typical examples of mixing improvements
have yielded:
• 50 % reduction in chlorine consumption
• 50 % reduction in raw material use; 75 % reduction in waste volume (pigment production)
• 50 % reduction in organic impurities in waste stream (waste treatment)
• 90 % reduction in surfactant use (powder draw-down process)
• 65 % reduction in batch time, and hence energy use (gel manufacturing)
• over-design of a new agitator avoided, resulting in 30 % reduction in power draw (paint
plant).
Operational data
Ensuring appropriate mixing is used will improve operability of the plant and will help avoid
lost batches.
Cross-media effects
Wahrscheinlich keine.
Applicability
Potentially applicable across most OFC processes. Opportunities are greatest when a new plant
is being designed, but retrofits can be cost effective for existing plants and processes. Less
opportunity is available for multipurpose, multiproduct plants, but consideration of mixing on
scale up can lead to the selection of the most appropriate vessel or identification when severe
process problems are likely and a retrofit is highly desirable.
OFC_BREF Dezember 2005 395