Integrierte Vermeidung und Verminderung der Umweltverschmutzung

3.2.43.3 Energy
Chapter 3
Steam requirements for single-stage evaporators range from 1.1 to 1.2 tonnes of steam per tonne
of evaporated water. Energy requirements may be reduced when using multi-effect evaporators.
In the case of double or third effect, the steam requirement lowers respectively to
0.6 - 0.7 and 0.4 tonnes of steam per tonne of evaporated water. The steam consumption can
also be reduced by applying mechanical or thermal vapour recompression (see
Sections 4.2.9.2.1 and 4.2.9.2.2) Sometimes exhaust gases can be used to recover energy from
other processes such as drying (see Section 3.2.44).
3.2.43.4 Noise
Noise is often produced from the evaporation processes, in particular from the thermal
compressor, the mechanical compressor, the steam ejectors and the high velocity of the fluids in
the pipework. This can usually be managed by applying appropriate acoustic insulation. Noise is
also generated in pumps due to cavitation.
3.2.44 Drying (liquid to solid) (F.2)
3.2.44.1 Water
The use of water is normally restricted to cleaning the equipment. The amount used greatly
depends on the type of equipment. During cleaning, waste water is generated containing soluble
organic material and SS. When air scrubbers are used, a waste water stream containing organic
material such as fine dust is generated.
3.2.44.2 Air emissions
In hot air drying, a gas/vapour is generated and exhausted into the air. This gas/vapour may
contain dust and VOCs, which originate from the product. This may cause an odour problem
which might require treatment prior to discharge. If drying is done using direct gas or fuel fired
burners, the exhaust gases might contain CO2, CO, SO2, NOx, depending on the heat source and
burner type. Food safety requirements must be respected, especially when drying very sensitive
products.
3.2.44.3 Solid output
A solid output may be generated when the equipment is emptied for a next batch or for
cleaning. This solid output can consist of raw materials, product residues, and dust which has
been recovered from the exhaust air. These solid products/dust can be recycled back into the
process or sold as animal feed.
3.2.44.4 Energy
For the evaporation of water, theoretically 0.611 kWh/kg (2.2 MJ/kg) energy is required. In
practice, due to energy losses in the process, the energy consumption for water evaporation
ranges from 0.694 – 0.972 kWh/kg (2.5 to 3.5 MJ/kg).
3.2.44.5 Noise
Noise may arise from the air inlet and outlet of the driers. If sound baffles are used to reduce the
noise at outlets, these baffles need to be checked periodically to remain effective.
RHC/EIPPCB/FDM_BREF_FINAL January 2006 141