Integrierte Vermeidung und Verminderung der Umweltverschmutzung

Chapter 3
3.2.45 Dehydration (solid to solid) (F.3)
3.2.45.1 Water
Water may be used in cleaning the equipment, with the resultant waste water containing
dissolved organic material and SS. Kilns for the drying of malt are cleaned dry.
3.2.45.2 Air emissions
In the hot-air dehydration process, air, with water vapour containing VOCs and dust, is released.
If dehydration is done using direct-fired burners, the exhaust gases might also contain CO2, CO,
SO2, and NOX, depending on the heat source and burner type. Depending on the type of raw
material or product, the dust may be glutinous and wet, e.g. meal from oilseed processing. Dry
dust can be filtered and wet dust can be recovered using cyclones. Odour may also be a
problem.
3.2.45.3 Solid output
Solid organic material may be generated when equipment is emptied for a next batch or for
cleaning. These outputs can consist of raw material, product residues and dust. These solid
products/dust can be recycled back into the process or sold as animal feed.
3.2.45.4 Energy
For the evaporation of water, theoretically 0.611 kWh/kg (2.2 MJ/kg) energy is required.
However, in practice, this very much depends on the type of drier used and can range from
0.556 – 1.08 kWh/kg (2.0 – 3.9 MJ/kg). Steam driers can have a considerably lower energy
consumption if they consist of more effects (multiple effect evaporation). Sometimes exhaust
gases from a combustion (CHP) plant are used to dry products, thereby reducing the direct
energy consumption. The energy consumption for dehydration can be further reduced by
increasing the dry substance content of the wet product. This can be achieved by preevaporation
or by using special dewatering equipment.
3.2.45.5 Noise
Noise may arise from the air inlet and outlet of the driers.
3.2.46 Cooling, chilling and cold stabilisation (G.1)
3.2.46.1 Water
Water may be used as the cooling medium in a once-through system. When cooling water is
recirculated, closed-circuit cooling towers can be used for heat removal.
3.2.46.2 Air emissions
In cryogenic cooling, emissions of gaseous N2 or CO2 occur. Leaking refrigeration equipment
can lead to emissions of refrigerant.
3.2.46.3 Energy
Electrical energy is needed to drive the pumps circulating the cooling water or the fans in air
cooling. Mechanical refrigeration systems generally require 0.3 – 1.0 kWh power per cooling
effect. However, overall, their energy consumption is significantly less than the total energy
required for the manufacture and use of liquid N2 or CO2.
142 January 2006 RHC/EIPPCB/FDM_BREF_FINAL