Integrierte Vermeidung und Verminderung der Umweltverschmutzung
Integrierte Vermeidung und Verminderung der Umweltverschmutzung Integrierte Vermeidung und Verminderung der Umweltverschmutzung
Chapter 2 The main raw materials used in Europe for the production of starch and its derivatives are cereals, i.e. maize, wheat, barley and rice, and potatoes of dedicated varieties. Each installation is usually technically dedicated to one raw material [10, Environment Agency of England and Wales, 2000, 84, European Starch Association, 2001]. Only starch production from maize, wheat and potatoes is described in this document. 2.2.8.1 Maize starch The commercial separation of pure starch from maize is achieved by a wet milling process which is generally considered to be efficient. The process is operated as an enclosed system in which process water is re-used in a closed circuit. The addition of fresh water is limited to one point in the production process. The raw material is washed using aspiration and screening to remove dust, chaff, broken grain, cobs and other extraneous material. The maize is soaked in water with sulphur dioxide (SO2) or sodium bisulphite (NaHSO3), for around 36 hours, in a process known as steeping. This removes solubles in the maize, softens the kernel to improve separation of the various components and reduces microbial activity. After steeping, the maize is passed through several grinding and separation operations until only starch and gluten remain. The grain is first ground coarsely and the germs are removed from the coarse grist. After removing the germ, the grist is finely ground and fibre is removed through a screening operation. Starch and gluten are separated, typically using centrifugal methods. This raw starch is washed with drinking water, using a countercurrent flow, in a series of four to six centrifuges. At one end, raw starch is the input and process water is the output and at the other end, refined starch is the output and fresh drinking water is the input. The starch, which at this stage is called refined starch, is then dewatered and dried. Refined starch is typically 99 % pure and 85 – 88 % dry solids. Native starch is refined starch, before physico-chemical modification. The gluten and fibre are collected separately as co-products. An example of a maize starch extraction process is shown in Figure 2.18. 92 January 2006 RHC/EIPPCB/FDM_BREF_FINAL
FW : PW : RPW : Fresh water Process water being recycled or treated (before discharge) Recycled process water Thermal energy Liquid Steep Liquor Evaporation Condensate Corn steep Liquor Thermal energy + Fibres Dewatering Drying Off vapours Wet sales CORN FEED NaHSO 3 or SO 2 RPW FW PW PW PW RPW RPW RPW RPW RPW Washing MAIZE Reception Dust Dry cleaning Steeping First grinding Degerminating Second grinding Thermal energy Sieving Separation Air emissions Starch Proteins Dewatering Dewatering Drying PROTEINS STARCH SLURRY Corn feed Chapter 2 RHC/EIPPCB/FDM_BREF_FINAL January 2006 93 Dust Air Germs Dewatering Drying DRY GERMS PW LIQUID MODIFIED SWEETENERS NATIVE STARCH STARCHES DRY SWEETENERS Thermal energy Figure 2.18: An example maize starch production process [84, European Starch Association, 2001] 2.2.8.2 Wheat starch Off vapours Air PW Off vapours The commercial separation of pure starch from wheat is achieved by a two-phase process. In the first phase, the wheat kernel is ground or converted into wheat flour by a dry milling process. The second phase then separates the ground wheat or the wheat flour into its separate components, i.e. starch, gluten, solubles and eventually fibre, by a wet separation process. The process is operated as an enclosed system in which process water is recycled in a closed circuit. Fresh water is used at some stages of the process. An example of a wheat starch extraction process is summarised in Figure 2.19. The process of washing raw wheat starch to produce refined starch is the same as that for maize starch (see Section 2.2.8.1).
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FW :<br />
PW :<br />
RPW :<br />
Fresh water<br />
Process water being recycled<br />
or treated (before discharge)<br />
Recycled process water<br />
Thermal<br />
energy<br />
Liquid Steep<br />
Liquor<br />
Evaporation<br />
Condensate<br />
Corn steep<br />
Liquor<br />
Thermal<br />
energy<br />
+<br />
Fibres<br />
Dewatering<br />
Drying<br />
Off vapours<br />
Wet sales CORN FEED<br />
NaHSO 3 or SO 2<br />
RPW<br />
FW<br />
PW<br />
PW<br />
PW<br />
RPW<br />
RPW<br />
RPW<br />
RPW<br />
RPW<br />
Washing<br />
MAIZE<br />
Reception Dust<br />
Dry cleaning<br />
Steeping<br />
First grinding<br />
Degerminating<br />
Second grinding<br />
Thermal<br />
energy<br />
Sieving<br />
Separation<br />
Air emissions<br />
Starch Proteins<br />
Dewatering<br />
Dewatering<br />
Drying<br />
PROTEINS<br />
STARCH SLURRY<br />
Corn feed<br />
Chapter 2<br />
RHC/EIPPCB/FDM_BREF_FINAL January 2006 93<br />
Dust<br />
Air<br />
Germs<br />
Dewatering<br />
Drying<br />
DRY GERMS<br />
PW<br />
LIQUID<br />
MODIFIED<br />
SWEETENERS NATIVE STARCH<br />
STARCHES<br />
DRY<br />
SWEETENERS<br />
Thermal<br />
energy<br />
Figure 2.18: An example maize starch production process<br />
[84, European Starch Association, 2001]<br />
2.2.8.2 Wheat starch<br />
Off vapours<br />
Air<br />
PW<br />
Off<br />
vapours<br />
The commercial separation of pure starch from wheat is achieved by a two-phase process. In the<br />
first phase, the wheat kernel is gro<strong>und</strong> or converted into wheat flour by a dry milling process.<br />
The second phase then separates the gro<strong>und</strong> wheat or the wheat flour into its separate<br />
components, i.e. starch, gluten, solubles and eventually fibre, by a wet separation process. The<br />
process is operated as an enclosed system in which process water is recycled in a closed circuit.<br />
Fresh water is used at some stages of the process. An example of a wheat starch extraction<br />
process is summarised in Figure 2.19. The process of washing raw wheat starch to produce<br />
refined starch is the same as that for maize starch (see Section 2.2.8.1).
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