Grain, dewatering

DisK Presses Figure 18-157 shows a disk press. The two disks, or press wheels, converge to a veiy narrow space at the bottom. This is the point of maximum compression, which can be more than 14 times the feed pressure. The press wheels have channels to cany the hquid from the dewatered product, and they are covered with a screen plate. Wheels 1.5 m (5 ft) in diameter are used on a large press that requires about 80 connected horsepower and produces just under 1 tonne/h (0.9 ton/h) of sohds (diy basis). Typical apphcations are fibrous materials such as coffee grounds, pineapple and citrus peels and wastes, alfalfa, and brewers spent grain. 

Other by-products of the brewing process are malt sprouts, brewers condensed solubles (produced from the mechanical dewatering of brewers grains) and brewers yeast. Most of the brewers grains are marketed in the wet form... 

The liquid left after distillation is subjected to centrifugation, where most of the suspended solids are separated. The clear liquid can be recycled by adding it back to the starch conversion stage. The moist cake released by the centrifuges is mixed with the syrup produced by the evaporator to form a homogenous mixture and is dewatered in dryers. The dryers produce a Distillers Dried Grains with Solubles (DDGS) meal, which can be formed into pellets. These are used in many applications, most prominently in animal feed. 

The grain size limitations for various dewatering systems are shown in Figure 4.7. A checklist for selection of drainage methods appears in Table 4.2. 

Dewatering methods are limited to grain size ranges, as shown in Figure 4.7. The finest treatment zone is labeled electro-osmosis. The electro-osmotic... 

Belt Filter Press Used to dewater fine grained sediments. Capable of obtaining relatively dry filter cake obtaining up to 45 - 70 % solids able to achieve solids capture of 85 - 95%. Generally best suited of filtration methods for mobile treatment systems. Performance is very sensitive to incoming feed characteristics and diemical conditions. Belts can deteriorate quickly in presence or abrasive material. Generates a substantial amount of waste water that must be treated. Medium... 

Chamber Filtration Used to dewater fine grained sediments. Capable of obtainii a relatively dry filter cake with a solids content up to 50 - 80 % able to achieve a high solids capture rate of up to 98%. Costly atsl energy intensive. Replacement of filter media is tiiiK consummg. Generates a wash water dut must subsequently be treated. HG ... 

Vacuum Rotary Filtration Used to dewater fine grained sediments capable of obtaining a filter cake of up to 35 - 40% solids and a solids capture rate of 88 - 95%. Least effective of tlie filtration metliods of dewatering. Energy intensive. Generates a wash water that must be treated. High... 

Percent solids achievable may represent values for optimal conditions and do not necessarily represent normally expected values. Dredged sediments are often fine-grained and difficult to dewater to the maximum indicated values. 

At the Hamburg harbour site, separation of the fine fraction is performed by cyclonage and up-stream classification before disposal. The deposition is made in alternating layers of 1.5 m fine-grained material and 30 cm of sand, the latter to drain excess water from the deposits. The rest of the separated sand fraction is used for the supporting dam. As we will see later, the costs of the Hamburg procedure are much higher than at Rotterdam, because of the efforts to separate and dewater the material. Capacities of both structures will be exhausted in about 10 to 15 years. 

LG Process. The large grain process for seawater magnesia. Greater density and grain size is achieved by using tube filter presses to dewater the slurry to the optimum 75% solids content. The product can be directly dead-burned. Refract J. May/June, 1976, pl3). 

Geotextile tubes for dewatering and decontamination of fine-grained soils... 

The previous chapter in this book, by Lawson (2015), reviewed the three options of geotextiles used as flexible forms bags, containers, and tubes. Fig. 21.1 shows dewatering and decontaminating fine-grained river and harbor sediments however, tube sizes are used invariably. Flexible soil-filled fabric tubes were made as early as 1957, but initially they were not successful. Eventually, in 1967 a patent was granted to a Danish firm, Aldek A.S., in conjunction with the Danish Institute of Applied Hydraulics. Aldek s system was developed further in 1970 (Zirbel, 1975). 

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