Floating bed
In technology, a fluidized bed is a mixture of solids with a liquid or a gas. The solids do not form a solid and compact layer, but are prevented from doing so by the liquid or gas by the flow resistance. The solids are fluidized with the liquid or gas . These mixtures behave largely like a homogeneous medium. While fluidization is predominantly referred to as floating bed in the two-substance system liquid / solids, the gas / solids system is referred to as a fluidized bed . More on this under fluidized bed . The information on properties and layer conditions given in the last article also largely apply to a floating bed and will not be repeated here.
Different designs of a floating bed are possible. A real floating bed is bounded by an upper boundary layer. A low-solids liquid phase is present above the boundary layer. Other types of floating beds are either bounded in the upper area by a fixed bed or the solids are in motion in the entire area of the liquid. In this case, however, the mixture is mainly called a fluidized bed .
Applications
The advantage of fluidized systems is the good mixing effect and the resulting easier reactions. The formation of dead spaces and poorly perfused areas with the possible concentration differences that can occur in the fixed bed are largely avoided. A favorable mass transfer between the two phases is achieved and the course of a chemical reaction is improved.
The solids are also classified in a floating bed . Larger and specifically heavy solids accumulate in the lower and smaller and lighter particles in the upper areas of the floating bed.
Below are some examples of technical-chemical processes with floating beds, taking into account the different types:
Combined floating bed with fixed bed
In the floating bed process , which was developed for the ion exchange of liquids (preferably water), a floating bed is formed. In this process, at least some of the ion exchange resins are fluidized and not part of the compact resin bed.
Real floating bed
One method with a fluidized bed is decarbonization in rapid reactors . In this process, the carbonate hardness in water is precipitated with milk of lime . In the reactors, fine sand particles, which serve as crystallization nuclei, form reactive hard grains on which calcium carbonate is deposited. These hard grains are fluidized in the upward flow of the treated water and form a floating bed with an upper boundary layer.
Real floating beds are formed during the backwashing of ion exchange resins. This enables the separation and discharge of undissolved dirt particles picked up during operation. However, it is only possible to flush out specifically lighter particles or particles with a higher flow resistance. A fluidized bed must not be formed during the backwashing, since ion exchange resins are then also rinsed out.
2-phase vortex floating bed
A relatively old method, however, is a mixture of fluidized bed and suspended, the suspension roasting in kilns. In this process the liquid phase is not present. A method used in practice on this basis is the roasting of sulphidic ores with the oxygen in the air to form oxides.
3-phase vortex floating bed
In the fluidized bed biofilm process , a cleaning process for waste water treatment , the phases liquid (water), gas (air or oxygen) and solid are used. The designs of the systems differ depending on the manufacturer. Mostly there is no floating bed, but a fluidized bed. Plastic particles, for example spheres, are circulated and whirled up intensively with air in the entire liquid or only in one chamber in the case of multi-chamber designs, depending on the design. The biomass required for cleaning and breaking down the pollutants in the water grows on the surface of the plastic particles and is largely fixed there.
Individual evidence
- ↑ G. Siegers, G. Wuttke: Lift bed and Rinsebett method. In: Power plant technology. 62, 1982, Jan. issue 1, p. 42.
- ↑ G. Baldauf, F. Schredelseker, M. Henkel, KW. Gatz, H. Sontheimer: Investigations on rapid decarbonization. In: gfw Wasser · Abwasser. 130 (1989), No. 11, pp. 569-577.
- ^ AF Holleman , E. Wiberg : Textbook of Inorganic Chemistry . 37-39 Edition. Walter de Gruyter, Berlin 1956, p. 206.
- ↑ W. Hosang, W. Bischhoff: Abwassertechnik. 11th edition. BGTeubner, Stuttgart / Leipzig 1998, ISBN 3-519-15247-9 .