Reactors vertical kilns

The chief examples are smelting for the recovery of metals from ores, cement manufacture, and lime burning. The converters, roasters, and kilns for these purposes are huge special devices, not usually adaptable to other chemical applications. Shale oil is recovered from crushed rock in a vertical kiln on a batch or continuous basis—moving bed in the latter case—sometimes in a hydrogen-rich atmosphere for simultaneous denitrification and desulfurization. The capacity of ore roasters is of the order of 300-700 tons/(day)(m3 of reactor volume). Rotary kilns for cement have capacities of 0.4-1.ltons/(day)(m3) for other purposes the range is 0.1-2. 

The blast furnace (Fig. 19-24f) is a vertical kiln in which fusion takes place in the lower section. This is a vertical moving-bed device iron oxides and coal are charged at the top and flow countercurrently to combustion and reducing gases. Units of 1080 to 4500 m3 (38,000 to 159,000 ft3) may produce up to 9 x 106 kg (20 x 106 lbm) of molten iron per day. Figure 19-24f identifies the temperature and composition profiles. Reduction is with CO and H2 that are made from coal, air, and water within the reactor. 

In addition to rotary and vertical kilns, hearth furnaces or fluidized-bed reactors may be used. These high-temperature reactors convert minerals for easier separation from gangue or for easier recovery of metal. Fluidized beds are used for the combustion of solid fuels, and some 30 installations are listed in Encyclopedia of Chemical Technology (vol. 10, Wiley, 1980, p. 550). The roasting of iron sulfide in fluidized beds at 650 to 1100°C (1202 to 2012°F) is analogous. The pellets have 10-mm (0.39-in) diameter. There are numerous plants, but they are threatened with obsolescence because cheaper sources of sulfur are available for making sulfuric acid. 

FIG. 19-24 Reactors for solids, (a) Temperature profiles in a rotary cement kiln, (b) A multiple-hearth reactor, (c) Vertical kiln for lime burning, 55 ton/d. (d) Five-stage fluidized-bed lime burner, 4 by 14 m, 100 ton/d. (e) A fluidized bed for roasting iron sulfides, (f) Conditions in a vertical moving bed (blast furnace) for reduction of iron oxides, (g) A mechanical salt cake furnace. To convert ton/d to kg/h, multiply by 907. 

FIG. 19-24 Reactors for solids, a) Temperature profiles in a rotary cement kiln, h) A multiple-hearth reactor, (c) Vertical kiln for lime burning, 55 ton/d. d) Five-... 

The counter-flow moving bed reactor is a type of gas-solid reactor in which the solid particles move downward from the top to the bottom of the bed and the gas stream flows upward from the bottom to the top. Vertical kilns and transport reactors are examples of a moving bed reactor. A schematic diagram of the moving bed reactor is shown in Figure 4.8. 

The process is usually carried out in rotary kilns, vertical multiple hearth furnaces or fluidized-bed reactors. Rotary kilns are the most versatile and widely used furnaces. They can be used for carbonization and/or activation and are available in a wide range of sizes. In this type of reactor the feed material is fed in granular or extrudate form. The vertical multiple hearth furnace consists of separate circular hearths, each of which can be maintained under different conditions of temperature and steam flow. Such reactors are usually used for activating carbonized material in granular form. The fluidised-bed reactor can be used for carbonization and/or activation. This type of reactor was used in a process developed to produce activated carbon from anthracite. 

Several processes of this type are very old, such as the fabrication of charcoal, the calcination of seaweed for producing potash, and the burning of limestone, and special reactors have been developed for each of these processes. Conventional technical reactors are vertical kilns, filled with solids that sink to the bottom... 

Vertical kilns are used in operations where no fusion or softening takes place, as in the burning of limestone or dolomite, though rotary kilns arc also used for these particular operations. The vertical kiln is the antecendent of modem moving-bed equipment, such as the pebble heater and catalytic reactors of this type. 

Different types of reactors are utilized for a wide variety of pyrolysis applications, including processing of waste plastics. The worldwide waste plastic pyrolysis systems utilize the fixed-bed designs of vertical shaft reactors and dual fluidized-bed, rotary kiln and multiple hearth reactor systems. The type of reactor used is chiefly based on material to be pyrolyzed and expected products from the pyrolysis. Stainless steel shaking type batch autoclave and stainless steel micro tubular reactors have also been used extensively [14]. Fluidized-bed reactors have been extensively used in producing raw petrochemicals from the pyrolysis of waste plastics [22, 24]. 

The most popular type of gasification furnace in Europe is the vertical shaft gasifier, used in the Andco-Torrax, Saarberg Fernvarme and Pyrogas process. Pyrolysis processes are often conducted in an indirectly heated rotary kiln reactor, e.g. in the Kiener, GMU or Krauss-Maffei process. Fluidized bed reactors are used at the universities of Hamburg, Eindhoven and Brussels and thus seem more popular in academic than in industrial spheres. 

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