Vertical kilns

Calcium oxide (lime) Rotary kilns, vertical and shaft kilns, fluidized bed furnaces Particulate matter Cyclones plus secondary collectors (baghouse, ESP, wet scrubbers, granular bed filters, wet cyclones)... 

Pelletizing (cf. tumbling agglomeration ) Green balls or pellets of ore or minerals are hardened by heat treatment with attendant loss of moisture and volatile matter. Pellet induration, pellet firing Travelling grate, rotary kiln, vertical shaft furnace... 

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. 

In spite of fhe distinctions described herein, most kilns, vertical or horizontal, when used for thermal processing, for example, calcination, oxidation, reduction, and so on, in a continuous operation... 

In the early days of cement manufacture the clinker was produced in shaft kilns (vertical kilns) which were manually charged and controlled It was a process involving strenuous physical labour and had the drawback of irregular operation, yielding a clinker of variable and often inferior quality. Besides, the capacity of such kilns was low. 

Dump lime is a physical shape of quicklime, derived from vertical kilns. 

Another thermally efficient kiln is the modem mixed-feed vertical kiln ia which coke is admixed with 8.5—20 cm lump limestone and charged into the top of the vertical kiln by a mobile, overhead charging system. However, use of this kiln is waning since the quaUty of mixed-feed kiln lime does not equal that of the other three kilns described above, owing to ash contamination from the coke and poorer reactivity and to the higher cost of coke in most areas. 

Many kilns that formerly were direct coal-fired or producer-gas verticals were retrofitted to natural gas firing with center-burners and after World War II, dramatically improving lime quaUty, kiln capacity, and fuel efficiency. By the 1960s, this improved vertical kiln had lost favor to rotary and other special kilns because of the supply and cost problems of oil and gas in the United States and the spectacular improvement in rotary kiln performance. Many natural gas-fired center burners were permanently closed and dismanded because they could not be converted to coal. However, the reverse occurred in Europe where the extensive oil and gas discoveries heightened interest in the new, advanced vertical kilns. 

Miscellaneous Kilns. A U.S. kiln, the Fluo-Sohds, appears to be another vertical kiln type, but this is its only similarity. It operates on a different principle. It utilizes as kiln feed only a discrete granulation of 0.225—2.4 mm (65—8 mesh) sizes. DeHcately controlled by air and exhaust gas pressure, the kiln feed of granules is fluidized as a dense suspension. Because it is instmmented, this kiln can produce a very reactive lime at better than average thermal efficiency. The kiln, however, has limited utifity because the cost of obtaining the kiln feed with many hard, compact limestones is prohibitive. 

Another method iavolves an electric-arc vaporizer which is >2000° C before burning (25,32). One of the features of the process is a rapid quench of the hot gas flow to yield very fine oxide particles (<0.15 nm). This product is quite reactive and imparts accelerated cure rates to mbber. Internally fired rotary kilns are used extensively ia Canada and Europe and, to a limited extent, ia the United States (24). The burning occurs ia the kiln and the heat is sufficient to melt and vaporize the ziac. Because of the lower temperatures, the particles are coarser than those produced ia the other processes. In a fourth process, ziac metal which is purified ia a vertical refining column is burned. In essence, the purification is a distillation and impure ziac can be used to make extremely pure oxide. Also, a wide range of particle sizes is possible (33). 

Raw Materials. The basic raw materials limestone and coke or coal (qv) should be high quaHty. Limestone should contain a minimum of 95—97% CaCO and a maximum of 1.5% MgCO, 1—1.5% Si02, 1% Fe202 plus AI2O2, and 0.006% phosphoms (see Lime and limestone). The limestone is first converted to lime in a rotary or vertical shaft kiln. The lime is screened to eliminate fines that interfere with the evolution of carbon monoxide in the smelting process. 

Vertical Kilns These Idlns are used primarily where no fusion or softening occurs, as in the burning of hmestone or dolomite, although rotary Idlns also are used for these operations. The blast furnace. Fig. 

Removal of volatile matter to about 0.5 wt% can be accomplished by calcming in a rotary kiln, rotary hearth, or vertical shaft calcmer All of these processes heat green coke to temperatures in excess of 1000°C where shrinkage and subsequent densification take place. The volatile components are comprised primarily of methane, ethane, hydrogen, and hydi ogen sulfide gases which can be employed as fuel for process heat. 

Kiviter A process for extracting oil and gas from shale, using a vertical kiln. The first unit was under construction in Estonia in the 1980s. 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime kilns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recovery furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

Parameters in the model are listed in Table I. The flow, structural, and boundary conditions are known quantities. The frequency factor and activation energy for coke burning were the values determined by Weisz and Goodwin (1966) from the experiments discussed earlier, and the catalyst diffusivity D was measured directly in the laboratory. The value of a was determined from direct observations of the CO/CO2 ratio in each zone of the operating kiln. The remaining parameters are known quantities. Thus, there are no adjustable parameters available to tune the fitting of predicted values to observed data, for the fraction of coke remaining and for the vertical temperature versus distance from the top of the kiln. 

Fig. 11. Simulation of y versus x for the Beaumont T-2 kiln operating with conventional green silica-alumina catalyst. Computed results are given by the solid curve. The observed values, obtained fix>m a vertical traverse, are given by the points. The operating conditions were as follows flow of air up—23,500 scfm (665 semm) flow of air down—13,600 scfm (385 semm) air temperature at inlet—120°F (4 >°C) O2 in air to kiln—21% catalyst circulation rate—348 tons/hr (3.16 x KF kg/hr) catalyst inlet temperature (1-ft level)—900°F (482°C) coke on catalyst (1-ft level)—1.5%.

The structure of a pyrites kiln is shown in Figs. 676 and 677. In Fig. 577 the pyrites is shown as inclosed on two sides by two sloping walls, the back and front walls being vertical. The mass of pyrites rests on... 

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