Spray calcination

Dead Seas Periclase Ltd., on the Dead Sea in Israel, uses yet another process to produce magnesium oxide. A concentrated magnesium chloride brine processed from the Dead Sea is sprayed into a reactor at about 1700°C (127,128). The brine is thermally decomposed into magnesium oxide and hydrochloric acid. To further process the magnesia, the product is slaked to form magnesium hydroxide which is then washed, filtered, and calcined under controlled conditions to produce a variety of MgO reactivity grades. A summary of MgO purities, for the various processes is given in Table 20. 

In some cases in which it is desirable to cool the product before removal to the outside atmosphere, the discharge end of the cyhnder is provided with an additional extension, the exterior of which is water-spray-cooled. In cocurrent-flow calciners, hot gases from the interior of the heated portion of the cylinder are withdrawn through a special extraction tube. This tube extends centrally through the cooled section to prevent flow of gas near the cooled-shell surfaces and possible condensation. Frequently a separate cooler is used, isolated from the calciner by an air lock. 

FIG. 12-72 Gas-fired indirect-heat rotary calciner with a water-spray extended cooler and feeder assembly (ABB Raymond/ Bartlett-Snow. )... 

Engelhard s in-situ FCC catalyst technology is mainly based on growing zeolite within the kaolin-based particles as shown in Figure 3-9A. The aqueous solution of various kaolins is spray dried to form micR)spheres. The microspheres are hardened in a high-temperature l,3f)(TF/704°C) calcination process. The NaY zeolite is produced by digestion of the microspheres, which contain metakaolin, and mullite with caustic or sodium silicate. Simultaneously, an active matrix is formed with the microspheres. The crystallized microspheres are filtered and washed prior to ion exchange and any final treatment. 

The solid base catalysts were prepared by dissolving Cs(N03)2 (Aldrich, 99%) in the minimum amount of distilled water before addition to the silica support by spray impregnation a method used to give a high dispersion of the metal salt on the support. The amount of each precursor added was calculated in order to give a 10% loading of metal on each catalyst. The catalyst was then dried in an oven overnight at 373 K. Prior to the reaction the catalyst was calcined in situ in a flow of N2 (BOC, 02 free N2) at 10 cm3 min"1 for 2 hours at 723 K. 

Nagai and Nishino [5.3] froze solutions of K2C03, Na2C03, MgS04 and A12(S04)3 18 H20 by spraying them into LN2, and freeze dried the frozen droplets at 0.13 mbar and 100 °C for 2-3 days. The dry product consisted of hollow and porous balls with a diameter from 150 to 200 pm, and had to be milled for 16 h in a ball mill to make it workable. The calcinated product had a spherical (0.1 pm diameter) or plate-like form of 0.2 to 2 pm. 

The catalysts were synthesized as films, with ceria prepared by spray pyrolysis of 0.1 M solutions of Ce(N03)3 onto nonporous alumina wafers held at 250 °C. The ceria was then calcined at 300 °C, resulting in a crystallite size of 10 nm. Pt, Pd, or Rh was vapor deposited onto the oxide film. For kinetics testing, the temperature was 300 °C. To determine the reaction order of H20, Pco was maintained constant at 0.026 atm. For the reaction order on CO, Ph2o was maintained constant at 0.02 atm. The kinetic parameters are tabulated in Table 69. 

The density specific gravity) of coke has a strong influence on future use and can affect the characteristics of the products such as carbon and graphite. The density (specific gravity) of coke can be measured conveniently by use of a pycnometer. In the test method (ASTM D5004), the mass of the sample is determined directly and the volume is derived by determining the mass of hquid displaced when the sample is introduced into a pycnometer. Oil or other material sprayed on calcined petroleum coke to control dust will interfere. Such oil can be removed by flushing with a solvent, which must be completely removed before the density determination. 

Catalysts are prepared by impregnation by spraying a solution of a metal salt onto pellets of a porous support until incipient wetness. The pellets are then dried and calcined to transform the metal into insoluble form. 

Figure 7.23 Schematic diagram of spray drying process for the formation of calcined magnesium zinc ferrite. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley and Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

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