Rate of calcination

X 20 cm, 2.5 x 5 cm, 1.3 x 0.6 cm, etc, or even narrower ranges, are more conducive to uniform calcination. As an example, if the size ranges between 1.25—15 cm, the small size would tend to be severely over-burned, or the large size would be incompletely calcined if the small size was properly burned. At constant temperature, the rate of calcination varies inversely with the size of the stone, increasing with smaller fractions. 

The high-level radioactive liquid wastes are stored in stainless steel 300,000-gal tanks located in underground concrete vaults pending their solidification in the Waste Calcining Facility (WCF). At present the liquid waste is stored for less than four years and is dependent in part on the rate of calcination and rate of waste generation. The tank farm consists of eleven 300,000-gal tanks and four special tanks of 30,000 gal each. 

To recap, the major variables influencing the rate of calcination of magnesite are ... 

Rates of calcination of different limestones under identical conditions can vary markedly (see section 15.3). For a given kiln output, a limestone with a slow calcination rate requires either a larger calcining zone, or higher temperatures in that zone, and due allowance should be made when designing the kiln and/or its refractory lining. 

For identical calcining conditions, different limestones may produce quicklimes with measurably different reactivities. While the differences in reactivity may not be significant in most operations, they could affect the suitability of the quicklimes for certain applications (e.g. aerated concrete). There may be several causes of such differences, e.g. rate of calcination, effects of impurities and the microstructure of the lime, (e.g. lime produced from oolitic and coarsely crystalline limestones is more prone to sinter and become less reactive [14.2]). 

Fig. 19. XRD patterns of nickel ferrite nanoparticles with heating rate of calcination of 10,...

Formation of emissions from fluidised-bed combustion is considerably different from that associated with grate-fired systems. Flyash generation is a design parameter, and typically >90% of all soHds are removed from the system as flyash. SO2 and HCl are controlled by reactions with calcium in the bed, where the lime-stone fed to the bed first calcines to CaO and CO2, and then the lime reacts with sulfur dioxide and oxygen, or with hydrogen chloride, to form calcium sulfate and calcium chloride, respectively. SO2 and HCl capture rates of 70—90% are readily achieved with fluidi2ed beds. The limestone in the bed plus the very low combustion temperatures inhibit conversion of fuel N to NO. ... 

The hydration rate of sodium tripolyphosphate to its stable hexahydrate, Na P O Q 6H20, directly affects detergent processing and product properties. The proportion of STP-I (fast-hydrating form) and STP-II (slow-hydrating form) in commercial sodium tripolyphosphate is controUed by the time—temperature profile during calcination. In most processes, a final product temperature of near 450°C results in a product containing about 30%... 

The temperature in the hottest part of the kiln is closely controlled using automatic equipment and a radiation pyrometer and generally is kept at about 1100—1150°C (see Temperature measurement). Time of passage is about four hours, varying with the kiln mix being used. The rate of oxidation increases with temperature. However, the maximum temperature is limited by the tendency of the calcine to become sticky and form rings or balls in the kiln, by... 

There have been several kinetic studies of the calcination of dolomite [29], a reaction of considerable technological importance. As in many reversible reactions, the rate of carbon dioxide release is sensitive to the prevailing pressure of this product (.Pco2) in the vicinity of the reaction interfaces. At low pressures (PCo2 < 12 Torr), reaction proceeds to completion in a single stage between 900 and 950 K... 

Catalytic reactions. The reaction was carried out at 543-643 K by using a flow reaction system with a mixtiue of EA, NH3, and Nz in the ratio of 1/50/25 at atmospheric pressure. The flow rate of the mixture gas was 76 cm min. Prior to the reaction, the catalyst was calcined at 773 K under O2 flow for 2 h. The reaction products were analyzed by an on-line gas chromatograph (FID) which was equipped with a 30-m capillary column (TCI701). 

Figure 8. Rate of carbon monoxide oxidation on calcined Pt cube monolayer as a function of temperature [27]. The square root of the SFG intensity as a function of time was fit with a first-order decay function to determine the rate of CO oxidation. Inset is an Arrhenius plot for the determination of the apparent activation energy by both SFG and gas chromatography. Reaction conditions were preadsorbed and 76 Torr O2 (flowing). (Reprinted from Ref. [27], 2006, with permission from American Chemical Society.)...

Preparation of mixed metal oxides - The sulfated metal oxides (zircoiua, titaiua and tin oxide) were synthesized using a two-step method. The first step is the hydroxylation of metal complexes. The second step is the sulfonation with H2SO4 followed by calcination in air at various temperatures, for 4 h, in a West 2050 oven, at the temperature rate of 240°C hSulfated zirconia Zr0Cl2.8H20 (50 g) was... 

Chemical stabilizers have been used to reduce the rate of oxygen-promoted degradation of polysaccharides at T>225°F. Methanol and sodium thiosulfate are the most commonly used (86). Sodium dithio-carbamate, alkanolamines, and thiol derivatives of imidazolines, thiazolines, and other heterocyclic compounds have also been tested for this application. Calcined dolomite (B7) and Cu(l) and Cu(ll) salts (88) have been reported to increase the thermal stability of HEC. 

Dealuminated samples were obtained by hydrothermal treatment of calcined MCM-22 (Si/Al = 15) at different temperatures (673, 773, 873 K) for 2-24 h under a saturated flow of a nitrogen/steam mixture (flow rate of 200 ml min"1). These steamed samples were further treated with 6N HNO3 solution at 353 K for 4 h in order to remove the extra-framework aluminum species. 

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