Calcining quality

The choice between an increase in calcine production rate and an improvement in product quality represents a classic operating trade-off in any production facility. Oxygen enrichment provides the capability to improve one or the other or a partial improvement of both. At a given enrichment level, greater productivity could be achieved if the calcine quality is maintained at the pre-enrichment level. Conversely, significant improvement in calcine quality can be achieved at the expense of a smaller increase in productivity. The choice must be made based upon the needs and relative economics of a given company. 

Fundamental to the basis for the calculation of the roaster operational data is a full mineralogical analysis and a complete definition of the chemical and physical properties of each concentrate. Data available from such analyses form the basis for an accurate mass and energy balance. The model then calculates all process ii ut data required for any prescribed output product requirements. Consistent calcine quality can be achiev only if the concentrates are properly assessed and predictions and consequent adjustments are made to the roaster input parameters. 

It is possible to modify the quality of the coke by calcination at high temperatures (1200-1400°C) this has the effect of reducing the volatile material and to increase the density. 

Luminescence. Limestone possesses only limited luminescent qualities, ranging from very faint or none with the impure types. However, quicklime is very luminescent at calcining temperatures, hence the term limelight. 

Cost and Quality. Many factors affect catalyst support cost including which raw materials are used, the purity of the raw materials, the chemical processing steps required, the fabrication method used, the severity of calcination conditions, and the extent of the quaHty assurance procedure. In... 

For best operation, the feed rate to rotating equipment should be closely controlled and uniform in quantity ana quality. Because sohds temperatures are difficult to measure and changes slowly detected, most rotating-equipment operations are controlled by indirect means. Inlet and exit gas temperatures are measured and controlled on direct-heat units such as direct dryers and kilns, steam temperature and pressure and exit-gas temperature and humidity are controlled on steam-tube units, and direct shell temperature measurements are taken on indirect calciners. Product temperature measurements are taken for secondaiy control purposes only in most instances. 

The quality of magnesium oxychloride cements is highly dependent on the reactivity of the magnesium oxide used in their preparation. Typically, such oxides are prepared by calcination of the basic carbonate (Eubank, 1951 Harper, 1967), but their reactivity varies according to the conditions under which such calcination is carried out. As the reactivity alters so does the amount of oxide that can be incorporated into a cement relative to the amount of aqueous MgClj (Harper, 1967). 

Later, Thangaraj et al. (275,281) developed a novel, improved route (prehydrolysis method) for the preparation of good quality TS-1 samples. In this method the silica source (tetraethyl orthosilicate TEOS) in Ao-propanol was first hydrolyzed with 20% aqueous TPAOH solution prior to the (dropwise) addition of titanium butoxide in dry iso-propanol under vigorous stirring. Crystallization was done statically at 443 K for 1-5 days and the solid was calcined at 823 K for 10 h. The TS-1 samples thus obtained exhibited high catalytic activity in hydroxylation reactions. 

Thermally efficient calcination of lime, dolomite, and clay can be carried out in a multicompartment fluidized bed (Fig. 17-28). Fuels are burned in a fluidized bed of the product to produce the required heat. Bunker C oil, natural gas, and coal are used in commercial units as the fuel. Temperature control is accurate enough to permit production of lime of very high quality with close control of slaking characteristics. Also, half calcination of dolomite is an accepted practice in fluidized... 

Dust control material is applied to calcined coke to help maintain a dnst-free environment. It adds weight to the coke and can have a negative effect on the quality of carbon and graphite artifacts made from the treated coke. Hence, a maximum amount may be specified. 

High-quality pigments called copperas reds are obtained by the thermal decomposition of FeS047 H20 in a multistage process (Fig. 22). If an alkaline-earth oxide or carbonate is included during calcination, the sulfate can be reduced with coal or carbon-containing compounds to produce sulfur dioxide, which is oxidized with air... 

Surfactant extractions have been attempted previously, but mainly for HMS materials (mesoporous silicas, prepared using neutral amines as the surfactant). Due to the much weaker S°I° interaction, compared to the S+I interaction, these surfactants can be extracted relatively easily [6], Some reports have been published on the extraction of the cationic surfactant, but the resulting material is mostly inferior to the calcined one and in most cases, still a posttreatment at high temperatures is required [7], We describe an extraction procedure for MCM-48, that does not require a post-treatment and that produces materials with a better quality than the calcined ones. 

It is demonstrated that thermogravimetry data for uncalcined MCM-41 samples can be used to predict the structural quality of the calcined materials. The method is based on the comparison of weight change derivatives for a sample under study with those for a series of well-characterized samples prepared under similar conditions. Thermogravimetry data were found useful for a qualitative estimation of the overall sample quality, phase purity, degree of structural collapse and, in favorable cases, pore size of calcined MCM-41 materials. 

The DTG curves for uncalcined HR-B2 and B3 still exhibited some similarity to those of good-quality samples, such as HR-A1 - A3, but resemble more closely the DTG curve for an uncalcined lamellar phase [22], XRD revealed the presence of hexagonally ordered domains in the calcined HR-B2 and B3 samples, whereas adsorption data showed the presence of ordered pore domains of the size in accord with the XRD interplanar spacing (see Table 2). 

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