Maximum pulverization

The maximum pulverization does not occur at the maximum oxidation rate. With 21% oxygen, the maximum oxidation rate occurs at 480°C, but the maximum pulverization occurs at the lower temperatures (see Tests 20, 5, 7, 8, 9, and 10). This observation appears to support the theory that if the oxidation is carried out too rapidly, the U3O8 on the surface of the fragments inhibits further oxidation and pulverization. Therefore, if maximum pulverization is desired, the oxidation should be carried out at a temperature less than that where the maximum oxidation rate occurs. 

To obtain maximum pulverization at minimum time, the oxidation temperature should be decreased as the material is oxidized. To minimize the induction period, the oxidation should begin at... 

For maximum heat economy, recovered exhaust heat is employed for preheating of the incoming sohds and combustion air. The fuels used may be gas, oil, or pulverized coal. 

In coal pulverizers it is desirable to supply heated air to vaporize the water in the coal. However, the temperature of this heated air should not be so high that ignition could occur. Craig (1G) in studying this problem discusses the effect of coal concentration of flame velocity. Maximum flame velocity occurs at an air-fuel ratio of about 5 to 1. Godbert and Greenwald (3G) report the effect of fineness on the flammability of coal dusts. 

Because pulverized coal boilers are designed to bum fuel in suspension, small TDF are typically used.7 TDF is often a maximum of 1-inch in diameter, but can be as small as 1/4-... 

Chemical desulfurization techniques have a common drawback. They require pulverizing the coke to expose maximum surface area to the reactant(s). Thus, the end product is low sulfur coke with no... 

Pulverization is the most expensive part of all rock reduction, more energy must be expended to accomplish it, and consequently this stage has received, and should receive, a maximum of study and attention. 

A newly introduced model cyclone firing unit (Figure 6) permits a longer retention time in the centrifugal field so that normal pulverized fuels and granular materials with maximum grain diameter of 3 mm can be burnt. 

Jaw crusher feed diameter 0.1 to 1.5 m reduction ratio 5 1 to 10 1 capacity 1 to 300 kg/s Mohs hardness <9 (reduction by compression). Gyratory crusher feed diameter 0.75 to 1.5 m reduction ratio 5 1 to 10 1, usually 8 1 capacity 140 to 1,000 kg/s Mohs hardness <9. More suitable for slabby feeds than jaw crusher (reduction by compression). Roll crusher feed diameter 1 cm reduction ratio 5 1 to 10 1 capacity 0.3 to 20 kg/s Mohs hardness <7.5. Suitable for softer, friable, and nonabrasive materials. OK for wet and sticky materials. Cone crusher and short head cone feed diameter <25 cm reduction ratio 5 1 to 10 1, usually 7 1 capacity 5 to 300 kg/s Mohs hardness <8. Usually secondary or tertiary crusher. Impact crusher pulverizers, shredders, or smooth roll feed diameter 1 cm with a reduction ratio of 7 1 to 10 1 capacity 0.3 to 50 kg/s. Mills, hammer, feed diameter 10 mm, reduction ratio 10 1 to 50 1, capacity 0.01 to 5 kg/s Mohs hardness <4.5. Maximum fines feed not hard or abrasive. Mills, ball, and rod feed diameter 0.5 mm with a reduction ratio of 10 1 to 50 1 Mohs hardness <9. Mills, autogenous, semiautogenous feed diameter 200 mm, reduction ratio 10 1 to 50 1 capacity 0.1 to 100 kg/s Mohs hardness <6. Mills, fluid energy feed diameter 50 pm reduction ratio 10 1 to 50 1 capacity <2 kg/s Mohs hardness <4.5. 

It is often possible to reduce air-input requirements- by removing the hazardous material at the point of discharge by loccd ventilation. This lowers the ta value in Eq. (8-5), which assumes possible disposal of hazardous material within the entire enclosed volume of the enclosure being ventilated. Hoods and exhaust ducts are placed over such equipment as open filter presses, pulverizers, open tanks, and over laboratory benches and equipment to catch the maximum amount of vapor or dust without interfering with normal operation and maintenance. Local air velocities in the region of pickup will depend on density of the hazardous material or its particle size if a dust or fume. Air velocities greater than 200 fpm are usually employed for industrial operations, while chemical laboratory fume hoods range from 70 to 125 fpm when fully opened. 

All vanadium sulfides can be S3mthesized from the elements. An intimate mixture of the finely pulverized components, in the proper proportions. Is placed in sintered clay tubular crucibles these are inserted in quartz tubes, which are then evacuated and melt-sealed. The tubes are then slowly heated and finally maintained for a long time at a maximum temperature of 1000-1300°C. Contact between the vanadium metal and the quartz must definitely be avoided. 

The temperature regimes in which this corrosion occurs are summarized in Figure 3.2. The data generally show that K2S2O7 will form from K2SO4 and SO3 at 400°C when SO3 concentration is at least 150 ppm as the temperature increases, the SO3 requirement increases, so that, at 500°C, at least 2000 ppm SO3 will be required to form liquid K2S2O7. Sodium pyrosulfate can form at 390°C with = 2500 ppm SO3, but at 485°C, 2% by volume SO3 will be required. Based on these results and the anticipated maximum level of 3500 ppm SO3 in a pulverized-coal boiler, Reid (1971) concluded that pyrosulfates can contribute to metal loss in the waterwall and economizer tubes but may not be a cause of corrosion in superheaters and reheaters in conventional systems (Natesan 2002). 

GrindabiUty is normally measured by determining the number of revolutions in a pulverizer that are required to achieve a given size reduction. This is an indirect measure of the amormt of work required for that size reduction. GrindabiUty increases slowly to a maximum at 90% carbon and decreases rapidly beyond this point. Hardness is ascertained by meastrring the size of the indentation left by a penetrator of specified shape pressed onto the coal with a specified force for a specified time. It changes only slightly between 70 and 90% carbon and increases rapidly beyond 90% carbon. 

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