Cement, Energy and Environment

larger than the maximum grain size of the sample. Fine size reduction Selection of a suitable fine– grinding mill is based primarily on the condition of the pre– crushed material mixture, the feed quantity and the required analytical fineness. In addition , the abrasion of the grinding tools should be taken into account. Due to the unfavourable breaking properties displayed by most of the residual waste samples, analytical fineness such as is known in the fields of mineralogy and agrology will hardly be achieved. Grind size between 200 and 5001Jm are generally adequate for the most important analyses on waste samples. If the sample material contains mainly hard, brittle components such as glass, ceramics or bone splinters, ball mills are the mills of choice, especially planetary ball mills such as Reisch's PM 100 CM. Grinding sets with different useable volumes and of various ceramic and metallic materials make this mill suitable for a wide range of applications. Supplementary to the grinding tools, abrasive components of the sample material act on the softer substances as an additional grinding aid . In planetary ball mills very high energy levels are transferred to the grinding balls by the superposition of the rotary motions of the sun wheel and grinding jars. With this energy input it is possible to obtain a high final fineness with a very good degree of homogenization. Waste mixtures consisting mainly of cellulose and plastic residues, in other words with a tough, fibrous product structure, are best pulverized with rotor mills. Reisch's Ultra Centrifugal Mill ZM 200 with its patented cassette system and easy handling is ideally suited for this job. An exchangeable ring sieve is placed around a horizontally rotating rotor. The material to be ground is fed to the mill through a hopper and is ground between rotor and ring sieve by impact and shearing. The aperture size of the ring sieve determines the degree of fineness. Experience shows that aperture sizes of 0.5 or 1mm are fully adequate for obtaining analytical fineness. When preparing samples for heavy metal analysis, care must be taken to ensure that grinding tools (rotor and ring sieve) of titanium are used to prevent contamination of the sample by traces of heavy metal. To improve the breaking properties of soft, ductile and elastic materials, these can be embrittled with liquid nitrogen before they are fed into the mill. This is recommendable when the residual waste contains large portions of thermoplastics or soft rubber. When ground at room temperature these materials would melt in the grinding chamber and clog it. Another possibility is the addition of dry ice or dry ice snow to the material before grinding. ====~~~~~~------------------------------~--- In every mechanical crushing process contamination of the sample through abrasion from the grinding tools can be expected. This abrasion depends on the hardness and feed size of the sample material and its dwell time inside the grinding chamber. In the case of fine grinding in particular, where higher energy levels are needed than for pre-crushing processes, this abrasion should be given special attention. It is therefore important to take the basic composition of the respective materials into account when selecting grinding sets and tools. Retsch provides a PDF document "Material Analyses of Grinding Tools" on its website which can be downloaded for free. Courtesy: International Cement Review, December 2009, Pp76-77. Renewable Energy RECENT REGULATORY AND POLICY INTERVENTIONS FOR PROMOTING RE The NAPCC (National Action Plan on Climate Change), announced by the Hon'ble Prime Minister on 30 June 2008, envisages several measures to address global warming . One of the suggested measures is to increase the share of RE in total 53