Traditionally, ball Mills are employed in cement industry for raw material, fuel and product grinding. Ball mills work with an established technology and offer certain advantages. However, they may have higher energy demands. By making use of a suitable kind of the greater number of efficient roller mill technologies – either as a replacement or in combination with ball mills – considerable energy savings is possible without compromising product quality. These micro powder mill concepts are applicable to cement manufacturing:
Vertical roller mills: In these mills materials are crushed from a rotating grinding table and 2 to 6 grinding rollers positioned slightly less than 90 degrees from your table surface and pressed hydraulically against it. Main features of Vertical Roller Mills include:
relatively low power consumption (under 10 kWh/t – for medium raw material hardness and medium fineness);
ability to combine grinding, drying (using waste heat from kiln system) and separation;
power to manage larger variations in mass flow rate (30 to 100% of mill capacity).
Vertical roller mills can be purchased in an array of capacities – 5 to 1200 t/h.
Chinese flag As outlined by National Development Reform Commission of China, VRMs have the following generic power consumption values when useful for different purposes in the cement plant:
The life-time period of the wear resistant material is reported to vary between 8000 to 12000 hours. In China, market penetration of VRMs in the building materials sector was anticipated to reach 50% throughout the eleventh five-year development period, requiring a smart investment of around 1.08 billion RMB, and holding a prospective to minimize energy consumption by 500 GWh (NDRC, p.51).
VRMs are placed in new cement plants with dry systems, as well as often replace ball mills during plant modernization, where the raw material moisture content articles are under 25%. At the time of 2010, VRMs for raw material preparation had a penetration rate of 45% in Chinese market. During the twelfth five-year period, the industry penetration of the technology is anticipated to attain 80% (MIIT, 2012. p.20)
Horizontal roller mills: Here materials are crushed within Coal Grinding Mill tube that also contains a grinding roller which is hydraulically pressed up against the inside top of the tube. Horizontal roller mills use 65-70% in the energy used in ball mills.
Roller press (high-pressure grinding rolls): With this technology materials are crushed between two counter-rotating rollers. These rollers are approximately 2 m in diameter and 1.4 m long. Roller presses use 50-65% of the energy employed in ball mills.
It is very important to keep up a constant temperature once the mill. In cases like this, it is achieved by automatic charge of a cold air valve letting cold air in to the hot air through the clinker cooler. At the entrance of your mill there must be a small negative pressure to avoid dust leaking out. This pressure needs to be regulated since an overly high negative pressure can cause an excessive volume of false air to leak in the system. The stress is maintained by controlling the damper just before the heat booster fan.The feed rate on the mill is controlled by constant monitoring in the noise level in the mill.
The operator will decide when you ought to start the grinding plant and often also when to stop it again.Start and quit from the individual machinery occurs in particular sequences controlled by the electrical interlocking system. The electrical interlocking system may, however for safety reasons, also cause a computerized stop in the operation. This could, for instance, become the case if your coal meal silo is filled to capacity or maybe if calcium carbonate grinding mill exit temperature exceeds the top of these two maximum alarm limits.
Today, coal of varying quality is commonly used, and blending is therefore necessary. Fig. 27 shows a good example of short term storage for coal by using a high blending effect. The primary issue with coal 98devhpky pile is “spontaneous combustion.”Coals vary a whole lot within the tendency to adopt up oxygen. In general,the tendency is relatively low for high rank (low volatile) coals. It is higher for coals of high bed moisture content, high oxygen content,and volatile content, all of these characterize a low rank coal. A key point in the heating process will be the total surface area of the coal exposed to the air: the greater the surface, the higher the risk for that coal to absorb and react with oxygen.
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