Traditionally, ball mills are being used in cement industry for raw material, fuel and product grinding. Ball mills make use of an established technology and provide certain advantages. However, they may have higher energy demands. By making use of an appropriate sort of the better efficient roller mill technologies – either as a substitute or together with ball mills – considerable energy savings can be accomplished without compromising product quality. The next micro powder mill concepts are applicable to cement manufacturing:
Vertical roller mills: Over these mills materials are crushed from a rotating grinding table and 2 to 6 grinding rollers positioned slightly under 90 degrees in the table surface and pressed hydraulically against it. Main features of vertical roller mills include:
relatively low power consumption (below 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 Based on National Development Reform Commission of China, VRMs possess the following generic power consumption values when useful for different purposes in the cement plant:
The life-duration 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 likely to reach 50% throughout the eleventh five-year development period, requiring a great investment of about 1.08 billion RMB, and holding a prospective to reduce energy consumption by 500 GWh (NDRC, p.51).
VRMs are positioned 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 less than 25%. Since 2010, VRMs for raw material preparation experienced a penetration rate of 45% in Chinese market. Through the twelfth five-year period, the marketplace penetration from the technology is predicted to attain 80% (MIIT, 2012. p.20)
Horizontal roller mills: Here materials are crushed inside of Coal Grinding Mill tube which also has a grinding roller that is hydraulically pressed against the inside surface of the tube. Horizontal roller mills use 65-70% in the energy found in ball mills.
Roller press (high-pressure grinding rolls): With this technology materials are crushed between two counter-rotating rollers. These rollers are as much as 2 m in diameter and 1.4 m long. Roller presses use 50-65% from the energy found in ball mills.
It is very important to keep a constant temperature once the mill. In such a case, it can be achieved by automatic control of a cold air valve letting cold air in the hot air from your clinker cooler. On the entrance from the mill there ought to be a small negative pressure to avoid dust leaking out. This pressure should be regulated since an overly high negative pressure might cause an excessive quantity of false air to leak into the system. The strain is maintained by controlling the damper ahead of the heat booster fan.The feed rate towards the mill is controlled by constant monitoring of the noise level from your mill.
The operator will decide when you should start the grinding plant and quite often also the best time to stop it again.Start as well as prevent in the individual machinery happens in a few sequences controlled through the electrical interlocking system. The electrical interlocking system may, however for safety reasons, also cause a computerized stop in the operation. This may, for example, be the case when a coal meal silo is filled to capacity or maybe calcium carbonate grinding mill exit temperature exceeds top of the 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 having a high blending effect. The key trouble with coal 98devhpky pile is “spontaneous combustion.”Coals vary a whole lot inside the tendency for taking up oxygen. In general,the tendency is relatively low for high rank (low volatile) coals. It is actually higher for coals of high bed moisture content, high oxygen content,and volatile content, all of these characterize a minimal rank coal. A key point in the heating process may be the total surface section of the coal open to the air: the larger the surface, the higher the risk for the coal to soak up and interact with oxygen.