Drying Coal mill

mill coal grinder plant

mill coal grinder plant

For drying and grinding of coal and feeding to the kiln, the following three systems are employed as shown in Fig. 23.

  • Direct firing
  • Semi-direct firing
  • Indirect firing

Among the above systems, the direct firing system is extensively used because its equipment is simple, construction cost is low and operation is simple. But, for purposes of accurately controlling the feed amount to the kiln and limiting the primary air volume to the minimum, the indirect firing system is most preferable. It is possible to remodel the system “a” into the system “c’\ But, it is necessary to pay special attention to prevent spontaneous combustion and explosion of coal powder. A mill type in popular use is either a single barrel air swept mill or a roller mill.

Direct Coal Firing Mill Notation:

  • Raw Coal Silo
  • Weigh Belt Feeder
  • Air-swept Ball Mill (Tirax-mill)
  • Air Heater (Auxiliary Firing)
  • Separator
  • Cydone Collector
  • Circulating Air Fan
  • Primary Air Fan
  • Rotary Kiln
  • Satellite Coders (Unax-cooler)

Semi-direct Coal Firing Mill Notation:

  • Raw Coal Silo
  • Weigh Belt Feeder
  • Air-swept Ball Mill (Tirax-mill)
  • Air Heater (Auxiliary Firing)
  • Separator
  • Cydone Collector
  • Circulating Air Fan
  • Primary Air Fan
  • Rotary Kiln
  • Satellite Coolers (Unax-cooler)
  • Feed Hopper (Working Bin)

In-direct Coal Firing Notation:

  • Bowl Mill
  • Weigh Belt Feeder
  • Damper
  • Raw Coal Silo
  • Vent Fan
  • Dust Collector
  • Rooster Air Heater
  • DustTrap
  • Clinker Cooler
  • Rotary Kiln
  • Primary Air Fan
  • Primary Air Damper
  • Storage Silo for Ground Coal
  • Rotary Valve
  • Cydone Collector

Finish grinding mill

Generally, in connection with the cement quality, the initial strength is enhanced by improving the finenessof the product but the long-term strength is not enhanced, so that excessive fine grinding should be avoided even to prevent waste of power. The Blaine value [cmVg] and the residual content [%] on a sieve with 88 (or 90) micron apertures (88 \xR) are available as the unit for the degree of the fineness of the product. The Blaine value is used for usual operation management due to its simplicity in measurement. This unit will, however, be insufficient when some improvement is to be made. The Blaine value indicates an increment in the specific surface area of the object to be ground, that is, the amount of energy consumed for grinding, while the 88 jxR value represents the residual rough particle content not contributing directly to the strength of the product. Although there is a correlation between these two values for the fineness of the products produced from the same system, an attempt to improve the grinding efficiency means nothing other than an attempt to achieve a lower 88 |iR value with a lower Blaine value. JIS, for example, specifies that ordinary portland cement should have a Blaine value of 2500 or more [cm2/g] but it provides no prescription for 88 pR [%]. When the residue on a 88 p. sieve is too high,there may be some cases where the prescribed value 70 or more [kgf/cm*] for 3 days, or 150 or more [kgf/cm2] for 7 days cannot be cleared. In this connection, the international standard for the 88 nR value of cement is within the range of 1 to 2 [%], while that for the Blaine value is within the range of 3,050- 3,300 [cmVg]. The particle size distribution of the product varies substantially depending on the mill types, and the product by the open circuit process has a broad particle size distribution as compared to the product by the closed circuit process. And, when half-burned raw material is mixed in the clinker, an unusually high Blaine value is sometimes obtained because such material is easilv ground. In particular, when a number of mills with different sizes and systems are used, to avoid erroneous judgments, it is desirable to control the Blaine value together with 88 |xR. In the closed circuit process, a dynamic separator is provided to avoid excessive grinding of the product and mixing of coarse particles. Though various types of separators have been developed, mechanism to adjust a critical panicle diameter by a balance of circulating ascending current and whirling current is common, so that such separators are generically called air separators. Even including the power for the separator and the attached fan, power consumption by the closed circuit process is 10 to 15% less than by ,the open circuit process. Since each separator is designed so as to allow changing of classification properties, a key point to efficiently operate this system is to control the feed quantity to the mill so as to keep an appropriate circulation rate (generally 200 to 300%) by taking into consideration the grindability of the clinker and the desired fineness of the product. In case of trying to improve the fineness of the product with the open circuit mill whose length is about three times of its diameter, that is, relatively short, it may be successfully done by installing a separator and changing to the closed circuit process. A detailed description on the efficiency improvement of the mill itself is provided above in the paragraph on the raw mill. To avoid repetition, no further description is made here. To maintain the optimum medium filling amount is important for any kind of ball mill. It is advisable that once the optimum operation conditions have been determined, the operation sound of the mill shell at that time should be memorized or the noise level and frequency characteristics should be measured when measuring instruments are available. Thereafter, the difference from these in the sound will allow judging whether the operation conditions are appropriate or not. When the operation technique attains this level, an acoustic feed control system using a microphone can be successfully introduced. Needless to say, operating the mill under an overload condition must be avoided. To reduce the load of the finishing mill intentionally because of its higher sintering capacity compared to the kiln, however, is not recommendable except for such special cases as electric power supply being limited. Usually, it will be more profitable to operate the mill with full load and thereby reduce the operation hours for the day. Especially when power is supplied from the public power supplier, prior negotiation should be made with the supplier side so that operation can be done intensively during the nighttime zone with less power demand. This should bring about mutual merits. In the finish grinding process, grinding with blast furnace slag blended in the clinker increases electric power unit consumption rate in this process. In some cases, also fuel may be required. However, these increases in the unit consumption rate are by far smaller than the total energy unit consumption required for burning clinkers. Therefore, this will result in larger conservation of the energy unit consumption in terms of value per product cement ton. It should, however, be noted that this will make no sense if it brings about some discount in the product price because of the decline in the product quality. Closest attention should be paid to the quality control of the base clinker and the mixtures.

Conclusion

The cement industry in Japan has drastically changed its production process from the wet process to the dry process and promoted the NSP system as increasing production scale. Since energy cost of total cement production cost is large, energy conservation is an important matter in technical improvement activities. The cement production cost depends on the adopted production process. The wet process cannot defeat the dry process as regards energy consumption. At the technical level of quality and productivity, there is no reason why the adoption of the dry process should be impeded. The improvement of a cement plant, however, needs large investment. The timing of the investment of process improvement must be carefully determined taking into consideration the budgetary condition of enterprises and the outlook of the cement market. Before improving a process, activities of “good housekeeping” and “equipment improvement” should be applied to promote energy conservation.

Categories: Grinding Mill Tags: , ,

One Response to “ Coal mill ”

  1. Demand:clinker grinding unit | Materials: clinker | SAMIR JABAL From New Turkey Says:

    We idetails and price of clinker grinding unit 40 to 50 ton per houre output size 50mm

Products Quick Links