In the past ten years, the application technology of vertical roller mill grinding system has developed faster and faster. In the long-term use process, the process of secondary fine powder collection has many drawbacks. For example, the inlet of the first-stage cyclone tube is too fast, the maintenance workload is increased, the system is leaking heavily, affecting the pumping force of the updraft in the mill, and the mill output is reduced; the circulating fan before the bag filter has a short service life (generally Less than one year), after the dusty gas wears the fan impeller, the balance is out of balance, resulting in noise and vibration, which affects the safe operation of the equipment; thus the control of the system process parameters is difficult to achieve a good state, and the grinding efficiency is reduced.
With the development of the bag dust collector cleaning technology and the material of the filter bag, the use performance of the domestic high-concentration bag dust collector is more and more stable and reliable. Among them, the gas box pulse bag dust collector allows the dust concentration of the inlet to reach 1000-13009/m3, which fully meets the requirements of the first-class fine powder collection of the vertical roller mill system, which simplifies the process flow, reduces equipment, and reduces the workshop floor space. The safe operation rate is improved.
The vertical grinding grinding process collected once in the outer circulation of the grinding mill maintains the characteristics of the “rough material grinding external circulation process” and the exhaust gas after the system purification can be used as the circulating wind waste heat utilization, and removes the high failure rate of the cyclone cylinder and the circulating fan. The impact of the grinding process parameters is small, timely adjustment, production control optimization can be achieved. This process has become a widely adopted design for vertical roller mill grinding systems.
Vertical grinding cement grinding first-level closed-circuit process, mainly divided into two parts: grinding functional zone and mixed functional zone. The grinding function zone mainly realizes the separate grinding of cement clinker and mixed materials, and the mixed functional zone mainly realizes the synthesis and configuration of various varieties of cement according to different product standards. The vertical roller mill is self-contained in a closed-circuit grinding system. Since the operating parameters of the cement vertical roller mill are not the same as the raw material grinding, it is easy to produce unreasonable cement particle composition, less fine powder, low early cement strength, serious bleeding phenomenon, etc. In addition, the cement component is more raw than the raw material. The wearability is poor, and the grinding roller and the grinding disc are seriously worn. Therefore, the vertical roller mill grinding cement has high requirements on the material of the equipment, the structure of the classifying device should be improved, and the operation and maintenance also has certain difficulty. Until July 2000, the vertical grinding and final grinding system applied to cement grinding in China was completed and put into production in Anhui Zhujiaqiao Cement Company. The system adopts the German-made Loesche mill LM46, with an annual output of 700,000 tons of slag cement. The process flow is shown in Figure 4-8. It is essentially a process line in which clinker and slag are separately ground and then cement is synthesized. This avoids the difficulty in controlling the distribution of cement multi-component particles during the gas classification process, and provides convenient conditions for ensuring the quality of the cement.