How to operate raw material grinding system economically

In the cement production process, the production efficiency of raw material grinding system has a certain extent influence and restriction to the cement clinker production management level and profitability, because firstly the main energy consumption of cement clinker production is electricity and fuel, and the power consumption of grinding system accounts for about 65%-70% of the cement production power consumption (that of new type roller press system is 30%-40%), which is an important component of cement manufacturing cost; secondly, the low efficiency of raw material grinding system will lead to insufficient amount of raw material, which can seriously affect the operation level of the rotary kiln, and that will directly increase the cast of single ton of clinker; thirdly, raw material shortage situation caused by inefficient operation of grinding system is bound to make the daily inspection and maintenance work of the grinding mill into a passive state, the production will also enter the vicious cycle. Therefore, managing well the raw material grinding system to continuously improve the economic operation is the issue that the cement clinker production enterprises must face.

1. The main factors affecting the operating efficiency of raw material grinding system

1.1 The effects of the size and grade of limestone on the yield of the mill. Raw materials are mainly composed of: limestone, sandstone (low silica sandstone), iron powder (iron ore), fly ash (slag), the proportion of limestone (the most important raw material ingredient) is 80%-83%.

1) When the limestone particle size is too large, the over-large particles will keep putting up instantly the grinding roller, as so to hamper a good grinding layer formation, increase the mill vibration value, and even cause vibration stop. When the limestone grain size is too large, the grindability is worse, so that mill rejects increase, the external circulation rises, and the output of the grinding mill will become low. If increasing the grinding pressure to to adapt to raw material, will increase the mill running current of the mill will increase; if mill vibration occurs during operation, the equipment will be damaged worse.

2) If limestone contains excessive mud, powder material is too much, cohesiveness is poor, the particle size distribution of raw materials will be unreasonable, resulting in unstable material layer and mill cycle increasing. That will cause collapse phenomenon, make the mill vibration value becomes large, and shut down the mill because of vibration, so as to affect the operation efficiency of grinding mill and decrease the output.

3) When the grade of limestone is bad, it can be distinguished from the surface view. The black stone in limestone is easy to change. When the poor grade limestone enters the mill, the amount of slag will be increased, and the outer circulation will be increased, so that the output of the mill will decrease.

1.2 The influence of main parts wear and equipment failure on production

1.2.1 Grinding roller shell and grinding table liner

GRMR vertical roller mill of our company (CHAENG - Great Wall Machinery) is the host equipment of raw material grinding system. the service lives of grinding roller shell and grinding table lining not only depend on steel material but also on the particle size and grade of the raw materials. If limestone is too large, the circular grinding frequency will increase, which will make the abrasion of the liner greater, when worn is up to a certain extent, grinding efficiency decreases, slag quantity rejected by mill increased, and then the output of vertical roller mill will decline greatly.

1.2.2 Nozzle ring and air guide cone

Nozzle ring and air guide cone of vertical roller mill are the key components of vertical roller mill. Their main function is to form vortex wind, so that the dusty gas enters the dynamic separator according to a certain trajectory. If the nozzle ring and the air guiding cone wear situation reaches a certain degree, the trajectory of vortex air will change, which will not only affect the powder selection efficiency, but also increase the wear of other parts of vertical roller mill.

1.3 The influence on energy consumption of system air leakage

Under the condition that the total air volume of the system is constant, the air leakage of the vertical roller mill will decrease the wind speed at the nozzle ring, which will lead to the increase of the cyclic load and the high pressure difference, and in the case wear and vibration will be easy to occur. In order to keep the wind speed at the nozzle ring, the working load of the circulating fan and tail fan will be increased, so the energy consumption will increase and the output of vertical roller mill will be reduced to a certain extent. The air leakage in other parts of the grinding system will also affect and increase the load of the circulating fan. Common outside leakage points usually appear in the main body of the grinding mill (upper part of hydraulic tension rod, overhaul door and slag discharge mouth), cyclone separator and air duct (channel) and so on.

2. Relevant measures

2.1 Control the grade and crushing size of limestone

2.2 Strengthen the inspection and maintenance of raw material preparation system equipment

1) Check work of raw material vertical roller mill shouldn’t be less than 2 times a week.

2) Attaches great importance to the lining of grinding roller and grinding table’s repair and recycle use. In principle, welding and repair of high chromium liner can’t be more than 3 times. The repaired linings shall be subject to acceptance and crack inspection of the main dimensions, and the contact area and clearance shall be checked during the assembly process to ensure that the lining assembly meets the technical requirements.

3) Focus on inspection and maintenance of belt conveyor anti-rain cover and raw materials warehouse, prevent belt machine and raw material warehouse from water leaking.

2.3 Pay attention to maintenance of hydraulic and lubrication system

1) Serious leakage of hydraulic cylinders should be commissioned by professional manufacturers to repair, to avoid the unintended consequences caused by imperfect work conditions, overhaul environment pollution and other reasons.

2) The hydraulic and lubrication lines shall be checked and maintained regularly.

3) Perform sampling inspection on the lubricating oil of main reducer and grinding roller periodically, and filtering or replacing lubricant according to the situation.

2.4 Remove the air leaking point in time

Raise awareness of negative impact on production and circulation fan energy consumption caused by the system air leakage, strengthen inspection and repair work for system are leakage, so as to timely eliminate air leakage.