Roots blower is used in rotary kiln firing system

The two 2500T/D production lines of the customer are equipped with roots blower with different speeds in the firing system respectively. Line 1 is equipped with low-speed Roots blower and Line 2 is equipped with high-speed Roots blower. After years of comparison of production and application, the low-speed Roots blower used in line 1 has stable performance and low failure rate, so it is more suitable for production and application.

No. 1 production line low speed Roots blower

1. Features of the blower
1) The roots blower at low speed has large volume and mass, and the designed motor is of large power. For example, the volume of JGR (A) 250D Roots blower fitted to line 1 is twice that of SRLA20 Roots blower fitted to line 2, with an additional mass of 1444kg and A motor power of 20kW.
2) Bearing lubrication shall be completely lubricated by oil pool. In the front and rear ends of roots blower gear and bearing transmission, there are lubricating oil pools, N320 medium load industrial gear oil is used to lubricate the gear and bearing. In the gearbox, lubrication of the bearing is achieved by the operation of the gear. In the drive bearing tank on the other side, the bearing is lubricated by an oil swing pan on the drive shaft. Both tanks are equipped with circulating water to cool down.

2. Application in production
Line 1 has been in use for more than 5 years. During this period, the Roots blower operates normally, and the air volume and pressure meet the requirements of calcining in rotary kiln. There has been only one failure of coal roots blower at the kiln end. The reason of the fault is the wear of rotor bearing, the radial clearance of the bearing increases, so that the impeller of the blower has abnormal sound in the operation. During the maintenance, the bearing was replaced, so that the blower back to normal.

No. 2 production line high speed Roots blower

1. Features of the blower
1) The roots blower with high speed is small in size, small in mass and small in power of the designed motor. The whole blower appears small and exquisite, handling and installation is more convenient. The impeller profile adopts the improved compound profile, which has high volume utilization coefficient and high efficiency.
2) Bearing lubrication adopts two methods: oil pool lubrication and grease lubrication. On one side of the transmission gear (auxiliary drive), there is a fuel tank, which is filled with N320 medium-load industrial gear oil. The bearing is lubricated by splashing gear oil from the gear operation. On the main transmission side, the bearing of the spindle is lubricated with grease. The grease adopts lithium base grease ZL-3, and the bearing seat is provided with a pressure spring type oil filling hole. The fuel tank and bearing housing are provided with circulating water for cooling.

2. Application in production
In the more than 2 years of use, the coal conveying, primary blower and kiln end blower all have faults to some extent. The reason for the failure is that the main transmission bearing is easily damaged.

3. Cause of failure of roots blower with high speed
The main fault of roots blower at high speed is the short life of main transmission bearing. This is because the main bearing lubrication grease, roots blower and in operation, the impeller by compressed air forced air supply, produce high temperature and load, while bearing outdoors with circulating water cooling, but the blower impeller shaft is passed to the bearing inner sleeve heat cannot be eliminated in time, such failure caused by bearing grease is easy to wear and prolong the life of the bearing is shorter, the general is 1 ~ 2 years. And the auxiliary drive sideslip lubrication oil lubricated bearing, bearing lubrication is better, the service life is longer.

4. Application comparison of two roots blower
1) power consumption
High speed Roots blower, motor power is small. The total capacity of Roots blower of line 2 is 60kW lower than that of Line 1.

40kW×24h/d×30d/ month × November/year = 316800kWh/ year

2) maintenance
Due to the high speed Roots blower failure rate is higher, in the maintenance, obviously more investment than the low speed Roots blower. At present, it is not possible to change the main transmission bearing of roots blower with high speed to lubricating oil, because this requires changing the housing and structure of the blower.
To maintain the normal operation of Line 2, the following measures have been taken:

5. Exchange and standby measures
1) Three Roots blower supplying coal powder at kiln head and kiln tail for general use.
This is also the original design requirements. The pipes of 3 blower are connected with each other and equipped with valve control. When a roots blower fails, as long as the valve of the roots blower is closed and the spare roots blower and valve are started, it can meet the urgent need of production.
2) Roots blower of kiln end decomposition furnace and roots blower of coal powder feed at kiln end are used in general.
3) The kiln head roots blower cannot be used interchangeably with other blowers. In case of failure, the kiln has to be stopped for maintenance.

6. Improve the working environment of roots blower main transmission bearing
1) Increase the circulating water of the main transmission bearing and reduce the running temperature of the bearing.
2) When the weather is hot in summer, the blower with axial flow will reduce the overall temperature of roots blower.
3) Increase the lubrication frequency of bearings from once to twice per shift.

Therefore, the high speed Roots blower design small, save energy, in order to achieve the required wind pressure, air volume, the design with high speed to compensate. However, when the speed is increased, the main transmission grease lubrication is not suitable for bearing lubrication, thus shortening the service life of the bearing. The low-speed Roots blower has large volume and large impeller, so the low-speed meets the requirements of production and application. However, the motor with large power is needed, and its consumption of electric energy is larger than that of the high-speed Roots blower. So both designs have their pros and cons. In short, the low-speed Root blower is more suitable for customers’ sintering system because of its advantages such as balanced drive, long service life and low failure rate, as well as higher requirements on equipment operation rate for rotary kiln calcination.