A company has built a 4000t/d cement clinker production line, its pulverized coal metering and conveying system is equipped with two rotor scales, and the pulverized coal preparation workshop is located at the kiln head. The coal feeding system at kiln head and kiln tail is equipped with Roots blower. The actual operating gauge pressure of the Roots blower at kiln head is 15kPa, and the Roots blower at kiln tail is 23kPa. There are problems such as large motor power selection and high noise (about 110dB).
01
Working principle and maintenance requirements of air suspension fan
The air suspension fan is an integrated machine of permanent magnet motor and high-pressure centrifugal fan, sharing one shaft. The fan adopts small impeller with high speed to ensure high air pressure and sufficient air volume; With the technology of dynamic air bearing and permanent magnet direct drive motor as the core, the fan shaft can be self suspended at about 30000 r/min; The impeller adopts three-dimensional flow design. Compared with Roots blower, the air suspension blower saves more power because it reduces the friction loss of equipment operation, has no mechanical wear, and has a semi permanent life (starting and stopping have friction, the manufacturer promises a service life of 30000 times of starting and stopping, and the laboratory has reached 50000 times). In addition, the air suspension fan can also meet the stable production of the kiln without adding lubricating oil and cooling water during operation, which is convenient for maintenance and improves the site environment.
If the air suspension fan needs to be maintained during production and operation, just clean or replace the filter cotton outside the equipment box in time according to the pressure difference prompt; The high-precision filter element shall be cleaned again during the shutdown period. In addition, the ventilation area of the plant should be large enough, and filtering facilities can be added at the plant vent to further improve the indoor environment.
02
Selection and installation requirements of air suspension fan
In August 2019, the company selected one Kingston air suspension fan to feed coal at the kiln tail and one Leitz air suspension fan to feed coal at the kiln head in November. Keep the original standby Roots blower, power supply and circuit. When selecting the fan, there is a certain margin of power and the fan air pressure is more than 1.25 times of the working air pressure, so as to ensure that the raw air volume will not decrease and meet the production requirements. The site photo of the original Roots blower is shown in Figure 1, and the selection parameters of Roots blower and air suspension blower are shown in Table 1. Before the installation of air suspension fan, it is necessary to block the air leakage outlet of the plant and install ventilation and dust removal windows to ensure the environmental health of the plant. See Figure 2 for site photos of ventilation and dust removal windows.
03
Technical transformation effect
After the transformation, the air suspension fan runs stably and can meet the production requirements of the kiln. The site photos of the air suspension fan are shown in Figure 3 and Figure 4, and the operation picture is shown in Figure 5.
3.1 Significant power saving effect
(1) Energy saving (energy saving rate) of coal feeding air suspension fan at kiln tail: 117-75=42kW (36%). If the annual operation is 300d, the annual power saving is about 302400kw, and the electric charge is calculated as 0.6 yuan/kw · h, the annual electric charge can be saved by 181440 yuan.
(2) Energy saving (energy saving rate) of coal feeding air suspension fan at kiln head: 60-42=18kw (30%). If the annual operation is 300d, the annual power saving is about 129600kw, and the electricity charge is calculated as 0.6 yuan/kw · h, the annual electricity charge can be saved by 77760 yuan.
3.2 The plant environment is effectively improved and the noise reduction effect is significant
(1) By changing the equipment from water cooling to air cooling, and changing the bearings to oil-free lubrication, it is no longer necessary to add lubricating oil and cooling water, which greatly improves the plant environment.
(2) In terms of noise reduction, the original coal feeding Roots blower at kiln head and kiln tail has a large noise of about 110dB. After it is replaced by suspension blower, the noise is significantly reduced, about 70-80dB, and the noise is reduced by about 20%.
3.3 Clinker quality improvement
See Table 2 for comparison of 3d and 28d compressive strength of clinker before and after technical transformation.
Table 2 Comparison of Clinker Compressive Strength, MPa
04
epilogue
(1) The company has adopted two air suspension fans to replace the original coal feeding Roots fans at the kiln head and kiln tail, and the power saving effect is obvious, and the technical transformation effect exceeds the expectation.
(2) The air suspension fan is air-cooled. Under the condition of high temperature in summer, the bearing temperature is normal and the equipment operates well.
(3) Considering the calculation of power saving, maintenance and overhaul costs, it is estimated that the investment in equipment reconstruction can be recovered in about 2 years.
(4) The air volume, air pressure and speed of the air suspension fan can be adjusted. At present, the key point of maintenance is to clean the box filter cotton to ensure that the differential pressure is within the effective range. In case of sudden power failure and coal accumulation in the pipeline of the equipment, the impact on the fan startup needs to be verified, and the reasonable setting of the outlet pressure of the suspension fan (or the conveying outlet pressure of the pulverized coal scale) still needs to be explored.
