Selection of Oxidation Blower in Power Plant Flue Gas Desulfurization Project

The desulphurization project is the one-time investment and continuous operation investment in the construction of thermal power plants with the highest investment in environmental protection projects, and it is difficult for enterprises to obtain corresponding profit returns. Therefore, in the more mature limestone-gypsum wet flue gas desulfurization technology used in thermal power plant flue gas desulphurization projects, the selection of equipment will directly affect the economic and technical characteristics of the entire project investment. As a key equipment in the entire desulfurization operation, the selection of the oxidation fan is directly related to the investment and operation of the entire project.

In the current limestone-gypsum wet flue gas desulfurization project, the commonly used oxidation fans include Roots blower (double-blade, triple-blade) and centrifugal blower (multi-stage centrifugal, unipolar centrifugal). This article describes the characteristics of the two blowers. A comparative analysis.

1 Roots Blower Features

1) The impeller and shaft are of integral structure, and the impeller is not worn. The fan performance is permanent and can be continuously operated for a long time;

2) It has hard exhaust characteristics. When the pressure changes, the flow rate changes very little. In the design pressure range, the flow rate of the pipe network changes little when it is changed, and it is suitable for the work place where the flow requirement is stable and the resistance change is large;

3) Due to the impact pulsation during the operation of the Roots blower, the noise of the Roots blower is high and it will have a great impact on the surrounding environment.

At present, most domestic power plant desulphurization projects use domestic Roots blowers.

2 Centrifugal blower features

1) The structure is relatively compact, occupying a small area;

2) Smooth operation: The optimized design of the impeller minimizes the axial force, and has an efficient impeller, and is corrected by the static and dynamic balance, so that the entire machine runs smoothly. Without any vibration damping device, the bearing Amplitude ≤ 0.04mm;

3) The noise is low. When the fan is running, there is no mechanical friction. The reasonable blade shape is used to minimize the noise. The noise generated by a centrifugal blower is high-frequency noise, and noise can be provided as long as there is an obstacle, so there is almost no noise outside the fan room.

In the actual application of power plant desulphurization, the centrifugal fan has the characteristics of large fluctuations in the flow rate of the absorption tower, and the corresponding air volume adjustment device is required. And because the provision of pressure depends to a large extent on the speed increase, and the speed is provided by the balance, lubrication and material properties and other restrictions, so the centrifugal blower control and maintenance

This is particularly important, making the fan structure complex and increasing the number of points of failure.

3 Comparison of Roots Blower and Centrifugal Blower in Practical Engineering Applications

(1) Fan efficiency

The multi-stage centrifugal blower adopts multi-stage impeller, and the efficiency is lost in the transmission process, generally about 80%. The Roots blower is a volume-type fan, and the pressure is increased by changing the volume of the air chamber, and the efficiency is about 70%. Therefore, when selecting the model under the same working conditions, there are certain differences in shaft power of various fans. Multistage centrifugal blowers can save about 15% energy compared to the corresponding Roots blowers. The

(2) Noise

The centrifugal blower has a noise level of 95dB (A) (no noise reduction) and is a high-frequency noise. Roots blower noise is inherently high (up to 110 dB(A)) and is low-band noise. The high-frequency noise is slightly silenced and it is easy to achieve noise reduction. The low-frequency noise of the Roots blower is difficult to handle, the noise spreads far, and it makes the human hearing very uncomfortable.

(3) Fan drive facilities

The Roots blower adopts a belt drive and the overall operation is relatively stable. However, when the installation or maintenance is not proper, the belt is easy to slip. Centrifugal blower adopts gear box + coupling transmission, bearing adopts sliding bearing, low-speed end adopts cylindrical watts, and high-speed end adopts tilting watts structure, which ensures stable operation of bearing during high-speed rotation, but the complete system is more complex and has more failure points. It is easy to cause the danger points of the fan to increase and the requirements for the protection system are high.

(4) Equipment cost

Due to the high rotational speed of the centrifugal blower, wear of many components, such as blades, is relatively large, and the requirement for the fan bearings is high. Therefore, the multi-stage centrifugal blower blade material is made of aluminum alloy and the overall milling process is used, resulting in the overall price of the centrifugal blower being relatively expensive. At current market prices, the price of a multi-stage centrifugal high-speed fan is about 3 times or more higher than that of a Roots blower.

4 Conclusion

In general, the performance of the Roots blower and centrifugal blower has its own advantages and disadvantages. The biggest advantage of a Roots blower relative to a centrifugal blower is the price; the biggest advantage of a centrifugal blower over a Roots blower is the efficiency of the blower. Therefore, in the selection of fans in power plant flue gas desulfurization projects, comprehensive trade-offs must be taken into consideration. It is most important that these three factors be unified in production, technically advanced, and economically reasonable.