FLUENT6 ． By using FLUENT6 . 计算流体动力学软件对内滤式反吹风清灰方式的布袋除尘器内的流场 、 压力进行数值模拟，并通过改变过滤风速对布袋除尘器内流场和压力的影响进行计算绘图，得出了一些有规律的结论，为布袋除尘器的设计和运行提供了参考依据 。 1 Computational fluid dynamics software numerically simulates the flow field and pressure in a bag filter with an internal filter type reverse blower and ash cleaning method , and calculates and plots the influence of the filtering wind speed on the flow field and pressure in the bag filter with Some regular conclusions were reached, which provided a reference basis for the design and operation of the bag filter .
、 前 1.Before Say:
GB 13223 － 2011 《 火电厂大气污染物 排放标准 》 的实施，比较旧标准新标准中规定的烟尘排放标准更加严格 。 With the implementation of the new GB 13223-2011 " Emission Standards for Air Pollutants of Thermal Power Plants " , the smoke and dust emission standards specified in the new standards of the old standards are more stringent . 。 Judging from the current flue gas dust removal technology, the main choices are electric dust collector and bag dust collector . 。 Because the electrostatic precipitator is greatly affected by changes in the working conditions and load of the boiler, the change in the specific resistance of the dust and other characteristics of the dust greatly affect the dust removal efficiency of the electrostatic precipitator .
。 Therefore, with the gradual increase of flue gas purification requirements, conventional electrostatic precipitators will face severe challenges. More and more coal-fired power plants will use bag dust collectors to handle flue gas, and their investment and operating costs will gradually increase. Drop, in some cases even lower than the electrostatic precipitator . 。 In the situation of reducing the total amount of smoke and dust, bag dust collectors will become the first choice . 。 The effect of the bag filter is closely related to the filtering wind speed. The study of the effect of the filtering wind speed on the performance of the bag filter is particularly important .
除尘机理： 2. Dust removal mechanism:
。 The filtering process of the general bag filter is actually divided into two stages. First, the dust-containing gas passes through the cleaning filter. At this time, the fiber is the main filter . 。 When the amount of dust trapped on the filter material continues to increase, part of the dust is embedded in the filter material, and part of the dust is attached to the surface to form a dust layer. At this stage, the filtration of dust-containing gas mainly depends on the dust layer. It plays a more important role than filter media and significantly improves the collection efficiency . 。 For industrial bag filters, the filtration process is mainly performed in the _ stage .
It can be seen that the collection efficiency of the bag filter is high, mainly due to the role of the dust layer formed on the filter material. The filter cloth mainly plays the role of forming and supporting the dust layer, and the primary dust layer should be kept when cleaning. Excessive dust removal will cause a significant decrease in efficiency and accelerate filter bag damage.
Figure 1 shows the classification efficiency curves of the same filter material under different conditions. It can be seen from Fig. 1 that the collection efficiency of the clean filter material _, after the dust accumulation _, and after the dust cleaning is reduced.
Figure 1 Capture efficiency under different conditions of filter material
Dust-collecting filter material, 2—filter material after shaking, 3—cleaning filter material
3. The main factors affecting the performance of the bag filter:
The performance of the bag filter is closely related to the dust layer on the filter bag, the characteristics of the filter material, the characteristics of the dust, and the filtering wind speed.
3.1 Impact of dust layer:
When the filter material purifies the dust-containing gas, there is no dust layer on the filter material, and the ability to trap dust is low; when the dust layer is formed, it has a good trapping effect on dust.
3.2 Impact of dust characteristics:
The dust particle size has a great influence on the filtration efficiency of the bag filter. For 1μm dust particles, the classification filtration efficiency can reach 95%; for dust particles larger than 1μm, the filtration efficiency can be more than 99%. The more charge the dust particles carry, the higher the filtering efficiency. With this feature, the use of the charge before or at the entrance of the bag filter can capture 99% of dust particles above 1.6 μm. 99%.
3． 3. Influence of filter characteristics:
In the woven filter cloth, the surface of the short-fiber fabric has many fluff, and it is easy to form a stable primary dust, and its filtration efficiency is higher than that of the long-fiber fabric.
3． 4. Impact of filtering wind speed:
Appropriate filtering wind speed can easily cause dust to form a dust layer on the surface of the filter bag, which is conducive to dust collection.
4. Use FLUENT to perform numerical simulation calculation in the bag:
A bag calculation model was established with GAMBIT, and a non-coupling, implicit solver was used to solve the problem with the FLUENT-2D solver. Assuming that the inlet pressure and outlet pressure are constant, the flow field and pressure at different filtered wind speeds are calculated. In the pressure and speed distribution chart, the inlet is inlet, and the three outlets are outlet1, outlet2, and outlet3; directly below is the inlet inlet.
Just above is outlet outlet1, on the left is outlet2, and on the right is outlet3. a. The inlet pressure is -2487Pa, the outlet pressure is -3987Pa, and the filtering wind speed v = 1. 1m / min, the pressure and velocity distribution inside the bag are shown in Figures 2 and 3.
2 Figure 2 Pressure map
From the pressure distribution chart at this time, it can be clearly seen that the pressure distribution at the same position on both sides of the bag is the same. The pressure at the outlet is small, and the pressure is greater toward the center of the bag, which forms a closed pressure. Field, the pressure is normally distributed from the edge of the bag to the center of the bag and gradually increases.
3 速度分布图（ Vmin = 0 ． Figure 3 Speed distribution ( Vmin = 0) . ， Vmax = 1 ． 008234471m / s , Vmax = 1 . ） 120005m / s )
From the velocity distribution chart at this time, it can be clearly seen that the speed at the same position on both sides is the same. The speed of the inlet _, the speed gradually decreases in the y-axis direction and the speed of outlet1 is small. From this figure, we can know that the dust particles are At the entrance where the speed is high, _ is fast. When the thickness of the deposit at the entrance increases, the speed will gradually increase along the y-axis direction. After the ash at the entrance is removed, the speed at the entrance will change to _ again, The speed is small where the gray layer is thick. But the difference is that the speed distribution in the middle is slightly more, and the overall speed distribution is uniform.
b. The inlet pressure is -2487Pa, the outlet pressure is -3987Pa, and the filtering wind speed v = 1. 0m / min, the pressure and velocity distribution inside the bag are shown in Figures 4 and 5.
Figure 4 Pressure distribution diagram
Compared with Figure 2, it can be clearly seen from the pressure distribution diagram at this time that the pressure distribution at the same position on both sides of the bag is the same. A closed pressure field is formed, and the pressure is normally distributed from the edge of the bag to the center of the bag and gradually increases. But the difference is that the closed pressure field moves negatively to the y-axis and the pressure center moves down.
Figure 5 Velocity distribution diagram (Vmin = 0.0101489489m / s, Vmax = 1.111524m / s)
Compared with Figure 3, the velocity distribution is not uniform at this time. c. The inlet pressure is -2487Pa, the outlet pressure is -3987Pa, and the filtering wind speed v = 0. 9m / min, the pressure and velocity distribution inside the bag are shown in Figures 6 and 7.
6 Figure 6 Pressure map
Compared with Figure 4, the pressure distribution at this time is very uneven. Two pressure centers appear at the center of the bag and at the upper exit, making the pressure field in the bag very chaotic.
Fig. 7 Velocity distribution diagram (Vmin = 0.202188188 m / s, Vmax = 1. 21229 m / s) Fig. 8 Pressure map
Compared with Figure 5, the flow field distribution at this time is very chaotic. The velocity distribution does not gradually decrease from the inlet, and the velocity at outlet1 is greater than the inlet velocity. This situation is not conducive to the collection of dust by the bag, and it is easy to damage the bag. bottom.
d. The inlet pressure is -2487Pa, the outlet pressure is -3987Pa, and the filtering wind speed v = 0. 8m / min, the pressure and velocity distribution inside the bag are shown in Figures 8 and 9. Compared with Figure 6, although there is only one pressure center at this time, the pressure distribution_unevenness starts from the inlet of the bag, and the pressure center moves almost to outlet1.
9 Figure 9 Vmin = 0 ． 02780255m / s ， Vmax = 1 ． 578396m / s ） Velocity distribution diagram ( Vmin = 0. 02780255m / s , Vmax = 1. 578396m / s )
Although the speed distribution is uniform compared to Figure 7, it is not that the speed at the entrance is large and gradually decreases along the y-axis positive direction, but on the contrary, the speed at outlet1 can easily damage the bottom of the bag. ,
5. Concluding remarks:
According to FLUENT6. 1 Computational fluid dynamics software numerically simulates the flow field and pressure in a bag filter with an internal filter type reverse blower and ash cleaning method, and calculates the effect of the flow field and pressure in the bag filter
by changing the filtering wind speed The following conclusions are reached: When the filtration speed is reduced, the flow field in the bag has serious turbulence at the bottom of the bag, and the pressure center field changes from one to multiple. This situation causes the dust layer to be too thick at the bottom of the bag , It is easy to damage the bottom of the bag, causing ash leakage and affecting the dust removal efficiency; it is recommended to filter the wind speed at 1. 0 to 1. 1m / min.