Pipes conveying dusty air are different from those conveying clean air. On the one hand, because the dust in the air settles in the pipeline, the pipeline is gradually blocked and the flow resistance increases, which affects the normal work of the dust removal system; On the other hand, due to the friction and collision between dust and the pipe wall during transportation, the pipeline wears quickly.
Therefore, the following points should be paid attention to in pipeline design:
1. When determining the pipe diameter of each section, the lowest flow velocity in the pipeline should be considered. The so-called minimum velocity refers to the minimum airflow velocity necessary to prevent dust from depositing and blocking in the pipeline. This speed depends on the nature of the dust. Table 8- 13 lists the minimum speed of all kinds of dust. In addition, the higher the flow velocity in the pipeline, the better. If the flow velocity is too high, although the cross-sectional area of the pipeline can be reduced, it will increase the pressure loss in the pipeline network, thus increasing energy consumption and friction on the pipeline. Therefore, when setting up the pipe network, several factors should be integrated to select the flow velocity in the pipeline to determine the diameter of the pipeline. Generally speaking, the vertical section velocity is 8 ~10m/s and the horizontal section velocity is16 ~ 20m/s. ..
Table 8- 13 Minimum design velocity of pipeline
2. The pipeline should be installed vertically or obliquely as far as possible, and the inclination angle of the inclined pipeline should be greater than the natural angle of repose of dust. Under special circumstances, the pipeline can also be laid horizontally. However, the length of the horizontal pipe should be as short as possible, with the longest not exceeding 10 ~ 15m, and there should be maintenance and cleaning holes on the pipe.
3. The minimum diameter in the pipeline is not less than 80mm; For fine dust; For coarse dust is not less than100 mm; ; For coarse dust, not less than 130mm.
4. In order to reduce airflow resistance and save energy, the bend requires a certain radius of curvature. When the pipe diameter is d < d< 100mm, r > 3d when d = 100 ~ 150 mm, r > 2.5d when d≥ 160mm, r > 2d.
5. The branch pipe should be connected with the main pipe at the top or side. In this way, the dust deposited in the branch pipe easily falls into the main pipe to prevent the branch pipe with smaller diameter from being blocked by dust. The included angle between connecting tees should not be greater than 30, generally15.
6. For the connection between the air duct and the inlet of the fan, it is best to use a straight inlet. If space is limited, you can use the elbow entrance. The connection of fan outlet pipe should be considered to avoid vortex as much as possible. As shown in figure 8-2 1 and figure 8-22.
Figure 8-2 1 Fan Inlet Pipe Connection
Figure 8-22 Fan outlet pipe connection
The pipeline resistance can be calculated by the relevant formula of fluid mechanics, but the density of dusty air should be calculated by formula (8-4) according to the dust concentration.