In the dedusting system Ventilation pipe construction Several problems needing attention in design
A complete dedusting system includes dust hood Ventilation duct , dust remover and fan.
The construction of ventilation duct (referred to as duct) is the channel for conveying dusty airflow, which connects the dust hood, dust remover, fan and other parts into a whole. Whether the construction design of ventilation pipeline is reasonable or not directly affects the effect of the whole dust removal system. Therefore, various problems in pipeline design must be considered to obtain a more reasonable and effective scheme.
1. Piping components
1.1 Elbow is a common component for connecting pipes, and its resistance is related to such factors as bend diameter d, radius of curvature R, and the number of bends. The larger the radius of curvature R, the smaller the resistance. However, when R is greater than 2~2.5d, the resistance of the bend will not be significantly reduced, but the space occupied is too large, making it difficult to arrange the system pipes, components and equipment. Therefore, from the practical point of view, R is generally taken as 1~2d in the design, and 90 ° bends are generally divided into 4~6 sections.
1.2 Tee in the dedusting system of the centralized air network, the air flow convergence component - tee is often used. When the air flow velocity of two branch pipes in the combined tee is different, the ejecting effect will occur, accompanied by energy exchange, that is, the energy will be lost if the flow velocity is large, and the energy will be gained if the flow velocity is small, but the total energy will be lost. In order to reduce the resistance of the tee, the ejection phenomenon should be avoided. When designing, the airflow velocity of the two branches and the header is equal, that is, V1=V2=V3, so the relationship between the sectional diameters of the two branches and the header is d12+d22=d32. The resistance of the tee is related to the airflow direction. The included angle between the two branch pipes is generally 15 °~30 ° to ensure smooth airflow and reduce resistance loss. Tees cannot be connected in a T-shape because the resistance of the tee connected in a T-shape is 4 to 5 times greater than that in a reasonable connection mode. In addition, try to avoid the use of four-way as much as possible, because the airflow in the four-way has a great interference, which seriously affects the air suction effect and reduces the efficiency of the system.
1.3 When the gas in the diffuser flows in the pipe, if the section of the pipe suddenly changes from small to large, the gas flow also suddenly expands, causing a large shock pressure loss. In order to reduce the resistance loss, a smooth transition diffuser is usually used. The resistance of the diffuser is caused by the formation of vortex zone due to the inertia of the air flow when the cross section is enlarged. Involute angle а The larger the eddy current area, the greater the energy loss. When a exceeds 45 °, the pressure loss is equivalent to the impact loss. In order to reduce the resistance of the diffuser, reduce the diffuser angle a as much as possible, but the smaller a is, the longer the diffuser is. Generally, 30 ° is appropriate for the angle of involution a.
one point four Ventilation engineering The interface between the construction pipeline and the fan and the outlet fan will produce vibration during operation. In order to reduce the impact of vibration on the pipeline, a section of hose (such as canvas hose) is used at the place where the pipeline connects with the fan. Straight pipes are generally used at the outlet of the fan. When it is required to install elbows at the outlet of the fan due to the limitation of the installation position, the direction of the elbow shall be the same as the rotation direction of the fan impeller. The air flow at the outlet of the pipe is discharged into the atmosphere. When the air flow is discharged from the pipe outlet, all the energy of the air flow before discharge will be lost. In order to reduce the dynamic pressure loss at the outlet, the outlet can be made into a diffuser with a small diffuser angle. No hood or other objects shall be set at the outlet, and the exhaust air flow velocity shall be reduced as far as possible.
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