Discussion on the Design of Dust Removal System in Textile Mill

At present, the textile technology and equipment at home and abroad are constantly updated, new technologies and equipment are emerging in endlessly, and the matching dedusting technology is also constantly improved. The main task of the dust removal system is to collect the impurities discharged from different parts scattered on each equipment, and use wind power to transport them to the dust removal equipment for dust and gas separation, so as to classify the dust and impurities, facilitate recycling and utilization, purify the air, and recycle or discharge according to the situation. A complete dust removal system must have three basic elements, namely dust removal equipment, pipeline network, and fan. In addition to the good quality and performance of the equipment itself, the reasonable configuration between the systems is more important. If the configuration is not good, even if the equipment is good, it will not be helpful.

1 Dust removal equipment

Dust removal equipment is an important component of the system, and the dust removal air volume is the key. In daily work, the air volume processed by the equipment when achieving dust removal effect is the dust removal air volume. The air volume for selecting dust removal equipment should be determined based on the total air volume required by the dust source, generally greater than 10% of the total air volume required, depending on the nature of the dust. The higher the concentration and viscosity of the dust, the more margin will be left, otherwise it will be less. For example, in the stage of cleaning and carding, there is a lot of miscellaneous cotton and dust, and the selected dust collector has a larger margin; However, the dust in the return air of the air conditioner is relatively small and less, and the margin can be reduced. Dust filters have become an essential set of dust removal equipment in textile mills. The dust filter combination machines produced by textile mills use two-stage air treatment equipment, with the first stage being a fiber pre-separator, including a disc pre-separator, fiber compactor, and suction fan. The main function is to filter, separate, and collect fibrous impurities in the air. The filter mesh size of the disc pre separator is generally 50-120 mesh, depending on the nature, length, and quantity of the fibers. The wind speed on the filter screen of the disc pre-separator should not be too high, and the general processing wind speed is 2.5-4.5m/s. The second stage is a multi-layer circular cage separator using WS-1, JM2, or JM5B filter materials, including multi-layer circular cages, sealing boxes, dust compactors, and dust collection fans. The main purpose is to filter, separate, and collect particulate dust in the first stage dust removal air, so that the workshop air is purified and reused or discharged, which can reduce air conditioning load and save energy. The filter material is also selected based on the performance of the impurities being treated, with a processing wind speed of around 0.69m/s and a resistance of generally around 100Pa. Reasonable configuration of two-stage air treatment equipment can achieve a dust filter efficiency of over 99%, and the dust content of the filtered air is less than 0.85mg/m ³, The fiber processing capacity can reach 50-80kg/h, with a total resistance of no more than 250pa. Two unit machines can be used separately according to needs. The processing air volume of LF102A-215 series dust filter combined machine is shown in Table 1

2. Dust removal pipeline network

The dust removal pipeline network is an important link in the dust removal system, serving as a bridge and hub connecting various equipment. It emits dust or harmful gases to designated locations and serves as a channel for improving the environment. The design of the dust removal pipeline system is relatively complex and needs to be flexible and variable. Its design and configuration need to change according to the process, model, exhaust method, exhaust volume, and pipeline organization form of the textile host. The quality of the design will directly affect the selection of fans and the dust removal effect. Therefore, it is necessary to understand the precautions to be taken when designing the dust removal pipeline network.

The main function of the dust removal pipeline network in a textile factory is to transport dispersed dust and fiber impurities to designated locations for recycling or destruction, in order to clean the indoor environment and improve the working environment of workers. This involves the issue of pneumatic conveying.

Pneumatic conveying pipelines can be divided into two types: vertical pipelines and horizontal pipelines. Vertical pneumatic conveying is achieved by utilizing upward airflow to generate friction on objects. When the friction force is greater than gravity, it will increase the relationship between air transport and wind speed, as shown in Figure 1.

To suspend an object in the air, it is necessary to make: F2 ≥ F1

In the formula: F1- the gravity of the object in the air;

F2- The upward frictional force of air flow on an object.

F₁=W-VRg=W-W/Rw × R=W(1-R/Rg)

In the formula: V - Volume of the object

R-density of air

W - the gravity of an object;

Rw is the density of an object.

F₂=CAR/2g × (U-Ug) ²

In the equation: μ Air flow rate

C - Resistance coefficient of air

A - The projected area of an object perpendicular to the direction of airflow movement

G - Gravitational acceleration

Ug - The speed at which an object moves upwards.

When moving at a constant speed, i.e. F ₁=F ₂, it can be inferred that:

When the object is suspended, Uw=0, at this point μ Is the minimum value, where the speed is either the levitation speed or the terminal speed. Of course, its speed is also related to the factors of air and impurities themselves.

The velocity of pneumatic conveying on a horizontal pipeline must be increased to a certain value to cause the object to detach from the pipe wall and move in suspension (also known as suspended motion). At this time, the flow velocity is called the velocity of air flow. The horizontal pneumatic conveying is more complex, with the airflow direction perpendicular to the gravity direction of the object. The object itself is in an unstable state (in a rolling state before reaching takeoff), making its suspension and motion state more complex. Therefore, when choosing the airflow speed, it is generally based on the velocity of the airflow when objects are suspended in the vertical pipeline. In the dust removal system of textile mills, waste cotton or cotton fibers are generally used, which have a large volume and low density. It is generally not necessary to reach the clearance speed in the horizontal direction. Only the frictional force F ₂ generated by the wind speed is greater than the rolling (or sliding) friction generated by the cotton fibers and the pipeline, but in reality, it is basically determined based on the vertical wind speed. The total pipeline wind speed used in general textile factories is 12-15m/s, as shown in the table

In the pipeline system, dust and impurities are collected through multiple branch pipes in the main pipeline and transported to the dust filter. This form is suitable for textile equipment that requires dust removal, with similar air volume and pressure, but a large number and dense arrangement. For example, in carding machines and combing machines, to ensure that the air volume between each branch pipe is basically consistent, it is necessary to ensure that the resistance between each pipe is basically the same, with a difference of no more than 10%, which is stricter than the requirements of air conditioning pipe networks. Because the adjustment amount of the dust removal pipeline itself is small, but it is impossible to add valves to the pipeline, as that will affect the transportation of materials. Therefore, it is necessary to ensure that the static pressure value of the main pipe at the connection between each branch pipe and the main pipe is basically consistent, so that the working conditions connected to the dust collection point are the same. Reasonable diameter reduction of the main pipe is often used to reduce the dynamic pressure value to offset the resistance between the two interfaces of the main pipe, ensuring that the static pressure value of the main pipe remains unchanged. The local resistance of the pipeline accounts for a significant portion of the total resistance, so it is necessary to minimize the resistance and reduce fan energy consumption during construction. The factors that affect the local resistance of the pipeline network include: tees, elbows, reducers, etc. The included angle of the tee is generally made to 15 ° -30 °; The curvature radius of the elbow is generally greater than 1.5 times the pipe diameter, and the number of intermediate sections should be as much as possible; The diameter of pipelines should generally be reduced to an angle of less than 60 ° on both sides; The diameter of the main pipeline is generally less than 650mm, which is too large and not conducive to material transportation. Dust and debris are prone to sedimentation and blockage; The dust removal equipment should regularly replace the filter material, otherwise it will increase resistance and increase the fan load.

The total resistance between each pipe section connected to the same dust removal equipment unit should be balanced. Due to the fact that various textile equipment may not work simultaneously, and in order to avoid affecting the operation of other equipment during equipment maintenance, it is necessary to directly connect to the dust filter through a separate pipeline, such as flower cleaning equipment and auxiliary machinery. Due to the varying exhaust air volume required by the production equipment and its own air pressure (such as the air volume required by A045 cotton condenser of 4500m) ³/ h. The self outlet wind pressure is 500Pa; The required air volume for FA106 cotton opener is 3400m ³/ h. Their own outlet wind pressure is -600Pa, and their distance to the dust filter is also different. The wind pressure of commonly used dust filters during operation is generally around -1800Pa (depending on the fan), and the negative pressure value is limited. Sometimes, the distance is too far, resulting in too much pipeline resistance. The required negative pressure value of the equipment cannot be reached, and a relay fan needs to be added to increase the negative pressure. Therefore, it is necessary to reasonably consider the characteristics of production equipment and their distance to the dust filter, and calculate the pipe diameter based on this.

3 fans

The fan is the power equipment of the dust removal system, and the fan used is generally a centrifugal fan for dust removal, with a large air volume and high air pressure; Impellers are all without front disc blades, which will not produce fiber winding, hanging flowers, blockage, or spark phenomenon. The air volume of the fan should be matched with the supporting dust removal equipment, generally leaving a 10% margin. The total pressure of the main fan is equal to the total resistance of the supporting dust removal system, the negative pressure required by the equipment's dust discharge or suction port, and the sum of the fan outlet resistance and discharge resistance, with an appropriate margin left. This is the total resistance of the pipeline system, and then the fan is selected based on the calculated value. Fans are generally selected based on air volume, taking into account air pressure. It generally has multiple levels, and the middle value of the fan air volume should be chosen to be close to the calculated value. By analyzing the characteristic curve of the fan and the pipeline network characteristic curve, it can be seen that the fan is generally at the high point of fan efficiency, which is conducive to energy conservation. But there is no need to put the equipment in a state of low efficiency and high energy consumption for temporary savings.

4 Conclusion

The dust generated during the textile production process not only affects the indoor environment, but also affects the outdoor environment. Long term work in this environment can easily lead to occupational diseases. Therefore, it is necessary to improve dust removal technology, reduce dust in the textile workshop, ensure the working environment, and improve work efficiency.