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Analysis of problems that should be paid attention to in the design of ventilation ducts in industrial plants
In recent years, the rapid development of industrial economy has correspondingly enhanced the production capacity of enterprises. In the process of technological transformation, it directly affects the air quality in the plant, makes operators feel uncomfortable, and further reduces the production level. Therefore, it is urgent to study how to optimize The internal environment of the factory building, and scientifically designed ventilation ducts can dissipate a large amount of waste heat and harmful gases in the factory building, thereby improving the indoor air quality. Therefore, combined with the actual situation, the measures to solve the problem of ventilation duct design are put forward.
1 Design and application of ventilation ductsin industrial plants
Due to the different functions of most factories, the floor area, span between columns and the height of the factory building are relatively large. There are complex process equipment and platform distribution inside the factory building, and there are a large number of daylighting windows and industrial doors and windows. If the factory building is rebuilt in the future, When designing ventilation ducts, various factors must be fully considered to ensure the rationality of ventilation settings. At present, natural ventilation is given priority in ordinary factory buildings. When natural ventilation cannot meet the requirements, ventilation ducts need to be designed. For single-storey factory buildings with complex process equipment and pipelines, roof-type exhaust fans are usually used to exhaust air, and side walls are equipped with air intake louvers for natural air intake. Or design the roof air intake fan to enter the wind. Based on the way the ventilator is installed on the roof, although the purpose of ventilation can be achieved, it cannot effectively improve the air quality inside the workshop. In addition, avoid short circuits when installing the ventilator on the roof. In the event of roof leakage, not only must waterproofing be done during civil construction, but also rain-shielding equipment must be installed when designing fans on the roof. There are a lot of process equipment and pipelines inside the plant, together with the water supply and drainage pipelines and electrical bridges, often form relatively complex pipelines, but the size of the ventilation pipelines is relatively large, and the pipelines require a large floor space. Therefore, the design of the ventilation fan Ducts are relatively short, which effectively eliminates interference between ventilators. When designing ventilation ducts, it is necessary to scientifically set the number of ventilation and air changes in consideration of the different application functions of the factory building. For some factory buildings where many doors and windows are often opened, it is necessary to carefully check the air leakage of the doors and windows to affect the ventilation.
2 Problems that should be paid attention to in the design of ventilation ducts in industrial plants
Factory buildings generally use civil beams to divide the smoke prevention area. Considering that the size of the ventilation duct is too large, it needs to occupy a lot of space. If it is installed separately, it will waste a lot of space. The system is integrated with multiple smoke prevention areas, so that the ventilation and smoke prevention system has higher requirements on the electrical control, which increases the difficulty of control accordingly. For those without ventilation and smoke exhaust fans, high temperature resistant fans should be selected as far as possible, and fire and smoke prevention work should be done well according to the requirements of regulations. For the cleanliness requirements of the workshop or the part where the harmful gas exceeds the standard, combined with the environmental pollution requirements proposed by the national department, scientifically design dust removal and purification, usually carry out fresh air supply, and discharge it to the outside after processing the return air. At this time, the air volume of dust removal and ventilation should be considered as a whole , Scientifically design the air supply and exhaust volume, reduce harmful substances polluting the indoor environment, and ensure that the space ventilation meets the clean requirements.
This article takes an industrial factory building as an example. When designing ventilation ducts, first mark each duct, mark the length of the duct and the position of the exhaust point. Determine the most unfavorable loop, and then combine the air volume and design flow velocity of each pipeline to determine the section size and unit frictional resistance of each pipe section of the most unfavorable loop. Combined with the minimum wind speed of the pipeline and considering the air leakage of the pipeline, the local frictional resistance of the pipeline is calculated.
2.1 Division of the ventilation system
When different air supply requirements are generated in the workshop, or the workshop area is relatively large, there are many air supply and exhaust points. In order to improve the management and operation level, multiple air supply and exhaust systems are generally designed. Typically includes fans, piping and equipment. The principles of division include: ① Those with the same treatment air requirements and indoor parameters can be classified as one system; ② Those with the same production procedures, operating shifts and time can be classified as one system; ③ Those with independent exhaust systems ④ Divide the dust removal system to meet different temperature and humidity. It is very likely to cause condensation in the pipeline after mixing, so the system should be designed separately; A system is jointly designed with a small amount of exhaust points, and the total resistance of the system is improved after setting the exhaust points. The basic principle of dividing the system: the distance between the exhaust points of the workshop is not large, and considering the economic benefits, a ventilation system should be designed.
2.2 Pipe material and shape
2.2.1 Selection of pipe section shape
There are two types of pipe sections, namely circular and rectangular. Compared with the two, when the cross-sectional area is the same, the resistance of the circular shape is small, the material is saved, and the strength is high; when the diameter of the circular air duct is relatively small, it is easier to manufacture and convenient for heat preservation. However, circular pipe fittings increase the difficulty of lofting and production; it is difficult to effectively match the building and structure during the layout process, which affects the aesthetics of the layout. When the pipe produces a higher flow rate, the diameter is reduced accordingly, so the round pipe is selected.
2.2.2 Pipe material
General pipeline materials include thin steel plates, heat-resistant and wear-resistant alloy steels, slag gypsum boards, bricks, and concrete. In places where the temperature of dusty gas and dust is relatively low, the pipe material only needs to be wear-resistant, and ordinary steel pipes can be used. In the vicinity of the metal melting furnace, considering that the internal temperature reaches 500 °C, the selected material should be resistant to high temperature, and should maintain wear resistance due to the inclusion of dust, and further select a material with high hardness and wear resistance. According to the requirements of this part, wear-resistant and heat-resistant alloy steel is used.
2.3 Scientific layout of ventilation ducts
When arranging local ventilation ducts, it is necessary to comprehensively consider the overall setting of the ventilation system, and closely contact other specialties, not only to ensure coordination, but also to comply with various regulations. If there are a large number of exhaust points in the ventilation pipe, choose a large-section manifold to directly connect with each branch pipe; when laying out the ventilation pipe, keep it as straight as possible to further prevent the complicated design of local pipe fittings; the gas contains liquid droplets during transportation , Set the ventilation pipes to slope, and install the water seal pipe at the lower part of the ventilation pipes, so as to better eliminate the accumulation of liquid; install adjustment and measurement equipment on the ventilation pipes, so as to effectively control the system in operation.
2.4 Ensure the temperature balance of the ventilation duct
When the ventilation duct transports the air, it consumes a lot of heat and cooling capacity, and attention should be paid to maintaining the balance of the air temperature, which requires thermal insulation measures to deal with the ventilation duct. The insulation structure of ventilation ducts generally includes three parts, namely insulation layer, moisture-proof layer and protective layer. Among them, the insulation layer is the core insulation part of the ventilation duct, the function of the moisture-proof layer is to prevent water or steam from contacting the insulation material, and the protection layer is to avoid damage to the insulation layer and the moisture-proof layer.
2.5 Intake and exhaust outlets of the ventilation system
In the industrial ventilation process, set the air inlet in the outdoor air clean area, and at the same time, pay attention to choose the wind direction above the air outlet, the height is obviously lower than the air outlet, and at the same time prevent the short circuit between the air outlet and the air inlet. The gas cylinder that discharges new pollution sources generally cannot be lower than 15 m. For two exhaust cylinders with the same pollutants, if the spacing is obviously smaller than the sum of the geometric heights, the gas distribution cylinders can be equivalently combined into one. The air outlet usually discharges the air containing toxic substances, which should be effectively diluted and diffused by the atmosphere. At this time, the air outlet should be set on the positive and negative pressure areas of the airflow, and the wind cap should not be installed, so as to prevent rainwater from entering the ventilation duct.
2.6 Do a good job in fire prevention and explosion protection
When there is a risk of fire and explosion in the design of the ventilation system, not only must the air volume meet the standard, but also set up facilities to detect the concentration of combustibles and explosives, select explosion-proof fans, install explosion-proof doors, and avoid accumulation of combustibles and explosions in the ventilation ducts. dead corner of things.
To sum up, industrial plants usually have a relatively large indoor space, and the types of internal pollution sources are complex. They are generally treated in a centralized manner and require specialized air supply and exhaust systems. Therefore, when designing the ventilation ducts of industrial plants, it must be considered as a whole to avoid design problems of ventilation ducts. Therefore, the scientific design of ventilation ducts should not only achieve the ventilation target but also reduce the cost as much as possible. This is also the focus of this paper.
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