In general, the harmful substances in the plant operation environment will reach the operator through the propagation path after the generation of the source. Therefore, the control measures of the operation environment can be controlled from three sources: the source, the propagation path, and the exposed person. From the point of view of engineering control, it is best to control the pollutants near the place where the pollutants occur and avoid the spread of harmful substances. In order to ensure the safety and hygiene of employees and a good working environment, engineering improvements should be made to their operating environment. For the improvement of hazardous environments such as harmful gases, vapors, or dust, one or two types of consolidation can be used to solve the hazards of exposure to hazardous substances. The following is a brief description of the overall ventilation and local exhaust systems commonly used in factories:
One, the overall ventilation system plant to prevent ventilation is mainly controlled by the overall ventilation (dilution ventilation) and local exhaust two main forms. Among them, the overall ventilation is the most basic type of ventilation system. Its main function is to provide fresh outside air at the workplace, dilute the harmful concentration in the workplace, and discharge the harmful substances out of the air by the flow of air. Therefore, in terms of the relationship between air and harmful substances, overall ventilation includes two basic mechanisms: mixing and replacement. The former mix fresh air with contaminated air to achieve dilution, while the latter replaces contaminated air with fresh air. In the labor safety and hygiene regulations, the relevant ventilation regulations regulate the timing, principles, and basic performance requirements of the overall ventilation device. However, the flow pattern of air in the room has a significant effect on the overall ventilation performance, and is often a factor that cannot be accurately ascertained. The geometric status of the room, compartments, equipment layout, distribution of temperature and pressure, configuration of intake and exhaust ports, and forced ventilation caused by manpower are the influencing factors of indoor airflow.
The overall ventilation has different interpretations and calculations in different applicable situations. For the purpose of controlling Indoor Air Quality (IAQ), the overall ventilation is to provide fresh air, maintain proper temperature and humidity for comfort, and to control the operating environment as a prerequisite, diluting it with fresh air. Contaminated air to achieve industrial safety and sanitation purposes. Since air has the characteristics of flowing from high pressure to low pressure, in order to consider the distribution of air flow in the plant and to avoid the accumulation of harmful substances in poor ventilation, we generally expect that the delivery and exhaust air will be mechanically forced and carried out via air supply and exhaust ducts. The system is designed to dilute the concentration of harmful substances, and if properly designed, it is extremely effective for the removal of low-concentration non-toxic or low-toxic pollutants with low occurrence and wide distribution. In terms of pollution control benefits, according to the American Conference of Governmental Industrial Hygienists (ACGIH), the overall ventilation is less suitable for workplaces where dust or fumes are emitted because of its generally high toxicity. If the whole ventilation device is used, a large amount of ventilation is required, and the speed and amount of dust and fumigation produced are generally large. Therefore, it is highly susceptible to local high concentration and cannot be controlled by this device. Therefore, this type of system ventilation is not a design that the ventilation design engineer will first consider. However, this device is a very practical solution to the situation where the source of contamination hazards is even and wide or the position is uncertain. Considering the overall ventilation design required for different environmental sources and different sources of pollution, we must first consider the calculation of ventilation volume. Currently, the calculation method of total ventilation and ventilation volume depends on (1) the number of operators (2) the size of the workplace (3) evaporation. Different conditions such as rate, threshold limit value (TLV) and lower explosion limit (LEL) are estimated separately.
2. Partial Exhaust System The local exhaust device is to remove air pollutants from the source or near the source of the pollutants and reduce the concentration of pollutants in the breathing zone of the workers. It is the most effective way to control the air pollution in the workplace. The method of things. The local exhaust system consists of four major components, including hoods, air ducts, air cleaners, and fans. In many cases, the overall ventilation system and the local exhaust system will be used together. The overall planning should be considered with reasonable consideration. Play its effectiveness.
The hood is the opening of the local exhaust system. Its role is to limit or reduce the diffusion of pollutants from the source, and to guide the airflow to capture the pollutants in the most effective way. Then the pollutants are transported through the duct to the air purification unit for disposal. . Whether the local exhaust device is good and effective is related to the type and location of the hood, and it has a great impact on the ventilation system in terms of economy and engineering. Taking dust as an example, after the dust source has been determined and quantified, engineering and economic evaluation operations can be started. The standard dust-proof local exhaust system is included in each dust generation source to install gas hoods, guide air ducts, and dust collection filters. Device and fan motor. Generally speaking, the closer the dust collection hood is to the dust source, the better the system economic efficiency is; the farther the hood is from the dust source, the worse the dust collection rate and the greater the amount of exhaust air demand. Basically, the size and cost of the dustproof system are directly proportional to the amount of polluting air. Each dust generating machine should be individually evaluated. How to correctly estimate the amount of air delivered is an effective and economical dustproof operation. Therefore, the hood design is very important. The key. If the hood is poorly designed, not only dust cannot be effectively controlled, dust emission starts to obstruct vision, worker's health is affected, the recurring cost of dust cleaning of the plant structure is increased, and mechanical over abrasion caused by dust is increased. Electrical and electronic components Damage repair costs. It not only wastes the energy of the system operation, but also increases the risk of fire. Therefore, it has a great impact on the overall economic efficiency. Therefore, at the beginning of the system design and planning, it is necessary to select the appropriate size and type of gas hood according to the operating method, the proliferation status, and properly evaluate the exhaust volume and pressure loss, control the wind speed, etc., based on the appropriate system design.
Since ventilation control engineering is widely used in various industries, from the wood industry in traditional industries, heat treatment operations, pickling industry, sand blasting, hot-dip galvanizing, grinding, mixing and petrochemical industries, plastics, plastics Industry, rubber industry, etc.; even the optoelectronics and semiconductor industry's process stations such as wet cleaning stations and local scrubbers all use ventilation systems (overall ventilation and local exhaust systems) to capture and process harmful emissions during processing. substance. As the ventilation control system is commonly used in the industrial sector, the provision of ventilation technology guidance is increasingly important. In the case of coaching companies in the past, it was often found that due to improper design of ventilation systems, or failure to perform regular inspections and maintenance, the systems could not achieve their intended functions, and the operators not only wasted many resources and costs, but also failed to effectively improve the quality of the environment. Safety and health with employees.
Third, ventilation engineering test method The purpose of the ventilation test is to assess the performance of the ventilation system to ensure that it meets the design requirements, but also can be used as a reference for maintenance and repair of ventilation facilities after the actual operation. Ventilation testing methods are as follows:
(1) Flow visualization: As the gaseous pollutants are eliminated by the flow of air, the flow state of the air flow has an absolute influence on the capture efficiency of the pollutants, and the visualization of the airflow is the distribution of the observation flow field. To make a qualitative assessment of the ventilation system. The general visualization method is to emit smoke in the flow field, and then observe the direction of the smoke flow to understand whether there are vortexes, reverse flow, or leakage that reduce the ventilation performance, and use it as a reference for improving the design. Drying ice, titanium tetrachloride, white wax oil, etc. are commonly used as smoke releasing materials for general industrial ventilation. However, if it is used in a clean room, these substances are not suitable because they may cause particulate contamination, resulting in degradation of the cleanroom class. Generally, the overall ventilation of a laminar flow clean room is often suspended by a wire at the air outlet. At this time, the yaw angle of the wire must not exceed 14 degrees, and it is judged whether the flow field is a parallel laminar flow. In addition, pure water can be atomized using ultrasonic waves to visualize the flow field as smoke-releasing substances.
(2) Experimental measurement method: The use of experimental equipment to directly measure important fluid flow characteristics, including pressure, flow rate, and flow rate. The commonly used experimental measurement equipment includes a hot wire speedometer, a Pitot tube, an ultrasonic anemometer, a pressure gauge, an impeller tachometer, and the like. The advantage of this method is that it can make a quantitative analysis of the flow field, and the result is also the most accurate. The disadvantage is that there must be enough points to be measured. Therefore, it takes a lot of manpower, material resources, and time.
(3) CFD simulation method: In the ventilation control engineering of the plant, many literatures use commercial software such as PHOENICS, CFX, FLUENT, STAR-CD, FIDAP, etc., all using Computional Fluid Dynamics (CFD). Solve a set of equations that describe physical problems such as continuous, momentum, energy, and other equations to obtain the flow characteristics of various gases, including flow fields and pressure fields. With the maturity of CFD technology and the rapid improvement of computer computing capability, CFD simulation has become the main tool of R&D units. Its advantage is that it can quickly obtain results and make corrections in real time to reduce the risk of misdesign of system engineering. Therefore, both functional and economic benefits. However, because the calculation result is not easy to verify, the calculation result must be compared with the data measured by the instrument to verify the correctness of the numerical deviation and ensure the correctness of the calculation result.
IV. CONCLUSIONS AND RECOMMENDATIONS Factory ventilation technology has been in place for many years. For the past in terms of overall ventilation and local exhaust, whether it is from the perspective of improving industrial safety or improving the quality of production, its role is increasingly important. neglect. In the past, technology was developed based on past operations. Since the production volume of the process, the size of the machine platform, and the scope of the plant operation area have been gradually expanded, the scope of relative pollution sources has also been increased proportionately, with the past technology being fully applied to the current scene. The operation may have its own difficulties. Even if it is the correct principle, technical amendments must be made to meet the on-site requirements. The entire ventilation system itself, in addition to the need to design for actual operating conditions, in order to meet regulatory and production needs, but also pay attention to its operating conditions and make regular inspections. In order to further prevent the occurrence of unexpected events, it is also possible to use the system's operation and maintenance records as a reference for designing or improving the system in the future.
One, the overall ventilation system plant to prevent ventilation is mainly controlled by the overall ventilation (dilution ventilation) and local exhaust two main forms. Among them, the overall ventilation is the most basic type of ventilation system. Its main function is to provide fresh outside air at the workplace, dilute the harmful concentration in the workplace, and discharge the harmful substances out of the air by the flow of air. Therefore, in terms of the relationship between air and harmful substances, overall ventilation includes two basic mechanisms: mixing and replacement. The former mix fresh air with contaminated air to achieve dilution, while the latter replaces contaminated air with fresh air. In the labor safety and hygiene regulations, the relevant ventilation regulations regulate the timing, principles, and basic performance requirements of the overall ventilation device. However, the flow pattern of air in the room has a significant effect on the overall ventilation performance, and is often a factor that cannot be accurately ascertained. The geometric status of the room, compartments, equipment layout, distribution of temperature and pressure, configuration of intake and exhaust ports, and forced ventilation caused by manpower are the influencing factors of indoor airflow.
The overall ventilation has different interpretations and calculations in different applicable situations. For the purpose of controlling Indoor Air Quality (IAQ), the overall ventilation is to provide fresh air, maintain proper temperature and humidity for comfort, and to control the operating environment as a prerequisite, diluting it with fresh air. Contaminated air to achieve industrial safety and sanitation purposes. Since air has the characteristics of flowing from high pressure to low pressure, in order to consider the distribution of air flow in the plant and to avoid the accumulation of harmful substances in poor ventilation, we generally expect that the delivery and exhaust air will be mechanically forced and carried out via air supply and exhaust ducts. The system is designed to dilute the concentration of harmful substances, and if properly designed, it is extremely effective for the removal of low-concentration non-toxic or low-toxic pollutants with low occurrence and wide distribution. In terms of pollution control benefits, according to the American Conference of Governmental Industrial Hygienists (ACGIH), the overall ventilation is less suitable for workplaces where dust or fumes are emitted because of its generally high toxicity. If the whole ventilation device is used, a large amount of ventilation is required, and the speed and amount of dust and fumigation produced are generally large. Therefore, it is highly susceptible to local high concentration and cannot be controlled by this device. Therefore, this type of system ventilation is not a design that the ventilation design engineer will first consider. However, this device is a very practical solution to the situation where the source of contamination hazards is even and wide or the position is uncertain. Considering the overall ventilation design required for different environmental sources and different sources of pollution, we must first consider the calculation of ventilation volume. Currently, the calculation method of total ventilation and ventilation volume depends on (1) the number of operators (2) the size of the workplace (3) evaporation. Different conditions such as rate, threshold limit value (TLV) and lower explosion limit (LEL) are estimated separately.
2. Partial Exhaust System The local exhaust device is to remove air pollutants from the source or near the source of the pollutants and reduce the concentration of pollutants in the breathing zone of the workers. It is the most effective way to control the air pollution in the workplace. The method of things. The local exhaust system consists of four major components, including hoods, air ducts, air cleaners, and fans. In many cases, the overall ventilation system and the local exhaust system will be used together. The overall planning should be considered with reasonable consideration. Play its effectiveness.
The hood is the opening of the local exhaust system. Its role is to limit or reduce the diffusion of pollutants from the source, and to guide the airflow to capture the pollutants in the most effective way. Then the pollutants are transported through the duct to the air purification unit for disposal. . Whether the local exhaust device is good and effective is related to the type and location of the hood, and it has a great impact on the ventilation system in terms of economy and engineering. Taking dust as an example, after the dust source has been determined and quantified, engineering and economic evaluation operations can be started. The standard dust-proof local exhaust system is included in each dust generation source to install gas hoods, guide air ducts, and dust collection filters. Device and fan motor. Generally speaking, the closer the dust collection hood is to the dust source, the better the system economic efficiency is; the farther the hood is from the dust source, the worse the dust collection rate and the greater the amount of exhaust air demand. Basically, the size and cost of the dustproof system are directly proportional to the amount of polluting air. Each dust generating machine should be individually evaluated. How to correctly estimate the amount of air delivered is an effective and economical dustproof operation. Therefore, the hood design is very important. The key. If the hood is poorly designed, not only dust cannot be effectively controlled, dust emission starts to obstruct vision, worker's health is affected, the recurring cost of dust cleaning of the plant structure is increased, and mechanical over abrasion caused by dust is increased. Electrical and electronic components Damage repair costs. It not only wastes the energy of the system operation, but also increases the risk of fire. Therefore, it has a great impact on the overall economic efficiency. Therefore, at the beginning of the system design and planning, it is necessary to select the appropriate size and type of gas hood according to the operating method, the proliferation status, and properly evaluate the exhaust volume and pressure loss, control the wind speed, etc., based on the appropriate system design.
Since ventilation control engineering is widely used in various industries, from the wood industry in traditional industries, heat treatment operations, pickling industry, sand blasting, hot-dip galvanizing, grinding, mixing and petrochemical industries, plastics, plastics Industry, rubber industry, etc.; even the optoelectronics and semiconductor industry's process stations such as wet cleaning stations and local scrubbers all use ventilation systems (overall ventilation and local exhaust systems) to capture and process harmful emissions during processing. substance. As the ventilation control system is commonly used in the industrial sector, the provision of ventilation technology guidance is increasingly important. In the case of coaching companies in the past, it was often found that due to improper design of ventilation systems, or failure to perform regular inspections and maintenance, the systems could not achieve their intended functions, and the operators not only wasted many resources and costs, but also failed to effectively improve the quality of the environment. Safety and health with employees.
Third, ventilation engineering test method The purpose of the ventilation test is to assess the performance of the ventilation system to ensure that it meets the design requirements, but also can be used as a reference for maintenance and repair of ventilation facilities after the actual operation. Ventilation testing methods are as follows:
(1) Flow visualization: As the gaseous pollutants are eliminated by the flow of air, the flow state of the air flow has an absolute influence on the capture efficiency of the pollutants, and the visualization of the airflow is the distribution of the observation flow field. To make a qualitative assessment of the ventilation system. The general visualization method is to emit smoke in the flow field, and then observe the direction of the smoke flow to understand whether there are vortexes, reverse flow, or leakage that reduce the ventilation performance, and use it as a reference for improving the design. Drying ice, titanium tetrachloride, white wax oil, etc. are commonly used as smoke releasing materials for general industrial ventilation. However, if it is used in a clean room, these substances are not suitable because they may cause particulate contamination, resulting in degradation of the cleanroom class. Generally, the overall ventilation of a laminar flow clean room is often suspended by a wire at the air outlet. At this time, the yaw angle of the wire must not exceed 14 degrees, and it is judged whether the flow field is a parallel laminar flow. In addition, pure water can be atomized using ultrasonic waves to visualize the flow field as smoke-releasing substances.
(2) Experimental measurement method: The use of experimental equipment to directly measure important fluid flow characteristics, including pressure, flow rate, and flow rate. The commonly used experimental measurement equipment includes a hot wire speedometer, a Pitot tube, an ultrasonic anemometer, a pressure gauge, an impeller tachometer, and the like. The advantage of this method is that it can make a quantitative analysis of the flow field, and the result is also the most accurate. The disadvantage is that there must be enough points to be measured. Therefore, it takes a lot of manpower, material resources, and time.
(3) CFD simulation method: In the ventilation control engineering of the plant, many literatures use commercial software such as PHOENICS, CFX, FLUENT, STAR-CD, FIDAP, etc., all using Computional Fluid Dynamics (CFD). Solve a set of equations that describe physical problems such as continuous, momentum, energy, and other equations to obtain the flow characteristics of various gases, including flow fields and pressure fields. With the maturity of CFD technology and the rapid improvement of computer computing capability, CFD simulation has become the main tool of R&D units. Its advantage is that it can quickly obtain results and make corrections in real time to reduce the risk of misdesign of system engineering. Therefore, both functional and economic benefits. However, because the calculation result is not easy to verify, the calculation result must be compared with the data measured by the instrument to verify the correctness of the numerical deviation and ensure the correctness of the calculation result.
IV. CONCLUSIONS AND RECOMMENDATIONS Factory ventilation technology has been in place for many years. For the past in terms of overall ventilation and local exhaust, whether it is from the perspective of improving industrial safety or improving the quality of production, its role is increasingly important. neglect. In the past, technology was developed based on past operations. Since the production volume of the process, the size of the machine platform, and the scope of the plant operation area have been gradually expanded, the scope of relative pollution sources has also been increased proportionately, with the past technology being fully applied to the current scene. The operation may have its own difficulties. Even if it is the correct principle, technical amendments must be made to meet the on-site requirements. The entire ventilation system itself, in addition to the need to design for actual operating conditions, in order to meet regulatory and production needs, but also pay attention to its operating conditions and make regular inspections. In order to further prevent the occurrence of unexpected events, it is also possible to use the system's operation and maintenance records as a reference for designing or improving the system in the future.
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