Biological laboratory fume hood system design and application

1, the function and application of the fume hood

The main function of the fume hood is to control various harmful gases, water vapor, odors, and residual heat generated during the experiment to be controlled in the fume hood and side-by-side to the outside so as to protect the user's safety and prevent the pollutants in the experiment. The purpose of the laboratory diffusion.

The fume hood has a wide range of applications in various biochemical and physical and chemical laboratories. It plays a role in protecting the purity of experimental samples, ensuring the accuracy of experimental results, maintaining the cleanliness of the laboratory environment, improving labor hygiene conditions, and improving work efficiency. Crucial role.

Fume hoods can be used in physical and chemical laboratories and biological laboratories as well as in clean laboratories, but not in biosafety level 3 and 4 laboratories.

2. Domestic and foreign standards on fume hoods

The foreign standards for fume hoods are: German Standard DIN 12927 (1990), French Standard NFX15-211 (1996), British Standard BS7989: 2001 (2001), Australian Standard AS/NZS2243.9: 2003 (2003) , US Standard ANSI/AIHAZ 9.5: 2003 (2003) and SEFA-9. China's standards for fume hoods are all industry standards, including: “Fume Hood” JB/T6412.1999, “Laboratory Variable Air Fume Hood” JG/T222.2007, “No Duct Self-cleaning Hood” ( Reviewer) JB/Txxxx.2011.

3, the performance of the fume hood

The performance of fume hoods is usually measured in three parameters: capture efficiency, suppression efficiency, and efficiency of removing harmful gases. Good capture efficiency can be achieved through two approaches. The first is to maintain a reasonable surface velocity of the hood opening, followed by a reasonable layout of the fume hood. Reasonable design of the fume hood cabinet and maintaining the proper surface wind speed of the fume hood is the key to obtain high restraint efficiency. The efficiency of removing harmful gases is achieved by the height of the outdoor vents and the appropriate wind speed.

3.1 Design Principles

The number of fume hoods deployed in the workplace varies depending on the type of experimental study. Generally, the configuration of the institute and the university is that the chemical research laboratory is equipped with one fume hood for each researcher, and the biological research laboratories 6 to 10 researchers share one fume hood, and the physics laboratory may be set up for the entire department. Taiwan fume hood. The type of fume hood should be selected and the number of fume hoods should be determined according to the nature of the experiment and the laboratory process requirements. Considering various factors comprehensively, determine the form of the fume hood exhaust system and the supplementary air system, and determine the position of the ventilation room and the ventilation shaft. The principle of safety, practicality, efficiency, and economy should be adopted to allow harmful gases to be discharged as soon as possible, not to pollute the environment and operators, and to make all the gaseous pollutants in the experiment within the fume hood. It should be combined with the process and construction profession to reasonably determine the location of the fume hood in the laboratory. The fume hoods should be installed in areas with little air flow interference, and should be kept away from the entrances, air outlets, and frequent passages of personnel to avoid unorganized air currents from interfering with the exhaust flow field of the fume hoods. At the same time, they should be kept away from precision instruments to avoid fume hoods. Exhaust air affects instrument operation. According to the BS7258 standard, when the fume hood is parallel to the draught, the front end should be kept at a distance of 1m from the door edge; when the fume hood is perpendicular to the draught, the proximal end should be kept at a distance of lm from the door, and the fume hoods facing each other should be kept between them. 3m net distance. According to the construction project environmental impact assessment report and its approval opinions, as well as the composition of pollutant gases, determine the exhaust gas treatment measures that need to be taken, select the treatment equipment, and meet the discharge port setup requirements. For example, the French standard XPX15-203 requires that the discharge port be at least 3m above the roof; or at least 125% of the height of the building. China's "National Civil Engineering Design and Technical Measures: HVAC, Power" stipulates: investigation measures. Reasonably arrange the air duct, shorten the length of the pipeline as far as possible, reduce the resistance of the air duct, and reduce the fan power and noise. Since water vapor or reagents evaporate into the exhaust during the experiment, condensation occurs in the exhaust ducts in winter and cold regions. Therefore, horizontal exhaust ducts should be sloped 29/00 to 3 inches and should be avoided as much as possible. The wind pipe should be turned upside down so as not to accumulate condensate; if necessary, drain pipes with manual closed valves should be installed at the lowest point of the exhaust pipe and exhaust fan.

Reasonably select and arrange exhaust fans. Exhaust fan selection and placement should consider the following factors:

(1) The material of the first exhaust fan should be resistant to corrosion. Generally, the centrifugal fan should be selected so that the motor is placed outside the exhaust gas.

(2) Considering the possibility of construction and future laboratory changes, the fan air volume and pressure head must take into account certain margins.

(3) To reduce noise and vibration, the fan speed should not exceed 1450 r/min. Reasonably determine the fan installation position, the fan position should consider the following factors:

1 Due to the noise and vibration of the fan, the installation site should be as far away as possible from rooms where noise and vibration are limited, and be relatively centralized; it is easy to install and maintain.

2 Fans should be arranged in the engine room as much as possible, especially in cold and cold areas, which is not only sound-proof and vibration-proof, but also antifreeze.

3 The exhaust fan should be arranged close to the discharge outlet, such as the top floor or the roof, to keep the indoor exhaust ducts under negative pressure, so as to prevent the leakage of air from adversely affecting other rooms through which the duct passes.

4 Determine the control mode of the fume hood exhaust system and the make-up system. Air-conditioned rooms should consider room pressure control and be combined with the building control system of the entire laboratory building.

3.2 System Design

3.2.1 Determination of Surface Wind Speed

At present, China does not have national standards and regulations that clearly specify the wind speed at the hood surface. Engineering design is usually based on the design manual's recommended values, or Party A and process requirements, as shown in Table 1.

3.2.2 exhaust system form

The common forms of the fume hood exhaust system mainly include the following types. See Table 2.

3.2.3 Air Supply System Form The common form of the air supply system for the fume hood is shown in Table 3.

3.2.4 Control System Forms The common forms of control systems for fume hoods are shown in Table 4.

3.2.5 Waste gas treatment

In general, physical and chemical experiments will use a variety of reagents. The exhaust gas components in the fume hood are complex and varied, and the concentration of harmful substances is not high. Generally, they can be discharged directly. Exhaust treatment is only required in some special cases.

(1) When a large amount of strong acid and alkali are used in the experiment, an exhaust gas purification tower can be used to treat the exhaust with the principle of acid-base neutralization.

(2) When radionuclides are used in experiments, the exhaust air should be discharged after treatment with a high-efficiency air filter.

(3) When ammonia is used in the experiment or the test product contains ammonia, odor, or trace carcinogens, the exhaust air should be discharged through activated carbon filtration. For the adsorption of gaseous substances should be selected granular activated carbon, the activity of CCL4 should be higher than 60%.

(4) When marking experiments are conducted in a fume hood, the exhaust port should be equipped with an iodine filtration device.

(5) When the fume hood is used for mercury-containing experiments, the exhaust outlet shall be drained after absorbing potassium permanganate and sodium hypochlorite solution absorption devices or sulfur-loaded activated carbon.

4 fume hood application example analysis

4.1 one-to-one system

The University of Life Sciences has a total building area of ​​27,000mz. There are 102 fume hoods. The exhaust fans of all the fume hoods are placed in the five fan rooms on the roof. The laboratory has a fresh air and a comprehensive exhaust system. Natural supplement wind.

A university science building, a total construction area of ​​380O0m2. A total of 47 fume hoods, mainly in the 11-14 layer of chemical, biological and environmental laboratories, exhaust fan exhaust fan are placed on the 15-story roof.

This exhaust fan corresponds to a fume hood system, which is flexible and does not interfere with each other and is well received by the experimenters. In these two universities, the use of fume hoods during the day is not long, so the environmental parameters of the laboratory are not affected. If the fume hood is used for a long time, the comfort of the laboratory may be affected.

4.2 Sharing System

The total floor area of ​​a new building of a university’s chemistry school is 19,700 m2. The one-to-many system with 2 to 4 fume hoods and 1 exhaust fan is used. The standard configuration of each laboratory is to set 3 fume hoods (2 for 1.8m, 1 for 1.5m or 1.2rn), and 2 room exhaust outlets (located on suspended ceilings) for each laboratory configuration 1 Bench exhaust fan and a variable frequency controller. Each fume hood is equipped with a displacement sensor, which automatically adjusts the exhaust volume of the system as the opening (lifting) amplitude of the glass door is changed, so as to maintain the constant surface wind speed of the fume hood (the wind speed is 0.5m/s~0.1) m/s). When the glass doors of all the fume hoods are closed (down to the end), the electric air valve on the air outlet on the ceiling will automatically open, exhausting the air through the two air outlets on the ceiling. When the door of any fume hood is opened, the ceiling exhaust vent is closed.

Each floor has a fresh air system. A part of the fresh air is sent to the corridor, and part of it is sent to the laboratory through the ceiling air outlet. The fresh air system sends cold air in summer, natural wind in the transition season, and no air in winter.

The characteristics of common exhaust systems for fume hoods and rooms are:

(1) The displacement sensor is used to directly control the frequency converter. No sensor is installed in the air duct to avoid the corrosion and pollution of the sensor. The variable air volume control is realized at a lower cost.

(2) The amount of air exhaust is directly adjusted by the lift of the glass door, and the control is simple.

(3) The energy-saving effect is good. When the small amount of air is exhausted, it can not only save electricity, but also reduce the loss of cold and heat.

(4) When the air is exhausted at low speed, indoor and outdoor noise is reduced.

(5) The surface wind speed of the fume hood door is approximately 0.5m/s when it is fully opened from half open to full open, and the wind speed is approximately 1m/s when the door opening height is less than 300mill, and the wind speed increases. The wind speed is unstable.

4.3 VAV system

The VAV system is widely used in R&D labs of foreign companies. Only a VIP hood control system is used in a laboratory and office building of a life science research institute in China and an entry-exit inspection and inspection bureau building.

The laboratory and office building of a life science research institute has a total construction area of ​​18000mE. There are 8 ventilation systems with variable air volume fume hoods, 6 fume hoods connected in parallel with each system, and frequency converters for sending and discharging fans. Air heat exchangers are provided between the sending and exhausting winds to recover the exhaust energy.

A floor of 14-19th floor of the Entry-Exit Inspection and Quarantine Building is a laboratory. There are 36 fume hoods in the entire building. The exhaust system uses variable air volume valves and inverters to control the exhaust and make-up of the fume hoods according to the pressure gradients of the corridors, rooms, and fume hoods. At the same time, the exhaust of the fume hood is discharged after being purified by the acid mist absorption tower.

The variable air volume fume hood system has good surface wind speed control and comfortable laboratory environment, but if frequency control is performed according to the wind speed of each fume hood, frequent operation of the damper, lag in adjustment, vibration and noise of the fan and so on will occur. When the inverter is applied, it is often difficult to achieve stepless adjustment.

4.4 No filter system

When the experiment scale is small, and the experimental intensity and frequency are not high, the non-tube filter type fume hood is preferred because of its simple installation, flexible use, and safety and energy saving features. Since no-pipe filter fume hoods are equipped with molecular filters, exhaust fans and anemoscopes, sub-high-efficiency filters or high-efficiency filters [5] can also be used as long as the pollutants in the exhaust can be absorbed by the filter. The density of tuyere in the tuyere is lower than the value specified in GBZ2.1—2007 and GBZ2.2—2007 (the strictest value in PC-TWA, PC-STEL, and PC.MAC). The filtered air does not need to be discharged outside. Recycling in the laboratory, operation can achieve significant energy savings. Li Qiang and others from Tongji University once used Shanghai as an example to calculate the energy consumption and cost savings of a ductless filter type fume hood with an exhaust capacity of 2300m3/h, and saved a total of 79207kWh of fresh air cooling for the whole year. 34106kWh heat, energy consumption costs 55170 yuan.

The net gas-type fume hoods of this type of ductless filtration system have been used by many institutions such as the Shanghai Institute of Materia Medica, the Chinese Academy of Sciences, the Beijing Veterinary Drugs Supervision Office, and the Beijing Sihuan Pharmaceutical Factory.

5 Summary

The selection of the fume hood exhaust system is affected by a number of factors, which need to be determined after analysis according to the specific situation. As long as the system is reasonable, which system can achieve satisfactory results.

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