Design of biological laboratory fume hood system

1. Function and application of fume hood

The main function of the fume hood is to control various harmful gases, water vapor, odor, residual heat, etc. generated during the experiment operation in the fume hood and discharge it to the outside to prevent the user from being safe and prevent the pollutants in the experiment. The purpose of 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 the sanitary conditions and improving work efficiency. Crucial role. Fume hoods can be used in physical and chemical laboratories, as well as in clean laboratories, but not in biosafety tertiary and tertiary laboratories.

2, the performance of the fume hood

Fume hood performance is typically measured in three parameters: capture efficiency, inhibit efficiency, and eliminate harmful gases. Good capture efficiency can be obtained in two ways, firstly to maintain a reasonable surface wind speed in the fume hood opening, and secondly to properly arrange the fume hood. A reasonable design of the fume hood cabinet and a reasonable surface wind speed to maintain the opening of the fume hood are the key to achieving high suppression efficiency. The efficiency of removing harmful gases is achieved by the height of the outdoor vent and the appropriate wind speed.

2.1 Design Principles

The number of fume hoods in the workplace depends on the type of experimental study, and the difference is large. Generally, the configuration in the institute and the university is that the chemical research laboratory has one fume hood per researcher, and six to ten researchers in the biological research laboratory share one fume hood. The physics laboratory may have one department. A fume hood. The type of fume hood should be selected to determine the number of fume hoods based on the nature of the experiment and laboratory process requirements. Considering various factors, determine the form of the fume hood exhaust system and the air supply system, and determine the location of the ventilation room and the ventilation shaft. The principle of safety, practicality, efficiency and economy should be adopted so that harmful gases can be removed as soon as possible, not polluting the environment and operators, and all the gaseous pollutants in the experiment should be controlled within the fume hood. It should be combined with the process and construction expertise to properly determine the location of the fume hood in the laboratory. The fume hood should be placed in a place where there is little interference from the airflow, as far as possible away from the doorway, the air supply port and the frequent passage of personnel to avoid interference caused by the unorganized airflow to the exhaust flow field of the fume hood. At the same time, it should also be away from precision instruments and avoid the fume hood. Exhaust air affects instrument operation. According to BS7258 standard, when the fume hood is parallel to the wind, the front end should be kept 1m away from the door edge; when the fume hood is perpendicular to the wind, the near end should be kept 1m away from the door edge, and the fume hoods should be kept between the oppositely arranged fume hoods. 3m clear distance. According to the construction project environmental impact assessment report and its approval opinions, as well as the pollutant gas composition, determine the exhaust gas treatment measures to be taken, select the treatment equipment, and meet the discharge port setting requirements. For example, the French standard XPX15-203 requires a discharge port that is at least 3 m above the roof; or at least 125% of the building height. China's "National Civil Engineering Design Technical Measures: HVAC, Power" provisions: check measures. Reasonably arrange the duct, minimize the length of the pipeline, reduce the duct resistance, and reduce the fan power and noise. Since water vapor or reagents are often evaporated into the exhaust during the experiment, condensation may occur in the exhaust ducts in the cold and cold regions in winter. Therefore, the horizontal exhaust duct should have a slope of 29/00 to 3 ‰ and try to avoid The air duct is turned up and down to avoid accumulation of condensate; if necessary, a drain pipe with a manual closed valve should be installed at the lowest point of the exhaust duct and the exhaust fan. Reasonably select and arrange the exhaust fan. The following factors should be considered for the selection and arrangement of exhaust fans:

(1) Firstly, the material of the exhaust fan should be corrosion resistant. Generally, the centrifugal fan should be selected to make the motor be outside the exhaust gas.

(2) Considering the possibility of construction and future laboratory changes, the fan air volume and the indenter must consider a certain margin.

(3) In order to reduce noise and vibration, the fan speed should not be higher than 1450r/min.

Reasonable determination of the installation position of the fan, the fan position should consider the following factors:

1 Due to the noise and vibration of the fan, the installation location should be as far as possible away from the room with restrictions on noise and vibration, and relatively concentrated; easy to install and maintain.

2 The fan should be placed in the machine room as much as possible, especially in the cold and cold areas, which is convenient for sound insulation and antifreeze.

The 3 exhaust fans should be placed as close as possible to the discharge port, such aDisposable Vape, Electronic Cigarettes, vapes the top floor or the roof, so that the exhaust ducts in the room are kept under negative pressure to prevent the air leakage from adversely affecting other rooms through which the air ducts pass.

4 Determine the control mode of the fume hood exhaust system and the air supply system. Air-conditioned rooms should be considered for room pressure control and combined with the building control system of the entire laboratory building.

2.2 system design

2.2.1 Determination of surface wind speed

At present, China does not have national standards and specifications to clearly define the wind speed of the fume hood. The engineering design is usually determined according to the recommended value of the design manual, or the requirements of Party A and the process.

2.2.2 Waste gas treatment

Usually, physical and chemical experiments will use a variety of reagents. The gas composition in the exhaust of the fume hood is complex and variable, and the concentration of harmful substances is not high, and it can generally be directly discharged. Exhaust air treatment is only required in some special cases.

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

(2) When radioactive nuclear elements are used in the experiment, the exhaust air should be discharged after being treated by a high-efficiency air filter.

(3) When ammonia or experimental products containing ammonia, malodor or trace carcinogens are used in the experiment, the exhaust air should be discharged after being filtered by activated carbon. For the adsorption of gaseous substances, granular activated carbon should be selected, and the activity of carbon tetrachloride should be higher than 60%.

(4) When marking experiments in the fume hood, the vent filter should be equipped with an iodine removal device.

(5) When the fume hood is used for mercury-containing experiments, the exhaust vents shall be set up with potassium permanganate and sodium hypochlorite solution absorption devices or sulfur-loaded activated carbon for adsorption.

2.2.3 The characteristics of the ventilation system shared with the room are:

(1) The inverter is directly controlled by the displacement sensor, and the sensor is not installed in the air duct, which avoids corrosion and pollution of the sensor, and realizes variable air volume control at a lower cost.

(2) The air volume is directly adjusted by the lifting of the glass door, and the control is simple.

(3) The energy-saving effect is good, and the small air volume can save electricity and reduce the loss of heat and heat.

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

(5) When the ventilation door is half open to full opening, the surface wind speed is about 0.5m/s, and when the door opening height is less than 300mill, the surface wind speed is about 1m/s, and the wind speed increases. The surface wind speed is unstable.