Laboratory ventilation system engineering is to control the spread and harm of air pollution by means of ventilation dilution or ventilation elimination, and it is a building environment control technology to ensure the quality of indoor and outdoor air environment. Ventilation system is a complete set of devices to realize the function of ventilation, including air inlet, air outlet, air supply pipe, fan, cooling and heating, filter, control system and other ancillary equipment.
Mechanical ventilation is generally used in laboratory ventilation engineering, and ventilation power devices, comprehensive ventilation and local ventilation equipment, such as fume hood, atomic absorption hood and universal exhaust hood, are mainly used for ventilation.
Fume hood:
Fume hood as an important safety equipment in the laboratory, it can provide an effective way of local ventilation.
Use environment:
Carry out experimental operations on flammable, explosive and volatile toxic and harmful substances, and carry out qualitative and quantitative experimental operations on items with unknown performance.
Structure style of fume hood:
Three-section desktop (upper cabinet, operating table top and lower cabinet); Desktop fume hood walk-in floor fume hood.
Fume hood type:
Steel wood hood, all-steel fume hood, FRP fume hood, PP fume hood.
In order to make the exhaust volume of each single equipment meet the design requirements and ensure that each ventilation equipment does not affect the normal operation of other ventilation equipment when running alone, a ventilation frequency conversion system is adopted.
Principle of frequency conversion system:
When part of the fume hood is not in use or the angle of the electronic air valve of the fume hood changes, The ventilation volume of the main pipe changes, and the pressure difference of the main pipe also changes. When the pressure difference sensor detects the change of the pressure difference of the air pipe, it transmits it to the frequency converter through the signal line, and the frequency converter automatically adjusts it to control the rotating speed of the motor of the fan, so as to achieve the purpose of controlling the exhaust air volume.
Frequency conversion mode:
Constant air volume frequency conversion/variable air volume frequency conversion control mode control method; The system is designed according to the air volume of all ventilation equipment, When the exhaust air volume of each ventilation equipment is constant, the angle controlled by the electronic air regulating valve installed at the end of the tuyere and the frequency of fan operation controlled by the frequency converter (static pressure of fixed pipeline or PLC programming) meet the exhaust air volume of ventilation equipment in use, increase the passing air flow when the switch is closed, and reduce the air flow when the switch is opened.
Advantages:
Energy saving. By switching the fume hood and room air supply to a low air flow rate, obvious energy saving can be realized. High-quality flow control is realized by using fast and stable adjustment method. Compared with VAV control system, the equipment cost of control system is low.
Disadvantages:
A high-low (or maximum-minimum) switch is made between two predetermined wind flow values. The opening position of the adjusting door is unknown, and the surface wind speed may be high or low, which may reduce the safety.
Variable frequency control mode of air volume:
In the process of adjusting the door moving, the face wind speed of the fume hood is kept constant, the opening of the valve is controlled, and the frequency converter controls the running frequency of the fan to meet the air volume required by the set face wind speed of the fume hood and achieve the control effect of constant face wind speed of the fume hood. At the same time, it ensures the dust collection capacity of fume hood and saves energy significantly.
Advantages:
Energy saving. By switching the fume hood and room air supply to a low air flow rate, obvious energy saving can be realized. High-quality flow control is realized by using fast and stable adjustment method. Compared with VAV control system, the equipment cost of control system is low.
Disadvantages:
A high-low (or maximum-minimum) switch is made between two predetermined wind flow values. The opening position of the adjusting door is unknown, and the surface wind speed may be high or low, which may reduce the safety.
Variable frequency control mode of air volume:
In the process of adjusting the door moving, the face wind speed of the fume hood is kept constant, the opening of the valve is controlled, and the frequency converter controls the running frequency of the fan to meet the air volume required by the set face wind speed of the fume hood and achieve the control effect of constant face wind speed of the fume hood. At the same time, it ensures the dust collection capacity of fume hood and saves energy significantly.
Advantages:
When the adjusting door is closed, the energy saving is remarkable; When adjusting the position change, keep the correct surface wind speed and increase the safety; The inherent alarm and monitoring function is a typical component of VAV system, while increasing safety. Because the VAV control system is easy to adapt to system changes, the flexibility of the laboratory will increase. As the wind flow decreases, the sound level will decrease.
Disadvantages:
If the regulating door remains open, there will be problems of high air flow and high operating cost. The cost of control system will cause high investment cost. Because the general adjustment position determines the air volume, incorrect adjustment door management will affect the investment recovery, sound effect and uneven situation. Different VAV systems have different performance, and different systems have different control speed, regulation ratio, stability and maintenance needs.
The laboratory will produce corresponding waste gas in the daily operation process. If it is directly discharged into the atmosphere without treatment, it will inevitably pollute the surrounding environment and cause damage to human body. According to the inorganic waste gas contained in the waste gas, different waste treatment schemes are made according to different types of waste gas.
Inorganic waste gas: nitrogen oxides, sulfides, hydrogen chloride, hydrogen cyanide. Hydrogen chloride, sulfur dioxide and other inorganic waste gas.
Organic waste gas: mainly includes aromatics: benzene, toluene, xylene, styrene, etc.; Aldehydes and ketones: formaldehyde, acetaldehyde, glutaraldehyde, butyraldehyde, acetone, cyclohexanone, methyl ethyl ketone, acetophenone, etc.; Esters: IsoJ acetate, ethyl acetate, butyl acetate, methyl acetate, banana oil, etc.; Alcohols: Methanol ethanol, butanol, propanol ethylene glycol, etc.
Working principle of activated carbon adsorber:.
Chemical smog and harmful gases enter the activated carbon adsorber through the fan, and the activated carbon and smoke molecules undergo oxidation reaction and adsorption reaction, and are hydrolyzed into carbon dioxide and water, thus reducing environmental pollution.
Working principle of water spray purification tower;
The fan drives the chemical acid mist through the water spraying device, In case of neutralized liquid sprayed into fine mist, the waste gas is absorbed to the surface of fine droplets and discharged into the collection tank. Clean air is further filtered and demistered and then discharged into the atmosphere. The liquid is pumped from the collection tank to the upper nozzle by a pump, and then discharged into the collection tank after neutralization reaction with the waste. After treatment, the waste liquid is discharged to the outside or recycled.