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Laboratory waste gas treatment system design

Views: 12     Author: China xicheng     Publish Time: 2021-06-04      Origin: China xicheng

In the design of laboratory exhaust gas treatment system, the following 5 matters need to be paid attention to:

Design Basis

The design of the laboratory exhaust gas treatment system must follow the national ventilation, fire protection, environmental protection, energy saving and other standards and regulations, including: "Heating, Ventilation and Air Conditioning Design Code" (GBJ19-87-2003), "Ventilation and Air Conditioning Engineering Quality Inspection and Evaluation Standard" (GBJ304-2002), "Concise Ventilation Design Manual" (GB50194-2002), "Code for Construction and Acceptance of Compressor, Fan, Pump Installation Engineering" (JBJ29-2002), "Construction and Acceptance of Low-Voltage Electrical Apparatus for Electrical Installation Engineering" Standards (GB50254-96), Comprehensive Emission Standards of Air Pollutants (GB16297-1996), Ambient Air Quality Standards (GB3095-1996), Environmental Noise Standards for Urban Areas (GB3096-93), Architectural Design "Fire Protection Code" (GB50016-2006), "Design Standard for Energy Efficiency of Public Buildings" (GB50189-2005), etc.

Exhaust gas purification mechanism

1. Organic waste gas purification

The most commonly used and most mature activated carbon adsorption method is used to purify the organic waste gas discharged from the physical and chemical laboratory. The essence of the activated carbon adsorption method is to use the characteristics of activated carbon adsorption to absorb the organic solvent and organic waste gas in the low-concentration and high-volume exhaust gas into the activated carbon and concentrate, and the gas after the activated carbon adsorption and purification is directly evacuated, which is a process of adsorption and concentration. The adsorption process is reversible and easy to desorb and regenerate. Due to the unbalanced and unsaturated molecular gravity or chemical bonding force on the solid surface, when the exhaust gas comes into contact with the porous solid material with a large surface area, the pollutants in the exhaust gas are adsorbed on the solid surface to mix it with the gas Separation to achieve the purpose of purification. The adsorption device uses activated carbon as the adsorbent, and the purification rate of organic waste gas (hydrocarbons, halocarbons, ketones, esters, ethers, alcohols, superimposed monomolecular objects and other organic substances) is high, and the efficiency is as high as 95%.

Laboratory fume hood equipment

2. Inorganic waste gas purification

For the purification of harmful inorganic gases, the currently commonly used acid mist spray method is adopted. According to the principle of acid-base neutralization, the acid mist spray method uses lye as the spray medium, fully contacts with the exhaust gas, and can effectively treat water-soluble gases such as HCL, HF, H2SO4, HCN, H2S, and the efficiency is as high as 98%. 3.3 Composition of exhaust gas treatment system The exhaust gas treatment system of the physical and chemical laboratory is composed of exhaust gas purification device, anti-corrosion fan, electric air valve, fire damper, ventilation terminal, ventilation pipe and frequency conversion control system. After purification treatment, the exhaust gas can meet the emission requirements specified by the state, and the system noise is controlled within the allowable range specified by the state.

Exhaust gas purification device

For organic waste gas: use activated carbon adsorption purification box, for inorganic waste gas: use glass fiber reinforced plastic anticorrosive acid mist spray tower.

1. Anti-corrosion fan

The anti-corrosion fan is made of acid and alkali resistant glass fiber reinforced plastic material, low noise, the foundation adopts a vibration damping device, and the foundation and the exhaust gas purification device adopt a soft connection form.

2. Ventilation duct

According to the actual situation, the ventilation duct should be rectangular or circular, and flame-retardant PVC pipe or stainless steel pipe should be selected. The selected ventilation ducts have the characteristics of acid and alkali resistance, corrosion resistance, water resistance, fire resistance, wear resistance, heat resistance, etc., and the design pressure of all ducts is less than 1500Pa.

3. Ventilation end

According to the characteristics of each laboratory, the ventilation terminal of the building laboratory is divided into the following methods, as shown in the table

4. Electric damper

The electric air valve is rectangular or circular according to the actual situation, and the opening and closing of the indoor switch is controlled, and the opening of the valve can be adjusted. The valve body is made of cold-rolled steel plate and the surface is sprayed with plastic. The drive adopts a high-quality low-noise hysteresis synchronous motor.

5. Fire damper

According to fire protection requirements, a fire damper is installed on the laboratory air duct where the ventilation duct is installed. When the temperature in the duct reaches 70°C, it will automatically cut off the pipe connection with other laboratories.

6. Frequency conversion control system

In order to achieve the purpose of energy saving and economic operation, the ventilation system adopts the static pressure sensor variable frequency control system with the best comprehensive performance. The air volume of each ventilation terminal device can be controlled by the static pressure sensor to control the frequency conversion adjustment. The control system is stable and the circuit layout is relatively simple. Moderate cost.

Exhaust gas treatment system layout

1. Layout design ideas

Comprehensively consider the nature of the exhaust gas emitted by each laboratory and the structure of the room, according to the principle of equal emphasis on economy and applicability, while reducing system noise as much as possible and striving for a beautiful layout. Based on this idea, the laboratories that can be combined for purification treatment are combined into an independent ventilation system; in order to ensure that the terminal noise of the system is ≤60dB, the selected fan power is as low as possible; in addition, the fan and purification device are placed on the roof of the building, and the exhaust gas is purified Discharge at high altitude afterwards.

2. Example: layout design plan

The laboratory exhaust gas treatment system design makes full use of the four ventilation shafts reserved in the building. A total of 19 sets of ventilation systems are designed in the laboratories on the first to fifth floors: 16 sets of activated carbon adsorption boxes are used to purify organic waste gas, 2 sets of acid mist spray towers are used to purify inorganic waste gas, and 1 set does not require purification. The exhaust system adopts a combination of partial exhaust of the fume hood and a top-suction exhaust hood for exhaust, or adopts a fixed-point exhaust method that combines top exhaust louvers and a universal exhaust hood for exhaust. All ventilation systems adopt static pressure sensing automatic frequency conversion variable air volume control system to ensure high-quality control performance and safety performance. Take the combustion performance laboratory as an example, the exhaust gas treatment system is shown in the figure.

Laboratory ventilation system installation case

Combustion performance The exhaust gas generated in the three laboratories is collected by a combination of fume hoods and local exhaust air of the equipment, and is pumped by the roof fan through the ventilation duct to the acid mist spray tower and discharged at high altitude after purification.

Exhaust gas treatment system calculation

The calculation of the exhaust gas treatment system is to design or select the various components of the system according to the requirements of the air volume and air pressure of the system. The following factors are mainly considered when calculating the air volume:

  1. The wind speed in the branch pipeline of the ventilation system is 5-8m/s, and the wind speed in the dry pipeline is 8-10m/s.

  2. The designed air volume of a single 1500mm×800mm×2350mm fume hood is 1200~1500m3/h.

  3. The designed air volume of the top exhaust louver is 300~500m3/h.

  4. The designed exhaust volume of the atomic exhaust hood is 350~500m3/h (specifically, the ventilation cross-sectional area is 400mm×400mm).

  5. The exhaust air volume of the universal exhaust hood is 160~300m3/h (specially refers to the ventilation cross-sectional area of 300mm×300mm).

  6. The number of air changes in the overall exhaust air of the general laboratory: 6-12 times/h.

The following factors are mainly considered in the calculation of wind pressure:

  • When the moving door of the fume hood is opened to the highest position, the resistance of the fume hood should be ≤ 70Pa.

  • The resistance of the universal exhaust hood is about 100Pa.

  • The resistance of the top exhaust louver is about 40Pa.

  • The resistance of standard components such as acid mist spray tower, activated carbon adsorption box, electric damper, etc. can be inquired according to the selected model.

  • The resistance of the air pipe (including pipes, elbows, tee, etc.) is calculated at 6-8Pa/m. 

Taking the combustion performance laboratory as an example, the exhaust gas treatment system is calculated as follows: combustion performance room 1 has 8 fume hoods, and the designed air volume is 12000m3/h; combustion performance room 2 has 4 equipment partial air outlets, and the designed air volume is 1000m3/h. h; There are 2 local exhaust vents for the 3 equipment in the combustion performance chamber, and the designed processing air volume is 500m3/h; the total exhaust air volume is 13500m3/h. The design wind speed of the main pipe is taken as 8.9m/s, so the diameter of the main pipe is calculated to be 600mm×700mm. The acid mist spray tower BFP-5 is selected according to the required air volume, with a processing air volume of 14000m3/h and a piezoresistance of 500Pa. The calculated pressure loss between the end of the ventilation and along the way is about 450Pa. In this way, according to the pressure resistance and air volume, the FRP anticorrosive fan BF4-72-8C is selected, the power is 7.5kW, the speed is 1120r/min, the air volume is 12000-23000m3/h, and the air pressure is 800-1200Pa.

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