How to deal with chemical laboratory exhaust gas?

Laboratory waste gas is divided into organic waste gas and inorganic waste gas, and there are four commonly used laboratory waste gas treatment methods in SICOLAB

1) Combustion method, (2) Absorption method, (3) Activated carbon adsorption method, (4) Condensation method.

The composition of the exhaust gas produced in the process of experiments is often complex and diverse, and the degree of damage to human health varies according to this characteristic. At present, the treatment methods of gaseous pollutants can generally be divided into two categories: wet and dry, and it is necessary to choose high-efficiency and low-cost methods according to the characteristics of chemical laboratory exhaust gas. Classification of laboratory waste gas treatment methods:

1) Wet waste gas treatment; (2) Dry waste gas treatment; (3) Adsorption of activated carbon.

Now there are two types of treatment methods: wet and dry

1. Wet treatment is to install the absorption tower spray outside the laboratory, reasonably select the absorption liquid according to the type of waste gas, atomize the spray from the top of the absorption tower, and pressurize the exhaust gas from the bottom of the absorption tower.

2. Dry waste gas treatment refers to the process of adsorbing a component or some components of the mixture on the solid surface by using the unbalanced molecular gravity or chemical bonding force existing on the solid surface when the gas mixture is in contact with a porous solid. The solid with adsorption is called adsorbent, and the advantages of this method are that the equipment is simple, the operation is convenient, and it is easy to realize automatic control. However, due to the different physical and chemical properties of adsorbents, they have strong pertinence, so the treatment of waste gas containing different harmful substances must be equipped with adsorbents with different physical and chemical properties in order to play a good role in gas purification; If the time for the exhaust gas to pass through the adsorbent is short, the content of harmful substances in the exhaust gas is too high, and the effect of exhaust gas purification will not be ideal; When the exhaust gas passes through the adsorption medium, the power of the fan must be increased to ensure the normal wind speed of the ventilation system because the air flow is blocked by the solid medium.

The adsorbent needs to be replaced or regenerated regularly to ensure the normal operation of the absorption device. Therefore, this method needs to invest a certain amount of cost and manpower in practical application, and this method is generally used for the treatment of waste gas with relatively stable types and low content of harmful substances in the exhaust gas, so as to facilitate the use of a targeted adsorbent. Dry waste gas treatment generally uses organic gas activated carbon adsorption device, the principle of which is that activated carbon has many micropores and a large specific surface area, relying on molecular gravity and capillary action, solvent vapor and volatile substances can be adsorbed on its surface, and according to the boiling point of different substances, the adsorbed substances are precipitated with steam.

When steam is used as the unsorption medium, the precipitated organic solvent vapor and water vapor are condensed through the condenser and enter the separation barrel after separation.

Chemical laboratory wastes include chemical waste, biological waste, radioactive waste, etc. Waste in chemical terms refers to the emissions generated in chemical experiments, which basically or completely lose their use value within a certain range of time and space, and cannot be used.

According to the physical form, chemical waste can be divided into three types: waste gas, waste liquid and waste residue, referred to as "three wastes". Classification according to the nature of laboratory waste:

1. Chemical waste. Chemical wastes include organic and inorganic wastes. Organic waste includes some highly toxic organic samples, such as pesticides, benzopyrene, aflatoxins, nitrosamines, etc.

2. Biological waste. Biological waste includes laboratory specimens such as blood, urine, feces, sputum and vomit; Testing supplies such as laboratory equipment, bacterial culture media, and positive bacterial specimens.

3. Radioactive waste. Radioactive waste includes radioactive markers, radioactive standard solutions, etc.

The target pollutants emitted by the laboratory are ranked according to the potential emission intensity and the necessity of control: small molecule gas pollutants, specific organic pollutants (formaldehyde, xylene, methanol), biological pollutants (pathogenic microorganisms and their aerosols), odors, other tvocs (ethers, benzene and other macromolecular organic compounds), and particulate matter. There are many kinds of waste gas, and one method cannot be used to deal with it simply, and appropriate treatment methods and devices should be used for different types of waste gas.

Waste gas treatment processes include high-efficiency filtration, activated carbon adsorption, photocatalytic decomposition, water spraying, wet chemistry, combustion, etc. Considering the inherent characteristics of the laboratory, high-efficiency filtration, wet chemistry and combustion methods are not applicable, and activated carbon, spray, and photocatalytic waste gas treatment processes are mostly used.

(1) Activated carbon adsorption technology

For organic waste gas, activated carbon adsorption or absorption liquid ten activated carbon treatment method is used, the amount of activated carbon filling must ensure that the removal rate of the main organic emissions (non-methane total hydrocarbons, aniline) is greater than 90%, the wind resistance of the equipment is not more than 400pa, the activated carbon filling method should be easy to take out the replacement or regeneration, and the box material is made of flame-retardant PP or 304 stainless steel.

(2) Spray adsorption technology

For the inorganic exhaust gas, the horizontal water mist spray tower or spray water washing box is used for alkali absorption treatment, and the exhaust gas is introduced into the spray tower through the exhaust fan, and the microvortex is formed through the disturbance action of the spoiler ball, which is fully integrated with the downward dispersion atomization spray liquid, and the pollutants in the exhaust gas are transferred from the gas phase to the liquid phase, so as to achieve the purpose of purifying the air. The purified exhaust emissions meet the GB162971996 "Comprehensive Emission Standard for Air Pollutants", the wind resistance of the equipment is not more than 400Pa, the box material is made of flame-retardant PP or 304 stainless steel, and the device material must be strong, corrosion-resistant and fire-resistant.

(3) Mixed waste gas adsorption technology

The mixed waste gas should be treated with water washing (lye) + activated carbon adsorption, the removal rate of the main organic emissions (non-methane total hydrocarbons, aniline) is greater than 90%, the purified exhaust gas emissions meet the national standards, the wind resistance of the equipment is not more than 400pa, and the device must be strong and corrosion-resistant. Effective defogging measures must be in place between the washing unit and the activated carbon unit.

(4) Regeneration treatment device

In order to reduce operating costs, the use of activated carbon regeneration treatment devices is encouraged to ensure that activated carbon can be recycled more than five times, and no secondary pollution will be produced in the reliving process.

(5) Photocatalytic technology of nano-semiconductors

The MNOXoX-TiO2 complex was used as the catalyst, the catalyst was attached to the titanium mesh by sol-gel method, and the vacuum ultraviolet lamp of a specific wavelength was selected as the catalytic light source. Through photocatalysis, electron-hole pairs are generated, and macromolecular organic matter in the gas stream is oxidized and decomposed, so as to remove pathogenic microorganisms and decompose some water-insoluble macromolecules into soluble small molecules.

(6) Building exhaust gas treatment control and monitoring system(7) Laboratory indoor ventilation equipment and accessories

The commonly used exhaust equipment in the laboratory mainly includes: fume hood, atomic absorption hood, universal exhaust hood, ceiling-mounted exhaust hood, countertop exhaust hood, etc.

At present, there are several ways to treat the waste gas and exhaust gas generated by the laboratory:

1. Condensation method. The use of steam cooling condensation, ** high concentration of organic steam and mercury, arsenic, sulfur, phosphorus, etc.

2. Combustion method. Combustible substances are heated and oxidized to convert pollutants into carbon dioxide and water, thereby purifying exhaust gases.

3. Absorption method. Take advantage of the property that some substances are easily soluble in water or other solutions, so that the harmful substances in the exhaust gas enter the liquid to purify the gas.

4. Adsorption method. The exhaust gas is put into contact with porous solids (adsorbents) and the harmful substances are adsorbed on the surface of the solid to separate the pollutants.

5. Catalyst method. Using the different catalytic activities of different catalysts for various substances, the pollutants in the exhaust gas are converted into harmless compounds or substances that are easier to remove than the original state, so as to achieve the purpose of purifying harmful gases.

6. Filtration method. Exhaust gases containing radioactive materials must be filtered through filters and discharged into the atmosphere.

7. Customized two-stage activated carbon adsorption device with alarm: designed according to the two basic principles of adsorption (high efficiency) and catalytic combustion (energy saving). That is, adsorption concentration and catalytic combustion method.

After the dust removal, the exhaust gas enters the adsorption bed, and the system adopts more than two adsorption beds, alternately used, a catalytic combustion chamber, and the device adopts an independently programmed PLC system to achieve fully automatic operation, and the system purification rate can reach more than 90%.

Hello landlord, according to the questions you raised, the following will be answered in detail for you:

Harmful gases produced or volatilized in secondary school chemistry laboratories must be treated harmlessly. The treatment method can be summarized as follows:

1. Physical treatment methods

Adsorption method: put an appropriate amount of activated carbon or newly made charcoal powder in a container with residual exhaust gas, and shake or leave it for a long time.

Dissolution method: such as waste gas can be absorbed by water, benzene, toluene, etc. can be absorbed by alcohol, bromine vapor can be absorbed by carbon tetrachloride and so on.

Reflux method: This method is suitable for gases that are easily liquefied. For example, a long glass tube is connected to the device to prepare bromobenzene, so that the volatile gas is liquefied into liquid under the cooling of air, and flows back into the reaction device along the inner wall of the long glass tube.

Bagged method: such as CO reduction cuo or, the treatment of CO and exhaust gas in the experiment is to pass the exhaust gas into a deflated balloon or plastic bag.

2. Chemical treatment methods

Combustion method: This method can be used for CO exhaust gas treatment.

Precipitation method: For example, gas is passed into a saturated solution to convert it into Cus precipitation.

Caustic method: This method can be used for all acid waste gas treatment (e.g., etc.).

The treatment methods of laboratory waste gas include combustion method, absorption method, activated wood carbon adsorption method and condensation method.

Combustion method: including high-temperature combustion and catalytic combustion, the former requires additional fuel combustion, therefore, the use of heat energy should be considered when using this method; Catalytic combustion has low energy consumption, but in the early stage of work, it needs to be heated with electric heating to the ignition temperature, so it is not suitable for frequent start-up and shutdown occasions. Considering that the heat of the high-temperature combustion method** exceeds the heat energy required for production, it is not suitable.

However, the direct use of catalytic combustion is too much investment.

Absorption method: that is, the appropriate absorbent (such as diesel, kerosene, water and other media) is used to absorb in the absorption tower, and the solvent is separated from the absorption solution after absorption to a certain concentration. Due to the difficulty of separating the mold agent from the absorbent before the cavity, its application is limited.

Activated carbon adsorption method: the use of porous activated carbon or activated carbon fiber adsorption organic waste gas, saturation with low-pressure steam regeneration, regeneration of solvent waste gas after condensation, water separation, solvent, suitable for discontinuous treatment process, especially for low concentration of organic waste gas in the solvent has a good effect.

Condensation method: The cold medium is mainly used to treat the high-temperature organic waste gas vapor, which can be an effective solvent. The quality of the treatment effect is related to the temperature of the refrigerant, and the treatment efficiency is relatively lower than that of other methods, and it is suitable for the treatment of high-concentration waste gas.

Precautions for the treatment of laboratory exhaust gas

1. Treatment of combustible gas.

1. For the emission of combustible gas, if the emission is large, you should choose a place with fewer people as much as possible, pay attention to the prohibition of fire around, and prepare corresponding fire extinguishers, sand and water.

2. The staff should stand on the side of the gas outlet to prevent gas spraying and injuring people.

3. When the combustion method is used, a pressure reducing valve should be installed to control the speed of the combustible gas, and try to release the gas slowly so that it can be fully burned in the combustion device.

2. Treatment of inert gases.

1. Regret touching the discharge in an appropriate place outdoors.

2. If the cylinder or instrument is indoors, it can be connected to the exhaust pipe to lead it to the outdoors and discharge it slowly.

3. Treatment of combustible gas.

1. The powder, petroleum, grease and flammable substances adhered to the container valve or the use of appliances are cleaned before the gas can be treated.

2. It is strictly forbidden to treat combustible gas and combustible gas in the same place near it to prevent the occurrence of accidents.

3. In the vicinity of the combustible gas, there should be no ignition source, no combustibles and explosive materials.