laboratory-exhaust-gas

Laboratory waste gas has diverse components (such as acidic and alkaline gases, organic solvent volatiles, and small amounts of toxic gases). Treatment requires targeted, separate purification. The following is a typical process flow chart:

Laboratory Waste Gas Treatment Process
1. Waste Gas Separation and Collection
- Universal exhaust hoods, fume hoods, and dedicated gas collection ducts are used to separate waste gases by their properties (e.g., separate acidic, alkaline, and organic waste gases to avoid mixed flows and reactions).
- Fans provide negative pressure to transport each type of waste gas to the corresponding pretreatment unit.
2. Separation and Pretreatment
- Acidic waste gas enters the acid mist scrubber, where it reacts with an alkaline solution (such as NaOH solution) sprayed into the scrubber to remove acidic substances such as HCl and SO₂.
- Alkaline waste gas enters the alkaline mist scrubber, where it reacts with an acidic solution (such as dilute H₂SO₄) to remove alkaline gases such as NH₃. - Organic waste gas: Preliminary filtration through an activated carbon filter removes large particles to prevent clogging of subsequent equipment.
3. Core Purification
- After pretreatment, mixed waste gas (or single organic waste gas) enters the core purification unit:
- Low-concentration organic waste gas: Photocatalytic oxidation equipment uses UV light to decompose VOC molecules, and ozone assists in the oxidation of these molecules into harmless substances.
- Medium- and high-concentration organic waste gas: Switch to an activated carbon adsorption tower (filled with granular activated carbon) to efficiently adsorb organic solvents such as benzene, toluene, and acetone.
- Toxic gases (such as Cl₂ and H₂S): Add a dedicated chemical absorption tower (e.g., Cl₂ is absorbed with a Na₂S₂O₃ solution).
4. Deep Purification and Discharge
- After core treatment, the waste gas enters a high-efficiency demister to remove residual water vapor and mist droplets.
- Finally, it is discharged through an exhaust stack at least 15 meters high. Some laboratories may need to install online monitoring instruments (to monitor VOCs and acid and base concentrations) to ensure compliance with standards.

The key to this process is "classified collection + quality-based treatment" to avoid secondary pollution caused by the mixing of different exhaust gases. Multi-stage purification also adapts to the characteristics of laboratory exhaust gases: low air volume, multiple components, and intermittent emissions.

Low-concentration exhaust gases from university laboratories can be treated with a two-stage activated carbon adsorption chamber. This two-stage cascade adsorption device is designed for low-concentration, multi-component laboratory exhaust gases (such as small amounts of VOCs, organic solvent volatiles, and small amounts of acidic/alkaline gases). Its core function is to utilize the physical adsorption properties of activated carbon to purify exhaust gases step by step, ensuring compliance with emission standards. Its features and adaptability are as follows:

Core Features
- Staged purification for more reliable efficiency:
The primary adsorption chamber first absorbs the majority of pollutants in the exhaust gas (especially those with relatively high concentrations). The remaining trace pollutants then enter the secondary adsorption chamber for deeper purification. This dual adsorption process significantly reduces the risk of saturation failure in a single adsorption chamber. The overall purification efficiency typically reaches 85%-95%, meeting stringent laboratory exhaust emission standards (such as GB 16297). - Adaptable to laboratory exhaust characteristics:
Laboratory exhaust is often emitted intermittently (e.g., during experimental operations, not continuously) and has complex components (possibly containing ethanol, acetone, formaldehyde, etc.). The two-stage adsorption design can cope with this volatility—even if the momentary concentration of a particular pollutant is slightly elevated, the two-stage adsorption system can provide a safety net to prevent excessive emissions.
- Flexible maintenance and manageable costs:
The activated carbon in the two-stage adsorption chamber can be replaced separately (the first stage has a higher adsorption load and requires more frequent replacement), eliminating the need for complete replacement, reducing consumables waste. Furthermore, the activated carbon loading volume is typically small (suitable for low-volume laboratory exhaust), resulting in lower maintenance costs than large industrial equipment, making it suitable for the budgets of school laboratories.

Applicable Scenarios and Precautions
- Suitable for chemistry, biology, and materials science laboratories, treating organic waste gases that are not high-concentration or corrosive (strong acidic gases, for example, require prior neutralization).
- Regular monitoring of adsorption performance (e.g., using odor and VOC detectors) is required, and saturated activated carbon should be replaced promptly to prevent pollutant penetration after saturation. If the exhaust gas contains dust or particulate matter, a pre-treatment device (such as a filter) should be installed before the adsorption chamber to prevent clogging of the activated carbon pores and affect adsorption efficiency.

This design balances purification effectiveness with the actual needs of the laboratory and is a common solution for small-scale decentralized exhaust gas treatment, effectively reducing the impact of laboratory exhaust gas on the surrounding environment.