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As the core equipment of wet scrubbing method in industrial waste gas treatment, the spray tower can remove pollutants such as hydrogen sulfide, ammonia, VOCs and odor through gas-liquid contact.
Its treatment effect depends on absorbent selection, gas-liquid contact efficiency and process parameter design.
The following is the structured description of treatment schemes, principles and technical key points for different pollutants:
1. Core Principle and Absorbent Selection of Spray Tower for Various Pollutants
The core logic of the spray tower: Waste gas enters from the bottom of the tower and makes countercurrent contact with the absorption liquid sprayed from the top. Pollutants transfer to the liquid phase through physical dissolution or chemical reaction. The purified gas is discharged through a demister. The pollutant-containing absorption liquid requires subsequent treatment or regeneration.
Pollutant Type | Core Treatment Principle | Recommended Absorbent | Key Reaction Equation | Treatment Efficiency |
|---|---|---|---|---|
Hydrogen Sulfide | Mainly chemical absorption. Alkaline absorption liquid reacts with hydrogen sulfide to generate salts. | 1. Sodium hydroxide solution2. Sodium carbonate solution3. Ammonia water4. Alkali liquid + desulfurization catalyst (such as iron ion and quaternary ammonium salt) | - | Conventional alkali washing: 80%-95%With catalyst: 95%-99% |
Ammonia | Mainly chemical absorption. Acidic absorption liquid reacts with ammonia to generate ammonium salts, supplemented by physical dissolution. | 1. Sulfuric acid solution2. Hydrochloric acid solution3. Phosphoric acid solution | - | 90%-99% (depends on acid concentration and liquid-gas ratio) |
VOCs | Only applicable to VOCs with high water solubility (such as alcohols, aldehydes and ketones), mainly physical dissolution. Water-insoluble VOCs (such as benzene and toluene) need cosolvents or combined processes. | 1. Clean water (for water-soluble VOCs)2. Special absorbent (such as diesel oil and washing oil for partial water-insoluble VOCs)3. Water + surfactant (improve gas-liquid contact effect) | No obvious chemical reaction, dominated by dissolution equilibrium | Water-soluble VOCs: 60%-85%Water-insoluble VOCs: <30% (poor effect when used alone) |
Odor | Odor is mostly mixed pollutants (including hydrogen sulfide, ammonia, mercaptan, amines, etc.). Combined absorbents are used to remove sulfur-containing and nitrogen-containing odor components. | 1. Alkali liquid + oxidant (such as sodium hypochlorite)2. Two-stage spraying with acid and alkali liquid3. Biological absorption liquid (such as activated sludge supernatant, suitable for low-concentration odor) | Mercaptan oxidation reaction | Mixed odor: 75%-90%; Biological absorption: over 90% |
2. Key Process Design Points
For mixed waste gas with multiple pollutants (such as waste gas from chemical industry, pharmaceutical industry and breeding industry), the following parameters of spray tower shall be optimized to avoid mutual interference in pollutant treatment.
2.1 Segmented Spraying Design
If the waste gas contains both hydrogen sulfide and ammonia, double towers in series or single tower with two-stage spraying shall be adopted.
The first stage: Acidic absorption liquid removes ammonia;
The second stage: Alkaline absorption liquid removes hydrogen sulfide;
Avoid direct mixing of acid and alkali liquid to prevent reagent failure and salt blockage.
2.2 Gas-Liquid Contact Efficiency Optimization
Packing selection: Porous packing (such as Pall ring, cascade ring and polypropylene packing) is selected to increase gas-liquid contact area. Turbulent ball tower can be used for high-concentration waste gas (spherical packing moves with air flow for sufficient contact).
Liquid-gas ratio (L/G): The liquid-gas ratio is controlled at 2−5 L/m³ for hydrogen sulfide and ammonia removal; it shall be increased to 5−10 L/m³ for VOCs treatment.
Spray pressure: The nozzle pressure is controlled at 0.2−0.4 MPa to ensure atomization effect, and the optimal droplet diameter is 100−200 μm.
2.3 Absorption Liquid Circulation and Regeneration
After alkali liquid absorption, elemental sulfur can be recovered by oxidative regeneration (introducing air or oxygen to oxidize sulfide);
The ammonium salt solution generated by acid absorption can be recycled as chemical fertilizer raw material or discharged after biochemical treatment up to standard;
Avoid cyclic use of saturated absorption liquid, otherwise the treatment efficiency will drop sharply.
2.4 Defogging and Anti-Blocking Design
A baffle demister or wire mesh demister is installed at the top of the tower to remove liquid droplets entrained in gas and prevent subsequent pipeline corrosion or secondary pollution;
Clean packing and nozzles regularly (online flushing system can be designed) to prevent salt crystallization and particle blockage.
3. Applicable Scenarios and Limitations
3.1 Applicable Scenarios
Medium and low concentration, large air volume mixed waste gas (such as chemical workshop tail gas, breeding farm odor and sewage treatment station waste gas);
Working conditions requiring pretreatment to remove particles and soluble pollutants (it can be used as the pre-treatment unit for subsequent catalytic combustion and activated carbon adsorption).
3.2 Limitations
Low treatment efficiency for water-insoluble VOCs (such as aromatic hydrocarbons and halogenated hydrocarbons), which needs to be combined with activated carbon adsorption, catalytic combustion (CO/RCO) and other processes;
It produces pollutant-containing wastewater, which needs supporting wastewater treatment system to avoid secondary pollution;
Anti-freezing measures shall be taken in low-temperature winter environment to prevent absorption liquid from freezing.
4. Typical Application Case
Take pharmaceutical factory fermentation waste gas (containing hydrogen sulfide, ammonia, VOCs and odor) as an example:
Process flow: Grille + two-stage spray tower + activated carbon adsorption + induced draft fan + discharge;
The first spraying stage: 5% sulfuric acid solution removes ammonia with a removal rate of 95%;
The second spraying stage: 3% sodium hydroxide + desulfurization catalyst removes hydrogen sulfide and part of water-soluble VOCs with a removal rate of 98%;
Activated carbon adsorbs residual water-insoluble VOCs and odor, and the final waste gas is discharged up to standard.
