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The spray tower is a common gas-liquid contact purification equipment for chemical waste gas treatment. Its core principle is to realize countercurrent or cocurrent contact between spray liquid and waste gas, and remove pollutants through absorption, neutralization and dissolution. According to the composition and properties of different chemical waste gases, targeted treatment schemes are adopted. The specific classification and applications are as follows:
Ⅰ. Core Treatment Schemes Classified by Spray Liquid Type
1. Alkaline Spray Scheme (For Acidic Waste Gas)
Applicable Waste Gas: Common acidic waste gas in chemical production such as HCl, H₂S, SO₂, partial NOₓ and fluorides, which are generally discharged from pesticide, electroplating and acid pickling processes.
Spray Liquid Formula: Solutions such as NaOH (Sodium Hydroxide), Na₂CO₃ (Sodium Carbonate) and Ca(OH)₂ (Calcium Hydroxide). The concentration is controlled at 2%–10% and adjustable according to waste gas concentration.
Purification Principle: Acid-base neutralization reaction. Typical chemical reactions are listed as follows:
HCl + NaOH = NaCl + H₂O
SO₂ + 2NaOH = Na₂SO₃ + H₂O
Process Characteristics: Simple equipment structure and low operating cost. It is necessary to regularly detect the pH value and replenish chemicals to prevent the decline of neutralization capacity.
2. Acidic Spray Scheme (For Alkaline Waste Gas)
Applicable Waste Gas: Alkaline waste gas such as ammonia (NH₃) and amines, which are generated in chemical fertilizer production, pharmaceutical and synthetic fiber processes.
Spray Liquid Formula: Dilute sulfuric acid (H₂SO₄) and dilute hydrochloric acid (HCl) with a concentration of 1%–5%.
Purification Principle: Acid-base neutralization to generate soluble salts. Typical chemical reaction is listed as follows:
2NH₃ + H₂SO₄ = (NH₄)₂SO₄
Process Characteristics: Prevent nozzle blockage caused by salt crystallization. An online cleaning device is recommended for auxiliary application.
3. Water / Solvent Spray Scheme (For Water-soluble / Solvent-soluble Waste Gas)
Applicable Waste Gas: Water-soluble organic waste gas (methanol, ethanol, acetone), partial inorganic waste gas (ammonia), and specific solvent-soluble waste gas (benzene series dissolved in diesel oil and engine oil).
Spray Liquid Formula: Clean water or special organic solvent. A small amount of surfactant can be added to improve gas-liquid contact efficiency for organic waste gas treatment.
Purification Principle: Realize gas-liquid mass transfer separation by utilizing the solubility of pollutants in liquid.
Process Characteristics: No secondary pollution. Solvent-containing spray liquid needs recycling treatment to avoid material waste.
4. Oxidative Spray Scheme (For Reductive and Odorous Waste Gas)
Applicable Waste Gas: Odorous waste gas such as H₂S, mercaptan and amines, as well as partial refractory organic waste gas from rubber industry, chemical production and landfill leachate treatment.
Spray Liquid Formula: Oxidant solutions such as NaClO (Sodium Hypochlorite), H₂O₂ (Hydrogen Peroxide) and KMnO₄ (Potassium Permanganate). A small amount of acid and alkali can be added to adjust pH value for enhanced oxidation effect.
Purification Principle: Strong oxidants decompose pollutants into harmless substances. For example, H₂S is oxidized into SO₄²⁻ and Cl⁻ by NaClO.
Process Characteristics: High deodorization efficiency. Oxidants shall be dosed quantitatively to avoid chemical waste and secondary pollution caused by excessive addition.
Ⅱ. Combined Spray Tower Schemes (For Complex Chemical Waste Gas)
A single spray tower is difficult to treat chemical waste gas with complex components. Combined processes are widely adopted in practical projects:
1. Multi-stage Series-connected Spray Towers
Typical combination: Acidic spray tower + Alkaline spray tower + Water washing tower. It is applicable for mixed waste gas containing acidic, alkaline and water-soluble pollutants to remove different contaminants step by step.
2. Spray Tower + Activated Carbon Adsorption
The spray tower firstly removes particulate matter, acidic and alkaline substances. The activated carbon adsorption tower treats residual organic waste gas to improve terminal purification effect. Suitable for coating and chemical synthetic waste gas.
3. Spray Tower + UV Photocatalysis / Plasma
The spray tower pre-removes macromolecular and water-soluble pollutants. Subsequent photocatalysis or plasma equipment decomposes refractory small-molecule organic compounds. Applicable for high-concentration and complex chemical organic waste gas.
4. Spray Tower + Biological Treatment
Pollutants are dissolved into the liquid phase by the spray tower and then flow into biological filters or biotrickling filters for microbial degradation. Suitable for low-concentration and biodegradable organic waste gas such as alcohols and esters.
Ⅲ. Key Design Points of Spray Tower Process
1. Gas-liquid Contact Mode
Countercurrent spraying is preferred. Waste gas enters from the tower bottom while spray liquid sprinkles downward from the tower top. Long gas-liquid contact time ensures higher purification efficiency.
2. Nozzle Selection
Spiral nozzles and hollow cone nozzles with excellent atomization effect are selected to avoid blockage and ensure uniform liquid coverage inside the tower.
3. Filler Selection
Polypropylene pall rings and cascade rings are added to expand gas-liquid contact area and improve mass transfer efficiency. Acid and alkali resistant fillers are required for corrosive waste gas.
4. Tail Water Treatment
Spray wastewater shall be collected and treated through neutralization, coagulation sedimentation and oxidation. Qualified wastewater can be discharged or recycled to avoid secondary pollution.
Ⅳ. Application Scope and Limitations
Application Scope: Pretreatment of medium and low-concentration acidic, alkaline, water-soluble, odorous chemical waste gas and particulate-containing waste gas.
Limitations: Low purification efficiency for water-insoluble and refractory high-concentration organic waste gas (such as benzene, toluene and xylene). Auxiliary equipment is required for combined treatment.
