+86 15853145085
For the treatment of four types of pollutants including hydrogen sulfide (H₂S), ammonia (NH₃), VOCs and odor, the process shall be selected according to pollutant properties, concentration, air volume and emission requirements. Some processes can realize the cooperative treatment of multiple pollutants. The mainstream processes and cooperative treatment schemes for each pollutant are as follows:
1. Hydrogen Sulfide (H₂S) Treatment Process
H₂S is an acidic and reducing toxic gas with a rotten egg smell. The core of treatment is to remove sulfur elements by oxidation or fix pollutants through acid-base neutralization.
1.1 Alkali Liquid Absorption Method
Principle: Use alkaline solutions such as NaOH and Na₂CO₃ for spray absorption to generate sodium sulfide or sodium hydrosulfide. It is applicable to low-concentration H₂S waste gas.
Advantages: Simple equipment, low investment and convenient operation; it can be integrated with ammonia absorption process.
Disadvantages: Waste liquid requires secondary treatment, which is easy to cause secondary pollution; limited treatment efficiency for high-concentration H₂S waste gas.
1.2 Dry Oxidation Method (Iron Oxide Method / Activated Carbon Adsorption Oxidation)
Iron Oxide Method: The iron oxide desulfurizer reacts with H₂S to generate iron sulfide, and regenerates by introducing air after saturation.
Activated Carbon Adsorption Oxidation Method: Activated carbon adsorbs H₂S and oxidizes it into elemental sulfur through surface catalysis.
Advantages: No secondary waste liquid, high treatment efficiency (over 99%), suitable for low-concentration and small-air-volume waste gas.
Disadvantages: The desulfurizer needs regular replacement or regeneration, and the operating cost increases with the rise of air volume.
1.3 Biological Method (Biological Filter / Biological Trickling Filter)
Principle: Microorganisms (such as sulfur-oxidizing bacteria) convert H₂S into elemental sulfur or sulfate.
Advantages: Low operating cost, no secondary pollution, suitable for cooperative treatment of medium and low concentration malodorous waste gas.
Disadvantages: Large floor area and susceptible to temperature and humidity.
1.4 Catalytic Oxidation Method (Claus Process / Selective Catalytic Oxidation)
Claus Process: High-concentration H₂S (>15%) is combusted to generate SO₂ firstly, and then reacts with unreacted H₂S under the action of catalyst to generate elemental sulfur.
Selective Catalytic Oxidation: Directly oxidize H₂S into elemental sulfur under low-temperature catalyst.
Advantages: Realize sulfur resource recovery of high-concentration H₂S with high treatment efficiency.
Disadvantages: High investment and complex process, applicable to high-concentration H₂S waste gas in coal chemical industry and petroleum refining industry.
2. Ammonia (NH₃) Treatment Process
NH₃ is an alkaline and water-soluble gas with pungent odor. The core of treatment is acid-base neutralization or catalytic decomposition.
2.1 Acid Liquid Absorption Method
Principle: Use acidic solutions such as sulfuric acid and hydrochloric acid for spray absorption to generate ammonium salts such as ammonium sulfate and ammonium chloride.
Advantages: Simple equipment, high efficiency (over 95%), and ammonium salts can be recycled as fertilizer.
Disadvantages: It is necessary to control the pH value of absorption liquid to prevent ammonia escape; multi-stage absorption is required for high-concentration ammonia waste gas.
2.2 Biological Method
Principle: Nitrifying bacteria convert ammonia nitrogen into nitrate or nitrite.
Advantages: Low operating cost, no secondary pollution, and it can be used for cooperative treatment of H₂S and odor.
Disadvantages: Sensitive to inlet gas concentration (NH₃ concentration shall be less than 500mg/m³) with long startup cycle.
2.3 Catalytic Decomposition Method
Principle: Decompose NH₃ into N₂ and H₂O under high temperature (300~400℃) and catalyst condition.
Advantages: No secondary pollutants, suitable for high-temperature and low-concentration ammonia waste gas.
Disadvantages: High investment and high energy consumption; dust and sulfur impurities need to be removed by pretreatment.
2.4 Adsorption Method
Principle: Adsorb NH₃ by adsorbents such as acidic activated carbon and zeolite.
Advantages: Simple operation and small floor area, suitable for low-concentration and small-air-volume waste gas.
Disadvantages: Adsorbents need regular regeneration or replacement with high operating cost.
3. VOCs Treatment Process
VOCs have complex components (such as hydrocarbons, alcohols and esters). The process shall be selected according to concentration, boiling point and flammability, which is divided into recovery method and destruction method.
3.1 Recovery Method (Suitable for medium and high concentration VOCs with recovery value)
3.1.1 Activated Carbon Adsorption Method
Principle: Use the porous structure of activated carbon to adsorb VOCs, and regenerate by steam desorption after saturation.
Advantages: Low investment and simple operation, suitable for low-concentration and large-air-volume VOCs.
Disadvantages: Not applicable to high-boiling and easily polymerized VOCs; activated carbon needs regular replacement.
3.1.2 Zeolite Rotor Adsorption Concentration + Incineration
Principle: The zeolite rotor adsorbs and concentrates low-concentration VOCs, and the concentrated gas is sent to the incinerator for destruction.
Advantages: High treatment efficiency (>95%) and low energy consumption, suitable for large-air-volume and low-concentration VOCs.
Disadvantages: Relatively high investment; dust and humidity need to be removed by pretreatment.
3.1.3 Condensation Recovery Method
Principle: Convert VOCs from gaseous state to liquid state for recovery by cooling and pressurization.
Advantages: Realize resource recovery, suitable for high-concentration and high-boiling VOCs (such as gasoline and organic solvents).
Disadvantages: High energy consumption and low treatment efficiency for low-concentration VOCs.
3.1.4 Membrane Separation Method
Principle: Use selectively permeable membrane to separate VOCs from air, and recover or destroy after enrichment.
Advantages: Low energy consumption and no secondary pollution, suitable for medium and high concentration VOCs.
Disadvantages: The membrane is easy to be blocked, requiring pretreatment and high investment.
3.2 Destruction Method (Suitable for low-concentration VOCs without recovery value)
3.2.1 Catalytic Combustion (CO)
Principle: Under the action of catalyst, VOCs are oxidized and decomposed into CO₂ and H₂O at low temperature (200~400℃).
Advantages: Low energy consumption and high treatment efficiency, suitable for medium and low concentration VOCs.
Disadvantages: The catalyst is easy to be poisoned (sulfur and chlorine impurities need to be removed by pretreatment) with relatively high investment.
3.2.2 Thermal Combustion (TO)
Principle: VOCs are directly combusted and decomposed at high temperature (600~800℃).
Advantages: Wide treatment range and no catalyst required, suitable for high-concentration VOCs with complex components.
Disadvantages: High energy consumption, waste heat recovery needs to be considered.
3.2.3 Photocatalytic Oxidation (UV Photolysis)
Principle: Ultraviolet light excites catalysts such as TiO₂ to generate hydroxyl radicals for oxidative decomposition of VOCs.
Advantages: Simple equipment and low operating cost, suitable for low-concentration malodorous VOCs.
Disadvantages: Treatment efficiency is greatly affected by humidity and dust, and intermediate by-products are easily generated.
3.2.4 Plasma Method
Principle: High-energy electrons are generated by high-voltage plasma to crack VOCs molecular chains.
Advantages: Small floor area, suitable for cooperative treatment of low-concentration VOCs and odor.
Disadvantages: High energy consumption, limited treatment efficiency for high-concentration VOCs, and easy to produce ozone.
4. Odor Treatment Process
Odor is mostly mixed pollutants (including H₂S, NH₃, VOCs, mercaptan, etc.), which requires cooperative treatment, and broad-spectrum processes are preferred.
4.1 Biological Method (Mainstream Process)
Process Type: Biological filter, biological trickling filter, biological scrubber.
Principle: Microorganisms degrade mixed odor pollutants into harmless substances.
Advantages: Low operating cost and no secondary pollution, suitable for medium and low concentration mixed odor (such as municipal sewage, garbage disposal and chemical waste gas).
Disadvantages: Large floor area and susceptible to temperature and pH value.
4.2 Advanced Oxidation Processes (AOPs)
Principle: Generate hydroxyl radicals through ozone oxidation, Fenton oxidation and other methods to oxidize and decompose odor molecules.
Advantages: High treatment efficiency and fast reaction speed, suitable for high-concentration and refractory odor.
Disadvantages: High energy consumption, ozone needs on-site preparation, and tail gas ozone removal is required.
4.3 Combined Adsorption-Oxidation Method
Principle: Activated carbon or zeolite adsorbs odor, combined with catalytic oxidation or photo-oxidation for advanced treatment.
Advantages: High treatment efficiency and wide application range, suitable for low-concentration multi-component odor.
Disadvantages: Relatively high operating cost, and adsorbents require regular maintenance.
4.4 Chemical Scrubbing Method
Principle: Use mixed scrubbing liquid of acid, alkali and oxidant (such as sodium hypochlorite) to neutralize and oxidize odor pollutants.
Advantages: Fast treatment speed and compact equipment, suitable for high-concentration water-soluble odor.
Disadvantages: A variety of scrubbing liquids need to be configured, and waste liquid requires secondary treatment.
5. Multi-Pollutant Cooperative Treatment Scheme
In practical engineering, most waste gas is mixed waste gas containing H₂S+NH₃+VOCs+odor. The recommended combined processes are as follows:
5.1 Chemical Scrubber + Biological Filter
Process Flow: Waste gas → Pretreatment (dedusting and cooling) → Acid-base scrubber (remove H₂S and NH₃) → Biological filter (degrade VOCs and residual odor) → Discharge.
Application: Medium and low concentration mixed waste gas (such as pharmaceutical, chemical and breeding waste gas).
5.2 Zeolite Rotor Concentration + Catalytic Combustion + Alkali Scrubber
Process Flow: Waste gas → Pretreatment → Zeolite rotor (concentrate VOCs) → Catalytic combustion (destroy VOCs) → Alkali scrubber (remove combustion by-product SO₂) → Discharge.
Application: Waste gas dominated by large-air-volume and low-concentration VOCs with a small amount of H₂S (such as coating and printing waste gas).
5.3 Plasma + Photocatalytic Oxidation + Activated Carbon Adsorption
Process Flow: Waste gas → Plasma (crack macromolecular VOCs and odor) → Photocatalytic oxidation (advanced degradation) → Activated carbon adsorption (terminal purification) → Discharge.
Application: Low-concentration refractory mixed odor (such as waste gas from garbage transfer station and sewage treatment plant).
