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Ⅰ. Scheme Background and Application Scope
1. Characteristics of Pharmaceutical Waste Gas
The waste gas generated in the pharmaceutical industry has complex components, containing volatile organic compounds (VOCs) such as benzenes, alcohols, esters, ketones and amines. Part of the waste gas is mixed with dust, acidic or alkaline substances and trace catalyst residues. It features large concentration fluctuation, complex composition, obvious peculiar smell and strong potential toxicity. Direct discharge will seriously pollute the atmospheric environment and fail to meet national environmental protection standards, including Non-organized Emission Control Standard for Volatile Organic Compounds (GB 37822-2019) and Emission Standard of Air Pollutants for Pharmaceutical Industry (GB 37823-2019).
2. Applicable Scenarios
This scheme is applicable to medium and low-concentration VOCs waste gas (concentration range: 500-5000mg/m³) produced in chemical synthesis pharmacy, biopharmaceutics and pharmaceutical preparation production. It is especially suitable for pharmaceutical waste gas with large air volume, low concentration and no excessive catalyst toxicants (such as sulfur, chlorine and heavy metals). The system can realize standard emission and odor elimination of waste gas.
Ⅱ. Technical Principle of Catalytic Combustion
Catalytic Oxidation (CO) is a thermal oxidation process. Under the action of catalysts, VOCs are oxidized and decomposed into harmless CO₂ and H₂O at a relatively low temperature (250-400℃), accompanied by heat release. The core chemical reaction formula is shown as follows:
VOCs + O₂ → CO₂ + H₂O + Heat
Compared with traditional thermal combustion (600-800℃), catalytic combustion has the advantages of low energy consumption, high purification efficiency, no secondary pollution and simple operation.
Catalyst is the core component of this technology. Precious metal catalysts (Pt/Pd supported type) or non-precious metal composite catalysts (MnO₂-CeO₂/Al₂O₃) are adopted in this scheme. The catalysts have high activity, excellent thermal stability and long service life (≥8000 hours), which can efficiently decompose various organic pollutants in pharmaceutical waste gas.
Ⅲ. Process System Design
1. Overall Technological Process
Waste Gas Collection → Pretreatment System → Heat Exchanger → Catalytic Combustion Reactor → Standard Discharge
(1) Waste Gas Collection
Closed air collecting hoods and negative-pressure pipelines are adopted to cover exhaust sources such as reaction kettles, dryers and storage tanks. The collection efficiency of unorganized waste gas is ≥90%.
(2) Pretreatment System
Dust Removal: High-efficiency bag dust collector is installed to remove dust particles (particle size ≥1μm) and prevent catalyst blockage. The dust removal efficiency is ≥99%.
Acid & Alkali Removal: If the waste gas contains acidic or alkaline substances, a spray washing tower with dilute NaOH or H₂SO₄ solution is equipped to adjust the pH value to 6-8, avoiding equipment corrosion and catalyst poisoning.
Dehydration Treatment: High-efficiency mist eliminator (mist removal rate ≥99.5%) and activated carbon dehydration layer are applied to reduce the moisture content of waste gas to ≤10% and prevent catalyst deactivation.
(3) Heat Exchanger
A plate heat exchanger is adopted to preheat raw waste gas by utilizing high-temperature tail gas (350-400℃) after catalytic combustion. The temperature of inlet gas rises to 200-250℃ to reduce auxiliary heating energy consumption. The heat recovery efficiency is ≥75%.
(4) Catalytic Combustion Reactor
Structure: Vertical fixed-bed reactor is adopted. The catalyst bed is divided into two layers (upper protective bed and lower main reaction bed) to ensure uniform gas distribution.
Auxiliary Heating: Electric heating or natural gas heating is equipped. Auxiliary heating is started to maintain reaction temperature when VOCs concentration is lower than 1000mg/m³. When the concentration exceeds 1500mg/m³, the waste heat from combustion can maintain stable reaction to realize self-heating operation.
Reaction Conditions: Reaction temperature: 280-350℃; space velocity: 10000-20000h⁻¹; gas retention time: ≥0.5s; VOCs removal efficiency: ≥95%.
(5) Standard Discharge
The purified waste gas is discharged through a chimney with a height of ≥15m. All emission indicators comply with GB 37823-2019, with VOCs emission concentration ≤60mg/m³, removal efficiency ≥80% and odor concentration ≤2000 (dimensionless).
2. Core Equipment Parameters
Equipment Name | Specification Parameters | Material Requirements |
|---|---|---|
Bag Dust Collector | Air volume: 5000-50000m³/h; filtration velocity: 1.2-1.5m/min | Filter bag: PTFE; Shell: Q235 with anti-corrosion coating |
Spray Washing Tower | Empty tower velocity: 0.8-1.2m/s; spray density: 15-20m³/(m²・h) | Tower body: FRP or 304 stainless steel |
Plate Heat Exchanger | Heat exchange area: 50-300m²; pressure loss ≤1500Pa | Plate: 316L stainless steel |
Catalytic Combustion Reactor | Design pressure: -500~+500Pa; maximum reaction temperature ≤450℃ | Shell: Q235 with high-temperature resistant coating; Inner tank: 316L stainless steel |
Catalyst | Specific surface area ≥200m²/g; compressive strength ≥100N/cm; operating temperature: 250-400℃ | Carrier: Honeycomb ceramic or γ-Al₂O₃ |
Ⅳ. System Operation and Control
1. Operation Control Logic
Start-up Stage
Start the induced draft fan first. After the system negative pressure is stabilized, turn on the auxiliary heating system to raise the catalyst bed temperature to 280℃, and then introduce waste gas into the reactor.
Operating Stage
Real-time monitor waste gas concentration, reaction temperature and system pressure. The PLC control system adjusts fan frequency and heating power to maintain stable reaction temperature. When VOCs concentration exceeds 80mg/m³, the system automatically switches to the bypass adsorption device (standby activated carbon bed) to ensure standard emission.
Shutdown Stage
Cut off the waste gas intake firstly, keep the induced draft fan running until the catalyst bed temperature drops below 100℃, and then shut down the fan and auxiliary equipment.
2. Safety Protection Measures
Explosion Prevention: Explosion relief sheets (explosion relief pressure: 0.1MPa) are installed on the reactor and pipelines. Combustible gas detectors are arranged in the workshop (alarm concentration ≤25% of LEL), linked with emergency shutdown devices.
Fire Prevention: Fireproof and thermal insulation materials are adopted for equipment and pipelines. All electrical equipment adopts explosion-proof type (Ex dⅡBT4).
Catalyst Poisoning Prevention: Regularly monitor waste gas composition. Waste gas containing sulfur, chlorine, heavy metals and other toxicants is prohibited from entering the reactor. Advanced pretreatment is required if gas components change.
Emergency Treatment: Emergency exhaust pipelines and standby adsorption devices are equipped. The system will switch to emergency mode in case of sudden failure to avoid direct exhaust of pollutants.
Ⅴ. Operation Maintenance & Cost Analysis
1. Daily Operation and Maintenance
Daily Inspection: Monitor operating parameters (temperature, pressure, air volume), clean dust hoppers, and check the liquid level and pH value of the spray tower.
Weekly Inspection: Detect temperature distribution of catalyst bed, clean dust on the heat exchanger surface, and test safety alarm devices.
Monthly Inspection: Sample and detect exhaust gas concentration, replace dehydration adsorption materials, and inspect the operating condition of fans and motors.
Annual Maintenance: Replace or regenerate catalysts, conduct comprehensive equipment maintenance, and calibrate detection instruments.
2. Cost Estimation (Taking 10000m³/h air volume as an example)
Equipment Investment: Approximately 800,000-1,200,000 RMB (including pretreatment system, reactor, heat exchanger and control system).
Operating Cost:
Energy Consumption: Power consumption is about 5-10kW・h/h during auxiliary heating stage; natural gas consumption is about 5-10m³/h under low-concentration working conditions. The annual energy cost is about 150,000-300,000 RMB.
Consumables: Annual catalyst replacement cost is 80,000-120,000 RMB; annual replacement cost of filter bags and adsorption materials is 30,000-50,000 RMB.
Labor Cost: 2-3 workers per shift; annual labor cost is about 100,000-150,000 RMB.
Investment Payback Period: Approximately 3-5 years (including environmental subsidies and energy-saving benefits).
Ⅵ. Scheme Advantages
High Purification Efficiency: The VOCs removal efficiency is ≥95% with excellent odor elimination performance, meeting strict environmental protection requirements of the pharmaceutical industry.
Energy Saving and Consumption Reduction: Waste heat recovery system is equipped with a high proportion of self-heating operating conditions. The energy consumption is 30-50% lower than traditional thermal combustion.
Safe and Reliable: Perfect explosion-proof, fireproof and emergency systems are configured to adapt to the characteristic of large concentration fluctuation of pharmaceutical waste gas.
Simple Operation: PLC automatic control system reduces manual intervention and lowers overall operation and maintenance costs.
Environmental Compliance: It meets national and local environmental protection standards and can pass official environmental acceptance.
