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15862552103
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No. 4058 Linhu Avenue, Luxu, Lili Town, Wujiang District, Suzhou City, Jiangsu Province
Suzhou Dingyu Energy saving Equipment Co., Ltd
Design and Selection of Chemical Waste Gas Fans
Date: 2025-08-20Read: 9
Chemical waste gas fan is the core equipment for treating corrosive, high-temperature, flammable, explosive or particulate industrial waste gas. Its design and selection are directly related to production safety and environmental compliance.
1、 Challenges of harsh working conditions and core design objectives
1. Corrosive gases
• Typical media: hydrochloric acid mist (HCl), chlorine gas (Cl ₂), hydrogen sulfide (H ₂ S), ammonia gas (NH3), organic solvent vapors (such as acetone, benzene derivatives).
Design response: The overcurrent components (impeller, volute) need to be fully covered with anti-corrosion coating, and ordinary stainless steel (such as 304) is prohibited.
2. High temperature and phase transition risk
• Exhaust gas temperature: 150 ℃~450 ℃ (coal-fired flue gas, reactor exhaust).
• Deadly problem: Acid dew point corrosion (such as sulfuric acid condensation corrosion of carbon steel) requires maintaining a wall temperature>dew point temperature of 15 ℃.
3. Explosive environment
• Dust explosion: Aluminum powder, coal powder, resin powder (concentration>20g/m ³ can explode).
Gas explosion: Organic waste gas reaches the lower explosive limit (LEL).
Design response: Explosion proof certification+Static elimination+Non sparking structure.
4. Particle abrasion
Hard particles: catalyst dust, silicon powder (hardness>Mohs 7).
• Adhesive adhesion: Tar and polymer coagulation (causing dynamic imbalance).
2、 Detailed Explanation of Core Structure Design
1. Impeller - Balance of Corrosion and Wear Resistance
• Material selection
Strong acid environment (HCl/H ₂ SO ₄): Hastelloy C276 (resistant to 120 ℃/70% sulfuric acid) or titanium alloy Gr5 (resistant to wet chlorine gas).
Hydrofluoric acid (HF): Monel alloy 400.
Organic solvents: Carbon steel lined with plastic (PP/PTFE) or full plastic fiberglass reinforced plastic (FRP).
High temperature dust: Dual phase steel 2205+tungsten carbide thermal spraying (HVOF coating).
• Structural reinforcement
Backward tilting blades: reduce particle adhesion rate (60% less fouling than forward tilting blades).
Strengthening rib design: Enhance rigidity and prevent deformation (deformation under high temperature conditions<0.3mm).
2. Spiral shell (casing) - double-layer protective system
• Substrate: Carbon steel shell (8-12mm thick).
• Internal protection:
• Lining scheme:
• Rolling lining PTFE: 2mm thick, resistant to all organic solvents (operating temperature -50 ℃~180 ℃).
Rubber lining: 5mm thick natural rubber (resistant to 90 ℃/50% sulfuric acid).
Overall plan: FRP molded shell (maximum temperature resistance of 150 ℃).
3. Sealing system - zero leakage lifeline
• Mechanical seal:
Double end face seal: Two pairs of silicon carbide friction pairs+isolation buffer (pressure>exhaust gas pressure 0.2MPa).
Gas blocking: nitrogen purging (purity 99.999%, flow rate 10L/min).
• Solution: Magnetic coupling transmission (no shaft seal design, eliminating leakage points).
4. Drive and control system
Explosion proof motor: Ex d IIB T4/Ex tD A21 IP66 (dust explosion-proof dual certification).
Variable frequency speed regulation: Adapt to air volume fluctuations (± 30% change in air volume under chemical working conditions).
• Security monitoring:
Bearing temperature: PT100 temperature measurement>85 ℃ alarm (shutdown threshold 95 ℃).
Vibration monitoring: piezoelectric sensor>4.5mm/s interlock shutdown.
3、 Anti corrosion Material Science Matrix
| Corrosive medium | Material selection | Tolerance limit | Taboo |
|---|---|---|---|
| Hydrochloric acid (gaseous) | Hastelloy C276 | 120 ℃/37% concentration | 316L stainless steel (perforated for 48 hours) |
| Hydrofluoric acid (HF) | Monel 400 | 80 ℃/any concentration | Fiberglass/Ceramic (Dissolved) |
| High temperature chlorine gas | Titanium alloy Gr5 | 350 ℃/dry chlorine gas | Titanium chloride explosion occurs at temperatures above 400 ℃ |
| Concentrated sulfuric acid (smoke) | Carbon steel lined with lead | 80 ℃/93% concentration | Lead lining detachment when flow rate>2m/s |
| Organic solvent vapor | PTFE lining | Full concentration corrosion resistance | Common failure of metal materials |
4、 Strict scenario application cases
1. Chlor alkali industry
• Medium: Wet chlorine gas (containing free chlorine and water vapor).
Fan scheme: titanium alloy impeller+FRP snail shell+nitrogen seal (to prevent chlorine gas leakage).
2. Tail gas from pesticide factories
• Medium: H ₂ S+organic sulfur+pesticide dust.
Fan scheme: Hastelloy C276 integral casting impeller+PTFE lined volute shell+explosion-proof motor.
3. Lithium battery injection workshop
• Medium: NMP solvent vapor (explosive limit 0.8%~9.5%).
Fan scheme: All aluminum spark free impeller+Ex tD explosion-proof certification+electrostatic grounding<1 Ω.
4. Gas purification in coking plant
• Medium: High temperature gas containing tar, H ₂ S, NH ∝.
Fan scheme: dual phase steel impeller+steam tracing system (anti tar condensation)+automatic flushing nozzle.
5、 The Golden Rule of Selection
1. Four step analysis method
Step 1: Media analysis
Clearly define the composition, concentration, and dew point temperature of the exhaust gas (to prevent condensation corrosion).
Step 2: Working condition mapping
Exhaust gas temperature, dust content, and explosion characteristics (LEL value/dust Kst).
Step 3: Performance Calculation
Air volume=design value x 1.3 (safety margin), air pressure=pipe network resistance x 1.2.
Step 4: Material selection
Select materials based on corrosion rate<0.1mm/year (Hastelloy>Titanium>Dual phase steel>316L).
2. Avoiding cost traps
Misconception: "304 stainless steel is universal" → In reality, perforation occurs in a chloride ion environment for 6 months.
Correct solution: Choose Monel for the hydrofluoric acid scenario (cost is twice that of titanium alloy, but lifespan is extended by five times).
6、 Maintenance strategy and lifespan assurance
1. Key points of daily monitoring
Sealing system: If the nitrogen pressure fluctuates by more than 10%, it needs to be checked immediately.
Vibration trend: If it increases by more than 15% for three consecutive days, a warning of impeller scaling will be issued.
2. Lifespan of key components
Mechanical seal:>24 months (isolation fluid needs to be changed quarterly).
Lining layer: PTFE lining>10 years, rubber lining>5 years.
3. Decision Points for Major Maintenance
Impeller corrosion: blade thickness reduction>10% forced replacement.
• Dynamic balance failure: If the residual unbalance exceeds G2.5 level, it needs to be returned to the factory for calibration.
