Core Operating Conditions of Incineration Flue Gas

The flue gas generated by waste incineration contains acidic gases such as HCl, SO₂, and HF, along with a large amount of fly ash and acid dew point condensation water.
The fan is exposed to combined effects of:

• Abrasive wear caused by dust particles
• Acid dew point corrosion
• Chloride ion pitting corrosion

Under such harsh conditions, ordinary carbon steel may fail within 3–6 months.

Therefore, the fan protection system must be designed comprehensively from six aspects:

1. Upstream flue gas pretreatment
2. Anti-wear structural design
3. Material selection for corrosion resistance
4. Surface strengthening technology
5. Sealing and insulation protection
6. Operation and maintenance management

1. Upstream System: Reduce Dust and Corrosive Media at the Source

1.1 Dust Control — Reduce Particle Erosion

• Install bag filters and cyclone pre-dust collectors before the fan inlet to reduce dust concentration below 50 mg/m³, preventing large fly ash particles from directly impacting the impeller blades.
• Install flow guide plates inside the duct to reduce uneven airflow, turbulence, and local erosion at the blade leading edge and volute tongue.
• Install ash discharge valves at low points of the duct to regularly remove accumulated ash and prevent large ash deposits from entering the fan.

1.2 Corrosion Control — Avoid Acid Dew Point Corrosion (Critical)

• Maintain the flue gas temperature at the fan inlet 15–25℃ above the acid dew point.
  Normally, the temperature should be maintained above 160℃ to prevent condensation of hydrochloric acid and sulfuric acid films during startup, shutdown, or low-load operation.
• Apply complete external insulation and weather protection to the duct and fan casing to prevent external condensation caused by low surface temperature.
• Install condensate drainage pipes at the lowest points of the duct system to discharge chloride-containing acidic condensate and prevent backflow into the fan.
• Add a hot air bypass system to maintain stable gas temperature during low-load operation and avoid dew point corrosion.

2. Structural Optimization: Prevent Dust Accumulation, Erosion, and Blockage

2.1 Impeller Design (Wear Resistance + Anti-Fouling)

• Use backward-curved straight blades with fewer blades and larger flow passages to reduce dust adhesion and buildup.
• Avoid curved blades that easily accumulate sticky dust.
• Thicken the blade leading edge and design it with a rounded guide profile to reduce erosion.
• Reinforce the front and rear plates of the impeller.
• Install replaceable wear-resistant liners at the volute tongue, which is the most vulnerable wear area.
• Provide cleaning ports on the impeller for online compressed-air cleaning to prevent dust accumulation and imbalance.
• Upgrade dynamic balancing level to G4.0 to handle vibration caused by uneven dust deposition.

2.2 Casing and Transmission Structure

• Increase the thickness of the volute casing plate and smooth the internal surface to reduce dust accumulation.
• Install large inspection doors for convenient cleaning and maintenance.
• Use a C-type external bearing housing to completely isolate bearings from flue gas.
• Apply double shaft sealing systems (labyrinth seal + air purge seal) with instrument air injection to prevent dust and corrosive gas entering the bearing chamber.
• Install cooling discs on the shaft to prevent high temperature transfer to bearings.
• Upgrade all fasteners to 316L stainless steel or Hastelloy alloy bolts to prevent premature corrosion failure of small components.

3. Material Selection by Different Flue Gas Sections

3.1 Before Desulfurization Section

High-temperature gas (200–350℃), high dust concentration, high HCl content

Impeller:

• Preferred material: Hastelloy C-276 alloy, offering excellent resistance against chloride pitting and strong HCl corrosion.
• Cost-effective option: 310S stainless steel + wear-resistant overlay layer.

Casing:

• Carbon steel Q245R with internal glass flake anti-corrosion lining.

Volute Tongue Wear Area:

• High chromium cast iron or tungsten carbide wear-resistant liners.

3.2 After Desulfurization Section

Clean flue gas (140–180℃), high humidity, chloride enrichment

Impeller:

• 316L stainless steel + wear/corrosion-resistant surface coating.
• For extremely severe conditions: titanium alloy or C276 Hastelloy alloy.

Casing:

• Carbon steel base material + double-layer glass flake coating
• Total coating thickness ≥ 1.2 mm
• Resistant to acidic mist corrosion.

3.3 Materials That Should Be Avoided

Ordinary 304 stainless steel is not suitable for waste incineration flue gas applications.

Due to chloride ions in the gas, 304 stainless steel may suffer from:

• Pitting corrosion
• Local perforation
• Early failure within 3–6 months

It should never be directly used for fan wetted/flow-contact components.

4. Surface Strengthening: Wear and Corrosion Protection Coatings

Solution A: Dual-Function Wear and Corrosion Protection for Impeller Blades

Process:

1. Sand blasting treatment to Sa2.5 grade
2. Apply transition layer:
   • Plasma sprayed NiCrAlY alloy coating
   • Prevents thermal expansion mismatch and coating peeling
3. Apply surface layer:
   • Laser cladding WC-CoCr tungsten carbide ceramic coating

Advantages:

• Excellent resistance against fly ash erosion
• Blocks acidic media penetration
• Operating temperature up to 450℃
• Service life more than 3 times longer than ordinary coatings

Solution B: Heavy-Duty Anti-Corrosion Protection for Casing

Internal casing treatment:

• Epoxy primer
• Two layers of glass flake coating

Advantages:

• Resistant to high-temperature acid mist
• Prevents coating peeling under heat and moisture conditions

Ordinary paint should be avoided because it easily fails under high temperature and humid environments.

Solution C: Simple Overlay Repair

For temporary field repair:

• Apply Cr-C-B wear-resistant welding overlay on blade leading edges.
• Creates a hard wear-resistant layer suitable for emergency maintenance.

5. Sealing and Insulation Protection

Shaft Sealing

Use:

• Perfluoroelastomer sealing rings
• Metal bellows structure

Performance:

• Resistant to 180℃ acidic flue gas
• Prevents gas leakage and shaft corrosion

Complete Equipment Insulation

Apply:

• Aluminum silicate insulation layer
• External metal protective cover

Purpose:

• Maintain casing wall temperature above dew point
• Prevent external condensation

Flange Protection

Install:

• PTFE gaskets

Purpose:

• Prevent cold air infiltration through gaps
• Avoid local cooling and condensation corrosion

6. Operation and Maintenance Management

Extend Service Life by More Than 50%

• During startup and shutdown, always activate hot air supply.
• Never allow cold and humid flue gas to enter a cold fan.
• After shutdown, keep the fan running for 30 minutes to remove internal moisture.
• Clean impeller deposits with compressed air every 7–15 days.
• Inspect deposits and coating condition monthly.
• Regularly monitor:
  • Flue gas temperature
  • Dust concentration
  • HCl concentration

Immediately adjust operation if:

• Dust removal system fails
• Temperature drops below acid dew point

Establish coating repair records:

• Repair blistered glass flake coatings
• Repair damaged coating areas immediately
• Prevent corrosion penetration into the base metal

7. Recommended Complete Configuration for Waste Incineration ID Fans

Aerodynamic Design

• Backward-curved straight blade impeller
• Large flow passages
• Replaceable wear liner at volute tongue
• External bearing housing
• Nitrogen or air purge sealing system

Materials

• C276 alloy impeller
• Carbon steel casing
• Glass flake internal anti-corrosion lining

Surface Treatment

• Laser cladding tungsten carbide wear-resistant and corrosion-resistant coating on blades

System Protection

• Upstream dust removal
• Flue gas temperature control
• Complete equipment insulation
• Condensate drainage system
• Online air cleaning system

Operation Control

• Strictly avoid acid dew point operation
• Regular dust removal
• Regular coating inspection and maintenance

Conclusion:
For centrifugal fans used in waste incineration plants, simply upgrading the material is not enough. The most reliable solution is a combination of proper system design + wear-resistant structure + corrosion-resistant materials + surface strengthening + strict operation control, which can significantly improve fan reliability and extend service life under extreme high-dust and high-corrosion conditions.