Q235 Large Capacity Corrosion Resistant Steam Boiler Induced Draft Fan

This article's table of contents introduction:

1. Core Components of Your Specification
2. Typical Fan Design (for this application)
3. How to Select the Correct Fan (Parameters Needed)
4. Common Manufacturer Standards & Potential Pitfalls
5. Recommendation for a Supplier Inquiry

It seems you are looking for an Induced Draft (ID) Fan specifically designed for a Q235 steel, large-capacity, corrosion-resistant steam boiler.

This is a highly specific industrial requirement, usually found in facilities burning high-sulfur fuels (like heavy oil or certain coals) or operating in recovery processes (like in pulp & paper).

Here is a detailed breakdown of what this specification means and how to select or specify this fan.

Core Components of Your Specification

• Q235 Steel: This is a Chinese standard (GB/T 700) low-carbon structural steel (equivalent to ASTM A36 or S235JR). It means the fan housing is made of this material.

  • Pros: Good weldability, low cost, moderate strength.
  • Cons: Not corrosion resistant by itself. Q235 will rust rapidly in a wet, acidic flue gas environment.
  • Implication: The fan is built from Q235 for structural rigidity, but must have an internal corrosion protection lining (e.g., rubber, epoxy, or stainless steel cladding).

• Large Capacity: This implies a very high volumetric flow rate (e.g., >100,000 m³/h or >60,000 CFM). The fan will be a large, double-inlet (D.I.) or radial design, often requiring heavy-duty bearings and a robust base frame.

• Corrosion Resistant: This is the critical challenge. Standard Q235 is not corrosion resistant. To achieve this, the fan must be modified. Common methods include:

  • Flue Gas Dew Point: The fan must handle gases containing SOx/NOx which form sulfuric/nitric acid upon condensation. The fan must keep gas temperatures above the acid dew point or use acid-proof materials.
  • Solutions: Rubber lining (hard or soft), glass flake lining (vinyl ester), or using a higher alloy for the impeller (e.g., 316L, 2205 Duplex, or Hastelloy for extreme cases) while the housing remains Q235.

• Steam Boiler Induced Draft Fan:

  • Function: Sucks flue gas out of the boiler, creating negative pressure (draft) inside the furnace.
  • Environment: Handles hot, dusty, corrosive, and humid gas.
  • Key Metrics: Static pressure (usually 2000-6000 Pa), high temperature capability (typically 120°C to 200°C), and dust erosion resistance.

Typical Fan Design (for this application)

The most common design for this heavy-duty application is a Centrifugal Fan with Backward-Curved or Radial Blades.

How to Select the Correct Fan (Parameters Needed)

You (or a manufacturer) must provide these parameters to get the right fan:

1. Gas Flow Rate (m³/h or CFM): At actual operating temperature (e.g., 150°C).
2. Total Static Pressure (Pa or mmWG): Resistance of the boiler, economizer, scrubber, and ductwork.
3. Gas Temperature (°C): Normal operating AND maximum peak temperature (e.g., 180°C normal, 250°C transient during soot blowing).
4. Gas Composition: % of O₂, CO₂, SO₂, H₂O. Crucial for corrosion.
   • High sulfur (S>1%) → High risk of Acid Dew Point. Need Acid Dew Point calculation.
   • Presence of Chlorides (Cl) → Very aggressive corrosion (pitting). Requires High Molybdenum SS (e.g., 6Mo) or FRP.
5. Dust Content (mg/Nm³): Determines if a Radial blade (for high dust) or Backward blade (for clean gas) is needed.
6. Altitude: Affects air density and motor power.

Common Manufacturer Standards & Potential Pitfalls

• Chinese Standard: Look for GB/T 3235 (Fan basic parameters) and JB/T 8699 (High-temperature fans).
• Critical Issue: Corrosion at Welds: The weld area between Q235 and any lining is the weakest point. If the lining fails, acid attacks the Q235, leading to rapid failure (often within weeks).
• Vibration: A large impeller must be dynamically balanced (G2.5 or better). Unbalance due to uneven corrosion/dust buildup is the #1 cause of shutdown.
• Motor: The motor must be rated for the ambient temperature and altitude. For large capacity fans, a YJKK (large HV motor) or YE3 (IE3 high efficiency) is common. High starting torque may be required.

Recommendation for a Supplier Inquiry

If you are sourcing this, your Request for Quotation (RFQ) text should look like this:

RFQ: Large Capacity Steam Boiler ID Fan

Application: Q235 Steel Boiler Induced Draft Flow Rate: [e.g., 200,000 m³/h at 140°C] Static Pressure: [e.g., 3500 Pa] Gas Temp: 140°C (Peak 180°C) Gas Type: Flue gas from coal/heavy oil (Sulfur content: 1.5%) Casing Material: Q235B, rubber lined (thickness: 4mm) or glass flake lining (Vinyl Ester) for acid protection. Impeller Material: SS316L (to resist dew point corrosion). Shaft Material: 40Cr. Bearings: SKF/FAG heavy-duty split type. Drive: V-Belt with motor on slide rails. Inlet Damper: Radial louver type. Balancing: ISO 1940 G2.5.

Final Warning: Do not use a standard Q235 fan without a proper corrosion-resistant lining for a steam boiler, especially if the fuel has any sulfur content. The boiler's flue gas will reach its acid dew point during startup or low-load operation, and within 6-12 months, the impeller will disappear and the casing will have holes. You need a lined fan or an FRP (Fiberglass Reinforced Plastic) fan for the most corrosive cases.