The core function of boiler flues

Boiler flues are gas passages connecting the boiler body to the chimney, used to transport combustion flue gas and exhaust it outside the furnace. Their design must consider fluid mechanics, structural strength, corrosion prevention, insulation, and safety and environmental protection. The following explains this from the perspectives of function, design points, and typical problems:

Core Functions

Flue gas transport: Ensure low flue gas flow resistance (pressure drop ≤10Pa/m), preventing ash accumulation and blockage;

Heat recovery: Reduce flue gas heat loss through insulation design (heat loss ≤5%), improving boiler thermal efficiency;

Safety protection: Prevent flue gas leakage (leakage rate ≤0.5%), withstand internal pressure (positive pressure flues must withstand 10kPa pressure).

Typical Problems and Solutions

1. Ash Accumulation and Blockage

Cause: Low flow rate (<10m/s), poor flow in bends, insufficient flue slope (slope should be ≥3%);

Solution: Install soot blowers (steam or sonic soot blowing, spacing 10~15m), install ash hoppers at the bottom (inclination ≥60°, with electric airlock).

2. Corrosion and Leakage

Example: Perforation in flues after wet desulfurization (pH=4~5) due to condensation corrosion;

Solution: Line with polytetrafluoroethylene (PTFE) plates (thickness 3~5mm, bonding strength ≥5MPa), or use brick lining (acid-resistant ceramic tiles + resin mortar, seam width ≤2mm).

3. Vibration and Noise

Cause: Airflow pulsation (flow rate ≥25m/s easily produces eddy current vibration), fan resonance;

Measures: Install silencers (insertion loss ≥25dB), add dampers to flue supports (natural frequency avoids 30~100Hz resonance zone).

Environmental Protection and Energy-Saving Design Trends

Low-resistance design: Use CFD simulation to optimize the flow field, making the flue system resistance ≤1500Pa (traditional design is about 2000~2500Pa), reducing induced draft fan power consumption;

Condensate recovery: Low-temperature flues have condensate collection systems (recovery rate ≥80%), used for boiler makeup water or desulfurization process water, saving 10~15% water;

Green materials: Promote inorganic anticorrosion coatings (such as water-based zinc silicate coatings, VOC content ≤50g/L), replacing solvent-based coatings, meeting environmental emission requirements.