The core function of a boiler flue.

Category: Industry News

Time: 2025-03-05

The boiler flue is a gas‑flow passage that connects the boiler body to the chimney, serving to convey combustion exhaust gases and discharge them outside the furnace. Its design must balance multiple requirements, including fluid dynamics, structural strength, corrosion resistance and thermal insulation, as well as safety and environmental protection.

The boiler flue is a gas‑flow passage that connects the boiler body to the chimney, serving to convey combustion exhaust gases and discharge them to the atmosphere. Its design must balance multiple requirements, including fluid dynamics, structural integrity, corrosion protection and thermal insulation, as well as safety and environmental considerations. The following discussion will address these aspects from the perspectives of function, key design considerations, and common issues.

Core Features

Flue gas conveyance: Ensure low flue gas flow resistance (frictional loss ≤ 10 Pa/m) to prevent ash deposition and blockages.

Heat Recovery: By employing an insulated design (with heat loss ≤ 5%), flue gas heat losses are minimized, thereby enhancing boiler thermal efficiency.

Safety Protection: Prevents flue gas leakage (leakage rate ≤ 0.5%) and withstands internal pressure (positive-pressure flues must be capable of withstanding 10 kPa).

Typical Problems and Solutions

1. Ash accumulation and blockage

Causes: excessively low flow velocity (<10 m/s), inadequate flow guidance at bends, and insufficient flue gas duct slope (the slope should be ≥3%).

Solution: Install sootblowers (steam‑ or sonic‑type, spaced 10–15 m apart), and provide an ash hopper at the bottom with a discharge chute having a slope of ≥60°, equipped with an electric airlock.

2. Corrosion Leakage

Case: After wet flue gas desulfurization, the flue duct (pH = 4–5) developed perforations due to corrosion caused by condensate.

Solution: Line the interior with polytetrafluoroethylene sheets (3–5 mm thick, with an adhesion strength of ≥5 MPa), or use a brick‑and‑tile lining (acid‑resistant ceramic tiles bonded with resin mortar, joint width ≤2 mm).

3. Vibration and Noise

Causes: airflow pulsation (vortex-induced vibration is likely to occur when the flow velocity exceeds 25 m/s) and fan resonance.

Measures: Install a silencer (insertion loss ≥ 25 dB) and add dampers to the flue duct supports (to shift the natural frequency away from the 30–100 Hz resonance zone).

Trends in Environmental Protection and Energy-Efficient Design

Low‑Resistance Design: Utilizing CFD simulations to optimize the flow field, the flue gas system achieves a pressure drop of ≤1500 Pa (compared to approximately 2000–2500 Pa in conventional designs), thereby reducing the power consumption of the induced draft fan.

Condensate Recovery: A condensate collection system is installed in the low‑temperature flue gas duct (with a recovery rate of ≥80%) to supply boiler make‑up water or desulfurization process water, achieving a water‑saving rate of 10–15%.

Green materials: Promote inorganic anti-corrosion coatings (such as waterborne zinc silicate coatings, with VOC content ≤ 50 g/L) to replace solvent-based coatings, thereby meeting environmental emission standards.

Keywords: The core function of a boiler flue.

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