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Dual-Layer Structure Principle
The twin wall flue system adopts a coaxial double-layer design, consisting of an inner and outer pipe with an annular air cavity in between. The inner pipe serves as the main flue gas passage, efficiently discharging high-temperature exhaust gases. The outer pipe, made of high-temperature-resistant stainless steel or galvanized steel, provides mechanical protection and thermal insulation. The air layer in the cavity acts as a thermal barrier, utilizing air's low thermal conductivity (0.023 W/(m·K)) to significantly reduce heat transfer from the inner pipe. This works similarly to the insulation layer in a vacuum flask.
Ventilation and Heat Dissipation
The air cavity includes a ventilation system, available in natural and mechanical modes.
Natural ventilation relies on the thermal buoyancy of the hot flue gases (chimney effect). Cool air enters from the base, heats up, and exits at the top. This method is suitable for small-scale residential systems or low-energy applications.
Mechanical ventilation uses variable-speed fans to force air circulation, with temperature sensors automatically regulating airflow. This approach is common in industrial applications where flue gas temperatures exceed 400°C.
The moving air quickly dissipates heat from the inner pipe, keeping the outer wall temperature below 50°C. This prevents burn hazards and allows for heat recovery through integrated exchangers, improving energy efficiency by 15% to 20%.
Safety Protection Mechanism
The twin wall flue system offers dual-layer protection to ensure safety.
The primary protection resists external forces such as wind, rain, snow, and physical impacts. The inner pipe, typically made of 316L stainless steel, resists corrosion caused by acidic flue gases.
The secondary protection ensures that, in case of an inner pipe failure, the sealed outer pipe can temporarily contain leaking gases. A condensate collection tray at the cavity base prevents harmful gas leakage. In gas boiler rooms, nitrogen can be introduced into the cavity to maintain a positive pressure environment, eliminating the risk of flammable gas accumulation and explosion.
High Efficiency and Energy Saving: Dual Heat Management
The insulating air cavity reduces the flue gas outlet temperature by 80 to 120°C compared to single-wall systems. For instance, an industrial boiler's flue gas temperature can drop from 280°C to 160°C. When used with an economizer, over 30% of the sensible heat in the exhaust can be recovered to preheat combustion air or process water. Field data from a food processing facility shows a 12% annual reduction in fuel consumption and approximately 200 tons of CO₂ emissions saved.
Safety and Reliability: Full-Cycle Protection
The outer pipe material complies with Class A standards for flame resistance according to GB 8624-2012. The inner pipe is pressure-tested at 1.5 times its working pressure. In high-rise kitchen environments, the system can withstand typhoon wind loads up to 1.2 kPa (Grade 9). A 50 mm layer of fire-resistant rock wool inside the cavity helps slow fire spread, meeting GB 51251-2017 fire safety standards for smoke and exhaust systems.
Noise Reduction: Noise Reduction Design
The annular air cavity, combined with damping materials, provides effective noise control. When filled with 50 mm thick glass wool (NRC = 0.85), it can reduce flue gas noise by 15 to 20 dB(A), lowering sound levels from 90 dB(A) to below 70 dB(A). Tests in a commercial kitchen showed outdoor noise levels near residential buildings at just 55 dB(A), well within national environmental standards.
Easy Installation: Modular Quick-Connect System
The system is modular with flanged connectors. Each standard pipe segment weighs no more than 30 kg and can be installed by two workers using quick clamps. No welding is required on-site. Custom components such as elbows and reducers can accommodate complex building layouts. For example, a vertical flue running through three floors can be fully assembled in just four hours—reducing installation time by 60% compared to traditional welded systems.
Long Service Life: Materials and Maintenance Combined
The inner pipe is made from Inconel 600, capable of withstanding temperatures up to 1200°C. The outer pipe uses aluminized zinc-coated steel with over 1000 hours of salt spray resistance. Annual maintenance, such as cavity cleaning via access ports, supports a design lifespan of 20 years—2.5 times longer than conventional carbon steel single-wall flue systems.
