Finned tubes, which are designed to enhance heat exchange efficiency by adding fins to the surface of the heat exchange tubes to increase their external (or internal) surface area, thereby improving the heat exchange efficiency, are a type of heat exchange tube.
Key performance requirements for finned tubes
Finned tubes, as heat exchange elements, operate under high-temperature flue gas conditions for extended periods, such as in boiler heat exchangers where the finned tube environment is harsh, with high temperatures, pressures, and corrosive atmospheres. This necessitates that finned tubes possess high performance specifications.
1) Corrosion Resistance
2) Wear Resistance
3). Lower contact thermal resistancentact resistance）
4) High Stability
5) Dust-Resistant Ability
Our company has been committed to the development and research of integrated finned tubes, and now they are widely used in boilers, chemical industry, shipbuilding, waste heat power generation, and more.
Applied in various fields such as home decoration. The overall finned tube is extensively utilized in the boiler industry as a heating surface, fully showcasing its advantages.
In the heating surface of boilers, superheaters, economizers, air preheaters, etc., are all utilizing integral finned tubes, which are currently performing very well. This is due to the following six advantages of integral finned tubes:
1. Integral finned tubes can enhance heat exchange efficiency (area and heat transfer coefficient). Under the same base tube conditions: (with the tube)
For φ32X4, with an airfoil height of 12 and airfoil spacing of 12, 1 meter is equivalent to: 4 meters of a light tube or a 2.6-meter membrane structure (spacing 62X3, flat steel 30X3) or a 1.5-meter flat steel coiled and welded fin tube (flat steel 12X3).
2. The integral finned tube is abrasion-resistant. As the fins of the integral finned tube are formed as one with the base tube, the crystal structure is consistent.
Performance is stable, and what's more, the fins are in a sand dune shape, which aligns with the temperature gradient shape when heated. The outer surface temperature of the fins is consistent when heated, resulting in uniform thermal stress with no concentration, thus avoiding weak points in strength. (The main cause of wear is due to high-temperature spots, which should be σ low.) Additionally, the fins have a guiding effect on flue gas, making the various parameters (temperature, flow rate, ash content, etc.) of the flue gas more uniform while guiding it, preventing the occurrence of flue gas bias flow and concentrated erosion on a specific area or part. Therefore, they are more wear-resistant. Typically, the light tubes at 30° radial, elbow ends, and side-by-side with walls are where wear is severe.
3. The overall finned tube stiffness is significantly enhanced. The stiffness depends on the moment of inertia, with the overall finned tube having a moment of inertia 4.76 times that of the corresponding plain tube. (For φ32X4, the moment of inertia is 35168 mm²), while the finned tube's moment of inertia is 167613 mm². The spacing between supports for plain tubes is 2.71m (3.55m for old specifications), and for finned tubes, it's 5.28m (6.91m for old specifications). When calculating the wall temperature reaches around 460°, the spacing between supports will decrease, leading to the phenomenon where several rows of tubes on the upper economizer break between supports. This phenomenon is characterized by clean断面, and no material issues have been identified.
4. Integrated finned tube does not accumulate ash. The reason for ash accumulation is due to Karman vortices: as flue gas flows through the tube, a negative pressure zone forms on the back of the tube, where the gas flow velocity is zero or even reverses, causing the flue gas to accumulate here and ash to adhere to the tube surface. Ash has a high thermal resistance, and as it accumulates, the thermal resistance increases, reducing the heat transfer and raising the exhaust gas temperature, thereby decreasing the boiler's efficiency. However, the finned tube guides the flue gas, overcoming the Karman vortices and also sorting out the ash distribution, ensuring it is evenly dispersed in the flue gas. Since its operation, Hualu Hengsheng Group has not accumulated ash.
(No dust removal facilities installed), the experimental report conducted by Xi'an Jiaotong University also confirms this.
5. Stable thermal conductivity. The monolithic structure serves as the heating surface, and after years (without exaggeration) of operation, the flue gas temperature of the boiler fluctuates minimally, with no instances of economizer tube bursting.
6. Long service life. Under the same operating conditions (coal quality, temperature, heating surface position), finned tubes ensure a lifespan more than double that of plain tubes. Generally, if the lifespan of plain tubes is 3 to 4 years, the lifespan of finned tubes is at least 7 to 8 years longer. Regarding the structural arrangement of the 240t/h boiler that you are interested in, the following is the proposed modification scheme for the economizer:
(1) Misplaced structure: S1XS2 = 100x75?
To prevent low-temperature corrosion, the lower two rows of economizers are treated with thickening, featuring a 34X6 fin height and a fin spacing of 12.
(3) To reduce wear, the two upper rows of each economizer are treated with additional thickness, featuring 34X6 fin height and a fin spacing of 12.
(4) Other finned tubes: 32X4 fins, fin height 10, fin spacing 12.
(5) Elbows are shielded by smoke baffles, preventing them from being washed by smoke.
(6) Maintain a low airflow velocity. (Wear is proportional to the cube of the airflow velocity.)