Finned tubes, designed to enhance heat exchange efficiency, typically increase the surface area (either external or internal) of the heat exchange tubes by adding fins, thereby improving the heat exchange efficiency. Such a type of heat exchange tube.
Main 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 environment is severe—high temperature, high pressure, and corrosive. This necessitates that finned tubes possess high performance specifications.
1) Corrosion Resistance
2) Anti-wear Performance
3). Lower contact thermal resistancentact resistance）
4) High Stability
5) Dust-Resistant Ability
Our company has been dedicated to the development and research of integral finned tubes, which are now widely used in boilers, chemical industry, shipping, waste heat power generation,
Home decoration and various other fields see its application. In the boiler industry, as a heating surface, it is widely used, fully showcasing the advantages of the integral finned tube.
In the heating surface of boilers, superheaters, economizers, and air preheaters are all utilizing integral finned tubes, which are currently performing exceptionally well. This is due to the following six advantages of integral finned tubes:
1. Integrated finned tubes can enhance heat exchange efficiency (area and heat transfer coefficient). Under the same base tube condition: (with the tube)
For φ32X4, with a fin height of 12 and fin spacing of 12, 1 meter is equivalent to: 4 meters of light tube or 2.6 meters of membrane structure (spacing 62X3, flat steel 30X3) or 1.5 meters of flat steel coiled and welded fin tube (flat steel 12X3).
2. The integral finned tube is wear-resistant. Due to the integral fins being formed as one with the base tube, the crystal structure is consistent.
The performance is stable, and the fins have a sand dune shape, which aligns with the temperature gradient shape when heated. The outer surface temperature of the fins remains consistent during heating, ensuring uniform thermal stress without concentration, thus eliminating weak points in strength. (Wear is primarily due to high-temperature spots, hence the low σ value.) Additionally, the fins guide the flue gas, making the gas's various parameters (temperature, flow rate, ash content, etc.) more uniform. This prevents skewed flow of flue gas, avoiding localized or targeted erosion. Therefore, they are more wear-resistant. Typically, the light tubes at locations such as 30° radial left and right, end bend, and side-by-wall pipes experience severe wear.
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 smooth tube. (The moment of inertia for φ32X4 is 35,168 mm²), while the finned tube's moment of inertia is 167,613 mm². The spacing between supports for smooth tubes is 2.71m (3.55m for the old tube specification), and for finned tubes, it is 5.28m (6.91m for the old tube specification). When calculating the wall temperature reaches approximately 460°, the spacing between supports will decrease, which is why some users have experienced several rows of tubes on the upper economizer bending between supports. This phenomenon is characterized by a clean break, and no material issues have been identified.
4. Integral finned tubes do not accumulate soot. The reason for soot accumulation is due to Karman vortices: as flue gas flows through the tubes, a negative pressure zone forms on the back of the tubes, where the gas flow velocity is zero or even reverses, causing the flue gas to accumulate here, and the soot to adhere to the tube surface. Soot has a high thermal resistance, and as it accumulates, the thermal resistance increases, resulting in less heat transfer and an increase in exhaust gas temperature, thereby reducing the efficiency of the boiler. However, the finned tubes guide the flue gas, overcoming the Karman vortices and also sorting out the distribution of soot, making it uniformly distributed in the flue gas. Since its operation, Huaxia Hengsheng Group has not accumulated soot.
(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 of (dust-free) operation, the flue gas temperature of the boiler shows minimal fluctuations, with no incidents of economizer tube burst.
6. Long service life. Under the same operating conditions (coal quality, temperature, heat exchange surface position), finned tubes ensure a lifespan twice 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. Regarding the structural arrangement of the 240t/h boiler, the proposed economizer retrofit scheme is as follows:
(1) Misalignment Structure: S1XS2 = 100x75?
(2) To prevent low-temperature corrosion, the two lower rows of the economizer are treated with increased thickness, with a fin height of 10 (34x6) and a fin spacing of 12.
(3) To reduce wear, the two upper rows of each economizer are treated with added thickness, featuring 34X6 fin height and 12 fin spacing.
(4) Other finned tubes: 32X4 fin height 10, fin spacing 12.
(5) Elbows are shielded by smoke baffles, protecting them from direct smoke wash.
(6) Maintain a low airflow velocity. (Wear is proportional to the cube of the airflow velocity.)