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 heat exchange tubes.
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) Anti-corrosion properties
2) Wear Resistance
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, shipbuilding, waste heat power generation,
Applies across various fields such as home improvement. In the boiler industry, as a heating surface, the advantages of the integral finned tube are fully utilized.
In the heating surface of boilers, superheaters, economizers, and air preheaters 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 tube)
For φ32X4, with a fin height of 12 and fin spacing of 12, 1 meter is equivalent to: 4 meters of glass 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 overall finned tube is wear-resistant. Due to the fins of the overall finned tube being formed as one with the base tube, the crystal structure is consistent.
The performance is stable, and the fins are in a sand dune shape, which matches the temperature gradient shape when heated. The surface temperature of the fins remains consistent during heating, ensuring even thermal stress without concentration, thus eliminating weak points in strength. Moreover, the fins have a guiding effect on the flue gas, making the various parameters (temperature, velocity, ash content, etc.) of the flue gas more uniform. This prevents any biased flow of the flue gas, avoiding localized or specific area abrasion. Therefore, they are more wear-resistant. Typically, the light pipes experience severe wear at locations such as the radial 30° angles, elbow ends, and side walls adjacent to walls.
3. The overall finned tube stiffness is significantly enhanced. The stiffness depends on the moment of inertia, and the moment of inertia of the overall finned tube is 4.76 times that of the corresponding plain 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 of the 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 bend between supports. This occurrence features a clean break, and no material issues have been identified.
4. Integral finned tubes do not accumulate dust. The reason for dust accumulation is caused by Karman vortices: as the flue gas flows through the tubes, a negative pressure zone forms on the back of the tubes. In this area, the flow velocity of the flue gas is zero or even reversed, causing the flue gas to accumulate here, with dust adhering to the surface of the tubes. The thermal resistance of the dust is relatively high; the thicker the dust accumulates, the greater the thermal resistance becomes, resulting in less heat transfer and an increase in exhaust gas temperature, thereby reducing the boiler's efficiency. However, the finned tubes guide the flow of flue gas, overcoming the Karman vortices and also sorting out the distribution of dust, making it uniformly distributed in the flue gas. Since its operation, Hualü Hengsheng Group has not accumulated any dust.
(No ash 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 shows minimal fluctuations, with no instances of economizer tube bursting.
6. Long service life. Under the same operating conditions (coal quality, temperature, heat 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 longer. Regarding the structural arrangement of the 240t/h boiler, the following is the discussion on the economizer retrofitting plan:
(1) Misaligned structure: S1XS2 = 100x75?
(2) To prevent low-temperature corrosion, a thickening treatment is applied below the lower economizer with two rows, featuring a fin height of 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 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.)