In the field of thermal power generation, square finned tubes usually refer specifically to H‑type finned tubes (also called rectangular finned tubes), which consist of two symmetrical square/rectangular fins welded to the base tube. They are not merely decorative; rather, they are core components that enable high efficiency and energy savings in thermal power plants. Below are their primary applications and value.

Square finned tubes are mainly installed in the tail‑flue pass of utility boilers, which is the final heat‑exchange zone between flue gas and the working fluid (water or steam):

• Economizer: Uses high‑temperature flue gas to preheat boiler feedwater, lowering the exhaust gas temperature and improving boiler thermal efficiency (a drop of 15–20 °C in exhaust temperature can increase boiler efficiency by about 1 percentage point).

• Air Preheater: Recovers waste heat from flue gas to preheat combustion air, enhancing furnace combustion and reducing incomplete‑combustion losses.

• Heat Recovery Steam Generator (HRSG): In combined‑cycle gas turbine (CCGT) plants, it recovers heat from the gas turbine’s hot exhaust to generate steam for driving a steam turbine.

Compared with traditional spiral or circular finned tubes, the square design performs significantly better under the harsh conditions typical of power plants:

1. Excellent Erosion/Wear Resistance (Critical for Preventing Tube Bursts)
   In coal‑fired plants, flue gas carries large amounts of fly ash that severely erodes tube surfaces. The H‑type fins create straight gas‑flow channels, guiding ash particles to pass through the gaps between fins rather than causing the “swirl‑cutting” wear seen with spiral fins. Their service life against erosion is typically 2–3 times longer than that of spiral‑finned tubes, greatly reducing unplanned outages due to tube bursts.

2. Superior Self‑Cleaning and Anti‑Fouling Performance
   The square fin roots are perpendicular to the base tube, so there are few “dead zones” where ash can accumulate. In addition, the larger and more uniform gas‑flow cross‑section allows the flue gas’s own kinetic energy to carry away loose ash, preventing the sharp efficiency drop caused by fouling (particularly beneficial for low‑grade, high‑ash coals).

3. High Heat‑Transfer Efficiency and Low Flue‑Gas Pressure Drop
   The fins substantially extend the heat‑transfer surface (typically 5–8 times that of a bare tube), and the square configuration creates intense boundary‑layer disturbance when gas flows across the tube bundle, enhancing convective heat transfer. At the same time, the gas‑side pressure drop is about 10–20% lower than that of spiral‑finned tubes, reducing induced‑draft fan power consumption.

4. High Structural Rigidity and Vibration Resistance
   The paired square fins act like “stiffening ribs” connecting the base tubes, giving the entire tube bank greater rigidity. This effectively resists low‑frequency flow‑induced vibration, extending the equipment maintenance interval.

• Coal‑fired / Biomass Power (Main Application)
  Particularly suitable for plants burning low‑grade or high‑ash coals, they are the preferred solution for addressing wear and fouling in the tail‑flue heat‑exchange surfaces.

• Waste‑to‑Energy Incineration
  Flue gas contains not only ash but also highly corrosive acid gases. Square finned tubes can be easily fitted with wear‑resistant shields, and their surfaces are less prone to sticky ash buildup, ensuring long‑term stable operation.

• Concentrated Solar Power (CSP) – Molten‑Salt Heat Exchange
  In tower‑type or trough‑type CSP plants, they are used in the steam‑generation system to intensify heat transfer between molten salt and water/steam. The increased heat‑transfer area helps reduce equipment footprint and accommodates the thermal‑shock stresses from frequent startup/shutdown cycles typical of CSP.

In thermal‑power applications, material selection must account for low‑temperature dew‑point corrosion (sulfuric‑acid dew‑point corrosion):

• For low‑temperature sections (where exhaust temperature is below the acid dew point), ND steel (09CrCuSb), 316L stainless steel, or even enamel‑coated surfaces are commonly used.

• For high‑temperature sections, heat‑resistant steels such as 20G or 15CrMoG are selected to ensure creep strength at elevated temperatures.

• During design, the fin pitch (typically 10–25 mm) and fin height must be accurately calculated to balance heat‑transfer performance and ease of cleaning.

The core value of square finned tubes in thermal power generation lies in their ability to safely, efficiently, and durably extract waste heat from flue gas in the severely challenging environment of “high dust, high erosion, and high corrosion.” They are a key technical detail that enables modern large‑scale coal‑fired units to reduce coal consumption and achieve energy‑saving and emission‑reduction targets.