Boiler World Update

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Multi-rifled seamless cold drawn boiler tubes: A revolution in power generation

Marking a significant technological advancement towards achieving enhanced efficiency and reliability in power generation, multi-rifled seamless cold-drawn boiler tubes represent innovation in boiler & seamless tube technology. These advanced tubes are essential in modern heat exchangers and boilers, especially in large coal-fired power plants, where they help achieve energy-efficient heat transfer and excellent operation.

Understanding Multi-Rifled Seamless Cold Drawn Boiler Tubes

    (A) Definition and Construction

Multi-rifled seamless cold-drawn boiler tubes are engineered with precision to enhance heat transfer efficiency within boilers. Unlike traditional tubes, which may have a smooth inner surface, these tubes feature intricate rifling patterns on the inside. These rifled surfaces create turbulence in the flow of gases or liquids, thereby increasing heat transfer rates and overall boiler efficiency.

    (B) Material and Manufacturing Process

These tubes are typically crafted from high-quality carbon steel or alloy steel, chosen for their robustness and thermal conductivity properties. The manufacturing process involves cold drawing seamless tubes from solid billets, ensuring uniformity in wall thickness and precise dimensional control. Rifling is then imparted through specialized machinery that creates helical grooves along the inner surface of the tube.

What is the USP of Rifled Tubes?

Rifled tubes are distinguished by their internal spiral grooves or rifling, which induce centrifugal forces within the mass flow. This leads to the separation of water from the steam fraction, forcing water towards the tube wall and thereby optimizing the heat transfer process. Unlike traditional tubes, the presence of these internal ribs does not compromise the mechanical properties of the tube, ensuring durability and strength while enhancing performance.

Key Advantages of Multi-Rifled Seamless Cold Drawn Boiler Tubes

    (1) High Heat-Transfer Efficiency

The primary advantage of rifled tubes lies in their superior heat-transfer efficiency. By promoting the spiral rotation of the fluid within the tube, rifled tubes prevent the formation of insulating steam films on the tube walls. This is particularly crucial in the high-pressure boilers of large power plants, where steam films can significantly raise the tube temperature and reduce efficiency. The rifling raises the dryness limit of steam at which Departure from Nucleate Boiling (DNB) occurs, effectively doubling this limit and thereby improving the boiler’s overall efficiency.

    (2) Reduced Fouling

The rifled surfaces not only enhance heat transfer but also mitigate the accumulation of deposits such as scale, ash particles, and other contaminants. By inducing turbulent flow, these tubes minimize fouling on the inner surfaces, thereby reducing maintenance downtime and prolonging the operational lifespan of boilers. This advantage is particularly crucial in environments prone to high levels of impurities and varying operating conditions.

Manufacturing Precision through Cold Drawing

Achieving high dimensional accuracy in rifled tubes has been made possible through the cold drawing process. This manufacturing technique involves forming grooves using a combination of a plug and a die, with the plug rotating during the process to create the spiral grooves on the tube’s interior surface.

The rib height (H), a critical dimension of the rifled tube, is influenced by the reduction of drawing and the base tube dimensions. Precision in this process ensures consistent performance and reliability of the tubes in demanding environments.

Technical Specifications and Dimensions

(1) Tube Dimensions:

  • – Outer Diameter (OD): Typically ranges from 25 mm to 80 mm, depending on the application and boiler capacity.
  • – Wall Thickness: Varies from 3 mm to 12 mm, ensuring robustness and durability under high-pressure conditions.

(2) Rifling Specifications:

  • – Rifling Depth: Usually ranges from 0.1 mm to 0.5 mm, creating precise helical grooves that optimize turbulence for maximum heat transfer efficiency.
  • – Rifling Pitch: The distance between successive rifling grooves varies based on design specifications and operational requirements.

What are the applications and advantages?

Rifled tubes are primarily used in the furnace walls of high-pressure boilers, where they play a crucial role in enhancing heat transfer and preventing the formation of steam films. The advantages of using rifled tubes include:

– Improved Heat Transfer Rate: Even at higher steam quality levels, rifled tubes maintain an excellent heat transfer rate, ensuring efficient operation of the boiler.

Integration of rifled tubes in the furnace walls to enhance heat transfer efficiency can achieve 15% increase in thermal efficiency, resulting in significant fuel savings and improved plant performance.

– Efficient at Low Mass Flux Levels: They provide excellent heat transfer even when the mass flux levels are low, making them versatile and reliable under varying operational conditions.
Installation of rifled tubes in the HRSG may ensure efficient heat transfer at low mass flux levels maintaining a consistent steam production with reduced maintenance costs and enhanced operational flexibility.

– Reduction in Tube Wall Temperature: By optimizing the rifling geometry, the mean metal temperature of the tube wall is reduced, enhancing the safety and lifespan of the tubes.
Implementing rifled tubes with optimized rifling geometry in the boiler’s furnace walls not only enhances operational safety by minimizing thermal stresses but also extended the lifespan of the tubes. The reduction in tube wall temperatures also ensures compliance with safety standards.

– Operational Efficiency: The ability to increase the heat transfer rate through optimized rifling geometry contributes to the overall efficiency and performance of the power plant.

Installing rifled tubes with advanced rifling geometry into the cogeneration facility’s boiler system significantly increases the heat transfer rate within the boiler, enhancing thermal efficiency. This improvement can allow the facility to generate more electricity from the same amount of fuel, achieving a 12% increase in overall efficiency. As a result, operational costs can be reduced by 8%.

Meeting the Demands of Power Generation

The unique design and precise manufacturing process of Multi-Rifled Boiler Tubes make them a key component of modern power generation, offering unparalleled efficiency and reliability. Even with the energy industry continuing to evolve, these tubes are sure to play a critical role in meeting the world’s growing energy demands.

Author:

Mr. Sheoshankar Ramsamunjh Mishra

Vice President – Quality Control

Lalbaba Seamless Tubes Private Limited