In catalytic cracking units, it bears the critical task of burning off coke from coked catalysts. As the "protective armor" of the regenerator, the structural design of the lining directly impacts equipment lifespan and operational efficiency. What are the advantages and disadvantages of traditional turtle mesh lining versus the new turtle mesh-free lining? Why do modern units prefer the latter? Let’s delve into this key technology.
The Dual Mission of Lining: Insulation and Wear Resistance
The regenerator operates at high temperatures of 650-730°C, with internal catalysts moving at high speeds in a fluidized state, causing severe wear on the vessel walls. The lining must meet both insulation and wear resistance requirements: on one hand, it must reduce heat loss to keep the carbon steel shell at a safe operating temperature; on the other hand, it must withstand the continuous erosion by catalyst particles. The early widely used turtle mesh double-layer lining, which supports the wear-resistant layer with a metal grid, offers good integrity but suffers from inherent drawbacks such as complex structure, long construction cycles, and susceptibility to deformation at high temperatures.
Technological Breakthrough of Turtle Mesh-Free Lining
The turtle mesh-free single-layer lining, introduced in the 1980s, uses Ω-shaped anchor bolts to secure insulation and wear-resistant materials mixed with stainless steel fibers. This innovative design absorbs thermal expansion stress through meltable plastic caps at the top of the anchor bolts. The lining offers good integrity and moderate thermal conductivity, preventing equipment overheating while avoiding acid gas dew point corrosion. In high-temperature areas such as regenerators and coke burners, turtle mesh-free lining demonstrates significant advantages: construction efficiency increases by 40%, maintenance costs decrease by 30%, making it particularly suitable for harsh operating conditions with coke burning intensities of 100-250 kg/(t·h).
Application Differences Due to Structural Variations
In practical applications, different areas have varying requirements for linings. The settler, due to its lower operating temperature (<540°C) and the risk of oil and gas penetration, still retains the turtle mesh double-layer structure, using the grid to isolate and prevent coke expansion caused by lining cracks. Oil and gas pipelines and risers, which are prone to coking, also use turtle mesh lining. Notably, after the 2004 overhaul, some units replaced the circulating inclined pipe with a single-layer turtle mesh-free lining, reflecting continuous advancements in material technology.
Technical Specifications for Lining Maintenance
Lining inspections must strictly adhere to standards: turtle mesh bulging deformation within 250mm requires no treatment; cracks wider than 3mm or deeper than one-third of the thickness must be repaired. For turtle mesh-free lining repairs, each repair area must have at least three anchor bolts, and the repair cross-section should be shaped like an inverted "八" to ensure bonding strength. During construction acceptance, a 0.5kg hand hammer should be used to tap at 350mm intervals for inspection, requiring clear, solid sounds without hollow spots, with thickness deviations controlled within ±5mm. After furnace drying, surface cracks in turtle mesh-free lining must not exceed 3mm in width, and through cracks are strictly prohibited.
The evolution from turtle mesh to turtle mesh-free lining reflects advancements in material science for refining equipment. Modern lining technology not only addresses the inherent flaws of traditional structures but also provides equipment assurance for achieving stringent targets such as regenerated catalyst carbon content below 0.2%, or even 0.05%-0.1%. With the continuous development of new anchor systems and wear-resistant materials, lining technology will continue to progress toward higher efficiency and durability, laying a solid foundation for the long-term operation of catalytic cracking units.
