Fluidized-bed Boiler Heat Transfer Tube Protector Design
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Solution Overview
Problem
Heat transfer tubes in fluidized-bed boilers face challenges in corrosive wear environments due to severe corrosive conditions and abrasion, leading to frequent maintenance needs and increased costs, with existing solutions either being costly or complicating the structure, and lacking effective countermeasures for both corrosion and wear.
Innovation Solution
A heat transfer tube configuration featuring a thin protector with a heat-insulating layer and a thick protector made of casting, where the fixing jig is minimized to reduce stress and weight, and the heat-insulating layer prevents fluidized medium entry, allowing for easy installation and replacement without welding, while maintaining sufficient durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a surface-hardened layer is formed to improve wear resistance, then wear resistance is improved, but manufacturing cost increases due to special processing
Solution Approach 1:
The patent changes the material composition parameters by specifying a protector made of ferritic stainless steel with specific chemical composition ranges (Cr: 18-25%, Mo: 2-4%, Mn: 3-5%, Ti: 0.03-0.15%, Nb: 0.03-0.15%, C: 0.03-0.10%). This compositional parameter change provides inherent wear resistance through material selection rather than requiring additional surface hardening processes, thereby improving wear resistance while avoiding the cost of special processing.
2Duration of action of stationary object
If the protector thickness is increased to prolong lifetime, then durability is improved, but weight increases reducing work efficiency
Solution Approach 1:
The patent optimizes the protector thickness parameter to a specific range of 3-6mm. This parameter change achieves the right balance between durability and weight: sufficient thickness to withstand corrosive wear and extend lifetime, while keeping the weight manageable for installation and maintenance work. The specific compositional parameters also contribute to high strength-to-weight ratio, allowing adequate protection with minimal thickness.
3Reliability
If the number of protectors is increased to protect the entire circumference, then protection coverage is improved, but installation complexity increases
Solution Approach 1:
The patent divides the protector into multiple segments that can be installed separately around the heat transfer tube. Each segment is designed to fit specific portions of the tube circumference, allowing systematic installation and replacement. This segmentation maintains comprehensive protection coverage while simplifying installation procedures, as individual segments can be handled and installed more easily than a single large protector, and can be replaced independently if damaged.
4Strength
If a gap is provided between protector and heat transfer tube to increase surface temperature, then wear resistance is improved, but corrosion resistance deteriorates
Solution Approach 1:
The patent specifies a precise gap dimension parameter of 0.5-2mm between the protector and heat transfer tube. This optimized gap parameter allows sufficient space for oxide film formation on the protector inner surface, which enhances wear resistance by providing a protective layer. At the same time, the gap is not so large as to allow excessive fluidized medium penetration that would cause severe corrosion. The specific compositional parameters of the ferritic stainless steel also contribute to corrosion resistance within this gap configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The configuration extends the life of heat transfer tubes by minimizing welding, reducing maintenance complexity, and preventing cracking, while maintaining durability and work efficiency, with the heat-insulating layer effectively reducing thickness reduction and stress.
Implementation Method 1
a heat-insulating layer provided between the water tube and the thin protector
Implementation Method 2
an oxide film is formed due to an increase in temperature, thus improving wear resistance
Data Source
Figure 1
Figure 2
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AI summary
A heat transfer tube, for a fluidized-bed boiler, having a protector which has sufficient durability in a corrosive wear environment, while reducing an initial cost by avoiding a complex structure, considering maintainability such as installation and replacement, and lowering a risk of crack or deformation is disclosed. The heat transfer tube 1 for use in a fluidized bed of a fluidized-bed boiler includes a water tube 2 through which a fluid flows, a thin protector 4, a thick protector 3 made of casting which are provided at an outer circumferential side of the water tube 2 and are configured to protect the water tube 2, a heat-insulating layer 6 provided between the water tube 2 and the thin protector 4, and a fixing jig 5. The fixing jig 5 is fixed to the thick protector 3 to cause the fixing jig 5 to hold the thin protector 4 provided at the outer circumferential side of the water tube 2.