Stainless Steel Spiral Coil Tube for High-Efficiency Low-NOx Coal Powder Burners
Product Overview
The stainless steel spiral coil tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered component designed for application in Spiral Coil Type High-Efficiency Low-NOx Coal Powder Burners. These coil tubes serve as critical heat transfer elements within burner systems, where they facilitate the controlled combustion of pulverized coal while simultaneously minimizing the formation of nitrogen oxides (NOx). The spiral coil geometry provides an exceptionally high surface-area-to-volume ratio, enabling efficient radiant heat absorption and rapid heat exchange within the combustion chamber.
Derived from extensive research and practical application in coal-fired boiler systems, these coil tubes represent a significant advancement in combustion technology. The spiral arrangement of the tubes within the burner throat creates a swirling flow pattern that promotes more complete fuel combustion, reduces flame temperature peaks, and inherently suppresses thermal NOx generation—addressing both efficiency and environmental compliance objectives.
Material & Properties
The coil tubes are fabricated from austenitic stainless steel grades selected for their superior resistance to oxidation, thermal fatigue, and corrosion under the demanding conditions of coal-fired combustion environments.
- Primary Alloy Grades: Type 310S (UNS S31008), Type 309 (UNS S30908), and Type 347H (UNS S34708) are the most commonly specified grades, chosen based on the maximum operating temperature and gas composition within the burner.
- Chromium (Cr) Content: Typically 19–26%, providing a robust passive oxide layer that resists high-temperature oxidation and sulfidation.
- Nickel (Ni) Content: 24–32%, ensuring excellent thermal stability and resistance to thermal cycling fatigue.
- Stabilizing Elements: Titanium (Ti) or Niobium (Nb) additions in grades such as 347H prevent intergranular sensitization during prolonged exposure to temperatures between 425°C and 870°C.
- Maximum Operating Temperature: Up to 1150°C (Type 310S) and 1200°C (Type 309), accommodating the peak flame temperatures encountered in coal powder burner systems.
- Thermal Conductivity: 22–26 W/(m·K) at operating temperatures, ensuring efficient heat transfer from the combustion gases to the working fluid.
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C (20–1000°C), requiring careful consideration in coil design to accommodate differential thermal expansion.
- Tensile Strength: Minimum 520 MPa at room temperature; retains significant strength at elevated temperatures (≥ 200 MPa at 900°C).
- Surface Finish: Hot-rolled or cold-worked finish with controlled surface roughness (Ra ≤ 12.5 μm for hot-rolled; Ra ≤ 3.2 μm for cold-worked), minimizing fouling and ash deposition.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Spiral Coil Tube (盘管 / Coil Tube) |
| Item No. | 685 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Material Grade | 310S / 309 / 347H (Austenitic Stainless Steel) |
| Outer Diameter (OD) | φ19 mm – φ76 mm (customizable) |
| Wall Thickness | 1.5 mm – 6.0 mm |
| Coil Pitch | 25 mm – 150 mm (adjustable per burner design) |
| Coil Diameter | 200 mm – 1200 mm |
| Coil Length | Up to 20 m per continuous coil |
| Maximum Operating Temperature | 1150°C – 1200°C |
| Design Pressure | Up to 2.5 MPa (water/steam side) |
| Bend Radius | R ≥ 3D (D = tube outer diameter) |
| End Treatment | Beveled, threaded, or flanged (per customer specification) |
| Applicable Standards | ASTM A213, ASME SA-213, EN 10216-5, GB/T 14976 |
Manufacturing Process
The production of high-quality stainless steel spiral coil tubes involves a rigorously controlled multi-stage manufacturing process:
- Material Selection and Inspection: Raw material is sourced from certified mills with full mill test certificates (MTC). Incoming steel is subjected to chemical composition analysis (spectrometry) and mechanical property verification prior to processing.
- Tube Forming: Seamless stainless steel tubes are produced via hot-rolling or cold-drawing processes in accordance with ASTM A213 or ASME SA-213 standards. The dimensional tolerances are held to ±0.05 mm for outer diameter and ±0.1 mm for wall thickness.
- Coil Forming (Spiral Bending): Tubes are fed into a computerized spiral coiling machine that precisely forms the helical geometry. The coiling process utilizes a hydraulic mandrel system to ensure uniform bend radii without inducing wrinkles, ovality, or wall thinning beyond acceptable limits (≤ 10% wall reduction at the inner bend radius).
- Heat Treatment: Post-forming solution annealing is conducted at 1050°C – 1150°C followed by controlled air cooling or water quenching. This step restores full austenitic microstructure, eliminates residual stresses from cold forming, and maximizes corrosion resistance.
- Surface Cleaning and Passivation: The finished coils undergo acid pickling and passivation to remove surface scale and contaminants, establishing a uniform chromium-rich oxide film critical for long-term oxidation resistance.
- Quality Inspection: Each coil is subjected to dimensional measurement, hydrostatic pressure testing (1.5× design pressure), visual inspection for surface defects, and optional eddy current testing for internal flaw detection.
Applications
These spiral coil tubes are engineered for use in a variety of demanding industrial applications:
- Low-NOx Coal Powder Burners: The primary application domain. The spiral coil arrangement within the burner throat creates a controlled swirl that enhances fuel-air mixing, promotes complete combustion, and reduces peak flame temperatures—thereby lowering thermal NOx emissions by 30–50% compared to conventional burner designs.
- Industrial Boilers and Waste Heat Recovery Systems: Used as radiant and convective heat transfer tubes in high-temperature furnace environments.
- Heat Exchangers: Deployed in high-temperature gas-to-liquid and gas-to-gas heat exchange applications requiring corrosion-resistant materials.
- Petrochemical Processing: Applied in reforming furnaces, cracker coils, and other high-temperature process heating systems where oxidation resistance is paramount.
- Power Generation: Integrated into ultra-supercritical (USC) and supercritical boiler systems where advanced materials are required to handle elevated operating conditions.
- Environmental Compliance Systems: Supporting flue gas treatment and selective non-catalytic reduction (SNCR) systems in coal-fired power plants.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all products meet international standards and regulatory requirements:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification reflecting commitment to environmentally responsible manufacturing.
- ASME Section I / IV — Compliance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code for pressure-containing components.
- EN 10204 3.1 / 3.2 — Third-party inspection certification for material and product conformity.
- GB/T 19001 — Chinese national standard for quality management systems.
- CE Marking — Conformity with European directives for machinery and pressure equipment where applicable.
Unique Selling Points
1. Optimized Spiral Geometry for Low-NOx Combustion: The coil tube design is specifically engineered based on computational fluid dynamics (CFD) research for spiral coil type high-efficiency low-NOx coal powder burners, delivering superior combustion efficiency and significantly reduced NOx emissions.
2. Advanced Material Selection: Use of high-nickel austenitic stainless steels (Type 310S, 309, 347H) provides exceptional resistance to thermal fatigue, high-temperature oxidation, and sulfidation in aggressive coal-fired environments.
3. Precision Manufacturing: Computer-controlled spiral coiling ensures dimensional accuracy and geometric consistency across all production runs, guaranteeing reliable performance in burner assemblies.
4. Customizable Configurations: Tube dimensions, coil pitch, coil diameter, and end treatments are fully customizable to match specific burner designs and operational requirements.
5. Full Traceability: Each coil tube is accompanied by complete material traceability documentation, including mill certificates, heat treatment records, and inspection reports, ensuring full compliance with regulatory and project specifications.
Conclusion
The stainless steel spiral coil tube (Item No. 685) from Wenzhou Jixing Metal Materials Co., Ltd. represents a technologically advanced solution for modern low-NOx coal combustion systems. By combining premium austenitic stainless steel materials with precision spiral forming technology, these products deliver the thermal performance, mechanical durability, and environmental compliance required by today's most demanding industrial applications. The product line is the direct outcome of applied research into spiral coil type high-efficiency low-NOx coal powder burner technology, bridging the gap between academic innovation and industrial deployment.