Application of Novel Three-Channel Double-Recirculation Pulverized Coal Burner in Henan City Power Plant Unit 3 Boiler

Literature Overview

This paper, published in Power Generation (Thermal Power Generation) in 2004, describes the design and field application of a novel three-channel double-recirculation pulverized coal burner developed by Xi'an Electric Power College and Henan City Power Plant. The burner was installed on the Unit 3 boiler to address two critical operational problems: excessive oil consumption during boiler start-up and poor load-following capability during operation. The results demonstrated significant reduction in start-up oil consumption, high continuous operation reliability, and wide load adaptability.

Technical Context and Engineering Relevance

From the perspective of piping and welding engineering, the burner system represents a critical interface between the fuel supply piping network and the boiler furnace. The three-channel design implies a complex manifold arrangement where pulverized coal, combustion air, and flue gas recirculation streams converge. Each channel requires dedicated piping connections with specific flow characteristics, pressure ratings, and temperature tolerances. The double-recirculation feature means that flue gas is extracted from the furnace and reintroduced through separate channels, creating thermal cycling conditions that impose significant demands on the metallurgical integrity of the burner throat, nozzle assemblies, and associated piping.

Piping System Considerations

The burner piping system must accommodate several distinct service conditions simultaneously:

The convergent geometry at the burner throat creates stress concentration zones that require careful welding design. The weld joints connecting the burner mounting flange to the boiler furnace wall are particularly critical, as they experience thermal cycling between start-up and shutdown operations. Based on my experience with similar boiler burner installations, the weld metal selection should match or exceed the creep strength of the base metal at the maximum operating temperature.

Welding and Fabrication Insights

The fabrication of a three-channel burner involves multiple dissimilar material welds. The burner nozzle is typically made from cast steel or forged alloy steel, while the inlet piping may be carbon steel. The transition welds must be designed with appropriate preheating temperatures and post-weld heat treatment to prevent cold cracking and ensure adequate toughness in the heat-affected zone. For high-temperature recirculation channels, the welding procedure specification should include controlled interpass temperatures and possibly in-situ stress relief to minimize residual stress accumulation.

The double-recirculation arrangement introduces additional piping loops that increase the total weld count and potential leak points. During commissioning, each recirculation loop must undergo hydrostatic testing at 1.5 times the maximum operating pressure, with particular attention to the expansion joints and flexible connections that accommodate thermal displacement between the stationary boiler structure and the burner assembly.

Key Technical Points and Study Insights

The paper's core contribution lies in demonstrating that a three-channel design with independent recirculation paths can simultaneously achieve low-NOx combustion and stable flame anchoring across a wide load range. From a piping engineering standpoint, this translates to the need for precise flow control at each channel inlet, which requires well-designed control valve assemblies with reliable actuator connections.

One important observation is that the burner's wide load adaptability—from minimum stable combustion load to full rated capacity—imposes variable thermal expansion demands on the burner-to-furnace weld joints. In my engineering practice, I have seen failures at these joints when the expansion compensation was inadequately designed. The burner mounting system must incorporate sufficient flexibility, either through expansion bellows in the air duct or through properly designed sliding supports on the furnace wall, to prevent fatigue cracking of the welds.

The high continuous operation reliability reported in the paper suggests that the burner design incorporated appropriate metallurgical considerations for the high-temperature components. The burner throat and register vanes, which are directly exposed to flame temperatures exceeding 1200°C, must be fabricated from materials with adequate thermal fatigue resistance. Common choices include Cr-Mo steels (such as 12Cr1MoV) for the structural components and refractory-lined cast steel for the hottest sections.

Engineering Practice Integration

When applying lessons from this literature to actual burner installation projects, several quality control checkpoints are essential:

1. Weld joint radiographic testing on all critical burner-to-furnace connections, with acceptance criteria per ASME Section V or equivalent national standards.
2. Hardness survey of the heat-affected zone on high-temperature alloy welds to verify that the PWHT was effective in preventing brittle microstructures.
3. Dimensional inspection of the burner throat to ensure the three-channel geometry matches the design specifications, as deviations affect flame shape and combustion efficiency.
4. Leak testing of all flue gas recirculation connections using helium or nitrogen trace methods, given the potential for CO ingress into the recirculation stream.

The successful application of this burner technology at Henan City Power Plant validates the engineering concept, but the long-term reliability depends heavily on the quality of the piping and welding workmanship at the burner interfaces. Engineers should treat the burner piping system as an integral part of the boiler pressure boundary and apply corresponding levels of design scrutiny, fabrication control, and inspection rigor.