What issues should be considered when installing a burner in a boiler?

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This post was last edited by zgj2405 on 2010-5-2 at 12:10. The burner is a key component for combustion in boiler equipment. The quality of boiler operation, its safety, efficiency, and the length of its operational cycle are all closely related to the quality of the burners. The quality of a burner is influenced by every aspect, from its design to installation and operation. In other words, the problems that arise during the operation of a boiler related to the burner are the result of one or more factors such as unreasonable design, errors during installation, inadequate operation and tuning, variations in coal quality, or mismatches between the boiler and related equipment. As engineering and technical personnel on the production front line, their main concern is the installation and operational tuning of burners. The quality of installation is the prerequisite and foundation for proper operational tuning. When burners are assembled on-site, various problems can arise, such as deviation, tilting, upward or downward inclination. As a result, the burner may stop functioning during operation, carbon buildup may occur, the nozzle may be damaged, the boiler’s combustion may be incomplete leading to low thermal efficiency and reduced output, the airflow may cause wear and damage to the pipes, uneven airflow patterns and large variations in heat load may lead to pipe rupture, and it may also accelerate the degradation of metal materials. Therefore, when installing or maintaining burners on-site, due attention should be paid to the importance and methods of proper installation, as well as to remedial measures for defects and problems, in order to ensure the safe, economical, and stable operation of the boiler. On-site assembly must comply with the installation procedures and drawings, as well as the connection methods (the combination of these components among themselves and their connection to external pipelines), to ensure adequate and uniform cooling of the nozzles, proper expansion of the burner, and proper fixation of the supports during assembly. 1 The installation shall comply with the requirements of the drawings. 1.1 Reference positioning: The burner shall be assembled on site with its position determined in accordance with the requirements of the drawings. Generally, for reasons of safety and ease of construction, the position of the lower row of secondary air nozzles (or rather, the lowest row of nozzles) is used as a reference point during installation; all other nozzles are installed with reference to this point. Therefore, this reference point must be accurate – the elevation must be correct, the horizontal position must be correct, all nozzles in the lower row must be at the same horizontal level, and their length extending into the furnace must meet the requirements specified in the drawings. 1.2 The burner assembly shall meet the requirements specified in the drawings as well as the installation specifications. After the reference positions of each burner group are established, the ideal airflow centerline should lie on the imaginary tangent circle at the center of the furnace; the installation of all other nozzles shall also comply with the requirements outlined in the drawings. The basic requirement is: (1) The centers of the nozzles in the same group of burners must be on the same vertical plane. 　　(2) The ideal centerlines of the airflow from each nozzle in the same group of injectors should lie on the same generatrix of the imaginary tangential circular cylinder at the furnace center. 　　(3) The elevation of each nozzle and the relative distance (height) between the nozzles shall meet the requirements of the drawings. 　　(4) The inclination angle of each nozzle shall meet the requirements of the drawings. 　　(5) The nozzles of the burners in each group of the same type should be on the same plane. 　　(6) The length of the same nozzle extending into the furnace for each group of injectors is equal. 　　This work is crucial in installation projects. Care should be taken to meet the requirements of the drawings and installation procedures as closely as possible; in other words, errors should be minimized, and proper installation records should be kept. 2 Connection of the burner (1) During on-site assembly, inadequate site conditions and limited space, along with the heavy weight of the burner components and the difficulty in moving them, pose significant challenges to the installation process. Even so, the nozzle must not be separated from the pipe that should be connected to it and aligned with its center. In other words, the nozzle must not be installed separately and then connected to the pipe, in order to prevent bending of the airflow or deviation of the airflow’s centerline. 　　(2) During on-site assembly, due to the limitations imposed by the boiler frame’s location, there is a lack of space when connecting the burner to external pipes, or bends are required. On-site installers focus more on whether the two can be connected, ignoring a factor that is even more important than connection: the length of the straight pipe section between the elbow and the outlet section of the nozzle. Based on field experience, this length should be no less than 2.5 times the equivalent diameter of the nozzle outlet cross-section. Otherwise, it is easy to result in an uncertain airflow direction and uneven wind speed at the outlet section; if it is primary air, it is easy to cause uneven distribution of air and powder in the outlet airflow. As a result, phenomena such as erosion of the tubes during operation, coking, unstable combustion leading to easy extinguishment, and burnout of the nozzles occur. 　　(3) When connecting the burner to external pipes, it is not allowed to use force such as pushing or pulling to make the connection, nor should the pipes be bent at large angles. 3　Cooling of the nozzle 　Uneven wind speed at the nozzle, uneven powder content, poor material quality, an unreasonable design of the nozzle’s air duct structure, as well as changes in coal quality and load levels, all affect the cooling of the nozzle. For example, if the wind speed at the nozzles is uneven, the wall temperature in areas with lower wind speeds will be higher, and the powder content there will also be higher. For nozzles with low wind speeds, the flame is close to the nozzle; the high temperature at the nozzle can cause it to deform or even get damaged. Therefore, materials that are heat-resistant and possess a certain degree of thermal strength should be used, especially in primary nozzles where the wind speed is low and there is dust present. It is generally made of heat-resistant steel. If ordinary materials are used, it is prone to burning out. In terms of the structural design of the nozzle air duct, if the elbow is located near the nozzle, or if the damper is positioned near the nozzle, or if the oil gun remains inserted in the air duct for an extended period, all these factors affect the cooling of the nozzle. 4 Expansion of burners All burners expand due to heat during operation. If insufficient expansion clearance is provided during installation, deformation will occur during operation; this is especially true for burners with large outlet cross-sections, where deformation of the nozzle walls can lead to burnout. For ordinary small-diameter combustion nozzle nozzles, provided that the wind speed is uniform and appropriate, it is not necessary to provide a dedicated expansion gap. An excessively high regional heat load, that is, changes in boiler load, inadequate operation and tuning, as well as changes in coal type, can all lead to an excessively high regional heat load, which in turn can cause the burner to burn out. This is a very important factor contributing to the unsuccessful application of the dual-channel, multi-coal-type stable combustion main burner in our plant’s 35t/h boiler. 5 Temporary fixation during installation Temporary fixation is an important step in the process of installing burners. It includes: the base, brackets, and fixing points. The requirement is: a solid foundation is needed; generally, a concrete foundation is used ； The bracket must be stable and reliable ； The fixation must be secure; do not use materials such as wooden planks or bricks that can cause errors as supports ； Furthermore, the temporarily fixed burner cannot be used as a support for scaffolding, nor can it serve as any other point for lifting, suspension, or bearing loads. 　　The above are the issues to be considered when assembling burners on-site, and they encompass most of the problems that may arise during the installation of other types of burners as well. Stating its significance lies not only in the need to pay sufficient attention during installation, but also in the fact that even more care must be taken during operation, maintenance, inspection, and renovation. Based on the requirements of the installation and maintenance procedures, this is done to ensure that the injectors after installation, maintenance, or modification meet the operational requirements. Besides the points mentioned above, are there any other things to keep in mind?