【Haichuan Pyrolysis Furnace】Structural features, construction techniques, and process optimization measures for the refractory lining of ethylene pyrolysis furnaces

2. Construction technology for the refractory lining of ethylene cracking furnaces – Parallel construction method. The so-called parallel construction method refers to a technique in which the refractory lining is installed simultaneously in the radiation section, transition section, convection section, and smoke collection box. This construction method employs network construction technology and carries out coordinated organization of the work. The key construction techniques are as follows: for the pouring materials in the radial section and the convective section, horizontal laying is used for lining; expansion joints are formed in one go using wooden molds. For lifting and installation, a \"modular\" construction technique is employed, in which two convective section segments are fastened to the furnace tubes together for reinforcement. In the radial section, hard bricks are drilled using an impact drill, and the grooves for brick hooks are cut using an alloy steel saw blade on a brick cutting machine. This concurrent construction method is an optimal construction technique, suitable for the renovation of fire-resistant linings in various ethylene plants introduced into the country as well as existing ethylene plants, thereby significantly improving economic and social benefits.

Material selection and management measures for the refractory lining of ethylene cracking furnaces: The following steps are necessary for managing the refractory lining. First, when purchasing refractory materials in person, it is essential to conduct sample inspections directly from the manufacturer’s production line or warehouse, and then send these samples to relevant refractory material research institutes for analysis of their physical and chemical properties, in order to ensure the quality of the refractory materials. Second, the refractory materials need to be stored and managed properly: since they must be protected from moisture and water during storage, it is necessary not only for workers to handle them carefully but also to set up sheds at the construction site, lay bamboo planks on the ground, and allow a greater number of stacking layers than specified. Third, technical training should be provided to the workshop workers: operators need to be trained on the standards for constructing furnaces and the specific methods for installing refractory linings in ethylene cracking furnaces. Case studies of common problems that arise during the operation of these furnaces should also be used to help them carry out timely inspections and repairs of the refractory lining during actual operations.

Analysis of key points for using refractory linings during construction (1) Precautions for use: When using refractory linings in daily operations, it is important to avoid rapid changes in temperature when starting up or shutting down the furnace. It is also necessary to adjust the size and position of the expansion joints as required; otherwise, this can lead to cracking or detachment of the refractory lining in the convection section. In the event of cracking or detachment, the refractory lining should be replaced promptly, and the position of the expansion joints adjusted accordingly. Structural characteristics, construction techniques, and process optimization measures for the refractory lining of ethylene cracking furnaces (2) Maintenance: Ceramic fiber modules are commonly used for the refractory lining of the radiation chamber. However, ceramic fibers tend to crystallize and degrade over time when exposed to high temperatures, which leads to shrinkage of the lining. Therefore, it is necessary to regularly inspect and maintain the refractory lining (at least once a year). When inspecting the refractory lining made of ceramic fibers, attention should be paid to whether there are gaps between the modules and at the corners of the furnace wall. It is also necessary to check whether the ceramic fibers have become thinner, as well as whether the fasteners holding the modules in place are loose or damaged. Furthermore, it is necessary to inspect and repair the refractory materials in the expanding areas of the brick wall based on the surface temperature of the exterior wall.

Sealing method for the furnace tubes and the roof lining of an ethylene cracking furnace: Anchors are welded to the inner wall of the roof lining area of the cracking furnace, and then combustible material is wrapped around the corresponding furnace tubes that pass through the holes in the roof, or sleeves made of combustible material are fitted over those furnace tubes. The thickness of the combustible material or of the sleeves corresponds to the allowable distance between the outer wall of the furnace tubes and the insulation layer on the inner wall of the roof holes. A layer of insulation made of zirconium fibers is sprayed onto the inner wall of the roof lining area, after which a wire mesh is fixed between this zirconium fiber insulation layer and the anchors; another layer of zirconium fiber insulation is then sprayed onto the wire mesh. Repeat the process several times in the order above until the anchor bolts are covered by the zirconium fiber insulation layer and the desired thickness is achieved. This sealing method for the furnace tubes and the refractory lining of the furnace top in ethylene cracking furnaces can effectively address the sealing issues at these areas; it is simple to implement, allows for rapid construction, and can significantly extend the service life of such furnaces.

3. Optimized construction techniques for the refractory lining of ethylene cracking furnaces: During the actual operation of ethylene cracking furnaces, in order to genuinely improve the quality of the refractory lining installation and reduce heat transfer, it is necessary to employ appropriate construction techniques to ensure a long service life for the refractory lining, thereby achieving low energy consumption and lower surface temperatures of the furnace, as well as extending its operational life. It is necessary to ensure an appropriate thickness for the insulation layer, as under prolonged exposure to high temperatures, the steel plates constituting the furnace body tend to deform, and cracks can form between the modules and these steel plates, allowing air convection to occur. This leads to a reduction in the thermal efficiency of the pyrolysis furnace, resulting in higher energy consumption. Therefore, during the operation of the refractory lining in ethylene cracking furnaces, the zirconium fiber blanket between the zirconium fiber modules and the steel plates must meet certain thickness requirements. Controlling the size of expansion joints: Light fire-resistant brick walls have high requirements regarding expansion joints, and certain measures must be taken during on-site construction to ensure the proper size of these joints. For example, plastic pieces can be manufactured in accordance with the required expansion joint dimensions; during construction, these plastic pieces can be placed between two adjacent fire-resistant bricks of the expansion joint to ensure accurate sizing. To better control the expansion joints in the vertical direction, the refractory bricks at both ends of these joints are processed during construction, ensuring that the zirconium fiber blankets inside the joints can return to their original state immediately after cooling. This prevents the formation of gaps when heating is resumed, thereby reducing heat loss. Spraying a high-temperature erosion-resistant coating on the surface of zirconium-containing fiber modules: After the installation of these modules, spraying a high-temperature erosion-resistant coating on their surface can prolong the time before the fibers crystallize and become fragmented due to exposure to high-temperature air currents over extended periods.