Catalytic cracking BPDIE without turtle shell mesh lining and construction technology

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Abstract on the use of BPDIE lining without scale-resistant mesh and its construction techniques in catalytic cracking: In response to the problems associated with the thermal insulation and wear-resistant linings in the regenerators of catalytic cracking units, this study investigated the mechanical spraying process for using new types of thermal insulation and wear-resistant lining materials, including the selection of such materials, the welding of insulation pins, the placement of construction joints, and the control of water volume. It solves problems such as high rebound rate of large particles. The mechanically sprayed lining has proven to have good performance after operational testing; it improves the efficiency of lining installation and reduces the energy consumption of the equipment. Keywords: Catalytic cracking, Wear-resistant lining, Mechanical spraying, Tortoise-shell mesh-free lining. A New Lining Material for Catalytic Cracking Regenerators. SHU Hai-tao and WANG Guan-bao (Industrial Equipment Inspection Co., Guangzhou Petrochemical General Works, Guangzhou 510726). Abstract: A new heat-insulating and wear-resistant lining material is used in the regenerators of catalytic cracking units to replace the conventional materials. A process for applying this new material to the walls of the regenerators via mechanical spray coating has also been developed. The new lining proves to be of high quality, which helps to reduce the energy consumption of the cracking units. Keywords: Catalytic cracking, Abrasion resistance, Mechanical spray coating. Heat-insulating and wear-resistant linings are important components of the inner walls of regenerators and reactors in catalytic cracking units. Over the past few years, with the advancement of catalytic cracking process technology, the operating load on these units has increased and the operating temperatures have risen, making the existing tortoise-shell mesh linings increasingly inadequate to meet the requirements for safe, stable, and long-term operation of these units. The main problems associated with it are its complex structure, numerous construction steps, long construction period, high cost, and short service life. The short service life is manifested in the fact that, after operation, differences in thermal expansion due to high temperatures can cause the welds to separate from the lining, leading to warping, cracking, and bulging. This results in extensive repair work for the lining, makes such repairs difficult, and makes it hard to ensure the quality of the repairs; as a consequence, the wear-resistant layer often peels off, the insulation layer gets eroded, and the metal wall overheats. These drawbacks are all related to the turtle shell mesh structure. To this end, it is necessary to develop and promote the use of a new type of turtle-shell mesh lining structure, as well as the corresponding lining materials and construction techniques. We have carried out research on the industrial application of BPDIE crack-free mesh linings for mechanical spraying in catalytic cracking units, in collaboration with organizations such as Beijing Design Institute and Yixing Zhangze Refractory Ceramics Factory. This work involved processes such as investigation and research, selection of lining materials, simulation tests, industrial application, and temperature monitoring, and satisfactory results have been achieved. 1 Material selection: The BPDIE heat-insulating and wear-resistant lining spraying material was chosen. Through multiple laboratory tests and medium-scale simulated spraying trials, it was found to meet the operational requirements as well as the requirements of the spraying process; its performance parameters are shown in Table 1. 　　Building on the existing technique of manually applying coatings to the BPDIE lining, significant improvements were made to the material in order to maintain the excellent performance of the original BPDIE lining and to meet the requirements of the spraying process. 　　Using the original BPDIE-G insulation lining material, and after multiple adjustments to the particle size and grading, the results of the spraying tests showed that the main component of this lining material is clay hollow spheres, making it unsuitable as a spraying coating. Due to its high strength, hollow spherical shape, and smooth glaze coating on its surface, it possesses the elasticity of a table tennis ball, which results in an extremely high rebound rate. Screening results of the dry mixture before spraying: aggregates larger than 1.2 mm accounted for 45.4%, whereas after spraying this figure was only 23.36%–13.56%. In other words, the rebound loss rate for aggregates larger than 1.2 mm ranges from 48.5% to 70%. Table 1 Performance specifications of thermal insulation lining material BPDIE-G and wear-resistant lining material BPDIE-D

| Parameter | BPDIE-G | BPDIE-D |
|-----------|---------|---------|
| Contractual specification | Measured value | Contractual specification | Measured value |
| Unit weight / kg·m⁻³ | 110°C: 1520–1680; 815°C: 1440–1600 | 1300–1450; 1200–1450 | 2720–2880; 2640–2800 |
| | 2450–2600; 2380–2550 | | |
| Flexural strength / MPa | 110°C: —; ≥2.2 | 540°C: —; ≥2.2 | 6.5–10 |
| | | 815°C: 2.1–3.5; ≥2.15 | 5.6–8.5; 5–8 |
| Compressive strength / MPa | 110°C: —; 10–15 | 540°C: —; 65–95 | |
| | | 815°C: 4.2–6.3; 9–13 | 35–55; 45–70 |
| | | 1100°C: 4.2–6.3; 8–12 | | |
| Linear strain rate / % | 815°C: –0.1––0.3; –0.1––0.25 | – | –0.1––0.2 |
| | 1100°C: –0.1––0.3; –0.2––0.25 | | ≤–0.6 |
| Thermal conductivity / W·m⁻¹·K⁻¹ | 540°C: 0.5; ≤0.4 | 1.56; ≤1.4 | |
| | 815°C: 0.53; ≤0.45 | 1.41 | |

Note: The method for determining thermal conductivity is the flat-plate method. 　　Large-grained expanded perlite, lightweight brick sand or ceramsite, glass beads, etc., were used to replace the clay hollow spheres in the BPDIE-G lining material; the binder, alumina cement, remained unchanged. Admixtures were added as appropriate. Considering the crushing and rebound of the lightweight aggregates during the spraying process, the proportion of coarse particles in these aggregates was increased accordingly. According to spraying simulation tests, the rebound loss rate for aggregates larger than 1.2 mm was only about 15%. The wear-resistant lining BPDIE-D basically retains the original materials; considering the high hardness of bauxite clinker, which results in significant rebound loss during spraying, the content of coarse particles has been appropriately increased. To achieve the correct mix ratio for the sprayed concrete, the mix ratios of the BPDIE-G insulation coating and the BPDIE-D wear-resistant coating were appropriately modified. Through the above modifications, the spraying test yielded relatively satisfactory results. 2 Tests without tortoise-shell mesh lining 2.1 Industrial application tests on the flue at the regenerator outlet The regenerator is a key equipment in catalytic cracking units; before adopting tortoise-shell mesh lining in regenerators, we first conducted industrial application tests on the horizontal section of the flue at the regenerator outlet with a diameter of φ2200mm under conditions similar to high temperatures, in order to evaluate the technical properties of the lining material. On this horizontal flue, the manual application method was used, with the BPDIE lining material produced by Yixing Zhangze Refractory Porcelain Factory. There are two layers of lining without a tortoise-shell mesh; the total thickness of these layers is 100 mm, of which the thermal insulation layer is BPDIE-G with a thickness of 60 mm, and the wear-resistant layer is BPDIE-D with a thickness of 40 mm. The total area covered by this lining is 40 m2. After one year of use, an inspection was conducted: the flue gas temperature inside the flue was around 600–650°C, while the surface temperature of its outer wall was 130°C. The temperature of the outer wall adjacent to the flue, which was lined with a tortoise-shell mesh, was 145°C. No local overheating was observed on any of the outer walls that did not have such a tortoise-shell mesh lining. Tests have shown that the combination and use without a turtle shell mesh lining perform well. 2.2 Mechanical spraying without a turtle-shell mesh lining Mechanical spraying involves using spraying equipment to propel semi-dry powdered material, which has been mixed with water in a certain proportion under the action of compressed air, as a high-speed airflow toward the surface to be treated, thereby achieving a tight and secure bond. We fabricated an arc-shaped steel plate based on the curvature of the φ9.6m regenerator; the structure is shown in Figure 1 (units: mm). Using the Allentown N-2 type spraying machine, the mechanical spraying technique for BPDIE linings without a turtle-shell pattern was developed through research. The samples were sent to the Luoyang **Refractory Materials Quality Inspection and Testing Center and the Department of Inorganic Materials at South China University of Technology for testing [1,2], and their properties such as thermal conductivity, density, high-temperature flexural strength, compressive strength, and linear expansion rate all met the required standards. 3 Construction of regenerator without tortoise-shell mesh lining: During the overhaul of the catalytic cracking unit, 180 m2 of lining was replaced in the dense-phase section of the regenerator. The original lining with a turtle-shell mesh was removed, and a new lining without such a mesh was applied mechanically. The lower end of the new lining is located 3 meters away from the center of the loading/unloading hole; the total height of the new lining is 5.5 meters, as shown in Figure 2. Figure 1: Diagram of the mechanically sprayed lining test plate. Figure 2: Schematic diagram of the regenerator. 3.1 Removal of the old lining and rust removal: The wear-resistant lining inside the grid structure is broken away using an iron chisel, exposing the end plates of the insulation nails; the grid structure is then removed by welding. Remove the insulation lining and all existing insulation nails. Use an iron shovel and wire brush to clean the rust and deposits from the inner wall. 3.2 Welded anchoring of insulation nails The V-shaped insulation nails are arranged in a cross-shaped pattern with vertical and horizontal lines, at an interval of 200 mm; this interval is reduced to 160 mm in some areas. After welding, the quality of each weld must be checked individually. 3.3 Handling of the interface between old and new linings The thickness of the original turtle-shell mesh lining was 100 mm, while that of the new turtle-shell mesh lining is 120 mm. There is an interface at the junction of the old and new linings; the structure of this interface is shown in Figure 3. By utilizing the oil and gas barriers located every 0.5 m on the inner wall of the existing regenerator, the interface was placed near these barriers. Angle steel measuring 30 mm × 30 mm × 4 mm was used to weld the turtle-shell mesh lining to the oil and gas barriers. Each section of this connecting angle steel was 600 mm long, and three holes with a diameter of φ12 mm were drilled in each section, so that it could be welded to the wall of the device using anchor bolts. The wear-resistant layers of the old and new linings are connected by a 45° sloped transition. Figure 3 Structure of the interface between the old and new linings 3.4 Placement and treatment of construction joints The lining is sprayed from bottom to top, with each spraying session covering a height of about 1.2 m. Four construction joints are arranged in a circumferential direction, while only one longitudinal construction joint is left. The interfaces of these construction joints are made as 45° beveled edges. The construction joints between the thermal insulation layer and the wear-resistant layer are spaced at least 200 mm apart. 3.5 Mechanical spraying of thermal insulation lining: Mix bauxite cement with aggregate in a certain mass ratio in a mixer for 3–5 minutes; after mixing evenly, add 6%–7% clean water to prevent the dry material from producing dust. This semi-dry mixture must be used up within 60 minutes; it is strictly prohibited to add water again and mix it once more. At the same time, all preparations prior to spraying should be completed; the semi-dry mixture should be filled into the spray machine’s tank until it is full. The operator is located on the loading/unloading platform, while the gun operator is inside the regenerator. The two work in coordination with each other. Spraying begins once the machine is started. Each spraying pass covers a width of 1.2–1.5 meters and a height of 1.2 meters, with the spray gun being about 1 meter away from the work surface. To ensure a dense coating on the lining, and to reduce the amount of material that rebounds during spraying, the pressure at the spray outlet is kept at around 0.2 MPa. The amount of water used is controlled by the gun operator, who aims to achieve a situation where there is minimal rebounding without any dripping. The spray machine must continue to supply material regularly, with refilling taking place approximately every 3 minutes. To control the thickness of the insulation layer, markings are made on the V-shaped anchor bolts before starting construction. When the insulation layer reaches the desired thickness of 70 mm, leveling is carried out. During spraying, the spray gun must move continuously; it is not allowed to stay in one spot for too long. 3.6 Mechanical spraying of wear-resistant layer lining: After the insulation layer has been sprayed, it must be allowed to cure for 8 minutes; once a visual inspection confirms that everything is in order, the insulation material exposed at the areas where the V-shaped nails are located must be removed completely before the wear-resistant layer can be sprayed. 　　Pure calcium aluminate cement and aggregate are placed in a mixer in a mass ratio and mixed for 3–5 minutes; after thorough mixing, a small amount of water is added to prevent the dry materials from producing dust. Then, using the dry mixture as a base, 3% stainless steel wire fibers are added; while mixing dry, the fibers are evenly incorporated using a brush. Mixing is continued for 8–10 minutes until uniformity is achieved. This semi-dry mixture must be used up within 45 minutes, and re-mixing or reuse is strictly prohibited. The semi-dry material is loaded into the feed cylinder of the spraying machine, and spraying is carried out continuously. The spraying technique is as described earlier; the thickness of the wear-resistant lining can be monitored and controlled using pins during the spraying process, ensuring that the lining thickness remains within an error range of ±3 mm. Once the desired thickness of 50 mm is achieved through spraying, the surface can be leveled and polished. The wear-resistant layer lining must have a smooth surface, without any through-cracks, bulges, or delamination. After completing the spraying process, mist the surface with water using a sprayer for 48 hours for curing, followed by natural curing for at least 5 days, after which the furnace drying process prior to operation can begin. 4 Application effects of a regenerator without a turtle-shell mesh lining A total of 5 measurements were taken of the surface temperature of the outer wall of the regenerator before and after replacing the turtle-shell mesh lining. The measurement points were at sections 1-1, 2-2, and 3-3 at the location where the lining in the dense-phase section of the regenerator was replaced (see Figure 2); the circumference was divided into 12 zones (see Figure 4), and the measurement data are shown in Table 2. Figure 4: Distribution diagram of the 12 areas around the circumference. As can be seen from Table 2, with a tortoise-shell mesh lining, the average temperature of the outer wall was high from the early stages of operation, reaching 148.8°C; after 7 months, this average temperature increased by 28.4°C. This indicates that turtle-shell mesh linings, due to inherent structural flaws, are prone to defects such as warping, cracking, and bulging during use at high temperatures. This can be explained by the increase in wall rise, as well as confirmed by the visual inspection of the equipment during overhauls. For those without a turtle-shell mesh lining, as can be seen from Table 2, their outer wall temperatures are generally lower. The local temperatures reached as high as 179°C and 172°C due to the detachment of the scale-resistant lining inside the inclined tubes between the regenerator and the riser during temperature measurement; this caused the surface temperature of those inclined tubes to rise sharply to around 600°C, thereby affecting the surface temperature of the outer wall of the regenerator in zone 4 that is located nearby. Even under these conditions, the average temperature of the outer wall of the regenerator increased by 7.1°C after 7 months, and by 7.5°C after 8 months. Taking into account the errors associated with the two different temperature measurement methods, it can be said that the average temperature of the outer wall of the regenerator changes very little. Operation with a mesh liner is stable, and it is capable of meeting the requirements of the cyclic operation of catalytic cracking units. Table 2 Measurement Data of the Outer Wall Surface Temperature of the Regenerator Operating Time/Month Infrared Temperature Metering Instrument Surface Temperatures at 12 Points Along the Perimeter/°C Average Temperature/°C 1 2 3 4 5 6 7 8 9 10 11 12 With scale net: 0 Thermal camera*: 150.1 151.3 147.0 154.1 143.7 148.4 147.0 ———— 148.8 With lining: 7 Thermometer: 174.0 176.0 206.0 175.0 178.0 176.0 167.0 156.0 166.0 193.0 197.7 161.3 177.2 Without scale net: 0 Thermometer: 122.5 140.5 151.5 107.5 106.5 144.5 133.5 125.0 138.0 156.5 119.5 133.0 131.5 With lining: 7 Thermal camera**: 126.6 140.0 157.0 179.0 144.5 135.5 135.1 127.2 132.6 144.7 122.2 118.1 138.6 8 Thermal camera**: 125.9 141.7 158.8 172.0 148.8 139.0 135.3 127.2 133.3 146.2 119.5 120.0 139.0 *Measurements commissioned to Maoming Petrochemical Company ； **Entrusted to South China University of Technology for measurement. 　　Compared with those with a turtle-shell mesh lining, the former has a lower average surface temperature on its outer wall, resulting in significant energy-saving effects. According to the calculation results provided by the Department of Inorganic Chemistry at South China University of Technology, the overall thermal conductivity of the new lining is 11.84 W/(m²·°C). If this same value is used for the old lining as well, and assuming an ambient temperature of 20°C in all calculations, the average heat dissipation per unit area for the new and old linings is respectively 1404.2 W/m² and 1525.0 W/m², resulting in an energy savings of 120.8 W/m² per unit area. After all the regenerators are replaced with linings without turtle-shell mesh, assuming a lining area of 1000 m2, energy savings of approximately 0.43 GJ per hour are achieved, which equates to 83 tons of fuel oil saved per year. 5 Conclusions (1) The successful large-scale application of mechanically sprayed domestic BPDIE lattice-free linings in the dense-phase section of catalytic cracking unit regenerators indicates that breakthrough progress has been made both in the technical properties of the materials and in the techniques for applying such linings. 　　(2) The main technical properties of mechanical spraying without a scale mesh lining, such as the thermal coefficient and high-temperature flexural strength, meet or exceed the manufacturer’s specifications. 　　(3) Through mechanical spraying tests and on-site construction practices, technical issues such as the rebound of large particles during mechanical spraying of BPDIE without a turtle-shell mesh lining were resolved, thereby creating the necessary construction technical conditions for its wider application in the future. 　　(4) During the replacement of the regenerator lining, a new structure for the interface between the old and new linings was developed, paving the way for the gradual replacement of the new lining without a scale net. 　　(5) Mechanical spraying without a scale-proof mesh lining not only reduces the labor intensity compared to manual construction, but also speeds up the construction process, shortens the maintenance cycle, and increases work efficiency by over 40%. 　　(6) The mechanically sprayed BPDIE without a tortoise-shell mesh lining has withstood over a year of operational testing, and no overheating has been observed; it can meet the requirements for long-term operation of catalytic cracking units. References:1. Guangzhou Petrochemical Complex. Test Report on Surface Temperature of the Regenerator Liner Without Scale-Preventing Mesh in the Refinery Catalysis System (I). Department of Inorganic Materials, South China University of Technology, 1993. 2. Guangzhou Petrochemical Complex. Performance Evaluation Report of the Regenerator Liner Without Scale-Preventing Mesh in the Refinery Catalysis System (I). **Refractory Materials Quality Supervision, Inspection and Testing Center, 1993