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1. What requirements must be met when repairing the furnace wall brick structure? (1) The furnace wall bricks must come with a certificate of conformity; if no such certificate is available, a thorough inspection is necessary before they can be used. (2) When laying bricks, it is necessary to strictly follow the brick-laying specifications and construction drawings. (3) If the furnace wall bricks are lightweight clay-based refractory bricks, they must be constructed using clay-based refractory mortar (medium grain). (4) The brick joints shall not be larger than 3 mm. (5) The mud filling in the brick joints must be complete and uniform, with a fullness rate of not less than 95%. (6) The fire-facing side of the brick must not be missing any edges or corners, nor shall it be modified in any way. (7) When laying bricks, only a wooden hammer may be used for alignment; the use of an iron hammer is strictly prohibited. (8) The brick joints on the surface should be hooked. 2. What filler is used for the expansion joints in firebrick furnace walls? In the past, asbestos rope was basically used to fill the expansion joints in the firebrick furnace walls of heating furnaces. Practice has shown that after a period of operation, most of the asbestos ropes in the expansion joints get burned out, losing the elasticity required for them to function as expansion joint fillers; some even turn into loose ash. Therefore, it is recommended that asbestos rope not be used in expansion joints where the furnace temperature is above 400°C. In the areas of the furnace where there are high-temperature flue gases, using ceramic fiber-filled bricks to fill the expansion joints is an ideal material. 3. How many types of clay-based refractory bricks are there? The raw materials for clay-based refractory bricks are refractory clay or kaolin. This type of brick contains <65% SiO2 and 30%–40% Al2O3. This type of brick is widely used in the heating furnaces of petrochemical plants; it is divided into two types: lightweight refractory clay bricks (QN) and clay bricks (NZ). 4. What are the advantages and disadvantages of using vertical and horizontal laying methods for the refractory brick lining of the radiation chamber in cylindrical heating furnaces? It is desirable that the inner surface of the refractory bricks forming the lining of the radiation chamber in such furnaces have a relatively smooth circular shape; however, since expensive special-shaped bricks are not desired, ordinary straight refractory bricks (230×114×65 mm) TZ-3 and wedge-shaped refractory bricks (114×65/55×230 mm) TC-23 are generally used in combination with vertical laying. Since the thickness of the refractory bricks in the wall of the cylindrical furnace is 114 mm, the width direction (114 mm) of the above two types of bricks aligns with the thickness direction of the furnace wall. If laid horizontally (with the long sides parallel to the ground), many noticeable short straight sections will appear on the inner surface of furnaces with a smaller diameter. The bricks in each layer will also be unevenly aligned vertically, and the joints between the bricks on the back side of the furnace wall will be relatively large. Therefore, horizontal laying should only be used for furnaces with a larger diameter; for furnaces with a smaller diameter, vertical laying (with the long sides perpendicular to the ground) is recommended. The disadvantage of vertical stacking is that it is difficult to ensure the verticality of each brick, and it is hard to arrange the vertical joints in the brick wall in a regular pattern; moreover, construction is more difficult compared to horizontal stacking. Vertical construction is carried out using TZ-3 and TC-23 in combination, but the number of TC-23 bricks used per layer is independent of the diameter of the cylindrical furnace. Under the condition of a wall thickness of 114 mm, the quantity of TC-23 used per layer is 71 pieces. 5. Can the furnace walls of cylindrical furnaces be entirely lined with lightweight heat-resistant concrete? At present, the bottom, top, convection chamber, and chimney of cylindrical furnaces are mostly lined with lightweight heat-resistant concrete, while the furnace walls of the radiation chamber are mostly constructed from bricks. It is technically entirely possible to replace the brick lining of the furnace walls in the radiation chamber with a lightweight heat-resistant concrete lining, but whether the lining or bricks is more cost-effective depends on factors such as supply sources and construction experience; therefore, there is no consistent conclusion yet. Except for the expansion joints where special-shaped bricks are used, the furnace walls of the radiant chamber in cylindrical furnaces can be constructed in other areas using standard straight bricks (TZ-3) and wedge-shaped bricks (TC-23), making the structure simple as well. 6. What is the maximum operating temperature for lightweight heat-resistant concrete linings? The maximum operating temperature for lightweight heat-resistant concrete linings must not exceed 900°C. Great care must be taken during use; improper usage can lead to serious consequences. 7. What is the composition and mix ratio of lightweight heat-resistant concrete linings? The lightweight heat-resistant concrete linings used in the heating furnaces of petrochemical plants are made by mixing bauxite cement, ceramsite (or lightweight clay brick sand), and vermiculite with water. The most commonly used ratio, both domestically and internationally, is: (1) Manual application: alumina cement: ceramsite (or lightweight brick sand): vermiculite = 1:2:4 (by volume). (2) Mechanical spraying: bauxite cement: ceramsite (or lightweight brick sand): vermiculite = 1:2.5:4.5 (by volume). The lining material must meet the following requirements: (1) Bauxite cement: It must comply with **standards. (2) Ceramsite should be washed by water; only those ceramsite particles that float on the surface should be used, with a loose density of 600–700 kg/m3. The gradation of ceramsite particle sizes is shown in Table 14-3. Table 14-3 Gradation of ceramsite particle sizes Particle size/mm Mass percentage/% Remarks Manual application Mechanical spraying 5–1.0 5–1.2 30 40/% Hard-shelled ceramsites 1.2–0.3 >1.2 <0.3 /30/40/1 5 Produced by crushing hard-shelled ceramsites (3) Vermiculite: The dry bulk density should not exceed 150 kg/m3; unvitrified or over-vitrified vermiculite is prohibited. The gradation of vermiculite particles is shown in Table 14-4. Table 14-4 Particle size distribution of vermiculite: Particle size/mm, Mass/%; 5–1.2, 1.2–0.3, <0.3: 45, 40, 15. (4) Construction water: Only clean tap water must be used. The large particles in ceramsite and vermiculite aggregates can improve the thermal insulation properties of the lining and reduce its density ； Small and medium-sized particles can fill the gaps between larger particles ； Use less cement ； Increase strength and improve workability. During construction, an appropriate amount of water that meets drinking standards should be added to the lining. The water-cement ratio (the mass ratio of water to cement + powder of admixtures) should be determined through testing based on specific conditions. An excessive water-cement ratio causes a large amount of water to be removed from the lining after drying and heating, resulting in an increase in pores, a decrease in strength, and an increased residual shrinkage of the concrete. The water-cement ratio for manual application is generally between 1.2 and 1.5. The moisture content of mechanically sprayed material is 50%–60%. Appropriate adjustments should be made based on conditions such as the temperature, humidity, and moisture content of the materials at the construction site. It is generally appropriate to hold the material in the hand, with water droplets squeezing out between the fingers without dripping. 8. Why is bauxite cement used as the binder for lightweight heat-resistant concrete linings? Bauxite cement has a fire resistance rating of over 1400°C, and it hydrates rapidly. During setting, the initial setting should not occur earlier than 40 minutes, and the final setting should not occur later than 10 hours. Due to its advantages such as temperature resistance and increased strength, it is used as a binder for lightweight heat-resistant concrete linings. The bauxite cement lightweight heat-resistant concrete lining undergoes an exothermic reaction during the curing period; therefore, cooling by spraying water is required for curing, and the high-temperature steam curing method used for ordinary concrete is strictly prohibited. During construction, it is necessary to completely avoid the mixing in of other impurities such as cement and lime. 9. Why are ceramsite and vermiculite used as aggregates in lightweight heat-resistant concrete linings? Both ceramsite and vermiculite are lightweight heat-resistant aggregates; concrete made using these two materials has a low density, which is why it is referred to as a lightweight heat-resistant lining. Ceramsite is produced by firing clay or shale at high temperatures. Expansive vermiculite is produced by heating raw vermiculite to a certain temperature; as the water contained within it evaporates rapidly, its volume increases. Ceramic beads have high strength, while vermiculite offers good thermal insulation properties. A lightweight, heat-resistant lining that uses bauxite cement as a binder and ceramsite and vermiculite as aggregates is an ideal lining material for heating furnaces in petrochemical plants, in terms of operating temperature, strength, and thermal insulation performance. 10. What are the two methods used for constructing lightweight heat-resistant concrete linings? What are the advantages and disadvantages of each method? The two methods for constructing lightweight heat-resistant concrete linings are manual application and mechanical spraying; the advantages and disadvantages of these methods are shown in Table 14-5. 14-5 Advantages and disadvantages of manual application and mechanical spraying: Construction method – Manual application, Mechanical spraying; Material loss – Water-cement ratio; Difficulty of construction – Easy to master; Suitable for constructing vertical walls or furnace roofs; Liner’s pressure resistance – Expansion joints need to be provided, about 10%; Easy to apply; Can be done according to design requirements; Formwork is required; Difficult to construct on furnace roofs; Lower cost; Easier to apply; High amount of rebound, with losses of around 50%; Not easy to master; Requires experienced workers; Due to rebound, the actual ratio varies significantly; No formwork is needed; Faster construction speed; But spraying equipment is required; Higher cost; More difficult to apply. 11. Should expansion joints be provided when constructing lightweight heat-resistant concrete linings? Expansion joints should generally be provided in refractory brick furnace walls, while expansion joints are necessary for lightweight heat-resistant linings, as refractory bricks and lightweight heat-resistant linings have different expansion and contraction properties. The expansion of refractory bricks increases as the temperature rises, while lightweight heat-resistant linings expand slightly when the temperature goes up, but they experience significant contraction upon cooling – this is known as residual contraction. In subsequent operations, if the maximum heating temperature does not exceed that of the first heating, the expansion and contraction of the lining as the temperature rises and falls will occur along the straight line shown in Figures 14–1, moving back and forth. Therefore, large-area linings do not need to have large expansion joints like refractory brick walls; instead, expansion joints with a width of 3–5 mm and a depth of about 1/3 of the lining’s thickness are sufficient, spaced every 1–2 meters. The purpose of this expansion joint is: (1) as the lining expands slightly during the first heating process, the expansion joint can reduce the internal stresses resulting from this expansion. (2) Due to the large residual shrinkage of the lining, significant cracks occur after cooling; expansion joints allow these cracks to appear in designated locations in a more regular manner. (3) Expansion joints allow cracks to stop at those joints and not continue to extend, thereby distributing contraction cracks evenly and preventing the formation of cracks that are too long or too wide. file:///C:\Users\Blackfox\AppData\Local\Temp\ksohtml\wpsF931.tmp.jpg 12. What kind of material is ceramic fiber? What are its basic properties? Ceramic fiber, also known as ceramic fiber mat, is a fibrous material produced by melting high-temperature resistant refractory materials such as corundum using an arc, and then spraying the resulting material with compressed air; it is also referred to as ceramic fiber cotton. Using ceramic fiber cotton, various ceramic fiber products can be manufactured. The Al2O3 content in domestic ceramic fiber mat scorpions is 62% and 45% respectively; the former can be used at temperatures of 1150–1200°C, while the latter can be used at 1000°C. Ceramic fiber felts are classified into three types based on the binder used: ceramic fiber rigid felts (with aluminum phosphate as the binder), ceramic fiber flexible felts (with latex, polyaluminum, water glass, methyl cellulose, or a composite binder of latex and aluminum phosphate), and ceramic fiber wet felts (with silica sol as the binder). Based on the properties of the ceramic fiber mat and the temperature of the heating furnace, a hard mat can be used for the hot face layer of the furnace wall. The dimensions of the ceramic fiber products are 600×400×20(10) mm. The basic properties of ceramic fiber mat are as follows: (1) It can operate at high temperatures, up to 1000°C. (2) The density of ceramic fiber felt is below 200 kg/m3 (usually 160 kg/m3), which is only 1/6 to 1/7 of that of lightweight heat-resistant linings. (3) The heat capacity is only 1/9 that of lightweight heat-resistant linings and lightweight clay refractory bricks. (4) Ceramic fibers remain stable at high temperatures, with very low residual shrinkage; therefore, there is no need for contraction or expansion joints, making construction convenient. (5) Low thermal conductivity. At a hot surface temperature of 600°C (average temperature of 366°C), the guide coefficient is 0.078 W/(m•K) ； At 900°C (average temperature of 551°C), it is 0.096 W/(m•K) ； At 1100℃ (with an average temperature of 678℃), it is 0.125 W/(m•K), which is about 1/8 of that of lightweight clay refractory bricks and 1/10 of that of lightweight heat-resistant linings. (6) It has good sound insulation performance. The ceramic fiber coating can reduce high-frequency noise with frequencies below 1000 Hz, and it can also absorb some low-frequency noise. (7) It has a certain tensile strength. (8) Good chemical stability. (9) It has good elasticity (78% elasticity at room temperature), making it easy to transport and install. (10) It has good resistance to air flow erosion, capable of withstanding air flow speeds of 30–50 m/s. 13. What precautions should be taken when using ceramic fiber felt? (1) It is strictly prohibited to store ceramic fiber felt outdoors. (2) The ceramic fiber felt must be kept dry and protected from rain. (3) Stepping on the ceramic fiber mat is strictly prohibited. (4) When using ceramic fiber felt, open the box as needed and handle it gently. (5) When applying ceramic fiber mat during construction, it is strictly prohibited to apply high-temperature adhesives over large areas on the furnace wall; instead, an area should be applied adhesive to and then the mat applied to it, depending on the size of the mat. (6) It is strictly prohibited to collide with the surface of the already applied felt. 14. What is the maximum operating temperature for ceramic fiber mats? For the ceramic fiber mats currently produced in China, the maximum temperature at which they can be used over a long period of time is 1000°C. 15. What is the general maximum allowable temperature for the outer wall of the heating furnace’s furnace wall? To reduce heat loss from the furnace walls of the heating furnace’s radiation chamber and convection chamber, it is required that the temperature of the outer wall of these furnace walls not exceed 80°C. 16. What are the requirements for painting and coating heating furnaces? Painting and coating heating furnaces is very important, as the quality of this work directly affects the furnace’s service life. Therefore, the following requirements must be met when applying paint: (1) Selection of paint: A red lead anti-rust paint should be applied first to the metal surface, followed by a second layer of lead paint, alkyd enamel, or phenolic enamel. Qualified thinner must be used for paint thinning. ①Before construction, the drying time of the paint and the condition of the dried paint film should be tested; it can only be used if they meet the requirements. ②Before painting, the metal surface should be polished and rust-free, with no dirt present. ③The construction site must be clean; work should not be carried out in conditions of extreme cold, frost, rain, fog, snow, or humidity. ④Apply the first coat of paint within 8 hours after rust removal, and wait at least 24 hours before applying the second coat. ⑤To ensure the quality and protective properties of the paint film, each coat should not be applied too thickly; instead, multiple applications should be used. ⑥The primer should be compatible with the topcoat; careful selection is necessary when using it, otherwise it will affect the durability of the paint film. (2) Regulations for painting and coloring: ① The bottom, body, and convection chamber of the heating furnace shall be painted dark green. ②The chimney is painted black. ③The platforms, ladders, and railings are painted dark gray.