industrial kiln

This post was last written by Nani_Summary of thermal insulation design specifications edited by This specification does not apply to the design of equipment and pipelines with special requirements for nuclear energy, aviation, and aerospace systems, as well as the insulation engineering of buildings, cold storages, and buried pipelines. GBT 4272-2008 General Principles of Insulation Technology for Equipment and Pipelines 1 Scope This standard specifies the terms and definitions related to insulation materials and their products, general requirements for performance requirements of insulation structural materials, insulation design, insulation structure, construction and acceptance of insulation projects, testing of insulation project effects, maintenance, inspection and safety regulations for insulation projects. This standard is applicable to thermal insulation projects with external surface temperatures of equipment, pipes and accessories between -196°C and 650°C. Insulation projects in other temperature ranges can be implemented with reference to this standard. GBT 8174-2008 Testing and evaluation of the insulation effect of equipment and pipelines 1 Scope This standard specifies the terms and definitions, test methods, test requirements, test organization and preparation, data processing, test uncertainty, insulation effect evaluation engineering quality analysis and test report content for the surface temperature test evaluation of equipment and pipeline insulation structures. This standard is applicable to the testing and evaluation of the thermal insulation effect of equipment, pipes and accessories in the general industrial sector. It is not applicable to the testing and evaluation of the thermal insulation effect of buildings, cold storage, national defense or scientific research, as well as some with special requirements. GBT 8175-2008 Guidelines for Thermal Insulation Design of Equipment and Pipelines 1 This standard specifies the basic principles of thermal insulation design, the performance requirements and selection principles of insulation layer materials and main auxiliary materials, thermal insulation calculations, cold insulation calculations, and the main construction technical requirements for thermal insulation structures and thermal insulation projects. This standard applies to general equipment and pipelines. It is not suitable for equipment and facilities with special requirements such as ship nuclear power and the lining of industrial furnaces and boilers. Temporary facilities during construction, pipes of various thermal instrumentation systems and heat tracing pipes are not subject to this standard. GBT 16618-1996 General Principles of Industrial Furnace Insulation Technology 1 Model This standard specifies the basic principles for industrial furnace insulation design, structural selection, insulation layer thickness calculation and material selection, as well as construction and acceptance. This standard is applicable to industrial furnaces used in melting, heating, heat treatment, sintering and other processes. This standard does not apply to furnaces or parts with special lining requirements such as metal smelting, ships, nuclear energy, boilers, etc. SHT 3010-2013 Specification for the design of thermal insulation engineering for petrochemical equipment and pipelines 1 Scope This specification specifies the design requirements for thermal insulation materials, insulation calculations, and insulation structures for petrochemical equipment and pipelines. This specification is applicable to the design of thermal insulation engineering for petrochemical equipment and pipelines. This specification does not apply to the design of internal insulation liners of equipment and pipelines and pipeline insulation projects with special requirements. Please pay attention to the scope of application of the above standards. There are few standards for calculating the thickness of industrial kiln insulation layers. GBT 16618-1996 is a general rule and is just a summary. Thickness calculations can refer to the above-mentioned standard flat wall economic thickness calculations, or other professional books or papers summarized by experts. Other: Reference to the issue of maximum allowable heat loss in equipment and pipe insulation https://bbs.hcbbs.com/thread-251233-1-1.html or attachment: Discussion on allowable heat loss and design methods of GB50264-97

I have never been able to tell the difference between industrial boilers and industrial kilns. Thank you to the original poster. Happy New Year!

It would be great if it can be helpful, :) Happy New Year to each other

Causes and treatment measures for ringing and balling in rotary kilns Various types of cement rotary kilns have encountered ringing problems. Loop formation significantly reduces the cross-sectional area of ​​the kiln, seriously affects the ventilation in the kiln, hinders material movement, and has a certain impact on the output, quality, safe operation, coal consumption, and power consumption of the rotary kiln. Especially in rotary kilns with frequent ring formation, it not only destroys the normal thermal system in the kiln, but also harms the health of operators and causes economic losses to production. 　　There are many factors that cause ring formation in rotary kilns, which are related to the nature of raw materials, ingredients of raw materials, ash content and fineness of fuel, kiln type, reduction atmosphere in the kiln and thermal system, etc. In the actual production process, calcining clinker with a high silicic acid rate is beneficial to reducing ring formation, but white cement clinker with a high silicic acid rate can also form rings. As for the impact of coal ash, all oil-burning cement rotary kilns also form rings. Therefore, the looping problem is more complicated. Now, based on the experience and understanding in production, we will talk about the prevention and treatment of rings in cement rotary kiln. 　　1 Formation of rings There are many factors that form rings in the rotary kiln, but the generation and solidification of the liquid phase are the main processes of ring formation. The lining temperature, material temperature, coal ash and raw meal composition are the main factors that determine the generation and solidification of the liquid phase. During the clinker calcination process, the raw material appears in a liquid phase at about 1200°C. The viscosity of the liquid phase begins to decrease at around 1250°C, and the amount of liquid phase increases. Due to the sudden drop in temperature of the material layer covering and the heat dissipation on the surface of the cylinder, the liquid phase solidifies on the kiln wall to form a kiln skin. The kiln continues to operate, and the kiln skin is exposed to high temperatures and melts off. It is covered with materials again, and the liquid phase solidifies again, and so on. If a lot sticks on and a little falls off, the kiln skin will become thicker, otherwise it will become thinner. Under normal circumstances, the thickness of the kiln skin can be maintained at about 200mm. If the melting and solidification processes are balanced within this temperature condition and area, the kiln skin will not thicken. When less melts and more solidifies, its thickness grows to a certain extent, forming a ring. When the temperature difference between the lining material and the material is large, under sufficient liquid phase conditions, the ring body becomes thicker and thicker. 　　1.1 The formation of the front knot ring The front knot ring (also known as the kiln mouth ring) is a ring knotted at the end of the firing zone of the rotary kiln. Under normal calcination conditions, the material temperature is 1350~1450°C, the liquid phase amount is about 24%, and its viscosity is relatively large. When the clinker leaves the firing zone, the liquid phase begins to cool, and the liquid phase entering the cooling zone has basically solidified. There is a large temperature difference at the junction of the firing zone and the cooling zone, and the material temperature at the kiln mouth is higher than the kiln skin temperature. When the clinker enters the cooling zone, the high-temperature clinker with liquid phase covers the lower-temperature end kiln skin, and it will quickly bond and become thicker and thicker, eventually forming a front ring. During the calcination process, when the temperature in the high-temperature part of the firing zone is too concentrated, a large temperature difference appears at the junction of the cooling zone and the firing zone. In addition, the amount of high-temperature rapid-burning liquid phase increases and the viscosity is small. When the clinker enters the cooling zone, there is still a large amount of liquid phase that cools rapidly near the junction, promoting the growth of the front ring. 　　1.2 Formation of clinker ring The clinker ring (also known as the second ring) is the ring between the firing zone and the exothermic reaction zone in the kiln. It is also the most harmful ring in the rotary kiln. During the clinker calcination process, when the material temperature reaches 1280°C, the liquid phase viscosity is relatively large, and the clinker ring is most easily formed. It is relatively strong after cooling and is difficult to remove. Under normal calcination conditions, the inner diameter of the clinker ring is often melted and falls off, maintaining the normal inner diameter of the ring. If there is too much liquid phase in the temperature range of 1250 to 1280°C, a clinker ring is often formed that hinders production. The clinker ring is usually formed at the boundary of the firing zone or further away. Initially, the kiln skin behind the firing zone gradually grows and becomes thicker. When it develops to a certain extent, a clinker ring is formed. The length of the kiln skin in severe clinker circles can even grow several times the length of the normal kiln skin. For example, a 3.6m65m three-stage cyclone preheater kiln in a white cement plant had a severe clinker ring during trial production. The kiln skin in the kiln is 52m long (measured from the kiln head guard iron), and the thickest part of the ring reaches 1050mm. As a result, trial production could not be carried out and the kiln was forced to be shut down. 　　2 Prevention and treatment of loops 2.1 Prevention of loops The main factor in the formation of loops and clinker loops is that the material produces a liquid phase at a certain temperature and area, and loops are prone to occur under the condition of a large temperature difference between the lining material and the material. Therefore, the way to prevent loop formation is to appropriately reduce the initial liquid phase in the material and minimize the temperature difference between the lining material and the material. 　　(1) Choose an appropriate ingredient plan to stabilize the ingredients of raw materials and improve the calcining operation level. Generally speaking: burning materials with high saturation ratio and high silicic acid rate is not easy to form rings, but it is very difficult to calcine, which is detrimental to the protection of kiln skin and clinker quality. When burning materials with low saturation ratio and low silicic acid rate, the sintering range is narrow, the amount of liquid phase is large, the particles are coarse, the calcination is difficult to control, and rings are easy to form. Materials with high saturation ratio and low silicic acid rate or low saturation ratio and high silicic acid rate can be easily burned without forming rings. Therefore, the batching plan should adopt a higher saturation ratio and a higher silicic acid rate to appropriately reduce the flux minerals, which is beneficial to preventing ring formation. For example, a cement 2.5m45m five-stage suspended preheater kiln has a batching plan that has been put into operation for more than two years: KH=0.9±0.02, SM=2.0±0.1, AM=1.3±0.1. Loop formation is frequent, and the output per hour is as low as 7.0t/h. The adjusted batching plan: KH = 0.94 ± 0.02, SM = 2.4 ± 0.1, AM = 1.1 ± 0.1, using the "thin material rapid rotation" operation, the looping problem has been basically solved, the kiln's rapid rotation rate and operation rate have been improved, and the output of the clinker table has stabilized at more than 10t/h. In addition, materials with high alumina content have high C3A content, high liquid viscosity, and are easy to form loops. In the batching plan, the aluminum oxygen rate value should be reduced under the condition of appropriately reducing the amount of liquid phase in the material. 　　(2) Reduce the fineness of pulverized coal, strengthen the mixing of air and coal, and eliminate incomplete combustion. The fineness of pulverized coal is coarse, the ignition speed is slow, the burning time is long, and the heat of the flame is dispersed. In the case of insufficient secondary air volume and poor ventilation, the material preheating is not good. The primary air volume is insufficient, the wind speed and wind pressure are reduced, and the air and coal are not mixed well, which may easily lead to incomplete combustion and the formation of reducing flames. Especially in rotary kilns that use single-channel coal injection pipes, the oxygen in the primary air is difficult to reach the central area of ​​the flame due to severe oxygen deficiency. A large amount of carbon particles and CO cannot be burned in the firing zone, but are burned in the decomposition zone or even at the end of the kiln. At the same time, a large amount of CO is generated in the firing zone, which reduces part of the iron oxide in the material to ferrous oxide, forming FeOSiO2, a low melting point compound. The FeOSiO2 liquid phase at about 1100℃ can promote the formation of silicon calcite [2(CaOSiO2)CaCO3], and the silicon calcite is formed in the liquid phase at 1180~1220℃, which is most likely to cause the liquid phase in the firing zone to appear in advance, bonding unmelted materials together, causing rings. To this end, controlling the fineness of pulverized coal to less than 10% during production, and improving the coal air injection system of single-channel coal-injection pipes, or using double-channel or three-channel coal-injection pipes to ensure full combustion of pulverized coal are important measures to prevent ring formation. 　　For example, a 4.4/4.15/4.4m180m wet rotary kiln in a cement plant once used a coal injection pipe with a nozzle diameter of 330mm and a flat head length of 750mm. The ash content of pulverized coal is as high as 40%, the fineness of pulverized coal is about 13%, and rings form frequently. After thermal calibration, the measured primary air volume is 16040Nm3/h, the primary wind speed is 70m/s, and the secondary air volume is 205400m3/h. Because the caliber of the coal injection nozzle is too small, the primary air volume is too small, the primary air speed is high, and the flat head of the nozzle is too long and inert, the fineness of the pulverized coal is larger than that of the coarse ash, resulting in a long black flame, concentrated heat in the high temperature zone, and the pulverized coal cannot be completely burned within the range. Later, a coal injection pipe with a diameter of 345mm and a flat head length of 550mm was used. The fineness of the pulverized coal was reduced to less than 10%, and the ash content of the pulverized coal was controlled at about 30%. The measured primary air volume is 17500Nm3/h. The primary wind speed is 63.6m/s and the secondary air volume is 236470m3/h. The flame in the kiln is smooth, clear, lively and powerful, the high-temperature zone is in the right position, the low-temperature part is not prolonged, the main kiln skin is lengthened (10-12m), the auxiliary kiln skin is shortened (5-6m), the heat is reasonably distributed in the kiln, the ringing situation is basically improved, and the clinker output, quality and operation rate are improved. 　　(3) In production, it is necessary to determine an economical and reasonable output index and operate the rotary kiln appropriately and quickly, which is a beneficial measure to prevent ring formation in the rotary kiln. Rings are mostly formed when the kiln output is high, often because the conditions for increasing the kiln output exceed the specified maximum air extraction capacity, resulting in incomplete combustion of the fuel. When the kiln output increases to a certain limit, the amount of coal used increases, a large amount of coal ash settles, and the reducing atmosphere in the kiln is thick. The operation must increase the exhaust air, the air flow speed in the kiln increases, the flame elongates, and the liquid phase appears in advance, which makes it easy to form a clinker ring. For this reason, in terms of production management, it is necessary to strengthen the quality control of raw materials and fuels, stabilize the composition of raw materials entering the kiln, and maintain uniform feeding. On the basis of strengthening pre-firing, measures such as fast turning of thin materials, long-flame smooth burning, stabilizing the thermal system, and increasing the fast turning rate are very effective in preventing loop formation. 　　2.2 Treatment of Rings During the operation of the rotary kiln, the formed front rings or clinker rings must be discovered and dealt with in a timely manner. When processing loops, the alternating hot and cold method is generally used to increase the temperature difference as much as possible so that the loop body collapses due to temperature changes. 　　2.2.1 Pre-ring processing When the pre-knot ring is not high, it will have little impact on the calcining operation. The thickness of the material layer of the firing belt can be increased, the residence time of the material in the firing zone can be extended, and the heat radiation from the firing belt to the front of the kiln can be reduced. However, when the front ring knot is high, it not only affects the fire watching operation, but also affects the ventilation and flame shape in the kiln. Large pieces of clinker cannot roll out, and the kiln skin and lining of the fired belt are easily damaged. At this time, the air coal should be adjusted or the coal injection pipe should be moved in time. 　　(1) The ring is located far away from the discharge port. Most of the rings are formed when the kiln skin is in good condition, the calcination is normal, the high temperature zone is in a suitable position, and the coal injection pipe is inside for a long time. During processing, you don't need to turn off the exhaust air or reduce the feeding amount. Just pull out the coal injection pipe and burn it. 　　(2) The ring is located close to the discharge port. This is mostly due to the poor condition of the kiln skin, the flame being too long, and the ring formed when the coal injection pipe is outside for a long time. There are two methods of operation: one is the operation of not reducing feeding. When the incoming material is too low, pull out the coal injection pipe, increase the primary and secondary air temperatures, increase the secondary air volume, control the tail temperature to the lower limit, increase the firing temperature, move the firing zone forward, and the fire point falls on the circle position and is gradually burned. During operation, the amount of coal should be added or subtracted in time, and the amount of incoming material and flame changes should be grasped. If the flame is found to be elongated or compressed, it should be adjusted in time to prevent damage to the kiln skin and light-fired products leaving the kiln; the second is to reduce the feeding operation. Appropriately reduce the feeding amount and the secondary air volume. When the tail temperature is low, pull the coal injection pipe to the outermost position. After the material with poor pre-burning enters the firing zone, the flame can be shortened and forced to calcine, so that the front ring will be burned away with strong fire. This method is forced when the coal injection pipe cannot be burned after being pulled out. Because the coal injection pipe is pulled out too much, and the raw material is very close, the black flame is very short, and it is impossible to maintain the normal flame shape. During the operation, more attention must be paid to the changes in the incoming material, and more frequent inspection is required. 　　2.2.2 Treatment of clinker rings When dealing with clinker rings, different treatment methods must be adopted according to the characteristics and distance of the rings to achieve better results. Generally, the method of alternating hot and cold treatment is used. When burning the far circle, cold is the main method, and when burning the close circle, burning is the main method. 　　(1) When the kiln skin in the kiln grows long and thick or has slight ring roots, pull out the coal injection pipe to move the position of the combustion zone, lower the temperature of the ring part, change the location of the coal ash settling, and make the thick and long kiln skin gradually collapse. Adjust the combination of air and coal to accelerate the combustion of pulverized coal so that the low-temperature parts at both ends of the high-temperature zone are not prolonged and prevent the ring roots from continuing to grow. 　　(2) When the thick and long kiln skin in the kiln is improperly or not handled in time, causing the periodic fast and slow running speed to increase, causing the thick kiln skin to develop and form a clinker ring. First, determine the position and thickness of the ring and the material accumulation behind the ring. Then reduce the feeding amount, generally to 70% to 80% of the normal feeding amount. Increase the flame temperature, strengthen pre-firing, gradually increase the kiln speed, keep the kiln rotating quickly, and remove the accumulated material behind the circle. When the material accumulation behind the circle is reduced, the coal injection pipe can be extended into the kiln, and the coal injection nozzle can be raised appropriately to move the high temperature area of ​​the flame toward the circle body. At this time, the exhaust air should not be increased too much to prevent the flame temperature from decreasing. After burning for 4 to 5 hours, the coal injection pipe is pulled out and burned. This process is repeated to cause the ring body to collapse due to temperature changes. When dealing with clinker rings, it is necessary to appropriately change the raw material composition, reduce the amount of liquid phase in the material, appropriately change the coal mix, and use coal with high volatile matter and low ash content to ensure complete combustion of pulverized coal to prevent the development of clinker rings. 　　When handling the clinker ring, you must protect the kiln skin and avoid excessive concentration of the flame. After treatment, the ring root is still very strong, and if the kiln skin and lining material are seriously damaged, the kiln should be stopped to remove the ring. 　　3 Conclusion There are many factors that cause loops in rotary kilns. As long as the main reasons for loops are found out, and based on the principle of "prevention first, removal as a supplement", only timely discovery, timely treatment, and correct methods during the calcination operation can the loop problem be truly solved. Thereby achieving high-quality, high-yield, low-consumption, safe and civilized production of the rotary kiln. Repost

For the calculation process of the steady-state single-layer insulation thickness of the furnace, please ask Haiyou experts for guidance. Calculate (single layer) by controlling the outer surface temperature of the insulation layer. Note: Equipment design temperature ℃t=700. Input equipment surface temperature ℃ts=50. Enter the average temperature of the insulation layer based on the process. ℃tp=375 tp=(t+ts)/2 The thermal conductivity of the insulation material at tp temperature W/m·℃λ1=0.105 Enter the search criteria, refer to the thermal conductivity reference equation Material thermal conductivity reference equation coefficient λ=λ0+b* (t+ts)/2 Ambient temperature ℃ta=25 Enter the heat release coefficient from the equipment surface to the surrounding air W/(m2·k)α=11.16461252 α=K(ts-ta)^(1/4)+(C1-2 * Radiation coefficient W/(m2·k4)C1-2=4.536 C1-2=ε1 * C0 Radiation coefficient of black body W/(m2·k4)C0=5.67 Constant blackness of metal ε1=0.8000 Enter industrial electric furnace table 6-3-1 Heat dissipation plane position coefficient K=2.5600 Enter vertical wall: 2.56 ； Heat dissipates upward from the stove top: 3.26 ； Heat dissipation downwards from the bottom of the furnace: 2.1. Then the thickness δ of the insulation layer is: mδ=0.2445 δ=(λ/α) * ((t-ts)/(ts-ta)) Calculation of economic thickness of insulation layer (single layer) Equipment design temperature ℃t=700 Input equipment surface temperature ℃ts=50 Input value based on process Average temperature of insulation layer ℃tp=375 tp=(t+ts)/2 The thermal conductivity of the insulation material at tp temperature W/m·℃λ1=0.105 Enter the search criteria, refer to the thermal conductivity reference equation Material thermal conductivity reference equation coefficient λ=λ0+b * (t+ts)/2 Ambient temperature ℃ta=25 Enter the heat release coefficient from the equipment surface to the surrounding air W/(m2·k)α=11.16461252 α=K(ts-ta)^(1/4)+(C1-2 * Radiation coefficient W/(m2·k4)C1-2=4.536 C1-2=ε1 * C0 Radiation coefficient of black body W/(m2·k4)C0=5.67 Constant blackness of metal ε1=0.8000 Enter industrial electric furnace table 6-3-1 Heat dissipation plane position coefficient K=2.5600 Enter vertical wall: 2.56 ； Heat dissipates upward from the stove top: 3.26 ； Heat dissipation downwards from the bottom of the furnace: 2.1. Thermal energy price yuan/(10^5KJ) fn=7 input is based on local actual price or estimate: fn=c * 1000 * PF/(qFηB) annual operation time, hτ=8000. Enter the annual operation generally based on the unit cost of the insulation structure for 8000 hours/m3Pi=1045. Enter the compound interest to calculate the annual amortization rate of the investment repayment of the insulation project, %S=0.187444018 S=i * (1+i)^n/((1+i)^n-1) Annual interest rate, %i=10%. Enter compound interest, which is generally 8%-12%. Number of interest-bearing years, enter n=8, which is generally 5-10 years. The thickness of the insulation layer δ is: mδ=0.2606 δ=1.897 * 10^(-3) * ((fn * λ * τ(t-ta))/Pi * s)^(1/2)-λ/α Calculation of heat loss on the insulation surface Flat wall heat loss W/m2Q=262.4696722 Q=(t-ta)/(δ/λ+1/α) Calculation of the outer surface temperature of the insulation layer Outer wall temperature ℃ts=48.50907134 ts=Q/α+ta

This post was last written by Nani_Edited by heat transfer * Tutorial This article is a tutorial for fools. The method can be extended to engineering professional courses such as fluid mechanics, materials mechanics, engineering thermodynamics. ps: Tutorials for fools are similar to popular science, so that people who have never studied this course can understand it. When writing tutorials for fools, the most taboo thing is to give people the feeling of being blind and touching the elephant. Right now: No matter how concise the language is, it must give the most overall framework of something, rather than using many words to describe parts, otherwise people who have not learned it will sound confused. At the same time, we should also pay attention to turning abstraction into concreteness and using correct and vivid life experiences to replace abstract and obscure theories. If you are a person who knows nothing about "Heat Transfer" and are studying * Before studying Heat Transfer, it is necessary to know in advance what "Heat Transfer" is about and what you can do after studying "Heat Transfer". This is the most elementary and intuitive understanding of a subject. To answer the above question, let’s give a specific example first: The heating power of the laptop CPU is 90 watts. The maximum temperature that the CPU can withstand is 80 degrees Celsius, and the room temperature is 20 degrees Celsius. What area of ​​aluminum flakes should be used for heat dissipation? Give another example: In the winter in the north, heating is required. The room area is 40 square meters. The boiler boiler boiled the water to 80 degrees Celsius and asked how many sets of radiators are needed to ensure that the room temperature reaches 25 degrees Celsius. "Heat Transfer" is to solve the above problems. For everyone, the above two examples have certain life experience. In this way, I have a more concrete intuitive feeling about "Heat Transfer". With this feeling, I will summarize "Heat Transfer" in a relatively abstract way.: “"Heat Transfer" is such a subject: Use the laws of heat transfer and calculus as a tool to solve problems related to heating and heat dissipation in practical engineering. ”——by Chen Erxi Now, you have a preliminary understanding of the subject of heat transfer. No matter how rudimentary your preliminary understanding is, it can still guide you when you are confused. To make a digression: To determine whether you truly understand a course, you can ask yourself if you can highly summarize the subject in one sentence. You can test it yourself. For example, "Mechanics of Materials", my "Mechanics of Materials" was prepared in two or three days before the exam. * +For surprise, read the preface and table of contents first, and then draw a conclusion.: "Mechanics of Materials" is a: It is a subject that studies the relationship between the deformations such as "tension and compression", "bending" and "twisting" that objects of various materials endure, and the "force" that the object endures. A formula can be used to establish a relationship between each deformation and force. Memorize the formula, be able to solve the equation, and then see how to superimpose and handle the situation where multiple deformations exist at the same time. (Kind tips: Please go to class on time, don’t skip classes, don’t place your hopes on a surprise attack before the exam, because if you walk too much at night, you will always encounter ghosts, anyway, I have encountered them) Level 1: "Heat Transfer" is such a subject: Use the laws of heat transfer and calculus as a tool to solve problems related to heating and heat dissipation in practical engineering. It is used to solve problems such as the need to use heating in winter in the north. The room area is 40 square meters. The boiler boiler boiled the water to 80 degrees Celsius and asked how many sets of radiators are needed to ensure that the room temperature reaches 25 degrees Celsius. And the heating power of the laptop CPU is 90 watts. The maximum temperature that the CPU can withstand is 80 degrees Celsius, and the room temperature is 20 degrees Celsius. What area of ​​aluminum flakes should be used for heat dissipation? These kind of questions. ===================== second floor: In nature, there are three ways of heat transfer between two objects with temperature differences.: Heat conduction, heat convection, heat radiation. (This is something taught in elementary school science class) There is a stove in the room. When I warm myself by the fire, I will feel the heat. This is thermal radiation. When I touch the stove with my hand, it feels hot. This is heat conduction. The stove will warm the entire room, which is convection. So heat conduction means that two objects with a temperature difference come into contact with each other and then transfer heat. Thermal convection is the transport of heat through flowing liquid or gas. Thermal radiation is to emit heat directly without relying on anything. No matter which way heat is transferred, there is a corresponding equation to solve the problem. As long as you determine the method of heat transfer, fill in the corresponding equation, and then you will definitely be right to solve the equation. ======================= third floor: What equations should be listed in this level? The corresponding equations for the three heat transfer modes are:: The above "text version" of the equation can be understood by elementary school students. However, all the equations above are universal theorems, equivalent to nonsense, too broad in scope, and not very targeted. In order to better solve a specific problem, some conditions need to be added for constraints. These constraints are initial conditions and boundary conditions. Give a chestnut: Brother Erxi grew 5 centimeters in three years of high school. Please ask Brother Erxi for his current height. The above problem can be expressed as an equation:: known: Δh=5cm, it is impossible to solve for h, and constraints must be added: Junior high school graduation height h0=180.4 The known quantity at the initial moment is called the initial condition. Constraints such as minimum and maximum values ​​are called boundary conditions. It can also be considered that the initial conditions represent values ​​at a certain time. Boundary conditions represent values ​​at a certain location. So, for any heat transfer problem, our solution is as follows: List the governing equations - add boundary conditions and initial conditions - solve the equations. In the above picture, I have listed all the equations for heat conduction, convection and radiation. In fact, only one type needs to be listed. =============================== fourth floor: This level needs to turn the literal equations from the previous level into partial differential equations. Don't be afraid. First, the literal equation of heat conduction is: The variable of the heat of the object = the heat generated by the object itself - the heat flowing out of the object becomes a partial differential equation: The derivation process is as follows: Then convert the system of literal equations of thermal convection into a system of partial differential equations: Finally, the literal equation of thermal radiation is turned into a partial differential equation: ============================ fifth floor: Regarding the basic knowledge of heat transfer, I probably covered it in more than a thousand words and a few pictures. However, heat transfer is a whole book, so what is the rest of the book about? The rest of the content is all calculation examples. It is not so much an example of heat transfer as an exercise in the course "Methods of Mathematical Physics". * question. Heat transfer problems in actual science and engineering all use these three methods to exchange heat. The most complicated is just a combination of multiple heat exchange methods. In actual heat transfer problems, the known conditions are ever-changing, but the governing equations are always the above three sets of formulas. What changes are only the initial conditions and boundary conditions, and what changes are only one-dimensional problems and multi-dimensional problems. Of course, when these change, the method of solving equations changes. The rest of heat transfer is about solving the same equations for different conditions, using different mathematical methods. If you have difficulty in learning heat transfer, it may be because you are not good at mathematics. You should learn mathematics well. Reposted on Zi Zhihu - Tuihu (formerly known as Chen Erxi)

Analysis of common industrial furnaces Industrial furnaces are commonly used processing and heating equipment for raw materials and products in industrial enterprise production. There are many types of furnaces with similar names, but their functions are quite different. According to the classification of furnaces in the "Emission Standard of Air Pollutants for Industrial Kilns" (GB9078-1995), combined with my own practical understanding in recent years, I checked some reference materials and sorted out and analyzed the common types of furnaces. The hot blast furnaces and annealing furnaces commonly used in industry are not mentioned in the "Emission Standard of Air Pollutants for Industrial Furnaces and Kilns" (GB9078-1995). Which type of furnace do they belong to in the "Emission Standard of Air Pollutants for Industrial Furnaces and Kilns" (GB9078-1995)? Yes Heat treatment furnace or heating furnace? Also, what is the difference between a smelting furnace and a melting furnace? What are calciners and roasting furnaces used for? Are converters and electric arc furnaces for steelmaking industrial furnaces? Although these questions are simple, not every front-line environmental protection worker can make it clear. 1. Hot blast furnace is a drying furnace commonly used in industrial enterprises for drying raw materials or products to remove moisture. Most of them use high-quality anthracite coal as fuel. The hot flue gas generated by fuel combustion is used to directly contact the raw materials or products to conduct heat, causing the raw materials or products to lose moisture and dry. Therefore, the characteristic of hot blast furnace is that the raw materials or products lose moisture and dry, which belongs to drying furnaces and kilns (Category 6) in the "Emission Standard of Air Pollutants for Industrial Furnaces and Kilns" (GB9078-1995). It is neither a heating furnace nor a heat treatment furnace. 2. Heat treatment furnace (Category 5 of the "Industrial Furnace Air Pollutant Emission Standards") is a furnace that performs heat treatment on metal or non-metal raw material workpieces. Heat treatment refers to controlling the heating or cooling rate to produce the required properties (such as hardness or ductility) of the raw workpiece. Therefore, the characteristic of the heat treatment furnace is a kiln that produces the required properties of the raw workpiece. In the "Emission Standard of Air Pollutants for Industrial Kilns" (GB9078-1995), heat treatment furnaces are divided into two types: metal heat treatment furnaces and non-metal heat treatment furnaces. Metal heat treatment furnaces in industrial production include quenching furnaces and annealing furnaces. Annealing refers to heating the metal material workpiece to a certain temperature at a certain speed, controlling it for a certain time, and then allowing it to slowly cool at a certain speed to change the internal structure or grade of the metal in order to facilitate processing or obtain the expected flexibility, electrical properties, magnetism, etc. Quenching refers to immersing the red-hot casting in water or oil or other liquids, taking it out immediately, and cooling it quickly. The purpose is to improve the hardness and strength of the alloy. Therefore, the annealing furnace commonly used in industry belongs to the heat treatment furnace (Category 5) in the "Emission Standard of Air Pollutants for Industrial Kilns" (GB9078-1995). 3. Heating furnace (Category 4 in the "Emission Standards of Air Pollutants for Industrial Furnaces") generally refers to a kiln that heats metal or non-metal raw workpieces to a certain temperature in order to facilitate the processing of raw material workpieces. Therefore, the characteristic of the heating furnace is to increase the temperature of the material to a certain temperature and temporarily change its organizational structure and performance. The purpose is to make the raw material workpiece easy to process and shape at high temperature. For example, before rolling or forging steel billets in a steel factory, the steel billets must be heated to make them soft and easy to roll. In the "Emission Standard of Air Pollutants for Industrial Furnaces" (GB9078-1995), heating furnaces are divided into two types: metal rolling furnaces, forging heating furnaces and non-metal heating furnaces. 4. Smelting furnaces and melting furnaces are Class 1 and Class 2 industrial furnaces respectively in the "Emission Standards for Air Pollutants from Industrial Furnaces" (GB9078-1995). Smelting furnaces include four types: iron-making blast furnaces, steel-making furnaces, ferroalloy smelting furnaces, and non-ferrous metal smelting furnaces. Melting furnaces include cupola furnaces, iron-melting furnaces, metal melting furnaces, non-metal melting furnaces, and smelting furnaces. There is only one word difference between these two types of furnaces, and the difference lies in this word. "Smelting" is to use fire or heating to melt substances and make them pure, tough or concentrated. “Melting" is the process of heating a solid substance to a certain temperature to turn it into a liquid state. Therefore, the characteristic of a smelting furnace is to cause chemical and physical changes in the material, change the structure and composition of the material, melt the material, and make it pure, tough or concentrated. The characteristic of the melting furnace is that the material only undergoes physical changes, and the material changes from solid to liquid to facilitate operations such as molding and casting without changing the chemical composition of the material. 5. Iron ore sintering furnaces belong to the third category of industrial furnaces in the "Emission Standards for Air Pollutants from Industrial Furnaces" (GB9078-1995). Iron ore sintering furnaces include two types: sintering machines and pellet furnaces. "Sintering" means heating small pieces of ore or powder to make them bond. Iron ore sintering furnaces combine iron ore powder, A kiln in which raw materials such as coke dust and white ash are mixed and sintered into large pieces of ore. Its main feature is to sinter small pieces of various powdery raw materials into large pieces for the next step of blast furnace ironmaking. 6. Non-metal baking (forging) kilns belong to Category 7 industrial kilns in the "Emission Standard of Air Pollutants for Industrial Furnaces" (GB9078-1995). "Baking" means baking with a low fire, and "baking" means burning and heating (minerals, etc.) without melting them to remove volatile components to change their chemical composition or physical properties. “The original meaning of "forging" is to put it in a fire. "Calcining" is to heat materials to high temperatures without melting them. The purpose is to produce useful physical and chemical changes in order to transform or remove certain unwanted substances. For example, heating limestone removes carbon dioxide to produce quicklime. Therefore, the characteristic of the roasting furnace is to bake with low fire to remove the volatile components in non-metallic minerals and change the chemical composition or physical properties of the substance. The characteristic of the calciner is to produce useful physical and chemical changes in the materials, transforming or removing certain unwanted substances. 7. Converters and electric arc furnaces are not mentioned in the "Emission Standard of Air Pollutants from Industrial Furnaces" (GB9078-1995). The converter is a steel-making furnace. The pig iron from the iron-making blast furnace is injected into the converter, and an appropriate amount of scrap steel is added, and then into the converter. Oxygen is blown into the furnace. Oxygen serves as an oxidant for decarburization, desulfurization and dephosphorization. Oxidation of carbon, sulfur and phosphorus can also generate a large amount of heat to heat the converter. The converter body is cylindrical and is mounted on a horizontal axis. It can be rotated and the molten steel can be easily poured out. The characteristic of the converter is to blow oxygen into the high-temperature molten iron to oxidize the carbon, sulfur, and phosphorus in the iron; the electric arc furnace is also a type of steel-making furnace. It is a furnace that uses the continuous spark discharge (i.e., arc) generated when the positive and negative electrodes are close to a certain distance to generate high temperatures to make steel. When gas discharge forms an arc, the energy is very concentrated, and the temperature in the arc zone is above 3000°C. For smelting metals, electric arc furnaces have greater process flexibility than other steel-making furnaces. They can effectively remove impurities such as sulfur and phosphorus. The furnace temperature is easy to control and are suitable for the smelting of high-quality alloy steel. Electric arc furnaces can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces and resistance electric arc furnaces according to the arc form. Therefore, converters and electric arc furnaces are both steel-making furnaces, that is, Class 1 smelting furnaces in the "Emission Standard of Air Pollutants for Industrial Furnaces" (GB9078-1995). 8. Category 9 industrial furnaces in the "Emission Standard of Air Pollutants for Industrial Furnaces" (GB9078-1995) are ceramic enamel tile kilns. Ceramic enamel tile kilns are divided into tunnel kilns and other kilns. Tunnel kilns are characterized by continuous, tunnel-stepping flame heating, large output, and stable product quality. They are mainly used for the firing of refractory materials, ceramics and chemical powders. According to the temperature, it is divided into two categories: high temperature tunnel kiln and medium temperature tunnel kiln. Tunnel kilns have various structural forms. The lining can be heavy refractory bricks or light refractory bricks. The kiln roof can be an arched roll structure or a flat ceiling structure. The outer shell can be a metal steel plate structure or a red brick exterior wall structure. The fuel can be natural gas, liquefied gas, oil, gas, coal, etc. 9. The preface of the "Emission Standard of Air Pollutants from Industrial Kilns" (GB9078-1995) states: "This standard applies to the management of industrial kilns that use solid, liquid, gaseous fuel and electric heating except for coke ovens, incinerators, and cement industries." Therefore, coke ovens, incinerators, and rotary kilns and shaft kilns in the cement industry are all industrial kilns. However, these types of kilns are very complex and important and are listed separately to implement their respective standards. Coke oven is a kiln equipment that decomposes and distills coal to produce coke; an incinerator is a piece of equipment used to process hazardous wastes. By controlling the temperature and residence time of hazardous wastes incinerated in the furnace, hazardous wastes are completely oxidized and decomposed to produce harmless substances; the cement industry clinker is calcined. There are two categories of burning equipment: rotary kiln and vertical kiln. The cement industry rotary kiln is a rotary bedroom cylindrical cement clinker calcining equipment. It is a kiln that burns the ground and prepared raw materials into clinker under the action of high temperature. The cement industry vertical kiln is a static vertical cylindrical clinker calcining equipment.

Indicators to pay attention to when purchasing refractory bricks: The high-temperature service properties of refractory materials are properties measured at high temperatures, such as: Refractoriness, reburning line changes, thermal shock resistance, slag resistance, load softening temperature and creep, etc., these properties reflect the state of refractory materials in use to a certain extent. Understanding these properties is of great reference for the selection and use of refractory materials. 1. Refractory resistance Refractory resistance refers to the high temperature resistance of materials. Raw materials such as mullite, kyanite, andalusite and sillimanite need to be measured for refractoriness to understand the purity of the raw materials. Impurity components, especially impurities with strong flux effects, will reduce the refractoriness. Method for measuring refractoriness: Construct refractory raw materials or materials into triangular pyramids. The length of the upper base of the triangular pyramid is 2mm, the length of the lower base is 8mm, and the height is 30mm. Then it is placed on the same cone plate as the high-temperature standard cone, heated at a specified heating rate, and the sample cone is compared with the standard cone. Due to the emergence of high-temperature liquid phase, the sample cone gradually softens and bends toward the bottom due to its own gravity. The temperature at which the apex of the cone bends down to contact the cone disk is the refractoriness. The refractory degree is expressed by the standard cone number that bends at the same time as the sample. The bending conditions of the sample cone at different melting stages are shown in Figure 1. Figure 1 The bending situation of the sample cone at different melting stages a - before the melting begins; b - at a temperature equivalent to the refractory degree; c - at a temperature higher than the refractory degree. The refractory degree, melting point and service temperature must be clearly distinguished.: (1) Refractoriness and melting point have different meanings. The melting point is the equilibrium temperature at which a single crystalline substance melts from solid to liquid. Refractoriness is the melting range of various minerals. It is true that the melting point of crystal minerals is high, and the temperature of the eutectic formed by their interaction is correspondingly high. (2) Refractory resistance cannot be misunderstood as the temperature at which refractory materials can be used under high temperature. Because it has completely softened to the point of losing its mechanical strength. For example, the bonded part of alkaline refractory materials melts first at a lower temperature, and its damage is based on the softening of the bonding agent. This temperature is much lower than the refractory degree of the material. Generally, the use temperature of clay bricks is about 200~250℃ lower than the refractory degree. 2. Change in the reburning line: The change in the reburning line refers to the residual expansion or contraction that occurs after the sample is heated to a specified temperature, kept warm for a certain period of time, and cooled to room temperature. The change in the reburning line is one of the important indicators for evaluating the quality of refractory products. The volume of refractory products expands or shrinks after reburning, indicating that the refractory products are not fully fired due to insufficient temperature and holding time or uneven temperature during the firing process. If the change index of the reburning line of refractory products exceeds * * The specified value is bound to be used in industrial kilns. Due to the high temperature, some physical and chemical changes continue to occur, causing the volume of the product to expand or contract, and the size to change greatly, causing changes in the brick seams of the furnace body, thus affecting the integrity of the furnace lining, and in serious cases causing structural damage to the furnace body. Therefore, the firing system must be standardized so that the reburning line of the product changes within the specified value. The change in the reheat line is calculated according to the following formula: 3. Thermal shock resistance Refractory materials are the basic materials of industrial kilns. It is bound to be affected by temperature during use, sometimes by sudden changes in temperature. Thermal shock resistance refers to the ability of refractory materials to resist thermal stress caused by rapid changes in temperature without damaging it. my country's sample testing conditions: 1100℃, water cooling; expressed in times. There are many reasons that affect the thermal shock resistance index of refractory materials, so there are many expressions. Now use the following relationship to briefly explain: From the above imperfect relational formula (the above formula does not take into account the shape and size of the material, heating (cooling) conditions, local stress generated during sudden temperature changes, etc.), it can be seen that there are the following main factors that affect the thermal shock resistance of the material.: (1) The elastic modulus is low; (2) The linear expansion coefficient is small; (3) The main mineral of the refractory material has high thermal conductivity; (4) The composition and main structure of the combination are appropriate. In the refractory production process, the basic ways to improve the thermal shock resistance of refractory products are as follows:: (1) Change the phase composition of the product to obtain low-expansion minerals, or the superposition of low-expansion minerals, etc.; (2) Appropriately select and control the production conditions to make the composition and main structure of the combination appropriate, such as forming micro-cracks, increasing the material particles of certain products, etc. Table 1 lists the expansion coefficient and other properties of several refractory materials. Table 1 Expansion coefficients and other properties of several refractory materials 4. There are many types of industrial kilns that resist CO corrosion. Refractory materials will be subject to various erosions in industrial kilns, such as erosion from molten steel and molten iron, the influence of slag (acidic or alkaline slag), temperature changes, thermal stress, and the damage effects of changes in atmosphere (especially reducing atmosphere) on refractory materials. Therefore, refractory materials need to have corresponding characteristics according to the working environment of industrial kilns, among which CO corrosion resistance is one of them. CO corrosion resistance refers to the ability of refractory materials to resist cracking or disintegration in a CO atmosphere. When refractory products encounter a strong CO atmosphere at about 500°C (300~600°C range), a chemical reaction of 2CO=CO2+C will occur. The separated free carbon will be deposited around the iron points of the product, causing the product to crack or be damaged. During the blast furnace smelting process, the refractory products cracked and the organizational structure is loose due to the above reasons in the 400~600°C part of the furnace body, which is one of the important reasons for the damage of the blast furnace lining. Reducing the iron oxide content and porosity of refractory products can enhance their resistance to CO erosion. 5. Load softening temperature The load deformation index of refractory materials at high temperatures is expressed by the load softening temperature. It is the product's resistance to the combined effects of high temperature and load. It also indicates the softening range in which refractory products exhibit significant plastic deformation. This indicator is often used as a basis for determining the maximum service temperature of refractory materials. According to the load softening temperature index of refractory products, it can be judged under the conditions under which the refractory material loses its pressure-bearing capacity during use. At the same time, the internal microstructure of the refractory material can also be inferred. 6. High-temperature creep. High-temperature creep refers to the relationship between the deformation and time of refractory materials under constant high temperature and a certain load. High-temperature creep indicators include the strength, temperature and time of refractory materials at high temperatures, indicating the deformation rate of refractory products at a certain temperature and within a certain period of time. The above indicators of commonly used refractory brick products need to be considered. In different high-temperature industrial kilns, due to different use environments and working conditions, the main indicators and factors considered for different parts of refractory bricks depend on the situation. For example, for refractory brick products used in hot blast furnaces, in addition to the material content, the most important thing is to look at the thermal shock stability index. ----"Industrial Furnace Energy Saving Technology"