Method for calculating temperature of inner wall based on condensation heat transfer process of blast furnace gas pipeline

Abstract

The invention provides a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline. The method for calculating the temperature of the inner wall based on the condensation heat transfer process of the blast furnace gas pipeline comprises the following steps: S1, calculating the thermal resistance of convective heat transfer between the inner wall of the gas pipeline and blast furnace gas; s2, calculating the thermal resistance of heat conduction between the gas pipe walls; s3, thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline is calculated; and S4, calculating the corrosion temperature of the inner wall surface of the blast furnace gas pipeline according to the total thermal resistance, the blast furnace gas temperature and the environment temperature. According to the method for calculating the inner wall temperature based on the condensation heat transfer process of the blast furnace gas pipeline, the heat resistance of each part of the blast furnace gas in the heat transfer process is calculated on the basis of the heat convection and heat conduction process, and the scientific and systematic method for calculating the inner wall temperature of the blast furnace gas is established; the corrosion condition of the blast furnace gas pipeline can be conveniently predicted, and the safe operation of the blast furnace gas pipeline can be monitored.

Description

Technical Field

[0001] The present invention relates to the technical field of blast furnace ironmaking, and in particular to a method for calculating the inner wall temperature of a blast furnace gas pipeline based on a condensation heat transfer process. Background Art

[0002] A blast furnace is a closed, countercurrent reactor operating continuously at high temperature and high pressure. It is also the largest single piece of equipment in the steel industry, involving complex internal processes such as the interaction between gas and charge, as well as heat and mass transfer between the materials. Blast furnace gas, a byproduct of blast furnace smelting, contains chloride and sulfate ions, which can cause internal corrosion in blast furnace gas pipelines.

[0003] According to actual production data from the company, the blast furnace gas temperature before the TRT and pressure reducing valve block is generally above 100°C, higher than the dew point, and there is no condensate accumulation or corrosion perforation within the pipeline. However, significant corrosion has occurred in the lower section of the blast furnace gas pipeline at the TRT outlet, the pressure reducing valve block outlet, and the rear section. This is related to a significant drop in blast furnace gas temperature and pressure, reaching the dew point of water-containing wet blast furnace gas.

[0004] Current research on the effect of temperature on corrosion rates in gas pipelines primarily relies on setting a temperature variable to investigate the corrosion rate. As the temperature increases, the corrosion rate increases. However, there is still a lack of methods to calculate the specific corrosion temperature of the inner wall of a gas pipeline.

[0005] Therefore, it is necessary to provide a method for calculating the inner wall temperature based on the condensation heat transfer process of blast furnace gas pipeline to solve the above technical problems. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a method for calculating the thermal resistance of each part of blast furnace gas in the heat transfer process based on the process of heat convection and heat conduction, and establish a scientific and systematic method for calculating the inner wall temperature of blast furnace gas, which makes it easy to predict the corrosion of blast furnace gas pipelines and monitor the safe operation of blast furnace gas pipelines. The method for calculating the inner wall temperature based on the condensation heat transfer process of blast furnace gas pipelines plays a role in monitoring the safe operation of blast furnace gas pipelines.

[0007] To solve the above technical problems, the present invention provides a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline, comprising the following steps:

[0008] S1: Calculate the thermal resistance of convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas;

[0009] S2: Calculate the thermal resistance of heat conduction between the gas pipe walls;

[0010] S3: Calculate the thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline;

[0011] S4: Calculate the corrosion temperature of the inner wall of the blast furnace gas pipeline based on the total thermal resistance, blast furnace gas temperature and ambient temperature.

[0012] Preferably, in S1, the method for determining the thermal resistance of convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas is: calculating the convective heat transfer coefficient between the inner wall of the gas pipeline and the blast furnace gas, the thermal resistance of convective heat transfer being the inverse of the convective heat transfer coefficient, and calculating the heat transfer coefficient based on Nusselt's assumptions about the heat transfer process in the condensation stage in the blast furnace gas pipe and a formula after correcting the average heat transfer coefficient.

[0013] Preferably, in said S2, the method for determining the thermal resistance of heat conduction between the gas pipe walls is: calculating the thermal resistance of heat conduction between the gas pipe walls based on the number of layers inside the gas pipe, the diameter of each layer of the pipe wall, the interface temperature between each layer interface and the thermal conductivity coefficient of each layer.

[0014] Preferably, in S3, the method for determining the thermal resistance of the convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline is: calculating the convective heat transfer coefficient from the outside of the gas pipeline to the outer wall of the gas pipeline, and calculating the convective heat transfer coefficient based on the Nusselt number in the convective heat transfer process, the wall thickness of the outer layer of the gas pipeline and the thermal conductivity of the air.

[0015] Preferably, in heat transfer at a fluid boundary surface, the Nusselt number is the ratio of the amount of convective heat to the amount of conductive heat across the boundary.

[0016] Preferably, in said S4, the method for determining the corrosion temperature of the inner wall of the blast furnace gas pipeline is: according to the thermal resistance of the convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas, the thermal resistance of the heat conduction between the gas pipe walls, and the thermal resistance of the convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline, the total thermal resistance of the heat transfer process is calculated, and the corrosion temperature of the inner wall of the blast furnace gas pipeline is calculated in combination with the blast furnace gas temperature and the ambient temperature.

[0017] Compared with related technologies, the method for calculating the inner wall temperature based on the condensation heat transfer process of blast furnace gas pipelines provided by the present invention has the following beneficial effects:

[0018] The present invention provides a method for calculating the inner wall temperature of a blast furnace gas pipeline based on the condensation heat transfer process. The method analyzes the heat transfer coefficient of the condensation stage based on the heat transfer process during the condensation stage within the blast furnace gas pipeline. The method corrects the average heat transfer coefficient of the Nusselt hypothesis for the condensation heat transfer process based on the Nusselt hypothesis, establishing a scientific method for calculating the heat transfer coefficient of the condensation stage within the blast furnace gas pipeline and clarifying the heat transfer coefficient of the condensation heat exchange stage. After determining the heat transfer coefficient of the condensation stage heat transfer process within the gas pipeline, a method for calculating the inner wall temperature of the pipeline is proposed, providing a basis for subsequent analysis of the corrosion temperature of the blast furnace gas pipeline. By calculating the inner wall temperature of the blast furnace gas pipeline, the corrosion temperature of the inner wall of the gas pipeline can be better analyzed, the corrosion condition of the gas pipeline can be further predicted, and the safe transportation of blast furnace gas can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to the present invention;

[0020] Figure 2 This is a physical model of the convection condensation process of wet gas in a horizontal tube in a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to the present invention;

[0021] Figure 3 A schematic diagram of a blast furnace gas pipeline in a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to the present invention;

[0022] Figure 4 This is a table of the values ​​of the constant C and the coefficient n in the correlation formula for large-space natural convection experiments. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Please refer to Figure 1 、 Figure 2 、 Figure 3 and Figure 4 ,in, Figure 1 This is a flow chart of a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to the present invention; Figure 2 This is a physical model of the convection condensation process of wet gas in a horizontal tube in a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline of the present invention. Figure 3 A schematic diagram of a blast furnace gas pipeline in a method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to the present invention; Figure 4 This is a table of values ​​for the constant C and coefficient n in the correlation equation for large-space natural convection experiments. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline includes the following steps:

[0025] S1: calculating the heat resistance of the convection heat exchange between the inner wall of the gas pipeline and the blast furnace gas;

[0026] The determination method of the heat resistance of the convection heat exchange between the inner wall of the gas pipeline and the blast furnace gas is: calculating the convection heat exchange coefficient between the inner wall of the gas pipeline and the blast furnace gas, and the heat resistance of the convection heat exchange is the inverse of the convection heat exchange coefficient. According to the assumptions of Nusselt for the heat transfer process of the blast furnace gas pipeline condensation stage and the formula after correction of the average heat transfer coefficient, the heat transfer coefficient is calculated.

[0027] The heat transfer coefficient of the blast furnace gas pipeline condensation stage is calculated as follows: the heat transfer process of the blast furnace gas pipeline condensation stage is complex, so Nusselt makes the following assumptions: the acceleration of the condensation thin liquid film is not taken into account in the calculation process; the interface is in a saturated temperature state; the influence of supercooling degree is not taken into account; the temperature of the thin liquid film is linearly distributed from the inner wall surface to the gas-liquid interface. The average heat transfer coefficient based on the above assumptions is corrected to obtain the following heat transfer coefficient calculation formula:

[0028]

[0029] wherein λ L represents the thermal conductivity of the condensate, W / (m 2 ·K); ρ L , ρ G are the density of the blast furnace gas condensate and the density of the blast furnace gas, respectively, kg / m 3 ; r, r' are the latent heat of the gas condensate and the corrected latent heat, respectively, N·s / m 2 ; g is the acceleration of gravity, m / s 2 ; c p is the specific heat of the condensate at constant pressure, kJ / kg·K; μ L is the viscosity of the gas condensate, N·s / m 2 ; t s , t w are the blast furnace gas temperature and the pipe wall temperature, respectively, ℃. The values are respectively the thermal conductivity of the condensate λ L 0.599 W / (m 2 ·K), the density of the blast furnace gas condensate ρ L 1.5 kg / m 3 , the density of the blast furnace gas ρ G 1.3 kg / m 3 , the acceleration of gravity g 9.8 m / s 2 , the viscosity of the gas condensate μ L 0.003 N·s / m 2 , the radius of the blast furnace gas containing the protective layer pipeline d4 2.271 m, the blast furnace gas temperature and the pipe wall temperature ts , t w The temperatures are 50℃ and 25℃ respectively, and the latent heat of gas condensate r is 2257.2N·s / m 2 , condensate constant pressure specific heat c p The corrected latent heat r' of the gas condensate is 2296.4 N·s / m 2 The condensation heat transfer coefficient h1' is calculated to be 4.484W / (m 2 ·℃).

[0030] S2: Calculate the thermal resistance of heat conduction between the gas pipe walls;

[0031] The method for determining the thermal resistance of heat conduction between gas pipe walls is as follows: the thermal resistance of heat conduction between gas pipe walls is calculated based on the number of layers inside the gas pipe, the diameter of each layer of pipe wall, the interface temperature between each layer interface and the thermal conductivity of each layer.

[0032] The thermal resistance of the blast furnace gas pipe wall is calculated as follows: If the blast furnace gas pipeline is regarded as a pure carbon steel metal pipeline, the thermal resistance of the blast furnace gas pipeline wall is only the thermal conductivity resistance of the metal carbon steel. However, in actual production, steel companies are aware of the corrosion caused by gas condensate due to temperature drop and convective heat transfer, so they will adopt some insulation measures to slow down the convective heat transfer on the pipeline. Therefore, when studying the overall thermal resistance of the blast furnace gas pipeline wall, the blast furnace gas pipeline is approximately regarded as a pipe wall sleeve with three layers of uniform material, namely the protective layer, the insulation layer, and the pipeline wall. Figure 3 As shown, the heat transfer of the blast furnace gas pipeline can be regarded as the heat transfer of three layers of cylindrical walls. The blast furnace gas flowing in the pipe is at a temperature of T, ℃; the air outside the pipe is free convection, and the temperature is t, ℃. The temperature of the inner wall of the pipe, the interface temperature between the pipe wall and the insulation layer, the interface temperature between the insulation layer and the protective layer, and the edge temperature of the protective layer are t1, t2, t3, and t4, ℃ respectively; the diameter of the pipe wall cavity, the diameter of the pipe wall (including the inner layer), the diameter of the insulation layer (including the inner layer), and the diameter of the protective layer (including the inner layer) are d1, d2, d3, and d4, m respectively. The thermal conductivity coefficients of the pipe wall, insulation layer, and protective layer are λ1, λ2, and λ3, W / (m 2 K). The heat flux of the blast furnace gas pipeline composed of three layers of material is:

[0033]

[0034] According to the definition of thermal resistance, the thermal resistance of the blast furnace gas pipeline composed of three layers of material is:

[0035]

[0036] where r i d iCorresponding radius, m.

[0037] The diameters of the pipe wall cavity, pipe wall (including inner layer), insulation layer (including inner layer), and protective layer (including inner layer) are d1, d2, d3, and d4, respectively, which are 4.5m, 4.52m, 4.54m, and 4.542m. The thermal conductivity coefficients λ1, λ2, and λ3 of the pipe wall, insulation layer, and protective layer are 45W / (m 2 ·K), 0.02W / (m 2 ·K), 0.03W / (m 2 ·K). The thermal resistance of the blast furnace gas pipeline is calculated to be 0.36978℃ / W.

[0038] S3: Calculate the thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline;

[0039] The thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline is determined by calculating the convective heat transfer coefficient from the outside of the gas pipeline to the outer wall of the gas pipeline. The convective heat transfer coefficient is calculated based on the Nu number (in heat transfer at a fluid boundary (surface), the Nusselt number (Nu) is the ratio of convective heat transfer to conductive heat transfer across the boundary), the wall thickness of the outer layer of the gas pipeline, and the thermal conductivity of air.

[0040] Calculation of natural convection heat transfer coefficient outside the blast furnace gas pipe. Considering that the heat transfer outside the blast furnace gas pipe is caused by the flow driven by the uneven temperature field of the fluid itself, the convection heat transfer outside the blast furnace gas pipe is defined as large space natural convection with uniform wall temperature as the boundary condition. In this case, the wall temperature is recorded as t w The ambient temperature (i.e. the fluid temperature not affected by the wall temperature) is t ∞ , and the temperature difference in Newton's cooling law and Graf's number is taken as t w -t ∞ According to heat transfer theory, the large-space natural convection experimental correlation formula widely used in engineering calculations is:

[0041]

[0042] Where, Nu m is the Nu number composed of the average surface heat transfer coefficient, and the subscript m indicates that the qualitative temperature is the average temperature of the boundary layer t m =(t ∞ +t w ) / 2. In the calculation of Nu m Before calculation, the size of Gr should be determined in order to select the appropriate constant C and coefficient n, so the following formula is used for calculation:

[0043]

[0044] Where g is the acceleration due to gravity, m / s 2 ;ν is kinematic viscosity, m 2 / s; l is the characteristic length, m. Δt is t w -t ∞ , considering blast furnace gas as an ideal gas, the volume expansion coefficient α in the Gr number is V =1 / t m The constant C and coefficient n of the horizontal cylinder determined by a large amount of experimental data are shown in Table 1. Therefore, the natural convection heat transfer coefficient h2 of the large space outside the blast furnace gas pipe is:

[0045]

[0046] The acceleration due to gravity g is 9.8 m / s 2 , wall temperature t w The ambient temperature is 25℃, t ∞ At 20°C, the kinematic viscosity ν is 0.00001506m 2 / s, the characteristic length l and d are both 4.542m, and the volume expansion coefficient α V is 0.0444, and the thermal conductivity of air is λ is 0.0259W / (m 2 ·K), the calculated heat transfer coefficient h2 is 7.13302306665549E+93.

[0047] S4: Calculate the corrosion temperature of the inner wall of the blast furnace gas pipeline based on the total thermal resistance, blast furnace gas temperature and ambient temperature.

[0048] The method for calculating the corrosion temperature of the inner wall of the blast furnace gas pipeline is as follows: the total thermal resistance of the heat transfer process is calculated based on the thermal resistance of the convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas, the thermal resistance of the heat conduction between the gas pipe walls, and the thermal resistance of the convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline, and the corrosion temperature of the inner wall of the blast furnace gas pipeline is calculated in combination with the blast furnace gas temperature and the ambient temperature.

[0049] Among them, the calculation formula for the temperature of the inner wall surface of the blast furnace gas pipeline during the condensation convection heat transfer stage is:

[0050]

[0051] The calculation formula of heat flux q' is:

[0052]

[0053] The blast furnace gas temperature T' is 50℃, the natural environment temperature t is 20℃, and the temperature of the inner wall of the blast furnace gas pipeline during the condensation convection heat transfer stage is calculated to be 14.02℃.

[0054] Compared with related technologies, the method for calculating the inner wall temperature based on the condensation heat transfer process of blast furnace gas pipelines provided by the present invention has the following beneficial effects:

[0055] The present invention provides a method for calculating the inner wall temperature of a blast furnace gas pipeline based on the condensation heat transfer process. The method analyzes the heat transfer coefficient of the condensation stage based on the heat transfer process during the condensation stage within the blast furnace gas pipeline. The method corrects the average heat transfer coefficient of the Nusselt hypothesis for the condensation heat transfer process based on the Nusselt hypothesis, establishing a scientific method for calculating the heat transfer coefficient of the condensation stage within the blast furnace gas pipeline and clarifying the heat transfer coefficient of the condensation heat exchange stage. After determining the heat transfer coefficient of the condensation stage heat transfer process within the gas pipeline, a method for calculating the inner wall temperature of the pipeline is proposed, providing a basis for subsequent analysis of the corrosion temperature of the blast furnace gas pipeline. By calculating the inner wall temperature of the blast furnace gas pipeline, the corrosion temperature of the inner wall of the gas pipeline can be better analyzed, the corrosion condition of the gas pipeline can be further predicted, and the safe transportation of blast furnace gas can be ensured.

[0056] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline, characterized in that: The following steps are involved: S1: Calculate the thermal resistance of convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas; S2: Calculate the thermal resistance of heat conduction between the gas pipe walls; S3: Calculate the thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline; S4: Calculate the corrosion temperature of the inner wall of the blast furnace gas pipeline based on the total thermal resistance, blast furnace gas temperature and ambient temperature.

2. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to claim 1, characterized in that: In S1, the method for determining the thermal resistance for convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas is as follows: the convective heat transfer coefficient between the inner wall of the gas pipeline and the blast furnace gas is calculated, where the thermal resistance for convective heat transfer is the inverse of the convective heat transfer coefficient. The heat transfer coefficient is calculated based on Nusselt's assumptions about the heat transfer process during the condensation stage in the blast furnace gas pipeline and a formula that corrects the average heat transfer coefficient.

3. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to claim 1, characterized in that: In S2, the method for determining the thermal resistance of heat conduction between the gas pipe walls is: calculating the thermal resistance of heat conduction between the gas pipe walls based on the number of layers inside the gas pipe, the diameter of each layer of the pipe wall, the interface temperature between each layer interface, and the thermal conductivity coefficient of each layer.

4. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to claim 1, characterized in that: In S3, the method for determining the thermal resistance of the convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline is: calculating the convective heat transfer coefficient from the outside of the gas pipeline to the outer wall of the gas pipeline, and calculating the convective heat transfer coefficient based on the Nusselt number during the convective heat transfer process, the wall thickness of the outer layer of the gas pipeline, and the thermal conductivity of air.

5. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to claim 4, characterized in that: In heat transfer at a fluid boundary surface, the Nusselt number is the ratio of the amount of heat transferred by convection to the amount of heat transferred by conduction across the boundary.

6. The method for calculating the inner wall temperature based on the condensation heat transfer process of a blast furnace gas pipeline according to claim 1, characterized in that: In S4, the method for determining the corrosion temperature of the inner wall of the blast furnace gas pipeline is as follows: the total thermal resistance of the heat transfer process is calculated based on the thermal resistance of convective heat transfer between the inner wall of the gas pipeline and the blast furnace gas, the thermal resistance of heat conduction between the gas pipe walls, and the thermal resistance of convective heat transfer from the outside of the gas pipeline to the outer wall of the gas pipeline, and the corrosion temperature of the inner wall of the blast furnace gas pipeline is calculated in combination with the blast furnace gas temperature and the ambient temperature.

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