Pellet roasting temperature control method based on online process simulation

Abstract

A pellet roasting temperature control method based on online process simulation, the method comprising the following steps: 1) establishing a pellet roasting process simulation model based on the heat and mass balance of the solid phase and the gas phase during the pellet roasting process; 2) inputting the global constant of the model, and performing process simulation on the first drying stage, the second drying stage, the preheating stage, and the roasting stage in sequence; 3) obtaining the pellet temperature simulation value at the end point of the roasting stage, comparing it with the roasting end temperature setting threshold, and using the deviation between the simulation value of the roasting end temperature and the setting threshold to adjust the roasting stage burner gas flow rate, thereby achieving control of the actual roasting temperature of the pellets. The present invention realizes control of the actual roasting temperature of the pellets based on online process simulation, avoiding the error caused by indirect judgment due to the inability to directly measure the roasting temperature of the pellets in the prior art, avoiding the waste of roasting energy, and improving the quality of pellet mineral products.

Description

Technical Field

[0001] The invention relates to a method for controlling the temperature of pellet roasting, and in particular to a method for controlling the temperature of pellet roasting based on online process simulation, and belongs to the field of preparation of raw materials for iron and steel metallurgy. Background Art

[0002] The pellet roasting process not only involves complex heat and mass transfer between the heat carrier and the pellet material layer and grate bed, but is also accompanied by physical and chemical reactions such as free water evaporation and condensation, crystallization water and carbonate decomposition, Fe3O4 and S oxidation, and fixed carbon combustion.

[0003] The roasting of green balls into pellets requires a large amount of heat to heat the pellets to the required temperature, achieve solid consolidation, and obtain pellets with a compressive strength of not less than 2500N to meet the needs of subsequent smelting. The roasting of pellets is carried out in a closed container. Since the roasting temperature is as high as 1250°C and the moving bed is kept in continuous operation, the existing technical means cannot directly measure the temperature of the material layer. It can only indirectly judge whether the material layer has reached the specified roasting temperature based on the exhaust temperature of the roasting section, which often causes the roasting temperature to be too high or too low. Overburning of pellets not only wastes energy, but also leads to a decrease in their metallurgical properties; underburning of pellets leads to their quality failing to meet the requirements.

[0004] The quality of pelletized ore products depends largely on whether the pellets reach the specified roasting temperature at the end of high-temperature roasting. Therefore, how to control the roasting temperature of the pellets is particularly important. Summary of the invention

[0005] In view of the defects existing in the above-mentioned prior art, the present invention proposes a method for controlling the roasting temperature of pellets based on online process simulation. The method establishes a roasting process simulation model, and sequentially simulates each process section in the roasting system to obtain a simulated value of the pellet temperature at the end point of the roasting section, compares the simulated value of the pellet temperature with the ideal roasting end point temperature setting threshold, and uses the deviation between the two to adjust the gas flow rate of the roasting section burner to achieve control of the actual roasting temperature of the pellets. The method avoids the error caused by indirect judgment due to the inability to directly measure the roasting temperature of the pellets in the prior art, thereby avoiding the waste of roasting energy and improving the quality of pellet mineral products.

[0006] According to an embodiment of the present invention, a method for controlling the temperature of pellet roasting based on online process simulation is provided.

[0007] A pellet roasting temperature control method based on online process simulation, the method comprising the following steps:

[0008] 1) Based on the heat and mass balance of the solid phase and the gas phase during the pellet roasting process, a simulation model of the pellet roasting process is established.

[0009] 2) Input the global constants of the model and simulate the process of drying stage 1, drying stage 2, preheating stage and roasting stage in sequence.

[0010] 3) Obtain the simulated value of the pellet temperature at the end point of the roasting section, compare it with the set threshold of the roasting end temperature, and use the deviation between the simulated value of the roasting end temperature and the set threshold to adjust the roasting section burner gas flow rate, thereby achieving control of the actual roasting temperature of the pellets.

[0011] In the present invention, in step 1), the establishment of a pellet roasting process simulation model specifically includes the following sub-steps:

[0012] 101) On the roasting system, a grate bed layer, a bottom material layer, and a green ball layer are arranged in order from bottom to top, and the grate bed layer, the bottom material layer, and the green ball layer form a moving bed. A coordinate system is established along the running direction of the moving bed with time t as the horizontal axis and height y as the vertical axis.

[0013] 102) Grid the moving bed: In the height direction, the same grid density is used for the bed material layer and the raw ball layer, and the grid height is less than or equal to the diameter of the pellets. In the time direction, the step size is set to 1s.

[0014] 103) Based on the heat balance and mass balance, the solid phase energy equation, solid phase mass equation, gas phase energy equation and gas phase mass equation are constructed for each grid respectively, and the Ergen equation is applied to each grid respectively.

[0015] In the present invention, in step 2), the process simulation of a certain process section in the drying stage 1, the drying stage 2, the preheating stage, and the roasting stage is specifically as follows:

[0016] The inlet temperature TnA, exhaust temperature TnB, inlet pressure PnA and exhaust pressure PnB of the process section are detected online to obtain the measured pressure difference ΔPn=PnA-PnB of the process section. The feed of the process section is the pellets output from the previous process section. The pellet temperature and the inlet temperature of the process section are used as initial conditions. The initial porosity ε and the initial gas flow rate Gn of the process section are set. The simulated exhaust temperature TnB' of the process section is calculated by the heat and mass balance equation (i.e., equations 1-4), and the simulated pressure difference ΔPn' of the process section is calculated by the Ergen equation (i.e., equation 5). The deviation dTn=TnB'-TnB between the simulated exhaust temperature TnB' and the measured exhaust temperature TnB of the process section, and the deviation dPn=ΔPn'-ΔPn between the simulated pressure difference ΔPn' and the measured pressure difference ΔPn of the process section are calculated. The temperature deviation and pressure difference deviation of the process section are used as feedback to correct the porosity and gas flow rate, and then the temperature distribution T of the solid phase on the y-axis at the junction of the process section and the next process section is calculated by the heat and mass balance equation. s(t,y), that is, the terminal temperature TnS of the pellets in this process section.

[0017] Wherein: n represents the corresponding nth process stage.

[0018] In the present invention, the temperature deviation and the pressure difference deviation are used as feedback quantities to correct the porosity and the gas flow rate, specifically:

[0019] If dTn∈[-10, 10] and dPn∈[-100, 100], no adjustment is required, and the initial porosity ε and the initial gas flow rate Gn of this process section remain unchanged.

[0020] like and / or The gas flow rate is adjusted by the formula Gn'=Gn*(1-dPn / ΔPn), and / or the porosity is adjusted by the formula ε'=ε*(1-dTn / TnB), so that the adjusted pressure difference deviation dPn∈[-100, 100] and the adjusted temperature deviation dTn∈[-10, 10].

[0021] Where: Gn' represents the adjusted gas flow rate of the nth process stage. ε' represents the adjusted porosity.

[0022] In the present invention, step 3) is specifically:

[0023] According to the process simulation of the roasting stage in step 2), the pellet temperature simulation value T4S at the end point of the roasting stage is obtained. The roasting end temperature setting threshold is T con , calculate the deviation between the simulated value of the roasting end point temperature and the set threshold value ΔT = T4S-T con The initial gas flow rate Q of the roasting stage burner is set, and the roasting end temperature deviation ΔT is used as feedback to adjust the roasting stage burner gas flow rate, thereby obtaining a suitable gas supply and realizing the control of the pellet roasting temperature.

[0024] In the present invention, the roasting end point temperature deviation ΔT is used as a feedback amount to adjust the roasting stage burner gas flow rate, specifically:

[0025] If ΔT∈[-10, 10], no adjustment is required at this time, and the initial gas flow Q of the burner in the roasting section remains unchanged.

[0026] like Then, by the formula Q'=Q*(1-ΔT / T con ) to adjust the burner gas flow rate of the roasting section so that the adjusted ΔT∈[-10,10]. At the same time, ensure that the roasting section is within the adjusted dT4∈[-10,10], dP4∈[-100,100].

[0027] Where: Q' represents the adjusted burner gas flow rate of the roasting section.

[0028] In the present invention, in sub-step 103), the energy and mass equations of the solid phase and the gas phase are specifically:

[0029] Solid phase energy conservation equation:

[0030] Solid mass conservation equation:

[0031] Gas phase energy conservation equation:

[0032] Gas phase mass conservation equation:

[0033] In the above equation: s is the solid phase density, kg / m 3 . C s , C g are the specific heat capacities of the solid and gas phases, kJ / (kg·K). s , T g are the temperatures of the solid phase and the gas phase, K. h is the effective heat transfer coefficient, kJ / (m 2 ·s). A is the heat transfer area, m 2 / m 3 . R i is the rate of reaction i, kg / (m 3 ·s). ΔH i is the enthalpy of reaction i, kJ / kg. α i is the distribution coefficient of the heat of reaction i in the gas phase. j is the density of component j in the pellet, kg / m 3 . G is the gas flow rate, kg / (m 2 ·s) B i is the gaseous reaction product of reaction i.

[0034] In the present invention, in sub-step 103), the Ergen equation is specifically:

[0035]

[0036] In the above equation: ΔPn' is the simulated pressure difference of the nth process section, Pa. H is the height of the material layer, m. ε is the porosity, %. ρ g is the gas density, kg / m 3 μ is the gas dynamic viscosity, kg / (m·s). ω is the gas flow rate, m / s. d is the average diameter of the particles, m. is the shape factor of the particle.

[0037] Preferably, in sub-step 102), in the height direction, the grate bed layer adopts a grid density different from that of the base material layer and the raw ball layer, and the grate bed layer is divided into no less than 4 layers of grids.

[0038] In the present invention, the global constants of the model described in step 2) specifically include: the effective length of the roasting system, the length of each process section in the roasting system, the total thickness of the cloth, the thickness of the base material layer, the thickness of the pellet layer, the operating speed of the roasting system, the amount of green balls fed, the components of each substance in the green balls, and the initial temperature of the green balls.

[0039] Generally speaking, the quality of pellet products depends on whether the pellets reach the specified roasting temperature at the end of high-temperature roasting, so the control of the roasting temperature of the pellets is particularly important. Since the existing technical means cannot directly measure the temperature of the pellets in each process section in the roasting system, it can only be judged indirectly by the gas temperature in the wind box, which often has a certain error, resulting in a waste of roasting energy and causing fluctuations in the quality of the pellet products, resulting in product quality failing to meet the requirements. Based on this, the present invention proposes a method for controlling the roasting temperature of pellets based on online process simulation. The method is based on the heat and mass balance (i.e., heat or energy balance, mass balance) of the solid phase and the gas phase during the roasting process, establishes a simulation model for the roasting process of pellets, and performs process simulation on each process section in the roasting system in turn to obtain a simulated value of the pellet temperature at the end point of the roasting section, compares the simulated value of the pellet temperature with the ideal roasting end point temperature setting threshold, and uses the deviation of the two to adjust the gas flow of the roasting section burner to achieve control of the actual roasting temperature of the pellets. The method performs process simulation through online detection data, thereby achieving the purpose of automatically controlling the pellet roasting temperature, avoiding the error caused by indirect judgment due to the inability to directly measure the pellet roasting temperature in the prior art, thereby avoiding the waste of roasting energy and improving the quality of pelletized mineral products.

[0040] It should be noted that the simulated value of the roasting end temperature (i.e., the simulated value of the pellet temperature at the end point of the roasting section) refers to the temperature of the surface pellets at the end of the roasting section obtained by process simulation. The set threshold of the roasting end temperature refers to the range of surface pellet temperatures determined by the properties of the roasting raw materials and product quality requirements. When the simulated value of the roasting end temperature is within the range of the set threshold, the roasting temperature is appropriate and the gas flow of the roasting section burner does not need to be adjusted. When the simulated value of the roasting end temperature exceeds the range of the set threshold, the roasting temperature is adjusted (increased or decreased) as needed, and fed back to the roasting section burner control system to adjust (increase or decrease) the gas flow of the burner as needed.

[0041] In step 1) of the present invention, the method for establishing a simulation model of the pellet roasting process is:

[0042] 101) On the roasting system, a grate bed layer with air permeability, a bottom material layer, and a green ball layer are arranged in order from bottom to top, and the grate bed layer, the bottom material layer, and the green ball layer form a moving bed. A coordinate system is established along the running direction of the moving bed with time t as the horizontal axis and height y as the vertical axis.

[0043] 102) Grid division of the moving bed: In the height direction, the bed layer and the raw ball layer use the same grid density, and the grid height is less than or equal to the pellet diameter; while the grate bed layer uses a different grid density from the bed layer and the raw ball layer, and the grate bed layer can be divided into no less than 4 layers of grids. In the time direction, the step size is set to 1s.

[0044] When dividing the grids, the present application requires that the grid height of the base material layer and the raw ball layer does not exceed the diameter of the pellets, so as to accurately obtain the temperature distribution of the pellets in the height direction, and then determine the temperature of each layer of pellets. As for the grate bed layer, generally speaking, the thickness of the grate bed layer is about 10 mm, which is relatively close to the diameter of a pellet, but the heat transfer of the grate bars has a greater impact on the thermal balance. Therefore, in order to improve the calculation accuracy, the grate bed layer needs to be divided into several more layers, but too many layers of division will affect the calculation speed of the program. After comprehensive consideration, the grate bed layer can be divided into no less than 4 layers of grids, for example, 4 to 8 layers, preferably 4 to 6 layers. For example, in the height direction, the grate bed layer is divided into 4 layers of grids.

[0045] For the grid with coordinates (t, y) in the moving bed, taking the temperature parameters as an example, the gas phase inlet temperature is Tg(t, y), the outlet temperature is Tg(t, y+1), the solid phase inlet temperature is Ts(t, y), and the outlet temperature is Ts(t+1, y).

[0046] 103) Based on heat balance and mass balance, solid phase energy equation, solid phase mass equation, gas phase energy equation and gas phase mass equation are constructed for each grid. Specifically, they include:

[0047] Solid phase energy conservation equation:

[0048] Solid mass conservation equation:

[0049] Gas phase energy conservation equation:

[0050] Gas phase mass conservation equation:

[0051] In the above equation: s is the solid phase density, kg / m 3 . C s , C g are the specific heat capacities of the solid and gas phases, kJ / (kg·K).s , T g are the temperatures of the solid phase and the gas phase, K. h is the effective heat transfer coefficient, kJ / (m 2 ·s). A is the heat transfer area, m 2 / m 3 . R i is the rate of reaction i, kg / (m 3 ·s). ΔH i is the enthalpy of reaction i, kJ / kg. α i is the distribution coefficient of the heat of reaction i in the gas phase. j is the density of component j in the pellet, kg / m 3 . G is the gas flow rate, kg / (m 2 ·s) B i is the gas reaction product of reaction i. During the whole process of pellet roasting, a series of physical and chemical reactions will occur in the pellet layer. i in the above equations 1-4 represents one of the many reactions. Pellets often include multiple material components. j in the above equations 1-4 represents one of the many components.

[0052] The Ergen equation is applied to each grid separately. The Ergen equation is specifically:

[0053]

[0054] In the above equation: ΔPn' is the simulated pressure difference of the nth process section, Pa. H is the height of the material layer, m. ε is the porosity, %. ρ g is the gas density, kg / m 3 μ is the gas dynamic viscosity, kg / (m·s). ω is the gas flow rate, m / s. d is the average diameter of the particles, m. is the shape factor of the particle.

[0055] For any grid in the moving bed, as long as the inlet parameters such as temperature, density, specific heat capacity, etc. are given, the outlet parameters of the grid can be calculated using equations 1-4, and the outlet parameters of the grid become the inlet parameters of the next grid. The pressure drop of the gas flow through the grid can also be calculated based on the Ergen equation.

[0056] In step 2) of the present invention, the process simulation of the first drying stage, the second drying stage, the preheating stage, and the roasting stage is performed in sequence, which means that after the process simulation model is established, the global constants of the model are input, and the intake parameters and exhaust parameters of the first drying stage (mainly including intake pressure, exhaust pressure, intake temperature, and exhaust temperature) are detected online. Since the feed of the first drying stage is all green balls, the natural temperature of the green balls and the intake temperature of the process stage are used as boundary conditions to simulate the temperature distribution of the pellets in the material layer height direction at the end point of the first drying stage, and use it as the initial condition of the adjacent process stage (i.e., the second drying stage), thereby simulating the temperature of the pellets in the subsequent process stages in sequence. Taking the process simulation of a certain process stage as an example, it is specifically as follows:

[0057] The inlet temperature TnA, exhaust temperature TnB, inlet pressure PnA and exhaust pressure PnB of the process section are detected online to obtain the measured pressure difference ΔPn=PnA-PnB of the process section. Among them, when the process section adopts blast operation (for example, drying stage 1, i.e. blast drying stage), the inlet temperature of the process section is the gas temperature in the bellows, the exhaust temperature is the gas temperature in the furnace hood, the inlet pressure is the pressure in the bellows, and the exhaust pressure is the pressure in the furnace hood. When the process section adopts exhaust operation (for example, drying stage 2, preheating stage, roasting stage), the inlet temperature of the process section is the gas temperature in the furnace hood, the exhaust temperature is the gas temperature in the bellows, the inlet pressure is the pressure in the furnace hood, and the exhaust pressure is the pressure in the bellows.

[0058] The feedstock of this process section is the pellets output from the previous process section. The pellet temperature and the inlet temperature of this process section are used as the initial conditions (when this process section is a drying section, the natural temperature of the raw pellets is used as the initial condition). The initial porosity ε and the initial gas flow rate Gn of this process section are set. The multiple partial differential equations of the energy and mass conservation model (i.e., equations 1-4) are iteratively calculated by the finite element method or the difference method through a computer program to obtain the simulated exhaust temperature TnB' of this process section. At the same time, the simulated pressure difference ΔPn' of this process section is calculated by the Ergen equation (i.e., equation 5) (the simulated pressure difference ΔPn' here is the pressure drop of multiple grids in the height direction of the material layer when the airflow passes through). The deviation dTn=TnB'-TnB between the simulated exhaust temperature TnB' and the measured exhaust temperature TnB of this process section, and the deviation dPn=ΔPn'-ΔPn between the simulated pressure difference ΔPn' and the measured pressure difference ΔPn are calculated. The temperature deviation and pressure difference deviation of the process section are used as feedback to correct the porosity and gas flow rate. Then, the multiple partial differential equations of the energy and mass conservation model (i.e., equations 1-4) are iteratively calculated by the computer program using the finite element method or the difference method to obtain the temperature distribution T of the solid phase on the y-axis at the junction of the process section and the next process section. s(t,y), that is, the end temperature TnS of the pellets in this process section is obtained. When the process simulation reaches the roasting section, the temperature simulation value of the pellets at the end point of the roasting section can be obtained.

[0059] Where: n represents the corresponding nth process section. n = 1, represents the first process section, i.e. drying section 1. n = 2, represents the second process section, i.e. drying section 2. n = 3, represents the third process section, i.e. preheating section. n = 4, represents the fourth process section, i.e. roasting section.

[0060] It should be noted that the pellet temperature simulated at the end point of each process section is actually the temperature distribution of the pellet at that position in the direction of the material layer height, and the temperature of the pellet in the direction of the material layer height has a gradient, that is, the end point pellet temperature of each process section is not a fixed value. Therefore, this application defines the simulated value of the roasting end point temperature as the temperature of the surface pellet at the end of the roasting section.

[0061] The porosity described in this application refers to the ratio of the pore volume to the total volume in the material layer, and the porosity is a parameter that is difficult to measure accurately. The gas flow rate of the process section refers to the heat carrier flow rate entering the process section. When the process section adopts the blast operation, the heat carrier passes through the moving bed from bottom to top, and conducts convection heat transfer with the grate bed layer, the bottom material layer, and the pellet layer; when the process section adopts the exhaust operation, the heat carrier passes through the moving bed from top to bottom, and conducts convection heat transfer with the pellet layer, the bottom material layer, and the grate bed layer; wherein, the physical and chemical reactions during the roasting process mainly occur in the pellet layer. The present invention first sets the initial porosity and the initial gas flow rate of the corresponding process section, and then corrects the porosity by the deviation between the simulated exhaust temperature of the process section and the measured exhaust temperature, and corrects the gas flow rate by the deviation between the simulated pressure difference of the process section and the measured pressure difference, thereby obtaining the porosity and gas flow rate under the conditions of the measured exhaust temperature and the measured pressure difference, and also makes the online process simulation of the present application more accurate. Then, the temperature distribution of the pellets on the y-axis at the junction of the process section and the next process section can be calculated, that is, the terminal temperature of the pellets in the process section is obtained, and the pellet temperature is used as the initial condition of the next process section.

[0062] In the present invention, the temperature deviation and the pressure difference deviation (i.e., the deviation between the simulated value and the measured value) are used as feedback quantities to correct the porosity and gas flow rate, specifically:

[0063] If the temperature deviation dTn∈[-10, 10] and the pressure difference deviation dPn∈[-100, 100], that is, the temperature deviation and the pressure difference deviation are small and still within the acceptable range, no adjustment is required at this time. Keep the initial porosity ε and the initial gas flow rate Gn of this process section unchanged and continue to simulate the roasting process.

[0064] like That is, dPn>100 or dPn<-100, then the gas flow rate is adjusted by the formula Gn'=Gn*(1-dPn / ΔPn); if That is, dTn>10 or dTn<-10, at this time, the porosity is adjusted by the formula ε'=ε*(1-dTn / TnB); the final adjusted pressure difference deviation must satisfy dPn∈[-100,100], and the adjusted temperature deviation must satisfy dTn∈[-10,10]. Where: Gn' represents the adjusted gas flow rate of the nth process section. ε' represents the adjusted porosity.

[0065] In step 3) of the present invention, according to the process simulation of the roasting stage in the above step 2), the pellet temperature simulation value T4S at the end point of the roasting stage is obtained. The roasting end temperature setting threshold is T con , calculate the deviation between the simulated value of the roasting end point temperature and the set threshold value ΔT = T4S-T con The initial gas flow rate Q of the roasting stage burner is set, and the roasting end temperature deviation ΔT is used as feedback to adjust the roasting stage burner gas flow rate, thereby obtaining a suitable gas supply and realizing the control of the pellet roasting temperature.

[0066] The roasting end point temperature deviation ΔT is used as feedback to adjust the roasting stage burner gas flow rate, specifically:

[0067] If ΔT∈[-10, 10], that is, the deviation between the simulated value of the roasting end temperature and the set threshold value is small, no adjustment is required at this time, and the initial gas flow Q of the roasting section burner can be kept unchanged.

[0068] like That is, ΔT>10 or ΔT<-10, at this time, the formula Q'=Q*(1-ΔT / T con ) to adjust the gas flow of the roasting section burner. When the analog value of the roasting end temperature is lower than the set threshold, the roasting temperature needs to be increased, that is, it is fed back to the roasting section burner control system to increase the gas flow; when the analog value of the roasting end temperature is higher than the set threshold, the roasting temperature needs to be lowered, that is, it is fed back to the roasting section burner control system to reduce the gas flow; until the adjusted analog value of the roasting end temperature is within the range of the set threshold, that is, ΔT∈[-10, 10]. It should be noted that in the process of adjusting the gas flow of the roasting section burner, the intake temperature T4A, exhaust temperature T4B, intake pressure P4A and exhaust pressure P4B of the roasting section detected online in real time will also change accordingly. Therefore, while adjusting the burner gas flow, it is also necessary to ensure that the temperature deviation and pressure difference deviation of the roasting section after adjustment meet the requirements, that is, dT4∈[-10, 10], dP4∈[-100, 100].

[0069] In this application, the set threshold of the roasting end temperature is the surface pellet temperature range determined by the roasting raw material properties and product quality requirements, that is, the set threshold of the roasting end temperature is related to the roasting raw material. The inventor of this application has obtained suitable pellet roasting end temperatures for different types of ores through multiple experiments and relevant experience, as shown in Table 1 below.

[0070] Table 1 Suitable pellet roasting end point temperature T for different minerals con

[0071] Magnetite proportion, % Hematite ratio, % <![CDATA[T con ,℃]]> 0 100 1300 10 90 1290 20 80 1280 30 70 1270 40 60 1260 50 50 1250 60 40 1240 70 30 1230 80 20 1220 90 10 1210 100 0 1200

[0072] Note: Generally speaking, the threshold is set as a temperature range, and Table 1 lists only one suitable temperature value within the range for different types of minerals.

[0073] Compared with the prior art, the present invention has the following beneficial technical effects:

[0074] 1. The present invention establishes a simulation model for the pellet roasting process, and simulates each process section in the roasting system in turn to obtain a simulated value of the pellet temperature at the end point of the roasting section, compares the simulated value of the pellet temperature with the ideal roasting end point temperature setting threshold, and uses the deviation between the two to adjust the gas flow rate of the roasting section burner to achieve control of the actual roasting temperature of the pellets, thereby solving the problem that the existing technical means cannot directly measure the roasting temperature of the pellets.

[0075] 2. The present invention realizes the control of the actual roasting temperature of the pellets based on online process simulation, avoiding the error caused by indirect judgment due to the inability to directly measure the roasting temperature of the pellets in the prior art, thereby avoiding the waste of roasting energy and improving the quality of pelletized mineral products.

[0076] 3. The present invention focuses on the effect of the porosity of the material layer on the pressure drop of the material layer, sets the porosity of the material layer and the gas flow rate of each process section, and then corrects the porosity by the deviation between the simulated exhaust temperature and the actual exhaust temperature of the corresponding process section, and corrects the gas flow rate by the deviation between the simulated pressure difference and the actual pressure difference, thereby obtaining the porosity and gas flow rate that meet the conditions of the actual exhaust temperature and the actual pressure difference, and thus being able to more accurately simulate the pellet temperature of each process section, and also making the online process simulation of the present application more accurate, so as to guide production practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 It is a flow chart of the pellet roasting temperature control method based on online process simulation of the present invention;

[0078] Figure 2 It is a flow chart of the process simulation for a certain process section of the roasting system in the present invention;

[0079] Figure 3It is a structural schematic diagram of each process section of the roasting system in the present invention;

[0080] Figure 4 is a cross-sectional view of the moving bed in the present invention;

[0081] Figure 5 It is a schematic diagram of the solid phase and gas phase trends in a certain process section of the present invention;

[0082] Figure 6 A schematic diagram of meshing the moving bed and establishing a coordinate system in the present invention;

[0083] Figure 7 Schematic diagram of coordinates of a grid in the present invention. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0085] According to an embodiment of the present invention, a method for controlling the temperature of pellet roasting based on online process simulation is provided.

[0086] A pellet roasting temperature control method based on online process simulation, the method comprising the following steps:

[0087] 1) Based on the heat and mass balance of the solid phase and the gas phase during the pellet roasting process, a simulation model of the pellet roasting process is established.

[0088] 2) Input the global constants of the model and simulate the process of drying stage 1, drying stage 2, preheating stage and roasting stage in sequence.

[0089] 3) Obtain the simulated value of the pellet temperature at the end point of the roasting section, compare it with the set threshold of the roasting end temperature, and use the deviation between the simulated value of the roasting end temperature and the set threshold to adjust the roasting section burner gas flow rate, thereby achieving control of the actual roasting temperature of the pellets.

[0090] In the present invention, in step 1), the establishment of a pellet roasting process simulation model specifically includes the following sub-steps:

[0091] 101) On the roasting system, a grate bed layer, a bottom material layer, and a green ball layer are arranged in order from bottom to top, and the grate bed layer, the bottom material layer, and the green ball layer form a moving bed. A coordinate system is established along the running direction of the moving bed with time t as the horizontal axis and height y as the vertical axis.

[0092] 102) Grid the moving bed: In the height direction, the same grid density is used for the bed material layer and the raw ball layer, and the grid height is less than or equal to the diameter of the pellets. In the time direction, the step size is set to 1s.

[0093] 103) Based on the heat balance and mass balance, the solid phase energy equation, solid phase mass equation, gas phase energy equation and gas phase mass equation are constructed for each grid respectively, and the Ergen equation is applied to each grid respectively.

[0094] In the present invention, in step 2), the process simulation of a certain process section in the drying stage 1, the drying stage 2, the preheating stage, and the roasting stage is specifically as follows:

[0095] The inlet temperature TnA, exhaust temperature TnB, inlet pressure PnA and exhaust pressure PnB of the process section are detected online to obtain the measured pressure difference ΔPn=PnA-PnB of the process section. The feed of the process section is the pellets output from the previous process section. The pellet temperature and the inlet temperature of the process section are used as the initial conditions. The initial porosity ε and the initial gas flow rate Gn of the process section are set. The simulated exhaust temperature TnB' of the process section is calculated by the heat and mass balance equation, and the simulated pressure difference ΔPn' of the process section is calculated by the Ergen equation. The deviation dTn=TnB'-TnB between the simulated exhaust temperature TnB' and the measured exhaust temperature TnB of the process section, and the deviation dPn=ΔPn'-ΔPn between the simulated pressure difference ΔPn' and the measured pressure difference ΔPn of the process section are calculated. The temperature deviation and pressure difference deviation of the process section are used as feedback to correct the porosity and gas flow rate, and then the temperature distribution T of the solid phase on the y-axis at the junction of the process section and the next process section is calculated by the heat and mass balance equation. s (t,y), that is, the terminal temperature TnS of the pellets in this process section.

[0096] Wherein: n represents the corresponding nth process section.

[0097] In the present invention, the temperature deviation and the pressure difference deviation are used as feedback quantities to correct the porosity and the gas flow rate, specifically:

[0098] If dTn∈[-10, 10] and dPn∈[-100, 100], no adjustment is required, and the initial porosity ε and the initial gas flow rate Gn of this process section remain unchanged.

[0099] like and / or The gas flow rate is adjusted by the formula Gn'=Gn*(1-dPn / ΔPn), and / or the porosity is adjusted by the formula ε'=ε*(1-dTn / TnB), so that the adjusted pressure difference deviation dPn∈[-100, 100] and the adjusted temperature deviation dTn∈[-10, 10].

[0100] Where: Gn' represents the adjusted gas flow rate of the nth process stage. ε' represents the adjusted porosity.

[0101] In the present invention, step 3) is specifically:

[0102] According to the process simulation of the roasting stage in step 2), the pellet temperature simulation value T4S at the end point of the roasting stage is obtained. The roasting end temperature setting threshold is T con , calculate the deviation between the simulated value of the roasting end point temperature and the set threshold value ΔT = T4S-T con The initial gas flow rate Q of the roasting stage burner is set, and the roasting end temperature deviation ΔT is used as feedback to adjust the roasting stage burner gas flow rate, thereby obtaining a suitable gas supply and realizing the control of the pellet roasting temperature.

[0103] In the present invention, the roasting end point temperature deviation ΔT is used as a feedback amount to adjust the roasting stage burner gas flow rate, specifically:

[0104] If ΔT∈[-10, 10], no adjustment is required at this time, and the initial gas flow Q of the burner in the roasting section remains unchanged.

[0105] like Then, by the formula Q'=Q*(1-ΔT / T con ) to adjust the burner gas flow rate of the roasting section so that the adjusted ΔT∈[-10,10]. At the same time, ensure that the roasting section is within the adjusted dT4∈[-10,10], dP4∈[-100,100].

[0106] Where: Q' represents the adjusted burner gas flow rate of the roasting section.

[0107] In the present invention, in sub-step 103), the energy and mass equations of the solid phase and the gas phase are specifically:

[0108] Solid phase energy conservation equation:

[0109] Solid mass conservation equation:

[0110] Gas phase energy conservation equation:

[0111] Gas phase mass conservation equation:

[0112] In the above equation: s is the solid phase density, kg / m 3 . C s , C g are the specific heat capacities of the solid and gas phases, kJ / (kg·K). s , T g are the temperatures of the solid phase and the gas phase, K. h is the effective heat transfer coefficient, kJ / (m 2 ·s). A is the heat transfer area, m 2 / m3 . R i is the rate of reaction i, kg / (m 3 ·s). ΔH i is the enthalpy of reaction i, kJ / kg. α i is the distribution coefficient of the heat of reaction i in the gas phase. j is the density of component j in the pellet, kg / m 3 . G is the gas flow rate, kg / (m 2 ·s) B i is the gaseous reaction product of reaction i.

[0113] In the present invention, in sub-step 103), the Ergen equation is specifically:

[0114]

[0115] In the above equation: ΔPn' is the simulated pressure difference of the nth process section, Pa. H is the height of the material layer, m. ε is the porosity, %. ρ g is the gas density, kg / m 3 μ is the gas dynamic viscosity, kg / (m·s). ω is the gas flow rate, m / s. d is the average diameter of the particles, m. is the shape factor of the particle.

[0116] Preferably, in sub-step 102), in the height direction, the grate bed layer adopts a grid density different from that of the base material layer and the raw ball layer, and the grate bed layer is divided into no less than 4 layers of grids.

[0117] In the present invention, the global constants of the model described in step 2) specifically include: the effective length of the roasting system, the length of each process section in the roasting system, the total thickness of the cloth, the thickness of the base material layer, the thickness of the pellet layer, the operating speed of the roasting system, the amount of green balls fed, the components of each substance in the green balls, and the initial temperature of the green balls.

[0118] Example 1

[0119] Taking the pellet production of 400Mt / a belt roaster as an example, the effective length of the roaster is 126m (section I: 9m; section II: 15m; section III: 18m; section IV: 30m; section V: 9m; section VI: 33m; section VII: 12m), the total thickness of the cloth is 400mm, the bottom material layer height is 100mm, the raw ball layer height is 300mm, and the roaster running speed is 4.0m / min. The above parameters are used as global constants of the model. In the roasting section, the burner gas volume Q=35m 3 The temperatures and pressures of the furnace hood and wind box of each section measured at 1000 rpm and 2000 rpm are shown in Table 2 below.

[0120] Table 2 Measured temperature and pressure of furnace hood and wind box in each process section

[0121] Section I Section II Segment III Segment IV Furnace hood temperature, °C 100 360 900 1250 Bellows temperature, ℃ 260 115 200 450 Furnace hood pressure, Pa -50 -50 -50 -50 Bellows pressure, Pa 3950 -4250 -4250 -4550

[0122] Note: For the process section with blast operation, the intake temperature is the gas temperature in the bellows, the exhaust temperature is the gas temperature in the furnace hood, the intake pressure is the pressure in the bellows, and the exhaust pressure is the pressure in the furnace hood; for the process section with exhaust operation, the intake temperature is the gas temperature in the furnace hood, the exhaust temperature is the gas temperature in the bellows, the intake pressure is the pressure in the furnace hood, and the exhaust pressure is the pressure in the bellows.

[0123] Input the global constants of the model, and the iron ore raw materials are composed of 50% each of magnetite and hematite. First simulate stage I (i.e., drying stage), with boundary conditions T1A = 260°C, T1B = 100°C, P1A = 3950Pa, P1B = -50Pa, ΔP1 = P1A-P1B = 4000Pa, at which time the feed is all green balls, T0S = 25°C. Set the initial porosity ε = 0.5, the initial gas flow G1 = 6*10 4 m 3 / h, the simulated exhaust temperature T1B' = 102°C of the process section is calculated by the computer program through the difference method of multiple partial differential equations of the energy and mass conservation model (i.e., heat and mass balance equations 1-4), and the simulated pressure difference ΔP1' = 4285Pa of the process section is calculated by the Ergen equation (i.e., equation 5). At this time, dP1 = ΔP1'-ΔP1 = 285Pa, and the gas flow rate is adjusted to G1' = 6*10 4 *(1-285 / 4000)=5.57*10 4 m 3 / h, and continue to calculate T1B'=84℃, ΔP1'=3885Pa. At this time, dP1=ΔP1'-ΔP1=-115Pa, and the gas flow rate is adjusted to G1'=5.57*10 4 *(1+115 / 4000)=5.73*10 4 m 3 / h, and then we can calculate T1B'=88℃, ΔP1'=3980Pa. At this time, dP1=ΔP1'-ΔP1=-20Pa, which satisfies dP1∈[-100,100], but dT1=T1B'–T1B=-12℃, and adjust the porosity to ε'=0.5*(1+12 / 100)=0.56, and then we can calculate T1B'=112℃, ΔP1'=4035Pa. At this time, dP1=ΔP1'-ΔP1=35Pa, which satisfies dP1∈[-100,100], but dT1=T1B'–T1B=12℃, and adjust the porosity to ε'=0.56*(1-12 / 100)=0.49, and then we can calculate T1B'=96℃, ΔP1'=3970Pa. At this time, dP1=ΔP1'-ΔP1=-30Pa, satisfying dP1∈[-100, 100], dT1=T1B'–T1B=-4℃, satisfying dT1∈[-10, 10], and jumping out of the loop. Then, the multiple partial differential equations of the energy and mass conservation model (i.e., heat and mass balance equations 1-4) are iteratively calculated by the computer program using the difference method to obtain the temperature distribution of the solid phase on the y-axis at the junction of sections I and II, that is, the temperature distribution of the pellets in the material layer height direction at the end position of section I.

[0124] Continue to simulate stage II (i.e. drying stage II), boundary conditions T2A = 360°C, T2B = 115°C, P2A = -50Pa, P2B = -4250Pa, ΔP2 = P2A-P2B = 4200Pa, and the feed material is the ball output from stage I. Set the initial porosity ε = 0.5, the initial gas flow rate G2 = 8*10 4 m 3 / h, the simulated exhaust temperature T2B' of this process section is calculated by the heat and mass balance equation to be 110°C, and the simulated pressure difference ΔP2' of this process section is calculated by the Ergen equation to be 4085Pa. At this time, dP2 = ΔP2'-ΔP2 = -115Pa, and the gas flow rate is adjusted to G2' = 8*10 4 *(1+115 / 4200)=8.22*10 4 m 3 / h, continue to calculate T2B'=127℃, ΔP2'=4225Pa. At this time, dP2=ΔP2'-ΔP2=25Pa, satisfying dP2∈[-100,100], but dT2=T2B'–T2B=12℃, adjust the porosity to ε'=0.5*(1-12 / 115)=0.45, continue to calculate T2B'=120℃, ΔP2'=4180Pa. At this time, dP2=ΔP2'-ΔP2=-20Pa, satisfying dP2∈[-100,100], dT2=T2B'–T2B=5℃, satisfying dT2∈[-10,10], jump out of the loop, and then calculate the temperature distribution of the solid phase on the y-axis at the junction of section II and section III through the heat and mass balance equation, that is, the temperature distribution of the pellets in the material layer height direction at the end position of section II.

[0125] Continue to simulate stage III (i.e. preheating stage), boundary conditions T3A = 900 °C, T3B = 200 °C, P3A = -50Pa, P3B = -4250Pa, ΔP3 = P3A-P3B = 4200Pa, at this time the feed material is the ball output from stage II. Set the initial porosity ε = 0.5, gas flow rate G3 = 10*10 4 m 3 / h, the simulated exhaust temperature T3B'=170℃ of this process section is calculated by the heat and mass balance equation, and the simulated pressure difference ΔP3'=4125Pa of this process section is calculated by the Ergen equation. At this time, dP3=ΔP3'-ΔP3=-75Pa, which satisfies dP3∈[-100,100], but dT3=T3B'–T3B=-30℃, the porosity is adjusted to ε'=0.5*(1+30 / 200)=0.58, and T3B'=215℃, ΔP3'=4050Pa are calculated. At this time, dP3=ΔP3'-ΔP3=-150Pa, and the gas flow rate is adjusted to G3'=10*10 4 *(1+150 / 4200)=10.36*10 4 m 3 / h, and then T3B'=220℃, ΔP3'=4250Pa. At this time, dP3=ΔP3'-ΔP3=50Pa, which satisfies dP3∈[-100,100], but dT3=T3B'–T3B=20℃, and the porosity is adjusted to ε'=0.58*(1-20 / 200)=0.52, and then T3B'=202℃, ΔP3'=4180Pa are calculated. At this time, dP3=ΔP3'-ΔP3=-20Pa, satisfying dP3∈[-100, 100], dT3=T3B'–T3B=2℃, satisfying dT3∈[-10, 10], and jumping out of the loop. Then, the temperature distribution of the solid phase on the y-axis at the junction of sections III and IV is calculated through the heat and mass balance equation, that is, the temperature distribution of the pellets in the material layer height direction at the end position of section III is obtained.

[0126] Continue to simulate stage IV (i.e. roasting stage), boundary conditions T4A = 1250℃, T4B = 450℃, P4A = -50Pa, P4B = -4550Pa, ΔP4 = P4A-P4B = 4500Pa, and the feed material is the ball output from stage III. Set the initial porosity ε = 0.5, the initial gas flow rate G4 = 180*10 4 m 3 / h, the simulated exhaust temperature T4B'=455℃ of this process section is calculated by the heat and mass balance equation, and the simulated pressure difference ΔP4'=4450Pa of this process section is calculated by the Ergen equation. At this time, dP4=ΔP4'-ΔP4=-50Pa, satisfying dP4∈[-100,100], dT4=T4B'–T4B=5℃, satisfying dT4∈[-10,10], and then the temperature simulation value T4S=1220℃ of the surface pellets at the end point of the roasting section is calculated by the heat and mass balance equation. As can be seen from Table 1, under the raw material conditions of 50% magnetite + 50% hematite, the appropriate roasting end temperature T con is 1250℃, that is, ΔT=T4S-T con =-30℃, adjust the gas volume of the roasting section burner to Q'=35*(1+30 / 1250)=35.84m 3 / t. At this time, the measured values ​​are T4A=1270℃, T4B=460℃, P4A=-50Pa, P4B=-4550Pa, ΔP4=P4A-P4B=4500Pa, and the initial values ​​of porosity ε and gas flow rate G4 are kept unchanged. T4B'=465℃, ΔP4'=4450Pa are calculated. At this time, dP4=ΔP4'-ΔP4=-50Pa, satisfying dP4∈[-100,100], dT4=T4B'–T4B=5℃, satisfying dT4∈[-10,10]. Then, the simulated value of the end temperature of the pellet roasting, T4S=1245℃, is calculated by the heat and mass balance equation, satisfying ΔT=T4S-T con∈[-10, 10], jump out of the loop calculation, and the optimal gas supply for the roasting section is 35.84m 3 / t.

Claims

1. A pellet roasting temperature control method based on online process simulation, the method comprising the following steps: 1) Based on the heat and mass balance of the solid phase and the gas phase during the pellet roasting process, a simulation model of the pellet roasting process is established; specifically: 101) On the roasting system, a grate bed layer, a bottom material layer, and a raw ball layer are arranged in sequence from bottom to top, and the grate bed layer, the bottom material layer, and the raw ball layer form a moving bed; along the running direction of the moving bed, a coordinate system with time t as the horizontal axis and height y as the vertical axis is established; 102) The moving bed is divided into grids: in the height direction, the bottom material layer and the raw ball layer use the same grid density, and the grid height is less than or equal to the pellet diameter; in the time direction, the step size is set to 1s; 103) Based on the heat balance and mass balance, the solid phase energy equation, solid phase mass equation, gas phase energy equation and gas phase mass equation are constructed for each grid, and the Ergen equation is applied to each grid; the Ergen equation is specifically: In the above equation: ΔPn' is the simulated pressure difference of the nth process section, Pa; H is the height of the material layer, m; ε is the porosity, %; ρ g is the gas density, kg / m 3 ; μ is the gas dynamic viscosity, kg / (m·s); ω is the gas flow rate, m / s; d is the average diameter of the particles, m; is the shape factor of the particle; 2) Input the global constants of the model, and simulate the process of the first drying stage, the second drying stage, the preheating stage, and the roasting stage in turn; specifically: detect the inlet temperature TnA, the exhaust temperature TnB, the inlet pressure PnA, and the exhaust pressure PnB of the process stage online, and obtain the measured pressure difference ΔPn=PnA-PnB of the process stage; the feed of the process stage is the pellets output from the previous process stage, and the pellet temperature and the inlet temperature of the process stage are used as the initial conditions, and the initial porosity ε and the initial gas flow rate Gn of the process stage are set, and the process stage is calculated by the heat and mass balance equation. The simulated exhaust temperature TnB' of the process section is calculated, and the simulated pressure difference ΔPn' of the process section is calculated by the Ergen equation; the deviation dTn=TnB'-TnB between the simulated exhaust temperature TnB' of the process section and the measured exhaust temperature TnB, and the deviation dPn=ΔPn'-ΔPn between the simulated pressure difference ΔPn' and the measured pressure difference ΔPn of the process section are calculated; the temperature deviation and the pressure difference deviation of the process section are used as feedback quantities to correct the porosity and gas flow rate, and then the temperature distribution T of the solid phase on the y-axis at the junction of the process section and the next process section is calculated by the heat and mass balance equation. s (t,y), that is, the final temperature TnS of the pellets in this process section; where n represents the corresponding nth process section; 3) According to the process simulation of the roasting section in step 2), the pellet temperature simulation value T4S at the end point of the roasting section is obtained; the roasting end point temperature setting threshold is T con , calculate the deviation between the simulated value of the roasting end point temperature and the set threshold value ΔT = T4S-T con ; Set the initial gas flow Q of the roasting section burner, and use the roasting end temperature deviation ΔT as feedback to adjust the roasting section burner gas flow, so as to obtain the appropriate gas supply and realize the control of the pellet roasting temperature.

2. The pellet roasting temperature control method according to claim 1, characterized in that: The temperature deviation and the pressure difference deviation are used as feedback quantities to correct the porosity and the gas flow rate, specifically: If dTn∈[-10,10], At this time, no adjustment is required, and the initial porosity ε and the initial gas flow rate Gn of this process section are kept unchanged; like and / or The gas flow rate is adjusted by the formula Gn'=Gn*(1-dPn / ΔPn), and / or the porosity is adjusted by the formula ε'=ε*(1-dTn / TnB), so that the adjusted pressure difference deviation dPn∈[-100, 100] and the adjusted temperature deviation dTn∈[-10, 10]; Where: Gn' represents the adjusted gas flow rate of the nth process stage; ε' represents the adjusted porosity.

3. The pellet roasting temperature control method according to claim 1, characterized in that: The roasting end point temperature deviation ΔT is used as a feedback amount to adjust the roasting section burner gas flow rate, specifically: If ΔT∈[-10, 10], no adjustment is required at this time, and the initial gas flow rate Q of the burner in the roasting section remains unchanged; like Then, by the formula Q'=Q*(1-ΔT / T con ) to adjust the burner gas flow rate of the roasting section so that the adjusted ΔT∈[-10, 10]; at the same time, ensure that the roasting section is within the adjusted dT4∈[-10, 10], dP4∈[-100, 100]; Where: Q' represents the adjusted burner gas flow rate of the roasting section.

4. The method for controlling the temperature of pellet roasting according to any one of claims 1 to 3, characterized in that: In sub-step 103), the energy and mass equations of the solid phase and the gas phase are specifically: Solid phase energy conservation equation: Solid mass conservation equation: Gas phase energy conservation equation: Gas phase mass conservation equation: In the above equation: s is the solid phase density, kg / m 3 ; C s , C g are the specific heat capacities of the solid and gas phases, kJ / (kg·K); T s 、T g are the temperatures of the solid phase and the gas phase, K; h is the effective heat transfer coefficient, kJ / (m 2 ·s); A is the heat transfer area, m 2 / m 3 ; R i is the rate of reaction i, kg / (m 3 ·s); ΔH i is the enthalpy of reaction i, kJ / kg; α i is the distribution coefficient of the reaction heat of reaction i in the gas phase; w j is the density of component j in the pellet, kg / m 3 ; G is gas flow rate, kg / (m 2 ·s); B i is the gaseous reaction product of reaction i.

5. The method for controlling the temperature of pellet roasting according to any one of claims 1 to 3, characterized in that: In sub-step 102), in the height direction, the grate bed layer adopts a grid density different from that of the base material layer and the raw ball layer, and the grate bed layer is divided into no less than 4 layers of grids.

6. The method for controlling the temperature of pellet roasting according to any one of claims 1 to 3, characterized in that: The global constants of the model described in step 2) specifically include: the effective length of the roasting system, the length of each process section in the roasting system, the total thickness of the material, the thickness of the base material layer, the thickness of the pellet layer, the operating speed of the roasting system, the amount of raw balls fed, the composition of each substance in the raw balls, and the initial temperature of the raw balls.

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