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High temperature liquid flow detection system and its application in zinc distillation

in the smelting process of non-ferrous metals, the flow of metal liquid is a very important process parameter. For example, in the process of zinc distillation, the stability of liquid zinc flow directly affects the life of the distillation tower, and has a great impact on the purity of refined zinc and the recovery rate of valuable metals. Therefore, using reasonable detection means to accurately detect the flow of molten zinc has become an urgent problem for zinc smelters. However, in actual production, the temperature of molten zinc is very high (generally between 600 ~ 650 ℃) and has strong corrosivity, so it is impossible to detect its flow with a general flowmeter. Although many high-temperature flow meters have come out, there is no report of instruments that can detect fluid flow above 600 ℃. Soft sensing technology is to detect those important variables that are difficult to detect directly by means of software. Its basic principle is to select a group of secondary variables that are easy to detect in industry and closely related to the primary variable (i.e. the variable to be measured) according to some optimal criteria, and realize the estimation of the dominant variable by using computer software by constructing a certain numerical relationship. At present, people have conducted extensive research on soft sensing technology and achieved great results [2 ~ 4]. In this paper, a method of indirect flow measurement, weighing method, is proposed by using soft sensing technology. Based on the basic principle of orifice outflow in fluid mechanics, it analyzes the main factor affecting the flow - the influence of liquid level height (i.e. liquid weight) on the flow; Through the orifice outflow test, the flow values under different weights are obtained, and then the mathematical model between flow and weight is established by using the least square method. Finally, the actual flow is calculated by the weight value detected by the load cell. 1 flow detection principle in order to detect the flow of molten zinc from the smelting furnace into the rectification tower, a transitional square launder is added between the smelting furnace and the rectification tower. The molten zinc flows into the launder from the smelting furnace, and then flows out of a round hole on its side wall to the rectification tower. In this way, the weight of molten zinc flowing out of the round hole per unit time is the flow of molten zinc to be detected. The liquid zinc flows out of the round hole of the launder. From the point of view of hydromechanics, it is actually the flow out of the orifice. 1.1 basic theory of orifice outflow liquid outflow through orifice is a widely used practical problem, and its basic principle can be shown in Figure 1 [1]. Under the action of gravity, the liquid in the container flows out of the small hole on its side wall. According to the theory of fluid mechanics, the volume flow at this time can be expressed by formula (1): in the formula, CD represents the flow coefficient, a represents the area of the small hole, G represents the gravitational acceleration, and H represents the liquid level height. 1.2 weighing principle it can be seen from formula (1) that the volume flow QV of liquid depends on the flow coefficient CD, orifice area a and liquid level height H. The main factors affecting CD are orifice Reynolds number Re and orifice shape and area. The Reynolds number Re is jointly determined by the shape, area, liquid level height of the orifice and the dynamic viscosity V of the liquid. For the round hole, the shape of its orifice has been determined, so the main factors affecting QV are the liquid level height h, orifice diameter D and operating viscosity V, which are expressed by the mathematical formula as follows: qv=f (h, D, V) (2) however, in the process of zinc rectification, there will be a layer of zinc oxide solid floating on the surface of the liquid zinc, and its thickness is uneven, so it is not convenient to measure the liquid height h of the liquid zinc in the launder. However, the weight of zinc oxide is very light, which can be completely ignored for the liquid zinc in the launder, and measuring the weight of the liquid zinc in the launder is more capacity. Since the size of the launder is known, the liquid level height h of the molten zinc is directly proportional to the ratio of the weight of the molten zinc (the part higher than the round hole) and the density of the molten zinc. Therefore, equation (2) can be changed to: qg=f[g/(s· ρ zn),D,v] · ρ In Zn (3), QG represents the weight flow of zinc liquid, and s represents the bottom area of the launder. Zinc tourist density ρ Zn and kinematic viscosity V are determined by their temperature. In actual production, the temperature range is 600 ~ 650 ℃. In this way, we can know that the variation range of density is 6.81 ~ 6.77g/ml, and the variation range of kinematic viscosity is 0.3568 ~ 0.3261 μ m2/s。 Because their changes are small and have little impact on the flow, they can be regarded as constants (the later test results of structural optimization guided weight method can prove that such simplification is reasonable and will not have a great impact on the accuracy of the model). In addition, the size of the launder is determined by the fact that the development of solid metal air battery industry still faces many technical bottlenecks, that is to say, the bottom area of the launder and the diameter of the orifice are tested by positive Xuan wave; It is also a constant. In this way, the flow is only related to weight, which can be expressed digitally as: qg=f (g) (4). Therefore, as long as the relationship between flow and weight is found, the flow detection problem can be transformed into a weight detection problem. The measurement of weight is relatively easy, which is the basic principle of weighing method. 2 fitting of flow model 2.1 the force value, displacement, stiffness, curve and other data can be used to form a standard experimental report for printing orifice outflow test. In order to find out the relationship between the flow and weight of molten zinc in the launder, we have done the following orifice outflow test. First fill the launder with liquid zinc, and then open the round hole to let the liquid zinc flow out freely. In the process of liquid zinc flowing out, keep measuring the weight of liquid zinc (the part of liquid zinc higher than the position of the small round hole) in the launder. In the test, measure every second until the liquid level of zinc in the launder is equal to the orifice (that is, the weight of zinc is close to zero, and at this time, the zinc will not flow out). Let the weight of zinc liquid be expressed by G (T), then its flow rate QG (T) can be expressed as: QG (T) = (d/dt) g (T) (5)

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