TWI443339B - Method for on-line measuring the content of ferrous ions in concentrated acid - Google Patents

Description

Method for online detection of ferrous ion content in concentrated acid

This invention relates to a method of detection, and more particularly to a method of detecting the content of ferrous ions in a concentrated acid on-line.

At present, most of the steel mills in the industry have an Acid Regeneration Plant (ARP). The task of this regenerative acid plant is mainly to treat the waste hydrochloric acid (HCl) solution produced after the hot and cold rolling process to clean the steel. In the regenerative acid plant, the waste hydrochloric acid solution is calcined into an iron oxide subsidiary product, and at the same time, the hydrochloric acid solution is recovered to continue to clean the steel.

During the entire roasting operation, the concentrated acid is the calcined raw material, and the content of ferrous ions contained in the concentrated acid is the most important quality control item. At present, the method for detecting the content of ferrous ions contained in the concentrated acid is conventionally sampled and then analyzed by ethylene diaminetetraacetic acid (EDTA) titration.

However, due to manual offline sampling analysis, the steps are cumbersome and time consuming. For example, currently only sampling and analysis can be performed every 4 hours, so only one set of test data can be provided as the basis for the operation of the roasting process. Therefore, such a detection method will lead to a relatively long window period of the quality control of the factory, which will cause delay in the process quality control, and lead to the regulation of hysteresis, thereby reducing the stability of the roasting process.

Such regulation hysteresis can seriously affect the production of iron oxide in the roasting process. For example, when the content of ferrous ions in the concentrated acid is too high, supersaturated crystallization occurs, and the line for transporting the concentrated acid is clogged. On the other hand, when the content of ferrous ions in the concentrated acid is too low, there may be a problem that the purity of the iron oxide product is insufficient and the productivity is too low.

Therefore, there is a need for a method for detecting the content of ferrous ions in a concentrated acid in order to improve the conventional deletion of the ferrous ion content in the concentrated acid by manual means.

Therefore, one aspect of the present invention is to provide a method for detecting the content of ferrous iron in a concentrated acid by using a thermodynamic test and a regression analysis to obtain an equation for the relationship between the content of ferrous ions and the density of concentrated acid, and using the line. The method of measuring the density of the concentrated acid enables the on-line detection of the ferrous ion content in the concentrated acid. Thereby, the composition of the concentrated acid can be adjusted immediately before the roasting process, and the stability of the roasting process can be significantly improved.

Another aspect of the present invention provides a method for detecting the content of ferrous ions in a concentrated acid on-line, and detecting ferrous ions in a concentrated acid on the line, thereby avoiding the conventional manual sampling and potential by using the method of the present invention. The time-consuming, labor-intensive and delays in the quality control of the titration analysis can effectively assist the stable operation of the production.

In accordance with the above object of the present invention, a method for detecting the ferrous ion content in a concentrated acid on-line is proposed, which comprises the following steps. The concentrated acid is delivered to a calciner at a predetermined temperature using a transfer tube comprising a hydrochloric acid component, a ferrous chloride (FeCl ₂ ) component, and an aqueous solvent. The hydrochloric acid component has a predetermined content, and the hydrochloric acid component has a first density, the ferrous chloride component has a second density, and the aqueous solvent has a third density. A specific gravity device on the line is arranged in the conveying pipe in front of the baking furnace. The fourth density of the concentrated acid is measured using the aforementioned in-line specific gravity device. The content of one of the ferrous chloride components is calculated using a first equation, a predetermined content of the aforementioned hydrochloric acid component, a first density, a second density, and a third density. Wherein, the first equation is the fourth density = the third density × the weight fraction of the aqueous solvent + the first density × the weight fraction of the hydrochloric acid component + the second density × the weight fraction of the ferrous chloride component.

According to an embodiment of the invention, the solution inlet and the solution outlet of the above-mentioned in-line specific gravity device are in communication with the delivery tube.

According to another embodiment of the present invention, the above-mentioned on-line specific gravity device is connected to a distributed control system, and after measuring the fourth density of the concentrated acid, the method for detecting the ferrous ion content in the concentrated acid on the above-mentioned line further comprises The measured fourth density is transmitted in a Distributed Control System (DCS).

According to still another embodiment of the present invention, the step of calculating the content of the ferrous chloride component is carried out in a decentralized control system.

According to the above object of the present invention, there is further provided a method for detecting the ferrous ion content in a concentrated acid on-line, which comprises the following steps. Transferring the concentrated acid to a calciner at a predetermined temperature by using a transfer tube, wherein the concentrated acid comprises a hydrochloric acid component, a ferrous chloride component, and a water solvent, and the predetermined temperature is 75 ° C And the content of the hydrochloric acid component is 400 g / liter. A specific gravity device on the line is arranged in the conveying pipe in front of the baking furnace. The density of the concentrated acid was measured using this in-line specific gravity device. The ferrous ion content in the ferrous chloride component is calculated using a program and the aforementioned concentrated acid density. Among them, the equation is ferrous ion content = -902.818 + 803.4678 × density of concentrated acid.

In order to improve the problems caused by the conventional detection method, the present invention proposes a method for instantaneously detecting the content of ferrous ions in a concentrated acid on the line. In one embodiment, when detecting the ferrous ion in the concentrated acid, the relationship between the concentrated acid density and the ferrous ion content can be established.

In general, the concentrated acid in a steel plant is mainly a solution composed of a hydrochloric acid component, a ferrous chloride component, and an aqueous solvent. Among them, since the hydrochloric acid component and the ferrous chloride component are the main electrolyte components in the concentrated acid solution, the concentration of the hydrochloric acid component and the ferrous chloride component affects the concentrated acid solution. Therefore, in an embodiment, the relationship between the density and the weight fraction of the aqueous solution of hydrochloric acid and the aqueous solution of ferrous chloride at temperatures of 30 ° C, 35 ° C and 40 ° C can be established by means of measurement and regression analysis, respectively.

Since the aqueous hydrochloric acid solution is volatile and difficult to measure its density, the density of the aqueous hydrochloric acid solution is well documented in the literature. Therefore, the present embodiment utilizes literature, such as Perry's Chemical Engineers' Handbook, to provide a density (kg/l) data of aqueous hydrochloric acid solution at different temperatures, as shown in Table 1 below, for regression analysis. The mode of density versus concentration of aqueous hydrochloric acid was obtained. Then, the density of the aqueous hydrochloric acid solution at 30 ° C, 35 ° C and 40 ° C was calculated.

According to the results of the regression analysis, the density of the aqueous hydrochloric acid solution at different hydrochloric acid contents of the aqueous hydrochloric acid solution at 30 ° C, 35 ° C and 40 ° C can be obtained, respectively. Further, based on the results of the regression analysis, the prediction equations (1), (2), and (3) of the relationship between the density and the weight fraction of the aqueous hydrochloric acid solution at 30 ° C, 35 ° C, and 40 ° C can be obtained as follows.

Where ρ _HCl is the density of aqueous hydrochloric acid solution, It is the weight fraction of water in an aqueous hydrochloric acid solution, and W _HCl is a weight fraction of a hydrochloric acid component in an aqueous hydrochloric acid solution.

Please refer to Fig. 1 and Fig. 2, which are schematic diagrams showing the comparison of the mode prediction and the literature value (experimental value) of the aqueous hydrochloric acid solution at 30 ° C and 40 ° C, respectively. It can be seen from Fig. 1 and Fig. 2 that the values obtained by the mode prediction are close to the literature values at 30 ° C or 40 ° C, showing the predictions obtained after the experimental and regression analysis. The results were quite consistent with the literature values.

When measuring the density of the aqueous solution of ferrous chloride, an appropriate amount of ferrous chloride is added to the distilled pure water, and a quantitative volume is prepared at a temperature of 30 ° C, 35 ° C and 40 ° C, and the density is calculated by weighing. The experimental results are shown in Table 2 below.

According to the results of the regression analysis, the density of the aqueous solution of ferrous chloride at different ferrous chloride contents at 30 ° C, 35 ° C and 40 ° C can be obtained respectively. Further, based on the results of the regression analysis, the prediction equations (4), (5), and (6) of the relationship between the density and the weight fraction of the aqueous solution of ferrous chloride at 30 ° C, 35 ° C, and 40 ° C can be obtained as follows.

among them, Is the density of the aqueous solution of ferrous chloride, Is the weight fraction of water in the aqueous solution of ferrous chloride, It is the weight fraction of the ferrous chloride component in the aqueous solution of ferrous chloride.

Please refer to Fig. 3 and Fig. 4, respectively, which are schematic diagrams showing the comparison of the mode prediction and experimental values of the aqueous solution of ferrous chloride at 30 ° C and 40 ° C, respectively. It can be seen from Fig. 3 and Fig. 4 that the values obtained by the mode prediction are quite close to the experimental values at 30 ° C or 40 ° C, showing the predictions obtained after the experimental and regression analysis. The results were quite consistent with the experimental values.

An experiment for measuring the density of an aqueous solution of a mixture of hydrochloric acid and ferrous chloride is carried out by adding an appropriate amount of a hydrochloric acid component to distilled pure water, and arranging it into an acid solution having a similar acid concentration in the field, and adding a different amount of ferrous chloride component. Weighed and gained density. The experimental results at temperatures of 30 ° C and 40 ° C are shown in Table 3 below.

The density pattern of the aqueous solution of the mixture of hydrochloric acid and ferrous chloride is added by the above equations (1) to (6), and the density is expressed as a function of temperature, and the following equation (7) is obtained.

Where ρ _mix is the density of the aqueous solution of the mixture of hydrochloric acid and ferrous chloride, and ρ _HCl is the density of hydrochloric acid, It is the density of ferrous chloride. Further, ρ _{i , 0} is the density of a material at a reference temperature T ₀ , ρ _i is the density of the compound at temperature T, ρ _{i , 1 is} the temperature coefficient of the density of the material, wherein the reference temperature T ₀ and The unit of temperature T takes the unit K of the absolute temperature.

Table 4 below lists the temperature, the density of water, hydrochloric acid and ferrous chloride, and the temperature coefficient of water, hydrochloric acid and ferrous chloride at a reference temperature of 30 ° C (T ₀ = 303 K). Table 5 below lists the densities of water, hydrochloric acid and ferrous chloride at temperatures of 30 ° C (303 K), 35 ° C (308 K) and 40 ° C (313 K).

Please refer to Fig. 5, which is a comparison chart of predicted density and experimental value of an aqueous solution of a mixture of hydrochloric acid and ferrous chloride. As can be seen from Fig. 5, when the hydrochloric acid component is 2 wt%, 5 wt% and 10 wt%, the predicted density of the aqueous solution of the mixture of hydrochloric acid and ferrous chloride is quite close to the experimental value.

In one embodiment, the content of the hydrochloric acid component in the concentrated acid of the roasting process of a general steel factory can be regarded as a fixed value, that is, 400 g/l, and the temperature of the concentrated acid is a constant value of 75 °C. Therefore, after unit conversion and simple linear regression, the calculation formula of the following equation (8) can be obtained.

Y=-902.818+803.4678×X (8)

Wherein Y is the ferrous ion content in g/l; and X is the density of the concentrated acid consisting of the hydrochloric acid component, the ferrous chloride component and the aqueous solvent, and the unit is g/cm ³ .

Please refer to FIG. 6 , which is a linear regression diagram showing a relationship between the density of concentrated acid and the content of ferrous ions according to an embodiment of the present invention. It can be seen from Fig. 6 that the relational expressions listed in equation (8) are confirmed to have a coefficient of determination (R-Square; R2) close to 1, indicating that the equation (8) has an extremely high degree of coincidence. Therefore, in this embodiment, the density value of the concentrated acid is detected, and the density value is substituted into the equation (8) to obtain the ferrous ion content Y.

Please refer to FIG. 7 , which is a schematic diagram of a device for detecting a ferrous ion content in a concentrated acid on line according to an embodiment of the present invention. In this embodiment, the concentrated acid after cleaning the steel material is transferred to the calcining furnace 108 of the regenerated acid plant by the transfer pipe 100 to perform high-temperature baking to produce an iron oxide subsidiary product, and the hydrochloric acid solution is recovered. In general, the concentrated acid mainly contains a hydrochloric acid component, a ferrous chloride component, and an aqueous solvent.

In one embodiment, the concentrated acid has a predetermined temperature and the hydrochloric acid component of the concentrated acid has a predetermined content. For example, the preset temperature may be 75 ° C, and the preset content of the hydrochloric acid component is 400 g / l. Moreover, from the above analysis and experimental procedures, the density of the hydrochloric acid component, the ferrous chloride component and the water solvent at the preset temperature is a known value.

When the concentrated acid is transported by the transfer pipe 100, the linear specific gravity device 102 may be disposed in the transfer pipe 100 in front of the baking furnace 108. Both the solution inlet 104 and the solution outlet 106 of the in-line specific gravity device 102 are in communication with the delivery tube 100. By this design, the concentrated acid carried by the conveying pipe 100 can pass through the in-line specific gravity device 102. In this way, the density of the concentrated acid can be measured instantaneously on the line of the on-line specific gravity device 102 as the concentrated acid passes through the on-line specific gravity device 102.

In one embodiment, after measuring the density of the concentrated acid, the above equation (7) can be utilized. And the predetermined content of the hydrochloric acid component, that is, the weight fraction of the hydrochloric acid component, and the density of the concentrated acid, and the known water density, the hydrochloric acid component density, and the ferrous chloride density are substituted into the equation (7). In this way, the weight fraction of water and the weight fraction of ferrous chloride, that is, the content of water and ferrous chloride, can be calculated. From the calculated content of the ferrous chloride component, the ferrous ion content can be determined. Therefore, the procedure for instantaneously detecting the ferrous ion content in the concentrated acid on the line is completed.

In one embodiment, as shown in FIG. 7, a decentralized control system 110 can be additionally provided and the in-line specific gravity device 102 can be coupled to the decentralized control system 110. Thus, the in-line specific gravity device 102 can transmit data of the density values of the concentrated acid it measures to the decentralized control system 110. In addition, the above equation (7) can be And the known weight fraction of hydrochloric acid components, water density, hydrochloric acid component density and ferrous chloride density are first built into the decentralized control system 110. In this way, when the on-line specific gravity device 102 transmits the measured concentrated acid density value to the distributed control system 110, the distributed control system 110 can calculate the content of the water and the ferrous chloride component, thereby calculating the ferrous iron. Ion content. Therefore, the field operator can instantly know the content of ferrous ions in the concentrated acid from the screen of the distributed control system 110.

At this time, the content of ferrous ions entering the concentrated acid in the baking furnace 108 can be adjusted manually according to the ferrous ion content detected on the line to improve the process stability. In another embodiment, a control program for adjusting the amount of ferrous ions in the concentrated acid may also be built into the decentralized control system 110. Therefore, when the distributed control system 110 receives the value of the concentrated acid density measured by the on-line specific gravity device 102, the ferrous ion content can be calculated, and the ferrous ion content is automatically adjusted to enter the baking furnace according to the calculated ferrous ion content. The content of ferrous ions in the concentrated acid in 108.

In another embodiment, when the preset temperature of the process is 75 ° C and the content of the hydrochloric acid component is 400 g / liter, the above equation (8), Y = -902.818 + 803.4678 × X can be utilized, and The density value X of the concentrated acid measured is substituted into equation (8). In this way, the content of ferrous ions can be calculated, and the procedure for instantaneously detecting the ferrous ion content in the concentrated acid on the line is completed. Of course, equation (8) can also be built into the decentralized control system 110, and the ferritic ion content can be automatically calculated by the decentralized control system 110.

Please refer to FIG. 8 , which is a comparison diagram of detection results of an on-line density detection method and an artificial potentiometric titration analysis method according to an embodiment of the present invention. It can be seen from Fig. 8 that the trend of the test results obtained by the two methods is quite consistent, so the process quality values are close. Further, from Fig. 8, it can be found that the deviation between the on-line detection density method and the artificial potential titration analysis method of one embodiment of the present invention is 2.8%. In addition, after the embodiment of the present invention is linearized, the process stability is much better than the artificial potentiometric titration analysis method.

It is apparent from the above embodiments of the present invention that one of the advantages of the present invention is that the method of the present invention uses thermodynamic tests and regression analysis to obtain an equation for the relationship between the content of ferrous ions and the concentration of concentrated acid, and uses the online measurement to measure the density of concentrated acid. The way, the ferrous ion content in the concentrated acid can be detected on the line. Thereby, the composition of the concentrated acid can be adjusted immediately before the roasting process, and the stability of the roasting process can be significantly improved.

It can be seen from the above embodiments of the present invention that another advantage of the present invention is that the method of the present invention can detect the ferrous ions in the concentrated acid on the line, so that the traditional manual sampling and potentiometric titration analysis can be avoided by using the method of the invention. Time-consuming, labor-intensive, and delays in process quality control, which in turn can effectively assist in stable operation of production.

While the present invention has been described above by way of example, it is not intended to be construed as a limitation of the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

100. . . Duct

102. . . Online specific gravity device

104. . . Solution inlet

106. . . Solution outlet

108. . . roaster

110. . . Decentralized control system

The above and other objects, features, advantages and embodiments of the present invention will become more apparent and understood.

Fig. 1 is a schematic diagram showing the comparison of the mode prediction and the literature value (experimental value) of the aqueous hydrochloric acid solution at 30 °C.

Fig. 2 is a schematic diagram showing the comparison of the mode prediction and the literature value (experimental value) of the aqueous hydrochloric acid solution at 40 °C.

Figure 3 is a schematic diagram showing the comparison of the mode prediction and experimental values of the aqueous solution of ferrous chloride at 30 °C.

Figure 4 is a schematic diagram showing the comparison of the mode prediction and experimental values of the aqueous solution of ferrous chloride at 40 °C.

Figure 5 is a graph comparing the predicted density of the aqueous solution of the mixture of hydrochloric acid and ferrous chloride with the experimental values.

Figure 6 is a graph showing a linear regression of a relationship between the density of a concentrated acid and the content of ferrous ions in accordance with an embodiment of the present invention.

Figure 7 is a schematic view showing a method of detecting a ferrous ion content in a concentrated acid on-line according to an embodiment of the present invention.

Figure 8 is a graph showing a comparison of detection results of a line density detection method and an artificial potential titration analysis method according to an embodiment of the present invention.

100. . . Duct

102. . . Online specific gravity device

104. . . Solution inlet

106. . . Solution outlet

108. . . roaster

110. . . Decentralized control system

Claims (8)

A method for detecting the content of ferrous iron in a concentrated acid on-line, comprising: transferring the concentrated acid to a baking furnace by using a conveying pipe at a preset temperature, wherein the concentrated acid comprises a hydrochloric acid component and a chlorination a ferrous component, and a monohydrate solvent having a predetermined content, wherein the hydrochloric acid component has a first density, the ferrous chloride component has a second density, and the aqueous solvent has a third density; a line of gravity is disposed in the delivery tube in front of the roasting furnace; a fourth density of the concentrated acid is measured by the in-line specific gravity device; and a first equation, the predetermined content, the first density, the second is utilized Density and the third density, calculating a content of the ferrous chloride component, wherein the first equation is the fourth density = the third density × the weight fraction of the aqueous solvent + the first density × the hydrochloric acid component Weight fraction + the second density x the weight fraction of the ferrous chloride component. A method for detecting a ferrous ion content in a concentrated acid as described in claim 1, wherein a solution inlet and a solution outlet of the linear specific gravity device are in communication with the delivery tube. The method for detecting the content of ferrous iron in a concentrated acid on line, as described in claim 1, wherein the on-line specific gravity device is connected to a decentralized control system, and after measuring the fourth density of the concentrated acid, the line is concentrated and detected. The method of ferrous ion content in the acid further comprises transferring the measured fourth density to the decentralized control system. A method for detecting a ferrous ion content in a concentrated acid as described in claim 3, wherein the step of calculating the content of the ferrous chloride component is carried out in the distributed control system. A method for detecting the content of ferrous iron in a concentrated acid on-line, comprising: transferring the concentrated acid to a baking furnace by using a conveying pipe at a preset temperature, wherein the concentrated acid comprises a hydrochloric acid component and a chlorination a ferrous component, and a monohydrate solvent, the preset temperature is 75 ° C, and the content of the hydrochloric acid component is 400 g / liter; a specific gravity device on the line is disposed in the conveying pipe before the baking furnace; Measuring a density of the concentrated acid; and calculating a ferrous ion content of the ferrous chloride component using a program and the density, wherein the equation is the ferrous ion content = -902.818 + 803.4678 × the density. A method for detecting a ferrous ion content in a concentrated acid as described in claim 5, wherein a solution inlet and a solution outlet of the linear specific gravity device are in communication with the delivery tube. The method for detecting the ferrous ion content in a concentrated acid on line, as described in claim 5, wherein the on-line specific gravity device is connected to a decentralized control system, and after measuring the density of the concentrated acid, the line detects the concentrated acid. The method of ferrous ion content further comprises transferring the measured density to the decentralized control system. A method for detecting a ferrous ion content in a concentrated acid on line as described in claim 7, wherein the equation is stored in the distributed control system, and the step of calculating the ferrous ion content in the ferrous chloride component is This is done in the decentralized control system.