RU2322519C2 - Method for controlling process of pelletizing loose finely divided materials - Google Patents

Abstract

FIELD: processes and equipment for pelletizing loose materials such as iron ore charges.

SUBSTANCE: method comprises steps of feeding charge to palletizing apparatus; monitoring outlet of formed pellets and changing parameters of process such as charge humidity, efficiency of pelletizing process, revolution number of pelletizing apparatus for providing maximum yield of ready pellets; separating by screening from pelletized charge and inspecting yield of pellets with size consisting of 0.8 - 1.0 of upper limit value of undersize products of screening; then changing process parameters.

EFFECT: increased yield of pellets of standard class, shortened time period of palletizing process.

5 dwg, 1 tbl

Description

The invention relates to the metallurgical or other industry and can be used in the manufacture of pellets.

A known method of controlling the granulation process, in which to increase the yield of standard pellets measure the content of large and small substandard fractions in the pellets, and depending on their ratio, control the rotation speed or the angle of inclination of the pelletizer to the horizon [1]. This method requires the simultaneous measurement of three classes of pellet fineness, and the control system has a large delay time.

There is also known the prototype method of controlling the pelletizing process by changing the speed of rotation of the granulator, the angle of inclination of the plate to the horizon, the addition of water or a binder depending on the mismatch between the set and current values of the number of suitable raw pellets and charge consumption [2].

The disadvantage of this method is that the control of the current value of the number of suitable raw pellets and pelletizing performance, even with optimal values of the adjustable parameters, do not allow us to obtain a suitable class of a narrow range of fineness and to optimize the process, since the yield of a class is significantly affected by the pelletization rate in the pelletizer itself, characterized by uncontrolled parameters. In addition, in this method, it is necessary to initially set the parameters of the pelletizer to be such that “a predetermined number of suitable raw pellets” is formed. However, this approach is not the best due to the fact that the process of granulation is not very predictable. A decrease in the yield of a narrow class of fineness leads to a loss of gas permeability of the calcined layer of pellets and a corresponding excessive consumption of fuel. An increase in the proportion of substandard size classes leads to cost overruns and a decrease in the quality of marketable products.

An object of the invention is to increase the yield of conditioned pellets.

The problem is solved in that in the known method, including changing the process parameters, the output of granules with a size of 0.8-1.0 is isolated and controlled from the value of the upper limit of the fineness of the under-sizing product of the screen and, after that, by changing the moisture content of the charge, the charge rate and speed pelletizer achieve the maximum amount of output of the granules.

The essence of the invention lies in the fact that since granules with a size of 0.8-1.0 from the value of the upper limit of the fineness of the under-sieve screen product in the subsequent (and only) movement in the pelletizer fall into the finished product, the conditions under which the maximum number of granules is formed, close in size to the upper limit of the sieve product of the screen will be optimal. At the same time, the yield of pellets of a suitable class is also optimal and the range of sizes of finished pellets is narrowed. The pelletization rate in the pelletizer is determined by the productivity of the initial charge, the pelletizer rotation speed and processes in the pelletizer itself, such as the statistical nature of the layering of the initial particles on the granule nuclei, the uneven formation and destruction of the granule nuclei. With high productivity and speed of rotation of the pelletizer, the limitation of the process is the growth of nuclei. If there is insufficient rate of increase in the mass of granules, the pellets of different sizes are squeezed out from the pelletizer by the flow of the mixture, decreasing the yield of standard pellets of a narrow size class. At the same time, with a decrease in productivity, an increase in the residence time of the material in the pelletizer occurs, which leads to a decrease in the yield of the conditioned fraction. Therefore, the control of granule formation in the production of pellets due to the control of the yield of formed granules with a size of 0.8-1.0 from the value of the upper limit of the sieve of the screening product is necessary to optimize the process.

The regulation of the parameters for the selection of a given value of the average diameter of the pellets is known. However, in the proposed technical solution, the control of rotation speed and productivity of the initial charge is carried out after separation and control of the output of granules with a size of 0.8-1.0 from the upper limit of the sieve product of the screen. This combination of operations is not known and allows you to obtain the desired particle size distribution of the pellets at the maximum output of a narrow class of conditioned fraction. The proposed combination and sequence of operations allows to improve the quality of the pellets and increase the gas permeability of the layer of pellets and, accordingly, reduce fuel consumption during hardening heat treatment.

Figure 1 shows the allocation scheme of the particle size class of 7-9 mm, which is 0.8-1.0 from the upper limit of the sieve product of the screen, and the implementation of the method of controlling the process of pelletizing. In Fig.2 is a graph of the dependence of the output of the fineness class 7-9 mm on the performance of the charge, Fig.3 is a graph of the dependence of the output of the fineness class of 7-9 mm on the rotational speed of the pelletizer, Fig.4 is a graph of the dependence of the output of the fineness class 7- 9 mm from changes in the moisture content of the mixture.

Pelletization process control by the proposed method is as follows. According to the diagram shown in FIG. 1, a material is discharged from pelletizer 1, including both finished products and an intermediate product. All this goes to the first screen 2, where the finished product 9 is extracted, which is fired by conveyor 3. Intermediate product 10 goes to the second screen 4, the cell size of which is 0.8 of the cell size of the first screen 2. The number of over-the-counter products 11 of the second screen size 0.8-1.0 from the upper limit of the under-sieve product of screen 2 is measured by the device 5 and a signal proportional to this quantity is fed to block 6, where the law of control of the pelletizing process is formed so that the amount of notch the second product of the second screen 11 was the maximum. The under-sieve product of the first and second screens and the over-sieve product of the second screen are combined on the conveyor 7 and fed as a circulation load by the conveyor 8 to the pelletizer loading area with the initial charge. After passing through the pelletizer, the volume of granules measured by block 5 is allocated by the first screen as a finished product of a narrow size class 9.

The proposed method is verified as follows. At the industrial drum pelletizer of the Poltava Mining Association, pellets from iron ore concentrate were received, which were sent for firing. The size of the finished pellets was 9-15 mm with an average of 13.5 mm. For optimal operation of the firing unit, according to technical standards, pellets of a narrow particle size class of 9-13 mm are required, providing high gas permeability of the layer due to the uniformity of the particle size distribution, with an average diameter of pellets of 12 mm. Pellets of this size after firing have high strength and abrasion resistance without a significant drop in the gas permeability of the layer and the performance of the machine. The charge sent to pelletizing consisted of iron ore concentrate with a grain size of 97% class minus 0.074 mm and 87.5% class minus 0.050 mm, with a content of bentonite of 0.5% and 0.1% limestone (pellets not fluxed). The moisture content of the mixture was 9.7-9.8%.

Pelletization process control was carried out as follows. After reaching the steady-state operation of the pelletizer, representative samples of the under-sizing product of the screen were taken according to the standard method, the output of granules minus 9 plus 7 mm was isolated and recorded. size from 0.8-1.0 from the upper limit of the sieve product of the screen. At the exit of the pelletizer, the roller screen had a slot size of 9 mm. After a time equal to the time of a single passage of material in the pelletizer, a sample of finished pellets was taken. Then, the productivity was successively changed relative to the initial one, equal to 110 t / h by 10 and 20%. In this case, the output of the class minus 9 plus 7 mm and finished pellets was recorded. The rotation speed of the drum remained at the initial level of 11 rpm. Then, setting the pelletizer productivity equal to 110 t / h, the pelletizer rotation speed was changed by 10 and 20%. At the same time, the output of granules of 7–9 mm and finished pellets was recorded. Similarly, we measured the yield of the class minus 9 plus 7 mm and the finished pellets with a change in the moisture content of the charge by changing the content of bentonite by 10% relative to the original. The results are presented in figure 2, 3 and 4, respectively.

From the presented graphs it can be seen that there is an optimal region of the ratio of parameters at which the process is going in the best way and the yield of granules is maximum. The table shows the output values of the classes of over-sizing products of the screens of the first and second, and Fig. 5 shows the dependence of the yield of finished pellets on the output of the class 0.8-1.0 on the upper limit of the sieve product of the screen 2.

Table Class output, mm P, t / h ν rpm W% 90 one hundred 110 120 130 9 10 eleven 12 13 8.6 9.8 10.9 7-9 2,5 3,1 3.6 3.6 2.7 3,1 3.3 3.6 3,5 3.3 2,4 3.6 3,1 +9 8.5 9.3 9.25 9.15 8.75 8.3 8.6 9.0 9.1 8.3 7.5 9.9 8.6

The application of the proposed method for controlling the process of pelletizing granular fine materials provides the following advantages compared to existing methods:

1) an increase in the yield of pellets of a conditioned class, a reduction in the time of pelletizing;

2) increasing the gas permeability of the layer of pellets and a significant reduction in fuel consumption during their hardening heat treatment.

Information sources

1. USSR author's certificate No. 771176, cl. C22B 1/16, 1980.

2. Patent for invention No. 2026378, class. C22B 1/24, publ. 1995.01.09

Claims (1)

A method of controlling the process of pelletizing bulk finely divided materials, including feeding the mixture into a pelletizer, controlling the yield of formed granules and changing the moisture content of the mixture, charge performance and rotational speed of the pelletizer to ensure the maximum output of the finished granules, characterized in that they are screened from the pelletized mixture and carried out control of the output of granules with a size of 0.8-1.0 from the value of the upper limit of the size of the size of the sieve product of the screen, and then change the mentioned th parameters.

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