Crushing Plant Design and Layout Considerations
The work of doing a research about Crushing Plant Design and Layout Considerations is necessary to bring further profit, reasonable crush plant is the fundamental of efficient crushing production. The main factors of crushing plant quality as following paper of crushing plant design and layout considerations.
1 Considerations of stone crusher plant design
The basic purpose of crushing ore is to achieve a certain particle size requirement for ore, raw materials or fuel. In ore dressing, the purpose of crushing ore is: (1) supply the most reasonable ore feeding size for rod grinding, ball milling, or provide qualified grinding medium for autogenous mill and gravel grinding; (2) make coarse-grained embedded minerals monomer preliminarily dissociated, create convenience for the coarse grain dressing methods, such as heavy medium separation, jig concentrate, dry magnetic separation and washing dressing; (3) to make high-grade iron ore reach the required grain size so that it can be smelted directly.
Different purposes require different particle sizes, and thus there are many types of crushing processes.
1.1 Crushing stage
The crushing stage is the most basic unit of the ore-crushing process. Different crushing stages and different combinations of crusher and sieve require different ore crushing processes.
The basic forms of the crushing stage are as follows: (a) one stage crushing; (b) one stage crushing with prescreening; (c) one stage crushing with control screening; Both (d) and (e) one stage crushing with prescreening and control screening, the difference is (e) type with pre-screening and control-screening operations on the same plate.
The two-stage crushing and over two stages crushing is a combination of different crushing stages, so there are many possible schemes. However, a reasonable crushing process can be determined according to the number of broken stages required and the necessity of applying pre-screening and control screening.
1.2 Determination of crushing stage
The number of crushing stages depends on the maximum grain size of the crude ore, the required particle size of the final crushing product, and the crushing ratio that can be achieved in each broken section, that is, the total crushing ratio required and the crushing ratio of each section.
The maximum grain size in the ore is related to the occurrence conditions of the ore, the scale of the mine, the mining method, and the transportation and handling methods of the ore. Open-pit mining depends mainly on the size of the mine and the volume of the loading shovel, typically 500 to 1300 mm. When mining underground, it depends mainly on the size of the mine and the mining method, generally 300 ~ 600 mm.
The size of the broken final product varies depending on the purpose of the crush. For example, the feeding of the autogenous mill is 300 to 500 mm, the particle size of the iron-rich ore smelting in the blast furnace is divided into two stages of 25 ~ 30 and 25 ~ 30 mm. The reasonable ore size of the rod mill is 20 ~ 40, the ball mill has a reasonable ore size of 10 to 25 mm. The reasonable final crushed product size depends mainly on the requirements of the process and the results of technical and economic comparisons.
When determining the optimum final particle size of the ball mill, the total technical and economic effects of crushing and grinding should be considered. The larger the particle size of the crushed product, the higher the crusher’s production capacity and the lower the crushing cost; however, the grinding machine’s production capacity will be reduced and the grinding cost will increase. On the contrary, the smaller the particle size of the crushed ore, the smaller the production capacity of the crusher and the higher the cost of crushing; but the production capacity of the grinding machine will increase and the grinding cost can be reduced. Therefore, the crushing and grinding should be considered comprehensively, and the particle size which minimizes the total cost should be selected as the suitable crushing final product particle size. The practice has proved that the most suitable ore size of the grinding machine is 10~25 mm. As the production scale of the concentrator is larger, the grain size of the grinding machine is reduced, and the economic effect is greater.
The crushing ratio of each crushing stage depends on the type of crusher, the type of crushing stage, the hardness of the ore processed, and the like. The crushing that can be achieved by the common crusher is shown in the Table below. When the hard ore is treated, the crushing ratio is small; when the soft ore is processed, the crushing ratio is large.
1.3 Determination of pre-screening and control screening
Pre-screening is to pre-screen the qualified grain size before the ore enters the crushing section, which can reduce the number of minerals entering the crusher and increase the production capacity of the crusher; at the same time, it can prevent the ore from being crushed. When processing with ore with higher water content and more fine ore, the wet mineral powder will block the crushing chamber of the crusher and significantly reduce the production capacity of the crusher. The use of pre-screening to remove wet and fine mineral powder can cause more normal working conditions for the crusher.
Therefore, the application of the pre-screening is mainly determined based on the content of the fine-grained grade in the ore (less than the fraction of the width of the discharge port of the crusher). The higher the fine fraction content, the more advantageous it is to use pre-screening. Studies have shown that technically and economically, pre-screening favorable ore, in which the limit content of fine-grain grade is related to the crushing ratio of the crusher.
From this, it can be seen that when the ore size characteristic is a straight line, it is always advantageous to use pre-screening regardless of the crushing ratio. In most cases, the grain size characteristics of the ore are concave, so pre-screening before crushing is economically cost-effective. However, due to the need to increase the height of the plant by using pre-screening, when the production capacity of the coarse crusher is sufficient, or when the direct filling is used, the pre-screening may not be provided.
The fine fraction content in the second crushing section and the third crushing section is mainly determined by the grain size characteristics of the ore discharging of the previous section of the crusher. According to the actual measurement, the grain size characteristic curves of various coarse crushers and medium crushers are mostly concave, that is to say, fine particles are dominant, so the second crushing section and the third crushing section are pre-screened. necessary. Only when there is a surplus in the production capacity of the selected crusher, it is not necessary to pre-screen before the crushing.
The purpose of screening is to control the particle size of the crushed product and to maximize the production capacity of the crusher. Because some of the crushing products of various crushers have a coarse fraction which is larger than the width of the discharge opening, such as the short-head cone crusher when crushing the medium-breakable ore, the product has a grain size greater than the width of the discharge opening takes 60%, the maximum particle size is 2.2 ~ 2.7 times of the discharge port; even worse when breaking the broken ore. The content of the coarse fraction (greater than the size of the discharge port) and the maximum relative particle size Z (that is, the ratio of the maximum particle to the size of the discharge port) in the crushed products of various crushers are shown in the table below.
After control sieving, the unqualified granules are returned to the crusher, just as the closed loop of the grinder and the classifier is beneficial to improve the grinding efficiency. Control screening can improve the production capacity of the crusher. However, the use of control screening will increase the investment and complicate the equipment configuration of the crushing workshop. Therefore, it is generally only used in the last crushing section to check and screen, and combined with the pre-screening to form a pre-screening closed loop.
It is thus necessary to pre-screen in each of the crushing stages; the control screening is generally only used in the last crushing section.
2 Considerations of crushing plant layout
2.1 Two stages of crushing flow sheet
The crushed product obtained by the two-stage open crushing process has a coarse particle size and is only used in a simple small ore dressing plant or an industrial test plant. The first stage may not be pre-screened. In this case, when the mud and water in the ore are high, a small concentrator can also be used in order to make the production work normally.
The small ore dressing plant handles the ore mining with small granularity in the underground mining, and the second section adopts the two-stage closed-circuit crushing process when the relatively large crushing impact crusher is used.
2.2 Three stages crushing process sheet
The basic types of the three-stage crushing process are three-stage open circuit and three-stage one closed circuit.
The three-stage and the one-closed crushing process has been widely used as a preparation for grinding. Whether it is underground or open-pit mining ore, as long as the ore is not high in mud, it can be effectively adapted. Therefore, the concentrators of different scales can be used.
Compared with the three-stage and one-closed process, the three-stage open-circuit crushing process has a coarser particle size, but it can simplify the equipment configuration of the crushing plant and save capital investment. Therefore, this process can be used when the grain size of the ore is not critical and the coarse grinding of the grinding section is carried out by rod grinding, as well as the treatment of muddy ore with high moisture content and terrain limitation. When dealing with ore with high moisture content, it is not as easy to block the screen and the crushing chamber as the three-stage closed circuit process. The three-stage open-circuit and rod-grinding crushing process do not require complex closed-circuit screening and return product transportation operations, and the rod mill is less affected by the ore-grain size change, and the ore-mining particle size is uniform, which can ensure the lower-stage grinding operation. The operation is stable; at the same time, the production process produces less dust, which can improve the sanitary conditions. This process can be used when coarser grain sizes (re-election plants) or brittleness (tungsten, tin ore) and large specific gravity (lead ore) minerals are required. Only very hard ore and very large-scale concentrators are treated. In order to reduce the crushing ratio of each section or increase the total crushing ratio, the four-stage crushing process is considered.
2.3 Crushing flow with the washing process
When the amount of ore containing mud (-3 mm) exceeds 5-10% and the water content is more than 5 ~ 8%, the fine fraction will bond into a mass, which will deteriorate the production conditions of the crushing process, such as blockage of crushing cavity and sieve hole, prone to equipment failures, in severe cases, production cannot be carried out. At this point, the washing facility should be added to the crushing process. Increasing the washing equipment will not only fully exploit the potential of the crushing equipment, but also make the production work normally. Improve labor intensity, and increase the recovery rate of useful metals and expand the use of resources.
The washing process is generally set before or after coarse crushing, depending on factors such as the ore size, water content and structure of the washing equipment. Commonly used washing equipment includes washing sieve (trommel screen, grid sieve, vibrating screen, cylindrical sieve) spiral trommel washing machine, cylinder trommel scrubber washing machine, etc. The net mine after washing, some need to be broken, and some can be used as a qualified grade. Washed mud, if the grade is close to the tailings grade, can be discarded; if the grade is close to the original grade, it needs to be sorted.
Due to the different features of the mineral ore, the way of washing and the treatment of fine mud are different, so the process is diverse. as an example, The ore is a skarn type copper deposit with 6-11% mud and about 8% water. The washing process is shown in the upper, and the crushing process is three sections and one closed circuit. In order to make the crusher safe and normal production, the first washing is carried out on the sieve, the product is sieved for coarse crushing, and the sieved product is washed into the vibrating screen. After the second washing, the product on the sieve enters the medium crushing. The product under the sieve is graded and delimed into the spiral classifier. The classified sand return is combined with the final crushed product. The graded overflow is buffered by the thickener, and after dehydration, it is separately fine. mud grinding, flotation.
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