Concentration of new technology and new technology - the basic principle of concentration (2)
The Ï… is expressed as the speed n:
The above formula shows that for a certain weight of ore particles, the centrifugal force increases with the increase of the radius of gyration and the number of revolutions. However, increasing the number of revolutions is more likely to increase the centrifugal force than increasing the radius of gyration.
In the centrifugal concentration dehydration operation, the ratio of the centrifugal acceleration to the gravity acceleration is commonly used to indicate the operating characteristics of the device, and is referred to as the centrifugal separation factor K, and its value is equal to:
The larger the separation factor is, the stronger the centrifugal force is, and the more easily the ore is precipitated. From the formula, increasing the rotation speed of the ore in the machine or increasing the radius of gyration can improve the separation effect.
In the process of centrifugal sedimentation, the centrifugal acceleration changes with the radius of rotation of the ore particles, so the sedimentation velocity of the ore particles is also a variable. In addition, the centrifugal force lines of the ore particles are not parallel to each other, and therefore the direction of the centrifugal force acting on each of the ore particles is also different. Therefore, the general gravity settlement law is not completely suitable for centrifugal sedimentation.
The centrifugal dewatering equipment currently used in mineral processing is a spiral discharge horizontal sedimentation centrifuge and a hydrocyclone. Vertical centrifugal dewatering machine used more coal plants in the election.
(IV) Gravity Settlement Test and Concentration Area Calculation The purpose of the settling test is to determine the sedimentation characteristics of solid materials in the slurry. The factors affecting the sedimentation performance of the material mainly include the pulp properties, such as the particle size composition of the material, the solid density, the density of the pulping liquid, the foam, the properties of the agent and the electrolyte in the slurry, and the operational factors such as the concentration of the ore and the ore. Mineral amount and its fluctuation range, pulp temperature, use of coagulant, etc. Through the sedimentation test of representative pulp, it is an important basis for selecting and designing the thickener to find out the relationship between the factors. Using the sedimentation test, the original data of the design concentrator, such as slurry settling time, unit settlement area and possible underflow concentration, can be obtained directly or indirectly through appropriate calculations. It is relatively easy to design a thickener using empirical and semi-industrial tests. However, intermittent settling tests are often a simple and feasible method due to time and financial constraints and the difficulty of preparing representative ore samples.
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The sedimentation test is generally carried out in a 2000 ml measuring cylinder. There are various methods for testing, but the contents tested are basically the same. Finally, the sedimentation curve of the slurry should be drawn, as shown in Fig. 4. In order to facilitate the selection of different methods to determine the sedimentation velocity of the slurry, the sedimentation test should generally provide the following data:
(1) the weight of the slurry sample, gram;
(2) dry solid weight, gram;
(3) solid density, g / cm 3 ;
(4) liquid density, g / cm 3 ;
(5) volume concentration of pulp, g / liter; weight concentration, %;
(6) temperature of the pulp, °C;
(7) the final volume of the slurry settling, the rise and the height, in millimeters;
(8) concentration and density of the clarified liquid;
(g) The height of the sedimentation interface corresponding to the different settling time during the 24 hour sedimentation process, mm. The necessary fashion must provide a different settling time t corresponding to the concentration of the clarified liquid, the weight concentration of milligrams per liter and grit, %, as shown in Figure 4 (d).
According to the settlement test, there are three main methods for calculating the unit settlement area:
(1) When the settlement interface is clear, the sedimentation curve has no obvious critical compression point, or the required underflow concentration is lower than the slurry concentration under the critical state, the map method should be adopted. The H-t sedimentation curve obtained by the settlement test is replaced by two straight line approximations, as shown in Fig. 1. The sedimentation curve is replaced by the fold line H o KL, then H o K is the free settling process line, KL is the compression process line, and K is the critical point. The sedimentation velocity of the particle group can be obtained by the following formula:
Where υ p ——— the sedimentation velocity of the particle group when the pulp concentration is p, m/h;
H o ———the starting height of the pulp surface in the measuring cylinder, m;
H K ———the height of the critical point, m;
t k ———the time elapsed from the start of settlement to the critical point, h;
t o ———the moment when the settlement begins, h.
The sedimentation area required to treat each ton of solids, ie the unit concentration area, can be calculated from the value of p, calculated by equation (9):
Where a p ——— the sedimentation area required to treat one ton of solid material when the slurry concentration is p, m 2 /t · h; corresponding to different υ p
Different a p can be obtained. When calculating the concentrator area, the maximum value a max should be selected.
K———the correction factor is generally 1.05～1.20. When the test is representative, the accuracy is high, the feeding amount and the property are stable, and the designed thickener has a large diameter, take a small value;
C 1 ——the solid content per unit volume of the test slurry, t/m 3 ;
C 2 ———The solid content per unit volume of the underflow of the designed concentrator, t/m 3 ; determined according to the test data and with reference to the production data of similar factories and mines.
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