Third, the choice and calculation of the thickener
1. The determination of the type and specification of the concentrator is generally based on the nature of the material being processed, the production and construction conditions, and the magnetic technical data provided by the experimental study. In foreign countries, the manufacturer calculates and selects based on the information provided by the user, and then recommends it to the user. In China, it is selected by the user or the design unit. For large scale production beneficiation plant, as far as possible in the case of using a large conditions thickener. Foreign data shows that the use of large-diameter concentrators can save about 25% of reinforced concrete and save about 50% of construction costs.
(1) Peripheral transmission concentrator
The peripheral transmission concentrator supporting the truss with the reinforced truss, the truss and the steel truss support are combined as a whole, with good rigidity and high strength. However, the truss structure has a water surface in the working and middle, and has a stirring effect on the clear layer, which is not conducive to the sedimentation of the fine particle material and affects the water quality of the overflow. The truss is a peripheral drive concentrator with a cantilever structure. The technical requirements for the surrounding track are not strict. The truss operation has less influence on the settlement layer and the overflow water quality is better.
(2) Large center drive concentrator
The central drive concentrator with central pedestal support (using hydrostatic bearings) has low frictional resistance and high effective transmission torque. The eccentric concentrator with precision ball bearings prevents damage when the load is too large. Arm and drive. Used to process iron, copper ore dressing products.
The large caisson center column concentrator adopts a hollow column foundation structure, which can accommodate discharge materials, electronic control, process pipe network and auxiliary facilities, and provide a space space for equipment operation and maintenance. The underflow of the equipment is piped from the hollow column to the subsequent operation point through the bridge, which can save the construction cost of the underground passage and the pump house. The underflow of this type of concentrating tank is discharged in parallel by a multistage pump. When the peak load occurs, the sand pump can handle it by itself until the concentration of the slurry in the collecting trench around the center column is reduced to a normal value. This method of discharging can make the pulp have a higher line speed and prevent the discharge port from being blocked. If a short circuit occurs in the discharge, the underflow concentration becomes lean and the suction head of the pump increases. In production, we should try to prevent short circuit in mine discharge. The pipeline installation cost of this type of thickener is high, the suction pipe of the pump is easy to block, and the maintenance is difficult. However, the structure is simple, the operation is convenient, the transmitted torque is large, and the operation is stable and reliable.
The cable center drive concentrator has a diameter of 12 meters to 75 meters. The steel wire rope can automatically adjust the data of the float up and down and left and right to measure the load inside the concentrator. Under uniform load conditions, the concentrator can obtain the best working condition by input data processing. The machine is suitable for dewatering operations with volatility and intermittent loads. The automatic compensation of the position of the dice can prevent the production balance load in the pool, so the ore concentration is uniform, and the torque can be adjusted by itself to ensure the normal operation of the equipment.
The multi-layer central drive concentrator has a simple structure, a small floor space, low power consumption, and low capital cost. This type of thickener should be used when the field is tight and requires sufficient settlement area. The device delivers less torque and a smaller diameter for use in small to medium concentrators.
The flocculating agent is added to the feed of the same-effect concentrator (the sloping plate can also be installed in the tank), and is sent to the settling portion of the concentrator after being stirred. The machine has a small footprint and high concentration efficiency. It is suitable for processing fine-grained materials and materials that must be dehydrated indoors. It is also suitable for the expansion of production capacity of old factories.
2. Calculation of the 浓缩 type thickener
In order to determine the area, structural size and number of concentrators operating under certain conditions, technical calculations of the concentrator must be performed. Due to the complexity of the sedimentation process of the mineral material in the continuous operation of the rake concentrator, there is no accurate calculation method. Some foreign companies design concentrators based on experience and different research methods, such as simulation, graphic method, initial settling velocity method, and empirical quota method.
At present, China's concentrator calculation is based on the production capacity of the unit's concentrated area and the sedimentation speed of the slurry in the static sedimentation test to determine the required effective settlement area, the size of the concentrator and the number of units. The production practice of China's concentrator shows that in the current situation, the more realistic calculation method should be determined through the settlement test and referring to the actual production data of similar mines. The overflow water quality requirements should be considered while meeting the underflow concentration requirements. When black metal ore with the use of a ring of water required solids content of less than 0.5% in the overflow; nonferrous metal mines should be minimum loss of metal.
The production capacity per unit area of ​​the concentrator is related to the particle size, density, concentration of feed and underflow, slurry composition, foam viscosity, slurry temperature and material value of the treated material particles or flocs. The production capacity per unit area is generally determined according to semi-industrial test or static sedimentation test. In the absence of test conditions, it can be determined by reference to the production index of similar factories and mines. Examples of the production capacity of different concentrates per unit of concentrated area are listed in Table 5.
Table 5 concentrator production capacity per unit area
Material characteristics of the concentrator | Production capacity per unit area, (r/m 2 .d) |
Overflow of mechanical classifier (before flotation) Lead oxide concentrate and lead-copper concentrate Lead sulfide concentrate and lead-copper concentrate Copper concentrate and copper-bearing pyrite concentrate Yellow iron concentrate Molybdenite concentrate Zinc concentrate Antimony concentrate Flotation iron concentrate Magnetically selected iron concentrate Manganese concentrate White tungsten ore flotation concentrate and medium mine Fluorite flotation concentrate Barite flotation concentrate Flotation tailings and medium mines | 0.7 to 1.5 0.4 to 0.5 0.6~1.0 0.5 to 0.8 1.0 to 2.0 0.4 to 0.6 0.5 to 1.0 0.5 to 0.8 0.4 to 0.6 3.0 to 3.5 0.4 to 0.7 0.4 to 0.7 0.8 to 1.0 1.0 to 2.0 1.0 to 2.0 |
(1) Concentrated area calculation
The following methods can be used to calculate the concentrated area:
1 Calculate the concentrator area using semi-industrial test production quota indicators using the following empirical formula:
K
A=K---
q
(1)
Where A-concentrator total effective area, m 2 ;
q—The weight of the solid material treated per unit area of ​​the concentrator, t/(m 2 .d), under the condition of meeting the requirements of overflow water quality, the visit value is determined by experiment. For lack of test data, refer to Table 5 for selection;
W—the weight of solids in the feed, t/d;
K - slurry fluctuation coefficient. Generally, for the industrial test, K=1, for the simulation test, K=1.05～1.20; when the ore sample is representative, the quantity and properties of the ore are stable, and the larger diameter of the concentrated enthalpy is selected, the small value can be taken, and vice versa. .
2 Calculate the concentrator area according to the static settlement test or simulation test data:
A=KQ0C0amax
(2)
or
A=KWamax
(3)
Where A - the total area of ​​the required thickener, m 2 ;
K-factor, take 1.05~1.2, the value principle is the same as (1);
Q 0 — design feed amount, m 3 /d;
c 0 — the unit volume of the designed ore is solid weight, t/m 3 ;
a max — the maximum settling area required to concentrate each ton of solid material, m 2 /(td -1 ) determined by experiment;
W—the solids weight fed to the concentrator, t/d.
3 In the absence of test data and no actual empirical data, the settlement speed of the solid material can be approximated according to the Stokes formula, and then the area of ​​the concentrator is approximated by the following formula:
W(R 1 -R 2 )K
A=-------------
86.4v 0 K 1
(4)
Where A - thickener area, m 2 ;
W—the solid weight fed to the thickener, t/d;
R 1 , R 2 — the liquid-solid ratio of the slurry before and after concentration;
K 1 — the effective area factor of the concentrator, generally 0.85 to 0.95; the concentrator above ø12m takes a large value;
K-mineral fluctuation coefficient, depending on the ore grade. When the diameter of the thickener is less than 5m, take 1.5, and when it is larger than 30m, take 1.2;
v 0 — the free settling velocity of the largest particle in the overflow in water, mm/d.
The settling velocity can also be approximated by (5):
v 0 =545(δ-1)d 2
(5)
Where δ - solid material density, gcm 3 ;
v 0 — the free settling velocity of the largest particle in the overflow in water, mm/s;
d—The maximum diameter of solid particles in the overflow, mm, the maximum particle size in the overflow of the concentrate is generally 5 μm, and the maximum should not exceed 30-50 μm when concentrated.
For flocculation settling, v 0 can only be determined by experiment. The calculation of the A value should be selected over the entire concentration range between the feed and the underflow, where the maximum is the cross-sectional area of ​​the settling tank. The area of ​​the concentrator must ensure that the slowest settled particles in the slurry have sufficient residence time to settle to the bottom of the tank. Therefore, the concentrator overflow velocity v (or rising water flow velocity) must be less than the sedimentation velocity of the largest particle in the overflow. The area of ​​the selected concentrator shall be checked by (6) and shall be maintained at v < v 0 . The overflow speed is calculated as follows:
V
V=---×100
A
(6)
Where v - rising water flow velocity, mm / s;
A—concentrator area, m 2 ;
V-concentrator overflow, m 3 /s. [next]
(2) Thickener depth calculation
The depth of the rake concentrator determines the residence time of the slurry in the compression layer. In order to ensure the concentration of the bottom stream, the slurry must have sufficient residence time in the concentrator. Therefore, the concentrator should have a certain height, namely:
H=h c +h p +h Y
(7)
Where H is the total height required for the thickener, m;
h c — the height of the clarification zone, which is about 0.5 to 0.8 m;
Hp—the height of the arm movement zone, m; can be calculated by the following formula;
D
h p =----tga
2
(7a)
D—the bottom diameter of the thickener, m;
A—bottom horizontal inclination, usually a=12°;
hY—the height of the compression zone, m; can be calculated by trial and test:
(1+δ.R C )t
hY=------------
24δamax
(7b)
Where t is the time required for the slurry to concentrate to the specified concentration (measured), h;
Δ—mineral density, g/cm 3 ;
a nax — the maximum clarification area required to clarify one ton of dry ore, m 2 /(td -1 );
R c — The average liquid to solid ratio of the slurry in the compression zone can be calculated as the average of the liquid to solid ratio and the liquid to solid ratio (both measured) of the ore discharge to the critical point.
When the domestic concentrator uses the domestic serial concentrator, its structural size has been fixed. When using this type of standard concentrator, the height h Y of the compression zone should meet the following requirements:
h Y ≤H-(hc+hp)
(8)
When the calculated h Y does not satisfy the requirement of equation (8), the area of ​​the thickener should be increased.
(3) Calculation of the diameter of the thickener:
(9)
Where D-concentrator diameter, m;
A—the cross-sectional area of ​​the concentrator, m 2 .
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