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D Reciprocating vacuum pump Reciprocating vacuum pump is also known as piston vacuum pump. The structure is shown in Figure 5.
(II) Selection and calculation of vacuum pump The water ring type and jet type vacuum pump have simple structure, convenient operation and maintenance, and are not afraid of misty corrosive filtrate mixing. Therefore, it is not necessary to provide a second stage steam-water separator in the filtration process. These two types of vacuum filtration operations for beneficiation plant better adaptability, price 20% lower than reciprocating pumps about, but the former is about twice higher power consumption, while its pumping capacity varies with the temperature of the water seal.
SK type water ring vacuum pump has larger pumping capacity than SZ type, lower power consumption and higher efficiency, up to 48~53%. It has small vibration during operation and reliable operation. Its maximum inspiratory capacity can reach 120 m 3 /min.
The SZ type water ring vacuum pump has a simple structure and convenient operation. At the same time, the waste water in the steam separator can be used to supplement the water consumption of the water ring in the pump. Therefore, the new water consumption is lower than that of the SK type pump, which is about 35%.
The water jet pump is suitable for use in small and medium-sized concentrators where the filter cake moisture requirements are not too strict. The pump has a simple structure, is easy to manufacture, and has a low cost. No moving parts during operation, low noise, easy operation and maintenance. The separated filtrate can be recycled, consumes less electricity and consumes less water. Steam blast pumps can also be used in concentrators with cheap steam sources.
Reciprocating vacuum pump, due to its high working environment requirements, can not pump gas containing liquid, at the same time the equipment structure is complex, the material processing and processing precision requirements are high, the operation and maintenance is not convenient, etc., the new concentrator is very Less adopted. However, the power consumption of the pump is lower than that of the SZ water ring vacuum pump, and the working efficiency is high, up to 65-70%. Therefore, a few concentrators are still using this pump.
Determining the specification of the vacuum pump depends primarily on the amount of air drawn by the filter cake during washing and draining and the required vacuum gauge pressure. These two indicators should generally be obtained through the filtrate test. In the absence of test data, the total pumping capacity and number of vacuum pumps can be determined based on the amount of pumping required per unit of filtration area and the total area of ​​filtration. [next]
When filtering viscous fine-grained materials or iron concentrates, the amount of minerals is large, the filter cake is thick, and the wind consumption is high. Generally, the air suction volume is 1.2-1.5 m 3 /(m 3 · min). The capacity and number of vacuum pumps are determined. The calculation shall be based on the amount of suction when the degree of vacuum is zero (ie, the measured pressure is 101 kPa).
The shaft power of the vacuum pump can be calculated as follows:
Where N - the shaft power of the vacuum pump; KW;
L 1 - the work done by drawing 1 m 3 of gas from the vacuum space, J/m 3 ;
Q——the actual inspiratory volume, m 3 /min;;
η—The full efficiency of the vacuum pump is generally 0.7 to 0.85, depending on the type of construction of the vacuum pump and the type of compression process to be followed.
When considering the adiabatic compression process, the work done by the vacuum pump is:
In the formula L 1 - the meaning is the same as above, J / m 3 ;
K - adiabatic index. The adiabatic index of air is 1.4;
P 1 - absolute suction pressure, Pa;
T 1 - air temperature at the beginning of compression, °K;
T 2 - the air temperature at the end of compression, °K.
(III) Selection of air blower When using various types of cylinder type internal filter type, disc type vacuum filter machine and filter press machine, it is necessary to use low pressure air to blow off the filter cake, and the absolute pressure is generally 112.8 to 225.6 kPa (ie The gauge pressure is 9.8 ~ 124.6 kPa), the lower limit of the magnetic separation concentrate, the upper limit of the flotation concentrate. Excessive pressure will affect the life of the filter cloth and consume more power.
There are many types of low pressure fans. The concentrator generally uses a fixed-capacity Roots blower or a Yee blower. The characteristics of these two blowers are that the machine itself does not compress the air it conveys, but the pressure is increased when the amount of air in the space of the exhaust container (such as the wind bag and the exhaust pipe) is increased. The air from the atmosphere is reverse-compressed, and the flow rate of the blower is constant and does not change with the magnitude of the wind pressure. This is another feature of the constant-capacity fan. [next]
The structure of the Roots and Yeh-type blowers is shown in Figures 6 and 7, respectively.
The actual inspiratory volume of a Roots blower can be calculated as follows:
Where Q is the actual amount of inhalation, m 3 /min;
A - the cross-sectional area of ​​each rotor, m 2 ;
D——the diameter of the rotor, m;
L——the length of the rotor along the axial direction, m;
N——rotor revolutions per minute, r/min;
Λ——pressure transmission coefficient, the main product is determined by the leakage condition, generally 0.75~0.85.
The operating pressure of the Ye's blower is higher than that of the Roots blower, but the construction is more complicated.
Concentrator desired gauge pressure antiquity as more than 29.4 kPa (0.3 kg / cm 2), optional water ring compressor.
In small-scale concentrating plants, when the requirements for concentrate water are not strict, it is also advantageous to blow the filter cake out of the exhaust gas discharged from the water ring or water jet vacuum pump, but the control pressure must be controlled at 9.8 kPa (0.1 kg/cm). 2 ) Above. This saves the blower but reduces the thermal efficiency of the vacuum pump.
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