Selection and calculation of interstage screen in carbon in
2020-07-07 10:11Introduction：There are vibrating screens, curved screens, peripheral screens and bridge-typescreens.The vibrating screen wears a lot on the carbon, and the curved screen is easily blocked,at present, bridge-type screen is widely used.According to the d
There are vibrating screens, curved screens, peripheral screens and bridge-type screens. The vibrating screen wears a lot on the carbon, and the curved screen is easily blocked ,at present, bridge-type screen is widely used.According to the different shapes of the screen mesh, the bridge screen is divided into chute plane screen, trapezoidal screen and cylinder screen.The slurry flow through the bridge－type screen is related to the area of the screen mesh, but in actual production, the depth of the contact between the screen and the slurry is generally approximately fixed, so the length of the screen mesh is only selected in practice.The total length of screen mesh required for each adsorption tank is:
L=Q/Q0 (7.1-3)
In the equation L -- the total length of screen mesh required for each adsorption groove, m;
Q -- slurry flow rate, m3/h;
Q0 -- the amount of slurry that can pass through the length of each meter, m3/(m•h)
Generally, the contact depth between the bridge-type screen of the 24mesh screen and the slurry is 100 ~ 200mm, and the slurry flow rate per unit screen length is 15 ~ 25m3/(m•h).
For ease of operation and maintenance, the bridge-type screen mesh of each groove is generally divided into several blocks, which are calculated as follows:
n=L/L0 (7.1-4)
In the equation n-- number of bridge-type screen mesh needed for each adsorption tank, block;
L0 -- selected length of each bridge-type screen, m.
In order to prevent the loss of large amounts of activated carbon when replacing the screen mesh, the number of each adsorption tank bridge-type screen mesh should not be less than 4.
If peripheral screen is used, the length of the screen shall not be less than 15% of the circumference of the adsorption groove.
In order to ensure free flow of slurry, the bridge-type screen chute must have a slope of more than 10%.
In practice, the overflow weir is usually installed in the chute of the bridge-type screen close to the screen net, as shown in figure
7.1-1.In order to reduce the pressure difference of the slurry on both sides of the screen, prevent the blockage of the screen and extend the service life of the screen.The bottom of the overflow weir has a 2 ~ 3mm slit, so that most of the slurry through the screen flow out of the slit, another part of the overflow from the top of the overflow weir.The overflow weir is adjustable so that the width of the slit can be adjusted according to the slurry flow.The height of the overflow weir depends on the depth of contact between the screen and the slurry, which is generally 100 ~ 200mm. It can also be calculated as follows:
H=Kν2/(2g) (7.1-5)
ν=2Q/(3A) (7.1-6)
In the equation, H -- height of overflow weir, m;
K -- loss coefficient of hydraulic head, usually 1.5;
ν——the velocity of slurry in the slit, m/s;
g -- gravity, m/s2;
Q -- the slurry flow rate through the screen, m3/s;
A -- slit area, m2.
Low pressure air is used to clean the screen surface of the bridge-type screen to prevent blockage caused by activated carbon clinging to the screen.The calculated pressure of the low-pressure wind is usually around 35kPa.According to experience, the required low pressure air volume per unit length screen is 1.0m3/(m•min).Based on this, the total amount of air required under standard state can be calculated. The amount of air under pressure can be calculated according to the conversion formula, and then the low-pressure fan is selected.
