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The coarse filter process calculation

The coarse filter process calculation

1.General
This calculation method is according to the petroleum chemical pipe filter and the bottom valve filter, reference standard SH/T 3411-1999, HG-T 21637-1991 . This calculation method only used for calculate the filtration international filtration area and the Starting pressure drop, it don’t suit for the The filter shell GB150 standard execution.

2.Filter area calculation
According to the criterion SH/T3411-1999, the Definition of the effective filtration area will be: the filter internal support structure opening area minus the pore area. So when calculate the effective filtration area, we should consider of the effective area of the support structure and the filter mesh. According the the criterion, the Permanent filter’s effective filtration and the pipe sectional area ratio will not less than 1.5. For this project, the filter will based on the temporary filter criterion, the effective filtration area and the pipe sectional area ration will not less than 3.0.

2.1 The pipe sectional area calculation S1:
For this project, the filter inlet and outlet of the pipe diameter: nDN200 , S1=(0.2/2)2×3.14=0.0314 m2
2.2 The filter effective filtration area calculation S2
According to the standard area ration 3, S2/ S1=3,S2= S1×3=0.0314×3=0.0942 m2
2.3 The filter filtration mesh area calculation:
According to the project requirement, the filtration will be 0.8mm, the surface area is 0.45m2
We choose the basket filter surface weran 0.56m2, the basket filter support part open area 50%, 24 mesh filter mesh(it could filter the particle size more than 0.785mm ) the effect opening area is 56%. Then, the basket filter effect area S=0.56×0.5×0.56=0.157 m2, the effect filter area more than 2.2, the computed result 0.0942m2, so the filter area is available.

3. The Starting Pressure Drop Calculation
According to the reference formula, if calculate the pressure drop, we need the following physical quantity: Reynolds number, the equivalent length, fluid density and viscosity, etc.

The Computational Formula
Δ p --- pressure drop (Pa)
λ---- the coefficient of friction (dimensionless)
L ---- equivalent straight pipe length (mm)
D ---- pipe diameter (mm)
Re---- Reynolds number
ω ---- fluid velocity (m/s)
μ ---- fluid viscosity (cP)
ρ ---- fluid density (kg/m3)

According the the parameters, calculation the pressure drop:
ω=(120644/780)/0.0314/3600=1.37 m/s
=780×200×1.37/0.45=474933
λ=64/ Re=64/474933=0.00014
the equivalent length L equal 55*103( use the standard equivalent length)
Then =0.00014×(780/2)×(1.37)2×(55×103/200)=28 Pa
So the filter starting pressure drop is 28pa.
During normal operation, Many element will influence the pressure drop of the filter, such as the content of the solid particle in the fluid and so on. So it is hard to calculate the relationship between the filter pressure drop and the operate time. We advise to replace the basket filter if the pressure drop is 0.1-0.2 M pa, and the Filter the design strength equal or more than 0.4mpa.

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