Problem SetProblem # 1 Continuous Screening
Given:
a. Effective dimension of 35 mesh screen (6ft x 20ft)
b. Undersize flow rate = 50 tons/hr
Mesh Size Feed Size Oversize Undersize
6/8 0.075 0.08 0.02
8/10 0.125 0.145 0.055
10/20 0.1 0.17 0.09
20/28 0.125 0.15 0.085
28/35 0.125 0.28 0.1
35/48 0.175 0.175 0.15
48/65 0.225 0.15
65/100 0.05 0.25
100/150 0.1
Required:
a. Effectiveness of screening operation
b. Capacity of each 35-mesh screen
Solution:Effectiveness
Let A= desired material (undersize)
Overall mass balance:
(equation 1)
Component mass balance:
(equation 2)
Solving equations 1 and 2 simultaneously,
F=86.3636 tons/hrR=36.3636 tons/hr
effectiveness = 0.53
Capacity
Using the throughflow method of Matthews,
Where A = screen area, ft2
Ct=throughflow rateCu=unit capacityFoa=open-area factorFs=slotted-area factor
Assuming that the screen has square openings,Fs=1Foa=(a/(a+d))2
where a=clear opening dimensiond=diameter of wire
From Table 19-6 of Perry’s Chemical Engineers’ Handbook, 7th editiond=0.0114in and a=0.165in (mesh 35 screen)
Foa=(a/(a+d))2
=(0.0165/(0.0165+0.0114))2
Foa=0.3497514163
Cu=0.4765289256 tons/hr-ft2
=11.44tons/24hr-ft2 =22880
tons/24hr-ft2