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