Bar Screen Design

MANUAL BAR SCREEN DESIGN

Objective: Screens are used in wastewater treatment for the removal of coarse solids. General design basics: S.N o

Description Bar spacing is in range "he screen is mounted at an angle of from hori#ontal Bar si#e +inimum approach velocit, in the bar screen channel to prevent grit deposition +a*imum velocit, between the bars to prevent washout of solids through the bars

Standard value  to ! $!%&'

Unit cm degree

( thic) * .! wide '.$!

cm m-s

'.

m-s

/*ample:  0verage  0verage 1low 2 !''' !''' m3-da, m3-da, 4ea) flow factor2 (.$! 4ea) flow 2 35!' m3-da, 6elocit, considered2 '.5 m-s  0ngle of inclination is !' o Depth-width ratio 2 (.! Space between bars2 3' mm and thic)ness of bar2 (' mm (. "he cross section of the bar screen channel is determined from the continuit, e7uation

8 2 0* 6 9here 82 flow rate m3-sec  02 ;hannel ;hannel cross section section area area m 62 6elocit, m-s

 028-6  02 '.$( m3-s '.5 m-s  02'.5 m

 0rea2 channel width m * channel depth m d-92(.! d2 (.! 9  0rea 2 width * (.! width  9idth 2 '.5 m (.! 92 '.5< m d2 '.5< m * (.! d2(.'3 m

. "he cross section of the bar screen is given b, the following e7uation

 0b 2 0-Sin= 9here  0b 2 bar screen cross section m > 2 inclination angle of the screen

 0b 2 '.5 m- sin !'  0b 2 '.( m

3. "he net area of the bar screen available for flow is given b, the following e7uation:

 0net 2 0b

S S?tbar 

9here

tbar  2

thic)ness of the screen bars m

S 2 space between bars m

 0net 2 '.( m

3' mm 3'mm? ('mm

 0net

2 '.5<$ m

1rom continuit, e7uation: 6 02 6 b 0net 6b 2 '.5 @ '.5-'.5<$ 6b 2'.5(3 m A'. its OC

$. "he head loss through the bar screen is given b, the following e7uation:

( 2

6b% 6 g

( '.&

9here (2 ead loss 62 approach velocit, m-s 6b2 6elocit, through opening m-s

g2 acceleration due to gravit, m-s 1or clear screen: ( 2

'.5(3 % '.5

(

@.<(

'.&

(2'.''('
1or $!E clogged screen:

 0net 2 !!E  0net 6 02 6b 0net 6b 2 '.5 @ '.5-'.5<$@'.!! 6b2 (.(( m-s ( 2

(.((% '.5 @.<(

( '.&

(2'.'53( m !. "he number of bars in the screen is given b, the following e7uation: n tbar ? Fn%(S 2 9 n@('?Fn%(3'25< n ('? n 3'25<?3' n2(&.< bars2sa, (< nos.

5. 9etted perimeter  42 w ?  d 42 wetted perimeterm 92 width of channel m d2 depth of channel m

42'.5<?@(.'3 42 .&< &. ,draulic radius H2 wd-w?d H2'.5<3@(.'3-.&! H2'.!5 m <. Slope +anning e7uation v 2 )n - n H-3 S(-

F(

where v 2 cross%sectional average velocit, Fm-s )n 2 (.' for SI units  0 2 cross sectional area of flow Fm  n 2 Manning coefficient of roughness H 2 h,draulic radius Fm S 2 slope of pipe Fm-m N2 '.'(3 S(-2 v@ n- H -3 S(-2 '.5@'.'(3-'.!5 '.55 S(-2 '.''&<-'.$'5< S2 '.'((& m-m