PROCESS DESIGN CALCULATIONS FOR TUBE SETTLER IN WATER TREATMENT PLANT 5.0 (C) TUBE SETTLER Raw water Flow Recycle Flow Design Flow
= = = = = = = = =
Shape of unit Length/ Breadth of Tube Settler provided
= =
100 5 100+5 105 4 105/4 26.250 26250.000 1093.750 Square 11.40
Tube Pack Data: Shape Cross sectional area Hydraulic radius Settling area : 60° Slope Settling area : 55° Slope Vertical Space between Tubes Angle of inclination
= = = = = = =
Hexagonal - Chevron 120 x 44 mm x mm 0.015 m 11 m²/m³ 13 m²/m³ 0.044 m 55 °
Settling area of Tube Pack, corresponding to the inclination, based on the effective volume of Tube Pack
= = = = = = = = = = = = = = = = = = = = = = =
1.00 m³/m²/h 0.70 1* 0.7 0.70 m³/m²/h 0.00000080 m²/s 20.00 °C 0.000001003 m²/s 0.0000008/0.000001003 0.798 0.7*0.798 0.558 m³/m²/h 0.700 m³/m²/h 1.000 11.4*11.4 129.960 m² 129.96*1 129.960 m³ 11.4*1 *(1/TAN55°) 7.982 m³ 129.96-7.982 121.978 m³ 121.978*13 1585.709 m²
Actual Settling rate on the horizontal projected area of Tube Pack
=
1093.75 / 1585.709 0.690 m³/m²/h 0.70 m³/m²/h Hence O.K.
Number of units provided So, Design flow per Tube Settler
Select, Settling rate on the horizontal projected area of Tube Pack Apply the probability factor,as recommended by theTube Pack Vendor Revised Settling rate on the horizontal projected area of Tube Pack Kinematic viscosity of water at 30°C Design temperature of water Kinematic viscosity of water at 20°C Correction Factor for Settling rate, w.r.t. Kinematic viscosity Corrected Settling rate Selected Settling rate on the horizontal projected area of Tube Pack Selected vertical depth of Tube Pack Plan area of the Tube Settler Volume of Tube Pack provided Loss of volume of Tube Pack, on account of inclination Effective volume of Tube Pack
<
Mld Mld Mld nos. Mld m³/d m³/h m
Check for the performance of the Tube Settler: Sedimentation takes place in the length following the transition length and it will retain all particles with a settling velocity less than Vs.
Vs
= V. k / { [sin θ + (Ls/d)cos θ ] }
Where, Vs = Settling velocity, m³/m²/h
Ls = Settling length of Tube d = depth of water in a Tube at right angle to the direction of flow, m θ = angle of inclination of Tube Pack to the horizontal k = a coefficient = 1.33 for Hexagonal Tubes Schiller formula to calculate transition length:
Lt = 0.0288 NR .D Where, Lt = Transition length V = Average velocity of flow in the Tubes, m³/h.m² = U / sin θ U = Average upward velocity, m³/h.m² = Surface loading rate of the Settling Tank = Rate of flow / Tube entrance area ν = Kinematic viscosity of water, m²/s NR = Reynolds Number
=
0.00000086
m²/s
Ls = L - Lt Where, L = Length of Tube Ls = Settling length of Tube Plan area of the Tube Settler
= 11.4*11.4 = 129.96 m² The tube entrance area is reduced due to the thickness of the tube pack and also due to the supporting structure provided. The support width of minimum 60 mm is recommended at a centre-to-centre distance of 1000 mm, in a square grid. No. of supporting angles, lengthwise @ 1m c-c spacing = (11.4/1)+1 = 12.40 nos. Say = 13.00 nos. No. of supporting angles, breadthwise @ 1m c-c spacing = (11.4/1)+1 = 12.40 nos. Say = 13.00 nos. = 65.000 mm Width of supporting angle of standard size, provided = 0.065 m Plan area lost by the supporting angles of width 65 mm = (11.4*13*0.065)+(11.4*13*0.065 -(13*13*0.065*0.065) = 0.768 m² = 3.00 % of plan area Plan area lost by the thickness of the Tube Pack = 3%*129.96 = 3.899 m² Total area of obstruction for flow through Tube Pack = 0.768+3.899 = 4.667 m² Tube entrance area = 129.96-4.667 = 125.293 m² Average upward velocity, U = 1093.75/125.293 = 8.730 m/h Average velocity of flow in the Tubes, V = U / sin θ = 8.73 / sin 55° = 10.657 m/h = 0.003 m/s Hydraulic radius, R ( = CSA / Wetted perimeter) Equivalent diameter, D ( = 4 R)
= = =
0.01500 4*0.015 0.060
Reynolds Number, NR
=
VR
m m
ν = =
0.003*0.015/0.00000086 51.632
Transition length of Tube
Settling length of Tube, Ls
Relative settling length of tube = Ls/d Coefficient k for Hexagonal shaped Tubes Vs
= = = = = = = = =
0.0288*NR*D 0.0288*51.632*0.06 0.089 m L - Lt 1-0.089 0.911 0.911/0.044 20.700 1.33
m
=
V. k / { [sin θ + (Ls/d)cos θ ] }
= = >
10.657*1.33/((sin55°+20.7*cos55°)) 1.117 m³/m²/h 0.690 Hence O.K.
= = = = =
11.40 1093.75
= = = = = = = = = =
0.025 m/s 1093.75 / 3600 / 0.025 12.15 m² 12.15 / 11.4 1.066 m 1.00 m 0.30 m 0.65 + 1 + 1.066 + 1 + 0.3 4.016 m 4.05 m Hence O.K.
= = = = = = = = = = = <
250 m³/m/d 26250/250 105.000 m 105/(2*(11.4-(1/TAN 55°) 4.907 6.000 nos. 6*2*((11.4)-(1/TAN55°)) 128.398 m 1093.75 / 128.398 8.52 m³/m/h 204.44 m³/m/d 250.00 m³/m/d Hence O.K. 30.000 Mld 30000.000 m³/d 30000 / 128.398 233.65 m³/m/d
Unit Size Length / Breadth of Tube Settler provided Flow per Tube Settler Approx.liquid height above the top of the tube pack Vertical Height of Plates Horizontal velocity in the clarification shall be 0.02 to 0.03 m/s. Horizontal Velocity in the clarification zone selected C/S area of clarification zone required below Tube Pack Height of the Clarification zone required Depth of the sludge compression zone provided Space provided for sludge scrapper Side water depth of unit required SWD provided
Provide V-Notch weir plates on the inner side of overflow launders. Recommended weir loading for Tube Settler Length of weir to be provided No.of overflow launders to be provided Say Approx.length of weir provided in each Tube Settler Discharge rate at design flow over the weir
Design Hydraulic flow per Tube Settler Discharge rate at design Hydraulic flow over the weir
= = = =
Size: 4 Nos. Tube Settlers, each of 11.4 m x 11.4 m x 4.05 m SWD
0.65 1.00
m m³/h 0.3038 m³/s m m
