Page 327 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

282 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

‘‘blend number,’’ n t 5R ¼ 36. Thus, n (2 s) ¼ 36, after a final K is determined. A heat exchanger is used to
and n 20 rps. In other words, with more time in cool circulated fluids.
the reactor, the pumping rate can be reduced. Required
Hint: (a) Determine from Equation 10.37 the time for Design an experimental program such that a P vs. R
C=C i ¼ 0.90, which is t=u ¼ 0.10. This is the time t ¼ set curve is generated. The curve will be used to design
t(five passes). Then calculate, n ¼ K=t(five passes). prototype systems of various sizes.
10.15 Q(impeller) for Five Passes 10.20 Calculate Flow of Liquid Alum and Ratio of Alum
to Raw-Water Flows
Given
Back-mix reactor with Rushton impeller and let Given
3
3
Q(basin flow) ¼ 0.1 m =s and u(basin flow) ¼ 10 s. For a raw-water flow, let Q(raw water) ¼ 1.00 m =s
(22.8 mgd) and let C(alum) ¼ 26 mg as Al 2 (SO 4 ) 3 14
Required
H 2 O=L.
Determine Q(impeller).
10.16 Calculation of n for 0.99 Blending Required
Calculate the flow of liquid alum required as a neat
Given
solution. Reference is Section 10.3.4.2.
Select a Rushton impeller–basin system and let n ¼ 10
10.21 Injection of Neat Alum
rps (as a first trial to be adjusted after calculation of
3
power, etc.) Assume, Q(raw-water) ¼ 1.000 m =s. Given
3
For a raw-water flow, let Q(raw water) ¼ 1.00 m =s
Required
(22.8 mgd) and let C(alum) ¼ 26 mg as Al 2 (SO 4 ) 3 14
Calculate t 5R for five passes through the impeller and
H 2 O=L. Neat alum solution, i.e., ‘‘liquid-alum,’’ is to
determine the detention time, u(raw water). Reference
be injected into the core zone of a jet mixer that
is Section 10.4.1.2.
disperses the raw-water flow in a 500 mm (20 in.) pipe.
10.17 Volume of Back-Mix Reactor
Required
Given
Determine the nozzle size for a single jet of neat alum.
Assume that the raw-water flow for coagulation
6
is 3.785 10 L=day (1.0 mgd). Assume that the coagu- Reference is Section 10.3.4.2.
10.22 Exploration of Mariotte Siphon for Small-System
lation chemistry regime is adsorption–destabilization.
Alum Feed
Required
Given
Determine the volume of a back-mix reactor. Refer-
The engineer for a small community, e.g., 2000 per-
ence is Sections 10.4.1.2 and 10.4.1.5.
sons, must select for alum-feed system for coagulation
10.18 Geometric Similitude
using a rapid mix. For reference, Example 10.4 pro-
Given
vides a context.
Consider a Rushton impeller–basin system with four
4
impeller blades. The system is to operate at R 10 . Required
3
Let u ¼ 10 s and Q m ¼ 0.076 m =min (20 gpm), Consider whether the use of a Mariotte siphon (see
3
Q p ¼ 0.438 m =s (10 mgd). Glossary) might be considered in lieu of a metering
pump for alum feed (for a possible ‘‘passive’’ alum-
Required
feed system).
(a) Calculate V m and V p . (b) Determine the dimen-
10.23 Design of Jet-Mixer System
sions of each basin.
Given
10.19 Imposing Similitude for Design
Raw water is delivered to a WTP by a 1067 mm
Given
(42 in.) pipeline from Horsetooth Reservoir with
A new impeller using a Rushton-type basin
water surface elevation 61 m (200 ft) above the plant.
(J=T ¼ 0.10) is to be tested by means of a model; for Let T ¼ 208C for working purposes.
3
most tests, u ¼ 10 s and Q p ¼ 0.00126 m =s (20 gpm).
Required
A variable speed direct current motor has been
State how the operation should be adjusted to account
installed with maximum power 2 kW; assume that
for the flow variation. How would you design the
the efficiency is 0.7 and is constant over all rotational
system to provide for the operating flexibility?
velocities. The model has been fitted with a bearing
10.24 Design of Second and Third Jet Rings
plate and scale to read torque; the rotational velocity is
measured by a strobe. The maximum rotational velocity Given
of the impeller is n(max) ¼ 3600 rpm. For working Raw water is delivered to a WTP by a 1067 mm
purposes, assume that the curve follows the standard (42 in.) pipeline from Horsetooth Reservoir with
viscous flow range curve and that for the level part, water surface elevation 61 m (200 ft) above the plant.
P ¼ K ¼ 0.5. The calculations will have to be revised Over the annual cycle, 2 T 168C. Example data