Page 482 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Cake Filtration 437

500
70
Filter-Cel
C-512
400 60
50
Pressure loss (kPa) 300 Nominal Pressure limit 40 Pressure loss (psi)

Hyflo
30
200

100 C-535 20
C-545 10
0 0
0 50 100 150 200 250
Time (h)
FIGURE CD14.10 Headloss versus time plots for five grades of diatomite as calculated by Table CD14.2.

T ¼ 118C, on the headloss versus time outcome. The independent
Turbidity ¼ 4 NTU variables include: Grade of DE, HLR, temperature, and
2
HLR ¼ 3.66 m=h (1.5 gpm=ft ) W(pre-coat).
r w ¼ 998 kg=m 3
g ¼ 9.81 m=s 2
r(pre-coat) ¼ 144 kg=m 3 14.3 DESIGN
r(cake) ¼ 144 kg=m 3
C(body feed) ¼ 25 mg=L The first task of design is to select a particular diatomite
technology, for example, pressure or vacuum, septum type,
Required orientation, etc. The sizing of equipment is next, including
(a) Calculate, from Equation 14.8, a plot of h L versus t.
specification of appurtenances, for example, tanks, pumps,
(b) Show the effect of doubling the HLR to HLR ¼
pipes, etc., and the control system.
7.32 m=h.
(c) Describe the effect of increasing C(body feed).
14.3.1 DIATOMITE TECHNOLOGIES
Solution
The steps for solution are enumerated below. A variety of equipment types is available from manufacturers
that relate to septum housing, septum type, and the method
1. Equation: The calculation of headloss is given by the of cleaning. To illustrate the kind of filter housing=septum
equation from Baumann et al. (1962): assembly available, Figure 14.11 shows a pressure filter
with retractable housing, which permits a dry-cake discharge.

m W(pre-coat) The same catalog source has a wide variety of tank–septum
h L ¼ v
r g k(pre-coat) r(pre-coat)
w

C(body feed) v t
(14:8)
þ
k(cake) r(cake)
The mass loading of body feed per unit area of
septum, W(cake), is
W(cake) ¼ C(body feed) v t (14:7)

2. Spreadsheet: Table CD14.2 is set up to calculate
headloss in accordance with Equation 14.8. For
the spreadsheet, let r(cake) ¼ r(pre-coat) ¼ dry
density. For example from Table 14.1, r(Hyflo dry
3
density) ¼ 144 kg=m .

Discussion
The spreadsheet, Table CD14.2, may be used to FIGURE 14.11 Pressure tank=septum assembly. (Courtesy of
explore the effect of any of the independent variables Durco Filters by Ascension Industries, North Tonawanda, NY.)