Chemical Engineering September 2021 - 52

TABLE 3. CORRECTION FACTORS FOR TYPICAL FILTER MEDIA AT
VARIOUS TEMPERATURES
Water
temperature,
°C
30
25
20
15
10
5
1.0 mm
anthracite
1.10
1.00
0.91
0.80
0.70
0.61
2.0 mm
anthracite
1.06
1.00
0.93
0.86
0.79
0.71
0.5 mm
sand
1.13
1.00
0.90
0.79
0.69
0.61
ensure efficient backwash operation
and minimal media loss.
Minimize risks of media loss from
temperature variations. At 85%
water level and 30°C, the tuned
backwash flowrate during the hot
day (Qhot) is 300 m3/h. This system
utilizes 1.0 mm of anthracite and 0.5
mm of sand.
Historically, the temperature could
drop significantly, to 20°C (water
density is 998 kg/m3), thus requiring
a lower backwash flowrate (denoted
by Qcold in Figure 10). From
Table 3, the derating factor (Cd) for
1.0 mm anthracite is 0.91/1.10 (a
ratio between correction factors at
20°C and 30°C, highlighted in blue
in Table 3) or 0.83. In the same fashion,
Cd for 0.5 mm sand is 0.90/1.13
(highlighted in green in Table 3) or
0.80.
The authors recommend using the
lower Cd for correction to minimize
the risks of filter media loss. From
Equation (2), Qcold can then be calculated
as follows:
Qcold = 0.80 × 300 m3/h = 240 m3/h
From the pump characteristic
curve in Figure 10, the corresponding
∆H for cold season (denoted by
∆Hcold in Figure 10) is 22.0 m water.
Thus, Pdischarge
- Psuction = 998
kg/m3 × 9.81 m/s2 × 22.0m =
215,388.4 Pa (2.15 bars)
When the water temperature is
20°C, one can use 2.15 bars pump
differential pressure as a first guess,
then observe the actual backwash
performance and adjust as needed.
Final recomendations
For poorly designed or existing systems
where no flowmeter is available
for backwash flow monitoring, the
outlined tuning technique has been
proven to be highly effective and
52
1.0 mm
sand
1.09
1.00
0.91
0.83
0.73
0.64
provide consistent
backwash flowrate.
The authors
recommend installing
a dedicated
flowmeter for new
units or retrofits to
the existing plant
for early detection
of any anomalies.
Although it
still requires a field
check to ensure
problem-free backwash operation,
the proposed technique is nonetheless
useful to verify the accuracy of
a flowmeter.
Create a transparent logging system
to ensure everyone involved in
process monitoring can track the
status of valve maintenance. For example,
the unit engineer can create
a dedicated section in the shift report
for any critical valves currently
under maintenance.
Communicate with all instrument
technicians to ensure they fully understand
the effects of positioning
bolts on filter operation. For troublesome
clarifiers, where sludge carryover
is frequent, the authors recommend
setting the backwash flowrate
at 10% above the design value to
handle potential clarifier upsets.
One may consider installing a realtime
sludge level detector for better
sludge level monitoring.
Create a task for a field operator
in charge to monitor the backwash
operation, at least once a month for
every filter.
Seasonally or quarterly, conduct
backwash
performance
evaluation.
The optimal backwash flowrate for
each season should be appropriately
documented for future reference. Be
careful when extending the time interval
between each backwash, for example,
from 24 to 36 hours, as trapped flocs/
particles will become more difficult to
remove. A backwash flowrate or duration
should be adjusted accordingly to
ensure efficient backwashing.
The same tuning technique can
also be applied to other systems with
similar configurations, such as activated
carbon filter or sand filters in
wastewater treatment units.
■
Edited by Scott Jenkins
References
1. Filter Maintenance and Operations Guidance Manual, AWWA Research
Foundation, 2002.
2. Handbook of Industrial Water Treatment, Suez, [Online] Available at
www.suezwatertechnologies.com.
Authors
Nattapong Pongboot is a senior
consultant at Global R&D Co. Ltd
(Samut Prakarn, Thailand); Email:
nattapong.globalrd@gmail.com or
nat.pongboot@gmail.com; Phone:
+66-87-665-6015. Pongboot is
an experienced chemical engineer
with broad experience in refining
and petrochemical technologies.
Earlier in his career, he spent several
years solving problems in water treatment plants.
Before partnering with Global R&D, he held various technical
roles with Honeywell UOP, PTT Global Chemical
and SCG Chemicals with good exposure to process design,
plant operation, troubleshooting and optimization.
Additionally, he is also a technical instructor for www.
chemengedu.com. He obtained both B.Eng (ChE) and
M.Eng. (ChE) degree from Kasetsart University.
Wiroon Tanthapanichakoon is
currently the managing director of
Global R&D Co. Ltd. (Samut Prakarn,
Thailand (Email: wiroont.globalrd@gmail.com;
Phone: +6683-177-8108.
Tanthapanichakoon
has several-years of combined experience
with ExxonMobil and SCG
Chemicals in Thailand. He has authored several international
papers and technical articles, and also holds some
technology patents under his name. He founded a chemical
engineering training platform called " ChemEngEdu "
(www.chemengedu.com). He has conducted several
public and in-house training courses on topics in chemical
engineering, process and equipment design and
scale-up for more than 2000 engineers. He is a senior
professional engineer in Thailand.
Wirinya Karunkeyoon is a process
engineer with PTT Global
Chemical (Thailand; Email:
Wirinya.k@pttgcgroup.com;
Phone: +66- 3897-1759 or +6683-233-6244).
Karrunkeyoon has
several years of experience in
water treatment, power generation
and diesel hydrotreating. She is
currently affiliated with PTT Global
Chemical (Site 6: Refinery) in Thailand. She obtained her
B.Eng. (ChE) degree from King Mongkut's University of
Technology North Bangkok and M.Eng. (ChE) degree
from King Mongkut's University of Technology Thonburi.
Kanyaporn Lertwimolkasem is
affiliated with PTT Global Chemical,
and is an experienced process
engineer
(Kanyaporn.L@pttgcgroup.com
or Kanyaporn.lert@
gmail.com). She has expertise in
water treatment, power generation,
steam reforming, mercaptan
oxidation and crude distillation.
She is currently works at the PTT
Global Chemical Site 6 Refinery in Thailand. Before PTT
Global Chemical, she spent two years working for Technip
Engineering. She obtained both B.Eng. (chemical
engineering) and M.Eng. (chemical engineering) degrees
from King Mongkut's University of Technology in
Thonburi in Bangkok, Thailand
CHEMICAL ENGINEERING WWWCHEMENGONLINECOM
SEPTEMBER 2021
http://www.suezwatertechnologies.com http://www.chemengedu.com http://www.chemengedu.com http://www.group.com
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