Design of Pressure sand filter for drinking water treatment plant. Filtration Capacity required is 100 cum per hour. Can any one suggest h...
Published on by Sandeep Pandharkar, Consultant for Engineering, Procurement & Construction for Water & Wind projects
7 Comments
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Sandeep,
There are many books to be found out there on media filtration design, which would provide you technical fundamentals on design of you system. Once such book that might provide you the technical reference you are seeking is “Filter Troubleshooting and Design Handbook”: By Richard P. Beverly.
Manufacturers of Media Filtration products, such as Evoqua, will have their own design practices. Most proprietary to try and sustain some level of competitive advantage on what has really become a commodity type of technology.
The media you have chosen has defined design flow specifications as provided by the manufacturer, which you has identified. The required media depth, specified media design flux (gpm/ft2), and market standard vessel diameters will define your vessel size. Pressure vessel MFG’s will have common shell diameters based upon their tooling. Although you can have any custom diameter fabricated, the cost is not justified in terms of beneficial filter performance. The standard diameter that most closely supports your design requirements will define your vessel diameter. I use the following rules of thumb in choosing a design flux rate, if not specifically defined by the media MFG.
Service Flux rate Anticipated % Particle Removal
(gpm / sq.ft.) (Particles > 40 mm) (Particles < 40 mm)
15 70% 50%
12 80% 60%
10 90% 70%
8 96% 75%
Pressure loss through the unit, both during service and backwash, will of course depend on your media profile, but will also be dependent upon your internal distribution design. There are various distribution designs. Most common for MMF would be a hub and radial design for lower collection and a splash plate upper distributor. Typical design pressure loss for such distribution is ~3-4psid.
Hope this helps.
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Hello,
Mr Sundance Rogers,
Mr Steven Johnson.
The data available from manufacturer of PF is as follows :
Operating Pressure = 5 kg/ cm2
Flow rate = 105 m3/hour
Media = Zeosorb( Germany) The website provides this info:
www.watchwater.com/pdf/suspended-solids-tss/zeosorb...
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Operation conditions and exchange capacity:
Bed depth 400 - 1000 mm
Freeboard 30 - 50 %
Service flow rate 20 - 48 m/h
Back wash flow rate 25 - 50 m/h
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Diameter of pressure vessel = 2400 mm (as per mfg) (How is this arrived ? )
Height = 2000 mm
Material of PF is Carbon steel.
To Filter untreated drinking water of 15 NTU at inlet to PF.
Temperature of Water = 20 deg C
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I have to choose a suitable pump for back washing, for which I need to first arrive at correct back wash flow required.
Also, I want to know how much residual pressure remains at the drain outlet after backwashing, so that the residual head can be used for further flow by gravity.
What could be the head loss after back washing ?
Where can I find a scientific method of " How to design a PF" ?
Sandeep
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Mr Sundance Rogers,
Mr Steven Johnson.
Thank You.
Will go thru your advice.
Will provide the info as given by the mfg of PF.
Regards,
Sandeep
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Well, it seems the message board wants to truncate my messages. The links provided will give you some access to pre-engineered media solutions that may be of interest, while also providing additional design detail that may be of help to you. My apologies the info is not coming through here as typed.
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It would appear that the content of the previous message did not come through. Let's try that again:
Backwash Design for conventional MMF
Temp (F) Flow(gpm/ft2)
< 5µm.
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Mr. Pandharkar,
I agree with Mr. Johnsons summary and would only add:
As a general design baseline for conventional media filtration I use the following temperature corrections for backwash design.
Temperature (F) Flow (gpm/ft2)
http://www.evoqua.com/en/brands/IPS/Pages/vantage-pti-hf-mmf.aspx
Cross flow < 5µm
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Sandeep,
Your question generates more questions that you will need to answer in order to design your system. Here are a few:
1) What are you trying to filter? TSS, Organics, Iron&Manganese, Etc. Your media will be dependent on your process water specifications required. Your flow rate of 100 m3/hr is about 440 gal/min (gpm). Based on the service rate of the media you choose (expressed in flow per area) usually media's are in the 5 gpm / ft2 to 6.25 gpm / ft2. The next question is how big do you make your tanks based on this service rate and you BW rate below. Normally you want to size your tanks based on common tank sizes you can manufacture and handle in your area. This flow would normally require (5) 54" dia x 60" side sheet tanks, or (4) 60" dia x 60" side sheet tanks.
2) Your design backwash rate is dependent on the media you choose and the water temperature. Usually you would refer to the manufacturer's media specs. There you will find backwash rate charts based on water temperature. A typical multi-media (gravel, sand, Anthracite) will have a BW rate of 15 gpm/ft2, Next Sand (high performance filtering media) can have a BW rate of 17 gpm / ft2 and Catalytic Media (OxiPlus 75) can be as high as 25 gpm / ft2 of surface area. All these are based on 60 Degrees F.
3) Tanks can be made of Carbon Steel, Stainless Steel or FRP (Fiberglass Reinforces Plastic). If CS is desired then usually the head and shells are of pressure vessel grade quality steel such as SA-516-Grade 70 CS. The attachments such as clips and supports are usually A36 CS.
4) Tank design is usually completed by the supplier of the pressure vessel. But, in most average filtering cases 100 psi (6.9 Bar) is a good average design pressure. Usually this results in a shell wall thickness of 3/16" (4.76mm) and head of 1/4" (6.35mm) depending on temperature. Of course your tank supplier should confirm the calculations based on his procedures, etc. so check with them first.
Good luck
Regards,
Steven Johnson
Watersurplus