Biwater Treatment Achieves A Positive Result To A Negative Transient Pressure Challenge

Biwater Treatment Ltd,part of the BiwaterGroup plc,offer consultancy services to thewater industry around the world.SimonJohnson,Senior Operations Engineerexplains how they used FloMASTER toprovide cost effective solutions to theircustomers.

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""FloMASTER is the right tool to solve problems which have a high impact on the safety and reliability of a plant and cannot be solved by most other solutions""

Simon Johnson,Senior Operations Engineer,Biwater

The Challenge

Biwater Treatment designed and installed apressurized filter and membrane plant atBroadford water treatment works (WTW).

In brief the plant consists of a filtration unitpositioned downstream of a pumpingstation which in turn is supplied,via agravity fed suction main,with water fromthe Allt a Mhuilinn river,1.2 km away.

During commissioning of the plant the siteengineers observed that the primary filtersfrequently blocked which triggered abackwash cycle.On site investigationsrevealed that,following the onset of thebackwash cycle,which caused a suddenincrease in flowrate through the intakepumps,air was entering the system,collecting on the filter screen and causingfurther blockage.

The Solution

Since the on-site investigations lead to theassumption that air was entering thesystem and the most likely route wasthrough air valves situated at intervalsalong the suction main,the next stage wasto prove this and then propose a costeffectivesolution.

Once it could be numerically proven thatthe negative pressure transients caused theair valve on the suction main to open,thetask was then to propose a solution.Thesimplest and most cost effective way camein the form of a bladder type surge vesselto absorb the rate of change of flow.Furthermore air release valves were fittedto the filter vessels.

The Results

From the initial simulation that proved thepressure in the suction main was causingthe air valves to open and identify whichbackwash flow rates were the cause,themodel was then modified to include thebladder type surge vessel and predict theoptimum size and connection diameters tothe existing system.Figures 1 and 2 showthe pressure transients at the most criticalpoint before and after the surge vessel isadded.The addition of the surge vesseland air release valve on the filters atBroadford has reduced the frequency ofthe backwash cycle from typically 5minutes to over 60 minutes and theensured that clean safe water can beproduced as economically as possible.Theuse of FloMASTER reduced the time toquantitatively identify the cause of reportedproblems and investigate cost effectivesolutions,faster and more accurately thantraditional testing.

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