Water Audit Article CE 1205

8/2/2019 Water Audit Article CE 1205

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Avariety of factors dictate thewater-treatment needs of anychemical process plant. Forinstance, many industriesdepend on high-quality inlet

water to produce their end products.Meanwhile, wastewater generated bychemical process operations must betreated to meet local, state and fed-

eral environmental guidelines. Manyindustrial plants are also working toreduce the total volume of water theyuse, to conserve this valuable and in-creasingly costly resource.

For these reasons, it is vitally im-portant that a facilitys water- andwastewater-treatment systems oper-ate in the most efficient and cost-ef-fective manner. By carrying out a com-prehensive, onsite water assessment,engineers can gain critical insight intotheir operations and uncover ways toensure cost-effective operation andguarantee consistent compliance withwater-quality standards while con-

serving water. And in many cases, suchan assessment can help engineers toimprove operations and maintenancepractices in a way that reduces costsand downtime.

Water assessments:The what and why

A water assessment consists of a re-view of all equipment that is used totreat process water and wastewaterat the plant. Process operators should

conduct a water assessment wheneverthey suspect a possible problem, eitherbecause they are not getting the de-sired quality and quantity of water, orbecause the individual unit processesare performing below expectations orspecifications (this aspect is discussedin detail later).

However, you dont have to waituntil there is a problem. Perhapsyour water-treatment equipment isold and youre wondering if it wouldmake sense to upgrade or replaceindividual components or the wholesystem. Perhaps you would like toknow if your plant is using water in

the most efficient manner to reduceoperating costs and encourage re-cycling and reuse. By conducting awater assessment at your facility, youcan identify equipment that needs tobe tuned up or replaced, and deter-mine whether additional equipmentshould be added to enhance the treat-ment capabilities of the existing sys-tem, in terms of economics, through-put volume or pollutant-removalcapabilities.

The system-wide evaluation willalso give you the opportunity to evalu-ate whether any additional equipmentthat may be needed as a result of theassessment should be handled as apurchased, permanently installed sys-tem, a build-own-operate system, or atemporary mobile system. Such a de-cision will depend on the site-specificoperational needs and budget. In gen-eral, it also makes sense to schedulean assessment before every scheduledplant outage, so that any work thatneeds to be done can be completed inan orderly fashion during the plannedfacility downtime.

Feature Report

Jeff Miladin

USFilter

Cover Story

WATER ASSESSMENTS:

In Searchof Hidden

DividendsA close lookat all aspects of yourwater- and wastewater-treatment systems

can reveal opportunities for cost savings,

improved operation, reduced downtime

and better water conservation


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Some unit operations or processesare, by nature, prone to developingwater-related problems. For example,reverse osmosis (RO) systems maydevelop problems if their membranesare not cleaned properly, or at ap-propriate intervals, to maintain theirdesign performance and throughput.Improper cleaning, or cleaning that isdone too late, may cause irreversibledamage to the RO membranes andresult in compromised system flow or

diminished product water quality.A timely water assessment can also

ensure that you are prepared for ashort-term or emergency water systemoutage by developing a comprehen-sive plan to manage these situations.The plan would take into account iden-tified weaknesses in the existing sys-tem and provide for a way to addressthe failure of those components. Thisplan could include adding provisionsfor emergency mobile equipment, im-proving system redundancy, or simplymaking sure the plant has the properspare parts inventory for high-wearparts. It should also include detailed

instructions on what the plant shoulddo operationally to minimize the im-pact of a water-related failure.

Diagnosingwater-related problemsThe following symptoms are often en-countered in chemical process plants,and may indicate a water-relatedproblem: Reduced product flow or quality Reduced run lengths on ion ex-

change applications Increased pressure differentials

across units Increased consumption of acid/caus-

tic/brine for regeneration systemsthat experience long periods of ser-

vice Online system instrument read-

ings that disagree with those of labinstruments that are used to verifythe accuracy of, or to help diagnoseproblems with, the water-treatmentsystem instruments

In addition, the following events cancreate water-related problems: Changes in makeup water source

Seasonal variations in makeupwater sources (such as minerals,turbidity, and temperature)

Running systems beyond their de-

sign limits (for instance, in emer-gency situations)

Whats involved?A water assessment can be as com-prehensive as reviewing all aspects ofall process operations, including thoserelated to process control, instrumen-tation, vessels, piping, influent anddischarge water quality, or it may beas simple as reviewing one specificpart of the process. As a general ruleof thumb, a full-fledged, comprehen-

sive water assessment is called for ifany of the following criteria are met:your system has been in service forover five years, has been poorly main-tained, is operating less efficientlyor is not meeting final water qualityspecifications.

An assessment that is designed tooptimize your process typically in-

volves the following protocol: A workteam is established to evaluate thefacilitys water-related operation andmaintenance activities, and review

any seasonal variations in plant in-fluent water quality, or changes in de-mand for process or wastewater flows.The team reviews maintenance logsto make sure proper maintenance hasbeen carried out at appropriate inter-

vals, and that all systems are beingoperated at the correct flows and pres-sure according to design data and as-sociated process and instrumentationdrawings (P&IDs). A thorough inspec-tion is carried out for each unit op-eration, if required. For example, the

team might perform the following ac-tivities during an assessment of an ionexchange vessel: Inspect, repair, rebuild vessels (veri-

fying lining integrity), internals (in-cluding distribution plumbing andstrainers), and valves, and verifythe proper operation and control ofeach

Inspect, test, add and replace the ionexchange resin as needed

Regenerate saturated resin to en-sure the performance of the system

Audit the brine, acid and causticconsumption of the resin-regenera-tion system

USFilter

FIGURE 1. Proper instrumentation and calibration are es-sential to verifying system performance and alerting plantpersonnel to problems before they get out of control


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Upgrade all controls Fix any system leaksOnce the inspection is complete, theoverall system operation should be

verified against the system P&IDs. Ifmodifications are required to meet de-

sign flows or water quality, they can beimplemented at this time.

How long willan assessment take?The time it takes to do an assessmentwill vary, depending on who conductsit and whether it is carried out as afull-fledged, complex assessment ofall water-related aspects of the en-tire facility, or one that reviews just asingle part of the process. Assessmentwill proceed more quickly when design

drawings and other documentation arereadily available from plant personnel.It may take longer when critical docu-mentation has to be reconstructed.

Third-party service providers typi-cally take 30 to 60 days to do an as-sessment from start to finish. Thisincludes developing the scope of theassessment, performing the equip-ment review, and creating an assess-ment report. The assessment report

verifies the scope of the project anddetails the current and desired condi-tion of the system, and then outlinesthe remedial steps needed to reach thedesired outcomes.

What about cost?The cost of a water assessment reflectsthe time spent by internal plant per-sonnel or external third-party serviceproviders to conduct the assessment.

A likely outcome of the effort is that

the need for upgrades or repairs willbe identified, so the costs associatedwith repairing or replacing the equip-ment once any problems have beenidentified must also be factored in.

Although you may be reluctant tospend money to upgrade an older sys-tem still producing water of sufficientquality, this decision could be short-sighted, as water-related failuresmay have a dramatic impact on plantoperations. When deciding whether ornot to repair or upgrade the system,

you must weigh the cost of the repairagainst the long-term potential gainsin efficiency, or improvements in sys-tem performance, as well as the costsassociated with unscheduled inter-ruptions in process water availabilityor insufficient water- and wastewa-ter-treatment capabilities. Table 1provides several examples that canhelp you to decide whether a waterassessment is recommended for yourspecific situation.

Should you do an assessment?How do you know whether or not youshould do an assessment? Lets use a

real situation to help answer thisquestion.

One mining operation operates alarge water-softening system thatfeeds the entire plant complex. Overthe last year, the facility experienced

shorter run lengths than expectedfrom the ion exchange resin beds. Sincethe raw water hardness had remainedunchanged, the plant elected to in-crease the feed rate of the regenerantbrine, fearing that the brine-injectionpumps were not pumping as well asthey had before. However, even afterhaving raised the brine flowrate, theplant did not experience any meaning-ful increases in the run lengths of thewater softeners. Having thus tried allthe easy things, plant managers de-

cided to engage a third-party serviceprovider to perform a water assess-ment to determine how best to solvethe problem.

An inspection inside the softenervessel revealed low resin levels andchanneling inside the resin bed, whichhad resulted from a distribution sys-tem failure. The channeling had con-tributed to the short run lengths. Theinspection also revealed that the ves-sel lining had failed in a few areas.The assessment team developed aplan with the mine operation person-nel that met the production needs.

During the overhaul of the water-

FIGURE 2. Since the performance of pretreatment systems can dictate theoverall success of any water-treatment system, regular verification and valida-tion of filtration media and valve performance is important

Cover Story

Dont wait for system

failure to pay attention

to your water-relatedsystems. Regular,

early assessment can

ensure that inlet

and outlet water

flows at the

expected rate

and meets qualityspecifications

USFilter


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softening system, resin was restoredto its proper level, the distributionsystem was repaired, and a new linerwas installed. To verify that the unitwas being operated correctly and tofind out if the regeneration sequence

was correct, the assessment team per-formed an elution study, for confirm-ing the effectiveness of the regenera-tion process. The team discovered thatwhile the sequence and brine dosagewere correct, the pressures in the sys-tem had varied considerably. This hadprobably caused the resin to becomebackwashed out of the system duringa high-pressure spike, and it may havecontributed to the distribution systemfailure, as well. The assessment teaminstalled a pressure-regulating valve,

and the flow problems were therebyeliminated.

Lessons learnedDiscussed below are some examples ofhow a water assessment helped fourindustrial plants to optimize their op-erations.Helping with an expansion proj-ect. A power plant expansion in theU.S. Southeast required 10 million gal-lons of water total to start up two newunits. The raw feed was surface waterfrom a 40-acre power plant reservoir,which required pretreatment withchlorine, polymer feeds and media

filtration to remove unwanted organ-ics and suspended solids. A water as-sessment determined that the bestresponse to this short-term, high-flowrequirement was to install a mobiledemineralization system provided as

part of a temporary system for hy-draulic test and steamblow (a processthat is used during the commissioningphase of any power plant, to clean theplant steam piping before it is put intoservice). The system would supply1,000 gal./min of boiler feedwater forthis steamblow project.

The third-party water-assessmentteam supplied the plant with mobiledemineralizer trailers, complete withpretreatment, and has now been oper-ating the system for six years as part

of a permanently installed build-own-operate system. The system continuesto meet the customers water specifi-cations and budget for the steam plantproject.

Addressing an issue with agingequipment. A water assessmenthelped a petroleum refinery in theU.S. Gulf Coast to solve a problemwith its filtration system. The refineryhad installed nine automatic valvelessgravity filters for filtering clarifiedriver water.

After almost 40 years in service,however, the units were showing signsof aging. A complete system evaluation

showed that the replacement strain-ers installed in the units did not meetO.E.M. specifications and were im-properly designed, allowing filtrationmedia to be lost. Further inspectionalso determined that the replacement

media was not properly sized. Besideshaving improper strainers and media,the equipment suffered from corrosionand lack of maintenance. The water-assessment team determined thatinstalling original manufacturer-de-signed stainless steel strainers wouldeliminate the problem.

However, an inspection of the in-dividual vessels revealed that a fewof them furthermore had structuraland operational problems that couldnot be corrected with typical repair

methods. The water-assessment teamrecommended structural repair and/orreplacement specific to each unit, andsuggested operational changes thatmade an immediate impact on unitoperation.

Since the initial inspection, refinerypersonnel have replaced the mediaand strainers in three of the nine

vessels, and have ordered new AVGFunits to replace two whose conditionwas too poor to be repaired. This im-mediately improved the water qualityfrom the filters that were repaired,and brought a corresponding improve-ment in the operation of downstream

TABLE 1. EXAMPLES OF WATER ASSESSMENT RECOMMENDATIONS FOR SPECIFIC SITUATIONS

Situation Seriousness Action

The water plant, and each unit process (clarification, filtration, ROand demineralization) are producing the quality and quantity ofwater needed and expected. The required inputs of chemicals,

energy, labor and maintenance are in line with design specifica-tions. Wastage via backwash, reject and regeneration is also inline with design specifications.

Green light Consider future water requirements, pos-sible raw-water alternatives, emerging en-vironmental restrictions and contingency

plans to maintain current high level ofperformance.

The overall water plant is producing the desired quality andquantity of water, but individual unit processes are performingbelow expectations or specifications.

Yellow light Conduct water assessment to focus onspecific unit process, before downstreamunits or overall water plant performance iscompromised.

The overall water plant is producing the desired quality andquantity of water, but required inputs in terms of chemicals, en-ergy, labor or maintenance are above expectations, specifica-tions or industry norms.

Yellow light Address water plant or unit process inef-ficiency that is resulting in higher opera-tional costs. Conduct water assessment tooptimize performance and reduce costs.

The overall water plant is producing the desired water quality andquantity, but wastage via backwash reject or regenerations is

above expectations, specifications or industry norms.

Yellow light Address water plant or unit process inef-ficiency that is resulting in higher opera-

tional costs. Conduct water assessment tooptimize performance and reduce costs.

The overall water plant is not producing the quality or quantity ofwater needed and expected. Manufacturing operations may becompromised or curtailed if the situation is not remedied quickly.

Red light Conduct water assessment immediatelyand consider using mobile water treatmentto safeguard manufacturing operations.


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equipment. As soon as all nineunits are repaired or replaced,the plant expects to reap sav-ings in terms of water-treatment

chemicals, improved operationof plant cooling exchangers, andreduced cost associated with de-mineralizer operation.Helping a plant stay onlinewith mobile treatment. Whena U.S. Midwest steel plant wasinvestigating its water-treatmentoptions, a water assessment sug-gested that outsourcing was thebest solution. By contractingtheir water-treatment operationsto a third-party service provider,

plant personnel would be able tofocus their resources upon theircore business. When market con-ditions turned downward, how-ever, the plant personnel endedup putting their outsourcingplans on hold.

In the meantime, the plantspretreatment system failed, andthe facility required a mobilepretreatment system to get itsproduction back online quickly. Ifit had shut down its steel production,

the plant would have lost more than amillion dollars per day. A combinationof five mobile trailers produced thewater quality needed for its process.

Had the relationship with the exter-nal water-treatment vendor not beenformed during the earlier water as-sessment, and had the vendor not un-derstood the customers requirements,the plant would have been forcedto constantly blow down its boilers,resulting in higher water, fuel andchemical costs.

Helping a refinery plan for anoutage. A Gulf Coast refinery hadscheduled a one- to two-week outagefor its cold-lime softening system,which clarified the incoming waterwhile reducing hardness. It initiallysought to install a filtration system toreplace the clarifier during the outage;however, an assessment of its currentwater condition and systems deter-mined that the desired water qualityand predictable flowrates could not beguaranteed, due to high turbidity ofthe incoming water.

In addition, the use of filtrationalone (in lieu of the existing water-

softening system) would not address

the abundance of hardness miner-als in the inlet water. After furtherreview of the specifications, therefinery determined that the bestsolution was to install mobile clari-fication equipment on a temporarybasis, to provide treated inlet waterthat met specifications while the ex-isting system was taken off-line forscheduled maintenance. Mobile clar-ifiers, combined with a side-streamzeolite softener, were able to producethe same quality of water as a tem-

porary system.Three clarifier trailers were deliv-

ered to the site, providing a total flow-rate of 3,500 gpm, with a maximumturbidity of 5 NTU. Delays duringmaintenance work on the refinerysexisting clarifier required that themobile units remained onsite for anadditional five weeks.

The mobile clarifiers met the speci-fied water flow and quality, and al-lowed the refinery to complete main-tenance on its existing system withoutinterrupting production. The ability touse a trailer-mounted mobile clarifierprevented an unscheduled outage at

the refinery, and allowed the re-quired maintenance work to bedone in an orderly manner.

Getting organizedWhen a chemical process operatordecides to hire an outside water-assessment team, plant person-nel should assemble the followingtypes of plant documentation anddata to help facilitate the assess-ment:Documentation: System operating manuals P&IDs for the water-treatment

system Schedule of preventive mainte-

nance done on the systemData related to: Wastewater produced by water-

treatment system (compare ac-tual performance with systemdesign and analyze any excur-sions)

System acid/caustic consump-tion

Replacement history for car-tridge filters, resin, membranes,and media

Makeup water and product water-

quality measurements Operating schedule (hours/days/

week/year)Inlet water and wastewater are essen-tial parts of most chemical process op-erations, and the ability to treat waterso that it meets process specificationsand regulatory thresholds is of criticalimportance to the smooth operationof the facility. By conducting timelywater assessments, operators canidentify opportunities for improve-ment, and take steps to rectify sub-par

performance in the most orderly andcost-effective manner, thereby mini-mizing the risk of system failures orunscheduled downtime.

Edited by Suzanne Shelley

Cover Story

AuthorJeff Miladin is vice-president of industrialsales for USFilter, a part of Siemens WaterTechnologies (22211 Palomino Way, Santa Clar-ita, CA, 91321; Phone: 805-312-2132; Email:[email protected]. He has been involvedwith industrial water treatment for more than18 years. His experience includes both water-treatment equipment and chemical treatment ina variety of industrial sectors, including power

generation, chemical process operations, hydro-carbon process operations, mining, pulp & paper,and primary metals. Miladin holds a B.S. degreein mechanical engineering from California Poly-technic University in Pomona, Calif.

FIGURE 3. Reverse osmosis membranes canbe cleaned onsite or off-site, depending on yourfacilitys needs. Auditing membrane conditionon a regular basis can alert you to other issueswithin your water-treatment system

USFilter

Reprinted from the December 2005 Chemical Engineering magazine. 2005 Access Intelligence, LLC.

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Water Audit Article CE 1205