Presentation on theme: "When is Reverse Osmosis Right for Boiler Pre-Treatment"— Presentation transcript:
1 When is Reverse Osmosis Right for Boiler Pre-Treatment
2 RO BenefitsReduced fuel costs through lower heat loss / increased boiler cyclesReduced boiler system chemical treatment costsImproved operation & Steam PurityReduced riskImproved condensate corrosion controlReduced external treatment costs; particularly if previously using cold or hot lime softening, ion exchange and / or re-generable DIRemove / reduce hazardous acid and caustic chemicalsExtended ion exchange resin life
3 What to consider when looking at RO for boiler pretreatment Cycles of concentrationSize of plant – steam productionFW QualityMake-up alkalinity, Dissolved mineral breakdown% FW make up - % hot condensate returnPressure deaerator or FW tank?Feed water piping and pump constructionIs there a use for RO reject (cooling tower MU)Chemical Program types- Separates, all-in-ones, powders, liquids, etc.
4 Questions to help you qualify feasibility of replacing demins with RO/EDI Is the customer concerned with handling acid and caustic?What is the conductivity of the influent water? The higher the dissolved solids in the influent water, the greater the potential benefits.How much acid and caustic are used and what is the cost?What is the cost of power?Can the plant effectively use the RO reject water? Or will the increase in water consumption and waste volume be an issue?Is this a new installation or is the customer considering replacement of or renovating an existing demineralizer system?Just as in the case of placing an RO ahead of a demineralizer system, things such as power costs, total dissolved solids limits in the water and the cost of regenerants become an issue. Again, dealing with the RO reject is an issue and must be thoroughly examined. Even if it becomes a waste stream, the RO reject is typically much better then the acid and caustic waste the plant currently deals with.Higher influent water conductivity will make the RO systems work harder to remove the dissolved solids but as long as the silt density index or SDI requirements for the RO can be met, then this combination is quite effective.Next slide please.
5 ASME GUIDELINES Table 1 - Watertube Boiler with Superheater/Turbine All Pressures: FW dissolved oxygen < 7 ppb (with DA) Feedwater pH: ( psig) / pH (> 901 psig)Boiler FeedwaterBoiler WaterTotalTotalSpecificDrumHardnessSilicaalkalinityConductancePressureIronCopper(ppm)(ppm)(ppm)(mhos/cm)(psig)(ppm Fe)(ppm Cu)CaCOSiOCaCO(Unneutralized)3230 to 3000.1000.0500.3001503503500300 to 4500.0500.0250.300903003000451 to 6000.0300.0200.200402502500601 to 7500.0250.0200.200302002000751 to 9000.0200.0150.100201501500901 to 1,0000.0200.0150.050810010001,001 to 1,5000.0100.0100.0002-1501,501 to 2,0000.0100.0100.0001-100Note: All limits are expressed “less than” the value specified (e.g., < ppm)
6 Impact of feedwater quality on boiler operational efficiency Fuel-to-steam efficiencyFuel is 70 – 80% of boiler operating costsWater & Sewer costs 3 – 5%But - Feedwater quality has enormous impact on boiler efficiency & fuel costsReliability and availabilityIndustry statistics – Tube failures due to waterside mechanisms are the leading cause of unscheduled Boiler outagesFuelWater & Sewer
7 Impact of feedwater quality on boiler operational efficiency Steam puritySteam purity is a direct function of boiler water dissolved solids contentSuperheater and turbine reliabilityHigh-purity processesSemiconductorsPharmaceuticalsCatalytic hydrocarbon / chemical processesFood and beverage processing/sterilizationComfort humidificationMedical and research steam sterilization processes
8 Boiler feedwater quality considerations Boiler pressure and superheater/turbine steampurity requirements generally definepretreatment and feedwater qualityrequirements. In general –Softened or single pass RO-quality make-up < 600 psigGenerally demineralized or RO/EDI make-up > 900 psi
9 Resin Based Pretreatment Performance Typical BoilerOperatingPressure (psig)Typical EffluentQualitySystemThis is just a rough summary or survey of what one would expect of the water quality out of various types of pretreatment equipment. Question the group on how well their equipment performs versus this profile.
10 Benefits for the Customer Conversion from Softened to RO Makeup Improved steam purity & safetyImproved purity of products/processes contacted by steamReduced steam contaminationEnhanced regulatory complianceImproved steam equipment reliability, efficiency & longevityImproved safety - Reduced chance of catastrophic failureImproved turbine efficiencyImproved steam heat transfer efficiencyReduced total cost of operation (must qualify carefully)Improved steam system heat transfer efficiencyImproved boiler thermal efficiencyReduced chemical treatment costsReduced regenerant costsBy providing better quality feedwater there is better quality steam being produced. This means control valves, processes that have direct steam contact, steam turbines used for electric generators, compressor or pump drives are less prone to failure. Superheaters remain free of boiler salts and maintain operating reliability. Steam expansion joints and steam headers do not suffer from caustic embrittlement that would lead to cracking of these stressed components.As the steam is pure, there are no concerns with contaminated product or product recalls or disposals.Even in systems that might experience mechanically induced steam purity problems, the fact that the water is more pure to start with means the resultant level of solids in the steam would be lessened when RO feedwater is used.Introducing less solids in the boiler means our internal treatment chemicals do not have to work as hard and are able to do a better job. This will greatly improve the reliability of the boiler.Next Slide Please.
11 Questions to help you qualify feasibility of pursuing RO conversions from NaZ RO will generally reduce our overall boiler chemical revenue by a factor of 60-80% . Is customer looking to reduce chemical?Is there a significant operational or efficiency issue that can be solved by higher purity FW?Does the plant lack blowdown heat recovery equipment (or is it inoperable)?Is there competitive pressure or a bid that is compelling you to consider RO as a solution?Are current average cycles of concentration < 10?As I just said the inclusion of an RO can significantly reduce the chemical usage. For example in a plant producing 100,000 lbs per hour steam, with 70% condensate return going from 8 to 50 cycles, without any other changes, will reduce the boiler chemical volume from 40,000 to 15,000 lbs per year.If the inclusion of the RO would get the customer to realize better condensate quality without requiring more amine feed,especially if they are limited due to regulatory issues on the amount of chemical treatment they can supply, then you could be quite a hero at the account. This a powerful selling point This is what value added selling is all about.Increased condensate return means less makeup and better quality feedwater. RO water has less alkalinity so that condensate corrosion of steel and copper surfaces is minimized leading to cleaner boilers and better heat transfer.Think about adding that RO when the steam purity problems can not be solved by changes in system operation, chemical feeds or other means. The better quality water provided by the RO versus the softener could be just what the customer needs.Increased overall plant thermal efficiency is often achieved by increasing boiler cycles but only if the plant does not have blowdown heat recovery such as blowdown flash tanks and blowdown heat exchangers. When this equipment is installed and operating properly, there will be very little of the energy savings realized by operating the boiler at higher cycles. Be careful to consider this before even broaching the subject of RO with a customer or prospect when this is the major thrust you are using.If a competitor has not done their homework and proposes RO and the main point they are making is energy recovery, point out to your customer or prospect the fallacy of the argument when heat recovery equipment is in place. This will close down the competitive thrust into this account while gaining you instant credibility.Next Slide Please.
12 Technical considerations in conversions from Na Zeolite to Reverse Osmosis Makeup RO permeate carbon dioxide considerations & reduction strategiesCorrosivity of RO permeateAlloy considerationsPreferred methods of pH adjustmentConsider boiler feed pump alloysSelection of oxygen scavengerInternal treatment program considerationsCondensate corrosion discussion & pH control rangeIn replacing a softener with an RO unit we must be conscious of the quality of the product water. RO permeate will be much lower in all species as the RO will remove >98% of all soluble species in the influent water. Gases will not be removed by the RO. The permeate will be acidic, typically pH 5-6, due to the presence of carbonic acid. For this reason piping resistant to corrosion will need to be installed. Such a change will maintain the purity of the permeate while maintaining the piping and pump network. Typically the change in metallurgy is to stainless steel or plastic.An alternative to metallurgy changes, would be to adjust the pH of the permeate using caustic or an amine. Both will protect the downstream piping but there are tradeoffs to consider.Adding caustic is cheap and effective but it will also affect the feedwater alkalinity, conductivity and boiler water pH. Adding amine will possibly be the better approach.Adding an amine will allow CO2 to be vented from the water in the deaerator and the amine will recycle. This will reduce the overall system demand for neutralizer. The amine in the feedwater will also not affect the boiler water chemistry.In a softened water system,the oxygen scavenger is often sulfite based. It is cheap, effective and the impact on cycles is typically not significant as they are already low. When we have gone to RO quality water the change to a sulfite replacement such as DEHA, hydroquinone, or one of the other organic scavengers maybe preferred. These products are effective, have limited effect on boiler water conductivity and will have benefits in the protection of the condensate as in the case of DEHAAll polymer or other solubilizing internal treatment technology is now a real possibility with RO quality feedwater. Cleaner boilers, higher cycles, and easy testing are all benefits to be derived by changes to soluble versus the older precipitating programs.Next slide please.
13 Zeolite Softening & Dealkalization AdvantagesInexpensive – Capital & operating costsSimple-to-operateDurableSafe & inexpensive sodium chloride regenerantLimitationsNo reduction in total dissolved solids (TDS)FW quality can limit boiler cyclesNot suitable for high-pressure boiler operation (> 900 psig)No silica reductionNo alkalinity reduction without dealkalizer
14 Resin-based demineralization AdvantagesReduction in all dissolved solidsEnables high cycles operationSuitable for high-pressure boilersCan tailor to specific purity needsExcellent silica rejectionExcellent alkalinity/CO2 rejectionLimitationsStrong acid/caustic required for regenerationCaustic costs high & variableLimited anion resin lifeSilica and sodium leakageManpower intensiveOperating costs directly proportional to TDS
15 Reverse Osmosis Advantages Limitations Rejection of all dissolved solidsOperating costs not directly dependant on TDSEnables high cycle boiler operationRequires no chemical regenerants (acid/caustic)Not labor intensiveVersatile pairings with resin-based systemsIdeal for mobile applicationsLimitationsRO alone not suitable for HP boiler feedwater > 1000 psig with turbineHigher electrical costs than resin-based systems (high-pressure pumps)Generates significant reject stream (typically 20 – 30% of input stream)Does not reject CO2 (g)
16 Potential membrane solutions for Boiler systems RO in front of existing demineralizersRO to replace or augment softenersRO/EDI to replace resin-based demineralizer - Mixed-bed quality trainUltrafiltration in front of demin. or RO to replace traditional filtration/clarification
17 Key input variables for modeling & analysis EconomicEnvironmentalTDS of influent waterCapital equipment costs (RO)Caustic costsElectrical power ratesInfluent water costsSewerage costsVolume or Vol/TDS-basis?Can plant reuse RO reject?Credits or incentives for reuseRegenerant neutralization costsDifferential labor costsReduction of acid/caustic inventoryPersonnel safety - chemical exposureWater scarcity issuesDischarge/permitting issuesThis can be a critical factor because direct sewerage of the RO reject stream may be costly
18 Case 1 - Potential Benefits in the Addition of RO ahead of Demineralizer Reduced acid & caustic regenerant costs90 – 95% reduction in regenerant usage is typicalReduced operator laborReduced high TDS regenerant neutralization dischargeExtended ion exchange resin life40 – 50% extension in resin life typicalGreatly reduced regen. cycles & reduced iron/organic foulingImproved feedwater & steam qualitySodium & silica slippage & breaks significantly reducedBy installing an RO system ahead of the demineralizer we lower the consumption of acid and caustic due to the reduced number of regeneration cycles. This reduction in regenerant usage can be on the order of 90-95%.As the number of regenerations is reduced, so too is the operator time required to monitor or conduct the regeneration. In addition, where manual intervention by the operator is required such as checking of regenerant strengths, handling drums of acid and caustic or initiating steps in the regeneration sequence operator time is minimized. Other advantages are the worker exposure to chemicals is greatly reduced minimizing the potential for injury from chemical burns or physical injuries and the time and expense required to neutralize the waste stream is also vastly reduced.As we reduce the chemicals used in the demineralizer system, the amount of chemical discharge from regeneration is significantly reduced as well. This could be a major benefit where a customer is faced with a plant discharge limitation issue.The inclusion of the RO would make this a more environmentally friendly technology.This is even more of a benefit when we are looking at eliminating the need for acid and caustic entirely as is the case with RO-EDI.The presence of the RO will generally extend resin life by as much as 40-50%. Organic fouling of the anion resin will be greatly reduced as will iron fouling of the cation resin. Colloidal silica is also significantly reduced by using RO prior to a demineralizer.Next slide please.
19 Capital and operating cost of RO included RO Preceding Demineralizer Example with relatively inexpensive water and sewerage RO cost justified above approx. 200 ppm TDSDemin.ROCapital and operating cost of RO included
20 Capital and operating cost of RO included RO Preceding Demineralizer Example with more expensive water and sewerage RO cost justified above approx. 400 ppm TDSROCapital and operating cost of RO included
21 Case 1 Summary - RO in front of Demineralizer Annual cost savings based on water production and savings per 1000 gallons
22 Case 2 - Potential Benefits Conversion from Softened to RO make-up Improved steam purity > Process/TurbineImproved condensate corrosion control > High-alkalinity watersMinimizes operating and maintenance expenses > Boiler waterside and steamside failuresMaintains optimal thermal performance > Boiler and steam heat transfer efficiencyReduced chemical treatment costs > Higher cycles operation – less wastage > Lower steam system treatment requirements
23 Typical Problems encountered in Softened water boiler systems Steam purity issuesDeposit controlCondensate CorrosionWhat are some of the typical problems encountered in a softened water boiler feedwater system?Lower operating cycles leading to higher fuel bills.Increased risk of steam purity problems due to lower quality feedwater. This low quality feedwater can not be concentrated too highly or carryover will take place leading to superheater, turbine or other critical system components being compromised. Additionally, the customer’s final product quality can be adversely affected leading to product recall, wastage, and negative publicity..With lower quality feedwater the total alkalinity in the feedwater will be higher. This will lead to greater potential condensate corrosion levels. Higher condensate treatment cost and the potential for greater deposits in the boiler due to inadequate corrosion protection will also occur.Next slide pleaseExpansion JointFailure
24 A look at fuel and water savings when increasing boiler cycles noting a natural cost of $8 per decatherm.
25 Potential Energy Loss Versus Waterside Scale Thickness Iron & SilicaHigh Iron Content76543"Normal" ScaleEnergy Loss (%)211/641/323/641/16Scale Thickness (Inches)