to be posted session b hawkins - turi.org b... · • demineralizer systems in power plants ......
TRANSCRIPT
11/15/2017
1
Reducing Chemicals in Water Demineralization Systems
TUR Process Characterization And Options Review
Some practical experience
Maura Hawkins
Water Demineralization Systems:
What we will cover
• Why Demineralize?• Demineralizer Systems in power plants• The Basics of Cation/Anion Demineralization Systems
• Chemical use • Process Characterization• Options
Maura Hawkins
Water Contaminants
Water Contaminants
All natural waters contain varying amounts of suspended and dissolved solids and gases
Salts and minerals
Ca, Mg, Fe, Al, Silica, silt, oil etc.
Organics and VOCs
Bacteria, minerals, charged ions, pharmaceuticals, caffeine, fertilizers, cleaning agents, debris or
Anything else naturally or man‐made
All natural waters contain varying amounts of suspended and dissolved solids and gases
Salts and minerals
Ca, Mg, Fe, Al, Silica, silt, oil etc.
Organics and VOCs
Bacteria, minerals, charged ions, pharmaceuticals, caffeine, fertilizers, cleaning agents, debris or
Anything else naturally or man‐made
Maura Hawkins
11/15/2017
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Water Treatment Systems
How is water
treated?
To remove the impurities in the water, water needs to be treated. The treatment system can depend on the use of the water.
Filtration Coagulation Clarification Neutralization Deaeration Ion removal including distillation, ion exchange, precipitation
and separation and membrane separation
Maura Hawkins
Water Treatment Systems
Who uses demin water?
What applications use demin water • Lab applications, testing and hospitals • Electronics manufacturers • Manufacturers – rinsing, spraying, washing• Laser cutting• Steam applications• Pharmaceutical manufacturing• Cosmetics• High‐pressure boiler water feed
What applications use demin water • Lab applications, testing and hospitals • Electronics manufacturers • Manufacturers – rinsing, spraying, washing• Laser cutting• Steam applications• Pharmaceutical manufacturing• Cosmetics• High‐pressure boiler water feed
Maura Hawkins
Power Plants ‐ Large Demineralized Water Users
Boiler Water Feed
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Circulation water pump
HRSG
Maura Hawkins
Heat Recover Steam Generator (HRSG) (Boiler)
Maura Hawkins
Power Plant Boiler Makeup Water Sources
• The boiler receives the feed water, which consists of varying proportion of recovered condensed water (return water) and fresh water, which has been purified in varying degrees (make up water).
• The make‐up water is usually treated by some process before use.• Feed‐water composition therefore depends on the quality of the make‐up water and the amount of condensate returned to the boiler.
• The boiler receives the feed water, which consists of varying proportion of recovered condensed water (return water) and fresh water, which has been purified in varying degrees (make up water).
• The make‐up water is usually treated by some process before use.• Feed‐water composition therefore depends on the quality of the make‐up water and the amount of condensate returned to the boiler.
Make‐up water
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Water Source
• Well• Lake• River• WWTP
Discharge• Process
Wastewater• City water
Maura Hawkins
Demineralization Systems
Why Demin?
• The deposition of dissolved salts and suspendedimpurities will form a scale on boiler equipment andcreate excessive pressure and thermal stress thusdegrading metal and restricting flow.
• Harmful dissolved salts may react with various parts ofthe boiler through which it flows, and corrode thesurfaces.
• Boiler feed water treatment is required to removedissolved and suspended impurities from water beforefeeding it to boiler.
• The deposition of dissolved salts and suspendedimpurities will form a scale on boiler equipment andcreate excessive pressure and thermal stress thusdegrading metal and restricting flow.
• Harmful dissolved salts may react with various parts ofthe boiler through which it flows, and corrode thesurfaces.
• Boiler feed water treatment is required to removedissolved and suspended impurities from water beforefeeding it to boiler.
Maura Hawkins
Demineralization Systems
Why Demin?
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Demineralization Systems
Maura Hawkins
Water Treatment Systems
What is demin water?
Water in its purest form consists of Hydrogen (H+) and Hydroxyl (OH‐) ions, which combine to create H2O. When considering a water’s purity, anything found in water other than the Hydrogen and Hydroxyl ions, are an impurity.
The process of deionization exchanges all of the charged ions found in water for Hydrogen and Hydroxyl ions. This process helps to form the water molecule, H2O. The deionization or ion exchange process results in a true water “blank”.
Maura Hawkins
Demineralization Systems
Deionization entails removal of undesirable electrically charged (ionized) dissolved substances by binding them to positively or negatively charged sites on a resin as the water passes through a column or columns packed with this resin in a process called ion exchange.
These systems are often two or three vessels ‐ one containing a cation‐exchange resin in the hydrogen (H+) form, the other containing an anion resin in the hydroxyl (OH‐) form and a mixed bed containing both. Water flows through the cation column, where all the cations are exchanged for hydrogen ions. The water then flows through the anion column where all the negatively charged ions are exchanged for hydroxide ions which then combine with the hydrogen ions to form water (H2O). Some systems have a third mixed bed for polishing.
Maura Hawkins
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Maura Hawkins
Maura Hawkins
Demineralization Systems –Regeneration
At some point the resin bed becomes exhausted and not able to function at peak performance.
• This may be indicated by o Increased effluent conductivityoPoor effluent qualityoDecreased flow ratesoExcessive rinse volumesoResin exchange sites will run out of mobile ions
• At this point the resin bed needs to be regenerated to restore the ability to exchange ions
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Demineralization Systems –Regeneration • Regeneration carried out using a strong acid for the cation
(as a source of hydronium ions) and liquid caustic (sodium hydroxide) as a source of hydroxyl ions for the anion.
• Resin is regenerated using sulfuric acid and sodium hydroxide (caustic) to regenerate the cation and anion respectively.
• First the resin is backwashed with water to fluff the resin and wash out any entrained particles.
• The system draws a set amount of regenerant chemical for a specified period of time and at a specified flowrate.
• Finished by a slow and fast rinse.
Maura Hawkins
Demineralization Systems
Power plants generally have at least two demineralizer trains. One train is in service while the other is regenerating.
Prior to entering the demineralizer train: • Raw water is passed through a dual media filter to removed suspended solids and reduce turbidity.
• Filtered water is directed to a large water storage tank. • Water for steam cycle makeup is drawn from this tank and passed through an activated carbon filter to remove dissolved gases.
Maura Hawkins
Sulfuric Acid or Sodium Hydroxide
Regenerant
To waste
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11/15/2017
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Demineralization Systems and TURYear ID SIC Chemical Manf'd Processed
Otherwise Used
Total Used
Generated as Byproduct
Point Air Emission
Total Releases
Discharge to POTW
Transfer Off‐Site
2013 274425 4911SODIUM HYDROXIDE 0 0 29007 29007 28678 0 0 0 0
2013 306579 4911SODIUM HYDROXIDE 0 0 75840 75840 9475 0 0 0 0
2013 306586 4911SODIUM HYDROXIDE 0 0 326836 326836 7488 0 0 0 0
2013 315603 4911SODIUM HYDROXIDE 0 0 41061 41061 7805 0 0 0 3
2013 315656 4911SODIUM HYDROXIDE 0 0 23620 23620 1181 0 0 0 0
2013 402959 4911SODIUM HYDROXIDE 0 0 471694 471694 0 0 0 0 0
2013 50773 4961SODIUM HYDROXIDE 0 0 49807 49807 49242 0 0 0 0
2013 205912 4931SODIUM HYDROXIDE 0 0 125442 125442 120145 0 0 0 0
TOTAL 1,143,307
2013 274425 4911SULFURIC ACID 380 0 46468 46848 32727 380 380 0 0
2013 306579 4911SULFURIC ACID 0 0 81375 81375 0 0 0 0 0
2013 306586 4911SULFURIC ACID 290 0 476030 476320 642 290 290 0 352
2013 315603 4911SULFURIC ACID 185 0 43023 43208 16956 91 91 0 11771
2013 315656 4911SULFURIC ACID 3747 0 28925 32672 8086 693 693 0 0
2013 342837 4911SULFURIC ACID 476 0 112797 113273 487 476 476 0 0
2013 402959 4911SULFURIC ACID 0 0 280784 280784 0 0 0 0 0
2013 50005 4911SULFURIC ACID 0 0 42136 42136 0 0 0 0 0
2013 50773 4961SULFURIC ACID 81 0 88106 88187 57415 0 81 0 0
2013 205912 4931SULFURIC ACID 274 0 165747 166021 135172 0 274 0 0
TOTAL 1,370,824
Maura Hawkins
TUR Chemicals
Demineralization Systems and TUR :
Applying TUR
Characterizing the Process
It pays to spend some time to understand the process, the numbers and what issues affect the use of regenerant chemicals – NaOH and H2SO4.
In concept it is relatively simple, but there are a lot of factors – each plant and process has its unique attributes.
Look at the demin system in the context of the whole facility.
Pay close attention to materials handling and process monitors.
It is all about the process
Think about and write down what factors affect the performance of the system as whole within the facility and specifically within the process unit.
Maura Hawkins
Demineralization Systems and TURProcess Flow Diagram
Applying TUR
DEMINERALIZATION PROCESS FLOW DIAGRAM
Unit of Product = gals of water demineralized
Maura Hawkins
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Demineralization Systems and TURPFD
Applying TUR
FACILITY PROCESS FLOW DIAGRAM
Unit of Product = MW
Maura Hawkins
26© Toxics Use Reduction Institute University of Massachusetts Lowell
Evaluate Remaining Options• Technical evaluation• Hazard evaluation
• Economic evaluation
Eliminate Options• Technically infeasible
• Not TUR
For each toxic in the production unit:
TUR Option ID and Evaluation
Identify Evaluate
Maura Hawkins
Demineralization Systems and TUR
TUR Options
TUR Options by Category for Ion Exchange Demineralizers
INPUT SUBSTITUTION: • No good options here• Chemistry is chemistry – you need the regenerant• Could use HCl instead of sulfuric for cation regeneration, but this is not common and has issues
PRODUCT REFORMULATION:• No good options here• Product is either gallons of water demineralized or MW
IN‐PROCESS (INTEGRAL) RECYCLING OR REUSE• No good options here
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11/15/2017
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Demineralization Systems and TUR
TUR Options
TUR Options by Category
PRODUCTION UNIT MODIFICATION:
There are other ways to demineralize water instead of onsite ion exchange systems• Off‐site ion exchange systems – use a trailer on site and send beds offsite for regen.
• Purchase demineralized water – vendor supplied system. • Reverse osmosis systems ‐ force water through a semi‐permeable membrane to filter water.
• Electrodeionization (EDI) ‐ uses an electric field to remove ions and polar species from an aqueous stream. EDI is often used with reverse osmosis to replace ion exchange resin‐mixed beds, which require onsite or offsite chemical regeneration.
Maura Hawkins
Demineralization Systems and TUR
TUR Options
TUR Options by Category
PRODUCTION UNIT MODIFICATION (CONT.):
Change the water source – use more city/municipal water instead of ground water, surface water, POTW discharge or process wastewater
Add Equipment to Pretreat Raw Water Soften and/or dealkalize via ion exchange which use a salt solution
(NaCl) for regeneration Filters to remove particulates and other impurities Decarbonator to remove CO2 prior to the anion bed Carbon filter to remove chlorine, organics and particles
• Combine Pre‐treatment Systems and Replacement Systems
Maura Hawkins
Demineralization Systems and TUR
TUR Options
TUR Options by Category:
PRODUCTION UNIT MODERNIZATION• Replace resin with newer more efficient resins
IMPROVED OPERATIONS AND MAINTENANCE• Optimize the operation of the resin beds • Reduce the amount of makeup water needed by improving
condensate return or producing less export steam • Extensive valve and vent leak repair; install steam traps • Reduce the frequency and amount of regens • Install a conductivity probe on the demin inlet to assist in
optimizing the performance of the system • Meter regenerants
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Demineralization Systems and TUR
TUR Options
• Evaluate Cost based on $$/1000 gal demineralized • Major factors are Cost of Chemical – can swing up and down yr. to yr. Source and Cost of Water – city water costs more Resin Quality and Life – higher quality $$ Average Maintenance Costs Amount of Run Time – If capacity factors are low, less incentive (big issue in power markets)
Ongoing Capital Expenditures – can be high to keep an old system running
Economic Evaluation
Maura Hawkins
Demineralization Systems and TUR
Challenges
• Getting the process down and understanding all the parts of the site specific plant steam cycle
• Getting good numbers and calculations
• Making predictable estimates of ROI
• Aging systems and maintenance costs
• Unpredictable plant run time
• The changing power markets
• The reality that things change
Maura Hawkins
Demineralization Systems and TUR
Next year is a planning year.I hope you get all your credits!
Thank You
Maura Hawkins