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Navajo Generating Stationj gWater Balance Model
Case StudyCase StudyHypothetical Plant Water Systems
Reconfig rationPresented at:
2013 Southwest Chemistry Workshop
Reconfiguration
Presented by:Daniel J. Robinette, P.E.
Rocky Mountain Water Engineering
Introduction by:Rob Peterson
Salt River Project
July 16- 18, 2013
Presentation Outline Introduction Case 1 – Current Configuration
“As-Built” Water Balance Case 2 – Reconfiguration
“What-If” Hypothetical Water Balances Subcase 1 - Current ZLD Equipment (Brine
Concentrators and Crystallizer) Subcase 2 – Adiabatic Scrubber Purge Dryer Subcase 3 – Adiabatic Scrubber Purge Concentrator
Interesting ZLD Chemistry Interesting ZLD Chemistry Conclusions Questions Questions Contact Information
Introduction
This Case Study is hypothetical. It is not intended as a “Design Review” of g
the existing Navajo Generating Station. It’s sole purpose is to demonstrate how a
Water Balance Model (WBM) can be used to evaluate design alternatives.
Hypothetical Case Study The Navajo plant was built in the late 1970s and
early 1980s. Scrubbers were added in the 1990s. At the time the plant was built, and the Scrubbers
were added the plant water systems werewere added, the plant water systems were configured to meet the needs of the circumstances that were driving forces for decisions that were made 30 to 40 years ago.
This Case Study is therefore not intended as a iti f h th NGS t tcritique of how the NGS water systems were
originally configured, but rather how a new plant might be configured if it were built today.
Key Case Study Question1. If a “new” coal-fired power plant equipped with cooling
towers and forced-oxidation limestone scrubbers were built today at a site with source water nearly saturated in
y y
y y“hardness”, would it be advantageous to:
A. Use the conventional configuration of:1) Lime Soda softening the cooling tower makeup water1) Lime Soda softening the cooling tower makeup water
in order to achieve high Cycles of Concentration (COC),
2) Using raw water as makeup to the Scrubbers to assure low chlorides concentration with no voluntary scrubber purge, and
3) Achieving ZLD with electrically driven Brine Concentrators and Crystallizer?Concentrators and Crystallizer?
2. Or, might it be preferable to take the following approach?
Key Case Study Question (cont )
B. Reconfiguration
Key Case Study Question (cont.)
g1. Do not Lime-Soda soften the Cooling Tower Makeup water,
but rather,2. Operate the Cooling Towers at moderate Cycles of
Concentration and treat with sulfuric acid and a low-dose of scale inhibitor for “insurance” against scale during upsets,
3. Configure the Scrubber as a Wastewater Pre-Concentrator by sending the Scrubber 100% of the moderately cycled upsending the Scrubber 100% of the moderately cycled-up cooling tower blowdown and implementing a voluntary purge to control chloride to moderately low concentrations within the Scrubber.
4. Employ ZLD equipment that is driven by hot flue gas to reduce the voluntary scrubber purge stream to a solid waste or manageable liquid waste instead of using electrically d i B i C t t d C t llidriven Brine Concentrators and Crystallizers.
What Is a Water Balance Model?
A WBM is a set of Excel workbook files
What Is a Water Balance Model?
A WBM is a set of Excel workbook files (modules) that are linked together to form a model that simulates a power plant’s p pthermodynamic power cycle, combustion, flue gas, water and solids systems.
Chemistry plays a major role in a WBM. A powerful equilibrium model capable of
f i l h i t t k hperforming complex chemistry tasks such as “Boil-Down” analyses is included.
Why Use a Water Balance Model?
A WBM is needed to evaluate “what-if”
Why Use a Water Balance Model?
A WBM is needed to evaluate what-if case studies aimed at optimizing the plant water systems.y
Thermodynamics supplants the need to install and maintain flow meters on major jstreams. Flow rates are accurately determined by
i lt d h t b lsimultaneous mass and heat balances. Computational capabilities give WBMs
power to pay back initial investmentpower to pay-back initial investment.
Conventional ConfigurationFlow Rates Reflect 3 Units Operating at Peak Generation in July Water Volumetric Flowrate
Dry Solids Mass Flowrate
Excesss Condensate"High‐Value" Water Excess Disti llate
Raw Water to Scrubber ‐ Softened Raw Water to Cooling Towers ‐ Cycled‐Up CT Blowdown to Traditional ZLD Equipment
80
737 6582.7
0.2gpmkpphRaw Water
(Lake Powell)
EvaporationAux. Steam
Quick Lime
FerricSulfate
mg/L Boron
mg/L Boron
Stripped CO2
20,820
737
332
658
0.9 14
3.8
0.1
1
9.921,170
21,2078.6
21,9088.6
0.1
24,135
8.7
Boiler Makeup Water
Treatment System
Soda Ash
Stripped CO2Disti l late
Reactivators (2)F
mg/L Clmg/L TDS
227.71,088
990
37
15128.5
8.6
3.92,901
8.598
6.015,588
Evaporation
mg/L BoronHigh Flowrate mg/L Boron& High TDSSent to ZLDEquipment Salts
Dumpate
1.2
27
2,928
8.5
9.74.1
6.066
Ponds SO2 Absorbed Sulfuric Acid
u pateInvoluntary PurgeEntrained in Gypsum
BrineConcentrators (3) Crystallizer (1) mg/L Boron
mg/L Chloride Vapor Vapormg/L TDS Compressor Compressormg/L Boron Power (Total): Power:
Scrubbers (3) Cooling Towers (3) bhp bhpkW‐hr/hr kW
6 70,343
41
719627
644.4
9400
6,5305 126
1918
79
23
198
SD-2 , 3 & 4
Ponds 60-2A, B, C & D
GypsumLimestone
Oxidation O2
kW hr/hr kW6275,126
COC = 20.0
COO = 20.0
COC = 11.1
COO = 31.1
COC = 3.0
COO = 34.1
COC = 92
COO = N/A
Alternative Configuration w/ Conventional ZLD Equipment
Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July Water Volumetric Flowrate:(Surge Ponds Not Shown) Dry Solids Mass Flowrate:
CondensateStripped CO2 from Distil lateSulfuric Acid
No Lime‐Soda Softening ‐ Scrubber Integrated Into Water Balance as Wastewater Pre‐Concentrator ‐ Conventional ZLD Equipment
20,82042
110
gpmkpph
0.5
Raw Water (Lake Powell)
Aux. SteamEvaporation
Evaporation
Sulfuric AcidAddition
mg/L Boron
mg/L Boron
110
1529.924,133 6.3
8
23,801
3320.1
9.721
2,901
p
mg/L BoronF
mg/L TDS
New VoluntaryPurge
6,1189.1
55
2,981
7.4
9.13,133
27
4 8
226.8
NewBoiler Makeup
Water Treatment System
SO2 RemovedSulfuric Acid
Purge
mg/L Boron1) Scrubbers are integrated into the Water mg/L Chloride
Balance as "pre‐concentrating" ZLD mg/L TDSequipment driven by "free" flue gas heat. mg/L Boron SaltsVoluntary Purge prevents high chlorides. Involuntary Purge
Entrained in Gypsum2) Lime‐Soda Softening at Front‐End of Plant mg/L Chloride
becomes obsolete and unneccessary mg/L TDS Dumpate
KEYS TO RECONFIGURED WATER BALANCE 142044
940058 939
1
76
5.0168
4.8
940058,939
64486
1.60.7
Ponds
Limestone
Oxidation O2
becomes obsolete and unneccessary. mg/L TDS Dumpate
3) Brine Concentrators and Crystallizer are"unloaded" by pre‐concentrating Scrubbers. Brine
Concentrators (1 + 1) Crystallizer (1) mg/L Boron4) Boron remains soluble in "wetted" areas, Scrubbers (3) Vapor Vapor
but Boric Acid could form localized vapor Compressor Compressorpockets in non‐wetted areas. Power (Total): Power:
Cooling Towers (3) bhp bhpkW‐hr/hr kW‐hr/hr
912716
457399
4.23608
58,93920SD-2 , 3 & 4
Ponds 60-2A, B, C & D
Gypsum
9400 mg/L ClkW‐hr/hr kW‐hr/hr716 399
COC = 7.8
COO = 7.8
COC = 15.6
COO = 23.8
COC = 3.0
COO = 26.8
COC = 2.6
COO = 29.4
Alternative Configuration using Scrubber as Wastewater Pre-Concentrator and Adiabatic Scrubber Purge DryerPre Concentrator and Adiabatic Scrubber Purge Dryer
Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July Water Volumetric Flowrate:(Surge Ponds Not Shown) Dry Solids Mass Flowrate:
Stripped CO2 from
No Lime‐Soda Softening ‐ Scrubber Integrated into Water Balance ‐ Adiabatic Scrubber Purge Dryer and Fabric Filter for ZLD
20,820
gpmkpph
0.5
Raw Water (Lake Powell)
Evaporation
Evaporation
ppSulfuric AcidAddition
Hot Flue Gas fromAir Preheater Inlet Ductdeg F Boiler
Furnace9.823,953 720
9.9
0.5
24,285Atomizer
3320.1
3,069
Evaporation
mg/L Boron Warm FlueGas returnto Scrubber deg F
mg/L TDS Inlet Duct
New Voluntary
7.4 1685.0
27 168
3503,133
6,1659.7
NewBoiler Makeup
Water Treatment System
SO2 RemovedSulfuric Acid
Purge
1) Scrubbers are integrated into the Water mg/L Chloride SaltBalance as "pre‐concentrating" ZLD mg/L TDS Disposalequipment driven by "free" flue gas heat. mg/L BoronVoluntary Purge prevents high chlorides. Involuntary Purge
Entrained in Gypsum2) Lime‐Soda Softening at Front‐End of Plant mg/L Chloride
becomes obsolete and unneccessary /L TDS t h dditi l C l B R t58 939
64486
5 15
5.0940058,939
9400
1
76
445.0168KEYS TO RECONFIGURED WATER BALANCE
ADDITIONAL FUEL CONSUMPTION
Limestone
Oxidation O2
becomes obsolete and unneccessary. mg/L TDS tph additional Coal Burn Rate required to evaporate total scrubber purge
3) Brine Concentrators and Crystallizer are from 3 generating units to total dryness.replaced by Adiabatic Dryer and Fabric Filterdriven by hot flue gas.
Scrubbers (3) Scrubber Purge Dryer4) Threat of Boron vapor buildup is eliminated. and
Fabric Filter (1 + 1)Cooling Towers (3)
58,939 5.15
Gypsum
9400 mg/L Cl
COC = 7.8
COO = 7.8
COC = 15.6
COO = 23.8
COC = ∞
COO = ∞
Alternative Configuration w/ Adiabatic Scrubber Purge Concentrator (No Fabric Filter)Concentrator (No Fabric Filter)
Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July Water Volumetric Flowrate:(Surge Ponds Not Shown) Dry Solids Mass Flowrate:
Stripped CO2 fromSulfuric Acid
No Lime‐Soda Softening ‐ Scrubber Integrated into Water Balance ‐ Flue Gas Driven Adiabatic Purge Concentrator (No Fabric Filter)
20,820
gpmkpph
0.5
Raw Water (Lake Powell)
Evaporation
Evaporation
Sulfuric AcidAddition Hot Flue Gas from
Air Preheater Inlet Ductdeg F Boiler
Furnace
Cooled
7209.9
24,285
23,953
3320.1
3,064
9.8
p
Cooled Flue Gas
mg/L Boron andEvaporateto Scrubber
mg/L TDS140 ‐ 180 deg F Entrainment
Separator
New Voluntary
6,1659.7
27
7.4
163
3,133
NewBoiler Makeup
Water Treatment System
SO2 RemovedSulfuric Acid
New VoluntaryPurge
60 %wt Slurry1) Scrubbers are integrated into the Water mg/L Chloride
Balance as "pre‐concentrating" ZLD mg/L TDS Slurryequipment driven by "free" flue gas heat. mg/L Boron DisposalVoluntary Purge prevents high chlorides. Involuntary Purge
Entrained in Gypsum2) Lime‐Soda Softening at Front‐End of Plant mg/L Chloride
becomes obsolete and unneccessary. mg/L TDS tph additional Coal Burn Rate
1
76
44 168
64486
940058,939
5.0
55.0
KEYS TO RECONFIGURED WATER BALANCE
58,939 5.009400
Limestone
Oxidation O2
y mg/L TDS tph additional Coal Burn Rate required to evaporate total scrubber purge
3) Brine Concentrators and Crystallizer are from 3 generating units to 60 %wt solids.replaced by Adiabatic Concentrator withEntrainment Separator driven by hot flue gas.
Scrubbers (3)4) Threat of Boron vapor buildup is eliminated.
Cooling Towers (3) Scrubber Purge Concentrator (1 + 1)
, 5.00
Gypsum
9400 mg/L Cl
COC = 7.8
COO = 7.8
COC = 15.6
COO = 23.8
COC = 33.3
COO = 57.1
Interesting ZLD Chemistry
Crystallizer Streams Module can be used
Interesting ZLD Chemistry
to Perform “Boil-Down” Simulations The solubilities of various species in the Boil-
Down analysis were customized to match RCCDown analysis were customized to match RCCtest run results.
As a general rule, the solubilities of species in g , pconcentrated brine are increased by two orders of magnitude over the solubilities in deionized waterdeionized water.
Boil-Down results are plotted on the following phase diagram.
WBM Boil-Down Results for Crystallizer Plotted on Na, Mg, Cl, SO4 Phase Diagram (at 221 deg F)SO4 Phase Diagram (at 221 deg F)
Thenardite and Mirabilite
ThenarditeAnyhydrous Sodium Sulfate
MirabiliteHydrated Sodium SulfateAnyhydrous Sodium Sulfate
Na2SO4Na2SO4 10H2O
Na2SO4 + 10H2O Na2SO410H2OCool
2 4 2 2 4 2MW = 142 MW = 180 MW = 322
5.07 gpm1.0 tph 2.27 tph
5 gpm of water is consumed for each ton per hour (tph) of Thenardite produced as it cools to form Mirabilite.
“Absorbable” Trace Species in Coal from S bb Ch i t D i T t BScrubber Chemistry During Test Burn
Design
Coal Combustion Products Imported from Boiler FurnaceCoal Concentration of Constituents Absorbed
TestTest Design
Boron StrontiumSilica Zinc
Bromide
Design Test
ppm
Test Design
ppm ppbCations (Total Dissolved) Anions (Total Dissolved)
2.864.72 126.522.77
General Cations (continued)ppm
ppm 5 32BromideChloride
Arsenic FluorideCadmium Fulvate
NitrateCobalt Nitrite
ppb ppmppb
ppb ppm
1497.50
2,325ppmppt ppm
5 17
ppm 5.32
0.000761.04 394
18.51.76
Cobalt NitriteChromium o‐Phosphate
Lead AmmoniumLithium Barium
pptppb ppm
41 ppm5.17
Non‐Conserved (N/C) Ionsppb ppb12.70 ‐57ppb 5ppb48 70
3.6334.394
Lithium BariumMagnesium CalciumManganese SulfateMercury AluminumNickel CopperP t i I
635.5‐40.00
25.70
ppbpptppb ‐240
ppm
pptb 50 00
39.74
564
1 62
ppb
ppbppm
‐5ppbppm
48.70
301368
Potassium IronSeleniumSodium
48.90ppb ‐50.00
480
1.62ppmppbppb
Tracking Species from Coal and Source Water
Case
nfig
-on
Case
nfig
-on
Case
nfig
-on
Case
nfig
-on
PurgeCooling Tower
BlowdownCrystallizerBlowdown
Brine Concen-trator Blowdown
Scrubber
9 71
600 115
Base
Reco
urat
i oCa
se
Base
Reco
urat
ioCa
se
Base
Reco
urat
ioCa
se
Base
Reco
urat
i oCa
se
Boron, mg/L B 6 1 1,918 486 66 1,420 198 3,608Silica, mg/L SiO2 950 150 176 242 125 89pH 7.4 7.4 6.8 6.8 6.0 6.0 6.0 6.0
s Calcium 551 705 600 189 108 111
nion
s Chloride 1,512
4,830
Catio
ns
78,995 80,304
Magnesium 237 252 7,982 4,574 2,632 13,372 7,960 32,768Potassium 101 40 678 635 1,119 1,858 3,384
604 9,422 9,411 16,786 27,520Sodium 4,140 806 9,533 12,055 45,958 35,255
50,766 71,552Fluoride 6 3 258 11 67 32 102 84Nitrate 105 42 589 642 1 162 1 878 3 522 4 884
4.2
Tot Susp Solids 23,011 5,904 210,394 53,063
An
Liquid Flow, gpm 1,088
8,781 3,442 37,403 30,523 84,111 85,492Nitrate 105 42 589 642 1,162 1,878 3,522 4,884Sulfate 128,760 189,730
Tot Diss Solids 15,615 6,118 70,343 58,962 150,972 168,174 270,278 390,301
2,981 64 232 98 55 33 22
1 1 0 2 3 4 0 6Diss Solids Flow, kpph 8.5 9.1 79 81 7.4 4.6 4.4
8.5 4.8 7.9 4.8Tot Solids Flow, kpph
23.4 31.1 26.4 34.1 29.0Note: All concentration units are in mg/L as substance unless otherwise noted.
Cycles Oof Concentration 20.0 7.8 N/A 15.6 11.1 3.0 3.0 2.6Cycles of Operation 20.0 7.8 N/A
Susp Solids Flow,kpph 1.1 0.2 3.4 0.6
Conclusions For new coal-fired plants, it is indeed feasible for
FGD Scrubbers to be integrated into the Plant Water Balance as Wastewater Pre ConcentratorsWater Balance as Wastewater Pre-Concentrators.
Lime-Soda softening at the front-end of a coal-fired power plant may be an obsolete technology,fired power plant may be an obsolete technology, especially if FGD Scrubbers are integrated into the Water Balance.
Adiabatic Scrubber Purge Concentrators and/or Dryers that are driven by flue gas may be a “best practice” technology for any new coal-fired powerpractice technology for any new coal fired power plant.
Conclusions (cont.) The WBM is a valuable tool for strategic
planning. For example, it can be used to predict what
would happen to water chemistry if the plant switched from one source of coal to anotherswitched from one source of coal to another.
Contact Information For general inquiries and questions
di thi t ti l
Contact Information
regarding this presentation please contact:
Dan Robinette Dan Robinette Rocky Mountain Water Engineering, LLC Phone: (720) 870-7818 E-Mail: [email protected]
Rob Peterson Salt River Project Salt River Project Phone: (928) 645-6384 E-Mail: [email protected]