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)

Sodium Sulfates are HygroscopicSodium Sulfates are Hygroscopic Below 35 deg C (95 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.

That’s a Wrap

Questions Comments Comments Criticisms

Witi iWiticisms Emotional outbreaks Thank you!

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: DanRobinette@RMWE.biz

Rob Peterson Salt River Project Salt River Project Phone: (928) 645-6384 E-Mail: Rob.Peterson@SRPnet.com