Navajo Generating Station Water Balance Model

Transcription

1 Navajo Generating Station Water Balance Model Case Study Hypothetical Plant Water Systems Reconfiguration Presented at: 2013 Southwest Chemistry Workshop Presented by: Daniel J. Robinette, P.E. Rocky Mountain Water Engineering Introduction by: Rob Peterson Salt River Project July 16-18, 2013

2 Introduction Presentation Outline 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 Conclusions Questions Contact Information

3 Introduction This Case Study is hypothetical. It is not intended as a Design Review of 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.

4 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 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 critique of how the NGS water systems were originally configured, but rather how a new plant might be configured if it were built today.

5 Key Case Study Question 1. 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 hardness, would it be advantageous to: A. Use the conventional configuration of: 1) 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? 2. Or, might it be preferable to take the following approach?

6 Key Case Study Question (cont.) B. Reconfiguration 1. 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-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 driven Brine Concentrators t and Crystallizers.

7 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 thermodynamic power cycle, combustion, flue gas, water and solids systems. Chemistry plays a major role in a WBM. A powerful equilibrium model capable of performing complex chemistry tasks such as Boil-Down analyses is included.

8 Why Use a Water Balance Model? A WBM is needed to evaluate what-if case studies aimed at optimizing the plant water systems. Thermodynamics supplants the need to install and maintain flow meters on major streams. Flow rates are accurately determined by simultaneous mass and heat balances. Computational capabilities give WBMs power to pay-back initial investment.

9 Conventional Configuration Raw Water to Scrubber Softened Raw Water to Cooling Towers Cycled Up CT Blowdown to Traditional ZLD Equipment Flow Rates Reflect 3 Units Operating at Peak Generation in July Water Volumetric Flowrate gpm 0.2 Dry Solids Mass Flowrate kpph Raw Water FerricSulfate 80 (Lake Powell) Excesss Condensate 2.7 "High Value" Water Excess Distillate Aux.Steam Quick Lime 737 Evaporation Boiler Makeup mg/l Boron 14 24,135 Soda Ash Water Treatment 21,170 System ,207 20, mg/l Boron , Stripped CO2 Distillate 990 Reactivators (2) F 37 1, Evaporation 8.5 2, mg/l Cl 15,588 mg/l TDS mg/l Boron 66 High Flowrate mg/l Boron & High TDS 2,928 Sent to ZLD 1.2 Equipment Salts 9.7 SO2 Absorbed Sulfuric Acid Ponds Dumpate Involuntary Purge SD-2, 3 & 4 23 Entrained in Gypsum Limestone Brine 198 Oxidation O2 79 Gypsum Concentrators (3) Crystallizer (1) mg/l Boron 9400 mg/l Chloride Vapor Vapor 6 70,343 mg/l TDS Compressor Compressor 1918 mg/l Boron Power (Total): Power: Scrubbers (3) Cooling Towers (3) 6,530 bhp 719 bhp ,126 kw hr/hr 627 kw COC = 92 COC = 20.0 COC = 11.1 COC = 3.0 Ponds 60-2A, B, C & D COO = N/A COO = 20.0 COO = 31.1 COO = 34.1

10 Alternative Configuration w/ Conventional ZLD Equipment No Lime Soda Softening Scrubber Integrated Into Water Balance as Wastewater Pre Concentrator Conventional ZLD Equipment Evaporation Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July (Surge Ponds Not Shown) Raw Water 42 (Lake Powell) 20, Stripped CO2 from Distillate Sulfuric Acid Evaporation ,133 Addition mg/l Boron 23, , Water Volumetric Flowrate: gpm Dry Solids Mass Flowrate: kpph Condensate Aux.Steam 8 21 mg/l Boron New 7.4 Boiler Makeup mg/l Boron Water Treatment 2,981 3, F System ,118 mg/l TDS 27 SO2 Removed Sulfuric Acid New Voluntary 55 Purge KEYS TO RECONFIGURED WATER BALANCE Limestone mg/l Boron 1) Scrubbers are integrated into the Water 9400 mg/l Chloride Balance as "pre concentrating" ZLD 1 58,939 mg/l TDS equipment driven by "free" flue gas heat. Oxidation O2 486 mg/l Boron Salts Voluntary Purge prevents high chlorides. Involuntary Purge Entrained in Gypsum ) Lime Soda Softening at Front End of Plant 9400 mg/l Chloride becomesobsolete obsolete and unneccessary. 58,939 mg/l TDS Ponds Dumpate SD-2, 3 & ) Brine Concentrators and Crystallizer are "unloaded" by pre concentrating Scrubbers. Gypsum 4.2 Brine 3608 Concentrators (1 + 1) Crystallizer (1) mg/l Boron 4) Boron remains soluble in "wetted" areas, Scrubbers (3) Vapor Vapor but Boric Acid could form localized vapor Compressor Compressor Ponds pockets in non wetted areas. Power (Total): Power: 60-2A, B, C & D Cooling Towers (3) 9400 mg/l Cl 912 bhp 457 bhp 716 kw hr/hr 399 kw hr/hr COC = 7.8 COC = 15.6 COC = 3.0 COC = 2.6 COO = 7.8 COO = 23.8 COO = 26.8 COO = 29.4

11 Alternative Configuration using Scrubber as Wastewater Pre-Concentrator and Adiabatic Scrubber Purge Dryer No Lime Soda Softening Scrubber Integrated into Water Balance Adiabatic Scrubber Purge Dryer and Fabric Filter for ZLD Raw Water (Lake Powell) 24, Evaporation 20, Stripped CO2 from Sulfuric Acid Addition Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July (Surge Ponds Not Shown) Evaporation 23, ,069 Water Volumetric Flowrate: Dry Solids Mass Flowrate: Atomizer gpm kpph Hot Flue Gas from Air Preheater Inlet Duct deg F Boiler Furnace New Boiler Makeup 7.4 mg/l Boron Warm Flue 168 Water Treatment 3,133 Gas return 5.0 System 9.7 to Scrubber 350 deg F 6,165 mg/l TDS Inlet Duct SO2 Removed Sulfuric Acid New Voluntary Purge KEYS TO RECONFIGURED WATER BALANCE 44 Limestone ) Scrubbers are integrated into the Water 9400 mg/l Chloride 5.0 Salt Balance as "pre concentrating" ZLD 1 58,939 mg/l TDS Disposal equipment driven by "free" flue gas heat. Oxidation O2 486 mg/l Boron Voluntary Purge prevents high chlorides. Involuntary Purge 64 Entrained in Gypsum 76 2) Lime Soda Softening at Front End of Plant ADDITIONAL FUEL CONSUMPTION 9400 mg/l Chloride becomes obsolete and unneccessary. 58,939 mg/l TDS tph additional lcoal 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 Filter Gypsum driven by hot flue gas. Scrubbers (3) Scrubber Purge Dryer 4) Threat of Boron vapor buildup is eliminated. and Fabric Filter (1 + 1) Cooling Towers (3) 9400 mg/l Cl COC = 7.8 COC = 15.6 COC = COO = 7.8 COO = 23.8 COO =

12 Alternative Configuration w/ Adiabatic Scrubber Purge Concentrator (No Fabric Filter) No Lime Soda Softening Scrubber Integrated into Water Balance Flue Gas Driven Adiabatic Purge Concentrator (No Fabric Filter) Raw Water (Lake Powell) 24, , Evaporation 20, Stripped CO2 from Sulfuric Acid Addition Flow Rates Reflect 3 Generating Units Operating at Peak Capacity in July (Surge Ponds Not Shown) Evaporation 3,064 Water Volumetric Flowrate: Dry Solids Mass Flowrate: gpm kpph Hot Flue Gas from Air Preheater Inlet Duct 720 deg F Boiler Furnace Cooled New Flue Gas Boiler Makeup 7.4 mg/l Boron and Water Treatment 3,133 Evaporate System 9.7 to Scrubber 6,165 mg/l TDS deg F Entrainment SO2 Removed Separator Sulfuric Acid New Voluntary KEYS TO RECONFIGURED WATER BALANCE Limestone Purge %wt Slurry 1) Scrubbers are integrated into the Water 9400 mg/l Chloride Balance as "pre concentrating" ZLD 1 58,939 mg/l TDS Slurry equipment driven by "free" flue gas heat. Oxidation O mg/l Boron 5.0 Disposal Voluntary Purge prevents high chlorides. Involuntary Purge 64 Entrained in Gypsum 76 2) Lime Soda Softening at Front End of Plant 9400 mg/l Chloride becomes obsolete and unneccessary. 58,939 mg/l TDS 5.00 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 with Gypsum Entrainment Separator driven by hot flue gas. Scrubbers (3) 4) Threat of Boron vapor buildup is eliminated. Cooling Towers (3) 9400 mg/l Cl Scrubber Purge Concentrator (1 + 1) COC = 7.8 COO = 7.8 COC = 15.6 COO = 23.8 COC = 33.3 COO = 57.1

13 Interesting ZLD Chemistry Crystallizer Streams Module can be used to Perform Boil-Down Simulations The solubilities of various species in the Boil- Down analysis were customized to match RCC test run results. As a general rule, the solubilities of species in concentrated brine are increased by two orders of magnitude over the solubilities in deionized water. Boil-Down results are plotted on the following phase diagram.

14 WBM Boil-Down Results for Crystallizer Plotted on Na, Mg, Cl, SO4 Phase Diagram (at 221 deg F)

15 Sodium Sulfates are Hygroscopic Below 35 deg C (95 deg F)

16 Thenardite and Mirabilite Thenardite Anyhydrous Sodium Sulfate Na 2 SO 4 Mirabilite Hydrated Sodium Sulfate Na 2 SO 4 10H 2 O Na 2 SO H 2 O Cool Na 2 SO 4 10H 2 O MW = 142 MW = 180 MW = tph 5.07 gpm 2.27 tph 5 gpm of water is consumed for each ton per hour (tph) of Thenardite produced as it cools to form Mirabilite.

17 Absorbable Trace Species in Coal from Scrubber Chemistry During Test Burn Coal Combustion Products Imported from Boiler Furnace Coal Concentration of Constituents Absorbed Design General Test Design Test Cations (continued) Boron ppm Strontium ppm 2.86 Silica ppm 4.72 Zinc ppb Cations (Total Dissolved) Anions (Total Dissolved) Bromide ppm Chloride ppm 2, Arsenic ppt 149 Fluoride ppm 1.76 Cadmium ppb 7.50 Fulvate Nitrate ppm ppb Cobalt ppb Nitrite ppm Chromium ppt 41 o Phosphateppm Non Conserved (N/C) Ions Lead ppb Ammonium ppb 57 Lithium ppb Barium ppb 55 Magnesium ppm Calcium ppm 368 Manganese ppb Sulfate ppm 301 Mercury ppt 564 Aluminum ppb Nickel ppb Copper ppt 240 Potassium ppm Iron ppb Selenium ppb Sodium ppb 480

18 Tracking Species from Coal and Source Water Cooling Tower Blowdown Scrubber Purge Brine Concentrator Blowdown Crystallizer Blowdown Case Base Reco uratio Case Case Base Reco uratio Case Case nfigon nfigon nfigon nfigon Case Boron, mg/l B 6 1 1, , ,608 Silica, mg/l SiO ph Calcium Magnesium ,982 4,574 2,632 13,372 7,960 32,768 Potassium ,119 1,858 3,384 4,830 Sodium 4, ,533 12,055 45,958 35,255 78,995 80,304 Chloride 1, ,422 9,411 16,786 27,520 50,766 71,552 Fluoride Nitrate , , , ,884 Sulfate 8,781 3,442 37,403 30,523 84,111 85, , ,730 Tot Diss Solids 15,615 6,118 70,343 58, , , , ,301 Tot Susp Solids 23,011 5, ,394 53,063 Liquid Flow, gpm 1,088 2, Diss Solids Flow, kpph Susp Solids Flow,kpph Tot Solids Flow, kpph Cycles Oof Concentration N/A Cycles of Operation N/A Note: All concentration units are in mg/l as substance unless otherwise noted. Cations An nions Base Reco uratio Case Base Reco uratio Case

19 Conclusions For new coal-fired plants, it is indeed feasible for FGD Scrubbers to be integrated into the Plant Water Balance as Wastewater Pre-Concentrators. Lime-Soda softening at the front-end of a coal- 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 power plant.

20 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 another.

21 That s a Wrap Questions Comments Criticisms Witicismsi Emotional outbreaks Thank you!

22 Contact Information For general inquiries and questions regarding this presentation ti please contact: Dan Robinette Rocky Mountain Water Engineering, LLC Phone: (720) Rob Peterson Salt River Project Phone: (928)