### Au g ust 2008 ( A p ril 2009 Revision ) 

## DOE/NETL-402/080108 

# Water Requirements for Existing and Emerging Thermoelectric Plant Technologies

## Disclaimer

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither th e United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any info rmation, apparatus, product, or process disclosed, or represents that its use w ould not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwis e does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Th e views and opinions of authors expressed therein do not necessarily state or reflect those of the United States Government or any agency thereof.

## Water Requirements for Existing and Emerging Thermoelectric Plant Technologies

DOE/NETL-402/080108

August 2008 Revised April 2009

NETL Contact:

Phil DiPietro Office of Systems, Analyses & Planning National Energy Technology Laboratory (NETL)

Prepared by:

Kristin Gerdes Christopher Nichols Office of Systems, Analyses & Planning, NETL

National Energy Technology Laboratory www.netl.doe.gov

i

### Table of Contents
Executive Summary ........................................................................................................... 1

1 Background .................................................................................................................. 2

1.1 Water Usage in Thermoelectric Plants .................................................................. 2

1.2 Objective .............................................................................................................. 3

1.3 DOE Water Reduction Effort ............................................................................... 3

2 Cooling Water Systems ................................................................................................ 3

3 Water Requirements for Power Generation Platforms .............................................. 5

3.1 Data Sources and Comparison ..................................................................................... 5
3.2 Subcritical and Supercritical PC plants ...................................................................... 7
3.3 IGCC plants ................................................................................................................... 8
3.4 NGCC plants ............................................................................................................... 10
3.5 Nuclear Plants ............................................................................................................. 11
4 Carbon capture and water usage ............................................................................... 11

4.1 Water consumption factors ........................................................................................ 13
4.2 Cooling water duty factors ......................................................................................... 15
5 Next Steps ................................................................................................................... 17 Appendix A ..................................................................................................................... A-1 Appendix B ..................................................................................................................... B-2 References ...................................................................................................................... R-1

ii

### List of Tables

Table ES-1. Water consumption and coolin g duty factors for thermoelectric power plants .......... 1 Table 3-1. Water intensive processes utilized by different IGCC gasifier designs 3 ..................... 10 Table 4-1. Impact of efficiency and water use by CDR equipment on water consumption associated with carbon capture for pl ants using wet recirculating cooling towers ...................... 14 

### List of Figures

Figure 1-1. Water flow schematic for power plants ....................................................................... 2 Figure 2-1. Cooling water system configurations .......................................................................... 4 Figure 2-2. Average total cost and number of cooling systems by type .......................................... 5 Figure 3-1. Water consumption for nuclear and greenfield bituminous coal and natural gas thermoelectric power plants utilizing wet cooling towers ............................................................... 6 Figure 3-2. Water flow schematic for a green field subcritical pulverized coal power plant utilizing a wet cooling tower and a wet FGD .................................................................................. 7 Figure 3-3. Water flow schematic for a green field supercritical pulverized coal power plant utilizing a wet cooling tower and a wet FGD .................................................................................. 8 Figure 3-4. Water flow schematic for a greenfie ld IGCC plant utilizing a wet cooling tower ....... 9 Figure 3-5. Water flow schematic for a greenfie ld NGCC plant utilizing a wet cooling tower .... 10 Figure 3-6. Water flow schematic for a nuclear plant utilizing a wet cooling tower 6 ................. 11 Figure 4-1. Comparison of net plant effic iencies (HHV basis) with and without CDR 3 .............. 12 Figure 4-2. Comparison of water consumption factors with and without carbon capture for greenfield plants using wet recirculating cooling towers – net power basis ................................ 13 Figure 4-3. Comparison of water consumption factors with and without carbon capture for greenfield plants using wet recirculating cooling towers – thermal input basis ........................... 15 Figure 4-4. Comparison of cooling water duty factors for greenfield plants – net power basis . 16 Figure 4-5. Comparison of cooling water duty factors for greenfield plants – thermal input basis

............................................................................................................................... ........................ 17

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## Executive Summary In light of the critical relationship between pow er generation and water, it is necessary to understand the water-related impacts associated with deployment of the advanced power platforms included in the National Energy Technology Laboratory (NETL) research
program. Table ES-1 shows water consumption and c ooling duty factors for several power generation platforms, with and without carbon dioxide (CO 2 ) capture. There is almost a fourfold increase in water consum ption per net kWh between the lowest water consuming platform (NGCC) and the highest (Nuclear). Also the addition of CO 2 capture and compression increases water c onsumption by 50% to 90%. Many of the advanced power platforms use less water and have a lower increase in water demand associated with incorporation of CO 2 capture equipment than do current technologies. The water consumption factors in Table ES-1 are based on a cooling system in which the effluent cooling water from the steam cycle co ndenser and other water coolers is cooled in an evaporative cooling tower and re-circula ted. “Consumption” re presents water that must be made up to account for both evapora tion in the cooling tower and a relatively small amount that is consumed in unit ope rations within the generation process. Table ES-1 also presents cooling duty factors, or thermal cooling load per kWh of net generation. These factors enable one to esti mate the impacts of different cooling water system configurations (e.g., once-through, wet cooling, dry coo ling). The percent change with the addition of CO 2 capture is different for cooling duty and water consumption because cooling duty does not include process water requirements.

Table ES-1. Water consumption and cooling duty factors for thermoelectric power plants i

Without CO 2 Capture With CO 2 Capture % Change With CO 2 Capture
Water Consumption Factors (gallons per MWh net power)*

Nuclear 720 -- Subcritical PC 520 990 +90% Supercritical PC 450 840 +90% IGCC, slurry-fed 310 450 +50%
NGCC 190 340 +80% Cooling Duty Factors (MMBtu per MWh net power)

Subcritical PC 4.7 11 +130% Supercritical PC 4.1 9.3 +130% IGCC, slurry-fed 3.0 3.7 +20%
NGCC 2.0 4.2 +110%
* Based on a cooling water system utilizing wet recirculating cooling towers

i Factors derived from the NETL Report “Cost and Performance Baseline for Fo ssil Energy Power Plants study, Volume 1: Bituminous Coal and Natural Gas to Electricity”; adjustments described in Appendix A.

Water Requirements in Emerging Thermoelectric Plant Technologies 1The factors in Table ES-1 are developed fo r the purpose of deriving the water-related impacts from different power plant deployment s cenarios, such as those forecasted by the National Energy Modeling System (NEMS) and MarKal models. The body of this report presents the calculation methodologies and data sources used to estimate the factors set forth in Table ES-1 . This information will enable analysts to adjust the factors to represent the impact of advanced technologies in th e areas of power generation, CO 2 capture and compression, and cooling water systems. 

## 1 Background Water, once considered a nearly inexhaustible resource, is increasingly limited, and water requirements for electricity production must compete with other demands, such as agriculture and sanitation. The 2007 drought in the southeastern U.S. underscored this issue with several nu clear power plants in the region reducing their output by up to 50% due to low river levels in August 2007. 1 Future water-related impacts on the industry may also come in the form of regulation. The Environmental Protection Agency is developing regulations under §316(b) of the Clean Water Act that will require the location, design, construction and capacity of coo ling water intake structures to reflect the best technology available for minimizi ng adverse environmental impact. 

### 1.1 Water Usage in Thermoelectric Plants The water-related impacts of fossil fuel thermo electric power plants ar e a function of (1) the cooling and process water needs, and (2) the system used to provide the cooling water. Thermoelectric power plants use wate r primarily to cool and condense the steam used to drive the turbines, w ith relatively minor amounts of water used for process steam make-up and other water-intensive processes, Figure 1.1-1

.

Figure 1.1-1. Water flow schematic for power plants

Water Requirements in Emerging Thermoelectric Plant Technologies 2About 43% of existing thermoelectric powerplant generating capacity employ a oncethrough cooling water system where water is drawn from a water body, used to condense steam, and then returned at a higher temperature. 2 More recently once-through cooling water systems have incorporated cooling to wers that lower the temperature of the discharge water. Further reduction in water w ithdrawal can be achieved in a recirculating system where the bulk of the water is cooled in evaporative cooli ng towers and reused with a lesser amount discharged and made up. A still further reduc tion in water use is possible in dry cooling systems – beneficial for arid regions – that use closed loop air cooling thus eliminating lo sses due to evaporation. 

### 1.2 Objective In December 2006, NETL participated in a De partment of Energy (DOE)-wide peer review of the analyses that are conducted to show the bene fits of the DOE research and development portfolio. One of the recommenda tions from the peer review panel was for DOE to consider the water-related impacts asso ciated with advanced thermoelectric plant technologies. This report provides the water use factors for use in deriving the waterrelated impacts from different power plan t deployment scenarios, such as those forecasted by the National Energy Modeling System and MarKal models.



### 1.3 DOE Water Reduction Effort This report highlights the wate r-related advantages of adva nced power platforms within the NETL research portfolio. However, due to the critical relationship between power generation and water, NETL has also initiated a research program to specifically develop advanced technologies to reduce water consum ption by thermoelectric power systems. The NETL Existing Plants – Emissions and Ca pture (EPEC) program contains a diverse research portfolio of water projects that ha ve the potential to significantly reduce the water-related impacts of thermoelectric pl ants. The EPEC program focuses on four technology pathways: (1) use of nontraditional s ources of process and cooling water; (2) innovative water reuse and recovery; (3) advanced cooling technologies; and (4) advanced water treatment and detection technology. Many of the efforts involve integration with existing power plant operatio ns, but are also applicable to advanced thermoelectric technologies. More information on the NETL efforts can be found at: http://www.netl.doe.gov/technologies/coalpower/ewr/water/index.html 

## 2 Cooling Water Systems For a cooling water system, water us age can be described as either consumption such as the water evaporated to the atmo sphere in a cooling tower or withdrawal which is equal to consumption plus any water returned to it s source. There are two basic cooling system configurations – once-th rough and recirculating, Figure 2-1 . In a once-through cooling system, water from an external water sour ce passes through the steam cycle condenser and is then returned to the source at a higher temperature with some level of contaminants. This system withdraws a significant amount of water, but consumes little at the plant site (evaporati on may, however, occur after th e water is returned to its source). To minimize the thermal impact to the water source, a cooling tower may be added in a once-through system to allow air c ooling of the water (with associated losses on site due to evaporatio n) prior to returning the water to its source.

Water Requirements in Emerging Thermoelectric Plant Technologies 3In a recirculating system, cooling water ex its the condenser, goes through a fixed heat sink and is then returned to th e condenser. This configurat ion results in relatively low
water withdrawal , but consumption occurring at the plant site is high relative to a oncethrough configuration. Typical heat sink options for recircul ating systems are mechanical or natural draft cooling towers and cooling pond s. In cooling towers , the water is cooled by the air to near the wet-bulb temperature using the principle of evaporation. Water flows over high surface area packing which serves to increase contact time with the air and maximize heat transfer. Mechanical draft cooling towers use fans to push or pull air through the towers, while natural draft cooli ng towers utilize larg e concrete chimneys facilitating a natural air current up the tower. While they require less power, natural draft towers are extremely large and generally only used at facilities w ith high cooling water requirements.

Once-Through Recirculating

Wet Cooling Dry Cooling

Wet Cooling Tower 

## Cooling Requirement

Mechanical Draft Natural Draft Cooling Pond Direct Indirect

Dry Cooling Tower

Figure 2-1. Cooling water system configurations

Make-up water to the cooling to wer is required to replace the water that evaporates to the atmosphere. Evaporation losses are typi cally the largest contributor to water consumption in a cooling tower system and can be estimated based on the cooling water flow rate and the cooling water temperature rise. As water evaporates in the cooling tower, a ny dissolved solids that came in with the raw make-up water will concentrate. To contro l the water chemistry and thus avoid scale formation and corrosion in the cooling wate r system, water must be discharged in a “blowdown” process. The required blowdown rate is highly dependent on the make-up water quality and is often determined based on cycles of concentr ation – the ratio of dissolved solids in the cooli ng water relative to the make-up water. With poor make-up water quality, the maximum allowable cycles of concentration is low requiring a high blowdown rate. A mid-range blowdown rate (c orresponding to a wate r quality requiring a cycles of concentration of 4) would be one third of the evaporation losses or 25% of the total make-up cooling water flow. 3 The water discharged as part of the blowdown process may be returned to the original source or sent to a water tr eatment facility. The

Water Requirements in Emerging Thermoelectric Plant Technologies 4quantity discharged (the blowdown) is th e primary difference between the raw water withdrawal and the water consumption in a wet recirculati ng cooling tower system. When water availability is low, a dry cooling system may be utilized. Dry cooling can be either direct or indirect and in each case us es convective heat transfer to provide cooling, eliminating evaporation losses. In direct dr y cooling systems, the turbine exhaust steam enters condenser tubes and is c ooled by ambient air. In an indirect system, cooling water is used to condense the steam, as in a wet re circulating system. Then the cooling water flows through tube bundles that are cooled in a mechanical or natural draft cooling tower. Cooling water make-up requirements can be nearly eliminated by use of dry cooling systems, but process and steam make -up water requirements are unaffected. Wet recirculating systems are roughly 40% more expensive than once-through systems, while dry cooling systems are 3 to 4 times more expensive than a wet recirculating system. 4 Figure 2-2 shows the average total cost and number of cooling systems for fossil/biomass-fueled steam plants in the U.S. for 2005. While most systems currently employ once-through cooling, environmental regulations and permitting requirements will likely push developers to choose recirculating or dry cooling options in the future.

19 28 27 182

0 100 200 300 400 500 600

Once through Recirc Cooling pond Other (includes dry)Number of systems

0 50 100 150 200 250 300Cooling system cost ($/kW) Number of systems: 1969 and before Number of systems: 1970 and later Cooling system cost

Figure 2-2. Average total cost and number of cooling systems by type 5



## 3 Water Requirements for Power Generation Platforms
3.1 Data Sources and Comparison In the 2007 NETL report, “Cost and Perfor mance Baseline for Fossil Energy Plants, Volume 1: Bituminous Coal and Natural Gas to Electricity” (N ETL Baseline), various greenfield thermoelectric plant technologi es were designed and costed. Water

Water Requirements in Emerging Thermoelectric Plant Technologies 5consumption, while not the primary focus of the NETL Baseline report, was quantified for pulverized coal (PC), natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC) plants. The analysis in Sections 3 and 4 of this report stems from these designs. ii For the coal-based platforms, th e water use factors are specific to bituminous coal.
Figure 3-1 compares water consumption for six th ermoelectric generation platforms using the design water consumption values from the NETL Baseline report (coal- and natural gas-based systems) and a 2002 EPRI report (nuc lear). The units ar e gallons of water consumed per net kWh of generation. All else equal, more efficient platforms will consume less water per kWh of net generation. However, other factors such as the steam cycle conditions, steam turbine contribu tion to gross power and process water requirements will impact the water usage for each technology.

0 100 200 300 400 500 600 700

NGCC

Shell IGCC

(Dry fed)

GEE IGCC (Slurry fed)

Supercritical PC

Subcritical PC

Nuclear Water Consumption (gal/MWh net)

Gasifier FGD Cooling Tower

Figure 3-1. Water consumption for nuclear 6 and greenfield bituminous coal and natural gas thermoelectric power plants utilizing wet cooling towers

NGCC and IGCC power plants have lower water consumption due to the fact that around 2/3 of a combined cycle power plant’s output comes from the combustion turbines which require minimal water when compared to the st eam cycle. Like PC plants, nuclear power generation is all from a steam cycle; however , nuclear plants utili ze lower pressure and temperature steam, and as a result require more steam and cooling water relative to the power produced.

ii The water requirements associated with each techno logy that were determined by the NETL Baseline report were adjusted based on a more detailed wate r analysis. The key assumptions related to water consumption and withdrawal used in the original study and a description of the subsequent adjustments are described in Appendix A. These adjusted factors are utilized throughout this report.

Water Requirements in Emerging Thermoelectric Plant Technologies 6

### 3.2 Subcritical and Supercritical PC plants As the least efficient type of fossil fuel power plant examined here, a subcritical PC plant also consumes the most water per kW of power produced. Due to the lower steam pressure as compared to a supercritical plan t, less energy can be transferred from the boiler to the turbine, so more steam flow, and thus more cooling water flow is required to generate the same electricity. Schematics hi ghlighting the water fl ows in a subcritical and a supercritical PC plant with a wet FGD unit can be seen in Figure 3-2 and Figure 3-3

. A PC plant fitted with a wet FGD unit will re quire make-up water. In an FGD, the flue gas enters a large vessel wher e it is sprayed with a slurry of about 10% limestone and 90% water. The sulfur in the flue gas and calcium in the limestone create a slurry of calcium sulfate (a gypsum). Although much of the water is removed from the gypsum by a dewatering process and then recycled, some is contained in the gypsum and must be made up. Water is also lost from the plant in the form of water vapor in th e flue gas. Although most of it was generated during combustion or was inherent coal moisture (approximately 11 wt% for bituminous coal), some of this water is from the FGD system. In the steam cycle, the boiler feedwate r (BFW) system requires blowdowns and subsequent make-up water. Because BF W make-up water is treated to remove impurities, the blowdown and make-up rates are not significant compared to the cooling water system requirements.

Water vapor Steam Turbine

Wet FGD Water vapor 

### Flue gas Steam cycle Cooling water

Boiler

Condenser Cooling tower

Raw water source (river, lake, ocean, well, municipal system, etc.) Wet gypsum Cooling water blowdown: 65-225 gal/MWh* FGD make-up: ~70 gal/MWh BFW make-up: ~10 gal/MWh Cooling tower make-up: 505-665 gal/MWh* BFW blowdown

*Range represents cycles of concentration from 3 to 8

Figure 3-2. Water flow schematic for a greenfield subcritical pulverized coal power plant utilizing a wet cooling tower and a wet FGD

Water Requirements in Emerging Thermoelectric Plant Technologies 7*Range represents cycles of concentration from 3 to 8 Water vapor Steam Turbine

Wet FGD Water vapor 

### Flue gas Steam cycle Cooling water

Boiler

Condenser Cooling tower

Raw water source (river, lake, ocean, well, municipal system, etc.) Wet gypsum Cooling water blowdown: 55-195 gal/MWh* FGD make-up: ~60 gal/MWh BFW make-up: ~10 gal/MWh Cooling tower make-up: 440-580 gal/MWh* BFW blowdown

Figure 3-3. Water flow schematic for a greenfi eld supercritical pulverized coal power plant utilizing a wet cooling tower and a wet FGD 

### 3.3 IGCC plants An IGCC power plant’s water profile is si gnificantly lower than either sub- or supercritical PC plants as shown in Figure 3-4 . This is mainly due to the fact that the gas turbine, which requires minimal cooling wate r, produces around 60% of the plant’s entire electrical output. Hot exhaus t gas from the gas turbine pa sses through a heat recovery steam generator (HRSG) to drive a steam cycle. It is worth noting that an IGCC’s steam cycle operates at a lower pressure than a PC plant’s does (1800 psig, as compared to 2400 psig for subcritical and 3500 ps ig for supercritical plants) , hence an IGCC plant consumes more water per MWh produced from the steam turbine than does a PC plant. iii
In addition to the use of cooling water for the steam condenser, an IGCC plant has cooling requirements for seve ral other gas proces sing steps. In the air separation unit (ASU), cooling water is required to cool co mpressed air prior to the cryogenic ASU cold box. In an IGCC’s acid gas removal (AGR) unit, hydrogen sulfide removal occurs through absorption by a chemical or physical solvent that then must be regenerated using heat. Cooling water is primarily utilized in the regenerator tower condenser and to cool

iii For the GEE IGCC configuration modeled in NETL’s baseline report, the steam turbine has a capacity of 299 MW and requires 3,485 gpm of make-up water associated with the condenser, yielding 699 gal/MWh gross for just the steam turbine condenser. For the PC plant, the cooling water make-up requirement is lower at 555 gal/MWh gross power. However, if th e power output of the entire IGCC plant including the steam and gas turbines is accounted for, then the GE plant’s cooling water make-up requirement is 271 gal/MWh gross power.

Water Requirements in Emerging Thermoelectric Plant Technologies 8the regenerated solvent. Fi nally, a relatively small amount of cooling water is required for compressor intercoolers in the tail gas treating unit (TGTU).

Water vapor Water vapor 

### Syngas Steam cycle Cooling water

Condenser Cooling tower

Gasifier HR SG

BFW make-up: ~5 gal/MWh Cooling tower make-up:

275-430 gal/MWh* Gasification process make-up:

25-55 gal/MWh* Cooling water blowdown: 35-145 gal/MWh*

Raw water source (river, lake, ocean, well, municipal system, etc.) AGR/ASU/TGTU Cooling Gas Turbine Steam Turbine

SWS BFW blowdown Wet Waste

*Range represents different gasifier technologies/designs and cooling water cycles of concentration from 3 to 8

Figure 3-4. Water flow schematic for a greenfield IGCC plant utilizing a wet cooling tower

IGCC plants also have water make-up require ments related to the gasification process itself. In the gasifier, coal, oxygen and st eam are reacted to produce a combustable gas called syngas. Each of the different IG CC gasifier designs modeled in the NETL Baseline report utilizes water for di fferent sub-processes as shown in Table 3-1 . In gasifiers marketed by Shell and ConocoPhillips (E-GAS), humidification of the syngas stream makes up a large porti on of the gasifier’s water demand. Syngas humidification along with steam and nitrogen dilution of th e syngas aids in minimizing formation of NO X during combustion in the gas turbine burner section. The E-GAS and General Electric Energy (GEE) gasifiers are slurry fed meaning that water is added to the coal prior to gasification. A portion of the water is consumed in the gasification process as it is converted to syngas. For these slurry fed designs, molten slag leaving the gasifier is quenched in water, then the slurry of wate r and slag drops out of the stream and is disposed of. Although some of the slurry water can be recovered, significant make-up is still required. In each of the designs, sc rubbing of the syngas with water occurs. It was assumed that some process water can be recovered and utilized in other processes or otherwise recycled within the system. Fo r example, the quench and scrubber water are sent to a sour water stripper (SWS) where th e impurities are removed from the water. As modeled, a portion of the blowdow n from the SWS effluent is recycled to meet other process water needs. Filtering or clean up require ments to facilitate this type of internal recycle were not evaluated in de tail in the NETL Baseline report.

Water Requirements in Emerging Thermoelectric Plant Technologies 9Table 3-1. Water intensiv e processes utilized by different IGCC gasifier designs 3

GEE CoP E-GAS Shell
Ash Handling 

### 8 8 8 Slurry/Slag Handling 

### 8 8 Quench/Scrubber 

### 8 8 8
Humidifier 

### 8 8
Gasifier Steam 

### 8
Gas Turbine Dilution 

### 8
3.4 NGCC plants NGCC plants do not consume water for slurryin g or desulfurization and the gas turbine generates 65%-70% of th e total plant power outpu t. The result is a configuration with a low water profile. The NGCC design does, however, consume roughly 25% more water relative to power generation from the steam turbine than does a subcritical PC plant, despite operating under similar steam conditions. This difference stems from the heat source for the BFW heater systems. In th e NGCC design, the BFW heating occurs in the heat recovery steam generator (HRSG). In the PC design, extraction steam must be used for BFW heating. A schematic of a greenfiel d NGCC plant’s water requirement is shown in Figure 3-5

.

Water vapor

Steam Turbine Water vapor 

### Combustion Steam cycle Cooling water

Condenser Cooling tower HR SG

Gas Turbine

BFW make-up: <5 gal/MWh Cooling tower make-up:

215-285 gal/MWh* Cooling water blowdown: 25-95 gal/MWh*

Raw water source (river, lake, ocean, well, municipal system, etc.) BFW blowdown

Figure 3-5. Water flow schematic for a greenfield NGCC plant utilizing a wet cooling tower

Water Requirements in Emerging Thermoelectric Plant Technologies 10

### 3.5 Nuclear Plants In a nuclear plant, energy from the decay of uranium heats pressurized water which is then used to produce steam in the steam gene rator (SG). All power produced comes from the steam cycle as it does for PC plants. Nu clear plants have a hi gher cooling tower load relative to net power generation. This is because the steam conditions are limited by metal brittleness effects from the nuclear reactor thereby reducing efficiency. Figure 3-6 shows the water requirements for a nuclear power plant.

*Cycles of concentration from 5 to 10 SG Water vapor Steam Turbine 

### Nuclear reaction Steam cycle Cooling water

Condenser Cooling tower

Cooling

tower make-up: 800-1100 gal/MWh Cooling water blowdown: 60-200 gal/MWh*

Raw water source (river, lake, o cean, well, municipal system, etc.) Pressurized Water Reactor

Figure 3-6. Water flow schematic for a nuclear plant utilizing a wet cooling tower 6



## 4 Carbon capture and water usage The NETL Baseline report designed and costed thermoelectric plants with the capability to capture carbon dioxide for each of the fo ssil energy plant technologies. Based on the technologies used in these de signs, installing carbon dioxide recovery (CDR) equipment increases the water requirement per net pow er generation of a plant, due both to a reduction in the plant efficiency ( Figure 4-1 ) and to the cooling water and process water requirements associated with carbon dioxide capture and compression.

Water Requirements in Emerging Thermoelectric Plant Technologies 110% 20% 40% 60%Plant Efficiency No CDR
CDR

No CDR 36.8% 39.1% 38.2% 41.1% 50.8%
CDR 24.9% 27.2% 32.5% 32.0% 43.7% Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure 4-1. Comparison of net plant efficiencies (HHV basis) with and without CDR

The CO 2 recovery method for PC and NGCC plants used in the NETL Baseline study is a monoethanolamine (MEA) recovery unit ba sed on the Fluor Econamine FG Plus technology. The data presented here are specif ic to that technology, however, research in this area is ongoing and systems with improved efficiency, costs, and/or water balances are being pursued. To meet the specifications of the Econamine process, a polishing scrubber simultaneously cools the flue gas and reduces the SO 2 concentration to less than 10 ppmv. The gas then contacts the MEA, which absorbs the CO 2 . The CO 2 -laden MEA is then steam-heated to release the CO 2 . The MEA is recovered and reused, and the carbon dioxide is cooled and compressed for shipment. Overall, t he CDR facility involves a number of subprocesses which collectively require a sign ificant amount of cooling water. This includes flue gas cooling, water wash cooling, absorber inte rcooling, reflux condenser duty, reclaimer cooling, the lean solvent cooler, and CO 2 compression interstage cooling. At the same time, however, the cooling water requiremen ts associated with the steam turbine condenser are reduced slightly relative to the power from the steam turbine as low pressure extraction steam is routed to th e MEA regenerator condenser. In addition, a portion of the cooling water that is evaporated is offset by collecting water that condenses as the CO 2 is cooled and compressed. In a plan t without CDR equipment, this water would generally leave the st ack as water vapor. For IGCC plants, a high level CO 2 recovery will require a water-gas shift reactor and a physical-absorption based scrubber. The water-gas shift react or increases the CO 2 and hydrogen concentration in the syngas str eam by converting carbon monoxide to CO 2 and hydrogen by the addition of steam over a catalyst bed. CO 2 is then removed from the gas stream using a two-stage Selexol proce ss. The greater concentration of CO 2 in the IGCC process allows use of this physical-solvent. Th is results in less of an increase in cooling water requirements compared to the chemical solvent used in the Econamine process for PC and NGCC plants. The remaining increase in cooling duty is due to an increase in the ASU cooling requirements and the addition of CO 2 compressor intercoolers.

Water Requirements in Emerging Thermoelectric Plant Technologies 12

### 4.1 Water consumption factors iv
Utilizing the design conditions and assumpti ons of the NETL Baseline report, water consumption factors (net of the blowdown from the cooling water system) for each of the plant technologies with a nd without CDR equipment were developed. Raw water withdrawal factors which show the entire volume of water withdrawn for cooling water and process use is provided in Appendix B.
Figure 4-2 compares the water consumption relative to net power generation. In the PC and NGCC cases, water consumption per ne t generation increases by 90% and 76%, respectively, with the addition of CO 2 capture. The bulk of th e increase is from higher cooling tower load related to the utilizati on of the cooling water-intensive chemicalabsorption CO 2 recovery method at the back end of the power plant. In the IGCC slurry fed case, CO 2 recovery occurs prior to combusti on so the water consumption factor increases by only 46%. More than half of this increase is due to water-intensive processes in the gasifier and in the water gas shift (WGS) process.

0 200 400 600 800 1,000Water Consumption(gal/MWh net) Cooling Tower
FGD
WGS
Gasifier

Total 517 985 452 844 309 452 295 475 192 338 Cooling Tower 449 884 392 759 290 355 243 355 192 338

FGD 68 101 59 86
WGS 52 49
Gasifier 19 45 53 71 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure 4-2. Comparison of water consumption factors with and without carbon capture for greenfield plants using wet recirculating cooling towers – net power basis

The reason for increases in cooling water consumption per net power generation is a combination of the reduction in efficiency and the additional cooling water and process water for CDR equipment. Table 4-1 shows the total increase in water consumption for carbon capture and breaks it down into the ex pected water increas e due to the lower efficiency of the carbon capture platform a nd the increased water usage due to additional cooling and process water for CDR processes.

iv See Appendix A for key information on the basis for these factors.

Water Requirements in Emerging Thermoelectric Plant Technologies 13Table 4-1. Impact of efficiency and wat er use by CDR equipment on water consumption associated with carbon capture for plan ts using wet recirculating cooling towers

Plant Type Impact of Efficiency Impact of Water Use by CDR Processes Total Increase in Water Consumption for Carbon Capture
Increase in Water Consumption Due to CO 2 Capture, gal/MWh net (%)

Subcritical PC 247 (48%) 221 (43%) 468 (90%) Supercritical PC 198 (44%) 195 (43%) 393 (87%) IGCC (slurry fed) 54 (18%) 89 (29%) 143 (46%) IGCC (dry fed) 84 (28%) 96 (32%) 180 (61%)
NGCC 31 (16%) 114 (60%) 146 (76%)

Figure 4-3 shows the water consumption factors on a HHV thermal input basis which essentially removes the impact of the effici ency reductions and only concentrates on the water use by the CDR equipment. On this basis, most of the increase in water consumption for the IGCC cases is due to pr ocess water usage including the addition of the steam for the WGS reaction and water dema nd associated with gasifier operation. The change in water consumption associated with the cooling water system for the IGCC cases is primarily due to compression cooling. This information is also useful if polic y and economic considerations point to the implementation of carbon capture for existing PC or NGCC plants. Should a plant be retrofitted with CDR equipment, the net power output of that plant would be reduced and thus the increase in water consumption for th at specific plant would not increase by the 90% or 76% quoted above. For example, for an existing subcritical PC plant based on the design used in this evaluation, the water consumption assuming a constant coal feed rate would increase by 30% or require roughl y 16 gallons of additional make-up water per MMBtu of thermal input (HHV). This addi tional requirement is almost entirely for the cooling tower load. As a result, if a pa rticular plant has maximized its water draw, the additional water requirements are only a ssociated with the cooling tower load and could thus be achieved with conversion to r ecirculating or the addi tion of a dry cooling system.

Water Requirements in Emerging Thermoelectric Plant Technologies 140 10 20 30 40 50 60 70 80 90 100Water Consumptionper HHV Thermal Input(gal/MMBtu) Cooling Tower
FGD
WGS
Gasifier

Total 55.7 71.8 51.8 67.4 34.6 43.1 35.5 44.5 28.6 43.2 Cooling Tower 48.4 64.4 45.0 60.5 32.5 33.8 29.2 33.2 28.6 43.2

FGD 7.3 7.4 6.8 6.8
WGS 4.9 4.6
Gasifier 2.1 4.3 6.3 6.7 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure 4-3. Comparison of water consumption factors with and without carbon capture for greenfield plants using wet recirculating cooling towers – thermal input basis



### 4.2 Cooling water duty factors v The water consumption factors for the cooli ng requirements described above can only be applied to wet recirculating cooling towers. Knowing the cooling duty associated with the cooling water systems for plants with and without CO 2 capture allows application of this data to once-through or dry cooling systems. Utilizing the design cooling duty from the NETL Baseline report for various proces ses within the plants, factors for cooling water duty per net power generation and per coal feed rate were developed as shown in Figure 4-4 and Figure 4-5

. The cooling water duty follows a similar patt ern to the water consumption factors with the increase related to CO 2 capture for NGCC and PC plants being far greater than for the various IGCC cases. For PC and NGCC plants, the increase in the cooling tower load is primarily due to the cooling needed for the amine process with some increased load due to CO 2 compressor intercoolers. The condenser duty actually decreases with the addition of CDR equipment both per net power and relati ve to the coal feed rate. The reason for this decrease is that a por tion of the steam from the steam turbine is routed to the Econamine system and condensed in th e solvent regenera tor reboiler. For the IGCC cases, a significant portion of th e additional water consumption associated with CDR capability is due to the gasifier and WGS process, so th e cooling tower load increase is less significant than the over all water consumption increase. The minor increase in additional cooling system load is due to the reduced efficiency of the CDR

v See Appendix A for key information on the basis for these factors.

Water Requirements in Emerging Thermoelectric Plant Technologies 15configuration, additional cooling load on the AGR unit and the addition of CO 2 compressor interstage coolers. Again this info rmation can be used to evaluate the cooling water needs for retrofitting an existing PC or NGCC plant with CDR equipment with the added flexibility to evaluate dry and once-through cooling systems.

0 2 4 6 8 10 12Cooling Water Duty(MMBtu/MWh net) CO2 comp intercool
Econamine
Miscellaneous ASU & TGT intercool
AGR Condenser

Total 4.7 10.7 4.1 9.3 3.0 3.7 2.5 3.7 2.0 4.2 CO2 comp intercool 0.39 0.36 0.25 0.22 0.13

Econamine 6.13 5.54 2.91

Miscellaneous 0.10 0.15 0.09 0.14 0.03 0.04 0.03 0.04 0.04 0.04
ASU & TGT intercool 0.36 0.49 0.27 0.43

AGR 0.10 0.32 0.14 0.32
Condenser 4.58 4.00 3.99 3.27 2.53 2.61 2.09 2.69 1.97 1.08 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure 4-4. Comparison of cooling water duty factors for greenfield plants – net power basis

Water Requirements in Emerging Thermoelectric Plant Technologies 160.0 0.2 0.4 0.6 0.8 1.0Cooling Water Dutyper HHV Thermal Input(MMBtu/MMBtu) CO2 comp intercool Econamine Miscellaneous ASU & TGT intercool AGR Condenser

Total 0.50 0.78 0.47 0.74 0.34 0.35 0.30 0.35 0.30 0.53 CO2 comp intercool 0.03 0.03 0.02 0.02 0.02

Econamine 0.45 0.44 0.37

Miscellaneous 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.01
ASU & TGT intercool 0.04 0.05 0.03 0.04

AGR 0.01 0.03 0.02 0.03
Condenser 0.49 0.29 0.46 0.26 0.28 0.25 0.25 0.25 0.29 0.14 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure 4-5. Comparison of cooling water duty factors for greenfield plants – thermal input basis 

## 5 Next Steps To extend and improve the factors presen ted here, the following next steps are recommended:

• Refine the water consumption and withdr awal factors presented here with a specific focus on water requirements. Process simulations will be used as
necessary.

• Develop water consumption and withdrawal factors for an integrated gasification fuel cell (IGFC) platform.

• Develop water consumption and withdraw al factors for plant designs with oxyfuel combustion.

• Develop water consumption and withdrawal factors for low rank coal for each of the coal-based platforms.

• Develop factors for solid residuals fo r each of the coal-based platforms.

Water Requirements in Emerging Thermoelectric Plant Technologies 17

## Appendix A

Key assumptions in the 2007 NETL baseline report:

- Raw water makeup is assumed to be provided 50% by a publicly owned treatment works and 50% from groundwater

- Cooling water circulation and losses we re determined using the following:

o Design ambient wet bulb temperature of 51.5 oF to achieve a cooling water temperature of 60 oF (8.5 oF approach)

o Cooling water temperature range of 20 oF

o Evaporative losses of 0.8% of the circulating water flow rate per 10 oF of
range

o Drift losses of 0.001% of the ci rculating water flow rate

o Blowdown rates = evaporated losses / (cycles of concentration – 1)

 Mid-range cycles of concentration of 4 was used (measure of water quality)

- Blowdown from other processes in the plant we re assumed to be routed to the cooling water system, backing out makeup water, as follows:

o PC and NGCC cases with CO 2 capture: condensed wa ter resulting from the cooling and compression of CO 2 (for non CO 2 capture cases, this water leaves with the flue gas) vi

o All cases: the boiler feedwater blowdow n is routed to the cooling water system

- Note that cooling water and process water requirements will vary significantly with process conditions such as temperature

Adjustments to water requirements detailed in the 2007 NETL baseline report:

- In the baseline report, for the PC and IGCC cases, an engineering estimate for miscellaneous cooling duty requirements of 100 MMBtu/hr was added (75 MMBtu/hr for the NGCC cases). This number was adjusted in this analysis as follows:

o PC cases: assumed to be 55 MMB tu/hr for the subcritical no CO 2 capture cases and was scaled based on coal feed rate for all other PC cases

o IGCC cases: assumed to be 20 MMBtu/ hr for the GEE IGCC no capture case and was scaled based on coal feed rate for all other IGCC cases

o NGCC cases: assumed to be 20 MMBtu/hr for both cases

- In the baseline report, cooling duty a ssociated with the ASU and the TGTU intercoolers was documented, but not utili zed in determining the cooling water circulation rate. The cooling duty and a ssociated cooling water requirements were added for these processes in this analysis.

vi Note that this was a significant change between the May 2007 report and the Revised August 2007 report

Water Requirements in Emerging Thermoelectric Plant Technologies B-1

## Appendix B

Below are the raw water withdrawal factors corresponding to th e discussion in Section 4

. This analysis incorporates all water wit hdrawn for various uses in the plant.

0 200 400 600 800 1,000 1,200 1,400Raw Water Withdrawal(gal/MWh net) Cooling Tower Boiler Feedwater FGD WGS Gasifier

Total 667 1,326 582 1,142 406 571 376 593 256 471 Cooling Tower 590 1,213 515 1,044 382 469 320 468 254 468

Boiler Feedwater 8 12 8 12 5 5 4 5 2 3

FGD 68 101 59 86
WGS 52 49
Gasifier 19 45 53 71 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure B-1. Comparison of raw water withdrawal factors with and without carbon capture for greenfield plants using wet recircula ting cooling towers – net power basis

0 20 40 60 80 100 120Raw Water Withdrawalper HHV Thermal Input(gal/MMBtu) Cooling Tower Boiler Feedwater FGD WGS Gasifier

Total 71.9 96.6 66.7 91.1 45.5 54.3 45.3 55.6 38.1 60.2 Cooling Tower 63.7 88.4 59.0 83.3 42.9 44.6 38.5 43.8 37.7 59.8

Boiler Feedwater 0.9 0.9 0.9 0.9 0.5 0.5 0.4 0.5 0.4 0.4

FGD 7.3 7.4 6.8 6.8
WGS 4.9 4.6
Gasifier 2.1 4.3 6.3 6.7 No CDR CDR No CDR CDR No CDR CDR No CDR CDR No CDR CDR

Subcritical PC Supercritical PC IGCC (slurry fed) IGCC (dry fed) NGCC

Figure B-2. Comparison of raw water withdrawal factors with and without carbon capture for greenfield plants using wet recirculati ng cooling towers – thermal input basis

Water Requirements in Emerging Thermoelectric Plant Technologies B-2

## References

1 Energy Velocity Suite, Nuclear Regulatory Commission Outage query. http://www1.ventyx.com/v elocity/vs-overview.asp

2 National Energy Technology Laboratory (NETL), “Estimating Freshwater Needs to Meet Future Thermoelectric Generation Requirements” Report DOE/NETL-400/2008/1339, Revised September 2008. http://www.netl.doe.gov/technologies /coalpower/ewr/pubs/2008_Wat er_Needs_Analysis-Final_10-2- 2008.pdf

3 National Energy Technology Laboratory (NETL), “Cost and Performance Baseline for Fossil EnergyPower Plants study, Volume 1: Bituminous Coal and Natural Gas to Electricity” Report DOE/NETL2007/1281, Revised August 2007. http://www.netl.doe.gov/energy-analyses/pubs/Bituminous%20Baseline_Final%20Report.pdf

4 R.Tawney, Z. Khan, J. Zachary (Bechtel Power Co rporation), “Economic and Performance Evaluation of Heat Sink Options in Comb ined Cycle Applications”, Journal of Engineering for Gas Turbines and Power

, April 2005, Vol. 127.

5 U.S. Department of Energy, Energy Information Ad ministration (EIA). Form EIA-767: Annual SteamElectric Plant Operation and Design Data. 2005 data. http://www.eia.doe.gov/cneaf/electricity/page/eia767.html

6 Electric Power Research Institute (EPRI), “Water & Sustainability (V olume 3): U.S. Water Consumption for Power Production – The Next Half Century”, Palo Alto, CA: 2002. 1006786.

Water Requirements in Emerging Thermoelectric Plant Technologies R-1