TECHNOLOGY CHOICE AND WATER CONSUMPTION FOR COAL ELECTRICITY PRODUCTION WITH CARBON CAPTURE AND STORAGE

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1 Proceedings of the ASME 2014 Power Conference POWER2014 July 28-31, 2014, Baltimore, Maryland, USA POWER TECHNOLOGY CHOICE AND WATER CONSUMPTION FOR COAL ELECTRICITY PRODUCTION WITH CARBON CAPTURE AND STORAGE Christopher Harto Washington, DC, USA Ellen White Argonne, IL, USA Robert Horner Washington, DC, USA Jenna Schroeder Washington, DC, USA ABSTRACT Water consumption is an important consideration when evaluating technologies for carbon capture and storage (CCS). It may in fact become a critical factor in certain regions where water is increasingly a source of conflict. For this reason, water consumption has the potential to become a challenging obstacle to adoption of CCS technologies. This analysis seeks to improve understanding of relative water costs of different CCS technology options. It also helps to identify areas where water use may in fact become a challenge and reveal opportunities for technological improvements that can help minimize these challenges. A life cycle assessment approach was utilized to analyze both the water consumption from carbon capture and storage projects. While there have been previous analyses that have looked at the direct water consumption for some capture processes, there have been few studies that have taken a detailed look at water consumption throughout the complete life cycle of the of electricity production with CCS. This effort expands the system boundaries beyond those of previous analysis while evaluating a range of system configurations to facilitate technology comparison. The range of system configurations considered in this analysis included both pre and post combustion capture systems and multiple sequestration scenarios. The system boundaries for the analysis include fuel production, fuel transport, combustion, capture, CO2 transport, and storage. Water consumption for conventional fossil fuel systems are also calculated for comparison purposes. The results show that while all carbon capture technology pathways result in a net increase in water consumption relative to conventional coal generation, the choice of technology, especially capture technology, can play a significant role in minimizing the increase in water consumption. Integrated gasification combined cycle coal plants with carbon capture were found to be significantly more water efficient than either conventional power plants with post combustion capture or plants utilizing oxy-combustion processes. Also, while other stages of the life cycle do consume water, the volumes were small relative to the power plant operations and capture stages. INTRODUCTION Throughout the past decade, much discussion and debate has centered on the viability and value of carbon capture and storage as a strategy to reduce carbon emissions. A growing question surrounding carbon capture and storage (CCS) concerns the amount of water that may be required. While limited analyses have been performed looking at CCS water consumption, they tended to focus solely on the direct water consumption resulting from carbon capture and consider a single or a limited number of technologies. More comprehensive analysis is required to adequately address questions surrounding water consumption for CCS. Most importantly, analysis is needed that considers a wider range of technology options and expands the boundaries of the analysis 1 Copyright 2014 by ASME

2 to consider the complete life cycle of the CCS process from fuel production to sequestration. METHODOLOGY The methodology selected for this analysis is a hybrid life cycle assessment. Hybrid life cycle assessment combines a traditional process based life cycle assessment approach with an economic input-output life cycle assessment (EIO-LCA) approach to expand the system boundaries and include impacts for process where detailed information may not be available (Williams 2004). The process based approach requires direct information about all the direct water consumption from each life cycle stage. It can be more accurate for a specific system when the required data can be obtained. However, in many cases all the data required is not available and thus this approach has a tendency to leave out potentially important components of the life cycle for which data is not available. The EIO-LCA methodology only requires information about the cost of different life cycle components and some information about the sectors of the economy to which these costs can be attributed. The model considers economic impacts for entire sectors of the economy including the impacts resulting from input materials from other economic sectors. The results are normalized per dollar of economic output from the individual sectors to produce impact factors in terms of impact per dollar of output. This approach produces a much more complete accounting of all impacts from the full life cycle of a process. The limitation is that it is not good at distinguishing impacts from similar products from the same economic sector as they are all assumed to have the same impacts per dollar spent. The specific model to be used is the EIOLCA.net model developed by Carnegie Mellon University. It includes impact factors for 428 specific economic sectors (CMUGDI 2014). For this analysis the process based approach was used to calculate direct water consumption from fuel mining and power plant operations. The EIO-LCA methodology was used for power plant construction, CO 2 transportation, and CO 2 injection. Processes considered outside of the system boundary for this analysis include: transportation of coal, manufacture of chemicals consumed within the capture process, offsite solid waste disposal (water consumption associated with onsite environmental controls and waste handling are included within the power plant operations stage), and decommissioning. The EIO-LCA methodology used to estimate water consumption follows the approach used by Harto et al. (2010). This approach combines direct water consumption from the different economic sectors with the indirect water consumption from energy production from those sectors. EIO-LCA water factors in gallons per dollar of economic activity were taken directly from Harto et al. when available for the sector of interest or calculated using the same approach (2010). A total of seven core scenarios were analyzed along with sensitivity analysis around some key parameters. The power plants and capture systems included in the analysis are: Subcritical pulverized coal (PC) with post combustion amine capture Supercritical PC with post combustion amine capture Oxycombustion at subcritical coal plant Integrated gasification combined cycle (IGCC) with capture Subcritical PC without capture Supercritical PC without capture IGCC without capture The impact of transportation distance and storage within deep saline aquifers within different regions and utilization for enhanced oil recovery (EOR) are evaluated for their impact on the overall water consumption impact on the life cycle. The specific scenarios are based upon recent modeling for technoeconomic analysis by Argonne and NETL (Doctor 2011, NETL 2010). LIFE CYCLE STAGES A total of five key life cycle stages were evaluated: coal mining, power plant construction, power plant operations, CO 2 transportation, and CO 2 storage. Key parameters for the seven LCA scenarios are shown in table 1. Coal Mining Water is required for coal mining. However, the quantity of water varies depending on the type of mining being employed. Surface mining generally requires less water per metric ton of Table 2. Coal Mining Water Consumption (gal/metric ton) Type of Mining Value Source Surface mining 6 Mavis 2003 Surface mining 25 Nicot et al Surface mining 8 BLM 2008 Surface mining 13 Elcock 2010 Underground 91 NETL 2009 Underground 130 Elcock 2010 Combined USGS Copyright 2014 by ASME

3 Table 1. Key Life Cycle Scenario Parameters Parameter a Source: NETL 2012 SubPC no CCS SubPC Amine SuperPC no CCS SuperPC Amine IGCC no capture IGCC w/ capture Oxyfuel Source Doctor 2011 Doctor 2011 NETL 2010 NETL 2010 NETL 2010 NETL 2010 Doctor 2011 Gross Power Output (MW) Net Output (MW) Capacity factor Capture % 0 90% 0% 90% 0 90% 98% Coal Consumption (metric ton/hr) Coal Type Illinios #6 Illinios #6 Illinios #6 Illinios #6 Illinios #6 Illinios #6 Illinios #6 CO2 pipeline flow (metric ton/hr) Plant lifetime Power Plant Total Capital ($/kwnet) 1,216 2,268 1,647 2,913 1,987 2,711 2,411 Storage cost ($/metric ton) a Pipeline cost ($/metric ton) a Table 4. Summary of Water Consumption LCA Results (gallon/metric ton) SubPC no SubPC SuperPC SuperPC IGCC no IGCC w/ LCA Stage CCS Amine no CCS Amine capture capture Oxyfuel Coal Power Plant Construction Power Plant Operations CO2 Transport CO2 Storage Total Copyright 2014 by ASME

4 coal. A summary of the literature data on water consumption for coal mining is shown in table 2. Average values for both surface and underground mining of 13 and 110 gallons per metric ton are used in this analysis. The default coal used in this analysis was Illinois #6, which is an underground mined bituminous coal with characteristics defined by NETL in their guidelines for systems analysis (NETL 2005). Results were also calculated based upon Wyodak-Anderson sub-bituminous coal from the powder river basin, which is surface mined and Pocahontas #3 high quality bituminous coal from VA which is underground mined. Power Plant Construction Although direct water consumption is expected to be limited for power plant construction, large quantities of energy go into construction as well as manufacturing of equipment which can lead to non-trivial indirect water consumption. Power plant capital costs from techno-economic analysis shown in table 1 were used to calculate the water consumption for plant construction using EIOLCA water factors. Rather than use a single water consumption factor for one sector, an EIOLCA factor for power plants was developed by combining the factors for three sectors: turbine and generator sets, general industrial machinery and equipment, and new construction. The factors from the three sectors were combined based upon their relative contribution to the total power plant cost from data from the supercritical pulverized coal plant scenario (NETL 2010). Power Plant Operations Power plant operations have been the primary focus of previous analyses that have looked at water consumption for CCUS. Water is consumed in a number of processes in the operation of a coal power plant; however the most significant in most cases is for cooling. For all scenarios recirculating cooling was assumed. This assumption was made due to the fact that upcoming EPA regulations (316(b)) will require that most new power plants utilize recirculating cooling and existing once through cooling systems will be largely phased out over time. Dry cooling is also an option but it is not commonly utilized for large coal power plants due to the significantly higher capital costs, larger land area required, and additional energy penalties experienced (Zhai et al. 2011). In addition, the energy penalty for dry systems increases when the ambient temperature increases, which is also when the demand for power is typically the highest. In addition to cooling, water is consumed for boiler feed water make-up and for emissions controls such as flue gas desulfurization and fly ash management. Capture systems can increase water consumption through two mechanisms. They increase parasitic loads on the power plant requiring more cooling water per net MWh generated. Amine systems also have a direct water consumption component. Water consumption for the operations phase was taken directly from the relevant techno economic analyses for which the scenarios were based. The values for the supercritical pulverized coal and IGCC scenarios were taken directly from the report (NETL 2012). The subcritical pulverized coal and oxyfuel scenarios required extraction of additional values from the Aspen models upon which the original analysis was based (Doctor 2011). CO 2 Transportation Power plants often are not located near suitable storage reservoirs. Thus pipeline networks are required to transport CO 2 from the power plant to injection wells or oil fields for EOR. Water can be consumed both in the construction of pipelines and from energy consumed for recompression of the CO 2 along the pipeline. The default pipeline distance of 100km utilized in most NETL techno-economic analyses was used for the core scenarios. In these scenarios CO 2 is compressed sufficiently at the power plant and no additional recompression is required for transportation and injection. Water consumption was also calculated for longer transportation distances where recompression was required. The EIOLCA water factor for the natural gas pipeline sector was selected for analyzing transportation water consumption as it was deemed to be the most appropriate for CO 2 pipelines, although it is recognized there will be some error associated with this assumption. Pipeline costs were taken from NETL s techno-economic analysis and are shown in Table 1 (NETL 2012). Pipeline costs were assumed to be liner with pipeline length so costs for longer pipelines were calculated by multiplying the cost of the 100 km pipeline by the distance. Energy consumption for recompression was calculated based upon literature estimates for longer pipelines and water consumption was calculated by assuming energy consumed was a parasitic load on the power plant (Singh et al 2011). CO 2 Storage There are two primary methods for CO 2 storage; injection into a deep saline aquifer and injection for enhanced oil recovery. Water is consumed both directly and indirectly (through energy consumption) in the drilling and construction of injection and monitoring wells. Injection for storage in a deep saline aquifer is assumed to be the default storage strategy in the core scenarios. The EIOLCA water factor for petroleum and natural gas drilling was selected for use for injection wells. The default cost for CO 2 storage was taken as the average of four cost estimates for different locations around the country (IL, ND, MT, and east TX) (NETL 2012). The high and low values from this range are also evaluated in the sensitivity 4 Copyright 2014 by ASME

5 analysis. It was assumed that no additional pumping and compression is required for injection and that all compression occurs either in the power plant operations and transportation stages. This is consistent with the NETL techno-economic analyses (NETL 2010). efficiency of the supercritical system aids in reducing water consumption relative to the less efficient subcritical system. Water consumption for EOR is assumed to be minimal due to the fact that EOR often takes place utilizing existing oil wells for injection. For this analysis the system boundary was set such that once the CO 2 is transferred to an oil company for use, the impacts associate with its use become part of the life for oil production, and are no longer allocated to power production. Thus water consumption for EOR is set to zero. RESULTS The water consumption results for the core scenarios are shown in Table 4 and figure 1. They show that the assumption made by other studies, that the operations stage of the life cycle is the most significant, is largely valid. Coal mining also accounts for a non-trivial amount of water consumption on the order of 5-10% of the total. In addition, we find that the IGCC system is by far the most water efficient option both with and without capture. Figure 1. Water Consumption Results by LCA Stage Figure 2 shows the results in terms of water consumption per metric ton of CO 2 stored for each capture scenario. This was calculated by comparing the change in water consumption from the same power plant type with and without capture with the quantity of CO 2 stored. This helps illustrate the relative water efficiency of the different capture technologies. It also helps to better understand the direct tradeoff between reducing emissions and increasing water consumption. It shows that IGCC is definitely the most water efficient CCUS technology, followed by oxyfuel systems. Both amine capture systems require a significant quantity of water, although the higher Figure 2. Water Consumption per Ton of CO 2 Stored SENSITIVITY ANALYSIS The impact of some key parameters on water consumption was explored for the coal mining, transportation, and storage life cycle stages. For coal mining two additional types of coal were evaluated, one that was lower in quality, but surface mined, and one that was higher quality and underground mined. For transportation, longer pipeline distances were evaluated, including distances that required additional recompression of the CO 2. For storage, in addition to the average cost for storage, the high and low costs estimated by NETL were also used as well as one scenario for EOR. The results of the analysis are shown in Table 5. For the coal scenarios both result in lower water consumption on a per MWh basis. The lower quality, surface mined coal (Wyodak-Anderson) from the Powder River Basin has less energy content, and thus more coal must be consumed per MWh of power produced. However, surface mining requires less water per unit of coal so the total water consumption is much lower. The higher quality underground mined Pocahontas #3 coal has higher energy content than Illinois #6, so less is required per MWh, and thus the water consumption is also lower, but not nearly as low as surface mined coal. The additional transportation scenarios consist of longer pipeline lengths which require additional compression. Water consumption for the baseline case is essentially insignificant relative to other stages of the lifecycle. However, for longer pipeline lengths the water consumption for transportation can exceed water consumption for coal (surface mined) and storage in some cases. 5 Copyright 2014 by ASME

6 Table 5. Summary of Sensitivity Analysis for Coal Mining, Pipeline Length, and Storage Site (gallon/metric ton) Coal Type Coal Type SubPC Amine SuperPC Amine IGCC w/ capture Oxyfuel Illinois #6 a,c Wyodak-Anderson c Pocahontas #3 a Pipeline Length Pipeline Length SubPC Amine SuperPC Amine IGCC w/ capture Oxyfuel 100km a km km Storage Site Storage SubPC Amine SuperPC Amine IGCC w/ capture Oxyfuel Baseline a Low High EOR a Default value for LCA scenarios; b Underground mine; c Surface mine For storage, the impact of storage cost was evaluated from a low of $5.8/ton to 17.9 $/ton (NETL 2012). The resulting water consumption varies similarly, although in all cases it is small relative to the operations stage. The water consumption for EOR is assumed to be zero as the actual storage is outside the system boundary and any impacts associated with oil production instead. However, it is possible that in many cases the CO 2 may have to be transported further to reach the oil field, resulting in increased water consumption in the transportation stage which could counteract some or all of the water savings relative to deep saline aquifers. In addition, this analysis shows a clear tradeoff between water and climate impacts for coal generation technologies. The CCUS technologies were found to consume anywhere from 200 to 700 gallons of water per ton of carbon stored. With this in mind it will be important to consider which CCUS technologies are selected and where they are deployed. Given that water is a regional resource and CO 2 emissions have a global impact, it may be possible to deploy CCUS technologies more widely in areas with abundant water resources and minimize its use in areas that are more arid and water stressed. ACKNOWLEDGMENTS CONCLUSIONS The life cycle water consumption for a number of CCUS technologies was estimated. The results clearly illustrate that water consumption can vary widely depending upon the capture technology selected. IGCC was found to be the most water efficient technology followed by oxyfuel, and post combustion capture systems respectively. Even among post combustion capture systems, the efficiency of the underlying power plant can have a large impact upon the water consumption of the system. Overall the results show that the power plant operations life cycle stage is by far the most important in terms of water consumption, although coal mining can contribute 5-10% to the life cycle. This project was supported by funding from the U.S. Department of Energy, National Energy Technology Laboratory, under Contract DE-AC02-06CH The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. REFERENCES Bureau of Land Management (BLM), 2008, Final Environmental Impact Statement for the West Antelope II Coal Lease Application, WYW Casper, Wyoming, U.S. Department of the Interior, BLM, Casper Field Office. Carnegie Mellon University Green Design Institute (CMUGDI), 2014, Economic input output life cycle assessment (EIO-LCA), US 1992 US Department of Commerce Model, Available at: 6 Copyright 2014 by ASME

7 Doctor, R.D., 2011, ANNUAL REPORT Future of CCS Adoption at Existing PC Plants Economic Comparison of CO2 Capture and Sequestration from Amines and Oxyfuels, ANL/ESD/12-9, December. Elcock, D., 2010, "Future U.S. Water Consumption: The Role of Energy Production," Journal of the American Water Resources Association (JAWRA) 46(3): Harto, C., R. Meyers and E. Williams, 2010, Life Cycle Water Use of Low-Carbon Transport Fuels, Energy Policy 38: Mavis, J., 2003, Water Use in Industries of the Future: Mining Industry. Industrial Water Management: A Systems Approach, C. M. Hill, New York, NY, Center for Waste Reduction Technologies, American Institute of Chemical Engineers: National Energy Technology Laboratory (NETL), 2005, Carbon Capture and Sequestration Systems Analysis Guidelines, Pittsburgh, PA, U.S. Department of Energy. NETL, 2009, NETL Life Cycle Inventory Data Unit Process: Underground Mine, Illinois No. 6 Bituminous Coal, Operation, Pittsburgh, PA, U.S. Department of Energy. NETL, 2010, Cost and Performance Baseline for Fossil Energy Plants, Volume 1: Bituminous Coal and Natural Gas to Electricity, Revision 2 DOE/NETL-2010/1397, Pittsburgh, PA, U.S. Department of Energy. NETL, 2012, Updated Costs (June 2011 Basis) for Selected Bituminous Baseline Cases, DOE/NETL- 341/082312, Pittsburgh, PA, U.S. Department of Energy. Nicot, J.-P., A. K. Hebel, S. M. Ritter, S. Walden, R. Baier, P. Galusky, J. Beach, R. Kyle, L. Symank and C. Breton, 2011, Current and Projected Water Use in the Texas Mining and Oil and Gas Industry, Austin, TX, Texas Water Development Board. Singh, B., A.H. Stromman, and E. Hertwich, 2011, Life cycle assessment of natural gas combined cycle power plant with post-combustion carbon capture, transport and storage, International Journal of Greenhouse Gas Control, 5: United States Geological Survey (USGS), 2009, Methods for Estimating Water Withdrawals for Mining in the United States, 2005, Scientific Investigations Report Williams, E., 2004, Energy intensity of computer manufacturing: hybrid assessment combining process and economic input output methods, Environmental Science & Technology 38: Zhai, H., E.S. Rubin, and P.L. Versteeg, 2011, Water Use at Pulverized Coal Power Plants with Postcombustion Carbon Capture and Storage, Environmental Science & Technology 45: Copyright 2014 by ASME