Commercial Viability of Near-Zero Emissions Oxy-Combustion Technology for Pulverized Coal Power Plants

Transcription

1 Commercial Viability of Near-Zero Emissions Oxy-Combustion Technology for Pulverized Coal Power Plants Andrew Seltzer Zhen Fan Horst Hack Foster Wheeler North America Corp., USA Minish Shah Kenneth Burgers Praxair Inc., USA Presented at The 37 th International Technical Conference on Clean Coal & Fuel Systems Clearwater, Florida USA June 3-7, 2012

2 Commercial Viability of Near-Zero Emissions Oxy-Combustion Technology for Pulverized Coal Power Plants Andrew Seltzer a (Andrew_Seltzer@fwc.com) Zhen Fan a (Zhen_Fan@fwc.com) Horst Hack a (Horst_Hack@fwc.com) Minish Shah b (Minish_Shah@praxair.com) Kenneth Burgers b (Kenneth_Burgers@praxair.com) a Foster Wheeler North America Corp., Perryville Corporate Park, Clinton, N.J., 08809, USA b Praxair, Inc., 175 East Park Drive, Tonawanda, NY ABSTRACT Oxyfuel combustion is one of the leading options for capturing and sequestering CO 2 from coalfired power plants. Praxair and Foster Wheeler are working on an oxy-coal power plant design that is based on Foster Wheeler s oxyfuel boiler technology and Praxair s Near Zero Emissions CO 2 processing unit (CPU) for purifying CO 2 -rich flue gas. This oxyfuel boiler is designed to efficiently use either air or oxygen as the coal oxidant. Near Zero Emissions is an advanced CPU technology that significantly reduces air emissions compared to conventional CPUs, while achieving significantly higher CO 2 capture rates. Foster Wheeler performed detailed performance analysis for retrofitting oxy-fuel technology to an existing 460 MWe (gross) pulverized coal power plant burning either low sulfur PRB fuel or high sulfur bituminous fuel. Flue gas recycle rates were selected such that furnace gas temperatures and wall heat fluxes in oxy-firing mode are approximately the same as when airfiring. Emissions generated in the boiler were predicted by 3-D CFD simulations. Praxair developed additional simulations using DOE s design basis guidelines and 550 MW net power output and Foster Wheeler s oxyfuel power plant design. Technoeconomic evaluations were performed for (a) retrofitting oxyfuel technology to an existing power plant and (b) building a new oxyfuel power plant. For both scenarios, evaluations were done for (a) an airfired plant without CCS, (b) an oxyfuel plant with a conventional CPU and (c) an oxyfuel plant with a Praxair Near Zero Emissions CPU. INTRODUCTION Coal-fired power plants currently account for more than 40% of man-made worldwide carbon dioxide emissions [1]. Oxyfuel combustion is one of the most promising methods of removing carbon dioxide from the exhaust gases of a coal power plant. Oxyfuel combustion is based on combusting coal with oxygen and recycled flue gas, to produce carbon dioxide and water vapor as the main components of the exhaust gas. This allows the carbon dioxide to be much more easily captured from the exhaust gas than in air combustion where nitrogen is the dominant flue gas component.

3 Since oxyfuel combustion is still a developing technology, it is advantageous to design oxyfuel combustion boilers with combustion conditions similar to those of air-fired boilers. Moreover, producing similar combustion conditions in the boiler allows oxyfuel to be readily adaptable to retrofit applications, which is especially important since coal firing is currently the dominant means of power generation (43% worldwide, 50% USA) [1]. Foster Wheeler has addressed the need for operational flexibility by designing the boiler to operate either under conventional combustion with air or under oxy-fuel conditions (Flexi-Burn concept) *. Oxyfuel combustion CO 2 capture technology presents an excellent opportunity for achieving near zero emissions from the coal-fired power plants. In the oxyfuel technology, the volume of flue gas is reduced by factor of five (on a dry basis) due to elimination/reduction of nitrogen from combustion. The entire volume of CO 2 -rich flue gas must be compressed for purification, thus further reducing the volume of flue gas. Integration of the trace impurities (SOx, NOx and Hg) removal in the CO 2 purification unit could significantly lower the capital investment compared to that for the air-fired operation. Praxair is developing a near zero emissions (NZE) CO 2 processing unit (CPU) that will leverage this synergy [2, 3]. The conventional CPU process is subject to several limitations. CO 2 capture rates are typically limited to a maximum of about 90% of the CO 2 contained in the flue gas. As power plants age and air intrusion increases, the CO 2 contained in the flue gas becomes diluted and degrades the ability of the conventional CPU to capture CO 2. A conventional CPU has no unit operations for the purpose of removing SOx, NOx and CO from the flue gas. These compounds are typically distributed between the process condensate, the CPU vent and the purified CO 2. To meet SOx and NOx purity specifications of the captured CO 2 from a conventional CPU, hot flue gas in the boiler island must be treated by an SCR and the CPU feed must be treated by an FGD. Vent Vacuum pressure swing adsorption CO 2 -Rich Oxyfuel Flue Gas FG Cooler/ Condenser H 2 O CO 2 -Rich Recycle Compressor Focus of current project Activated Carbon Dryer VPSA Catox Expander Cold Box Vent Cold Box > 95% CO 2 Hg bar Condensate Dilute acid Figure 1 - Near zero emissions CPU Process Schematics * Flexi-Burn is a trademark of Foster Wheeler Energia Oy, registered in the US, EU, Finland

4 The Near Zero Emissions CPU (Figure 1) includes several improvements to overcome the limitations of the conventional CPU process. An activated carbon process is used to remove SOx and NOx from compressed flue gas and convert these compounds to sulfuric acid and nitric acid. A CO 2 vacuum pressure swing adsorption (VPSA) process is used to capture and recycle CO 2 that would otherwise be vented to atmosphere, and increasing CO 2 capture rates to ~99%. A catalytic oxidation unit eliminates CO emissions to air by converting CO to CO 2. The NZE CPU technology will reduce emissions of CO 2, SOx, Hg and CO by >99% and NOx emissions by >95% compared to an air-fired pulverized coal power plant. The benefits of the technology include mitigation of air ingress problem, capital and operating cost savings for SOx and NOx removal, reduction in CO 2 capture cost and production of high purity CO 2 stream for sequestration. These benefits will translate to lower cost of electricity for power plants with CO 2 capture. This paper presents the power plant performance analysis for retrofitting existing coal power plant with oxyfuel technology and technoeconomic comparison of NZE CPU technology vs. conventional CPU in retrofit and greenfield scenarios. POWER PLANT PERFORMANCE ANALYSIS A power plant performance analysis was conducted for retrofitting oxy-fuel technology to an existing power plant burning low sulfur PRB fuel or high sulfur bituminous fuel [4]. The reference plant is a subcritical pressure (2415psia/1000ºF/1000ºF) power station generating 460 MWe gross and 418 MWe net (air-firing). The air-fired plant has a net efficiency of 35.8/36.7%. The power plant employs a natural circulation boiler, a selective catalytic reactor (SCR), a wet flue gas desulfurization (FGD) and a baghouse. The furnace heat transfer surfaces consist of waterwalls, radiant superheater partial division walls, and convective finishing superheater and reheater tube banks. Final main steam temperature is controlled by spray water attemperation, while reheat steam temperature is controlled by a HRA (Heat Recovery Area) gas flow proportioning damper. A wet FGD is applied to remove the SOx. For NOx control, the furnace is equipped with low NOx burners and air staging (over-fire air). Modifications to adapt the plant to accommodate oxyfuel firing include the addition of flue gas recirculation ducts, oxygen distribution piping, ASU/CPU steam extractions, CPU flue gas cooler, increased HRA economizer size, low pressure economizer downstream of the air-heater, a quench tower, and increased cooling tower size. Heat is extracted from the boiler via steam and hot water for ASU and CPU thermal loads. Ammonia to the SCR is shut-off, but the SCR catalyst remains in place. Limestone fed to the FGD is reduced to the amount required to remove SOx from the recycled primary gas stream and partially from the recycled secondary gas stream for bituminous-firing. Emissions generated in the boiler were predicted by 3-D CFD simulations. For PRB-firing overfire gas (OFG) was set at 25% of the total combustion gas (the same as for air-firing). For bituminous-firing over-fire gas was shut off to increase NOx so as to shift emission control duty to the CPU.

5 The quantity of flue gas recirculation was selected to minimize changes to the boiler by approximately matching heat transfer and maximum metal temperatures. The flue gas recirculation flow to the boiler is 68%/72% (PRB/bituminous). The oxyfuel plant has a power plant net efficiency of 36.4/37.1% (without including the power consumption of the ASU and CPU, but including heat extraction to the ASU and CPU Figure 2 presents the gas temperature and furnace water wall heat flux for PRB-firing. For PRB-firing the SO 2 at furnace exit is 500 ppmv compared to air-firing at 210 ppmv. The SO 2 is 465 ppmv (0.23 lb/mbtu) to the CPU compared to air-firing at 52 ppmv (0.13 lb/mbtu) to the stack. For the recycled primary flue gas, 98% SO 2 is removed by the wet-fgd and water quenching producing a SO 2 concentration of 12 ppmv. Air-Fired O2-Fired Air-Fired O2-Fired ºF Btu/hr-ft 2 Gas Temperature Wall Heat Flux Figure 2 - Gas Temperature and Wall Heat Flux PRB-Firing For bituminous-firing, the wet FGD is used to treat the recycled primary gas and 36% of the secondary gas to reduce the SOx concentration in the furnace to 4080 ppmv compared to airfiring at 2050 ppmv. The SO 2 is 3840 ppmv (1.62 lb/mbtu) to the CPU compared to air-firing at 35 ppmv (0.08 lb/mbtu) to the stack. For the FGD treatment of the recycled primary flue gas and 36% of the secondary flue gas, 99% SO 2 is removed by the wet-fgd and water quenching producing a SO 2 concentration of 43 ppmv in the recycled flue gas. For air-firing, the ratio of SO 3 /SO 2 at the furnace outlet is 0.57%/0.65 (PRB/bituminous). For oxy-firing, the ratio of SO 3 /SO 2 at the furnace outlet is 0.61%/0.73 (PRB/bituminous). The outlet

6 SO 3 was determined to be independent of the amount of SO 3 in the recycle flue gas since SO 3 is destroyed in the high temperature regions of the furnace and formed only in the upper sections of the furnace. Furthermore, the ratio of SO 3 /SO 2 was determined to be independent of the amount of SO 2 in the recycle flue gas. For PRB-firing, the SCR outlet SO 3 concentration is 6.2 ppm for oxy-firing versus 2.5 ppm for air-firing. Outlet SO 3 concentration is 5.8 ppm (3.6 lb/bbtu) for oxy-firing versus 1.3 ppm (4.0 lb/bbtu) for air-firing. For the recycled primary flue gas 90% SO 3 is removed by the wet-fgd and water quenching producing a SO 3 concentration of 0.7 ppmv. For bituminous-firing, the SCR outlet SO 3 concentration is 50 ppm for oxy-firing versus 24 ppm for air-firing. Outlet SO 3 concentration is 47 ppm (25 lb/bbtu) for oxy-firing versus 2.4 ppm (7.3 lb/bbtu) for air-firing. For the recycled primary flue gas 95% SO 3 is removed by the wet-fgd and water quenching producing a SO 3 concentration of 2.7 ppmv. For PRB oxy-firing the NOx was predicted to be 156 ppm at the boiler outlet (0.056 lb/mbtu to CPU) compared to the air-fired NOx of 147 ppm (0.22 lb/mbtu) at the boiler outlet and 36 ppm at the SCR outlet (0.062 lb/mbtu to stack). For bituminous oxy-firing the NOx was predicted to be 391 ppm at the boiler outlet (0.127 lb/mbtu to CPU) compared to the air-fired NOx of 166 ppm (0.25 lb/mbtu) at the boiler outlet and 40 ppm at the SCR outlet (0.069 lb/mbtu to stack). For oxy-firing the outlet CO mole fraction was predicted to be about 2.2 times that of air-firing for both PRB-firing and bituminous-firing. The outlet CO was determined to be independent of the amount of CO in the recycle flue gas since CO is destroyed in the high temperature high oxygen regions of the near burner region. For PRB-firing the outlet CO is predicted to be 280 ppm (0.06 lb/mbtu to the CPU) compared to the air-fired emission of 128 ppm (0.13 lb/mbtu to the stack). For bituminous-firing the outlet CO is predicted to be 284 ppm (0.05 lb/mbtu to the CPU) compared to the air-fired emission of 133 ppm (0.14 lb/mbtu to the stack). For PRB-firing, mercury exits the furnace at 18 ppbv and is reduced to 10 ppbv (15.7 lb/tbtu) by the SCR catalyst before exiting to the CPU compared to the air-fired boiler outlet (to stack after wet FGD) Hg of 1.4 ppbv (10.5 lb/tbtu). For bituminous-firing, mercury exits the furnace at 1.7 ppbv and is reduced to 1.0 ppbv (1.3 lb/tbtu) by the SCR catalyst before exiting to the CPU compared to the air-fired boiler outlet Hg of 0.2 ppbv (1.1 lb/tbtu). For the recycled primary flue gas all Hg is essentially removed by the wet-fgd and water quenching by cooling the fluegas to a low temperature. A summary of the power plant emissions is presented in Table 1.

7 Table 1 - Emissions Summary in Air-Fired and O 2 -Fired Modes Low Sulfur PRB High Sulfur Bit. Air Fired at Stack O2 Fired to CPU Air Fired at Stack O2 Fired to CPU ppmv lb/mbtu ppmv lb/mbtu ppmv lb/mbtu ppmv lb/mbtu CO SO SO NOx NH HCl PM VOC ppbv lb/tbtu ppbv lb/tbtu ppbv lb/tbtu ppbv lb/tbtu Hg TECHNO-ECONOMIC ANALYSIS Techno-economic analysis was performed to determine the value of Praxair s NZE CPU in comparison to a conventional CPU. Retrofit and greenfield scenarios were analyzed. In the retrofit scenario, only equipment addition to the air-fired plant was considered. Additional equipment needed in each of the oxyfuel retrofit cases was determined based on the need to achieve the desired CO 2 purity. In the greenfield scenario, both equipment addition and removal compared to the air fired reference plant were considered in order to optimize each of the oxyfuel cases. Assumptions The design guidelines reported by the DOE were used in this analysis [5]. Power Plant The pulverized coal power plant based on a subcritical steam cycle and fired with low sulfur PRB coal was used in all the cases. Net output in both air and oxy-firing modes is set to 550 MW (net). The Flexi-Burn concept was included in the design of the steam generator. For the retrofit case, the air-fired power plant was assumed to be without the SCR and FGD. Because of the age of the boiler island, high air intrusion rates (10%) were assumed. For oxyfuel retrofit with conventional CPU, an SCR was added in order to enable the purified CO 2 from the CPU to achieve a NOx concentration of <100 ppmv. An FGD was also added to treat the recirculated primary gas and the CPU feed in order to prevent corrosion in the pulverizer and to enable the purified CO 2 from the CPU to achieve a SOx concentration of <100 ppmv. For oxyfuel retrofit with NZE CPU, no SCR was added in the boiler island and FGD was required only to treat the primary recirculated flue gas (RFG). In the retrofit scenario, it was assumed that the capital cost of the boiler island has been significantly depreciated.

8 For the greenfield cases, the air-fired power plant included a full size SCR and a full size FGD. Because the boiler island is new, low air intrusion rates (2%) were assumed. For the greenfield oxy-coal plants using a conventional CPU, the boiler island included a full size SCR and a partial size FGD for treating the primary RFG and the CPU feed. For the greenfield oxy-coal plants using a NZE CPU, the boiler island included an FGD for treating the primary RFG. Air Separation Unit An advanced cryogenic air separation unit (ASU) was used to supply 97% (by vol.) oxygen to the furnace. No co-products, such as nitrogen or argon were made in the ASU. CPU The CPU was assumed to produce >95% CO 2 at 2200 psia with trace impurity concentrations of <100 ppm for SOx and <100 ppm for NOx. The NZE included all the equipment shown in Figure 1. The conventional CPU excluded the following equipment: Activated carbon process for SOx/NOx removal CO 2 VPSA for increasing CO 2 capture Catalytic oxidation unit for reducing CO emissions Cost and Performance Comparison Retrofit Scenario Overall performance is shown in Table 2. Gross efficiency of the boiler island is about %, higher in oxy-fired mode than in air-fired mode. Because of the high air intrusion rate, the flue gas contains a low concentration of CO 2 causing the conventional CPU to capture only 78.2% of the CO 2 contained in the flue gas. The CO 2 VPSA in the NZE CPU increases the CO 2 capture rate to 97.7%. Net efficiency decreases by 8.3% when using the conventional CPU and by 9.3% when using the NZE CPU. The main reason for higher parasitic load in the NZE CPU is power consumed in separating and compressing additional CO 2 that is captured. Table 2. Overall Performance Retrofit Scenario Air or Oxy Firing Air Oxy Oxy CPU Type None Conv. NZE Contained O 2 from ASU, tpd 0 13,473 13,898 Coal Rate, tpd Fuel HHV, MWth Gross Power, MWe Net Power, MWe Gross Eff (HHV) 39.8% 40.4% 40.5% Net Eff (HHV) 36.8% 28.5% 27.5% CO 2 Captured, tpd 0 13,309 17,156 CO 2 Capture Rate, % 0.0% 78.2% 97.7%

9 A comparison of emissions for the retrofit cases is shown in Table 3. The Praxair NZE CPU outperforms the conventional CPU for emissions of CO 2, SOx, NOx, and CO, while eliminating the need for an SCR and using a much smaller FGD. It also produces CO 2 containing lower concentrations of SOx and NOx. Table 3. Emissions and CO2 Purity Comparison Retrofit Scenario Air or Oxy Firing Air Oxy Oxy CPU Type None Conv. Praxair Stack/CPU Vent Flow and Composition Total Flow, 1000 lbs/hr CO 2, % vol 13.73% 28.88% 4.31% SOx, ppmv NOx, ppmv CO, ppmv Emission Reduction (Compared to Air-Fired) CO % 96.89% SOx 99.9% ~100% NOx 99.6% 99.8% CO 23.7% 99.2% CO 2 Purity by Volume CO 2, % 95.35% 95.00% SOx, ppm 82 2 NOx, ppm CO, ppm The cost comparison is shown in Table 4. Unit capital when using the NZE CPU is about $110/kW higher than for the conventional CPU. The higher cost in this scenario is mostly due to the cost of the CO 2 VPSA and larger flue gas compressor needed to achieve high CO 2 capture. The increase in COE for the NZE CPU is higher due to increased CO 2 capture rate. The cost advantage of NZE CPU is apparent when CO 2 capture costs are compared. Cost of captured CO 2 using the NZE CPU is $10.5/ton less than captured CO 2 cost using the conventional CPU. Cost of avoided CO 2 for the Praxair CPU is $17.7/ton less than the cost using the conventional CPU.

10 Table 4. Cost Comparison Retrofit Scenario Air or Oxy Firing Air Oxy Oxy CPU Type None Conv. NZE Unit Capital Costs, $/kw $350 $1880 $1990 Cost of electricity, $/MWh $34.8 $94.7 $98.5 CO 2 Capture Cost, $/ton $59.6 $49.1 CO 2 Avoided Cost, $/ton $83.9 $66.2 Greenfield Scenario Overall performance is shown in Table 5. Gross HHV efficiency of the boiler island is about 1% higher in oxy-fired mode than in air-fired mode. Net HHV efficiency decreases by 7.2 % when using the conventional CPU and by 7.5% when using the Praxair CPU. Because of the low air intrusion rate associated with the new boiler island, the flue gas contains a higher concentration of CO 2 and results in higher CO 2 capture rates. The conventional CPU captures 91.9% of the CO 2 contained in the flue gas and the NZE CPU captures 99.3% of the contained CO 2. Table 5. Overall Performance Greenfield Scenario Air or Oxy Firing Air Oxy Oxy CPU Type None Conv NZE Contained O 2 from ASU, tpd 0 13,843 13,950 Coal Rate, tpd Fuel HHV, MWth Gross Power, MWe Net Power, MWe Boiler Island Gross Eff (HHV) 39.8% 40.8% 40.8% Total Plant Net Eff (HHV) 36.3% 29.1% 28.8% CO 2 Captured, tpd 0 15,289 16,661 CO 2 Capture Rate, % 0.0% 91.9% 99.3% A comparison of emissions in air-fired mode and oxy-fired mode with conventional and Praxair CPU s is shown in Table 6. Emissions of SOx and NOx for the greenfield air-fired case are lower than for the retrofit case because of the inclusion of the SCR and FGD. The emissions from the conventional CPU are lower than in the retrofit case because the lower air intrusion rate results in a lower rate of gas vented from the CPU. The Praxair CPU again outperforms the conventional CPU for emissions of CO 2, SOx, NOx, and CO, while eliminating the need for an SCR and using a much smaller FGD.

11 Table 6. Emissions Comparison - Greenfield Air or Oxy Firing Air Oxy Oxy CPU Type None Conv Praxair Stack/CPU Vent Flow and Composition Total Flow, 1000 lbs/hr CO 2, % vol 12.87% 37.91% 5.70% SOx, ppmv NOx, ppmv CO, ppmv Emission Reduction (Compared to Air-Fired) CO % 99.1% SOx 99.5% % NOx 98.3% 98.9% CO 55.5% 99.6% CO 2 Purity by Volume CO 2, % 95.54% 95.45% SOx, ppm 65 2 NOx, ppm CO, ppm The cost comparison for the greenfield scenario is shown in Table 7. The unit capital cost when using the NZE CPU is about the same as the conventional CPU. The difference in between the air-fired and oxy-fired systems is about $2630/kW. The COE for a conventional CPU and a Praxair CPU are almost equivalent. Cost of captured CO 2 using the NZE CPU is $5.1/ton less than captured CO 2 cost using the conventional CPU. Cost of avoided CO 2 for the Praxair CPU is $6.8/ton less than the cost using the conventional CPU. Table 7. Cost Comparison Greenfield Scenario Air or Oxy Firing Air Oxy Oxy CPU Type None Conv. NZE Unit Capital Costs, $/kw $2350 $3990 $3980 Cost of electricity, $/MWh $84 $148.8 $148.6 CO 2 Capture Cost, $/ton $56.1 $51.0 CO 2 Avoided Cost, $/ton $71.5 $64.7

12 CONCLUSIONS A conceptual oxyfuel Flexi-Burn design was developed based on the retrofit of a subcritical PC power plant burning either low-sulfur PRB or high-sulfur bituminous coal. By proper selection of the quantity of flue gas recycle flow, the boiler can be used in oxy-fuel mode without major modifications. Boiler retrofit challenges mostly center on the flue gas recycle and the oxygen distribution systems. These challenges include physical routing of ducts and pipes, selection of materials to avoid corrosion, and proper mixing of gases. Overall power plant retrofit constraints include proximity to geologic sequestration, space availability (especially for ASU and CPU), and access to additional water supply for increased cooling load. The cost of electricity for retrofitting an old power plant with CCS compare reasonably well (only ~15% higher) with a greenfield plant without CCS. This suggests that if CCS is required in the future, retrofitting should be considered. The Praxair near zero emissions CPU achieves much higher CO 2 capture rates than a conventional CPU. The difference becomes more significant at high air intrusion rates such as those anticipated in older boilers. For a greenfield plant, unit capital of an oxyfuel power plant using a NZE CPU is about the same as a power plant using a conventional CPU. Cost of electricity is also about the same. Captured CO 2 cost when using a Praxair CPU is about $51/ton and avoided CO 2 cost is about $65/ton, as compared to $56/ton captured CO 2 and $71.5/ton avoided CO 2 when using a conventional CPU. Compared to a conventional CPU, Praxair s NZE CPU achieves better environmental performance, CO 2 purity, and CO 2 capture rates while lowering the CO 2 capture costs. ACKNOWLEDGEMENT This material is based upon work supported by the U.S. Department of Energy under Award Number DE-NT REFERENCES [1] International Energy Outlook 2008, Energy Information Administration, September [2] M. Shah, N. Degenstein, M. Zanfir, R. Solunke, R. Kumar, J. Bugayong, and K. Burgers. Purification of oxy-combustion flue gas for SOx/NOx removal and high CO 2 recovery. 2nd Oxyfuel Combustion Conference, Yeppoon, Australia, September [3] M. Shah, N. Degenstein, M. Zanfir, R. Solunke, R. Kumar, J. Bugayong and K. Burgers. Near zero emissions oxy-combustion flue gas purification NETL CO2 Capture Technology Meeting, Pittsburgh, USA. August [4] A. Seltzer, Z. Fan, H. Hack, and M. Shah. Simulation and prediction of pollutants in a Flexi-Burn TM oxyfuel pulverized coal power plant. 35th International Technical Conference on Coal Utilization & Fuel Systems, Clearwater, USA. June [5] Pulverized Coal Oxycombustion Power Plants. DOE/NETL-2007/1291. Volume 1: Bituminous Coal to Electricity. Final Report. Revision 2, August 2008.