Performance Improvements for Oxy-Coal Combustion Technology

Transcription

1 Performance Improvements for Oxy-Coal Combustion Technology John Wheeldon Technical Executive, Electric Power Research Institute Second Oxy-Combustion Conference Yeppoon, Queensland 12 th to 15 th September 2011

2 Worldwide Demand for Electricity Increasing Multiple societal benefits offered by electricity: elevates quality of life Projected generation 25.0 x 10 9 MWh in 2020, 35.2 x 10 9 MWh in % 16% hydro 2% others Without fossil fuels nuclear is the only mass generator. 21% 14% 5% 18% Nuclear Renewables Liquids Natural gas Coal World Power Generation: x 10 9 MWh Source: DOE-EIA International Energy Outlook 2010 Can renewables supply all power required at acceptable cost? Diversity of supply essential to cost control. The challenge is how to strike a balance between protecting the environment and keeping electricity affordable. 2

3 EPRI s PRISM-MERGE Analysis Two portfolios: full- and limited-technologies reduce CO 2 emissions to ~1905 levels by 2050, an 80% reduction. US Data Population, millions ~296 ~84.2 CO 2, billion tons ~6000 ~1200 CO 2, tons/capita ~ 419 ~ Levels match those of proposed US legislation, which also values CO 2 at $25/ton. Limited portfolio: no CCS or plug-in electric vehicles (PEVs) and nuclear remains at 2007 levels. Heavily dependent on gas. Full portfolio: coal and gas with CCS, expansion of PEVs, and increased nuclear power. By 2050 full portfolio COE increases 80% relative to 2007 prices: limited portfolio COE increases 210%. 3

4 Assumptions Used in Economic Calculations Unless stated otherwise Capacity factor 85% Coal price $1.71/GJ ($1.8/MBtu) and coal is sub-bituminous Gas price $4.71/GJ ($5.0/MBtu) Cost of CO 2 emitted $26.5/tonne ($25/ton) Cost of CO 2 transmission and storage $10/tonne ($9.1/ton). Cost of electricity levelized over 30 years. Plants located in Kenosha, Wisconsin and incorporate state-of-the art environmental controls. Ultra-supercritical (USC) pulverized coal steam conditions 290 bar/600 C/620 C (4200 psia/1110 F/1150 F). Advanced ultra-supercritical (A-USC) pulverized coal steam conditions 345 bar/730 C/760 C (5000 psia/1350 F/1400 F). 7FB (60 Hz) gas turbine firing temperature 1430 C (2600 F) 4

5 Points to Bear in Mind Results are preliminary. Based on different studies adjusted to common basis: close to equal footing but more work required. Costs include projected realistic improvements: objective to show potential of technologies. It is a snap shot: technologies will evolve and costs will change. New technologies and innovations will emerge. Demonstration essential to prove technology and improve designs: only the most cost-effective will be commercialized. Development activities need to be focused on commercial offering by 2025 otherwise coal may miss the boat. Source: Shell 5

6 CO 2 Emissions from Current Power Plants USC PC 2 x 7FB Net output, MW Capacity factor, % TPC, $M TPC, $/kw Efficiency, % (HHV) lb CO 2 /MWh emitted Cost of electricity, $/MWh Capital Fixed O&M Variable O&M Fuel CO 2 S&T CO 2 emitted TOTAL Dispatch cost, $/MWh x 7FB

7 Making CO 2 Emissions from USC Equivalent to those from NGCC Cost, $/MWh COE Dispatch 20 0 USC USC + PCC NGCC USC dispatch not affected USC + PCC with 65% capture efficiency achieving CO 2 emissions of 850 lb/mwh, same as NGCC 7

8 Effect of 98% Post-Combustion CO 2 Capture USC dispatch reduced slightly Capture cases have CO 2 emissions of 46 lb/mwh NGCC is now coal equivalent 8

9 When CO 2 Capture Included, Higher Generating Efficiency Lowers Levelized Cost of Electricity 70 COE Increase over Case Without CCS, % Based on current post-combustion capture (PCC) technology with KS-1. Oxy-combustion projected to be similar. Pittsburgh #8 Relative COE will fall as technologies improve. PRB 35% - DOE target Generating Efficiency Without CCS, % (HHV) Capture only. Transportation and storage costs also reduced by improved efficiency 9

10 Effect of Increasing Coal Plant Generating Efficiency Cost of electricity Dispatch cost 100 Cost, $/MWh USC PCC USC OXY A-USC OXY NGCC PCC NGCC PCC 40% CF Oxy cases based on 660-MW USC PC with projected enhancements to ASU. All CCS cases have CO 2 emissions of 46 lb/mwh 10

11 Source of Power Losses from OXY USC MW Air-blown USC OXY USC Gross output Power block ASU (1) 71.7 CPU 67.3 BOP Losses Net output (1) Includes projected improvements ASU + CPU = 139 MW, 20% of gross output 11

12 Two Approaches to Lowering Cost of CCS Evolutionary approach: improved current technologies to be as cost-effective as possible. Revolutionary approach: develop new technologies with potential to lower cost of CCS. 12

13 Effect of CO 2 Purity and Capture Efficiency on Oxy-Combustor Performance Base Case 1 Case 2 CO 2 captured, % CO 2 purity, vol. % > >99.99 O 2 content, vol. % <20 ppm 0.4 vol. % <20 ppm Net output, MW TPC, $M Efficiency, % (HHV) lb CO 2 /MWh emitted COE, $/MWh Dispatch cost, $/MWh Case 3A Case 3B vol. % 4.1 vol. % Little difference in alternative CO 2 purification approaches. High oxygen not acceptable for EOR applications and may not satisfy pipeline purity criteria. 13

14 Revolutionary Developments Chemical looping offers 20 percent reduction so COE would be around $100/MWh For NGCC with PCC COE is around $75/MWh. Ion Transfer Membrane is a new technological approach that lowers cost of oxygen production. Extensive activity to develop improved technologies to capture CO 2 from flue gas where partial pressure is only 0.12 bar (1.7 psi) Technologies include membranes, solvents, and sorbents Could these be adapted to capture/separate oxygen from either atmospheric or pressurized air? For example, the metal-organic framework materials have very high specific surface and a very large number of structural variations. Replacing steam with supercritical CO 2 as working fluid Potentially adds 3% points to efficiency as well as lowering capital cost. 14

15 Evolutionary Improvements For low sulfur coal, remove FGD and capture acid gases in CPU. Neutralize sulfuric, nitric, and hydrochloric acids in limestone digester Potential by-product sales but fickle market. Improve compressor designs to lower power losses Designed to handle acid gases All power plant technologies benefit but coal more so as CO 2 /MWh higher. Do steam turbine drives offer advantages? Identify most cost-effective heat integration measures through rigorous modeling In USA, DOE is funding the Carbon Capture and Storage Simulation Initiative Studies must be realistic and comply with boiler design and operational requirements. 15

16 Evolutionary Improvements (continued) Cyclone burners displaced because of high NO X emissions but oxycombustion mechanism and CPU can over come this Coarser fuel using crushers not mills so lower maintenance and power consumption. Oxy flue gas contains 4.5 wt % of oxygen delivered by ASU and is 25 vol.% of CPU vent stream Using membrane to remove oxygen lowers ASU duty. Complete materials development programs identifying most cost effective materials especially for water walls: also US DOE funded project. Pressurized operation. Lower capital costs, less energy consumed in recycle, recovery of latent heat at higher pressure. 16

17 Evolutionary Improvements (continued) Reduce recycle and increase oxygen content of combustion gas CFB well suited to this: intrinsic heat dissipation through solids circulation Boiler cost reduced 30% and recycle gas rate by 70%. Accommodate design changes to reduce load at when COE peaks For 3 hours in July electricity in Texas selling for over $3000/MWh. By switching off ASU (72 MW) and using LOX, revenues increase by $648k Or vent some CO 2 and pay the levy. Eliminate pipeline by storing CO 2 on own reservation Can save $5/MWh: may influence plant location. Limiting water usage becoming increasingly important Oxy has inherent advantage over PCC: maximize it. Ideas may not be additive; achieving one may preclude another Again good modeling capability may help establish the optimal benefits. 17

18 Need for Demonstration Once the most economic design options are identified they need to be demonstrated to prove that they are operationally practical Economic benefits could be negated by increased maintenance costs. Demonstration is an essential step to commercialization Design and operational experience identifies cost reduction measures But it is expensive so how can cost be reduced? Likely still need public private partnership but cost can be limited by retrofitting an existing unit. EPRI has been investigating the cost of retrofitting post-combustion CO 2 capture technology and is now preparing to do something similar for oxy combustion Compared to new unit study identified capital savings of up to $3300/kW. 18

19 Closing Comments Reducing CO 2 emissions is a formidable challenge and will come with a marked increase in the cost of electricity. To minimize the cost increase all power generation technologies will need to play a part including coal with CCS Fuel diversity is essential to keep electricity prices competitive. Oxy-combustion appears to be a cost-competitive coal option, but in keeping with all technologies costs must be reduced Technology innovations are needed Reality-based modeling can help sort through the options. Technology needs to be commercially available around 2025 so it is essential that demonstration projects come into service in the next 5 to 8 years. 19

20 Together Shaping the Future of Electricity 20