COMPARING FLEXIBLE CO_2 CAPTURE IN GAS- AND COAL-DOMINATED ELECTRICITY MARKETS

摘要

Coal-fired power plants are a source of inexpensive, reliable electricity for many countries. Unfortunately, their high carbon dioxide (CO_2) emissions rates contribute significantly to global climate change. With the likelihood of future policies limiting CO_2 emissions, CO_2 capture and sequestration (CCS) could allow for the continued use of coal while low- and zero-emission generation sources are developed and implemented. This work compares the potential impact of flexibly operating CO_2 capture systems on the economic viability of using CCS in gas- and coal-dominated electricity markets. The comparison is made using a previously developed modeling framework to analyze two different markets: 1) a natural-gas dominated market (the Electric Reliability Council of Texas, or ERCOT) and 2) a coal-dominated market (the National Electricity Market, or NEM in Australia). The model uses performance and economic parameters for each power plant to determine the annual generation, CO_2 emissions, and operating profits for each plant for specified input fuel prices and CO_2 emissions costs. Previous studies of ERCOT found that flexible CO_2 capture operation could improve the economic viability of coal-fired power plants with CO_2 capture when there are opportunities to reduce CO_2 capture load and increase electrical output when electricity prices are high. The model was used to compare the implications of using CO_2 capture systems in the two electricity systems under CO_2 emissions penalties from 0-100 US dollars per metric ton of CO_2. Half the coal-fired power plants in each grid were selected to be considered for a CO_2 capture retrofit based on plant efficiency, whether or not SO_2 scrubbers are already installed on the plant, and the plant's proximity to viable sequestration sites. Plants considered for CO_2 capture systems are compared with and without inflexible CO_2 capture as well as with two different flexible operation strategies. With more coal-fired power plants being dispatched as the marginal generator and setting the electricity price in the NEM, electricity prices increase faster due to CO_2 prices than in ERCOT where natural gas-plants typically set the electricity price. The model showed moderate CO_2 emissions reductions in ERCOT with CO_2 capture and no CO_2 price because increased costs at coal-fired power plants led to reduced generation. Without CO_2 prices, installing CO_2 capture on coal-fired power plants resulted in moderately reduced CO_2 emissions in ERCOT as the coal-fired power plants became more expensive and were replaced with less expensive natural gas-fired generators. Without changing the makeup of the plant fleet in NEM, a CO_2 price would not currently promote significant replacement of coal-fired power plants because there is minimal excess capacity with low CO_2 emissions rates that can displace existing coal-fired power plants. Additionally, retrofitting CO_2 capture onto half of the coal-based Heel in NEM did not reduce CO_2 emissions significantly without CO_2 costs being implemented because the plants with capture become more expensive and were replaced by the coal-fired power plants without CO_2 capture. Operating profits at NHM capture plants increased as CO_2 price increased much faster than capture plants in ERCOT. The higher rate of increasing profits for plants in NEM is due to the marginal generators in NEM being coal-based facilities with higher CO_2 emissions penalties than the natural gas-fired facilities that set electricity prices in ERCOT. Overall, coal-fired power plants were more profitable with CO_2 capture systems than without in both ERCOT and NEM when CO_2 prices were higher than USD25/ton.