Coal combustion in O₂/CO₂ mixtures compared with air

Abstract

n 1996, coal was used to generate 25% of the electricity produced worldwide. Because of its large reserves, coal will certainly continue I to play a major role in energy production in North America and worldwide. During the past decade concern has grown about greenhouse gas emissions (CO, , CH, , N, O) and their potential impact on climate change. Since coal-fired power plants account for about 1 1 % of CO, emissions, clean and efficient combustion technologies need to be developed for use in existing and new coal-fired power generation plants.To reduce CO, , one of the most attractive solutions in the medium term is to remove CO, from flue gas stacks. Studies on post-combustion treatment of stack gases from conventional power plants have demonstrated that the energy penalties for CO, separation are high (Smith and Thambimuthu, 1991; Riemer, 1993). Therefore, CO, capture and sequestriation technologies must be developed that offer substantially reduced costs and, when possible, with value-added benefits.One application that offers secondary economic benefits while reducing CO, emissions from coal-fired power generation plants i s the use of CO, in enhanced oil recovery (EOR) operations. The potential for CO, use in EOR is relatively large in the USA and Canada. For example, in Western Canada, it is estimated that about 277 million tonnes of CO, can be stored over a 15-year period through EORoperations. The estimated CO, capacity in this time frame could reduce up to 5% of the annual Canadian CO, emissions. Another very attractive application is the use of CO, for enhanced coal bed methane (CBM) recovery. Methane i s produced from deep coal seams by injecting CO, and with the CO, being retained underground with its preferential adsorption in the coal seams. In the longer term, other environmentally sound, albeit more costly, methods of gas disposal such as in aquifers and disused gas and oil wells can be found for the permanent stroage of CO, removed from coal-fired power generation plants.Conventional technologies for removing CO, from the stack gas in existing coal-fired power plants are expensive because CO, i s diluted (typically about 14 vol% on a dry basis) and because the flue gas needs to be pretreated. The cost of gas separation can be reduced by increasing the concentration of CO, in the flue gas. This can be achieved by increasing the oxygen in the feed gas and, eventually, by recycling part of the flue gas (weller et al., 1985). Coal combustion at higher oxygen concentration is particularly attractive, not only because it helps reduce the cost of CO, separation in the flue gas, but also because it reduces the volume of inert gas present such as nitrogen, thus increasing boiler *Authors to whom correspondence may be addressed. E-mail addresses: ecroiset@ uwaterloo.ca; kelly. thambimuthu@nrcan.gc.ca thesent address: Department of Chemical Engineering, University of Sydney, NSW 2006, Australia.As part of CO, abatement strategies for climate change, we are investigating coal combusion behaviour in various...

Oxy-fuel combustion of coal and biomass, the effect on radiative and convective heat transfer and burnout

“…Around mid-1990s, a research consortium led by IHI funded by NEDO did the first pilot scale studies in Japan [11][12][13][14]. During the later part of the 1990s, CANMET [15][16][17] and a research consortium led by Air Liquide [18,19] did further pilot scale studies on this aspect of combustion. Lui et al [20] performed laboratory scale studies on a small downshot reactor firing a bituminous coal in mixtures of O 2 /CO 2 .…”

SO2 effects on CO oxidation in a CO2 atmosphere, characteristic of oxy-fuel conditions

“…This reduction is likely due to an increase in the retention of sulphur by ash and the formation of deposits in the furnace due to the recirculation of the flue gas. However, other studies suggest that SO 2 emissions are almost independent of the combustion media [8], being governed only by the oxygen concentration [9] or by the sulphur content of the fuel [10]. Additionally, and due to the accumulation of SO 2 in the system, a higher fraction of SO 2 is oxidized to SO 3 , which can involve serious implications due to corrosion in the boiler and CO 2 transportation systems.…”

Sulfur fate during bituminous coal combustion in an oxy-fired circulating fluidized bed combustor

“…Two main different conclusions were obtained. Some investigators [3][4][5][6] observed that the conversion of sulfur in coal to SO 2 decreased in O 2 /CO 2 combustion compared with traditional air combustion because high SO 3 concentrations in the flue gas during O 2 /CO 2 combustion resulted in sulfur retention by ash or deposits in the furnace. Whereas, Zheng and Furimsky argued that CO 2 plays no insignificant role for the sulfur release compared oxygen by equilibrium calculations [7].…”