تجارت کردن در انتشار آلاینده های گاز اسید و دی اکسید کربن در نیروگاه های سوخت فسیلی با جذب کربن

This paper investigates the impact of capture of carbon dioxide (CO2) from fossil fuel power plants on the emissions of nitrogen oxides (NOX) and sulphur oxides (SOX), which are acid gas pollutants. This was done by estimating the emissions of these chemical compounds from natural gas combined cycle and pulverized coal plants, equipped with post-combustion carbon capture technology for the removal of CO2 from their flue gases, and comparing them with the emissions of similar plants without CO2 capture. The capture of CO2 is not likely to increase the emissions of acid gas pollutants from individual power plants; on the contrary, some NOX and SOX will also be removed during the capture of CO2. The large-scale implementation of carbon capture is however likely to increase the emission levels of NOX from the power sector due to the reduced efficiency of power plants equipped with capture technologies. Furthermore, SOX emissions from coal plants should be decreased to avoid significant losses of the chemicals that are used to capture CO2. The increase in the quantity of NOX emissions will be however low, estimated at 5% for the natural gas power plant park and 24% for the coal plants, while the emissions of SOX from coal fired plants will be reduced by as much as 99% when at least 80% of the CO2 generated will be captured.

Nitrogen oxides (NOX), sulphur oxides (SOX) and carbon dioxide (CO2) are among the gases that are generated during the combustion of fossil fuel for the production of electricity. NOX and SOX form acid gases that have a negative impact on the environment, causing acidification, eutrophication of water masses, smog formation, etc. ( Tzimas and Peteves, 2001; EEA, 2005; IEA GHG, 2006). CO2 is a greenhouse gas that contributes to global climate change when discharged to the atmosphere ( IPCC, 2005; IEA GHG, 2006). The emissions of NOX and SOX from power plants have decreased significantly since the 1970s as a result of the development and deployment of technologies that can remove them from the flue gases and convert them into inert substances (e.g. nitrogen and gypsum). These technologies include flue gas desulphurization (FGD) and selective catalytic reduction (SCR). Newly built power plants in Europe can now achieve low NOX and SOX emission levels in compliance with the Large Combustion Plant (LCP) Directive (2001/80/EC). 1 Furthermore, technologies are currently under development to capture the CO2 in the flue gases of power plants and store it for long periods of time in suitable geological formations or use it for enhanced oil recovery purposes ( IPCC, 2005; Tzimas et al., 2005b). However, concerns have been raised, for example, in the recent deliberations for the preparation of the second phase of the European Climate Change Programme (DG ENV, 2006), that the application of CO2-capture technologies may increase the emissions of acid gas pollutants (NOX and SOX). This is a customary concern with trade-off issues between emissions upon the adoption of mitigation options. As an example of such a case, a reduction in CO2 emissions from gas turbines, by increasing the combustion temperature and hence the turbine efficiency, typically results in an increase in the generation of NOX. The possible increase in emissions of acid gas pollutants due to CO2 capture may have implications for the compliance of individual plants with the LCP Directive, as well for the compliance of European States with the National Emissions Ceiling Directive (2001/81/EC), and its successors, that sets upper limits for the total annual emissions of acid gas pollutants from each Member State of the European Union. This paper intends to clarify this issue by estimating the difference in the quantities of acid gas pollutants and CO2 emitted by fossil fuel fired power plants with and without CO2 capture. Two power generation options are investigated: natural gas combined cycle plants (NGCC) and pulverized coal (PC) plants. Post-combustion capture of CO2 using special chemical solvents, such as alkanolamines, is considered in this paper as this technology has been utilized for many years by the chemical and petrochemical industries and is expected to have a major role in forthcoming demonstration projects and early deployment of carbon capture and storage (CCS) technologies. Finally, the importance of considering an integrated approach for air pollution control for each plant is highlighted in the paper. Such an approach can facilitate the design and assist the selection of the most efficient options to reduce CO2 emissions from power plants using capture technologies.

The capture of CO2 is not likely to increase the quantity of emissions of acid gas pollutants (SOX and NOX) from a power plant. On the contrary, the low selectivity of the solvents used to capture the CO2 from the flue gases will also remove some quantities of NOX (in form of NO2) and SOX. The NOX emissions from the power generation sector, however, are likely to increase when carbon capture technologies are implemented on a large scale, due to the reduced efficiency of power plants that capture CO2. The increase of NOX emissions from natural gas and coal plants will be rather low, estimated at 5% and 24%, respectively, while at least 80% of the CO2 generated will be captured. Moreover, the SOX emissions from pulverized coal plants will also decrease driven by the need to reduce solvent losses. The reduction will depend on the solvent used and may vary between 96% and 99%. The power plant efficiency penalty is expected to decrease over time by technology improvement and by the development of new technology options. A comprehensive and integrated assessment of air pollution management at the plant level has to be performed prior to the deployment of CCS technologies. Integrated gasification combined cycle (IGCC) technology is an alternative option for using coal to generate electricity. This technology is characterized by lower acid gas emissions than pulverized coal plants with carbon capture. CO2 capture from an IGCC plant (pre-combustion capture) can be done more easily and with a lower efficiently penalty than in a PC plant (post-combustion capture). Acid gas emissions may also have to be further reduced when the captured CO2 has to be used in specialized applications such as for enhanced oil recovery.