The new Canadian laws on CO2 emissions aim to lower the emissions of coal-fired power plants down to those of natural gas combined cycle units: 420 kg CO2/MWeh. In order to meet these requirements, calcium looping and two process variants are investigated through process simulations using Aspen Plus V8.2. The combination of calcium looping and chemical looping combustion, replacing the required air separation unit, is a way to reduce the energy penalty of the capture process. The addition of copper as an oxygen carrier in two different process configurations is compared to calcium looping and shown to reduce the efficiency penalty from 7.8% to 4.5% points but at the price of circulations rates up to about 3800 kg/s. The other improvement path studied is the implementation of calcium looping to a pressurized fluidized bed combustion unit. The pressurized carbonator acts as a reheater for the gas turbine and operating the carbonator at temperatures up to 798°C results in a reduction of the energy penalty from 5.1% to 3.1% points.

This thesis analyses two strategies for decreasing anthropogenic carbon dioxide (CO2) emissions: to capture and store CO2, and to increase the use of biomass. First, two concepts for CO2 capture with low capture penalties are evaluated. The concepts are an integrated gasification combined cycle where the oxygen is supplied by a membrane reactor, and a hybrid cycle where the CO2 is captured at elevated pressure. Although the cycles have comparatively high efficiencies and low penalties, they illustrate the inevitable fact that capturing CO2 will always induce significant efficiency penalties. Other strategies are also needed if CO2 emissions are to be forcefully decreased. An alternative is increased use of biomass, which partially could be used for production of motor fuels (biofuels). This work examines arguments for directing biomass to the transport sector, analyses how biofuels (and also some other means) may be used to reduce CO2 emissions and increase security of motor fuel supply. The thesis also explores the possibility of reducing CO2 emissions by comparatively easy and cost-efficient CO2 capture from concentrated CO2 streams available in some types of biofuel plants. Many conclusions of the thesis could be associated with either of three meanings of the word sense: First, there is reason in biofuel production – since it e.g. reduces oil dependence. From a climate change mitigation perspective, however, motor fuel production is often a CO2-inefficient use of biomass, but the thesis explores how biofuels’ climate change mitigation effects may be increased by introducing low-cost CO2 capture. Second, the Swedish promotion of biofuels appears to have been governed more by a feeling for attaining other goals than striving for curbing climate change. Third, it seems to have been the prevalent opinion among politicians that the advantages of biofuels – among them their climate change mitigation benefits – are far greater than the disadvantages and that they should be promoted. Another conclusion of the thesis is that biofuels alone are not enough to drastically decrease transport CO2 emissions; a variety of measures are needed such as fuels from renewable electricity and improvements of vehicle fuel economy. / QC 20100823