Environmental assessment of German electricity generation from coal-fired power plants with amine-based carbon capture

One of the most important sources of global carbon dioxide emissions is the combustion of fossil fuels for power generation. Power plants contribute more than 40% of the worldwide anthropogenic CO(2) emissions. Therefore, the increased requirements for climate protection are a great challenge for the power producers. In this context a significant increase in power plant efficiency will contribute to reduce specific CO(2) emissions. Additionally, CO(2) capture and storage (CCS) is receiving considerable attention as a greenhouse gas (GHG) mitigation option. CCS allows continued use of fossil fuels with no or little CO(2) emissions given to the atmosphere. This could approve a moderate transition to a low-carbon energy generation over the next decades. Currently, R&D activities in the field of CCS are mainly concentrated on the development of capture techniques, the geological assessment of CO(2) storage reservoirs, and on economic aspects. Although first studies on material and energy flows caused by CCS are available, a broader environmental analysis is necessary to show the overall environmental impacts of CCS. The objectives in this paper are coal-based power plants with and without CO(2) capture via mono-ethanolamine (MEA) and the comparison of their environmental effects based on life cycle assessment methodology (LCA). This LCA study examines the environmental and human health effects of power generation of five coal-based steam power plants, which differ in the year of installation (2005, 2010, 2020), the conversion efficiency, and in the ability and efficiency to capture CO(2). For the removal of CO(2) from combustion and gasification processes in power plants, three main technology concepts exist: (1) pre-combustion technology, (2) oxyfuel combustion systems, and (3) post-combustion separation. As post-combustion technology shows the highest level of maturity, this study concentrates on this route, focusing on capture using mono-ethanolamine (MEA). The analysis regards the post-combustion retrofit of coal power plants with MEA to be a general option in 2020. Material and energy flows are balanced on the level of single processes as well as for the whole process chains. The life cycle inventory clearly shows decreasing inputs and outputs according to the efficiency increase from 43% to 49% in case of the power plants without CO(2) capture. In case of the MEA plants, all inputs and emissions raise, according to the additional energy consumption, except CO(2) and sulphur dioxide. The strong decrease of SO(2) partly results from the necessary improvement of desulphurisation if MEA wash is used. The influence of up and downstream activities on the results is determined. For the MEA plants, a considerable effect of up and downstream activities on the overall results is observed. Finally, the inventory results are assigned to selected impact categories. Global warming (GWP), human toxicity (HTP), acidification (AP), photo-oxidant formation (POCP), eutrophication (EP), and primary energy demand are adopted as impact categories. The impact assessment indicates decreasing impacts for all categories with increasing combustion efficiency for the coal plants without carbon capture. As expected, the GWP for the MEA plants is much lower than for the power plants without CO(2) capture. In contrast to this, the HTP and the EP are much higher (up to three times) for the MEA plants. Sensitivity analysis reveals that the origin of coal and the corresponding transport distances have a significant impact on the overall results. Furthermore, it is concluded from the sensitivity analysis that for CCS systems the length of CO(2) pipeline has a negligible effect in comparison with the effect of capture efficiency. The LCA is completed by a normalisation of the environmental impact categories. The development of combustion efficiency in case of the power plants without CO(2) capture has the main influence on the decreasing mass flows at the input side. The energy penalty of the MEA plants affects the use of the inputs into the opposite direction. Although the power producer's focus is on the power plant, the sense of a life cycle assessment is an integrated environmental assessment of the full life cycle of a product (here 1 kWh) including up and downstream processes. Therefore, the inventory results are presented without and with up and downstream processes. The inventory analysis clearly shows the significant influence of the up and downstream processes on the overall emissions. This influence is higher for the MEA plants than for the power plants without capture. In case of CO(2) emissions, the significance of up and downstream processes is especially considerable (approx. 30%). Sensitivity analysis reveals that the origin of coal and the corresponding transport distances have a significant impact on the overall results. The results point out that the reduction of carbon dioxide emissions into the atmosphere is achieved at the expense of increasing other emissions and corresponding environmental impacts. In most cases the influence of up and downstream processes is significant. Therefore, life cycle approaches are necessary to get a holistic evaluation. It also shows that the implementation of new techniques can change the environmental assessment of the process chain and, thus, positive and negative effects have to be compared and weighed up against each other. As there exist several possible technical options for CO(2) capture, further studies are necessary to compare the overall environmental effects of competing capture concepts such as pre-combustion and oxyfuel technology. Additionally, gas separating membranes should be part of further studies as they have the potential to contribute to all three main capture technology routes. Further studies with more detail and reliable inventories for CO(2) compression and liquefaction as well as for gas conditioning as an interface between CO(2) capture and transport are needed. Furthermore, the environmental effects including long-term CO(2) emission from the storage sites are recommended.