Life Cycle Assessment of the process of carbon capture and storage

Anna Śliwi ńska, Dorota Burchart-Korol, Krystyna Czaplicka-Kolarz

Central Mining Institute, Katowice, Poland asliwinska@gig.eu

Abstract Carbon capture and storage (CCS) is a very important process aiming at decreasing of carbon emission, which is considered to implement in energy generation from coal. However, capturing of CO2 leads to lower efficiency of energy generation from coal, which is associated with negative consequences for the environment. The purpose of the life cycle assessment was to evaluate both the environmental benefits and negative consequences resulting from capturing and storage of carbon dioxide created during conversion of coal. Analyses were performed on the example of an IGCC power plant where carbon dioxide is removed from the fuel gas before combustion. The processes of capture, transport and injection of carbon dioxide into underground storage were taken into account within the system boundary. The most important categories of environmental impact were assessed, among others: greenhouse gas emission, fossil fuel depletion, human toxicity, land occupation and transformation. Technical parameters which impact the energy and material consumption and therefore also the magnitude of environmental burdens were investigated. The assessment was based on data concerning the safe storage of carbon dioxide in Poland.

Introduction Environmental benefits and burdens of the process of carbon capture and storage were evaluated using life cycle assessment (LCA) method. The technique of sequestration has generated much interest and there is a rich literature on the environmental impact of the process of CO2 sequestration from the perspective of the whole life cycle of power systems. In this paper environmental aspects related to the carbon capture and storage (CCS) were assessed using Polish conditions. The market of energy in Poland is based mainly on coal and according to the Energy Policy of Poland until 2030 (2009), coal still will be important source of energy in the future, thus the process of CCS is seemed as a chance to reduce emission of carbon dioxide emission. In Poland underground storage in deep saline formations is the most probably method of carbon dioxide storage. It is envisaged that the captured CO2 will be compressed, transported via pipeline to the chosen place of storage and then injected into porous rock formation with high salinity. Wachowicz et al. (2010) presented the following parameters of the stream of CO2 transported to underground storage:

− temperature 27°C − pressure 12 MPa, − density 900 kg/m3, − mass flow rate of CO2 100 – 300 Gg/year,

Carbon dioxide after injection is slowly dissolving in a brine and after very long time a part of the gas can react with the rock (mineralisation). Underground storage of CO2 contributes to a significant reduction of a global warming potential of coal power plants. However the LCA method indicates that other consequences of carbon capture and storage are increasing fossil depletion and reduction of overall efficiency of the power production. Other environmental consequences of CCS chain, including CO2 transport, injection and storage as well related to infrastructure are uncertain and difficult to assess. This paper aim was quantification of the environmental burdens of the CCS chain in Polish conditions and identification of key parameters influencing the results of LCA.

Methods Life Cycle Assessment (LCA) is used in assessment of environmental impact of the processes and products in a broad perspective. This method has two main advantages.

1. It enables to assess various single categories of environmental impact as well as aggregated environmental indicators. LCA takes into account not only emission of greenhouse gases and energy consumption, but also impact on for example human health or fossil fuel depletion.

2. It takes into account environmental interventions from the analysed power plant, such as emissions and wastes, but also environmental burdens associated with other processes, for example mining and transport of coal to power plant, construction of the plant, processes of production of consumed materials, depletion of water and many others.

The aim of the paper was evaluation of both the environmental benefits and negative consequences resulting from capturing and storage of carbon dioxide created during conversion of coal in the power plant on the example of Integrated Gasification Combined Cycle (IGCC). In the frames of the paper two variants were assessed: IGCC power plant without CCS and IGCC power plant with CCS. All results were related to production of 1 MWhe of electricity transferred to the grid. Processes and operations included in the assessment are shown on the simplified scheme of the system boundary (Fig. 1).

Coal gasification

Gas treatment

Combined cycleH2 + CO

Coal

Power

Environmental interventions:Emission to airSolid wastesWastewater

IGCC Power Plant

Construction of the plant

Solvent Water

Compression of CO2 + dehydratation

Compression station Power

Transport via pipelineConstruction

of the pipeline

Emission of CO2

Injection of the gas into saline formation

Injection station

Power from the grid

Compression of CO2 + dehydratation

Drilling worksEmission from the

storage place

Emission

CCS chain

LIFE CYCLE OF THEINFRASTRUCTURE

LIFE CYCLE OF THE PROCESS

CO2

Fig. 1. Simplified scheme of the system boundary used in the life cycle assessment Source: The authors The assessment was performed using the method ReCiPe (Goedkoop et al., 2009). Environmental assessment with the method ReCiPe covers environmental problems listed in the Table 1. Results can be weighted to one value representing the overall potential of environmental impact expressed in the eco-points, which represent one thousandth of the average environmental load caused by one European inhabitant within one year. The higher points represent the worse environmental impact. Table 1. The list of environmental impact categories accounted in the method ReCiPe Damage category

Human health Ecosystem Resources

Climate change Human health

Climate change Ecosystems Fossil depletion

Ozone depletion Terrestrial acidification Metal depletion Humane toxicity Freshwater eutrophication Photochemical oxidant formation

Terrestrial ecotoxicity

Particulate matter formation

Freshwater ecotoxicity

Ionising radiation Marine ecotoxicity Agricultural land occupation Urban land occupation

Impact categories

Natural land transformation

Source: the authors

Impact categories of the damage category ‘human health’ aim to express the number of years lived disabled (YLD) and the number of years of life lost (YLL) resulting from respiratory and carcinogenic effects, effect of climate change, the depletion of the ozone layer, and ionising radiation. The damage models takes into account many variables, like temporary changes in concentration, dose, exposure, or occurrence. The damage category ‘ecosystem’ is reflected by the diversity of species within it, and is expressed in terms of the number of species that disappear in a given area as a result of contamination (PDF – Potentially Disappeared Fraction). The damage includes the area or volume of the impact and the time period. The ReCiPe method uses the term ‘species density’ to express the importance of the disappearance of species. Third category ‘Resources’ reflects depletion of resources due to the extraction.

Results of the Life Cycle Inventory The stage of Life Cycle Inventory (LCI) include collecting following data: energy inputs, raw material inputs, products, co-products, waste, releases to air, water, soil and other important environmental aspects (EN-ISO 14044:2006). In the assessment the public project of energy systems operation, including IGCC prepared by US DOE (Cost and Performance..., 2010) was used. The project assumes capturing of 90% of carbon dioxide from the gas using the absorber with Selexol. Data related to construction and liquidation of power plant, production of materials consumed and disposal of waste generated by IGCC were taken from previous works (Śliwi ńska i Czaplicka-Kolarz, 2012). Data concerning the CCS chain, including infrastructure and processes of compression, transport, injection and storage were based mostly on Wachowicz et al. (2010). Infrastructure Infrastructure included: compression station before pipeline, pipeline and injection station. Recompression stations compensating drop of pressure during transport probably will not be necessary in case of Poland, where the considered distance of transport is less than 150 km. The compression station is related to occupation of the area of 100 m2 (industrial area). The pipeline has following parameters:

− Dimensions of the pipeline: the width of 4 m, length of 30 km gives the area occupied; it was assumed that about 25% of the area occupied by the pipeline was transformed from arable

− To minimise risk of leakages resulting from the pipeline corrosion by transported gas, carbon manganese steel should be used for pipeline construction. Assumed thickness of steel was about 6,3 mm. The process of steel production ‘Steel, low-alloyed, at plant/RER U’ (Classen et al., 2009) from the database ecoinvent was used. Outer diameter of the pipeline designed for annual transport of 200 Gg of CO2 is 0,162 m. Calculated amount of steel used for construction of 1 km of the pipeline equals 12,3 Mg.

− The pipeline would be supported on concrete pedestals, distance between pedestals is 5,5 m. Pipes would be insulated by mineral wool (thickness of insulation 150 mm) secured with galvanized steel and painted with epoxy paint (thickness of 300 µm). Calculated consumed amounts of mineral wool equals 4,74 Mg/km and of epoxy paint equals 266 l/km of the pipeline.

− Data for processes of drawing and transport of pipes were taken from the ecoinvent process ‘Pipeline, natural gas, high pressure distribution network’ (Faist Emmenger et al. 2007).

The processes of compression, transport, injection and storage of CO2 The stream of carbon dioxide to transport should be dried to avoid corrosion and compressed to 12 MPa. It was assumed that electricity needed for compression was produced in IGCC plant and then overall efficiency of power production in the case with CCS was lower than in the case without CCS. Transport of CO2 via pipeline can impact environment through leakages. In the paper it was assumed that the annual emission of CO2 from the pipeline equals to 0,1315 t/km. The operation of injection results in consumption of electricity – national mix of power consumption was used in analyses. Estimated emission of carbon dioxide from the underground storage is equal to 0,0085wt% of the stored amount. Such emission will change in time and should be modelled dynamically. Here only the first year of the storage was accounted.

Results of the Life Cycle Assessment LCA results of the two variants of the IGCC plant: without CCS and with CCS calculated using the method ‘ReCiPe’ are presented in the Table 2 (‘midpoint’ – environmental impacts expressed in equivalent units) and Table 3 (‘endpoints’ – environmental damages expressed in damage units). Table 2. Results of life cycle impact assessment in different impact categories using the method ‘ReCiPe Midpoint’ Impact category Unit IGCC IGCC_CCS Climate change kg CO2 eq 860,3487 291,6286 Ozone depletion kg CFC-11 eq 6,77E-07 8,06E-07 Terrestrial acidification kg SO2 eq 0,100434 0,121541 Freshwater eutrophication kg P eq 0,010667 0,0128 Marine eutrophication kg N eq 0,005323 0,006394 Human toxicity kg 1,4-DB eq 7,988205 9,597212 Photochemical oxidant formation kg NMVOC 0,103697 0,124574 Particulate matter formation kg PM10 eq 0,033746 0,040758 Terrestrial ecotoxicity kg 1,4-DB eq 0,001079 0,001291 Freshwater ecotoxicity kg 1,4-DB eq 0,166341 0,200018 Marine ecotoxicity kg 1,4-DB eq 0,164527 0,19783 Ionising radiation kg U235 eq 7,124007 8,509316 Agricultural land occupation m2a 26,72736 31,93776 Urban land occupation m2a 3,462034 4,454684 Natural land transformation m2 0,022898 0,027326 Water depletion m3 2,702442 3,137927 Metal depletion kg Fe eq 0,644364 0,777794 Fossil depletion kg oil eq 285,837 341,4835 Source: the authors

Table 3. Results of life cycle impact assessment in different damage categories using the method ‘ReCiPe Endpoint’

Damage category

Unit IGCC IGCC_CCS Impact category IGCC IGCC_CCS

Climate change Human Health 98,8% 95,9% Ozone depletion 0,0% 0,0% Human toxicity 0,5% 1,6%

Photochemical oxidant formation 0,0% 0,0% Particulate matter formation 0,7% 2,5%

Human Health

DALY 1,2*10-3 0,4*10-3

Ionising radiation 0,0% 0,0% Climate change Ecosystems 94,0% 81,4%

Terrestrial acidification 0,0% 0,0% Freshwater eutrophication 0,0% 0,0%

Terrestrial ecotoxicity 0,0% 0,0% Freshwater ecotoxicity 0,0% 0,0%

Marine ecotoxicity 0,0% 0,0% Agricultural land occupation 4,4% 13,5%

Urban land occupation 1,0% 3,2%

Ecosystems species.yr 7,3*10-6 2,8*10-6

Natural land transformation 0,6% 1,8% Metal depletion 0,1% 0,1% Resources $ 47,3 56,5 Fossil depletion 99,9% 99,9%

Source: the authors The shares of different stages of the CCS chain, including compression, transport and injection of carbon dioxide, in total environmental impact in each of the two selected categories are shown in the Table 4. Table 4. The share (%) of the CCS chain in total impact in selected impact categories

Impact category CO2_compression CO2_transport CO2_injection CO2_storage Climate change 97,4 0,13 1,9 0,4 Fossil depletion 99,6 0,0002 0,4 0,03 Source: the authors

Discussion Comparison of the results of LCA of two analysed variants which are shown in the Table 2 demonstrates that the CCS chain leads to two opposite environmental effects. Implementing the CCS process allows to achieve the goal – reduce emission of greenhouse gases (GHG) to air, which is given in the row ‘Climate change’. However when considering the sum of GHG emitted in the life cycle this reduction is lower than declared 90%. Emission of GHG in the case ‘IGCC_CCS’ represents more than 30% of the GHG emission for the base case ‘IGCC’. Parallel with the reduction of GHG emission, the environmental impacts in all other impact categories are higher for the variant ‘IGCC_CCS’. Calculated damages to the environment in each of the impact category shown in the Table 3 indicate that climate changes contribute to the most important consequences both for human health and ecosystems. Therefore worsening of the environmental impacts in other categories may be considered as relative less important than benefits from reduction of such amounts of GHG emission. However it should be clearly stated, that such conclusion depends on the used methodology ‘ReCiPe’ and the model used in this method for conversion of environmental impacts expressed in equivalent units to environmental damages expressed in damage units.

Analyses of the individual stages in the CCS chain were performed. The shares of the impact of each stage in the total impact of the CCS chain were presented in the Table 4. The obtained results showed that the most important element in terms of environmental of the CCS chain is compression of captured carbon dioxide. Contributions to the total calculated environmental impact made by the other stages: CO2 transport, injection and storage are much lower. In fact emission of carbon dioxide from the pipeline and storage place comparing to the emission associated with electricity consumed in stages of compression and injection is negligible. This share depends on the distance of the storage place – in this paper it was assumed only 30 km of the pipeline. Accidental releases of carbon dioxide were not included in the analyses. Moreover assumption of the transport of CO2 by trucks or ships would lead to other proportions. Environmental impact associated with the injection of the gas into saline formation results mainly from the consumption of electricity. As consumption of the Polish mix of energy was assumed, injection contributes to consumption of fossil fuels in Poland. Share of this stage depends on parameters characteristic for the storage place, among others: porosity, depht, injection pressure. All analysed processes include ‘overhead’ impacts associated with material and energy consumption for infrastructure. For example, construction of the pipeline requires large amounts of steel, insulation – mineral wool, cement, fuel to transport pipes etc. The scale of environmental impacts resulting from the construction is significant, nonethelles this operation occures only once in the investment stage. Such type of the impact is divided by the life time – in case of the pipeline by 30 years – and the calculated ‘overhead’ is proportionally attributed to the functional unit. The contribution made by the infrastructure to the total environmental impact of the CCS chain is negligible.

Summary Environmental impacts of two variants of power production from coal were compared using the life cycle assessment (LCA) method. Analyses were performed on the example of an IGCC power plant without and with carbon capture and storage (CCS). Contributions of different stages of the CCS chain in the total environmental impact were investigated. Following processes and infrastructure were included: compression and compressor station, transport and pipeline, injection and injection station and storage of carbon dioxide captured from the syngas in the power plant before combustion. Results showed that IGCC with CCS has lower potential of climate change expressed in kg CO2eq, i.e. it has lower ‘carbon footprint’ than IGCC without CCS. On the other hand, analyses confirmed that the process of carbon capture and storage caused higher impact in other environmental categories, especially fossil fuel depletion. More detailed analysis of the CCS chain for pre-combustion capture process indicated that the most important cause of environmental impact of the CCS chain in each impact category was the consumption of additional electricity in the process of carbon dioxide compression before transport.

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Acknowledgements This paper is a part of the ongoing Research Task ‘Development of coal gasification technology for high production of fuels and energy’ funded by the National Center for Research and Development under the Strategic Programme for Research and Development entitled: ‘Advanced energy generation technologies’