Techno-economic analysis of CO2 capture concepts
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The estimates of post combustion CO2 capture costs reported in the literature ranges typically from 50 €/tCO2 to 130 €/tCO2, reflecting differences in the cost estimation methods used, scopes of the analyses, and assumptions made. This variation in calculated costs is important when evaluating the feasibility of a technology and highlights the importance of ensuring consistency and transparency in cost estimations. A project named CO2stCap is being run in Norway and Sweden with the aim to provide cost effective solutions based on partial CO2 capture to reduce carbon emissions in emission intensive process industries like steel & iron, cement, pulp & paper and metallurgical production of silicon for solar cells. This PhD is a part of this project CO2stCap with the aim to establish a methodology for performing techno-economic analysis that highlights the effects of different technical and economic assumptions on the overall cost of a capture plant and identifies the crucial factors. The input is a simplified process flow diagram and an equipment list. Simulation of the process is performed via a software such as Aspen Hysys for mass and energy balances, which are essential for equipment dimensioning and cost calculations. For cost estimation, a practical engineering economic method has been introduced named Enhanced Detailed Factor (EDF) method where capital expenditure (CAPEX) is being calculated based on individual installation factors (named enhanced detailed installation factors in this thesis) and the individual equipment cost. An enhanced detailed installation factor sheet is presented in the work that is used for the CAPEX estimation. The proposed techno-economic analysis methodology is applied to a Base case that involves the amine-based post combustion capture of CO2 (85% capture rate) from the flue gas of a cement industry, giving a capture cost of 63 €/tCO2. The Base case results show that the steam cost, electricity cost, and capital cost are the main contributors. This method can provide an overview of the main cost drivers, and a sensitivity analysis of the variable input parameters can be performed simply and quickly. The results obtained using this method can be valuable in the early phase of the project (concept screening or study estimates) and contribute to reasonable decision making. This developed tool for techno-economic analysis has also been applied to partial CO2 capture from flue gas of a cement plant. It is not obvious whether a high removal efficiency from a part of the flue gas (termed as part-flow) or a low removal efficiency from the total flue gas (termed as full-flow) is the optimum solution, hence both case studies were analysed. Besides, a task is to compare the EDF cost estimation method with a simple Lang factor method. It is found that a full-flow alternative is the energy optimum while a part-flow alternative treating 80% of the exhaust gas is the cost optimum. The major cost drivers were identified via the EDF method while the Lang factor method is not designed to provide these details. This work shows that the calculated optimum is dependent both on the criteria used and on the selected method. Hence, there is a need of consistency in cost estimates when it comes to comparing cost from different studies. While it is generally recognized that the utilization of waste heat has potential to reduce the energy-associated costs for CO2 capture, the cost of waste heat recovery is seldom quantified. In this work, the cost of heat-collecting steam networks for waste heat recovery for solvent regeneration is estimated. Two types of networks are applied to waste heat recovery from the flue gases of four process industries (cement, silicon, iron & steel, and pulp & paper) via a heat recovery steam generator. The results show that the overall cost (CAPEX+OPEX) of steam generated from one hot flue gas source is in the range of 1–4 €/t steam. The CAPEX required to collect the heat is the predominant factor in the cost of steam generation from waste heat. The major contributor to the CAPEX is the heat recovery steam generator, although the length of the steam pipeline when heat is collected from two sources or over long distances is also important for the CAPEX. With only excess heat, it is often not possible to capture all the CO2 emissions, hence there is a need for extra steam/energy for the capture plant to achieve a higher CO2 capture efficiency. This work analyses three steam production options i.e., coal fired boiler, natural gas fired boiler and biomass fired boiler. A proposed steam network is analysed. Steam production based on natural gas is calculated to be more economical than steam production based on coal or biomass, although the calculated steam cost is extremely sensitive to market conditions such as fuel price, which varies across the world. Natural gas has the highest boiler efficiency and it also gives the lowest amount of CO2 in the flue gas. Although coal has the cheapest fuel cost, it is not the cheapest steam production option. Biomass boilers give the highest steam cost that is mainly due to the higher purchase cost of biomass (wood pellets), but an advantage is that the CO2 present in the flue gas is neutral. This work emphasizes the importance of technical and economic assumptions and the selected cost estimation method in estimating the CO2 capture cost. A methodology for techno-economic analysis has been presented in this thesis, in particular the EDF cost estimation method that has the potential to perform the detailed cost estimates efficiently and highlights the factors that require further analysis, hence eases the process of decision making.
Består avPaper 1: Ali, H., Eldrup, N.H., Normann, F., Andersson, V., Skagestad, R., Mathisen, A. & Øi, L.E.: Cost estimation of heat recovery networks for utilization of industrial excess heat for carbon dioxide absorption. International Journal of Greenhouse Gas Control 74, 2018, 219-228. https://doi.org/10.1016/j.ijggc.2018.05.003
Paper 2: Ali, H., Øi, L.E. & Eldrup, N.H.: Simulation and Economic Optimization of Amine-based CO2 capture using excess heat at a cement plant. Proceedings of the 59th International Conference of Scandinavian Simulation Society, SIMS 2018, 58-64, 2018. https://doi.org/10.3384/ecp1815358
Paper 3: Ali, H., Eldrup, N.H., Normann, F., Skagestad, R. & Øi, L.E.: Cost Estimation of CO2 Absorption Plants for CO2 Mitigation – Method and Assumptions. International Journal of Greenhouse Gas Control 88, 2019, 10-23. https://doi.org/10.1016/j.ijggc.2019.05.028
Paper 4: Ali, H., Øi, L.E., Eldrup, N.H., Skagestad, R. & Mathisen, A.: Steam Production Options for CO2 Capture at a Cement Plant in Norway. Proceedings of the 14th Greenhouse Gas Control Technologies Conference (GHGT-14), Melbourne 21-26 October 2018. https://ssrn.com/abstract=3366165