An Integrated Process and Network Solution for CO₂ Utilisation

Global warming is directly related to the increasing GHG emissions from both natural and anthropogenic sources. The contribution of CO₂ emissions towards this phenomenon has propelled the international community to initiate research programs that aim to mitigate the emissions through process efficiency improvements, in addition to capturing CO₂ from flue gases at the power plant stacks. Such options have become especially attractive for implementation when they are economically viable. In this regard, one of the most promising technological driven approaches is through Carbon Capture and Utilisation (CCU). Programs within CCU aim to reduce CO₂ emissions from electricity production and other chemical process industries by capturing CO₂ for utilisation in applications such as Enhanced Oil Recovery (EOR) within the oil and gas industry. The optimum utilisation of CO2 as feedstock potentially enhances the efficiency of chemical conversion processes resulting in useful products of economic value.The objective of this thesis is to introduce a methodology which integrates the design and modelling of multiple CCU network elements. The modelled network includes CO₂ sources, transport and utilisation options that potentially provide economic benefits through the dynamic allocation of CO₂ to sinks applications. The assessment case study is applied within the industrial sector of the State of Qatar in order to create new economic opportunities. The methodology considers various chemical conversion processes of multiple sink applications, including the synthesis of chemicals and materials such as Fischer-Tropsch Gas-to-liquid (GTL) production that utilise CO₂ within the GTL process in order to increase the yield of value-added products for different reformers, and to compare the results with the conventional GTL process. The methodology comprises of four stages: (a) initial development of a geospatial database, which involves the collation of data regarding the industries identified as CO₂ emission sources and utilisation sinks, and the transportation network that links them; (b) systems modelling representing integration of processes using a pipeline network models; (c) techno-economic and environmental assessment of the CCU network for the formulation of objective functions; and (d) multi-period and multi-objective CCU network optimisation representing a dynamic model which is sensitive to economic variables, such as the fluctuation in prices of the value-added products.The methodology utilises data gathered from the local industries in Qatar that have been identified as potential CO₂ users, including representatives from the fertiliser industry (QAFCO), chemical additives (QAFAC), and the Gas-to-Liquid (GTL) fuel industries. It is demonstrated that the market prices of the products are a key factor in the decision making for the model that enable to define the optimal solution for CCU objectives based on the different scenario assessments considered in this study. Several indicators are considered as part of the evaluation; profitability considering the CAPEX and OPEX, and the environmental performance considering the direct and indirect CO₂ emissions. The methodology includes a an Aspen HYSYS simulation for the gas to liquids (GTL) process as a potential sink for CO₂ utilisation, which includes a model which demonstrates the efficiency enhancement of the Fischer-Tropsch process through CO₂ injection. In the model, syngas production in the reforming units is simulated for three cases; two cases for auto-thermal reforming (ATR) with varying steam flow rates and a case for steam-methane reforming (SMR). The objective is to demonstrate the enhancement in the total refined products, and the optimisation of the growth probability (α) in the Anderson–Schulz–Flory (ASF) relationship and H2:CO proportion. The study also introduces a hazard identification (HAZID) and quantitative risk assessment (QRA) methodology for large-scale carbon capture and utilisation networks, which capture the resilience level of the CO₂ network. It does this by incorporating the business continuity management system (BCMS) in evaluating the readiness of the entire network to respond to the significant threats that could potentially cause economic disruptions. The objective is to measure the robustness of the network through risk assessments and computation of a resilience index, which provides an indication of the ability of the critical components to withstand against the system failures. The GTL plant model simulation indicates that the ATR reformer operating at a steam flow rate 3223 T/D and a CO₂ flow rate 1500 T/D represents an optimal scenario for product enhancement. Accordingly, the outcomes demonstrate that the optimal output for carbon dioxide utilisation ranges from 1.62 Mt/y to 6 Mt/y, which corresponds to a potential annual revenue ranging from 0.48 to 4.35 billion US dollars. Based on the solutions obtained for the Qatar case study, the maximum carbon dioxide utilisation occurs at the Pearl gas-to-liquids plant (up to 16%), whereas the major revenue is generated from the methanol-hydrogen plant, contributing as much as 59% of the total revenue in the proposed fixed network design. In terms of assessing the robustness of the CO₂ network, the computed resilient index is 0.42 which indicates the potential for economic loses and environment impact as a result of disruptions. Possible mitigation necessitates an alternative system to be installed in the form of either a new pipeline parallel to the network, or by means of CO₂ storage to be located at Mesaieed which will serve more than 60% of the sinks.