(738f) Achieving Carbon-Neutral Supply of Power, Methanol and Ammonia through the Energy-Chemical Nexus

In order to combat climate change, the Paris Agreement has aimed to keep the global temperature rise in this century well below 2 °C, and preferably 1.5 °C, above pre-industrial levels [1]. Despite the controversy in exact definition of pre-industrial periods, the annual average global surface temperature in 2019 has already increased by 0.98 °C relative to 1951-1980 average temperatures which is clearly after the (First) Industrial Revolution [2]. Furthermore, according to the Intergovernmental Panel on Climate Change (IPCC), the trend of increasing annual anthropogenic CO₂ emission persists in the recent years [3]. Among the various sources of global greenhouse gas (GHG) emission, energy sector has become the world’s largest GHG emitter [4].

The decarbonization of energy sector at national scale is usually country-specific in order to fully realize the potential of inter-sectorial synergies [5]. In this work, China is selected as the country under investigation considering its large amount of CO₂ emission [6] and the government’s determination in emission reduction [7,8]. It is believed that the concept of energy-chemical nexus could potentially help the country achieve a low-carbon future by integrating the development of energy and chemical sectors that lead in national CO₂ emission [9]. Therefore, this study aims to evaluate the preliminary feasibility of forming such nexus in China across a timeframe of over 40 years in the future from temporal, spatial and sectorial perspectives. For the concreteness of this analysis, electricity is selected as the representative product for energy sector as it currently constitutes more than 45% of China’s total energy related CO₂ emission [10]. For chemical sector, both methanol and ammonia are selected considering China’s current role as the world’s largest producer and consumer of both chemicals [11,12]. Also, the recent development of active, stable and selective heterogeneous catalysts for methanol and ammonia synthesis further improve their competitiveness as future liquid energy carriers [13,14].

In this study, electricity generation from both fossil fuels and renewable resources, with or without carbon capture and storage (CCS) facilities, are considered. For methanol and ammonia production, apart from conventional fossil-based synthesis, hydrogen supplied by water electrolysis and carbon dioxide captured from power plants can also be used as feedstock to facilitate inter-sectorial integration. In order to quantitatively assess the impact of energy-chemical nexus on climate change, two relevant planetary boundaries, namely atmospheric CO₂ concentration (ppm) and energy imbalance at top of atmosphere (W/m²), are involved. Unlike conventional comparative life cycle assessments whose results are most meaningful when a comparison between different options is concerned, planetary boundaries analysis provides a set of evaluation criteria for absolute sustainability based on the safe operating spaces of fundamental Earth system processes [15]. Finally, subject to the operation constraints of various technologies and emission constraints from the carbon neutrality target, a nexus optimization model is developed to study the optimal planning of energy-chemical nexus in China from 2018 to 2060 with forecasted product demands, resource capacities and technology capital and operating costs.

References

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