Abstract

Hydrate-based CO2 sequestration has emerged as one of the possible methods for the long-term storage of CO2 as hydrates within the geological media, notably under marine sediments. In this direction, a thermodynamic model for the phase equilibria of CO2 hydrates in pure water and THF solutions (≤ 5.56 mol%), based on the fugacity approach is employed to predict the three-phase (LHV) equilibrium pressures and the fractional occupancy of CO2 and THF molecules in small and large cages. The hydrate, vapor, and liquid phases are modeled using the van der Waals-Platteeuw solid solution theory, Peng-Robinson-Stryjek-Vera equation of state, and the modified UNIFAC method, respectively. The model-predicted equilibrium pressures are in excellent agreement with experimental data with an AAD of 1.55%. The presence of THF has greatly reduced the CO2 hydrate equilibrium pressures. The cage occupancy results revealed the reduction in small cage occupancy of CO2 at (≥) 1.296 mol% THF and a continuous substantial decrease in large cage occupancy of CO2 with increased THF concentration. However, the overall hydrate stability is ensured by the large cage occupancy of the large molecule THF in larger fractions. This study is an important precursor for future hydrate-based CO2 sequestration.

Abstract

Air-source heat pump, as an efficient and clean heating methods, have significant potential in the electrification of energy terminals within public buildings. This study delves into the suitability of air-source heat pumps for use in public buildings located in severe cold, cold, and hot-summer and cold-winter regions. Considering the performance adjustments required under defrosting and low-temperature conditions, the heating system is constructed using the TRNSYS software. The hourly operational characteristics and dynamic control strategies of heat pump clusters are simulated and analyzed across various climate regions and public building types. The results reveal a positive correlation between the COP of heat pump systems and outdoor temperature, with COP values of 1.64 (Harbin), 2.57 (Beijing), and 2.81 (Shanghai), alongside average operation numbers of 16.6 (Harbin), 7.5 (Beijing), and 2.6 (Shanghai). Notably, the COP remains unaffected by the type of public building. This study aims to offer valuable insights for the application and regulation of air-source heat pumps in public buildings.