• Energy Research

Abstract Absorption is considered as the most mature method for CO2 capture from the flue gas. This paper introduces the current state of CO2 absorption technology. In addition, we discuss the barriers associated with the absorption technology for CO2 capture and present future perspectives through recommendations for future research and development. Four activities to improve the CO2 absorption process are considered in this study, i.e., utilization of alternative solvents, utilization of alternative process modifications and process intensification, optimization of process flowsheet, and energy integration with other sections of the power plant. Two research priorities on the absorber and desorber equipment and CO2 solvents in the future research work are illustrated.

Abstract Carbon Capture, Utilization and Storage (CCUS) is one of the essential components for mitigating CO2 emissions. This special issue of Applied Energy includes research and review articles on CCUS technologies and applications. Recent developments in CO2 capture technologies with emphasis on post-combustion processes are highlighted. CO2 utilization in fuel production and other chemical processes, and CO2 storage are also presented, along with detailed discussion of life cycle assessments and techno-economic analyses to evaluate the various CCUS processes.

Abstract This work presents a profitability analysis of a novel route to produce biomethane and synthetic natural gas through Power-to-Gas technology. Differently to traditional Power-to-Gas processes, the process configuration herein proposed allows to produce biomethane even if a source of hydrogen is not available. The novelties of this work are both the new process configuration and the comparison among results for several plant sizes (100, 250, 500, and 1000 m3/h) under two representative EU scenarios (Spain and Germany). The main finding of this work is that no profitable results can be obtained at the present natural gas prices, evidencing the need of incentives. Largest plant could reach profitability under reasonable subsidies (12–15 €/MWh). The forecasted cost reduction for H2 production and CO2 methanation are also analysed. The results show that subsidies are needed even in the most optimistic scenario. A corollary of this study is the current technological great challenge to develop low carbon routes which push forward the transition towards sustainable societies.

The circular economy is calling for the rapid use of already-developed renewable energies. However, the successful implementation of those new fuels is limited by economic and political issues. For instance, in the Brandenburg region, Germany, biogas production from anaerobic digestion of biomass and wastes is a current alternative. However, the upgrading biogas to biomethane is still challenging and the economic viability is unknown. Therefore, we performed an economic analysis for biogas upgrading to biomethane in the Brandenburg region. Five biogas plant sizes were analyzed by the method of discounted cash flow. This method yields the net present value of the projects, thus revealing the profitability or non-profitability of the plants. Results indicate profitable outputs for medium and large plants, with net present values between 415 and 7009 k€. However, the smallest plants have net present values from -4250 to -3389 k€, thus needing further economic efforts or subsidies to reach profitability. Indeed, biomethane prices should range between 52.1 and 95.6 €/MWh to make these projects profitable. Combinations of 50% of investment subsidized and 11.5 €/MWh feed-in tariffs subsidies could make the projects reach profitability. These findings reveal that political actions such as green policies and subsidies are needed to implement green energy. This case study should serve as a potential tool for policy-makers toward a sustainable bioeconomy.

Abstract In this paper, an integrated power generation system of Kalina cycle system (KCS) and organic Rankine cycle (ORC) with LNG cold energy exploitation and CO2 capture is introduced. The composite circulation system can fully recover and use the medium and low temperature waste heat to reduce the greenhouse gas emissions. To evaluate the system performances, the thermodynamics model was established and the system was simulated by using Aspen HYSYS software. Thermodynamic analysis has been performed to study the effects of turbine inlet temperature, NH3 mass fraction, evaporation pressure and CO2 capture pressure on the KCS/ORC integrated system. The optimal conditions were also investigated and identified. Exergy analysis of the components operated on KCS or ORC has also been demonstrated. The results showed that the optimal values of the network output, thermal efficiency and CO2 captured quantity of the system were respectively 394.685 kW, 53.25% and 0.3 t/tCO2 (0.6 t/tLNG), while the evaluation indexes of the power recovery efficiency and exergy efficiency were respectively 36% and 41.42%. The exergy loss efficiency of each component was examined. It was indicated that the whole system has significant advantages in waste heat recovery.

With the ongoing exploration and development of oil and gas resources all around the world, applications of petrophysical methods in natural porous media have attracted great attention. This special issue collects a series of recent studies focused on the application of different petrophysical methods in reservoir characterization, especially for unconventional resources. Wide-ranging topics covered in the introduction include experimental studies, numerical modeling (fractal approach), and multiphase flow modeling/simulations.

Predicting the performance of solar water heater (SWH) is challenging due to the complexity of the system. Fortunately, knowledge-based machine learning can provide a fast and precise prediction method for SWH performance. With the predictive power of machine learning models, we can further solve a more challenging question: how to cost-effectively design a high-performance SWH? Here, we summarize our recent studies and propose a general framework of SWH design using a machine learning-based high-throughput screening (HTS) method. Design of water-in-glass evacuated tube solar water heater (WGET-SWH) is selected as a case study to show the potential application of machine learning-based HTS to the design and optimization of solar energy systems.

Abstract With the increase of liquified natural gas trade, more and more attention has been paid to the liquified natural gas cold energy utilization. In order to better recover and utilize liquified natural gas cold energy, a novel combined cooling, heating and power system based on liquified natural gas cold energy utilization and exhaust gas waste heat recovery is proposed in this paper. The system consists of a three-stage organic Rankine cycle, a Kalina cycle and liquified natural gas direct expansion. To evaluate the performance of the combined cooling, heating and power system, a mathematical model was established, and through the thermodynamic analysis the net output power, thermal efficiency, and exergy efficiency of the system were 1257.708 kW, 43.43%, and 70.4%, respectively. The effects of the pump and compressor outlet pressure, n-hexane mass flow rate in the first Rankine cycle, turbine inlet temperature, and isentropic efficiency of the turbines on the system performance were analyzed. Moreover, exergoeconomic analysis is used to calculate the total product unit cost of the combined cooling, heating and power system, which was found to be 51.1 $/GJ. In addition, single- and multi-objective optimizations of the system were performed. The multi-objective optimization results show that the maximum exergy efficiency and minimum total product unit cost of this novel combined cooling, heating and power system were 80.49% and 48.04 $/GJ, respectively. This work shows a great potential in utilizing the liquified natural gas cold energy and waste heat of exhaust gas by a combined cooling, heating and power system.