A conventional exergy analysis can highlight the main components having high thermodynamic inefficiencies, but cannot consider the interactions among components or the true potential for the improvement of each component. By splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts, the advanced exergy analysis is capable of providing additional information to conventional exergy analysis for improving the design and operation of energy conversion systems. This paper presents the application of both a conventional and an advanced exergy analysis to a supercritical coal-fired power plant. The results show that the ratio of exogenous exergy destruction differs quite a lot from component to component. In general, almost 90% of the total exergy destruction within turbines comes from their endogenous parts, while that of feedwater preheaters contributes more or less 70% to their total exergy destruction. Moreover, the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction; however, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. A large part of the avoidable exergy destruction within feedwater preheaters is exogenous; while that of the remaining components is mostly endogenous indicating that the improvements mainly depend on advances in design and operation of the component itself.

Distributed energy system, a decentralized low-carbon energy system arranged at the customer side, is characterized by multi-energy complementarity, multi-energy flow synergy, multi-process coupling, and multi-temporal scales (n-M characteristics). This review provides a systematic and comprehensive summary and presents the current research on distributed energy systems in three dimensions: system planning and evaluation, modeling and optimization, and operation and control. Under the regional environmental, resource, and policy constraints, planning distributed energy systems should fully integrate technical, economic, environmental, and social factors and consider device characteristics, system architecture, and source-load uncertainties. Further, this review presents four modeling perspectives for optimizing and analyzing distributed energy systems, including energy hub, thermodynamics, heat current, and data-driven. The system’s optimal operation and scheduling strategies, disturbance analysis, and related control methods are also discussed from the power system and thermal system, respectively. In all, more research is required for distributed energy systems based on an integrated energy perspective in optimal system structure, hybrid modeling approaches, data-driven system state estimation, cross-system disturbance spread, and multi-subject interaction control.

Solar aided power generation (SAPG) is an efficient way to make use of low or medium temperature solar heat for power generation purposes. The so-called SAPG is actually ‘piggy back’ solar energy on the conventional fuel fired power plant. Therefore, its solar-to-electricity efficiency depends on the power plant it is associated with. In the paper, the developed SAPG model has been used to study the energy and economic benefits of the SAPG with 200 and 300 MW typical, 600 MW subcritical, 600 MW supercritical, and 600 and 1000 MW ultra-supercritical fuel power units separately. The solar heat in the temperature range from 260 to 90°C is integrated with above-mentioned power units to replace the extraction steam (to preheat the feedwater) in power boosting and fuel-saving operating modes. The results indicate that the benefits of SAPG are different for different steam extracted positions and different power plants. Generally, the larger the power plant, the higher the solar benefit if the same level solar is integrated. Copyright © 2010 John Wiley & Sons, Ltd.

Compressed air energy storage (CAES) is a commercial, utility-scale technology that provides long-duration energy storage with fast ramp rates and good part-load operation. It is a promising storage technology for balancing the large-scale penetration of renewable energies, such as wind and solar power, into electric grids. This study proposes a CAES-CC system, which is based on a conventional CAES combined with a steam turbine cycle by waste heat boiler. Simulation and thermodynamic analysis are carried out on the proposed CAES-CC system. The electricity and heating rates of the proposed CAES-CC system are lower than those of the conventional CAES by 0.127 kWh/kWh and 0.338 kWh/kWh, respectively, because the CAES-CC system recycles high-temperature turbine-exhausting air. The overall efficiency of the CAES-CC system is improved by approximately 10% compared with that of the conventional CAES. In the CAES-CC system, compressing intercooler heat can keep the steam turbine on hot standby, thus improving the flexibility of CAES-CC. This study brought about a new method for improving the efficiency of CAES and provided new thoughts for integrating CAES with other electricity-generating modes.

In order to understand the pyrolysis mechanism of β-O-4 type lignin dimers, a pyrolysis model is proposed which considers the effects of functional groups (hydroxyl, hydroxymethyl and methoxyl) on the alkyl side chain and aromatic ring. Furthermore, five specific β-O-4 type lignin dimer model compounds are selected to investigate their integrated pyrolysis mechanism by density functional theory (DFT) methods, to further understand and verify the proposed pyrolysis model. The results indicate that a total of 11 pyrolysis mechanisms, including both concerted mechanisms and homolytic mechanisms, might occur for the initial pyrolysis of the β-O-4 type lignin dimers. Concerted mechanisms are predominant as compared with homolytic mechanisms throughout unimolecular decomposition pathways. The competitiveness of the eleven pyrolysis mechanisms are revealed via different model compounds, and the proposed pyrolysis model is ranked in full consideration of functional groups effects. The proposed pyrolysis model can provide a theoretical basis to predict the reaction pathways and products during the pyrolysis process of β-O-4 type lignin dimers.