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Abstract With the increasing penetration of renewables, microgrid integration has been considered as one of the most promising approaches to enhance the utilizations of various types of energy resources in smart distribution systems. In the near future, with the higher levels of intermittent renewables are envisaged, the distribution network operators will face significant challenges to the control and operation of distribution networks dispersedly. Consequently, the development of effective and motivating ancillary service schemes in a decentralized way for executing real-time control and reducing calculation and communication burden is still in its infancy and needs to be researched. To address this issue, this paper explores an optimal voltage regulation method with the participants of multi-microgrids based on multiple agent systems. Without an arbitration agent, peer agents in the multiple agent system calculate voltage sensitivities by local and neighbourhood measurements only. In this paper, a bi-level game model is proposed for voltage control process. In the upper-level, the distribution network operator searches the reasonable incentive mechanism based on the Stackelberg game. In the lower-level, microgrids make voltage control strategies autonomously based on a static game among microgrids. In the proposed method, microgrids participate in voltage control in distribution networks as ancillary service providers while maximizing their own profits. Meanwhile, the distribution network operator reduces the infrastructure reinforcement and avoids unnecessary renewable energy curtailment. Finally, the feasibility and effectiveness of the proposed method has been demonstrated on a modified IEEE 33-bus system.

Abstract A great portion of the primary energy is consumed by space heating and cooling in buildings. The need for utilizing more renewable energy in the building sector remains critical for ensuring the energy and environment sustainability. Geothermal energy is one of the renewable energy sources that we have an easy access to for supplying low-grade thermal energy with a low impact on the environment. The methods of utilizing geothermal energy for buildings include such as ground source heat pumps and earth to air heat exchangers (EAHEs). In this paper we presented the comprehensive performance analysis and deduced an easy-to-apply regression model for predicting the cooling capacity of an EAHE. A one-dimensional steady-state control volume model was developed and applied to simulate the performance of the EAHE. It couples both heat and mass transfer between the air and the tube. The model was calibrated by comparing against the experimental data from an existing renewable energy testing facility. After the calibration, six factors, namely the air temperature, the air relative humidity, the air velocity at the inlet of EAHE, the tube surface temperature, and the tube length and diameter on the performance were analyzed using the calibrated model. The polynomial regression models for predicting the cooling capacities including total, sensible and latent cooling capacity with high accuracy were obtained. The easy-to-apply formulas can be of great use in the design and application of EAHEs.

Abstract Depleted shale gas reservoirs may be candidates for conversion to injection wells for the long-term geologic storage of CO2, but the decision to transition from production to injection depends on economic and policy factors that may be uncertain. This paper aims to comprehend the uncertainty inherent to the underlying assumptions of CO2 sequestration and their impact on the injection decision. We view and analyze the production to injection transition decision as a kind of options problem, where the owner of a producing well can choose to exercise the option to stop producing natural gas and start injecting CO2. Our approach integrates a detailed reservoir model for shale-gas production and CO2 injection in the Marcellus shale formation with a multi-period decision problem under uncertainty in future prices for CO2 and produced natural gas. With no uncertainty, the modeling framework is able to identify the optimal timing of the transition to CO2 injection as a function of natural gas prices and a hypothetical CO2 price. We find that a CO2 price of approximately $15 per tonne to be needed in order to incentivize a producer to transition to CO2 injection earlier. If these prices are uncertain, we find that the option to delay CO2 injection has value even when CO2 prices are relatively high and natural gas prices are low, although the option value is highly sensitive to the choice of discount rate and the option value to delay injection is generally very low when CO2 prices are $20/tonne or higher. Our modeling suggests that commitment in carbon pricing regimes is of equal importance to the choice of the price level.

Abstract Colorless Distributed Combustion is a combustion technique to reduce pollutants emission, reduce noise, enhance flame stability, promote a uniform thermal field distribution in the flame, and mitigate combustion instability. To achieve these conditions, hot reactive gases must be entrained into the oxidizer to reduce the oxygen concentration, which slows down the reaction rate to broaden and homogenize the reaction front. This paper focuses on the development of a distributed combustion index that will predict transition to favorable distributed combustion conditions over a range of conditions. Distributed conditions were achieved by adding either N2 or CO2 dilution to the oxidizer stream to simulate hot gas entrainment. The index developed here is for either N2 or CO2 dilution and focuses on the effects of heat release intensity, equivalence ratio, and mixture preheat temperature. The results show heat release intensities in the range of 5.72–9.53 MW/m3-atm to have minimal effect on the oxygen concentration corresponding to transition to distributed combustion. In contrast, equivalence ratio and preheat temperature provided strong effects on this transition. Decrease in equivalence ratio from 0.9 to 0.6 required increased oxygen concentration for transition to distributed conditions by some 4% with N2 as the diluent and only 3% with CO2 as the diluent. Increase in mixture preheat temperature from 300 to 700 K decreased oxygen concentration transition requirements by some 3% with N2 and 2% for CO2. Emission levels obtained showed ultra-low NO and CO under favorable distributed combustion condition. The distributed combustion index development presented here is aimed to help guide in the design and development of novel next generation of advanced colorless distributed combustors with much reduced further experimentation.

This paper investigates thermal mixing caused by the inflow from one or two round, horizontal, buoyant jets in a water storage tank, which is part of a thermal solar installation. A set of experiments was carried out in a rectangular tank with a capacity of 0.3 m3, with one or two constant temperature inflows. As a result, two correlations based on temperature measurements have been developed. One of the correlations predicts the size of a zone of homogenous temperature, referred to herein as the mixing zone, which develops when a single hot inflow impinges on the opposite wall of the tank. The other identifies the degree of mixing resulting from the interaction between a hot inflow and a cold inflow located below the hot one. The correlations are combined with energy balances to predict the amount of hot water available in a tank with open side inlets and the corresponding temperatures of the outflows. Outdoor measurements were also performed in a solar installation, in which a commercial water storage tank with a 1.5 m3 capacity, heated by a solar collector array with a useful surface area of 42.2 m2, drives a LiBr–H2O absorption chiller. Comparison of the predicted and measured outflow temperatures under a variety of weather conditions shows a maximum difference of 3 °C.

The devolatilisation step of coal is a vital stage in both air–coal and oxy-coal combustion and there is interest in whether methods of estimating the reaction parameters are similar for both cases. A network pyrolysis model, the FG-DVC (Functional Group-Depolymerisation Vaporisation Cross-linking) code was employed to evaluate the effect of temperature (1273–1773 K) and heating rate (104–106 K/s) on the devolatilisation parameters of two coals of different rank. The products distribution between char and volatiles, and volatiles and NH3/HCN release kinetics were also determined. In order to assess the accuracy of the FG-DVC predictions, the values for nitrogen distribution and devolatilisation kinetics obtained for a temperature of 1273 K and a heating rate of 105 K/s were included as inputs in a Computational Fluid Dynamics (CFD) model for oxy-coal combustion in an entrained flow reactor (EFR). CFD simulations with the programme default devolatilisation kinetics were performed. The oxygen content in oxy-firing conditions ranged between 21% and 35%, and air-firing conditions were also employed as a reference. The experimental coals burnouts and oxygen concentrations from the EFR experiments were employed to test the accuracy of the CFD model. The temperature profiles, burning rates, char burnout and NO emissions during coal combustion in both air and O2/CO2 atmospheres were predicted. The predictions obtained when using the CFD model with FG-DVC coal devolatilisation kinetics were much closer to the experimental values than the predictions obtained with the ANSYS Fluent (version 12) program default kinetics. The predicted NO emissions under oxy-firing conditions were in good agreement with the experimental values. The present study was carried out with financial support from the Spanish MICINN (Project PS-120000-2005-2) co-financed by the European Regional Development Fund. L.A. and J.R. acknowledge funding from the CSIC JAE program, which was cofinanced by the European Social Fund, and the Asturias Regional Government (PCTI program), respectively. MG acknowledges financial support from E.ON UK, and for an EPSRC Dorothy Hodgkin Postgraduate Award. We also thank Dr L Ma for helpful discussions. Peer reviewed

Abstract Global demand for methanol as both a chemical precursor and a fuel additive is rising. At the same time, numerous renewable methanol production pathways are under development, which, if commercialized, could provide significant environmental benefits over traditional methanol synthesis pathways. However, it is difficult to compare technologies at different maturity levels, with differing feedstocks, and with significant differences in overall process design. Thus, there is a need to harmonize the analyses of renewable pathways using a consistent techno-economic approach to evaluate the potential for commercialization of various pathways. This analysis uses a novel cross-comparison method to assess near-term and long-term viability of both low- and high-maturity level technologies. The techno-economic assessment considers cost factors critical to market acceptance combined with carbon- and energy-efficiency assessments of three renewable pathways compared with a commercial baseline. We find that biomass gasification to methanol represents a near-term viable pathway with a high technology readiness level and commercially competitive market price. If cost-reducing technological improvements can be realized and scaled up in the CO2 electrolysis pathways, the potential for higher carbon efficiencies may help drive market adoption of these more modular, direct conversion pathways in future markets as they present an opportunity to better support global decarbonization efforts through efficient waste carbon utilization.