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Abstract Grape pomace is a by-product of the wine making industry with great availability and energetic potential. Torrefaction is a pre-treatment that may enhance the biomass quality as a fuel, and consists in exposing the biomass to an inert atmosphere at a temperature between 200 °C and 300 °C. This study evaluates the combustion characteristics of raw and torrefied grape pomace in a thermogravimetric analyzer and in a drop tube furnace. Initially, the raw grape pomace was torrefied in an argon inert atmosphere at 260 °C. Subsequently, the combustion of the raw and torrefied grape pomace was examined in the thermogravimetric analyzer through non-isothermal runs at a heating rate of 10 °C/min from room temperature to 800 °C. Finally, the combustion of both biomass residues was evaluated in the drop tube furnace at 1100 °C. The data reported includes gas temperature, major gas species concentration and particle burnout measured along the axis of the drop tube furnace. The main conclusions of this study are (i) for the devolatilization stage, the thermogravimetric data yielded apparent activation energy values of 84.9 and 85.2 kJ mol−1, and for the char oxidation stage of 137.5 and 109.2 kJ mol−1 for the raw and torrefied grape pomace, respectively; (ii) the NOx concentrations along the drop tube furnace were always higher for the combustion of the torrefied grape pomace than for the combustion of the raw grape pomace because the former residue has a higher nitrogen content; and (iii) the burnout values along the drop tube furnace were always lower for the combustion of the torrefied grape pomace than for the combustion of the raw grape pomace because the former residue has a lower volatile content and a higher fixed carbon content.

Given the significant amount of installed generation-capacity based on wind power, and also due to current economic downturn, the subsidies and incentives that have been widely used by wind-power producers to recover their investment costs have decreased and are even expected to disappear in the near future. In these conditions, wind-power producers need to develop offering strategies to make their investments profitable counting solely on the market. This paper proposes a multi-stage risk-constrained stochastic complementarity model to derive the optimal offering strategy of a wind-power producer that participates in both the day-ahead and the balancing markets. Uncertainties concerning wind-power productions, market prices, demands' bids, and rivals' offers are efficiently modeled using a set of scenarios. The conditional-value-at-risk metric is used to model the profit risk associated with the offering decisions. The proposed model is recast as a tractable mixed-integer linear programming program solvable using available branch-and-cut algorithms. Results of a case study are reported and discussed to show the effectiveness and applicability of the proposed approach.

Distributed energy resources (DERs) change the supply-demand balance of power systems. To better manage these resources, they are operated as micro-grids (MGs) in both grid-connected and standalone modes. In the presence of MGs, the decision making framework in power systems is changing from the centralized structure into the decentralized one. In such framework, modeling the operation problem of MGs with the participation in energy and reserve markets in the presence of uncertainties is considered as an important challenge. Most of the studies use probability distribution functions (PDFs) to model the uncertain parameters. In this paper, the operation problem of a grid-connected MG is modeled while the MG operator (MGO) faces with uncertainties of renewable energy sources (RESs) without considering their PDFs. For this purpose, an information gap decision theory (IGDT)-based approach is employed to model the uncertain behavior of RESs as well as to control the risk level of the MGO on the optimal scheduling of DERs. To investigate the effectiveness of the model, a modified 15-bus low voltage MG us used as a test system. The results show that optimal decisions of the risk-averse MGO are different from those of a risky one.

This paper describes anaerobic thermophilic sludge digestion (55 °C) in a continuously stirred tank reactor (CSTR) on a pilot-plant scale (150 L). The experimental protocol was defined to examine the effect of the increase in the organic loading rate on the efficiency of the digester and to report on its steady-state performance. The reactor was subjected to a programme of steady-state operation over a range of solids retention times (SRTs) of 75, 40, 27, 20 and 15 days and organic loading rates (OLR) in the range 0.4–2.2 kg VS/(m3 day). The digester was fed with raw sludge (containing approximately 35 kg/m3 volatile solids (VS)) once daily during the 75-day SRT period, twice daily during the 40-day SRT period and three times a day during the 27-, 20- and 15-day SRT periods. The reactor was initially operated with an organic loading rate of 0.4 kg VS/(m3 day) and an SRT of 75 days. The volatile solids removal efficiency in the reactor was found to be 73%, while the volumetric methane production rate produced in the digester reached 0.02 m3/(m3 day). Over a 338-day operating period, an OLR of 2.2 kg VS/(m3 day) was achieved with 49.1% VS removal efficiency in the pilot sludge digester, at which time the volumetric methane production rate content of biogas produced in the digester reached 0.4 m3/(m3 day). The chemical oxygen demand (COD) mass balance obtained indicated that COD used for methane generation increased when the SRT was decreased or when the influent organic loading rate was increased. This implies that the amount of COD used in the anabolism route decreased with SRT due the microbial population becoming adapted to new operational conditions and more COD being used to generate methane.

This work presents a crude bioethanol fueled integrated power system for backup and off-grid applications. The system is based on ethanol steam reformation to hydrogen that is used in polymer electrolyte fuel cells to produce electricity. We introduce the system design and overall system specifications, and report the experimental process of defining specifications for the produced hydrogen quality, a key variable affecting the final system cost, efficiency and durability. Results from development of individual subsystems are also presented together with discussion on the complete system integration.

One of the major goals of engine designers is the reduction of fuel consumption and pollutant emissions while keeping or even improving engine performance. In recent years, different technical issues have been investigated and incorporated into internal combustion engines in order to fulfill these requirements. Most are related to the combustion process since it is responsible for both fuel consumption and pollutant emissions. Additionally, the most critical operating points for an engine are both the starting and the warming up periods (the time the engine takes to reach its nominal temperature, generally between 80°C and 90°C), since at these points fuel consumption and pollutant emissions are larger than at any other points. Thus, reducing the warm-up period can be crucial to fulfill new demands and regulations. This period depends strongly on the engine cooling system and the different strategies used to control and regulate coolant flow and temperature. In the present work, the influences of different engine cooling system configurations on the warm-up period of a Diesel engine are studied. The first part of the work focuses on the modeling of a baseline engine cooling system and the tests performed to adjust and validate the model. Once the model was validated, different modifications of the engine coolant system were simulated. From the modelled results, the most favourable condition was selected in order to check on the test bench the reduction achieved in engine warm-up time and to quantify the benefits obtained in terms of engine fuel consumption and pollutant emissions under the New European Driving Cycle (NEDC). The results show that one of the selected configurations reduced the warm-up period by approximately 159 s when compared with the baseline configuration. As a consequence, important reductions in fuel consumption and pollutant emissions (HC and CO) were obtained.

Abstract CIEMAT is promoting experiences on heliostats for replacement of damaged facets on CESA-1 field, design of new modules for Phoebus-like plants and innovative high-risk options for the future. Glass-metal facets, stretched membranes, glass fiber and holographic concentrators are being considered in a number of developments.

Abstract This study employs the decomposition analysis of CO2 emissions for the period from 2000 to 2012. This technique computes five effects that drive changes in CO2 emissions in five subsectors of the Portuguese tourism industry. The energy over fixed capital, the capital over labour productivity, and the tourism intensity are the most important effects in accommodation, food and beverage services. The carbonisation index constitutes an important effect in transports. The capital over labour productivity intensity effect has the strongest influence, while the carbonisation index exerts a positive influence upon CO2 emissions in tour operators and travel agencies. The energy over gross fixed capital and tourism intensity effects predominate in cultural, sports and recreational services. The results of the econometric analysis further confirm the statistical significance of the aforementioned effects. Policy recommendations are provided.