Ehsan Houshfar , Terese Løvås and Øyvind Skreiberg
Article: Experimental Investigation on NO_x Reduction by Primary Measures in Biomass Combustion: Straw, Peat, Sewage Sludge, Forest Residues and Wood Pellets
Energies 2012, 5(2), 270-290; doi:10.3390/en5020270 - published online 8 February 2012
Show/Hide AbstractAbstract: An experimental investigation was carried out to study the NO_x formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NO_x level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO₂, C_xH_y, O₂, NO, NO₂, N₂O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NO_x reduction of 50–80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NO_x emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NO_x showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1–25% of the fuel-N content is converted to NO_x depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NO_x reduction and low fuel-N conversion to NO_x. Tops and branches did not show desirable NO_x reduction and made the combustion also more unstable. N₂O emissions were very low, typically below 5 ppm at 11% O₂ in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere.

Wei-Min Lin , Keh-Chin Chang , Yi-Mei Liu and Kung-Ming Chung
Article: Field Surveys of Non-Residential Solar Water Heating Systems in Taiwan
Energies 2012, 5(2), 258-269; doi:10.3390/en5020258 - published online 7 February 2012
Show/Hide AbstractAbstract: To develop indigenous alternative and renewable energy resources, long-term subsidy programs (1986–1991 and 2000–present) for solar water heaters have been enforced in Taiwan. By the end of 2010, the total installed area of solar collectors had exceeded 2 million square meters. However, over 98% of solar water heaters were used in residential systems for hot water production, with the areas of installed solar collector being less than 10 square meters. There were only 98 systems with area of solar collectors installed exceeding 100 square meters put into operation from 2001 to 2010. These systems were mainly installed for water heating in dormitories, swimming pools, restaurants, and manufacturing plants. In the present study, a comprehensive survey of these large-scale solar water heaters was conducted. The objectives of the survey were to assess the system performance and to collect feedback from individual users. It is found that lack of experience in system design and maintenance are the key factors affecting reliable operation of a system. Hourly, daily and long-term field measurements of a dormitory system were also examined to evaluate its thermal efficiencies. Results indicated that thermal efficiency of the system is associated with the daily solar radiation. Hot water use pattern and operation of auxiliary heater should be taken into account in system design.

Angel Sánchez , Rocio Maceiras , Angeles Cancela and Mónica Rodríguez
Article: Influence of n-Hexane on in Situ Transesterification of Marine Macroalgae
Energies 2012, 5(2), 243-257; doi:10.3390/en5020243 - published online 6 February 2012
Show/Hide AbstractAbstract: The purpose of this work is to investigate the influence of n-hexane addition on in situ transesterification of a solid raw material for biodiesel production. Extraction and reaction of macroalgae oil has been performed simultaneously in a batch reactor adding n-hexane with the reactants. In order to analyze the influence of n-hexane on the transesterification, the reaction was also carried out with sunflower oil. The results show that the presence of n-hexane does not have an important effect on the transesterification. It was also observed that this method requires large quantities of methanol to carry out the reaction. The best reaction conditions for in situ transesterification of marine macroalgae were 300:1 methanol-to-oil molar ratio, 1% catalyst concentration, 60 °C reaction temperature and 11 h reaction time, resulting in a methyl esters yield of 17.1%. Thus, biodiesel production from macroalgae by transesterification in situ could be feasible, using hexane for the extraction and eliminating the previous extraction. This integrated method is thus effective and technically attractive.

Fernando R. Mazarrón , Jaime Cid-Falceto and Ignacio Cañas
Article: Ground Thermal Inertia for Energy Efficient Building Design: A Case Study on Food Industry
Energies 2012, 5(2), 227-242; doi:10.3390/en5020227 - published online 2 February 2012
Show/Hide AbstractAbstract: The search for energy efficient construction solutions is still pending in the agro-food industry, in which a large amount of energy is often consumed unnecessarily when storing products. The main objective of this research is to promote high energy efficiency built environments, which aim to reduce energy consumption in this sector. We analyze the suitability of using the thermal inertia of the ground to provide an adequate environment for the storage and conservation of agro-food products. This research compares different construction solutions based on the use of ground thermal properties, analyzing their effectiveness to decrease annual outdoor variations and provide adequate indoor conditions. The analysis undertaken is based on over five million pieces of data, obtained from an uninterrupted four year monitoring process of various constructions with different levels of thermal mass, ranging from high volume constructions to others lacking this resource. It has been proven that constructive solutions based on the use of ground thermal inertia are more effective than other solutions when reducing the effects of outdoor conditions, even when these have air conditioning systems. It is possible to reach optimal conditions to preserve agro-food products such as wine, with a good design and an adequate amount of terrain, without having to use air conditioning systems. The results of this investigation could be of great use to the agro-food industry, becoming a reference when it comes to the design of energy efficient constructions.

Diego Vicinanza , Lucia Margheritini , Jens Peter Kofoed and Mariano Buccino
Review: The SSG Wave Energy Converter: Performance, Status and Recent Developments
Energies 2012, 5(2), 193-226; doi:10.3390/en5020193 - published online 31 January 2012
Show/Hide AbstractAbstract: The Sea-wave Slot-cone Generator (SSG) is a Wave Energy Converter based on the wave overtopping principle; it employs several reservoirs placed on top of each other, in which the energy of incoming waves is stored as potential energy. Then, the captured water runs through turbines for electricity production. The system works under a wide spectrum of different wave conditions, giving a high overall efficiency. It can be suitable for shoreline and breakwater applications and presents particular advantages, such as sharing structure costs, availability of grid connection and recirculation of water inside the harbor, as the outlet of the turbines is on the rear part of the system. Recently, plans for the SSG pilot installations are in progress at the Svaaheia site (Norway), the port of Hanstholm (Denmark) and the port of Garibaldi (Oregon, USA). In the last-mentioned two projects, the Sea-wave Slot-cone Generator technology is integrated into the outer harbor breakwater and jetty reconstruction projects. In the last years extensive studies have been performed on the hydraulic and the structural response of this converter, with the aim of optimizing the design process. The investigations have been conducted by physical model tests and numerical simulations and many results have been published on both conference proceedings and journals. The main scope of this paper is reviewing the most significant findings, to provide the reader with an organic overview on the present status of knowledge.

Yanghui Li , Yongchen Song , Weiguo Liu and Feng Yu
Article: Experimental Research on the Mechanical Properties of Methane Hydrate-Ice Mixtures
Energies 2012, 5(2), 181-192; doi:10.3390/en5020181 - published online 30 January 2012
Show/Hide AbstractAbstract: The mechanical properties of methane hydrate are important to the stability of borehole and methane extraction from a methane hydrate reservoir. In this study, a series of triaxial compression tests were carried out on laboratory-formed methane hydrate-ice mixtures with various methane hydrate contents. Axial loading was conducted at an axial strain rate of 1.33%/min and a constant temperature of −10 °C. The results indicate that: (1) the deformation behavior is strongly affected by confining pressure and methane hydrate content; (2) the failure strength significantly increases with confining pressure when confining pressure is less than 10 MPa, and decreases with methane hydrate content; (3) the cohesion decreases with methane hydrate content, while the internal friction angle increases with methane hydrate content; (4) the strength of ice specimens are higher than that of methane hydrate-ice mixture specimens; Based on the experimental data, the relationship among failure strength, confining pressure and methane hydrate content was obtained, and a modified Mohr-Coulomb criterion considering the influence of methane hydrate content on shear strength was proposed.