Forest treatment residues for thermal energy compared with disposal by onsite burning: Emissions and energy return

Mill residues from forest industries are the source for most of the current wood-based energy in the US, approximately 2.1% of the nation's energy use in 2007. Forest residues from silvicultural treatments, which include limbs, tops, and small non-commercial trees removed for various forest management objectives, represent an additional source of woody biomass for energy. We spatially analyzed collecting, grinding, and hauling forest residue biomass on a 515,900 ha area in western Montana, US, to compare the total emissions of burning forest residues in a boiler for thermal energy with the alternatives of onsite disposal by pile-burning and using either natural gas or #2 distillate oil to produce the equivalent amount of useable energy. When compared to the pile-burn/fossil fuel alternatives, carbon dioxide emissions from the bioenergy alternative were approximately 60%, methane emissions were approximately 3%, and particulate emissions less than 10 μm were 11% and 41%, respectively, for emission control and no-control boilers. Emissions from diesel consumption for collecting, grinding, and hauling biomass represented less than 5% of the total bioenergy emissions at an average haul distance of 136 km. Across the study area, an average 21 units of bioenergy were produced for each unit of diesel energy used to collect, grind, and haul biomass. Fossil fuel energy saved by the bioenergy alternative relative to the pile-burn/fossil fuel alternatives averaged 14.7–15.2 GJ t^?1 of biomass.     

End of life of fuel cells and hydrogen products: From technologies to strategies

End-of-Life (EoL) technologies and strategies are needed to support the deployment of fuel cells and hydrogen (FCH) products. This article explores current and novel EoL technologies to recover valuable materials from the stacks of proton exchange membrane fuel cells and water electrolysers, alkaline water electrolysers, and solid oxide fuel cells. Current EoL technologies are mainly based on hydrometallurgical and pyro-hydrometallurgical methods for the recovery of noble metals, while novel methods attempt to recover additional materials through efficient, safe and cost-competitive pathways. Strengths, weaknesses, opportunities and threats of the reviewed EoL technologies are identified under techno-economic, environmental and regulatory aspects. Beyond technologies, strategies for the EoL of FCH stacks are defined mainly based on the role of manufacturers and recovery centres in the short-, mid- and long-term. In this regard, a dual role manufacturer/recovery centre would characterise long-term scenarios within a potential context of a well-established hydrogen economy.     

Biomass integrated gasification combined cycle with reduced CO2 emissions: Performance analysis and life cycle assessment (LCA)

Performance analysis and life cycle assessment (LCA) of an integrated gasification combined cycle (IGCC) fed with biomass with upstream CO₂ chemical absorption has been carried out. The main working conditions have been determined by mean of partial exergetic analysis. A sensitivity analysis with respect to the CO₂ absorbing solution composition has also been carried out. The reachable efficiency ranges between 35% and 36%, depending on gas turbine technology level. In comparison with efficiency values previously found for an IGCC fed with coal with upstream CO₂ chemical absorption (38–39%), the configuration studied seems to be attractive because of the possibility of operating with a simplified scheme (without H₂S removal process) and at atmospheric pressure and for the possibility of using biomass in a more efficient way with respect to conventional combustion systems. Due to the lower efficiency, the specific CO₂ emission results higher (170 kg/MW h) with respect to the cycle fed with coal and CO₂ removal (130 kg/MW h). Moreover, the CO₂ balance has been determined with respect to the entire life cycle of the plant, including the construction, operation, dismantling and the biomass growing phases.     

Energy consumption and GHG emissions of GTL fuel by LCA: Results from eight demonstration transit buses in Beijing

Gas-to-liquids (GTL) as an alternative to diesel is considered to be one of the technical options to reduce petroleum consumption in the on-road transportation sector. Between May and August 2007, a joint demonstration program by Tsinghua University, Beijing Transit, Cummins Corporation and Shell Corporation was carried out in Beijing. The program focused on the supply systems and vehicle use of GTL fuel. The demonstration fleet was formed by four transit buses fueled with GTL and four with diesel. It was demonstrated that GTL has good compatibility with diesel in terms of fuel supply system and vehicle use. This paper compares the energy consumption and GHG emissions of diesel and GTL fuel supply chains by life cycle analysis based on demonstration results. The results indicate GTL’s large range (reported 54–70%) in synthesis efficiency, as the key factor in determining energy consumption and GHG emissions within the GTL fuel supply chain. For the probable case (GTL synthesis efficiency: 65%), the life cycle energy consumption and GHG emissions of GTL fuel are 42.5% and 12.6% higher than that of diesel. For two sensitivity analysis cases (GTL synthesis efficiency: 54% and70%), energy consumptions are 74.2% and 31.2% higher and GHG emissions are 27.3% and 7.4% higher than that of the diesel fuel supply chain. If the efficiency of the GTL synthesis process is improved to 75%, then the GHG emissions level of the GTL fuel supply chain can be reduced to the same level as the diesel fuel supply chain.     

Hydrogen production by biological processes: a survey of literature

Hydrogen is the fuel of the future mainly due to its high conversion efficiency, recyclability and nonpolluting nature. Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermochemical and electrochemical processes. They are mostly controlled by either photosynthetic or fermentative organisms. Till today, more emphasis has been given on the former processes. Nitrogenase and hydrogenase play very important role. Genetic manipulation of cyanobacteria (hydrogenase negative gene) improves the hydrogen generation. The paper presents a survey of biological hydrogen production processes. The microorganisms and biochemical pathways involved in hydrogen generation processes are presented in some detail. Several developmental works are discussed. Immobilized system is found suitable for the continuous hydrogen production. About 28% of energy can be recovered in the form of hydrogen using sucrose as substrate. Fermentative hydrogen production processes have some edge over the other biological processes.     

Production of enriched methane by a molten-salt concentrated solar power plant coupled with a steam reforming process: An LCA study

Enriched Methane is a gas mixture consisting of methane and a certain amount of hydrogen (10–30%vol) that finds out several applications such as fuel of Internal Combustion Engines (ICEs). To produce EM, a steam reforming reactor whose heat duty is supplied by a molten-salt stream heated up by a concentrating solar power (CSP) plant can be used, in order to generate the hydrogen steam by solar energy. In fact, molten salts at temperatures up to 550 °C can allow to reach the necessary thermal level inside the reactor to promote steam reforming reaction.     

Cofiring versus biomass-fired power plants: GHG (Greenhouse Gases) emissions savings comparison by means of LCA (Life Cycle Assessment) methodology

One way of producing nearly CO₂ free electricity is by using biomass as a combustible. In many cases, removal of CO₂ in biomass grown is almost the same as the emissions for the bioelectricity production at the power plant. For this reason, bioelectricity is generally considered CO₂ neutral. For large-scale biomass electricity generation two alternatives can be considered: biomass-only fired power plants, or cofiring in an existing coal power plant. Among other factors, two important aspects should be analyzed in order to choose between the two options. Firstly, which is the most appealing alternative if their Greenhouse Gases (GHG) Emissions savings are taken into account. Secondly, which biomass resource is the best, if the highest impact reduction is sought. In order to quantify all the GHG emissions related to each system, a Life Cycle Assessment (LCA) methodology has been performed and all the processes involved in each alternative have been assessed in a cradle-to-grave manner. Sensitivity analyses of the most dominant parameters affecting GHG emissions, and comparisons between the obtained results, have also been carried out.     

Assessment of finishing processes by exhaustion principle for textile fabrics: An exergetic approach

This study reveals the exergetic assessment of exhaustion processes for textile fabrics using actual operational data. The objective of the current work is to address the effects of the exhaust method parameters on exergy destruction and consumption rates. Additionally, a case study for cotton and polyester finishing processes was performed. The process temperature and time, water inlet temperature and liquor ratio were found to be the main parameters that affect exergy destruction rates. The effects of carry-over on exergy destruction rates were also investigated. It was shown that, 23% and 50% of total exergy destruction rate were occurred by the bleaching and the washing steps for cotton finishing, respectively, while 32% of total was accounted for the dyeing step of polyester finishing. The exergy efficiency of the finishing processes was obtained to be between 4.6% and 34.8% depending on the process variables. High temperature processes had higher exergy efficiency values.     

CFD analysis of nonlinear processes in pulse tube refrigerators: Streaming induced by vortices

Streaming in the pulse tube refrigerator is a crucial nonlinear flow and heat transfer phenomenon which considerably affects the refrigeration temperature and performance. The third type streaming in the pulse tube refrigerator is studied using computational fluid dynamics method for the first time. A two-dimensional simulation of an inline inertance tube pulse tube refrigerator (ITPTR) is performed for different operating frequencies with the help of the FLUENT® package. The streaming is found to be formed due to the generation, evolution and shedding of vortices and pressure drops which are induced by the hydrodynamic and thermodynamic asymmetries along the refrigeration system. The pressure drops due to abrupt changes of the tube cross sections at both hot and cold ends in the pulse tube are calculated and the mass flow rate of the streaming is predicted. The geometry, temperature gradient and especially frequency are revealed as the main factors influencing the streaming patterns and final refrigeration performance. The numerical results agree well with the substantial experiments and indicate further suppression and optimization methods.     

Anti-reflection (AR) coatings made by sol–gel processes: A review

Traditionally, various vacuum-based processes, depending on material systems and properties, and chemical etching process have been used for producing different types of anti-reflection (AR) coating on different substrate materials. In this paper, the development of sol–gel derived AR coating on different substrates for various applications in the past 40 years are reviewed. These coatings possess good uniformity in thickness and properties which have met requirements for various applications. The major approaches to fabricate AR coating and their characteristics have been discussed. This paper outlines the major solution coating processes and design principles of AR coatings. Major fabrication processes used in AR coating technologies have been compared. Different solution chemistries developed for producing different materials for AR coating preparation have been extensively reviewed. The optical performance of different types of sol–gel-derived AR coatings have been summarized and comparison to the commercial AR coating produced by traditional technologies have been discussed. The sol–gel AR coating has been shown to possess comparable or superior performance to those produced by vacuum-based processes.     

Production of synthetic gasoline and diesel fuel by alternative processes using natural gas and coal: Process simulation and optimization

The problem of producing synthetic liquid fuels by alternative routes is addressed. Industrial processes known as gas to liquid (GTL) and coal to liquid (CTL) are considered and compared to a hybrid process presently developed, which combines features of both GTL and CTL.     

Biomass to bio-ethanol: The evaluation of hybrid Pennisetum used as raw material for bio-ethanol production compared with corn stalk by steam explosion joint use of mild chemicals

The second generation biomass to bio-ethanol production is of growing interest. Energy crop were becoming important for second generation biomass to bio-ethanol production for their growth advantages. Hybrid Pennisetum as a new hybrid energy crop was selected as a model to compare with corn stalk. As pre-treatment methods, steam explosion and its combined action with dilute sulfuric acid, bisulfite, and mixed dilute acid and bisulfite were selected. The enzymatic hydrolysis demonstrated that the cellulose conversion is a strong function of the pre-treatment method applied, with corn stalk providing slightly better results. With dilute acid steam explosion (DA-SE), conversions were 67.6% and 54.5% for corn stalk and pennisetum, respectively. This can be attributed to the higher Cr. I of pennisetum (65.03%) than of corn stalk (54.05%). The cell lumen of pretreated pennisetum was smaller than for corn stalk as shown in SEM photos, meaning there was a substantially higher enzyme accessible surface and porosity in pennisetum, thus responsible for the higher cellulase adsorption of pretreated pennisetum. DA-SE was the most effective pre-treatment method, but the inhibitors' concentration was higher than in other methods. Combined dilute acid and bisulfite can moderately remove hemicelluloses and lignin. Cr. I values, lignin content, accessible surface and porosity were supplied the energy crop evaluation standards for bio-ethanol production.     

U.S. energy demand and supply scenarios: A retrospective appraisal of the U.S. National Academy of Sciences Study by the Committee on Nuclear and Alternative Energy Systems (CONEAS)

The paper presents the highlights of the report by the Committee on Nuclear and Alternative Energy Systems (CONAES) issued in January 1980 by the National Academy of Sciences.The study spans the time period from 1975, taken as a reference point, to the year 2010, with the year 1990 as a convenient mid-point.The anticipated energy demand is based on the assumption that the Gross National Product (GNP) during this period will grow at an average rate of either 2 or 3% and that the cost of energy will either remain constant, double or quadruple. The combination of these factors provides eight different scenarios for energy demand.The estimate of energy supply from various sources is worked out as a function of sociopolitical conditions which may either remain substantially unchanged, enhance energy supply by appropriate political action, or else will drive the growth of energy supply to the limit. These assumptions were the starting point for preparing three scenarios for the energy supply, each with a different mix of energy derived from various sources.By combining the eight demand scenarios with the three supply scenarios, a set of integrated scenarios for the period under study was worked out and analyzed.One conclusion arrived at is that, depending on the policies implemented, vastly different figures (with variations up to 2:1) can be forecasted for energy requirements in the year 2010, without significantly affecting either the standard of living or the lifestyle of Americans.