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Guest Editorial

J. Energy Resour. Technol. 2018;140(4):040301-040301-1. doi:10.1115/1.4039892.
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Biomass energy is a promising sustainable alternative for rapidly depleting fossil fuels. This form of energy is widely being considered by policy makers, scientific researchers, and engineers worldwide since the energy issue is of serious concern for global economy, environment, standards of living, and productivity. The use of biomass energy can effectively narrow the increasing energy gap between energy availability and energy use. Furthermore, it can also help mitigate environmental issues as biomass is renewable, sustainable, carbon-neutral, abundantly available, and it provides low emissions levels of NOx, SOx, and hydrocarbons. Efficient use of biomass energy depends on good understanding of the fundamentals of resource characteristics, conversion processes, and specific utilization system(s) of biomass energy conversion. Therefore, the main motivation of this special issue of ASME Journal of Energy Resources Technology (JERT) is to bring together original articles on the fundamentals and applications of biomass energy with respect to resource characteristics, conversion processes, reaction properties, and utilization systems of biomass energy.

Topics: Biomass
Commentary by Dr. Valentin Fuster

Review Article

J. Energy Resour. Technol. 2018;140(4):040801-040801-8. doi:10.1115/1.4039737.

Biobutanol is an attractive, economical, and sustainable alternative fuel to petroleum oil which are depleting in sources due to the diminishing oil reserves and creating an increase in the concentrations of greenhouse gases in the atmosphere. Alternative routes to sustainable bacterial fermentation for the production of biobutanol are being sought and prepared for commercialization. The challenges for implementing an economically competitive fermentation process for biobutanol production include the availability of cheaper feedstock by improvement toward large-scaled production, improvement of fermentation efficiency, and better strategies for solvent recovery. The development of biobutanol production was analyzed and various methods to increase the fermentative butanol production were discussed in detail. It was found that the implementations of metabolic engineering of the Clostridia sp., advanced fermentation techniques, and utilization of renewed substrates are among the potential and economically viable technology in the production butanol production. Besides, this review outlines several challenges and potential future work for the advancement of fermentative butanol production.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):040802-040802-6. doi:10.1115/1.4039604.

As compared with the conventional electrical heating pyrolysis, microwave-assisted pyrolysis (MAP) is more rapid and efficient due to its unique heating mechanisms. However, bio-oil production from MAP of biomass is strongly dependent on the operation parameters. Based on the recent researches, this study reviews the effects of the main operation parameters including microwave power, pyrolysis temperature, and pyrolysis time on the bio-oil yield obtained from MAP of biomass. The results show that microwave power, pyrolysis temperature, and pyrolysis time usually increase the bio-oil yield initially and decrease the bio-oil yield finally. The reported optimal microwave powers, pyrolysis temperatures, and pyrolysis times were mainly in the ranges of 300–1500 W, 400–800 °C, and 6–25 min, respectively. The mechanisms for bio-oil produced from MAP of biomass as affected by the main operation parameters were also analyzed.

Commentary by Dr. Valentin Fuster

Research Papers: Energy From Biomass

J. Energy Resour. Technol. 2017;140(4):041801-041801-5. doi:10.1115/1.4037814.

Supercritical water gasification (SCWG) is an efficient and clean conversion of biomass due to the unique chemical and physical properties. Anthracene and furfural are the key intermediates in SCWG, and their microscopic reaction mechanism in supercritical water may provide information for reactor optimization and selection of optimal operating condition. Density functional theory (DFT) and reactive empirical force fields (ReaxFF) were combined to investigate the molecular dynamics of catalytic gasification of anthracene and furfural. The simulation results showed that Cu and Ni obviously increased the production of H radicals, therefore the substance SCWG process. Ni catalyst decreased the production of H2 with the residence time of 500 ps while significantly increased CO production and finally increased the syngas production. Ni catalyst was proved to decrease the free carbon production to prohibit the carbon deposition on the surface of active sites; meanwhile, Cu catalyst increased the production of free carbon.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(4):041802-041802-13. doi:10.1115/1.4038624.

Dual fuel diesel (DFD) engines have been gaining popularity due to the flexibility of using both bio and fossil liquid and gaseous fuels. Further, the efficient combustion in DFD mode with bio liquid and gaseous fuel can greatly reduce the greenhouse gas emissions as well as the dependency on fossil diesel. In recent times, a host of investigation has been done in normal dual fuel diesel (nDFD) mode with pure diesel and biogas. However, the engines with ethanol blended with diesel and intake charge (biogas–air mixture) with preheating have not been studied. In the present study, 5% ethanol blended with diesel (E5) and biogas with preheating are used in dual fuel engine (DFD-E5) to find their performance and emission characteristics. In order to have a direct comparison of performances, an engine with pure diesel (E0) and biogas with preheating is also tested in dual fuel mode (DFD-E0). In all the cases, the effect of total equivalence ratio on engine overall performance has also been investigated. In DFD-E5 mode, and at the maximum torque of 21.78 N·m, the brake thermal efficiency (BTE) increases by 2.98% as compared to nDFD mode. At the same torque, there is no trace of carbon monoxide (CO), whereas there is a reduction of hydrocarbon (HC) emission by 62.22% with respect to pure diesel (PD) mode. The nitrogen of oxides (NOx) is found to decrease in DFD modes in contrast to PD mode.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):041803-041803-10. doi:10.1115/1.4039601.

In this study, the syngas composition exiting a biomass gasifier is investigated to determine the effect of varying selected gasification parameters. The gasification parameters considered are the mass flow rate of steam, the gasification agent, the mass flow rate of oxygen, the gasification oxidant, and the type of biomass. The syngas composition is represented by its hydrogen, carbon monoxide, carbon dioxide, and water fractions. The oxygen fed to the gasifier is produced using a cryogenic air separation unit (CASU). The gasifier and the air separation unit are modeled and simulated with aspenplus, where the gasification reactions are carried out based on the Gibbs free energy minimization approach. Finally, the syngas composition for the different types of biomass as well as the different compositions of the three types of the biomass considered are compared in terms of chemical composition. It was found that for each type of biomass and at a specified steam flow rate there is an air to the air separation unit where the gasification of the biomass ends and biomass combustion starts and as the volatile matter in the biomass increases the further the shifting point occur, meaning at higher air flow rate. It was found for the three considered biomass types and their four mixtures that, as the volatile matter in the biomass increases, more hydrogen is observed in the syngas. An optimum biomass mixture can be achieved by determining the right amount of each type of biomass based on the reported sensitivity analysis.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):041804-041804-7. doi:10.1115/1.4039602.

Biofuels derived from cellulosic biomass offer one of the best near- to midterm alternatives to petroleum-based liquid transportation fuels. Biofuel conversion is mainly done through a biochemical pathway in which size reduction, pelleting, pretreatment, enzymatic hydrolysis, and fermentation are main processes. Many studies reveal that biomass particle size dictates the energy consumption in the size reduction. Biomass particle size also influences sugar yield in enzymatic hydrolysis, and biofuel yield in fermentation is approximately proportional to the former enzymatic hydrolysis sugar yield. Most reported studies focus on the effects of biomass particle size on a specific process; as a result, in the current literature, there is no commonly accepted guidance to select the overall optimum particle size in order to minimize the energy consumption and maximize sugar yield. This study presents a comprehensive experimental investigation converting three types of biomass (big bluestem, wheat straw, and corn stover) into fermentable sugars and studies the effects of biomass particle size throughout the multistep bioconversion. Three particle sizes (4 mm, 2 mm, and 1 mm) were produced by knife milling and were pelletized with an ultrasonic pelleting system. Dilute acid method was applied to pretreat biomass before enzymatic hydrolysis. Results suggested 2 mm is the optimum particle size to minimize energy consumption in size reduction and pelleting and to maximize sugar yield among the three particle sizes for big bluestem and wheat straw biomass. Nevertheless, there is no significant difference in sugar yield for corn stover for the three particle sizes.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):041805-041805-9. doi:10.1115/1.4039782.

In order to enhance biogas production in the anaerobic digestion of duckweed, and duckweed with excess sludge as single and mixed substrates, the effects of hot alkali pretreatment and variation of the ratio of substrate to inoculum were investigated. The results showed that the delayed stage of anaerobic gas generation could be shortened when the two substrates were mixed during methane production, to give a cumulative gas yield of 2963 mL, which was 11% higher than the calculated value for the complementary substrate. The methane content was 57%, which was 13% higher than that from the duckweed group and 9% higher than from the excess sludge group. Furthermore, the methane yield was improved by 8% after the duckweed was pretreated with hot alkali. When the substrate to inoculum ratio was 1:1, the maximum biogas production of 3309 mL was achieved, with a methane yield of 1883 mL which, respectively, increases of 151 mL and 304 mL compared with the worst group (1:2.5).

Topics: Biogas , Methane , Proteins
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):041806-041806-18. doi:10.1115/1.4039869.

A large potential is contributed to the energetic utilization of biomass, whereby thermochemical gasification seems to be especially interesting. In order to contribute to a better understanding of the thermochemical conversion process in the gasifier, mathematical models are used. An intensive effort is made in development of mathematical models describing the gasification process and a large number of models, considerably differing in their degree of simplification, and their applications are reported in literature. In the present article, a brief review of models applied, mainly focused on equilibrium models, is provided and a robust and flexible modified stoichiometric equilibrium model, for modeling a novel gasifier, is presented.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2017;140(4):042001-042001-7. doi:10.1115/1.4038383.

Cyclone gasification technology is commonly used for biomass fuels with small particle sizes, such as rice husks and wood chips. This paper explored the effects of gasification intensity and equivalence ratio on the performance characteristics of an autothermal cyclone gasifier. Increasing the gasification intensity caused the syngas' heating value, the cold gasification efficiency and the carbon conversion rate to increase to a maximum for an intensity of 885.24 kg/(m2 h) before then decreasing as the gasification intensity was further increased. Increasing the equivalence ratio from 0.23 to 0.32 increased the overall temperature of gasifier, decreased the tar content (from 6.84 to 4.96 g/N·m3), and increased the carbon conversion rate (from 47.2% to 62.3%). Increasing the equivalence ratio to 0.26 also increased the syngas' heating value to its maximum of 4.25 MJ/N·m3, which then decreased with further increases in equivalence ratio. A similar trend was observed for the gasification efficiency, which ranged from 30% to 37%. From these tests, a gasification intensity of 885.24 kg/(m2 h) and an equivalence ratio of 0.26 appeared optimal for the autothermal cyclone air gasification of biomass process studied here.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2017;140(4):042002-042002-8. doi:10.1115/1.4038406.
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Combustion of biomass and co-combustion with fossil fuels are viable means of reducing emissions in electricity generation, and local biomass resources are appealing to minimize life cycle emissions. In the Rocky Mountain Region of the U.S., a bark beetle epidemic is causing widespread forest death and associated safety hazards. This biomass has potential to be a feedstock resource, thereby achieving dual goals of improving forest health while supplying biomass for uses such as co-firing with coal in power plants. In this study, combustion and co-combustion of healthy pine (HP) and beetle kill pine (BK) with coal were conducted to assess the interchangeability of these feedstocks in raw and torrefied forms. HP and BK pine were torrefied at 200, 250, and 300 °C to increase energy density and improve grindability, both of which aid in seamless integration into power plants. Grindability was assessed for both feedstocks at each torrefaction condition. The raw feedstocks were pyrolyzed to assess their relative compositions. Raw and torrefied feedstocks were then combusted alone and co-combusted with sub-bituminous Powder River Basin coal using thermogravimetric analysis (TGA). Modulated TGA was used to derive kinetic parameters of coal, raw and torrefied biomass, and coal-biomass blends. Results show increased grindability and pyrolysis mass loss of BK as compared to HP, which are attributed to the degraded state of the wood. Combustion and co-combustion show favorable interchangeability of the HP and BK, and additive behavior when co-combusted with coal.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2018;140(4):042003-042003-10. doi:10.1115/1.4039315.

Municipal solid waste (MSW) may be a suitable feedstock for thermochemical conversion. Current technologies process the MSW into refuse-derived fuel (RDF) fluff before conversion. Bench- and pilot-scale densification trials were conducted to determine the parameters required to produce a high quality feedstock from the MSW-RDF material in pellet form. The RDF was densified, as well as the biodegradable (paper and wood) fraction of the RDF stream to compare quality of pellets for the two material compositions. A single pelleting trial was conducted to examine the compaction parameters that would produce high quality pellets: sample material, grind size, moisture content, temperature, and pelleting pressure. It was determined that quality pellets, for both materials, were formed at a grind size of 6.35 mm at 16% moisture under pelleting conditions of 90 °C and 4000 N applied load. Pilot-scale pelleting was then completed to emulate industrial pelleting process utilizing the parameters from the single pelleting trials that were deemed to produce quality pellets. All of the samples produced durable pellets (88–94%), with the ash content around 20%. A techno-economic feasibility study determined that 6.35 mm diameter pellets could be produced for an average cost of $38/Mg, although the aggressive process of the size reduction required indicates that it may not be a technically feasible option.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Energy Resour. Technol. 2018;140(4):044501-044501-5. doi:10.1115/1.4039603.

Biomass is a promising alternative energy source for fossil fuel with the advantages of abundance, renewability, environmental friendliness, etc. This makes the development of biomass technology be of great potential and interesting. The experiments of biomass fast pyrolysis were performed in a microquartz reactor for rice husk (RH), corn stalk (CS) and birch wood (BW), and scanning electron microscope (SEM), energy dispersive spectrometer, and Raman microscope were then applied to analyze the collected chars. The average char yields of RH, CS, and BW pyrolyzed at 800 °C were 29.64%, 18.67%, and 8.64%, respectively. The morphological structures of RH and CS were mainly reserved in chars, while the raw surface textures of BW disappeared during the fast pyrolysis. The silicon concentrations in RH char and CS char were much higher than BW char, and the graphitization degree of CS char was the lowest among the three biomass chars.

Commentary by Dr. Valentin Fuster

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