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

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.

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

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