Torrefaction is a mild pyrolysis, which has been explored for the pretreatment of biomass to increase the heating value and hydrophobicity. Due to its potential applications for making torrefied ...pellets, which can be used as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes, torrefaction and densification have attracted great interest in recent years from both academia and bioenergy industry. This paper provides a comprehensive review of research progresses in this area, drawing on major contributions from two major research groups of the authors on torrefaction and densification at Canada and Taiwan as well as literatures. It is revealed that torrefaction of various biomass species and their major components, lignin, cellulose and hemicelluloses have been extensively studied in thermogravimetric apparatus (TGA) under both inert (N2) and oxidative (O2, H2O) environments to elucidate the weight loss as a function of temperature, particle size and time. It was found that the higher heating value and saturated water uptake of torrefied biomass were a strong function of weight loss, which represents the degree of torrefaction. When torrefied sawdust is compressed into torrefied pellets, more mechanical energy is consumed and higher die temperature is required to make torrefied pellets of similar density and hardness as regular pellets. Simple economics analyses based on laboratory scale experimental data showed that because of the potential savings from pellets transport, handling and storage logistics, the overall cost for torrefied pellets can be lower than regular pellets in European market for both European and Canadian pellets. The gasification could be improved in terms of both energy efficiency and syngas quality because of the removal of oxygenated volatile compounds from torrefied biomass.
Wang et al examine carbon-supported Pt-based alloy electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells. They focus on particle size, shape, and composition ...manipulation, as well as their impact to activity. They provide information on theoretical studies, experimental studies on the control of carbon-supported Pt-alloy particle size, experimental studies on the control of carbon-supported Pt-alloy particle shape, and experimental studies on the control of carbon-supported Pt-alloy composition.
•The characterization methods of electrostatics in fluidized beds are outlined.•Charge generation and distribution phenomena in fluidized beds and the underlying mechanisms are discussed.•The ...interplay between electrostatics and hydrodynamics in fluidized beds is reviewed.•Practical applications of tribocharging fluidized beds are presented.•The CFD simulations of fluidized bed systems including electrostatic charges are compared.
Gas-solid fluidized beds, by their nature, are associated with intense and frequent collisions of solid particles with each other and with the vessel wall, causing tribo-electrification. Accumulation of electrostatic charges in fluidized bed reactors can result in severe problems such as agglomeration, wall fouling, nuisance and hazardous discharge, all reducing the process performance and raising significant safety concerns. Tribo-charging of particles in fluidized beds has also been exploited in a number of useful applications. In this review, the characterization methods of electrostatics and the mechanisms of charge generation and distribution in fluidized beds are presented, followed by an account of the interplay between the hydrodynamics and electrostatic phenomena. Furthermore, techniques of electrostatic charge control in fluidized beds are reviewed, and applications of tribo-electrostatic fluidization systems are summarized. Finally, computational fluid dynamics simulations of the electrostatic effects on the hydrodynamic characteristics of fluidized beds are outlined.
The reduction kinetics of α-Fe2O3 to metallic iron by carbon monoxide at temperatures of 1023 to 1223K was experimentally investigated in a micro fluidized bed reactor with in-situ mass spectrometer ...analysis of product gases. Results indicate that the overall reduction process could be separated into two parts that proceed in series. The first part represents a single-step reaction Fe2O3→Fe3O4 which takes place fast and covers the conversion from 0 to 1/9. The second part represents a two-step reaction Fe3O4→Fe which is a combination of two single-step reactions: Fe3O4→FeO and FeO→Fe that occur in parallel and cover the range of conversions from 1/9 to 1.0. The reduction from Fe2O3 to Fe3O4 can be reasonably described by the first-order reaction model, while the reduction from Fe3O4 to Fe could be described by a parallel reaction model based on Johnson-Mehl-Avrami (JMA) equation. The apparent activation energies for Fe2O3→Fe3O4, Fe3O4→FeO and FeO→Fe were determined as 30.60±0.75 to 52.99±0.78KJ/mol, 52.44±0.10 to 80.83±0.12KJ/mol and 45.74±0.25 to 92.12±0.27KJ/mol, respectively, and were found to increase with increasing CO concentration.
Display omitted
•A micro fluidized bed reactor was used to investigate the reduction of α-Fe2O3.•The reduction of hematite was interpreted as a two-stage process.•The first stage was reasonably analyzed by the first-order reaction model.•The second stage was successfully described by the JMA equation using SPSS.
H2-fed polymer electrolyte membrane fuel cells (PEMFCs) are the most advanced fuel cell technology to date and continue to be of great interest as prospective energy sources in numerous applications, ...including for low/zero-emission electric vehicles, distributed power generators in homes, and small portable electronic devices. However, the commercialization of PEMFC technology has been greatly hindered by certain challenges, mainly the sluggish kinetics of the oxygen reduction reaction at the cathode and the high cost of Pt-based cathode catalysts, the latter presently accounting for over 55% of the total PEMFC cost. To overcome the limited stability of state-of-the-art Pt/C, Pt and Pt-alloy catalysts supported on modified carbon materials have garnered significant interest in recent years. It is therefore timely to compile a review that focuses on Pt and Pt-alloy catalysts supported on modified carbon materials, examining their current R&D status, applications, challenges, and future prospects. This review provides a systematic and comprehensive survey of current Pt and Pt-alloy PEMFC cathode catalysts in terms of materials selection and design, synthesis methods, and structural features, emphasizing how these various aspects relate to the catalysts' physicochemical characterization and performance, and with the aim of shedding light on the future direction of PEMFC research.
A techno-economic assessment was conducted to estimate the capital and operating costs of a hypothetic biofuel system based on hydrothermal liquefaction (HTL) of forest residues in British Columbia. ...Three scenarios were investigated to understand how supply chain designs could influence the system's economic performance. The minimum selling price (MSP) of HTL biofuels was found to be 63%–80% higher than that of petroleum fuels. Converting forest residues to bio-oil and wood pellet before being transported to the conversion facility can lower the variable operating cost but not the MSP of HTL biofuels, due to the considerable increase in capital investment. Processing parameters such as the yield of bio-oil and biofuel can significantly influence the MSP of HTL biofuels, therefore, technology advancement can make great contribution in reducing the production cost. Alternatively, a high carbon tax is needed to make the HTL biofuels competitive with petroleum fuels.
•Techno-economic assessment of HTL biofuel system with three supply chain designs.•Densified forest residues lower variable operating cost but not the minimum fuel selling price.•Carbon tax and technology advancement are needed to make HTL biofuels competitive.•Bio-oil and biofuel yield significantly influence the minimum selling price of HTL biofuels.
Display omitted
•Thermal kinetics of pyrolysis and subsequent in-situ gasification of torrefied biomass pellets were studied.•Both torrefaction and densification treatments delayed the thermal ...decomposition of biomass pellets during pyrolysis.•In-situ gasification reactivity of torrefied pellet char decreased with the increase of torrefaction temperature.•Changed biomass properties by torrefaction and densification led to different pyrolysis/gasification kinetics.
Torrefaction followed by densification improves the heating value, grindability, and logistical treatment efficiency of biomass. Study of the pyrolysis and gasification of torrefied biomass pellets has great significance for the efficient conversion and utilization of biomass. In this study, the thermal behavior and reaction kinetics of pyrolysis and following in-situ CO2 gasification of torrefied corn stalk pellets were investigated in a macro-thermogravimetric analyzer. Torrefaction reduced the amounts of volatiles released during pyrolysis and the maximum pyrolysis rate of pellets decreased with the increase of torrefaction temperature. A three-pseudocomponent model applied for the pellet pyrolysis process suggested that the contribution of hemicellulose reduced as indicated by a decrease in activation energy, while lignin contributed more to the overall kinetics with the increased torrefaction temperature. The gasification of chars after the pyrolysis of torrefied pellets based on the nucleation and growth model indicated that as the torrefaction temperature increased, the gasification reactivity decreased, as implied by the evolutions of pore structures, ash compositions and graphitized crystal structures of the pellet pyrolysis chars. The higher activation energy increased the reaction resistance during the pellet gasification process. The results showed that torrefaction and densification together influenced the reaction behavior, reactivity and overall kinetics of biomass.
► An oxidation torrefaction kinetics model was developed based on TGA data. ► Sawdust was torrefied in a fluidized bed reactor using oxygen-laden combustion flue gases. ► Torrefied sawdust was ...compressed into pellets of properties similar to regular pellets.
Oxidative torrefaction of sawdust with a carrier gas containing 3–6% O2 was investigated in a TG and a fluidized bed reactor, with the properties of the torrefied sawdust and pellets compared with traditional torrefaction without any O2, as well as the dry raw material. It is found that the oxidative torrefaction process produced torrefied sawdust and pellets of similar properties as normally torrefied sawdust and corresponding pellets, especially on the density, energy consumption for pelletization, higher heating value and energy yield. For moisture absorption and hardness of the torrefied pellets, the oxidative torrefaction process showed slightly poor but negligible performance. Therefore, it is feasible to use oxygen laden combustion flue gases as the carrier gas for torrefaction of biomass. Besides, torrefied sawdust can be made into dense and strong pellets of high hydrophobicity at a higher die temperature than normally used in the production of traditional control pellets.
The ash content of biomass has some negative impacts on the efficient utilization of biomass for the production of value-added products. In this paper, the techniques of ash removal from Mountain ...Pine Beetle (MPB) killed pine bark and switchgrass were examined systematically. Size fractionation was found to be effective for ash removal not only for the heterogeneous switchgrass but also for the homogeneous pine bark. Inorganic constituents of untreated samples and treated samples showed that leaching by water and four dilute acid solutions was effective in removing most of ash from both biomass samples. The inorganic element distributions in ash of pine bark samples before and after the acid leaching showed that substantial reductions were achieved in different main elements, Al (66%), Ca (90%), Fe (66%), K (92%), Mg (98%), Na (100%) and S (25%). For switchgrass, most of the element concentrations were reduced by water leaching because of its high content of water-soluble metals in the ash. For the purpose of practical applications of the two types of biomass, especially the underutilized pine barks, different leaching methods should be evaluated to identify the most suitable method for the removal of inorganic constituents.
► Fractionation could remove up to 20% ash content from both heterogeneous switchgrass and homogeneous pine bark samples. ► Water leaching could remove up to 40% ash content for switchgrass because of its high content of water-soluble inorganic constituents. ► Water leaching was ineffective in reducing ash content from pine bark because of its low content of water-soluble inorganic constituents. ► Leaching by dilute acid solutions removed most organic constituents from both bark and switchgrass.
Oxidation–reduction reaction pathways at the carbon/catalyst junction during CO2 co-gasification. Display omitted
•Ash minerals have two-fold effects on biomass/fossil fuels co-gasification ...kinetic.•For low potassium contents, inhibitory effect was observed during co-gasification.•For K/Al>1M ratios, biomass enhanced coal gasification significantly.•Biomass rich in minerals and fossil fuels poor in aluminosilicates are recommended.
Recent environmental regulatory sharp curbs on fossil fuel power plants have obliged industries to incorporate alternative sources of fuels for energy production. Cost and recovery of synthetic catalysts are major challenges in carbonaceous materials catalytic gasification. Biomass rich in alkali metals can be added as fuel and also to provide inexpensive natural catalysts to boost fossil fuel gasification. Biomass/fossil fuel co-gasification could provide bridging energy production based on renewable and fossil fuels. In this work, CO2 co-gasification of switchgrass and sawdust with coal and fluid coke was conducted in a thermogravimetric analyzer. Gasification kinetics were inhibited or enhanced, depending on the potassium concentration in the mixture. For low K/Al and K/Si molar ratios, the coal ash sequestered the biomass potassium needed for KAlSiO4 formation, and thus, no catalytic effect was observed until the biomass-to-coal mass ratio reached 3:1, where the switchgrass ash supplied enough potassium to more than satisfy the minerals in the coal ash. For high K/Al and K/Si molar ratios, unreacted residual potassium acted as catalyst, enhancing coal gasification. Fluid coke contained much lower Al and Si than for the coal. Hence, the gasification kinetics of fluid coke were significantly augmented by blending the coke with switchgrass due to the abundance of potassium in the biomass.
PDF
