Steam‐air blown bubbling fluidized bed biomass gasification (BFBBG): Multi‐scale models and experimental validation

During fluidized bed biomass gasification, complex gas‐solid mixing patterns and numerous chemical and physical phenomena make identification of optimal operating conditions challenging. In this work, a parametric experimental campaign was carried out alongside the development of a coupled reactor network model which successfully integrates the individually validated sub‐models to predict steady‐state reactor performance metrics and outputs. The experiments utilized an integrated gasification system consisting of an externally‐heated, bench‐scale, 4‐in., 5 kWth, fluidized bed steam/air blown gasifier fed with woody biomass equipped with a molecular beam mass spectrometer to directly measure tar species. The operating temperature (750–850°C) and air/fuel equivalence ratio (ER = 0–0.157) were independently varied to isolate their effects. Elevating temperature is shown to improve the char gasification rate and reduce tar concentrations. Air strongly impacts the composition of tar, accelerating the conversion of lighter polycyclic‐aromatic hydrocarbons into soot precursors, while also improving the overall carbon conversion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1543–1565, 2017     

Photochemical free-volume generation in poly(methyl methacrylate) photoresists

The dissolution rates of poly(methyl methacrylate) [PMMA] thin films on quartz substrates are studied by a combination of laser interferometry and fluorescence quenching methods. In this way one can monitor the penetration, rate of the solvent (2-butanone, 2-pentanone) into the film. When these films were prepared containing 2 to 8 percent Meldrum's diazo (1) as a dopant, the dopant acted as a mild retarder of film dissolution. Upon irradiation at 254 nm, 1 is converted to CO, N₂ + acetone, and this process leads to a pronounced acceleration' of the PMMA film dissolution rate.     

环氧丙烯酸树脂的合成及其改性

采用丙烯酸(AA)对环氧树脂(EP)进行光活性改性制备环氧丙烯酸树脂(EA),通过单因素试验法优选出制备EA的最佳反应条件。结果表明:制备EA的最佳反应条件是以N′N-二甲基苯胺为催化剂,w(催化剂)=2.5%(相对于反应物总质量而言);以对苯二酚为阻聚剂,w(阻聚剂)=0.1%(相对于反应物总质量而言);反应温度为90℃,反应时间为2.0～3.5h。当w(引发剂)=1.0%时,EA的固化性能较好。采用多元醇先对EP进行改性,然后再进行光活性改性,可明显降低产物的黏度。     

马来松香/SiO2杂化材料的研究

采用溶胶-凝胶法,以正硅酸乙酯（TEOS）为原料,制备硅溶胶;松香与马来酸酐熔融加成反应,生成马来松香;在对甲苯磺酸催化作用下,硅溶胶与马来松香发生酯化反应,生成马来松香／SiO2杂化材料。产物酸值较松香明显降低;FT-IR结果表明,其组份间以Si-O-C键键合;XRD结果表明,其为非晶态;DSC结果表明,其玻璃化转变温度㈣随着SiO2含量的增大而上升。     

Stability of Y-Ti-O nanoparticles during laser deposition of oxide dispersion strengthened steel powder

This study investigated the feasibility of a direct energy deposition process for fabrication of oxide dispersion strengthened steel cladding. The effect of the laser working power and scan speed on the microstructural stability of oxide nanoparticles in the deposition layer was examined. Y-Ti-O type oxide nanoparticles with a mean diameter of 45 nm were successfully dispersed by the laser deposition process. The laser working power significantly affected nanoparticle size and number density. A high laser power with a low scan speed seriously induced particle coarsening and agglomeration. Compared with bulk oxide dispersion strengthened steel, the hardness of the laser deposition layer was much lower because of a relatively coarse particle and grain size. Formation mechanism of nanoparticles during laser deposition was discussed.     

COMPARISON OF EXPERIMENTAL AND MODELLING STUDIES FOR THE MICROWAVE DRYING OF IRONBARK TIMBER

Temperature profiles through boards during the microwave-assisted drying of Australian Ironbark timber have been investigated in this work in order to explore evidence for timber degrade via “charring” at internal temperatures below those required for pyrolysis (Brooke et al., 1998). A previously published model (Turner and Jolly, 1990a) describing one-dimensional microwave power absorption, based on the solution of Maxwell's equations, has been reviewed and significant limitations identified and overcome. Improvements included the use of a linear-mixing approach for the dielectric constants, the incorporation of temperature and moisture dependencies for these dielectric properties and the inclusion of diffusion within an overall system model. A control-volume technique has been used for predicting both moisture and temperature distributions within the timber, with a second-order finite-difference method being used to solve Maxwell's equations. The final model showed     

THE ELECTRODEWATERING OF SEWAGE SLUDGES

Electrodewatering (EDW), the enhancement of conventional pressure filtration by an electric field, is an emerging technology with the potential to improve dewatering especially for difficult materials. CSIRO has many years of experience in EDW, ranging from bench scale tests to demonstration trials. A recent programme has investigated the applicability of EDW to aerobic wastewater treatment sludges which are particularly difficult to dewater using conventional equipment.

The bench scale filtration experiments produced cakes with solids contents of 35-46 wt% using EDW, compared with 24-30 wt% using pressure filtration alone. This paper : • describes how the dewatering results were achieved;

•identifies a relationship between moisture removal limits by EDW and the forms of water within the sludge;

•shows the results of preliminary attempts to mathematically model the EDW process     

Evolution of Microstructure and Mechanical Properties of Oxide Dispersion Strengthened Steels Made from Water-Atomized Ferritic Powder

Nano-structured oxide dispersion strengthened (ODS) steels produced from a 410L stainless steel powder prepared by water-atomization was studied. The influences of Ti content and milling time on the microstructure and the mechanical properties were analysed. It was found that the ODS steels made from the Si bearing 410L powder contained Y–Ti–O, Y–Ti–Si–O, Y–Si–O, and TiO₂ oxides. Most nanoparticles produced after 80 h of milling were aggregated nanoparticles; however, after 160 h of milling, most aggregated nanoparticles dissociated into smaller individual nanoparticles. Perfect mixing of Y and Ti was not achieved even after the longer milling time of 160 h; instead, the longer hours of milling rather resulted in Si incorporation into the Y–Ti–O rich nanoparticles and a change in the matrix morphology from an equiaxed microstructure to a tempered martensite-like microstructure. The overall micro-hardness of the ODS steel increased with the increase of milling time. After 80 and 160 h, the microhardnesses were over 400 HV, which primarily resulted from the finer dispersed nanoparticles and in part to the formation of martensitic phases. Tensile strength of the 410L ODS steels was comparable with that of ODS steel produced from gas-atomized powder.     

Effective parameter estimation within a multi-dimensional population balance model framework

This study considers optimization problems with multi-dimensional population balance models embedded. The objective function is formulated as a least-squares problem, minimizing the difference between target data and simulated model output and the goal is to find model parameter values that best fit the data. Results show that derivative-free methods, such as the Nelder–Mead simplex method, fail to converge to an optimal solution. A similar result was obtained with gradient-based methods such as BFGS, quasi-Newton, Newton, Gauss–Newton, Levenberg–Marquardt and SQP, and with a stochastic genetic algorithm. It was hypothesized that three main issues could contribute to these convergence failures: (1) gradients were calculated based on finite differences, and as a result of improper step size determination, the numerical error could be prohibitive resulting in inaccurate derivative information, (2) the parameters may not be identifiable and (3) numerical instability could occur during the course of optimization. To circumvent these issues, this work addresses the calculation of derivative information based on automatic differentiation and sensitivity analysis to ensure increased accuracy. Issues such as parameter identifiability are also dealt with by analyzing an accurate Fisher information matrix. Given the computational burden in calculating accurate Jacobians and Hessians, compounded by the potential nonsmoothness introduced into the objective function as a result of granule nucleation, other optimization strategies may be warranted and this work addresses those accordingly. Overall, by systematically assessing the problem formulation and mechanisms, the results show that substantial improvements in convergence can be achieved by utilizing appropriate optimization techniques, thus leading to more successful and optimal parameter estimation.     

Ferroelasticity in a metal–organic framework perovskite; towards a new class of multiferroics

A metal–organic framework perovskite, [(CH₂)₃NH₂][Mn(HCOO)₃], exhibits a weakly first order ferroelastic phase transition at ～272 K, from orthorhombic Pnma to monoclinic P2₁/n, and a further transition associated with antiferromagnetic ordering at ～8.5 K. The main structural changes, through the phase transition, are orientational ordering of the azetidium groups and associated changes in hydrogen bonding. In marked contrast to conventional improper ferroelastic oxide perovskites, the driving mechanism is associated with the X-point of the cubic Brillouin zone rather than being driven by R- and M-point octahedral tilting. The total ferroelastic shear strain of up to ～5% is substantially greater than found for typical oxide perovskites, and highlights the potential of the flexible framework to undergo large relaxations in response to local structural changes. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show some of the characteristic features of ferroelastic materials. In particular, acoustic dissipation below the transition point can be understood in terms of mobility of twin walls under the influence of external stress with relaxation times on the order of ～10^?7 s. Elastic softening as the transition is approached from above is interpreted in terms of coupling between acoustic modes and dynamic local ordering of the azetidium groups. Subsequent stiffening with further temperature reduction is interpreted in terms of classical strain–order parameter coupling at an improper ferroelastic transition which is close to being tricritical. By way of contrast, there are no overt changes in elastic or anelastic properties near 9 K, implying that any coupling of the antiferromagnetic order parameter with strain is weak or negligible.