Fast microflow kinetics and acid catalyst deactivation in glucose conversion to 5-hydroxymethylfurfural

Application of multiple swirl burners in pilot-scale entrained bed gasifier for short residence time

CFD modelling of supercritical water reforming of glycerol for hydrogen production

On 10 November 2018, during the RELAMPAGO field campaign in Argentina, South America, a thunderstorm with supercell characteristics was observed by an array of mobile observing instruments, including three Doppler on Wheels radars. In contrast to the archetypal supercell described in the Glossary of Meteorology, the updraft rotation in this storm was rather short lived (~25 min), causing some initial doubt as to whether this indeed was a supercell. However, retrieved 3D winds from dual-Doppler radar scans were used to document a high spatial correspondence between midlevel vertical velocity and vertical vorticity in this storm, thus providing evidence to support the supercell categorization. Additional data collected within the RELAMPAGO domain revealed other storms with this behavior, which appears to be attributable in part to effects of the local terrain. Specifically, the IOP4 supercell and other short-duration supercell cases presented had storm motions that were nearly perpendicular to the long axis of the Sierras de Córdoba Mountains; a long-duration supercell case, on the other hand, had a storm motion nearly parallel to these mountains. Sounding observations as well as model simulations indicate that a mountain-perpendicular storm motion results in a relatively short storm residence time within the narrow zone of terrain-enhanced vertical wind shear. Such a motion and short residence time would limit the upward tilting, by the left-moving supercell updraft, of the storm-relative, antistreamwise horizontal vorticity associated with anabatic flow near complex terrain.

Event Abstract Back to Event Evolution of tensile properties of UHMWPE after short residence times in the melt state followed by high pressure molding Beatrice Yeung1, Pierangiola Bracco2, Thomas S. Thornhill1 and Anuj Bellare1 1 Brigham & Women's Hospital, Harvard Medical School, Department of Orthopedic Surgery, United States 2 University of Turin, Department of Chemistry, Italy Introduction: Consolidation of ultra-high molecular weight polyethylene (UHMWPE) powder during molding has received considerable attention due to damage associated with incomplete UHMWPE fusion in total joint replacement prostheses components [1],[2]. In this study, we studied the early stage fusion of UHMWPE powder in the melt state using a unique high pressure process that enables the polymer to be maintained in the melt state for very short times. Figure 1 outlines the phase diagram of polyethylene and the path taken to enable UHMWPE to reside in the melt state for specific time intervals. This is possible since the polymer enters the melt state isothermally via depressurization at elevated temperature compared to conventional compression molding wherein melting occurs via increase in temperature at moderate pressures, which is a slow process due to the low thermal conductivity of UHMWPE. We measured the tensile properties of the resulting UHMWPE to evaluate fusion of the consolidated polymer. Materials and Methods: GUR 1020 UHMWPE powder (Celanese, Oberhausen, Germany) was compression molded at 180˚C and 10 MPa pressure for 2 hours, and served as the control. A high pressure cell was used to apply 300 MPa pressure to the UHMWPE powder, heated to 180˚C, depressurized and maintained in the melt state for 5, 30 and 60 minutes respectively (HP-5min, HP-30min and HP-60min, respectively), re-pressurized to 300 MPa, cooled and depressurized. ASTM 638 type V specimens were prepared (n=5) and subjected to tensile testing at 10mm/min crosshead speed. The tensile modulus, yield stress, maximum strain and tensile strength were measured. A Differential scanning calorimeter (DSC) was used to measure the degree of crystallinity using a heat of fusion of 293 J/g (n=3). Results: DSC revealed a crystallinity of 53.1 ± 0.9%, 66.4 ± 0.3%, 71.1 ± 3.3%, 71.5 ± 2.5% and 70.0 ± 1.8% for Control UHMWPE, UHMWPE powder, HP-5min, HP-30min and HP-60min, respectively. There was no statistically significant difference in crystallinity for the HP UHMWPEs (p>0.05, ANOVA). The tensile modulus of the Control UHMWPE was approximately three times lower than those of the HP group (see Table 1). The HP UHMWPEs also had a higher yield stress and UTS compared to the Control but there was no statistically significant difference among the HP UHMWPEs. The maximum strain of HPE-5min and HP-10min was significantly lower than that of the Control but this was not the case for HP-60min. Discussion: This study showed that it took 60 minutes of melt fusion for the maximum strain of UHMWPE to attain a value close to that of the control, in which the polymer resided in the melt state for 2 hours. Such a rapid evolution of tensile properties indicates that co-crystallization of polymer chains across powder boundaries must play a significant role in consolidation since diffusion of chains across powder boundaries would likely take several hours to days. The study also shows that high pressure molding provided a high modulus UHMWPE with high yield stress, tensile strength and comparable maximum strain at 60 minutes of residence time in the melt state. Conclusions: The fusion of UHMWPE resin powder in the melt state results in rapid evolution of tensile properties during high pressure molding providing a UHMWPE with high tensile properties compared to conventional molding. Figure 1. Phase diagram of polyethylene indicating processing route. Table 1. Tensile properties of UHMWPEs

Biomass and sewage sludge are attracting increasing interest in power plant technology as a source of carbon dioxide-neutral fuels. A new way to reduce the consumption of fossil fuels could be the co-combustion or co-gasification of coal and biomass or coal and sewage sludge. In both cases, pyrolysis is the first step in the technical process. In order to obtain detailed information about the pyrolysis of coal/biomass and coal/sewage sludge mixtures as well as unblended fuels, the ‘Institut für Verfahrenstechnik und Dampfkesselwesen (IVD)’ at the University of Stuttgart has carried out investigations using an electrically heated entrained flow reactor. One application of substitution of fossil fuels could be the utilization of pyrolysis gas or gas generated in a gasification process as a reburn fuel in conventional boilers fired with fossil fuels. Investigation showed that generated gas from coal, biomass and sewage sludge pyrolysis and gasification have high NOx reduction efficiencies compared to methane or low calorific gases using it as a reburn fuel in coal fired boilers. In order to take advantage of this pretreatment process the release of organic as well as of mineral compounds during the pyrolysis or gasification has to be investigated. For coal pyrolysis and gasification the reactions are known since there was a lot of research all over the world. Biomass or sewage sludge have other structures compared to fossil fuels and contain alkali, chlorine and other problematic compounds, like heavy metals. The release of those elements and of the organic matter has to be investigated to characterize the gas and the residual char. The optimum process parameters regarding the composition of the generated gas and the residual char have to be found out. The IVD has studied the co-pyrolysis of biomass and sewage sludge together with a high volatile hard coal. The main parameters to be investigated were the temperature of the pyrolysis reactor (400°C–1200°C) and the coal/biomass and coal/sewage sludge blends. Besides co-pyrolysis experiments test runs with unmixed main fuels were carried out with the hard coal, straw as biomass, and a sewage sludge. It was expected that the high reactivity of biomass and sewage sludge would have an effect on the product composition during co-pyrolysis. The test runs provided information about fuel conversion efficiency, pyrolysis gas and tar yield, and composition of pyrolysis gas and tar. Besides gas and tar analysis investigations regarding the path of trace elements, like heavy metals, alkali, chlorine and nitrogen components, during the pyrolysis process varying different parameters have been carried out. The fuel nitrogen distribution between pyrolysis gas, tar and char has been analyzed as well as the ash composition and thus the release of mineral components during pyrolysis. Increasing reaction temperatures result in a higher devolatilization for all fuels. Biomass shows a devolatilization of up to 80% at high temperatures. Hard coal shows a weight toss of approx. 50% at same temperatures. Sewage sludge devolatilizes also up to 50%, which is nearly a total release of organic matter, because of the high ash content of about 50% in sewage sludge. Gaseous hydrocarbons have a production maximum at about 800°C reaction temperature for all feedstocks. Carbon monoxide and hydrogen are increasingly formed at high pyrolysis temperatures due to gasification reactions. Mineral elements are released during straw pyrolysis, but within the hot gas filtration unit further recombination reactions and condensation of elements on panicles take place. There is no release of mineral elements during sewage sludge pyrolysis and only a slight release of heavy metals at high pyrolysis temperatures. The effect of co-pyrolysis depends on the feedstocks used in association with the panicle size. The co-pyrolysis test runs showed that a synergetic effect exists when using sewage sludge and hard coal. There is a higher char production related to the unmixed fuels; gas and tar formation are lowered. Co-pyrolysis test runs with biomass and coal did not show this effect on the pyrolysis products. Reasons for this behaviour could be a difference in particle size and material structure which influences the devolatilization velocity of the fuels used or the relatively short residence time in the entrained flow reactor. It seems possible that coal pyrolysis is influenced by the reaction atmosphere, generated in co-pyrolysis. In the co-pyrolysis of coal and sewage sludge, the sludge degases much faster than coal because of the structure of sewage sludge and its small panicle. The coal pyrolysis taking place afterwards in the reaction tube occurs in a different atmosphere, compared to the mono-pyrolysis experiments. The devolatilization of coal in the co-pyrolysis experiments together with straw was not disturbed by the gaseous products of straw pyrolysis, because the large straw particles showed a delayed degasing compared to the coal particles.

Particle Size Distribution and yield control in continuous Plug Flow Crystallizers with recycle

In a real gas turbine the fluid dynamics and the thermal conditions that prevail in the hot gas path and near hot parts walls are rather complex. This type of machine features indeed a very specific set of operating conditions, including: high gas temperatures and velocities, complex gas streamlines combined with a wide range and fast variability of operation load. The artifacts caused by internal cooling devices and thermal barriers or anti-corrosion coatings add to this complexity. For these reasons, predicting the fate of ash particles approaching or impinging a hot part represents a real challenge. In addition the particular conditions that prevail in the combustors, especially: the pressurized and very oxidizing flames, the high temperature but short residence time, make the chemistry of ash formation fairly complex as well. A work recently undertaken by GE Energy and LERMPS shows that HVOF (High Velocity Oxy-Fuel) facilities represent interesting tools to simulate the “in-flame generation” of ash particles and their fate when impinging on a part wall, provided the test conditions, especially the thermal and velocity fields, are properly adjusted and controlled. The paper summarizes the development of HVOF experiments specifically devised to study the formation of ash particles with controlled chemistry and their deposition onto hot parts.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

Reaction pathways of glucose during esterification: Effects of reaction parameters on the formation of humin type polymers

The overall scope of this project is to monitor the free radicals during coal depolymerization under SRC-II preheater/reactor conditions. Understanding the nature and behavior of the free radicals may not only provide significant mechanistic information for the depolymerization of coal, but it could also impact the design of coal liquefaction processes. Our uniquely designed apparatus will allow us to monitor free radicals and how they are affected by, among others, short residence times, temperature and pressure changes. All components of Task I have been completed successfully. Specifically, an experimental design for Task II (screening of main process variables) has been developed; a detailed experimental procedure for obtaining data at high pressures and high temperatures has been developed; and the scheme to separate reacted coal has been outlined and tested. As part of the special cavity testing and development of experimental procedure, it was determined that data can be obtained 3 to 4 minutes after the initiation of the heating process to achieve a high temperature (450/sup 0/C). Thus, we expect that we will be able to gain significant information on free radical formation and behavior within the first several minutes of subjecting coal to high temperatures and pressures. The free radical concentration can be measured to +-20%. Preliminary results indicate that some of the process variables may cause several-fold changes in the free radicals. A new Varian Associates instrument has been purchased to carry out this work. The next phase of the work will involve the investigation of temperature and pressure effects, heating rate changes, short residence times and the use of process derived solvent.

Low temperature and long residence time pretreatments have been proposed as an alternative to conventional pretreatments within a centralized biorefinery, allowing for a decentralized pretreatment without high energy costs. Ammonia fiber expansion (AFEX™) pretreatment may be uniquely suitable for decentralized pretreatment, and this study considers the possibility of decreasing the temperature in AFEX pretreatment of corn stover. AFEX pretreatment at 40°C and 8 h produced comparable sugar and ethanol yields as conventional AFEX pretreatment at high temperatures and short residence time during subsequent hydrolysis and fermentation. Increasing the ammonia loading at these temperatures tends to increase digestibility, although the moisture content of the reaction has little effect. This study suggests a greater flexibility in AFEX pretreatment conditions than previously thought, allowing for an alternative approach for decentralized facilities if the economic conditions are appropriate.

NO2-promoted oxidation of methane to formaldehyde at very short residence time. Part I: Experimental results

Hyporheic exchange flows were simulated using MODFLOW and MODPATH to estimate relative effects of channel morphologic features on the extent of the hyporheic zone, on hyporheic exchange flow, and on the residence time of stream water in the hyporheic zone. Four stream reaches were compared in order to examine the influence of stream size and channel constraint. Within stream reaches, the influence of pool‐step or pool‐riffle sequences, channel sinuosity, secondary channels, and channel splits was examined. Results showed that the way in which channel morphology controlled exchange flows differed with stream size and, in some cases, with channel constraint. Pool‐step sequences drove hyporheic exchange in the second‐order sites, creating exchange flows with relatively short residence times. Multiple features interacted to drive hyporheic exchange flow in the unconstrained fifth‐order site, where pool‐riffle sequences and a channel split created exchange flows with short residence times, whereas a secondary channel created exchange flows with long residence times. There was relatively little exchange flow in the bedrock‐constrained fifth‐order site. Groundwater flow models were effective in examining the morphologic features that controlled hyporheic exchange flow, and surface‐visible channel morphologic features controlled the development of the hyporheic zone in these mountain streams.

Collisions, adsorption and self diffusion of gas in nanometric channels by molecular dynamics and stochastic simulation and the case of helium gas in graphitic slit pore

Study on formation mechanism of three types of carbon nanoparticles during ethylene pyrolysis in thermal plasmas