High Feed Flow Rate Research Articles

Hydrogen Production by Methanol Reforming in Supercritical Water: Suppression of Methane Formation

The reforming of methanol is carried out in supercritical water at 276 bar and 700 °C to produce H2 along with CO, CH4, and CO2. The reactions are catalyzed by the wall of the tubular reactor made of Inconel 600, which is an alloy of Ni, Cr, and Fe. Experiments are conducted to study the effects of the pressure, residence time, and steam-to-carbon ratio on the H2 yield. The residence time is varied by changing the length of the reactor as well as the feed flow rate. Both the experimental results and equilibrium calculations show that, as the pressure is increased, methanation of CO and CO2 takes place, resulting in a loss of H2. In addition, the methane formation is favored at a high residence time and low steam-to-carbon ratio. In this study, the following three strategies are proposed for the suppression of methane formation during the production of H2 from methanol in supercritical water: (1) operation at a low residence time by having a small reactor length or a high feed flow rate; (2) addition of a small amount of K2CO3 or KOH in the feed; (3) utilization of the surface catalytic activity of the reactor made of Ni−Cu alloy. All three of these strategies resulted in a significant reduction in the methane formation and corresponding enhancement in the H2 production.

Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment

Filtration performance and fouling of nanofiltration (NF) and reverse osmosis (RO) membranes in the treatment of dairy industry wastewater were investigated. Two series of experiments were performed. The first one involved a NF membrane (TFC-S) for treating the chemical-biological treatment plant effluents. The second one used a RO membrane (TFC-HR) for treating the original effluents from the dairy industry. The permeate flux was higher at higher transmembrane pressures and higher feed flowrates. The curves of permeate flux exhibited a slower increase while the feed flowrate decreased and the pressure increased. Membrane fouling resulted in permeate flux decline with increasing the feed COD concentration. Furthermore, the flux decline due to the COD increase was found higher at higher pressures for both NF and RO membranes.

Combating Deactivation in Methane Non-Oxidative Dehydrocyclization via Hydrogen Feed Pulsing

The non-oxidative dehydrocyclization of methane was carried out over Ru–Mo/HZSM-5 catalyst in a fixed-bed catalytic reactor between 873 and 973 K. The catalyst, prepared by incipient wetness co-impregnation, was highly selective towards benzene production. The formation and deposition of low-H/C carbonaceous species was found to be more important at high temperatures and high methane space velocities. Intermittent hydrogenation of the catalyst by periodically switching from CH4 stream to pure hydrogen in the feedstream contributed significantly to the regeneration of active sites through hydrogenation of the carbonaceous species. Coke removal from the catalyst during H2 exposure was confirmed through temperature programmed oxidation and mass spectrometry analyses of spent catalyst. Alternating sequences of dehydrocyclization and hydrogenation under moderate and high feed flow rates resulted in improving catalyst stability due to efficient reduction of coke formation. These results might suggest an option for maintaining relatively high catalyst activity towards benzene production for prolonged reaction times.

Comparing and Modeling the Dehydrogenation of Ethanol in a Plug-Flow Reactor and a Pd−Ag Membrane Reactor

In this study the performance of a membrane reactor was compared to that of a plug-flow reactor for the dehydrogenation of ethanol. The membrane consisted of a 2.2 μm Pd-Ag film (23 wt% Ag) deposited on the inside of an asymmetric α-alumina membrane tube (SCT). The membrane tube was packed with a 14.5 wt% Cu on SiO 2 catalyst. The effects of the sweep gas flow rate, the ethanol feed flow rate, and the temperature on acetaldehyde yield and selectivity were investigated. A model was developed using measured kinetic data and membrane permeance data to predict the performance of the membrane reactor. The membrane reactor performed significantly better than the plug-flow reactor at all temperatures tested. The best results were obtained at 275°C, where the total ethanol exit conversion increased from 45% (plug-flow reactor) to 60% at low feed flow rates and from 36% to 46% at high feed flow rates. The acetaldehyde selectivity for the membrane reactor increased from the lower 80% range to above 90% at 275°C. The model underpredicted the total ethanol conversion, indicating that the measured reaction rate parameters for a differential reactor were lower than those for the membrane reactor.

Pervaporation dehydration of ethanol–water mixtures with chitosan/hydroxyethylcellulose (CS/HEC) composite membranes: I. Effect of operating conditions

Composite hydrophilic pervaporation membranes were prepared from chitosan blended with hydroxyethylcellulose using cellulose acetate as a porous support. The membranes were tested for dehydration performance of ethanol–water mixtures of ethanol concentrations 70–95 wt.% in the laminar flow region, at temperatures 50–70°C and at permeate pressures of 3–30 mmHg. The composite membrane showed an improved dehydration performance compared with dense CS/HEC membrane developed earlier. The effects of operating conditions also revealed that pervaporation of low water content feed carried out at high feed flow rate and at low temperature and permeate pressure was an advantage.

Air Separation by a Small-Scale Two-Bed Medical O2 Pressure Swing Adsorption

A small-scale two-bed six-step pressure swing adsorption (PSA) process using zeolite 13X was performed to provide oxygen-enriched air in the medical system. The binary mixture N2/O2 (79/21 vol %) was used for PSA experiments. Cyclic behaviors of the PSA process were investigated from unsteady- to steady-state conditions. Also, effects of various operating parameters on the PSA performance such as the P/F ratio, adsorption pressure, feed flow rate, and adsorption step time were investigated experimentally under the nonisothermal condition. The effect of the P/F ratio was noticeably changed according to the adsorption pressure and feed flow rate conditions. The higher the adsorption pressure, the slower the increasing rate of purity and the higher the decreasing rate of recovery. However, as the adsorption pressure became higher, the effect of the P/F ratio on the O2 purity became smaller. Furthermore, the effect of adsorption pressure on the O2 purity and recovery was diminished gradually to the increase of the P/F ratio. The feed flow rate also had a strong effect on the O2 purity. As for the product purity, the low feed flow rate began to lose its advantage with an increase in the P/F ratio. The recovery and productivity at a high feed flow rate was higher than those at a low feed rate even under the high product purity region. The dominant operating factor to determine the O2 purity was changed from the adsorption pressure to the feed flow rate as the P/F ratio was changed from low to high values. The modified linear driving force (LDF) model similar to a solid-diffusion model predicted the transition behavior of the cyclic process better than the LDF model.

00/03361 Development and application of a generalised steady-state electrochemical model for a PEM fuel cell

The surface adsorption effect of CO on the hydrogen permeability of a 12.5 micron-thick Pd77Ag23 membrane has been evaluated quantitatively under experimental conditions close to the operating conditions of the highly-efficient membrane reformer (MRF) system developed by Tokyo Gas. The permeability of the membrane was measured in the conditions of CO concentration between 1 and 5 vol.% at a temperature and pressure of up to 500 °C and 0.6 MPa, respectively. High feed flow rates and a microchannel module configuration were applied in the flux measurements to ensure that the results are obtained with limited influence of concentration polarization adjacent to the membrane surface and hydrogen depletion along the microchannel length. While the CO inhibition effect was close to negligible at 500 °C, it was significant at lower temperatures. At a feed pressure of 0.2 MPa, the CO inhibition effect was only 0.2% at a CO concentration of 1 vol.% and the effect was 3.6% at a CO concentration of 5 vol.% at 500 °C. The CO inhibition effect were 3.4% for 1 vol.% CO and 14.1% for 5 vol.% CO at 400 °C. Measurements were also carried out at a high feed pressure of 0.6 MPa to evaluate the pressure dependence of the CO inhibition effect. The CO inhibition effect decreased to 0.7% at a CO feed concentration of 5 vol.% at 500 °C. Lower CO inhibition effect were also observed at 450 and 400 °C compared to the data obtained with the feed pressure of 0.2 MPa, while the inhibition levels were almost the same at 350 °C. Though the CO inhibition effect is larger at a lower feed pressure of 0.2 MPa, the effect was only 0.2% at 1 vol.% CO at 500 °C, which is close to the operating conditions of the MRF system. This study quantitatively revealed that the CO inhibition effect on hydrogen flux is extremely small when the membrane is operated at temperatures equal to or higher than 500 °C, even for state-of-the-art thin membranes. The performance of the Tokyo Gas MRF seems thus mainly limited by concentration polarization effects.

Separation Characteristics of Ternary Gas Mixtures in Serial Cells of Polysulfone Hollow Fibre Membranes

Separation characteristics of CO 2 , O 2 , and N 2 gas mixtures are measured in a series configuration of hollow fibre polysulfone membranes. One, two, and three separation cells in series are used in the experiments and are operated in the counter current mode. The measurements are performed as a function of the reject flow rate and pressure. Measured data are compared against predictions of the countercurrent flow model. Measurements and analyses include variations in the stage cut as well as species permeance, removal, recovery, permeate enrichment, and reject depletion. Measurements and model predictions are closely matched with percentage errors of less than 10%. Operation with three cells in series results in larger stage cuts and higher species recovery in the permeate stream. This is associated with lower purity in the permeate and reject streams. The highest permeate enrichment is found for the permeate stream in the first cell for the two and three cells system. This is caused by the constant reject flow used in various configurations. As a result, higher feed flow rates are used for the two and three cells in series, which reduces the gas residence time in the first cell and makes separation more selective.

Modeling of Degradation of Solutions Containing Nitrogen and Carbon Compounds in Aerated Submerged Fixed-Film (ASFF) Bioreactors

The biodegradation reaction rates of waste-water solutions containing nitrogen and carbon compounds were studied in an aerated submerged fixed film (ASFF) reactor with four compartments. A solution containing sucrose (carbon source) and ammonium chloride (nitrogen source) was considered in this study. The kinetic models considered in the analysis were the variable order model and the Monod model. Measurements and analysis were performed as a function of organic and hydraulic loading for the reactor. Analysis of the kinetic data was carried out in the first compartment and in the combined section of the reactor which included the second, third, and fourth compartments. The reaction order for carbon removal in the first compartment was found to vary over a range of 1–2 and drops to a range of 0.7–1.2 in the combined section. Lower reaction orders were obtained for nitrogen removal which varied from 0.6–1 in the first compartment and the combined section. Upon application of the Monod model for the two reactions, similar trends to those of the variable order model were obtained for carbon and nitrogen removal in both sections of the reactor. The calculated Monod constants for carbon removal were one to two orders of magnitudes larger than those for nitrogen removal. Measured removal rates of carbon in the first compartment were two orders of magnitudes higher than the nitrogen removal rates in the same compartment. However, the removal rates of both components are comparable in the combined section, especially at high feed flow rates. This behaviour was consistent with literature data on simultaneous removal of carbon and nitrogen compounds, where high concentrations of carbon resulted in severe reduction in the removal rates of nitrogen compounds.

A Model for Continuous Foam Concentration of Proteins: Effects of Kinetics of Adsorption of Proteins and Coalescence of Foam

Abstract A model for concentration of proteins from dilute solutions in a continuous foam fractionation column is proposed. This model accounts for (1) kinetics of adsorption of proteins in the liquid pool as well as in the foam, (2) liquid drainage from thin films due to Plateau border suction and disjoining pressure, (3) gravity drainage of liquid from Plateau borders, and (4) bubble coalescence in the foam. Protein enrichment and recovery were found to increase as the liquid pool height increased, eventually attaining constant values (corresponding to adsorption equilibrium), thus demonstrating the strong dependence of protein separation on adsorption kinetics. Higher enrichments and lower recoveries were obtained for smaller gas velocities, larger bubble sizes, and higher feed flow rates. Enrichments as well as recoveries were higher at lower feed concentrations. Coalescence was found to lead to higher enrichments and lower recoveries, this dependence being stronger for larger inlet bubble sizes.

Non-contacting control of objects by pulse width modulated air-jet actuators and optical position feedback

In many areas of the food manufacturing industry use of contacting mechanical devices to manipulate the products frequently causes damage to the products and/or gives rise to system jamming particularly at higher feed flow rates. Techniques for manipulating objects by non-contacting means, namely by power air-jets, have been under development at Birmingham University. The advantage of non-contacting technology is the increase of flow rates of manufactured products beyond that currently sustainable by mechanical means without causing damage and system hold-ups. In the present paper, a technique for motion control of objects is presented which utilizes pulse width modulated fast acting power air-jets with piezotranslator drive stages, a transputer based digital image processor for position feedback and fuzzy logic techniques for the control algorithm.

Separation in a gas centrifuge at high feed flow rate

The separation of a binary gas mixture for high feed flow rates such that the E¼ vertical shear layer is nonlinear is considered. Numerical solutions for the velocity field and the temperature within the centrifuge are computed using the method originally described by Bennetts & Hocking (1973). These solutions are inputs to the separation problem which is characterized by a concentration boundary layer also of width of O(E¼). Results are presented for a wide range of parameters and the effect of thermal drive strength is examined in detail. Surprisingly the numerical results indicate that the analytical solution for the separation factor given by Conlisk, Foster & Walker (1983) may be used far outside its strict asymptotic region of validity.