In this study, dynamic analysis of diffusion and convective flows in the pores of calcined limestone pellets, which are used for the removal of acidic gases from flue gases, has been studied using the single pellet moment technique. Experiments have been conducted in a diffusion cell by using nitrogen gas (carrier) flowing through both faces of the pellet. Prior to the diffusion experiments limestone powders were calcined in an atmosphere of N2 at 800°C. Effective diffusivity of helium has been determined by giving a pulse of helium to the upper face of the calcined limestone pellet and by comparing the response peak on the lower face of the pellet with theoretical expressions. The values of effective diffusivities increased with increasing temperature and pellet porosity. Convective flow contribution to the diffusion flux was found to increase with the increase of pressure drop across the pellet.
A macroporous adsorption resin, DF01 (cross-linked polystyrene, particle size 0.3–1.0 mm, specific area 400–420 m2 g–1), was selected from twelve kinds of resins and used to adsorb alkaloids from Sophora alopecuroides L. The adsorption capacity of DF01 on total alkaloids was as high as 17 mg cm–3 at pH 10.0 and the NaCl concentration of 1.0 mol L–1. Alkaloids were desorbed by ethanol/water (80:20, v/v) of pH 3.0 and 96% of the adsorbed alkaloids were eluted. The alkaloid monomers were separated by gradient elution with ethanol/water solutions of different volume ratios at reduced pressure. The major alkaloid monomers were obtained with a purity of over 90%.
Osmotic dehydration experiments of “difficult- to-filter” bentonite slurry were conducted with the aid of the high osmotic pressure brought about by hypertonic solution. In the experiments, osmotic dehydration was conducted by submerging a dialysis membrane tube containing bentonite slurry in polyethylene glycol solution. It was found that this method is quite effective for dehydration of “difficult-to-filter” slurry. It was clarified that the dehydration behaviors can be analyzed separately divided into two parts; filtration and subsequent consolidation. In the filtration period, the dehydration behaviors were well described by the Ruth filtration rate equation, in consideration of the compressibility of the filter cake. Also, the dynamic behaviors of dehydration in the consolidation period were accurately described by the modified Terzaghi model. The variations over time of the mass of the bentonite slurry during osmotic dehydration were well evaluated using in combination with the Ruth filtration rate equation and the modified Terzaghi model.
An emulsion of Omani heavy crude oil was prepared to reduce its viscosity, and combusted in a test boiler to investigate its combustibility and to analyze its flue gas composition, e.g., CO, SO2, NOx, and dust. The emulsion was evaluated to be suitable for use as a combustion fuel due to its lower environmental impact and lower possibility of high-temperature corrosion of boiler materials, in comparison with a commercial emulsion fuel, Orimulsion.
Using an anodic alumina supported silver catalyst with a low Ag loading (1.68 wt%), NOx adsorption and NOx-TPD/-TPSR measurements in different gas streams were conducted to investigate the formation, consumption and reactivity of surface adsorbed NOx species. And, the reactivity difference between NO and NO2 was also discussed by using non-steady and steady state tests. No remarkable uptake of NO was found in “NO only” adsorption. Introducing oxygen greatly promoted the formation of surface nitrite and nitrate species. Much more surface nitrate species were observed in NO2 adsorption, accompanied by gaseous NO released. The oxidation reaction of NO with oxygen into NO2 was believed to play an important role in the formation of nitrate during the coadsorption of NO and O2. The result of TPSR indicated that the surface nitrate species could be effectively and preferentially reduced by propene. When introducing oxygen into propene stream of TPSR test, the significantly increased amount of reacted nitrate undoubtedly showed the importance of oxygen in activating propene. The selective reduction of NOx under oxygen-rich conditions was considered to pass through the selective reduction of the adsorbed nitrate species with the activated propene with oxygen. The reactivity difference between NO and NO2 was attributed to the stronger NOx adsorption capacity and oxidation ability of NO2 than NO. With oxygen increasing, however, the difference gradually decreased, and finally disappeared in extremely excess oxygen. Besides the decreased difference in NOx adsorption capacity and gaseous reactivity between NO2 and NO, a slower activation rate of propene with oxygen was a supplementary interpretation for the complete disappearance of the difference in 15% oxygen.
With more stringent environmental regulations or acts being implemented, the research on developing a desulfurization/denitrification technology with high efficiency and cost performance becomes very urgent. In this paper, TiO2 catalyst with the addition of different promoters and additives were tested in a laboratory scale plasma reactor. Promoters are V2O5 and K2O–V2O5, and additives are H2O and H2O2, respectively. The experimental results indicate that the promoters (V2O5 and K2O–V2O5) are considerably effective in promoting the activity of TiO2 catalyst in the presence of plasma, which causes the SO2 oxidation rate to increase. Meanwhile, K2O–V2O5 (K-promoter) is found to be a better promoter than V2O5. Except for promoters, the additives (H2O, H2O2) also have an important impact on SO2 oxidation in the case of simultaneously using plasma and TiO2 catalyst.
Motivated by the common non-minimum phase property of dead time and right-half-plane (RHP) zero, this paper presents a Smith-like scheme for control of systems with RHP zeros. It is shown that RHP zeros and possible dead time can be removed from the characteristic equation of the scheme so that the control design is greatly simplified, and enhanced performance is achievable. By model reduction, a unified design with a single tuning parameter is presented for processes of different order. The relationships between the time domain specifications and the tuning parameter are developed to ease the design trade-off. Simulation examples are presented to demonstrate the effectiveness of the proposed scheme. For robustness, it is shown that our design ensures a gain margin of 2 and phase margin of π/3, as well as 100% perturbation of the RHP zero or uncertain time delay of |ΔL| ≤ τ/0.42.
In this paper, a simple and effective model reduction method for linear delay systems is proposed. It makes use of our newly developed robust identification algorithm from system step responses and can guarantee stability of reduced order models.
In this paper, several linear PID control methods for unstable processes with time delays, which have recently been reported in the literature, are studied in terms of a comprehensive set of control performance specifications. Their applicability and achievable performance are indicated with regard to different cases of normalized time delay for ease of user’s choice of the methods. By analyzing these methods’ pros and cons, a modified method which combines their respective strengths using simple linear time-variant and nonlinear control strategies is obtained and demonstrated with performance enhancement.
In the lactic acid fermentation, the lactic acid bacterium does not grow in a culture containing only sugar. In order for the normal growth of lactic acid bacteria, nutrients such as nitrogen source and vitamin are usually required. In general, both yeast extract and peptone are used as nutrients for lactic acid fermentation, but they are not economical. In this work, we adopted typical food wastes as the nutrients instead of yeast extract and peptone, and the lactic acid fermentation was performed. As a result, it was found that the lactic acid production on the sakekasu (sake filter cake) addition was more than that on the addition of the yeast extract and peptone.
The water diffusion and the water desorption behavior of sugars and pasta-like foods for temperatures between 283 K and 323 K were investigated by isothermal drying experiments and desorption isotherm measurement. The equilibrium water content in low water activity increased with a decrease in temperature for sucrose and maltodextrin whereas the values did not change significantly with temperature for pasta-like foods. The water diffusion coefficient of sucrose was much lower than those of pasta-like foods. Because of these two factors, the drying rates at low temperatures for pasta-like foods were higher than those for sucrose.
The dynamic process or structural studies of adsorption and desorption phenomena on the fluid interface has not been clearly established because of its difficulties in experimental instrumentation. In this work, we focused on the bubble coalescence phenomenon, which is known to be strongly affected by trace impurities such as 1 ppm or smaller. We measured the time course of the scattered He-Ne laser intensity irradiated at the contact surface of two bubbles, and the bubble coalescence time was determined in an aqueous solution of n-butanol with concentrations of 5.0, 7.5, and 10.0 mol/m3. The butanol concentration was so dilute that surface tension was little affected. At each butanol concentration, the bubble coalescence time varied with bubble age, which is the elapsed time from the formation of a bubble. The coalescence time quickly increased in a few seconds since its formation. After that, it gradually increased till the age of a few hundreds seconds, and then suddenly increased again. The initial value of the bubble coalescence time at the bubble age of zero could not be determined because of the difficulty in experiment, however, the value just after the first increase clearly depended on the butanol concentration. The bubble age at the onset of the second sudden increase also clearly depended on the butanol concentration. The slope between the first and the second sudden increase was larger for the higher butanol concentration. The dependence of the bubble coalescence time on the bubble age obtained in this work can be a help to elucidate the dynamic process of adsorption and desorption at the interface.
Non-equilibrium H2 production from ethanol was achieved with precious metal catalysts using a CO2 absorption ceramic. The ceramic consisted of lithium silicate, which was granulated and coated with coarse alumina particles. H2 production in steam reforming of ethanol was enhanced and CO production was suppressed significantly in the presence of the CO2 absorption ceramic. The optimum temperature region for non-equilibrium H2 production was 500–550°C. For example, at a temperature of 500°C, at atmospheric pressure and with a 1 wt% Rh/CeO2 catalyst, the H2 concentration was 91 mol%-dry, which was considerably higher than that at the chemical equilibrium of 63 mol%-dry, and it was 1.4 times higher than that obtained without the CO2 absorption ceramic. A highest H2 concentration of 96 mol%-dry was obtained at 550°C. The CO concentration decreased dramatically at 500°C from 1.5 mol%-dry to less than the detection limit, which was about 1 × 10–2 mol%-dry. It was markedly lower than that of the chemical equilibrium. Similar results were also obtained with a 1 wt% Pt/CeO2 catalyst. At 500°C in particular, the concentration of H2 was fairly high at 89 mol%-dry and the CO concentration was lower than the detection limit. Carbon deposition was not observed visually in each case. It is concluded that non-equilibrium H2 production from ethanol with a precious metal catalyst in the presence of the CO2 absorption ceramic has a high potential for application to a non-equilibrium reactor for proton exchange membrane fuel cell (PEMFC) systems. A markedly low concentration of CO and a fairly high concentration of H2 will contribute to simplifying the complicated system configuration and to improving PEMFC performance, respectively.
Adsorption and nonthermal plasma degradation of gaseous acetaldehyde was studied in a novel plasma discharge reactor, in which fibrous activated carbon was used as both an electrode and adsorbent. After a sheet of fibrous activated carbon put onto a glass plate was saturated with 50 ppm of acetaldehyde gas, 10 kV of high voltage AC was applied to fibrous activated carbon. The barrier discharge was generated at around the sheet of fibrous activated carbon. Acetaldehyde adsorbed in the fibrous activated carbon was removed during the plasma treatment, and complete decomposition of acetaldehyde was achieved within 60 min. We also examined the recycle of fibrous activated carbon. After complete degradation of adsorbed acetaldehyde in fibrous activated carbon with discharge was finished, the fibrous activated carbon could be reusable for the adsorbent and degradation with discharge. The fibrous activated carbon used in our study was able to reuse at least five times without any significant decrease of adsorption ability. These results suggested that continuous treatment with spontaneous adsorption and nonthermal plasma degradation of VOCs is possible by using fibrous activated carbon as the high voltage electrode.
Utilization of the picosecond (100 ps) laser ionization was successful in measuring the mass spectra attributed to di-, tri-, tetra-, penta-, and hexa-chlorinated biphenyls. It was confirmed that the quantitative limit of this method in real-time (1 min) was 10 μg/m3N (equivalent to 1/10 of the value established as the statutory limit for PCBs in the ambient air of the workplace environment). Further evaluations of measurement accuracy based on comparisons with the results of the conventional method (gas sampling and GC-MS) demonstrated a coefficient of variation within 30%. We undertook the measurement of the exhaust gas and the work environment atmosphere in PCBs treatment plants using the LI-IT-TOFMS method, confirming that the monitoring system could be operated appropriately by the introduction of an internal standard gas (2,4-dichlorinated toluene), and that it was possible to make continuous long-term measurements for over 500 h (total measurement time, >6000 h).
Thin-layer of magnesium hydrogenphosphate was prepared over a glass plate by a sol–gel technique using sodium diphosphate and magnesium nitrate to be employed for the continuous removal and recovery of aqueous ammonium. Although it had been reported before that magnesium hydrogenphosphate was prepared with sodium alginate together with sodium diphosphate and magnesium nitrate in the sol–gel technique, the present study revealed that the employment of sodium alginate resulted in the formation of a thin-layer of magnesium hydrogenphosphate that could be easily peeled off from the glass plate. The preparation procedure described in the present study afforded a rather stable thin-layer of magnesium hydrogenphosphate which does not peel off from the glass plate even after repeated use in the removal and recovery of aqueous ammonium. The possibility for the employment of the thin-layer of magnesium hydrogenphosphate for repeated use of the removal and recovery of aqueous ammonium was described.