Possibility to convert the tar vapor in the hot coke oven gas (COG) to a synthesis gas was investigated. Tar condensed from an actual COG as well as model compounds such as benzene, naphthalene, and pyrene were used as the reactants. Experiments of the pyrolysis and catalytic steam reforming of the tar in a helium, a steam, and a simulated COG atmospheres were carried out. More than 80% of tar could be decomposed in several seconds by pyrolysis at temperature ≥1000°C The coke yield reached 80% and the main gas products were methane and hydrogen. Coke deposition was reduced in the presence of steam by steam gasification of the coke. When the tar was pyrolyzed in the simulated COG, coke deposition from methane in addition to the deposition from the tar was observed at high temperature. The reverse shift reaction forming carbon monoxide and steam also occurred during the tar pyrolysis in the simulated COG. The coke formation was not reduced greatly even in the presence of the reforming catalysts.
We have recently presented a new coal solvent extraction method that enhances the extraction yield dramatically. The method extracts coal using a flowing stream of either tetralin or 1-methylnaphthalene under 10 MPa at 200 to 400°C. The extract yield reached 65 to 80% for bituminous coals at 350°C, and the extract was almost free from mineral matters. Thus, this method was found to be effective to recover clean fuels from bituminous coals under rather mild conditions. To extend the extraction method to low rank coals and to make the method practically applicable, coal derived oils, carbol oil and creosote oil, were used in addition to tetralin in this study. Twenty kinds of coals were subjected to the extraction by tetralin and the coal derived oils at 350°C. Almost all sub-bituminous coals and brown coals examined were surprisingly extracted by 80% in the carbol oil at 350°C. It was also found that the extract was almost free from mineral matters and that most of sulfur was retained in the coal through the extraction by tetralin, whereas most of sulfur including pyritic sulfur was transferred into the soluble fraction through the extraction by the carbol oil. Thus, it was clarified that the proposed method was effective to produce a large amount of clean fuels from low rank coals under rather mild conditions.
Studies on coal gasification in CO2 at elevated temperatures and high heating rates are necessary to develop IGCC technology. Coal gasification is a very complicated phenomenon, which makes a generalized understanding and description of gasification reactivity of a coal highly important. With a unique fluidized bed, the reactivity of seven coals was investigated at elevated temperatures and high heating rates. A modified random pore model was proposed to unify the gasification reactivity of coals obtained by us. It was identified that the coal reactivity can be unified with a master curve described by the new model for all the coals, temperatures and heating rates examined in this work. This model can also satisfactorily unify the experimental gasification data in literature. The modified random pore model can predict the experimental data with an error within about 5%. The error of the prediction by the modified random pore model is about one-third smaller than that of the prediction by the random pore model. It is recommended as a sub-model for simulation of coal gasification in practical gasifiers.
The distribution of alkali elements in coal is of the utmost importance for determining their transformation during combustion, however, little is known of it because of their lower concentration in coal. From this viewpoint, several advanced techniques were used in this study to investigate the evolution of alkali elements during combustion of two Chinese coals at 1200°C. The contents of alkali elements were analyzed using Inductively Coupled Plasma (ICP) spectroscopy; their distribution in raw coals and the combustion residues were analyzed by computer controlled SEM (CCSEM); moreover, the particulate matters in the emission gas were collected by a Low Pressure Impactor (LPI) to study the vaporization of these elements in combustion. The results indicate that the organically bound alkali-based compounds totally vaporized during coal pyrolysis, meanwhile, the included ones fragmented into ultra-fine particles with a size of about 1.0 μm, a portion of which entered into a gas atmosphere and changed into particulate matters. On the other hand, the excluded alkali elements have bimodal distribution in raw coals, in which the fine particles fragmented and changed into particulate matters, the large portion having a size of about 20.0 μm kept unchanged till the carbon had burnt out. For the vaporized alkali elements in the particulate matters, they had a bimodal sized-distribution; fine particles of about 0.4 μm were formed from combination of fine Na/Al-Si, NaCl, Na2SO4 and Na3PO4 less than 0.1 μm in size. They could capture the trace elements, too, and a portion of them coagulated into large particles in the particulate matters. The different vaporization behavior of sodium and potassium was also addressed using XPS analysis.
Upgrading of low-rank coal by means of a combined process of vacuum drying and tar coating has been conducted in order to suppress low-temperature oxidation and spontaneous combustion of coal. Some advantages on improvement of devolatilization and control of low-temperature oxidation have been observed. This upgrading technique was able to produce the upgraded coals comparable to bituminous coal particularly in moisture, volatile matter and carbon contents. Total weight loss and devolatilization significantly increased with an increase of the upgrading temperature, from 29.5 and 10.5%, respectively at 200°C to 36.5 and 21.9%, respectively, at 300°C. Moreover, upgraded coals showed a lower propensity to oxygen attack and low-temperature oxidation.
The low temperature oxidation of four coals ranging from brown coal to bituminous coal was investigated. The coal oxidation was carried out using 16O2 or 18O2. Isotope 18O2 was used for the oxidation experiment of coal to clarify the release behavior of oxygen-containing gases during the oxidation of the coal sample and the devolatilization of oxidized coal. During the oxidation of coal and the temperature-programmed heat-treatment of oxidized coal, CO (m/z = 28, 30), CO2 (m/z = 44, 46, 48) and H2O (m/z = 18, 20) were analyzed with a quadrupole mass spectrometer. It was found that the gas release profiles were dependent on the coal rank. In the case of high rank coal, the amounts of H218O, C18O and C18O18O released than those of H216O, C16O and C16O16O. Oxygen chemisorped in low rank coal is easily released as inorganic gases during the heat treatment. The oxygen incorporated into the coal structure during the oxidation treatment plays more important role for the decrease in the caking property than oxygen in raw coal. The coal structural changes, which may be due to cross-linking and the decrease in hydrogen donor ability of oxidized coal, strongly affected the caking property of coal.
A kind of porous alumina was employed as bed material of bubbling fluidized bed coal combustion instead of non-porous silica sand. The effect of the bed material on emissions of N2O and NOx was evaluated using a bench-scale combustor. The present porous alumina suppressed N2O emission. This result is explained by the catalytic activity of porous alumina to decompose N2O. In addition, NOx emission with porous bed material was nearly the same as or lower than that for the sand bed. Thus the decrease in N2O without increasing NOx was attained. A modification of desulfurization by limestone was proposed. Fine limestone particles were employed as sorbent in order to conduct SO2 capture in the freeboard. By employing fine particles, the contact between volatile matter and limestone, which is known to increase the emission of NOx, was avoided. Thus the increase in NOx emission during limestone feed was avoided.
The authors thought that Trimethylolethane (TME) hydrate had a great potential as a brand-new phase change material (PCM) due to organic hydrate, which was no flammable and no corrosive against metals. The present paper investigates the physical properties, phase separation and corrosiveness against metal about TME hydrate. The phase separation phenomena of TME hydrate in the stagnant melt was investigated on condition that the hydrate was used with a capsule type heat storage system. Furthermore, the corrosiveness of TME hydrate against metals had evaluated to ascertain the possibility of being used as a metal heat exchanger. It was confirmed that the melting point of TME hydrate is 302.8 K and heat of fusion is 218 kJ/kg. Moreover, basic physical properties were measured, such as specific heat capacity, thermal conductivity and density. It was found that TME hydrate can be used as a heat storage material without thickening agent under some concentration. The concentration of TME that occurs phase separation changes according to the melting temperature and retention time in a general system condition. Also, it was found that TME hydrate has no corrosiveness against aluminum, copper, carbon steel and stainless steel. It was suggested that metal heat exchangers made of copper and aluminum could be used for TME hydrate.
For efficient heat recovery of high temperature waste heat in the form of latent heat, the stable utilization technology of encapsulated phase change material, PCM, without leak was studied. In the experiments, lead pellets were selected as a PCM, then encapsulated by a nickel film based on an electro-plating method, and next were tested by cyclic heating for practical use. At the same time, thermal stress model was developed, validated by the measured data and implemented to study the effect of the film thickness on the strength of capsules. The results of the cyclic test showed that the obtained PCM has enough strength by increasing the film thickness or decreasing PCM diameter. The developed stress model also well predicted the relationship between the film thickness and PCM diameter for estimating the required thickness of the Ni layer. The developed methodology will be useful for designing the encapsulation of any PCMs.
The application of ultrasound, which has been shown to be useful for the supercooling relaxation and solidification enhancement of erythritol as an organic phase change material in our previous study, was further investigated. Experiments on the solidification of erythritol were conducted using a visualization setup with a cooling vertical double-pipe. Functions of ultrasonic irradiation parameters, in particular, amplitude and irradiation mode in relation to its physical effects were investigated. It was shown that melt with a higher degree of supercooling facilitates the crystal formation in the presence of ultrasound. Together with the rapid propagation of crystals by secondary nucleation and effective bulk mixing, restoration of supercooled melt to its melting temperature was promptly attained at higher acoustic amplitudes. Pulsed and continuous irradiation modes were compared. The results demonstrated that continuous irradiation led to sustained secondary nucleation. In other words, ultrasonic irradiation enabled constant fragmentation and effective dispersion of crystals by the mixing of erythritol melt.
Ultrasonic decomposition of (4-Chloro-2-methyl phenoxy)acetic acid (MCPA) in aqueous solution was performed at a frequency of 500 kHz under an argon atmosphere. We investigated the mechanism of ultrasonic degradation of MCPA by observing the decomposition time evolution of MCPA and the behaviors of chloride ion, TOC (total organic carbon), and byproducts formed through the ultrasonic degradation process of MCPA. At a constant power of 21.4 W, MCPA was completely decomposed after 180-min sonication and the ultrasonic decomposition of MCPA followed a pseudo first order reaction kinetics. Much of its chlorine atoms were mineralized in solution after 360-min sonication. On the other hand, it was difficult to achieve complete mineralization of carbon, and about 60% of the initial TOC remained in aqueous solution after 360 min. Based on the GC-MS analysis, byproducts such as 4-chloro-2-methyl phenol (CMP), 4-chlorocathecol, methylhydroquinone, cresol, acetic acid and formic acid were detected in the aqueous solution to which ultrasonic irradiation was applied. The CMP concentration increased during the early period of irradiation reaching a maximum concentration at about 60 min followed by its decrease until CMP became undetectable at 180 min. Decomposition of MCPA by ultrasonic irradiation resulted in the increase in acetic acid concentration until 120 min, after which no further increase was observed. Conversely, formic acid concentration was observed to increase only during the duration of sonication experiment.
Adsorption equilibria of ethanol and methanol vapors on activated carbon fibers (ACF) and granular one (GAC) were measured at 30 and 50°C, and adsorption isotherms over a wide temperature range were predicted from the experimental equilibrium curves. The cooling effect in an ideal cycle of adsorption refrigerators was estimated under the typical operating temperature conditions from the predicted isotherms. The results obtained showed that the ACF with large surface area has high adsorptive capacity for both ethanol and methanol vapors. The cooling effect estimated for the ACF/methanol pair exceeded 300 kJ/kg, and these values were greater than those for the GAC/methanol pair. Furthermore, we could successfully prepare ACF with high bulk density (HD-ACF) from phenol resin fibers without adding any binders. The prepared HD-ACF has a dense structure with smooth fibers, and has micropores mainly in the range of the radius below 2 nm. The HD-FAC adsorbed rapidly ethanol and methanol vapors comparable to the felt-type ACF. The cooling effect on the apparent volume basis showed an extremely high value of 177 MJ/m3 for the HD-ACF/methanol pair. Therefore, we concluded that it is feasible to apply this working pair to adsorption refrigerators.
Typical adsorptive desiccant cooling process mainly consisting of a rotary dehumidifier and a sensible heat exchanger can be driven with low-temperature heat energy like solar energy or waste heat, and it has been expected to be alternative air conditioning equipment considering various energy/environmental problems such as global warming. However, the fact that the cooling performance is decreased significantly as ambient humidity increases was also found. This is mainly due to a simultaneous increase of humidity and temperature in the process outlet air of dehumidifier. For the use of the cooling process in high humid condition, two process configurations were proposed and investigated by means of simple calculation. One of the proposed configurations, the 4-wheel cycle with double stage dehumidification, indicated a sufficient cooling performance for the use in factories or laboratories even though the ambient humidity was nearly 20 g/kg. Furthermore, the process performance was improved more with water spray evaporative cooling at the inlet of a regeneration air stream in the pre-dehumidification section. This means that lower humidity and lower temperature of air supplied to the process inlet of the dehumidifier is strongly required to give the cooling process a sufficient performance for actual use. Meanwhile, it was found that lower temperature heat around 50–60°C could drive the 4-wheel desiccant cycle in a moderate ambient humidity. The other, a 3-wheel cycle equipped with a total heat exchanger, gave us a reasonable improvement in the cooling effect and COP with less additional investment than that for the 4-wheel cycle.
Composite particles of calcium chloride and expanded graphite were prepared for promoting the reaction of gas-solid chemical heat pumps that generate cold heat by using waste heat or solar energy. Analyses with SEM and mercury porosimetry revealed that fine particles had been created in small pores of the expanded graphite powder by a procedure developed in this study. TG analysis for the reaction with methanol vapor showed that the reaction rate of composite particles with a large specific surface area was about 1.6 times as large as that of untreated calcium chloride.
A magnesium oxide/water chemical heat pump using a 10-W class packed bed reactor was examined experimentally to evaluate the thermal performance of the heat pump. A developed reactant having high durability for repetitive operation was packed in the cylindrical reactor. The magnesium oxide hydration was studied under reaction pressures up to 405 kPa, which were higher than one of previous work. Heat generation at around 100–240°C was measured by the hydration under the heat amplification mode operation. The magnesium hydroxide dehydration was capable to store the surplus exhaust heat from a cogeneration system and surplus night-time electricity. The heat storage density of the heat pump was sufficiently competitive with that of a conventional sensible heat water storage system. The heat pump was expected to be applicable for load leveling in a cogeneration system by chemically storing surplus heat during low heat demand and supplying heat during peak demand.
In the low temperature gasification of wood biomass, fluidized beds may exhibit defluidization problems caused by tar. These problems may be avoided by using porous particles as a bed material to capture the tar. Using wood chips, we studied the tar capture behavior of various porous particles and the influence of fluidization on the tar capture performance under pyrolysis conditions. The results of thermobalance experiments showed that γ-alumina, sepiolite and activated clay had high tar capture performance. The tar capture depended on the specific pore surface area and pore volume of the particles, with particles having higher pore surface and volume showing greater tar capture. Furthermore, micropores in the particles were used for capture of the tar, and this promoted carbonization. The results of a small fluidized bed experiment showed that porous particles were able to capture the tar even under fluidized bed conditions, and that defluidization did not occur at a low weight ratio of the wood chip to the bed material.
In a biomass integrated gasification/gas turbine (BIG/GT) system, a novel configuration with external heat source using GT exhaust was proposed and evaluated. The proposed system was compared to the conventional configuration of the BIG/GT system with an internal heat source obtained by partial combustion of biomass. The system integration and evaluation were performed using a commercial process simulation tool, ASPEN Plus. The proposed system comprises energy recuperation technologies: heat, steam, and thermochemical recuperations. An improvement in the system performance was confirmed in the proposed BIG/GT system in comparison with the conventional system by means of the integration of external heating feature in gasifier using the exhaust as the heat source.
In the combustion of low vapor pressure liquid fuel, it is necessary for instantaneous ignition to preheat the liquid fuel evaporator at any required time. For example, in the kerosene vaporizing type boiler for home use, electric power is consumed in the preheating kerosene vaporization to supply hot water, even on standby. To avoid the preheating process by electric power during the standby period, the technology that can vaporize liquid fuel instantaneously needs to be developed. From this viewpoint, the application of the ultrasonic atomization was proposed to ignite liquid fuel without any heating process. Similar trials had already been done but no stabilized combustion was accomplished by ultrasonic atomizing, using an MHz frequency. In this work, a kerosene pre-mixed burner equipped with a 1.7-MHz ultrasonic oscillator was manufactured and the characteristics of the atomization of kerosene, stable combustion region and NOx emission on this ultrasonic atomization burner are examined. The relatively quick ignition with a few seconds delay was realized. The atomization of kerosene was obtained at the rate of 0.75 g/min, which is proportional to the time and the average kerosene droplet size, 3.1 μm, produced by 1.7 MHz ultrasonic oscillation. 0.54 kW load was obtained by using this combustor. Stable combustion was obtained around 0.7 in the equivalence ratio. The stable combustion was defined as [CO]/[CO2] < 0.002 for combustion exhaust gas. 23 ppm of low NOx emission (O2 0% base) is accomplished in the stable combustion region as it can provide the balance between both primary and secondary air flow rates.
A zero-emission fuel cell vehicle system using a thermally regenerative fuel reformer, which had a performance of carbon dioxide fixation from a reformed gas, was proposed. A packed-bed regenerative reforming reactor containing a reforming catalyst and calcium oxide was examined for methane steam reforming under atmospheric pressure. It was demonstrated that carbon dioxide was well fixed by chemical absorption of calcium oxide in a preliminary experiment. The methane reforming, carbon monoxide shifting and calcium oxide carbonation proceeded simultaneously in the regenerative reactor. The carbonation of calcium oxide fixed the carbon dioxide generated through the reforming, and the hydrogen purity of effluent gas was raised beyond the equilibrium amount of a conventional fuel reformer. The vehicle system was expected to improve the efficient utilization of surplus thermal energy and surplus electricity by utilizing them for the regeneration of the reformer.
The HCl evolution behavior in the process of sulfation of KCl, CaCl2 and NaCl was studied by using a lab-scale gas flow-type tubular reactor, in simulated conditions of municipal waste incinerations, under mixed gas of SO2: 0.3–1.3 vol%, O2: 2.5–15 vol%, H2O: 5–20 vol%, in the temperature range of 623–1123 K. The sulfation rates of KCl, CaCl2 and NaCl changed distinguishably with the temperature above 923 K, for each inorganic chloride of KCl, CaCl2 and NaCl. Comparing the time-changes of the concentration of HCl released from KCl, CaCl2 and NaCl, the rate of HCl evolution from CaCl2 was the highest; the maximum concentration of HCl discharged from CaCl2 was more than 5 times higher than those from NaCl and KCl at 923 K. The reaction kinetic parameters like the rate constant and the reaction orders with respect to SO2, O2 and H2O partial pressure for the sulfation of NaCl, KCl and CaCl2 were determined. It was suggested that the mechanism of formation of HCl by sulfation of KCl, CaCl2 and NaCl was different above and below the temperature range of 850–900 K. A higher sulfation rate of KCl, CaCl2 and NaCl might be attributable to a partial melting and/or volatilization of these inorganic chlorides at the temperatures higher than the temperature range of 850–900 K. The effect of SO2 partial pressure on the sulfation rate was 2–4 times larger for NaCl than for KCl and CaCl2. For the sulfation of KCl, the reaction order with respect to the O2 partial pressure was almost a half of that of NaCl. On the other hand, the rate of sulfation of CaCl2 was almost independent on the O2 partial pressure. The dependence of H2O partial pressure on the sulfation rates of KCl, CaCl2 and NaCl was almost the same in lower temperatures of 623–923 K. However, the reaction order with respect to H2O at 923–1123 K became 2–4 times larger than that in the lower temperature regions.
A catalyst support with both small pores and large pores, as well as a distinct bimodal pore structure, has excellent advantages in industrial solid-catalysis reactions because the large pores provide pathways for rapid molecular transportation and the small pores serve a large area of active surface. A simple preparation method of bimodal supports was developed by introducing SiO2 or ZrO2 sol into large pores of an SiO2 gel pellet directly. The pores of the obtained bimodal supports distributed distinctly as two kinds of main pores. On the other hand, the increased BET surface area and decreased pore volume, compared to those of original silica gel, indicated that the obtained bimodal support formed according to the designed route. The obtained bimodal support loaded with cobalt was applied in slurry-phase Fischer–Tropsch synthesis (FTS). The bimodal catalyst presented the best reaction performance in slurry-phase FTS with a high reaction rate and low methane selectivity, because the spatial promotional effect of the bimodal structure and the chemical effect of the porous zirconia were available inside the large pores of original silica gel.
The reaction of iron carbide with steam was examined under constant temperatures and a constant heating rate using a temperature-programmed thermogravimetry-GC/MS. Coproduction of pure Fe and H2 from iron carbide coincides with reduction of Fe3O4 and subsequent oxidation of produced Fe by steam which formed FeO. A carbon conversion of 94% and an Fe yield of 80% were achieved, providing rapid heating and low steam concentration (10%).
Thermal efficiency of the IS (sulfur-iodine) thermochemical hydrogen production cycle process was investigated. The heat and mass balance of the process were calculated with various operating conditions, and the effects of these conditions on the thermal efficiency were evaluated. The flowsheet of the H2SO4 decomposition designed by Knoche et al. (1984) was used. An electro-electrodialysis (EED) cell for the concentration of HI and a hydrogen permselective membrane reactor for decomposition of HI were applied to the process. Sensitivities of four operating conditions (the HI conversion ratio at the HI decomposition reactor, the reflux ratio at the HI distillation column, the pressure in the HI distillation column, and the concentration of HI after the EED cell) were investigated. The concentration of HI had the most significant effect on thermal efficiency. The difference of the efficiency was 13.3%. Other conditions had little effects within 2% of the efficiency. Effects of nonideality of the process (electric energy loss in the EED cell, loss at heat exchangers and loss of the waste heat recovery as electric energy) were evaluated. The difference of the efficiencies by the loss in the EED cell was 11.4%. The efficiency decreased by 5.7% by the loss at heat exchangers. The loss of the waste heat recovery lowered the efficiency by 6.3%. The result shows that the development of the EED cell, heat exchangers and electric recovery is effective in improving thermal efficiency. The operating conditions such as the HI concentration after the EED cell should be optimized to obtain the maximum thermal efficiency after the developments of the apparatuses. Change of the state of nonideality needs the optimization of the concentration. The thermal efficiency of the total process was 56.8% with ideal operating conditions of the EED cell, heat exchangers and high performance waste heat recovery.