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Kouichi Miura, Kazuhiro Mae
1994 Volume 20 Issue 6 Pages
733-746
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Recently flash pyrolysis of coal has been attracting great attention as a means to recover valuable chemicals under rather mild conditions. In this paper several features and problems related to the flash pyrolysis of coal are examined. The effect of the operating conditions including the heating rate is examined to elucidate the factor controlling the yields of total volatiles and liquid products. The mechanism by which the yield of total volatiles increase during the flash pyrolysis is examined with the aid of a pyrolysis model presented by Niksa et al. It is clarified that the amount of the tar precursor called “metaplast” and the formation rate of noncondensable gases are closely related to the yield of total volatiles. An explanation is given to a debate on the applicability of the first-order reaction model to the pyrolysis reaction. Then a procedure to determine true activation energies from the first-order reaction model is presented. The methods proposed for controlling the pyrolysis reaction under mild conditions are collected from the literature and reviewed. Finally, several new pyrolysis methods proposed by the authors, which realize significant increases in the total volatiles and the yields of benzene, toluene, and xylene under mild conditions, were introduced.
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Hisao Makino, Masayoshi Kimoto
1994 Volume 20 Issue 6 Pages
747-757
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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As an energy source for thermal power stations, coal will be most important because the minimum reserve of coal is many times more than that of other fossil fuels whose depletion is feared. The supply of coal is expected to be stable in the future. In pulverized coal combustion. which is a major coal utilization technology, it is necessary to develop flue gas cleaning technology to control environmental pollutants.Especially, NO
x control technology is very important because selective catalytic denitrification equipment is of high cost and it has a limited removal performance.So, it is very important to develop low NO
x combustion technology which controls NO
x formation in pulverized coal combustion.
In this paper, the concept of low NO
x combustion and the trends of research and development in this field are introduced in detail. The newest low NO
x combustion technology, which accelerates low air ratio combustion near the burner and uses formation and intensification of the reduction flame, is investigated. The combined low NO
x combustion technology, which comprises the use of a low NO
x burner, secondary fuel injection and intensified two stage combustion, can significantly reduce the NO
x emission in pulverized coal combustion.
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Yasuo Hatate, Yoshimitsu Uemura, Shigeho Tanaka, Yasuhiro Tokumasu, Ya ...
1994 Volume 20 Issue 6 Pages
758-765
Published: November 10, 1994
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Hydrogen production performance was examined at comparatively low temperatures (ca. 800°C) and atmospheric pressure using a spouted bed type coal gasifier with draft tube, proposed as a new reactor for coal conversion technology. This re-actor has the following favorable points; 1) plug flow is predominant in the gasification zone, 2) classification of feed coal particles is not necessary and 3) air can be used instead of oxygen. A hot model study was carried out via cold model study at a 1 kg/h coal-feed rate. Above 80% contents of hydrogen and carbon monoxide were achieved in exit gases produced.
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Fumiki Ueda, Nobuo Yoshida, Ryouichi Hashimoto, Tadayoshi Muramatsu, K ...
1994 Volume 20 Issue 6 Pages
766-773
Published: November 10, 1994
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The characteristics of an oxygen-blown entrained-bed coal gasifier have been investigated by using a 50t/d piolot plant. Cold-gas efficiency reached a maximum with an appropriate oxygen/coal ratio. Combining char recycle, a cold-gas efficiency as high as 78% and a carbon conversion efficiency of 98% have been achieved. It was found that adding an appropriate amount of oxygen to the recycled char was very important to avoid an excessive amount of char recycle. By controlling the relative amount of oxygen supplied separatery to the upper and lower burners, a favorable temperature distribution in the gasifier could be realized. Thus, a H
2-CO-rich gas can be produced while the temperature of the lower part of the gasifier is high enough to allow stable slagging of the molten ash. In the early stage of pilot plant operation, ash deposit build-up occured and plugged the exit of the gasifier. This interfered with the long-term operation and it has been overcome by decreasing the amount of oxygen to the upper burners and by lowering the temperature in the upper region of the gasifier. Finally, the pilot plant had been successfully operated continuously for as long as 1149 hours.
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Yuichi Fujioka, Jung Wei Shih
1994 Volume 20 Issue 6 Pages
774-783
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Coal gasification experiments for six kinds of coal under partial combustion with oxygen were conducted using a pressurized fluidized bed reactor of about 10cm diameter at temperatures of 11001400K and coal feed rates of 2-6kg/h. The feed coal particles were prepared large enough so as not to be entrained by freeboard gas.Analysis of carbon and ash mass balances shows that the carbon content of the fluidized bed is dependent on carbon conversion and has no relation to coal feed rate, gasification temperature and H
2O feed rate. It is suggested that the fine char high in carbon content that is carried over by the gasification gas decreases the carbon conversion and is mainly produced during devolatization of coal. It is also suggested the production of fine char during gasification and combusion scarcely decreases carbon conversion. Under these conditions, maximum carbon conversion from 0.92 to 0.98 is attainable.
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Yuichi Fujioka, Yoshihiko Tsuchiyama, Kimishiro Tokuda, Fumiya Nakashi ...
1994 Volume 20 Issue 6 Pages
784-792
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Experiments on the reaction between limestone and hydrogen sulfide were conducted with fixed bed and fluidized bed experimental apparatus under high pressures and temperatures. This study made it clear why desulfurization efficiency was low when limestone was directly fed into a coal fluidized bed gasifier. The first reason is that the residence time of limeston in the gasifier is too short. The second reason is that the oxidation rate of CaS is larger than the formation rate of CaS. When the rate of CaS formation was nearly equal to the rate of calcination, the CaS mole fraction of limestone was above 60 %. Passing coal gasification gas through a limestone fluidized bed in the fluidized bed experimental apparatus decreased H
2S concentration at the fluidized bed to about 140 ppm.
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Effects of gases formed on reactivity
Yoshiyuki Nishiyama, Kazuhiko Terada
1994 Volume 20 Issue 6 Pages
793-798
Published: November 10, 1994
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Steam gasification of three different ranks of coal with or without catalysts was conducted using a vertical quartz tube as the reactor. Various amounts of coal were charged and the effects of pyrolysis/gasification products on the reactivity of coal-catalyst systems were examined. For Taiheiyo coal without added catalyst, carbon conversion per a unit weight of coal decreased with the bed height indicating the suppressive effect of the products. With sodium catalyst, deactivation was almost negligible. With calcium, iron or nickel, the deactivation was intermediate between the sodium-loaded and non-catalytic cases. For Taiheiyo and Loy Yang coals, the composition in CO and CO
2 was in equilibrium with the steam partial pressure. This indicates the occurrence of a water gas shift reaction downstream of the reaction bed. For Blair Athol coal, equilibrium was attained only with catalysts active for a shift reaction, i.e., calcium or chromium. The amount of tar decreased for Blair Athol coal with nickel or iron as catalyst suggesting that secondary decomposition occurs for some coal/catalyst systems.
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Takayuki Takarada, Ukiya Komori, Takenori Atsuta, Nobuyoshi Nakagawa, ...
1994 Volume 20 Issue 6 Pages
799-804
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Potassium-loaded Yallourn brown coal was prepared with KCl using an ion-exchange technique. The K-loaded brown coal char was physically mixed with a higher rank coal char, Liddell coal, in a fluidized bed and the mixture was gasified in carbon dioxide (0.1 MPa) with the fluidized bed at 750°C. Potassium catalyst incorporated into Yallourn coal not only significantly enhanced the reactivity of Yallourn coal char, it also did so for Liddell coal char. It was found that potassium compound easily transfer from K-loaded coal char to unloaded coal char by collision in the fluidized bed. The catalytic effectiveness on the gasification of Liddell coal char was dependent on the particle size. The intimate direct contact between K-exchanged coal char and higher rank coal char was very important for this catalytic coal gasification system. The partial deactivation of potassium catalyst due to reaction with mineral matter in Liddell coal was observed.
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Shigeyuki Uemiya, Hiroyuki Yoshitake, Jicheng Bi, Tadashi Kimura, Tosh ...
1994 Volume 20 Issue 6 Pages
805-812
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Gasification of Taiheiyo coal char was conducted using a continuous fluidized bed coal gasifier (I.D. 78.1 mm) with a center nozzle and conical distributor. Effects of bed temperature and jet velocity on gas concentration profiles were investigated at different levels of carbon conversion. The results demonstrated that combustion and steam gasification occurred mainly in the jet and in the annulus region, respectively. Gas concentration profiles in the grid zone were independent of gas interchange between the jet and annulus because it was fast compared with gasification at the experimental temperature. In the grid zone, the relative contributions of gasification and combustion in the continuous gasifier were found to have similar tendency to a smaller batch gasifier. Scale effect on the gas interchange between the jet and annulus was observed between two gasifiers having different inner diameters of 78.1 and 43.0 mm. Further study using computer simulation is necessary to confirm the scale effect.
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Atsushi Morihara, Syuntaro Koyama
1994 Volume 20 Issue 6 Pages
813-819
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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The gasification process discussed in this paper consists of a two-stage process, combustion and gasification, in a one-room reactor. The development of a calculation method for particle residence time is important because of the residence time effects on the efficiency of gasification. The average particle residence time was calculated by using the density profiles of particles in the outer gas. The density profiles were calculated by particle motion equation and diffusion by turbulence. The effect of upper burner flow rate and outer diameter on average particle residence time can be determined with our model.
Furthermore the particle residence time was measured by a pulse response method at room temperature and atmospheric pressure by using a flow model for the furnace of the coal gasifier. The calculated results agree with the experimental data.
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Toshiro Tsuji, Toshiharu Shibata, Osamu Uemaki
1994 Volume 20 Issue 6 Pages
820-826
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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A mathematical model has been developed for the continuous spouted bed coal gasifier which had been developed previously by the authors. The model based on a gasification rate equation and balance equations, assumes the spout and annulus to be two well mixed tanks.
The devolatilization data and steam-char reaction rate of Taiheiyo coal were measured using a small scale fixed bed equipment. With these data and the model equations, performance characteristics such as carbon conversion, steam conversion, gas yield and gas composition of a spouted bed gasifier were calculated for selected operating conditions.
The results were compared with the previous experiments for Taiheiyo coal by the authors. The dependence of reactor performances on oxygen feed rate and steam feed rate are illustrated well by this model.
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Akihiro Kataoka, Takashi Ihara, Wojciech Nowak, Hitoki Matsuda, Masano ...
1994 Volume 20 Issue 6 Pages
827-833
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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A circulating fluidized bed gas combustor equipped with an internal nozzle in the bottom part of the riser for low calorific and difficult-to-burn gases was proposed. Flue gas characteristics of the proposed system were measured and discussed with regard to NOx emission. The effects of such parameters as the solid circulation rate, air ratio, particle temperature, particle property, ratio of the gas flow from the nozzle to the total gas flow and combustion load on NO
x emission were investigated.It was possible to decrease NO
x emission by use of this equipment due to the following factors.
-a decrease of the bed tempenature by circulating solid particles,
-bed temperature control by operation with a suitable air ratio,
-high heat transfer in the bed due to high heat capacity of solids,
-a decrease of the bed temperature and the two stage combustion effect by control of the ratio of gas flow from the nozzle to total gas flow.
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Masayuki Taniguchi, Kiyoshi Narato, Kazuyuki Ito, Hiroshi Miyadera, Ka ...
1994 Volume 20 Issue 6 Pages
834-842
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Ignition and combusion behaviors were observed for pulverized coal particles which were suspended in a laminar upward flow and were heated by a single pulse Nd : YAG laser. The surface temperature of the particles was estimated to increase at a rate of about 10
6K/s. For a bituminous coal, observations with high-speed video revealed that the coal particles ignited heterogeneously 1-2ms after the laser pulse operation and this was followed by the evolution of volatile materials and their combustion in the gas phase. A rate constant of surface oxidation reaction of the bituminous coal at a temperature range between 800K and 1400K was calculated by an analysis of the ignition temperatures of the particles. The reaction order for oxygen partial pressure was 1.0 and the activation energy was 50KJ/mol, which coincide with published values determined by heterogeneous reaction theory. Ignition temperature varied several hundred degrees for the same coal and experimental conditions due to the difference of chemical characteristics of particles. This corresponded to a three-times variation in the frequency factors.
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Ichiro Naruse, Yasuyukim Yamamoto, Hirofumi Itoh, Kazutomo Ohtake
1994 Volume 20 Issue 6 Pages
843-848
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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One of the main sources of N
2O production is considered to be exhaust gas released from low temperature coal combustors. In this study N
2O formation/destruction characteristics in pulverized coal combustion under low temperature condition are discussed by changing coal types. The experimental apparatus is a one dimensional electrically heated laminar flow reactor. By calculating the mass balance of nitrogen included in both the sampled burning particles and combustion gas, the effect of gas species including nitrogen (HCN and NH
3) on N
2O formation is studied experimentally.
N
2O is mainly produced during volatile matter combustion. Coals which emit more HCN than NH
3 produce higher N
2O concentration. After volatile matter combustion, N
2O concentration increases again and NO concentration decreases gradually. This result can be explained by means of the mass balance of nitrogen. An increase in N
2O in char combustion may be caused not only by the reaction between NO and carbon in char : NO + (char-C) -NCO and NCO + NO→N
2O +CO, but also the reaction between nitrogen in char and NO : (char-N) +NO→N
2O. The conversion from fuel nitrogen to N
2O increases with a decrease in the burning fraction and with a decrease in the fuel ratio. This tendency depends on the difference of temperature and combustion atmosphere surrounding coal particles.
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Hiroshi Moritomi, Yosizo Suzuki, Michitaka Ikeda, Koichi Suzuki, Kin-i ...
1994 Volume 20 Issue 6 Pages
849-856
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Nitrous oxide (N
2O) is responsible for the global destruction of stratospheric ozone and for greenhouse warming. To explain N
2O emissions from coal at low combustion temperature, we have studied the mechanisms by using a batch reactor. In this paper, based on four formation sources, that is direct formation from char (Dc), indirect formation by homogeneous reaction with coal volatile, fast or first volatile (IMv), indirect formation by homogeneous reaction with char volatile, slow or second volatile (IMc) and indirect formation by heterogeneous reaction over char (IT), respective contributions to N
2O formation were evaluated by comparing the fuel nitrogen conversion to N
2O. Two coals and a petroleum coke were used as fuel. The contribution of char and volatiles to N
2O formation were elucidated by using the chars devolatilized at various temperature. The contributions of gas phase reactions and heterogeneous reactions were studied by using a short reactor to reduce the gas phase reactions. As a result, the contribution of Dc was estimated to be between 0%and 30% IMv between 20% and 30% and IMc between 40% and 70%. The contribution of IT was strongly dependent on NO concentration around char particles, which was about 20% in circulating fluidized bed combustion.
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Eiki Kasai, Fumio Saito
1994 Volume 20 Issue 6 Pages
857-864
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Combustion experiments of carbonaceous fuel composites were carried out in order to reduce the amount of NOx emitted from the iron are sintering process. The fuel composites prepared were : 1) coke granules having adhering layers of Ca (OH)
2 and Fe
2O
3 mixture and of synthetic calciumferrite (CFs) powders and 2) iron-bearing coke obtained by admixing of iron are powder with coal.
The averaged conversion ratio of fuel N into NO
x during combustion of the coke granules is lower than that of the normal coke particles. Further reduction of the conversion ratio is achieved for the combustion of coke granules having adhering layer of CF powders. It was confirmed that the presence of Fe
2O
3 and CFs accelerated the reduction of NO into N
2 by CO in the range from 873 to 1393 K. Admixed iron are powder with coal is reduced to metallic iron grains during the coking process and the content of fuel N in the obtained coke samples appreciably decreases. Conversion ratio into NO
x during combustion of the coke samples also decreases. This method enables us to reduce significantly the amount of NO
x emission by about 50% in comparison to that for normal coke particles.
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Shigeyuki Uemiya, Makoto Miyata, Toshinori Kojima
1994 Volume 20 Issue 6 Pages
865-871
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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The elution of toxic trace elements, As, Mo, Pb, V and alkaline earth, elements Mg and Ca from fly ash disposed from a commercial pulverized coal combustor was investigated. Buffer solutions of pH = 3, 5, 7 and 11 were permeated through the layer of the fly ash. A part of each element was eluted rapidly within 1 h, but the rest hardly eluted thereafter. This result indicates the presence of two or more parts remainder was with different leachability. In particular, high levels of elution were observed for As and Mo irrespective of pH. Elements with high volatility, such as As, were eluted easily from the fly ash because of their condensation on the surface of ash. It was found that elution was expressed as a function of time, t, as
Xt/ (1 +
Yt). In this equation,
X and
X/Y show the initial rate and maximum elution, respectively. There was a positive relation between the initial rate and maximum elution.
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Toshinori Kojima
1994 Volume 20 Issue 6 Pages
872-879
Published: November 10, 1994
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Combustion of granulated and carbonized coal with various ash contents was carried out and the amounts of 27 elements including trace elements in the residual ash were measured by ICP-AES. Vaporization of several elements from the ash was observed at high burning temperature. Leaching of the elements from the crushed or pulverized ash into pure or acidic water was conducted. It was clearly observed that the solubility of most of the elements detected decreased with maximum burning temperature and drastic decreases were found at a certain temperature for several elements. It is suggested that the solubility of the elements from the ash is restricted by the vitrification of ash.
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Eiji Sasaoka, Kazuyoshi Tanaka, Yoshihiko Inami, Yusaku Sakata, Shigea ...
1994 Volume 20 Issue 6 Pages
880-888
Published: November 10, 1994
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To develop catalysts for simultaneous removal of SO
x and NO
x in a flue gas, Al
2O
3, TiO
2, ZrO
2, SiO
2 oxides were prepared as catalysts and their catalytic activities for simultaneous removal were measured. The modification of these catalysts by the addition of Na was also examined. In this process, SO
2 and NO are catalytically oxidized to SO
3 and NO
2 and then fixed on the catalyst surface. The role of SO
2 for NO oxidation and the role of NO for SO
2 oxidation were also investigated. The experiments were carried out using a fixed-bed flow reactor under atmospheric pressure at 130°C. The inlet gas was mainly composed of SO
2 (250 ppm), NO (250 ppm), O
2 (5%), CO
2 (10%), H
2O (10.3%) and N
2 (balance gas).
The main results obtained were as follows : (1) Al
2O
3, TiO
2 and ZrO
2 were active for simultaneous removal, (2) The contribution of the solid base character of the metal oxides to their catalytic activities was suggested from the results of the experiments using NaY and H-NaY zeolite and confirmed by experiments in which the effects of Na addition to the metal oxides on their activities were examined, (3) SOX and NOx were assumed to be adsorbed on the same sites of the catalysts and SOX was adsorbed more strongly than NO
x and, (4) The presence of SO
2 in gas phase was indispensable for NO oxidation and NO in gas phase accelerated the SO
2 oxidation.
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Noriyuki Kobayashi, Tomoyasu Hirano, Yoshinori Itaya, Masanobu Hasatan ...
1994 Volume 20 Issue 6 Pages
889-893
Published: November 10, 1994
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The effect of coexisting H
2O with high concentration on the population balance between CO
2 (001) and CO
2 (100) levels was theoretically investigated in order to develop a CO
2 gas dynamic laser (CO
2-GDL) using combustion of hydrocarbons as a converter of thermal energy to photo energy. It was found that the population inversions between the two levels sufficient to obtain laser emission can be realized when combustion gas with methane/air at a stoichiometric ratio is adiabatically expanded so as to achieve a Mach number of 5.0 through the supersonic nozzle. The ratio of the number densities reaches on maximum at H
2O concentration of 0.4 and the location where the peak appears shifts upstream with increasing H
2O concentration. The magnitude of the population inversion increases with increasing C/H of fuel at a constant N
2 concentration. The width in the streamline keeping the population inversion, however, becomes narrow at a high concentration of H
2O.
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Noriyuki Kobayashi, Yoshinori Itaya, Masanobu Hasatani
1994 Volume 20 Issue 6 Pages
894-901
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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In order to develop a CO
2 gas dynamic laser that is driven by thermal energy generated from combustion of fossil fuel or nuclear power generation, an unsteady flame propagation combustor was developed that was applicable as a driving gas generator. In this study, the fundamental characteristics of the combustor using methane/air at normal pressure were experimentally investigated. It was found that the combustor has a wide turn-down ratio of up to 48 digit. This means the combustor can be controlled over a wide load. The combustion of methane/air was well promoted because combustion occurred through at the entire combustion chamber. The values of burning velocity were fifteen times greater than the laminar one. With fuel lean conditions, the period of combustion for a cycle can be assumed by employing the dimensionless values of normalized period by mean residence time of supplied gas. Also, burning velocity can be predicted using normalized burning velocity by mean gas velocity of supplied gas in the combustor.
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Akio Honji, Osamu Sato, Shigeru Yasukawa
1994 Volume 20 Issue 6 Pages
902-911
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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The future Japanese energy system up to the year 2030 was estimated using the linear programming model MARKAL with four scenarios used with two kinds of economical growth and two imported fuel prices. The system cost discounted to 1985 at the rate of six percent per year was chosen as the objective function. The effects of carbon tax were also evaluated. In the high fuel price scenarios, carbon dioxide emissions are larger in 2010 than that in the low fuel price scenarios, because the consumption of coal, which is much cheaper than oil and natural gas is increased. On the contrary, emission is decreased in 2030 because the supply of steam coal is at the upper bound in every scenario, and nuclear and renewable energy are thus utilized more.
In cases where a carbon tax is levied, annual carbon dioxide emissions decrease by up to about one half in 2030 compared with cases without carbon tax, though the system cost per GDP is almost the same. In this case, the nuclear and renewable energies are utilized at almost the maximum and then additional reduction of carbon dioxide emissions is only minimal even with the rise of fuel prices.
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Shoichi Takao, Yoshitaka Imori
1994 Volume 20 Issue 6 Pages
912-917
Published: November 10, 1994
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Changes in properties of a highly loaded coal water mixture (CWM) by weathering of feed coal were investigated. As the duration of weathering of the feed coal was increased, the maximum reachable concentration to obtain CWM with a viscosity of 1 Pa · s decreased and also the amount of sedimentation during two-week storage increased.
It was found that the amount of sulfate formed by oxidation of iron sulfide in the feed coal increased during weathering causing the acidification of the produced CWM. Hydrophilic functional groups on the coal surface were thus increased resulting in a decrease of “free water, ” which is needed for a good fluidity. It was considered that acidification and an increase of hydrophilic functional groups on the coal surface were the main causes of the degradation of coal slurriability.
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Kouichi Miura, Kenji Hashimoto, Kazuhiro Mae, Shinji Inoue
1994 Volume 20 Issue 6 Pages
918-925
Published: November 10, 1994
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Co-pyrolysis of coal, biomass, and waste plastics was examined as a means to increase the total conversion and the liquid yield as compared with separate pyrolysis of each substance. First, co-pyrolysis of a coal or a cellulose simply mixed with waste plastics, a polyethylene-derived wax, Orinoco tar or a coal liquefaction residue was performed using a Curie-point pyrolyzer. Only the combination of the cellulose and the polyethylene-derived wax realized increases in total conversion and liquid yield. This clarified that intimate contact at molecular level and matching of the pyrolysis rates between both substances are essential for the co-pyrolysis to be effective. Based on the above results we presented a new co-pyrolysis method of coal and wax. The coal was oxidized by hydrogen peroxide at 298K to increase oxygen functional groups, namely non-covalent bonding sites, then it was swollen by the wax. The modified and swollen coal was pyrolyzed at 1037K, which realized significant increases in the total volatiles and the liquid yield. The increases were found to be realized through the suppression of crosslinking and the acceleration of hydrogen transfer from wax to coal.
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Kouichi Miura, Kenji Hashimoto, Kazuhiro Mae, Hideyuki Wakiyasu
1994 Volume 20 Issue 6 Pages
926-933
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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We have recently developed two types of pyrolysis methods. One is flash pyrolysis of coal preswollen with a hydrogen donor solvent in an inert atmosphere (method I). This method increased significantly the yields of total volatiles and tar. The other is the pyrolysis of coal in an atmosphere containing a solvent vapor (method II). This method controlled the secondary gas phase reactions to increase the yields of benzene, toluene and xylene (BTX) selectively. In this paper, flash pyrolysis of coal-solvent slurry was proposed as a means to realize the two methods in practical processes. A coal-methanol mixture prepared from an Australian brown coal (Morwell) was pyrolyzed in a free fall pyrolyzer at 923-1123K. This method realized significant increases in the yields of total volatiles, tar and BTX. At 1023K, the yields of tar and BTX reached surprisingly high levels of 23.3 and 7.8kg/100kg-coal, respectively. Addition of a hydrogen donor solvent to the coal-methanol slurry realized further increases in the yields of total volatiles and tar. Addition of water to the slurry was also examined to utilize the coal-water slurry in this pyrolysis method.
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Tadahiro Murakata, Kenya Takahashi, Ikuo Morishita, Shimio Sato
1994 Volume 20 Issue 6 Pages
934-940
Published: November 10, 1994
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Coal degradation by anodic oxidation using an electron mediator was studied for alkaline coal slurry. To oxidize a coal effectively with insignificant oxygen generation, a suitable mediator system was sought on the basis of experimental results of redox potential of coals and an anode potential at which oxygen was generated. The experimental results showed that a redox couple Fe (CN)
3-6 + e= Fe (CN)
4-6mediated effectively electrolysis of an alkaline slurry of Taiheiyo coal and was found to be suitable as the mediator system. To know whether or not the mediator system can be applied to other coals, the rate of a chemical reaction step involved in the anodic coal oxidation was studied for various coals. The results showed that the rate of the chemical reaction step decreased with higher rank coals. Thus, the present mediator system was suggested to be efficient for relatively low rank coals.
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Yuan C. Fu, Katsuya Ishikuro, Makoto Akiyoshi, Mitsuyoshi Yamamoto, Ta ...
1994 Volume 20 Issue 6 Pages
941-945
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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This study deals with hydrodesulfurization of a sulfur-containing model compound using syngas and steam. Dibenzothiophene could be hydrodesulfurized with syngas and steam in the presence of petroleum solvent and NiMo catalyst at high pressure and 673K. Although the conversion was not as extensive as that observed with hydrogen, the extent of desulfurization increased with the increase of H
2/CO mole ratios in syngas. With the amount of water at H
2/CO mole ratios of 0.3-0.6, an active water-gas shift reaction occurred. Hydrodesulfurization of dibenzothiophene carried out in H
2/CO-D
2O and D
2-CO-H
2O systems yielded deuterated products of cyclohexylbenzene and biphenyl in both systems. Some deuteration of the unreacted dibenzothiophene and solvent also occurred. These results indicate that active deuterium produced via water-gas shift reaction of CO with D
2O as well as hydrogen in the gas phase could both participate in the hydrodesulfurization along with the hydrogen/deuterium exchange reaction with substrates.
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Ikusei Nakamura, Kaoru Fujimoto
1994 Volume 20 Issue 6 Pages
946-951
Published: November 10, 1994
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A new type of coal/petroleum residue separate co-processing method, which is composed of vacuum residue cracking with coal-based catalyst and activation of brown coal for preparation of the cracking catalyst, is proposed. Vacuum residue was cracked by using a disposable metal supported active carbon catalyst in the presence of hydrogen (5.0-7.0 MPa) to produce high quality distillates and coke without significant hydrogen consumption. Even the most inferior vacuum residue, such as Maya VR, was cracked completely. The active carbon was prepared by treating brown coal with carbon dioxide at temperatures around 850°C to produce tar, carbon monoxide and water. Carbon monoxide and water can be converted into hydrogen and carbon dioxide by a water-gas shift reaction. The hydrogen can be supplied to hydrocracking of residual oil and upgrading of product oil. The carbon dioxide may be utilized appropriately for coal activation.
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Hiromoto Usui, Shuichi Morita, Takashi Saeki, Toshio Tsujino, Hiromu I ...
1994 Volume 20 Issue 6 Pages
952-958
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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The present investigation is aimed at finding a way to develop a thermal preconditioning process of a CWM for a coal gasification process. The liquid water in a CWM was evaporated very rapidly in a thermal preconditioner. Two-phase flow consisting of coal particles and steam was obtained at the exit of the thermal preconditioner, and this gas-solid mixture was considered as the feed material for an entrained-flow coal gasifier. Also, an analysis of a coal gasification process proved that the cold gas efficiency and the oxygen demand were considerably improved as a result of the incorporation of a thermal preconditioning process into a coal gasification process. Thus, it was concluded that the thermal preconditioning process proposed in this study was effective for increasing the gasification efficiency if the heat recovery for the thermal preconditioner was carried out appropriately.
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Toshimasa Takanohashi, Masashi Iino, Kazuo Nakamura
1994 Volume 20 Issue 6 Pages
959-964
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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A computer simulation using computer-aided molecular design (CAMD) was applied to the construction of three-dimensional coal structure. The molecular models for pyridine soluble constituent of Chinese bituminous coal (Zao Zhuang coal) with various lengths of intercluster bonds, which each connect two aromatic clusters, were constructed, and the energy-minimum conformation was determined by CAMD of the molecular mechanics and the molecular dynamics. The density of the molecular models was also determined by simulation using CAMD. The simulated density of the structure in which the length of intercluster bond is two carbon atoms was found to be in good agreement with that determined experimentally.
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Tadafumi Adschiri, Kouichi Nakada, Satoshi Ogasawara, Kunio Arai
1994 Volume 20 Issue 6 Pages
965-970
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Specific features of solid catalyzed reaction in supercritical fluid were discussed through the comparison of denitrogenation of coal tar pitch by using NiMo-Al
20
3 catalyst in supercritical fluid (toluene/tetralin mixture) and in liquid (1-methyl naphthalene/tetralin mixture). Basic nitrogen compounds reacted faster than neutral nitrogen compounds on the solid-acid-catalyst in both cases. At 703 K and 15 MPa, and in the range of particle sizes from 0.11 to 0.85 mm where denitrogenation proceeded under chemical reaction control, the reaction rate in supercritical fluid was higher than that in the liquid.
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Katsuyasu Sugawara, Yasuhito Tozuka, Keiko Abe, Takuo Sugawara
1994 Volume 20 Issue 6 Pages
971-975
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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Kinetic parameters were determined for the release rates of volatile matter and sulfur from coals at temperatures of 1120K to 1550K by using a free-fall pyrolyzer which enabled coal particles to be heated at the rate of 2 × 10
4Ks
-1. The release rate of volatile matter increased with the increase of heating rate while each coal showed a different dependency of ultimate volatile yield on the heating rate and final temperature. The desulfurization extents of organic sulfur were larger than the ultimate volatile yields. The release rate of organic sulfur increased with the increase in heating rate.
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Atsushi Tsutsumi, Hiromichi Kameyama, Takashi Asano, Kunio Yoshida, At ...
1994 Volume 20 Issue 6 Pages
976-981
Published: November 10, 1994
Released on J-STAGE: November 12, 2009
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The liquefaction of low-rank coal with supercritical water has been studied at 400°C and 25.3 MPa using a semi-batch microreactor. Liquid yield up to 41wt% is attained in less than 7 min. Subsequent gasification of residue takes place.
2D-n. m. r. spectral analysis of liquids products in supercritical and the results of mass balance suggests that both hydrolysis and condensation reactions contribute to oxygen removal during supercritical water liquefaction of coal.
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