To convert coal into clean gases, various types of gasifier have been being developed.Recently, based on the requirement to attain both large throughput and high efficiency during gasification, there is a tendency that the temperatures in the gasifier, especially those in the char partial oxidation zone, rise, and sometimes they rise over the melting point of ash.To avoid the agglomeration of particles, the bed is stirred at a certain interval, or relatively high gas velocities are achieved in the fixed-bed gasifiers.Some attempts, such as distributor improvement and attainment of high temperature without ash agglomeration, are made for the fluidized-bed gasifiers.In the entrained-bed gasifiers, ash is melted to completely utilize the carbon contained in the coal.In this paper, the tendency to aim high gasification temperatures is summarized, and the methods to realize such high temperatures are discussed.
Combination of the pyrolysis method, previously invented by the authors, and the semi-micro gasification method, presented in the current JIS method for the nitrogen in coke, was investigated in order to establish a new method for the determination of nitrogen in coal. Hongay and Yubari coal were selected as typical coals of anthracite and bituminous coal, respectively, to investigate the optimum conditions of the method.The optimum analytical procedure is demonstrated as follows. A coal sample of 0.1g, pulverized up to under 149pm in diameter, was accurately weighed out, and mixed with powdered soda lime of 1.5g.The mixture was distributed in a sample boat, and uniformly covered with FeCl3-Al2O3 catalyst of 2.0g, prepared by mixing FeCl3 aq.soln and active Al2O3 for column chromatography and drying.The boat was inserted into the hot zone of a pyrolysis tube heated at 900-1, 000°C.The nitrogen in the sample was pyrolyzed in the presence of steam (3.0g/min of flow rate) and converted to ammonia quantitatively within 10 min.The ammonia was determined by the conventional titration method. The method was applied to various coals, and the results agreed with those obtained by the current JIS method (semi-micro Kjeldahl method).
Infrared spectra of FeSO4, Na2edta, MgSO3-14NO and15NO systems, and those of related substances were measured in aqueous solution phase.The results showed that EDTA present in the solution forming a complex of Fe (II) edta (υaCOO, 1, 597cm-1), NO is absorbed to the complex through the formation of NO-Fe (II) edta coordinate bond (υNO 1, 775, vaC00 1, 610cm-1), and that the coordinated NO react with S03-to form imido-di-sulfonate or nitriro-tri-sulfonate and or compound analogous to them (υ S0, 1, 260, 1, 230, 1, 030em-1).Stretching vibration frequency of the coordinated14NO, 1, 775cm-1, suggests that the edta has no activity to promote the reduction of the NO.It was found that a part of the Fe (II) is oxidized to Fe (III) in the present reaction, which is considered to be probably caused from the absorbed NO.It should be also noted that Fe (II) edta-NO (1, 775cm-1) was distinguishably observable from Fe (II)-NO (1, 810cm-1), as well as Fe (II) edta (1, 597cm-1) from Fe (II) edta (1, 620cm-1) with the use of IR technique.
In order to obtain fundamental informations on hydrogasification of coal, thermogravimetric curves were measured for chars prepared by heat-treatment of coals at temperature range from 400°C to 900°C. Kinetic analysis of hydrogasification was done with the following equation in which the rate was expressed in terms of unit surface area; Rate constant= (-dw/dt) /S= (-dw/dt) /Cmiddot;w2/3=1/Ck where w and S are weight and sruface area of samples, respectively.C is a constant depending on both shape factors and density. It was found from the results that k value was generally larger for chars than those for original coals and a maximum value of k was obtained for the char heat-treated at 600°C. As the rate was closely related to the internal surface area of each sample, the reaction would be thought to proceed in such a way that gaseous H2 molecule could enter even into a considerably small pore of the solid to react with carbon.
Heat?treatment of coal?asphalt mixtures were performed using a bench scale pipe reactor in order to determine the effect of heating rate on solubilization of coals by solvolysis.Coals tested were a bituminous coal (C: 82.6%) and a brown coal (C: 76.3%), and Khaf ii asphalt (vacuum residue) was used as a solvent for solvolysis reaction of coal. The asphalt or coal-asphalt mixture (1: 2 by weight) was continuously fed into th pipe reactor, which was heated at a temperature between 450 and 540°C by salt bath fo rapid heating.The inner diameter of the pipe reactor was 3 mm, and initial heating rate o coal slurry was estimated about 2700°C/min. After the heat-treatment, the yields of pitch, oil and gaseous product were determined (Fig.3), and then the solvent extraction of the pitch, analysis of the oil and gaseous product were carried out.It was shown that the viscosity of pitch was remarkably decreased with increasing in reaction temperature.(Fig.5) Dependence of the conversion of coal to solvent soluble matter on reaction temperature was determined from the result of solvent extraction, and maximum conversions for the bituminous coal and the brown coal were 73.2 and 46.7%, respectively.(Fig.9 and 11) It was found that the conversion of brown coal by the rapid heating using the pipe reactor was higher than that by slow heating using batch-wise reactor in solvolysis, because of the predominant thermal decomposition reaction over the polymerization reaction of coal and asphalt in the pipe reactor.Considerable amounts of ethylene and propylene were formed as gaseous products, and olefin-rich oil was obtained.(Fig.6 and 7) At a temperature above 520°C, however, the formation of benzene insoluble matter from the solvent was observed in the case of brown coal-asphalt mixture.
Proton F ID signals were obtained for 13 crude oils and 12 asphalts with a 20 MHz pulsed NMR spectrometer, and it was found that each signal consisted of several components which had different T2 values. 1/T2 value shows a fairly good relationship with, d154, (for crude oils), or softening temperature (for asphalts), From this relation, straight asphalts were thought to have different structures from blown and propane deasphaltd asphalts.
Emission and reduction of NOx during fluidized bed combustion were studied using dolomite as a bed material.Arabian Light vacuum residue was used as fuel oil in this work, since this oil has the lowest combustibility among various residual oils studied in the preceding work.Combustion efficiency & about 98% was attained with this fuel oil at 850°C and 20% excess air.Under these conditions, SOx+H2S concentrations were as low as 15 ppm, while 328 ppm of NOx was emitted.It was found, however, that NOx concentration could be reduced to 220 ppm by the addition of NH3 to the combustion system.Moreover, the mixture of H2 and NH3 was more effective in reducing NOx concentration.
In order to promote the reaction between NOx and NH3 the catalitic activity of dolomite loading various metal oxides was tested.As a result dolomite loading Fe2O3 was found to be the most active of the bed materials tested.NOx emission was reduced from 267 to 57 ppm by the addition of 2000 ppm of NH3 when this bed material was used.Furthermore, combustion efficiency at temperatures below 900°C was improved by loading Fe2O3 on the dolomite.The sulfer removing efficacy of the Fe2O3-dolomite was exactly same as that of dolomite, and the concentration of SOx+H2S in flue gases was as low as 10 ppm at 850°C.