Mitsunori Makino

Correlation of gasification reactivities with char properties and pyrolysis conditions using low rank Canadian coals

Abstract During the flash pyrolysis and flash hydropyrolysis of coals performed at relatively low temperatures (around 650 °C) to maximize liquid product yields, a large amount of char is obtained. It is expected that this char will be gasified to produce synthesis gas or to generate electricity. In this work the gasification rates of chars produced by flash pyrolysis or flash hydropyrolysis of different Canadian coals were measured to investigate the effects of pyrolysis conditions on char reactivity. Gasification measurements were made by the temperature programmed reaction (TPR) method in an air atmosphere. Data obtained were analysed using the Bhatia-Perlmutter model to obtain gasification rate parameters. These were used to represent char reactivity. In all cases, reactivity of a char decreased as the severity of the pyrolysis step increased. Several char properties such as pore surface area, amount of chemisorbed oxygen and residual volatile matter were measured in addition to the proximate and ultimate analyses to see if one or more of these properties would serve as a reactivity index. The amount of chemisorbed oxygen was found to be the best index.

Effects of hydrogen pressure on hydrogasification of Taiheiyo (Japan) coal

Abstract The non-isothermal hydrogasification of Taiheiyo coal is studied at hydrogen pressures up to 5 MPa and temperatures of 900 °C using a high-pressure thermobalance and tubular reactor. Gaseous products are analysed and liquid products obtained from the mass balance. Rates of formation of methane increased with temperature to two maxima, at 550 °C and at 750 °C. Corrections to rate are necessary because of appreciable weight losses. In the temperature range 650–800 °C the activation energy of methane formation is ≈ 115 kJ mol −1 . Below 55 °C, the pressure dependence of reaction is 0.3, becoming first order at higher temperatures. Rates of formation of methane and ethane indicate a similar mechanism of formation. Rates of formation of liquid hydrocarbons maximize at ≈ 450 °C and increase with hydrogen pressure.

Factors affecting methane evolution on pyrolysis of coal under pressure

Abstract In order to make clear the effect of pressure upon the gaseous products on pyrolysis of coal, experiments were carried out using a flow-type apparatus under helium pressure up to 900 °C, changing both the superficial velocity of carrier gas and the height of the coal bed. No significant pressure effects on the gaseous products were observed. An increase of methane evolution was found above 600 °C on account of the decrease in superficial velocity and the increase in height of the coal bed.

The effect of acid treatment of coal on H2S evolution during pyrolysis in hydrogen

Abstract The amount of H2S evolved during pyrolysis was analyzed by g.c.-m.s. for four types of raw coal samples, Taiheiyo, Datong, Wandoan and Mequinenza. These coals were treated with HNO3 or HF HCl solution, in which inorganic sulfur was eliminated by the acid treatment. In the case of HNO3-treated samples, the evolution of H2S in the low temperature region, below 500°C, was reduced by the chemical oxidation. At high temperatures, the amount of H2S evolution from acid-treated coal was markedly increased compared to the raw coals, especially Taiheiyo and Wandoan, through the elimination of minerals. From X-ray fluorescence analysis and X-ray powder diffraction of coal and char, it was confirmed that calcium in the raw coal has an important role for the fixation of sulfur during pyrolysis.

Relation between formation rates of methane and hydrogen on pyrolysis of coal under pressure

Abstract In an earlier paper 1 it became clear that secondary-methane formation occurs under certain experimental conditions during pyrolysis of coal. In order to study this more deeply, the evolution rates of methane and hydrogen were measured simultaneously for an anthracite and a lignite. The secondary-methane formation was accompanied by a corresponding decrease in hydrogen formation. It is suggested that secondary-methane formation occurs according to the equation C + 2 H 2 = CH 4 on an average and is proportional to the partial pressure of evolved hydrogen.

Measurement of CO2 Gasification Rate of Coal Char Under High Pressure and High Temperature Using a Mini Directly-Heated Reactor

A mini directly-heated reactor (mini-DHR) was constructed to measure the gasification rate handily under high CO2 pressure of ~ 2 MPa in the presence of other gases, such as CO and H2, at T = ~ 1,200°C. The mini-DHR was made of U-shaped SUS or Pt tubing of 3 mm I.D. The reactor itself was used as a heating element. An electric current of 75–150 A and a few volts were introduced to the reactor to heat up the reactor up to 900–1,200°C. About 1 mg of char was placed in a platinum mesh basket of 1.0 mm I.D. and 10 mm high. The basket with the char sample was placed just above a thermocouple in the reactor. The conversion of char, X, was estimated by weighing the remaining char sample. The X vs. t relationships obtained under various conditions were analyzed to formulate a gasification rate equation in the presence of both CO2 and CO for a char prepared from an Australian brown coal.

Study on reaction characteristics of coal hydrogasification.

In order to estimate a suitable condition for the production of high calorie gas by the hydrogasification of coal, Taiheiyo coal was gasified continuously with hydrogen, and the yield of each product or the composition of gas produced was measured. The experiments were carried out under conditions of 714-775°C and 0-50 kg/cm2G. The feed rate of the coal ranged from 0.256 to 1.47 kg/hr and of hydrogen ranged from 0.113 to 1.059 m3/hr.The volume of methane produced was in the range of 0.2 to 0.3 m3/kg-coal, and it depended strongly on the feeding ratio of coal to hydrogen. The other factors, such as the hydrogen pressure and the coal feed rate, did not affect obviously on the evolution of methan. The yield and the viscosity of tar decreased with the residence time of gas in a reactor. The coal conversion was ranged from 0.38-0.55 kg/kg-coal and it depended on the feeding ratio of coal to hydrogen. The total heat value of the residual char was in good linear relation to the coal conversion.

Study on Gasification of Coal under Pressure Hydrogasification at Lower Temperature Region

It has been known that the evolution of methane shows the maxima at about 550°Cand 750°C when a coal was heated in the atmosphere of pressurized hydrogen under non-isothermal condition.In order to make clear the hydrogasification phenomena in the visinity of the maximum at lower temperatare, 550°C, Taiheiyo coal and its carbonized products were gasified under a hydrogen pressure of 40 atm at constant temperatures, 400-600°C, for 5 hours to which the small scale batch-type gasifier was heated from outside electrically. Discussions were made taking both the changes with time in evolution rate of gaseous hydrocarbons and the conver-sions of carbon and hydrogen in the starting material to gaseous, liquid and residual products into account.It is suggested that at lower temperature below about 600°C the gaseous hydrocarbon is evolved not by the reaction between the hydrogen and the carbon itself in the coal but that between the hydrogen and the limitted active sites in the coal which are excited by the in-crease of temperature but depressed remarkably by the stop of the increase of temperature. The active sites in the carbonized coal heat-treated below reaction temperature were as effective as those in the untreated raw coal, while those in the carbonized coal above reaction tem-perature disappeard almost completely resulting in no evolution of gaseous hydrocarbons.

Studies on Gasification of Coal under Pressure Hydrogasification of Taiheiyo Coal under Non-isothermal Conditions

In order to clarify the hydrogasification reaction of coal, the change in weight loss and the corresponding gaseous products were measured at various hydrogen pres-sures under non-isothermal conditions.The evolutions of gaseous hydrocarbons by hydrogasification began from about 420°C, reached their respective maximam rate at the same temperature of about 550°C and then decreased irrespective of the hydrogen pressure. After showing the minima at about 600°C, the formations of methane and ethane again increased to the clear second maxima. It was found that below 600°C the ratio of the formation rate of ethane to that of methane remained constant regardless of the reaction temperature, but increased with increase in hydrogen pres-sure. This suggests that some active portion of carbon in coal structure will simultaneously produce gaseous hydrocarbons including ethylene and propane.Above 600°C, methane was predominatingly produced from fixed carbons at a rate proportional both to the hydrogen pressure and to the weight of residual coal.

Studies on Gasification of Coal Under Pressure

Rapid pyrolysis of Taiheiyo coal was studied at 900°C and argon pressure-50atm. An increase in argon pressure to 50atm caused the secondary decomposition of tarry materials in the interspace among coal particles, which led to an agglomeration of coal particles as well as an increase in char yield.It was suggested that the overall pyrolysis of coal proceeded with the following reaction sequence.Decomposition of coal → fast decomposition of volatile → slow reactions between product gases(primary decomposition) (secondary reactions)Compared with slow heating at 3.3°C/min, rapid heating of coal enhanced the yield of unsaturated gaseous hydrocarbons such as ethylene and propylene. The unsaturated hydrocarbons were converted to methane when the secondary reactions were forced to proceed by elevating the pressure or prolonging the residence time of product gases.Effect of pressure and product-gas residence time on the distribution of gaseous hydrocarbons were quantitatively well expressed by a reaction model which was concerned only in the last step in the above sequence.