Takuo Sugawara

Dynamic behavior of trace elements during pyrolysis of coals

Release behavior of sodium and potassium was followed during pyrolysis of coals in a nitrogen stream up to 1200°C. Sodium and potassium in coal and char were classified into five fractions by a serial dissolution method with H 2 O, CH 3 COONH 4 , HCl, H 2 SO 4 and HF solutions. Distribution of selenium in coal matrix and its release behavior were observed for density-separated samples during pyrolysis. The results showed that lower temperature release of potassium was observed during pyrolysis comparing to the sodium release. Fractions of H 2 O soluble and CH 3 COONH 4 soluble decreased, and fractions of H 2 SO 4 soluble increased with heat treatments for both alkali metals. Selenium was distributed unevenly in the coal matrix and its content was correlated well with pyritic sulfur content but not with organic sulfur content.

Dynamic behaviour of sulphur forms in hydropyrolysis of coals

Abstract Three kinds of noncaking steam coals were pyrolysed with the use of fixed beds in hydrogen streams at atmospheric pressure and 30 kg cm −2 , and up to 900 °C and 500 °C, respectively. To determine the inorganic forms of sulphur in char produced in reduced atmosphere, a quantitative analytical method has been described. A direct method to determine iron sulphide by modifying the Gladfelter and Dickerhoof method has been proposed. Sequential changes in the contents of various sulphur forms in the solid phase and hydrogen sulphide in the gas phase then followed. Desulphurization from the solid phase was characterized by the complex behaviour or organic and inorganic sulphur forms. A desulphurization scheme is proposed in this paper.

Effect of heating rate and temperature on pyrolysis desulfurization of a bituminous coal

Abstract Non-caking bituminous Ermelo coal was pyrolyzed using a fixed bed with thermogravimetric analyzer in a nitrogen stream at atmospheric pressure up to 1173 K with heating rate of 20–100 K/min. The desulfurization was assessed for final temperatures of 773–973 K. The sulfur content in residual char depended on the heating rate as well as the terminal temperature. Sulfur form analysis clarified that the change in total sulfur, which showed a minimum, was due to the change in organic sulfur during the course of pyrolysis. Sequential changes of sulfur forms at different heating rates were successfully simulated kinetically based on a proposed volume reaction model and desulfurization scheme which considers competing phenomena between the uptake reaction of hydrogen sulfide by the organic matrix and dispersion of hydrogen sulfide within a coal particle. Rapid pyrolysis using a free fall pyrolyzer confirmed that the high heating rate was favorable for sulfur removal from the solid phase.

Dynamic behaviour of sulphur forms in rapid hydropyrolysis of coal

Abstract Seven bituminous and sub-bituminous coals were rapidly hydrodesulphurized with a free-fall pyrolyser at atmospheric pressure, temperatures up to 1233 K and a heating rate of ≈ 6000 K s −1 . The observed changes in the contents of sulphur forms were successfully simulated kinetically. Organic sulphur content was reduced by 54–92% and pyritic sulphur was almost reduced to ferrous sulphide sulphur in a very short reaction time of −1 with the increasing ratio of internal surface area of 1–4, the frequency factor of the release rate of volatile organic sulphur to tar and gas increased from 1.1 × 10 5 to 3.4 × 10 5 s −1 and that of organic sulphur to tar increased linearly from 3 × 10 4 s −1 to 2 × 10 5 s −1 . The desulphurization results of total sulphur and char yield in rapid hydropyrolysis at atmospheric pressure and those in slow heating hydropyrolysis at high pressure are comparable. Comparing the observed rates of the desulphurization steps to those obtained under slow heating at high pressure treatments, rapid hydropyrolysis increases the frequency factors in the rate of release of organic sulphur to gas and tar by 2.5–10 times, while the frequency factors in the reduction rate of pyrite is suppressed by three to four orders. Rapid hydropyrolysis has potential as a pre-treatment process with high thermal efficiency for coal cleaning.

Preparation of zinc oxide varistor by a wet chemical method

Abstract A wet chemical method has been applied to synthesize zinc oxide varistor in order to obtain chemically pure and homogeneous product. Efficient yield was attained for precursors by a precipitation method using zinc acetate as a starting material with praseodymium oxide and cobalt chloride as additives. The calcination process, crystalline size of zinc oxide, additives distribution and voltage current curve were characterized for the samples, which were prepared by a wet chemical method with or without calcination, and by a ball-mill method for comparison.

Correlation of liquid-side mass transfer coefficient based on the new concept of specific power group

Abstract A new concept of a specific power group, proposed previously for correlating the mass transfer between a liquid and particles fixed in the liquid with a low level of turbulence, is discussed in comparison with the conventional concept of a specific power group from the Kolmogoroff theory. The new concept gives a single correlation equation of liquid-side mass transfer coefficients for single particles, fixed beds, and fluidized beds, which is practically the same as the correlation equations for stirred tanks, suspended bubble columns, and two-phase tube flow based on the conventional concept. The agreement induces the consideration of the relationship between specific power groups based on the new concept and the conventional one from the viewpoint of hydrodynamics. The energy dissipation rate for a particle, defined in the new concept, is extended to the particles suspended in a fully developed turbulence field and is hydrodynamically compared with the average energy dissipation rate defined conventionally in the turbulence field. It is revealed that the magnitude of the specific power group including the former energy dissipation rate almost agrees with that including the latter one. Thus, combined with the specific power group based on the conventional concept which has a simplicity in the calculation of its value for suspended particles, the specific power group based on our concept is useful as a general parameter in the study of mass transfer phenomena between a liquid and particles where the liquid is either quiescent or turbulent and the particles are fixed or suspended.

Dynamic behaviour of sulfur forms in rapid pyrolysis of density-separated coals

Abstract Non-caking bituminous coal was separated into three groups by sink-float in aqueous zinc chloride. These samples were rapidly pyrolysed in free fall at atmospheric pressure under nitrogen, at temperatures up to 1253 K and heating rates of 4000–6000 K s −1 . The differences observed in the dynamic behaviour of sulfur forms, devolatilization and internal structure resulted from variation in maceral composition. The ultimate extent and release rate of volatile matter increased with decreasing density of sample. The experimental results indicate that rapid heating promoted the devolatilization reaction for the volatile precursors contained in the low-density group. Rapid pyrolysis also promoted the development of internal structure for the low-density group composed of exinite and vitrinite, but not for the high-density group enriched in inertinite. The organic sulfur content was reduced by 76, 67 and 34% within 0.4 s, in order of increasing density. The reactivity of organic sulfur is considerably affected by the change in sulfur forms with maceral group composition.

XANES analysis of sulfur form change during pyrolysis of coals

Three kinds of coal and their density separated samples were rapidly pyrolyzed in a free-fall reactor under a nitrogen stream at a terminal temperature of 1253 K. X-ray absorption near edge structure analysis was applied to directly determine the sulfur forms in the coal and pyrolysis char. The results showed that the low-density group contained sulfide and sulfoxide, which could contribute to the high extent of organic sulfur removal. Thermally stable thiophenic sulfur was observed in the higher density groups as a major form of organic sulfur.

Characteristics of rapid hydropyrolysis of coals in a free fall pyrolyser

Abstract Five non-caking and two caking coals were pyrolysed rapidly using a free fall pyrolyser in a hydrogen stream at atmospheric pressure and at temperatures up to 1233 K, with a heating rate of ≈6000 K s −1 . Sequential changes in the yield of volatile matter and char internal surface area were followed for several treatment times, from ≈0.1 to 0.4 s. The pyrolysis rate was determined by considering changes in particle temperature, diameter and apparent density. Average rate constants of pyrolysis were correlated with the increasing ratio of internal surface area in the early stage of pyrolysis. Rapid-hydropyrolysis char was more favourable for gasification than slow-heating pyrolysis char.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in plywood combustion gas

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/DF) levels in plywood combustion gas were investigated for the effects of ammonium chloride (NH4Cl) and paint. For combustion systems in which neither NH4Cl nor paint were present in the plywood samples, total amounts of PCDD/DFs in the combustion gas were in the order of 35-529 ng/Nm3, and were higher in the systems with softwood trees than broadleaf ones, depending on the Cl concentrations. For the systems with added NH4Cl and no paint, and those without NH4Cl but were painted, higher PCDD/ DF rates were observed at combustion temperatures of 270 degrees C and 500 degrees C, respectively. However, for the systems with both NH4Cl and paint, their amounts in the range of 0.6-13 ng/Nm3 were the lowest in all systems. The PCDD/DF abundance profiles were similar to their patterns in pentachlorophenol (PCP). Furthermore, it was found that the 2,3,7,8-chlorine substituted penta- and hexa-CDDs contributed more than other 2,3,7,8-chlorine substitutes to toxicity equivalency (TEQ).