Article pubs.acs.org/EF
Hydrothermal Treatment of Brown Coal To Improve the Space Time Yield of a Direct Liquefaction Reactor Toshinori Inoue,† Osamu Okuma,‡ Kaoru Masuda,† Motoharu Yasumuro,§ and Kouichi Miura*,∥ †
Applied Chemistry Division, Kobelco Research Institute, Inc., 1-5-5, Takatsukadai, Nishi-ku, Kobe 651-2271, Japan Research Department, The New Industry Research Organization, 1-5-2, Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan § Coal and Energy Technology Department, Kobe Steel, Limited, 2-3-1, Shinhama, Arai-cho, Takasago 676-8670, Japan ∥ Department of Chemical Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishigyo-ku, Kyoto 615-8510, Japan ‡
ABSTRACT: The possibility of hydrothermal treatment (HTT) of brown coal at 200−350 °C was examined as a pretreatment method for improving the space time yield of a Victorian brown coal liquefaction reactor. Main reactions occurring during HTT below 350 °C were decarboxylation and dehydration, by which most of carboxylic groups were decomposed. Sodium and chlorine in the brown coal were almost completely removed below 250 and 300 °C, respectively, during HTT. Around 20−30% of Ca and Mg in the brown coal was also removed by HTT below 350 °C. The viscosity of the coal−solvent slurry prepared from a HTT coal was less than 1/10 of the viscosity of the coal−solvent slurry prepared from a just dewatered coal. This enabled the increase of the coal concentration of the coal−solvent slurry from 28 to 40 wt %. The significant increase of the coal concentration of the coal−solvent slurry prepared from the HTT coal was found to be realized mainly by the decrease of the pore volume of the coal particles through HTT. These results suggest that HTT will be a pretreatment method effective not only to increase the space time yield but to suppress the scale formation of the brown coal liquefaction process.
1. INTRODUCTION Recent worldwide oil consumption growth and the subsequent oil price increase have been demanding the necessity of alternative sources for petroleum-based fuel.1 Under such circumstances, effective processes liquefying abundant coal reserves have received greater attention again in several countries. Although coal reserves are very huge worldwide, about a half of the reserves is occupied by low-rank coals that have not been used effectively. Therefore, development of more effective liquefaction technologies of low-rank coals, such as brown coal, will become important.2 The reserve of the Victorian brown coal in Australia is very huge. However, its use is limited only for power generation near the coal mine. This is because the brown coal contains much water, reaching more than 60 wt %, and it ignites easily when dewatered, which prohibits its storage and transportation for international trading. To overcome this drawback and to meet the demand increase of liquid fuel, the brown coal liquefaction (BCL) process has been developed for the Victorian brown coal, and a pilot plant of 50 tons/day (dry basis) was constructed and had been successfully operated in Australia between 1985 and 1990.3 The BCL process is a twostage hydrogenation process that consists of four unit sections: dewatering, primary hydrogenation (liquefaction), de-ashing, and secondary hydrogenation, as shown in Figure 1. The BCL process, however, was not commercialized, because the price of coal-derived oil had not been competitive with that of petroleum in the 1990s when the process was developed. Despite the setback, continuous efforts have been made to improve the liquefaction process for reducing the oil production cost.3 To make the BCL process cost-competitive, however, several problems still exist to be solved. © 2012 American Chemical Society
In the BCL process, pulverized raw coal is dewatered in a solvent by the so-called slurry-dewatering system4 and then hydroliquefied at high temperature (
