The operation of coal liquefaction pilot plant has been carried out for 269 days, including 3 kinds of coal and the stable operation being continued 1920 h, since December 1996 to September 1998, in Kashima, Japan. Through the coal-in-operation, the high oil yield and long-term consecutive operability have been confirmed.
Nevertheless after a long operation, a variety of solid deposits have been found in several locations of the plant such as liquefaction reactors and hot high pressure separator. These were characterized using proximate, ultimate, ash component, optical microscopic, so on, and EDX analyses.
The deposit was found to consist of coal minerals, catalyst, inert and unliquified active macerals which were dispersed in carbonized pitch matrix.
The mineral particles containing catalyst and coal minerals are found to be agglomerated in several layers as found as the reactors. Such a feature of deposit suggests that the viscous slurry of high density was trapped on the bottom surface of the separator.
The pitch matrix is carbonized slowly around 400°C, to form composite solid of high densities, while the light fraction is washed out by the coal liquid during the operation.
Low temperature and solid particles dispersed in the pitch prohibit development of large anisotropy.
From these results, some ideas to prevent such depositing are proposed.
