Solid materials in the reactors of 150 tons of coal per day liquefaction pilot plant

After a long term operation of the 150 tons/d bituminous coal liquefaction pilot plant (PP), a variety of solids have been found deposited at several locations in the plant. Inorganic particles accumulated in the plant's liquefaction reactors and deposits on the wall of the hot-high-pressure separator (HHPS) and downstream piping of the letdown valve (LDV) were characterized in the present study, by conducting analyses using optical and scanning microscopes with an energy dispersive X-Ray spectrometer (EDX). The inorganic particles accumulated in the reactor consisted of several layers of coal minerals and a catalyst. Successive deposition of soluble minerals forms layers there of over the core of the solid mineral particles as SiO2 Massive solid deposits were found in the HHPS and the downstream piping of the LDV, containing coal minerals, a catalyst, inert and unliquefied active macerals dispersed in a carbonized pitch matrix. The inorganic particles were dispersed in the massive solid deposits, said particles having the same compositions as those found in the reactors. Such a feature of the solid deposits suggests that the solid mineral particles agglomerated in the reactors flowed out of the reactors and the heavy fraction of viscous slurry containing particles of high density was sedimented on the bottom surface of the HHPS and the downstream piping of LDV due to the low flow rate. The pitch fraction in the sedimented materials was carbonized slowly at around 400 degreesC, to form composite solid of carbon and inorganic particles, while the lighter fraction was washed out by the streaming coal liquid. Solid particles dispersed in the pitch prohibit development of large anisotropy through low temperature carbonization under a high viscosity. Some procedures are proposed to prevent such deposition in a long term operation. (C) 2001 Elsevier Science Ltd. All rights reserved.