A case history of a fixed bed, coal-derived oil hydrotreater

Abstract

With the apparent shrinkage in the worldwide supply of liquid hydrocarbon fuels, upgrading of coal-derived liquids to synthetic crude oils will eventually emerge as a commercial entity. Although the Char-Oil-Energy Development (COED) Project has been shelved in the short term, information about the reaction engineering of the upgrading of coal-derived liquids by hydrotreatment in the COED Process should be relevant to upgrading technologies for other coal liquefaction processes. The COED Process was developed by FMC Corporation and the Office of Coal Research (now DOE) in the late 1960's and early 1970's. The process produced a synthetic crude oil, medium Btu gas and char by multi-stage, fluidized bed pyrolysis of coal. The raw coal-tar produced by pyrolysis was upgraded to synthetic crude oil by catalytic, fixed-bed hydrotreatment. Raw coal-tar has different properties from petroleum-derived oils, and upgrading by hydrotreatment is not an off-the-shelf technology. A 30 barrel per day fixed-bed hydrotreater was constructed and operated at the COED pilot plant site. The pilot plant hydrotreater design was based on conventional petroleum residua hydrotreatment technology together with bench-scale hydrotreatment tests performed by ARCO in the 1960's utilizing coal-tars produced in a process development unit. The pilot plant hydrotreater did operate for about four years providing valuable information about the reaction engineering of the hydrotreatment process as well as providing numerous samples for applications studies performed by other DOE contractors and interested potential users of the COED syncrude. Of note, 50,000 gallons of COED syncrude were supplied to the U.S. Naval Ship Engineering Center for shipboard testing in the boilers of the U.S.S. Johnston on November 15–16th, 1973. This paper deals with the reaction engineering of the guard chamber and fixed-bed hydrotreatment reactors at the COED facility. Of major importance is the study of the role of the feedstock (pyrolysis coal-tar) properties and their effects on the catalysts utilized in the reactors. A working kinetic model has been derived that could allow a designer to optimize a particular set of design parameters and a plant operator to determine catalyst life. A quantitative comparison has been made of the effect of metals content of coal-derived oils and petroleum resids on catalyst deactivation.