Coal liquefaction is one of the most difficult processes for instrumentation. This paper describes technical problems and their countermeasures on direct liquefaction and solvent refining processes which operate under severe conditions.
A critical area of the process exsists between a coal slurry pump and a letdown valve where temperatures and pressures are extremely high. The rest of the process can be served by conventional instruments.
The difficulties of the process are due to high temperatures of up to 460t, high pressures of up to 300 bar, and clogging plus abrasion of coal solvent slurries. High viscosity and nonNewtonian nature of the slurries also create problems.
In the critical area, there seem to be no significant problems on temperature and pressure measurements: conventional products can be used with a few modifications.
Level in a gas liquid separator can be measured with a displacer, gamma ray level meter or dip tube with hydrogen purge.
The dip tube appears to be most practical although this system has a risk of clogged purge line in case of source pressure failure.
Regarding flow measurement, no flowmeter is satisfactory for high temperature, high pressure slurries. A venturi with solvent purge is the only usable type for the time being, although its accuracy is extremely poor. There used to be various ideas on letdown valve design, but an angle valve with tungsten carbide trim seems to have become most popular.
Basic instrumentation for coal liquefaction plant can be done with instruments modified from conventional products: no exotic instruments are needed.
