Fig. 3-15 Essential parts and equipment for tracer injection and detection of a coal liquefaction plant Time variation of tracer concentration is continuously monitored by neutron sources and detectors equipped at the upper outlets of the reactors. Coal slurries and tracers are introduced from at the bottom of reactors.

Fig. 3-16 Observed variation of neutron count rate (top) and calculated tracer concentration (bottom) versus elapsed time after injection of tracer

Fig. 3-17 Whole view of the test plant (Coal processing capacity 1 ton/day)

Development of technology for the liquefaction of coal is being promoted as a national project by the Ministry of International Trade and Industry (MITI). Conversion of the solid coal which is solid into the liquid state provides more practical fuel like oil. One of the essential aims of this project is to improve the design of a liquefaction plant by knowing the behavior of coal slurries in liquefaction reactors. For this purpose a tracer is injected into the plant which is under high temperature and high pressure. In such a case a radioactive tracer has been conventionally used. Recently it becomes more difficult to carry out such an experiment which might cause radioactive contamination at the site. Accordingly a non-radioactive tracer having a large neutron absorption coefficient (Gadolinium compound) was used to measure the count rate of transmitted neutrons at the outlet of the reactors as shown in Fig. 3-15. In this method the time variation of concentration of the tracer, namely the residence time distribution of materials in the reactor was determined in a test plant whose coal processing capacity was 2.5 tons per day (Fig. 3-16). Thus configurations of equipment for injection and detection of neutrons were optimized so as to get sufficient tracer detection sensitivity depending on the inner diameter and thickness of the pipes at the measuring point. Test plants of capacities of 1 ton/day (Fig. 3-17) and 150 tons/day are currently being constructed. JAERI is continuously contributing to the project in the technology of neutron absorption measurements for the tracer.

Reference O. Ishikawa, Applications of radioisotope techniques for coal liquefaction reactors, Radioisotopes, 45(5), 349 (1996).

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