Many fuel consumers such as electric power generators and cementmanufacturers have begun to use coal instead of fuel oil as an energy source because of therapid rise of fuel oil prices since the energy crisis in 1973. This trend is bringing about asurplus of residual oil in petroleum refineries. These surplus residual oils must be upgradedto more valuable distillates for effective utilization, although prices of crude oils have fallendown to low levels recently.
For this purpose, continued efforts are being made on residual oil processing. Difficultproblems, however, are encountered in processing heavy feeds because they contain largeamounts of sulfur, nitrogen, asphaltene, and heavy metals.
In recent years, many attractive upgrading processes have been investigated.
This paper reviews recent development of upgrading of heavy oils as follows:
1) Upgrading by fluid catalytic cracking with regular catalysts,
2) Upgrading by fluid catalytic cracking with newly developed catalysts,
3) Upgrading by hydrotreating processes,
4) Upgrading by slurry hydroconversion,
5) Upgrading by thermal cracking.
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