Preparation of low sulfur content heavy fuel oils

Claim 1

A PROCESS FOR MANUFACTURING HEAVY FUEL OILS OF IMPROVED QUALITY FROM HEAVY PETROLEUM OIL S HAVING OBJECTIONABLY HIGH VISCOSITIES AND SULFUR CONTENTS, COMPRISING SUBJECTING A RESIDUAL HYDROCARBON CHARGE STOCK THAT HAS A GRAVITY BELOW ABOUT 20* API AND A SULFUR CONTENT OF AT LEAST ABOUT 2 PERCENT, TO CATALYTIC HYDRODESULFURIZATION AT A HYDROGEN PARTIAL PRESSURE BELOW ABOUT 2000 P.S.I.G., AT A TEMPERATURE BETWEEN ABOUT 700*F. AND 850* F. AND AT A SPACE VELOCITY BETWEEN ABOUT 0.2 AND 10, THE TEMPERATURE AND SPACE VELOCITY BEING SELECTED WITHIN THE RANGES SPECIFIED TO YIELD PRINCIPALLY A RESIDUAL PRODUCT FREE FROM FURNACE IL AND LIGHTER MATERIALS THAT HAS A PENTANE-INSOLUBLES CONTENT THAT IS NOT GREATER THAN THE PENTANE-INSOLUBLES CONTENT OF THE CHARGE STOCK, SAID RESIDUAL PRODUCT HAVING A SOMEWHAT REDUCED VISCOSITY, SULFUR CONTENT AND POUR POINT AND BEING CHARACTERIZED BY AN INCREASED SUSCEPTIBILITY TO VISCOSITY REDUCTION BY VISBREAKING, AND SUBJECTING AT LEAST THE RESIDUAL PORTION OF THE HYDRODESULFURIZED PRODUCT TO A VISBREAKING TREATMENT AT A TEMPERATURE BETWEEN ABOUT 800*F. AND 1000*F., A PRESSURE BETWEEN ABOUT 50 AND 100 P.S.I.G., AND WITH A COIL VOLUME OF BETWEEN ABOUT 0.012 AND 0.050 CUBIC FEET OF COIL VOLUME ABOVE 750*F. PER BARREL OF THROUGHPUT PER 24-HOUR DAY, THE COMBINATION OF CONDITIONS BEING SELECTED TO FORM BELOW ABOUT 20 PERCENT 400*F. END POINT GASOLINE AND, SO AS TO YIELD PRINCIPALLY A HEAVY FUEL OIL PRODUCT HAVING STILL FURTHER REDUCED VISCOSITY, POUR POINT AND SULFUR CONTENT, AND THAT REQUIRES REDUCE QUANTITIES OF CUTTER OIL TO OBTAIN AN ACCEPTABLE VISCOSITY FOR USE AS A HEAVY FUEL OIL.