When a catalytic reformer at Humble Oil & Refining Company’s Baytown, Texas plant showed alarming pressure drop across the reactors after about 50 days’ operation principally as a result of plugging with iron sulfide scale, immediate steps were taken to investigate the source of scale and the importance of metal losses occurring in the system. Over 600 pounds of iron dust was removed from the reactor and the unit put back in operation. In a month’s time it was necessary to screen the catalyst again.
Heavy scale was found in the first exchanger on the reactor effluent stream both from the tubes and deposited from piping upstream. Catalyst was channeled and plugged.
When it became apparent the scaling was the result of sulfide attack and possibly severe corrosion in the furnace tubes and other components a testing program was begun. Several materials were tested at various locations in the stream by the electrical resistance method. Hydrogen sulfide content of the naphtha charge and recycle gas was determined.
Corrosion rates during operation on heavy naphtha varied from 0.15 to 0.4-inch on carbon steel and chrome alloys but the rate on 18-8 was about one-tenth that of the other metals. Chromium alloys through 12 percent in many instances showed corrosion rates higher than those of carbon steels.
In a laboratory pilot unit, tests indicated that aluminized steel generally showed good resistance and that hydrogen sulfide concentrations under 0.008 mol percent did not cause appreciable damage at temperatures about 1000 F. Humble plans to install a hydrofining unit to reduce sulfur content of the naphtha to about 40 ppm before it is charged to the naphtha reforming process. 3.2.2
