A significant number of refineries experience accelerated fouling in their delayed coking unit (DCU) furnaces, in many cases from asphaltenic feedstocks. Feeds to a DCU have traditionally come from the crude unit’s vacuum distillation tower bottoms, which contain a high concentration of asphaltenes.
High heat flux, feedstock quality (e.g., asphaltenes), and increased throughput often shorten desired run lengths, perhaps by as much as 75%. Bumping up against furnace tube skin temperature limits force refineries to shut their delayed coker units down for cleaning, thereby decreasing refinery profitability. Potential severe fouling can accompany processing of unstable asphaltenic feedstocks, particularly at high temperature furnace conditions.
Athlon Solutions recently reported the development of a proprietary chemical treatment program designed to reduce the impact of DCU furnace fouling along with the rate of skin temperature increase. The program results in extended run lengths, reduced fuel consumption and decreased overall greenhouse gas emissions. According to information available from Athlon, only one chemical injection location is required.
In one instance, a midcontinent refinery experienced significant fouling in their DCU furnace. Run lengths were often shortened to as little as 3 months due to a skin temperature limit of 1250°F. Athlon’s RPA 301 was injected into the inlet of the furnace at 50 ppm, resulting in a doubling of furnace run length. The engineering study followed by the improved system modifications resulted in annualized savings of about $1.25 million. Athlon says the chemical treatment program is economically viable even at reduced coker margins.
In other developments related to coker furnace fouling control, researchers at Baker Petrolite recently noted that the coking stability index (CSI) test used by refiners to determine the relative stability of coker furnace feedstocks, is more accurate than historical analytical methods that evaluate petroleum liquids stability.