Fluid Coking Process by ExxonMobil Research and Engineering

ExxonMobil’s Research & Engineering (EMRE’s) continuous thermal conversion process with fluidized bed reactor to convert heavy hydrocarbons (vacuum residuum, extra heavy oil or bitumen) to lighter liquid products and fuel-grade coke. Attractive when markets available for fuel-grade fluid coke, or if planned applications include present or future addition of a fluid bed boiler for cogeneration of steam and power as this combination has both heat integration as well as SOx removal benefits.

A fluid coking unit is similar in operation to an FCC unit but operates on much more difficult vacuum resid feeds. Instead of catalyst, fluid coke particles are circulated between the burner and reactor to transfer process heat. Feed, typically 1,050°F+ vacuum resid from the bottom of the vacuum pipestill, is pumped without the need for a preheat furnace directly to the scrubber (1) on the top of the reactor (2). The scrubber (1) has several functions: i) to further heat the feed by direct heat exchange with reactor effluent vapors, ii) to separate coke particles for return to the fluid bed reactor and iii) to recycle the higher boiling reactor effluent hydrocarbons (typically at 975+°F, but this can be adjusted to meet downstream gas oil processing requirements) back to the reactor with fresh feed.

Specially designed nozzles in the reactor (2) produce droplets of feed, which interact with the circulating coke particles. Gas and liquid thermal conversion products are removed from the top of the scrubber and a layer of coke is added to the circulating particles. Heat for the thermal cracking reactions is supplied by burning a fraction of the coke in the fluid bed burner (3). Hot coke circulates between the burner (3) and reactor (2), and cold coke returns to the burner (3). About 20% of the coke is burned with air to supply process heat requirements, eliminating the need for an external fuel supply. The rest of the coke is withdrawn from the burner and either sold as a product or burned in a fluid bed boiler in cogen projects.

Products: Liquid products produced are similar in yields and quality to delayed coking. These products are upgraded through conventional hydrotreating, hydrocracking or in a fluid catalytic cracker (FCC). Fluid coke is used as a solid fuel, with particular advantages in cement kilns or fluid bed boilers.

Competitive advantages:
• Continuous fluid bed process, coke conveyed pneumatically and contained in fluid solids and product silos.
• Process very heavy feeds from tar sands bitumen to Venezuelan heavy crudes.
• Internally heat integrated, minimal use of fuel gas, and lower coke production than delayed coking.
• Combination of fluid coking and fluid-bed boilers for COGEN has heat integration and SOx removal synergies.

Licensor: ExxonMobil Research and Engineering Co.

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