Faced with the loss of a fuel gas contract, CITGO was forced into a hard choice - make less fuel gas or reduce overall refinery throughput. CITGO has an excellent safety program and emphasises safe and reliable projects. Aggreko's engineering operation produced a comprehensive process design for each of the two projects.
Temperature control solution
Aggreko approached the refiner with solutions to reduce fuel gas generation. A review of the process units showed that if intermediate steam temperatures were reduced, more unsaturated gas would be absorbed, reducing gas flow to the fuel gas section of the plant.
Aggreko's recommended temperature control scheme (water-cooled version) and the process and economic logic for this solution was based on the quantity of gasoline to be cooled and the enthalpy to be removed. The gasoline inlet temperature is low enough to achieve the desired heat removal in one exchanger. The mechanical chiller was cooled by water; Aggreko supplied a dedicated portable cooling tower.
Two process points were identified: a mechanical chiller for API 51° gasoline; and a heat exchanger for cooling naphtha-range lean oil. CITGO accepted the solutions and embarked on a fast-track program to install them. From the initial point of discussion to project start-up took approximately six weeks.
The documentation permitted the refiner to carefully analyse the project for performance, safety and reliability. This documentation also facilitated a smooth and trouble-free installation and start-up.
The saturates plant process engineer reported an observation that fuel gas in his unit had been reduced by 500,000 scf/d. This is equivalent to about 340 barrels per day. The cost to benefit ratio was 6.8 to 1.