Application: Increase the throughput capacity by up to 50% and/or conversion in FCC units; process heavier feeds; overcome blower limitations, also temporarily.
Description: “Clean fuels” regulations are being implemented. Plus, the demand for transport fuels continually shifts toward more kerosine and diesel. The reason is that the regulations and the change in demand are totally independent developments. But both contribute to the requirement of more flexibility in fluid catalytic cracking units (FCCUs). Consequently, FCCUs require more flexibility to treat a wider range of feeds, especially heavier feeds, and increasing throughput capacity. Both goals can be achieved via oxygen enrichment in the FCC regeneration.
In the FCC reactor, long-chain hydrocarbons are cleaved into shorter chains in a fluidized-bed reactor at 450 –550°C. This reaction produces coke as a byproduct that deposits on the catalyst. To remove the coke from the catalyst, it is burned off at 650 –750°C in the regenerator. The regenerated catalyst is returned to the reactor.
Oxygen enrichment, typically up to 27 vol% oxygen, intensifies catalyst regeneration and can substantially raise throughput capacity and/or conversion of the FCC unit. Oxygen sources can be liquid oxygen tanks, onsite ASUs or pipeline supply. Oxygen consumption in FCC units fluctuates widely in most cases; thus, tanks are the best choice with respect to ease of operation, flexibility and economy.
For oxygen addition into the CS air duct, a number of safety rules must be observed. The oxygen metering device FLOWTRAIN contains all necessary safety features, including flow control, low-temperature and low-pressure alarm and switch-off, and safe standby operation. All of these features are connected to the FCC units’ process control system. An efficient mixing device ensures even oxygen distribution in the air feed to the FCC regeneration.
Economics: Oxygen enrichment in FCC regeneration is economically favorable in many plants. For example, one refinery increased throughput by 15%. The net improvement was a 26% increase in higher-value products, such as naphtha. Likewise, lower value products increased only 5%, as fuel gas. The net profit increased substantially. Installed cost for oxygen enrichment is typically below $250,000.
Operating costs will depend on the cost for oxygen and the duration of oxygen enrichment. Economical oxygen usage can be calculated on a case-by-case basis and should include increased yields of higher-value products and optional usage of lower-value feeds.
Contributor: Linde AG, Division Gas and Engineering.
