Turning FCC Flue Gas into Power

Energy efficiency and competitiveness are closely linked in refining. Wasted energy means higher operating costs. One of the best examples of energy recovery in a refinery is the FCC regenerator flue gas system.

The FCC Regenerator

The fluid catalytic cracking unit converts heavy gas oils into more valuable light products such as gasoline, olefinic LPG, and light fuel oils. About 40 percent of gasoline production in North America comes from FCC units. [1] In the FCC regenerator, coke that has deposited on the catalyst is burned off. This produces a large volume of hot flue gas, typically 1,300 to 1,400 degF at low to medium pressure (10 to 40 PSIG). That heat and pressure represent recoverable energy. [2]

Three Ways to Recover the Energy

Since the first FCC was commissioned in 1942, engineers have developed several approaches to capture the energy in regenerator flue gas. An expander-generator uses the flue gas to drive a turbine connected to a generator, producing electric power. An expander-blower uses the same principle but couples the turbine shaft to an air blower, which supplies combustion air back to the regenerator. A waste heat boiler uses the hot flue gas to generate steam.

Combining the Approaches

For greater efficiency, the expander options can be paired sequentially with a waste heat boiler. For example, an expander-generator followed by a waste heat boiler produces both electric power and steam from the same flue gas stream, similar in concept to a gas turbine cogeneration system.

References

[1] U.S. Energy Information Administration

[2] Handbook of Petroleum Refining Processes, Meyers, Chapter 3.2