Also known as: Resid catalytic cracker
The RCC is a variation of the FCC unit that is capable of taking heavier feed. The RCC takes atmospheric resid and VGO and cracks them using heat in the presence of a catalyst. The primary product is FCC gasoline, which is used in gasoline product blending. However, the RCC also produces lighter products that feed the alkylation unit and heavier products that can be blended into diesel and residual fuel oil.
The RCC is particularly valuable in a refinery that is trying to maximize gasoline production over residual fuel oil. The RCC yields a high volume of gasoline of pretty good quality (high-octane and low vapor pressure). However, its volume yield of diesel is low and of low quality (low-cetane), since it is made up of cracked material, which tends to have low cetane.
How it works
Heated feed is mixed with a heated catalyst and injected into a reactor, where the catalyst freely mixes with the feed as a fluid. As the feed is cracked, coke deposits on the catalyst, causing it to gradually deactivate. Cracked product is drawn off at the top of the reactor and is sent to a fractionator. Deactivated catalyst is drawn off the bottom of the reactor and is sent to a regenerator where the coke is burned off by injecting heat and air. The cleaned (regenerated) catalyst is then sent back to the reactor, and the cycle repeats.
The feed to the RCC includes streams that would otherwise be blended into fuel oil. Typical feeds include:
- Atmospheric resid - The bottoms from the atmospheric distillation tower, containing a mix of VGO and vacuum resid. Typically, the RCC uses atmospheric resid from a light, sweet crude or atmospheric resid that has been hydrotreated
- VGO - This heavy cut from the vacuum distillation is sometimes added to the RCC feed to increase throughput
- Coker gasoil - For refineries with a coker, this VGO range material from that unit is also a major feedstock for the RCC
The RCC produces a range of mostly lighter products, with the most significant being FCC gasoline. Typical products are:
- FCC gasoline - This is a naphtha boiling range material with octane and vapor pressure close to the quality specifications for finished gasoline. This is typically the largest product at around 50% of FCC output
- Cycle oils - The FCC produces a diesel range product called cycle oil. This is highly aromatic and often high in sulfur, which makes it a poor diesel blend stock. It is typically blended into lower quality diesel, used as a cutter stock in fuel oil blending, or sent to the hydrocracker for upgrading
- FCC slurry - The heaviest product from the the RCC is a highly aromatic resid stream, typically with high sulfur content. This is usually sent to fuel oil blending, used as feed for the coker, or used to make specialty products such as carbon black or needle coke
- FCC gas - The light ends from the RCC include both saturated and unsaturated C3s and C4s. This is typically sent to an unsaturated gas plant where the components are separated. The butylenes, and sometimes the propylenes, are fed to the alkyaltion unit if there is one. Lighter gases (ethane and methane) are sent to the refinery fuel system