Flexi-Coking

 

Flexi coking is one of the most important processes in a refinery as only 2% of coke is produced from the residue.

                                                 Pic Credit : link.springer.com



In Flexi-Coking process, feed after preheated to 315 − 350 C enters into the reactor o fluid bed of hot coke at a temperature of 510 − 540 C .The hot coke is recycled from the  heater at a rate enough to maintain the desired temperature. This recycled coke from the heater provides the heat of evaporation and sensible heat to the feed and enables the cracking process. 

Vapors and lighter fractions are obtained at the upper end which are passed through separators to separate the coke particles from the products and some high boiling cracked vapors are condensed and recycled to the feed.

 The coke produced is deposited as thin films in the bottom of the reactor bed and is stripped off with steam. 

The coke stripped off at bottom is sent to the heater where it is heated at around 590 C o and the hot coke is sent back to the reactor and the excess coke ,also known as purge coke, is withdrawn at the bottom of the heater. The gases at top of the heater are sent to tertiary cyclones and venturi scrubbers to separate out fine coke particles and then it is treated to remove the sulfur content.


 The coke then moves to gasifier where it reacts with steam and air to produce a fuel gas consisting of H2, N2, CO, CO2 .This gas from the top of the gasifier is sent back to the bottom of the heater to fluidize the heater bed and provide necessary heating to the coke and send it back to the reactor. 


Thus, it can be concluded that the major part of coke is used to heat the feed with the help of a gasifier which produces fuel gas which heats the coke in the heater.

Also, the main purpose of the heater is to transfer the heat from the gasifier back to the reactor bed.