Thermafor Catalytic Cracking (TCC)

Dr. Semih Eser: Thermafor catalytic cracking process provided significant improvement over the Houdry cat cracking in terms of the thermal efficiency. Now, this improvement came with the change in the reactor configuration from a fixed bed in Houdry to a moving bed of catalyst now. So the catalysts are not fixed, but they are moving by gravity so that the reaction can be now conducted in just one reactor instead of having multiple reactors and switching between those reactors.

There was an improvement in the catalyst as well. Instead of using natural silica-alumina, now there are synthetic alumina-silica beads with more controlled activity, more homogeneous activity of the sites that the cracking goes on, which, of course, makes the control of the reactions better compared to the Houdry cat cracking.

So the integration of the reactor and the catalyst regenerators, as you will see, has increased the thermal efficiency very significantly over the fixed bed, the Houdry cat cracking.

Now, you can see that the feed is introduced along with the catalyst from the top of the reactors. So the particles move down with gravity at controlled flow rates along with the feed. So as the cracking goes on, on the catalyst surfaces, there is the activation. There's still coking going on, on the catalyst particles. So by the time they reach the bottom of the reactor flowing with gravity, the catalyst reactivity has been reduced to a significant extent. The catalysts are now ready to be reactivated or regenerated.

Steam, as you can see, is introduced from the bottom of the reactor to strip off all the volatile products during cracking, and the products are sent to a fractionator for separating into gas, gasoline, LCO, heavy oil, and so forth.

So the used catalysts, then, leaving the reactor is sent to a furnace where hot air is introduced to burn off the coke on the surface of the catalyst to regenerate the active sites. And the regenerated catalysts, the hot particles now, are put on bucket elevators to be sent up to the top of the reactor to close the catalyst cycles.

So the thermal integration here is such that the heat that is generated by burning the coke heats the catalyst particles. And these are hot enough to actually have the cracking take place on the surface. You can see that there is no external heater in this reactor scheme in Thermafor Cat Cracking.

But there is still more heat losses, especially in this bucket elevator system, transporting the hot catalyst particles to the top of the reactor. Thermal efficiency, although much improved over the Houdry fixed bed process, there is still a lot of room for improvement in thermal efficiency through the integration of endothermic and exothermic reactions.

This diagram illustrates the flow and operation of the Thermafor Catalytic Cracking (TCC) process, introduced in 1942, showing a moving-bed system where catalyst particles continuously circulate between a reactor and a regenerator to improve thermal efficiency.

At a high level, the process shows feed entering a reactor with a downward-moving bed of catalyst particles, products being removed to a fractionator, and deactivated catalyst being regenerated and recycled back to the reactor using bucket elevators.

Process flow:
Gas oil feed, labeled “feed,” enters at the top of a vertical reactor. Inside the reactor, catalyst particles move downward by gravity while cracking reactions occur. Steam, labeled “steam,” enters near the bottom and carries cracked products out through a line labeled “Products to fractionator.” Spent catalyst exits the bottom, is regenerated with hot air, and is returned to the top of the reactor via a circulation loop labeled “Catalyst particles” and “Bucket elevators.”

Reactor section (left side):

• A tall vertical reactor vessel contains a packed moving bed of catalyst particles.
• The inlet at the top is labeled “feed,” indicating where gas oil enters.
• Catalyst particles also enter at the top and move downward through the reactor.
• As the feed contacts the catalyst, cracking reactions occur along the catalyst surfaces.

Product removal and steam stripping:

• A side inlet near the bottom labeled “steam” introduces steam into the reactor.
• The steam flows upward, carrying vaporized cracking products out of the reactor. 
• These products exit through a side outlet labeled “Products to fractionator,” leading to downstream separation.

Catalyst deactivation and removal:

• As catalyst particles move downward, coke builds up on their surfaces, reducing activity.
• The deactivated catalyst exits the bottom of the reactor and flows into a vessel below.

Regenerator section (bottom left):

• The lower vessel acts as a regenerator. 
• A line labeled “Hot air” enters this unit, where coke deposits are burned off the catalyst.
• This regeneration step restores catalyst activity and heats the particles.

Catalyst circulation loop (right side):

• A vertical loop labeled “Catalyst particles” shows the path of regenerated catalyst being recycled.
• Within this loop, a transport system labeled “Bucket elevators” lifts catalyst particles upward.
• Arrows indicate the upward movement of hot, regenerated catalyst back to the top of the reactor.

The diagram emphasizes continuous operation through a moving-bed design in which catalyst particles flow downward during reaction, are regenerated with hot air, and are mechanically lifted back to the reactor. The circulating hot catalyst supplies heat for the endothermic cracking reactions, improving efficiency compared to earlier fixed-bed processes.