Blog post published Nov 30, 2012 Blog: Go with the flow

Propane dehydrogenation: Part 2 – continuous catalytic reforming

This week we’ll go deeper to the propane dehydrogenation in part 2 about the role of continuous catalytic reforming and valves in propane dehydrogenation:

Does CCR sound familiar to you? This represents continuous catalytic reforming, typically used in producing high octane gasoline and aromatics where the catalyst is regenerated continuously, without stopping the reforming process. Catalytic reforming and continuous catalyst regeneration is commonly used also in producing propylene as a part of propane dehydrogenation (PDH) process.

What‘s the function of CCR (continuous catalyst regenerator) in PDH?

Over a period of time, due to the high operating temperature, the catalyst becomes coated with coke, a natural by-product of the process and it therefore requires regeneration. Catalyst activity is maintained by a continuous catalyst regenerator (CCR) or by shutting down reactors one by one and regenerating the reactor with regeneration air. The CCR is where the catalyst is continuously withdrawn from the reactor, regenerated, and then fed back to the reactor bed. A series of lock hoppers, typically four complete lock hopper arrangements, are used to move the catalyst from the reactor to the regenerator and eventually back into the reactor.

Why is CCR so important?

A constant non-declining yield is important for PDH economics. It is achieved by the CCR section to ensure that the reactors are continuously supplied with freshly regenerated catalyst and product yields are maintained at fresh catalyst levels. Critical valves – in catalyst handling lock-hoppers, venting, catalyst withdrawal and addition – play an extremely important role in successful catalyst regenerating process performance. Poorly performing valves in the process must be serviced because they will have a direct impact on the efficiency of the process. Valves should be specifically designed to meet the process requirements such as UOP specification 671.

Intelligent seat supported ball valve from Metso Automation.

Intelligent seat supported ball valve from Metso Automation.

For these critical valves in the CCR section, care must be taken in material selection and seat construction in order to avoid any wear or particles entering the seat cavities and adhering to sealing surfaces. Metal-seated valves, like Metso’s ball valves, have been widely used for critical catalyst handling applications. Hard coatings should be applied to raise the surface hardness of the ball to provide for long component life in this highly abrasive and frequent cycling (20 000 – 30 000 cycles annually) service. Special seat construction is recommended in this critical application, such as Metso’s solid-proof seat construction. This is extremely important as catalyst fines behind the seat can cause the required torque to increase beyond the maximum output capability of the actuator. This design has proved its long lasting tightness over years of frequent cycling and catalyst handling.

 In the CCR section, the catalyst addition system is the point in the process where new catalyst is added to replace the quantity of catalyst that is withdrawn and discarded from the system after it can no longer be regenerated. The new catalyst flows by gravity into the system through a catalyst addition hopper at ambient temperature. Soft-seated ball valves with catalyst friendly design, like Metso’s Jamesbury soft-seated ball valve with Xtreme seats, are typically used as the solution here.

Does intelligence bring added value here?

Predictive maintenance can be practiced with the help of the diagnostic devices, like Neles SwitchGuard SG 9000 which is an intelligent on-off valve controller that is specially designed to meet challenges of process critical on-off applications, such as valves in continuous catalyst regeneration.

Reliable catalyst handling valves with predictive maintenance capabilities will support successful catalyst regenerating process, which plays an important role in propane dehydrogenation process availability and sustainable production.

Related posts:
Propane dehydrogenation: Part 1 – markets and prospects
Propane dehydrogenation: Part 3 – reactor and product recovery

 





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