Can I reduce riser outlet temperature in our FCC unit while maintaining conversion level? Is a higher activity catalyst needed?
First published in PTQ Q4 2018
Nicolas Lambert, Technology Team Manager – RDS, FCC & Sweetening Segment, Axens
There is certainly an advantage in challenging the catalyst formulation in order to better suit your needs. This could result in a better conversion at same operating conditions or, as suggested, similar conversion at reduced riser outlet temperature (ROT). We will nevertheless leave aside the catalytic aspects of the question (which will surely be thoroughly handled by our esteemed partners) to focus on the process aspects.
FCC unit conversion level is directly related to the severity of the operation, thus to the ROT, which is your primary controlling parameter.
Nevertheless, there are some possibilities offered to compensate for loss of conversion due to reduction in ROT, such as:
- Increasing the cat/oil (C/O) through riser quench usage: this is also called ‘MTC’ for mix temperature control. This consists of injecting a heavy naphtha or LCO downstream of the feed injection point. This fluid will act as a thermal sponge upon vaporisation, impacting the temperature profile in the riser. The C/O is consequently increased in order to compensate for this quench and maintain ROT, resulting in a higher regenerated catalyst return flow rate. The new conditions are thus improving the feed conversion, especially with heavier feedstocks, through availability of more enthalpy for feed vaporisation. The usage of MTC could be accompanied with a decrease in ROT to satisfy your constraints while maintaining the conversion level, or even improving it, depending on the base line and extent of quench usage.
- Upgrading some internals: obviously, the conversion can be positively impacted by an upgrade of one or a combination of technology features of the FCC unit. For instance, usage of improved feed injectors will enhance the feed distribution for a better conversion. An upgrade of the riser termination device could also improve the products distribution. Ultimately, owing to a global improvement in unit performance, the ROT could be decreased to the necessary level without detrimental impact on your unit’s profitability.
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