PTQ Q1 2024 Issue

model shows the conversion yield reduces from 76.83 vol% in the base case to 72.18 vol% in Case 4. The reduced conversion yield in Case 4 has a 14% reduc- tion in the propylene yield and virtually none in the naph- tha yield, based on the selected catalyst type in the model. Moreover, a higher total steam feed rate to the reactor will increase the hydraulic load to the downstream system and could result in a pressure surge in the reactor and the asso- ciated systems. Feed temperature to riser Hydrocarbon feed to the FCC reactor typically passes through a preheat system, receiving heat rejected from exchangers in the downstream system. Excessive exchanger fouling or malfunctioning of the exchanger bypass control system could reduce the temperature of the reactor feed. Case 5 in Table 1 shows the Hysys model results for oper- ation with 20ºF less feed temperature to the reactor riser. With the reactor temperature kept the same in the mod- els for both Case 5 and the base case, more heat is needed in Case 5 to compensate for the 20ºF drop in the feed inlet temperature, and the catalyst circulation increases by about 1% in Case 5 relative to that in the base case. The resulting higher C/O from the increase in the catalyst circulation rate in Case 5 also leads to a slightly higher yield conversion. With the combustion air flow rate set the same in the models for Case 5 and the base case, the higher cat- alysts circulation rate in Case 5 reduces the excess oxygen content of the flue gas from the regenerator, and the vol% of

CO and CO 2 in the flue gas also increases. Compared to the base case, the Case 5 model calculates a slightly higher delta coke and about 0.8% higher CO 2 emission. Conclusion Based on the upset events due to process parameter changes previously discussed, the FCC model in Hysys seems useful for predicting reasonable details of perfor- mance consequences resulting from the selected upset events. The model apparently includes reaction kinetics parameters to calculate yield distributions, flue gas compo - sitions, and heat balances at varying operating conditions. Several catalyst type options with varying selectivity performances for specific yield distribution targets are also available in the model, along with the design and operat- ing options, such as combustion air oxygen enrichment and recycling a fraction of spent catalyst to the reactor riser. Utilising the model to simulate these options has not been included in this discussion but may be considered. Moreover, fine-tuning the model input parameters and ver - ifying the calculation results against actual operating data could likely make the model useful for quantitative assess- ment of consequences from upset events or for process design analysis and optimisation. Tek Sutikno is a Process Engineering Manager with Fluor and a Professional Engineer registered in 11 US states with more than 35 years of experience in the process industries. He holds BSc, MSc, and DEngr degrees in chemical engineering and a MBA degree, all from the University of Kansas. Email: tek.sutikno@fluor.com

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PTQ Q1 2024