Authors: Peter Blaser a, Ray Fletcher a, and Sam Clark a
aCPFD Software
Source: This paper was first presented at the AFPM Annual Meeting March 19-21, 2017.
Description: The FCC unit has a long history of upgrading low valued feed stocks into much higher valued LPG olefins and motor fuels. Potential for increasing profitability through modification of the configuration or design of FCCU components is often limited due to challenges in diagnosing the root causes of under-performance and the risk of possible negative impacts of implementing changes on operational reliability. Gains obtained via modifications to a stable but sub-optimal process can be quickly erased if unforeseen, adverse effects are experienced, particularly if the changes result in an unplanned shutdown. The result is a strong preference for the status quo over uncertainty, due to the lack of means to test proposed improvements prior to implementation.
In recent years computational particle fluid dynamics engineering simulation technology has emerged as a powerful tool enabling refiners to “look inside” their FCCU and test the effect of proposed changes to equipment and process design. Simulation is being used to address issues such as erosion, catalyst losses, afterburn and emissions by identifying the root causes of operational problems and the effect of potential solutions.
This paper describes many additional structural issues which are endemic to the FCC operation resulting in limitations in operational flexibility with subsequent negative impact on economics. These issues include items such as incomplete combustion of spent catalyst within the regenerator commonly referred to as the “salt and pepper” appearance of regenerated catalyst, erosion of reactor or regenerator hardware leading to unscheduled shutdowns or reduced cycle length, and poor aeration at the inlets of regenerated catalyst hoppers and along the length of the standpipes leading to poor fluidization and reduced catalyst circulation rates. Each of the above conditions results in limited operational flexibility with either direct or indirect negative impacts on profitability.