Oct-2024

APC advances FCC unit performance at Pemex Deer Park refinery

In addition to exploring the complex design and processes behind an advanced process control solution, the benefits gained are discussed in this case study.

Mohamed Abokor, Pemex Deer Park refinery
Michelle Wicmandy, KBC (A Yokogawa Company)

Article Summary

The global demand for light oils is on the rise, driven by factors such as increased energy consumption and geopolitical shifts. According to J. P. Morgan Research,¹ world oil demand is projected to reach 106.9 million barrels per day (mbd) by 2030, surpassing the levels of 2023 by 5.5 mbd. This upward trend is primarily fuelled by population growth and escalating energy consumption in developing nations, which outweigh energy efficiency initiatives in these economies.

Refiners are facing the challenge of meeting this growing demand for refinery products while dealing with the decreasing quality of crude oils and lighter product specifications due to environmental constraints. To navigate these complexities and achieve optimal performance, refineries are turning to technologies like advanced process control (APC). 

Built in 1929, the Pemex Deer Park refinery in Houston, Texas, serves as a prime example of a traditional refinery that has successfully integrated technology with legacy systems to achieve stellar results. With a production capacity of 340,000 barrels per day (bpd) for motor fuels, such as gasoline, diesel, and jet fuel, this refinery operates 24/7 year-round. To enhance its operations, the refinery implemented an APC system known as the Platform for Advanced Control and Estimation (PACE), which improves the efficiency of its fluid catalytic cracking (FCC) unit by reducing the fluctuation on key variables.

In addition to exploring the complex design and processes behind this solution, this case study discusses the benefits gained, including improved operator efficiency, tighter control over critical parameters, and optimised product yields.

FCC unit role
For more than 60 years, the FCC unit has been responsible for transforming heavy hydrocarbon petroleum compounds into valuable products like intermediate distillates, light olefins, and petrol. In fact, researchers claim the FCC unit is responsible for producing nearly 45% of the world’s gasoline supply.²

However, FCC units can be challenging to manage, as they require precise control over numerous interconnected processes and variables. To meet modern demands for fuel, the FCC unit is evolving with new technological advancements. APC technology has improved how refiners approach FCC unit optimisation to achieve new levels of efficiency and performance.

Traditional vs modern systems
Historically, the Deer Park refinery’s FCC unit relied on a traditional, siloed approach to process control. This setup involved the use of the Shell Multivariable Optimisation Controller (SMOC) and a separate real-time optimisation (RTO) system, each with its own dedicated interface. This fragmented approach created challenges for the operators, who had to navigate between three separate interfaces –APC, RTO, and a Robust Quality Estimator (RQE) – when trying to optimise and efficiently manage the FCC unit. To address these challenges, the refinery embarked on an APC migration project, adopting PACE technology to maximise its capacity to process residual feeds and enhance FCC unit profitability.

Unifying FCC unit operations
Due to changing market conditions and profitability targets, the Deer Park refinery needed to capture value by converting low-value feedstock into high-value products like gasoline through a high-temperature cracking reaction facilitated by catalyst. To reduce variation over key processes, designing the right application was crucial. Integrating a sophisticated control architecture within the FCC unit and its gas fractionator unit was essential.

With a single RTO loop, the refinery can enhance operational efficiency by seamlessly merging three applications:
· The first application focused on optimising operations of the reactor regenerator (R&R) and main fractionator (MFRAC).
· The second loop focuses on the rectified absorber (RA).
· The third loop is dedicated to the depropaniser (DC3) and debutaniser (DC4) columns.

This intricate control framework, with more than 25 manipulated variables and 71 controlled variables, works in tandem to form the foundation of the refinery’s operations to improve performance. An overview of the FCC unit is shown in Figure 1.

Reactor regenerator and main fractionator structure
This APC system consists of one application with two subcontrollers, which are responsible for managing the reactor regenerator, as well as the main fractionator in the FCC unit. The APC system uses five circulating reflux streams to control the main heat removal and product endpoints on the main fractionator.

The R&R subcontroller’s main purpose is to manage the combined carbon monoxide (CO) boiler and feed preheater, riser, reactor, and regenerator components to ensure these elements operate efficiently and effectively.

Meanwhile, the MFRAC subcontroller focuses on separating the hydrocarbon vapour from the overhead reactor into individual product streams. Each product stream is then directed to its respective destination for further refinement or blending into valuable liquid fuels as follows:
· Wet gas is compressed by the wet gas compressor and sent to the gas fractionator unit.
· Naphtha, Light cycle oil (LCO), heavy cycle oil (HCO) and slurry are routed to their final destinations for further processing.

This comprehensive control structure, with its ability to manage many different manipulated and controlled variables, has been instrumental in optimising unit throughput and producing high-value products such as gasoline, light olefins, and diesel fuels.

Efficient management of the various systems at Deer Park refinery was crucial to achieving value. APC systems, such as PACE, have proven to enhance operator efficiency, tighten control over critical parameters, optimise product yields and quality, and maximise economic performance. Key benefits that the refinery realised included:
· Enhancing operator efficiency
· Tighter control over critical parameters
· Optimising product yields and quality.