MPC Controller Selection

• Fuel Gas Stripper: A single sub-MPC controller has been selected for the fuel gas stripper control.
• Deethanizer: A single sub-MPC controller is designated for deethanizer control.
• Depropanizer: A single sub-MPC controller is chosen for depropanizer control.
• Debutanizer: A single sub-MPC controller is assigned for debutanizer control.
• Depentanizer/Hexane: A single sub-MPC controller is selected for depentanizer/hexane control.
• Overall-Plant MPC Controller: An overarching MPC controller will coordinate the operation of the sub-controllers, optimizing unit performance. In cases of excess capacity, this controller will maximize unit throughput.

Fuel Gas Stripper ARC Components

The Fuel Gas Stripper ARC includes the following features:

• Surge Volume Control (SVC):
  • On the tower bottom level, cascading onto the tower bottom flow.
  • On the overhead condenser accumulator, cascading onto the condenser refrigerant level to regulate refrigerant flow. A high level in the overhead accumulator will override the reflux drum level control (LC) to manage the refrigerant flow effectively.
• Pressure Control: Tower overhead pressure cascades onto the fuel gas flow, ensuring optimal operating conditions.
• Reflux-to-Feed Ratio Control: This component maintains the appropriate reflux ratio relative to the feed.
• Reboiler Heat Duty-to-Feed Ratio Control: This controls the reboiler heat duty in relation to the feed to ensure efficient thermal management.

Depropanizer ARC Components

• Surge Volume Control (SVC):
  • On the tower bottom cascading onto the tower bottoms flow.
  • On the overhead condenser accumulator cascading onto the overhead reflux.
• Pressure Control: Tower overhead pressure cascading onto overhead ethane flow to the cryogenic unit.
• Tower Control: Includes tower overhead-to-feed ratio control and tower reboiler duty-to-feed ratio control.
• Top Differential Control: Ensures stability in the tower operation.

Debutanizer ARC Components

• Surge Volume Control (SVC):
  • On the tower bottom cascading onto the tower bottoms flow.
  • On the overhead condenser accumulator cascading onto the overhead reflux.
• Pressure Control: Tower overhead pressure control cascading onto overhead vapor flow.
• Reflux Control: Overhead reflux-to-feed ratio and reboiler duty-to-feed ratio management.

Fuel Gas Stripper/Deethanizer MVC-Based Controls

A single stand-alone MPC controller is recommended for the fuel gas stripper and deethanizer. Objectives of the controller include:

• Stabilizing operations of both units.
• Maintaining C2 specifications in the deethanizer bottoms propane product.
• Optimizing the trade-off between reducing propane and ethane losses and energy consumption.
• Maximizing throughput for both the fuel gas stripper and deethanizer, limited by operational and equipment constraints.
• Operating both units at optimum pressure without violating tower constraints.

Depropanizer MVC-Based Controls

A single stand-alone MPC controller is recommended for the depropanizer and MPPD hydrogenation reactor. Objectives of the controller include:

• Stabilizing tower operations.
• Minimizing C4 in the overhead.
• Maximizing unit throughput limited by operational and equipment constraints.
• Operating the tower at optimum pressure without violating tower constraints.

Debutanizer MVC-Based Controls

A single stand-alone MPC controller is recommended for the debutanizer. Objectives of the controller include:

• Stabilizing tower operations.
• Controlling %C5 in the overhead and %C4/C5 in the bottoms.
• Maximizing unit throughput limited by operational and equipment constraints.
• Optimizing the trade-off between throughput, yield, and utility costs.
• Operating the tower at optimum pressure without violating tower constraints.

Depentanizer MVC-Based Controls

A single stand-alone MPC controller is recommended for the depentanizer/hexane tower. Objectives of the controller include:

• Stabilizing tower operations.
• Controlling top pentane, middle hexane, and C7+ bottom products.
• Maximizing unit throughput limited by operational and equipment constraints.
• Operating the tower at optimum pressure without violating tower constraints.

MPC Controller Implementation Plan

The MPC controller system implementation consists of the following phases:

1. Controller Design
2. Plant Testing and Model Identification
3. Factory Acceptance Testing
4. Controller Commissioning
5. Documentation

MPC Controller Design

Preliminary structures will be reviewed with plant technology and operations personnel to ensure that the recommended control structure addresses all process constraints. The reviewed configuration will serve as the basis for conducting plant tests and will be finalized post-testing.

Plant Testing and Model Identification

Data collection and identification software provided by ACSC will be utilized to develop dynamic models of the controllers. A pretest of the regulatory system will step through manipulated variables to monitor responses, providing insight into settling times and required move sizes.

ACSC will provide a guideline test procedure outlining independent variable moves and process states during the test, enabling control room operators to conduct tests without 24-hour engineer oversight.

Factory Acceptance Testing

Upon completion of plant testing and dynamic model identification, ACSC will install its proprietary simulation package to tune the controller and demonstrate its behavior in response to setpoint and disturbance changes during factory acceptance tests.

Controller Commissioning

Once the dynamic model is verified, the controller is commissioned in an online environment. Initially, the controller will operate in a predict-only mode to observe calculations without implementation, testing all functionalities. Tuning adjustments may occur at this stage based on actual performance, with operator training scheduled one month after commissioning to ensure direct exposure to the controllers.