Advanced Process Control Systems: Supporting Carbon Reduction Goals While Boosting Product Output

— Vincent Chang, Department Manager at AI Application Development Department, CTCI ASI, Group Intelligent Solutions Business.
— Yao-Hua Wang, Department Manager at Intelligent Service Department, CTCI ASI, Group Intelligent Solutions Business.
— Hao-Chia Hung, Engineer at AI Application Development Department, CTCI ASI, Group Intelligent Solutions Business

Using intelligent technology to promote sustainable development has become a global trend. Especially with the rapid advancement of technology, the implementation of Advanced Process Control (APC) in various industries has become increasingly widespread. Through high-speed computing, APC systems process large amounts of data and respond quickly, establishing a solid foundation for multivariable control in the production process. This significantly improves production efficiency, reduces costs, maximizes profits, and also brings energy-saving and carbon-reduction benefits. In this article, we will take the petrochemical industry as an example to share how the CTCI team, with its rich experience, assists clients in implementing APC systems in existing plants, enhancing operational efficiency and helping the industry move toward a more energy-efficient and carbon-reducing future.

The Implementation of an APC System and its Advantages

Developed by AspenTech in the U.S., Aspen DMC3™ is an APC application that helps companies achieve goals such as increased production, improved yield, reduced energy consumption, and enhanced product quality. Implementing an APC system is a gradual process that requires expert guidance and involves multiple stages including controller design, process analysis, on-site discussions, control loop tuning, pre-testing, model building, step testing, and advanced controller commissioning, before a full implementation of the system can be fully completed.  

I. Controller Design
The goal of implementing anAPC system is to enhance operational efficiency. Therefore, establishing target benefits is the premise of a controller's design. To maximize the effectiveness of  APC system implementation, the  target benefits should primarily focus on improving profitability, including increasing production output, enhancing product quality, and reducing energy consumption.

II. Process Analysis
Process analysis is a crucial step. The personnel involved in the APC system implementation and deployment  must thoroughly understand the production process and the operational data, and be able to analyze Piping and Instrumentation Diagrams (P&ID) to identify key control points in the production process, so that critical variables affecting the production can be determined. 

Take the case of a naphtha cracking plant project executed by the CTCI team as an example. The main processes for naphtha production include cracking reactions, quenching, and product separation and purification. By examining these procedures, we can see that parameters such as temperature, pressure, and flow rate can have an immediate impact on the quality and yield of the products. Therefore, during the process analysis phase, the team should focus on the patterns of these parameters' variations and their effects on production.

III. On-Site Discussion
After obtaining  results from the process analysis, discussions should be held with on-site operations supervisors, process engineers, and plant managers to jointly determine the manipulated variables (MV), controlled variables (CV), disturbance variables (DV), and limiting variables (LV) in the control system,  while gaining a detailed understanding of specific operational conditions.

IV. Control Loop Tuning
A well-tuned control loop can deliver better results in the advanced control system. To achieve this, when field instruments and control valves are in normal condition, it is necessary to switch important control loops from manual to automatic control mode,  allowing the advanced process controller to setpoints for each control loop. Additionally, each control loop must be finely tuned to ensure its response time and stability in automatic control mode. 

V. Pre-Test
Pre-test refers to making small adjustments to the setpoints of one control loop, recording changes in process measurements  or sampling analysis values, and observing how these changes affect other variables. This process helps in verifying  the interactions between variables and the effects of adjustments, providing data support for subsequent model building.

VI. Model Building
Building a operational model requires inputting the pre-test data into Aspen DMC3™ software  and establishing the gain of manipulated variables (MV) corresponding to process measurement values  under various disturbance variables (DV). Once the model is built, the process can use the established operational model to automatically apply setpoints to the relevant control points, maintaining stability  and product quality even under certain levels of disturbance. 

During model building, constant adjustment and validation of the model are required to ensure accuracy and stability. This process involves combining operational experience with data analysis, making iterative adjustments and optimizations.

VII. I/O Interface Preparation and Connectivity Testing
Communication between the APC controller and the on-site distributed control system (DCS) is conducted through Open Platform Communications (OPC) protocols for data reading and writing exchange. During this phase, proper hardware and software setup is essential to maintain stable data communication, allowing data to be read and written accurately and ensuring the precision of displayed data.

VIII. Step Change Test
The step change test involves switching the APC controller to calibration mode, formally connecting the advanced process controller to the process, and outputting the calculated setpoints to the process control loops to observe its response. This process is similar to the pre-test but covers a wider range, involving more control loops and variables.

In the step change test, the APC controller will automatically adjust various operational variables to ensure stability and responsiveness  in actual operations.

IX. Advanced Process Controller Deployment
The final step is to connect the advanced process controller (host) with the control system (DCS/PLC) inputs/outputs and activate the switch for actual intervention control. This process requires combining onsite conditions with data analysis to adjust and optimize the controller parameters for the best performance. Steps include: deploying and bringing the controller online, ensuring stable system operation, selecting conservative upper and lower limits and tuning parameters, making final adjustments according to on-site needs, saving the model and establishing baselines, and completing operator training.

Summary

The implementation of an APC system is a complex and detailed process, requiring constant adjustment and optimization based on operational experience and statistical analysis in order to achieve optimal control performance. 

By implementing the APC system, significant improvements in production efficiency, reduction in energy consumption, and decrease in operational variability can be achieved, which is of great importance to petrochemical production. Additionally, these results contribute to energy saving and carbon reduction benefits, achieving ESG goals and paving the way for the industry's transition to net-zero emissions.