Optimizing Process Control for Improved Margins
By Heath Stephens, P.E., Digitalization Leader
Advanced process control solutions (APC) are software-based platforms that are layered on top of a plant’s basic control system to improve performance. While a Basic Process Control System (BPCS), the DCS or PLC platform, is integrated into the plant to automate and regulate core operations, APC solutions can provide higher-level optimization by simultaneously managing multiple interrelated variables, reducing process variability, and improving throughput, energy efficiency, and product quality.
However, for any control system to work effectively, the existing control loops that govern process variables, such as pressure, flow, and temperature, must be tuned and maintained. Loop tuning ensures that the system responds in a balanced manner to setpoint changes or disturbances, avoiding both instability and sluggish performance. Properly tuned and maintained loop control is foundational system performance and must be optimized prior to layering in additional APC tools.
The Problem of Poorly Tuned Control Loops
In many facilities, control loops that have not been correctly tuned are disabled by engineers or operators and left in manual mode due to poor control results in unpredictable process behavior. Rather than correcting these systems, operators are left to manage the process manually, making frequent adjustments throughout their shifts in an attempt to keep the system in a relatively steady state. This approach to process control leads to inconsistent product outcomes and excessive demands on operators’ time and attention. The alternative, continuing to run the control loops with poor tuning, is that it accelerates wear on control valves due to the oscillations and frequent repositioning of the valve components, and wastes energy and other resources.
The cumulative impact of poor loop control rarely presents as a single point of failure. Instead, it slowly erodes performance across the system: lost efficiency, additional operator workload, and accelerated equipment degradation. These small inefficiencies compound over time, silently draining resources and often remain hidden until a push for APC or another effort exposes the underlying issues.
Small Fixes, Big Payoffs
In one typical scenario, a chemical manufacturer had not reviewed their PID parameters since initial startup. By deploying loop monitoring software and addressing equipment issues (such as worn valve packing and aging instrumentation), they were able to restore stability across their process units. The improvements were significant, even before advanced process control was introduced. Once the system was operating more consistently, the facility could take advantage of more sophisticated control strategies, including APC and AI applications.
Developing the Right Loop Tuning Program
Loop tuning involves more than adjusting proportional, integral, and derivative (PID) settings so that the feedback loop maintains a balanced response in both speed and stability as process conditions change. While poorly tuned loops can overshoot, oscillate, or react too slowly leading to inefficiencies and disruptions, a well-tuned loop responds quickly and reliably, maintaining stability and minimizing process variability.
However, improving loop performance is not just a matter of changing the PID settings. Physical issues in the field may be the cause of loop control issues. Whether it is worn control valves, miscalibrated sensors, poor installation, sizing, or sensor selection, too often control engineers are asked to “fix” a control loop from the control room, when a holistic approach to loop tuning is needed. Only an ongoing holistic approach can truly address control loop health.
A control loop health program should consist of:
- Software to monitor control loop performance and identify root causes of issues
- Software to provide tuning parameter suggestions (may or may not be part of the loop monitoring package)
- Instrument technician support to repair or replace faulty equipment
- Instrument engineer support to correct design issues with instrumentation and valves
- Control system engineer support to prioritize issues, address control loop strategy issues, and update loop tuning parameters
Establishing loop tuning and control optimization as a routine part of operations can prevent many operational challenges and inefficiencies. Tuning can be done incrementally, focusing on one unit or system at a time. A good control loop health program can save a company thousands of dollars a month in energy and raw material usage. Operators will also be freed from “babysitting” unreliable control loops and build more trust in their instrumentation and systems, while initially increasing the instrument technicians’ workload during the rollout. The instrument technicians will eventually get fewer work orders as control valves stop oscillating and wearing out components.
Delivering Advanced Insights with APC and AI
Advanced process control software builds on a plant’s existing base control system for further performance improvements through system-wide optimization. Today’s APC platforms increasingly use artificial intelligence (AI) and machine learning (ML) algorithms that analyze historical and real-time data to create a mathematical model of the system. Other industrial AI platforms provide early warnings of equipment failures or product deviations. These models can identify the complex relationships between process variables and product outcomes, uncovering new opportunities for optimization.
APC and industrial AI benefits go beyond improved efficiency. These solutions enable data-driven decision-making, increase product consistency, extend equipment life, optimize energy usage, and reduce operating costs.
For example, a manufacturer could train an APC model using historical process data. The resulting model may then predict how changes in control variables, like steam flow or column pressure, affect overall outcomes such as yield or energy use. Based on these insights, the APC system can automatically make minor setpoint adjustments that improve overall performance.
While APC is not a new concept and has been around for more than 30 years, some industries employ these solutions more commonly than others. For example, the oil and gas industry has largely integrated APC solutions into its refineries. In other industries, their use remains less commonplace. The two most commonly cited reasons for not implementing APC are perceived complexity/cost and the state of their existing control loops and instrumentation. Similarly, one of the most frequently cited reasons for APC and AI pilot projects failing is a lack of quality process data feeding them and poor process control to effect field changes.
To fully realize the benefits of advanced Industry 4.0 solutions, manufacturers must begin by ensuring their control loops are properly tuned. Without this groundwork, even the most sophisticated APC and AI platforms will struggle to deliver meaningful results. Tune the control loops first! To learn more about our range of support solutions, from software to field support, or to get started, contact Hargrove Controls & Automation today.
