Advanced process control powers developments in operations management

Nov. 8, 2004
Technology progression within advanced process control (APC) continues to evolve; however, it is the relationship among core APC developments, enabling technologies, and management practices that is producing a greater impact.

Technology progression within advanced process control (APC) continues to evolve; however, it is the relationship among core APC developments, enabling technologies, and management practices that is producing a greater impact. Improving economic conditions have not led to widespread hiring and increased capital spending. Process operators are instead mainly exploring continued advancements in operations technology to grow profits.

Examples of this strategy include using APC for improved process stability and reliable operating transitions; continued improvement in operations efficiency; remote and unattended operation of small plants; integration with higher-level planning, scheduling, and production optimization systems for larger plants; and the achievement of full-time operations best practices.

For process operators, technology advancements are best measured by impacts on the bottom line. An old self-evident premise of plant operations is that to achieve improvements in process operations, something must change: operating set points, process response to disturbances, adjustment of different variables, process operating strategy, etc.

If the way the process operates does not ultimately change, no software technology will provide bottom-line benefits. APC systems can produce these types of changes, resulting in significant economic benefits for companies that use this technology.

Operations management

APC algorithm and methodology improvements have led to more reliable and stable process transitions that enable operations strategies based on more frequent changes in production targets while maintaining or reducing staffing levels.

These strategies for where and how to operate units, plan for operating changes, connect business and operations tactics, and build inherent reliability and quality are known as "operations management."

APC is the "foundation" of operations management. APC is the connecting layer between the set points and valves that are actually moved in the process unit and the business strategies that determine how best to move them.

All higher-level production optimization systems (i.e., planning and scheduling, process optimization, quality management) must eventually have their strategies communicated to and then implemented by an APC system. As the quality and capability of the APC system improves, so does the effectiveness of these higher-level systems.

With this business focus, the most important developments in APC technology are those that directly address the needs of operations management.

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Table 1 details recent technology developments that have improved operations management and the economic value proposition of APC applications. These advancements have enhanced basic process operations, implemented optimization strategies that include process variables previously rarely adjusted, enabled redeployment of staff to more valuable operations functions, improved product quality, and increased production rates.

These results tie directly to the primary business targets for process operators: efficiency, reliability, reduced cost, improved quality, optimized staffing, and responsiveness to changing business needs.

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Fig. 1 exemplifies how recent developments in automated process testing promise to reduce implementation costs and improve the quality of APC applications.

Few applications of chemical process automated testing were reported before 2001; however, several practitioners have recently reported successful implementations on process applications, ranging from upstream processing to downstream refining units, and second-generation automated testing technologies are now commercially available. These systems allow for carefully designed set point changes in process variables, collect data from the resulting process response, and use this information to develop a process model that can be used for control and optimization.

Recent developments in signal design for chemical processes and in model identification technology used to analyze data are significantly reducing the time and personnel required to develop process models for APC applications. This reduces the cost of APC projects and increases the opportunities for APC applications, such as smaller and less-traditional process units like upstream oil and gas processing, and utility units.

System analysis

Significant academic research and commercial development has also focused on performance measurements for process and control system analysis. Improved tools for analyzing the performance of control systems and underlying valves and instrumentation, screening all system variables, and producing a prioritized list of suspected problems and potential solutions are becoming available (Fig. 2).

Performance analysis compares operations to benchmarks and prioritizes problem loops (Fig. 2).
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These developments enhance the work processes of engineers responsible for supporting many plant sites or a large individual site. Many companies now consolidate and then access the results of these tools from a central location, which enhances the capability for remote support. Issues addressed by recent technology developments include:

  • Poorly tuned control loops.
  • Sticking or poorly responding valves.
  • Excessive process disturbances.
  • Measurement signal noise.
  • Loop or signal saturation.
  • Unresponsive instrumentation.
  • Performance monitoring

Performance monitoring technologies are actively progressing for basic controls and instrumentation,

These technologies include:

  • Performance measurements that assess control and optimization performance against a benchmark.
  • Identification and definition of the unique state or conditions of process operations.
  • Assessment of the system's economic sensitivity to operating changes.
  • Tools for troubleshooting and debugging.

Small-scale processes

New technologies for smaller-scale (1-5 manipulated set points) and nonlinear chemical processes promise to broaden the applicability of APC to new process applications. Underlying these technologies are empirical nonlinear models suitable for APC.

"Bounded derivative nets" is a technology that enables the construction of reliable models that incorporate challenging process features such as nonlinear composition response, variable time response and process delay time, and significant changes in the importance of key variables depending on the process operating modes.

These capabilities enable the cost-effective construction of APC systems for smaller applications, including upstream oil and gas units, fuel gas systems, and specialty processing units. Deploying these applications on a large scale (i.e., multiple applications) is a preferred strategy because much of the information concerning how the process works is incorporated in the model structure; operators can often share data from multiple plants.

Because many of these solutions for specialty processes require custom models to address unique process characteristics and an APC system design tailored to specific business needs, they are often packaged and commercially provided as a solution for a type of processing unit rather than delivered as individual tools that must be "grassroots" configured.

Packaged solutions allow software developers to deliver the technology at a cost applicable to the prevailing process unit economics. Fuel gas optimization systems, sulfur plant control and optimization, and gas processing unit optimization systems are examples of packaged APC solutions that are commercially available.

Web capabilities

Networking and web capabilities continue to impact APC heavily. Some companies have constructed centralized support centers with significant remote capabilities; others have altered their models for implementing APC projects and some have instituted forms of remote plant operations.

Such tools as automated plant testing are easily monitored remotely, thereby enabling simultaneous construction of APC systems on multiple plants. Similarly, performance monitoring technology and tools enhance remote monitoring by providing clear benchmarks of expected performance and prioritizing issues that must be addressed.

Systems can often remotely apply updates and application improvements so that process troubleshooting is no longer limited to the resources or response time of people available on site. These capabilities reduce project and support costs, improve quality, and improve the economics of APC initiatives.

These more practical technology developments directly support the business rationales for operations management and are therefore frequently more significant than other more technical advances.

Other developments

Several other APC technology developments are promisingfor a continued progression in value from APC installations. These include improvements in modeling technology via enhanced state-space methods, mixed integer programming, new robust control concepts, and further development of performance monitoring and support tools.

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Technologies outside of APC could, however, significantly impact APC, real-time optimization, and other online process applications (Table 2).

Computing security is a major issue for users and vendors. The full use of computing technology, available at a low cost, is yet to be realized. Process modeling technology continues to evolve via additional methods for property estimation and the challenges of multiphase and reaction systems.

New developments in sensor technology supply new valuable, low-cost process information that can be used for control and optimization. Multivariate statistical methods continue to progress, offering definitive descriptions of process disturbances, improved quality control, clearer information from process measurements, and new process modeling techniques.

In addition, visualization technology may be the key to communicating more information concerning plant performance in a more absorbable and useful format. APC technology continues to progress. The most significant developments directly address the needs of operations management strategies adopted by many industry leaders. Recent developments reduce project costs, imporve capabilities, and provide an attractive opportunity for new applications on process units not traditionally considered cost-effective for APC.

The underlying principle of using technology and innovation to change the way process units operate will produce desired improvements in operating efficiency and reliability, production quality, and responsiveness to changing business conditions that a competitive environment demands.

The author

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William M. Canney ([email protected]) is a principal technologist with Aspen Technology Inc., Houston, and is responsible for APC technology development and contributing to AspenTech's overall technical direction. He has more than 20 years' experience with APC and multivariable process control technologies. Canney previously worked for FMC Corp., Union Carbide Corp., Praxair Inc., and Dynamic Matrix Control Corp. He has published articles and patents related to APC on several applications, including performance monitoring, refining, blending, cryogenic air separation, plastics, powders, and drying. Canney holds a BS in chemical engineering from the University of Wisconsin-Madison.