The global industrial marketplace has increased pressure on facility operators to remain both competitive and profitable. For chemical manufacturers, the challenge is to run processes, typically involving large and interconnected sets of operations, at their optimal conditions while simultaneously maintaining multiple safety margins at acceptable levels.
For a growing number of sites, advanced process control (APC) and real-time optimization (RTO) are playing a key role in meeting operational and business objectives.
Yet, some chemical makers still don’t embrace APC technology, often because of outdated fears. This article aims to help overcome this reluctance by explaining how proper planning, implementation and maintenance of an APC strategy can result in tremendous improvements in plant efficiency and performance.
The ABCs Of APC
First, let’s cover some basics. APC is an intelligent and active software layer that sits above the distributed control system (DCS) or regulatory control layer in a manufacturing automation hierarchy. APC and RTO applications are designed to reduce changeability of critical variables and continuously adjust the process to guarantee the desired end result. The applications depend upon an accurate mathematical model of the manufacturing process; building that model is the first step in any implementation.
Many plant operators have learned to trust APC technology and appreciate its ability to make them more effective in their jobs. Today’s APC applications provide robust analytical tools and decision-support capabilities. These include comprehensive “move cause” scenario support, easier problem identification and faster diagnostics, as well as enhanced visualization for presentation of crucial information and integration/access to non-APC information (Figure 1).
For example, APC coupled with soft sensor technology enables a chemical processing facility to determine product quality in real-time on-site without waiting for a laboratory-sample or an end-of-the-run analysis. This results from the ability to predict quality accurately in-process as well as from improved process stability.
APC also enhances operational stability and consistency. Product and batch transitions are performed more quickly and in a uniform manner, translating directly to greater operational efficiencies and lower transition losses. In addition, the technology allows a manufacturer to run closer to desired targets and push constraints with more confidence. This leads to increased throughput as well as decreased consumption of raw materials and energy.
Advanced control technology should appeal particularly to a processor faced with operator shortages and low head counts. Current economic conditions are driving more companies toward APC so they can make do with fewer staff.
Applying The Technology
In the 1980s and 1990s, APC tools and techniques sometimes were difficult to use and needed special hardware for implementation, which raised costs. With today’s powerful computers, APC now is available anytime and everywhere — at lower capital cost and with greater return on investment.
One of the main hurdles in APC deployment is gaining acceptance from operators, particularly because they must relinquish control to the intelligence embedded within the system and accept changes affecting long-established procedures. Winning over operators requires efforts on two fronts: resolving technical issues; and simultaneously advising all those involved about how jobs will be handled going forward.
Typically, APC implementation takes place during the normal steady-state phase of a unit’s lifecycle. Plant owners increasingly are looking to expedite the benefits of the technology by introducing it at the conclusion of the guarantee period and having it functional within 3–6 months after the plant becomes operational.
As a preliminary, you must tune up the existing instrumentation, valves, controllers and control infrastructure to maximum performance. This on its own may yield substantial improvements. However, it won’t suffice to meet the larger objectives of APC deployment — namely, taking advantage of every opportunity to drive optimization of the plant.
Next, you must install online control-quality-monitoring software and then analyze process data on poorly performing control loops to identify the system dynamic. Finally, you must calculate new and improved tuning parameters for the control system.