Advanced Process Control
The concept of APC, and the ways in which it can be tailored to industry-specific processes - given the right level of knowledge and expertise - offers a great potential for a metals industry seeking solutions that provide tangible and guaranteed returns. Today, APC is fundamental to the success of certain processes within many industries, and is increasingly being applied today in steel production.
Although it is technically advanced and not without complexities, APC can be considered simply as the autopilot for driving the plant to an optimum state around the clock. It is traditionally based on Model Predictive Control (MPC), a technology with proven ability to provide control solutions using constraints, feed-forward and feedback to handle multi-variable processes that feature delays and processes with strong interactive loops. Using a plant model and objective functions, MPC can predict system behavior some steps into the future – put simply, it produces a digital twin of any process and predicts the way it will act.
Based on this predictive functionality, APC is able to automatically adjust operational set points to ensure peak plant performance and productivity. Its ability to make frequent, small changes, avoids large corrections or over-compensation for changes in conditions, creating a stable process, before steadily and smoothly moving to and maintaining an optimal operating state (Fig. 1). In this way, APC is able to enhance quality, raise throughput and reduce energy use.
APC is already used in a variety of industries to facilitate operational change, offering significant ROI. In the cement industry, for example, APC has been used to optimize both horizontal and vertical grinding circuits to improve productivity. Given the similar process and equipment used across both the cement and metals industries, such examples offer practical insight into the sort of savings APC could offer to steel producers in their own grinding processes.
In one example, an APC solution for cement was installed on a grinding circuit that included a roller-press with static V-separator and single chamber ball mill, achieving an improvement in control with a 4% increase in production, a 3% saving in energy, and a 60% reduction in the standard deviation of the rate of returns (tph).
In the cement industry - which, like the steel industry makes use of sinter - APC
can also be used to optimize raw mix proportioning in the sinter plant, as it already does for the raw mix entering the cement plant pyroprocess. With varying iron ore characteristics posing challenges to the production of a consistent steel product, using APC to balance the dosing ratio of base, limestone, dolomite and coke has the potential to minimize chemical variation before material enters the sinter machine.
Following the implementation of APC in a range of other industries - not only cement but also mining and pulp and paper - and working together with steelmakers, ABB has now developed APC applications for metals plants covering processes that pose clear and established challenges to steel plant operations.