BeST uses Pavilion, Gensym and its own KICS technologies to supply optimised control solutions to complex control problems.
The nonlinear and multivariate control problem
Many manufacturing processes in industry are complex and difficult to control because:
* There are many conflicting and opposing goals to satisfy.
* The processes are nonlinear and multivariable in nature.
* The processes themselves are complex and not fully understood.
The above problems manifest themselves where the same control actions under seemingly similar process conditions produce totally different results. This occurs where the system response is highly nonlinear and system gains change and even change sign, therefore causing the output from the same control action to have widely differing consequences.
The problem of poorly understood processes is also a major source of confusion and frustration in the control of these processes. These processes are generally well modelled through first principles under laboratory conditions. However, under operating conditions the nature of the processes is extremely difficult to understand especially if one uses linear tools. This is particularly true for multivariate metallurgical and mineral processing applications with feedback.
Consequently, the optimisation in realtime, of such processes is generally very difficult and intractable. This generally applies to the generic but opposing goals of maximising throughout and efficiency, whilst maintaining product quality.
Adding to the problem, in many cases, is that one needs to perform this complex control within a highly constrained environment. One needs to take cognisance of real limitations such as motor power limits, or maximum temperatures in order to safeguard physical equipment such as motors, and refractory bricks.
Another growing issue is that many processes can be described as chaotic. What this means is that certain variables are almost guaranteed to bounce around the setpoint chaotically. This is not due to unmeasured disturbances, but the nature of the process itself. This does not mean that these processes have not and will not continue to be controlled, but rather that optimal control or regulation in presence of these disturbances if possible, will at best be sub-optimal.
Solution - optimal and intelligent model-based predictive control
A suitable solution to this problem has been the deployment of control solutions by BeST in conjunction with other industry partners and systems suppliers, such as PPC, Pavilion Technologies and Gensym.
BeST together with its partners have created solutions to the above type of control problem. It uses nonlinear model-based predictive control, coupled with realtime intelligent systems to produce an optimal and intelligent controller.
The core technology is the optimising model-based predictive control engine (Pavilion's Process Perfecter), which allows for the nonlinear steady state modelling of the process using neural networks, and the coupling of this to a model-based predictive dynamic controller. One of the most powerful features of the neural network technology from Pavilion is that it can be inverted in realtime, thus allowing for the determination of the settings to use to achieve certain production goals. This allows one to put setpoints and constraints on both inputs and outputs, hence providing for full dynamic optimisation on both manipulated and controlled variables. Types of constraints are; maximum rate of change, hard constraints, and soft, or fuzzy constraints
The controller constantly makes moves to manipulated variables such as valves and feed conveyors to control outputs like load, temperatures and gas composition. All of this is done in conjunction with various economic rules, prioritisations, and costings. A surrounding intelligent expert system 'KICS Wrapper' is used to monitor the instruments and perform intelligent signal processing to prepare the signals to be fed to the controller. The result is a robust controller that adapts to the plant instrumentation failures or uncertainties. This allows production staff to optimise according to various economic and operational strategies.
BeST says that a number of world firsts in terms of optimal control have been realised by this technology, and the most prominent in South Africa is the optimal control of a cement kiln 1,2,3. Other areas tackled by BeST include mills and furnaces. Worldwide the technology has been widely applied in other industries such as paper and pulp, food, and petrochemical.
BeST SA
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