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Porpoise Control Systems Our principal activity is the provision and implementation of plant control systems. To date we have supplied a number of elements of control schemes, mainly in the provision of the precise measurement equipment but also complete schemes concerning batch reactions. We have the capability of producing turn key closed loop control schemes on a wide variety of polymerisation processes, including LDPE, PP, PS, PET and PU. The full control of resin plants is now our main target. The opportunity arises because there is a need to improve on the currently accepted best practice, which places heavy reliance on calculated or modelled variables such as average molecular weight. This practice has indeed produced significant advances in polymerisation control and has been assisted by progressive improvements in many of the fundamental control issues such as gas analysis. The modelling approach has a fundamental weakness in that the calculated variable may not always accurately describe the reality. A typical failure mechanism in this type of scenario happens when the gas impurities poison the catalyst. In extreme circumstances a drive-off will result when the calculated variable shows tendencies out of sympathy with the controlling forces. Modern catalyst systems are very clever but their susceptibility to changes in feed gas and impurity levels requires a great deal of care. The drive-off is an extreme example but our approach, based on careful measurement of prime variables, will ensure that the control mechanisms will remain viable at all times including regression to a safety zone if the catalyst system is overwhelmed. The advantages of this approach are security of operation, optimum grade changes and more stable control during normal operations. A unique advantage is the tighter control of molecular structure which leads to more predictable processing for the end product. The costs of the implementation are reflected in the ex-reactor sampling and the Porpoise measurement equipment. For example, a PP system will require a sampler and dedicated P5 for ex-reactor control in addition to a P5 for fine control of the reactive extrusion process (the peroxide control) and finished product. In the cases of LDPE, PS, PU and PET the reaction properties can be measured on the finished product, thus saving the cost of a separate analyser. |
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