Increased production and improved quality on paper machines using advanced process control: Some European case studies

摘要

The paper describes results from some recent paper machine performance improvement projects undertaken in Europe using an approach called Advanced Process Control (APC), which is quite new to the pulp and paper industry. With APC, controllers can be designed that comprehend the real multivariable character of processes such as paper machines, in which many interacting variables determine both quality and production rates. The paper presents results showing that APC systems are able to reduce the standard deviations of key quality variables to a third of what they were, or better, and to improve machine efficiency, thus increasing production. APC systems are able to do this while at the same time optimising production costs and maintaining inputand output variables within specified operating ranges. Improved wet end stability is known to be a key to better runnability and product quality of paper machines and to the reduction of off-specification production loss. Significant technological developments in recent years have brought, firstly, a number of new sensors allowing much closer realtime scrutiny of wet end behaviour and, secondly, the means of adjusting average levels of fibre retention using retention aid dosage rates. Using APC, these two developments are able to be linked in order to improve paper machine stability. An APC wet end stability controller can be set the task of minimising wet end variation and stabilising the ash content of the sheet, by providing coordinated control of all the variables that influence the operation of the stock approach system and the wet end. With improved wet end stability as a platform, APC can then be used to meet other performance improvement objectives, for example better control of drainage to improve moisture control, to reduce variation in draw, to diminish specific dryer energy usage and hence to increase production in machines that are dryer bottlenecked. Each paper machine has its own operating priorities and constraints and therefore requires a controller design unique to that machine.Case study material is presented from some of our recent European APC paper machine application projects on newsprint, fine paper and multi-ply board machines.