Multi Stock Ratio Control - Feedforward weight controls for multiple headbox machines.

A Metso Automation IQControl for Optimized Multiple Headboxes.

Description

Multi Stock Ratio Control is an important tool for optimizing a multiply stock board machine. By controlling allocation of several stock types to multiple headboxes or formers, this control increases machine productivity, reduces cull, improves quality and saves on material cost.

Normally, the filler plies are configured to control MD weight (although any headbox/former can be selected by the operator to participate in MD weight control). If there is more than one filler ply, the operator can set the loading of each ply using ratio targets. Usually, the liners are run in constant coverage mode to ensure consistent surface properties and to minimize the use of the more expensive liner furnish.

Using consistency and speed measurements from each headbox, Multi Stock Ratio Control adjusts the stock flows to prevent disturbances entering the machine. This feedforward control mechanism is essential on board machines where there are substantial time delays between the wet end and the reel. The control is supervised by a MultiPredictive feedback weight controller using the reel or base sheet scanning measurements.

Multi Stock Ratio Control provides the operator with the tools needed to get quality on-spec fast after startup, keep weight on target, ensure that the high cost liners are maintained at their most effective setpoints and that the filler is maximized for the lowest total furnish costs.

Benefits to the papermaker

• Good control of sheet weight for a consistent, high quality product.
• Feedforward approach corrects wet end disturbances before the product is affected.
• Operator has the tools to manage liner coverage and filler ply loading.
• The control can be configured by the operator to match the machine setup for different grades.
• Wet end prediction used by operator during breaks, startups and other transient conditions ensures fast startups and recovery from upsets.
• Constant coverage control of liners for more consistent surface properties.

Technical features

• Prediction of oven dry or conditioned weight for the whole sheet and each ply.
• Operator can control ply weights using feedforward setpoints and/or ratio targets.
• Ply weights can be set even before the sheet gets to the scanner ensuring fast startups.
• When a liner coverage change is made, the Filler flows are automatically adjusted to prevent an upset from occurring.
• Operator can configure for each headbox/former which stock is being used for constant coverage or weight control mode. Ply loading can be set if there are several filler formers.
• Stock System Overview display presents the operator with all the information required to run the stock system on a single page.
• Oven dry or conditioned weight measurement from the scanner is used to adapt the feedforward model for drift in consistency measurement, retention, shrinkage etc.
• Multi Stock Ratio Control can either directly adjust the stock valve to control feedforward weight for each ply or adjust the setpoint of a dry stock flow or volumetric flow controller, if desired.
• The Operator Tracking feature provides history of setpoint entry and controls status changes.
• Thick Stock flow for each ply is included in this package as a low-level controller.

Engineering support features

• Multi Stock Ratio Control is equipped with a comprehensive set of tools for tuning, maintenance and troubleshooting.
• All operations are performed with dedicated tuning displays, which are carefully designed for each task and step.
• The control package is configured by standard system CAD tools.