House of card

The fierce winds across the Solvay Firth turn the blades of the generator windmills overlooking the Workington paperboard mill. Surrounded by the logs that feed the paper-making process, the plant produces high-quality board for boxes - notably, for upmarket brands of chocolate, and for software packages.

Demand for the product is rising steeply, as companies switch to new graphic printing techniques which require higher-quality board. Demand is also rising outside the mill's traditional Western Europe market - rising affluence on the Pacific Rim has created a market for more advanced packaging. The mill's operator, Iggesund Paperboard, has recently completed its 'MILLenniUm Project' (the acronym stands for 'Mill Uplift') to meet this demand, spending £51million on boosting the plant's capacity by almost 50 per cent, to 235 000tonnes per year.

Alongside a wide range of new processing equipment, the project included installation of a new drive system to allow the mill machinery to run at higher rates. Included in this was a new process control system. With Siemens providing the variable speed drives, as well as switchgear and one of the largest electric motors in the UK, Iggesund decided to give Siemens the task of updating the control system.

The MILLenniUm Project represented a major overhaul of the plant. The board produced at the Workington mill is a multilayer product, with the outer layers made from an ultrawhite, high-quality chemical pulp which has a smooth, glossy finish that is 'glazed' for printing. This chemical pulp is imported, but the inner layers are made from a lower-quality pulp, produced in-house from wood chips. This entire process, from log to board, is carried out at the plant, and much of the machinery to accomplish this was replaced.

The pulp mill, which turns the large woodchips into pulp, was completely rebuilt. The chip refiner was rebuilt and connected to a 17MW electric motor. The pulp screening system was also replaced, and a new peroxide bleaching system installed.

Further down the process, Iggesund refitted one of the mill's two boardmaking machines, installing extra steam-heated drying rollers at the 'dry end'; a new dryer hood; upgraded steam and condensate systems, and an entirely new electrical drive system to allow it to run at higher speeds. These incorporated machine sectional drives in the board machine, linked into variable speed drives in the pulp mill and to high-voltage switchgear.

The control system for both pulp mill and boardmaking machine, now housed in a single new control room, uses Siemens' Uniform Millwide Automation. Based around the PCS7 control system, this allows such parameters as speed, loading and tension profiles to be generated for the system as a whole or for each drive. This can help pinpoint paper breaks, for example, and warn when and where breaks are likely to happen.

The PCS7 control system is designed to replace the old control systems at papermills, which would typically have different systems for automation, process control and quality control. The single system covers process control, using Intel PCs; automation, using Siemens' SIMATIC S7 processors communicating with the process control level via industrial ethernet; and the field level, with the sectional drives communicating with the rest of the system via a Profibus network.

These components are all linked on Siemens' Millwide Information Management System (MIMS), which allows all the personnel at the plant to have access to process information from any location around the mill. It also links process control with overall production, allowing logistics, production planning and book-keeping to be integrated with the papermaking operation itself.

The system also functions as a simulation and archiving tool; it stores raw data which can be analysed in terms of energy usage, paper trimming, and product quality, and can be used in simulations to optimise the process, such as by scheduling the power plant to generate peak energy only when it is needed. Moreover, Siemens says, it produces reports from the process data, such as quality reports for the product's users which can be shipped with the reels of finished board.