Pulp & Paper - Paper Mill
Paper Machine Dry End
Uptime / machine breaks
Paper machine efficiency
The dryers are in series and are typically grouped into sections. A paper machine can have 3-4 sections. You will often see starch applied to writing and printing and other papers for sizing somewhere before the last dryer section. A calender stack (typically only two rolls, not four as shown) is at the end of the machine just before the reel to mechanically size the paper as well as apply a small amount of finishing. High finishing requires supercalenders. Supercalenders are often separate from the machine.
Some mills have a starch cooker, where raw starch is heated to a specific temperature for a specific period of time to control viscosity. Dilution with water controls the solids. Viscosity and solids are the two main KPI’s. This area is a good application for mag meters. Other mills simply purchase cooked starch and dilute it before adding it to the machine. In either case, a mag meter or Coriolis meter is used to apply the proper amount to the paper, based on weight of the paper (and the grade). A mass measurement here is useful.
Coated paper mills typically have their own mixing area to make their own coatings. This is often called the “Coater Kitchen”. Materials used in coatings can be proprietary, and are almost always expensive. Latex, starch, and titanium dioxide are some examples of ingredients. Some ingredients are mixed by hand and some with magmeters. Like the starch, the final coating is applied to the paper based somewhere before the last dryer section.
The amount is carefully metered, either by a mag or Coriolis meter, based on the weight of paper (and the grade). Again, a mass measurement is useful.
We have had success with mass flow on the steam to the dryers as well. Usually there is only one steam measurement for the main header going to all dryer sections.
As mentioned, supercalendering puts a high gloss on the paper. This is accomplished by multiple rolls with varying finishes to give the paper different finishing properties, and by the treatment with steam. Vortex has been especially successful for Supercalenders when mills are running a wide variety of grades that require a wide variety of glossiness. This can lead to low flow that other technologies can’t handle with the accuracy required by this control loop.