ULTRAMAX from Ultra-Dynamics has been successfully applied to the optimisation of a paper tissue making process for reducing greenhouse gas emissions. The quantitative objective of the project was to reduce the overall process energy cost while maintaining product quality and without loss of production rates. It was important that the energy savings be achieved in a short time without the need for major plant modifications. ULTRAMAX proved to be ideal for this optimisation project because of its dynamic nature.
In the paper mill, water was removed from the furnish by several forced-through air and vacuum stations and finally by the Yankee steam drum, from which the tissue is removed by the crepe blade. The tissue paper pulp consisted of a combination of hard and softwoods, plus various chemicals.
The aim was to balance the cost of energy among the various combinations of ways to remove the water and moisture to get the desired final tissue moisture of about 6%.
The desired scope of the optimisation project was determined by a project team formed for this purpose, including the Product Development Department to ensure product integrity. The project scope also included the constraints that required to be satisfied to maintain machine capability, safety, quality and reliability considerations.
The optimisation project consisted of mill adjustments made hourly as recommended by ULTRAMAX, following plant personnel approval. After three weeks of optimisation, a 7.1% reduction in energy costs was achieved.
As the optimum condition was achieved with the recycled air flow damper fully open, extrapolations using the optimisation tool indicated that a larger recycled air duct and fan capacity would provide further benefit. The cross-section of the duct was subsequently doubled and a further round of optimisation cycles was carried out with additional energy savings of 8.5%. The re-engineering cost represented only a fraction of extra annual savings in energy costs.
The total energy savings were therefore 15.6% and when ULTRAMAX was applied to the eleven other mills, similar benefits were achieved.