Energy Audit Uncovers Major Energy Savings for Paper Mill

Abstract

The results from a recent Stora Enso North America - Stevens Point Paper Machine #34 (PM34) dryer section rebuild will be reported. The rebuild, funded partially by the Wisconsin Focus on Energy program, improved the effectiveness of the dryer section. The mill used a four-step approach and the energy efficiency improvements were carefully documented to demonstrate the significant energy savings and production improvements achieved from each task. This paper tracks the results from the dryer section feasibility study through the installation of the Dryer Management System™ control software. The steps will be discussed as follows: 1. Dryer Section Feasibility Study. This report quantified the energy savings and outlined a plan to upgrade the dryer section. 2. Phase 1 of the Dryer Section rebuild. Steam system modifications and equipment upgrades in the after section were performed during the scheduled eight-hour monthly maintenance outages. 3. Phase 2 of the Dryer Section rebuild. The installation was continued in the pre-dryer section during the scheduled maintenance outages in the months that followed. 4. Phase 3 of the Dryer Section rebuild. The final stages of the project were completed during a 5-day outage. This included the installation of new valves, transmitters and a complete supervisory control system. The paper will describe the upgrade and tout the benefits of each step. The energy use and production history over a two-year time period will be reported. The paper will describe any problems encountered and solutions to overcome them. Observed benefits include energy savings of 4,000 pounds per hour steam and improvements in machine runnability and sheet quality. The expected energy benefits for paper companies like the one in this case study range from $100,000 to over $1 million per year. Machine production increases of up to 20 percent are also possible.