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Performance audits in the paper mill consist of wet-end and dry-end evaluations. The wet-end audit consists of evaluating the stock preparation and whitewater system design; evaluation of short circulation, performance, and capacity limits of stock screening and cleaning systems; and evaluation of pumps and water clarification equipment. Equipment performance must be compared with design values, and should be evaluated for additional capital investment requirements for upgrades and resulting economic return on investment (ROI).
Performance of the paper machine forming section must be evaluated for sheet dryness off the couch, fiber and filler retention, sheet drainage rates, and performance of the drainage elements. Evaluation of the forming section in some cases also helps identify formation and hydrodynamic problems that are commonly experienced in many mills. Individual and overall paper machine performance indexes must be compared with performance values for paper machines that produce similar grades of product.
The press section must be evaluated or good performance in achieving maximum sheet dryness. The performance of press section components--such as the nip, felt, Uhle box, and showers--must support the goal of maximum sheet dryness. The design should be optimized to minimize open draw and rewetting of the sheet. Recent press section designs include steam showers to improve sheet dewatering.
A performance audit in the dryer section of the paper machine includes identification of any capacity limitations in the dryer systems. The drying rate should be compared with TAPPI drying rates and other paper machines producing similar product grades. The efficiency of the condensate removal system must be evaluated for proper siphon size, siphon clearance, condensate evacuation, condensate piping, blowthrough steam, maintenance of adequate differential pressure between dryer groups, and system steam losses. The hood and ventilation system must be evaluated for proper hood balance,...