Optimizing the Utility System of a Tissue Paper Mill Using Pinch Technology

Abstract

A tissue paper mill in southern California had existing utility demands of 7.1 MW for the tissue mill (13 MW for the whole site), and 55 MM Btu/hr of fuel gas for the steam boiler. Total utility costs were $12 MM per year. The mill was seriously considering an 11 MW cogeneration system as a means of reducing operating costs. The expected benefits of the cogeneration project were $5.5 MM/yr of savings for an investment of $9 MM. A "pinch" study of the mill was initiated by SCE, with the customer's consent, to explore viable alternative projects that would result in comparable savings at equal or better payback and lower risk. The study identified a group of ten inter-related projects, including process heat recovery, a waste heat boiler and a 2.5 MW gas turbine. Combined savings were $4.5 MM/yr (37% of existing bill) at an estimated capital cost of $6.6 MM. The recommended approach was considered more attractive by the paper mill than the original plan because: (a) the benefits were obtained in a number of different areas -reduced fuel use, reduced power cost, reduced water makeup, reduced wastewater discharge to sewer, and reduced solid wastes to landfill (b) the smaller projects involved lower technical and economic risk, and were easier to implement.