A. Leshchinskaya. MICROWAVE WOOD CHIP TREATMENT USE IN CHEMICAL PULP MANUFACTURING (TECHNICAL-ECONOMIC ASSESMENT)

Abstract

MICROWAVE WOOD CHIP TREATMENT USE IN CHEMICAL PULP MANUFACTURING (TECHNICAL-ECONOMIC ASSESMENT) A. Leshchinskaya Plekhanov Russian University of Economics. 36 Stremyannyy Pereulok, 115093 Moscow, Russia, e-mail: alixfl@mail.ru] Keywords: chemical pulping, microwave wood modification, pulp, softwood, wood chips. Large volumes of cellulose are produced from wood chips by chemical methods. Low permeability of many wood species causes problems in the chemical pulp industry. These include: very long cooking times, high chemical consumption, large material losses, high energy consumption, and environmental pollution. New microwave (MW) wood modification technology can provide an increase in wood permeability for liquids and gases, which solves many of these problems. The technology works by applying intensive MW power to green wood, which generates steam pressure within wood cells. High internal pressure destroys weak elements of wood structure, opens pores and forms micro and macro cracks. A several thousand-fold increase in wood permeability can be achieved in species previously found to be impermeable to liquids and gases. It allows a significant increase in the speed of pulp cooking and improves a production processes. The study of the technology showed radical potential improvements in the pulp industry through: increase in mill throughput significant reduction of chemical consumptionreduction of energy consumption • increase in pulp quality and yield improvement of environmental performance. Pulp manufacturing process includs timber chipping, microwave chip treatment, steaming, cooking, washing, and pulp making. The use of MW wood chip treatment in pulp mills with outputs of 50,000 to 500,000 air dry tons (ADT) per year requires MW equipment with power from 1000 to 10,000 kW. Economic modelling of this technology used in different pulp mill conditions allowed assessment of the effect of capital costs, electricity costs, labour costs and other cost components to specific total costs of MW chip processing. Economic assessment of MW technology application showed that specific costs of softwood chip processing at electricity costs of 0.08 - 0.12 US$/kWh are 25.4 -33.7 US$/ADT of pulp. Electricity costs form the most significant part of the total specific costs of MW processing and form 51-69% shear in the total specific costs. Under the same conditions capital costs form 15-20% shear, and labour costs form 5-18% shear of the total specific costs. The electricity cost increase from $0.04 to $0.24/kWh provides specific MW processing cost rise by 2.7 to 3.1 times at pulp mill output range 50,000 to 500,000 ADT/year. New technology use allows benefits up to 7 – 22 Mil US$ per year for pulp mills with output of more than 200,000 ADT/year. The technology can be used by pulp mills with batch and continuous digesting and is not limited by mill throughput. Ecological impacts and high economic advantages of this MW technology application in pulp and paper industry provide good opportunity for commercialisation.