Influence of Cl and K on Operation and Design of Chemical Recovery Equipment, 2010 TAPPI/PAPTAC International Chemical Recovery Conference

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The main objective in this study is to evaluate the effect of NPE on the operation costs and design capacities of equipment in the chemical recovery cycle. Pulp mills are faced with the difficult task of operating facilities cost competitively, while meeting increasingly stricter environmental regulations. Consequently, mill closure tends to increase, causing the accumulation of undesirable elements in the kraft liquor cycle.

Total inorganic solids in black liquor increase in the presence of chlorine (Cl) and potassium (K). Such change will affect the operation of chemical recovery equipment. The objective here is to show the magnitude of these impacts and estimate operational costs by using different inputs for Cl and K contents in liquors. Pulp mill material and energy balances for each case are used for this purpose and a modern Brazilian pulp mill served as a base case model.

The results show that for one specific range, the solid content in black liquor can be 7% higher by increasing the mass percentage of Cl and K in black liquor. This difference reduces its high heating value by 6.2% and increases recovery boiler capacity by 6.5%. The evaporation load increases 6.6% along with steam consumption. This makes total electricity output up to 1.6MW lower due to reduced flow to condensing stage of steam turbine. The balances also demonstrate that some pumping costs can be 16% higher when operating from low to high concentration of Cl and K in black liquor.