Kraft Pulp Mill Internal Sulphuric Acid Production, 2000 Environmental Conference Proceedings

- S. Valeur, P. Fetissoff, D. Lawler, P. Bjorklund -- As effluent closure increases in Kraft pulp mills in response to environmental legislation, incoming sodium and sulphur may exceed natural losses, and the ratio of sodium to sulphur may change. In order to control this balance, mills may need to purge precipitator dust, SO2 scrubber liquor, etc., and add fresh makeup chemicals rich in either sodium or sulphur, such as NaOH or H2SO4. Elemental chlorine-free (ECF) mills may need to sewer all of their ClO2 generator by-product. There is a cost and an environmental impact of purging and sewering sodium - sulphur streams and making-up with purchased chemicals. Producing sulphuric acid from non-condensable gases (NCGs) will reduce the surplus of sulphur in tight mills and thus reduce the need to purge or sewer sodium - sulphur streams. In ECF mills, internal acid production permits more recycle of ClO2 generator by-product to the liquor cycle resulting in less purchased sodium and sulphuric acid. The sodium / sulphur balances and economic analyses presented in the paper will focus on the impact of internal sulphuric acid production on ECF mills. The potential benefits to the pulp mill described. The first plant in the world for producing sulphuric acid from NCG is now operating at a Swedish pulp mill, and the results are discussed.