Organic matter balance in ECF kraft mill fiberline.

Organic matter balances of an ECF kraft mill fiberline were studied in three different operational conditions of the oxygen delignification stage by implementing mill measurements, collecting routine mill data and combining them in a modified PROCELL steady state model. Dissolved volatile solids was the basic measurement for organic matter in liquid streams. Normal operation of the O2D0E(O)D1E(OP)D2 fiberline was described successfully. It was also possible to describe exceptional operating situations in the oxygen delignification stage and their effects on other parts of the production process reasonably well in order to focus studies on aspects requiring further attention. The existence of organic matter lost through complete degradation and volatile organic compounds in unit processes as well as its sensitivity to yield and operational situations is shown. The different perspectives of pulp production and wastewater treatment can be brought closer to each other using the approach in this study. The variation in the fractions discharged to wastewater treatment, although a relatively small share of the overall organic matter balance, will continue to become more important also for pulp production when effluent streams are increasingly turned back to the production line through further closure. Studies like the one presented here, can contribute to the evaluation of this development.

The role of organic matter lost in kraft pulping material balances .

Efficiency improvement in a pulp mill includes minimisation of environmental discharges simultaneously with the development of pulp quality and production economy. Material balances in production processes, including fate of sidestreams, are key in proceeding these matters. Different approaches of determining the material balances increase understanding of process behaviour. We have focused on measuring sidestream (carryovers, washing water, filtrate) dissolved organic matter (DOM) in fibreline unit process blocks of softwood ECF bleached kraft production. The DOM was analysed by traditional wastewater methods (volatile solids, organic carbon, chemical oxygen demand). The measured data was combined with primarily simulated water balances and routine operational mill data in a simulation model. From this balance, yield estimate included, lost organic matter through complete degradation (CD) and volatile organic compounds (VOC) can be calculated throughout the fibreline. The sensitivity of this considerable amount (23-35 kgDVS/adt in total) to various factors is discussed in this paper.