Sulfur Addition to Reduce CO Emissions

In autumn 2017, an experiment was conducted for the reduction of carbon monoxide (CO) emissions commissioned by Holmen Paper Braviken, one of the world’s most production-efficient paper mills. Digitalization has increased in recent years, which has resulted in a decreased demand for graphic paper. The goal of finding cost-reducing solutions in the manufacturing process has been increased in Holmen Paper Braviken to meet the rising price pressure and strengthen competitiveness. Braviken consumes large quantities of steam in the paper machines and some of this steam is produced in the solid fuel boiler. The solid fuel boiler combusts bark, wood chips, and water treatment sludge. When adding sulfur-rich water treatment sludge to the fuel mix, it has been observed that CO levels decrease without increasing NOx levels. To control the amount of sulfur addition, it has been proposed that pure sulfur can be microdosed into the fuel mix. A previous short-term experiment was conducted in Braviken during autumn 2016 with a successful result. The present study was conducted with the aim of mapping the effects of sulfur addition to the solid fuel boiler in Braviken concerning CO emissions. The possibility to operate the plant and interaction with the water treatment sludge have also been investigated. The study was performed through the construction of a microdosing system and a long-term attempt of sulfur addition. The result shows that the optimal sulfur concentration of Braviken’s solid fuel boiler for reducing CO emissions is 6 kg/h S (1.03 kg S/ton C). The interaction between elemental sulfur with the sulfur-rich water treatment sludge is complex, but with sulfur dosage a reduction of 42% CO can be achieved. NOx levels have not shown any change on the addition of sulfur. The study shows that CO emissions are at a more stable level with sulfur dosing. The result becomes difficult to analyze because the parameters varied. The effects of parameters should be investigated with the recommendation to perform a more prolonged experiment on sulfur addition.