The fate of nitrogen in the chemical recovery process in a kraft pulp mill. Part III: The effect of some process variables

The effects of some process variables on the fate of N in the chem. recovery cycles of pulp mills were studied.  The general picture of the relative flows of wood N in the cycle was the same for both hard and soft woods.  However, the wood species was of significance for the N concns. in the cycle as well as for the level of NO_x emissions from the boiler.  The different ways to handle secondary condensates caused some minor changes in the routes of N in the cycle.  The addn. of bio-​sludge (∼0.5 wt.​% of black liquor solids) to black liquor in the middle of the evapn. plant increased the N content of liquor by ∼30​%.  However, this addn. and the feed of the high-​concn., low-​vol. gases and MeOH to the recovery boiler did not result in any change in the share of the smelt N of the liquor N or in any increase in the levels of NO_x emissions in the boiler.