The effect of increased heat integration on the cost for producing DME via black liquor gasification

Paper in proceeding, 2009

Black liquor gasification is currently being developed as an alternative technology for energy and chemical recovery at chemical pulp mills. Substituting the recovery boiler with a black liquor gasification plant coupled to motor fuel production at a future market pulp mill will change the mill’s mass and energy balance from a surplus of both bark and electricity to a deficit. This study investigates the effect, on mass and energy balances and economy, of increased heat integration when a black liquor gasification plant producing DME is introduced to a kraft market pulp mill. By integrating the evaporation plant, the largest steam consumer at a pulp mill, with other parts of the mill and increasing the number of evaporation effects the need for live steam in the evaporation plant can be reduced by more than 50%. As a consequence, the mill’s need for external biomass decreases by 62%. At the same time, however, the need for external electricity increases by 35%. The additional operating cost, compared to a conventional mill with a recovery boiler, is dependent on the assumed biomass and electricity prices and the ratio between these prices. When a relatively low price ratio is assumed, the additional operating cost increases by approximately 2% when increased heat integration is considered. But when a relatively high ratio between the biomass and electricity prices is considered, increased heat integration decreases the additional operating cost by approximately 4%. The additional investment cost, compared to investing in a new recovery boiler, decreases by 10%. The cost for producing DME decreases by 1-5% depending on the assumed ratio between the biomass and electricity prices when increased heat integration is considered.