Figure 1 shows energy conversion system of the mill. All middle pressure steam (MP steam) to mill processes is taken from the turbine. Back pressure steam (BP steam) is also produced at the TMP plant and heat only boiler (HOB) to cover the whole heat demand of the mill. Feed water before the recovery and fluidized bed boilers is pre-heated using MP steam. BP steam is used for feed water pre-heating in the feed water tank. Condensates of MP and BP steams from the mill are collected into the separate condensate tanks before returning them back to the feed water tank of the power plant. Feed waters to the TMP plant and HOB are pumped from the condensate tank. Feed waters pumped to the TMP plant and HOB are not pre-heated. There are also other heat only boilers for peak load situations at the mill site but they can be ignored in this calculation. Table 1 shows known process values of the conversion process. Black liquor Recovery boiler 16 1 Fudized Bark bod boiler Pre-heater 13 Pump 10 12 Mass flow rate of black liquor 1711 t/d Mass flow rate of bark 345 t/d LHV of black liquor 14.2 MJ/kg LHV of bark 14.9 MJ/kg Figure 1. Energy conversion system of the mill Feed water tank Turbine 15 5 14 4 11, makeup water TMP Natural gas Boiler efficiency of recovery boiler 0.8 Boiler efficiency of fluidized bed boiler 0.87 Isentropic efficiency of turbine 0.82 Isentropic efficiency of pump 0.82 Table 1. Process values of the energy conversion process P, bar 84 84 Point 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 11 4 4 4 4 4 4 11 4 4 84 4 4 11 t, C 171 500 90 90 40 90 90 h. kJ/kg m.kg/s 16.0 99.0 15.3 15.3 99.7