DeltaVega

I don't think the value of quality you found is correct... stage 5 is defined by T = 525 C and P = 10 MPa this gives h = 3437.7 and s = 6.6777 Then when this is extracted through the turbine we have that at stage 6: P = 10 kPa and s = 6.6777 (which is the same entropy as stage 5) if you look at 10 kPa: s_f = 0.6493 s_g = 8.1502 and so s = 6.6777 gives you a quality of 80.35% not 88% (so this means in this question you need another reheat) now to answer your original question, follow these steps: Given 600MW and the time the plant is functional in one year find the heat transferred to the steam Then find the heat of combustion of coal then find the mass of coal given the heating value then use the wt% of sulfur to find the mass of sulfur