nRemember the law of conservation of mass. No element mass is lost or gained and the plant is at steady state.
nInput = Output so Mass of S in coal feed = Mass of S in Ash + Mass of S in stack gas, therefore:
n.01 (20,000 ton) = .02 (1000 ton) + S
n200 ton = 20 ton + S
nS= 200 ton – 20 ton = 180 ton