The current calculation methods for acid dew point of flue gas were summarized.Since the former Soviet Union method can not reflect the self-desulfurization ability of fly ash accurately

distinguish the sulfur form in coals and consider the effect of SO3

a method based on actual SO2 concentration in flue gas at inlet of the desulfurizing tower was proposed.This method uses the input coal composition

environmental parameters and unit operation parameters to figure out the combustible sulfur content

meanwhile

the actual boundary conditions like whether there is the SCR system are also considered.Three 600MW units firing lean coal

lignite coal and bituminous coal were taken as the example to give the detail calculation steps.The results indicate the proposed method was more reasonable.