To protect catalyst from ammonium sulfate/bisulfate deposition and subsequent poisoning

the minimum operation temperature at low load should not be violated.Therefore

the selective catalytic reduction(SCR)system should be down at low load.However

the exit NOxconcentration may not meet the emission standards.The application of economizer bypass is an effective way to solve this problem.Taking the SCR system of a 600MW coal-fired power plant as the example

the numerical simulation method was employed to obtain the optimum economizer bypass scheme.By using the optimum economizer bypass

the average flue gas temperature at inlet cross section of the first catalytic layer increases to 319℃

which is above the minimum operation temperature

and the maximum deviation of the flue gas temperature distribution in this cross section is 2.4%

which satisfies the minimum ammonia spraying temperature.