The evaporator is modelled by a flash separator in Aspen Plus. Under the operating conditions of 107 ℃ and 1 atm, the acid solution can be re-concentrated to 61 wt.%; whilst under 108 ℃ and 1 atm, the acid solution can be re-concentrated to 64 wt.%. Electricity is utilized to supply heating for the evaporator and efficiency of electricity to heat conversion is assumed to be 100%.