Evaporation plays a key role in the alumina production process, in which heat of steam with high temperature and high pressure is transferred to the sodium aluminate solution in order to evaporate the redundant water contained in the liquid, and increase the caustic ratio concentration for that the liquid can satisfy the conditions of recycling. Influenced by the change of input parameters in practical production, the concentration of output liquid shows fluctuation. Besides, the delay of the operation on t...