The ethylene column is a kind of separation devices used in the petro-chemical process. It is easy for the column to enter abnormal condition because of improper operation in the distillation process. The outlet temperature will decrease with reflux increasing in normal condition and the model gain is negative. However

if reflux continues to increase

plate efficiency will decrease then outlet temperature begins to rise and model gain becomes positive then the distillation comes into abnormal condition. A kind of model gain online identification method based on the least square method for ethylene column was proposed in this paper. The symbol of model gain was identified online and then if the ethylene distillation column enters abnormal condition could be determined according to identification of model gain. Normal and abnormal control systems of the ethylene column were established and the control effect of the column controller could be determined according to the identification result of model gain

making reflux and outlet temperature controlled in the permitted range of normal condition. It could guarantee the ethylene column to work under normal condition and achieve the control of ethylene column under normal and abnormal condition.