Load change problem synchronized with pipe network pressure increasing of three thermo-coupled columns in a cryogenic air separation unit was discussed.Due to the thermo-coupled features among the distillation columns

the simulation of the load change operation of a cryogenic air separation unit is difficult.Analytical results reveal that slight change of the operation variable can cause dramatic change of some other variables

which results in the difficulties of convergence due to inaccurate gradient approximation.The homotopy-based backtracking method(HBM)can efficiently deal with the load change simulation of the thermo-coupled system.The nitrogen block phenomena can also be simulated with this method.