The most common causes of slow running models are:

• The number of equations being solved is large (greater than 15).
• A phase in the model completely disappears (e.g. a solid phase dissolves completely) during the simulation. Very small volume phases can occasionally cause numerical problems within the solvers that cause a large number of steps to be taken.
• A discontinuity is present in the model solution caused by a calculate statement (e.g. ‘If’ statements used to implement a process control action)
• Rapid changes in profiled variables. A sudden change (a discontinuity) will force the solver to take small steps to capture the change accurately.
• The number of data points in the model is large (greater than 100). The solver will stop and report a value at times corresponding to each data point. This means that the more data points you have, the slower the run will be.
• Wrong choice of solver. Another solver may run the model more quickly.
• Model parameter inconsistencies (e.g. rate constants or concentrations are orders of magnitude too high). Check the model in the simulator windows.
• Other model inconsistencies (e.g. imposing pressure in a set volume gas phase).

Troubleshoot models that run slowly.