Abderrazak M. Latifi good question

Dear Aberrazak M. Latifi,

I suggest you to see links and attached file on topic.

https://www.psenterprise.com/products/gproms/custom

Article Process Systems Engineering, 2. Modeling and Simulation

Article A Modelling and Simulation Language for Combined Lumped and ...

Article Modelling and simulation of combined lumped and distributed ...

Article From discretization to regularization of composite discontin...

Best regards

I guess an approximate Integral function may be used to replace the actual Integral:

1. choose a large-enough Upper Limit of your Integral function: it is usually that the approximate integral value is close to the accurate value, when its Integral Upper Limit of is large enough;

2. choose a resonable Discretisation methods supported by gPROMS, like non‐uniform-interval Discretisation methods ( the code is like TRANSFORM( LOG, 4.0) ] ), which may greatly decrease computation load;

3. check the accuracy of the approximate Integral function;

4. if the accuracy of the approximate Integral is good enough, then it could be used in your model