First of all, thanks for providing such a splendid MFA tool to the scientific community!
For an MFA of the agri-food chain we are looking to model nitrogen flows, including the N speciation. We didn't really find a way in STAN to model and calculate the flows across species of a substance.
In that frame, we were wondering if there is a possibility to develop our own calculation plugin. And is it possible to share the sources of the (free) calculation algorithm that is shipped with STAN?
In STAN it is only possible to consider elements of the periodic table and compounds that are not transformed within processes because they obey the law of mass conservation. Thus, different N-compound and there transformations based on stoichiometric equations cannot be modelled in STAN.
Unfortunately, it is not possible to write your own plugin because STAN doesn't offer any API. Sorry for not having better news.
The nonlinear data reconciliation algorithm implemented in STAN is decribed in detail in
Cencic, O., Nonlinear data reconciliation in material flow analysis with software STAN. Sustainable Environment Research 2016, 26, (6), 291-298.