Additional constraints enable easy configuration

The data reconciliation model in yield accounting system is primarily a mass balance model. The streams in the mass balance model have measured mass quantities associated with them and data reconciliation gives the reconciled mass quantities by satisfying the mass balance constraints. When we build a data reconciliation model of the entire plant for the purpose of mass balancing, the number of streams will often exceed 1,000, for the majority of which it would be unrealistic and unnecessary to impose a component or enthalpy balance. For that reason, we usually configure component or enthalpy balances around some sections of the entire model. This has the disadvantage that we cannot impose balance constraints between each section because the intervening parts may not have components or enthalpy configured.

Figure: An example of a complex mass balance model

Where:

Xi is mass quantity of stream i

Cij is component composition of stream i and component j.

For the outputs of PR2 and PR3, assume that the third component or each triplet is a final product. Assume further that we would like to build a component balance for only a final product component between the feed stock and final product output, consistent with the mass balance for the entire plant. How can we impose such a component balance constraint? The conventional method would impose a component balance for PR1, PR2 and PR3 balance nodes respectively but there is no way to enforce a component balance between the X1, X2 and X3 streams when there is no component balance for the interior part of the model.

Our new approach would instead create an additional component balance model consisting of the third component of the X1, X2 and X3 streams, then impose additional constraints between the existing mass balance model and the additional component balance model like this:

The component balance model of the 3rd component of the streams

Figure: The component balance model of the 3rd component of the streams

Selectively building a component or enthalpy balance in this way can yield a great improvement of the accuracy of the reconciled mass quantities.