Correspondence/Rebuttal pubs.acs.org/est
Comment on “Solid Recovered Fuel: Materials Flow Analysis and Fuel Property Development during the Mechanical Processing of Biodried Waste” Enforcing plausibility constraints on these flows (i.e., making all of them non-negative) affects the results. For instance, the transfer coefficients for the plant input to the SRF output change by 1.5% (net calorific value), 3.4% (ash content), and 0.2% (total Cl content), respectively, relative to the reported values, if currently negative ferrous scrap flows are set to zero and positive ones are set to the value calculated from the mass balance of the process “Fe-metals mixing”. Although the resulting deviations between these possible and the reported values are small, it should be noted that they originate from a physically invalid model. Thus, they are the result of model inconsistencies and not of data uncertainties. These inconsistencies can be avoided by appropriate modeling and data handling. Third, Velis et al.1 state that their mass balancing procedure could be validated as STAN was used to reconcile the full set of mass balances and satisfying agreement between measured and modeled flows could be achieved. As physically impossible, negative flows occur in the system, the plausibility of the whole set of reconciled mass flows (at different material levels) is dubious, at least. We believe that the data reconciliation in STAN should have lead the authors back to the flow balancing step (refining input data for the MFA model) to adjust some of the assumptions on the allocation of nonconserved waste fractions (i.e., fractions which are (partly) generated during treatment and not present in the waste input, for example, Fines
