Local and System Exergy Losses in Cogeneration Processes

In cogeneration processes a major product appears as well as one or more by-products. The cumulative consumption of primary non-renewable exergy burdening the major product can be determined by means of the principle of avoided expenditures, assuming that the utilization of by-products eliminates the exergy consumption in the subprocess replaced by that utilization. The mentioned principle makes it usually possible to determine the consumption of raw materials and semi-finished products burdening the major product. That determination is, however, not possible if the by-product replaces some imported material, because such material burdens with the exergy consumption the total domestic production system.