One of the ways that the portland cement industry is seeking eco-efficiency gains is in waste co-processing and energy/material recovery - using the waste and by-products of other industries as fuels and raw materials for cement manufacture.1 These wastes and by¬products of other industries, such as tires and plastics (fuels) or blast furnace slag and fly ash (raw materials), are often referred to collectively as alternative fuels and raw materials (AFRs). The Portland cement industry has long desired to more fully utilize AFRs. However, antiquated New Source Review (NSR) rules required facilities to evaluate such changes to the kiln system using the future potential, less past actual, emissions increase calculation approach. The overly conservative future potential, less past actual, approach often led to the need for Prevention of Significant Deterioration or Non-Attainment New Source Review permitting (and/or the requirement to take unnecessary permit limitations to avoid NSR permitting) even if the actual change in emissions from the project was an emission reduction. As the portland cement industry has long known that utilizing many of the available AFRs would have very little impact on actual air emission rates, this calculus clearly undermined one of the fundamental tenets of the NSR rule's intent: the 'causation' between a particular physical change and a change in actual emissions.
Fortunately, recent reforms to the NSR rules allow plants to compare changes in actual emissions from the use of AFRs to major source pre-construction permitting applicability thresholds. Consequently, these changes often require only minor source construction permits, as opposed to major source NSR permits. This paper reviews some of the recent methods used for estimating the emission changes resulting from the use of AFRs for Clean Air Act (CAA) permitting purposes as well as the types of permit conditions resulting from such permitting.