After these data were developed, it became clear that no single method by itself could achieve all the required reduction. On the other hand, combining all three methods at full capacity on both types of furnaces (which would be prohibitively expensive if the company’s products are to remain competitively priced) much more than adequate. Therefore, the engineers concluded that they would have to use some combination for the method, perhaps with fractional capacities, based on their relative costs. Furthermore, because of the differences between the blast and the open-hearth furnaces, the two types probably should not use the same combination.
An analysis was conducted to estimate the total annual cost that would be incurred by each abatement method. A method’s annual cost included increased operating and maintenance expenses, as well as reduced revenue due to any loss in the efficiency of the production process caused by using the method. The other major cost is the start-up cost (the initial capital outlay) required to install the method. To make this one-time cost commensurable with the ongoing annual costs, the time value of money was used to calculate the annual expenditure that would be equivalent in value to this start-up cost.
This analysis led to the total annual cost estimates given in the table on the next page for using the methods at their full abatement capacities.