I judge the discussion in the Clearing the Air column in the August 2007 issue of Power Engineering (“How the Clean Air Act Promotes Pollution”) to be right on target.
The typical lifecycle of steam generating units makes whether the impact of generating unit modifications is to be evaluated on hourly or annual emissions critical to the justification of the contemplated modifications and to the owner’s actions to limit the expenditure level. Steam units are typically installed to serve a base load mode of operation and begin to experience deterioration by about age 20 that progresses sufficiently by about age 30 to require remedial action. The available remediation options are (1) retirement or mothballing, (2) life extension through changing the mode of operation and (3) life extension through refurbishment or through repowering by conversion to combined-cycle operation or by boiler replacement.
I have observed the retirement or mothballing choice to be rare. For example, I am aware of very few retired units that have been brought back into operation, am aware of several steam units being temporarily mothballed in response to excess capacity resulting from finally being able to operate nuclear units that had been delayed, and am not aware of any unit mothballed for a reason other that excess capacity that was brought back into operation. Refurbishment has become a common remediation option in recent years. Previously, the most common option was changing the mode of operation.
It is the life extension through refurbishment or repowering option that attracts the EPA’s attention. The EPA’s test compares the emissions expected from operations after refurbishment with the emissions from the two years of operations prior to the modifications. The more efficient usage of fuel that is inherent in the heat rate improvement from refurbishment will reduce hourly emissions for a given level of capacity and the increased hours of operation from the improved efficiency and reliability that moves a refurbished unit up in the dispatch-order will increase the annual emissions. Since the “before” and “after” test for emission changes must be done prior to making the modifications, the EPA compares historical operations with the post-refurbishment potential to emit, which assumes round-the-clock operation at maximum load for a year. The EPA’s assumption about future operations is inconsistent with how steam units actually operate.
If the modifications are anticipated to significantly increase the hours of operation, the unit can be expected to fail the EPA’s test, thereby leading to substantial expenditures for emission abatement that would not be triggered by an hourly test. Therefore, precisely when during the life of a steam unit the modifications occur and the owner’s reaction to the emissions situation become significant. Modifications occurring early enough in the life for the annual capacity factor to not change much may preclude failing the EPA’s test. However, this is an unlikely situation, because refurbishing a unit that has not yet deteriorated to the point where refurbishment is needed makes no sense. Therefore, the reaction of competent managers would be to attempt to increase the annual capacity factor for a couple of years in order to “game-the-system,” which is what the August 2007 column gets at.
The implications of when during the life of a steam unit the modifications occur are demonstrated by the Port Washington station of Wisconsin Electric Power Co. (WEPCO). Port Washington had 80 MW coal units installed in 1935, 1943, 1947, 1948 and 1950 (units 1 – 5) that had deteriorated sufficiently to require remedial action, and a 17 MW combustion turbine unit (unit 6) installed in 1969 that was not involved in the proposed modification project. WEPCO’s modification decision for units 1 – 5 resulted from a 1983 assessment study and was to be accomplished by replacing steam drums on all but unit 1 and replacing air heaters on all but unit 5. At the time the units were seldom operated and unit 5 had been taken out of service due to an equipment failure, which prompts me to interpret the modification project as more of a resurrection than a refurbishment. The project attracted the attention of the EPA, which filed an enforcement proceeding that caused the electric industry to become reluctant to use the term life extension.
The Court remanded the case to the EPA for further proceedings, which I believe led to the case being settled, but do not know the details of the settlement. However, it is my understanding that WEPCO opted to proceed with refurbishment of units 1 – 4 and to retire unit 5.
I have no knowledge of the magnitude of WEPCO’s project cost relative to either the cost of replacing the units or to the cost of the surviving units. However, I am aware that the modification costs that attracted the EPA’s attention in a later enforcement proceeding against the Tennessee Valley Authority amounted to less than 2 percent of the cost of replacing the units. When expressed in terms of an automobile having a replacement cost of $25,000, less than 2 percent represents the cost for replacing the tires.
John Ferguson, Richardson, Texas
Correction: Table 4 in “East River Repowering Project: Design, Construction and Operation” in the August 2007 issue gave the reverse osmosis permeate temperature in degrees centigrade. The temerperature should have been given in degrees Fahrenheit.