NEW AIR QUALITY REGULATIONS ANTICIPATED
Existing coal-fired power plants must meet stringent air and water quality regulations to ensure they do not pose an environmental hazard. In addition, because the Navajo plant is near a dozen or so National Parks, minimizing releases that contribute to haze or smog is also a critical element of operating the NGS. Controlling these gasses has been a priority for CAP and the power plant owners for decades. In the 1990s, ‘scrubbers’ were installed at the facility, at a cost of more than $400 million, which successfully reduced Sulfur Dioxide (SO2) emissions to below regulatory standards. NGS is also achieving high levels of particulate matter emissions control.
In 2008, aware that regulation on nitrogen oxide (NOx) emissions was pending, the Salt River Project (SRP), which operates the NGS, conducted a study of potential NOx-control technologies. Based on the study results, CAP and the power plant owners began installing low-NOx combustion technology at NGS. Installation of the first of three high-intensity burner assemblies was completed in 2009. Installation of the remaining two assemblies is scheduled for 2010 and 2011. The $43 million dollar project will reduce NOx emissions to well below the anticipated regulatory limit.
Low NOx burners control fuel and air mixing at each burner in order to create larger and more branched flames. This reduces peak flame temperature and results in less NOx formation. The improved flame structure also reduces the amount of oxygen available in the hottest part of the flame thus improving burner efficiency.
In August 2009, as part of its Regional Haze Program, EPA announced its intention to evaluate Best Available Retrofit Technology (BART) limits on NOx emissions at the Navajo Generating Station and the Four Corners Power Plant. In addition to low-NOx burners, the EPA is also considering a very different NOx control system known as Selective Catalytic Reduction (SCR).
SCR converts nitrogen oxides with the aid of a catalyst into gaseous nitrogen and water. A gaseous reductant, typically anhydrous ammonia, is added to a stream of exhaust gas and is absorbed onto a catalyst such as vanadium and tungsten, zeolites, and various precious metals. In automobiles, the catalyst is typically platinum.
According to studies conducted by the Salt River Project, the use of SCR would require between $660 million and $1.2 billion in additional capital expense (over and above the cost of low-NOx combustion technology), and add more than $13 million in annual operation and maintenance expense. The SCR technology would also require the daily importation of as many as two tanker trucks (about 31 tons) of anhydrous ammonia to support the control equipment.
SRP's studies also shows that SCR would produce no perceptible improvement in visibility in the region over that achievable with low-NOx combustion technology alone. This level of expenditure (and related operational difficulty and risk) would raise significant concerns about increases in the cost of power from NGS and about the operational reliability of NGS.
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