Air quality at Santan Generating Station
Construction of the natural gas generating facility at SRP's Santan site — built with state-of-the-art technology — has actually improved air quality in the metropolitan Phoenix airshed. It may sound like a contradiction to say that adding a new generating facility will reduce emissions, but it's a fact, and here's why:
The U.S. Environmental Protection Agency (EPA) and Maricopa County Environmental Services Department mandate that no new major emission sources can be added to the metropolitan Phoenix airshed unless existing emissions are reduced — no exceptions.
In addition to meeting stringent emissions standards set forth by the EPA and Maricopa County, SRP obtained offsets from other sources that exceeded total new plant emissions by 10% to 50% (the actual amount varies by combustion byproduct and the distance of the offsets from the facility), and made on-site improvements that ensured changes in emissions were insignificant.
The Maricopa County Environmental Services Department issued a renewed air quality permit for the Santan Expansion Project on Dec. 23, 2010. A copy of the permit can be obtained at Maricopa County Environmental Services Department, Air Quality Division, (602) 506-6010.
Protecting public health
Santan Generating Station continues to meet all government air quality standards to protect public health and:
- does not have any visible emissions or odors from the stacks
- has sound reduction technology to manage the noise.
The expanded generating facility incorporates state-of-the-art technology and clean-burning natural gas to meet air quality standards that protect public health and the environment. The plant will remain subject to federal, state and local air quality regulations, which primarily relate to combustion byproducts.
- Comparison of emissions pre- and post expansion of the Santan plant
- Typical configuration of a combined cycle combustion system
Note: Natural gas powers a combustion turbine, a process similar to that which powers a jet engine. The exhaust heat produced in this process is captured to create steam (a process similar to boiling water in a pressure cooker), which powers a second turbine. The exhaust is then filtered through catalytic cleaning systems before it is released through a stack.
In metropolitan Phoenix, the major sources of pollution continue to be automotive exhaust (on-road mobile sources) and dust caused by construction (included in non-road sources).
Industrial facilities like power plants are minimal contributors - 2% or less - of particulates (PM10) and carbon monoxide (CO). (Source: Maricopa County Environmental Services Department, Emissions Inventory)
Air quality monitoring
SRP has installed continuous emissions monitoring systems (CEMS) on all Santan units for monitoring emissions from the units. Each CEMS system consists of an extractive system with analyzers for the monitoring of nitrogen oxides (NOx) and CO and certified fuel flow meters to calculate emissions of PM10, volatile organic compounds (VOCs) and oxides of sulfur (SO2).
A sample of the flue gas is continuously extracted, conditioned and analyzed by a NOx analyzer, an O2 analyzer and a CO analyzer. This system results in the monitoring and recording of NOx and CO in pounds per hour (lb/hr).
The fuel usage is recorded in hundreds of standard cubic feet per hour and converted to lb/hr data for PM10, VOC and SO2.
Hourly data from the Santan CEMS are used to calculate "12-month rolling total" emissions for comparison with the limits specified in the Santan air quality permit. The "12-month rolling total" is calculated by adding up all of the emissions generated during the current month and the 11 previous months. It is a "rolling" total because it is calculated at the end of each month. For example, the 12-month rolling total emissions for January 2011 is the sum of all emissions generated between February 1, 2010 and January 31, 2011.
Graphs showing the 12-month rolling total emissions of NOx, CO, PM10 and VOC for recent months are posted here on a quarterly basis. Because there are separate permit limits for the existing Units 1-4 and the new Units 5-6, separate graphs are shown to distinguish the old from the new units.