The Arizona Department of Environmental Protection is taking comment until Jan. 26 on draft air permit changes that would allow installation of dry sorbent injection (DSI) on the coal-fired Cholla plant for Mercury and Air Toxics Standards (MATS) compliance.
Normal MATS compliance is due by no later than April 15, 2015. Arizona Public Service (APS) has already been granted a one-year extension by ADEQ, to April 16, 2016. The new DSI systems are expected in operation in March 2016.
“This permit revision incorporates the requirements to authorize the installation and operation of mercury reduction systems on Units 1, 3 and 4 to comply with Mercury and Air Toxics Standards,” said a permitting document. “The revision also incorporates the compliance schedule for installation and operation of mercury controls, mercury continuous emissions monitoring systems (CEMS) and boiler tuneup/burner inspection for Units 1, 3 and 4.”
Each mercury reduction system will consist of a silo and feeder injection train to inject the mercury absorbing sorbent into the flue duct of each unit. The sorbent is injected upstream of the particulate matter control device. The sorbent absorbs vapor phase mercury and is captured in the baghouse.
The Cholla plant operates four pulverized coal-fired, steam boilers which generate approximately 1,160 MW. Each unit is a tangentially-fired, dry bottom furnace. Unit 1, 3 and 4 are each equipped with fabric filter devices and Unit 2 is equipped with a mechanical dust collector for controlling particulate matter emissions. In addition, Unit 1 is equipped with a tray tower absorber system, Unit 2 is equipped with a four module flooded-disk scrubbers and four absorber towers, and Units 3 and 4 have spray tower absorber for controlling SO2 emissions. All four units are retrofitted with low-NOx burners (LNBs) and over-fire airsystems to reduce NOx.