Arizona Public makes progress on SCRs for last Four Corners coal units

Ongoing installation of selective catalytic reduction (SCR) equipment for NOx control at the surviving units of the coal-fired Four Corners Power Plant are among the recent projects for Arizona Public Service that are extending the lives of some of its fossil-fired assets.

John R. Lucas, the General Manager of Generation Engineering and Projects supporting Fossil Generation at Arizona Public Servic, described the projects in testimony filed June 1 at the Arizona Corporation Commission in support of a utility rate hike request.

Since the last rate case filing in 2011, the following changes have been made to the fossil generating assets:

  • June 30, 2013 — APS retired Saguaro steam Units 1 and 2, removing 210 MW of 1955 vintage natural gas generating capacity.
  • December 30, 2013 — APS retired Four Corners Units 1, 2 and 3 (560 MW of coal generating capacity) and purchased Southern California Edison’s 48% share of Four Corners Units 4 and 5 (739 MW), increasing APS’s share in Four Corners by 179 MW.
  • October 1, 2015 — APS retired Cholla Unit 2, removing 260 MW of coal generating capacity.

Between 2013 and 2015, APS retired 1,030 MW of fossil fueled generating capacity, including 820 MW of coal and 210 MW of old natural gas steam units. Overall, APS’s net ownership in fossil fueled generating capacity has decreased by 291 MW since the last rate case.

APS started the SCR project at Four Corners in early 2014 using a competitive-bid process to evaluate qualitative and quantitative metrics before completing an Engineering, Procurement and Construction (EPC) contract with a firm experienced in SCR projects. The open-book process was used to examine the cost estimates and the cost-estimate basis before completing the contract. APS’s share of the SCR project is projected to be approximately $400 million and $35 million to upgrade the condition of the FGD systems.

In 2016, infrastructure and the pilings/footings necessary to support the new equipment at Four Corners are under construction. The SCR must be operational at Four Corners Units 4-5 for one of the units by March 31, 2018, and by July 31, 2018, for the remaining unit.

In alignment with the U.S. EPA’s Federal Implementation Plan and a Consent Decree issued in June 2015 for Four Corners Units 4 and 5, APS must install SCR technology to reduce the NOx emissions to a level of 0.08 lb./mmBtu and replace sections of the Flue Gas Desulfurization (FGD) systems to meet 95% SO2 emissions removal from the flue gas created from coal combustion.

Two of the main environmental projects being completed in the post-Test Year Plant period include:

  • Installation of activated carbon injection system to reduce mercury emissions on Cholla Units 1 and 3. The scope of these projects is estimated to cost $6.7 million.
  • Overhaul of Four Corners Units 4 and 5 absorber modules to meet 95% SO2 removal and reduce moisture carry-over to the steam stack. The scope of these projects is estimated to cost more than $20 million.

In 2016, the utility entered a three-year period of major overhauls on the large coal units with planned outages for Cholla Unit 3 and Four Corners Unit 5 executed earlier this year. Investment in Four Corners Units 4 and 5 is imperative to improving the level of performance on these 770-MW units, Lucas noted. To reliably operate to 2038, the current asset end of life, APS has a three-year investment strategy to improve the health of Four Corners Units 4 and 5. Due to the decision to exit coal generation at Cholla by no later than the mid-2020s, the recently completed Unit 3 overhaul was reduced in scope to only those projects needed to maintain the unit’s safe, environmentally compliant and reliable operations through that time.

The Lucas testimony contains a long list of ongoing and recently completed projects on the various fossil plants of APS. For example:

  • Four Corners-Common Main Air Compressor Replacements. The purpose of the project is to increase Unit reliability and reduce annual O&M cost. This project will replace the existing 40 year old Allis Chalmers air compressors and ancillary equipment. Was due in-service on March 31 of this year.
  • Navajo coal plant-Navajo Reliability Project. The scope of this program to support APS’s share of Navajo Generating Station’s capital projects. Due in-service on June 30, 2017.
  • Four Corners-Unit 5 High Energy Valve Rebuild. The purpose of the project is to proactively avoid Main Steam Valve and Control Valve weld joint failures in order to eliminate potential safety risk and maintain long-term unit reliability. Was due in-service on April 1, 2016.
  • Saguaro-Combustion Turbine 2 Hot Gas Path/Major Inspection. The purpose of this project is to rebuild the 501AA and ancillary mechanical and electrical equipment to help ensure future 90% reliability going forward to 2025. Was due in-service on May 1, 2016.
  • West Phoenix-Combined Cycle 2 Major Inspection. The purpose of this project is to maintain unit reliability byconducting a major overhaul of the combustion turbine according to OEM recommended accumulated starts. Was due in-service on April 5, 2016.

As for prior major projects:

  • Redhawk Steam Turbine Generator Replacement — In 2015, APS completed a $50 million project to address steam turbine generator abnormalities on both Redhawk combined cycle units. In 2016, Redhawk Power Plant is projected to provide 20% of fossil generation for APS.
  • Douglas reliability — In late 2014, APS invested $5 million for a turbine overhaul and original control system replacement for the 1972-vintage, 16-MW generator located in Douglas, Arizona.
  • Yucca reliability — In 2015, APS completed the $2 million generator rotor rewind of Yucca CT3. The 55-MW combustion turbine is used for Yuma load pocket support during periods of peak demand.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.