The Coolidge Generating Station, a 575MW gas-fired simple-cycle peaking power plant located in Pinal County, Arizona, US, is planned to be expanded with 16 additional fast-start gas-fired units of 820MW capacity.

Salt River Project (SRP), Arizona’s largest community-based public utility delivering water and power to the Phoenix metropolitan area, owns and operates the facility. It acquired the power station from TransCanada (now TC Energy) for $448m in May 2019.

The SRP Board, in September 2021, approved the Coolidge expansion project to add new gas-fired units to the existing facility to meet the increasing peak electricity demand and support the integration of more renewable energy as part of the utility’s commitment to deliver half of its retail electricity from zero-carbon resources by 2025.

The company applied for a certificate of environmental compatibility (CEC) for the proposed expansion from the Arizona Corporation Commission (ACC) in December 2021. Construction works on the $830m expansion project are expected to start in the second half of 2022, with the first eight units scheduled to come online by 2024, followed by the remaining eight by 2025.

The new gas-fired units at the Coolidge power station will allow SRP to add more than 2GW of solar energy by 2025, while ensuring grid stability and reliable power supply during peak electricity demand.

Location and site details

The existing Coolidge gas-fired power plant is located on a 100-acre site near the intersection of Randolph Road and South Arizona Boulevard in Coolidge, Pinal County, Arizona, 90km south-east of Phoenix.

The new plant will be built on another 100-acre site lying immediately south of the existing facility. The power generation facilities will occupy 30 acres, whereas the new evaporation ponds and a new switchyard for the plant will occupy 16 acres and 46 acres, respectively.

Coolidge expansion plant make-up

The new 820MW simple-cycle gas-fired facility at the Coolidge generating station will be equipped with   16 LM6000PC aero-derivative gas turbines, each capable of ramping up to full production within ten minutes.

Each combustion turbine will utilise GE’s SPRayINTercooling (SPRINT) technology to increase the air mass flow by cooling the compression air with the injection of atomised water through spray nozzles. The SPRINT design will boost the power output of each LM6000PC gas turbine up to 51.25MW.

The new gas-fired units will also be equipped with water injection to the combustors, along with selective catalytic reduction (SCR) systems to control nitrogen oxide (NOx) emissions.

Each of the 16 simple-cycle units will have an exhaust stack measuring 85ft high and up to 12ft in diameter.

Power evacuation

The electricity generated by the Coolidge expansion project will be evacuated through four gen-tie lines connecting the new 500kV switchyard, which will interconnect the plant to the existing Pinal Central to Browning 500kV transmission line running along the western side of the site through two new 380m-long power lines.

Gas supply

The Coolidge expansion project is estimated to require up to 7,162 million British thermal units (Mbtu) of gas an hour to operate at full load. Natural gas will be supplied by the existing El Paso Natural Gas and TransWestern pipeline systems.

Infrastructure facilities

While the new plant will utilise the existing gas pipeline, transmission network and water wells at the site, it will require a new gas metering station and a new 500kV electrical switchyard. The project will also involve new ponds for wastewater discharge and stormwater management.

The existing Coolidge power station details

The existing 575MW gas-fired simple-cycle power plant was built by TransCanada between 2009 and 2011, with an estimated investment of $500m. It is equipped with 12 GE LM6000PC gas turbines, seven gas compressors and six generator step-up transformers.

Coolidge generating station can produce enough electricity to power 575,000 homes in the Phoenix metropolitan area during peak demand.

Contractors involved

GE will supply the LM6000PC gas turbines and generators for the Coolidge expansion project. It also supplied the turbines and generators for the existing plant, which was built under an engineering, procurement and construction (EPC) contract awarded to a joint-venture of the US-based general industrial construction company TIC, and engineering and design firm Parsons Brinckerhoff (now WSP).