APS Redhawk Power Station

The Client

APS (Arizona Public Service) has been a leading provider of electricity and energy products and services to the Western United States for over a century. With power plants located throughout the Southwestern U.S., APS provides natural-gas, coal and nuclear generated electrical power to the region.

Project Description and Challenges

APS commissioned the Redhawk Power Station in 2002. The plant is comprised of two 2x1 combined cycle natural gas-fired units to produce a total of 1060 MW of electrical power.

Critical to the planning and permitting of this facility was the source and utilization of water and the environmental impact of the station with respect to liquid emissions.

Based upon these issues, Redhawk was designed to use reclaimed municipal effluent from the nearby Palo Verde Nuclear Generating Station for its process water requirements. What is unique about this source of water is that it's supplied by several neighboring City of Phoenix municipal treatment facilities with their associated seasonable variability. The plant would also be designed to utilize well water as a contingency and achieve in either case, high-quality water for continuous re-use throughout the plant.

Zero Liquid Discharge (ZLD) Compliance

The second critical aspect of the plant is the permitted requirement as a Zero Liquid Discharge facility. Under this condition, no aqueous waste can be discharged from site operations into the environment.

To effectively meet this requirement, the wastewater treatment system must be designed to remove water contaminants and recycle high-quality water back into the process. This closed loop integration of the overall water and wastewater cycle must be achieved over the complete range of feed water conditions as well as support the varied operating conditions of the host station.

For successful production of high purity water, maintaining cooling tower conditions for high availability and compliance with the Zero Liquid Discharge mandate, APS needed a total systems approach to the design of the water treatment facility at Redhawk. HPD was chosen as the solutions provider for this project based on their ability to execute the design, construction and project management of the entire water treatment facility on a design-build basis.
HPD ZLD System

Project Design and Technology Solutions

APS chose proven and resilient technologies to successfully achieve the objectives of the Redhawk Power Station wastewater treatment facility. The Zero Liquid Discharge (ZLD) System had to reclaim water resources and reject waste properly as an integrated component of the power station. To accomplish this, the process utilized brine evaporation and crystallization systems, which were the key elements in the overall design.

The evaporator was designed to receive 450 gpm of high salinity blowdown from the cooling towers. The compressor-driven evaporator pre-concentrates the brine and produces high purity distillate for recycling to the cooling tower and service water system.

Concentrate from the evaporator is advanced to the crystallizer where the salts that form the impurities are crystallized and sent to a centrifuge for dewatering. The crystallizer is also compressor-driven and produces distillate that is combined with that of the evaporator for recycle.

The Results

HPD was the sole point of responsibility in providing a design-build solution for the complete wastewater portion of the plant which included:

• All major equipment
• Mechanical erection
• Buildings
• Utility piping and valves
• Electrical hardware and cabling
• Overall control system
• Insulation and painting
• Structural support and access steel
• Training of staff, commissioning
  and start-up support

The ZLD system was efficiently completed and commissioned by HPD in the promised time frame.

Since the startup of the integrated ZLD system, the Redhawk Power Station has successfully accomplished the goal of effectively recycling the waste created by cooling tower blowdown and producing highquality water while adhering to the Zero Liquid Discharge mandate.