Davis Water Treatment Plant Chemical System Improvements

Davis Water Treatment Plant Chemical System Improvements | San Antonio, TX

The corrosive nature and quality of the process chemicals  used at the City of Austin’s Davis WTP in conjunction with the age of the equipment resulted in deterioration of process and chemical equipment, piping and appurtenances. The existing chlorination system, piping, weigh scales and other modifications were installed in 1993 as part of the Safe Water Drinking Act Improvements project. Subsequent modifications were made to the actuators, ball valves, fittings and chlorine injection vaults in 2007.

There were six Wallace & Tiernan Series V-2000 chlorinators rated at 2,000 pounds per day (PPD). Davis WTP operations staff indicated that the backpressure on the system did not permit operating more than one chlorinator at a time. Operating only one chlorinator limited the chlorine feed rate at the injection vaults to 2,000 PPD. In addition, the City experienced failure of the existing PVC ball valves on the chlorine solution pipelines. The ball valves blistered and leaks created operational and safety concerns. This purpose of this project was to improve the chemical feed systems through modifying the existing systems.

• Replacement of the existing chlorinators with six new V- 2030 Wallace & Tiernan chlorinators with a maximum capacity of 3000 PPD each, and with an appropriately sized rotameter each to feed 2000 PPD of chlorine; Closing of the middle valve on the water supply header so that the 6-inch water supply pipeline would provide water to chlorinators 1, 2, and 3 and the 6-inch water supply pipeline provides water to chlorinators 4, 5, & 6.  This improvement would allow more than one chlorinator to be operated at the same time.
• Replacement of the two vacuum regulator check unit assemblies related to the chlorinator replacement. Each unit assembly would include: two pressure check-pressure relief valves, two vacuum regulators, four line valves, two strainers, and two pressure gauges.
• Replacement of the existing chlorine solution pipelines and ball valves with CPVC diaphragm valves in the Chemical Building and behind the chlorinators in the Chlorine Building.
• Installment of ultrasonic flow meters on the two 6-inch motive water supply pipelines to the chlorine injectors. This improvement would allow Davis WTP staff to monitor the motive water flow rate to the injectors and aid in monitoring the hydraulic operating requirements of the injectors, based on the injector curves, for troubleshooting.
• Installment of one pressure gauge on the motive water pipeline downstream of the backflow preventers (prior to the injectors) and a second pressure gauge immediately downstream of the injectors. The pressure gauges would allow Davis WTP staff to monitor motive water pressure at the injectors and injector backpressure. The water pressure data will permit monitoring the hydraulic operating requirements of the injectors for troubleshooting.