The Challenges of Designing and Constructing the World's Largest Ozone Facility

This paper chronicles the design, construction, and startup of the ozone facilities at Dallas Water Utilities' East Side Water Treatment Plant, which is the largest ozone generating facility in the world dedicated to the treatment of drinking water. The numbers associated with the plant are impressive: 6.5 mg/L ozone maximum dosage, 36,000 lbs per day of ozone generating capacity, nine ozone generators, almost 5.5 million gallons per day of cooling water used, four 2500 KVA and two 3000 KVA electrical feeders, two 30 ton per day vacuum swing adsorption oxygen generation units, and 60,000 gallons of liquid oxygen storage.The planning design, construction, and startup of this facility required a five-year project involving great effort to anticipate and cope with the issues unique to a facility of this size. The length of the construction and startup period itself was a major issue requiring addressing issues such as:Construction staging to maintain plant operations during construction and startup.Simultaneous startup of the ozone system with operation of East Side's existing disinfection scheme.Coordinating with the electrical utility during the initial days of deregulation.Adjusting treatment regimes resulting from various raw water blends because of construction shutdowns.The length of project construction and startup also presented several unanticipated changes to working conditions and schedule challenges, including mergers and acquisitions of two primary suppliers of equipment, as well as the aforementioned electrical utility deregulation. A prime example of these changes was Dallas' sudden need to replace the ozone generators at their Elm Fork WTP. To expedite this replacement, four of the ozone generators originally meant for installation at East Side were installed at Elm Fork. Thus, instead of nine generators to start up, the Ozone System Supplier (OSS) needed to coordinate startup for thirteen ozone generators at one time, a 45% increase in scope, at two sites separated by 30 miles. Adding to the complications was the OSS's relocation from New Jersey to North Carolina, resulting in loss of key staff and inconsistency in product manufacturing.Other areas examined in this paper are applying lessons learned from previous ozone designs including the need for adequate drainage for the contact basins and the need for OSS responsibility for the ozone control system, reliability features to ensure minimal impact on plant operations from feed gas supply to the electrical system such as paralleling of multiple transformers, switchgear, and ozone generator power supplies, project delivery using sole source supply of the ozone equipment and a two step procurement for the Owner; and designing the facility to showcase the City's leading edge in water treatment.The performance of the overall system exceeded expectations. Measured performance translated to 4.5% lower annual operational costs than bid. The VSA system performed especially well at 14% better efficiency than guaranteed.Overall, the projects highlighted these lessons learned:VSA vendors are not familiar with water treatment. These vendors normally operate in an industrial environment, as opposed to the municipal market. Such procedures as shop drawing submittals were not familiar ground to the vendor.Consider system wide impacts of shutdowns. Make sure the entire water treatment and distribution system is ready for restrictions in production at the plant under construction.Ozone generators can be installed quickly. This takes cooperation among all parties from OSS, Engineer, Constructor, and Owner.More confidence gained treating multiple water sources and blends. DWU staff has gained beneficial experience working with many blends of source waters needed during the construction.