KEYWORDS: Ozone, Cooling Water, Stand-Alone Treatment, and Large Capacity Cooling Tower
SUMMARY: The operational experience and performance of the successful use of ozone as a stand-alone cooling water treatment method are discussed. Several guidelines for design parameters and operational controls are presented. From a wide field of application experience, the author offers several lessons-learned relating to generator types, capacity, dosage, corrosion, and microbiological control. From the evolution of early struggles and disenchantment, specific information on what should be done is provided as well as what must be avoided. Unlike conventional chemical programs, ozone treatment based upon applied rates and dosages remain controversial, but case studies continue to explore and validate this emerging technology.
Introduction Prior to 1990, cooling towers at Kennedy Space Center (KSC) had been maintained using conventional chemical treatment consisting of a scale and corrosion inhibitor (two phase), and two alternating biocides to control bacteriological growth. Tower chemistry was controlled through discharge by blowdown to area surface waters. Stricter environmental regulations began to impact cooling tower operations. State regulatory code establishes the criteria for surface water quality, and therefore dictates the standards by which any waters discharged to surface water must comply. Due to chemical additives and operating water chemistry, the blowdown discharge could not meet the environmental regulatory criteria.
In 1990, NASA and the Base Operations Contractor, formerly EG&G Florida Inc., began to explore numerous avenues that would yield cooling tower environmental compliance. One of these considerations had been studied at KSC since as early as 1984, and at the NASA Jet Propulsion Laboratory prior to that. This technology was the application of ozone to cooling water treatment, which will be expanded upon from both a historical and technical viewpoint in this paper.
Background In 1992, Kennedy Space Center (KSC) modified six comfort-cooling towers from conventional chemical feed water treatment systems to ozone treatment systems. All systems were intended to operate at zero blowdown thereby significantly increasing the cycles of concentration of these towers. The feasibility of this practice was re-assessed as detrimental to operation and steps were taken to initiate limited blowdown to the sanitary sewer. Even the short-term period of zero blowdown culminated in severe scaling of condenser tubes, tube-heets, and housings. With environmental compliance being met and gaining concurrence from the appropriate organizations a realistic program approach began to emerge.
In reality, the ozone treatment program remained problematic due to poor equipment reliability and the undersizing of ozone generator capacity. These initial experiences, coupled with the changing climate of facility expansion/construction and chiller plant centralization, formed the evolutionary pathway for KSC in the application of ozone water treatment. Despite the treatment difficulties, water treatment personnel at KSC and supporting industrial resources (system and equipment supplier), remained confident in the technology application and the positive attributes that ozone demonstrated. With pensive feeling mounting within NASA, two independent A&E studies were conducted to investigate the most feasible treatment method for the cooling towers.