Northern Indiana Public Service Co. (NIPSCO)
1790 MW Schahfer Generating Station
Wheatfield, Indiana, USA
Senior Chemist, NIPSCO
Four (4) MIOX RIO M5 MOS generators
Units 14 & 15 installed 2010
Units 16 & 17*
Photosynthesis blocker (algaecide)
National Pollutant Discharge Elimination Permit (NPDES) restrictions limited cooling tower disinfection dosage to only two hours a day for each tower. During the warm weather summer months, the 2 hour/day restriction did not allow enough dosage to control microbiological growth in the cooling water. NIPSCO’s Chemical and Environmental Compliance Department was using a chemical regimen of sodium hypochlorite, sodium bromide, and a photosynthesis blocker (or algaecide) to treat water supplied to four cooling towers at the 1780 MW coal-fired power plant. The cooling water was allowed to reach 2-3 cycles of concentration, with the cooling tower blowdown being discharged into a 200-acre settling pond before discharged into the Kankakee River.
Due to open-air hotdecks exposed to the sun on two of the towers, algae control was an ongoing challenge. It was not uncommon to see spikes in Legionella surpass 200 colony forming units per milliliter (CFU/ml); above the 100 CFU/ml limitation triggering workers to wear respiratory equipment for health safety. At the time, NIPSCO had adopted the policy of posting Legionella level warning signs at all of the cooling towers.
When the utility first began considering a new disinfection regimen, sodium hypochlorite prices had nearly doubled to about $1.60-1.65 a gallon, so saving money was another primary driver to choosing a new water treatment program. Reducing the number of chemicals used for bio-control from three to down to one made the proposal more attractive to officials at NIPSCO, who have a forward-thinking reputation of working closely with environmental regulators in order to stay ahead of the regulatory curve.
STUDY DESIGN & RESULTS
In 2010 NIPSCO installed two MIOX RIO Mixed Oxidant Solution (MOS) systems on two of the four cooling towers at R.M. Schahfer Generating Station. After switching to MIOX, the two towers experienced minimized algae growth, better biocontrol and lower Legionella counts, cleaner condenser tube sheet and reduced differential pressure, and zero negative impact on corrosion rates.
The annual savings with MIOX amounts to approximately $158,500/year per tower. Additional savings have been realized by eliminating 2 hrs/week man-hours for scheduling, an 80% reduction in trucking delivery/unloading, elimination of handling chemical containers, and elimination of hazards associated with the previous treatment chemical regimen.
NIPSCO Schahfer Generating Station plans to convert all 4 of their cooling towers to MIOX for a total treatment capacity over 650,000 gpm recirculated water. The benefits from MIOX on-site chemical generation include improved worker safety in addition to savings over $600,000, clean condenser tube sheets, zero presence of algae or biofilm, and better corrosion rates.