Case Study - Power Plant Using Sea Water

Challenge:

The Northport Fossil Power Station on Long Island Sound treated one quadrant of a condenser with Mexel. The main problem stemmed from deposits of mud in the condenser tubes, which required hydro-blasting weekly to maintain efficiency. A secondary problem was mussel accumulations in the cellblocks (chambers that distribute the water to the four quadrants of each unit), the pipes to the circulating pumps, and the forebay. A crew of 17 persons was required to hydro-blast the condenser tubes and the four quadrants needed nightly cleaning. This expensive and timely procedure led Northport to test Mexel due to its reputation for fast and safe results.

Treatment:

The Northport Power Station has four 350MW units fired by oil or gas and cooling water is drawn directly from Long Island Sound. While the application’s focus was to address sedimentation, the plant experienced other fouling problems including corrosion, microfouling, and macrofouling. Northport had been using chlorine for treatment but growing environmental and economic pressures caused them to seek an alternative. During preliminary trials it was concluded that Mexel 432/0 showed promise in reducing the rate of fouling, so additional trials were performed treating the entire water flow of a Unit. Initial dosage was 4.5 ppm for 30 minutes per day. This was gradually reduced over six months to 3 ppm for 20 minutes per day.

Results:

The treatment altered the deposits’ nature and made them less adherent to the tubes. In addition, analysis determined that the treated unit’s deposits contained almost no organic matter demonstrating that Mexel had eliminated the biofilm from system surfaces. At the end of the season when the Unit was cleaned, there were no live mussels or hydroids in the forebay, cellblocks, or piping. In contrast, the untreated units accumulated normal-to-heavy amounts of mussels and hydroids. With regard to corrosion from the saltwater, Mexel post-treatment had no evidence of corrosion in the AL-6X tubed condenser. It was evident that treatment with Mexel had a positive effect on overall fouling. Furthermore, there was an increase in condenser efficiency of ~0.5% compared to the untreated units. This finding was also consistent with anecdotal data from European power plants.