Study of the Corrosive Effect on Aluminium and CP Titanium of Mixtures of Ammonia and Seawater That May Be Encountered in OTEC Heat Exchangers. Final Report

摘要

The design currently most favored for an Offshore Thermal Energy Conversion power plant would use an ammonia cycle energy system as powered by the small thermal differences existing between warm surface and deep ocean waters. A possibility therefore exists for ammonia or seawater leakage within the evaporator or condenser. The objective of this work is to assess the extent to which small concentrations of seawater would affect corrosion of aluminum and CP titanium by ammonia and the extent to which small concentrations of ammonia might affect the same alloys by seawater. Testing was conducted using coupons of aluminum alloys 3003-H14, 5052-H32, and 5086-H32, CP titanium, and aluminum alloy 5052-H32 as pretreated for 8 hours in boiling deionized water. Four pilot units were constructed to investigate different possible OTEC heat exchanger environments. Experimentation on ammonia leakage into seawater employed two units containing recirculating (approx. 6 gal.), temperature-controlled (5 exp 0 C or 30 exp 0 C) seawater at 5.6 and 2.5 fps with continuous seawater refreshment (2.0-0.5 gpm). Ammonia leakage was simulated in these two units by injection of ammonia hydroxide into the refreshment seawater. A third unit with the same seawater supply utilized seawater on a once-through, 5 fps, ambient temperature basis to simulate optimum, no-leak OTEC seawater service. Performance of the subject alloys in ammonia and ammonia containing seawater utilized recirculating ammonia with temperature controlled to 5 exp 0 C. The experimental procedure and test results are discussed. (ERA citation 04:048324)