The Reduction of NOx Emissions from Marine Power Plants

The EPA has proposed a 9.2 g/kWh NOx limit for maritime diesel engines. Gas turbines, which are always cleaner burning, have escaped maritime NOx mandates at this time. However, in Europe, increasingly stricter exhaust emission limits for shipboard turbines near high-pollution ports undergo periodic review. Anticipating these proposed mandates, the Navy has been directed by OPNAVINST 5090 1A to comply therewith. EPA studies show that two-cycle marine diesel configurations combining exhaust-gas recirculation, retardation of the timing of injection, intercooling, and an oxidation catalyst for combustion of particulates lower NOx-emission levels to 8.5 g/kWh. Water injection appears ineffective below water-fuel ratios of 0.4, and is not cost effective for achieving the required NOx emission objective, at least in two-cycle engines. The proposed diesel configuration eliminates any negative ship impact on the engine-room spaces from water-management systems and water logistics. Contrastingly, water injection into the combustor of gas turbines is a state-of-the-art development, which may be a low-risk, low-cost option for reduction of gas-turbine emissions. It is anticipated that the required pure water would be obtained from water purification plants and stored supplies. For presentation at the Air and Waste Management Association's 90th Annual Meeting and Exhibition, June 8-13, 1997, Ontario, Canada, Paper 97-A1399.