Reduction of NOx Emissions from Marine Power Plants

WP-42

Objective

The Navy has been directed to comply with anticipated state-imposed limits on emissions from a naval inventory of about 700 gas turbines and 2,700 diesel engines on ships operating within coastal waters. One low-risk, low-cost, state-of-the-art technology achieves low nitrogen oxide (NOx) emission from gas turbines by injecting water into the gas-turbine combustor. For diesel engines, the following appear necessary to achieve anticipated state-imposed emission standards: simultaneous use of injection timing retardation, exhaust-gas recirculation, and water injection. The impact of these emission-reducing technologies on complicated ship engines, including their ability to operate without unscheduled loss of power in a tactical situation, may be assessed only through realistic shipboard evaluation.

It was the objective of this project to establish within the Navy community, the credibility of these technologies as an acceptable method of reducing NOx emissions from Navy engines in a naval at-sea operating scenario.

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Technical Approach

A water-injection controller (WIC), designed and fabricated for injection of water into the combustor of an LM2500 gas turbine, was tested at the LM2500 test and land-based simulation facility at the Naval Ship Systems Engineering Station in Philadelphia, PA. Upon successful resolution of these and additional tests, the WIC system was installed on a guided missile frigate (FFG)-Class ship at the Norfolk, VA, shipyard. After ship integration, the WIC system and its automated emissions monitor underwent at-sea testing to assess the overall impact of the WIC system on the gas-turbine plant and ambient ship systems. In addition, a DDC 4-71 diesel engine was modified to retard the timing of fuel injection, to introduce exhaust gas recirculation, and to inject water in the form of an emulsified, fuel-water mixture. This manually-controlled system was tested at research facilities of the North Carolina State University prior to testing in a Yard Patrol craft at the Naval Academy in Anapolis, MD. Studies assessed the risks of erosion/corrosion in the fuel injectors, flame quenching, and/or cylinder misfiring. All ship-system impacts were accessed at-sea in the Yard Patrol.

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Results

Water-injection into the combustor of the LM2500 gas turbine engine reduced NOx emissions to the planned objective level of 42 ppm during steady-state engine operations at all levels of throttle output power. Tests for diesel engines showed that two-stroke, turbocharged marine diesel configurations combining exhaust-gas recirculation, retardation of injection timing, intercooling, and an oxidation catalyst for the combustion of volatile organic compounds (VOC) and particulates lowers NOx-emission levels to below Environmental Protection Agency (EPA) mandates. In addition, the technology for diesel engines reduced carbon monoxide and particulate matter (PM) emissions below mandated levels without loss of rated power. PM measurements averaged 0.25 g/kWh (less than half the proposed EPA standard of 0.54 g/kWh), with NOx levels below 9.0 g/kWh. This project was completed in FY 1998.

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Benefits

This technology can enable the Navy to operate as an ecologically-benign neighbor in domestic and global maritime environments. It also permits the Navy to avoid litigation and to operate in zones subject to strict limitations of NOx emissions, such as the California littoral region and congested European ports.

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