January 1, 2001 / Volume 35 , Issue 1 / pp. 17 A – 18 A Copyright © 2001 American Chemical Society
Technology Solutions
Preventing ship pollution before regulation The technology is now at hand to control pollution from large ships, marine engineers now agree. The International Maritime Organization (IMO), the United Nations' agency focusing on maritime safety and ship pollution prevention, has passed regulations that would limit fuel pollution, and engineers from around the world are developing technologies to comply with those regulations, even though they may not come into force. Shipping is a major source of SO x and NOx emissions (Environ. Sci. Technol. 2000, 34 (3), 65A). The IMO regulations, known as Annex VI, would limit these pollutants in the exhaust of most ships weighing over 500 tons and lower the amount of allowable sulfur in marine fuel. The regulations must be ratified by 50% of IMO countries to be binding, but, thus far, only 2 of the organization's 158 member countries have ratified them. The growing popularity of cruises and the rapid international delivery of business goods are driving the market for large marine ship engines, reports Michael L. Parker, head of engineering for Rolls-Royce's Marine Gas Turbines Division. International navies now use 968 engines on 388 ships, and the gas turbine engines on these vessels generally are in service for 30-40 years. Researchers investigating how to ameliorate marine ship pollution presented their work at the International Symposium on Marine Engineering held in Tokyo in October. For example, engineers in Denmark and Japan are devising new lubricant formulations and changing engine operating modes, so they can adapt more easily to the requirements of harbor and opensea operation. The “Intelligent Engine” developed in Denmark meets the suggested IMO regulations by modifying the combustion system, using water-emulsified fuel, and treating exhaust gas by selective catalytic reduction, according to Peter Sunn Pedersen, of the Research and Development Division of MAN B&W Diesel A/S, Denmark. Taken together, these advances can reduce NOx emissions by 80%, he says.
The modified design uses a computer-controlled fuel injection pump to achieve moderate emission reductions in the two-stroke engines that are used in 75% of large ships, Pedersen says. When combined with a fuel nozzle designed to control local temperature and the concentration of oxygen in the fuel spray area, the fuel injection pump has been shown in tests to reduce emissions of NOx by up to 25%, to below the IMO limits, which vary based on the ship's engine sizes. Although their use is not mandatory, these low-NOx nozzles are in all MAN B&W Diesel A/S's new motors. Also, a slide-type fuel valve reduces hydrocarbon and soot emissions by decreasing the amount of fuel that can seep out between fuel injections. However, Pedersen is still struggling with how to make the engine cool and clean exhaust gases to remove particles, heavy metals, unburned fuel, lubrication oil, and sulfuric acid, so recirculating the gases will not damage turbocharger components or air coolers. Exhaust gas recirculation has a large potential to reduce NOx levels, but practical problems such as what to do with the material removed must be resolved before commercial applications are possible, Pedersen tells ES&T . Conventional ship engines do not clean exhaust gases, he adds, noting that “this dirty waste product is sent directly to the atmosphere, if not cleaned out of the exhaust gas before recirculation.” In Japan, five manufacturers are in the final stages of developing what they call a “super marine gas turbine” engine intended for coastal shipping. The researchers hope to simultaneously reduce NOx emissions and increase thermal efficiency. The target 1200 °C inlet temperature for the turbine is 50-100 °C higher than what is used in conventional 2500-kW turbines. To raise the heat level of the new turbine, the Japanese researchers are building a plate recuperator with many layers of small fins a few millimeters high. They are also devising a highefficiency, combined axial and radial compressor. The use of these compressors will increase engine efficiency by working in low- and high-pressure stages, unlike most small gas turbines, which are limited to simple radial compressors. With higher temperatures, the blades need to be cooled better, according to Takao Sugimoto of Kawasaki Heavy Industries, Ltd. Japan does not currently regulate ship exhaust, although the country's land-based emission restrictions are increasingly stringent. But Japanese engine designers are evaluating the same kinds of combustion improvements as Denmark for retarding engine timing, and they are using water-emulsified fuel to counter the poor-quality fuel in marine engines. “Practical applications of [these regulations'] technology for two- and four-cycle engines are almost complete,” reports Hayato Yamashiro, of Japan's Ship Ocean Foundation. But when these clean technologies hit the market, they may be beset by stormy seas. The IMO venture from safety to pollution will raise technical and legal issues, the International Society of Marine Engineers predicts. “It's not going to be easy to police this,” says Stephen G. Dexter, product manager for AVL of Austria, suggesting on-board diagnostics as the ready practical solution. “Unfortunately, we cannot predict when Annex VI will be ratified,” says an IMO spokesperson. The rules would go into effect a year after the treaty's ratification, and the IMO will order an investigation if Annex VI is not ratified by 2003, she said. —SANDRA KATZMAN
