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Exhaust-gas recirculation cooler reduces pollutant emissions from 2- and 4-stroke maritime diesel engines

For maritime applications GEA offers an efficient solution for lowering nitric and sulfur oxide emissions (NOx and SOx)

The challenge posed by sustainability:

On large freight container ships, extensive use is made of low-speed 2-stroke diesel engines. They burn heavy oil and emit pollutants in the form of nitric and sulfur oxides (NOx and SOx). The International Maritime Organization (IMO) has issued regulations for maritime applications that stipulate the progressive reduction of such pollutants by 80 %, in stages, until 2016. In the first stage of these reductions, valid since July of 2010, IMO regulations entail stricter specifications limiting pollutant emission of NOx and SOx in heavily frequented shipping lanes under IMO control.

The initial situation:

Pressure and temperature demands placed on large diesel engines represent a challenge for the structural design of exhaust-emission control. Addition of an inert gas (such as exhaust gas) reduces the production of NOx, since the rapid oxidation of fuel molecules is inhibited by exhaust-gas molecules. Cooling the recirculated gas further intensifies the effect.
In large diesel engines, exhaust gases with pressures that can often reach more than 7 bar must be reliably cooled during such recirculation. An exhaust-gas recirculation cooler must withstand without difficulty the following conditions: a great temperature gradient of more than 600 °C, system-related pressure fluctuations, vibrations transmitted from the engine to the cooler, as well as corrosion from the effects of condensation in the exhaust gas. In addition, the cooler must operate at a high level of efficiency.

The solution:

In diesel engine operation, exhaust-gas recirculation is one of the most essential meas-ures for reduction of NO emissions. The lower the temperature of combustion, the smaller the share of NOx. A compact heat exchanger made of temperature- and corrosion-resistant stainless steel lowers exhaust-gas temperatures from as high as 700 °C to 50 °C before the exhaust gases are mixed with the air of combustion. Its finned-tube system, embedded in the water-passage structure, features newly developed fin geometry – which, in addition, minimizes the collection of dirt and debris. The surface structure of the stainless steel fins creates turbulence in the gas flow, which results in heat transfer over the entire surface.
The mode of operation of the GEA high-pressure exhaust-gas recirculation cooler is not only efficient, but just as impressively simple: a fraction of the exhaust gas is extracted from the cycle upstream of the turbocharger. The result is an increase in the charge air mass in the combustion chamber. Increased mass requires at the same time a greater amount of energy for its heating. This consequently lowers the temperature of combustion, which is critical for creation of NOx content.
Designed as a modular system, the GEA exhaust-gas recirculation cooler is available in versions for high and for low temperatures. In the low-temperature models, the condensation of sulfurous acid and water in the process is unavoidable. Moist carbon-particu¬late matter (soot) must be removed from the cooler. A condensate separator protects the downstream engine components from corrosion and reduces the particulate count of the exhaust gas recirculated to the air of combustion.
In its latest generation of exhaust-gas recirculation coolers, GEA has extended its technology already in use for heavy-oil systems to new application with low-speed 2-stroke diesel engines. A scrubber has been installed upstream of the cooler to desulphurize the exhaust gas. This injection of water significantly lowers the exhaust-gas temperature (to < 150 °C) before its entry into the cooler enclosure. During the cooling process, however, only part of the water evaporates. The remaining part remains in the liquid state and impacts with great exhaust-gas velocity onto the finned-tube block. The newly developed compact stainless steel finned-tube system is also sufficiently resistant to this impact – in addition to withstanding corrosion and erosion of the cooling fins.

The sustainable strengths:

This exhaust-gas recirculation cooler by GEA satisfies international regulations by the IMO for progressive reduction of emissions in maritime engines until 2016. An additional gas scrubber likewise enables 2-stoke diesel engines to effectively meet strict future SOx limits. In its low-temperature version, the exhaust-gas recirculation cooler moreover employs a downstream condensate separator that reduces the particulate count of the exhaust gas recirculated to the air of combustion.

The developers:

GEA Heat Exchangers provides one of the most extensive product portfolios on the heat exchange market worldwide for a wide range of applications. With GEA plate heat exchangers, shell and tube heat exchangers, air-cooled heat exchangers, air filter systems, synthetic fillings for numerous areas of application, wet cooling towers and dry cooling systems as well as air-conditioning technology GEA Heat Exchangers gives comprehensive coverage of the spectrum.

Thumbnail profile of the company:

Name: GEA Maschinenkühltechnik, subsidiary of GEA Heat Exchangers
Home office: Herne (Germany)
Solutions provided: indoor climate-control systems, refrigeration components, and solutions for commerce and industry
International activities: global
URL: www.gea.com, www.gea-heatexchangers.com