EGR economiser enhances waste heat recovery
Alfa Laval has introduced a pressurised exhaust gas recirculation (EGR) economiser, allowing companies complying with Tier III NOx limits through EGR to make fuel efficiency savings by improving waste heat recovery.
The high-pressure, in-line unit can be installed on MAN Diesel & Turbo engines before the jet sprays that cool exhaust gas before EGR. This means that the economizer can make waste heat recovery economical at lower engine loads – as low as 30% according to Alfa Laval – as well as offering an increase in steam quality and temperature, improving the amount of power that can be recovered.
John Pedersen, business manager boilers, combustion and heaters at Alfa Laval said: “By moving the break point for waste heat recovery from a medium engine load down to a low load, the Aalborg EGR-HPE enables even slower steaming,” says Pedersen. “That means fuel savings that quickly pay back the economizer, offset the EGR investment and lower CO2 emissions on top of the NOx reduction.”
By operating at even low engine loads, the Aalborg EGR-HPE creates the possibility of even slower steaming, said Pedersen. “Vessels can steam even slower, with huge fuel savings as a result. A vessel performing EGR and using the Aalborg EGR-HPE will be not only compliant with Tier III, but also substantially more fuel efficient.”
In a project supported by the Danish Energy-Technological Development and Demonstration Programme (EUDP) and developed in cooperation with Aalborg University, the EGR boiler has been rigorously tested aboard the Maersk Cardiff.
Ole Christensen, senior machinery specialist at AP Moller-Maersk, said: “As a front-runner in the pursuit of green technologies, we were keen to see what the Aalborg EGR-HPE could do. But while we were enthusiastic about the boiler’s potential, we were also somewhat uncertain as how it would handle the physical realities of EGR. The temperatures are twice as high as those of traditional waste heat recovery, and the gas pressures are far greater.”
The boiler was brought online with Maersk Cardiff’s two-stroke MAN B&W 6S80ME-C9 engine in November 2014. “Not only did the boiler survive,” says Christensen, “the results we have seen during testing are very promising.”
Alfa Laval believes that the EGR boiler has changed the balance of the NOx compliance question. “Suddenly EGR is not only a means of Tier III compliance, but also a means of radically improving the vessel’s energy efficiency. And that makes it a very different sort of investment,” concluded Pedersen.
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