Soot Deposits and Fires in Exhaust Gas Boiler - Martin's Marine ...

Soot Deposits and Fires in Exhaust Gas BoilerIntroductionThe demand for the highest possibleoverall fuel efficiency is reflected in developmentsover the last two to threedecades in the propulsion market foroceangoing ships. Today, this market isdominated by highly efficient two-strokelow speed diesel engines which run onlow quality fuels and utilise (recover) theexhaust gas heat by means of an exhaustgas boiler/economiser.In the same period, reduced specificfuel oil consumption, i.e. increasedthermal efficiency of the diesel engine,has resulted in lower exhaust gas temperatures.Based on ISO ambient referenceconditions (25°C air and 25°Ccooling water), and with the presentnominal ratings of the MC/MC-C andME/ME-C engines, the exhaust gastemperature after the turbocharger isabout 240-270°C, but may be lower forderated engines.The name “exhaust gas economiser” isoften used for an exhaust gas boiler whichis not able to operate separately, i.e.without its own steam drum. In thispaper, the name “exhaust gas boiler”will be used in general, also in caseswhere “exhaust gas economiser”, inprinciple, should have been used.Rise in soot fire incidentsAs a consequence of the lower exhaustgas temperatures and the remainingsteam consumption requirements, theexhaust gas boiler has been designedto become more and more efficient.This involves the use of a large heattransfer surface and thus a boiler designwith a low internal gas velocity as wellas tubes with “extended” surfaces.Furthermore, the quality of the fuels hasdecreased significantly during the sameperiod. Whereas the average fuel qualitymay not have deteriorated as muchNumber of soot fire/overheating incidents per year7060504030201001982 84 86 88 90 92 94 96 98 00 2002 2004YearFig. 1: Number of soot-fire-damaged exhaust gas boilers in DnV- classed vesselsThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net3