Engine designers and engine builders are striving to establish reliable and economical measures to have their engines meet the IMO NO(x) regulation Tier III, which is coming into force in 2016, requiring a drastic level of NO(x) reduction from ships and needing in fact a different technology from those for previous Tiers I or II. In order to ensure to provide ships with main engines complying with contemporary regulations even in/after the year 2016, Hitachi Zosen Corporation, who is not only an engine builder but also a catalyst manufacturer as well as an SCR manufacturer well-known in land applications, have developed a marine SCR system for large two-stroke diesel engines in collaboration with MAN Diesel & Turbo, an engine designer leading the market. The concepts of the system are (1) urea-SCR, (2) SCR located upstream turbine and (3) SCR operated on ordinary HFO. This paper presents mechanism and features of the system and test results from the testbed and the sea trial. Main themes are how such an SCR system works on a large two-stroke diesel engine run on HFO, of which exhaust gas generally is low temperature and contains a considerable amount of sulfur oxides, and how such an engine is controlled even in low load and/or transient conditions. The system ensures always high enough exhaust gas temperature to do SCR of high sulfur exhaust gas without utilizing any extra heating device, which consumes extra fuel, by making use of so-called 'cylinder bypass'. In low load conditions, a part of the scavenging air bypasses the cylinders and SCR line through the cylinder bypass line, and hence hot exhaust gas to the SCR. In transient conditions, the SCR bypass is controlled so as to charge the cylinders with an appropriate amount of scavenging air as necessary. This makes engine's quick acceleration possible. All these functions are automatically controlled. A number of various tests were performed not only in their SCR research laboratory but also with an actual product engine equipped with the SCR system on a testbed at Hitachi Zosen's engine factory in order to confirm that their technology was applicable also to marine-use and optimize it for marine application. After the successful tests on testbed, both the engine and the SCR system were transferred to install into a new-built ship, on board which the SCR system were intended to be field-tested in service, with the geometrically same SCR arrangement as well as the same control system as those for the testbed. The sea trial was performed to confirm that the engine with SCR functioned correctly and safely even in an actual ship system, and to measure and record its initial conditions before her delivery. During the sea trial, transient responses were tested in various cases, e.g. accelerations, decelerations, maneuverings and ahead/astern, and confirmed them as expected beforehand. Similar to the testbed results, 80% of NO(x) reduction ratio was achieved, and IMO's E3-cycle value of NO(x) emission was confirmed to be less than 3.4 g/kWh, which is the limit for low speed engines, also in the sea trial.
Development of Marine SCR System for Large Two-stroke Diesel Engines Complying with IMO NO(x) Tier III
2013
16 Seiten, 43 Bilder
Conference paper
English
Development of marine SCR system for large two-stroke diesel engines complying with IMO NOx Tier III
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