Mitsubishi Heavy Industries Technical Review Vol. 47 No. 3 (September 2010)
48Development of Selective Catalytic Reduction forLow-speed Marine Diesel Engines- Super-clean Marine Diesel R&D Project for the IMO NOx Tier III Regulations KATSUYA FUJITA*1

KATSUMI NOCHI*2

YUJI WAKATSUKI*3

AKIHIRO MIYANAGI*4

NAOHIRO HIRAOKA*4|1. Introduction
In response to strengthened International Maritime Organization (IMO) regulations, the“Super-clean Marine Diesel” research and development project was initiated and overseen by Japan
Marine Equipment Association and promoted by the Nippon Foundation, led by the Ministry ofLand, Infrastructure, Transportation and Tourism. Mitsubishi Heavy Industries, Ltd. (MHI) andAkasaka Diesels Ltd. are participants in this project, which aims to develop selective catalytic
reduction (SCR) for slow-speed diesel engines. We will complete a verification test for the firststep of this project using a land test rig this September. This article provides an outline of ouractivities to date.

|2. IMO Exhaust Gas Regulations
Air pollutant reductions from international ships and vessels have been actively discussed on
the IMO stage since Norway first proposed discussions at the IMO 26th Marine Environment
Protection Committee (MEPC26) meeting. A new protocol was adopted at the MARPOL73/78
session of the Conference of Parties in 1997, and its Appendix VI has been in effect since May
2005.

Figure 1*1

Exhaust gas regulations of the IMOManager, Industrial Energy Power Systems Department, Power Systems Headquarters*2Hiroshima Research and Development Center, Technical Headquarters*3

Manager, Marine Diesel Engine Business Unit, Kobe Shipyard & Machinery Works*4

Marine Diesel Engine Business Unit, Kobe Shipyard & Machinery Works

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 3 (September 2010)49

As shown in Figure 1, the Appendix VI Revision, which requires more stringent regulations,
was approved by the MEPC57 in 2008 and is effective from July 2010. The emission regulations
include nitrogen oxide (NOx), sulfur oxide (SOx) and particulate matter (PM) exhausted from maindiesel engines. SOx and PM will be implemented by sulfur content regulation for fuel.
NOx is mainly generated by combustion in the engine. It can be reduced to some extent byimproving the combustion itself. However, in the IMO discussions, the introduction of an SCR
system, which is already utilized in land facilities, has been considered, rather than consideration ofsmaller step-by-step improvements. In the Tier III NOx regulations of the Emission Control Area(ECA), which are expected to be in effect in 2016, NOx emission must be drastically reduced by
80% relative to the current Tier I regulations.

|3. Outline of the Research and Development of Super-clean Marine
Diesel Engines
In Europe, many SCR have been installed in midium-speed diesel engine ships due topolitical incentives in Sweden and other countries. Investigations have also been performed toinstall SCR systems in low-speed diesel engine ships.
Figure 2 shows an exhaust gas cleaning system using SCR. Figure 3 shows the same type ofhoneycomb catalyst that was used in the present tests.
The most critical problem when installing an SCR system in a ship is the deterioration of thecatalyst caused by the sulfur content in the fuel. The reducing agent ammonia reacts with the sulfur
content in fuel at ambient temperatures below 300C to produce ammonium hydrogen sulfate(NH4HSO4); this compound deposits on the catalyst surface and inhibits its performance. InEurope, the majority of engines that have adopted SCR systems have exhaust temperatures of300C or more and therefore do not suffer from this problem. However, low-speed diesel engines
operate with exhaust temperatures below 300C, and newer low-speed engines with remarkable
performance levels have exhaust temperatures below 250C. The lower exhaust temperature
decreases the amount of heat rejection, increasing the engine efficiency and decreasing fuelconsumption and carbon dioxide (CO2) emissions. Consequently, the purpose of this project is todevelop an SCR system compliant with the Tier III NOx regulations without impairing the highperformance obtained with low exhaust temperatures.
Land plant SCR systems are used in favorable environments with low-sulfur-content fuel andhigh-temperature conditions to attain high SCR performance with no catalyst deterioration. In somecases, SCR systems have been installed in low-speed diesel engine ships, but they are locatedupstream of the turbocharger, where the exhaust temperature is high. In these cases, a bypass isimplemented so that the SCR is only used under high-load stable voyage conditions to avoid thepossibility of significant ship operating problems at low speeds or unstable loads. However, NOxemissions also need to be reduced for coastal voyages and for midium- to low-speed voyages inseas that are close to land. An SCR system with stable NOx reduction performance at low
temperatures downstream of the turbocharger is required.

Courtesy of Sakai Chemical Industry Co., Ltd.

Figure 2

Exhaust gas purification with an SCR system

Figure 3

SCR honeycomb catalyst

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 3 (September 2010)50|4. Characteristics of an SCR with Low-temperature Exhaust Gas
and Aqueous ammonia Injection for Low-speed Engines
One of the largest domestic test rigs for low-speed diesel engine Mitsubishi–Akasaka
3UEC37LA (1 103 kW, 188 rpm), owned by Tokyo University of Marine Science and Technology,
was selected as our test rig. Figures 4 and 5 show the denitration tests with full-flow exhaust gas at
100% load that were mainly conducted in fiscal year 2008. The exhaust temperature was adjusted
by diluting the air, and NOx was measured at the SCR inlet and outlet to monitor the NOx removal
efficiency. The fuel used for the test was marine diesel oil (MDO) fuel, which has sulfur content of0.7%, reasonably obtainable and close to the planned 0.5%. The reducing agent was 25% aqueous
ammonia, for which ample low-temperature denitration results are available. Aqueous ammonia
provides a simple chemical reaction. The engine was operated for approximately 100 hours foreach case, noting that the engine could only be operated during the daytime due to facility
restrictions.

Figure 4

Test rig used in fiscal year 2008

Figure 5 Test rig photo from fiscalyear 2008In fiscal year 2009, the test rig was converted so that it had four small-flow branch lines ofdiesel engine exhaust gas, as shown in Figures 6 and 7, allowing four test results at a time andincreasing the number of test cases. The same reducing agent was used, but the MDO fuel had asulfur content of 0.07%. The exhaust gas conducted into the SCR system could be cooled withdiluted air and heated with an electric heater, and the performance degradation caused by theexhaust gas temperature and catalyst deterioration was examined. Regeneration of the deterioratedcatalyst was attempted by making use of elevated exhaust gas temperatures using the electricheater.

Figure 6

Test rig used in fiscal year 2009

Figure 7

Four line reactors

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 3 (September 2010)
51

The exhaust gas measurements during the engine tests consisted of continuous monitoring of
the CO, CO2, and O2 in addition to the NOx and ammonia to detect any leaks, and PM
measurements to determine the effect of dust. The amount of dust stuck to the catalyst surface wasrather high. The effects of a soot blower, diesel particulate filter (DPF), and electrostatic
precipitator (EP) were verified.
An outdoor tank of aqueous ammonia was installed next to the test room, and facilities suchas an absorption tank were used to treat the vapor. With these additions, the aqueous ammonia did
not cause any problems due to leaks for the entire test period spanning approximately two years.
Safety must be carefully evaluated before installing an aqueous ammonia supply in a ship. Our
study demonstrated that few safety issues should arise if sufficient equipment is used.

|5. SCR Verification Tests with the Engine at Tokyo University ofMarine Science and Technology
In the fiscal year 2008 test, the denitration performance of the catalyst gradually decreased
with operating time. The possibility of an uneven concentration of catalyst in the exhaust gas wasconsidered because of the unexpectedly low denitration rate from the initial stages of the test andthe analysis results of the catalyst. The exhaust gas flow was simulated, and the flow speed
distribution control was tested with porous plates to ensure uniform distribution of the reducing
agent on the catalyst surface in exhaust gas. With these countermeasures, the initial denitration rate
was improved to some extent.
However, the flow control could not stop the degradation of catalyst performance caused by
the sulfur content in the fuel. Class “A” heavy fuel with low sulfur content was used to verify thiseffect. Although the IMO Tier III NOx regulations do not refer to fuel limitations, the type of fuelwill be limited within the ECA. SOx and PM regulations in ECA, which come into effect in 2015,
state that the sulfur content in fuel must be 0.1% or less. If both regulations are considered, it islikely that fuel containing less than 0.1% sulfur will be used with an SCR system. Therefore, wedecided to test MDO fuel with a sulfur content of 0.07% in fiscal year 2009. The test results
showed a drastic improvement in the performance degrading speed, in contrast to our predictions,and the relationship with the sulfur content of the fuel was verified. Figure 8 shows the difference
in denitration performance according to fuel sulfur content.

Figure 8 Denitration performance with fuel sulfur content

In fiscal year 2009, the denitration performance was examined for different temperatures.
The tests also considered the catalyst regeneration effect due to heating and dust removal in theexhaust gas to reduce the amount of dust stuck to the catalyst. The optimum denitration conditions
were considered.
With the use of 0.07% sulfur content fuel, the catalyst performance was improved, and theMitsubishi Heavy Industries Technical Review Vol. 47 No. 3 (September 2010)52

degrading trend of the catalyst denitration performance was not significant. As a result, the effect ofchanging conditions was small. The parallel test operation allowed more accurate comparisons of
the test results and a better assessment of the denitration performance. A significant degradation of
the denitration performance was not apparent after 100 hours of operation at an exhaust gas
temperature of 250C, making the possibility of denitration with an SCR system more realistic.
Also, degraded catalyst was revitalized almost to the level of new catalyst performance by heating
to a temperature of approximately 350C. This heating regeneration can be done any time it isrequired, even while denitrating. Figure 9 shows the heating regeneration test results. Evaluation of
the catalyst durability of multiple regenerations has not yet been verified, and further tests arerequired.

Figure 9

Test results after heating regeneration|6. Conclusion
The exhaust gas denitrating tests carried out in fiscal years 2008 and 2009 at Tokyo
University of Marine Science and Technology were initially aimed at achieving a denitration rateof 80% using MDO fuel with 0.5% sulfur content. However, this target was changed to consider
fuel with a sulfur content of less than 0.1%. At the start of this research, denitration at exhaust
temperatures of 250C was not possible, and the implementation of the test itself was thought to besignificant. However, using fuel with a sulfur content of less than 0.1% enabled stable denitration
performance at low exhaust temperatures.
This research and development project will now proceed to the second step, which consistsof installing an SCR system in a ship with a low-speed diesel engine downstream of theturbocharger. Further investigation is needed to develop the regeneration method and ensure thedurability of the system. The knowledge attained in this study will be utilized for future practicaluse.
This research and development project was overseen by Japan Marine Equipment
Association and promoted by the Nippon Foundation. The participants were MHI and Akasaka
Diesels, Ltd. The supply and analysis of the catalyst was assisted by Sakai Chemical Industry Co.,
Ltd. and the test engine was provided by Tokyo University of Marine Science and Technology for along period of time. We would like to express our gratitude to these organizations and to the people
who made this study possible.