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Development and Installation ofMarine-use Hybrid SOx Scrubber Systemthat Complies with IMO SOx Emission Regulations

YUSUKE WATANABE*1

SHO KOYANAGI*2

As a solution to meet the International Maritime Organization (IMO) regulations on SOxemissions from ships, Mitsubishi Heavy Industries, Ltd. (MHI) and Mitsubishi Kakoki Kaisha, Ltd.
(MKK) jointly developed a marine-use flue gas desulfurization (FGD) system called the "HybridSOx Scrubber System." One of the advantages of this system is hybrid cleaning, which has twomethods for cleaning the flue-gas: the freshwater closed-cycle mode and seawater open-cycle
mode. These specifications provide sufficient FGD performance that is applicable in various
sailing areas. A packaged module that houses the elemental components enables the efficient use of
the limited area on a ship and shortens the construction work period. This system was delivered toKawasaki Kisen Kaisha, Ltd. ("K" Line) for its car carrier that entered service in February 2016.
The sea trials showed the sufficient desulfurization performance of this system under real maritime
conditions.

|1. IntroductionThe reduction of flue gas emitted from ships to the atmosphere has been urged and the sulfur
content standards for ship fuels have been tightened in stages to reduce SOx emissions from ships
under the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex
VI Regulation 14. In Emission Control Areas (ECAs) including the North Sea area, Baltic Sea area,and North American coastal zone, the sulfur content of fuel oils must be 0.1% or lower fromJanuary 1, 2015, under this Regulation. For outside the ECAs, the sulfur content is required to be0.5% or lower from as early as January 1, 2020. The ECAs may be further expanded, and there areindications that some countries will establish their own emission regulations.
Regulation 4 of MARPOL Annex VI allows the use of an exhaust gas cleaning system(EGCS) as an alternative to using low-sulfur fuel oil only if the EGCS reduces the sulfur content offlue gas from the fuel combustion engines to below the limits. Low-sulfur fuel oil is more
expensive than conventional heavy fuel oil, and it is unclear whether the supply capacity of
low-sulfur fuel oil can meet the increasing demand in the future. On the other hand, EGCSs allows
ship owners to keep using conventional inexpensive heavy fuel oil for which there is sufficient
supply capacity while meeting the SOx emission limits, so EGCSs are in greater demand and arebeing rapidly diffused, particularly for ships that travel in ECAs.

|2. Development of marine-use SOx scrubber system
To meet the increasing demand for EGCSs, MHI and MKK have jointly developed amarine-use wet-type FGD system, a type of EGCS, since 2010. MKK, a manufacturer of FGDsystems for onshore conditions, has significant production expertise. MHI built a scrubber
demonstration plant at MHI's Nagasaki Research & Development Center that treats flue gas from a2-stroke 1-cylinder diesel test engine (rated at 762 kW). Several tests were conducted to collectdata on the FGD performance of the scrubber system treating the diesel test engine, which foundthat the system sufficiently satisfies the regulation in terms of desulfurization performance at adesulfurization rate of 98% or higher. Figure 1 shows the appearance of the scrubber*1

Chief Staff Manager, Ship & Ocean Engineering Department, Shipbuilding & Ocean Development Division, Commercial Aviation &Transportation Systems*2 Ship & Ocean Engineering Department, Shipbuilding & Ocean Development Division, Commercial Aviation & Transportation Systems

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 2 (June 2016)49

demonstration plant. Figure 2 is an example of the SOx content variation at the SOx scrubber
outlet in the test.
The "Hybrid SOx Scrubber System" presented in this paper is a commercial productdesigned based on the demonstration results to meet the IMO MEPC.259 (68) "2015 Guidelines for
Exhaust Gas Cleaning System" (EGCS Guidelines). The EGCS Guidelines prescribe therequirements to ensure sulfur contents equivalent to fuel oils determined in Regulation 14.1 andRegulation 14.4 of MARPOL Annex VI.

Figure 1 SOx scrubber
demonstration plant

Figure 2 Behavior example of SO2 concentration at scrubber
outlet at FGD test

|3. Outline of Hybrid SOx Scrubber System
This system provides two hybrid cleaning methods: freshwater closed-cycle mode (Figure 3)
and seawater open-cycle mode (Figure 4). The former circulates the freshwater while neutralizing
it with NaOH for recycling, and the latter pumps seawater and directly splays it into the flue gas.
Thanks to its specifications, this system provides sufficient FGD capacity that is applicable invarious sailing areas including oceans, rivers, and bays.
This system consists of many elemental components such as a scrubber tower, pumps, a heatexchanger, a circulation water treatment unit, an exhaust & effluent monitoring unit and acompliance data storage unit, NaOH tanks, and sludge tanks. The scrubber tower is a multi-streamtype, where flue gas from several engines is treated in a single tower. This scrubber tower, whichhas quite a simple internal structures with no moving parts inside, is easy to maintain and thepressure loss is very low.

Figure 3

Freshwater closed-cycle mode

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Figure 4

Seawater open-cycle mode

|4. Features of Hybrid SOx Scrubber System
4.1

System automation

The elemental components of this system are integrated so as to be controlled and monitored
through a SOx scrubber operation panel in the machinery control room. Scrubber on/off and modeselection are done through the simple touch panel automatically without complicated valveoperations.

4.2

Component packaging

A container-type module, an ISO-standard container housing some of the main components(freshwater circulation pump, heat exchanger, NaOH tank and sludge tank), is also available.
Packaging these main components into a container enables the limited space on a ship to be used
more efficiently and shorten the duration of construction work. The container-type module can beinstalled even on an exposed deck depending on the type of ship. Figure 5 shows the layout of themain components that are installed separately inside a ship. Figure 6 shows the container-type
module housing the main components mounted on an exposed deck. The container-type module isalso easy to retrofit to ships already in service by adding just two components inside the ship: ascrubber tower in a funnel casing and a seawater pump to be mounted on the ship bottom. If
installed on the exposed deck of a delivered ship, the container-type module can be easily moved toanother ship for reuse when the older ship is retired.

Figure 5

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Figure 6
Layout example of container-type module
housing this system|5. System installation on a ship
5.1

Installation onto large-scale car carrier

A large-scale car carrier, the M.V. DRIVE GREEN HIGHWAY (Figure 7) with a
7,500-vehicle carrying capacity, was built under “K” Line’s DRIVE GREEN PROJECT aiming foran environmentally-friendly maritime industry. It is a flagship showcasing next-generation
environmental performance. In the Sox scrubber system in the car carrier, the flue gas pipes fromthe main engine and three power generation units are connected to the scrubber tower in the engine
casing, such that this system solely cleans flue gas that is equivalent to 15 MW-class engine
emissions in its entirety. A 40-ft container (Figure 8) housing the main components such as theheat exchanger and circulation water treatment unit is mounted on the exposed stern garage deck.
The NaOH and sludge are separately stored in the heater-equipped stainless ISO tank containers
mounted inside the ship.

Figure 7

Large-scale car carrier “M.V. Drive Green Highway”

Figure 8

Packaged module housing main components

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5.2Sea trials

During the sea trials of the car carrier, the FGD performance of this SOx scrubber system
was verified under real maritime conditions. Figure 9 shows the desulfurization rate against theliquid-to-gas ratio (or Liquid/Gas ratio, meaning the volume of the scrubbing water against thevolume of flue-gas). This system sufficiently desulfurizes the flue gas in both cleaning modes,
meeting the EGCS Guideline requirements by appropriately adjusting the Liquid/gas ratio. This
result is mostly consistent with the results of the demonstration plant test, verifying thedesulfurization performance expected for this system.

S.W.: Seawater open-cycle mode
F.W.: Freshwater closed-cycle mode

Figure 9

FGD performance of the marine-use SOx scrubber system|6. Conclusions
MHI and MKK jointly developed the marine-use FGD system called the "Hybrid SOx
Scrubber System." Thanks to its specifications, the system provides sufficient FGD performancethat is applicable in various sailing areas and operates automatically without complicated manualprocedures. Packaging the main components in a container makes it possible to use the limited
space on a ship more efficiently. During the sea trials of “K” Line’s large-scale car carrier, theM.V. DRIVE GREEN HIGHWAY, this system showed sufficient desulfurization performance
under real maritime conditions. The practical use of the system in ECAs is also planned.
The SOx scrubber system was developed and installed in cooperation with Nippon Kaiji
Kyokai (also known as ClassNK), "K" Line, Japan Marine United Corporation and MKK, withsupport from the ClassNK Joint R&D for Industry Program. We would like to express our deep
appreciation to ClassNK for various advices and to the other parties for their efforts in thesuccessful completion of this project.