Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
1

The Most Advanced SCR Technologies for Contributing
to Hydrogen-based Society and Other AQCS Products forReducing Environmental LoadAir Quality Control Systems
Business Unit
M i t s u b i s h i P o w e r, L t d .

Mitsubishi Power, Ltd. (Mitsubishi Power) is the only manufacturer in the world that can
provide the Air Quality Control Systems (AQCS), a comprehensive flue gas treatment system
including Selective Catalytic Reduction System (SCR), De-SOx system, Electrostatic Precipitators,etc., in an integrated manner, thereby contributing to environmental conservation. As regulations
on exhaust gas and wastewater become stricter around the world, further efforts for
decarbonization are required. This report presents the latest status of promising technologies asmeasures to deal with this requirement: 1. high-efficiency SCR system that contributes to ahydrogen society, 2. zero liquid discharge equipment for De-SOx system as a measure to minimize
wastewater from power plants and 3. SOx scrubber as a measure to comply with the relevant
exhaust gas control system’s regulation for marine engines.

|1. High-efficiency SCR system
Mitsubishi Power has achieved over 95% high-efficiency SCR system for gas turbine
combined cycle (GTCC) plants. This achievement was realized by adopting (i) technology for
reducing in NH3/NOx ratio distribution (high-performance ammonia injection nozzle andhigh-performance exhaust gas mixer) and (ii) exhaust gas seal structure compatible withhigh-efficiency SCR system. In addition, for the coming decarbonized society, we are planning (iii)application of the above high-efficiency SCR system technology to gas turbine power generation
facilities that use hydrogen and ammonia as fuel. The details of these efforts are described in thefollowing sections.

1.1 High-efficiency SCR technology(i) Technology for reducing in NH3/NOx ratio distribution
SCR system is needed ammonia injection into the exhaust gas containing NOx generated
in power generation facilities, etc. and converts into nitrogen and water with the following
chemical reaction over the De-NOx catalyst.
4NO + 4NH3 + O2 → 4N2 + 6H2O
Since NOx and ammonia react at a ratio of 1:1, in order to achieve high-efficiency SCRof 95% or more it is indispensable that injected ammonia is mixed with NOx in the exhaust gas
as completely as possible to reduce the NH3/NOx ratio distribution. We have developed andadopted a high-performance ammonia injection nozzle and a mixer that utilizes a swirling flow,
taking into consideration the NH3/NOx ratio distribution due to the temperature rise during
ammonia injection to succeed in reducing the NH3/NOx ratio distribution and achieving
high-efficiency SCR of 95% or more into practical use.
(ii) Exhaust gas seal structure compatible with high-efficiency SCR system
Since De-NOx system for GTCC is built into the Heat Recovery Steam Generator(HRSG), it is necessary to design the reactor (installed) with catalyst in consideration of thethermal expansion of the HRSG. However, due to this structure, exhaust gas that does not comeinto contact with the De-NOx catalyst and passes through clearance is generated. We havesucceeded in reducing the gas leaks (gas blowing through) by changing the exhaust gas seal

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
2structure inside the HRSG.
(iii) Application of SCR technology to hydrogen and ammonia fired GTCC
In the future, when hydrogen and ammonia are used as fuel for hydrogen andammonia-fired GTCC to reduce CO2, it is considered that NOx emitted from gas turbines
will increase compared to that from the natural gas used at present and more efficient SCR
system will be required. We are planning to realize such higher-efficiency SCR system byapplying the catalytic technology to reduce the ammonia injection amount and the NH3/NOx
ratio distribution , which increase as the NOx concentration at the inlet of the SCR system
becomes higher than that of normal GTCC that uses natural gas as fuel.

1.2 Achievements of high-efficiency SCR system
We have already delivered SCR system with a De-NOx efficiency of over 95% to thecombined cycle power plant demonstration facility at Takasago Works (T-point 2). This system
has achieved a De-NOx efficiency of 95% or more by adopting an exhaust gas seal structurecompatible with the NH3/NOX ratio distribution reduction technology and the high-efficiency
SCR system (Figure 1).

Figure 1 SCR system for combined cycle power plant demonstration facility
at Takasago Works (T-point 2)|2. WSD (Wastewater Spray Dryer) Zero Liquid Dischargeequipment that contributes to reducing environmental load
In recent years, for protecting health and improving water quality around the world,
regulations of wastewater from industrial facilities have been tightened including ELG's (EffluentLimitation Guidelines and Standards) in the United States, Action Plan for Prevention and Controlof Water Pollution (Water Ten Plan) in China, Water Pollution Control Low in Japan , BREF (BestAvailable Techniques Reference) in Europe, etc.
Conventionally, in thermal power plants, waste water from the wet-FGD was fed to thewastewater treatment equipment and contained heavy metals and other harmful components weresuppressed below the regulation standard values through multiple processes, and then discharged.
However, as mentioned above, in response to the growing need for dry flue gas treatment and Zero
Liquid Discharge (ZLD) technology, we have developed the Wastewater Spray Dryer (WSD),
which efficiently and inexpensively eliminates wastewater from wet flue gas De-SOx equipment bycontacting it with the heat source of exhaust gas, as an initiative that contributes to reduce
environmental load.
Figure 2 shows the flow of WSD. The WSD system draws part of the flue gas extracted
from the Air Heater (AH) inlet into the WSD chamber body and at the same time, dropletizes andsprays the desulfurized filtrate wastewater to make it contact with the exhaust gas, evaporate anddry up. Then the system returns this exhaust gas to the AH outlet and removes the evaporated salt
particles with a Dry Electrostatic Precipitator (ESP). The features of this WSD are as follows.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
3(i)Since ZLD can be efficiently realized by using the heat of the plant exhaust gas, utilities
such as steam heat sources required by other ZLD methods are not required.
(ii) By installing a damper in the duct connecting the WSD chamber body and the main fluesystem and closing the damper to disconnect the WSD system when necessary, the inside of
the WSD can be cleaned and maintained while the power plant is in operation. Therefore,
stable operation of all the power plant is possible.
(iii) Exhaust gas can be drawn into the WSD chamber body by using the differential pressure of
AH as a driving force and an air supply fan dedicated to the WSD system duct is not
required, so the equipment configuration can be simplified.
By 2016, we completed the WSD basic research and development(prediction of delay inevaporation rate of saltwater droplets, suppression of deliquescency of evaporated salt andtreatment method preventing elution of heavy metals) and pilot test demonstration(1) and made it
possible to design the appropriate capacity of the actual equipment through a simulation methodthat simultaneously analyzes thermal hydraulics and saltwater droplet evaporation (Figure 3).
After this research, in 2017, in cooperation with Chinese EPC business company : Beijing
Beike Ouyuan Technology Co., Ltd (OYST), we constructed the first WSD unit at Linfen Power
Station (a 300MW coal-fired power plant ) in Shanxi Province, China and started its operation(with a desulfurization wastewater treatment rate of 5 t/h). As a result of appropriately adjusting theoperation conditions and maintenance frequency based on operation data management incooperation with OYST , which also handles O&M of the power plants, this WSD has beenachieving long-term stable operation until now without causing any blockage in the outlet duct
(Figure 4).
Table 1 lists the reference project list of WSD. We have currently received orders for a totalof 14 WSDs in China and the United States and we are in the bidding stage for multiple projects.
As the next initiative, we are examining the practical application of a technology thatcombines WSD with desulfurized wastewater-concentrating and volume-reducing equipment.
For concentrating and volume-reducing desulfurized wastewater in the front stream of the ZLD
equipment, either a method of increasing the amount of filtrate returned to the absorber after
gypsum dewatering with desulfurization equipment or a method of passing the wastewater
discharged from the desulfurization equipment through a Reverse Osmosis membrane (ROmembrane) to extract a Brine Concentrate is used. In order to extend the life of the membrane andensure stable operation, we are now selecting the RO membrane type and its osmosis pressure andoptimizing the pretreatment method for preventing scaling and fouling and the backwash
frequency.
Figure 5 shows comparison for operation cost between the conventional type and WSD withRO membrane. It can be seen that WSD with RO has a total cost advantage over the conventional
type. When WSD and RO are combined, the power cost (heat source) and equipment cost can besignificantly reduced compared to when the WSD is used alone. This is the effect of the energy
saving due to the reduction of the amount of wastewater, the amount of heat source required andthe size reduction of the ZLD equipment. When WSD and RO are combined, the chemicals costincreases for pretreatment in the pretreatment system, but we are currently trying to find the waysof reducing it.
The WSD introduced in this report has the potential to be applied not only to thermal power
plants, but also to other industry facilities, so we will strive for technological progress to contributeto the environment and energy saving in order to apply the WSD to ZLD.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
4Figure 2

Flow of WSD

Figure 3 Simulation analysis example ofevaporation of wastewater droplets inside
WSD Chamber body
Table 1

WSD reference list (by licensee*)

Area

Delivery destination

Figure 4 Photograph inside outlet
duct at overhaul inspection ofactual WSD equipment*WSD technology licensed company

Power plant
capacity

Shanxi Province,
Linfen Power Station
1 × 300MW
China
Shanxi Province,
Houma Power Station
2 × 300MW
China
Hebei Province,
Jingneng Qinhuangdao
2 × 350MW
China
Power Station
Shanxi Province,
Jinneng Xiaoyi Power
2 × 350MW
China
StationGuangdong
Guangdong Dapu Yudean
2 × 660MW
Province, China Power Generation Co., Ltd.
Guangdong
Guangdong River Corp
2 × 300MWProvince, China
Power Station
2 × 660MW
Fuzhou Power Station ofJiangxi Province,
Datang International Power 2 × 1 000MW
China
Generation

Wastewater
treatment
amountNumber of
WSD units

5t/h

18t/h

112t/h210t/h220t/h

48t/h
16t/h

116t/h1Minnesota, USA

Boswell Energy Center1 × 650MW

24t/h

1Total―8 190 MW

119t/h14

Received orders : 13 units in China
1 unit in the United States

Plant state
In commercial
operation
In commercial
operation
Under
construction
Under
construction
Under
construction
Under
construction
Under
construction
Underconstruction―As of June 2021Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
5Figure 5 Comparison of total equipment and operating
cost (between conventional method, WSD andcombination of RO concentration and WSD)

|3. Marine SOx scrubbers that comply with IMO regulations
From January 2020, the International Maritime Organization (IMO) implemented a stricter
limit for sulfur in fuel oil of vessels operating in all sea areas based on their regulations. We
developed marine SOx scrubbers by marinizing the rectangular flue gas desulfurization system foronshore boilers, which has been improved over the years, so they have advantages in terms of theinstallation layout, especially in large container vessels and can be installed without the cargo loss.
In addition, these SOx scrubbers have a high sulfur removal efficiency and are compliant with theregulations of all sea areas including Emission Control Areas (ECAs), which are subject to theparticularly strict emission regulations. We have received SOx scrubber orders for 45 vessels so farand have contributed to reducing the global environmental load in all sea areas around the world.
This chapter introduces the latest situation surrounding this product.

3.1 Features of marine SOx scrubber
Marine SOx scrubbers use one of the following methods: open loop in which seawater is sent
as absorbent liquid to the absorption tower in one-pass system , closed loop in which a circulating
liquid containing chemicals such as caustic soda is used and hybrid in which the above twomethods are used in combination. We produced open-loop systems that can comply with ECA
regulation values and then received additional orders for hybrid systems that can be used even inareas where overboard discharge is prohibited (Non-Discharge Area) due to non-discharge
operation mode. We have also designed and developed smaller-capacity range products comparedto the existing models to expand our product lineup.
Figure 6 is an external view of the marine SOx scrubber. As the height/width ratio of therectangular scrubber tower can be changed relatively freely, the optimal layout in the limited spaceof a vessel becomes possible, achieving a higher volumetric efficiency than the existing cylindricalscrubbers. Especially for large container vessels, the scrubber can be installed without reducing thecontainer loading capacity, which indicates that the rectangular shape offers a considerable layoutadvantage. Figure 7 depicts an image of the layout of the scrubber on board a large container
vessel. This is an example of a large container vessel with two-island design with living area
separate from the engine casing in which the scrubber unit is accommodated, thus enabling theinstallation to be carried out without the cargo loss for container vessel.
In addition, the use of our scrubber can minimize the number of pieces of equipment byadopting a multi-stream method that handles gas from multiple engines in a single tower inconsideration of easy maintenance. Considering the risk of work inside the tower, we selected andadopted a spray nozzle structure that is not likely to require maintenance inside the tower as a resultof clogging.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 3 (September 2021)
6Figure 6 External view of marine SOx
scrubberFigure 7 Layout image of scrubber installedin large container vessel

3.2 Engineering for installation
We can provide engineering service for installation SOx scrubber to vessel with Mitsubishi
Shipbuilding Co., Ltd which is our partner company. Our service is provided to customers whowant the SOx scrubber to be installed on board their planned vessels more quickly, easily andsecurely. We do our best to support our customers' plans combining the knowledge of Mitsubishi
Power as a SOx scrubber manufacturer and of Mitsubishi Shipbuilding Co., Ltd., as a shipbuilding
yard. While this service is also available to vessel owners who want to retrofit the SOx scrubber on
their in-service vessels, the number of shipbuilders which are using this service for new built
vessels are increasing. Mitsubishi Shipbuilding Co., Ltd. can propose an installation plan
harmonious with any vessels whichever they are new built / retrofit, or vessel built by our company/ vessel built by another company.

3.3 Post-installation support and after-sales service
As support for customers we are strengthening after-sales service for marine scrubbers,
including periodical audit. We are promoting after sales support using our overseas network.

|4. Future development
Reflecting the global decarbonization trend, the needs for next-generation products forenvironmental technology have been increasing. As a supplier of comprehensive Air Quality
Control System (AQCS), Mitsubishi Power, Ltd. will continue to propose the optimum system
according to the regulations of the country where the product is introduced and the situation of theplant and contribute to the reduction of environmental load.

References(1)

Seiji Kagawa et. al, Development of Wastewater Spray Dryer (WSD) for Desulfurization Plants,
Mitsubishi Heavy Industries Technical Review Vol. 52, No. 4 (2015)