Mitsubishi Heavy Industries Technical Review Vol. 60 No.3 (September 2023)
1Growing Expectations for Ammonia as Clean Energy- Compressors to Meet Diverse Needs of Plant -Sales Group
Business Development Division
Mitsubishi Heavy Industries
Compressor Corporation
mco_info@mhi.com

Ammonia is used as fertilizer or for industrial applications. In the midst of moving forward
to carbon neutrality, in recent years, there is a growing expectation for its use as clean energy withno carbon dioxide emissions. As the technologies for ammonia production, transport and storage
have already been established, the technological development is progressing for applications inthermal power generation, industrial furnaces and marine fuel. It is also attracting attention for its
use as a carrier for transporting hydrogen, which is difficult to transport in large quantities.
Under such circumstances, the number of ammonia production plant projects is increasing
across the world. Diverse needs are emerging, such as low-carbonization, decarbonization andplant expansion/upgrade.
This report presents the features of Mitsubishi Heavy Industries Compressor Corporation’s(MCO) compressor package for ammonia plants, as well as the needs for low-carbonization,decarbonization and upgrading of existing plants.

|1. Compressors for ammonia plants
In the process of ammonia production (Haber-Bosch method), the compressors, which
compress air or gas, serve as the key role. Figure 1 shows the major compressors used in the
production process and their roles. As the efficiency and performance of compressors directly
affect the plant operation, their high reliability is indispensable.

Figure 1 Major compressors used in ammonia production process and their roles
With regard to our compressor delivery records for ammonia plants, we have supplied moreMitsubishi Heavy Industries Technical Review Vol.60 No.3 (September 2023)
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than 350 units across the world since our first delivery in South Korea in the 1960s, thereby
contributing to the stable operation of plants. Recently, we delivered to one of the world’s largest
ammonia plants (3,600 tons per day) in the United States. Table 1 lists our major deliveries.
Table 1 Major deliveries to ammonia plants
Production capacity(tons/d)
3,300

Year of delivery

Country2015

Saudi Arabia

2017

Uzbekistan

2,0002019

Nigeria

2,3002020

Saudi Arabia

3,3002021

USA*

3,600

*Blue ammonia|2. Features of our synthesis gas compressor train
The compression processes in ammonia production are shown in (1) to (5) in Figure 1. This
report focuses on the features of our synthesis gas compressor, which is the heart of the plant anddirectly affects ammonia production capacity.

2.1

Compressor train configuration

The synthesis gas compressor pressurizes a mixture of gases mainly consisting of hydrogenand nitrogen. As synthesis of ammonia needs high pressure and the pressure ratio between suction
and discharge is high, at least two compressors are necessary. (One for low pressure or LP and theother for high pressure or HP). Because of high-pressure service, vertically split (hereafter referred
to as V-type) single-shaft multi-stage compressor will be applied as shown in Figure 2. The V-type
compressor has a barrel type cylindrical outer casing, whose structure can withstand a high pressureof approximately 50-700 barg and even 1,000 barg experimentally. In this service, the V-type
compressor has been used in the range of 150-300 barg. Maintenance is performed by pulling out aset of compressor’s internal parts along the shaft axis.

Figure 2 Configuration of single-shaft multi-stage compressor withvertically split design (V-type)Figure 3 compares the train configurations between our synthesis gas compressor and theconventional compressor. In the conventional configuration, compressors are arranged in series
based on the single end shaft drive design. During maintenance, the compressor located inside has
to be removed/relocated to the maintenance area. However, our double end shaft drive design
allows compressors to be positioned on either side of the driver. This enables replacement of thecompressor’s internal parts without moving the compressor to another area. Because of thissuperior maintainability, our train configuration has been received favorably by many customers
and we have delivered more than 150 units.

Mitsubishi Heavy Industries Technical Review Vol.60 No.3 (September 2023)
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Figure 3 Comparison of train configurations between our synthesis gas compressor andconventional compressor

2.2

Boltless design of V-type compressor

As described above, V-type compressors are mainly used in high-pressure service. One of thefeatures of our compressors is the boltless design, which makes maintenance easy. A compressor
consists of a casing and the internal parts, and the internal parts of V-type compressor to be pulled
out along the shaft axis, one end of its cylindrical casing is open to allow a pull-out compressor
internal. Therefore, it is necessary to attach and bolt a lid to the open end of the casing in order tomaintain the internal pressure during operation. However, we have adopted the boltless design forour compressors using shear rings and retaining rings, thereby considerably shortening the required
time for compressor disassembly. There is also another big advantage in terms of safety, that is norisk of gas leak through gaps around the bolts (Figure 4).

Figure 4

2.3

Sealing structure of V-type compressor casing

Integrated type (detachable type) base plate with seal gas supply unit

In general, dry gas seal is equipped with compressor to prevent the gas leakage of internal
gas to outside. Dry gas seal has a micro-gap of 2-3μm between the rotating ring and the stationaryring. A seal gas supply unit is therefore required to supply filtered clean gas. Conventionally, it isMitsubishi Heavy Industries Technical Review Vol.60 No.3 (September 2023)
4installed outside the compressor base plate, and piping connection work between seal gas supply
unit and compressor is necessary at site. However, in recent years, we often receive requests to
install seal gas supply unit on compressor base plate and complete piping connection work before
delivery in order to considerably reduce the required time at site. This causes deterioration ofhandling ability, the higher transportation cost and influence to the restriction of transportation due
to increase of base plate size and weight. Therefore, we propose detachable type seal gas supply
unit on the base plate by cantilever structure as necessary. This option not only allows confirmationof piping connection between the seal gas supply unit and the compressor before delivery, but also
prevents increase of transportation cost, since seal gas supply unit can be removed from base plate
and which means the base plate size for transportation remains unchanged from conventional one(Figure 5). We are thus capable of making proposals according to the customer requests, like theconventional separate installation of seal gas supply unit and the compressor, the installation on thesame base plate, or the cantilever structure.

Figure 5 Integrated type (detachable type) base plate with Seal gas supply unit

2.4

Performance optimization

The concept of our compressors are: high efficiency by high-speed selection, high turbine
efficiency by matching rotating speed with the steam turbine, and the consequent reduction ofrequired power (i.e., reduction of steam consumption). High-speed selection is able to reduce
compressor size. This also contributes reduction of customer’s CAPEX (Capital Expenditure). On
the other hand, for the motor driven compressors, which are increasing in recent years, the rotating
speed of motor depends on the power supply frequency of a given area, which is different fromturbine. For example, in the case of a 4-pole motor of 60 Hz, rotating speed is fixed at a low speedof 1,800 rpm. Therefore, as shown in Figure 6, by applying a speed increasing gear between thedouble end motor and each compressor, the rotating speed of each of compressor (i.e., LP and HPcompressors) is adjustable and compressor performance can be optimized.

Mitsubishi Heavy Industries Technical Review Vol.60 No.3 (September 2023)
5Figure 6

Motor-driven compressor train configuration|3. Upgrading of existing plants
As the demand for ammonia rises, attention is placed on the upgrading of existing plants inaddition to the grass root plants. For the ammonia plants, there are many old plants which has low
production capability and old compressors with low efficiency. Replacement with the latest
compressor model not only expands the plant capacity, but also can help customers to improvetheir OPEX (Operating Expense) by high efficiency. When upgrading an existing plant, it ispreferable to minimize the scope of modification for keeping the investment costs low. Based on
our vast experience in replacing more than 350 units and technologies, we are capable to propose
optimization or minimization of the scope of modification according to the existing plantconditions or customer requests. For example, in case of plant capacity expansion project,
conventional design causes the larger size of compressor, and thus modification of existing
concrete foundation would be necessary. On the other hand, available period of the revamping
work is usually limited since the work to be done during plant turnaround period and evaluation ofsoundness for existing old foundation is quite difficult. However, by applying our uniquecustomized design, our compressor is fitted to the existing foundation as shown in Figure 7, themodification scope can be minimized and we can support customers in maximizing the return oninvestment.
Thus, replacement with our compressors can help customers to maximize the return on
investment with the improved OPEX of existing plants, as well as the reduction of CO2 emissions.

Figure 7 Example of replacement of existing compressor with our compressor(Plant capacity expansion project)Mitsubishi Heavy Industries Technical Review Vol.60 No.3 (September 2023)
6|4. For low-carbonization and decarbonization
Coupled with the movement for carbon neutrality, study for low-carbonization anddecarbonization of ammonia plants have been progressing in recent years. Blue ammonia which
captures CO2 generated in the production process, Green ammonia which is produced fromhydrogen obtained by water electrolyzer that uses electricity derived from renewable energy, areexpanding its use to fuel use as clean ammonia.
For achieving low-carbonization and decarbonization, CO2 compressors are required to inject
the captured CO2 into underground in blue ammonia plant etc. We have many supply records of
CO2 compressors for conventional urea plants and gas processing plants.
In the green ammonia plants, there is no reformer that generates high-pressure steam (Figure8), then the driver for the compressor is changed from a steam turbine using high-pressure steam toan electric motor. Also a booster compressor is required to mix hydrogen generated by waterelectrolyzer and nitrogen. We are developing a large-capacity hydrogen compressor to pressurize
pure hydrogen.

Figure 8Compressors in green ammonia production process|5. Future prospect
The use of ammonia as a fuel is attracting attention, and as background that its demand isincreasing, optimization requests of turbomachinery are also increasing to meet diverse plantdemands, such as construction of grass root plants, capacity expansion or efficiency improvement
for existing ammonia plants in operation. MCO will contribute to our customers and achieve thecarbon neutral society by proposing highly reliable single-shaft multi-stage compressors/drivers
based on our vast experience in grass root projects and revamping projects.