Mitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
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CO2 Compressors Contributing to Building
CCUS Value Chain

Mitsubishi Heavy Industries
Compressor Corporation
Sales Group, Business Development
Division

CCUS*1, a technology that can absorb, transport, use, and store carbon dioxide (hereafter,CO2) generated from industrial sectors, is garnering interest in response to the world's urgent needto decarbonize. CO2 is regarded to be the main contributor to global warming. So, the CCUS
technology extracts CO2 from exhaust gas, transfers it to storage locations via pipelines or liquefiedCO2 carriers, and injects it into strata like saline formations and depleted oil fields that can store
CO2 for a long time.
Mitsubishi Heavy Industries Compressor Corporation (MCO) designs, manufactures andsupplies two kinds of centrifugal compressors, single-shaft and multi-stage compressors andintegrally geared compressors. So, MCO is suitably placed to offer CO2 compressors best suited tocustomers' projects.
Large-scale CCUS initiatives are currently being planned all around the world. By improving
MCO's integrally geared compressor for large volume of CO2, MCO created a new integrallygeared compressor to satisfy the demands.
This report highlights the development of a CCUS value chain and describes MCO'stechnology for CO2 compressors as well as the features of the new integrally geared compressor.
*1

CCUS: Carbon dioxide Capture, Utilization and Storage|1. Compressors playing important roles in CCUS value chain
To achieve a CCUS value chain aimed to capture, transportation and injection of CO2,
compressors are required to effectively compress CO2 at each process are indispensable (Figure 1).
This chapter describes the models and features of MCO's CO2 compressors and the delivery records.

Figure 1 CCUS value chain and compressors

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1.1

Single-shaft and multi-stage compressor

Our single-shaft and multi-stage compressor design is structured to hold a rotor having
multiple impellers attached to a single shaft in one casing as shown in Figure 2. Gas entering
through a suction nozzle passes through the inside of the impellers attached to the high-speed
rotating rotor, thereby being compressed by centrifugal force to a predetermined pressure, and thecompressed gas is then discharged from the exhaust nozzle.
MCO has delivered over 100 CO2 compressors to fertilizer plants around the world since the1990s, and based on its extensive experience and track record, MCO has established corrosion
prevention technologies (stainless steel weld overlay, etc.) to deal with carbonic acid corrosion
caused by to CO2 and performance prediction technologies with consideration given to thecharacteristics of CO2 gas, which exhibits large changes in physical properties. When the pressureof CO2 with high density increases, the exciting force, which is produced at the impellers and theseal part and applied to the rotor, increases. We have used technologies such as high boss ratio
impellers to increase the rigidity of the rotor-build and a novel hole pattern seal to provide a
damping function to the seal part for implementing the stable operation of the rotor.
Our single-shaft and multi-stage compressor is suited for high-pressure or high-pressure ratio
injection services because of its structural features. In addition, when the CO2 capture amountincreases in the future, the capacity can be increased with the use of the existing casing and throughmodification of the impellers or internal parts.

Figure 2

1.2

Structure of single-shaft and multi-stage compressor

Integrally geared compressor

Our integrally geared compressor is structured to contain gears in the casing as shown in
Figure 3 and is generally composed of one gear wheel shaft and multiple pinion shafts. It has amultiple-shaft and multiple-stage structure, in which impellers are attached to both ends of eachpinion shaft, each impeller is equipped with a casing called a scroll, and gas discharged from ascroll flows in the next-stage scroll through the pipe and is compressed. Its suction pressure anddischarge pressure are about the same as those of the single-shaft and multi-stage compressor.
The gear wheel shaft is driven by a driving machine such as a motor, and its motive power isconveyed to the pinion shafts via the gears. The number of rotations of each pinion shaft is adjusted
according to the gear ratio to the gear wheel shaft, and each impeller can be rotated at the mostefficient rotation speed.
Furthermore, because of its structural feature (each impeller has a casing), a gas cooler canbe installed between a scroll and the next-stage scroll, allowing the inlet temperature of each
impeller to be decreased. As a result, the power required for compression of gas can be reduced. In
numerous cases where we deliver integrally geared compressors to customers, we deliver acompressor along with several associated devices such as gas coolers, lubricating oil equipment
and shaft seal systems.

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Compared to the single-shaft and multi-stage compressor, the integrally geared compressor issuited for compression of a large volume of gas and can be effectively used for compression of alarge volume of CO2 required upstream in a CCUS value chain.

Figure 3

1.3Structure of integrally geared compressor

Track record of our compressors for CCUS

Table 1 shows the delivery records (non-exhaustive) of our compressors for CCUS. A
single-shaft and multi-stage compressor with a discharge pressure of 200 bar was delivered to a gas
treatment plant in Algeria in 2003. Thereafter, we continued its development, and in 2019, acompressor with higher discharge pressure of 550 bar was delivered for a FPSO*2 in Brazil.
An eight-stage integrally geared compressor with a discharge pressure of 130 bar wasdelivered for the Petra Nova Carbon Capture Project in the United States in 2017 and its capacity
was about 5,000 tons/day, which, at that time, was the largest capacity in the world.
*2

FPSO: Floating Production, Storage and Offloading System

Table 1 Major delivery records of CO2 compressors for CCUS
Delivery year
Country
2003
Algeria
2015
Brazil2017
USA2019
BrazilDelivery destination
Gas treatment plant
FPSO
Carbon capture project
FPSO

Compressor type
Single-shaft and multi-stage
Single-shaft and multi-stage
Integrally gearedSingle-shaft and multi-stage|2. New integrally geared compressor package
CCUS has a history of nearly 50 years mainly in EOR (Enhanced Oil Recovery) and gas
treatment plants, and against the background of the recent trend toward decarbonization,
unprecedent amount of large-scale CCUS projects have been under consideration around the world.
CCUS, which is not for EOR but only for storage of CO2, is an upcoming area that has notbeen necessary in the past. Therefore, it is required to reduce the construction cost for capital
investment and the equipment maintenance cost as much as possible.
As such we made significant improvements of our integrally geared compressor suitable forcompression of large volume of CO2 and conducted product development according to the needs of
cost reduction, shorter site installation time and improved maintainability.

2.1

Development of new integrally geared compressor

For an integrally geared compressor, the size of the gear wheel is determined so that thescrolls provided for the respective impellers do not interfere with each other. Therefore, to control
the peripheral speed of the gears below the reference value, an integrally geared compressor needs
to be driven by an expensive 6-pole motor according to the size of the gear wheel. In addition, themaintenance space for the compressor was limited because the scrolls are placed close to eachMitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
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other.
In order to solve the cost and maintenance issues, we have developed a new integrally geared
compressor with a smaller gear wheel and an additional idle gear as shown in Figure 4. The
reduced size of the gear wheel allowed the compressor to be driven by a general-purpose 4-pole
motor which is cheaper than a 6-pole motor.
In addition, with an idle gear additionally arranged, the casing of the compressor became
wider and the distance between the scrolls became larger. As a result, it was also possible to securea large maintenance area surrounding the compressor, which was advantageous.

Figure 42.2

New integrally geared compressor (with an idle gear arranged)

Compact module to shorten site installation time and improved maintainability

In addition to the development of the new compressor, we made the whole integrally gearedcompressor package compact to shorten the site installation time and improve the maintainability.
High labor costs in facility construction have become a concern, especially in industrialized
nations where the introduction of CCUS has been pushed. In order to shorten the time for site
work, as shown in Figure 5, a compressor, a seal system and instrumentation devices are built in
one module, and the integrally geared compressor and its peripheral devices are configured in four
modules in consideration of the restrictions in transportation to the site, thereby minimizing thenumber of parts to be transported to the site. In addition, pipes between devices and instrumentation
devices are installed after the modules are set up and thus the number of days for site work isgreatly shortened.

Figure 5

Separate modules

Conventionally, the header of cooling water pipes was installed on the front side of the gas
cooler and placed on the pipe rack. To improve maintenance, we changed the layout, in which thecooling water pipes are buried or installed on the steel frame rack so that the bundles can be easily
pulled out during maintenance of the gas coolers. In this new integrally geared compressor,
ancillary facilities that hinder maintenance of the devices were also reduced.
Furthermore, the pipes around the compressor were arranged together to increase themaintenance space around the compressor, and the auxiliary piping connecting to the compressor,

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which must be disassembled at the time of maintenance, was divided into blocks, thereby
facilitating the disassembly and reassembly of the compressor at the time of maintenance.
Figure 6 shows the comparison views of the conventional and the new compact module
layout. Compared to the conventional, the new compact module has its footprint reduced by about
20% and can be easily installed in a limited space.

Figure 6 Comparison between the conventional layout and the new compact module layout|3. Toward achievement of carbon neutrality
MCO has abundant track records and technological capabilities in CO2 compressor andprovides optimal compressor packages for customers' CCUS projects by utilizing the features of its
single-shaft and multi-stage compressor and new integrally geared compressor. As a company of
the Mitsubishi Heavy Industries Group, we are actively contributing towards carbon neutrality bytaking advantage of the synergy with other products such as CO2 capture systems.