Reducing CO 2 with a Highefficiency Large Gas Engine
Cogeneration System
MASAHITO KOMIYAMA*1

MASAYOSHI KATSUMI*1
HIROYUKI ENDO*2

Amid mounting concern over global warming, power producers are turning their attention to electric power generation systems
fueled by natural gas, an energy resource with low CO2 emissions. For this purpose, Mitsubishi Heavy Industries, Ltd. (MHI) has
developed and practically supplied a large 6-MW-class gas engine, the MACH-30G. This report describes the design strategy forachieving total thermal efﬁciency with the MACH-30G, including the strategy to recover heat from exhaust gas and other sources.
Various approaches for improving thermal efﬁciency, quality control for site work using modular design, and other features of the newengine are also described.

1. Introduction
In light of the heightened need to reduce global warming
i n accorda nce w it h t he i mplement at ion of t he Kyoto
Protocol (2008 to 2012) and discussions at the COP 13 Bali
Conference to develop a roadmap for reducing greenhouseeffect gases after 2012, attention is turning to an engine
powered by natural gas, a fuel with low carbon dioxide (CO2 )emissions. When used in power generation systems, gas
engines have the additional merit of emitting very low levelsof sulfur oxide (SOx), the source of acid rain, and low levelsof nitrogen oxide (NOx), which is harmful to the humanbody. These engines are excellent for preserving the global
environment as a whole, as well as the climate itself.
T his paper i nt roduces t he ef f icienc y- i mprovement
technologies adopted for the MACH-30G,1 a large gas engineof 3000 kW or more. It also summarizes various advantagesof the gas engine cogeneration system, for example, interms of quality control at the site, a reduced construction
period involving modular design (the realization of MD), andreduced CO 2 emissions through improvements in the total
thermal efﬁciency.

Fig. 1 Power plant in the Yokohama Dockyard & Machinery
Works of MHI
MHI started operating the plant in October 2002, and since then has
achieved an availability factor of 99% or higher.

consumption in factories.
To recogni ze the needs of the customers who haveinstalled gas engine cogeneration systems and to verify
the reliability and improve the performance of gas engine
cogeneration plants, in 2002, MHI started operating a powergeneration plant with its first and second MACH-30G gas
engines in its Kanazawa factory at the Yokohama Dockyard &Machinery Works (Fig. 1). MHI has enhanced the efﬁciencyof actual engines using the test plant (see the results shownin Fig. 2), 2 and through the various improvement measures
shown in Fig. 2, MHI improved the efﬁciency from an initiallevel of 42.5% to 44.5% . The company has now targetedfurther improvement to a 48 % level of efficiency thoughvarious strategies.

2. Approaches to improve the efﬁciency of power
generation
In 2000, MHI developed the MACH-30G, a gas engine
i g n it ed by pi lot f uel oi l , wh ich wa s modeled a f t er aconventional spark ignition gas engine and diesel engine.
As of the end of 2007, customers have placed 138 orders for
MACH-30G gas engines in Japan in addition to 19 orders forengines overseas. The key selling points for customers havebeen environment-friendly performance and reduced energy*1 Yokohama Dockyard & Machinery Works*2 Yokohama Research & Development Center, Technical Headquarters

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Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)

50

Step 6Further improvement of combustion efficiency

49
48

Step 5
Improved combustion efficiency

47

Efficiency (%)

46

Step 4
Increase in the maximum firing pressure

45
44

Step 3
Application of a high-efficiency turbocharger
Improved combustion in the precombustion chamber

MACH30G
43

Step 2
Realization of the Miller cycle
Lean fuel:air mixture ratio

42

Step 1
Open/close timing for the intake and exhaust valvesSpecifications of the precombustion chamber
Pilot injection system

4140
39

FY 2001

2002

2003

2004

2005

2006

2007

2008 or later

YearFig. 2 Steps for improving efﬁciency
MHI has been taking steady measures to improve efﬁciency since the market release in 2002.

Exhaust gas system components
such as the exhaust gas boiler

Cooling tower

min7000

Ventilation blower room

Auxiliary area

Auxiliary units

Electrical room

Layout of the panels in the electrical room

Piping block

9000

Electrical room

29120
Fig. 3 Example of a 6 MW plant design
The plant design seeks to reduce the construction period and assure quality by modularizing the respective units of the gas engine plant.

Heat-recovery equipment and antipollution facilities suchas NOx-removal equipment are added in some cases, inaccordance with various needs of customers, and regulationsat installation sites.
By adopting a MD to modularize the basic auxiliaries andcombining modules in several cases, MHI has responded to
the various needs of customers and realized compatibility

3. Conﬁguration of the gas engine plant andrealization of MD
A gas engine plant has several components, such as
several auxiliaries for fuel gas, pilot fuel oil, lubricatingoil, cooling water, compressed air, intake air, exhaust gas,various electrical equipment, and an engine and generator.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)

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Service Center in
Yokohama Dockyard & Machinery Works, MHI

Customer’s cogeneration system
Telephone line network

Operation data management and failure diagnosis
are carried out by the remote-monitoring server.

MACH-30G• Data transmission at
regular intervals• Alarm transmission

Remote-monitoring server• Trend indication• Event history indication• Monthly report indication

Generator
Data logger

Printer
Personal computerfor monitoring• Printing a monthlyreport• Communication during
major accidents, andprediction• Dispatch a service
engineer

FAX

Cellular phone

Monitorfor supervision

Fig. 4 Remote monitoring system
This system connects the customer’s plant and MHI’s service center for service requiring extreme care.

between quality control for site work. Moreover, MHI has
reduced construction periods using several combinationsof specif ic modules consisting of engine and auxiliar yunits, and variable modules such as auxiliaries for exhaustequipment (Fig. 3). MHI enhances services for customers
by monitoring the operating conditions of engines remotelyand exploiting superior engine properties, such as quickstart capability, rapid loading for sudden load changes,
and minimal ef f iciency reduction with variation in air
temperature. In addition, the condition of the engines can bemeasured and analyzed during operation by collecting dataon the combustion pressure of each cylinder and various

kinds of temperature data for combustion control using a
remote monitoring system (Fig. 4).

4. Total thermal efﬁciency
To reduce CO 2 , the total thermal efﬁciency is importantin terms of not only the power generation efficiency butalso, heat recovery from the exhaust gas, cooling water, andlubricating oil. In one plant, a total thermal efficiency of
77% was achieved by raising this heat recovery efﬁciency to33% (a total thermal efﬁciency of 80% or higher is achieved
if low-temperature water recovery is included). This highefficiency reduces energy consumption and brings about
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Technical Review Vol. 45 No. 1 (Mar. 2008)27

a total expected CO 2 reduction of about 15,000 ton/year incomparison with a conventional plant, when calculated at twolevels:• A CO 2 reduction of about 9,000 ton/year through power
generation with natural gas.
• A CO 2 reduction of about 6,000 ton/year through heat(steam and hot water) recovery by cogeneration

References
1. Nakano, R . et al., Development of High Power K U30GA Gas
Engine, Mitsubishi Heavy Industries Technical Review Vol.38
No.4 (2001) p.202
2. Nakano, R. et al., Development of Advanced M ACH-30G Gas
Engine, Mitsubishi Heavy Industries Technical Review Vol.41
No.1 (2004) p.22

5. Conclusion
The solid record of the high-efﬁciency performance of theMACH-30G since its commercial release in 2002, together
with its enhanced reliability through the use of a remotemonitoring system and other measures, has convinced
customers to place more than 150 orders for this engine,both inside and outside Japan.
MHI will continue to support the efforts of its customers
to prevent global warming and improve economy throughenhanced efﬁciency and reliability.

Masahito Komiyama

Masayoshi KatsumiHiroyuki Endo

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 1 (Mar. 2008)28