Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
1Boiler Digital Twin Applying Machine Learning

HIDETOSHI AIKI*1

KAZUHIKO SAITO*2

KAZUHIRO DOMOTO*3 HIROTOMO HIRAHARA*4
KAZUTAKA OBARA*5

SOICHIRO SAHARA*6

Artificial Intelligence (AI)-related technologies based on statistical processing have been
attracting attention in recent years. While AI has a feature of learning data, in-service power
plants generate operational data every second. If AI could learn these data and help achieve better
operating conditions, it would be possible to build a more flexible control system, supplementing
the conventional-style control process. This report will describe the installation procedure for
Digital Twin, which can contribute to the enhancement of our clients’ earning capacity byincreasing the economic efficiency of power plants, and also presents an overview of Digital
Twin’s features, its system structure and an actual introduction example in Taiwan.

|1. Introduction
Recently, due to the various changes in the market such as electricity deregulation and theintroduction of renewable energy, flexible operational performance, O&M optimization andperformance improvement are in greater demand. Under such circumstances, there has been active
development in a wide range of services utilizing Information and Communication Technology(ICT) and data science (e.g., big data analysis and AI technology).
Digital Twin is an example of data science application, which collects information from
actual devices and plant facilities and reproduces it in a digital space on a computer network in realtime.
Mitsubishi Hitachi Power Systems (MHPS) began offering digital solution service“MHPS-TOMONI” in 2017, where cutting-edge technologies are applied to optimize the operationof thermal power plants to help boost the client’s earning capacity by increasing the plant’seconomic efficiency.
The list of services of “MHPS-TOMONI” for coal-fired boilers includes remote monitoring,anomaly prediction/early detection, performance diagnosis and efficiency improvement. Amongthem is Digital Twin for boilers as an efficiency-booster service. Digital Twin for boilers collects
the measurement data of thermal power boilers such as pressure, temperature and flow rate, utilizes
AI technology including machine learning and MHPS’s expertise as a boiler manufacturer, andreproduces a virtual boiler on a computer with the same behavioral patterns as the real unit,
providing feedback to the control system of the real unit on the optimum settings. Digital Twin isillustrated in Figure 1. We believe that the development of this technology will lead to theestablishment of automatic autonomous operation in the future.
This report will explain Digital Twin in terms of how it contributes to improved boiler
efficiency and reduced auxiliary power.

*1

Senior Chief Engineer, Power & Energy Solution Business Headquarters, Mitsubishi Hitachi Power Systems,Ltd.

*2Manager, Boiler Business Strategy Planning Department, Boiler Technology Integration Division, Mitsubishi Hitachi Power*3Manager, Boiler Engineering Department, Boiler Technology Integration Division, Mitsubishi Hitachi Power Systems,Ltd.

Systems,Ltd.
*4Boiler Business Strategy Planning Department, Boiler Technology Integration Division, Mitsubishi Hitachi Power Systems,Ltd.

*5Nagasaki Power Systems Service Department, Power Systems Service Headquarters, Mitsubishi Hitachi Power Systems,Ltd.

*6Control Systems Department, Project Management Division, Mitsubishi Hitachi Power Systems,Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
2Figure 1Digital Twin

|2. Machine learning model
Generally speaking, basic technologies for artificial intelligence include rule-based control
systems, deductive systems, machine learning and deep learning, whereas their applied
technologies include question answering systems, search engines, image recognition, naturallanguage processing and voice recognition. These are the technologies simulating (replicating withan engineering approach) one aspect of human intellectual activities.
The conventional control systems delivered to thermal power plants have an automatic
operation feature which is mainly “based on strict rules and operable under certain conditions,” anexample of which is the start-stop function of power plants.
On the other hand, there is a possibility to develop a more flexible automatic operation
feature by applying the above AI technologies. Machine learning is roughly classified into
supervised learning, unsupervised learning and reinforcement learning. In this regard, Digital Twinfor boilers adopts the kind of machine learning which would be classified as supervised learning to
replicate measurement data such as pressure, temperature and flow rate.

|3. Digital Twin installation work flow
The Digital Twin installation work flow consists of the following steps to solve clients’problems while achieving their understanding of the whole process. Each step will be described inFigure 2.

Figure 2(1)Digital Twin installation work flow

Assessment
This is where any issues related to improved plant operation, (i.e., the reduction of fuelconsumption, NOx amount, unburnt ash contents and auxiliary power) are discussed. A further
discussion is held as to whether Digital Twin construction would be a good solution for theexisting issues or whether there are any other ideas.
Meanwhile, to protect the operational data, a non-disclosure agreement is made with theclient prior to receiving a certain amount of data for our review. Then, the amount and qualityof the data is examined to determine whether a pre-trained model suitable for the purpose canbe created.

Mitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
3(2)PoC (Proof of Concept)
This is where a pre-trained model is created and its accuracy is improved. Furthermore, atable-top optimization study is conducted utilizing the pre-trained model to help the clientunderstand what kind of actual advantages can be gained by constructing Digital Twin.
Then, a pre-trained model with a high level of accuracy is constructed by making it learn
MHPS’s expertise as a boiler manufacturer (an enormous amount of knowledge/experience, as
well as a deep understanding of physical phenomena) and the client’s knowledge and expertiseon operation and maintenance.
(3) Installation
Boiler Digital Twin is installed in the actual power plant. The connection with the control
device is examined, communication is established with it and a combustion test and anoptimization test are run on-site before evaluating the advantages quantitatively.
(4) Additional learningThis is conducted upon the client’s request. Utilizing an additional dataset for learning,
the pre-trained model obtained in (3) above is updated.

|4. Overview of Boiler Digital Twin features(1)

The major features of Digital Twin are described below.
Monitoring feature
In terms of the main parameters of the boiler, operational data are indicated in the system
diagram rather than in a table, for the purpose of achieving a more user-friendly interface. The
data consist of the measurements of the water/steam system, air/gas system, instruments aroundthe mill and burner. A monitoring screen is shown in Figure 3.

Figure 3(2)

Monitoring screen

Prediction feature
Real-time prediction of process values is available utilizing a pre-trained model. In termsof coal-fired boilers, some process values (boiler properties) fluctuate depending on the
different kinds of coal used. However, MHPS has already experienced building a pre-trainedmodel which is capable of predicting the properties of multiple types of coal, as well as biomass
co-combustion, not just medium fuel-ratio coal which is the commonly used fuel.
(3) Optimization feature
Target values are set for major parameters which experienced engineers would consider
in combustion tuning. Digital Twin suggests the optimum settings that are economicallyefficient (i.e., reducing fuel consumption, ammonium consumption and auxiliary power) andhas no problem in terms of the setting parameters (i.e., satisfying the target values). Operatorsin power plants may choose to either reflect or not reflect the suggested optimum settings in theMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
4control device.
Settings for various operation terminals (e.g., damper opening settings) in power plantsthat are selected at the time of a test run are determined according to the design coal or test
coal. Various types of coal are used in the clients’ actual operation and boiler properties change
depending on the coal used. Boiler properties vary due to age after being used for many years.
The conventional control systems also allow the settings to be adjusted according to the changeof coal types. However, the flexible adjustments in the settings whenever a change occurs, asexplained above, would enable delicate optimum operation, cutting down on operational
expenses.
(4) Change in target values
Target values may be adjusted according to the client’s needs. For instance, it is possible
to conduct reduced NOx operation in consideration of environmental performance, operation
with reduced fuel consumption focusing on economic efficiency or having a good balanceamong environmental performance, economy and operational efficiency, as can be seen inFigure 4.

Figure 4

Optimum settings suggested by Digital Twin

|5. System configuration
MHPS has 2 solid accomplishments (Figure 5) in system configuration as follows.

Figure 5(1)System configuration

Configuration performing calculations with a server computer located inside the power plant:This is one form of system configuration where the plant control device is connected to a
Digital Twin server without any connection to external networks, which sends the optimum
setting parameters calculated on the server back to the control device. The optimum settings canMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
5(2)be obtained whenever the client needs them.
Configuration performing calculations with a server computer located outside the power
plant utilizing MHPS-TOMONI:
In this system configuration, operational data is transmitted to MHPS-TOMONI frompower plants via Netmation Secure Gateway (NSGW), MHPS’s data diode (unidirectionalcommunication). This allows calculations of the optimum setting parameters on a Digital Twin
server built in MHPS-TOMONI.
MHPS suggests the optimum setting parameters to the client based on the calculations
carried out according to the client’s needs such as changes in the types of fuel used. In thisconfiguration, the optimum setting parameters calculated on the server should be updated
manually, since they would not be fed back to the control device automatically.
In terms of security, utilizing MHPS’s NSGW can block access from networks outside of
the plant. Accordingly, a secure plant network can be achieved, fully protected from any
external attacks.
In addition to those mentioned above, better configurations will continue to be discussed
and proposed for our clients’ best interests.

|6. Installation of Taiwan Linkou Power Plant Unit 2
6.1Combustion tuning optimization feature (Steps 1 and 2) and operational cost
optimization feature (Step 3)

Below is the actual installation project of Digital Twin in Linkou Power Plant Unit 2(800MW) of Taiwan Power Company (Taiwan Power).
Step 1 consists of system configuration and the construction of a machine learning modelutilizing operational data from the actual device. In Step 2, optimization tests were carried out
where Digital Twin, dedicated to the optimization feature for combustion tuning (mainly inenvironmental and operational aspects), was installed as application software. Consequently, theadjustments to various parameters (indices) achieved a proper combustion balance, allowing
successful process optimization in terms of the environmental and operational performances.
In Step 3, a different feature, which predicts changes in process values in terms of economic
efficiency such as boiler efficiency and auxiliary power, was added to the features mentioned in
Steps 1 and 2, equipping the parameters suggested by Digital Twin with improved economic
effects (the operational cost optimization feature). Furthermore, the machine learning model has
become capable of handling multiple types of coal by learning data of various coal types. Figure 6illustrates the installation process of the Digital Twin adopted in Linkou Power Plant.

Figure 6

6.2

Digital Twin installation process

Installation results and effects

In Step 1, it was confirmed that creating a highly-accurate model is possible through a test
where a machine learning model would learn the trend of fluctuations in the installation process byapplying different values to multiple parameters. In Step 2, the process was optimized utilizing thepre-trained model. The optimization test includes “Overall optimization test with a good balance ofexhaust gas characteristics, steam temperature, etc.” and “Optimization test focusing on certain
process values (e.g., NOx)” while applying different target values. Figure 7 presents thecombustion tuning results from Steps 1 and 2. For example, when the limit value for NOx wasMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)
6100%, experienced engineers would make some adjustments to keep it down to around 70%,
whereas Digital Twin’s adjustments also achieved 69%, which confirmed Digital Twin was capableof adjusting the settings as good as the human engineers. Moreover, Digital Twin’s estimate thenwas 65%, which was quite accurate in light of the actual value. This tendency has been confirmedin terms of the spray valve opening, which needs to be within the control range, as well as themetallic temperature distributed on every panel.

Figure 7

Results of Digital Twin combustion tuning

In Step 3, a test focusing on operational cost optimization was performed while maintaininga certain amount of control margin for load change etc. Figure 8 gives the results of the cost
reduction effect achieved by the operational cost optimization feature in Step 3. The condition
before Boiler Digital Twin was installed is referred to as “the benchmark cost,” by contrast withwhich we evaluate the cost reduction realized as a result of the Boiler Digital Twin’s control. The
cost reduction effect varies depending on the types of coal or operational conditions. However, inthe test, the cost reduction effect was confirmed to be about 100 million yen a year.

Figure 8

Results of optimum operational cost adjustment by Digital Twin

|7. Conclusion
Our clients can enjoy various benefits from Boiler Digital Twin to suit their needs. Taiwan
Power Linkou Power Plant Unit 2 (800MW) demonstrated an operational cost reduction effectworth 100 million yen annually thanks to the introduction of Boiler Digital Twin.
In our work flow, the PoC phase is introduced prior to installation where we help our clients
understand the details and let them decide whether Digital Twin can be installed.
Among various AI technologies attracting global attention, some are being developed and putMitsubishi Heavy Industries Technical Review Vol. 55 No. 4 (December 2018)7

into practical use that are more advanced than the machine learning described in this paper. MHPS
will continue to develop new features which would contribute to solving our clients’ problems bycombining new technologies and the expertise we possess as a boiler manufacturer.

References(1)(2)

MHPS News (June 11, 2018) No.130
http://www.mhps.com/news/20180611.html
MHPS News (January 10, 2017)No.090
http://www.mhps.com/news/20170110.html