PT PLN is a government-owned company that manages the electric power industry in Indonesia, while PT Pertamina Geothermal Energy (PGE), also a government-owned company, develops geothermal steamfields. To ensure a stable power supply for North Sulawesi province, PLN and PGE have jointly built and are currently operating six geothermal power plants in Lahendong, which is located 30 km south of Manado, the provincial capital.
Indonesia’s population and economy are growing at a remarkable rate, and the country’s demand for electricity far outstrips supply. Despite holding 40 percent of the world’s geothermal reserves, enough to produce about 30,000 MW, the country has done relatively little till now to make use of this resource. However, the Indonesian government has signaled a strong intention to begin developing the country’s geothermal resources.
Geothermal energy is a clean and renewable power source, and plants of this type produce extremely little CO2, which is a major contributor to the greenhouse effect. For this reason, efforts to make use of this resource are gaining momentum, and its development is expected to bring great environmental and economic benefits.
At the Lahendong III geothermal power plant, Yokogawa installed the CENTUM CS 3000 distributed control system (DCS) with redundant controllers, a backup system, and a test system in 2008. Based on the success of these installed systems, Yokogawa subsequently received an order to install its CENTUM VP DCS at the Lahendong IV geothermal power plant in 2010.
Then, when carrying out projects to renovate the Lahendong I and II plants, PT PLN selected the CENTUM VP to replace the existing Bailey INFI 90 system that had been used to monitor and control the steam turbine auxiliary facilities as it was approaching the end of its useful life. The solid performance of the systems used, combined with Yokogawa's superior technical expertise in geothermal power generation, the proven quality of its products, and its extensive engineering and service network in Indonesia, were primary considerations in PT PLN's decision to go with the CENTUM VP solution again.
The Challenges and the Solutions
Automated plant and turbine startup and shutdown
Plant and turbine startup and shutdown procedures are very complex and time-consuming, and place great stress on both personnel and equipment. To eliminate operator errors during these critical processes, the CENTUM DCS has automated plant and turbine startup and shutdown procedures. The startup and shutdown sequences are executed in accordance with the logic design, and the DCS human machine interface (HMI) clearly shows the status of the sequence and the facility conditions. It also guides operators in the acknowledgement of messages and alarms and the triggering of interlock sequences. Operator intervention during the automated plant and turbine startup and shutdown processes is minimized, ensuring safe and smooth startup and shutdown. This greatly reduces operator workload and errors, shortens the startup and shutdown times, and mitigates thermal and physical stress on the turbine.
Geothermal power plants have less auxiliary equipment and their control loops are not as complex as those at fossil fuel power plants. In addition, they cost less to operate. It is therefore feasible and desirable to run a geothermal power plant nonstop at full load. When a plant is operated in this way, reliability is a key concern. And even when the plant’s DCS has redundant controllers and is extremely reliable, there is still a risk that it might fail in a corrosive environment. For this reason, Yokogawa has provided a backup system. This backup system includes the following features:
- Monitors by using a graphical user interface to ensure safety operation while the backup system is engaged
- Handles effective alarms
- Performs emergency operation in the event that the DCS fails
The backup system ensures that the plant can run safely without any interruptions.
Sequence-of-events (SOE) station
All events are precisely recorded with millisecond accuracy and displayed in a sequence of events (SOE) window for later analysis. Using this, operators can assess the cause of any problem and request a fix by maintenance personnel.
When application software needs to be modified, the revised software must be tested before it can be downloaded to the controller, requiring a plant shutdown. To maximize plant uptime, Yokogawa provided a test system that uses the test functions of the CENTUM CS 3000. This test system accurately replicates the plant control and graphical interfaces, and the software can be easily checked under the same conditions as with the actual plant system. It can be also used to train the operators.
The design and structure of the CENTUM CS 3000 and CENTUM VP systems for these geothermal power plants exceeded PT PLN’s high expectations. The use of the same HMI in both systems allows for complete consistency in the monitoring and control of the power plants and turbines at both plants. PT PLN greatly appreciates having the ability to automatically execute flawless plant and turbine startups and shutdowns.
In 2020, PGE selected Yokogawa’s CENTUM DCS to replace the existing control systems for its steamfield above ground system (SAGS) in Units 1-4. When this project is completed, both the SAGS and the power generators of Units 1-4 of the plant will be controlled by Yokogawa’s systems. The newly integrated system will maximize the potential of Industrial-Internet-of-Things devices when introduced, boosting productivity and efficiency.
Furthermore in 2021, PGE chose Yokogawa for the procurement of a 500-kW binary organic rankine cycle (ORC) power plant to be connected to the SAGS of Lahendong Units 1-4. The plant is scheduled to be commissioned at the end of the same year. This will increase the efficiency of power generation in the Lahendong area since the power produced using excess brine (hot water) from the reservoir will be used for the SAGS instead of using electricity generated from Units 1-4. The success of this project will incentivize the development of renewable energy in the country. PT PLN is looking forward to further collaboration with Yokogawa.
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