1:45 PM - 3:15 PM
[O11-P10] The potential and challenges of binary geothermal power generation
Keywords:binary power generation, geothermal resources
1. Background and Purpose
The Naruko district, part of Osaki City in Miyagi Prefecture where our school is located, is nationally renowned for its abundant hot spring water and diverse spring qualities. We learned that geothermal power generation, which utilizes local geothermal resources—a distinctive feature of this region—has significant advantages such as low environmental impact. However, it also faces the reality of low adoption rates in Japan compared to the resource potential. The utilization of geothermal energy is a critical component in building a sustainable society.
Among the power generation methods of geothermal energy is binary power generation. This method enables power generation with relatively low boiling-point media, allowing Japan to more fully harness its geothermal resources. We focused on binary power generation and, through literature surveys, embarked on this research to investigate its current state and challenges.
2. Methods
We collected information on geothermal power generation by visiting geothermal power plants and consulting reference materials. Additionally, we deepened our understanding by creating a geothermal power generation model.
3. Results
Regarding flash and dry steam methods, local investigations revealed that corrosion of the pipes used to extract the necessary hot water or steam from underground, as well as blockages due to impurities, often make it challenging to maintain a stable supply of hot water over an extended period. This necessitates digging new production wells each time, driving up maintenance costs for geothermal power facilities.
On the other hand, binary power generation—which utilizes the hot water from sources like hot spring origins—generates electricity by using the steam of low boiling-point catalysts. It allows power generation by leveraging heat during the cooling of high-temperature sources. Therefore, unlike the aforementioned methods, binary power generation is considered to reduce maintenance costs as there is no need to excavate new production wells.
Furthermore, binary power generation can be miniaturized, making installation relatively easy.
However, a disadvantage noted during visits to binary power plants was that some facilities had all foreign-made equipment. Additionally, frequent maintenance was required, with parts imported from overseas, which was a factor contributing to high overall maintenance costs for the facility.
Next, to enhance understanding, we created a simple geothermal power generation model of the dry steam method. Using an induction heater, pressure cooker, and other components, we conducted an experiment to replicate geothermal power generation.(figure1)
In the experiment, the energy conversion efficiency was below 0.01%, which was 1/4000th of the power consumption of the induction heater used.
To identify the cause of this efficiency, thermal imaging suggested heat loss near the steam outlet and the connection between the pressure cooker and the vinyl pipe. Methods to increase efficiency, such as using insulation to prevent heat loss and modifying propeller shapes, are necessary.
The geothermal power generation model produced in the experiment was also used beyond experiments, such as in presentations and outreach lessons, to promote knowledge about geothermal power generation.
Additionally, we are creating a binary power generation model(figure2,4). The design involves using alternative fluorocarbon as the medium due to its low boiling point properties. Efforts include sealing the room where the turbine rotates, and coupling the turbine with an external generator using magnets(figure3). To further develop concepts for non-contact magnetic binary power generation, we visited Prospine, a company in Osaki City that sells magnets.
4. Discussion and Future Challenges
If cost and maintenance frequency issues with binary power generation are resolved, it is expected to further accelerate the utilization of geothermal resources.
For the creation of the binary power generation model, experiments are planned at Tohoku University to use a low boiling-point medium (assuming 'R-1234yf' with a boiling point of 29°C) instead of water. Additionally, dry ice ethanol capable of cooling to -72°C will be used to cool the low boiling-point medium.
Moving forward, we aim to operate the binary power generation model, compare it with the completed dry steam method generation model, and utilize it in outreach lessons for elementary and middle school students to explain geothermal power generation.
The Naruko district, part of Osaki City in Miyagi Prefecture where our school is located, is nationally renowned for its abundant hot spring water and diverse spring qualities. We learned that geothermal power generation, which utilizes local geothermal resources—a distinctive feature of this region—has significant advantages such as low environmental impact. However, it also faces the reality of low adoption rates in Japan compared to the resource potential. The utilization of geothermal energy is a critical component in building a sustainable society.
Among the power generation methods of geothermal energy is binary power generation. This method enables power generation with relatively low boiling-point media, allowing Japan to more fully harness its geothermal resources. We focused on binary power generation and, through literature surveys, embarked on this research to investigate its current state and challenges.
2. Methods
We collected information on geothermal power generation by visiting geothermal power plants and consulting reference materials. Additionally, we deepened our understanding by creating a geothermal power generation model.
3. Results
Regarding flash and dry steam methods, local investigations revealed that corrosion of the pipes used to extract the necessary hot water or steam from underground, as well as blockages due to impurities, often make it challenging to maintain a stable supply of hot water over an extended period. This necessitates digging new production wells each time, driving up maintenance costs for geothermal power facilities.
On the other hand, binary power generation—which utilizes the hot water from sources like hot spring origins—generates electricity by using the steam of low boiling-point catalysts. It allows power generation by leveraging heat during the cooling of high-temperature sources. Therefore, unlike the aforementioned methods, binary power generation is considered to reduce maintenance costs as there is no need to excavate new production wells.
Furthermore, binary power generation can be miniaturized, making installation relatively easy.
However, a disadvantage noted during visits to binary power plants was that some facilities had all foreign-made equipment. Additionally, frequent maintenance was required, with parts imported from overseas, which was a factor contributing to high overall maintenance costs for the facility.
Next, to enhance understanding, we created a simple geothermal power generation model of the dry steam method. Using an induction heater, pressure cooker, and other components, we conducted an experiment to replicate geothermal power generation.(figure1)
In the experiment, the energy conversion efficiency was below 0.01%, which was 1/4000th of the power consumption of the induction heater used.
To identify the cause of this efficiency, thermal imaging suggested heat loss near the steam outlet and the connection between the pressure cooker and the vinyl pipe. Methods to increase efficiency, such as using insulation to prevent heat loss and modifying propeller shapes, are necessary.
The geothermal power generation model produced in the experiment was also used beyond experiments, such as in presentations and outreach lessons, to promote knowledge about geothermal power generation.
Additionally, we are creating a binary power generation model(figure2,4). The design involves using alternative fluorocarbon as the medium due to its low boiling point properties. Efforts include sealing the room where the turbine rotates, and coupling the turbine with an external generator using magnets(figure3). To further develop concepts for non-contact magnetic binary power generation, we visited Prospine, a company in Osaki City that sells magnets.
4. Discussion and Future Challenges
If cost and maintenance frequency issues with binary power generation are resolved, it is expected to further accelerate the utilization of geothermal resources.
For the creation of the binary power generation model, experiments are planned at Tohoku University to use a low boiling-point medium (assuming 'R-1234yf' with a boiling point of 29°C) instead of water. Additionally, dry ice ethanol capable of cooling to -72°C will be used to cool the low boiling-point medium.
Moving forward, we aim to operate the binary power generation model, compare it with the completed dry steam method generation model, and utilize it in outreach lessons for elementary and middle school students to explain geothermal power generation.