Systems & Solutions
Systems & Solutions
Geothermal power generation harnesses the thermal energy from the Earth's magma to create steam that drives the turbine and generator to generate power.
The steam flow used for geothermal power is generated by rainwater seeping underground and being heated by the magma. The amount of heat that magma produces is limitless, and rainfall is infinitely repeated, as a result of one of the Earth's atmospheric phenomena. As such, use of underground steam is a part of infinitely-repeated energy collection cycles, and geothermal therefore is renewable energy.
* A study says it takes about three billion years for the temperature of the mantle (4,000°C) to decrease by 300°C. ("Introduction to Geothermal Energy", The Geothermal Research Society of Japan)
About 30% of CO2 emissions in Japan come from power stations. In order to reduce CO2 emissions to mitigate global warming, it is desirable to adopt generation systems with less CO2 emissions such as geothermal power.
Different from generation by solar power or wind power which is affected by seasonal and weather factors, geothermal power utilizing the stable thermal energy of the magma is free from seasonal and weather factors and offers stable and sustainable power generation.
Japan is a volcanic country with abundant geothermal energy. This power generation uses 100% domestic geothermal energy and is free from the effects of the economic changes abroad and the supply fluctuations associated with import of fuel resources needed for generation. It allows for independent and stable power generation.
Toshiba's geothermal power generation systems have the following characteristics.
• Super rotor technology
• Small-scale geothermal power generation system
Long-term operation of a geothermal power plant faces some issues. One is a reduction in the output and performance due to attenuation of geothermal resources. Another is deterioration in the performance and reliability arising from aging and damaging specific to geothermal turbines because the turbines are constantly exposed to steam flows that contain corrosive substances. Super rotor technology is a collective term for Toshiba's technologies to counter such issues and improve the reliability and performance of geothermal power generation.
The photograph on the right shows a last stage blade which was used for 10 years. It clearly shows that the integrity of the blade is maintained.
More than 20 years have passed since the commercial operation began at a geothermal power station in the US to which Toshiba delivered a steam turbine and generator and a reduction in the main steam pressure and flow rate, as well as aging due to corrosion and erosion, have been observed. The geothermal steam of the power station is highly corrosive, and turbine manufacturers struggled with stress corrosion cracking (SCC). Among them, Toshiba was the only company that provided a highly effective technology that was unprecedented.
In this project, Toshiba mainly applied new design to the nozzle and rotor and replaced the parts.
For 8-10 years since then, the parts were used without maintenance or major inspections, and there has been no reduction in the performance observed. Toshiba will continue to offer solutions for various issues that geothermal power generation systems may face.
Even if the available area is limited, Geoportable™ may offer a generation system that meets your requirements. In one project, 2 MW-class Geoportable™ were used and the entire power generation system was fit into a 250 ㎡ area.
Turbine, generator and other components of Geoportable™ are standardized based on an optimal skid plan that takes into account transport and on-site installation work. The equipment is assembled on a skid at a factory under rigorous quality control and shipped from the factory, which enables installation in a short time and early commercial operation. Additionally, the system employs a tubular condenser. Unlike a direct-contact condenser, a tubular condenser has no limitation in the height difference from the cooling tower and, for the Waita Geothermal Power Plant, construction work such as excavation was not necessary.
Auxiliary equipment such as condenser, cooling tower, gas extraction system, and various pumps are optimized to minimize the power required to operate them. By curbing the use of extra power, the net power output is maximized.
At the Waita Geothermal Power Plant, for which Toshiba supplied systems and took charge of a part of the construction work, Toshiba's 2 MW-class Geoportable™ was adopted and has contributed to the plant's high availability factor.
* Availability factor falls between December 2014 and September 2016, excluding periods of planned inspection and maintenance by the customer.
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