We operate the Onuma and Sumikawa geothermal power plants in the Hachimantai area. Electricity generated at these plants supplies nearly all the demand of those who live in the Kazuno area. The following is how a geothermal power plant works, what it is and how it is connected to our everyday life.
1.Opening
Mitsubishi Materials Corporation had operated mining and refining businesses in Akita Prefecture. We knew that the unit cost of power must be cut as part of our cost lowering measures. In the mid-1960s, we explored possibilities to build the Onuma Geothermal Power Plant by using technology we acquired from our experiences on natural resource development. In the 1970s, Japan realized the necessity of developing alternative energy resources to oil, after the country went through two oil crises and the Iranian Revolution. That was when the Sunshine Program started. In the early 1980s, exploration for the Sumikawa Geothermal Power Plant began.
2.Characteristics of the Hachimantai Area
The Hachimantai area is made mainly of Quaternary volcanic rock. Although its surface is covered with thick greenery, extremely active geothermal activities can be detected underneath. It is an area suitable for geothermal development with resource potential. Fortunately, we were one of the community members of the area through the operation of the nearby Osarizawa Mine. We also had hydroelectric power plants in the area along the Komata River and elsewhere. These factors contributed to our geothermal power generation development in the region.
3.Principle of Geothermal Power Generation
Areas with high underground temperature and pressure often have high temperature geothermal water. When the pressure is high enough to suppress boiling, the geothermal water exists as a liquid. When the pressure lowers, the geothermal water boils and separates into steam and hot water. This is the principle of geothermal power generation. Geothermal water spouts out of the wells. Then, the steam rotates turbines and generates electricity. It is believed that rainwater and seawater that filters into the ground is heated from transmitted magma heat.
4.Excavation of Geothermal Wells
The depth of production wells at our geothermal power plants is 1,500 to 2,500 meters, while that of wells to retrieve geothermal water separated on the surface is 1,000 to 1,500 meters. The well is screened from the bedrock with a casing and cement, and the steel pipe through which the geothermal water enters and exits has slits. In order to reduce the surface land use as much as possible, all wells are grouped at a few pads. Because of this, they are excavated on an incline. The direction and the inclination are controlled on the surface when we sink a well.
5.Operation of Geothermal Power Plants
The Onuma Geothermal Power Plant began operation more than 25 years ago, while five years have passed since the Sumikawa Geothermal Power Plant began operation. Both plants have been operating smoothly. Moreover, their facilities are designed to harmonize with their surroundings.
6.Multipurpose Use
Waste steam from geothermal power plants can be directed into stream water to create hot spring water, while the separated hot water can be used to create warm water through the heat exchange process before sending it back underground. Such hot spring and warm water can be used at nearby hotels, swimming pools and horticultural facilities. The Onuma Geothermal Power Plant is making efficient use of geothermal resources.
7.Advantages of Geothermal Power Generation
Prevention of global warming is called for, and control over carbon dioxide emissions has become a major challenge. Geothermal power generation has been praised for its small carbon dioxide emissions. For Japan, a country with limited natural resources, the heat from magma, which brings about volcanic activity, is one of the most important domestic resources. That heat can be used efficiently in geothermal power generation.
1. Address
District of Kidometai, Hachimantai, Kazuno City, Akita Prefecture
2. Proprietor
Power generation: Tohoku Electric Power Co.
Steam production: Mitsubishi Material Co.
3. Power output
Installed capacity: 50,000kW
Authorized capacity: 50,000 kW
4. Geographical information of the power station
(1) Location
The power station is about 1,062 m above sea level in the district of Hachimantai occupying the southernmost part of Kazuno City, Akita Prefecture.
The Mount Hachimantai with an elevation of 1,613 m, which is on the border between Iwate and Akita Prefectures, is about 6 km southeast of the power station.
There is the spa of Hachimantai in the neighborhood, which has a regular bus service from Hanawa City.
(2) Relationship with the national park
While the power plant is outside the Towada-Hachimantai National Park, it is in a district designated as a forest area by the Law of National Land Planning.
5. History of development
Rough survey period I: 1965-1973
Mitsubishi Metal Co. (Mitsubishi Material Co. at present) conducted a regional survey to select the Sumikawa district as a promising area along with the Onuma district.
Rough survey period II: 1974-1980
Mitsubishi Material Co. implemented additional ground surveys and drilling of investigation wells.
Further, state-run surveys were also introduced, including Minute Investigations for Geothermal Development, Nationwide Geothermal Basic Investigations, Regional Surveys on Geothermal Structures, and Environmental Surveys for Geothermal Energy Development.
Steam spouting was confirmed in an investigation well N52E-SM-2, triggering off the start of a full-scale investigation.
Minute survey period I: 1981-1985
A cooperative development commenced between Mitsubishi Material Co. and Mitsubishi Gas Chemical Co., which drilled four investigative wells to confirm powerful steam spouting out of the well S-4.
A cooperative investigation committee with Tohoku Electric Power Co. was established to study the feasibility of construction of a 50-MW power plant.
Minute survey period II: 1986-1990
Mitsubishi Material Co. and Mitsubishi Gas Chemical Co. made a drilling plan of investigative wells for the construction of the 50-MW power plant.
Besides, state-run projects were introduced, which are concerned with Verification Surveys on Technologies for Geothermal Prospecting (in Sengan District) and Surveys for Promotion of Geothermal Development.
A three-month-long total discharge test test was implemented in 1990 to confirm the amount of steam equivalent to 50 MW, resulting in the conclusion of a basic agreement for development between Tohoku Electric Power Co. and Mitsubishi Material Co.
Construction and operation period: 1991-
After an environmental assessment between 1990 and 1991, a construction plan for the power plant was approved in March, 1992 to commence the construction work, and the business operation started in March, 1995.
6. General Geology
The Sumikawa district is in the northern part of Hachimantai area, one of the most prominent volcanic and geothermal regions in Japan.
In the neighborhood are distributed a lot of volcanoes, such as Hachimantai, Iwatesan, and Akita-Komagatake.
They are largely aligned in E-W or NE-SW direction. The Quaternary volcanoes are underlain by a N-S trending horst-graben structure.
The Sumikawa district is located at a junction between the N-S trending Hanawa trough and the E-W trending Hachimantai-Yakeyama-Moriyoshiyama volcanic row.
Such a tectonic setting is thought to have contributed to the formation of prominent geothermal resources in this area.
As a ground indication of geothermal activities in this district is cited the distribution of numerous hot-springs and fumaroles, such as Shibari, Zenikawa, Toroko, Akagawa, Sumikawa, Goshogake, Fukenoyu, Obuka, and Tamagawa from north to south.
Further, the Volcano Yakeyama have been recorded nine eruptions since 807.
The present area is underlain by siliceous shale in the pre-Daishima stage (A formation), andesitic to dacitic lavas and pyroclastics (B, C, and F formations) and the contemporaneous brown- to black-colored siltstone and shale (E formation) ranging from Daishima stage to the Funakawa stage. Further, they are covered by Quaternary lake sediments (K formation) and andesite lavas (L formation).