Engineering and design features of the Otake geothermal power plant

Abstract

Otake geothermal power plant, the first steam-water mixture type geothermal power plant in Japan, was accomplished in August, 1967, and is now operating successfully with 12,000 kW output. In comparison with the other geothermal power plants in the world, most of which use superheated steam at about 3–13 kg/cm 2 G, the features of Otake geothermal power plant are that it utilizes low-pressure saturated steam of 1.5 kg/cm 2 G separated from a mixture of hot water and steam. The design of this plant is based on the study and development of the following items: 1. (1) The study of the characteristics of the geothermal well. 2. (2) The study of the chemical properties of steam and hot water. 3. (3) The study of ideal material to be used for geothermal steam and water. 4. (4) The development of efficient water separators. 5. (5) The development of orifice water-level control method. 6. (6) The study of transmission of mixture of water and steam. 7. (7) The development of jet condensers. The features of this power plant are as follows: Rated output 10,000 kW Maximum output 13,000 kW Steam condition 1.5 kg/cm 2 saturated Condenser vaccum 687 mmHg Geothermal well 5 × 8 in.dia. Steam turbine Single cylinder impulse condensing Condenser Barometric spray type Cooling method Forced draft cooling tower Gas extractor Reciprocating type vacuum pump The steam condition was selected to get the maximum available energy from the geothermal well, and also to avoid power down in case of scale deposits. The condenser vacuum was selected considering all the factors, such as turbine output, turbine last blade length, size of both the condenser and cooling tower, and required number and power for cooling water pump, hot water pump, cooling tower fan and vacuum pump. In the case of geothermal power plants steam quantity is apt to increase in the future. Therefore, in order to be sure of stretched power operation in the future, turbines are designed to have a maximum output of 13,000 kW. The main problems of the geothermal plant which uses a mixture of hot water and steam are scale deposit and corrosion. This paper describes the design concept of the equipment which can withstand and work effectively against problems inherent to steam-water mixture type geothermal power plants. Overall inspection after 8670 hours of continuous operation showed no damaged to all the equipment.