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By technology classification

Osaka Gas believes that technologies serve as the foundation of corporate competitiveness, and considers R&D to be one of the most important elements in the strategy to make a difference.
For this reason, Osaka Gas works actively on R&D and commercialization of new technologies, as presented below.

Cryogenic power generation system recovering LNG's cryogenic energy and generating power for energy and CO2 emission savings

Cryogenic power generator

The 150 t/h LNG cryogenic power plant will reduce CO2 emissions by approximately 15,000 tons a year.

Fig. 1: Cryogenic power generation system from Osaka Gas

Recovery, in form of electric power, of cryogenic energy, which would otherwise be wasted from LNG vaporization facilities, reduces power consumption at LNG import terminals, and by extension CO2 emissions from thermal power plants.
Osaka Gas has operated cryogenic power generation systems safely and stably for more than 30 years, the longest such operating period in the world.

Osaka Gas is a pioneer in the field of LNG cryogenic power generation plants using the Rankine cycle.

LNG terminal
in Osaka Gas
No. of units Operation commenced Power output [kW] Process LNG
Senboku 2 1 Dec. 1979 1,450 Rankine 60
Senboku 2 1 Feb. 1982 6,000 Rankine +
Direct NG expansion
Himeji 1 Mar. 1987 2,800 Rankine 120

Advantages of cryogenic power generation

■The simple processes have the following advantages:

  1. 1. While complex systems exist regarding Rankine-cycle LNG cryogenic power generation plants, such as two-stage expansion turbines and many heat exchangers, Osaka Gas embraces a process design philosophy emphasizing simple configuration for ease of operation and maintenance.
  2. 2. Osaka Gas proposes a simple configuration for cryogenic power generation, consisting of three shell & tube heat exchangers and a radial turbine, as shown in Fig. 1.
  3. 3. Its area requirement is approximately 30 m × 35 m, excluding the maintenance area.
  4. 4. The carefully selected intermediate heating medium (IHM) does not require a high maintenance cost during operation for an extended period of time.
  5. 5. The system starts automatically from a cold standby state and reaches a rated power operation state within 20 minutes. It takes only 10 minutes or less when shifting the operation mode from power generation to vaporization.
  6. 6. The system operates continuously even in the event of failure in power generating facilities including the turbine, heat exchange medium circulation pump and hydraulic system for turbine, with the vaporizer's performance remaining intact. This eliminates the need for a reserve vaporizer intended to ensure continued natural gas supply.

■ High corrosion resistance
Heat exchanger tubes made of titanium resist corrosion caused by seawater passing through them. Consequently, they contribute to reduced maintenance cost.

■ Osaka Gas's cryogenic power generation facilities also offer the following advantages:

  1. 1. Their well-designed control system and safety system prevent seawater from freezing or clogging in heat exchanger tubes.
  2. 2. If an accident occurs, the only operation required is to close the LNG inlet shutoff valve, which actuates the safety system to shut down both vaporizer and power generator safely.

Electricity generated by cryogenic power generation (example)

■ Services from Osaka Gas (Examples)

  1. 1. Offers feasibility studies and FEED and EPC work.
  2. 2. Supplies main equipment such as three heat exchangers and turbines on an FOB Japan basis.
  3. 3. Provides well-written operation and maintenance manuals.
  4. 4. Supports operation and maintenance work.

Recoverable cryogenic energy and challenges

Cryogenic LNG (−160℃) has a potential for cryogenic energy recovery of some 240 kWh per ton of LNG if 100% recovery is achieved. We believe that recovering cryogenic energy as motive power is highly important from an energy-saving point of view. Based on this belief, Osaka Gas actively promotes technology development, such as novel cryogenic power generation systems and cold energy storage.

Working principles of cryogenic power generation system

Three types of LNG cryogenic power generation facilities are presently in operation: Rankine cycle, direct NG expansion, and Rankine cycle + direct NG expansion. The operating principle is explained below, taking as an example a Rankine cycle using propane as intermediate heating medium.
The LNG pressure is increased to 3.5 to 4.5 MPaG by LNG pumps. The LNG vaporizer transfers heat from propane gas to LNG. Veaporized LNG then enters the NG trim heater and is heated to 0ºC or higher by sea water. The liquid propane condensed in the LNG vaporizer via heat exchange with LNG is pressurized by the circulation pump and sent to the propane vaporizer where it vaporizes at a pressure in accord with the temperature of sea water. Vaporized propane gas drives the turbine during the expansion process and generates electricity. Subsequently, the propane gas is condensed again in the LNG vaporizer.


Approaches taken by Osaka Gas toward cryogenic power plant development

Osaka Gas pioneered research and development of LNG cryogenic power generation facilities ahead of our competitors and constructed the first commercial unit. Since then, we have been actively working on R&D of LNG cryogenic utilization technology