less coal–is also highly effective in reducing GHG emissions.

So far, Japan has conducted many studies on coal-fired thermal power generation technology and has enhanced the efficiency of power generation. Currently, research and development are being carried out on advanced ultra-super critical thermal power generation, integrated coal gasification combined cycle system, integrated coal gasification fuel cell combined cycle system, etc.

Advanced ultra-super critical thermal power generation is a technology used to improve power generation efficiency by tweaking the steam condition of the current pulverized coal thermal power generation method to produce high temperature and high pressure. The integrated coal gasification combined cycle system is an integrated technology that generates electricity using coal gasification, gas turbines, and steam turbines. The integrated coal gasification fuel cell combined cycle system is a technology that further adds fuel cells.

If the power generation efficiency can be raised from the current 42% to 65% by adopting and popularizing these technologies, carbon dioxide emissions can be reduced by approximately 40%. Furthermore, by combining these technologies with CCS, carbon dioxide emissions can be reduced to almost zero.

CCS is a technology that separates/captures carbon dioxide from exhaust gas emitted from large point emission sources, such as thermal power plants, and stores or sequestrates the carbon dioxide underground in geological formations or in deep ocean masses for long periods of time to prevent carbon dioxide from being released into the atmosphere. This technology is composed of four components, namely, separation/capture, transport, compression, and storage. Separation/capture technology and storage technology are at the core of this technological development. Japan started basic research on this in the

Overview of a long-term pilot plant for CO₂ capture (Photo: courtesy of Mitsubishi Heavy Industries, Ltd.)

late 1980s. To date, small verification tests using compression up to the 10,000-ton level have been carried out to study storage stability. One of the major hurdles for the commercialization of CCS is cost reduction. To lower the cost of separation/capture, which accounts for approximately 60% of the CCS cost, Japan has been developing elemental technology such as a highly efficient absorbing solution. To popularize CCS, we need to have environmentally effective and efficient methods to manage CCS. Japan is also developing such methods.

## (C) High-efficiency Natural Gas Thermal Power Generation Technology

Compared to other fossil fuels, natural gas is a clean energy that exerts relatively little environmental impact. Therefore, in line with the “Basic Energy Plan,” Japan continues to promote the adoption and increased use of natural gas while making efforts to strike a balance with oil, coal, nuclear energy, and other energy sources.

When burning fuel, gas from the fuel can be used to turn the turbine and generate electricity. Such internal-combustion turbines are small and lightweight, and have many merits including high output and quick activation. The combined cycle system combines the thermal generation and steam power generation, in which the residual heat from internal combustion is used to produce high temperature and highly pressurized steam to turn the steam turbine. Because natural gas thermal combined cycle power generation uses the two kinds of turbines for power generation, its heat efficiency reaches the 50% or more level. One way to raise the efficiency of natural gas thermal power generation even higher is to raise the temperature at the entrance of the gas turbine. Since Japan developed and installed a gas turbine with a temperature of $ 1100\ ^{\circ}C $ at its entrance in the 1980s, the heat resistance performance has improved. The current commercialized gas turbine has reached a temperature of $ 1500\ ^{\circ}C $ at its entrance.

Development of the next-generation gas turbine, which has a temperature of $ 1700\ °C $ at the entrance, is being pursued as a national project. When this gas turbine is developed, high-efficiency natural gas thermal power generation, which uses such turbines, will have a heat efficiency up to 56%, delivering even higher performance. The development of the high performance gas turbine is expected to increase the performance of the integrated coal gasification combined cycle system as well.