Around 2020, the mixed gas referred to as "Hythane" which is formed by mixing hydrogen of up to 20% to natural gas is fed through the pipeline. Electricity is generated making use of the natural energy including the solar energy, the wind energy and the water energy, and water is electrolyzed to form hydrogen. Following this strategy, the CO2 concentration in the atmosphere will be stabilized from the present concentration of 360 ppm to about 450 ppm in the middle of the next century as shown in Fig.7, contrary to most expectations including the IPCC (Intergovernmental Panel on Climate Change), and then, it will be gradually dropped in tens of years. We feel reassured because the Institute known as its strict criticism in USA announced such a prediction to indicate that then, direction of our strenuous efforts is not mistaken. It is told that the natural gas pipeline has a semi-permanent service life once it is buried, and thus, it is also an effective and important social capital in the above-described age of hydrogen.
6. Prospect of Marine Engines
If the above-described strategy is followed, the CO2 emission should be reduced possible. The great proposition how the marine engines should be in such a "system energy" age will be discussed below. It goes without saying that the physical distribution by ships is necessary and essential for Japan which is surrounded by the seas and a large resources-importing country.
The first renewal timing of about 300 VLCCs (large oil tankers of 200,000 DWT or over) which were built in 1970s was estimated to be around 2000, and their engines are replaced by the long stroke engines with lower fuel consumption. The number of cylinders is reduced, and the cargo space is increased. However, taking into consideration the dimensions of the engine room and the loading of the fuel oil, it is difficult to say that the ships carry the cargo space or their own fuel. A quarter of the deadweight tonnage is occupied by the fuel oil for the ships engaged in the service between the Far East and Europe. Even when an effort is paid to the low fuel consumption, a large volume of fuel must be loaded if the speed and the output are increased so long as the oil-fired engines are used, leaving the essential problem unsettled.
In addition, if the new Annex of "MARPOL 73/78" of IMO is ratified, the regulation on emission of the air pollutant including NOx and SOx is applied to the ships of not less than 400 GT. Though the present regulated value is not stringent yet, the basic direction of regulation is sufficient to threaten the existence of the diesel engines as the marine main engines. If the technology for the countermeasures to reduce NOx and SOx is truly effective, it can not be achieved without any sacrifice of the economy. By the time around 2030 of the next renewal timing of the VLCCs, it is necessary to achieve the sufficient consideration on the next generation marine energy system, and to establish the preparation system therefor. It is difficult to imagine that the low grade fuel oil-fired diesel engine still maintains its life while sustaining the cost for the environmental countermeasures after 2030. Now that CO2 is discussed in addition to NOx and SOx, and it is a good timing to fully discuss how the next generation marine energy system should be.
The basic principle of the "system energy" described in the lecture is the assembly of the highly efficient energy system to suck the heat to the marrow from the high temperature to the low temperature by combining the established existing basic technologies with each other. This principle is based on the principle of the thermodynamics, and immobile so long as the heat engine is used. Other engines than the heat engine such as the fuel cell is not included. The engines in which natural gas, methanol or hydrogen is used for the fuel will be limited to medium to small ships for coastal services though in 2030. For the VLCCs and high-speed container carriers, the possibility of the nuclearpropelled ships should be sufficiently examined together with the highly efficient combined cycle engine as the "system energy" technology with A-oil for its fuel.
Two kinds are included in the combined cycle engines. The first one is the "turbo compound" engine, and the second one is the "gas turbine and steam turbine compound cycle" engine. In the "turbo compound" engine, the gas turbine is driven by the exhaust gas from the diesel engine, and the output of the turbine is applied to the driving force of the main shaft through the reduction gear simultaneously with the turbo-charging. The "gas turbine and steam turbine compound cycle" engine employs the regular land-based combined cycle, and its efficiency is increased by combining the possibly high-temperature gas turbine with the steam turbine.
