3. Subtask 3 : Conceptual design of the total system

3.1 Conceptual design of the total system

3.1.1 R&D Goals

In FY 1993 as the first year of this research project, an investigation was conducted on the present situation of each individual technology of the processes from the hydrogen production to its utilization as well as that of the similar overseas projects. Based on this investigation, eligible technologies were selected which were applicable to WE-NET system, and the base system for the conceptual design which was to be conducted from the FY 1994 onward, was established. Based on these results, in FY 1994, the conceptual design, cost estimate and sensitivity analysis were carried out on the system composed of hydrogen production utilizing solid polymer electrolytes water electrolysis, mass transportation and storage of hydrogen using liquid hydrogen and hydrogen combustion turbine in order to evaluate as a whole system the technology currently under R&D in WE-NET. From FY 1995 to 1996, transportation and storage system using methanol and ammonia, which could be composed of existing technologies, was selected, and then technical development themes were indicated through conceptual design, cost estimate and sensitivity analysis on the system, and also through comparison with the system using liquid hydrogen.

In last fiscal year, followings were studied from various aspects as the items regarding a whole system which is independent of large scale and concentrated utilization by liquid hydrogen utilizing renewable energy, based on various suggestions to the interim evaluation of the WE-NET research and development which had been conducted in FY 1996 by Agency of Industrial Science and Technology and also from a view point of introduction and diffusion of hydrogen energy through the public as early as possible.

1. Alternative hydrogen production methods
2. Technology for dispersed utilization of hydrogen
3. Technology for hydrogen gas transmission pipeline
4. Application of life cycle assessment concerning CO₂ emission from each system

In this fiscal year as the final year of the WE-NET Phase I, followings were studied as the items to carry the result of the study in the preceding fiscal year a step further, based on the results of research and development of the element technology of each subtask.

1. Elaboration of conceptual design of the liquid hydrogen transportation and storage system, etc.
2. Study on economic efficiency in the power generating system with the hydrogen combustion turbine using hydrogen produced by alternative hydrogen production methods.
3. Study on economic efficiency in the dispersed utilization system of hydrogen
4. Study on CO₂ emission factor in the alternative hydrogen production system

3.1.2 Results in fiscal year 1998

3.1.2.1 Elaboration of conceptual design of the liquid hydrogen transportation and storage system, etc.

(1) Review on input data used in the system such as facilities costs

1. Input data for the following items was reviewed, based on the progress of the R & D in each subtask until FY 1998.
   The power generating facilities with the hydrogen combustion turbine were classified into two categories: "cryogenic oxygen production facilities" and "power generating facilities with hydrogen combustion turbine." Facilities costs, an annual expense ratio and a scale factor, etc. were set to each category.

   i) Liquid hydrogen transportation and storage system conducted in FY 1994 (See Fig.i)

   ii) Liquid hydrogen transportation and storage system established in FY 1998 (See Fig.ii)

2. The facilities costs and annual expense ratio of the solid polymer electrolytes type water electrolysis facilities were reviewed.

3. The annual expense ratio of other facilities such as a hydrogen liquefier was reviewed.

(2) Estimation of power generating cost

3.1.2.2 Study on economic efficiency in the power generating system with the hydrogen combustion turbine using hydrogen produced by the alternative hydrogen production method.

(1) Hydrogen production by the coal gasification and power generating system with hydrogen combustion turbine (See Fig.(1))

The coal gasification furnace adopted a pressurized two-stage entrained flow bed partial oxidation method using oxygen as a gasifying agent. The system was composed of a combination of this process and a hydrogen combustion turbine.

The capacity of the oxygen production equipment must be large enough to supply oxygen to both a coal gasification furnace and a hydrogen combustion turbine. The hydrogen production cost is 19.2 yen/Nm³ (local factor 70%) in case of the coal consumption of 3,000 t/day and the hydrogen production of 149 x 10³Nm³/h.

The power generating cost in a power generating system with a hydrogen combustion turbine were 15.1 yen/kWh and the net system energy efficiency was 30.1%.

(2) Hydrogen production by natural gas reforming and power generating system with hydrogen combustion turbine (See Fig.(2))

The process, using natural gas as raw material, of producing hydrogen by steam reforming is predominantly adopted on the chemical industry requiring a large amount of hydrogen such as ammonia and methanol synthesizing plants. The system is composed of this hydrogen production process to which a hydrogen combustion turbine and oxygen production facilities is added.

The hydrogen production cost is 13.6 yen/Nm³ (local factor 70%) in case of the natural gas consumption by this method of 79.1 t/h and the hydrogen production of 200 x 10³Nm³/h.

The power generating costs in the power generating system with a hydrogen combustion turbine were 11.9 yen/kWh and the net system energy efficiency was 29.8%.

3.1.2.3 Evaluation of power generating cost in each system with hydrogen combustion turbine

In the WE-NET system, a system using liquid hydrogen is advantageous to others in terms of energy efficiency, and a system using methanol in terms of cost. As seen in the present cost review, the future progress in the research and development leaves much to be likely to reduce cost of the liquid hydrogen system.

Neither liquid hydrogen system nor ammonia system emits CO₂ while the methanol system emits CO₂. In the case of being recovered and processed of this CO₂, the power generating cost with the methanol system will increase by about 6 yen. Taking into consideration, therefore, the recovery and processing of CO₂ at present, a liquid hydrogen system is advantageous to others in terms of the power generation costs.

However, there is a considerably wide gap between the above-mentioned cost and the power generating costs of approximately 9 or 10 yen/kWh in an existing power generating system. It is desired that further research and development be conducted in the future.

Among the alternative hydrogen production systems, the natural gas reforming hydrogen production system had almost the same system energy efficiency as that of the coal gasification hydrogen production system, but was lower in the power generating costs than the coal gasification system.

In comparison with power generating cost by renewable energy using overseas hydraulic power generation in the WE-NET system, which has been an original plan, the power generating cost by fossil fuel reforming are lower even if CO₂ fixation processing cost are taken into consideration. However, considering the fact that the economic efficiency of the CO₂ fixation processing technology has not yet been established at this moment in time, it is necessary to compare these two systems carefully.

3.1.2.4 Study on economic efficiency in the distributed utilization system of hydrogen

(1) Schematic flowchart of a system for generating power by supplying hydrogen to hydrogen diesel facilities (Fig (1))

(2) Schematic flowchart of a system for generating power by supplying hydrogen to fuel cell (Fig (2))

(3) Schematic flowchart of a system for supplying hydrogen to hydrogen automobile (Fig (3))

(4) Rough estimate of the cost of generating power in hydrogen diesel and fuel cell and the cost of supplying hydrogen to hydrogen automobile. The rough estimate of power generating costs and hydrogen supply costs is as shown in the table.

3.1.2.5 Study on CO₂ emission factor in the alternative hydrogen production system

As a result, assuming that operation life of the system is 30 years, the CO₂ emission factor (g-C/kWh) is calculated to be 297 g-C/kWh for the coal gasification hydrogen production system and 166 g-C/kWh for the natural gas reforming hydrogen production system.

The CO₂ emission factor in the coal gasification hydrogen production system is about the same as that in the existing coal fired power generation system. The CO₂ emission factor in the natural gas reforming hydrogen production system is about the same as that in the existing LNG fired power generating system and power generating system by the methanol transportation and storage(See Table 3-1-2-5).

3.1.2.6 Development of system design software

3.1.3 Subject in future