JP2014118813A - Marine hot water power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a thermal power generating system with sea bottom hot water being applied as a heat source.SOLUTION: In order to suppress development cost and construction cost, the upper-most part of a power generating system major constituent element is set at a low depth from a sea surface or below and an entire system is moored at the sea bottom part, influence of tide power, ocean current and weather or the like over the power generation system is made minimum. Also, in order to suppress the cost, marine space down to the sea bottom is effectively utilized to constitute a steam generation and condensate system having a simple pipe structure. In order to make influence such as corrosion by salt contained in hot water minimum, hot water steam is not sent directly to a power generation turbine, but a heat exchanger is used to heat another thermal medium.

Description

The present invention relates to a geothermal power generation system using subseafloor hot water as a heat source.

Geothermal power generation is attracting attention as a clean energy supply source along with solar power generation and wind power generation. However, although geothermal power generation on land has been increasing year by year, the largest geothermal power plant in Japan has an output of 112 MW, which is about 1/10 of that of a nuclear power plant. Japan's total is 540 MW, which is just one medium-sized nuclear reactor.

In addition, existing onshore geothermal power generation has severe restrictions on installation. In the first place, it is difficult to get permission in a national park where there are many heat sources. In order to open up the forest and construct a power plant facility, it is necessary to investigate the impact on the surrounding natural environment. If there is a hot spring area nearby, the effect on the heat source supply to the area must be investigated. For this reason, it is necessary to determine the construction site, the steam well, and the location to dig the reduction well after careful geological survey.

We think that it would be useful if geothermal power generation could be realized using hot water under the ocean floor as a heat source.

However, various problems occur when installing power generation facilities in the ocean. First, since the available hot water contains salt derived from seawater, when steam is generated as it is from the hot water, the salt contained in the steam cannot be ignored such as the corrosive action on the internal structure of the piping and power generation turbine. Will have an impact.

When constructing a power generation system on an offshore fixed platform, the distance to the hot water source does not change due to tidal forces, ocean currents, weather, etc., and piping becomes easy. Cost.

When building on an offshore floating platform, it is difficult to absorb the fluctuations in the distance from the hot water source due to tidal forces, ocean currents, weather, etc., with the piping.

Further, when all the power generation systems are installed on the deep sea bottom, the development cost and the construction cost become enormous so that all the components can withstand the installation depth.

Using hot water containing salinity, the power generation medium such as pure water is evaporated by heat exchange by heat exchange, sent to the power generation turbine, and the low-temperature and low-pressure steam used for power generation is condensed by the condenser, and again Supplying to the steam generator minimizes the impact of salinity on piping and power generation turbines. In addition, the steam generator and condenser are installed in the sea, and the power generation turbine body is installed in the sea at a low depth. Corresponding to pressure, the development cost is minimized, and it is not necessary to construct an offshore fixed platform that requires a large construction cost. (Claim 1)

A steam generator with a simple tube structure that secures the heat exchange area mainly by its length is constructed by using the distance between the power generation turbine installed in the deep sea and the hot water supply port on the seabed. Reduce development and construction costs by simplifying the structure. In addition, the heat supply fluid and the heating fluid are counterflowed to increase heat efficiency by raising the hot water once and then exchanging heat. The hot water supply circulation is realized by the hot water supply pressure and the negative pressure from the descending hot water side generated by the temperature density difference between the rising hot water and the descending hot water. (Claim 2)

Similarly to the above, the condenser also uses a structure with a simple tube structure that uses the distance to the seabed to secure the heat exchange area mainly by its length, so that the development cost and construction Reduce costs. Condensate supply circulation is realized by the action of gravity, which always keeps the condensate level difference between the steam generation side and the steam condensate side constant against the pressure difference between the steam generation and the condensate. (Claim 3)

By mooring the above steam generator, condenser, and power generation turbine together on the seabed, the influence of sea level altitude fluctuations due to tidal forces can be eliminated. It is inevitable that the distance of fluctuates. In order to absorb this variation, the connection between the steam generator and the seafloor fixed part including the hot water supply port is connected with a pipe having a flexible structure. (Claim 4)

It is a schematic diagram showing the whole power generation system in the present invention.

FIG. 1 shows a schematic diagram of the overall configuration of the power generation system.

The power generation system includes a power storage plant ship 11 that floats on the sea, a power generation turbine ship 12 that is installed in a shallow sea and anchored at a fixed distance from the bottom of the sea by an anchor cable 31, a steam condensate pipe 22, a condensate pipe 23, a steam generation pipe 24, The steam pipe 25, the hot water rise pipe 28, the hot water down pipe 29, the hot water supply pipe 26 fixed to the sea bottom, the solid matter remover 13, and the soft water rise pipe 28 that connects the solid matter remover 13 and the hot water rise pipe 28. It consists of a structural tube 27, a main anchor 14 and the like.

However, when the land is close, it is possible to omit the power storage plant ship 11 and transmit power from the power generation turbine ship 12 to the land.

Since the power generation turbine ship 12 has a manhole 21 exposed on the sea, a worker can enter for maintenance work or the like.

The heat transfer pipe is only the steam condensate pipe 22 and the steam generation pipe 24, and the other pipes are constructed as heat insulation pipes.

Since the flexible tube 27 only needs to withstand the hot water supply pressure from the hot water supply tube 26, the flexible tube 27 is mainly made of a material that can withstand the high temperature of the hot water.

The buoyancy and its own weight including the main anchor 14 are adjusted so that sufficient ground friction is obtained between the main anchor 14 and the seabed for the entire seabed mooring portion. Also, in order to keep the swinging due to ocean currents, weather, etc. small, it is effective to increase the buoyancy of the upper structure part and make the main anchor heavy, but it is minimal considering the stress applied to each part of the structure. Keep on.

The anchor cable 31 lowered from the power generation turbine ship 12 to the part other than the main anchor 14 is also effective in suppressing swinging due to ocean currents, weather, etc., but also has a role of absorbing Coriolis force due to earth rotation.

In consideration of abnormal sea level descent due to a tsunami or the like, the lower part of the condensate pipe 23 and the steam generation pipe 24 is connected to the main anchor 14 with an anchor cable 31 with a certain margin (appropriate apparatus descent limit 56). Regarding the abnormal rise in sea level, a sufficient safety distance 57 is taken so that the power storage plant ship 11 does not ride on the power generation turbine ship 12, and the power line 32 and the anchor cable 31 connecting the ships are also taken into account the fluctuation due to the tidal force. Give extra length.

Solid water is removed from the hot water supplied from the hot water supply pipe 26 on the seabed by the solid material remover 13. This is to prevent solid matter from accumulating on the flexible structure tube 27 and the hot water rising tube 28 to cause clogging. The hot water that has passed through the solid substance remover 13 rises the flexible structure pipe 27 and the hot water rise pipe 28 by the supply pressure from the hot water supply pipe 26 and the negative pressure due to the hot water descending the hot water descending pipe 29. To do. The hot water that has reached the hot water descending pipe 29 heats the condensate inside the steam generating pipe 24, which is a heat transfer pipe, and descends the hot water descending pipe 29 while lowering the temperature itself by heat exchange. The hot water whose temperature has reached the bottom of the hot water downcomer 29 is discharged into the sea. Although it is possible to dig a reduction well and return it to the bottom of the sea without releasing it into the sea, it is not adopted in the configuration example of FIG. 1 in consideration of cost. The reason why the hot water is once raised and then exchanged is to increase the thermal efficiency by using a heat supply fluid and a heating fluid as a counter-flow type.

The steam generated by heating the condensate in the steam generation pipe 24 passes through the steam pipe 25 and reaches the power generation turbine ship 12 to rotate the power generation turbine and the generator. The electric power obtained by turning the generator is sent to the storage plant ship 11 and stored. Although the power storage method in the power storage plant ship 11 is not specified, it is conceivable to synthesize and accumulate carbon oxides using hydrogen obtained by electrolysis or using hydrogen as a raw material. The steam whose temperature has been lowered after being used for power generation in the power generation turbine ship 12 is further cooled in the steam condensate pipe 22 to be condensed and liquefied. The steam condensate pipe 22 is a heat transfer pipe and is cooled by the surrounding seawater. The cooled and liquefied condensate passes through the condensate pipe 23 and is supplied again to the steam generation pipe 24.

The condensate level on the steam condensate pipe 22 and the condensate pipe 23 side during power generation is the low-temperature side condensate level 41, and the condensate level on the steam generation pipe 24 and steam pipe 25 side is the high-temperature side condensate level 42. The difference between the two condensate levels is called the condensate level difference 54, and indicates the difference in vapor pressure between the high temperature side vapor pressure and the low temperature side vapor pressure.

The pressure in the condensate system pipe, the steam condensate pipe 22, the condensate pipe 23, the steam generation pipe 24, and the steam pipe 25 is lower than the pressure in the sea depth. Therefore, these tubes need to have compressive strength that can withstand negative pressure. At least, the entire pipe has a compressive strength that can withstand negative pressure equal to or higher than seawater pressure at the low-temperature condensate level depth 55.

The steam generation pipe upper limit depth 52 is limited by the temperature of hot water supplied from the hot water supply pipe 26. For example, when the hot water temperature is 200 degrees Celsius or higher, there is a risk of boiling if there is no pressure of about 16.5 atmospheres or more, so a depth of about 155 meters or more is required.

When hot water of 200 degrees Celsius or higher is obtained from the seabed at a depth of 1000 meters, assuming that the lower end of the hot water descending pipe 29 is about 20 meters from the seabed, the maximum length of the steam generation pipe 24 is about 825 meters. It can be secured. However, if the steam generation pipe 24 is secured at the maximum length, it is assumed that the condensate level difference (steam pressure difference) 54 is about 160 meters (about 16 atmospheres) and the height of the power generation turbine ship 12 is 10 meters. The length of the water pipe 22 cannot be secured. If the length of the steam generation pipe 24 is 725 meters, the length of the steam condensate pipe 22 can be secured to about 85 meters. It is necessary to determine the optimum values of these lengths from the heat transfer coefficient determined by the material of the steam condensate pipe 22 and the steam generation pipe 24. Moreover, you may adjust heat transfer amount not only by length but by thickness, the number, etc.

It is reasonable to consider that the place where there is a deep sea where enough hot water is available to generate electricity in the ocean is far away from the generation energy demand area. Therefore, energy transportation to the demand area becomes a problem. Assuming that there is a distance of up to several thousand kilometers to the demand area, the power supply by the transmission line is huge in terms of installation cost, and it is difficult to keep the transmission loss within an allowable range.

However, it is considered that the problem can be solved by electrolyzing seawater with the generated power to generate hydrogen and transport it as a secondary energy to the demand area. To that end, it is necessary to expect cost reductions through the development of mass transport technology for hydrogen. In addition, if technology that can efficiently produce hydrocarbon compounds such as methane and methanol from hydrogen and carbon dioxide is put into practical use, it can be used as a treatment plant for carbon dioxide generated in thermal power plants, and the produced hydrocarbon compounds. Can be transported to the demand area at a relatively low cost by applying the current natural gas transportation technology.

Conversely, it may be possible to bring the demand itself close to the power generation facility. It is also conceivable to construct a plant or the like that requires high power on land that is within the range where power can be transmitted from the power generation turbine ship, or tow a plant built on a floating floating platform and bring it close. If realized, there is a possibility that competitiveness can be secured as a plant that covers all electric power with renewable energy.

DESCRIPTION OF SYMBOLS 11 Power storage plant ship 12 Power generation turbine ship 13 Solid substance remover 14 Main anchor 21 Manhole 22 Steam condensate pipe 23 Condensate pipe 24 Steam generation pipe 25 Steam pipe 26 Hot water supply pipe 27 Flexible structure pipe 28 Hot water rise pipe 29 Hot water fall Pipe 31 Anchor cable 32 Power line 41 Low temperature side condensate level 42 High temperature side condensate level 51 Sea level altitude at low tide 52 Upper limit depth of steam generation pipe 54 Condensate level difference (steam pressure difference)
55 Low-temperature side condensate level depth 56 Device descent allowable limit 57 Safety distance

Claims (4)

It is a power generation system that uses seafloor hot water as a heat source. It is installed in the sea with a steam generator and condenser, and a power generation turbine system in a deep sea. A geothermal power generation system characterized by maintaining vertical stability with buoyancy. The hot water supply circulation of heat exchangers (steam generators) installed in the sea is the falling heat generated by the natural supply pressure of hot water and the density difference between the rising hot water and the falling hot water. 2. The geothermal power generation system according to claim 1, which is mainly realized by negative pressure from the water side. The condensate supply circulation of the condenser installed in the sea mainly has the function of gravity to keep the condensate level difference between the steam generation side and the steam condensate side constant against the pressure difference between the steam generation and the condensate. It implement | achieves, The geothermal power generation system of Claim 1 characterized by the above-mentioned. The geothermal power generation system according to claim 1, wherein the seabed fixed part and the seabed mooring part are connected by a flexible structure pipe.

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