"Salt difference energy"

Salinity difference can mean the chemical potential difference energy between seawater and freshwater or between two seawaters with different salt concentrations. It is ocean energy that appears in the form of chemical energy. There is mainly a junction with the river and the sea. At the same time, salt lakes and underground salt mines in areas rich in freshwater can also use salt differential energy. Salt difference can be the most renewable energy source in ocean energy.

There is a large infiltration pressure difference between fresh water and seawater. Generally, when the seawater salinity is 3.5%, the chemical potential difference between the seawater and the river water has an energy density equivalent to a head of 240m head. Theoretically, if this The pressure difference can be harnessed, sending 0.65 kw·h of electricity per cubic foot of fresh water flowing from the river into the sea. A river with a flow rate of 1m3/S can generate 2340kw of power output. In principle, this water level difference can be achieved using a semipermeable membrane at the junction of saline and freshwater. If the salinity does not decrease during this process, the resulting infiltration pressure can increase the saline water surface by 240m. With this water level difference, energy can be extracted directly from the hydro-generator. If this energy of all the rivers in the world is extracted with a very efficient device, about 2.6 TW of electricity can be obtained. Even more noticeable is the potential of salt deposits. In the Dead Sea, the osmotic pressure between fresh water and salt water is equivalent to a head of 5000m, and the large amount of dry salt in the salt pan has more dense energy.

It is always the scientist’s ideal to use the enormous potential of the salinity difference between the sea and the land estuary. In the 1970s, many countries conducted many investigations and studies to find ways to extract salt difference energy. In fact, it is very difficult to develop and use salinity difference energy resources. In the simple example cited above, fresh water will dilute the salt water. Therefore, in order to maintain the salinity gradient, it is necessary to continuously add salt water to the pool. If this process continues continuously, the surface of the pool will rise 240m above sea level. For such a head, it requires a lot of power to pump salt water. The best salt difference practical development systems that have been studied so far are very expensive. This system uses an electrolysis process (actually a salt battery) to extract energy from salt water. According to a report in 1978, the investment cost is about $50,000/kw. The reverse osmosis method can also be used to raise the water level, and then let the water flow through the turbine. This method can generate electricity up to 10 to 14 US$/kw·h. Another technically feasible method is based on the principle that fresh and brackish water have different vapor pressures: the water is evaporated and condensed in brine, and the turbine is turned by the steam flow. This process will make the turbine work like an open ocean thermal power plant. The cost of the machinery required for this method is also almost equal to that of the open ocean thermal energy conversion plant. However, this method is not strategic because it consumes fresh water, while the ocean thermal power plant produces fresh water. Salt difference energy research results show that other forms of ocean energy can be more worthy of research and development than salt differences.

It is estimated that the salt difference in the estuaries of the world can reach 30 TW, and 2.6 TW may be used. The salt difference in China can be estimated as 1.1 × 10 ^ 8kw, mainly concentrated in the major rivers to the sea, at the same time, China's Qinghai Province and other places there are many inland salt lakes can be used. The study of salt difference energy takes the research of the United States and Israel as the first, and China, Sweden and Japan have also conducted some researches. However, on the whole, the research on salt energy, a new energy source, is still at the level of laboratory experiments and there is still a long distance from the demonstration application.

Power generation applications

1, osmotic pressure method

2, steam pressure method

3. Electrodialysis cell method

latest progress

Statkraft began researching the salt difference energy utilization device in 1997. In 2003, it built the world's first laboratory specializing in salt difference energy. In 2008, it designed and built a salt difference power station with a power of 2 to 4 kW.