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Tidal energy principle
Tidal power generation is simply to build a dam in a bay or tidal estuary to form a reservoir, and place a hydro-generator set in or near the dam, and use the fluctuation of seawater level during tidal fluctuation to drive the hydro-generator set to generate electricity when seawater passes through the hydro-turbine. From the point of view of energy, it is to use the potential energy and kinetic energy of seawater to convert it into electrical energy through hydro-generators.
Tidal energy is one of the most mature marine energy in the world, and the tidal power generation abroad is developing rapidly. European countries, with vast oceans and long coastlines, are rich, stable and cheap tidal resources, and have always been at the forefront of the world in tidal development and utilization. France, Canada, Britain and other countries keep the leading edge in the research and development of tidal power generation.
China's coastline is tortuous and long, mainly concentrated in the coastal areas of Fujian, Zhejiang, Jiangsu and other provinces. The development of tidal energy in China began in 1950s. After years of research and pilot projects on tidal power station construction, the tidal power generation industry in China has not only matured technically, but also made great progress in reducing costs and improving economic benefits. A number of tidal power stations with good performance and remarkable benefits have been built.
Insufficient power supply is an important factor restricting the development of China's national economy, especially in the eastern coastal areas. Tidal energy has the advantages of renewable, clean and predictable. Under the background of optimizing the power structure and promoting the upgrading of energy structure in China, the development of tidal power generation conforms to the social trend and is conducive to alleviating the energy shortage in the eastern coastal areas. The construction of tidal power station can create good economic, social and environmental benefits and has great investment potential.
2. Principles
tidal power generation
In a bay or tidal estuary, you can see the sea or river fluctuating twice a day, which is called tide in the morning and sunseeker at night. This phenomenon is mainly caused by the tidal force of the moon and the sun and the rotation effect of the earth. Tide is a kind of renewable energy with huge reserves, inexhaustible, no need for mining and transportation, clean and pollution-free To build tidal power stations, there is no need to emigrate or flood the land, and there is no problem of environmental pollution. In addition, it can also be combined with tidal power generation to develop comprehensive utilization projects such as reclamation, aquaculture and marine chemical industry.
The principle of tidal power generation is similar to that of ordinary hydropower generation. By leaving the reservoir, seawater is stored in the reservoir at high tide and stored as potential energy. Then, when the tide ebbs, seawater is released, and the turbine is driven to rotate by the difference of high and low tide levels, and the generator is driven to generate electricity. The difference is that seawater is different from river water, and the accumulated seawater has a small drop, but a large flow and is intermittent, so the turbine structure of tidal power generation should be suitable for the characteristics of low head and large flow.
Tidal power generation is a kind of hydroelectric power generation. Dams, gates and factories are built in conditional bays or tidal ports to form reservoirs, so that the water level of the reservoirs and the tidal level in the open sea form a certain tidal difference (i.e. working head), thus driving the hydro-generator set to generate electricity.
The technology related to tidal power generation has made rapid progress, and a variety of mechanical equipment has been developed to convert tidal energy into mechanical energy, such as propeller turbine, axial flow turbine, open cycle turbine and so on. Japan even began to use satellites to provide tidal information. The utilization of tidal power generation is becoming more and more mature and has entered the practical stage.
3. Physical condition
There are two physical conditions for tidal power generation: first, the amplitude of tidal power generation must be large, at least several meters; The second coastal terrain must be able to store a large amount of seawater and can be used for civil engineering. The working principle of tidal power generation is similar to that of general hydropower generation, that is, dams are built in estuaries or bays to form natural reservoirs, and hydro-generator sets are installed in seawalls. Tidal power stations can be single reservoirs or double reservoirs. The single-reservoir tidal power station has only one dam and one reservoir. In the old single-reservoir tidal power station, seawater enters the reservoir at high tide, and the hydro-generator set is driven by the tidal difference between the reservoir and the sea surface at low tide. It can't generate electricity continuously, so it is also called single reservoir single program tidal power station. The new single-reservoir tidal power station can generate electricity at high tide and low tide by using the special design of the reservoir and the function of sluice, but it can't generate electricity only at low tide when the water level inside and outside the reservoir is the same. This kind of power station is called single reservoir and double program tidal power station, which greatly improves the utilization rate of tidal energy.
Therefore, in order to make the tidal power station generate electricity continuously all day, it is necessary to adopt the dual-reservoir tidal power station. The double reservoir tidal power station has two adjacent reservoirs, and the hydro-generator set is placed in the dam between the two reservoirs. A reservoir only enters water at high tide (high water level reservoir), and a reservoir only releases water at low tide; There is always a water level difference between the two reservoirs, so it can generate electricity all day. ? Because the water level difference of seawater tide is much lower than that of ordinary hydropower stations, the tidal power stations should adopt hydro-generator sets with low head and large flow. At present, all the water is flowing? Hydro-generator set has been widely used in tidal power station because of its small size, light weight, short pipeline and high efficiency.
It is predicted that the annual output of tidal power stations in the world will reach 3x10/kloc-0 ~ 6x1010kw h by 2000. Tidal power stations not only generate electricity, but also have broad comprehensive utilization prospects, among which the biggest benefit is to reclaim land from the sea and increase land, in addition to mariculture and develop tourism. Because of the above reasons, tidal power generation has attracted the attention of all countries in the world.
4. The law of tide occurrence
Tides also appear regularly. The occurrence of tides is related to the sun and the moon, and also corresponds to the traditional lunar calendar in China. On the first day of the first lunar month, the sun and the moon are on one side of the earth, so tidal force is the largest, which will cause a "spring tide". Near the 15th or 16th day of the first lunar month, the sun and the moon are on both sides of the earth, and the tidal force of the sun and the moon will also cause "spring tide". When the phases of the current month are the first quarter moon and the second quarter moon, that is, August and 23rd of the lunar calendar, the tidal force of the sun and the tidal force of the moon cancel each other out, so a "small tide" occurs. Therefore, there is a saying in agricultural proverbs that "the spring tide begins on the fifteenth day of the first lunar month, and beaches can be seen everywhere on the 23rd of the eighth lunar month". In addition, there was a climax on the first day. Because the moon moves eastward more than 13 degrees on the celestial sphere every day, which is about 50 minutes in total, that is, the transit time of the moon (1 lunar day =24: 50) is delayed by about 50 minutes every day, (there will be tides in the next transit, usually twice a day), so the time of high tide is also delayed by about 50 minutes every day.
Working people in China have summed up thousands of years' experience and put forward many tidal calculation methods (tidal pushing time), such as the eight-point tidal calculation method, for example, the concise formula is:
High tide =0.8h×[=0.8h×[ Lunar date-1 (or 16)]+ high tide interval.
When the above formula can be regarded as one-day high tide, for the normal semidiurnal tide sea area, add or subtract 12: 25 (or add or subtract 12: 24 for calculation convenience) to get another high tide time. If you add or subtract 6: 00 and 12 points, you can get the time of low tide-low tide. However, due to the complexity of the movements of the moon and the sun, the spring tide may sometimes be delayed by one or several days, and the climax during lunar day is often one hour or several hours later than the transit time on the moon. In some places, the tide will rise as soon as the lunar calendar is over. Therefore, the time and interval of high tide and low tide are different every day. ? Now the world has already developed the technology of tidal power generation. 19 13, Germany established the first tidal power station on the North Sea coast. The first tidal power station was built in Shandong in 1957. In August 1978, 1, Baishakou Tidal Power Station in Rushan County, Shandong Province started to generate electricity, with an annual output of 2.3 million kWh. On August 4th, 1980, China's first "single-reservoir bidirectional" tidal power station-Jiangxia tidal test power station was officially put into operation, with an installed capacity of 3,000 kilowatts and an average annual power generation of/kloc-0.07 million kwh, which was the second largest tidal power station in the world at that time, second only to the French Lance tidal power station (with an installed capacity of 240,000 kilowatts and an annual power generation of 540 million kwh).
5. Single reservoir unidirectional power station
That is, only one reservoir is used to generate electricity at high tide (or low tide). The Shashan tidal power station in Wenling City, Zhejiang Province, China is of this type. Single-reservoir two-way power station uses one reservoir, but it can generate electricity at high tide and low tide, but not at low tide, such as Shizhenkou tidal power station in Dongguan, Guangdong Province and Jiangxia tidal power station in Wenling, Zhejiang Province. Double-reservoir bidirectional power station uses two adjacent reservoirs, so that one reservoir can feed water at high tide and the other reservoir can discharge water at low tide, so that the water level of the former reservoir is always higher than that of the latter reservoir, so the former is called the upper reservoir and the latter is called the lower reservoir. The hydro-generator set is placed in the dam between the two reservoirs, and the water level difference between the two reservoirs is always maintained, so it can generate electricity all day.
Advantages Tidal energy is a clean, pollution-free and renewable energy that does not affect the ecological balance. Every day the tide rises and falls, and it goes on and on. Inexhaustible, inexhaustible. It can be developed into an important supplementary energy source for life, production and national defense in coastal areas.
It is a relatively stable and reliable energy source, which is little affected by natural factors such as climate and hydrology, and the total annual power generation is stable, not affected by high and low water years and high and low water periods.
Tidal power stations do not need to flood a large number of farmland to form reservoirs, so there are no complex problems such as population migration and flooding farmland. So what? Use seawalls to promote? Reclaim a large area of tidal flat by silting up land, combining aquaculture, water conservancy, marine chemical industry and transportation. Engage in comprehensive utilization. This is a prominent advantage for coastal areas with large population and little arable land.
There is no need to build high dams for tidal power stations. Even if the dam is damaged by natural disasters such as war or earthquake, it will not cause serious disasters to downstream cities, farmland and people's lives and property.
Tidal energy combines primary energy and secondary energy, does not need fuel, is not affected by the price of primary energy, and has low operating cost, so it is an economic energy. But like Hechuan hydropower station, it has the characteristics of large one-time investment and low power generation cost.
There are many units, so there is no need to set up standby units.
6. shortcomings
Tidal range and water head often change in one day, and the output is intermittent, without special adjustment measures, which brings inconvenience to users. However, the operation plan can be made in advance according to the tidal forecast and run in parallel with the large power grid to overcome its intermittence.
tidal power generation
When the tide changes for half a month, the tidal range can be doubled, so the annual utilization hours to ensure the output and installed capacity are also low.
Tidal power station is built in the estuary of harbor, and the dam depth is generally long, so it is difficult to construct, treat foundation and prevent siltation. Hometown construction and electromechanical? Large investment and high cost.
Tidal power station is a form of power generation with low head and large flow. On the contrary, the enemy turbine is bulky and consumes a lot of steel. The structure of water inlet and outlet buildings is complex. Moreover, seawater and marine life have corrosive and polluting effects on metal structures and marine structures because they are immersed in seawater, so special anti-corrosion and anti-adhesion treatment is needed for marine life.
The tidal cycle is lunar day (24 hours and 50 minutes), the monthly cycle is about 14 days, and the daily high tide lags behind by about 50 minutes. The demand-load diagram of daily electricity given on sunny days is not well coordinated. ? Although tidal power generation has the above shortcomings, it can be improved with the continuous improvement of modern technology. The first disadvantage can be made up by using two-way or multi-reservoir power generation, using pumped storage and regulating the power grid. Adopting modern floating caisson construction can save civil investment; The corrosion of seawater and the attachment of marine life can be overcome by using stainless steel production equipment, vinyl resin series coatings and cathodic protection.
7.
Foreground tide is a worldwide phenomenon of periodic sea level change. Because of the two gravitational sources of the moon and the sun, the sea level fluctuates twice a day and night. Tide, as a natural phenomenon, provides convenience for human navigation, fishing and salt drying. What's more worth pointing out is that it can also be converted into electric energy, bringing people light and motivation.
Tidal power generation is an undertaking with great potential. After years of practice, it has basically taken shape in working principle and overall structure, and can enter the stage of large-scale development and utilization. Tidal power generation has broad prospects.
At the beginning of the 20th century, some countries in Europe and America began to study tidal power generation. The first tidal power station with commercial and practical value was the French Reims Power Station built in 1967. The power station is located at the mouth of the Lance River in the Gulf of Saint Marlowe, France. The maximum tidal range at Langsi Estuary is13.4m, and the average tidal range is 8m. A 750-meter-long dam spans the Longs River. The dam is a highway bridge for traffic, and there are lock, sluice and generator room under the dam. There are 24 bidirectional turbine generators installed in the engine room of Langsi Tidal Power Station, which can generate electricity at high tide and low tide. The total installed capacity is 240,000 kilowatts, and the annual power generation is more than 500 million kWh, which is input into the State Grid.
1968, the former Soviet Union built an experimental tidal power station of 800 kilowatts in Yawan, Kiisla, near Murmansk in the north. 1980, Canada built an experimental tidal power station with 20,000 dry watts in the Bay of Fundy. Experimental power stations and pilot power stations are used to demonstrate and prepare for the construction of larger practical power stations.
Due to the competition of cheap electricity charges of conventional power stations, commercial tidal power stations are rarely built and put into operation. However, due to huge tidal energy reserves and many advantages of tidal power generation, people still attach great importance to the research and experiment of tidal power generation.
According to the calculation of oceanographers, the global tidal power generation resources are more than 654.38+0 billion kilowatts, which is also an astronomical figure. The general survey and calculation method of tidal energy is: firstly, select the sites suitable for tidal power station construction, then calculate the developable installed capacity of these sites, and add up the estimated resources.
There are more than 20 places in the world suitable for building tidal power stations, which are being studied, designed and built. These include Cook Bay in Alaska, Fendi Bay in Canada, Severn Estuary in Britain, San Jose Bay in Argentina, Vandimen Bay in Darwin, Australia, Kambe Estuary in India, Haipin Bay in Okhotsk, Russia and Incheon Bay in South Korea. With the progress of technology and the reduction of tidal power generation cost, large-scale modern tidal power stations will be built and used in 2 1 century.
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