Solar thermal power generation technology
Solar thermal power generation technology Li Bin, Li Anding (Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100080) Considering: 1 It is very important to realize low-cost investment and high-reliability operation of solar thermal power generation system; 2 to achieve large-scale development. Establish large-scale grid-connected systems ranging from tens of megawatts to hundreds of megawatts; 3 develop independent systems ranging from tens of kilowatts to 10,000 kilowatts to address the urgent needs of areas without electricity.
0 Overview Solar energy as a clean, inexhaustible energy source will account for a larger proportion of the energy structure. Solar thermal power emit not only power, may also be implemented at the same time heating, cooling, constitute a heat, power and cooling. Solar thermal power generation system by the collector system, a thermal transfer system, thermal storage systems energy storage, heat engine, generator etc. After concentrating solar collector systems, heat transfer concentrated solar energy system, the heat transmitted to the machine, by the heat engine to generate power to drive a generator to generate electricity, the heat source of the entire system from the solar energy, so called solar thermal power generation system.
1 Introduction 1.1 solar power tower tower solar thermal power generation system using solar heat generating system heliostat track the sun, and the sunlight focused on the center of the receiver receives the column, transformation of radiant energy focused on the receiver For heat energy, heating the working fluid, driving the turbine generator to generate electricity. Heliostat track the sun by the computer control to achieve the best focus. The tower solar thermal power generation system has a concentrating ratio of 300 1500 and an operating temperature of up to 1500 psi (1).
The design of the tower solar thermal power system was proposed by the former Soviet Union in the 1950s. The world's first grid-type solar thermal power plant was built in 1981 by France, the former Federal Republic of Germany and Italy. The system is installed in Sicily, Italy, and uses 182 concentrating mirrors. The total area of ​​the mirror field is 6,200 m2, and a regenerator consisting of nitrate is used. Its rated power is 1MW, steam temperature is 512T:, thermal power is 4.8MWU. The first 10MW tower solar thermal power station was built in southern California in 1982. The device is called Sun No. 1, which covers a total area of ​​291,000 square meters. The central receiver is located at the top of the 90.8 m high tower, producing 58T: high temperature steam. Each fixed mirror is mounted on the table beam. The position of the heliostat can be changed by a small power motor and gear box for two-axis tracking. The motor receives signals from the central control computer, so that the heliostat keeps track of the sun at any time. Gather the sunlight onto the receiver at the top of the tower. The maximum peak output of Sun 1 is 11 700 kW, and the annual average efficiency is less than 6%, which does not meet the original design requirements of 8.2%. The reason for the low efficiency is that the power consumption of the power station itself is too large; the installed capacity of the power station is small, and it is impossible to adopt a more efficient reheat steam turbine. The original design estimates the actual effective sunshine amount too high, and does not consider the mirror cleaning. problem. Sun 1 was later converted to the Sun No. 2 power station. The parameters of the Sun 2 power station are as follows: 1926 heliostats, molten salt heat storage systems, 300-foot central heat sinks, costing $40 million, and grid-connected tests run until 1998. The molten salt consists of 60% sodium nitrate and 40% potassium nitrate. It melts at 700 psi and becomes liquid when it is close to 〖000T.
1.2 trough concentrating thermal power generation system trough concentrating mirrors gather sunlight on a line, and a tubular collector is installed on this focal line to absorb the concentrated solar radiant energy. After the fluid in the tube is heated, it flows through the heat exchanger to heat the working medium, and generates electricity by means of a steam power cycle. The parabola is facing the sun for one-dimensional tracking (the device axis is placed north and south, then the east and west rotation tracking), the concentration ratio is between 10 and 100, and the temperature range is up to 400T:. This form of thermal power generation system was developed in the mid-1980s. So far, a 354 MW trough concentrating thermal power station has been installed in California. The working medium is heat transfer oil. The heat transfer oil can generate 390T superheated steam through the heat exchanger to drive the steam turbine. This system was developed by LUZ Company of the United States. Since 1984, we have developed a variety of systems of 14, 30 MW and 80 MW with a total installed capacity of 354 MW. The main feature of LUZ's technical route is the use of a large number of parabolic trough concentrators to collect direct sunlight and convert it into heat. . Each collector consists of a trough parabolic concentrator and a heat collecting element located on its focal line. Each collector element is a vacuum collector tube, 4 m long, and each 24 collectors are connected in series to form a collector with a length of 99 m. In combination, the 80 MW system requires 850 collector assemblies. Each assembly is placed horizontally from north to south. There are special sensors and computer controlled tracking system. The heat transfer medium is heat transfer oil. After it is heated in the vacuum heat collecting tube, it turns the water into high temperature and high pressure steam through a group of heat exchangers. To drive the steam turbine to generate electricity. This system requires the receiver parabolic area 470265m2 (680mX680m), HTF outlet temperature of the heat collector 391T :, to steam a steam pressure of 100 atmospheres, a Rankine reheat cycle thermal efficiency is 38.4%, from The highest instantaneous efficiency of solar radiant energy to electrical energy is 24%, and the annual average efficiency from solar radiant energy to electrical energy is 14%. Since solar energy is random, a conventional fuel (usually natural gas) is added to the working fluid circuit. Auxiliary boilers are in urgent need.
The core components of the LUZ power generation system are high-precision trough parabolic condensers and vacuum tube collectors. Since the temperature of the metal pipe wall is above 400T, the performance stability of the selective coating, the maintenance of the vacuum degree, and the sealing of the glass and the metal pipe are all difficult problems in the process. The surface of the heat absorbing tube of the heat collecting element adopts a high temperature resistant sputtering selective coating and has good stability.
Since LUZ built its first power generation system in 1984, the investment per kilowatt of installed capacity has dropped from $6,000 to $2,875; electricity costs have dropped from 24 cents kWh to 7.5 to 85 cents/(kWh). The average efficiency of the system is 10%. Now that the new absorption tube that directly produces high temperature and high pressure steam has been successfully developed, the heat transfer oil circuit can be eliminated, the system and operation cost can be reduced, and the operation safety can be increased. Sex.
1.3 Disc-type solar thermal power generation system By means of two-axis tracking, the parabolic dish mirror concentrates the received solar energy on the receiver of its focus. The receiver absorbs this portion of the radiant energy and converts it into thermal energy. A thermoelectric conversion device, such as a Stirling engine or a Rankine cycle heat engine, is installed on the receiver to convert thermal energy into electrical energy.
The capacity of a single-disc Stirling power plant ranges from 5 to 50 kW. Working with helium or hydrogen as a working medium, the energy conversion efficiency of the 800 Stirling engine is high. The dish system may be a separate device or may be composed of a group of disks to output a large amount of power. The earliest construction of the disc-type solar thermal power plant was Advanco and McDonnell Douglas.
Internationally, an experimental report on the assumptions and principles of thermoelectric semiconductors, thermionics, thermal photovoltaics, and the use of alkali metal thermoelectric direct converters (AMTEC) to form dish or trough solar thermal direct power generation was published, but it was not put into practical use. In the research stage.
1.5 The solar pool power generation system uses the solar pool phenomenon to generate energy, which was first proposed by Israeli scientists. The solar pool power generation system uses the salt water to generate different temperature gradients under the irradiation of sunlight due to different salt gradients to drive the steam turbine to generate electricity. Generally, the depth of the pool water is more than 6m, and the bottom of the pool is blackened to absorb direct and diffuse solar radiant energy. According to this principle, the bottom pool water can be heated to above 90t. The solar pool is usually divided into three layers along its depth: the top troposphere, which is very thin, with a low concentration of brine, which is caused by wind and surface heat loss; about 1 to 1.5 m in the middle, which is a non-troposphere, the salt of this layer The concentration increases with depth, and the increase in the salt gradient avoids the possibility of convection of the lower layer of warm water to the cooler upper layer, which acts as a transparent insulating layer.
Allow sunlight to penetrate, thus avoiding the hot convection of the hot water at the bottom; the lower part is the heat storage layer, about 24m deep, the concentration of salt is higher, and a certain depth has formed saturated brine. This layer of brine has a very high specific gravity, a nearly constant concentration and a relatively uniform temperature distribution. The thickness of this layer determines the heat storage capacity of the solar pool.
The 25m solar pool produced 96t of hot water; in 1973, with the support of the Israeli government, the Israel Scientific Research Foundation revisited the solar pool project and in 1977 set up a 150kW solar pool power generation system. The grid was successfully operated for seven years and the project was stopped because the land was recovered by the landowner. On this basis, in 1984, the BeithHa'ava plan was proposed. According to this plan, a 5MW solar pool power generation system should be established with partial support from the Israeli government. However, due to budget constraints, the area of ​​the solar pool only achieved the design area. At the same time, Australia established a 15kW solar pool power generation system. US power company Edison Sarton lake in California built a generating capacity of 5MW solar pond power plant, the United States has also established 70kW and 330kW thermal power cogeneration system for seawater desalination. In 1975, Clark et al used in power generation of the solar pond conducted a series of studies to provide hot water for the New Mexico uranium, to build world's largest solar cell for power generation in Southern California, its power generation capacity Israel has estimated that up to 600 in the Dead Sea coast has built three solar pond and the use of low temperature difference between the generator and the power plant Rankine cycle engine running at low temperature's first experimental solar pond power of 150kW of power plant, at the end of 1979 started to run, rather that cost the same power station, the price is only 1 to 2 cents / (kWh). It is the first step in Israel's plans to make extensive use of the solar pool's power generation plan; according to the plan, a series of solar pool power stations built around the Dead Sea will provide about 13% of Israel's national electricity demand. According to the United States national resources of solar radiation and salt resources census, the conclusion is: if all the available resources can be developed and utilized, it will meet about 12% of the country's electricity needs of the United States, which It is a very promising prospect. First, the Salt Lake Sun Pool Project was implemented in Southern California, and a large solar pool power plant with a final power generation capacity of 800 MW was built.
2 Development and current status of domestic solar thermal power generation technology In the late 1970s, Xiangtan Motor Factory and the United States cooperated to build a disc-type solar thermal power generation experimental device. Condenser mirror diameter 7.5m, made of alloyed aluminum, block forming, combined, surface-coated aluminum film, computer-controlled two-axis tracking system, heat absorption with heat transfer oil, then heat transfer to organic working fluid, drive turbine generator set Power generation, experimental device power generation 3kW. Institute of Electrical Engineering, Chinese Academy of Sciences, in the late 1970s, applied basic research work on solar thermal power generation, including solar collectors, solar radiation absorption coatings and Stirling engines. During the “Eighth Five-Year Plan†period, the Beijing Solar Energy Research Institute and the Institute of Electrical Engineering of the Chinese Academy of Sciences undertook the key technical research projects for solar thermal power generation. The Institute of Electrical Engineering of the Chinese Academy of Sciences developed a trough line focusing device for the trough parabolic collector system. The research has achieved gratifying results. The University of Science and Technology of China and the Institute of Electrical Engineering of the Chinese Academy of Sciences have done a deep research work on non-imaging CPC collection and heat transfer enhancement. These have laid the foundation for the research and development of solar thermal power generation technology in China.
3 Conclusion First, the realization of low-cost investment and high-reliability operation of power generation systems is crucial to the development of solar thermal power generation technology; secondly, to achieve large-scale development, the establishment of large-scale grid-connected systems of tens of megawatts to hundreds of megawatts, It not only saves conventional fuel, but also ensures the smooth operation of the system. At the same time, it should develop a convenient and practical independent system of several tens of kilowatts to 10,000 kilowatts in order to solve the urgent need in areas without electricity and electricity.
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