With the increasingly prominent problems of environmental pollution and waste of resources, the importance of new energy has become increasingly apparent. Solar energy has become widely used as a representative energy source in the new energy family. This paper introduces the current status and characteristics of solar thermal power generation and shows that solar thermal power generation has a good application prospect.
1 Solar power system
1.1 Introduction to Solar Energy
Solar energy is the energy generated by the continuous nuclear fusion reaction process inside the sun. It is the most important basic energy source for various renewable energy sources and the most abundant energy that humans can use. The annual radiant energy that the sun projects onto the ground is as high as 1.05×1018 kWh, which is equivalent to 1.3×106 million tons of standard coal, which is approximately 10,000 times more than the current annual energy consumption in the world. According to the current solar mass consumption rate, it can maintain 6×1010 years. It can be said that it is an inexhaustible source of energy.
Wind energy, water energy, ocean temperature energy, wave energy, biomass energy, and part of the tidal energy on Earth are all derived from the sun; even fossil fuels on the earth (such as coal, oil, natural gas, etc.) are fundamentally ancient since ancient times. The stored solar energy, so the scope of the broad scope of solar energy is very large, the narrow sense of the solar energy is limited to solar thermal energy, photoelectronic and photochemical direct conversion. Solar energy is both primary energy and renewable energy. It is rich in resources and can be used free of charge without transportation, without any pollution to the environment.
1.2 Solar Thermal Power Generation
Modern solar technology can synthesize sunlight and use its energy to produce hot water, steam and electricity. Solar Thermal Energy. The principle is to focus the sunlight reflected by the mirror on a glass tube called a receiver, and the hollow glass tube allows oil to flow through. The sunlight reflected from the mirror warms up the oil in the pipe, produces steam, and then drives the turbine to generate electricity.
In addition to using appropriate technology to collect solar energy, buildings can also harness the sun's light and heat by adding appropriate equipment, such as massive south-facing windows or building materials that absorb and slowly release solar heat. . In place, the long-term use of solar energy is already close to or even lower than traditional fossil fuels.
2 Solar CSP Control Technology
2.1 Status and Characteristics of Solar Thermal Power Generation Control System
For the solar thermal power generation control system, the characteristics of the power generation control system are similar to or equal to those of the conventional thermal power generation unit. The following describes the development status and characteristics of the solar thermal power generation island control system for the conventional thermal power unit distributed control system. ?
Based on the system structure and control model, a reasonable control system is designed and the parameter setting method is given. When the unit is running stably and the load operation is changed according to the grid load requirements, the unit parameters are operated within a reasonable range, and no over-temperature and over-pressure occurs. Trips and other faults are one of the main goals of the thermal power plant automation control system. The thermodynamic system of thermal power generating units is complex and there are many thermal protection projects. Under abnormal conditions, the unit's safety shutdown can be achieved to avoid major equipment damage due to operational errors. In addition, in order to achieve orderly start-up and shutdown of units and equipment, a number of sequential control loops are also provided. Typical thermal power plant control systems include: furnace SOE, boiler protection, furnace front oil system, sealed air, fire detection cooling air system, micro oil ignition system, pulverizing system and fire inspection, fuel oil and fire inspection system, and coordination System, water supply main control system, combustion main control, delivery points, induced draft, primary air system, superheated steam temperature, reheat steam temperature system, wind smoke system, boiler startup system, soot blowing system, desulfurization system, denitration system, steam turbine Body system, bypass system, regenerative heating system, generator cooling system, lubrication system, generator-transformer group, excitation system, plant power system, small turbine system, auxiliary workshop system, etc.
Thermal power unit automation equipment is mainly distributed control system DCS programming logic controller? PLC. DCS is generally used for host control, PLC is generally used to assist workshop control, such as coal control, chemical water treatment control. Although there are many types of distributed control systems, the most basic distributed control system generally has the structure shown in the figure. Among them, the controller (or field control station, process control station, distribution processing unit, etc.) belongs to the decentralized control part and is connected with the field instrument; the engineer station, operator station and server belong to the operation management part. The decentralized control section and the operation management section are connected together by a computer network. The distributed control system is connected to other systems through an open network interface.
2.2 Solar Thermal Power System Operation Mode
2.2.1 Ordinary morning start
The heliostats in each region are in their natural orientation, and are not in the standby state as shown in Figure 4 (Standby, ie, the focused rays of each heliostat are positioned in the air at several points). At this time, the whole plant starts to run. Called "Ordinary Morning Start", the basic logic of each module in the startup process determines the order. ?
2.2.2 Cold start
During the start-up operation of the whole plant, the heat absorber is affected by heat loss, and the state parameter at startup is corresponding to the surrounding environment. After the previous operation of the heliostat field, it is in the standby state as shown in FIG. 5 . Such operation is called For the whole plant "cold start." The logical sequence of each module's operation is the same as normal morning start except that the mirror field is started from the standby state instead of the natural orientation state. ?
2.2.3 Hot start
For some reasons such as irradiation, high wind, etc., which results in the decoupled operation of the heat sink and steam turbine, some heat absorbers with isolation doors can maintain steam with a certain pressure and temperature inside, when irradiation, wind speed, etc. Changes in external conditions, so that the heat exchanger to meet the start of the re-run is called "hot start", at this time will be able to reach the rated operating conditions in a relatively short period of time, depending on the design of the absorber. This type of startup is basically the same except that the mirror field is in the standby state instead of the natural orientation state, and the steam parameter can reach the rated value quickly to reduce bypass flow.
2.2.4 Normal operation
After the startup is completed, under the condition that there are no drastic changes in the external conditions, the whole plant is in normal operation, and the power generation of the entire plant is directly related to the change in irradiation.
2.2.5 cloud cover operation
When the intensity of the radiation projected onto the surface of the heat sink falls below the lower limit of the design of the heat sink to N (depending on the specific design) time step, the heliostat field begins to initiate the procedure of deflecting to the standby state; this results in When the inlet steam pressure of the steam turbine is lower than the set value (in order to ensure continuous connection with the power grid, the smaller the setting value is, the better), under the condition that the energy storage is sufficient, the steam energy is supplied to the steam turbine automatically by the energy storage system. If the irradiation intensity is restored before the heliostat field is fully deflected, the heliostat is again focused from the current position to the surface of the heat sink. The basic logic of the process is judged.
2.2.6 Night Shutdown
When the intensity of the condensing radiation projected onto the surface of the heat sink falls below the design lower limit in the evening, the process of automatically starting the mirror field from the position of the focused heat sink to the standby state is controlled, and the pressure regulating and temperature adjusting device is controlled to reduce The load brought by the steam turbine finally broke the generator set and the power grid.
2.2.7 Emergency operation
The accident mainly comes from the heat absorber and the mirror field. The fault of the heat sink mainly occurs in the water supply system, such as failure of the feed pump, mechanical or electrical failure of the pipeline, and the surface of the heat sink is still very strong at this time. Light distribution, so start the field of deflection of the heliostat must be enabled at the same time the water cooling system, and open the heat sink safety valve. The failure of the mirror field usually results from communication or power interruptions. At this time, the backup power must be enabled to bias the heliostat to the standby position.
This paper gives a detailed introduction of the current status and characteristics of solar thermal power generation control technology, and makes a related explanation for the operation mode of solar thermal power generation system power station. For today's serious environmental pollution, solar energy as the most favored green energy in new energy sources can not only alleviate the problem of environmental pollution, but also bring great business opportunities.
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