As the problems of environmental pollution and resource waste become
increasingly prominent, the importance of new energy has become more and more
obvious. As a representative energy in the new energy family, solar energy has
been widely used by people. This article introduces the current status and
characteristics of solar thermal power generation and illustrates that solar
thermal power generation has good application prospects.
1Solar power generation 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 among
various renewable energy sources and the most abundant energy available to
mankind. The radiant energy projected by the sun onto the ground every year is
as high as 1.05×1018 kilowatt hours, which is equivalent to 1.3×10.6 billion
tons of standard coal, which is approximately more than 10,000 times the current
annual energy consumption in the world. According to the current mass
consumption rate of the sun, it can last for 6×1010 years. It can be said that
it is an inexhaustible energy source.
Wind energy, water energy, ocean temperature difference energy, wave
energy, biomass energy and part of tidal energy on the earth all come from the
sun; even fossil fuels on the earth (such as coal, oil, natural gas, etc.) are
fundamentally Stored solar energy, so solar energy in a broad sense covers a
very wide range, while solar energy in a narrow sense is limited to the direct
conversion of photothermal, photoelectric and photochemical energy from solar
radiation. Solar energy is both a primary energy source and a renewable energy
source. It is rich in resources, free to use, does not require transportation,
and does not cause any pollution to the environment.
1.2 Solar thermal power generation
Modern solar technology can concentrate sunlight and use its energy to
produce hot water, steam and electricity. Concentrated solar energy (Solar
Thermal). 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. Sunlight reflected from the mirrors heats the oil in the tubes,
producing steam that drives a 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 incorporating appropriate
features into their design, such as large south-facing windows or using building
materials that absorb and slowly release the sun's heat. . In the right
locations, the long-term cost of solar energy is close to or even lower than
that of traditional fossil fuels.
2 Solar thermal power generation control technology
2.1 Current status and characteristics of solar thermal power generation
control system
For solar thermal power generation control systems, the characteristics of
the power generation control system are similar or identical to the control
systems of conventional thermal power generation units. The following describes
the development status and characteristics of the solar thermal power generation
island control system in terms of conventional thermal power generation unit
decentralized control systems.
Based on the system structure and control model, a reasonable control
system is designed, and a parameter setting method is given. When the unit
operates stably and with varying loads according to the power grid load
requirements, the unit parameters can be operated within a reasonable range
without over-temperature or over-pressure. Faults such as tripping are one of
the main targets of the thermal power unit automation control system. The
thermal system of thermal power generating units is complex and has many thermal
protection projects. Under abnormal circumstances, the unit can be safely shut
down to avoid major equipment damage caused by operating errors. In addition, in
order to realize the orderly start and stop of the units and equipment, several
sequence control loops are also set up. Typical thermal power unit control
systems include: boiler SOE, boiler protection, furnace oil system, sealing air,
fire detection cooling air system, micro-oil ignition system, pulverizing system
and its fire detection, fuel oil and its fire detection system, coordination
System, water supply main control system, combustion main control, distribution
system, induced draft, primary air system, superheated steam temperature,
reheated steam temperature system, air and smoke system, boiler starting system,
soot blowing system, desulfurization system, denitrification system, steam
turbine Main body system, bypass system, regenerative heating system, generator
cooling system, lubrication system, generator-transformer unit, excitation
system, factory power system, small steam turbine system, auxiliary workshop
system, etc.
The thermal power unit automation device is mainly a distributed control
system DCS programming logic controller PLC. DCS is generally used for host
control, and PLC is generally used for auxiliary workshop control, such as coal
transportation control, chemical water treatment control, etc. Although there
are many types of distributed control systems, the most basic distributed
control system generally has a structure as shown in the figure. Among them, the
controller (or field control station, process control station, distributed
processing unit, etc.) belongs to the decentralized control part and is
connected to the field instruments; the engineer station, operator station, and
server belong to the operation management part. The decentralized control part
and the operation management part are connected into a whole through the
computer network. Distributed control systems are connected to other systems
through open network interfaces.
2.2 Solar thermal power generation system power station operation mode
2.2.1 Ordinary early morning startup
The heliostats in each area are in their natural orientation positions and
are not in the standby state (Standby, that is, the focused light of the
heliostats in each area is positioned at several points in the sky) as shown in
Figure 4. At this time, the entire factory is started. It is called ordinary
early morning startup, and the basic logical judgment sequence of each module
during the startup process.
2.2.2 Cold start
During the startup operation of the whole plant, due to the influence of
heat loss, the state parameters of the heat absorber at startup correspond to
the surrounding environment. After the previous operation, the heliostat field
is in a standby state as shown in Figure 5. This type of operation is called A
cold start for the entire plant. The logical sequence of operation of each
module is the same as ordinary early morning startup except that the mirror
field is started from the standby state instead of the natural orientation
state.
2.2.3 Hot start
When the heat absorber and the steam turbine are decoupled due to certain
reasons, such as irradiation, strong wind, etc., some heat absorbers with
isolation doors can maintain a certain pressure and temperature of steam stored
inside. When irradiation, wind speed, etc. When external conditions change and
the heat absorber meets the requirements for restarting operation, it is called
a hot start. At this time, it will be able to reach the rated operating
conditions in a short time, depending on the design of the heat absorber. During
this type of startup, the rest are basically the same except that the mirror
field is in the standby state instead of the natural orientation state, and the
steam parameters can reach the rated value quickly to reduce bypass
circulation.
2.2.4 Normal operation
After the start-up is completed, the entire plant is in normal operation
under the condition that there are no drastic changes in external conditions,
and the power generation of the entire plant is directly related to changes in
irradiation.
2.2.5 Cloud cover operation
When the radiation intensity projected onto the surface of the heat
absorber is lower than the lower limit of the heat absorber design for N time
steps (determined by the specific design), the heliostat field begins to start
the process of deflecting to the standby state; this results in When the steam
turbine inlet pressure is lower than the set value (in order to ensure
continuous connection with the power grid, the smaller the set value, the
better), the energy storage system automatically generates steam to supply the
steam turbine under the condition of sufficient energy storage. If the
irradiation intensity recovers before the heliostat field is completely
deflected, the heliostat will be refocused from its current position to the
surface of the heat absorber. The basic logical judgment of the process.
2.2.6 Closure at night
When the intensity of concentrated light irradiation projected onto the
surface of the heat absorber in the evening is lower than the design lower
limit, the program for deflecting the mirror field from the position of the
focusing heat absorber to the standby state is automatically started, and the
voltage and temperature regulation devices are controlled to reduce The load
carried by the steam turbine eventually separates the generator set from the
power grid.
2.2.7 Accident emergency operation
The accident mainly comes from two aspects: the heat absorber and the
mirror field: The failure of the heat absorber mainly occurs in the water supply
system, such as the failure of the water supply pump, mechanical or electrical
failure in the pipeline. At this time, there is still a strong concentration on
the surface of the heat absorber. Therefore, when starting the heliostat field
deflection, the water spray cooling system must be activated and the safety
valve of the heat absorber must be opened. Failure of the mirror field usually
results from a communication or power supply interruption, in which case a
backup power supply must be activated to bias the heliostat to the standby
position.
3Conclusion
This article gives a detailed introduction to the current status and
characteristics of solar thermal power generation control technology, and
provides relevant explanations on the operation methods of solar thermal power
generation system power stations. In view of today's serious environmental
pollution, solar energy, as the most popular green energy among new energy
sources, can not only alleviate the problem of environmental pollution, but also
bring great business opportunities.
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