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Polaris Thermal Power Grid News: At present, the average coal consumption of coal power units with 300 MW and above in the mainland is about 305 g/(kW•h). According to the power generation capacity of coal-fired units in 2020 of 4.8 trillion kW•h, the annual consumption of standard coal is about 1.46 billion tons, and the co2 emissions are about 4.2 billion tons. According to relevant forecasts, by 2030, coal power CO2 emissions will be about 4 billion tons, which is close to the current level, and the carbon peak of the industry can be basically achieved. However, power generation is essentially a carbon industry, and emissions account for a large proportion. Technological progress in the power generation industry, especially breakthroughs in low-carbon technology, is the key support for achieving the mainland's goal of "30∙60 carbon peak carbon neutrality".
(Source: WeChat public account "Circulating fluidized bed power generation" ID: xhlhcfdAuthor: Wang Yueming)
Thermal power generation, especially coal-fired power generation, is currently the most comprehensive and economical form of power generation with the highest technological maturity. Theoretically, compared with nuclear power, hydropower, wind power, etc., thermal power generation is less constrained by resources, the layout is more flexible, and the installed capacity can be determined according to actual demand.
The development of coal power, on the one hand, depends on the overall demand for the power industry such as the level of economic development, resource endowments, environmental protection, and carbon emission reduction in the mainland, and on the other hand, it depends on the technical characteristics, technological maturity and economy of coal power. Therefore, in order to deeply study the development trend of coal power and obtain the reasonable proportion and structure of coal power under the background of "carbon peaking and carbon neutrality", it is necessary to comprehensively consider the two aspects of power demand and power generation technology development, and consider the energy saving and consumption reduction of existing units and the high efficiency of new units. At the same time, coal-fired power units need to be intelligent and flexible to meet the large-scale access of new energy power. Therefore, the focus should be on the study of high-efficiency coal-fired power technology, flexible peak shaving technology of coal-fired power units and carbon capture and utilization technology。
1 Research on the development of coal power
1.1 Characteristics and positioning of coal power
After several decades of development, the emission of pollutants from coal-fired power generation has been effectively controlled. By the end of 2020, almost all of the mainland coal-fired power units will reach ultra-low emission levels. However, thermal power generation units are obviously disadvantaged in terms of carbon emissions. At present, the carbon emissions per unit of coal-fired units in mainland China are as high as 879 g/(kW•h), and even the most advanced coal-fired power units have reached 756 g/(kW•h), which is much higher than the near-zero emission standard required to achieve carbon neutrality (carbon emissions per unit of power generation are less than 100 g/(kW•h)), so coal-fired power generation is the main area of carbon reduction in the mainland power industry.
Since the founding of New China 70 years ago, the mainland's electric power industry has developed rapidly, achieving a huge leap from small to large, from weak to strong, and from catching up to leading, and has made outstanding contributions to the mainland's economic and social development. In this context, coal power has developed rapidly, and with the continuous investment and support of the state, coal power technology has made great progress, and the capacity of individual units, unit parameters, number of units, and energy efficiency indicators have leapt to the forefront of the world. For a long time, coal-fired power generation has shown the characteristics of high proportion and large volume, and actually assumed the role of the main power supply and basic power supply in the mainland.
In recent years, the mainland's demand for diversified, clean and low-carbon energy utilization has become increasingly urgent, especially after General Secretary Xi Jinping put forward the goal of "30∙60 carbon peak carbon neutrality", the transformation of the energy industry, especially the power industry, is imperative. In the future, coal-fired power generation will surely undertake a new historical mission.
First of all, new energy power fluctuations are large and intermittent, before the mature application of large-scale, low-cost energy storage technology, an appropriate proportion of coal-fired power generation can provide sufficient moment of inertia for the stable operation of the power system, stabilize the fluctuations caused by the grid connection of a large proportion of new energy power generation, and ensure the safety of the power grid system. The power system requires thermal power generation, especially coal-fired power generation, to give full play to the important role of "bottom guarantee".
Secondly, coal power should actively change its role, from the traditional main power supply that provides electricity and electricity to the basic power supply that provides reliable power and peak regulation and frequency regulation capabilities, actively participate in auxiliary services such as peak regulation, frequency regulation, voltage regulation, and backup, improve the power system's ability to consume new energy power generation, and give more electricity to low-carbon electricity。
Finally, cogeneration of coal-fired generating units is an important guarantee for meeting the heating needs of mainland residents. Although cogeneration units currently account for 41% of thermal power units, they still cannot meet the growing heat demand in the mainland. Low-cost coal-fired power generation is the basis for low-cost electricity and heat consumption in the whole society, an important support for the mainland to ensure people's livelihood and energy use for social and economic activities, and is of great significance to promoting economic and social development and enhancing people's happiness.
1.2 Reasonable proportion of coal power in the total installed capacity
The scale of investment in coal power in the mainland has decreased year by year, with the average annual installed capacity of coal power in the "Eleventh Five-Year Plan" period being 68.62 million kW, and by the "13th Five-Year Plan" period, it has dropped to 35.38 million kW。 The scale of new installed capacity of coal power was surpassed by new energy in 2016, and the annual installed capacity of new energy power generation in 2020 is nearly 3 times that of coal power, and the proportion of installed capacity of coal power has historically dropped below 50%. With the "double carbon" goal proposed, the trend of further reducing the installed capacity of coal power is irreversible.
However, the reasonable power structure and power generation composition depend on the technical development level and economy of various types of generator sets, and also adapt to the overall needs of economic development level, resource endowment, environmental protection requirements and so on.
According to the forecast of the mainland's economic development and the electricity demand of the whole society, the total installed power supply capacity in the country will be about 2.874 billion kW in 2030, and the total annual power generation will be about 8.94 trillion kW•h. According to the demand for carbon peaking, the power generation industry needs to take the lead in peaking around 2025. The total annual carbon emissions of the power generation industry will be controlled at about 3.8 billion tons in 2030, and the carbon emissions per unit of power generation will be reduced to 425 g/(kW•h).
Under these conditions, it is estimated that in 2030, the installed capacity of coal-fired power generation will be 1.213 billion kW, accounting for 42.20% of the total installed capacity. Coal-fired power generation generated 4.85 trillion kW•h, accounting for 54.27% of the total power generation. Carbon emissions per unit of coal-fired power generation fall to around 750 g/(kW•h). The annual carbon emissions of coal-fired power generation are about 3.63 billion tons, and the total carbon emissions of the power generation industry are about 3.8 billion tons.
In 2060, according to the forecast of the mainland's economic development and the electricity demand of the whole society, the total installed power supply capacity in the country is about 7.092 billion kW, and the total annual power generation is about 16.5 trillion kW•h. Considering the demand for carbon neutrality alone, the power generation industry needs to reduce the carbon emissions per unit of power generation to less than 50 g/(kW•h) by 2060, and the total carbon emissions of the power generation industry in 2060 will be controlled at 800 million to 900 million tons. However, by 2060, the mainland still needs to maintain about 700 million kW of coal-fired generating units to ensure the safety of the mainland's energy and electricity supply and peak shaving and heating needs, and there is great uncertainty about the actual total carbon emissions of the power generation industry in 2060.
It is foreseeable that in the future, the installed capacity of coal power and the amount of power generation will be mainly subject to the dual constraints of carbon emission reduction targets and power supply security。 Starting from the carbon emission reduction target, coal power should continue to reduce its scale; but from the perspective of power supply security, coal power needs to continue to assume the roles of bottom guarantee, emergency backup, peak regulation and frequency regulation, new energy consumption, and even industrial heating and heating for a long period of time. As a result, coal power will continue to reduce its power generation capacity while meeting the security of power supply to achieve less carbon emissions. In addition to meeting the requirements of the "30/60" target, the schedule of the downward adjustment of its installed capacity and power generation capacity is also affected by the economics of power supply and environmental protection, and is closely related to factors such as the level of flexibility improvement, the maturity of efficient technology development, carbon capture integration, the economy and safety of carbon transportation and storage.
2 Low-carbon technology for coal power
2.1 Energy saving and efficiency improvement of existing units
2.1.1 Comprehensive technologies for low-carbon coal power consumption, energy conservation and efficiency improvement
The factors affecting the energy consumption characteristics of large coal-fired power units in mainland China include external conditions such as operating load, fuel characteristics and ambient temperature, as well as internal factors such as performance defects and operation management levels of the units themselves. In order to optimize the operation of the coal-fired power unit under full working conditions, it is necessary to diagnose the energy saving of the system, check the performance of each thermal equipment under full working conditions, and obtain the energy consumption characteristics of the thermal system.
Energy-saving diagnosis is based on comprehensive system energy consumption analysis and diagnosis, for all the main and auxiliary system of the unit, starting from the equipment selection, operation mode, existing problems and other aspects; combined with coal quality, environmental boundary conditions, operating mode, operating parameters, etc., the energy consumption indicators of the unit are analyzed and accounted for in detail, and the energy consumption level and energy-saving potential of the unit are obtained; and on this basis, the energy-saving transformation direction is pointed out for the power generation enterprises, and the targeted comprehensive energy-saving efficiency improvement technology is used to reduce the coal consumption of the unit.
The comprehensive transformation technology of coal-fired power consumption and efficiency improvement is to regard coal-fired power units as a whole, and adopt technical measures that are technically feasible, economically reasonable and environmentally and socially bearable in coal-fired power generation systems, so as to strengthen heat transfer and mass transfer, heat cascade utilization, rational utilization of energy, auxiliary machine efficiency improvement and speed regulation transformation and other optimized operation methods for the overall energy-saving and efficiency-improvement of coal-fired power units for technology orientation。
At present, the mature energy-saving technology is shown in Figure 1. For specific power plants, according to local conditions, one plant and one policy, different combinations of technologies can be used to achieve the best technical and economic results.
Figure 1 Integrated energy-saving technology system for thermal power units
2.1.2 Comprehensive efficiency improvement technology of unit life extension
The life extension technology of coal-fired power unit improvement parameters is an important means to improve the overall energy consumption level of coal-fired power units, energy saving and carbon reduction.
During the 14th Five-Year Plan period, there are 87 coal-fired power units of 200,000 kW and above that have reached the design period, with a total capacity of about 26 million kW. In the next 10 years (2021-2030), 252 coal-fired power units with a capacity of 200,000 kW and above will meet the design deadline, with a total capacity of about 82 million kW, accounting for about 7.6% of the current total coal power capacity (based on 1.08 billion kW at the end of 2020). Among them, there are 205 units of subcritical 300 MW and above, accounting for 88% of the capacity of the units that expire within 10 years.
According to the operating experience of foreign coal-fired power units, more than 24% of coal-fired power units have served for more than 30 years in the world. Nearly 50% of Japan's coal-fired power units have a service life of 30 to 39 years, and 25% of coal-fired power units have a service life of more than 40 years. The average service life of coal-fired power units in the United States is 42 years, and 11% of units have an operating life of more than 60 years. In the composition of continental coal-fired power units, the service life of 300 MW class subcritical units within 20 years accounts for 82.8%.
For units that have reached the design life, the economy of the unit can be greatly improved by extending the life of the unit and the synchronous implementation of the upgrading parameter transformation.
For subcritical units, only the steam temperature is increased, while the main steam pressure remains basically unchanged, which can reduce the coal consumption level of the unit and effectively reduce the amount of renovation engineering. The magnitude of the steam parameter increase is proportional to the difficulty of the solution and the scale of the investment.
2.2 Efficient coal-fired power generation technology
2.2.1 Ultra-high parameter ultra-supercritical coal-fired power generation technology
Ultra-high parameter supercritical coal-fired power generation refers to the further improvement of the parameters of coal-fired generating units from the current 600 °C level to 650 °C level or even 700 °C level, so as to achieve the purpose of improving power generation efficiency.
In the past few decades, coal-fired power units have been developing towards large capacity and high parameters. At present, the steam parameters of coal-fired power units around the world are stable at 600 °C, and some units are raised to 620 °C. The unit capacity is basically 600 MW and 1 000 MW. At present, China has put into operation more than 600 supercritical and ultracritical units with 600 MW ratings, and 137 supercritical 1,000 MW units have been put into production. In 2016, the state-of-the-art 1 000 MW class 600 °C/620 °C/620 °C ultra-supercritical secondary reheat unit was successfully put into operation, with a net efficiency of 47%. With the continuous investment and support of the state, the advanced clean and efficient power generation technology of coal has made significant progress, and the parameters, quantity and energy efficiency indicators of the units have leapt to the first place in the world.
In the field of 700 °C power generation technology, especially in terms of high-temperature nickel-based alloy materials, foreign countries have developed several nickel-based alloy materials suitable for 700 °C units, completed the conceptual design of 700 °C power plants, and basically made technical reserves for the construction of 700 °C units. The research of 700 °C power generation technology on the mainland is also keeping pace with the world. The relevant scientific research units have screened and developed a number of high-temperature alloy materials, built a 700 °C component verification platform in Huaneng Nanjing Power Plant, and completed the verification of key high-temperature components of 25 000 h, and the operation is in good condition. At the same time, experimental applications are also being carried out in the second phase of Ruijin Power Plant. In addition, the main steam pipe and high and medium pressure rotor alloys have been developed, and are currently undergoing industrial trial production and component performance verification.
Preliminary estimates: In 2025, the engineering demonstration of 650 °C grade ultra-supercritical coal-fired generating units will be realized, with a net efficiency of not less than 47%; in 2035, large-scale commercialization of 650 °C grade ultra-supercritical coal-fired generating units will be realized; in 2035, the engineering demonstration of 700 °C grade ultra-supercritical coal-fired generating units will be realized, with a net efficiency of not less than 50%; in 2045, large-scale commercial use of 700 °C grade ultra-supercritical coal-fired generating units will be realized。
On the basis of 700 °C ultra-supercritical steam power generation technology to further improve the temperature parameters, the efficiency of the power generation system is limited, even if the temperature reaches 800 °C, the net efficiency is difficult to break through 55%, and with the increase of temperature, the development cost and manufacturing cost of superalloy materials are multiplied, and the problem of material bottleneck is prominent. Therefore, after the commercial use of 700 °C grade ultra-supercritical coal-fired generating units, it is not recommended to develop to higher parameters.
2.2.2 Supercritical CO2 cycle for efficient coal-fired power generation
Supercritical CO2 cycle efficient coal-fired power generation technology is a new type of coal-fired power generation technology that uses supercritical CO2 instead of water as the circulating working medium and breton cycle instead of the Rankin cycle as the power cycle. In the 600 °C level, the power supply efficiency of supercritical CO2 circulating coal-fired generating units can be improved by 3 percentage points to 5 percentage points compared with traditional water circulation generating units, and the power supply efficiency of supercritical CO2 circulating coal-fired generating units can be improved by 5 percentage points to 8 percentage points compared with traditional water circulation generating units at 700 °C.
In 2004, the U.S. Department of Energy (DOE) began research and development of supercritical CO2 cycle power generation technology, with the goal of developing next-generation power equipment for nuclear power plants, solar thermal power generation, and waste heat utilization. In 2011, the U.S. Department of Energy began implementing the "Sunshot" program, which aims to commercialize the supercritical CO2 Breton circulation system. The R&D project is mainly for the development and testing of 10 MW supercritical CO2 generator sets, and the experimental tests are carried out at the Nuclear Energy Systems Laboratory (NESL) under Sandia National Laboratory in the United States. Since 2014, the U.S. Department of Energy has implemented a fossil fuel supercritical CO2 cycle power generation research program, which aims to make the supercritical CO2 closed cycle more efficient than the high-parameter hydrodynamic Lancian cycle by more than 5 percentage points.
From 2005 to 2011, sandia National Laboratory, with funding from the U.S. Department of Energy, first built a supercritical CO2 Breton cycle experimental loop device with a thermal power of 1.0 MW, with a design pressure of 15.2 MPa, a temperature of 538 °C, and an electrical power of 125 kW.
Europe and Japan are also stepping up their research into the supercritical CO2 cycle. EDF has carried out research on the closed supercritical CO2 cycle of coal combustion, and tokyo institute of technology, the Russian Academy of Sciences, and the University of Liege in Belgium have carried out semi-closed supercritical CO2 cycle research. Overall, for the study of the coal-based supercritical CO2 cycle, foreign countries are still in their infancy.
Mainland research in this field is basically synchronized with foreign research. Xi'an Thermal Research Institute Co., Ltd. (Xi'an Thermal Engineering Institute), the Chinese Academy of Sciences, the China Nuclear Power Research Institute, Tsinghua University, Xi'an Jiaotong University and other units have successively carried out supercritical CO2 cycle related research. The Ministry of Science and Technology of the People's Republic of China has successively supported key research and development projects such as "Research on Key Basic Issues of Supercritical CO2 Solar Thermal Power Generation", "Research on Basic Theory and Key Technologies of Ultra-high Parameter Efficient CO2 Coal-fired Power Generation", "Research on Basic Theory and Key Technologies of Megawatt-level Efficient compact New Marine Nuclear Power Devices", etc. After unremitting efforts, some of the achievements in the direction of supercritical CO2 cycle construction and supercritical CO2 flow heat transfer mechanism have reached the international advanced level.
Xi'an Thermal Engineering Institute's 5 MW supercritical CO2 cycle power generation verification platform (Figure 2) was completed in December 2020. With a maximum pressure of 21.5 MPa, a maximum temperature of 600 °C and a maximum flow rate of 306 t/h, the platform is currently the world's largest and highest-parameter supercritical CO2 cycle verification platform. The completion and operation of the platform will greatly promote the development and engineering application of new high-efficiency power generation technologies.
Figure 2 5 MW supercritical CO2 cycle power generation verification platform
At present, with the commissioning of the 5 MW supercritical CO2 power generation platform, key technologies and key equipment have been gradually verified and improved, and the engineering application research of this technology has been fully launched. Xi'an Thermal Institute and related units are conducting feasibility studies and preliminary designs for 50 MW supercritical CO2 solar thermal power generation, and it is expected to achieve 300 MW supercritical CO2 coal-fired power unit engineering demonstration around 2030, with a net efficiency of not less than 50%; in 2040, the engineering demonstration of large-scale supercritical CO2 coal-fired generating units with a net efficiency of not less than 55%.
2.3 Coal-fired power unit flexibility technology
In order to solve the problem of new energy consumption, coal power operation needs to be more flexible, and the peak regulation capacity needs to be more prominent and reliable. The peak shaving technology of coal-fired power units needs to focus on research or breakthroughs mainly includes two aspects: one is the depth of peak shaving, and the other is the speed of peak shaving. Thermal power is gradually changing from the traditional main power supply that provides electricity and electricity to a basic and regulated power supply that provides reliable capacity, peak regulation and frequency regulation and other auxiliary services to the power system while providing electricity and electricity.
With the increase of the proportion of new energy, the response ability of the power grid to a large load shedding in an instant should be greatly improved, and it is urgent to improve the ability to rapidly rise and fall the load of coal power from a technical point of view.
2.3.1 Boiler depth peak shaving technology
According to the different furnace type, coal quality and combustion equipment, most of the domestic coal-fired boilers currently have a low load and stable combustion capacity of 40% to 50% of the rated load, and the rated load is explored to 20% to 30% through transformation.
The boiler depth peak shaving mainly faces two problems: low load stable combustion and environmental protection standards.
The main technical measures to improve the low-load and stable combustion capacity of the boiler are: the fine operation adjustment of the boiler, the transformation of the boiler burner based on enhanced combustion, the transformation of the boiler milling system, the transformation of the coal quality mixed with high volatile emissions, and the combustion transformation of plasma, micro oil, and oxygen enrichment.
At present, the operating temperature of the denitrification device of most coal-fired power units is 300~420 °C. When the unit is deeply peak shaved, as the boiler load decreases, the smoke temperature at the inlet of the denitrification device will drop below 300 °C. In order to avoid the deviteration catalyst from losing its activity, the denitrification device needs to be withdrawn from operation, resulting in excessive nitrogen oxide emissions and the suspension of peak regulation of the unit. Therefore, for the units that cannot be put into the denitrification device during the deep peak shaving period, it is necessary to improve the smoke temperature of the denitrification device. The main low-load selective catalytic reduction (SCR) denitrification inlet smoke temperature improvement technologies include economizer flue gas bypass, economizer water side bypass, economizer grading arrangement, reheat extraction steam replenishment water, hot water recirculation and other technologies.
The above technical measures are all conventional means, which require different combinations for different units.
2.3.2 Control system peak regulation adaptability technology
The start-stop process control of continental thermal power units below 50% of the rated load is generally based on the start-stop process, and the control logic of the decentralized control system (DCS) fails to continuously operate below 50% of the rated load and even responds to the commissioning of peak regulation and frequency regulation.
The general target of the operating load range of deep peak shaving of thermal power units is 30% to 100% of the rated load. This is not only a simple widening of the operating load range, from the perspective of automatic regulation and control, the nonlinear characteristics of a large number of objects such as steam feed pumps, variable frequency pumps, control valves, etc. become non-linear with the widening of the working range. Many control loops matching 30% to 100% of the rated load range conditions become extremely difficult, resulting in the unit often manifested in some working conditions of automatic control operation abnormalities, to further improve the variable load rate index to the safe and stable operation of the unit brings great challenges.
When the unit is running deep peak shaving, a large number of equipment is running close to the limit, and the functional circuits such as auxiliary tripping, main fuel tripping and other protection and cutting automatic are very easy to threaten the safe and stable operation of the entire system if there is a malfunction or cutting manual. To achieve further deep peak shaving, control optimization for boiler combustion is required, and the logic needs to be modified (Figure 3).
Figure 3 Intelligent coordination and optimization control of coal-fired boilers
2.3.3 Thermoelectrolytic coupling technology
1) Turbine high and low bypass thermoelectrolytic coupling technology The design purpose of the steam turbine bypass is to coordinate the imbalance between the boiler steam production and the steam consumption of the steam turbine, to achieve a certain degree of thermolytic coupling, and to improve the adaptability of the unit to load, heat supply and operational flexibility. External heating can be achieved by using the existing bypass or the newly built bypass of the unit. The steam turbine bypass heating system is shown in Figure 4.
Figure 4 Steam turbine bypass heating system
Steam turbine high and low bypass heating can be divided into:
1) Low-voltage bypass for separate external heating;
2) High-pressure bypass part of the main steam external heating;
3) Steam turbine high and low bypass combined heating.
At present, the more applications are low-voltage bypass independent external heating and steam turbine high and low bypass combined heating.
2) Low-pressure cylinder zero-output thermal electrolytic coupling technology Heating units are generally affected by the low-pressure cylinder cooling steam flow limit and the way of operation with heat fixed electricity, and the peak regulation capacity is limited, it is difficult to adapt to the deep peak regulation demand of the power grid, and the heating capacity is also limited. Low-pressure cylinder zero output technology is an effective means to break through this problem. Figure 5 shows the low-pressure cylinder zero-output heating technology system. This technology is to close the low pressure cylinder inlet valve under the condition of high vacuum operation of the low pressure cylinder, and use the steam that originally entered the low pressure cylinder for heating, so as to realize the zero output operation of the low pressure cylinder of the steam turbine. Taking a unit as an example, after the low-pressure cylinder zero output transformation, the steam intake volume of the low-pressure cylinder is reduced, a large amount of steam is used for heating, the corresponding cold source loss is reduced, and the average coal consumption of power generation in the heating season is reduced by about 40 g/(kW•h). The low-pressure cylinder zero-output transformation technology breaks through the traditional heating unit operation theory, realizes the zero-output operation of the low-pressure cylinder of the unit, thereby greatly reducing the cooling steam consumption of the low-pressure cylinder, improving the electromechanical peak regulation capacity and heating and pumping capacity of the steam turbine, and can realize the online flexible switching of the pumped condensate operation mode and the zero output operation mode, so that the unit also has the characteristics of high back pressure unit heating capacity and flexible operation mode of the pumping condensate heating unit, which significantly improves the operational flexibility.
Fig. 5 Low-pressure cylinder zero-output heating technology system
2.3.4 Thermal storage coupling peak shaving technology
The current thermal power unit flexibility is poor, mainly because the boiler of the unit and the steam turbine have a strong coupling relationship, when the need for wide load operation, the steam turbine has a good load regulation ability, but the boiler is limited by the minimum stable combustion load, can not further reduce the load rate, limiting the peak regulation capacity of the unit. In order to increase the flexibility of thermal power units and apply for deep peak shaving, measures need to be taken to decouple the boilers and turbines of the unit.
Energy storage can be used to charge at the trough of the electricity load and discharge at the peak of the power supply to reduce the load spike. The substitution effect of the energy storage system can be used to release the capacity of coal power, thereby improving the utilization rate of thermal power units and increasing their economy.
At present, the engineering application can already be realized is the peak shaving technology of high-temperature molten salt storage thermal coupling thermal power unit, and its system structure is shown in Figure 6.
When the unit participates in the power grid peak regulation needs to reduce the output, keep the boiler load unchanged, by extracting part of the main steam and reheat steam into the heat storage module, after heat exchange, return to the corresponding thermal system interface of the unit according to the parameter matching, so as to realize the reduction of the output of the unit while storing part of the heat in the heat storage module; when the unit participates in the peak regulation of the power grid, it still keeps the boiler load unchanged, and extracts part of the steam or feed water from the corresponding thermal system interface of the unit according to the parameter matching. After the heat exchange, the steam or feed water is mixed with the corresponding thermal system interface according to the parameters, and the unit is returned to the unit to achieve an increase in the output of the unit.
When the unit requires low load operation, the boiler combustion amount is unchanged, the steam turbine load is reduced, the high-grade energy storage is stored by the heat storage medium, the load change is not affected by the minimum stable fuel load of the boiler, and the peaking load range and flexibility of the unit are increased, and the demand for deep peak shaving can be realized, and the peak regulation depth is reduced to 18% of the rated load.
Figure 6 Peak shaving technology of high-temperature molten salt storage and thermal coupling thermal power unit
When the unit requires high load operation, the boiler combustion rate is unchanged, and the heat storage medium is used to release heat to increase the load of the steam turbine and improve the energy utilization efficiency. The steam turbine unit can achieve continuous expansion of 5% during the peak period of the unit without other modifications.
2.4 Policy recommendations for peak shaving of coal-fired power units
In 2020, coal power generation capacity will be about 4.8 trillion kW•h, accounting for 65% of the total power generation of the whole society, with an annual utilization hour of 4 400 h and a load rate of about 50%. If the load rate is reduced to 30%, the annual utilization hours will be 2 600 h, and the annual power generation will be reduced to 2.8 trillion kW•h, which can make room for new energy grids and maintain the peak regulation backup function of coal power.
After the peak shaving of coal power, the coal burning volume of the entire industry was reduced by about 534 million tons/a, and the total co21.53 billion t/a reduction was made。 It is recommended to use emission reductions to make up for the cost gap and compensate for carbon trading for peak shaving standby coal-fired power units that free up space on the grid. For units that can meet the special requirements of the power system in a timely manner under extreme circumstances, special financial incentives are given to ensure that the peak shaving backup function of coal-fired power units is not abandoned and the stability of the entire power system is ensured.
3 Carbon capture and application technology
Carbon capture, utilization and storage (CCUS) refers to the separation of CO2 from industrial or other sources of emissions and transported to specific locations for use or storage to achieve long-term isolation of collected CO2 from the atmosphere (Figure 7). CCUS technology is an important technical component of the continent to achieve carbon peaking by 2030 and carbon neutrality by 2060.
Figure 7 THE CCUS system
CO2 geological storage refers to the process of storing captured CO2 in geological structures through engineering and technical means to achieve long-term isolation from the atmosphere. According to the classification of different storage geological bodies, it mainly includes technologies such as onshore saline water reservoir storage, seabed saline water reservoir storage, and depleted oil and gas field storage. Almost all of the technical elements required for the storage of onshore brackish aquifers exist in the oil and gas extraction industry, and the existing technical elements in the oil and gas industry can partially meet the needs of demonstration projects. For China, the degree of development of various technical elements of onshore saline reservoir storage is very inconsistent, of which monitoring and early warning, remediation technology, etc. are still only at the level of research and development. The storage of the seabed saline layer has some similarities with the storage of the terrestrial saline layer, but the engineering is more difficult. Foreign countries have many years of engineering practice experience, but there is no exemplary precedent in China.
3.1 Policy recommendations on carbon capture technologies
The installation of CCUS in thermal power can promote near-zero carbon emissions in the power system, provide stable and clean electricity, balance the volatility of renewable energy generation, and play an important role in inertia support and frequency control in avoiding seasonal or long-term power shortages. Therefore, the competitiveness of CCUS technology in the power system will continue to increase with full consideration for power system flexibility, reliability and carbon emissions.
The installation of CCUS in thermal power can avoid the early retirement of units that have already been put into production, and reduce the economic cost of achieving the goal of "carbon peaking and carbon neutrality". Carbon capture retrofit is the most attractive for some nearby thermal power plants that can store CO2 or utilize CO2, and the use of captured CO2 for oil flooding can greatly improve the economic benefits of CCUS technology. At the same time, considering incentives such as the carbon market and carbon tax, CCUS is expected to achieve commercial promotion in the future.
3.2 Technical and economic analysis of carbon capture
CO2 emissions in the power industry are low-concentration emission sources, and the capture cost is relatively high. Installing carbon capture devices will incur additional capital investments and operational and maintenance costs, etc. Taking the installation of thermal power plants as an example, the cost of the first generation of post-combustion capture technology (in terms of CO2, the same below) is about 300~450 yuan/t, the energy consumption (in terms of CO2, the same below) is about 3.0 GJ/t, and the power generation efficiency loss is 10 percentage points to 13 percentage points; the energy consumption of the second generation of combustion post-capture technology is about 2.0 to 2.5 GJ/t, and the power generation efficiency loss is 5 percentage points to 8 percentage points. In addition, under the realistic conditions that most projects are still based on tank trucks as the main mode of transportation, the introduction of CO2 transportation will also increase the operating cost of about 1 yuan / (t•km), and when the transportation distance reaches 100 km, the operating cost per ton will also increase by hundreds of yuan.
Carbon market trading can compensate for the deployment cost of CCUS technology to some extent. China is promoting the establishment of a national carbon trading market, and the power generation industry is the first entity to be included in the transaction. Overall, the current carbon quota turnover and turnover showed an upward trend, as of August 2020, the cumulative transaction volume of the carbon market in the pilot provinces and cities exceeded 400 million tons, and the cumulative turnover exceeded 9 billion yuan. It is predicted that by 2030, China's average carbon price (in terms of CO2, the same below) will rise to 93 yuan / t, and by 2050 will exceed 167 yuan / t. The development and gradual improvement of the carbon trading market in the future and the increase in carbon prices will offset some of the cost of CCUS. In general, in the short term, it is necessary to rely on subsidy policies to obtain partial application.
3.3 Application prospects of carbon capture technology
Due to technological maturity and cost reasons, mainland CCUS technology should still be based on research and development demonstration before 2030, and will not be developed on a large scale. Therefore, before 2030, the mainland's carbon emission reduction mainly relies on the vigorous development of energy conservation and efficiency and renewable energy technologies, CCUS technology is an important strategic reserve technology for the mainland to reduce greenhouse gas emissions in the future. After 2030, with the advancement of technology, the improvement of carbon prices, and the development of CO2 flooding and utilization technology, the potential of CCUS application value will be greatly released, becoming an important technical guarantee for the transformation of the continent's fossil energy-based energy structure to a low-carbon diversified energy supply system.
4 Conclusion
1) Coal power is a strategic force for the mainland's power security, and the mainland's construction of a socialist modern country and the satisfaction of the people's yearning for a better life require retaining a certain proportion of coal power shares. Coal combustion is the main source of CO2 emissions. As a result, coal power will continue to reduce its power generation capacity while meeting the security of power supply to achieve less carbon emissions. It is predicted that by 2030, the mainland needs to retain 1.213 billion kW of installed coal-fired power generation capacity; it will still need to maintain about 700 million kW by 2060 to ensure the safety of the mainland's energy and electricity supply and peak shaving and heating needs.
2) The low-carbon development of coal power is crucial to the realization of the mainland's "double carbon" goal. For the stock of coal-fired power units, it is necessary to vigorously carry out energy-saving and efficiency-improvement transformation to reduce coal consumption to less than 300 g/(kW•h). For units that have reached the design life, the economy of the unit is greatly improved by means of unit life extension modification and synchronous implementation of parameter modification. In addition, it is necessary to promote scientific and technological innovation, vigorously develop new and efficient power systems such as high-parameter supercritical technology and supercritical CO2 cycle, and reduce the coal consumption of new coal-fired power units to less than 250 g/(kW•h).
3) At the same time, comprehensively enhance the flexibility of coal-fired power units, vigorously develop technologies such as boiler deep peak regulation, thermal electrolytic coupling and energy storage coupling peak regulation, and improve the peak regulation adaptability of the control system, formulate peak regulation incentive policies, and provide support for large-scale access to renewable electricity。
4) In addition, it is necessary to reserve carbon capture and storage technologies, develop low-cost CCUS technologies, and strengthen policy guidance to ensure the realization of carbon neutrality goals by 2060.
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