A pumped storage power station with multiple upper reservoirs

Abstract

The application discloses a pumped storage power station with multiple upper reservoirs, and aims at the problem that the capacity of the upper reservoir of the pumped storage power station is limited by the topography of a mountain and cannot be expanded, proposes to use multiple upper reservoirs, and establish two sets of systems of underground pumped power generation and ground pumped water, reduce the number of generator units, reduce the excavation amount of the underground powerhouse, expand the pumped water flow, better match the daily characteristics of photovoltaic power generation, ensure that the pumped storage power station can realize daily circulation, and expand the scale and annual power generation of the pumped storage power station.

Description

Technical Field

[0001] This invention relates to the field of pumped storage power station technology, and in particular to a pumped storage power station with a multi-stage upper reservoir. Background Technology

[0002] Pumped storage power stations typically construct their upper reservoirs in mountain top basins. However, due to the constant natural weathering and geological processes that affect these basins, their area is often limited, making it difficult to expand the capacity of the upper reservoir and necessitating optimization. Summary of the Invention

[0003] The main difference between the new power system and the fossil energy power system is that wind and solar power replace coal power. Photovoltaic power generation generates electricity for 6-10 hours a day throughout the year, with very little or no power generation at other times. Due to the large-scale simultaneous nature of photovoltaic power generation, it will replace nighttime coal power as the main source of pumped water power for pumped storage power stations in the electricity market. This requires pumped storage power stations to pump water to fill the upper reservoir for 6-8 hours a day, and generate electricity for the remaining 10 hours or more. Existing pumped storage power stations have relatively small storage capacity. For example, a 1.2 million kilowatt pumped storage power station that can operate at full capacity for 6 hours continuously generates 1,200 hours of electricity per year, producing 1.44 billion kilowatt-hours annually. This is only equivalent to 26.7% of the annual power generation of a 1.2 million kilowatt coal-fired power station that operates for 4,500 hours per year. Due to the small scale of pumped storage power stations, the cost per kilowatt-hour over their entire life cycle is relatively high. Relying solely on the electricity price difference in the electricity market cannot guarantee a reasonable return, and the power system needs to pay capacity charges. If the scale of pumped storage power stations can be expanded, the annual power generation of pumped storage power stations can be increased. Under the premise that the intraday price difference in the electricity spot market is relatively fixed, the revenue from the electricity price difference can be increased, the capacity charge can be reduced, and a gradual transition to market-oriented units can be achieved. Under the premise of a fixed water head, the capacity of the upper and lower reservoirs is the main factor determining the energy storage capacity of a pumped storage power station. Among them, the power generation capacity that the upper reservoir can form is often the main constraint. The upper reservoir often utilizes the mountaintop to form a mountaintop basin, but the area of ​​the mountaintop is limited. For a pumped storage power station with a rated head of 500 meters and a capacity of 1.2 million kilowatts, the power generation capacity of the upper reservoir is 7-8 million cubic meters. This makes it difficult for the main pumped storage power stations to reach an energy storage capacity of more than 10 million kilowatt-hours. The lower reservoir is located at a lower elevation, making it relatively easier to form a larger capacity. To increase the energy storage capacity of a pumped storage power station, it is necessary to find ways to expand the power generation capacity of the upper reservoir.

[0004] The present invention adopts the following technical measures to solve the problem of expanding the storage capacity of the upper reservoir: when selecting the site for a pumped storage power station, there are often multiple intermediate mountain tops and intermontane depressions between the proposed upper mountain-top reservoir and lower reservoir, which can form a plurality of upper reservoirs with different height differences. For example, if the height difference between the upper reservoir and the lower reservoir is 600 meters, there may be a plurality of mountain tops or intermontane depressions suitable for reservoir construction at elevations of 500 meters, 450 meters and 350 meters from the lower reservoir. Then a plurality of upper reservoirs are constructed at these reservoir-forming positions, and each upper reservoir is connected to the same underground powerhouse through a separate water conveyance tunnel. The advantage of connecting to the underground powerhouse respectively is that it can solve the technical condition that the head difference of different upper reservoirs is too large to be met by the same unit in terms of head variation range. Reversible pump-turbines with different rated heads are used to connect to the upper reservoirs of different heights respectively. For example, at an elevation of 600 meters, there is a site where Upper Reservoir 1 with a capacity of 5 million cubic meters can be constructed, with a power generation capacity of 7.36 million kWh; at an elevation of 450 meters, there is a site where Upper Reservoir 2 with a capacity of 6 million cubic meters can be constructed, with a power generation capacity of 6.62 million kWh; at an elevation of 350 meters, there is a site where Upper Reservoir 3 with a capacity of 7 million cubic meters can be constructed, with a power generation capacity of 6.01 million kWh; the lower reservoir can have a storage capacity that can accommodate the above three upper reservoirs. In the same underground powerhouse, the No.1 water conveyance tunnel from Upper Reservoir 1 is connected via a bifurcated pipe to two 350,000-kW reversible pump-turbines, Unit 1 and Unit 2, with a rated head of 600 meters in the underground powerhouse. Optionally, the number of continuous full-load generation hours is selected as 12 hours (the full-load generation hours can be selected in the range of 8-14 hours according to the storage capacity of upper reservoirs at all levels and the power market situation in the region), and the number of generation hours matches the storage capacity of Upper Reservoir 1; similarly, Upper Reservoir 2 is connected via Water Conveyance Tunnel 2 and a bifurcated pipe to two 300,000-kW reversible pump-turbines, Unit 3 and Unit 4, with a rated head of 450 meters in the same underground powerhouse, and the number of continuous full-load generation hours is also 12 hours, with the power generation capacity matching the storage capacity of Upper Reservoir 2; Upper Reservoir 3 is connected via Water Conveyance Tunnel 3 and a bifurcated pipe to two 300,000-kW reversible pump-turbines, Unit 5 and Unit 6, with a rated head of 350 meters in the same underground powerhouse, and the power generation capacity matches the storage capacity of Upper Reservoir 3. In this way, the same underground powerhouse uses six units in pairs to solve the power generation problem of the three upper reservoirs with different rated heads. The key here is to extend the number of continuous full-load generation hours to more than 8 hours (the current usual 6 hours of continuous full-load generation hours is not feasible). Extending the number of continuous full-load generation hours to more than 8 hours can use fewer generator units and reduce the space of the underground powerhouse. However, since photovoltaic power generation lasts for 10 hours during the daytime in summer, the number of continuous full-load generation hours of the pumped storage power station supporting photovoltaics cannot exceed 14 hours, otherwise the continuous power generation duration in summer will be insufficient.With the power generation issue resolved, let's examine the pumping capacity. The daily photovoltaic power generation duration is 6-10 hours throughout the year, both winter and summer. The goal is to utilize this peak photovoltaic power generation time to fill the upper reservoir within 6-8 hours. Considering a 6-hour calculation, the upper reservoir has a capacity of 5 million cubic meters and a rated head of 600 meters. A 350,000 kW reversible turbine has a rated pumping flow rate of 57 cubic meters per second. Two turbines can pump 2.46 million cubic meters of water in 6 hours, leaving 2.54 million cubic meters unfilled. The upper reservoir has a capacity of... The first reservoir has a capacity of 6 million cubic meters and a rated head of 450 meters. The rated pumping flow rate of the 300,000 kW reversible turbine is 60 cubic meters per second. Two units can pump 2.59 million cubic meters of water in 6 hours, leaving 3.41 million cubic meters unfilled. The second reservoir has a capacity of 7 million cubic meters and a rated head of 350 meters. The rated pumping flow rate of the 300,000 kW reversible turbine is 76 cubic meters per second. Two units can pump 3.28 million cubic meters of water in 6 hours, leaving 3.59 million cubic meters unfilled. How can the insufficient pumping capacity be resolved? An additional surface pumping system is selected, pumping water in stages from the lower reservoir to upper reservoir 3, then from upper reservoir 3 to upper reservoir 2, and finally from upper reservoir 2 to upper reservoir 1. This separate surface pumping system, independent of the underground pumped power generation system, is established. Water is pumped from the lower reservoir through its associated pumped storage pump unit workshops, through a water conveyance tunnel to upper reservoir 3, then from upper reservoir 3 through its associated pumped storage pump unit workshops, through a water conveyance tunnel to upper reservoir 2, and finally through its associated pumped storage pump unit workshops, through a water conveyance tunnel to the uppermost upper reservoir 1. This completes the pumping process of the surface pumping system. This surface pumping system is independent of the power generation system above. The pumped storage pump unit workshops and water conveyance tunnels for each level are shared by the underground pumped power generation system; the shared features are the lower reservoir and the various upper reservoirs. Because the elevation difference between the various stages of the surface pumping system is relatively small, the flow rate of a 350,000 kW pumped storage pump, due to its reduced head, is much greater than that of a reversible pump-turbine in the underground pumped power generation system under pumping conditions. This overcomes the shortcomings of reversible units, such as small pumping flow and long pumping time. The combined pumping capacity of the surface and underground systems can fill all the upper reservoirs within 6-8 hours. At the same time, since the surface pumping system is only in pumping mode, the submergence depth of the pumped storage pump is not as great as that of a reversible pump-turbine. Vertical shaft semi-underground or pit semi-underground powerhouses are preferred as the form of pumped storage pump unit powerhouses. If the lower reservoir or the upper reservoir of the intermediate stage has open terrain or stepped terrain, surface-type pumped storage pump unit powerhouses can also be considered, because these forms of pumped storage pump unit powerhouses reduce investment compared to excavating underground powerhouse caverns. Underground pumped storage pump unit powerhouses should only be considered if the terrain and geological conditions are not suitable. The advantages of establishing underground pumped power generation systems and surface pumping systems are that they can reduce the number of generator units in underground power plants and reduce the excavation area of ​​underground power plants. They can also utilize surface-level stepped pumping to increase the pumping flow rate and improve pumping capacity.

[0005] To summarize the technical solution of this invention, a mountain depression with suitable head development conditions is found between the upper and lower reservoirs to form a multi-stage upper reservoir. These upper reservoirs are connected to different reversible pump-turbine units in the underground powerhouse through their respective water diversion tunnels. Reversible units that match the head of the corresponding upper reservoir are selected to solve the problem of large differences in head between different upper reservoirs (if two upper reservoirs have similar heads, and the head variation is within the applicable range of the same reversible unit, some water diversion tunnels can be combined and the same reversible unit can be shared to reduce investment). Based on the power generation capacity of the corresponding reservoir, and assuming a continuous full-load operation of 8-14 hours, the total power generation capacity and number of units of reversible pump-turbine turbines are configured to fully utilize the daily power generation time. With a water head of 300-600 meters, two existing mainstream 300,000 and 350,000 kW reversible pump-turbine turbines can basically cover the power generation capacity of the upper reservoir of 5-7 million cubic meters. In this way, the six units in one underground powerhouse can form a storage capacity of about three times that of a pumped storage power station with a single upper reservoir, which can effectively solve the problem of site selection difficulties for a single large upper reservoir. Simultaneously, an independent surface pumping system is added, utilizing water conveyance tunnels to connect the lower reservoir to the upper reservoirs at each level from low to high, ultimately connecting to the uppermost upper reservoir. This forms a cascade of independent surface pumping systems separate from the underground pumped power generation system. Because the elevation difference between adjacent upper reservoirs is greatly reduced, the head is shortened, and the flow rate of the same power storage pump increases. This creates conditions for increasing the pumping flow rate and compressing the pumping time to 6-8 hours. In addition to increasing the flow rate, the benefits of cascade pumping also include that each upper reservoir with different elevation differences is pumped and filled separately, without requiring extra work. Because the surface pumping system only operates in one direction and the head of adjacent stages is relatively small, a semi-underground powerhouse (vertical shaft semi-underground or pit semi-underground powerhouse) is preferred to meet the submergence depth requirements of the pumped storage units. If the intermediate reservoir has stepped terrain, a surface powerhouse can also be considered (meeting the submergence depth requirements of the units through the difference in terrain). The surface pumping system uses large-scale pumped storage pumps, thus forming two systems: an underground pumped power generation system from each level of upper reservoir to the underground powerhouse and then to the lower reservoir, and a surface pumping system from the lower reservoir to each level of upper reservoir. Since pumping is completed by both the underground pumped power generation system and the surface pumping system, the pumping capacity is increased. The total power of each pumped storage unit and the corresponding pipe diameter of the water conveyance tunnel are selected based on the capacity to fill each level of upper reservoir in 6-8 hours.

[0006] The technical effects achievable by this invention are as follows: ① Multi-stage upper reservoirs solve the problem of insufficient capacity expansion with a single upper reservoir, effectively increasing the energy storage capacity of pumped storage power stations. It is relatively easy to achieve the goal of tripling the power generation capacity of the upper reservoir. If the lower reservoir is an existing large reservoir, and terrain conditions permit, it is possible to achieve 5-6 times, or even higher, the energy storage capacity of existing pumped storage power stations. This provides a feasible technical solution for expanding the scale of pumped storage power stations and increasing annual power generation; ② Increase the continuous full-load operating hours of underground pumping systems, raising the current standard of 6 hours to 8-14 hours, reducing the need for underground pumping... The number of reversible pump-turbine units in the hydropower system reduces the space required for underground power plants, fully utilizes the daily power generation time, avoids power redundancy, and reduces investment; ③ The pumping capacity is increased by using large-scale energy storage pumps instead of adding reversible pump-turbines. Since large-scale energy storage pumps of the same 350,000 kW are cheaper than 350,000 kW reversible pump-turbines, and there is room for further power increase, it is not limited by the power limit of about 400,000 kW for reversible pump-turbines. In this way, the pumping capacity of reversible pump-turbines is retained, and the increased pumping capacity is solved by large-scale energy storage pumps, which can reduce the investment in pumping equipment and reduce pumping costs. ④ By utilizing a multi-stage surface pumping system, the pumping capacity of traditional pumped storage power stations is increased. Since the surface pumping system can be used to arrange the pumping pump unit plant in the ground shaft, it is free from the space limitations of underground plant. The pumping capacity can be expanded by opening up space. By utilizing the small head between the multi-stage pumping stages, the pumping flow rate is increased, overcoming the pumping capacity shortcomings of reversible pump turbines. It can fill the upper reservoirs of each stage in 6-8 hours, which can be precisely matched with the daily photovoltaic power generation and the low price period of the electricity market, ensuring that the power generation capacity of each upper reservoir can be circulated daily.

Claims

1. A pumped-storage power station with a multi-stage upper reservoir, characterized in that: ① A multi-stage pumped-storage power station comprises multiple upper reservoirs, and two independent systems: an underground pumped-storage power generation system and a surface pumping system; ② The underground pumped-storage power generation system includes upper and lower reservoirs, an underground powerhouse, a water conveyance tunnel, and reversible pump-turbine units; ③ In the multi-stage upper reservoirs, each upper reservoir with a different head is connected to a reversible pump-turbine unit in the underground powerhouse, matching the head of that upper reservoir, through an independent water diversion tunnel. The water diversion tunnels and connected units for each upper reservoir with a different head are not... Same as above; ④ The surface pumping system includes, in addition to the lower reservoir and upper reservoirs of various levels shared with the underground pumped power generation system, a pumped storage pump unit plant, large pumped storage pumps, and two adjacent water conveyance tunnels connecting the lower reservoir and the upper reservoirs of various levels with different elevation differences; ⑤ The surface pumping system can operate independently of the underground pumped power generation system, sending water from the lower reservoir through separate water conveyance tunnels, from bottom to top according to elevation differences, through large pumped storage pumps in the corresponding pumped storage pump unit plant, and gradually into the upper reservoirs of various levels.

2. The pumped-storage power station with a multi-stage upper reservoir as described in claim 1, characterized in that, The combined pumping capacity of the underground pumped power generation system and the surface pumping system is sufficient to fill all levels of upper reservoirs with water for power generation within 6-8 hours.

3. The pumped-storage power station with a multi-stage upper reservoir as described in claim 2, characterized in that, The underground pumped power generation system is configured with generator sets for 8-14 hours of continuous full-load operation.

4. The pumped-storage power station with a multi-stage upper reservoir as described in claim 1, characterized in that, The pumping and storage pump unit building of the aforementioned ground pumping system is a vertical shaft semi-underground building, a pit semi-underground building, or a ground-level building.