Supercritical carbon dioxide and steam coupled pi-shaped boiler and power generation system

Abstract

The invention discloses a supercritical carbon dioxide and steam coupled pi-shaped boiler and a power generation system, and relates to the field of heat energy engineering and power generation equipment. The problem that in the prior art, on the premise that the safety of a hearth is guaranteed, the requirements of a supercritical carbon dioxide boiler for a low-flow-resistance and high-efficiency system cannot be met at the same time is solved. A steam working medium loop and a supercritical carbon dioxide working medium loop are arranged at the same time. The hearth water cooling wall and the rear flue enclosure wall are both cooled through water working media. The supercritical carbon dioxide loop adopts a screen type heating surface to be arranged above the hearth and a horizontal flue, and comprises a primary reheating system to improve the efficiency. A steam loop adopts a reheating-free system, and efficient waste heat utilization is achieved through the economizer and the superheater which are connected in parallel. Through double-working-medium coupling and heat gradient utilization, efficient cooperation of the steam Rankine cycle and the supercritical carbon dioxide Brayton cycle is achieved at the same time. The invention is used for thermoelectric systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal energy engineering and power generation equipment, in particular to a boiler structure, and specifically to a supercritical carbon dioxide and steam coupled π-type boiler and power generation system. BACKGROUND

[0002] The supercritical carbon dioxide Brayton cycle, which uses supercritical carbon dioxide as the working medium, has broad application prospects in the fields of power generation, aerospace, etc. due to its compact system and high efficiency potential. In theory, the thermal efficiency of the supercritical carbon dioxide Brayton cycle can exceed that of the traditional steam Rankine cycle in the high-temperature and high-parameter range.

[0003] However, the conversion of this theoretical advantage into an actually usable supercritical carbon dioxide boiler system faces enormous engineering and technical challenges, with the core difficulty mainly originating from the unique properties of supercritical carbon dioxide working medium and its extreme sensitivity to system parameters.

[0004] Firstly, the cooling capacity of supercritical carbon dioxide in the boiler furnace is insufficient, and there is a risk of over-temperature pipe explosion. The boiler furnace is the main area where the combustion products release radiant heat, and the heating surface (usually referred to as "gas cooling wall") arranged inside it needs to withstand extremely high heat flux density. In traditional steam boilers, the water cooling wall using water as the working medium can effectively control the tube wall temperature within the material allowable range due to its extremely high latent heat of vaporization and excellent heat transfer performance. However, supercritical carbon dioxide is a single-phase fluid, and there is no phase change endothermic process, and its specific heat capacity, density and other physical properties will change dramatically in the near-critical region. The fundamental reason is that the convective heat transfer coefficient of supercritical carbon dioxide with the tube wall is significantly lower than that of water at the same mass flow rate. This means that the tube wall temperature of the supercritical carbon dioxide gas cooling wall will be much higher than that of the steam boiler water cooling wall when absorbing the same amount of heat. If the design concept of the steam boiler is directly applied, the supercritical carbon dioxide gas cooling wall will not be sufficiently cooled, which will easily lead to overheating of the metal material, reduction of strength, and ultimately cause pipe explosion accidents, seriously threatening the safe operation of the boiler. This inherent property difference makes the design criteria of conventional boilers unable to be directly applied to supercritical carbon dioxide furnaces, and the selection and design lack mature and reliable guiding principles, which is the primary technical bottleneck restricting the development of large-capacity supercritical carbon dioxide boilers.

[0005] Secondly, the supercritical carbon dioxide Brayton cycle efficiency is highly sensitive to the system pressure drop, which puts extremely strict requirements on the boiler flow resistance control. The efficiency core of the supercritical carbon dioxide Brayton cycle comes from the high density of the working medium near the critical point and the significant reduction of compressor power consumption. However, the full play of this advantage is extremely dependent on the maintenance of the high pressure state of the system. The fundamental reason is that the compression process of the cycle is close to the critical point, and the compressor power consumption is extremely sensitive to the change of the inlet pressure. As a main pressure component in the system, the internal flow resistance loss (pressure drop) of the boiler will directly cause the back pressure of the turbine to rise and the inlet pressure of the compressor to decrease. Studies have shown that a small pressure drop of the system will cause a significant increase in the power consumption of the compressor, thereby sharply offsetting the benefits of turbine output power, resulting in a significant decline in the efficiency of the entire cycle. Therefore, the supercritical carbon dioxide boiler must control its flow resistance at a very low level while ensuring efficient heat exchange.

[0006] This contradiction is particularly prominent in the convection flue of the boiler. For example, if the traditional boiler wall (the heat absorbing surface surrounding the flue) uses supercritical carbon dioxide as the cooling medium, due to its small temperature rise and large specific heat capacity, it requires a large mass flow rate to absorb the heat of the flue gas, which will result in a very high flow rate in the wall tube bundle and a large pressure drop. The pressure loss brought by the use of supercritical carbon dioxide to cool the wall is far lower than the loss of cycle efficiency, and from the system level, it is not worth the cost. Therefore, how to minimize all flow resistances of supercritical carbon dioxide in the boiler while meeting the heat exchange demand is another major challenge faced by designers.

[0007] In summary, the existing technology cannot meet the low flow resistance and high efficiency system requirements of the supercritical carbon dioxide boiler while ensuring the safety of the furnace. SUMMARY

[0008] The purpose of the present application is to solve the problem that the existing technology cannot meet the low flow resistance and high efficiency system requirements of the supercritical carbon dioxide boiler while ensuring the safety of the furnace, and to provide a supercritical carbon dioxide and steam coupled π-type boiler and power generation system.

[0009] The technical solution of the present application is:

[0010] A supercritical carbon dioxide and steam coupled π-type boiler, comprising a furnace, a front flue and a rear flue forming a π-type arrangement, the furnace is vertically arranged upwards, the front flue and the rear flue are respectively vertically arranged on the two sides above the outlet of the furnace, and the three together form a symmetrical structure in the shape of "π", and further comprising a steam working medium circuit and a supercritical carbon dioxide working medium circuit;

[0011] The steam working medium circuit comprises a parallelly arranged economizer, a water-cooled wall, a package wall serving as a rear flue wall, and a parallelly arranged superheater, which are sequentially connected according to the working medium flow; the supercritical carbon dioxide working medium circuit comprises a low-temperature superheater, a partition screen type superheater arranged above the furnace outlet, a subsequent partition screen type superheater arranged in the horizontal flue, and a final superheater, which are sequentially connected according to the working medium flow; and a low-temperature reheater and a final reheater sequentially connected for reheating of high-pressure turbine exhaust gas; wherein the water-cooled wall constitutes the peripheral wall of the furnace and is cooled by water working medium, the package wall constitutes the peripheral wall of the rear flue and is cooled by water working medium, and the partition screen type superheater and the subsequent partition screen type superheater are arranged above the furnace and in the horizontal flue for heating of the supercritical carbon dioxide working medium.

[0012] Further, the water-cooled wall is a vertical tube coil membrane wall structure, or is composed of a lower furnace spiral tube coil and an upper furnace vertical tube coil.

[0013] Further, the economizer comprises a front flue economizer and a rear flue economizer, and the front flue economizer and the rear flue economizer are arranged in parallel.

[0014] Further, the superheater comprises a front flue superheater and a rear flue superheater, and the front flue superheater and the rear flue superheater are arranged in parallel.

[0015] Further, the low-temperature reheater and the final reheater are arranged in the rear flue.

[0016] Further, the rear flue is configured as a double flue structure, and the rear flue economizer, the rear flue superheater, and the reheating heating surface of the reheating system of the supercritical carbon dioxide working medium circuit are arranged on the rear flue, respectively, for independent adjustment of the temperature of the working medium flowing through the interior thereof.

[0017] Further, the steam working medium circuit is a non-reheating system.

[0018] Further, the supercritical carbon dioxide working medium circuit is a primary reheating system.

[0019] The application also provides a power generation system using the aforementioned supercritical carbon dioxide and steam coupled π-type boiler to realize coupling of the steam Rankine cycle and the supercritical carbon dioxide Brayton cycle.

[0020] Compared with the prior art, the application has the following effects:

[0021] 1. The present application combines the high efficiency of supercritical carbon dioxide in high parameter area and the high efficiency of steam power generation in low parameter, and designs a supercritical carbon dioxide and steam double working medium cycle pi type boiler arrangement scheme, realizing the coupling of steam power generation Rankine cycle and supercritical carbon dioxide power generation Brayton cycle. On the one hand, it solves the design difficulty of large-capacity supercritical carbon dioxide boiler under the existing technical conditions, and at the same time, by selectively arranging supercritical carbon dioxide high-efficiency heat transfer heating surface in the boiler, the supercritical carbon dioxide heating resistance loss is greatly reduced, and the Brayton cycle efficiency is improved. On the other hand, the flue gas waste heat can still be effectively utilized by the steam boiler, making up for the deficiency of supercritical carbon dioxide power generation system in this respect.

[0022] 2. The present application arranges water working medium and supercritical carbon dioxide heating surface on a conventional boiler at the same time, realizes the step-by-step utilization of heat generated by fuel combustion, adopts water-cooled wall for the furnace to directly apply the mature steam boiler selection guide, solves the furnace selection difficulty, and adopts steam-cooled wall for the boiler rear flue to avoid the problem that the use of supercritical carbon dioxide as the wall cooling working medium has large pressure loss and small temperature rise, which has a great influence on the efficiency of supercritical carbon dioxide Brayton cycle. The supercritical carbon dioxide selects to use the screen heating surface above the furnace and in the horizontal flue, which has the advantages of high heat transfer efficiency and low resistance. The present application can realize the maximum power generation efficiency of high-parameter steam power generation and supercritical carbon dioxide power generation system at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the present application;

[0024] Wherein: 1, front flue economizer, 2, rear flue economizer, 3, front flue superheater, 4, rear flue superheater, 5, low-temperature superheater, 6, low-temperature reheater, 7, partition screen superheater, 8, subsequent screen superheater, 9, final reheater, 10, final superheater, 11, wall; DETAILED DESCRIPTION

[0025] Specific implementation one: combined with Figure 1The embodiment is described as follows. The embodiment includes a furnace, a front flue and a rear flue forming a π-shaped arrangement, the furnace is vertically arranged upward, the front flue and the rear flue are vertically arranged on both sides of the furnace outlet respectively, and the three together form a symmetric structure in the shape of π, and the embodiment further includes a steam working medium loop and a supercritical carbon dioxide working medium loop; the steam working medium loop includes a coal economizer, a water-cooled wall, a package wall 11 serving as a rear flue wall, and a parallelly arranged superheater in sequence and in communication according to the working medium process; the supercritical carbon dioxide working medium loop includes a low-temperature superheater 5, a partition screen type superheater 7 arranged above the furnace outlet, a subsequent screen type superheater 8 arranged in the horizontal flue, and a final stage superheater 10; and a low-temperature reheater 6 and a final stage reheater 9 in sequence and in communication for reheating the high-pressure turbine exhaust; wherein the water-cooled wall constitutes the four surrounding walls of the furnace and is cooled by water working medium, the package wall 11 constitutes the four surrounding walls of the rear flue and is cooled by water working medium, the partition screen type superheater 7 and the subsequent screen type superheater 8 are arranged above the furnace and in the horizontal flue, and are used for heating the supercritical carbon dioxide working medium.

[0026] The embodiment directly uses the water-cooled wall with mature technology to protect the furnace. Water will change into steam in the furnace, absorbs a large amount of heat (latent heat of vaporization), and can extremely reliably control the metal tube wall temperature within a safe range. The embodiment completely avoids the huge safety risk brought by the immature supercritical carbon dioxide gas-cooled wall technology, and makes it possible to build a large-capacity, high-parameter supercritical carbon dioxide boiler. The main supercritical carbon dioxide high-temperature heating surface (screen type superheater) is arranged in the furnace outlet and the spacious horizontal flue. The space is large, and the screen type structure with large pitch and sparse tube bundle can be used. When the supercritical carbon dioxide working medium flows in these screen type heating surfaces, the flow channel is short and smooth, and the working medium can absorb high-intensity radiation heat and convection heat at a low flow rate, so as to reduce the flow pressure loss to the minimum while ensuring the heat transfer effect, and the efficiency of the supercritical carbon dioxide cycle is preserved.

[0027] The embodiment uses the "mixed" layout to make the water and supercritical carbon dioxide working media "perform their respective functions" in the boiler - the water is responsible for "safety protection" and "waste heat recovery", and the supercritical carbon dioxide is responsible for "high-efficiency work", and finally safely realizes the coupling of the two advanced power cycles, and breaks through the technical bottleneck of the single supercritical carbon dioxide boiler.

[0028] Specific embodiment two: combination Figure 1 The water-cooled wall of the embodiment is a vertical tube ring membrane wall structure, or is composed of a lower furnace spiral tube ring and an upper furnace vertical tube ring.

[0029] In this way, the structure is simple, the cost is low, and the installation and maintenance are easy. The other components and connection relationships are the same as those of the specific embodiment one.

[0030] In a vertical tube coil membrane wall structure, all tubes are arranged parallel and straight around the furnace. The structure is very simple and easy to weld and assemble. The tubes are welded together with fins to form a continuous "membrane" (hence the name membrane wall), completely sealing the furnace and effectively preventing flue gas leakage, thus improving boiler efficiency and safety. The entire wall structure is flat, allowing for uniform absorption of radiant heat from the furnace flame.

[0031] Under ultra-high pressure (such as supercritical and ultra-supercritical), the density difference of the working fluid decreases, and the natural circulation capacity weakens. In vertical pipelines, the working fluid velocity may be uneven, and under certain operating conditions (such as low load), individual pipes may be at risk of overheating due to excessively slow working fluid velocity and insufficient cooling.

[0032] The lower furnace spiral tube coil and the upper furnace vertical tube coil fundamentally solve the problem of reliable cooling of the furnace water-cooled wall under supercritical pressure, ensuring that overheating does not occur under any load.

[0033] Specific implementation method three: Combining Figure 1 This embodiment describes an economizer comprising a front flue economizer 1 and a rear flue economizer 2, which are connected in parallel.

[0034] This configuration facilitates precise control of steam temperature; ensures balanced heat absorption in the flue, preventing localized wear; and improves the flexibility and reliability of system operation. Other components and connections are the same as in specific implementation methods one or two.

[0035] Specific implementation method four: Combination Figure 1 This embodiment describes a superheater comprising a front flue superheater 3 and a rear flue superheater 4, which are connected in parallel.

[0036] This configuration enables precise, flexible, and efficient control of the superheated steam temperature. Other components and connections are the same as in any of the three specific embodiments.

[0037] Specific Implementation Method Five: Combining Figure 1 In this embodiment, the low-temperature reheater 6 and the final-stage reheater 9 are arranged within the rear flue. This arrangement provides an optimal flue gas thermal environment for the safe, efficient, and controllable operation of the supercritical carbon dioxide reheat system. Other components and connections are the same as in any of the specific embodiments one through four.

[0038] Specific Implementation Method Six: Combination Figure 1In this embodiment, the rear flue of the embodiment is configured as a double flue structure, and the rear flue economizer 2, the rear flue superheater 4, and the reheating heating surface of the reheating system of the supercritical carbon dioxide working medium loop are arranged respectively to independently adjust the temperature of the working medium flowing through the inside thereof.

[0039] In this way, in order to solve the complex temperature adjustment problem of the multi-working medium coupled boiler, a partitioned, independent, and fine flue gas side adjustment scheme is provided, so as to ensure that the steam and the supercritical carbon dioxide two cycles can be operated efficiently and safely under the optimal design parameters. The other components and connection relationships are the same as any one of embodiments one to five.

[0040] Embodiment seven: in combination with Figure 1 In this embodiment, the steam working medium loop of the embodiment is a non-reheating system.

[0041] In this way, under the framework of double-working medium coupling, a strategic design selection is adopted to maximize the overall system efficiency, simplify the structure, and optimize the investment cost. The other components and connection relationships are the same as any one of embodiments one to six.

[0042] Embodiment eight: in combination with Figure 1 In this embodiment, the supercritical carbon dioxide working medium loop of the embodiment is a primary reheating system.

[0043] In this way, the thermal efficiency of the supercritical carbon dioxide Brayton cycle is significantly improved. The other components and connection relationships are the same as any one of embodiments one to seven.

[0044] Embodiment nine: in combination with Figure 1 In this embodiment, a power generation system is provided, which uses a supercritical carbon dioxide and steam coupled π-type boiler to realize the coupling of the steam Rankine cycle and the supercritical carbon dioxide Brayton cycle.

[0045] The steam boiler has been developed for a hundred years and is a very mature design. A large amount of experience data has been accumulated in the heating surfaces and temperature adjustment of each stage of the boiler. The present application simultaneously arranges the water working medium and the supercritical carbon dioxide heating surface on the conventional boiler of the furnace of the supercritical carbon dioxide boiler. The furnace adopts a water-cooled wall, which can directly apply the mature steam boiler selection guide (adopting a conventional vertical tube ring membrane wall or a lower furnace spiral tube ring and an upper furnace vertical tube ring), to solve the difficulty in selecting the furnace. The boiler rear flue also adopts a steam cooling package wall, which avoids the problem that the use of supercritical carbon dioxide as the package wall cooling working medium has a large pressure loss, a small temperature rise, and a large impact on the efficiency of the supercritical carbon dioxide Brayton cycle.

[0046] The supercritical carbon dioxide selects the screen heating surface above the furnace and the horizontal flue, has the advantages of high heat transfer efficiency and low resistance. The application can realize the high parameter steam power generation and the supercritical carbon dioxide power generation system in parallel, wherein the supercritical carbon dioxide is a primary reheating system, and the water working medium is a non-reheating system. The boiler is arranged in a π type, and double flues are arranged at the tail for temperature adjustment of the supercritical carbon dioxide working medium. For the water working medium process: the boiler feed water is preheated through the parallel front flue economizer 1 and rear flue economizer 2, then the undersaturated water enters the boiler water wall and the wall 11 to become micro-superheated steam, then enters the parallel front flue superheater 3 and rear flue superheater 4 to become superheated steam and is output externally. For the supercritical carbon dioxide process: the boiler feed gas is preliminarily heated through the low-temperature superheater 5, then is further heated through the partition screen superheater 7 and the subsequent screen superheater 8, and finally is heated to the rated gas temperature through the final superheater 10; the main gas is made to work through the high-pressure turbine, the exhaust gas enters the reheating process, the cold reheated gas is preliminarily heated through the low-temperature reheater 6, and then is heated to the required reheated gas temperature through the final reheater 9.

[0047] The above examples are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A supercritical carbon dioxide and steam coupled π-type boiler, comprising a furnace, a front flue and a rear flue arranged in a π-shape, wherein the furnace is arranged vertically upwards, and the front and rear flues are respectively arranged vertically on both sides above the furnace outlet, the three together forming a symmetrical "π"-shaped structure, characterized in that: It also includes a steam working fluid circuit and a supercritical carbon dioxide working fluid circuit; The steam working fluid circuit includes an economizer, a water-cooled wall, a wall 11 serving as the wall surface of the rear flue, and a superheater arranged in parallel, connected sequentially according to the working fluid flow. The supercritical carbon dioxide working fluid loop includes a low-temperature superheater (5) connected in sequence according to the working fluid flow, a partition screen superheater (7) arranged above the furnace outlet, a follow-up screen superheater (8) arranged in the horizontal flue, and a final stage superheater (10); and a low-temperature reheater (6) and a final stage reheater (9) connected in sequence for reheating the high-pressure turbine exhaust gas. Among them, the water-cooled wall forms the four sides of the furnace and is cooled by water, the wall (11) forms the four sides of the rear flue and is cooled by water, and the partition screen superheater (7) and the subsequent screen superheater (8) are arranged above the furnace and in the horizontal flue to heat the supercritical carbon dioxide working medium.

2. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 1, characterized in that, The water-cooled wall is a vertical tube membrane wall structure, or it is composed of a lower furnace spiral tube coil and an upper furnace vertical tube coil.

3. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 2, characterized in that, The economizer includes a front flue economizer (1) and a rear flue economizer (2), which are connected in parallel.

4. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 3, characterized in that, The superheater includes a front flue superheater (3) and a rear flue superheater (4), which are connected in parallel.

5. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 4, characterized in that, The low-temperature reheater (6) and the final stage reheater (9) are arranged in the rear flue.

6. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 5, characterized in that, The rear flue is constructed as a dual flue structure, with the rear flue economizer (2), the rear flue superheater (4) and the reheating surface of the supercritical carbon dioxide working fluid circuit reheating system arranged respectively, for independently adjusting the temperature of the working fluid flowing through it.

7. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 6, characterized in that, The steam working fluid loop is a non-reheating system.

8. A π-type boiler coupled with supercritical carbon dioxide and steam according to claim 7, characterized in that, The supercritical carbon dioxide working fluid loop is a single reheat system.

9. A power generation system, characterized in that, It uses a π-type boiler that couples supercritical carbon dioxide and steam as described in any one of claims 1-8 to achieve coupling of steam Rankine cycle and supercritical carbon dioxide Brayton cycle.

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