A high-low temperature dual-fluid solar receiver for a tower-type solar thermal power station and its design method

Abstract

The present invention discloses a high-low temperature dual-fluid solar receiver for a tower-type solar thermal power station and its design method. First, based on the magnitude of the heat flux density, a truncation criterion is used to classify the non-uniformly focused solar heat flux, and then combined with the truncated energy, a heat-absorbing tube row module for the high-heat flux region and a heat-absorbing tube row module for the low-heat flux region are designed to match. The fixed positions, truncated energy, working fluid flow rate, and operating conditions of the two modules are comprehensively matched and designed to obtain a high-low temperature dual-fluid solar receiver. Through iterative design, multiple groups of solar receivers that meet the set conditions are obtained, and the best design results are screened and output from them. The high-low temperature dual-fluid solar receiver includes a heat-absorbing tube row module for the high-heat flux region and a heat-absorbing tube row module for the low-heat flux region, which can respectively heat two heat transfer working fluids to achieve diversified and flexible utilization and reduce material costs, reduce radiative heat loss and improve energy utilization rate on the basis of two-stage energy utilization. The present invention can promote the efficient and low-cost comprehensive utilization of tower-type concentrating solar thermal power generation technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar thermal power generation, and particularly relates to a high-low temperature dual-fluid absorber for a tower-type solar thermal power station and a design method thereof. Background Art

[0002] To reduce the dependence on traditional fossil energy and improve the ecological environment, many countries are committed to promoting the utilization of renewable energy and realizing the commercialization of related industries. Solar energy has the advantages of rich reserves and no pollution, and is recognized as one of the important forms of future renewable energy utilization. Solar power generation technologies can be mainly divided into photovoltaic power generation and concentrating solar thermal power generation. Compared with photovoltaic power generation, concentrating solar thermal power generation technology can be combined with thermal energy storage technology to achieve continuous power generation day and night, and has obvious advantages in terms of dispatchability and reliability. The tower-type solar thermal power station has a relatively high concentration ratio, can achieve a higher operating temperature, and thus has the advantages of being suitable for large-scale power generation and having great potential for cost reduction, becoming the main direction of the future development of concentrating solar thermal power generation technology. The tower-type solar thermal power station mainly consists of a concentrating and heat-collecting subsystem, a heat storage and heat transfer subsystem, and a heat-work-electricity conversion subsystem. Among them, the concentrating and heat-collecting subsystem is the most obvious sign that distinguishes the tower-type solar thermal power station from traditional power stations.

[0003] The concentrating and heat-collecting subsystem is the key part of the tower-type solar thermal power station that focuses light energy and converts it into heat energy, and mainly consists of a heliostat field and an absorber. Among them, the absorber mainly has several typical structural forms such as a single-fluid exposed cylindrical tube bank absorber, a cavity-type tube bank absorber, a finned tube bank absorber, a porous medium volumetric absorber, and a particle absorber. Currently, the single-fluid exposed cylindrical absorber is the most widely used. During normal operation, the absorber receives the light energy reflected by the heliostat field and further transfers it to the internal heat transfer fluid (such as molten salt, heat transfer oil, water / steam, liquid metal, air, and particles) in the form of heat energy. This process involves the conversion of light to heat and complex multiple heat transfer processes such as conduction, radiation, and convection. Currently, some scholars have found that the uniformity of the focused solar heat flux will have a significant impact on the flow and heat transfer performance of the single-fluid exposed cylindrical absorber. That is, during actual operation, the non-uniform focused solar heat flux of the single-fluid exposed cylindrical absorber may cause local overheating, which will further lead to a significant heat radiation effect between the surface of the single-fluid exposed cylindrical absorber and the surrounding environment, and ultimately cause a large amount of radiation heat loss.

[0004] Currently, some scholars have started a series of studies on improving the thermal efficiency of a single - working - fluid exposed cylindrical absorber by improving the non - uniformity of the focused solar heat flux. For example, in terms of the heliostat field, some scholars have proposed various improved bionic heliostat fields based on the original bionic heliostat field. The results show that the improved heliostat field can converge more energy onto the single - working - fluid exposed cylindrical absorber while significantly improving the non - uniformity of the heat flux density, thereby enhancing the thermal efficiency of the single - working - fluid exposed cylindrical absorber. In terms of improving the structural form of the single - working - fluid exposed cylindrical absorber, some researchers have proposed a new type of finned absorber, which can significantly reduce radiation and reflection losses through the re - absorption effect and simultaneously reduce the peak heat flux density. Thus, while reducing the non - uniformity of the heat flux density, it improves the thermal efficiency to a certain extent.

[0005] It should be noted that under the condition of highly non - uniform heat flux density, the single - working - fluid exposed cylindrical absorber shows different energy absorption - loss situations at different layout positions. That is, at some positions, the heat flux density is low, the temperature is low, and the radiative heat loss is relatively low; at some positions, the heat flux density is high and the temperature is low, so the radiative heat loss is also relatively low; however, on the contrary, at some positions, the heat flux density is low and the temperature is high, resulting in a relatively high radiative heat loss. It can be seen that the distribution of the heat flux density of the single - working - fluid exposed cylindrical absorber is not consistent with the distribution of the radiative heat loss. Therefore, the non - uniform focused solar heat flux can be divided based on the magnitude of the heat flux density to find the area where the focused solar heat flux is consistent with the distribution of the radiative heat loss; at the same time, it is noted that there is only one kind of heat - transfer working fluid inside the single - working - fluid exposed cylindrical absorber, and its function is single.

[0006] Through research, it can also be found that current studies mainly focus on optimizing the layout of the heliostat field and the structural form of the single - working - fluid exposed cylindrical absorber itself, reducing radiative heat loss by improving the non - uniformity of the heat flux density, and thus enhancing the thermal efficiency of the absorber. However, in the actual production and application process, the workload and cost of building the heliostat field are huge, and the material cost and manufacturing difficulty of complex - structured absorbers such as finned absorbers cannot be ignored. Further work needs to be carried out on the effective utilization of the non - uniform focused solar heat flux of the single - working - fluid exposed cylindrical absorber and the innovative design of new absorber structures. Summary of the Invention

[0007] Aiming at the problems of high non - uniformity of the focused solar heat flux, large radiative heat loss, and single function of the single - working - fluid exposed cylindrical absorber in existing tower - type solar thermal power plants, the object of the present invention is to provide a high - and low - temperature dual - working - fluid absorber for tower - type solar thermal power plants and its design method. Based on the division of non - uniform focused solar heat flux, a high - and low - temperature dual - working - fluid absorber is designed to achieve two - stage utilization of energy, develop multiple functions of the absorber, and simultaneously significantly reduce radiative heat loss, improve the energy utilization rate and the thermal efficiency of the high - and low - temperature dual - working - fluid absorber.

[0008] A high-low temperature dual-working-fluid absorber for a tower-type solar thermal power station and its design method, specifically including the following steps:

[0009] Step 1: According to the rated installed capacity of the required tower-type solar thermal power station, use the currently common tower-type concentrating heat collection subsystem design software, such as the System Advisor Model (SAM) software based on analytical solutions, to obtain the heliostat field under the design conditions and the single-working-fluid exposed cylindrical absorber matched with it, as the starting point of the initial design of the present invention and the performance comparison object.

[0010] Step 2: Adopt the Monte Carlo ray tracing method, establish an optical model of the whole process of solar rays from the heliostat field to the single-working-fluid exposed cylindrical absorber through self-programming, use this model to calculate the concentrating process of the tower-type solar thermal power station for a whole year, and obtain the annual weighted heat flux density distribution of the single-working-fluid exposed cylindrical absorber; considering that the thermal efficiency of the absorber changes little within a year, select the noon of the spring equinox as the design point, and calculate the cut-off energy, thermal efficiency and heat loss of the single-working-fluid exposed cylindrical absorber at the design point. The single-working-fluid exposed cylindrical absorber uses a first heat transfer fluid, and the first heat transfer fluid will further heat the working fluid in the power cycle of the tower-type solar thermal power station to realize the power generation process. The material for manufacturing the single-working-fluid exposed cylindrical absorber is the first raw material.

[0011] Furthermore, the cut-off energy of the single-working-fluid exposed cylindrical absorber is the part of the light energy reflected by the heliostat field that irradiates on the tube wall surface, and can be directly calculated by the Monte Carlo ray tracing method. The process of calculating the thermal efficiency and heat loss of the single-working-fluid exposed cylindrical absorber in Step 2 is as follows:

[0012] S1: The calculation formula for the thermal efficiency of the single-working-fluid exposed cylindrical absorber is:

[0013] η R,th,1 =Q htf,1 / Q R,opt,1 ×100% (1)

[0014] In formula (1), η R,th,1 is the thermal efficiency of the single-working-fluid exposed cylindrical absorber; Q htf,1 is the energy absorbed by the first heat transfer fluid in the single-working-fluid exposed cylindrical absorber; Q R,opt,1 is the energy absorbed by the light-absorbing coating on the tube wall of the single-working-fluid exposed cylindrical absorber, and can be directly calculated by the Monte Carlo ray tracing method.

[0015] S2: The calculation formula for the energy absorbed by the first heat transfer fluid is:

[0016] Q htf,1 =q m,1 ×cp,1 ×(T out,1 -T in,1 ) (2)

[0017] In formula (2), q m,1 is the mass flow rate of the first heat transfer fluid; c p,1 is the specific heat capacity at constant pressure of the first heat transfer fluid; T in,1 is the temperature of the first heat transfer fluid at the inlet of the single - fluid exposed cylindrical absorber; T out,1 is the temperature of the first heat transfer fluid at the outlet of the single - fluid exposed cylindrical absorber.

[0018] S3. The calculation formula for the heat loss of the single - fluid exposed cylindrical absorber is:

[0019] Q loss,th,1 =Q R,opt,1 -Q htf,1 (3)

[0020] In formula (3), Q loss,th,1 is the heat loss of the single - fluid exposed cylindrical absorber.

[0021] The components of the heat loss of the single - fluid exposed cylindrical absorber are:

[0022] Q loss,th,1 =Q loss,rad,1 +Q loss,cond,1 +Q loss,conv,1 (4)

[0023] In formula (4), Q loss,rad,1 is the radiative heat loss of the single - fluid exposed cylindrical absorber; Q loss,cond,1 is the conductive heat loss of the single - fluid exposed cylindrical absorber; Q loss,conv,1 is the convective heat loss of the single - fluid exposed cylindrical absorber.

[0024] Step 3: Obtain the maximum annual weighted heat flux density of the single - fluid exposed cylindrical absorber. Take m% of the maximum annual weighted heat flux density as the truncation criterion. According to design experience, the value of m is generally recommended to be 1 - 30. Start the design with 1% of the maximum annual weighted heat flux density as the initial judgment truncation basis. The part of the annual weighted heat flux density at the middle position of the tube row greater than the truncation criterion is the high - heat - flux area. Correspondingly, the part of the annual weighted heat flux density near the edge of the tube row less than the truncation criterion is the low - heat - flux area. Design a high - heat - flux area absorber tube row module for the single - fluid exposed cylindrical absorber and determine the lengths of each tube row in the high - heat - flux area absorber tube row module. The high - heat - flux area absorber tube row module uses a second heat transfer fluid, and the second heat transfer fluid has the same function as the first heat transfer fluid. The material for manufacturing the high - heat - flux area absorber tube row module is the second raw material.

[0025] Step 4: Based on the spring equinox noon moment of the design point, calculate the cut-off energy, thermal efficiency, and heat loss of the heat-absorbing tube row module in the high heat flux area under the design conditions.

[0026] Furthermore, the cut-off energy of the heat-absorbing tube row module in the high heat flux area is the part of the light energy reflected by the heliostat field that irradiates on the tube wall surface, which can be directly calculated by the Monte Carlo ray tracing method. The process of calculating the thermal efficiency and heat loss of the heat-absorbing tube row module in the high heat flux area in Step 4 is as follows:

[0027] S1. The calculation formula for the thermal efficiency of the heat-absorbing tube row module in the high heat flux area is:

[0028] η R,th,2 =Q htf,2 / Q R,opt,2 ×100% (5)

[0029] In Equation (5), η R,th,2 is the thermal efficiency of the heat-absorbing tube row module in the high heat flux area; Q htf,2 is the energy absorbed by the second heat transfer working fluid in the heat-absorbing tube row module in the high heat flux area; Q R,opt,2 is the energy absorbed by the light-absorbing coating on the tube wall of the heat-absorbing tube row module in the high heat flux area, which can be calculated by the Monte Carlo ray tracing method.

[0030] S2. The calculation formula for the energy absorbed by the second heat transfer working fluid is:

[0031] Q htf,2 =q m,2 ×c p,2 ×(T out,2 -T in,2 ) (6)

[0032] In Equation (6), q m,2 is the mass flow rate of the second heat transfer working fluid; c p,2 is the specific heat capacity at constant pressure of the second heat transfer working fluid; T in,2 is the temperature of the second heat transfer working fluid at the inlet of the heat-absorbing tube row module in the high heat flux area; T out,2 is the temperature of the second heat transfer working fluid at the outlet of the heat-absorbing tube row module in the high heat flux area.

[0033] S3. The calculation formula for the heat loss of the heat-absorbing tube row module in the high heat flux area is:

[0034] Q loss,th,2 =Q R,opt,2 -Q htf,2 (7)

[0035] In Equation (7), Q loss,th,2 is the heat loss of the heat-absorbing tube row module in the high heat flux area.

[0036] The components of the heat loss of the heat-absorbing tube row module in the high heat flux area are:

[0037] Q loss,th,2 = Q loss,rad,2 +Q loss,cond,2 +Q loss,conv,2 (8)

[0038] In Equation (8), Q loss,rad,2 is the radiative heat loss of the heat absorption tube row module in the high heat flux region; Q loss,cond,2 is the conductive heat loss of the heat absorption tube row module in the high heat flux region; Q loss,conv,2 is the convective heat loss of the heat absorption tube row module in the high heat flux region.

[0039] Step 5: If the thermal efficiency of the heat absorption tube row module in the high heat flux region does not improve compared with that of the single - working - fluid exposed cylindrical heat absorber, then further select a larger truncation criterion (such as 2%), and repeat Steps 3, 4, and 5. If the thermal efficiency improves, then execute Step 6.

[0040] Step 6: Considering that it is necessary to ensure the temperature - rising effect of the second heat - transfer working fluid in the heat absorption tube row module of the high heat flux region to maintain the normal power generation of the tower - type solar thermal power plant, it is necessary to limit the truncation energy of the heat absorption tube row module in the high heat flux region, that is, it shall not be less than n% of the truncation energy of the single - working - fluid exposed cylindrical heat absorber. According to design experience, the value of n is generally 70 - 80. Taking 80 as the initial value, if the truncation energy of the heat absorption tube row module in the high heat flux region is less than 80% of that of the single - working - fluid exposed cylindrical heat absorber, then further select a larger truncation criterion (such as 3%), and repeat Steps 3, 4, 5, and 6; if the truncation energy of the heat absorption tube row module in the high heat flux region is greater than or equal to 80% of that of the single - working - fluid exposed cylindrical heat absorber, then execute Step 7.

[0041] Step 7: On the basis of determining the truncation criterion and the lengths of each tube row of the heat absorption tube row module in the high heat flux region, design a heat absorption tube row module for the low heat flux region for the single - working - fluid exposed cylindrical heat absorber, and further determine the lengths of each tube row of the heat absorption tube row module in the low heat flux region. On the basis of respectively determining the lengths of each tube row of the heat absorption tube row module in the high heat flux region and the heat absorption tube row module in the low heat flux region, the tube row lengths of the high - and low - temperature dual - working - fluid heat absorber can be determined. The heat absorption tube row module in the low heat flux region uses a third heat - transfer working fluid. The third heat - transfer working fluid can be other working fluids used to assist in realizing the functional diversity of the tower - type solar thermal power plant. When it is brackish water, methanol, R245fa, or heat - conducting oil, functions such as brackish water desalination, solar adsorption refrigeration, and power generation by solar - driven organic Rankine cycle and steam Rankine cycle can be realized. The material for manufacturing the heat absorption tube row module in the low heat flux region is the third raw material.

[0042] Step 8: After the position, truncation energy, flow rates of the two heat - transfer working fluids, and operating conditions of the heat absorption tube row module in the high heat flux region and the heat absorption tube row module in the low heat flux region are matched and designed, the two modules can be combined into a high - and low - temperature dual - working - fluid heat absorber.

[0043] A high-low temperature dual-fluid absorber for a tower-type solar thermal power station, comprising a high heat flux area absorber tube row module and a low heat flux area absorber tube row module; the low heat flux area absorber tube row module includes an upper half part and a lower half part of the low heat flux area absorber tube row module connected by a long connecting tube of the low heat flux area absorber tube row module, and the high heat flux area absorber tube row module is located between the upper half part and the lower half part of the low heat flux area absorber tube row module.

[0044] Furthermore, the high heat flux area absorber tube row module includes two flow paths, each flow path includes a number of absorber tube rows of the high heat flux area absorber tube row module that are interconnected, and both ends of each absorber tube row of the high heat flux area absorber tube row module converge to a header of the high heat flux area absorber tube row module, wherein a flow path inlet and a flow path outlet are respectively provided on the two headers of the high heat flux area absorber tube row module;

[0045] The upper half part of the low heat flux area absorber tube row module includes a number of upper half part tube rows of the low heat flux area absorber tube row module that are interconnected, and both ends of the upper half part tube rows of the low heat flux area absorber tube row module converge to a header of the upper half part of the low heat flux area absorber tube row module, and a flow path inlet of the low heat flux area absorber tube row module is provided on the header of the upper half part of the low heat flux area absorber tube row module;

[0046] The lower half part of the low heat flux area absorber tube row module includes a number of lower half part tube rows of the low heat flux area absorber tube row module that are interconnected, and both ends of the lower half part tube rows of the low heat flux area absorber tube row module converge to a header of the lower half part of the low heat flux area absorber tube row module, and a flow path outlet of the low heat flux area absorber tube row module is provided on the header of the lower half part of the low heat flux area absorber tube row module.

[0047] Furthermore, the heat transfer fluid in the low heat flux area absorber tube row module is brackish water, R245fa, methanol or heat transfer oil.

[0048] Step 9: Calculate the thermal efficiency, heat loss and material cost of the designed high-low temperature dual-fluid absorber at the design point, and compare with a single-fluid exposed cylindrical absorber.

[0049] Furthermore, in step 9, the overall process of calculating the thermal efficiency and heat loss of the high-low temperature dual-fluid absorber includes the following steps:

[0050] S1: The calculation formula for the thermal efficiency of the low heat flux area absorber tube row module is:

[0051] η R,th,3 =Q htf,3 / Q R,opt,3 ×100% (9)

[0052] In formula (9), η R,th,3 is the thermal efficiency of the low heat flux area absorber tube row module; Qhtf,3 The energy absorbed by the third heat transfer working fluid in the heat absorption tube row module in the low heat flux area; Q R,opt,3 The energy absorbed by the light-absorbing coating on the tube wall of the heat absorption tube row module in the low heat flux area.

[0053] S2. The calculation formula for the energy absorbed by the third heat transfer working fluid is:

[0054] Q htf,3 =q m,3 ×c p,3 ×(T out,3 -T in,3 )(10)

[0055] In formula (10), q m,3 is the mass flow rate of the third heat transfer working fluid; c p,3 is the specific heat capacity at constant pressure of the third heat transfer working fluid; T in,3 is the temperature of the third heat transfer working fluid at the inlet of the heat absorption tube row module in the low heat flux area; T out,3 is the temperature of the third heat transfer working fluid at the outlet of the heat absorption tube row module in the low heat flux area.

[0056] S3. The calculation formula for the heat loss of the heat absorption tube row module in the low heat flux area is:

[0057] Q loss,th,3 =Q R,opt,3 -Q htf,3 (11)

[0058] In formula (11), Q loss,th,3 is the heat loss of the heat absorption tube row module in the low heat flux area.

[0059] The components of the heat loss of the heat absorption tube row module in the low heat flux area are:

[0060] Q loss,th,3 =Q loss,rad,3 +Q loss,cond,3 +Q loss,conv,3 (12)

[0061] In formula (12), Q loss,rad,3 is the radiative heat loss of the heat absorption tube row module in the low heat flux area; Q loss,cond,3 is the conductive heat loss of the heat absorption tube row module in the low heat flux area; Q loss,conv,3 is the convective heat loss of the heat absorption tube row module in the low heat flux area.

[0062] S3. The calculation formula for the thermal efficiency of the high-low temperature dual working fluid absorber is:

[0063] η R,th =(Q htf,2 +Q htf,3 ) / ( Q R,opt,2 +Q R,opt,3)×100% (13)

[0064] In formula (13), η R,th is the thermal efficiency of the high-low temperature dual - working - fluid heat absorber, specifically the ratio of the sum of the thermal powers absorbed by the second heat - transfer fluid and the third heat - transfer fluid in the high - heat - flux area heat - absorbing tube row module and the low - heat - flux area heat - absorbing tube row module to the sum of the energies absorbed by the light - absorbing coatings on the tube walls of the high - heat - flux area heat - absorbing tube row module and the low - heat - flux area heat - absorbing tube row module.

[0065] S4. The calculation formula for the heat loss of the high - low temperature dual - working - fluid heat absorber is:

[0066] Q loss,th = Q loss,th,2 + Q loss,th,3 (14)

[0067] In formula (14), Q loss,th is the heat loss of the high - low temperature dual - working - fluid heat absorber.

[0068] S5. The calculation formula for the material cost of the single - working - fluid exposed cylindrical heat absorber is:

[0069] C1 = V1×A1 (15)

[0070] In formula (15), C1 is the cost of the first raw material of the single - working - fluid exposed cylindrical heat absorber, V1 is the usage amount of the first raw material in the single - working - fluid exposed cylindrical heat absorber; A1 is the unit price of the first raw material in the single - working - fluid exposed cylindrical heat absorber.

[0071] S6. The calculation formula for the material cost of the high - heat - flux area heat - absorbing tube row module is:

[0072] C2 = V2×A2 (16)

[0073] In formula (16), C2 is the cost of the second raw material of the high - heat - flux area heat - absorbing tube row module; V2 is the usage amount of the second raw material in the high - heat - flux area heat - absorbing tube row module; A2 is the unit price of the second raw material in the high - heat - flux area heat - absorbing tube row module.

[0074] S8. The calculation formula for the material cost of the low - heat - flux area heat - absorbing tube row module is:

[0075] C3 = V3×A3 (17)

[0076] In formula (17), C3 is the cost of the third raw material of the low - heat - flux area heat - absorbing tube row module; V3 is the usage amount of the third raw material in the low - heat - flux area heat - absorbing tube row module; A3 is the unit price of the third raw material in the low - heat - flux area heat - absorbing tube row module.

[0077] S9. The calculation formula for the material cost of the high - low temperature dual - working - fluid heat absorber is:

[0078] C=C2+C3 (18)

[0079] In formula (18), C is the material cost of the high and low temperature dual-media heat absorber, which is the sum of the material costs of the heat absorption pipe bank module in the high heat flux area and the heat absorption pipe bank module in the low heat flux area.

[0080] Step 10, compare the thermal efficiency, heat loss and material cost of the high-low temperature dual-fluid heat absorber and the single-fluid exposed cylindrical heat absorber. If the thermal efficiency of the high-low temperature dual-fluid heat absorber can be improved by at least 1% and the material cost can be reduced by at least 5%, proving that it has advantages in energy utilization and material cost, then execute step 11; otherwise, further select a smaller n value and return to step 6 for redesign.

[0081] Step 11: Save the design results of the tube row length, thermal efficiency, material cost, etc. of the high and low temperature dual-medium heat absorber.

[0082] Step 12, determine whether the current n value is greater than 70, if so, further select a smaller n value and return to step 6 to redesign; otherwise, execute step 13.

[0083] Step 13, screening the results saved in step 11, outputting the optimal design results of the tube row length, thermal efficiency and material cost of the high and low temperature dual working fluid heat absorber, and ending the design process of the high and low temperature dual working fluid heat absorber.

[0084] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0085] 1. The present invention provides a design method for a high-low temperature dual-fluid heat absorber. Based on the size of the heat flux density, the non-uniform focused solar heat flux is divided, and the high heat flux area heat absorption pipe row module and the low heat flux area heat absorption pipe row module are designed to heat the second heat transfer medium and the third heat transfer medium respectively. The high-low temperature dual-fluid heat absorber can find the area where the focused solar heat flux and the radiation heat loss are distributed in a consistent manner by dividing the non-uniform focused solar energy flow, realizing the two-level utilization of energy to heat the two working fluids, developing the diversity of the absorber functions, and significantly reducing the radiation heat loss of the high-low temperature dual-fluid heat absorber, thereby improving the energy utilization rate and the thermal efficiency of the high-low temperature dual-fluid heat absorber, and providing a new idea and theoretical method for the design of the absorber structure in the tower solar thermal power station.

[0086] 2. The high-low temperature dual-working fluid heat absorber provided by the present invention can heat the second heat transfer fluid with a higher temperature and the third heat transfer fluid with a lower temperature through the high heat flux area heat pipe row module and the low heat flux area heat pipe row module respectively. Since the service temperatures and physical properties of the two heat transfer fluids are different, materials with different temperature resistance performances and costs can be used to manufacture the high heat flux area heat pipe row module and the low heat flux area heat pipe row module respectively. And due to the lower service temperature of the low heat flux area heat pipe row module, the materials used have more advantages in terms of processability, manufacturing difficulty and market maturity, etc. At the same time, the cost of using the heat transfer fluid can be reduced by using the low-temperature heat transfer fluid. In summary, compared with the single-working fluid exposed cylindrical heat absorber, the high-low temperature dual-working fluid heat absorber can significantly reduce the cost of raw materials.

[0087] 3. The high-low temperature dual-working fluid heat absorber provided by the present invention can heat two heat transfer fluids simultaneously. On the basis of realizing the high-temperature working fluid thermodynamic cycle power generation function in the original tower-type solar thermal power station through the high heat flux area heat pipe row module, it can further heat low-temperature working fluids such as methanol, brackish water, R245fa and heat-conducting oil through the low heat flux area heat pipe row module, so as to realize processes such as solar adsorption refrigeration, solar desalination of brackish water, solar-driven medium-low temperature organic Rankine cycle and steam Rankine cycle power generation, etc., which involve multiple application fields. While developing the functional diversity of the heat absorber, it can be flexibly selected according to different usage requirements. In application, the high-low temperature dual-working fluid heat absorber can flexibly regulate the intercepted energy of the high heat flux area heat pipe row module and the low heat flux area heat pipe row module by combining with the heliostat field aiming strategy, and can also perform matching design on aspects such as the flow rate and flow path of the two heat transfer fluids, the header and connecting pipes, and the system process according to requirements. The high-low temperature dual-working fluid heat absorber has the advantages of flexible use and diversification, and may provide a reference for promoting the innovative integration development of the key technologies of tower-type concentrating solar thermoelectricity.

[0088] In summary, for the high-low temperature dual - working - fluid heat absorber and its design method described in the present invention, based on the magnitude of the heat flux density, the non - uniform concentrated solar heat flux is divided, and the region where the concentrated solar heat flux is consistent with the radiative heat loss is found. The heat - absorbing tube row module for the high - heat - flux region and the heat - absorbing tube row module for the low - heat - flux region are designed respectively. By heating two heat - transfer working fluids with different temperatures, the material cost is reduced, the radiative heat loss is decreased, and the energy utilization rate is improved. At the same time, the heat - transfer working fluid of the low - heat - flux region heat - absorbing tube row module can be flexibly and diversely selected according to the usage requirements and application scenarios, realizing the diversity of the heat absorber functions. This high - low temperature dual - working - fluid heat absorber can also be further combined with aspects such as the heliostat field aiming strategy, the flow path of the heat - transfer working fluid, the optimization of headers and connecting pipes, flow rate regulation, and the optimization design of the system process, to carry out the full - system integrated innovation design for the concentrating and heat - collecting process of the tower - type solar thermal power plant. The high - low temperature dual - working - fluid heat absorber and its design method described in the present invention can provide a reference for the innovative design concept of the heat absorber from the perspectives of function, efficiency, and cost, which is conducive to promoting the efficient and low - cost comprehensive utilization of the tower - type concentrating solar thermal power generation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 It is the flowchart of the implementation of the present invention.

[0090] Figure 2 It is the structural schematic diagram of the single - working - fluid exposed cylindrical heat absorber.

[0091] Figure 3 It is the annual weighted heat flux density distribution diagram after unfolding the single - working - fluid exposed cylindrical heat absorber.

[0092] Figure 4 It is the structural schematic diagram of the heat - absorbing tube row module for the high - heat - flux region.

[0093] Figure 5 It is the structural schematic diagram of the heat - absorbing tube row module for the low - heat - flux region.

[0094] Figure 6 It is the structural schematic diagram of the high - low temperature dual - working - fluid heat absorber.

[0095] Figure 7 It is the thermal efficiency comparison diagram between the single - working - fluid exposed cylindrical heat absorber and the high - low temperature dual - working - fluid heat absorber.

[0096] In the figure: 1 - short connecting pipe of single - working - fluid exposed cylindrical heat absorber, 2 - first flow path inlet of single - working - fluid exposed cylindrical heat absorber, 3 - second flow path inlet of single - working - fluid exposed cylindrical heat absorber, 4 - first long connecting pipe of single - working - fluid exposed cylindrical heat absorber, 5 - header of single - working - fluid exposed cylindrical heat absorber, 6 - first flow path outlet of single - working - fluid exposed cylindrical heat absorber, 7 - second flow path outlet of single - working - fluid exposed cylindrical heat absorber, 8 - tube bank of single - working - fluid exposed cylindrical heat absorber, 9 - second long connecting pipe of single - working - fluid exposed cylindrical heat absorber, 10 - low - heat - flux region, 11 - truncation criterion, 12 - high - heat - flux region, 13 - header of heat absorption tube bank module in high - heat - flux region, 14 - first flow path inlet of heat absorption tube bank module in high - heat - flux region, 15 - second flow path inlet of heat absorption tube bank module in high - heat - flux region, 16 - short connecting pipe of heat absorption tube bank module in high - heat - flux region, 17 - first long connecting pipe of heat absorption tube bank module in high - heat - flux region, 18 - first flow path outlet of heat absorption tube bank module in high - heat - flux region, 19 - second flow path outlet of heat absorption tube bank module in high - heat - flux region, 20 - tube bank of heat absorption tube bank module in high - heat - flux region, 21 - second long connecting pipe of heat absorption tube bank module in high - heat - flux region, 22 - flow path inlet of heat absorption tube bank module in low - heat - flux region, 23 - upper - half short connecting pipe of heat absorption tube bank module in low - heat - flux region, 24 - upper - half header of heat absorption tube bank module in low - heat - flux region, 25 - upper - half tube bank of heat absorption tube bank module in low - heat - flux region, 26 - upper - half of heat absorption tube bank module in low - heat - flux region, 27 - lower - half short connecting pipe of heat absorption tube bank module in low - heat - flux region, 28 - lower - half header of heat absorption tube bank module in low - heat - flux region, 29 - lower - half tube bank of heat absorption tube bank module in low - heat - flux region, 30 - flow path outlet of heat absorption tube bank module in low - heat - flux region, 31 - lower - half of heat absorption tube bank module in low - heat - flux region, 32 - long connecting pipe of heat absorption tube bank module in low - heat - flux region. Detailed implementation mode

[0097] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "upper", "lower", "front", "rear", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plural" is two or more. In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0098] Solar Two tower molten salt solar thermal power plant is the world's first commercial demonstration molten salt tower solar power plant with a rated installed capacity of 10 MW. The concentrating and heat collecting subsystem of the Solar Two tower solar thermal power plant includes an annular heliostat field and a single-fluid exposed cylindrical absorber, and the heliostat field includes 1926 heliostats. In order to make the purpose and technical solutions of the present invention clearer and easier to understand, the following further details the present invention by taking the concentrating and heat collecting subsystem of the Solar Two tower solar thermal power plant as an example. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0099] As Figure 1 shown, the specific implementation process of a high-low temperature dual-fluid absorber for a tower solar thermal power plant and its design method provided by the present invention is as follows:

[0100] Step 1: The existing literature materials have introduced in detail the concentrating and heat collecting subsystem of the Solar Two tower molten salt solar thermal power plant. From this, the layout of the heliostat field and the geometric parameters of the single-fluid exposed cylindrical absorber can be determined, including the height of the absorber from the ground, the diameter of the absorber, the height of the absorber itself, etc. The structure of the single-fluid exposed cylindrical absorber is as Figure 2As shown in the figure, each single - working - fluid exposed cylindrical absorber tube row 8 includes several absorber tubes arranged side by side, and they converge at both ends to the single - working - fluid exposed cylindrical absorber header 5, facilitating the flow of the heat - transfer working fluid within the entire single - working - fluid exposed cylindrical absorber. The single - working - fluid exposed cylindrical absorber short connecting pipe 1 connects the headers of adjacent tube rows. During operation, the heat - transfer working fluid enters the single - working - fluid exposed cylindrical absorber header 5 from the single - working - fluid exposed cylindrical absorber first flow path inlet 2 and the single - working - fluid exposed cylindrical absorber second flow path inlet 3 respectively, flows into each absorber tube through the single - working - fluid exposed cylindrical absorber header 5, then flows out from the single - working - fluid exposed cylindrical absorber header 5 at the other end, and then flows into the next traditional exposed cylindrical header through the single - working - fluid exposed cylindrical absorber short connecting pipe 1, repeating this process. After the heat - transfer working fluid crosses through the single - working - fluid exposed cylindrical absorber first long connecting pipe 4 and the single - working - fluid exposed cylindrical absorber second long connecting pipe 9, it finally flows out through the single - working - fluid exposed cylindrical absorber first flow path outlet 6 and the single - working - fluid exposed cylindrical second flow path outlet 7. The single - working - fluid exposed cylindrical absorber of the Solar Two tower molten - salt solar thermal power plant will be used as the design starting point and performance comparison object in this example.

[0101] Step 2: Use the Monte Carlo ray - tracing method to simulate the entire propagation process of solar rays from the heliostat field to the single - working - fluid exposed cylindrical absorber at all times throughout the year, and obtain the annual weighted heat - flux density distribution of the single - working - fluid exposed cylindrical absorber. To better carry out the design work of the proposed high - and low - temperature dual - working - fluid absorber, the single - working - fluid exposed cylindrical absorber is unfolded into a rectangular plane, and the annual weighted heat - flux density distribution after unfolding the single - working - fluid exposed cylindrical absorber is as Figure 3 shown. Select the spring equinox noon moment as the design point, and calculate the cut - off energy, thermal efficiency, and heat loss of the single - working - fluid exposed cylindrical absorber at the design point. Among them, the cut - off energy of the single - working - fluid exposed cylindrical absorber can be obtained through the Monte Carlo ray - tracing method.

[0102] Furthermore, the heat - transfer working fluid in the single - working - fluid exposed cylindrical absorber of the Solar Two tower molten - salt solar thermal power plant is a non - eutectic mixed nitrate of NaNO3 - KNO3 (60wt% - 40wt%) (hereinafter referred to as nitrate). After being heated to the target temperature in the single - working - fluid exposed cylindrical absorber, the nitrate will further heat the steam, and the steam will drive the steam turbine and the generator set to generate electricity. At the same time, since the working temperature of the nitrate is 290 - 565 °C, stainless steel 316L with better high - temperature resistance is selected as the material for manufacturing this single - working - fluid exposed cylindrical absorber. The process of calculating the thermal efficiency and heat loss of the single - working - fluid exposed cylindrical absorber is as follows:

[0103] S1: The calculation formula for the thermal efficiency of the single - working - fluid exposed cylindrical absorber is:

[0104] ηR,th,1 = Q htf,1 / Q R,opt,1 × 100% (1)

[0105] In formula (1), η R,th,1 is the thermal efficiency of the single - working - fluid exposed cylindrical absorber; Q htf,1 is the energy absorbed by the nitrate in the single - working - fluid exposed cylindrical absorber; Q R,opt,1 is the energy absorbed by the light - absorbing coating on the tube wall of the single - working - fluid exposed cylindrical absorber, which can be directly calculated by the Monte Carlo ray - tracing method.

[0106] S2. The calculation formula for the energy absorbed by the nitrate in the single - working - fluid exposed cylindrical absorber is:

[0107] Q htf,1 = q m,1 × c p,1 × (T out,1 - T in,1 ) (2)

[0108] In formula (2), q m,1 is the mass flow rate of the nitrate; c p,1 is the specific heat capacity at constant pressure of the nitrate; T in,1 is the temperature of the nitrate at the inlet of the single - working - fluid exposed cylindrical absorber; T out,1 is the temperature of the nitrate at the outlet of the single - working - fluid exposed cylindrical absorber.

[0109] S3. The calculation formula for the heat loss of the single - working - fluid exposed cylindrical absorber is:

[0110] Q loss,th,1 = Q R,opt,1 - Q htf,1 (3)

[0111] In formula (3), Q loss,th,3 is the heat loss of the single - working - fluid exposed cylindrical absorber.

[0112] The components of the heat loss of the single - working - fluid exposed cylindrical absorber are:

[0113] Q loss,th,1 = Q loss,rad,1 + Q loss,cond,1 + Q loss,conv,1 (4)

[0114] In formula (4), Q loss,rad,1 is the radiative heat loss of the single - working - fluid exposed cylindrical absorber; Q loss,cond,1 is the conductive heat loss of the single - working - fluid exposed cylindrical absorber; Q loss,conv,1 is the convective heat loss of the single - working - fluid exposed cylindrical absorber.

[0115] Step 3: According to Figure 3 it is obtained that the maximum annual weighted heat flux density of the single - working - fluid exposed cylindrical heat absorber is 7.46×10 7 kW / m 2 , and the m% (m = 1 - 30) of this value is used as the truncation criterion 11 for design in sequence. For the convenience of display, here 1%, 10%, 15%, 20%, 25%, and 30% of 7.46×10 7 kW / m 2 are taken as examples, that is, the values of the truncation criterion 11 are 7.46×10 5 kW / m 2 , 7.46×10 6 kW / m 2 , 1.12×10 7 kW / m 2 , 1.49×10 7 kW / m 2 , 1.87×10 7 kW / m 2 , and 2.24×10 7 kW / m 2 . As shown in Figure 3 , first, 7.46×10 5 kW / m 2 is used as the truncation criterion 11 to divide the non - uniform heat flux density of the single - working - fluid exposed cylindrical heat absorber, that is, the part of the heat flux density in the single - working - fluid exposed cylindrical heat absorber greater than 7.46×10 5 kW / m 2 is defined as the high - heat - flux area 12, and the part less than 7.46×10 5 kW / m 2 is defined as the low - heat - flux area 10. A high - heat - flux area heat - absorbing tube row module is designed for the high - heat - flux area 12 of the single - working - fluid exposed cylindrical heat absorber, and the lengths of each tube row of the high - heat - flux area heat - absorbing tube row module are determined; in order to facilitate the comparison of the thermal efficiency and heat loss of the single - working - fluid exposed cylindrical heat absorber and the high - heat - flux area heat - absorbing tube row module in Step 4, nitrate is also used as the heat - transfer working fluid in the high - heat - flux area heat - absorbing tube row module, and the role of nitrate here is the same as that in the single - working - fluid exposed cylindrical heat absorber. The same as the single - working - fluid exposed cylindrical heat absorber, stainless steel 316L is selected as the raw material for manufacturing the high - heat - flux area heat - absorbing tube row module.

[0116] Its structure is as shown in Figure 4As shown, the connection method of each part is similar to that of the single - working - fluid exposed cylindrical absorber. The specific structure is as follows: Each heat - transfer tube row module 20 in the high - heat - flux area includes several heat - transfer tubes placed side by side, and they converge at the header 13 of the heat - transfer tube row module in the high - heat - flux area at both ends, facilitating the flow of nitrate within the entire heat - transfer tube row module in the high - heat - flux area. The short connecting pipe 16 of the heat - transfer tube row module in the high - heat - flux area connects the headers of adjacent tube rows. During operation, nitrate enters the header 13 of the heat - transfer tube row module in the high - heat - flux area from the first flow - path inlet 14 and the second flow - path inlet 15 of the heat - transfer tube row module in the high - heat - flux area respectively, then flows into each heat - transfer tube, and then flows out from the header 13 at the other end, and then flows into the header of the next heat - transfer tube row module in the high - heat - flux area through the short connecting pipe 16 of the heat - transfer tube row module in the high - heat - flux area, and so on. After the nitrate crosses through the first long connecting pipe 17 and the second long connecting pipe 21 of the heat - transfer tube row module in the high - heat - flux area, it finally flows out through the first flow - path outlet 18 and the second flow - path outlet 19 of the heat - transfer tube row module in the high - heat - flux area.

[0117] Step 4: Based on the spring equinox noon moment at the design point, set the inlet and outlet temperatures of nitrate the same as those of the single - working - fluid exposed cylindrical absorber, and calculate the cut - off energy, thermal efficiency, and heat loss of the heat - transfer tube row module in the high - heat - flux area at this time. Among them, the cut - off energy of the heat - transfer tube row module in the high - heat - flux area can be directly calculated by the Monte Carlo ray - tracing method.

[0118] Furthermore, in step 4, the overall process of calculating the thermal efficiency and heat loss of the heat - transfer tube row module in the high - heat - flux area includes the following steps:

[0119] S1: The calculation formula for the thermal efficiency of the heat - transfer tube row module in the high - heat - flux area is:

[0120] η R,th,2 =Q htf,2 / Q R,opt,2 ×100% (5)

[0121] In formula (5), η R,th,2 is the thermal efficiency of the heat - transfer tube row module in the high - heat - flux area; Q htf,2 is the energy absorbed by nitrate in the heat - transfer tube row module in the high - heat - flux area; Q R,opt,2 is the energy absorbed by the light - absorbing coating on the tube wall of the heat - transfer tube row module in the high - heat - flux area.

[0122] S2: The calculation formula for the energy absorbed by nitrate in the heat - transfer tube row module in the high - heat - flux area is:

[0123] Q htf,2 =q m,2 ×c p,2 ×(T out,2 -T in,2 ) (6)

[0124] In Equation (6), q m,2 is the mass flow rate of nitrate; c p,2 is the specific heat capacity at constant pressure of nitrate; T in,2 is the temperature of nitrate at the inlet of the heat absorption tube row module in the high heat flux area; T out,2 is the temperature of nitrate at the outlet of the heat absorption tube row module in the high heat flux area.

[0125] S2. The calculation formula for the heat loss of the heat absorption tube row module in the high heat flux area is:

[0126] Q loss,th,2 = Q R,opt,2 - Q htf,2 (7)

[0127] In Equation (7), Q loss,th,2 is the heat loss of the heat absorption tube row module in the high heat flux area.

[0128] The components of the heat loss of the heat absorption tube row module in the high heat flux area are:

[0129] Q loss,th,2 = Q loss,rad,2 + Q loss,cond,2 + Q loss,conv,2 (8)

[0130] In Equation (8), Q loss,rad,2 is the radiative heat loss of the heat absorption tube row module in the high heat flux area; Q loss,cond,2 is the conductive heat loss of the heat absorption tube row module in the high heat flux area; Q loss,conv,2 is the convective heat loss of the heat absorption tube row module in the high heat flux area.

[0131] Step 5. Compare the thermal efficiency of the heat absorption tube row module in the high heat flux area with that of the single - working - fluid exposed cylindrical absorber. If the thermal efficiency of the heat absorption tube row module in the high heat flux area has not been improved, then further select 7.46×10 6 kW / m 2 as the truncation criterion and re - perform Steps 3, 4, and 5; if the thermal efficiency of the heat absorption tube row module in the high heat flux area has been improved, then proceed to Step 6.

[0132] Step 6. Considering that it is necessary to ensure the temperature - rising effect of nitrate in the heat absorption tube row module in the high heat flux area to maintain the normal power generation of the tower - type solar thermal power plant, it is necessary to limit the truncation energy of the heat absorption tube row module in the high heat flux area. According to design experience, first set the truncation energy of the heat absorption tube row module in the high heat flux area to be not less than n% of the truncation energy of the single - working - fluid exposed cylindrical absorber, where n = 70 - 80, with 80% as the initial value.

[0133] Further, if the truncation energy of the heat absorption tube row module in the high heat flux region is less than 80% of the truncation energy of the single - working - fluid exposed cylindrical heat absorber, a larger value of 1.12×10 7 kW / m 2 can be further selected as the truncation criterion, and steps 3, 4, 5, and 6 are repeated, and so on; if the truncation energy of the heat absorption tube row module in the high heat flux region is greater than or equal to 80% of the truncation energy of the single - working - fluid exposed cylindrical heat absorber, step 7 is executed.

[0134] Step 7: After the judgments in steps 5, 6, 10, 11, 12, and 13, finally determine 20% of the maximum annual weighted heat flux density, that is, 1.49×10 7 kW / m 2 as the finally selected truncation criterion 11. Referring to Figure 3 , the high - heat - flux region and the low - heat - flux region can be finally divided. Accordingly, the lengths of the tube rows in the high - heat - flux region heat absorption tube row module can be determined. On this basis, a low - heat - flux region heat absorption tube row module is designed for the low - heat - flux region 10 of the single - working - fluid exposed cylindrical heat absorber, and the lengths of its tube rows are also determined accordingly. The structure is as Figure 5 shown. In this embodiment, heat - conducting oil is used as the heat - transfer working fluid in the low - heat - flux region heat absorption tube row module. The working temperature of the heat - conducting oil is between 240 and 390 °C, which can play a role in pre - heating molten salt, heating feed water and steam in the Solar Two tower - type molten salt solar thermal power station. Considering the relatively low working temperature of the heat - conducting oil, stainless steel 304 with relatively poor temperature - resistance performance can be selected as the raw material for manufacturing the low - heat - flux region heat absorption tube row module;

[0135] The structure of the low - heat - flux region heat absorption tube row module is as Figure 5 shown. The specific structure is as follows: Each upper - half tube row 25 of the low - heat - flux region heat absorption tube row module includes several heat absorption tubes placed side by side and converges at both ends to the upper - half header 24 of the low - heat - flux region heat absorption tube row module, so as to facilitate the flow of heat - conducting oil in the entire low - heat - flux region tube row module. The upper - half short connecting pipe 23 of the low - heat - flux region heat absorption tube row module connects the headers of adjacent tube rows. Similar to the upper - half part 26 of the low - heat - flux region heat absorption tube row module, each lower - half tube row 29 of the low - heat - flux region heat absorption tube row module includes several heat absorption tubes placed side by side and converges at both ends to the lower - half header 28 of the low - heat - flux region heat absorption tube row module, so as to facilitate the flow of heat - conducting oil in the entire low - heat - flux region tube row module. The lower - half short connecting pipe 27 of the low - heat - flux region heat absorption tube row module connects the headers of adjacent tube rows. The upper - half part 26 of the low - heat - flux region heat absorption tube row module is connected to the lower - half part 31 of the low - heat - flux region heat absorption tube row module by the long connecting pipe 32 of the low - heat - flux region heat absorption tube row module.

[0136] During operation, the heat transfer oil flows into the upper header 24 of the low heat flux area heat absorption tube row module from the inlet 22 of the flow path of the low heat flux area heat absorption tube row module, then flows into each heat absorption tube, and then flows out from the upper header 24 of the low heat flux area heat absorption tube row module at the other end. After that, it flows into the upper header of the next low heat flux area heat absorption tube row module through the short connecting pipe 23 of the upper half of the low heat flux area heat absorption tube row module, and so on. The heat transfer oil flows into the lower header 28 of the low heat flux area heat absorption tube row module through the long connecting pipe 32 of the low heat flux area heat absorption tube row module, then flows into each heat absorption tube, and then flows out from the lower header 28 of the low heat flux area heat absorption tube row module at the other end. After that, it flows into the lower header of the next low heat flux area heat absorption tube row module through the short connecting pipe 27 of the lower half of the low heat flux area heat absorption tube row module, and so on. Finally, it flows out from the outlet 30 of the flow path of the low heat flux area heat absorption tube row module.

[0137] Step 8: After comprehensively considering the positions, cut-off energies, mass flow rates of the two heat transfer working fluids, and operating conditions of the high heat flux area heat absorption tube row module in Figure 4 and the low heat flux area heat absorption tube row module in Figure 5 , combine the two modules into a high-low temperature dual-working fluid heat absorber, and its structure is as shown in Figure 6 .

[0138] A high-low temperature dual-working fluid heat absorber for a tower-type solar thermal power station includes a high heat flux area heat absorption tube row module and a low heat flux area heat absorption tube row module. The low heat flux area heat absorption tube row module includes the upper half 26 of the low heat flux area heat absorption tube row module and the lower half 31 of the low heat flux area heat absorption tube row module. The high heat flux area heat absorption tube row module is located between the upper half 26 of the low heat flux area heat absorption tube row module and the lower half 31 of the low heat flux area heat absorption tube row module.

[0139] Among them, the high heat flux area heat absorption tube row module includes multiple high heat flux area heat absorption tube row module tube rows 20 arranged circumferentially, a high heat flux area heat absorption tube row module header 13, a high heat flux area heat absorption tube row module short connecting pipe 16, a high heat flux area heat absorption tube row module first long connecting pipe 17, a high heat flux area heat absorption tube row module second long connecting pipe 21, a high heat flux area heat absorption tube row module first flow path outlet 18, a high heat flux area heat absorption tube row module second flow path outlet 19, and other parts.

[0140] Each heat absorption tube row module tube row 20 of the high heat flux area includes several heat absorption tubes arranged side by side in sequence. The two ends of the heat absorption tubes converge to the high heat flux area heat absorption tube row module header 13. The high heat flux area heat absorption tube row module first flow path inlet 14 and the high heat flux area heat absorption tube row module second flow path inlet 15 are respectively arranged on two high heat flux area heat absorption tube row modules headers 13. Adjacent high heat flux area heat absorption tube row modules headers 13 are connected through the high heat flux area heat absorption tube row module short connecting pipe 16. The high heat flux area heat absorption tube row module is composed of twenty-four high heat flux area heat absorption tube row module tube rows 20. Every twelve high heat flux area heat absorption tube row module tube rows 20 form a flow path of nitrate, so it can be divided into two paths in total.

[0141] In the first flow path, nitrate flows in from the high heat flux area heat absorption tube row module first flow path inlet 14. After flowing through the first six high heat flux area heat absorption tube row module tube rows, the first six high heat flux area heat absorption tube row module tube rows are connected to the last six high heat flux area heat absorption tube row module tube rows through the high heat flux area heat absorption tube row module first long connecting pipe 17, and finally flows out through the high heat flux area heat absorption tube row module first flow path outlet 18 connected to the header of the last high heat flux area heat absorption tube row module tube row. Similarly, in the second flow path, nitrate flows in from the high heat flux area heat absorption tube row module second flow path inlet 15. After flowing through the first six high heat flux area heat absorption tube row modules, the first six high heat flux area heat absorption tube row module tube rows are connected to the last six high heat flux area heat absorption tube row module tube rows through the high heat flux area heat absorption tube row module second long connecting pipe 21, and finally flows out through the high heat flux area heat absorption tube row module second flow path outlet 19 connected to the last high heat flux area heat absorption tube row module header.

[0142] The low heat flux area heat absorption tube row module includes the upper half 26 of the low heat flux area heat absorption tube row module and the lower half 31 of the low heat flux area heat absorption tube row module.

[0143] The upper half 26 of the low heat flux area heat absorption tube row module is composed of twenty-four tube rows 25 of the upper half of the low heat flux area heat absorption tube row module. Each tube row 25 of the upper half of the low heat flux area heat absorption tube row module includes several heat absorption tubes placed side by side. The two ends of the heat absorption tubes converge to the upper half header 24 of the low heat flux area heat absorption tube row module. The heat transfer oil flows into the upper half 26 of the low heat flux area heat absorption tube row module through the low heat flux area heat absorption tube row module flow path inlet 22 connected to the upper half header of the first low heat flux area heat absorption tube row module. The adjacent upper half headers 24 of the low heat flux area heat absorption tube row module are connected and communicated through the short connecting pipe 23 of the upper half of the low heat flux area heat absorption tube row module. The structure of the lower half 31 of the low heat flux area heat absorption tube row module is similar to that of the upper half 26 of the low heat flux area heat absorption tube row module. The lower half 31 of the low heat flux area heat absorption tube row module is composed of twenty-four tube rows 29 of the lower half of the low heat flux area heat absorption tube row module. Each tube row 29 of the lower half of the low heat flux area heat absorption tube row module includes several heat absorption tubes placed side by side. The two ends of the heat absorption tubes converge to the lower half header 28 of the low heat flux area heat absorption tube row module. The adjacent lower half headers 28 of the low heat flux area heat absorption tube row module are connected and communicated through the short connecting pipe 27 of the lower half of the low heat flux area heat absorption tube row module. The upper half 26 of the low heat flux area heat absorption tube row module is connected to the lower half 31 of the low heat flux area heat absorption tube row module through the long connecting pipe 32 of the low heat flux area heat absorption tube row module. The heat transfer oil can thus flow from the upper half 26 of the low heat flux area heat absorption tube row module into the lower half 31 of the low heat flux area heat absorption tube row module and finally flow out of the low heat flux area heat absorption tube row module through the low heat flux area heat absorption tube row module flow path outlet 30 connected to the header of the low heat flux area heat absorption tube row module.

[0144] Step 9: Calculate the thermal efficiency, heat loss and material cost of the high and low temperature dual working fluid heat absorber at the design point, calculate the material cost of the single working fluid exposed cylindrical heat absorber, and compare the thermal efficiency, heat loss and material cost of the high and low temperature dual working fluid heat absorber and the single working fluid exposed cylindrical heat absorber.

[0145] Furthermore, in step 9, the overall process of calculating the thermal efficiency and heat loss of the high and low temperature dual working fluid heat absorber includes the following steps:

[0146] S1: The calculation formula for the thermal efficiency of the low heat flux area heat absorption tube row module is:

[0147] η R,th,3 =Q htf,3 / Q R,opt,3 ×100% (9)

[0148] In formula (9), η R,th,3 is the thermal efficiency of the low heat flux area heat absorption tube row module; Q htf,3 is the energy absorbed by the heat transfer oil in the low heat flux area heat absorption tube row module; Q R,opt,3 is the energy absorbed by the light absorption coating on the tube wall of the low heat flux area heat absorption tube row module.

[0149] S2. The calculation formula for the energy absorbed by the heat transfer oil in the heat absorption tube row module in the low heat flux area is:

[0150] Q htf,3 =q m,3 ×c p,3 ×(T out,3 -T in,3 )(10)

[0151] In formula (10), q m,3 is the mass flow rate of the heat transfer oil; c p,3 is the specific heat capacity at constant pressure of the heat transfer oil; T in,3 is the temperature of the heat transfer oil at the inlet of the heat absorption tube row module in the low heat flux area; T out,3 is the temperature of the heat transfer oil at the outlet of the heat absorption tube row module in the low heat flux area.

[0152] S3. The calculation formula for the heat loss of the heat absorption tube row module in the low heat flux area is:

[0153] Q loss,th,3 =Q R,opt,3 -Q htf,3 (11)

[0154] In formula (11), Q loss,th,3 is the heat loss of the heat absorption tube row module in the low heat flux area.

[0155] The components of the heat loss of the heat absorption tube row module in the low heat flux area are:

[0156] Q loss,th,3 =Q loss,rad,3 +Q loss,cond,3 +Q loss,conv,3 (12)

[0157] In formula (12), Q loss,rad,3 is the radiative heat loss of the heat absorption tube row module in the low heat flux area; Q loss,cond,3 is the conductive heat loss of the heat absorption tube row module in the low heat flux area; Q loss,conv,3 is the convective heat loss of the heat absorption tube row module in the low heat flux area.

[0158] S3. The calculation formula for the thermal efficiency of the high-low temperature dual working fluid heat absorber is:

[0159] η R,th =(Q htf,2 +Q htf,3 ) / ( Q R,opt,2 +Q R,opt,3 )×100% (13)

[0160] In formula (13), η R,this the thermal efficiency of the high-low temperature dual - working - fluid heat absorber, specifically the ratio of the sum of the thermal powers absorbed by the nitrate in the heat absorption tube row module in the high - heat - flux area and the heat - conducting oil in the heat absorption tube row module in the low - heat - flux area to the sum of the energies absorbed by the light - absorbing coatings on the tube walls of the heat absorption tube row module in the high - heat - flux area and the heat absorption tube row module in the low - heat - flux area.

[0161] S4. The calculation formula for the heat loss of the high - low temperature dual - working - fluid heat absorber is:

[0162] Q loss,th =Q loss,th,2 +Q loss,th,3 (14)

[0163] In formula (14), Q loss,th is the heat loss of the high - low temperature dual - working - fluid heat absorber.

[0164] Researchers have conducted experimental tests on the thermal efficiency of the single - working - fluid exposed cylindrical heat absorber in the Solar Two tower molten - salt solar thermal power plant, and selected 9 operating points. The specific operating parameters are shown in Table 1. The inlet and outlet temperatures of nitrate in the single - working - fluid exposed cylindrical heat absorber and the heat absorption tube row module in the high - heat - flux area are 290 °C and 565 °C respectively, and the inlet and outlet temperatures of the heat - conducting oil in the heat absorption tube row module in the low - heat - flux area are 240 °C and 390 °C respectively. Comparing the thermal efficiency of the single - working - fluid exposed cylindrical heat absorber and the designed high - low temperature dual - working - fluid heat absorber, the calculation results are as Figure 7 shown. Compared with the single - working - fluid exposed cylindrical heat absorber, the thermal power of the high - low temperature dual - working - fluid heat absorber has been significantly improved. The thermal efficiency improvement in the 9 operating conditions is between 1.11% and 4.89%, and the average thermal efficiency improvement value is 2.87%.

[0165] Table 1 Experimental test operating parameters

[0166]

[0167]

[0168] Furthermore, taking the 6th operating condition mentioned above as an example, as shown in Table 2, it is a data comparison of the radiative and convective heat losses of the single - working - fluid exposed cylindrical heat absorber, the heat absorption tube row module in the high - heat - flux area, the heat absorption tube row module in the low - heat - flux area, and the high - low temperature dual - working - fluid heat absorber. After calculation, compared with the single - working - fluid exposed cylindrical heat absorber, the convective heat loss of the high - low temperature dual - working - fluid heat absorber is reduced by 34.14%, and the radiative heat loss is reduced by 36.68%. The total heat loss is approximately the sum of the radiative heat loss and the convective heat loss. Therefore, the total heat loss of the high - low temperature dual - working - fluid heat absorber is reduced by about 36.00% compared with the single - working - fluid exposed cylindrical heat absorber.

[0169] Table 2 Comparison of heat losses between the single - working - fluid exposed cylindrical heat absorber and the high - low temperature dual - working - fluid heat absorber

[0170]

[0171] Since the row height of the single - working - fluid exposed cylindrical absorber and the designed high - low - temperature dual - working - fluid absorber is the same, the cut - off energy of the two absorbers is the same. By comparing the proportions of radiative heat loss and convective heat loss of the single - working - fluid exposed cylindrical absorber and the high - low - temperature dual - working - fluid absorber in the cut - off energy, the energy utilization rates of the two absorbers can be seen. Based on the heat losses of the single - working - fluid exposed cylindrical absorber and the high - low - temperature dual - working - fluid absorber listed in Table 2, it can be calculated that when the cut - off energies of the single - working - fluid exposed cylindrical absorber and the high - low - temperature dual - working - fluid absorber are equal, the thermal efficiency of the high - low - temperature dual - working - fluid absorber is increased by 2.78% compared with that of the single - working - fluid exposed cylindrical absorber. Thus, it can be seen that the high - low - temperature dual - working - fluid absorber significantly reduces heat loss while achieving two - stage energy utilization, and improves the thermal efficiency of the high - low - temperature dual - working - fluid absorber.

[0172] Since the price of a single absorber tube in the absorber varies greatly among different manufacturers, when calculating the material costs of the single - working - fluid exposed cylindrical absorber and the high - low - temperature dual - working - fluid absorber, only the cost price is calculated based on the mass of the required raw materials, excluding the labor cost of manufacturing the raw materials into absorber tubes. The single - working - fluid exposed cylindrical absorber in the Solar Two tower molten - salt solar thermal power station selects stainless steel 316L as the raw material. Through market research, it is found that the material cost price of stainless steel 316L is 45 yuan / kg, and the maximum temperature resistance is 900°C. The absorber tube row module in the high - heat - flux area also uses nitrate as the heat - transfer working fluid, so stainless steel 316L is still used as the raw material. For the absorber tube row module in the low - heat - flux area, since the temperature of the heat - transfer oil is relatively low, stainless steel 304 with a maximum temperature resistance of 800°C can be selected as the raw material. Through market research, it is found that the material cost price of stainless steel 304 is 30 yuan / kg. The cost price of the high - low - temperature dual - working - fluid absorber is the sum of the costs of the absorber tube row module in the high - heat - flux area and the absorber tube row module in the low - heat - flux area.

[0173] S5. The calculation formula for the material cost of the single - working - fluid exposed cylindrical absorber is:

[0174] C1 = V1×A1 (15)

[0175] In formula (15), C1 is the material cost of stainless steel 316L in the single - working - fluid exposed cylindrical absorber, V1 is the usage amount of stainless steel 316L in the single - working - fluid exposed cylindrical absorber; A1 is the unit price of stainless steel 316L in the single - working - fluid exposed cylindrical absorber.

[0176] S6. The calculation formula for the material cost of the absorber tube row module in the high - heat - flux area is:

[0177] C2 = V2×A2 (16)

[0178] In Equation (16), C2 is the material cost of 316L stainless steel in the heat absorption tube row module in the high heat flux area; V2 is the usage amount of 316L stainless steel in the heat absorption tube row module in the high heat flux area; A2 is the unit price of 316L stainless steel in the heat absorption tube row module in the high heat flux area.

[0179] S7. The calculation formula for the material cost of the low heat flux area heat absorption tube row module is:

[0180] C3 = V3 × A3 (17)

[0181] In Equation (17), C3 is the material cost of 304 stainless steel in the low heat flux area heat absorption tube row module; V3 is the usage amount of 304 stainless steel in the low heat flux area heat absorption tube row module; A3 is the unit price of 304 stainless steel in the low heat flux area heat absorption tube row module.

[0182] S8. The calculation formula for the material cost of the high and low temperature dual - working fluid heat absorber is:

[0183] C = C2 + C3 (18)

[0184] In Equation (18), C is the material cost of the high and low temperature dual - working fluid heat absorber, which is the sum of the material costs of the high heat flux area heat absorption tube row module and the low heat flux area heat absorption tube row module.

[0185] As shown in Table 3, it is the summary of the material cost estimates of the single - working fluid exposed cylindrical heat absorber, the high heat flux area heat absorption tube row module, the low heat flux area heat absorption tube row module, and the high and low temperature dual - working fluid heat absorber in the Solar Two tower - type molten salt solar thermal power station. It can be seen from the table that the estimated material cost price of the single - working fluid exposed cylindrical heat absorber with the same size is 137,800 yuan, while the estimated material cost price of the high and low temperature dual - working fluid heat absorber is 124,700 yuan. The estimated material cost price of the high and low temperature dual - working fluid heat absorber is reduced by 9.5% compared with that of the single - working fluid exposed cylindrical heat absorber.

[0186] Table 3 Comparison of Material Cost Estimates between the Single - Working Fluid Exposed Cylindrical Heat Absorber and the High and Low Temperature Dual - Working Fluid Heat Absorber

[0187]

[0188] In this example, heat transfer oil is used as the low-temperature heat transfer working fluid for design calculation. If the high-low temperature dual working fluid heat absorber aims to achieve functions such as solar brackish water desalination, solar adsorption refrigeration, and solar organic Rankine cycle, then brackish water (room temperature to 80 °C), methanol (room temperature to 150 °C), and R245fa (150 to 300 °C) should be used as the low-temperature heat transfer working fluids for the low heat flux zone heat pipe row module respectively. For applications in different temperature ranges between room temperature and 300 °C, since the outlet temperature of the low-temperature heat transfer working fluid is lower than 390 °C of the heat transfer oil in the example, the radiative and convective heat losses of the low heat flux zone heat pipe row module can be further reduced, and the lower the temperature of the low-temperature heat transfer working fluid, the smaller the heat loss. At the same time, for different low-temperature heat transfer working fluids, different materials can be further selected to manufacture the low heat flux zone heat pipe row module. Relatively speaking, materials with lower temperature resistance have more advantages in workability and manufacturing difficulty, and the market maturity is also relatively higher. Therefore, as the temperature of the low-temperature heat transfer working fluid decreases, the advantage of the high-low temperature dual working fluid heat absorber in terms of material cost will become more obvious.

[0189] Step 10: Compare the thermal efficiency, heat loss, and material cost of the single working fluid exposed cylindrical heat absorber and the high-low temperature dual working fluid heat absorber. If the thermal efficiency of the high-low temperature dual working fluid heat absorber can be increased by at least 1% and the material cost can be reduced by at least 5%, proving its advantages in energy utilization rate and material cost, then execute Step 11; otherwise, further select a smaller n value (n = 70 - 80), and return to Step 6 to re-design.

[0190] Step 11: Save the design results such as the tube row length, thermal efficiency, and material cost of the high-low temperature dual working fluid heat absorber this time.

[0191] Step 12: Determine whether the n value at this time is greater than 70. If so, further select a smaller n value and return to Step 6 to re-design; otherwise, execute Step 13.

[0192] Step 13: Screen among the results of Step 11, and select the high-low temperature dual working fluid heat absorber with the highest thermal efficiency and the lowest material cost as the best design result, output the design results of the tube row length, thermal efficiency, and material cost of the best high-low temperature dual working fluid heat absorber, and end the design process of the high-low temperature dual working fluid heat absorber. Under the application conditions of the Solar Two tower molten salt solar thermal power plant in this example, when the value of m is 20 and the value of n is 70, the advantages of the designed high-low temperature dual working fluid heat absorber in terms of thermal efficiency and material cost are the most obvious, so the corresponding design results can be output.

[0193] The above process shows that the high-low temperature dual-working-fluid absorber has advantages in terms of energy utilization efficiency and material cost, and the design method is practical and effective. The high-low temperature dual-working-fluid absorber can reduce material cost, decrease heat loss and improve energy utilization efficiency while realizing two-stage energy utilization. It can further flexibly control the intercepted energy of the heat absorption tube row module in the high heat flux area and the heat absorption tube row module in the low heat flux area by combining with the aiming strategy of the heliostat field. It can also perform matching design on aspects such as the flow rate and flow path of the two heat transfer working fluids, the header and connecting pipes, and the system process according to the usage requirements, and further carry out the full-system integrated innovation design for the concentrating and heat collection process of the tower-type solar thermal power plant.

[0194] The features of the present invention are as follows: (1) Aiming at the problems of high local surface temperature, large radiative heat loss and low thermal efficiency caused by the non-uniform focused solar heat flux of the single-fluid exposed cylindrical absorber, considering the different energy absorption-loss situations presented at different positions on the surface of the single-fluid exposed cylindrical absorber, the present invention divides the non-uniform focused solar heat flux based on the heat flux density and separately designs the high heat flux zone absorber tube row module and the low heat flux zone absorber tube row module. By heating two heat transfer fluids with different temperatures, while realizing the two-stage utilization of energy, different low-temperature heat transfer fluids can be flexibly adopted according to different usage scenarios and actual requirements to realize processes such as solar brackish water desalination, solar adsorption refrigeration, solar-driven organic Rankine cycle and steam Rankine cycle power generation, achieving the functional diversification of the tower-type solar thermal power station, and also providing new ideas and theoretical methods for the absorber structure design in the tower-type solar thermal power station; (2) Since the high heat flux zone absorber tube row module and the low heat flux zone absorber tube row module respectively adopt high-temperature and low-temperature heat transfer fluids, compared with the single-fluid exposed cylindrical absorber, the wall temperature of the low heat flux zone absorber tube row module can be significantly reduced, thereby greatly reducing the radiative heat loss, and finally improving the energy utilization rate and thermal efficiency of the high-low temperature dual-fluid absorber; (3) Since there are two heat transfer fluids in the high-low temperature dual-fluid absorber, in terms of the tube row material, two materials with different temperature resistance and costs can be respectively used to manufacture the high heat flux zone absorber tube row module and the low heat flux zone absorber tube row module. The material with lower temperature resistance has more advantages in terms of processability, manufacturing difficulty and market maturity. And in terms of the heat transfer fluid material, the cost of different low-temperature heat transfer fluids is also lower than that of the original single type of high-temperature heat transfer fluid. In summary, the high-low temperature dual-fluid absorption has certain advantages in terms of the costs of materials and heat transfer fluids. Different low-temperature heat transfer fluids can be selected according to different functions. The lower the temperature of the low-temperature heat transfer fluid, the more obvious the advantages of the high-low temperature dual-fluid absorber in terms of energy utilization rate and material cost; (4) Compared with the existing finned absorbers, the high-low temperature dual-fluid absorber can achieve the above advantages in terms of energy utilization rate, functional diversity and cost without increasing the overall manufacturing difficulty and the occupied space; (5) In practical applications, the high-low temperature dual-fluid absorber can be combined with the heliostat field aiming strategy to flexibly control the intercepted energy of the high heat flux zone absorber tube row module and the low heat flux zone absorber tube row module, and can also match and design the flow rates and flow paths of the two heat transfer fluids according to requirements, and optimize the flow paths, headers and connecting pipes of the heat transfer fluids to further reduce the material cost, and based on this, further carry out the integrated innovation design of the entire system for the concentrating and heat collection process of the tower-type solar thermal power station.

[0195] The implementation method given above is the basic idea for implementing the present invention. The implementation details of the present invention are only exemplified by the Solar Two tower molten salt solar thermal power plant, and are not limited to the installed capacity of the tower solar thermal power plant, the layout of the mirror field, the parameters of the heliostat, and the heat transfer working fluid used. The high-low temperature dual working fluid absorber and its design method proposed in this paper can still be used to design various absorbers in other tower solar thermal power plants. Any non-essential addition or replacement made by those skilled in the art according to the technical features of the present invention shall fall within the protection scope of the present invention.

Claims

1. A design method for a high-low temperature dual-fluid absorber of a tower-type solar thermal power station, characterized in that It includes the following steps: Step 1: Based on the rated installed capacity of the tower solar thermal power station, obtain the heliostat field under design conditions and the single - working - fluid exposed cylindrical receiver that matches it according to the traditional design method; Step 2: Calculate the annual weighted heat flux density distribution of the single - working - fluid exposed cylindrical receiver; Select a representative moment as the design point, and calculate the truncated energy, thermal efficiency, and heat loss of the single - working - fluid exposed cylindrical receiver at the design point; The single - working - fluid exposed cylindrical receiver uses the first heat transfer fluid, and the material for manufacturing the single - working - fluid exposed cylindrical receiver is the first raw material; Step 3: Find the maximum value of the annual weighted heat flux density of the single - working - fluid exposed cylindrical receiver, set a truncation criterion according to the maximum value of the annual weighted heat flux density, divide the tube rows into a high - heat - flux region and a low - heat - flux region, and determine the lengths of the tube rows in the high - heat - flux region absorber tube row module; The high - heat - flux region absorber tube row module uses the second heat transfer fluid, and the material for manufacturing the high - heat - flux region absorber tube row module is the second raw material; Step 4: Calculate the truncated energy, thermal efficiency, and heat loss of the high - heat - flux region absorber tube row module at the design point; Step 5: Judge whether the thermal efficiency of the high - heat - flux region absorber tube row module has increased compared with that of the single - working - fluid exposed cylindrical receiver: If the thermal efficiency has not increased, select a larger truncation criterion and jump to Step 3; if the thermal efficiency has increased, execute Step 6; Step 6, determine whether the cut-off energy of the high heat flux area heat absorption tube row module is less than that of the single working fluid exposed cylindrical heat absorber by n %: If the judgment result is yes, select a larger truncation criterion and jump to Step 3; if the judgment result is no, execute Step 7; Step 7: On the basis of determining the truncation criterion and the lengths of the tube rows in the high - heat - flux region absorber tube row module, design a low - heat - flux region absorber tube row module for the low - heat - flux region in the single - working - fluid exposed cylindrical receiver, and further determine the lengths of the tube rows in the low - heat - flux region absorber tube row module; The low - heat - flux region absorber tube row module uses the third heat transfer fluid, and the material for manufacturing the low - heat - flux region absorber tube row module is the third raw material; Step 8: Combine the high - heat - flux region absorber tube row module and the low - heat - flux region absorber tube row module into a high - and - low - temperature dual - working - fluid receiver; Step 9: Calculate the thermal efficiency, heat loss, and material cost of the designed high - and - low - temperature dual - working - fluid receiver at the design point; Step 10: Compare the thermal efficiency, heat loss, and material cost of the high-low temperature dual-fluid absorber and the single-fluid exposed cylindrical absorber. If both the improvement in thermal efficiency and the reduction in material cost of the high-low temperature dual-fluid absorber can meet the target values, then proceed to Step 11; otherwise, reduce n and return to Step 6; Step 11: Save the design results of this time, and the design results include the tube row lengths, thermal efficiency, and material cost of the high - and - low - temperature dual - working - fluid receiver; Step 12, determine n whether the value is greater than the threshold. If so, decrease n the value and return to Step 6; otherwise, execute Step 13; Step 13: Screen among the design results in Step 11, and select the design results of the tube row lengths, thermal efficiency, and material cost of the best high - and - low - temperature dual - working - fluid receiver as the final design results.

2. The design method of a high-low temperature dual-fluid absorber for a tower-type solar thermal power station according to claim 1, characterized in that In Step 3, use the percentage of the maximum value of the annual weighted heat flux density of the single - working - fluid exposed cylindrical receiver as the truncation criterion. The part of the annual weighted heat flux density greater than the truncation criterion is used as the high - heat - flux region, and the part less than the truncation criterion is used as the low - heat - flux region; Design the high - heat - flux region absorber tube row module according to the high - heat - flux region to heat the second heat transfer fluid to realize the subsequent normal power generation process of the tower solar thermal power station.

3. The design method of a high-low temperature dual-fluid solar receiver for a tower-type solar thermal power station according to claim 1, characterized in that, Through steps 4-7, determine the lengths of the tube rows of the high heat flux region heat absorption tube row module; on this basis, design a low heat flux region heat absorption tube row module for the low heat flux region of the single working fluid exposed cylindrical heat absorber in step 3, and determine the lengths of the tube rows of the low heat flux region heat absorption tube row module; the second heat transfer working fluid and the third heat transfer working fluid are respectively used in the high heat flux region heat absorption tube row module and the low heat flux region heat absorption tube row module; after the matching design of the positions, intercepted energies, flows of the two heat transfer working fluids, and operating conditions of the high heat flux region heat absorption tube row module and the low heat flux region heat absorption tube row module, combine the two modules into a high and low temperature dual working fluid heat absorber.

4. The design method of a high-low temperature dual-working fluid absorber for a tower-type solar thermal power station according to claim 1, characterized in that, In the said step 10, the target values are: the thermal efficiency of the high and low temperature dual working fluid heat absorber is increased by more than 1%, and the material cost is lower than 5% compared with the single working fluid exposed cylindrical heat absorber.

5. The design method of a high-low temperature dual-working-fluid absorber for a tower-type solar thermal power station according to claim 1, characterized in that, In the said step 2, establish an optical model of the whole process of solar rays from the heliostat field to the single working fluid exposed cylindrical heat absorber through self-programming, use the model to calculate the concentrating process of the tower type solar thermal power station for a whole year, and according to the annual weighted heat flux density distribution of the single working fluid exposed cylindrical heat absorber in the concentrating process of the tower type solar thermal power station.

6. The design method of a high-low temperature dual-fluid absorber for a tower-type solar thermal power station according to claim 1, characterized in that Further, in the step 3, the set truncation criterion is m %, m and the value ranges from 1 to 30.

7. A design method for a high-low temperature dual working fluid absorber of a tower-type solar thermal power station according to claim 1, characterized in that In the said step 6, n takes a value of 70 to 80.

8. A high-low temperature dual-fluid absorber for a tower-type solar thermal power station designed by the design method according to any one of claims 1-7, characterized in that, It includes a high heat flux region heat absorption tube row module and a low heat flux region heat absorption tube row module; the low heat flux region heat absorption tube row module includes the upper half of the low heat flux region heat absorption tube row module and the lower half of the low heat flux region heat absorption tube row module connected by the long connecting pipe of the low heat flux region heat absorption tube row module, and the high heat flux region heat absorption tube row module is located between the upper half of the low heat flux region heat absorption tube row module and the lower half of the low heat flux region heat absorption tube row module.

9. The high-low temperature dual working fluid absorber of a tower-type solar thermal power station according to claim 8, characterized in that The upper half of the low heat flux region heat absorption tube row module includes a plurality of mutually connected tube rows of the upper half of the low heat flux region heat absorption tube row module, and both ends of the tube rows of the upper half of the low heat flux region heat absorption tube row module converge to the upper half header of the low heat flux region heat absorption tube row module, and a flow path inlet of the low heat flux region heat absorption tube row module is arranged on the upper half header of the low heat flux region heat absorption tube row module; The lower half of the low heat flux region heat absorption tube row module includes a plurality of mutually connected tube rows of the lower half of the low heat flux region heat absorption tube row module, and both ends of the tube rows of the lower half of the low heat flux region heat absorption tube row module converge to the lower half header of the low heat flux region heat absorption tube row module, and a flow path outlet of the low heat flux region heat absorption tube row module is arranged on the lower half header of the low heat flux region heat absorption tube row module.

10. A high-low temperature dual-fluid absorber of a tower-type solar thermal power station according to claim 9, characterized in that The heat transfer working fluid in the low heat flux region heat absorption tube row module is brackish water, R245fa, methanol or heat transfer oil.

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