Parabolic trough solar thermal power station and its collector field, and method for obtaining the inner diameter value of the mother pipe in the field

Abstract

The present invention discloses a trough-type solar thermal power station and a heat collection field and a method for obtaining the inner diameter value of a mother pipe in the field, and relates to the technical field of solar thermal power stations. The heat collection field includes a cold molten salt mother pipe, a hot molten salt mother pipe and n heat collection loops, and the cold molten salt mother pipe and the hot molten salt mother pipe are arranged in the same way; the n heat collection loops are arranged in parallel between the cold molten salt mother pipe and the hot molten salt mother pipe; the cold molten salt mother pipe includes i pipe sections, i=1,2,…,n‑1. The inner diameter value of the i-th pipe section of the cold molten salt mother pipe is D c,i , the calculation formula is: #imgabs0#The inner diameter of the ith section of the hot molten salt mother pipe is D h,i , and its calculation formula is #imgabs1# The present invention can achieve balanced flow distribution without valve control through the same-path arrangement, thereby reducing the cost of valve installation, control and maintenance.

Description

Technical Field

[0001] The present invention relates to the technical field of photothermal power stations, and in particular to a trough photothermal power station and a heat collection field thereof, and a method for obtaining the inner diameter value of a mother pipe in the field. Background Art

[0002] With the accelerated development of renewable energy and clean electricity, my country launched the first batch of 20 solar thermal demonstration projects in 2016. As of 2020, the installed capacity of solar thermal power stations under construction and in operation in my country were 1,150MW and 220MW respectively.

[0003] During the design phase of a solar thermal power station, the optimal design of the solar island collector circuit is a prerequisite for the efficient operation and control of the subsequent system, and the flow balance of the collector circuit can ensure that the maximum temperature difference of the circuit is within a reasonable range, thereby avoiding problems such as overheating and blockage of the heat transfer fluid. Therefore, for large-scale solar island collector systems, how to achieve balanced distribution of multi-circuit flows is crucial.

[0004] Existing solar island solar collector systems mostly use valve adjustment to control the flow balance of multiple circuits. However, when the number of circuits is large, the number of valves installed increases, which leads to an increase in construction costs and control difficulties. Therefore, it is particularly important to develop a design scheme with a simple structure, no need for valve adjustment, and capable of achieving multi-circuit flow balance distribution in the solar collector system, and its corresponding calculation method for the development of the solar thermal power station industry.

[0005] The Chinese patent with publication number CN214120433U discloses a molten salt linear Fresnel type solar thermal power station in which cold and hot molten salts are distributed in the same way to achieve self-balanced molten salt temperature at the outlet of each collector loop. However, the patent does not limit the diameter of the mother pipe. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a trough-type solar thermal power station heat collection circuit, a method for obtaining the inner diameter value of a mother pipe, and a power station in view of the shortcomings of the existing technology, and provide a method for obtaining the inner diameter value of the mother pipe to achieve self-balancing of the flow of multiple heat collection circuits.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a solar collector field of a trough-type solar thermal power station, including a cold molten salt mother pipe, a hot molten salt mother pipe and n solar collector loops, wherein the cold molten salt mother pipe and the hot molten salt mother pipe are arranged in the same way; the n solar collector loops are arranged in parallel between the cold molten salt mother pipe and the hot molten salt mother pipe; the cold molten salt mother pipe includes i pipe sections, i = 1, 2, ..., n-1. The inner diameter value of the i-th pipe section of the cold molten salt mother pipe is D c,i , and its calculation formula is: m is the total flow rate of molten salt flowing in the collector field, D is the maximum diameter of the mother pipe, M c,iis the molten salt flow rate of the i-th section of the cold molten salt mother pipe. The inner diameter value of the i-th section of the hot molten salt mother pipe is D h,i , and its calculation formula is λ is the resistance loss coefficient of binary molten salt along the way, ρ c is the density of cold molten salt; w is the length of each section of cold / hot molten salt mother pipe, ξ c,i is the local resistance loss coefficient at the tee of the cold molten salt mother pipe, ρ h is the density of hot molten salt; w is the length of each cold / hot molten salt main pipe section, ξ h,i is the local resistance loss coefficient at the tee of the hot molten salt mother pipe, M h,i is the molten salt flow rate of the i-th section of the hot molten salt mother pipe.

[0008] Specifically, the molten salt flow rate M of the i-th section of the cold molten salt mother pipe is c,i The calculation formula is M c,i =M c,i-1 -m i ;m i is the actual molten salt mass flow rate in the i-th collector circuit, M c,0 = m; molten salt flow rate M of the ith section of the hot molten salt main pipe h,i The calculation formula is M h,i =M h,i-1 +m i , M h,0 =0.

[0009] Specifically, the local resistance loss coefficient ξ at the tee of the cold molten salt mother pipe is c,i Local resistance loss coefficient ξ at the tee of the hot molten salt main pipe h,i The value is 20λ. K is the roughness of the pipeline; d is the inner diameter of the heat collection loop pipe; Re is the Reynolds number.

[0010] Based on the same technical concept, the present invention also provides a method for obtaining the inner diameter value of a mother pipe in a collector field of a trough-type solar thermal power station. The method for obtaining the inner diameter value of each pipe section of the mother pipe comprises the following steps:

[0011] S1, establish the physical model of the solar collector field: set the total flow rate m of the molten salt flowing in the solar collector field, the inlet molten salt temperature ti of the solar collector field, the outlet temperature to and the inlet static pressure p; at the same time, set the number of loops n of the solar collector circuit, the length l of each loop, the length w of each mother pipe section, the maximum diameter D of the mother pipe and the inner diameter d of the solar collector circuit pipe;

[0012] S2, assuming that the molten salt flow rate in each collector loop pipe is an average flow rate, based on this assumption, the molten salt flow rate of each pipe section of the mother pipe is obtained, based on the equal molten salt flow rate of each pipe section of the mother pipe, the inner diameter value of each pipe section of the cold molten salt mother pipe is calculated, assuming that the pressure drop of the corresponding pipe sections of the hot molten salt mother pipe and the cold molten salt mother pipe is equal, based on this assumption, the inner diameter value of each pipe section of the hot molten salt mother pipe is calculated;

[0013] S3, obtain the actual molten salt mass flow rate in each thermal collector loop pipe; verify whether the calculated sum of the actual molten salt mass flow rates in the thermal collector loop pipe is equal to the set total molten salt flow rate m. If they are equal, calculate the ratio of the actual molten salt mass flow rate in each thermal collector loop pipe to the average molten salt flow rate. When the ratio ranges from 0.9973 to 1.0027, it is considered that the pipe diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe obtained in step S2 are valid values.

[0014] Specifically, based on the effective diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe verified in step S3, a standard diameter value is selected nearby, and step S3 is repeated.

[0015] Specifically, the specific implementation method of step S2 includes:

[0016] S201, assuming that the molten salt flow rate in each collector loop pipe is the average flow rate m av , m av =m / n; use formula M c,i =M c,i-1 -m av , calculate the molten salt flow M in the cold molten salt main pipe of each pipe section c,i ; Use formula M h,i =M h,i-1 +m av Calculate the molten salt flow rate M in the hot molten salt main pipe of each pipe section h,i ;M h,0 =0,M c,0 =m;

[0017] S202, assuming that the molten salt flow rate in each pipe section is equal, based on the formula Calculate the diameter D of each section of the cold molten salt main pipe c,i ; Assume that the pressure drop of each section of the hot molten salt main pipe is ΔP h,i Equal to the pressure drop ΔP of each section of the cold molten salt main pipe c,i , based on the formula Calculate the inner diameter D of the ith section of the molten salt main pipe h,i .

[0018] Specifically, the specific implementation method of step S3 includes:

[0019] S301, calculating the actual mass flow rate of molten salt in each heat collection loop pipe;

[0020] S303, judging whether the sum of the actual mass flow rate of the molten salt in each heat collection loop pipe is equal to the set total flow rate m, if not equal, returning to step S301; if equal, entering step S304;

[0021] S304, based on the formula Calculate the flow deviation coefficient α of the kth collector circuit k , when the flow deviation coefficient α k In the range of 0.9973-1.0027, the diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe obtained in step S2 are considered to be effective values.

[0022] If the flow deviation coefficient α k In the range of 0.9973-1.0027, the actual mass flow rate of molten salt in each collector circuit is approximately equal to the average flow rate, and it can be considered that the uniform distribution of the collector circuit flow rate can be achieved.

[0023] Specifically, the specific implementation method of step S301 includes:

[0024] S3011, obtain the actual mass flow rate m1 of the molten salt in the first heat collection loop pipe:

[0025] The outlet static pressure P of the first collector circuit h,1 Assignment, P c,1 =p, based on the formula ΔP k =P c,k -P h,k Calculate the static pressure difference ΔP1 between the cold and hot ends of the first heat collection loop, and calculate the actual mass flow rate m1 of the molten salt in the first heat collection loop based on the static pressure difference ΔP1;

[0026] ΔP k is the static pressure difference between the cold and hot ends of the kth collector circuit, P c,k is the static pressure at the cold end of the kth collector circuit, P h,k is the static pressure at the hot end of the kth collector circuit, k = 1, 2, …, n.

[0027] S3012, obtaining the actual mass flow rate of the molten salt in the second to nth heat collection loop pipes:

[0028] Based on formula M c,i =M c,i-1 -m i and M h,i =M h,i-1 +m i , get the molten salt flow M of the cold molten salt main pipe of the i-th pipe section c,i and the molten salt flow rate M of the hot molten salt main pipe h,i ;

[0029] Based on the formula Calculate the molten salt pressure drop ΔP of the cold molten salt main pipe in the i-th pipe section c,i , based on the formula Calculate the molten salt pressure drop ΔP of the hot molten salt main pipe in the i-th pipe section h,i ; and according to the formula P c,i+1 =P c,i -ΔP c,i And the formula P h,i+1 =P h,i -ΔP h,i The static pressure P at the cold end of the i+1th collector circuit is obtained respectively c,i+1 and hot end static pressure P h,i+2 ;

[0030] Get the static pressure difference ΔP between the cold and hot ends of the i+1th collector circuit i+1 , and based on the static pressure difference ΔP i+1 Calculate the actual mass flow rate m of the molten salt in the i+1th collector loop pipe i+1 .

[0031] Specifically, the actual mass flow rate m of the molten salt in the kth collector loop tube is calculated based on the static pressure difference between the cold and hot ends of the kth collector loop. k The formula is ξ k is the local resistance loss coefficient at the tee of the kth collector loop pipe.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) The present invention can achieve balanced flow distribution without valve control through the same-path arrangement, thereby reducing the cost of valve installation, control and maintenance.

[0034] 2) The present invention provides a method for calculating the inner diameter of each pipe section of the cold / hot molten salt mother pipe; the diameter of each pipe section of the cold molten salt mother pipe is calculated based on the equal molten salt flow rate of each section, and the diameter of each pipe section of the hot molten salt mother pipe is calculated based on the equal pressure drop of the hot molten salt mother pipe and the corresponding section of the cold molten salt mother pipe, and then the diameter is corrected with the standard pipe diameter. After the diameter value of the molten salt mother pipe is calculated, the ratio of the actual mass flow rate of the molten salt in each solar collector loop pipe to the average flow rate is calculated. When the ratio is in the range of 0.9973-1.0027, it can be seen that the actual mass flow rate of the molten salt in each solar collector loop pipe is approximately equal to the average flow rate, and it can be considered that the uniform distribution of the flow in the solar collector field can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The structure diagram of the solar collector field of a trough type solar thermal power station according to an embodiment of the present invention.

[0036] Figure 2 This is a model diagram of a solar collector field of a trough-type solar thermal power station according to an embodiment of the present invention.

[0037] Figure 3 This is a flow chart of a method for obtaining the inner diameter values ​​of each pipe section of a cold / hot molten salt mother pipe according to an embodiment of the present invention.

[0038] Figure 4 The distribution diagram of the flow rate in the tubes of each solar collector circuit corresponding to Table 4.

[0039] Figure 5 The flow deviation coefficient distribution diagram of each collector circuit corresponding to Table 4.

[0040] Figure 6 The figure is a comparison chart of theoretical calculation results and simulation software calculation results of an embodiment of the present invention.

[0041] Among them, 1 is a cold molten salt tank, 2 is a cold molten salt pump, 3 is a cold molten salt mother pipe, 4 is a heat collection loop, 5 is a concentrator, 6 is a hot molten salt mother pipe, 7 is a hot molten salt pump, and 8 is a hot molten salt tank. DETAILED DESCRIPTION

[0042] like Figure 1 As shown, a trough type CSP power station according to an embodiment of the present invention comprises a heat collection field, a cold molten salt tank 1, a hot molten salt pump 7 and a hot molten salt tank 8. The heat collection field comprises a cold molten salt mother pipe 3, a hot molten salt mother pipe 6 and n heat collection loops 4. Each of the heat collection loops 4 comprises two concentrators 5.

[0043] The cold molten salt mother pipe 3 and the hot molten salt mother pipe 6 are arranged in the same route, and the n heat collection loops 4 are arranged in parallel between the cold molten salt mother pipe 3 and the hot molten salt mother pipe 6. The cold molten salt tank 1 is connected to the inlet of the cold molten salt mother pipe 3 through the cold molten salt pump 2, and the outlet of the hot molten salt mother pipe 6 is connected to the hot molten salt tank 8 through the hot molten salt pump 7. The cold molten salt mother pipe 3 is arranged in a folded manner, and the inlets of the cold molten salt pump 2 and the n heat collection loops 4 are respectively arranged upstream and downstream of the cold molten salt mother pipe 3.

[0044] The heating path of the molten salt is as follows: it is pumped out from the cold molten salt tank 1 through the cold molten salt pump 2 and flows into the cold molten salt main pipe 3, and then the cold molten salt main pipe 3 turns back away from the side of the cold molten salt tank 1 and starts to diverge, enters each of the heat collection loops 4, is concentrated and heated by the concentrator 5, and then converges to the hot molten salt main pipe 6, and finally is pumped into the hot molten salt tank 8 through the hot molten salt pump 7.

[0045] Since the molten salt flowing in each of the heat collection loops 4 has the same flow path in the heat collection field, it is easy to achieve balanced distribution of multi-loop flow without valve regulation.

[0046] The cold molten salt mother pipe 3 includes i pipe sections, and the i-th pipe section is the pipe section of the cold / hot molten salt mother pipe between the i-th heat collection loop and the i+1-th heat collection loop, wherein i=1, 2, ..., n-1. Similarly, the hot molten salt mother pipe 3 includes i pipe sections. The inner diameter D of the i-th pipe section of the cold molten salt mother pipe 3 is c,i The inner diameter D of the i-th pipe section of the hot molten salt mother pipe 6 is h,i The calculation method includes the following steps:

[0047] S1, such as Figure 2 As shown in the figure, the physical model of the solar collector field is established: the total flow rate of molten salt flowing in the solar collector field is set to m, and the molten salt temperature at the inlet of the solar collector field is set to t i , outlet temperature t o and the static pressure p of the cold molten salt inlet; at the same time, set the length l of each of the heat collection loops 4, the length w of each mother pipe section, the maximum diameter D of the mother pipe, and the inner diameter d of the heat collection loop pipe.

[0048] The heat transfer medium flowing in the solar collector field is assumed to be binary molten salt, the component structure of the binary molten salt is: 60wt% NaNO3+40wt% KNO3, and the relationship between its physical properties and temperature is shown in formulas (1)-(4).

[0049] ρ m =2085.5-0.6258t m (1)

[0050] λ m =0.4407+1.926×10 -4 t m (2)

[0051] C p,m =1442.3+0.1735t m (3)

[0052]

[0053] in,

[0054] ρ m ——Density of binary molten salt, kg / m 3

[0055] λ m ——Thermal conductivity of binary molten salt, W / m / K

[0056] C p,m ——Specific heat capacity of binary molten salt, J / kg / K

[0057] μ——dynamic viscosity of binary molten salt, Pa·s

[0058] t m ——Temperature, °C

[0059] When designing the fluid in the pipeline, a relatively low flow velocity is selected, and the flow state is generally in the turbulent transition zone. The resistance loss coefficient λ of the binary molten salt along the way is calculated using the Arit-Suri formula, i.e., formula (5).

[0060]

[0061] in,

[0062] K——Roughness of the pipeline, m, with a value range of 0.0001-0.0002

[0063] d——Inner diameter of the pipe, m

[0064] Re——Reynolds number

[0065] S2, assuming that the molten salt flow rate in each collector loop pipe is an average flow rate, based on this assumption, the molten salt flow rate of each pipe section of the mother pipe is obtained, based on the equal molten salt flow rate of each pipe section of the mother pipe, the inner diameter value of each pipe section of the cold molten salt mother pipe is calculated, based on the equal pressure drop of the hot molten salt mother pipe and the corresponding pipe section of the cold molten salt mother pipe, the inner diameter value of each pipe section of the hot molten salt mother pipe is calculated; specifically including:

[0066] S201, the molten salt flow rate in each collector loop pipe is the average flow rate m av =m / n, and calculate the molten salt flow rate M in the cold molten salt main pipe of each pipe section according to formula (6): c,i ;

[0067] M c,i =M c,i-1 -m av (6)

[0068] Among them, M c,0 =m.

[0069] According to formula (7), the molten salt flow rate M in the hot molten salt main pipe of each pipe section is calculated h,i ;

[0070] M h,i =M h,i-1 +m av (7)

[0071] Among them, M h,0 =0.

[0072] S202, assuming that the molten salt flow rate of each pipe section is equal, the pipe diameter D of the i-th pipe section of the cold molten salt mother pipe is calculated according to formula (8): c,i ;

[0073]

[0074] According to formula (9), the pressure drop ΔP of each section of the cold molten salt main pipe is calculated: c,i;

[0075]

[0076] in,

[0077] ξ c,i ——Local resistance loss coefficient at the tee of the cold molten salt mother pipe. In this embodiment, this coefficient is 20λ

[0078] w——the length of each cold / hot molten salt main pipe section, m

[0079] p c ——density of cold molten salt, using inlet temperature t i Substitute into formula (1) to calculate, kg / m 3

[0080] Due to the pressure drop ΔP of each section of the hot molten salt main pipe h,i Equal to the pressure drop ΔP of each section of the cold molten salt main pipe c,i According to formula (9) and formula (10-1), formula (10-2) is obtained, and the inner diameter D of the i-th pipe section of the hot molten salt mother pipe is calculated based on formula (10-2): h,i .

[0081]

[0082]

[0083] in,

[0084] ξ h,i ——Local resistance loss coefficient at the tee of the hot molten salt mother pipe. In this embodiment, this coefficient is taken as 20λ

[0085] ρ h ——Density of hot molten salt, using outlet temperature t o Substitute into formula (1) to calculate, kg / m 3

[0086] S3, since the calculation in step S2 is based on assumptions, it may deviate from the actual situation. The static pressure difference at both ends of each collector loop is obtained by static pressure analysis. Based on the static pressure difference, the actual molten salt mass flow rate in each collector loop pipe is calculated, and it is verified whether the calculated sum of the actual molten salt mass flow rate in the collector loop pipe is equal to the set total molten salt flow rate m. If they are equal, the ratio of the actual molten salt mass flow rate in each collector loop to the average molten salt flow rate is calculated. When the ratio ranges from 0.9973 to 1.0027, it can be seen that the actual mass flow rate of molten salt in each collector loop pipe is approximately equal to the average flow rate, and it can be considered that the uniform distribution of the collector field flow rate can be achieved. That is, the pipe diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe obtained in step S2 are effective values, specifically including:

[0087] S301, obtain the actual mass flow rate m of the molten salt in each heat collection loop pipe k , k = 1, 2…, n; comprising the following steps:

[0088] S3011, obtaining the actual mass flow rate m1 of the molten salt in the first heat collection loop pipe;

[0089] Since the static pressure at the inlet of the solar collector field is set to p in step S1, that is, the static pressure at the cold end of the first solar collector circuit is P c,1 =p, the outlet static pressure of the first collector circuit is P h,1 The value is assigned as 0.001, and the static pressure difference ΔP1 between the cold and hot ends of the first collector loop is calculated according to formula (11). The actual mass flow rate m1 of the molten salt in the first collector loop pipe is calculated according to formula (12).

[0090] ΔP k =P c,k -P h,k (11)

[0091] ΔP k is the static pressure difference between the cold and hot ends of the kth collector circuit, P c,k is the static pressure at the cold end of the kth collector circuit, P h,k is the static pressure at the hot end of the kth collector circuit, k = 1, 2, …, n.

[0092]

[0093] ξ k is the local resistance loss coefficient at the tee of the kth heat collection loop pipe, and in this embodiment, the value is 20λ.

[0094] S3012, obtaining the actual mass flow rate of the molten salt in the second to nth heat collection loop pipes;

[0095] like Figure 2 As shown, the molten salt flow rate M in the cold molten salt main pipe of the i-th pipe section c,i The calculation method of is shown in formula (13), the molten salt flow rate M in the cold molten salt main pipe of the i-th pipe section h,i The calculation method of is shown in formula (14).

[0096] M c,i =M c,i-1 -m i (13)

[0097] M h,i =M h,i-1 +m i (14)

[0098] Since the molten salt in the first section of the hot molten salt main pipe comes from the first collector circuit, the molten salt flow rate M in the first section of the hot molten salt main pipe is h,1 Equal to the actual molten salt flow rate m1 of the first collector circuit, as shown in formula (15), the molten salt flow rate M of the cold molten salt main pipe of the first pipe section is calculated based on formula (16): c,1 .

[0099] M h,1 =m1(15)

[0100] M c,1 =m-m1(16)

[0101] The molten salt flow rate M of the first section cold molten salt main pipe is obtained c,1 and the molten salt flow rate M of the hot molten salt main pipe h,1 Substituting into equation (9) and equation (10-1) respectively, we can obtain the molten salt pressure drop ΔP of the cold molten salt main pipe in the first pipe section: c,1 And the molten salt pressure drop of the first section of the hot molten salt main pipe ΔP h,1 .

[0102] As explained in step S3011, the static pressure at the inlet of the solar field is p, that is, the static pressure at the cold end of the first solar collector loop is P c,1 =p, the outlet static pressure of the first collector circuit P h,1 Assigning a value of 0.001, the static pressure P at the cold end of the second collector circuit can be obtained according to equations (17) and (18) respectively: c,2 and hot end static pressure P h,2 .

[0103] P c,i+1 =P c,i -ΔP c,i (17)

[0104] P h,i+1 =P h,i -ΔP h,i (18)

[0105] Based on formula (11), the static pressure difference ΔP2 between the hot and cold ends of the second solar collector loop is obtained, and based on formula (12), the actual mass flow rate m2 of the molten salt in the second solar collector loop is obtained.

[0106] Using the same method, based on equations (13), (14), (9), (10-1), (17) and (18), the static pressure P at the cold end of the i+1th collector circuit is obtained: c,i+1 and hot end static pressure P h,i+1 .

[0107] Based on formula (11), the static pressure difference ΔP between the cold and hot ends of the i+1th collector circuit is obtained: j+1, and based on formula (12) obtain the actual mass flow rate m of the molten salt in the i+1th collector circuit j+1 .

[0108] At this point, the actual mass flow rate of molten salt in each collector circuit is obtained.

[0109] S302, as shown in formula (19), the sum of the actual mass flow of the molten salt in each heat collection circuit should be equal to the set total flow m. Therefore, after obtaining the actual mass flow of the molten salt in each heat collection circuit, it is determined whether the sum of the actual mass flow of the molten salt in each heat collection circuit is equal to the set total flow m. If not, the outlet static pressure P of the first heat collection circuit is adjusted. h,1 Reassign value and return to step S301.

[0110] If they are equal, go to step S303.

[0111]

[0112] S303, based on formula (20), calculate the flow deviation coefficient α of the kth heat collection circuit k When the flow deviation coefficient α k If the inner diameter value D of the i-th pipe section of the cold molten salt mother pipe obtained in step S2 is within the range of 0.9973-1.0027, it is considered that c,i and the inner diameter value D of the ith section of the hot molten salt mother pipe h,i When it is a valid value, multi-circuit flow balance can be achieved, and the process goes to step S4.

[0113]

[0114] S4, based on the inner diameter value D of the i-th pipe section of the cold molten salt mother pipe obtained in step S2 c,i and the inner diameter value D of the ith section of the hot molten salt mother pipe h,i , respectively select the nearest standard pipe diameter value, and repeat step S3. When the flow deviation coefficient α k In the range of 0.9973-1.0027, the selected standard pipe diameter value will be used as the final solution for the pipe diameter value of each pipe section of the cold molten salt mother pipe and the hot molten salt mother pipe to achieve self-balancing of the flow of multiple solar collector circuits.

[0115] Based on the above method, an embodiment of the present invention performs theoretical calculation and software simulation respectively, and compares the results of theoretical calculation and simulation. The details are as follows:

[0116] In the theoretical calculation part, the model parameters of the solar field are shown in Table 1. The diameters of each section of the cold and hot molten salt mother pipes are calculated according to the method of one embodiment of the present invention as shown in Table 2. Considering that in actual engineering applications, segment-by-segment diameter changes will increase the difficulty of pipeline manufacturing and installation, group diameter changes are adopted, and the diameters are set according to the groups in Table 3 and the mother pipe diameters of the groups.

[0117] According to the pipe diameter values ​​of each group in Table 3, the flow distribution in each collector loop pipe is calculated to obtain the molten salt mass flow rate at the outlet of each collector loop. The molten salt mass flow rate at the outlet of each collector loop can represent the molten salt mass flow rate in each collector loop pipe. The calculated molten salt mass flow rate in each collector loop pipe is divided by the average molten salt flow rate to obtain the flow deviation coefficient in each collector loop. See Table 4 for details.

[0118] From Table 4 we can get Figure 4 and Figure 5 , Figure 4 and Figure 5 The horizontal axes of are all the serial numbers of the collector circuits. Figure 4 The vertical axis is the mass flow rate of molten salt in each collector circuit. Figure 5 The ordinate is the flow deviation coefficient of each collector circuit, such as Figure 4 and Figure 5 As shown, in the 37th, 38th and 39th collector circuits, the molten salt mass flow rate is significantly different from the average flow rate, which is a reflection of the error accumulation. However, its flow deviation coefficient is still within the range of 0.9973-1.0027.

[0119] In the software simulation part, based on the data in Table 1 and Table 3, Apros software was used to simulate and obtain the mass flow rate at the outlet of each loop.

[0120] The results of theoretical calculation and simulation are compared, and the mass flow rate of each circuit outlet obtained by simulation using Apros software is compared with the mass flow rate of each circuit outlet in Table 4, as shown in Figure 6 As shown, Figure 6 The horizontal axis is the serial number of the heat collection loop, and the vertical axis is the mass flow rate of the molten salt in each heat collection loop pipe. Figure 6 It can be observed that the overlap of the two curves is relatively high, indicating that the error between the calculation method of the present invention and the simulation result is relatively small. Therefore, the calculation method of the diameter of the cold and hot molten salt mother pipes in the present invention has high validity and can achieve self-balancing of the flow in multiple solar collector circuits.

[0121] Table 1 Simulation model parameters of the thermal field

[0122] Model parameters unit Numeric Total flow of molten salt in the collector field m Kg / s 606.27 The design temperature of the molten salt inlet of the collector field is ti ℃ 290 The design temperature of the molten salt outlet of the collector field is to ℃ 550 The static pressure of the molten salt inlet of the collector field MPa 4.2 Inner diameter of heat collecting tube in heat collecting loop d mm 80 Length of collector circuit l m 1100 Total number of collector circuits n strip 40 Heat collector circuit spacing w m 25 Maximum diameter of mother pipe D mm 550

[0123] Table 2 Pipe diameter values ​​of each section of cold / hot molten salt main pipe

[0124]

[0125]

[0126] Table 3 Diameters of each pipe section after the mother pipe is grouped

[0127]

[0128]

[0129] Table 4 Molten salt mass flow rate and flow rate deviation coefficient of each collector circuit

[0130]

[0131]

Claims

1. A solar collector field of a trough solar thermal power station, comprising a cold molten salt mother pipe, a hot molten salt mother pipe and n solar collector loops, wherein the cold molten salt mother pipe and the hot molten salt mother pipe are arranged in the same route; the n solar collector loops are arranged in parallel between the cold molten salt mother pipe and the hot molten salt mother pipe; the cold / hot molten salt mother pipe comprises i pipe sections, i=1, 2, ..., n-1; It is characterized in that The inner diameter of the i-th section of the cold molten salt mother pipe is D c，i , and its calculation formula is: m is the total flow rate of molten salt flowing in the collector field, D is the maximum diameter of the cold / hot molten salt mother pipe, M c，i is the molten salt flow rate of the i-th section of the cold molten salt main pipe; The inner diameter of the ith section of the molten salt main pipe is D h，i , and its calculation formula is λ is the resistance loss coefficient of binary molten salt along the way, w is the length of each cold / hot molten salt mother pipe section, ρ c is the density of cold molten salt; c，i is the local resistance loss coefficient at the tee of the cold molten salt mother pipe, ρ h is the density of molten salt; h，i is the local resistance loss coefficient at the tee of the hot molten salt mother pipe, M h，i is the molten salt flow rate of the i-th section of the hot molten salt mother pipe.

2. The solar collector field of a trough solar thermal power station according to claim 1, characterized in that: Molten salt flow rate M of the i-th section of the cold molten salt main pipe c，i The calculation formula is M c，i =M c，i-1 -m i ;m i is the actual molten salt mass flow rate in the i-th collector circuit, M c，0 = m; molten salt flow rate M of the ith section of the hot molten salt main pipe h，i The calculation formula is M h，i =M h，i-1 +m i , M h，0 =0.

3. The solar collector field of a trough solar thermal power station according to claim 1 or 2, characterized in that: Local resistance loss coefficient ξ at the tee of cold molten salt main pipe c，i Local resistance loss coefficient ξ at the tee of the hot molten salt main pipe h，i The value is 20λ. K is the roughness of the pipeline; d is the inner diameter of the heat collection loop pipe; Re is the Reynolds number.

4. A method for obtaining the inner diameter value of a mother pipe in a collector field of a trough-type solar thermal power station according to any one of claims 1 to 3, characterized in that: Method for obtaining the inner diameter value of each section of the mother pipe The following steps are involved: S1, establish the physical model of the solar collector field: set the total flow rate m of the molten salt flowing in the solar collector field, the inlet molten salt temperature ti of the solar collector field, the outlet temperature to and the inlet static pressure p; at the same time, set the number of loops n of the solar collector circuit, the length l of each loop, the length w of each mother pipe section, the maximum diameter D of the mother pipe and the inner diameter d of the solar collector circuit pipe; S2, assuming that the molten salt flow rate in each collector loop pipe is an average flow rate, based on this assumption, the molten salt flow rate of each pipe section of the mother pipe is obtained, based on the equal molten salt flow rate of each pipe section of the mother pipe, the inner diameter value of each pipe section of the cold molten salt mother pipe is calculated, assuming that the pressure drop of the corresponding pipe sections of the hot molten salt mother pipe and the cold molten salt mother pipe is equal, based on this assumption, the inner diameter value of each pipe section of the hot molten salt mother pipe is calculated; S3, obtain the actual molten salt mass flow rate in each thermal collector loop pipe; verify whether the calculated sum of the actual molten salt mass flow rates in the thermal collector loop pipe is equal to the set total molten salt flow rate m. If they are equal, calculate the ratio of the actual molten salt mass flow rate in each thermal collector loop pipe to the average molten salt flow rate. When the ratio ranges from 0.9973 to 1.0027, it is considered that the pipe diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe obtained in step S2 are valid values.

5. The method for obtaining the inner diameter value of the mother pipe in the collector field of a trough type solar thermal power station according to claim 4, characterized in that: Based on the effective pipe diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe verified in step S3, a standard pipe diameter value is selected nearby, and step S3 is repeated.

6. The method for obtaining the inner diameter value of the mother pipe in the collector field of a trough type solar thermal power station according to claim 4, characterized in that: The specific implementation method of step S2 includes: S201, assuming that the molten salt flow rate in each collector loop pipe is the average flow rate m av , m av =m / n; use formula M c，i =M c，i-1 -m av Calculate the molten salt flow rate M in the cold molten salt main pipe of each pipe section c，i ; Use formula M h，i =M h，i-1 +m av Calculate the molten salt flow rate M in the hot molten salt main pipe of each pipe section h，i ;M h，0 =0,M c，0 =m; S202, assuming that the molten salt flow rate in each pipe section is equal, based on the formula Calculate the diameter D of each section of the cold molten salt main pipe c，i ; Assume that the pressure drop of each section of the hot molten salt main pipe is ΔP h，i Equal to the pressure drop ΔP of each section of the cold molten salt main pipe c，i , based on the formula Calculate the inner diameter D of the ith section of the molten salt main pipe h，i .

7. The method for obtaining the inner diameter value of the mother pipe in the solar trough power station collector field according to claim 4, characterized in that: The specific implementation method of step S3 includes: S301, calculating the actual mass flow rate of molten salt in each heat collection loop pipe; S303, judging whether the sum of the actual mass flow rate of the molten salt in each heat collection loop pipe is equal to the set total flow rate m, if not equal, returning to step S301; if equal, entering step S304; S304, based on the formula Calculate the flow deviation coefficient α of the kth collector circuit k , when the flow deviation coefficient α k In the range of 0.9973-1.0027, the diameter values ​​of the cold molten salt mother pipe and the hot molten salt mother pipe obtained in step S2 are considered to be effective values.

8. The method for obtaining the inner diameter value of the mother pipe in the solar trough power station collector field according to claim 7, characterized in that: The specific implementation method of step S301 includes: S3011, obtain the actual mass flow rate m1 of the molten salt in the first heat collection loop pipe: The outlet static pressure P of the first collector circuit h，1 Assignment, P c，1 =p, based on the formula ΔP k =P c，k -P h，k Calculate the static pressure difference ΔP1 between the cold and hot ends of the first heat collection loop, and calculate the actual mass flow rate m1 of the molten salt in the first heat collection loop based on the static pressure difference ΔP1; ΔP k is the static pressure difference between the cold and hot ends of the kth collector circuit, P c，k is the static pressure at the cold end of the kth collector circuit, P h，k is the static pressure at the hot end of the kth collector circuit, k = 1, 2, ..., n; S3012, obtaining the actual mass flow rate of the molten salt in the second to nth heat collection loop pipes: Based on formula M c，i =M c，i-1 -m i and M h，i =M h，i-1 +m i , get the molten salt flow M of the cold molten salt main pipe of the i-th pipe section c，i and the molten salt flow rate M of the hot molten salt main pipe h，i ; Based on the formula Calculate the molten salt pressure drop ΔP of the cold molten salt main pipe in the i-th pipe section c，i , based on the formula Calculate the molten salt pressure drop ΔP of the hot molten salt main pipe in the i-th pipe section h，i ; and according to the formula P c，i+1 =P c，i -ΔP c，i And the formula P h，i+1 =P h，i -ΔP h，i The cold end static pressure P of the i+1th collector circuit is obtained respectively c，i+1 and hot end static pressure P h，i+2 ; Get the static pressure difference ΔP between the hot and cold ends of the i+1th collector circuit i+1 , and based on the static pressure difference ΔP i+1 Calculate the actual mass flow rate m of the molten salt in the i+1th collector loop pipe i+1 .

9. The method for obtaining the inner diameter value of the mother pipe in the solar trough power station collector field according to claim 7, characterized in that: Calculate the actual mass flow rate m of the molten salt in the kth collector loop tube based on the static pressure difference between the cold and hot ends of the kth collector loop k The formula is ξ k is the local resistance loss coefficient at the tee of the kth collector loop pipe.

10. A trough type solar thermal power station, characterized in that: A solar collector field comprising the trough type solar thermal power station as described in any one of claims 1 to 3.

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