Sectional tower type photo-thermal system mirror field distribution control method

Abstract

The invention relates to the field of tower-type photo-thermal systems, and discloses a mirror field distribution control method for a segmented tower-type photo-thermal system, which comprises the following steps of: separately arranging an evaporation section tube panel and an overheating section tube panel of a heat absorber of the tower-type photo-thermal system, and calculating a theoretical power distribution ratio of the overheating section tube panel to the evaporation section tube panel; calculating the initial number of heliostats distributed to the overheating section tube panel according to the theoretical power distribution ratio; the sun position is given, and the optical efficiency of each heliostat is calculated; iterative calculation is carried out to obtain the final number of heliostats distributed to the tube panel of the overheating section; and the target point of each heliostat is optimized, and when the position of the sun changes, heliostat distribution is carried out again. According to the method disclosed by the invention, the influence of light spot overflow on the overheating section tube panel is avoided, the control difficulty of the mirror field projection energy flow is reduced, and the overall optical efficiency can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of tower photothermal systems, and in particular to a mirror field distribution control method for a segmented tower photothermal system. Background Art

[0002] The tower solar thermal system has the advantages of fewer energy conversion links and high heat collection efficiency. It can also save heat absorption and heat storage media and has high economic efficiency. However, the tower solar thermal system also faces the problem of difficult temperature control in the superheated section when producing superheated steam. This is mainly due to the small amount of steam in the superheated section tube screen at the initial startup, and its temperature is very sensitive to the delivered energy flow, so a more accurate energy flow control strategy is needed. Figure 1 As shown, its working principle is as follows: external make-up water enters the steam-water separator 6 through the deaerator and the feed water heater, and the liquid water after steam-water separation flows into the evaporation section tube panel 2 and is heated to saturated steam and water, and then enters the steam-water separator 6, wherein the separated saturated steam enters the superheating section tube panel 3, and the saturated steam in the superheating section tube panel 3 is heated to superheated steam, and finally the superheated steam is output for heating or power generation.

[0003] In the existing tower direct steam generation (DSG) system, the evaporation section tube screen and the superheating section tube screen of the absorber are adjacent, which will inevitably cause the light spot projected onto the evaporation section tube screen to overflow to the superheating section tube screen, causing the superheated steam temperature to fluctuate. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a segmented tower solar thermal system mirror field distribution control method, so as to avoid the influence of light spot overflow on the overheating section tube screen, reduce the difficulty of controlling the mirror field projection energy flow, and significantly improve the overall optical efficiency.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for controlling mirror field distribution of a segmented tower photothermal system comprises the following steps:

[0007] Step 1: Separate the evaporation section tube panel and the superheating section tube panel of the tower-type solar thermal system absorber, wherein the evaporation section tube panel is located at the top of the absorber tower, and the superheating section tube panel is located below the evaporation section tube panel;

[0008] Step 2, calculating the theoretical power allocation ratio of the overheating section tube panel and the evaporation section tube panel, assuming that the optical efficiencies of the heliostats are the same, and calculating the initial number of heliostats allocated to the overheating section tube panel according to the theoretical power allocation ratio; allocating the above number of inner circle heliostats within the field of view of the overheating section tube panel to the overheating section tube panel, and the remaining heliostats to the evaporation section tube panel;

[0009] Step 3, given the sun position, the target point of the heliostat is set as the geometric center of the superheating section tube screen or the evaporation section tube screen, and the optical efficiency of each heliostat is calculated;

[0010] Step 4, according to the calculated optical efficiency of the heliostat, the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen is calculated, and according to the relationship between the actual projected power ratio and the theoretical power allocation ratio, the number of heliostats allocated to the superheating section tube screen is adjusted, and the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen is recalculated until the requirement is met, and the iteration is stopped to obtain the final number of heliostats allocated to the superheating section tube screen;

[0011] Step 5, optimizing the target point of each heliostat so that the energy flow projected onto the superheating section tube screen or the evaporation section tube screen has less overflow and is evenly distributed;

[0012] Step 6: When the sun position exceeds the set range, return to step 3 and redistribute the heliostats.

[0013] In the above scheme, in step 2, the calculation method of the theoretical power distribution ratio of the superheating section tube panel and the evaporation section tube panel is as follows:

[0014] Mirror field projection power required for the evaporation section tube screen for:

[0015]

[0016] The mirror field projection power required for the overheating section tube panel for:

[0017]

[0018] The theoretical power distribution ratio Γ0 of the superheating section tube panel and the evaporation section tube panel is:

[0019]

[0020] Among them, H 1,out is the specific enthalpy of saturated steam at the outlet of the evaporation section tube panel, H 1,in is the water enthalpy at the inlet of the evaporation tube panel, v is the pipeline flow rate, η1 is the heat absorption efficiency of the evaporation tube panel, H 2,out is the specific enthalpy of superheated steam at the outlet of the superheated tube screen, and η2 is the heat absorption efficiency of the superheated tube screen.

[0021] In the above scheme, in step 2, the calculation method of the initial number m0 of heliostats allocated to the overheating section tube panel is as follows:

[0022] m0=Γ0*n

[0023] Where n is the total number of heliostats.

[0024] In the above scheme, in step 3, the optical efficiency η of the heliostat is calculated as follows:

[0025] η=η cos ·η sb ·η att ·η trunc ·η ref

[0026] Among them, η cos is the cosine efficiency, η sb is the shadow occlusion efficiency, η att is the atmospheric transmittance, η trunc is the cutoff efficiency and η ref is the specular reflectivity.

[0027] In the above scheme, in step 4, the calculation formula for the actual projected power ratio Γ of the superheating section tube panel and the evaporation section tube panel is as follows:

[0028]

[0029] Wherein, P1 is the power projected onto the evaporation section tube screen, P2 is the power projected onto the superheat section tube screen, I is the normal direct radiation value, A is the heliostat reflection area, m is the number of heliostats projected onto the superheat section tube screen, n is the total number of heliostats, and η 1,j represents the optical efficiency of the jth heliostat projected onto the evaporation tube screen, η 2,i It represents the optical efficiency of the i-th heliostat projected onto the superheated tube panel.

[0030] In the above scheme, in step 4, the difference δ between the actual projected power ratio Γ and the theoretical power allocation ratio Γ0 is calculated, and a threshold σ is set. If δ<-σ, the number of heliostats allocated to the overheating section tube screen is increased, and the iteration continues; if δ>σ, the number of heliostats allocated to the overheating section tube screen is reduced, and the iteration continues; if |δ|≤σ, the requirement is met and the iteration is stopped.

[0031] In the above scheme, in step 5, the DNI used for the target point optimization of the heliostat is the clear sky DNI of the sun's position on the design point day, and the target point optimization method used is a genetic optimization method or a simulated annealing algorithm.

[0032] In the above scheme, in step 6, for the northern hemisphere, the sun position is divided into 3×6 checkerboards in terms of altitude and azimuth, and the sun position at the center of the checkerboard is used as the sun position given in step 3 to allocate heliostats. Therefore, for the solar thermal mirror field, only 18 heliostat allocation schemes need to be set throughout the year, and the same allocation scheme is used in each checkerboard.

[0033] Through the above technical solution, the mirror field allocation control method of a segmented tower photothermal system provided by the present invention has the following beneficial effects:

[0034] 1. The present invention arranges the evaporation section tube panel and the superheat section tube panel separately, thereby eliminating the influence of spot overflow on the superheat section tube panel and reducing the difficulty of controlling the energy flow of the mirror field.

[0035] 2. After the evaporation section tube screen is set separately, due to the lower operating temperature, low-cost alloy steel can be used to save costs.

[0036] 3. The present invention dynamically allocates the number of heliostats projected onto the evaporation section tube screen and the superheating section tube screen according to different solar positions, thereby maximizing steam production.

[0037] 4. The present invention optimizes the target point of the heliostat so that the energy flow projected onto the superheating section tube screen or the evaporation section tube screen has less overflow and is evenly distributed.

[0038] 5. The present invention can dynamically adjust the allocation scheme according to the different positions of the sun caused by the change of time every day. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0040] Figure 1 The process flow chart for producing superheated steam for a tower-type CSP power station;

[0041] Figure 2 A schematic flow chart of a method for controlling mirror field allocation in a segmented tower photothermal system disclosed in an embodiment of the present invention;

[0042] Figure 3 It is the first form of segmented tower concentrating solar collector system;

[0043] Figure 4 It is the second form of segmented tower concentrating solar collector system;

[0044] Figure 5 It is the third form of segmented tower concentrating solar collector system;

[0045] Figure 6 Schematic diagram of the sun's position.

[0046] In the figure, 1. heat absorption tower; 2. evaporation section tube screen; 3. superheat section tube screen; 4. inner circle heliostat; 5. outer circle heliostat; 6. steam-water separator. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0048] The present invention provides a method for controlling the mirror field distribution of a segmented tower photothermal system. Figure 2 As shown, the following steps are included:

[0049] Step 1: Separate the evaporation section tube panel and the superheating section tube panel of the tower-type solar thermal system absorber, wherein the evaporation section tube panel 2 is located at the top of the absorption tower 1, and the superheating section tube panel 3 is located below the evaporation section tube panel 2.

[0050] Segmented layout such as Figure 3-Figure 5 As shown, the shape of the absorber evaporation section tube panel 2 is diverse, which can be an external cylindrical, regular polygon, cavity, flat plate or half of a regular polygon. When the shape of the evaporation section tube panel 2 is cavity, flat plate or half of a regular polygon, its orientation is determined according to the geographical location. The evaporation section tube panel 2 can withstand conventional industrial steam pressure below 8MPa, and can also meet higher pressure requirements by increasing the wall thickness, but the increase in wall thickness will affect the heat transfer rate and reduce the efficiency of the absorber. The material of the evaporation section tube panel 2 is determined according to the maximum operating temperature; the absorber superheating section tube panel 3 is located below the evaporation section tube panel 2, and its tube panel shape is also diverse. When the tube panel shape is cavity, flat plate or half of a regular polygon, the opening direction is determined according to the geographical location, and the material is determined according to the maximum operating temperature.

[0051] When the evaporation section tube screen 2 is cylindrical, the mirror field is arranged in a circular shape. When the evaporation section tube screen 2 is cavity-type, flat-plate-type or regular polygonal, the mirror field is arranged in a half-field, all located on the opening side of the evaporation section tube screen 2. The heliostats in the mirror field are divided into two parts, of which the inner circle heliostats 4 are close to the absorber, with a small spot and more precise energy flow control. Therefore, the inner circle heliostats 4 within the field of view of the superheated tube screen are assigned to the superheated section tube screen 3 that is more sensitive to energy flow, and the remaining heliostats are assigned as the outer circle heliostats 5 to the evaporation section tube screen 2 that is relatively insensitive to energy flow. The specific arrangement is determined according to the type of absorber. Figure 3 , Figure 4 and Figure 5 Typical segmented concentrating solar collector system configuration schemes are given. This tower-type concentrating solar collector system effectively avoids the impact of spot overflow on the overheating section tube screen, reduces the difficulty of controlling the projected energy flow of the mirror field, and at the same time, the mirror field adopts a half-field layout, and its relative position with the absorber is determined according to the geographical location, which can significantly improve the overall optical efficiency.

[0052] Step 2, calculate the theoretical power allocation ratio of the overheating section tube screen and the evaporation section tube screen, assuming that the optical efficiencies of the heliostats are the same, and calculate the initial number of heliostats allocated to the overheating section tube screen according to the theoretical power allocation ratio; allocate the above number of inner circle heliostats 4 within the field of view of the overheating section tube screen to the overheating section tube screen, and allocate the remaining heliostats as outer circle heliostats 5 to the evaporation section tube screen.

[0053] The calculation method of the theoretical power distribution ratio of the superheating section tube panel and the evaporation section tube panel is as follows:

[0054] Mirror field projection power required for the evaporation section tube screen for:

[0055]

[0056] Mirror field projection power required for the overheating section tube panel for:

[0057]

[0058] The theoretical power distribution ratio Γ0 of the superheating section tube panel and the evaporation section tube panel is:

[0059]

[0060] Among them, H 1,out is the specific enthalpy of saturated steam at the outlet of the evaporation section tube panel, H 1,in is the water enthalpy at the inlet of the evaporation tube panel, v is the pipeline flow rate, η1 is the heat absorption efficiency of the evaporation tube panel, H 2,out is the specific enthalpy of superheated steam at the outlet of the superheated tube screen, and η2 is the heat absorption efficiency of the superheated tube screen.

[0061] Assuming that the optical efficiency of the heliostats is the same, the initial number of heliostats allocated to the overheating section tube panel m0 is calculated as follows:

[0062] m0=Γ0*n

[0063] Where n is the total number of heliostats.

[0064] Step 3: Given the sun position, the target point of the heliostat is set as the geometric center of the superheating section tube screen or the evaporation section tube screen, and the optical efficiency of each heliostat is calculated.

[0065] The calculation formula of the optical efficiency η of the heliostat is as follows:

[0066] η=η cos ·η sb ·η att ·η trunc ·η ref

[0067] Among them, η cos is the cosine efficiency, η sb is the shadow occlusion efficiency, η att is the atmospheric transmittance, η trunc is the cutoff efficiency and η ref is the mirror reflectivity. The above parameters are obtained using the Monte Carlo ray tracing method.

[0068] Step 4: Calculate the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen based on the calculated optical efficiency of the heliostats. Adjust the number of heliostats allocated to the superheating section tube screen based on the relationship between the actual projected power ratio and the theoretical power allocation ratio. Recalculate the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen until the requirements are met. Stop the iteration and obtain the final number of heliostats allocated to the superheating section tube screen.

[0069] The calculation formula for the actual projected power ratio Γ of the superheating section tube screen and the evaporation section tube screen is as follows:

[0070]

[0071] Wherein, P1 is the power projected onto the evaporation section tube screen, P2 is the power projected onto the superheat section tube screen, I is the normal direct radiation value, A is the heliostat reflection area, m is the number of heliostats projected onto the superheat section tube screen, n is the total number of heliostats, and η 1,j represents the optical efficiency of the jth heliostat projected onto the evaporation tube screen, η 2,i It represents the optical efficiency of the i-th heliostat projected onto the overheating section tube screen. The optical efficiency is calculated using the calculation formula in step 3.

[0072] Calculate the difference δ between the actual projected power ratio Γ and the theoretical power allocation ratio Γ0, and set the threshold σ. If δ<-σ, increase the number of heliostats allocated to the overheating section tube screen, such as adding a heliostat on the original basis, and continue to iterate; if δ>σ, reduce the number of heliostats allocated to the overheating section tube screen, and continue to iterate; if |δ|≤σ, the requirement is met and the iteration is stopped.

[0073] Step 5, optimizing the target point of each heliostat so that the energy flow projected onto the superheating section tube screen or the evaporation section tube screen has less overflow and is evenly distributed.

[0074] The DNI used for the heliostat target point optimization is the clear sky DNI of the sun position at the design point, and the target point optimization method used is a genetic optimization method or a simulated annealing algorithm. The target point optimization method belongs to the existing method, is not within the protection scope of the present invention, and will not be described in detail.

[0075] Step 6: When the time change causes the sun position to exceed the set range, return to step 3 and re-allocate the heliostats.

[0076] For the northern hemisphere, the sun's position each day is divided into 3×6 grids in terms of altitude and azimuth, such as Figure 6 As shown, the sun position at the center of the chessboard is used as the sun position given in step 3 to allocate the heliostats. Therefore, for the solar thermal mirror field, only 18 heliostat allocation schemes need to be set throughout the year, and the same allocation scheme is used in each chessboard.

[0077] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the mirror field distribution of a segmented tower solar thermal system, characterized in that: The steps include: Step 1: Separate the evaporation section tube panel and the superheating section tube panel of the tower-type solar thermal system absorber, wherein the evaporation section tube panel is located at the top of the absorber tower, and the superheating section tube panel is located below the evaporation section tube panel; Step 2, calculating the theoretical power allocation ratio of the overheating section tube screen and the evaporation section tube screen, assuming that the optical efficiencies of the heliostats are the same, and calculating the initial number of heliostats allocated to the overheating section tube screen according to the theoretical power allocation ratio; Allocate the above number of inner circle heliostats within the field of view of the superheating section tube panel to the superheating section tube panel, and the remaining heliostats to the evaporation section tube panel; Step 3, given the sun position, the target point of the heliostat is set as the geometric center of the superheating section tube screen or the evaporation section tube screen, and the optical efficiency of each heliostat is calculated; Step 4, according to the calculated optical efficiency of the heliostat, the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen is calculated, and according to the relationship between the actual projected power ratio and the theoretical power allocation ratio, the number of heliostats allocated to the superheating section tube screen is adjusted, and the actual projected power ratio of the superheating section tube screen to the evaporation section tube screen is recalculated until the requirement is met, and the iteration is stopped to obtain the final number of heliostats allocated to the superheating section tube screen; Step 5, optimizing the target point of each heliostat so that the energy flow projected onto the superheating section tube screen or the evaporation section tube screen has less overflow and is evenly distributed; Step 6: When the sun position exceeds the set range, return to step 3 and redistribute the heliostats.

2. The method for controlling the mirror field distribution of a segmented tower solar thermal system according to claim 1, characterized in that: In step 2, the calculation method of the theoretical power distribution ratio of the superheating section tube panel and the evaporation section tube panel is as follows: Mirror field projection power required for the evaporation section tube screen for: The mirror field projection power required for the overheating section tube panel for: The theoretical power distribution ratio Γ0 of the superheating section tube panel and the evaporation section tube panel is: Among them, H 1,out is the specific enthalpy of saturated steam at the outlet of the evaporation section tube panel, H 1,in is the water enthalpy at the inlet of the evaporation tube panel, v is the pipeline flow rate, η1 is the heat absorption efficiency of the evaporation tube panel, H 2,out is the specific enthalpy of superheated steam at the outlet of the superheated tube screen, and η2 is the heat absorption efficiency of the superheated tube screen.

3. The method for controlling mirror field allocation of a segmented tower photothermal system according to claim 2, characterized in that: In step 2, the calculation method for the initial number of heliostats m0 allocated to the overheating section tube panel is as follows: m0=Γ0*n Where n is the total number of heliostats.

4. The method for controlling mirror field allocation of a segmented tower solar thermal system according to claim 1, characterized in that: In step 3, the optical efficiency η of the heliostat is calculated as follows: the=the cos ·or sb ·or att ·or trunc ·or ref Among them, η cos is the cosine efficiency, η sb is the shadow occlusion efficiency, η att is the atmospheric transmittance, η trunc is the cutoff efficiency and η ref is the specular reflectivity.

5. The method for controlling mirror field allocation of a segmented tower solar thermal system according to claim 1, characterized in that: In step 4, the calculation formula for the actual projected power ratio Γ of the superheating section tube panel and the evaporation section tube panel is as follows: Wherein, P1 is the power projected onto the evaporation section tube screen, P2 is the power projected onto the superheat section tube screen, I is the normal direct radiation value, A is the heliostat reflection area, m is the number of heliostats projected onto the superheat section tube screen, n is the total number of heliostats, and η 1,j represents the optical efficiency of the jth heliostat projected onto the evaporation tube screen, η 2,i It represents the optical efficiency of the i-th heliostat projected onto the superheated tube panel.

6. The method for controlling mirror field allocation of a segmented tower solar thermal system according to claim 1, characterized in that: In step 4, the difference δ between the actual projected power ratio Γ and the theoretical power allocation ratio Γ0 is calculated, and a threshold σ is set. If δ<-σ, the number of heliostats allocated to the overheating section tube screen is increased, and the iteration continues; if δ>σ, the number of heliostats allocated to the overheating section tube screen is reduced, and the iteration continues; if |δ|≤σ, the requirement is met and the iteration is stopped.

7. The method for controlling mirror field allocation of a segmented tower solar thermal system according to claim 1, characterized in that: In step 5, the DNI used for the target point optimization of the heliostat is the clear sky DNI of the sun's position on the design point day, and the target point optimization method used is a genetic optimization method or a simulated annealing algorithm.

8. The method for controlling mirror field allocation of a segmented tower solar thermal system according to claim 1, characterized in that: In step 6, for the northern hemisphere, the sun position is divided into 3×6 checkerboards in terms of altitude and azimuth, and the sun position at the center of the checkerboard is used as the sun position given in step 3 to allocate heliostats. Therefore, for the solar thermal mirror field, only 18 heliostat allocation plans need to be set throughout the year, and the same allocation plan is used in each checkerboard.

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