CN108413617B - High temperature vacuum tube bundle absorber for small tower system - Google Patents

Abstract

The invention discloses a high-temperature vacuum tube bundle heat absorber of a small tower system, which comprises: a plurality of vacuum heat-absorbing tubes whose mid-abdomen cross-section is elliptical or circular; The tubes include the inner metal flat tube or round tube and the outer glass tube, the inner metal flat tube or round tube and the outer glass tube are connected by expansion joints; in the upper part of the tube bundle, the front inlet metal tube and the rear outlet metal tube It is connected through the top corrugated pipe; in the lower part of the tube bundle, the rear inlet metal pipe is connected with the diverter, and the front discharge outlet metal pipe is connected with the collector; the exposed inner pipe and the corrugated pipe are covered with insulation materials, and the heat absorber The part near the inlet and outlet of the inner pipe is fixed on the heat absorption tower. The invention has strong ability to absorb reflected light, and at the same time, has small heat loss, and can receive light energy gathered by heliostats in different regions at different time periods.

Description

High temperature vacuum tube bundle absorber for small tower system

technical field

The invention relates to the technical field of solar energy utilization, in particular to a high-temperature vacuum tube bundle heat absorber of a small tower system.

Background technique

In the whole tower solar thermal power generation system, the heat absorber is the key to realize the light-to-heat conversion. The heat absorber receives the solar radiation energy projected from the heliostat and converts it into heat energy of the working fluid. The heat absorber is required to have the characteristics of small size and high energy conversion efficiency. The selection, size and structure of the heat absorber are all related to the number of heliostats, the arrangement of the heliostats, the type of working medium, and the required parameters of the heat absorber outlet.

The tower heat absorbers can be roughly divided into the following types: cavity heat absorbers, external heat absorbers, flat plate heat absorbers, fluidized bed heat absorbers, etc., but the current mainstream has only practical applications There are two types of cavity heat absorbers and external heat absorbers, each of which has its own advantages and disadvantages. The cavity-type heat sink has a small opening and small heat loss, but its small cavity opening size also limits the layout of the mirror field; the external heat sink can receive reflected light in 360° directions, which can make the heliostat field The overall layout is more reasonable, suitable for large-capacity systems, but because the heat sink is completely exposed to the environment, the heat exchange with the outside world is particularly large, so there is a large heat loss, so the thermal efficiency is relatively low.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high-temperature vacuum tube bundle heat absorber of a small tower system, which has a strong ability to absorb reflected light, and at the same time has a small heat loss, and can accept the heat collected by heliostats from different regions at different time periods. of light energy.

In order to solve the above-mentioned technical problems, the present invention provides a high-temperature vacuum tube bundle heat absorber of a small tower system, which includes: a plurality of vacuum heat-absorbing tubes with elliptical or circular midsection cross-sections, and the number of tube rows adopts double-row equilateral triangles. tube; the vacuum heat absorbing tube includes an inner metal flat tube or thick round tube 5 and an outer glass tube 4, and the inner metal flat tube or thick round tube 5 and the outer glass tube 4 are connected by an expansion joint; on the upper part of the tube bundle, The front inlet metal pipe 8 and the rear outlet metal pipe 6 are connected through the top corrugated pipe 7; in the lower part of the tube bundle, the rear inlet metal pipe 3 is connected to the diverter 2, and the front outlet metal pipe 9 is connected to the current collector 10; The bare inner pipe and corrugated pipe are covered with insulation material, and the heat absorber is fixed on the heat absorption tower through the part near the inlet and outlet of the inner pipe.

Preferably, the size of the cross-section of the outer tube of the vacuum heat absorbing tube is 20-200 mm.

Preferably, the vacuum heat-absorbing tubes are connected in series, in parallel or combined in series, and are arranged horizontally or vertically in the heat-absorbing surface.

Preferably, a selective absorption coating is provided on the side of the inner tube facing the mirror field, and a large amount of non-evaporable getter is arranged on the side facing away from the mirror field.

Preferably, the inner tube is provided with short fins on both sides of the long axis of the ellipse or on both sides of the diameter of the circle, and the shortest distance between the tip of the fins and the inner side of the glass outer tube is 2mm.

Preferably, the cross-section of the midsection of the vacuum heat absorbing tube is an ellipse or a thicker circle, and the two ends transition to a thinner circle.

Preferably, an insulating layer is arranged on the side and back of the arranged vacuum tube bundle, and the inner surface of the insulating layer is coated with a reflective coating.

Preferably, the heat absorber as a whole rotates around a vertical axis.

Preferably, corresponding counterweights are arranged on the top of the heat absorption tower.

The beneficial effects of the present invention are: (1) the primary light leakage rate is reduced, and the primary light leakage rate is greatly reduced by arranging double-row tubes and flattening the round tube into an oval tube; (2) in the upper part of the tube bundle, the front and rear tubes pass through corrugated Tube connection; in the lower part of the tube bundle, the circular inner tube at the inlet is connected to the diverter, and the metal tube at the outlet is connected to the collector; when the metal tube is heated and expanded, the elongation in the axial direction can be compensated by compressing the flexible bellows , which can reduce the stress of the connecting part between the tubes caused by the relative linear expansion difference caused by uneven heating; (3) The rotating mechanism at the bottom of the heat absorber can realize time-sharing concentration, which is suitable for the time-sharing concentration scheme The multi-tower concentrating system can accept the light energy gathered by the heliostats in different areas at different time periods, and compared with the conventional trough concentrating system of the vacuum tube heat absorber, the cosine efficiency has been significantly improved; (4) Let the fluid in the tube be heated more evenly, and improve the situation that the temperature of the fluid at the tube wall is higher than that of the tube core; (5) The invalid heat absorption length at both ends of the tube does not participate in heat absorption, so that all solar radiation is concentrated on the effective heat absorption section, avoiding The energy loss of solar radiation converging to the invalid heat-absorbing section; (6) The high-temperature metal inner tubes at both ends of the glass tube are close to each other, so the temperature is relatively high. Applying sufficient insulation to this part of the higher-temperature outer tube section can further reduce the overall absorption. (7) The trough-type concentrating system that is conventionally matched with the vacuum tube heat absorber has a theoretical limit of 100 times of the geometric light concentration ratio, but if the vacuum tube is combined with the planar heat absorber shown in the present invention , the geometric concentration ratio can reach hundreds of times, and the heat loss allocated to the unit condenser mirror surface will be lower under the same working temperature.

Description of drawings

Fig. 1(a) is a left view of the overall structure of the heat absorber of the present invention.

Fig. 1(b) is a front view of the overall structure of the heat absorber of the present invention.

Fig. 2 is a schematic diagram of the mirror field of the present invention.

Fig. 3 is a schematic diagram of the tower top heat absorber and counterweight of the present invention.

Fig. 4 is a schematic diagram of the arrangement of vacuum sleeves of the present invention.

Fig. 5 is an overall schematic diagram of the elliptical flat tube of the present invention.

Fig. 6 is a schematic diagram of different incident angles of the present invention.

Fig. 7 is a schematic diagram of light leakage rate curves of elliptical tubes and circular tubes with different angles according to the present invention.

Among them, 1. Cold working fluid inlet; 2. Diverter; 3. Rear inlet metal tube; 4. Glass tube; 5. Metal flat tube or thick round tube; 6. Rear outlet metal tube; 7. Top bellows ; 8. Front inlet metal pipe; 9. Front outlet metal pipe; 10. Current collector; 11. Hot working fluid outlet; 12. Counterweight; 13. Rotating mechanism; 14. Motor; 15. Heat absorber; 16. Tower pillar; 17. Mirror field.

Detailed ways

As shown in Figure 1(a) and Figure 1(b), a high-temperature vacuum tube bundle heat absorber of a small tower system includes: a plurality of vacuum heat-absorbing tubes with elliptical or circular mid-abdomen cross-sections, and the number of tube rows Double-row equilateral triangle tubes are adopted; the vacuum heat absorbing tube includes the inner metal flat tube or thick round tube 5 and the outer glass tube 4, and the inner metal flat tube or thick round tube 5 and the outer glass tube 4 are connected by expansion joints ; In the upper part of the tube bundle, the front inlet metal pipe 8 and the rear outlet metal pipe 6 are connected through the top corrugated pipe 7; The current collectors 10 are connected; the bare inner pipe and the corrugated pipe are covered with thermal insulation materials, and the heat absorber is fixed on the heat absorption tower through the part near the inlet and outlet of the inner pipe.

The shape of the tube in the present invention is an elliptical tube or a round tube, and the size can be arbitrary, ranging from 20 to 200 mm. The tube diameter can be adjusted according to the scale of the mirror field and the heat absorption of the working medium. The number of tube rows adopts double rows of regular triangle tubes, and the front and rear tube bundles are connected in series through flexible corrugated tubes, which does not limit the axial expansion and contraction. In the upper part of the tube bundle, the front and rear tubes are connected by corrugated pipes; in the lower part of the tube bundle, the metal tube at the inlet is connected with the diverter, and the metal tube at the outlet is connected with the collector. In order to reduce convection and radiation heat loss, the exposed inner tube is covered with insulation material. The heat absorber as a whole can rotate around the vertical axis to realize time-sharing concentration. The heat absorber is fixed on the heat absorbing tower through the inlet and outlet parts of the inner pipe. Corresponding counterweights are set on the top of the heat absorbing tower to balance the mass of the heat absorber. An insulation layer is arranged on the side and back of the arranged vacuum tube bundle, and the inner surface of the insulation layer is coated with a reflective coating, which can reflect the leaked light to the inner tube again. The heat-absorbing surface composed of tube bundles has a certain inclination angle according to the size of the mirror field. In the mirror field, the solar radiation energy is reflected to the inner tube through the heliostat, heating the working medium in the tube, and converting solar energy into heat energy of the working medium.

A large number of getters are arranged on the side of the elliptical or circular inner tube facing away from the mirror field, which has the advantage of prolonging the maintenance time of high vacuum in the tube.

Both sides of the elliptical or circular inner tube (not the front and back), that is, the direction of the long axis of the ellipse or both sides of the diameter of the circle, can have short fins to further reduce the gap between two adjacent tubes and reduce primary light leakage rate, but pay attention that the fins cannot touch the glass outer tube, and the distance between the fin tip and the inner side of the glass outer tube can be as short as 2mm.

In this example, the size of the unit mirror field is 100m×40m. According to the tower height of 32m and mirror height of 2m, the length of a single mirror field module is 100m from east to west, and 80m from north to south. The farthest heliostat is 140m away from the tower, as shown in Figure 2. The azimuth angle of the heat-absorbing surface is ±139°, so the angle between the center of the nearest row of heliostats and the center of the heat-absorbing surface and the plumb line is 27°, and the angle between the farthest row is 78°, that is, the heat-absorbing surface The elevation angle of the nearest and farthest heliostats facing the mirror field in the center is 78-27=51°, the maximum incidence angle in the elevation angle direction is 25.5°, and the included angle between the heat-absorbing surface and the ground is 52.5°. The angle between the center of the heat-absorbing surface and the center of the most southeast (or most southwest) heliostat and the east-west axis is 8.5°, so the azimuth angle of the heat-absorbing tower facing the mirror field is 81.5°, and the maximum incident angle is 40.8°. Therefore, the heat-absorbing tube should be placed vertically downwards, and its cylindrical shape is suitable for a larger azimuth angle, as shown in Figure 3.

When the tubes are arranged, the diameter of the outer tube is 90mm, the diameter of the inner tube is 40mm, and the distance between the same row of outer tubes is 5mm, that is, the distance between the center and the center of the circle is 5+45+45=95mm. Two rows of tubes are arranged, and then arranged in a triangular arrangement. Double-row tubes, as shown in Figure 4 and Figure 5. Considering that the round tube will have a large primary light leakage rate in the actual working process, we flatten the inner tube into an oval tube with a long semi-axis of 30mm and a short semi-axis of 5mm based on the equal perimeter.

Here the incident angle is defined as the angle between the light and the normal plane of the tube row plane, as shown in Figure 6. After analyzing the light leakage rate, it is found that the light leakage rate will change greatly at different angles of incidence:

(1) 0-9° incident, the light leakage rate is 0;

(2) 9°～30° incidence, the light leakage rate gradually increases, and the light leakage rate is the largest at 30° incidence, which is 0.35;

(3) 30°～45° incident, the light leakage rate gradually decreases, and the light leakage rate is 0 at 43° incident;

(4) 45°～53° incident, the light leakage rate is 0;

(5) 53°～60° incidence, the light leakage rate gradually increases, and the light leakage rate is the largest at 60° incidence, which is 0.33;

(6) When incident at 60° to 65°, the light leakage rate decreases gradually, and the light leakage rate at 65° incident is 0.

Figure 7 shows the light leakage rate curves when the heat-absorbing tubes are circular tubes and elliptical tubes respectively. It can be seen from the figure that when the incident angle of sunlight changes in the range of 0-48°, the primary light leakage rate varies at different incident angles. From 0 to 21%, the elliptical tube is better than the round tube in terms of light leakage rate. And because a reflective coating is set behind the tube row, a small amount of leaked light can be reflected back to the tube for absorption, so almost all the sunlight reflected by the mirror field is absorbed by the vacuum tube.

The working process of the heat absorber: the working medium first enters the splitter, from the splitter into the rear tubes to absorb heat, and then enters the front tube through the upper flexible bellows to fully absorb heat, and the working medium reaches the specified temperature by controlling the flow rate before entering Current collector, flow to the next section.

The heat absorber of the present invention has strong ability to absorb reflected light, and at the same time has small heat loss, and can receive light energy gathered by heliostats in different regions at different time periods.

Claims (6)

1. A high-temperature vacuum tube bundle heat absorber of a small tower system, characterized in that it comprises: a plurality of vacuum heat-absorbing tubes whose mid-abdomen cross-section is elliptical or circular, and the number of tube rows adopts double rows of regular triangle tubes; The heat absorbing tube includes an inner metal flat tube or thick round tube (5) and an outer glass tube (4), and the inner metal flat tube or thick round tube (5) and the outer glass tube (4) are connected by an expansion joint; In the upper part of the tube bundle, the front inlet metal pipe (8) and the rear discharge outlet metal pipe (6) are connected through the top bellows (7); in the lower part of the tube bundle, the rear inlet metal pipe (3) and the diverter (2) The metal pipe (9) at the front outlet is connected to the collector (10); the exposed inner pipe and corrugated pipe are covered with thermal insulation materials, and the heat absorber is fixed to the heat absorption tower through the part near the inlet and outlet of the inner pipe Above; the side of the inner tube facing the mirror field is provided with a selective absorption coating, and the side facing away from the mirror field is arranged with a large number of non-evaporable getters; Transition to a thinner circle; the heat sink as a whole rotates about a vertical axis. 2. The high-temperature vacuum tube bundle heat absorber of a small tower system according to claim 1, wherein the size of the cross-section of the outer tube of the vacuum heat absorbing tube is 20-200 mm. 3. The high-temperature vacuum tube bundle heat absorber of a small tower system as claimed in claim 1, wherein the vacuum heat absorbing tubes are connected in series, in parallel or in series and parallel, and are arranged horizontally or vertically in the heat absorbing surface. The way. 4. The high-temperature vacuum tube bundle heat absorber of a small tower system as claimed in claim 1, wherein the inner tube is provided with short fins on both sides of the major axis of the ellipse or on both sides of the diameter of the circle, and the fins are pointed The closest distance to the inner side of the glass outer tube is 2mm. 5. The high-temperature vacuum tube bundle heat absorber of a small tower system according to claim 1, wherein an insulating layer is arranged on the side and back of the arranged vacuum tube bundle, and the inner surface of the insulating layer is coated with a reflective coating. 6. The high-temperature vacuum tube bundle heat absorber of a small tower system according to claim 1, wherein a corresponding counterweight is arranged on the top of the heat absorption tower.