FALLING PARTICLE RECEIVER SYSTEMS WITH MASS FLOW CONTROL

Abstract

The present disclosure is directed to systems and methods to control particle mass flow rate in solar receivers and associated heat exchangers based on feedback from one or more temperatures of particles in the system.

Claims

1. A solar receiver system, comprising: a solar receiver having an inlet and an outlet; and one or more particle flow control devices disposed at the inlet of the solar receiver to control the flow of a plurality of particles through the solar receiver; the one or more particle flow control devices capable of receiving an input to change the flow of the plurality of particles based on a temperature measurement from a temperature measurement device in the solar receiver system.

2. The solar receiver system of claim 1 further comprising a hopper connected to the one or more particle flow control devices, the hopper discharging the plurality of particles.

3. The solar receiver system of claim 1 wherein the particle flow control devices comprise a flow control member.

4. The solar receiver system of claim 3 where in the flow control member comprises a slide gate device.

5. The solar receiver system of claim 1 further comprising a storage bin having an inlet and an outlet and connected to the outlet of the solar receiver.

6. The solar receiver system of claim 5 further comprising a heat exchanger having an inlet and an outlet and connected to the storage bin.

7. The solar receiver system of claim 6 further comprising one or more particle flow control devices disposed at the inlet of the heat exchanger.

8. The solar receiver system of claim 1 wherein the one or more particle flow devices comprise a particle temperature measuring device.

9. The solar receiver system of claim 8 wherein the particle temperature measuring device comprises one or more troughs.

10. A solar receiver system, comprising: a solar receiver; a heat exchanger comprising an inlet and an outlet, the heat exchanger configured to exchange heat from heated particles to a second medium; and one or more flow control devices to control the particle flow and temperature of particles into the heat exchange based on an input from a temperature measurement device.

11. The system of claim 10, wherein the second medium is a working fluid for a power cycle.

12. The system of claim 11, wherein the working fluid is supercritical CO.sub.2.

13. A solar receiver system, comprising: a solar receiver having an outlet; a storage bin for collecting and storing particles from the outlet; and one or more particle flow control devices disposed at locations within the system to control the particle flow or particle temperature of particles flowing into the solar receiver.

14. The system of claim 13, wherein the one or more particle flow control devices are controlled automatically by the measured particle temperature exiting the receiver.

15. The system of claim 13, wherein two or more particle flow control devices are programmed to accommodate a non-uniform irradiance on the particle curtain such that the mass flow of particles is greatest where the irradiance is highest, and vice-versa.

16. The system of claim 13, wherein the particle flow control devices are controlled automatically by the measured particle temperature entering the heat exchanger.

17. The system of claim 13, wherein the particle flow control devices are controlled automatically by the working fluid temperature exiting the heat exchanger.

18. The system of claim 13, wherein proportional-integral-derivative control methods are used to control the particle flow control devices to achieve a steady particle outlet temperature.

19. The system of claim 18, wherein proportional-integral-derivative control methods are used to control the particle flow control devices to achieve a steady working-fluid outlet temperature.

20. A method, comprising heating particles in a solar receiver in a solar receiver system; measuring temperature of the particles within the solar receiver system; and adjusting the flow of particles into the solar receiver based on the measured temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The figures depict embodiments of the present invention for purposes of illustration only, and are not necessarily drawn to scale. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.

[0024] FIG. 1 illustrates a falling particle solar receiver system according to an embodiment of the disclosure.

[0025] FIG. 2 shows a flow control device and hopper according to an embodiment of the disclosure.

[0026] FIG. 3 illustrates a multiple flow control arrangement according to an embodiment of the disclosure.

[0027] FIG. 4 illustrates a collection system to accurately measure the particle temperature exiting the receiver by immersing a thermocouple (not shown) in particles flowing through a funnel-shaped device.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present disclosure is directed to systems and methods to control the particle mass flow rate in a solar receiver and heat exchanger based on feedback from particle and/or working-fluid outlet temperatures.

[0029] FIG. 1 illustrates a falling particle solar receiver system 100 according to an embodiment of the disclosure. As can be seen in FIG. 1, the system 100 includes a falling particle solar receiver (receiver) 102, a high temperature storage bin 104, a heat exchanger 106, a low temperature storage bin 108, and a particle return system 110. In this exemplary embodiment, the receiver 102 is a multi-aperture falling particle receiver, however, in other embodiments, other solar receiver designs may be used.

[0030] Also, in this exemplary embodiment, the heat exchanger 106 transfers heat from the particles to supercritical CO.sub.2 for a Brayton power cycle. However, in other embodiments, other heat transfer materials may be used, such as, but not limited to air, water/steam, molten salt, and thermal oils. Also in this exemplary embodiment, the particle return system 110 is a bucket elevator; however, in other embodiments, other material conveyance devices may be used, such as, but not limited to skip hoists, screw elevators, and pneumatic lifts.

[0031] The system 100 further includes a particle mass flow control device 120 (see FIGS. 2 and 3) between a hopper 122 and the receiver 102. The hopper 122, which receives cool particles from the particle return system 110, provides a buffer volume of particles for the receiver 102. The hopper 122 includes a discharge opening or outlet (not shown) at the bottom of the hopper 122.

[0032] The particle flow control device (flow control device) 120 controls the amount of particles discharged from the hopper 122 to the receiver 102. The flow control device 120 can include a flow control member 121. In this exemplary embodiment, the flow control device 120 includes one flow control member 121. However, in other embodiments, the flow control device 120 may include one or more flow control members. The receiver 102 includes a corresponding inlet (not shown) to the outlet of the hopper 122. It should be appreciated that the system 100 includes control device operation components (not shown) for moving the flow control member 121 (see FIG. 2) across and between the outlet of the hopper 122 and the inlet of the receiver 102. In such a manner, the flow control device 120 regulates the amount of particles flowing from the hopper 122 to the receiver 102 from between full flow and zero flow, and thus, controls the amount of particles falling through the receiver 102.

[0033] Referring to FIG. 2, it can be seen how moving the flow control member 121 to the left across the width of the hopper discharge opening 124 effectively narrows the stream of discharged particles thereby creating a thinner particle curtain stream to the receiver 102. Similarly, as the flow control member 121 is disposed between the discharge opening 124 and the inlet to the receiver 102, the movement of the flow control member 121 can be understood as narrowing the receiver inlet. As such, the falling particle curtain, being irradiated on one-side, a thinner curtain results in less shading and more irradiance of particles toward the rear of the falling particle curtain through the receiver 102, resulting in higher average/bulk particle temperatures. If the flow control member 121 moves to the right, the hopper discharge opening 124 is effectively enlarged, and more particles will flow into the receiver 102. The higher particle mass flow rates result in lower average/bulk particle outlet temperatures.

[0034] In this exemplary embodiment, the flow control device 120 is a slide gate device. However, in other embodiments, the flow control device 120 may be a slide gate, hinged gate, rotary valve, ball valve, or other particle flow control device that can regulate the amount of particle flow through the device.

[0035] Also in this exemplary embodiment, the flow control member 121 is a solid member. However, in other embodiments, the flow control member 121 may include holes, slots or other openings to create a pattern release of particles from the flow control device. In an embodiment, a flow control device may include other flow control members that may partially or completely cover one or more of the openings in the hopper 122.

[0036] In an embodiment, the flow control member 121 can include a pattern such that when particles are released from the hopper 122 through the flow control member 121, the particles form a pre-determined pattern. A release pattern can be used so that the mass flow rate would not change the particle temperature at the receiver outlet. For example, a perforated plate with a single row of holes through which particles can fall through can be the gate, where the row of holes is perpendicular to the incoming rays of the particle receiver. In another embodiment, a slide gate may be used with slots that allow only every other hole to flow particles. This arrangement can be used to increase mass flow rate without changing temperature. In another embodiment, a slide gate may be pulled back further to allow all the holes to flow particles. In this embodiment, mass flow of twice as many particles may be achieved, but, unlike a continuous particle curtain, all of the particle streams through the holes still see the same amount of irradiance (no increased shading). Thus, the heating and particle temperatures will be the same in both modes of operation, despite the mass flow being increased by opening up twice as many holes.

[0037] The flow control device 120 is preferably sufficiently far enough from the receiver 102 so as not to overheat and cause sticking problems. The flow control device 120 can be actuated in a closed-loop feedback system to maintain the outlet temperature of the particles within a desired range. For example, if the particles are too cold, the flow control device 120 will close to reduce the particle flow, which increases the particle temperatures. If the particles are too hot, the flow control device 120 opens to increase the particle flow, which reduces the particle outlet temperatures. A control system for both the particle receiver 102 and heat exchanger 106 can be used to achieve desired particle and working fluid (e.g., supercritical CO.sub.2) outlet temperatures using PID methods by controlling the mass flow rate of particles and/or working fluid.

[0038] FIG. 3 shows a flow control arrangement 300 that includes three flow control devices 302 that control the flow of particles into three particle inlets of a receiver (not shown). In this exemplary embodiment, the flow control arrangement 300 includes three flow control devices 302. However, in other embodiments, the flow control arrangement 300 may include two or more flow control devices. Also, in this exemplary embodiment, the flow control devices are slide gates. However, in other embodiments, the flow control devices may be other embodiments as described above. Also, in this exemplary embodiment, receiver includes three particle inlets 304. However, in other embodiments, the receiver may include a single continuous inlet or a number of inlets corresponding to the number of flow control devices. FIG. 3 illustrates how this flow control arrangement can be scaled up to accommodate any size or capacity of the solar receiver system by simply increasing the number of slide gates or flow control systems.

[0039] Referring again to FIGS. 1 and 2, in another embodiment, particle mass flow may also be controlled by controlling the speed at which the particle return system 110 transports particles to the hopper 122. In this exemplary embodiment, the particle return system 110 is a bucket elevator, but a more continuous screw-type particle elevator can be used where the speed of the rotating casing controls the mass flow rate of the lifted particles. The particles are then distributed along a desired discharge slot before entering the receiver. The flow rate of the elevator can be actuated in a closed-loop feedback system to maintain the outlet temperature of the particles within a desired range.

[0040] The present disclosure is further directed to using a flow control device at the bottom and/or top of the heat exchanger to control the mass flow of particles through the heat exchanger. In this exemplary embodiment, a flow control device 120 is shown proximate to the outlet of the heat exchanger 106 to control the mass flow of the moving packed-bed of particles. In other embodiments, other heat exchanger designs such as fluidized-bed heat exchangers can be used in which the flow control device 120 is proximate to the inlet of the heat exchanger 106 to control the mass flow of particles. The flow control device 120 is used to ensure the appropriate amount of heat transfer to the working fluid (e.g., sCO.sub.2) and to reduce thermal shock to the system. In an embodiment, cold particles may be blended with the hot particles in the heat exchanger from a separate reservoir to minimize thermal shock during start-up.

[0041] The present disclosure is further directed to a method of operating a falling particle solar receiver system that includes measuring the temperature of the particles at one or more locations in the system including, but not limited to, the inlet of the feed hopper 122, the outlet of the feed hopper 122, the outlet of the receiver 102, at the high temperature storage bin 104, at the inlet to the heat exchanger 106, at the outlet of the heat exchanger 106, and at the low temperature storage bin 108. In such a manner, the heat transfer from the particles to another medium in the heat exchanger 106 can be maximized for the application.

[0042] Referring to FIG. 4, the present disclosure is further directed to a particle temperature measuring device 400 that includes one or more mini troughs (funnels) 402a-402e that collect the particles along the bottom of the receiver 102 so that the particles accumulate in the troughs 402a-402e (slightly) before passing by a thermocouple that is immersed in the particles near the bottom of each trough 402a-402e.

[0043] This particle temperature measuring device 400 allows for accurate measurement of the temperature of free-falling particles in situ. By having a series of the troughs 402a-402e, the temperature distribution of the particles falling along the length of the particle curtain stream can be measured. This can independently control each slide gate for particle release along the entire length of the potentially long curtain. Because the irradiance may be non-uniform, there is an advantage and increased efficiency to allow more flow where the irradiance is highest (typically in the middle) and less flow where the irradiance is lower (towards the outside).

[0044] While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.