CN100445686C - Method and device for mixed heat storage in high temperature slope layer in molten salt - Google Patents

Abstract

The invention provides a high-temperature inclined-temperature layer mixed heat storage device in molten salt, which comprises an injection part, a discharge part and a porous medium filler section of molten salt liquid, wherein the injection part and the discharge part are high-temperature shell-and-tube phase-change heat exchangers or low-temperature shell-and-tube phase-change heat exchangers; the porous medium filling section is provided with a foam silicon carbide ceramic piece which is used as a partition part and also used as a heat-developing and heat-storing piece of a solid medium. A hybrid heat storage method comprises the following steps: forming a thermocline in the device; in the heat release process, high-temperature molten salt liquid is pumped out from an outlet at the top of the device through a high-temperature phase-change shell-and-tube heat exchanger, enters the device through a low-temperature phase-change shell-and-tube heat exchanger from an inlet and an outlet at the bottom of the device after heat release, and releases heat by virtue of sensible heat exchange and phase-change heat exchange; in the heat storage process, low-temperature molten salt liquid is pumped out from a bottom outlet of the device through a low-temperature phase-change shell-and-tube heat exchanger, heated into high-temperature molten salt liquid, enters the device from the top of the device, and heat storage is carried out by sensible heat exchange and phase-change heat exchange.

Description

Method and device for mixed heat storage in high temperature slope layer in molten salt

technical field

The invention relates to a solar heat absorption and energy storage utilization technology, in particular to a method and device for mixing heat storage in a high-temperature slope temperature layer in a molten salt.

Background technique

The development and utilization of solar energy has become an important part of the energy strategy of today's society. Among the many factors restricting the development of solar energy, the low efficiency caused by the low-temperature utilization mode is the key to the weak competitiveness of the solar thermal power market. Increasing the temperature of solar thermal utilization and developing solar thermal power stations is one of the main ways to utilize solar energy on a large scale one. The high radiation density heat flow conversion, transportation and storage loop in the solar thermal power generation system is mainly composed of heat absorbers, steam generators and heat accumulators, so enhancing the energy conversion efficiency and storage density of thermal devices has become one of the key technologies for solar thermal power generation .

At present, the double-tank heat storage method of molten salt has become the main type of heat storage technology in solar thermal power generation systems, but the production of two heat storage tanks, the large amount of molten salt used, and high temperature maintenance lead to a relative comparison between the unit cost and the operation and maintenance cost. The space for reducing its electricity cost is very limited; another potential way is to use thermocline single-tank heat storage, and use molten salt thermocline single-tank heat storage system to replace the more common molten salt double-tank heat storage system , can greatly reduce the cost, but the effective heat storage capacity per unit volume of the system is reduced, and the injection and discharge structure of the molten salt liquid, that is, the diffuser and the liquid collector have relatively high requirements to reduce turbulence as much as possible. Each of the lower ends has an independent diffuser and liquid collector, forming two processes, which are respectively used for heat release and heat storage working conditions. The diffuser often uses multiple radially distributed circular tube diffusers, and the liquid collector adopts a The liquid collecting pipe with 3 to 5 interfaces has a complex structure, and the effect of import and export will produce certain disturbances; at the same time, stainless steel mesh needs to be configured as layered elements at intervals of about a certain distance in the porous media packing, so that the single tank axis of the thermocline The one-dimensional laminar flow movement ensures better maintenance of the inclined temperature layer in the tank. However, as a layered element, the stainless steel mesh has a small thermal conductivity and a low effective heat storage capacity per unit volume. It cannot be used as a heat storage material and has no obvious effect. Heat storage effect; and the porous media filler requires not only good chemical stability, but also good physical stability, so as not to form debris to block various channels.

In order to reduce the power generation cost of solar thermal power generation and improve the effectiveness and annual utilization rate of power generation, a medium-high temperature heat storage method and device with larger unit effective heat storage capacity, long-term stability, and lower manufacturing cost and operation and maintenance cost are required .

Contents of the invention

The purpose of the present invention is to overcome the shortcoming that existing molten salt heat storage system exists (manufacturing cost and operation and maintenance of double-tank molten salt system are relatively high; Complex, difficult to install and occupy the space in the tank, stainless steel mesh as layered equipment has low thermal conductivity, and the effective heat storage capacity per unit volume is low), the research and design can not only meet the requirements of solar thermal power generation for heat storage technology, but also can significantly The invention relates to a molten salt medium-high temperature thermocline mixed heat storage device which reduces manufacturing cost and improves the effective heat storage capacity per unit volume.

Another object of the present invention is to provide a method for mixing and storing heat in a high-temperature thermocline layer in molten salt realized by using the above-mentioned device.

The purpose of the present invention is achieved through the following technical solutions: a high-temperature ramp layer mixing heat storage device in molten salt, including an injection part for molten salt liquid, a discharge part, and a porous medium packing section, characterized in that: the injection part and the discharge part is a high-temperature shell-and-tube phase-change heat exchanger or a low-temperature shell-and-tube phase-change heat exchanger; the porous medium packing section is provided with a foamed silicon carbide ceramic sheet, and the foamed silicon carbide ceramic sheet serves as a separate layer It is also used as a sensible heat storage component of a solid medium.

The device is a single-tank structure, and the structural dimensions such as the diameter and height of the tank depend on the heat storage temperature and heat storage capacity. Both the bottom and the top of the tank body can adopt an elliptical head, and a safety valve is installed on the top elliptical head, and the tank body and the tank cover can be connected by flanges. The high-temperature shell-and-tube phase-change heat exchanger and the low-temperature shell-and-tube phase-change heat exchanger are installed in gaps in the tank. The heating wire is wound around the outside of the tank to maintain the molten salt in a liquid state, heat the porous medium and the tank, and balance heat loss when starting up. The outermost layer of the tank is wrapped with a glass fiber insulation layer. The thickness of the insulation layer depends on Heat storage temperature and requirements for heat loss.

The cylindrical shells of the high and low temperature shell-and-tube phase change heat exchangers are all made of stainless steel, the tube bundles are made of stainless steel tubes, and are evenly distributed in the shell, and the end covers at both ends are made of stainless steel plates, and one of the end covers is welded with a filling phase There is a connection pipe for vacuuming on the side of the interface for charging the phase-change heat storage material. The main structural difference between high-temperature and low-temperature phase-change heat exchangers is only the height and size of the tube bundle and shape.

The tube side of the high-temperature shell-and-tube phase-change heat exchanger flows through molten salt liquid, and the shell side is filled with high-temperature molten salt phase-change material. The high temperature molten salt phase change material with a suitable melting point is selected according to the upper limit working temperature of the application. The replacement of the heat exchanger simplifies the injection and discharge structure of the molten salt liquid, and increases the heat storage capacity.

The tube side of the low-temperature shell-and-tube phase-change heat exchanger flows through molten salt liquid, and the shell side is filled with low-temperature molten salt phase-change material. The low-temperature molten salt phase change material with a suitable melting point is selected according to the lower limit working temperature of the application. The heat exchanger also replaces and simplifies the injection and discharge structure of the molten salt liquid, and increases the heat storage capacity.

The porous medium packing section is the sensible heat storage section of the thermocline layer, and foamed silicon carbide ceramic sheets are evenly arranged at certain intervals in the porous medium packing section; the interval may be 100-150 mm. The foamed silicon carbide ceramic sheet not only replaces the stainless steel mesh as a layered element, but also can be used as a heat storage body, and has obvious heat storage effect.

The porous medium mixed with quartzite and siliceous sand is filled between the foamed silicon carbide ceramic sheets as the sensible heat storage material of the main solid porous medium.

A method of mixing heat storage in a high-temperature thermocline layer in molten salt realized by using the above-mentioned device, characterized in that it comprises the following steps:

(1) A thermoclinic layer is formed in the device: specifically, when the high-temperature molten salt liquid is extracted from the top inlet and outlet of the device, after heat exchange and cooling, it enters the device from the bottom inlet and outlet of the device; or when the low-temperature molten salt liquid is in the The inlet and outlet at the bottom of the device are drawn out, and after heating, when the inlet and outlet at the top of the device enter the device, there is a natural stratification with a large temperature gradient in the middle of the device, that is, the thermocline layer.

(2) At the beginning of the exothermic process, the device is filled with high-temperature molten salt liquid, and the high-temperature molten salt liquid is extracted from the top inlet and outlet of the device through a high-temperature phase-change shell-and-tube heat exchanger, and then enters from the bottom of the device after heat release. The outlet enters the device through a low-temperature phase-change shell-and-tube heat exchanger. The thermocline layer remains stationary for a period of time at the beginning of heat release. After a period of time, the thermocline layer begins to move upward steadily. And when it is close to the high-temperature phase change shell-and-tube heat exchanger, in a short period of time, the temperature at the outlet end drops significantly below the melting point of the high-temperature phase-change material, and then relies on the high-temperature phase-change heat, in a long period of time Keep the temperature constant, and finally the phase transformation heat basically ends, and the outlet temperature drops significantly in a short period of time.

(3) At the beginning of the heat storage process, the device is filled with low-temperature molten salt liquid, and the low-temperature molten salt liquid is extracted from the bottom inlet and outlet of the device through a low-temperature phase change shell-and-tube heat exchanger, heated to a high-temperature molten salt liquid, and released from the The inlet and outlet of the top of the device enter the device, and the thermocline layer remains stationary for a period of time at the beginning of heat storage. After a period of time, the thermocline layer begins to move down steadily. In the case of a tubular heat exchanger, the temperature at the outlet end rises significantly above the melting point of the low-temperature phase-change material in a short period of time, and then relies on low-temperature phase-change heat to maintain the temperature for a long period of time, and finally The phase transformation heat basically ends, and the outlet temperature rises significantly in a short time.

In the exothermic process and heat storage process, the foamed silicon carbide ceramic sheet is arranged in the sensible heat storage section of the thermocline layer instead of the stainless steel mesh as a layered element to perform auxiliary heat release or heat storage.

The foamed silicon carbide ceramic sheets are evenly arranged at intervals in the sensible heat storage section of the thermocline layer.

The working principle of the present invention is: the thermocline layer involved in the present invention is formed by utilizing the relationship between density and temperature, and is a natural stratification with a large temperature gradient in the middle of the device, which is similar to the isolation layer , so that the molten salt liquid above the thermocline layer keeps high temperature, and the molten salt liquid below the thermocline layer keeps low temperature. With the continuous extraction of molten salt liquid, the thermocline layer will move up and down, and the extracted molten salt liquid can maintain a relatively constant temperature. When the thermostat reaches the top or bottom of the tank, the temperature of the drawn molten salt can change significantly. In order to maintain the thermocline layer in the tank, it is necessary to strictly control the injection and discharge process of the salt solution, fill the tank with a porous thermal storage material with a reasonable porosity and configure layered elements with an optimal structure.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The effective heat storage capacity per unit volume is large. Due to the use of phase change heat storage in the high and low temperature shell and tube phase change heat exchanger, the heat storage capacity is greatly improved.

(2) The structure is simple, compact and easy to use. The high and low temperature shell-and-tube phase change heat exchanger is used as the structure of the diffuser and the liquid collector, which ensures the uniform flow of the fluid. Compared with the original thermocline thermal storage single tank system, the injection of molten salt and The discharge structure is relatively simple and practical; the foamed silicon carbide ceramic sheet is used instead of the stainless steel mesh as the layered element. Since the foamed silicon carbide ceramic is a three-dimensional interconnected pore network structure, it has high thermal conductivity, good thermal and chemical stability, and excellent mechanical properties. It not only enhances the heat transfer performance of the heat storage system, but also can be used as a porous heat storage material.

(3) Low manufacturing cost. Compared with the double-tank heat storage system, the manufacturing cost of the single-tank heat storage system is reduced. At the same time, the foamed silicon carbide ceramic sheet with low production cost can not only store sensible heat, but also reduce the amount of molten salt.

(4) The working temperature range is wide. The melting points of the high and low temperature molten salt phase change materials are selected according to the working temperature of the actual application. The thermocline layer in the middle section can keep moving steadily during the heat release and heat storage process, and the inlet and outlet temperatures maintain a relatively ideal temperature difference, which has a better heat storage effect.

Description of drawings

Fig. 1 is a structural schematic diagram of a high-temperature thermocline layer hybrid heat storage device in molten salt of the present invention.

Fig. 2 is a schematic diagram of separation of foamed silicon carbide ceramic sheets in the sensible heat storage section of the thermocline layer in the device shown in Fig. 1 .

Fig. 3 is a schematic structural view of the high and low temperature shell-and-tube phase-change heat exchangers in the device shown in Fig. 1 .

Fig. 4 is a schematic diagram of the heat storage principle of the device shown in Fig. 1 .

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

The specific structure of the present invention is shown in Figures 1 to 3, and it can be seen from Figure 1 that the high-temperature ramp layer hybrid heat storage device in the molten salt is a single-tank structure, and the structural dimensions such as the diameter and height of the tank body 7 mainly depend on Heat storage temperature and heat storage capacity. Both the bottom and top of the tank body 7 adopt elliptical heads, and a safety valve 9 is installed on the top elliptical head. The tank body 7 and the tank cover 10 are connected by flanges; The high-temperature shell-and-tube phase-change heat exchanger 1 and the low-temperature shell-and-tube phase-change heat exchanger 3 are arranged on the upper part of the tank body 7, and the low-temperature shell-and-tube phase-change heat exchanger 3 is arranged on the The lower part of the tank body 7, the cylindrical shells of the high and low temperature shell-and-tube phase-change heat exchangers 1 and 3 are all made of stainless steel, and the tube bundle 11 is made of stainless steel tubes, which are evenly distributed in the shell (see Figure 3). The cover is made of stainless steel plate, and one end cover is welded with an interface 12 filled with phase change heat storage material, and there is a vacuum connecting pipe (not shown in the figure) on the side of the interface filled with phase change heat storage material; high and low temperature phase change The main structural difference of the heat exchanger is only the height and size of the tube bundle and the shape. The middle section of the tank body is the thermocline layer sensible heat storage section 2, and a foamed silicon carbide ceramic sheet 5 is arranged in this section, and the foamed silicon carbide ceramic sheet 5 is arranged at intervals in the thermocline layer sensible heat storage section 2. 100-150mm is evenly arranged, and the porous medium mixed with quartzite and siliceous sand is filled between the foamed silicon carbide ceramic sheets 5, as the sensible heat storage material of the main solid porous medium, as shown in Figure 2. The tank body 7 is wound with a heating wire to maintain the molten salt in a liquid state, heat the porous medium and the tank body, and balance heat loss when starting. The outermost layer of the tank body 7 is wrapped with a glass fiber insulation layer. The choice depends on the heat storage temperature and the requirements for heat loss.

The high-temperature thermocline layer mixed heat storage method in molten salt of the present invention realized by using the above-mentioned device comprises the following steps (see Fig. 4):

(1) A thermoclinic layer is formed in the device: specifically, when the high-temperature molten salt liquid is extracted from the top inlet and outlet 8 of the device, after heat exchange and cooling, it enters the device from the bottom inlet and outlet 4 of the device; or when the low-temperature molten salt The liquid is pumped out at the inlet and outlet 4 at the bottom of the device, and after being heated, when it enters the device through the inlet and outlet 8 at the top of the device, there is a natural stratification with a large temperature gradient in the middle of the device, that is, the thermocline layer 6 .

(2) When the exothermic process begins, the device is filled with high-temperature molten salt liquid, and the high-temperature molten salt liquid passes through the high-temperature phase-change shell-and-tube heat exchanger 1 (the high-temperature shell-and-tube phase-change heat exchanger tube side flow Pass through the molten salt liquid, and fill the shell side with high-temperature molten salt phase-change material; select the high-temperature molten salt phase-change material with a suitable melting point according to the upper limit of the working temperature of the application) from the top inlet and outlet 8 of the device, and release heat from the bottom of the device The inlet and outlet 4 pass through the low-temperature phase-change shell-and-tube heat exchanger 3 (the tube side of the low-temperature shell-and-tube phase-change heat exchanger flows through the molten salt liquid, and the shell side is filled with low-temperature molten salt phase-change materials; the lower limit of the work depends on the application Temperature to select the low-temperature molten salt phase change material with a suitable melting point) into the device, and within a period of time when the heat is released, the thermocline layer 6 remains motionless. After a period of time, the thermocline layer 6 begins to move upward steadily. When the layer 6 moves up continuously and approaches the high-temperature phase-change shell-and-tube heat exchanger 1, the temperature at the outlet end drops significantly below the melting point of the high-temperature phase-change material in a relatively short period of time, and then relies on the high-temperature phase-change heat to Keep the temperature constant for a long period of time (during this process, the foamed silicon carbide ceramic sheets set in the sensible heat storage section of the thermocline layer balance and ensure the one-dimensional temperature distribution of the molten salt liquid, and perform auxiliary discharge heat), and finally the phase transformation heat basically ends, and the temperature at the outlet end drops significantly in a short period of time.

(3) At the beginning of the heat storage process, the device is filled with low-temperature molten salt liquid, and the low-temperature molten salt liquid is extracted from the bottom inlet and outlet 4 of the device through the low-temperature phase change shell-and-tube heat exchanger 3, and heated into high-temperature molten salt liquid After entering the device from the top inlet and outlet 8 of the device, the thermocline layer 6 remains stationary for a period of time at the beginning of heat storage. After a period of time, the thermocline layer 6 begins to move down steadily. And close to the low-temperature phase-change shell-and-tube heat exchanger 3, in a short period of time, the temperature at the outlet end obviously rises above the melting point of the low-temperature phase-change material, and then rely on the low-temperature phase-change heat, in a long period of time (in this process, the foamed silicon carbide ceramic sheet set in the sensible heat storage section of the thermocline layer balances and ensures the one-dimensional temperature distribution of the molten salt liquid, and performs auxiliary heat storage). The transformation heat is basically over, and the outlet temperature rises significantly in a short time.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (10)

1, high temperature mesolimnion mixed heat accumulation device in a kind of fuse salt, comprise injection part, discharging parts, the porous media packing section of fusion saline solution, it is characterized in that: described injection part and discharging parts are high temperature shell-tube type phase-change heat-exchanger or low temperature shell-tube type phase-change heat-exchanger; Described porous media packing section is provided with the foam silicon carbon potsherd as separating stratification part and sensible heat accumulation of heat assembly.

2, high temperature mesolimnion mixed heat accumulation device in the fuse salt according to claim 1, it is characterized in that: described foam silicon carbon potsherd evenly is arranged on the porous media packing section at regular intervals, fills quartzite and mix porous media with siliceous sand between the foam silicon carbon potsherd.

3, high temperature mesolimnion mixed heat accumulation device in the fuse salt according to claim 2 is characterized in that: the described 100～150mm that is spaced apart.

4, high temperature mesolimnion mixed heat accumulation device in the fuse salt according to claim 1 is characterized in that: be single jar structure form, high temperature shell-tube type phase-change heat-exchanger and low temperature shell-tube type phase-change heat-exchanger adopt the gap to install in tank body; The outer winding of described tank body followed heater strip, at tank body outermost parcel glass fibre thermal insulation layer.

5, high temperature mesolimnion mixed heat accumulation device in the fuse salt according to claim 4, it is characterized in that: described high temperature shell-tube type phase-change heat-exchanger and low temperature shell-tube type phase-change heat-exchanger be uniform stainless steel tube bank in its housing, described high temperature shell-tube type phase-change heat-exchanger and low temperature shell-tube type phase-change heat-exchanger two ends end cap adopt corrosion resistant plate, wherein be welded with on the end cap and fill the phase change heat storage material interface, fill the tube connector that the phase change heat storage material interface sides vacuumizes in addition.

6, a kind ofly utilize high temperature mesolimnion mixed heat accumulation method in the fuse salt that each described device of claim 1～5 realizes, it is characterized in that comprising the steps:

(1) in device, forms mesolimnion;

(2) when exothermic process begins, be full of the high-temperature fusion saline solution in the device, this high-temperature fusion saline solution is imported and exported extraction through high temperature shell-tube type phase-change heat-exchanger from the top of device, bottom from device after the heat release is imported and exported in low temperature shell-tube type phase-change heat-exchanger access to plant, just begun in heat release a period of time, it is motionless that mesolimnion keeps, after a period of time, mesolimnion moves on beginning to stablize, along with mesolimnion moves on constantly and during near high temperature shell-tube type phase-change heat-exchanger, in the short period of time, the temperature of the high-temperature fusion saline solution of the port of export drops to below the fusing point of high temperature phase change material (pcm) significantly, relies on the high-temperature phase-change heat exchange then, and holding temperature is constant in one long period, last phase-change heat-exchange finishes substantially, and the temperature of high-temperature fusion saline solution of section inner outlet end significantly descends in very short time;

(3) when heat-accumulating process begins, be full of the watery fusion saline solution in the device, this watery fusion saline solution is imported and exported extraction through low temperature shell-tube type phase-change heat-exchanger from the bottom of device, import and export in the access to plant from the top of device after being heated into the high-temperature fusion saline solution, just begun in accumulation of heat a period of time, it is motionless that mesolimnion keeps, after after a while, mesolimnion begins stable moving down, when mesolimnion constantly moves down and during near low temperature shell-tube type phase-change heat-exchanger, in the short period of time, the temperature of the watery fusion saline solution of the port of export is raised to more than the fusing point of low-temperature phase-change material significantly, relies on the low temperature phase change heat exchange then, and holding temperature is constant in one long period, last phase-change heat-exchange finishes substantially, and the temperature of watery fusion saline solution of inner outlet end significantly rises in very short time.

7, high temperature mesolimnion mixed heat accumulation method in the fuse salt according to claim 6, it is characterized in that: described high temperature shell-tube type phase-change heat-exchange organ pipe effluent is crossed the fusion saline solution, shell-side can high-temperature fusion salt phase transformation material is selected the high-temperature fusion salt phase transformation material of suitable fusing point according to the application scenario upper limit working temperature.

8, high temperature mesolimnion mixed heat accumulation method in the fuse salt according to claim 6, it is characterized in that: described low temperature shell-tube type phase-change heat-exchange organ pipe effluent is crossed the fusion saline solution, shell-side can watery fusion salt phase transformation material is selected the watery fusion salt phase transformation material of suitable fusing point according to application scenario lower limit operating temperature.

9, high temperature mesolimnion mixed heat accumulation method in the fuse salt according to claim 6, it is characterized in that:, the foam silicon carbon potsherd is set in mesolimnion sensible heat heat accumulating sections as becoming layer elements and assisting heat release and accumulation of heat at described exothermic process and heat-accumulating process.

10, high temperature mesolimnion mixed heat accumulation method in the fuse salt according to claim 9, it is characterized in that: described foam silicon carbon potsherd evenly is provided with every a segment distance in mesolimnion sensible heat heat accumulating sections.

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