Solar multi-stage latent heat recovery type sludge drying system and method

Abstract

The invention discloses a solar multi-stage latent heat recovery type sludge drying system and method.The system comprises a solar light gathering device, a solar heat storage device and a sludge drying device, and the sludge drying device is provided with a plurality of sludge drying spaces and a plurality of steam flowing spaces; the sludge drying space and the steam flowing space are sequentially arranged at intervals from top to bottom, the steam flowing space is separated from the sludge drying space above the steam flowing space through a supporting purification layer, and the steam flowing space is separated from the sludge drying space below the steam flowing space through a hydrophilic heat conduction layer and a hydrophobic heat conduction layer; a sunlight absorption layer and a transparent heat insulation layer are sequentially arranged above the uppermost sludge drying space; the solar energy utilization efficiency of the system can be improved, the energy consumption and the environmental influence can be reduced, and the problems of high energy consumption and complicated operation in the sludge drying process and the technical problems of low efficiency, easy secondary pollution and large occupied area of the solar drying technology can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge drying devices, and particularly relates to a solar multi-stage latent heat recovery type sludge drying system and method. Background Art

[0002] The high moisture content of sludge is a key issue restricting the subsequent treatment of sludge. Existing sludge drying technologies include electric energy sludge drying method, hot water drying method, steam drying method and waste heat of furnace flue gas sludge drying method. Among them, the electric energy sludge drying method has high energy consumption and is not suitable for sewage treatment plants with tight power supply and large sludge production; while the hot water drying method has high requirements for heat exchangers, and the hot water drying process may be restricted by the stability of heat sources and the supply of hot water; although the steam drying method has high drying efficiency, the steam drying equipment is usually complex and the maintenance cost is high; in the waste heat of furnace flue gas sludge drying method, harmful substances in the flue gas may cause secondary pollution to the sludge. In addition, when the flue gas temperature is low or the supply is insufficient, the drying efficiency will be affected.

[0003] Therefore, the existing sludge drying technologies generally have problems such as high energy consumption, large initial equipment investment, difficult operation and management, and high maintenance costs. As a clean energy, the application of solar energy in sludge drying can greatly reduce energy consumption and the operation management is relatively simple. However, the solar low-temperature drying technology is not yet mature, and has disadvantages such as low drying efficiency, easy to cause secondary pollution, and large floor area. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a solar multi-stage latent heat recovery type sludge drying system and method, which can improve the solar energy utilization efficiency of the system, reduce energy consumption and environmental impact, and can solve the problems of high energy consumption and complex operation in the sludge drying process, as well as the technical problems of low efficiency, easy to cause secondary pollution and large floor area of the solar drying technology.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a solar multi-stage latent heat recovery type sludge drying system is provided, which includes a solar concentrator, a solar heat storage device, and a sludge drying device. The sludge drying device includes a plurality of sludge drying spaces and a plurality of steam flow spaces. The sludge drying spaces and the steam flow spaces are arranged at intervals from top to bottom in sequence. The steam flow space and the sludge drying space above it are separated by a supporting purification layer, and the steam flow space and the sludge drying space below it are separated by a hydrophilic heat conduction layer and a hydrophobic heat conduction layer; above the uppermost sludge drying space, a sunlight absorption layer and a transparent heat insulation layer are arranged in sequence; the uppermost sludge drying space uses solar energy as a heat source to dry the sludge, and the remaining sludge drying spaces use the latent heat released by steam liquefaction as a heat source to dry the sludge; the solar concentrator provides heat for the sludge drying device during the day, and the solar heat storage device provides heat for the sludge drying device at night.

[0007] In some embodiments of the present invention, the supporting purification layer of the sludge drying device is in the shape of a drawer and is made of fiberboard. An adsorption material is coated above the fiberboard, and the coating thickness of the adsorption material is 0.1-1 mm.

[0008] In some embodiments of the present invention, the hydrophilic heat conduction layer includes a trough-shaped heat conduction plate made of hydrophilic foam copper. The grooves on the trough-shaped heat conduction plate serve as the steam flow space, and a water outlet is provided on the trough-shaped heat conduction plate.

[0009] In some embodiments of the present invention, the hydrophobic heat conduction layer includes a heat conduction plate. The surface of the heat conduction plate is chemically etched with a hydrophobic material to obtain a hydrophobic coating, and the thickness of the hydrophobic coating is 0.5-2 mm.

[0010] In some embodiments of the present invention, the solar concentrator includes a plurality of Fresnel lenses and a reflector. The Fresnel lenses are placed at different positions and simultaneously focus sunlight on the reflector, and the reflector reflects the focused sunlight to the sunlight absorption layer above the sludge drying device.

[0011] In some embodiments of the present invention, the solar energy storage device includes a molten salt tank and a heat conduction pipe. The photothermal material coating on the surface of the molten salt tank can absorb the focused sunlight and convert it into heat energy to be stored by the molten salt. The heat conduction pipe transfers the heat stored by the molten salt to the hydrophobic heat conduction layer above the sludge at night to further dry the sludge.

[0012] In some embodiments of the present invention, the hydrophilic heat conduction layer is located below the steam flow space, and the hydrophobic heat conduction layer is located above the sludge drying space.

[0013] In some embodiments of the present invention, a gap is formed between the supporting purification layer and the hydrophobic heat-conducting layer at a set distance, and the gap serves as a sludge drying space.

[0014] In a second aspect of the present invention, a working method of a solar multi-stage latent heat recovery type sludge drying system is provided, including:

[0015] Sunlight is absorbed by the sunlight absorption layer after passing through the transparent heat-insulating layer and is converted into heat.

[0016] The heat is transferred to the sludge in the sludge drying space through the hydrophobic heat-conducting layer for drying. The steam generated by the evaporation of water during the sludge drying process enters the steam flow space through the supporting purification layer.

[0017] The steam liquefies in the steam flow space to release latent heat. The heat is transferred to the sludge in the next-stage sludge drying space through the next-stage hydrophobic heat-conducting layer for drying. The steam generated by the evaporation of water during the sludge drying process enters the next-stage steam flow space through the next-stage supporting purification layer; this process is repeated to recover and utilize the latent heat of the steam in multiple stages.

[0018] One or more technical solutions of the present invention have the following beneficial effects:

[0019] (1) For the drying system provided by the present invention, the solar concentrating device is set to provide heat for the sludge drying device during the day, and the solar heat storage device is set to provide heat for the sludge drying device at night, enabling the continuous operation of the sludge drying device; at the same time, using solar energy, a rich clean energy source, the light energy is converted into heat energy through the sunlight absorption layer for sludge drying, greatly reducing energy consumption and effectively solving the problem of high energy consumption existing in current methods such as thermal sludge drying; by setting a transparent heat-insulating layer on the sunlight absorption layer, it can ensure that sunlight completely passes through and reduce heat loss.

[0020] (2) The present invention can achieve the directional transfer of the latent heat of sludge through the set hydrophobic heat-conducting layer and trough-shaped hydrophilic heat-conducting layer, etc., thereby realizing the multi-stage latent heat recovery of sludge, further improving the solar energy utilization efficiency, and solving problems such as low drying efficiency and large floor area in traditional solar sludge drying methods; the hydrophobic heat-conducting layer transfers heat to the sludge and at the same time ensures that the steam generated by the heated sludge will not liquefy on its surface. The sludge is heated and dried to generate hot steam; the hydrophilic heat-conducting layer ensures that the hot steam liquefies on its surface, absorbs the latent heat released by the liquefaction of the steam, and serves as a heat source to heat the next-stage sludge.

[0021] (3) The steam generated from the dried sludge can be purified by the provided support purification layer in the present invention, solving the problem of the generation of poisonous gases in the traditional sludge drying method, which is prone to cause secondary pollution; the support purification layer is prepared by coating adsorption materials such as activated carbon on a fiber board, and the adsorption and purification efficiency can reach more than 90%, without setting additional purification equipment, reducing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of the solar multi-stage latent heat recovery type sludge drying system of the present invention;

[0023] Figure 2 is a sectional view of the sludge drying device of the present invention;

[0024] Figure 3 is a schematic diagram of the principle of the sludge drying device of the present invention.

[0025] In the figure: 1, transparent heat insulation layer; 2, sunlight absorption layer; 3, hydrophobic heat conduction layer; 4, sludge; 5, support purification layer; 6, purified hot steam; 7, hydrophilic heat conduction layer; 8, water outlet; 9, Fresnel lens; 10, reflector; 11, molten salt tank; 12, heat conduction pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be further described below with reference to the drawings and embodiments.

[0027] Embodiment 1

[0028] In a typical embodiment of the present invention, a solar multi-stage latent heat recovery type sludge drying system is proposed, as Figures 1-3 shown, including a solar concentrator, a solar heat storage device and a sludge drying device. The sludge drying device includes a plurality of sludge drying spaces and a plurality of steam flow spaces. The sludge drying spaces and the steam flow spaces are arranged at intervals from top to bottom in sequence. The steam flow space is separated from the sludge drying space above it by the support purification layer 5, and the steam flow space is separated from the sludge drying space below it by the hydrophilic heat conduction layer 7 and the hydrophobic heat conduction layer 3; above the top sludge drying space, a sunlight absorption layer 2 and a transparent heat insulation layer 1 are arranged in sequence; the top sludge drying space uses solar energy as a heat source to dry the sludge, and the remaining sludge drying spaces use the latent heat released by steam liquefaction as a heat source to dry the sludge; the solar concentrator provides heat for the sludge drying device during the day, and the solar heat storage device provides heat for the sludge drying device at night.

[0029] In this embodiment, the solar concentrator includes a plurality of Fresnel lenses 9 and a reflector 10. The Fresnel lenses 9 are placed at different positions and simultaneously focus sunlight on the reflector 10. The reflector 10 reflects the focused sunlight onto the sunlight absorption layer above the sludge drying device. The solar energy storage device includes a molten salt tank 11 and a heat conduction pipe 12. The photothermal material coating on the surface of the molten salt tank 11 can absorb the focused sunlight and convert it into heat energy to be stored by the molten salt. The heat conduction pipe 12 transfers the heat stored by the molten salt to the hydrophobic heat conduction layer above the sludge at night to further dry the sludge.

[0030] In this embodiment, the support purification layer 5 includes a fiber board, and an adsorption material is coated above the fiber board. The coating thickness of the adsorption material is 0.1 - 1 mm. When the coating thickness of the adsorption material (such as activated carbon) is within the range of 0.1 - 1 mm, it can effectively adsorb the malodorous gases and volatile organic compounds (VOCs) generated during the sludge drying process. If the coating is too thick, it may lead to a decrease in adsorption efficiency and an increase in cost, while if it is too thin, it cannot meet the purification requirements.

[0031] The support purification membrane can be manually pulled out for loading sludge. At the same time, it has a purification function and can purify the malodorous gases and volatile organic compounds generated during the sludge drying process. The support purification layer 5 is in the shape of a drawer and is separated from the hydrophobic heat conduction layer 3 by a set distance to form a gap. The width of the gap is 0.5 - 2 cm, and the gap serves as the sludge drying space for placing sludge.

[0032] Specifically, the support purification layer is prepared by coating an adsorption material such as activated carbon on a fiber board. The thickness of the support purification membrane is 0.5 - 2 mm, and the area is 100 - 10000 cm 2 . Among them, the coating thickness of the adsorption and purification material such as activated carbon is 0.1 - 1 mm, and the adsorption and purification efficiency can reach more than 90%. In a specific implementation manner of this embodiment, activated carbon is coated on a fiber board to prepare a support purification membrane. The thickness of the support purification membrane is 1 mm, and the area is 100 cm 2 . Among them, the thickness of the activated carbon coating is 0.2 mm. The support purification layer is pulled out and flatly filled with sludge. The thickness of the sludge layer is 0.5 cm, and the area is 100 cm 2 .

[0033] In this embodiment, the hydrophilic heat conduction layer 7 includes a trough - type heat conduction plate made of hydrophilic foam copper. The grooves on the trough - type heat conduction plate serve as the steam flow space, and a water outlet 8 is opened on the trough - type heat conduction plate.

[0034] Specifically, the top opening surface of the trough-shaped hydrophilic heat-conducting layer is covered by a supporting purification layer. The trough-shaped hydrophilic heat-conducting layer can ensure the liquefaction of hot steam on its surface and absorb the latent heat released by the steam liquefaction, thereby further serving as a heat source to heat the next-stage sludge. The trough-shaped hydrophilic heat-conducting layer is made of a composite material such as hydrophilic copper foam and graphene by methods such as the template method. Its thickness is 0.5 - 2 mm, and the area is 100 - 10,000 cm 2 . After the steam liquefies on the surface of the hydrophilic heat-conducting layer, it flows towards the water outlet 8 due to the action of gravity, and thus the purified condensed water is discharged at the water outlet 8. The water outlet is arranged at the bottom of the lower side of the trough-shaped hydrophilic heat-conducting layer for collecting the condensed water after the steam liquefaction. In a specific implementation manner of this embodiment, the trough-shaped heat-conducting plate is made of hydrophilic copper foam obtained through commercial channels by the template method. Its thickness is 1 mm, and the area is 100 cm 2 , and its thermal conductivity is 500 W / (m·K).

[0035] In this embodiment, the hydrophobic heat-conducting layer 3 includes a heat-conducting plate. The surface of the heat-conducting plate is chemically etched with a hydrophobic material to obtain a hydrophobic coating. The thickness of the hydrophobic coating is 0.5 - 2 mm. The thickness of the hydrophobic coating directly affects the heat transfer efficiency. The thickness range of 0.5 - 2 mm can ensure efficient heat transfer to the sludge drying space, while preventing the steam from liquefying on its surface, thereby avoiding heat loss. At the same time, the coating thickness can enhance the durability of the hydrophobic heat-conducting layer and reduce material damage caused by the coating being too thin or too thick.

[0036] Specifically, the hydrophobic heat-conducting layer 3 is placed below the sunlight absorption layer 2, which can transfer the heat generated by the sunlight absorption layer 2 to the sludge for heating and drying. At the same time, its hydrophobic property can ensure the directional transfer of the latent heat of the steam. The hydrophobic heat-conducting layer is made of heat-conducting good plates such as copper plates, aluminum plates, and carbon plates by preparing a hydrophobic coating on its surface. Its thickness is 0.5 - 2 mm, and the thermal conductivity is 200 - 3,500 W / (m·K).

[0037] In a specific implementation manner of this embodiment, a copper plate obtained through commercial channels is chemically etched with a mixed solution of ferric chloride and hydrochloric acid to obtain a hydrophobic heat-conducting layer. Its thickness is 1 mm, and the area is 100 cm 2 , and the thermal conductivity is 400 W / (m·K).

[0038] In this embodiment, the upper part of the sunlight absorption layer 2 is closely attached to the transparent heat-insulating layer 1. The sunlight absorption layer can efficiently absorb a relatively wide band of sunlight and convert it into heat. The sunlight absorption layer 1 is made by coating with a photothermal material. The thickness of the sunlight absorption layer is 0.5 - 2 mm, and the area is 100 - 10,000 cm 2, the photothermal conversion efficiency is about 60 - 90%. The thickness of the sunlight absorption layer affects the photothermal conversion efficiency. A thickness range of 0.5 - 2 mm can ensure that the absorption layer efficiently absorbs sunlight and converts it into heat energy, while reducing heat dissipation to the outside. Among them, the sunlight absorption layer is made of low-cost photothermal materials such as graphene, copper oxide, and biochar through methods such as coating and chemical vapor deposition. In a specific implementation manner of this embodiment, graphene obtained through commercial channels is used to prepare the sunlight absorption layer by the coating method, with a thickness of 1 mm and an area of 100 cm 2 , and the photothermal conversion efficiency is about 85%.

[0039] In this embodiment, the transparent heat-insulating layer 1 uses high-temperature transparent materials, such as high-temperature transparent materials like quartz glass or fused alumina. While ensuring that sunlight can pass through it internally, it reduces the heat exchange between the light absorption layer at its bottom and the external environment, thereby further concentrating the heat in the system and reducing heat loss. The thickness of the transparent heat-insulating layer is 0.5 - 2 mm, and the area is 100 - 10000 cm 2 , and the sunlight transmittance is about 80 - 95%. The thickness of the transparent heat-insulating layer is 0.5 - 2 mm, and the transparent heat-insulating layer within this thickness range can effectively reduce heat dissipation while ensuring a high sunlight transmittance (80 - 95%).

[0040] In a specific implementation manner of this embodiment, quartz glass with a thickness of 1 mm and an area of 100 cm 2 is used as the transparent heat-insulating layer, and its transmittance within the solar spectrum range (about 300 nm to 2500 nm) reaches 85%.

[0041] In this embodiment, the hydrophilic heat-conducting layer 7 is located below the steam flow space, and the hydrophobic heat-conducting layer 3 is located above the sludge drying space.

[0042] The solar multi-stage latent heat recovery type sludge drying system provided in this embodiment is divided into multiple stages. Each stage includes a hydrophobic heat-conducting layer 3, a sludge drying layer 4, a support purification layer 5, and a hydrophilic heat-conducting layer 7. Among them, the first stage also includes a transparent heat-insulating layer 1 and a sunlight absorption layer 2. The heat source of the first stage is solar energy. Starting from the second stage, the heat source changes from solar energy to the latent heat of steam generated in the previous stage. The heat recovered from the latent heat depends on the selection of the above-mentioned photothermal materials, heat-conducting materials, etc., and can successfully dry the sludge in 2 - 3 stages. The entire system is inclined to obtain more solar flux, and the inclination angle is determined by the latitude of the application area. In the specific application process, different light absorption materials can be used to improve the sunlight absorption rate; the system structure can be adjusted, such as changing the material design of the transparent heat-insulating layer and the hydrophilic heat-conducting layer, to adapt to different application environments and improve efficiency; different thermal calculation methods can be adopted to determine the optimal system size parameters to achieve higher solar energy utilization efficiency.

[0043] The working principle of the solar multi-stage latent heat recovery type sludge drying system provided in this embodiment is as follows: Solar energy is obtained through the top light absorption layer to heat and dry the sludge. The transparent heat-insulating layer 1 ensures that sunlight completely penetrates and reduces heat loss. The sunlight absorption layer 2 efficiently absorbs sunlight and converts it into heat. The hydrophobic heat-conducting layer 3 transfers heat to the sludge 4, and at the same time ensures that the steam generated by the heated sludge will not liquefy on its surface. The sludge is heated and dried to generate hot steam. The supporting purification layer places the sludge 4 and has a purification function to purify the steam passing through it. The hydrophilic heat-conducting layer 7 ensures that the hot steam liquefies on its surface, absorbs the latent heat released by the steam liquefaction, and serves as a heat source to heat the next-stage sludge.

[0044] Example 2

[0045] In a typical implementation manner of the present invention, a working method of a solar multi-stage latent heat recovery type sludge drying system is provided, including:

[0046] The sunlight is absorbed by the sunlight absorption layer after passing through the transparent heat-insulating layer and converted into heat;

[0047] The heat is transferred to the sludge in the sludge drying space through the hydrophobic heat-conducting layer for drying, and the steam generated by the evaporation of moisture during the sludge drying process enters the steam flow space through the supporting purification layer;

[0048] The steam liquefies in the steam flow space to release latent heat, and the heat is transferred to the sludge in the next-stage sludge drying space through the hydrophobic heat-conducting layer of the next stage for drying. The steam generated by the evaporation of moisture during the sludge drying process enters the next-stage steam flow space through the next-stage supporting purification layer; this process is repeated to recover and utilize the latent heat of the steam in multiple stages.

[0049] Although the specific implementation manners of the present invention are described above in conjunction with the accompanying drawings, it is not a limitation to the protection scope of the present invention. Those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A solar multi-stage latent heat recovery sludge drying system, characterized in that: It comprises a solar energy concentrating device, a solar energy heat storage device and a sludge drying device, wherein the sludge drying device comprises a plurality of sludge drying spaces and a plurality of steam flow spaces, wherein the sludge drying spaces and the steam flow spaces are arranged in sequence from top to bottom, wherein the steam flow space is separated from the sludge drying space above it by a supporting purification layer, and the steam flow space is separated from the sludge drying space below it by a hydrophilic heat conductive layer and a hydrophobic heat conductive layer; a solar light absorption layer and a transparent heat insulating layer are arranged in sequence above the uppermost sludge drying space; the uppermost sludge drying space uses solar energy as a heat source to dry the sludge, and the sludge drying spaces of the remaining layers use the latent heat released by steam liquefaction as a heat source to dry the sludge; the solar energy concentrating device provides heat for the sludge drying device during the day, and the solar energy heat storage device provides heat for the sludge drying device at night.

2. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The supporting purification layer of the sludge drying device is drawer-shaped and made of fiberboard. The fiberboard is coated with adsorption material, and the coating thickness of the adsorption material is 0.1-1 mm.

3. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The hydrophilic heat-conducting layer comprises a groove-type heat-conducting plate, which is made of hydrophilic foam copper. The grooves on the groove-type heat-conducting plate serve as steam flow spaces, and a water outlet is provided on the groove-type heat-conducting plate.

4. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The hydrophobic heat-conducting layer comprises a heat-conducting plate, the surface of the heat-conducting plate is chemically etched with a hydrophobic material to obtain a hydrophobic coating, and the thickness of the hydrophobic coating is 0.5-2 mm.

5. The solar multi-stage latent heat recovery sludge drying system according to claim 1 is characterized in that: The upper part of the solar light absorption layer is in close contact with the transparent heat insulation layer. The solar light absorption layer is made by coating with a photothermal material. The thickness of the solar light absorption layer is 0.5-2 mm.

6. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The solar energy concentrating device comprises a plurality of Fresnel lenses and a reflector. The Fresnel lenses are placed at different positions and focus sunlight on the reflector at the same time. The reflector reflects the focused sunlight to the sunlight absorbing layer above the sludge drying device.

7. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The solar energy storage device includes a molten salt tank and a heat pipe. The photothermal material coating on the surface of the molten salt tank can absorb and focus sunlight and convert it into heat energy to be stored in the molten salt. The heat pipe transfers the heat stored in the molten salt to the hydrophobic heat-conducting layer above the sludge at night to further dry the sludge.

8. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The hydrophilic heat-conducting layer is located below the steam flow space, and the hydrophobic heat-conducting layer is located above the sludge drying space.

9. The solar multi-stage latent heat recovery sludge drying system according to claim 1, characterized in that: The supporting purification layer and the hydrophobic heat-conducting layer are separated by a set distance to form a gap, and the gap serves as a sludge drying space.

10. A working method of a solar multi-stage latent heat recovery sludge drying system as claimed in any one of claims 1 to 9, characterized in that: include: After passing through the transparent insulation layer, the sunlight is absorbed by the sunlight absorption layer and converted into heat; Heat is transferred to the sludge in the sludge drying space through the hydrophobic heat-conducting layer for drying. Steam generated by evaporation of water during the sludge drying process enters the steam flow space through the supporting purification layer. Steam liquefies in the steam flow space and releases latent heat. The heat is transferred to the sludge in the next sludge drying space through the next hydrophobic heat-conducting layer for drying. The steam generated by the evaporation of water in the sludge drying process enters the next steam flow space through the next supporting purification layer. This process is repeated to recycle the latent heat of steam in multiple stages. Furthermore, during the day, the solar concentrating device reflects sunlight to the solar absorption layer above the sludge drying device; at night, the solar heat storage device transfers the heat stored in the molten salt to the hydrophobic heat conductive layer above the sludge.

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