Interface photothermal steam-driven membrane filtration system

Abstract

The present invention discloses a membrane filtration system driven by interfacial photothermal steam, which includes a housing, a filtration membrane, a fresh water chamber, and a cylinder. The bottom of the housing is connected to the fresh water chamber through the filter membrane. The cylinder includes a cylinder body, a piston, and a piston rod. The piston rod is respectively connected to the cylinder body and the piston. The piston rod passes through the fresh water chamber and can expand and contract along the axial direction of the housing. The piston is arranged inside the housing and divides it into a pressure boosting chamber and a seawater chamber. A vacuum chamber is circumferentially arranged on the inner wall of the housing. A solar evaporator capable of continuously generating steam under sunlight irradiation is arranged in the pressure boosting chamber. A pressure detector and a temperature detector are arranged on the side of the pressure boosting chamber away from the seawater chamber. The present invention combines solar-based interfacial photothermal technology and membrane filtration technology, achieving a water production rate of up to 81 kg m-2 h-1 under 12 sun illuminations, which can be applied to high-throughput solar seawater desalination, greatly reducing the energy required for brine separation and having high energy efficiency.

Description

Technical Field

[0001] The present invention relates to a membrane filtration system, specifically a membrane filtration system driven by interfacial photothermal steam. Background Art

[0002] In recent years, with the growth of the population and the rise of industrialization, the demand for energy and fresh water resources has been increasing day by day. Although the water resources on the earth are abundant, with a reserve of 1.386 billion cubic kilometers, 97.5% of them are seawater with a salt concentration of 3.5 wt%, and seawater desalination is required to become potable fresh water. Solar-based seawater desalination technology has pointed the way for green and sustainable seawater desalination technology. Especially, solar interfacial photothermal steam technology, through the spectral design of the sunlight absorber, enables it to absorb most of the sunlight and makes the solar photothermal effect occur at the gas-liquid interface, only heating the water on the liquid surface rather than the whole water body, significantly improving the energy efficiency of water evaporation, and the energy conversion efficiency can reach more than 90%, making the solar-based seawater desalination technology a very promising technology for application.

[0003] Although the solar interfacial photothermal evaporation technology already has a high energy efficiency now, but because in the evaporation process, in addition to the sensible heat part of water, it is also necessary to overcome the huge evaporation enthalpy of water, which is about 2455.6 kJ kg- 1 at room temperature (298 K), which greatly limits the water evaporation rate of the solar interfacial photothermal technology. The evaporation rate of a single-stage solar interfacial photothermal evaporator is 1.47 kg m- 2 h- 1 now under one sun. Some solar-based multi-stage evaporation and low-pressure evaporators, although further increasing the water production, still have a large evaporation enthalpy. For example, under one sun, the output of a 10-stage evaporator can increase to 2.94 kg m- 2 h- 1 , but it is difficult to meet the demand for high water production.

[0004] In addition, there is another mature membrane filtration technology for seawater desalination, which separates salt ions and water molecules by pressurizing seawater to pass through filtration membranes such as reverse osmosis (RO) or nanofiltration (NF). Its theoretical thermodynamic separation energy is far lower than the evaporation enthalpy of water. For seawater with a salt content of 35000 ppm, the thermodynamic theoretical energy consumption of the constant temperature and constant pressure reverse osmosis filtration process is 1.6 kWh m- 3 . Even in the actual RO membrane process stage with a water recovery rate of 50%, the actual energy consumption is only 1.8 kWhm- 3 (6.48 kJ kg- 1) Its actual energy consumption has already approached its thermodynamic limit. It can be seen that membrane filtration is a seawater desalination technology with very low separation energy, but current membrane filtration technologies require a large amount of electrical energy and generate a large carbon footprint. Even for membrane filtration technologies driven by photovoltaic power generation, their efficiency and output are limited by the photovoltaic efficiency.

[0005] In summary, achieving a highly efficient and high-throughput seawater desalination technology based on solar photothermal is a very great challenge. Summary of the Invention

[0006] Objective of the Invention: In order to overcome the deficiencies in the prior art, the objective of the present invention is to provide an interfacial photothermal steam-driven membrane filtration system that avoids water evaporation and has a high water production rate.

[0007] Technical Solution: An interfacial photothermal steam-driven membrane filtration system described in the present invention includes a housing, a filtration membrane, a fresh water chamber, and a cylinder. The bottom of the housing is connected to the fresh water chamber through the filter membrane; the cylinder includes a cylinder body, a piston, and a piston rod. The piston rod is connected to the cylinder body and the piston respectively. The piston rod passes through the fresh water chamber and can expand and contract along the axial direction of the housing. The piston is arranged inside the housing and divides it into a pressure boosting chamber and a seawater chamber; a vacuum chamber is circumferentially arranged on the inner wall of the housing to suppress heat conduction and convection; a solar evaporator capable of continuously generating steam under sunlight irradiation is arranged in the pressure boosting chamber; a pressure detector and a temperature detector are arranged on the side of the pressure boosting chamber away from the seawater chamber to monitor the steam temperature and pressure.

[0008] Furthermore, the solar evaporator includes a solar absorber, a heat insulator, and an evaporation medium. The solar absorber is arranged on the surface of the heat insulator away from the piston, and the solar absorber floats on the upper surface of the evaporation medium. The solar absorber is made with a porous carbon foam as the framework and then sprayed with carbon nanotubes. The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 15 - 25 nm, which are used to improve the sunlight absorption rate and hydrophilicity. The heat insulator is made of aluminosilicate foam material for floating and heat insulation. The porosity of the aluminosilicate foam material is 50 - 70%, and the thickness is 5 - 6 mm. The evaporation medium is ethanol or water.

[0009] Furthermore, the housing is made of stainless steel and light-transmitting quartz glass materials.

[0010] Furthermore, the filtration membrane includes a reverse osmosis (RO) membrane and a nanofiltration (NF) membrane.

[0011] Furthermore, the seawater chamber is connected to a seawater tank. The pressure boosting chamber is connected to a condenser to collect the excess steam.

[0012] Furthermore, the pressure of the steam rises to 8 - 12 atmospheres, reaching the starting pressure of the filter membrane. The piston moves towards the fresh water chamber to filter water. After the water filtration is completed, the remaining steam is discharged into the condenser. After the pressure in the pressure boosting chamber returns to normal pressure, the water inlet stage begins.

[0013] Working principle: Combine the high - energy - efficiency solar interfacial photothermal evaporation technology with the membrane filtration seawater desalination technology with low separation energy to improve the water production rate of solar seawater desalination. Use solar interfacial photothermal to generate high - pressure steam, and then push seawater through the RO / NF membrane to separate water molecules from salt ions. The working process of the photothermal water filtration system device is divided into four stages: pressure boosting stage, water filtration stage, exhaust stage, and water inlet stage. First, use solar interfacial photothermal technology to generate high - temperature and high - pressure steam in the pressure boosting chamber until the steam pressure reaches the starting pressure of the filter membrane. Then, open the piston fixed by the cylinder barrel body. The high - pressure steam pushes the piston and seawater below, enabling the seawater to pass through the RO / NF membrane to complete the water filtration process and separate water molecules from salt ions. After the filtration is completed, the remaining steam in the pressure boosting chamber is discharged to the condenser. Finally, by setting the seawater tank at a height above the seawater chamber, while the electric cylinder pushes the piston back to its original position, seawater is continuously fed into the seawater chamber by gravity. After the water inlet process is completed, the next cycle of work begins.

[0014] Usage method: Place this device under concentrated sunlight to boost the pressure. When the appropriate pressure is reached, open the switch of the cylinder to control the piston and start water filtration. After the filtration is completed, discharge the remaining steam and fill the seawater chamber with water to start a new cycle.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0016] 1. Combine the solar - based interfacial photothermal technology and membrane filtration technology. By designing and building a photothermal water filtration system and preparing a solar evaporation body, a water production rate as high as 81 kg m- 2 h- 1 is achieved under 12 - sun illumination, which can be applied to high - throughput solar seawater desalination;

[0017] 2. Use solar interfacial photothermal to generate high - pressure steam, and then push seawater through the RO / NF membrane to separate water molecules from salt ions. This method avoids the direct evaporation of water molecules, does not need to overcome the evaporation enthalpy of water, greatly reduces the energy required for brine separation, has high energy efficiency, and can also achieve a high - throughput seawater desalination rate;

[0018] 3. The housing is assembled from stainless steel and light-transmitting quartz glass materials, which limits the expansion ratio of steam to 1-8, further improving the water production rate. Starting the RO membrane and NF membrane through the solar evaporator is beneficial to expanding its application fields, such as seawater desalination, wastewater treatment, and separation of divalent and monovalent ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the present invention;

[0020] Figure 2 is a schematic structural diagram of the solar evaporator 9 of the present invention;

[0021] Figure 3 is an electron microscope image of the solar absorber 901 of the present invention at a scale of 500 μm;

[0022] Figure 4 is an electron microscope image of the solar absorber 901 of the present invention at a scale of 200 nm;

[0023] Figure 5 is a schematic working principle diagram of the present invention;

[0024] Figure 6 is a working process diagram of the present invention;

[0025] Figure 7 is a real-time pressure change curve of the steam 8 in the pressure boosting chamber 5 of the present invention under different sunlight conditions;

[0026] Figure 8 is a real-time temperature change curve of the steam 8 in the pressure boosting chamber 5 of the present invention under different sunlight conditions;

[0027] Figure 9 is a real-time pressure change curve in the pressure boosting chamber 5 when starting the NF membrane under 12 sunlights of the present invention;

[0028] Figure 10 is a real-time pressure change curve in the pressure boosting chamber 5 when starting the RO membrane under 12 sunlights of the present invention;

[0029] Figure 11 is a relationship curve between the water production rate and the sunlight multiple of the present invention;

[0030] Figure 12 is a bar chart of the rejection rates of different ions of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] As Figure 1, the vacuum chamber 7 circumferentially arranged on the inner wall of the housing 1 of the interfacial photothermal steam-driven membrane filtration system is used to isolate heat conduction and convection. The bottom of the housing 1 is fixedly connected to the fresh water chamber 3 through the filter membrane 2. The cylinder 4 includes a cylinder main body 401, a piston 402 and a piston rod 403. The piston rod 403 extends outside the cylinder main body 401, passes through the fresh water chamber 3 and can expand and contract along the axial direction of the housing 1. The piston rod 403 is fixedly connected to the piston 402. The piston 402 is arranged inside the housing 1 and divides the housing 1 into a pressure boosting chamber 5 and a seawater chamber 6. There is a solar evaporator 9 in the pressure boosting chamber 5 that can continuously generate steam 8 under sunlight irradiation. One side of the pressure boosting chamber 5 away from the seawater chamber 6 is connected to a pressure detector 10 and a temperature detector 11 to monitor the temperature and pressure of the steam 8. The housing 1 is assembled from stainless steel and light-transmitting quartz glass materials. The filter membrane 2 includes a reverse osmosis membrane (RO) and a nanofiltration membrane (NF). The seawater chamber 6 is connected to a seawater tank 12. The pressure boosting chamber 5 is connected to a condenser 13 for collecting the excess steam 8.

[0032] The cylinder 4 also includes a compressed air machine, an electric control device, seals, etc. When compressed air is input into the cylinder chamber in the cylinder main body 401, the piston 402 rises to the top of the seawater chamber 6; when the compressed air is discharged from the cylinder chamber, the piston 402 returns to the bottom of the seawater chamber 6. The intake and exhaust of the cylinder 4 are completed by the compressed air machine, and the piston 402 realizes reciprocating linear motion.

[0033] As Figures 2 to 4 , the solar evaporator 9 includes a solar absorber 901, a heat insulator 902 and an evaporation medium 903. The solar absorber 901 is arranged on the surface of the heat insulator 902 away from the piston 402, and the solar absorber 901 floats on the upper interface of the evaporation medium 903. The evaporation medium 903 is preferably ethanol or water. The solar absorber 901 uses porous carbon foam as the skeleton and is then sprayed with carbon nanotubes. The model of the carbon foam is PPI110, with 110 pores per inch and a thickness of 3 mm. The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 15 - 25 nm to improve the sunlight absorption rate and hydrophilicity. The heat insulator 902 is made of aluminosilicate foam material with a porosity of 50 - 70% and a thickness of 5 - 6 mm for floating and heat insulation.

[0034] As Figure 5 , sunlight irradiates the solar evaporator 9 from the top of the housing 1, and interfacial photothermal generates high-pressure steam 8, which pushes seawater through the RO / NF membrane to realize the separation of water molecules and salt ions.

[0035] As Figure 6 , the working process of the interfacial photothermal steam-driven membrane filtration system is divided into four stages: the pressure boosting stage, the water filtration stage, the exhaust stage and the water intake stage.

[0036] First, use the solar interface photothermal technology to generate high-temperature and high-pressure steam 8 in the pressure-boosting chamber 5 until the pressure of the steam 8 reaches the starting pressure of the filtration membrane 2 for filtering water. Ethanol is selected as the evaporation medium 903 for the interface photothermal effect. The real-time pressure of ethanol vapor 8 in the pressure-boosting chamber 5 under different sunlight densities is as Figure 7 shown. As can be seen from Figure 7 , under 2, 3, 5, 8, 10, and 12 sunlights, its final steady-state pressures reach 2.1, 3.4, 6, 8.4, 9.7, and 11.2 atmospheres respectively. The greater the concentration ratio of sunlight, the faster the pressure boost speed and the higher the final steady-state pressure reached. Figure 8 Figure Figure 8 shows the temperature change of the steam 8 under different sunlight concentration ratios. It can be seen that when under 2, 3, 5, 8, 10, and 12 sunlights, the temperature of the steam 8 increases with time. Among them, when under 12 sunlights, the steam 8 has the highest and fastest temperature increase. Therefore, this embodiment is carried out under 12 sunlights, and the starting pressure is selected as 11 atmospheres.

[0037] Next, open the piston 402 fixed by the cylinder body 401 of the air cylinder 4. The high-pressure steam 8 pushes the lower piston 402 and seawater, enabling the seawater to pass through the filtration membrane 2, completing the water filtration process and separating water molecules and salt ions.

[0038] Then, after the filtration is completed, the remaining steam 8 in the pressure-boosting chamber 5 is discharged to the condenser 13.

[0039] Finally, by setting the seawater tank 12 at a height higher than the seawater chamber 6, the seawater therein removes pollutants through pre-treatment. While the air cylinder 4 pushes the piston 402 back to its original position, the seawater is continuously fed into the seawater chamber 6 by gravity. After completing the water inlet process, the next cycle of work can begin.

[0040] As shown in Figure 9 , under 12 sunlights, during the pressure-boosting stage, the pressure of the steam 8 rises to 9.95 atmospheres, which has reached the starting pressure of the filtration membrane 2 (NF membrane), and water filtration begins. After the water filtration ends, the remaining steam 8 is discharged into the condenser 13. After the pressure in the pressure-boosting chamber 5 returns to atmospheric pressure, the water inlet stage begins.

[0041] As shown in Figure 10 , under 12 sunlights, when the pressure of the steam 8 in the pressure-boosting chamber 5 reaches 11.2 atmospheres, it reaches the starting pressure of the filtration membrane 2 (RO membrane), and water filtration begins. After the water filtration ends, the remaining steam 8 is discharged into the condenser 13. After the pressure in the pressure-boosting chamber 5 returns to atmospheric pressure, the water inlet stage begins.

[0042] As shown in Figure 11 , the RO membrane is activated under 12 sunlights, and its water production rate reaches 81 kg m- 2 h-1 (The ratio of water production rate to incident solar flux is 6.75 kg kWh- 1 ). The NF membrane is started under 5 sunlights, and its water production rates under 5, 8, 10 and 12 sunlights are 40 kg m- 2 h- 1 , 78.2 kg m- 2 h- 1 , 134.5 kg m- 2 h- 1 , 180.4kg m- 2 h- 1 .

[0043] The ion rejection rate of the interfacial photothermal steam-driven membrane filtration system was tested under 12 sunlights and 10000 ppm feed solution conditions. As Figure 12 shown, the RO driven by the interfacial photothermal membrane filtration system has rejection rates of 99.98%, 99.96%, 99.98%, 99.5%, 99.97% for Ca 2 +, Mg 2 +, Na+, F- respectively, and the ion concentrations in the filtered fresh water are all lower than the World Health Organization drinking water standards. The NF driven by the photothermal membrane filtration system has rejection rates of 97.6%, 97%, 97.3%, 73.5%, 97.3% for Ca 2 +, Mg 2 +, Na+, F- respectively.

[0044] Comparative Example

[0045] The rest of the structure of this comparative example is the same as that of the embodiment, and the only difference is that: the solar evaporator 9 is replaced by a photovoltaic cell, and it is found that: the energy consumption is too large, the cost increases significantly, and the output decreases.

Claims

1. An interfacial photothermal steam-driven membrane filtration system, characterized in that: It includes a housing (1), a filter membrane (2), a fresh water chamber (3) and a cylinder (4). The bottom of the housing (1) is connected to the fresh water chamber (3) through the filter membrane (2). The cylinder (4) includes a cylinder body (401), a piston (402) and a piston rod (403). The piston rod (403) is respectively connected to the cylinder body (401) and the piston (402). The piston rod (403) passes through the fresh water chamber (3) and can expand and contract along the axial direction of the housing (1). The piston (402) is arranged in the housing (1) and divides it into a pressure boosting chamber (5) and a seawater chamber (6). A vacuum chamber (7) is circumferentially arranged on the inner wall of the housing (1). A solar evaporator (9) capable of continuously generating steam (8) under sunlight irradiation is arranged in the pressure boosting chamber (5). A pressure detector (10) and a temperature detector (11) are arranged on the side of the pressure boosting chamber (5) away from the seawater chamber (6). The solar evaporator (9) includes a solar absorber (901), a heat insulator (902) and an evaporation medium (903). The solar absorber (901) is arranged on the surface of the heat insulator (902) away from the piston (402). Both the solar absorber (901) and the heat insulator (902) float on the upper surface of the evaporation medium (903). The solar absorber (901) is made by using porous carbon foam as the skeleton and then spraying carbon nanotubes. The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 15 - 25 nm. The evaporation medium (903) is ethanol.

2. The interfacial photothermal steam-driven membrane filtration system according to claim 1, wherein: The heat insulator (902) is made of aluminosilicate foam material. The porosity of the aluminosilicate foam material is 50 - 70%, and the thickness is 5 - 6 mm.

3. The interfacial photothermal steam-driven membrane filtration system according to claim 1, wherein: The housing (1) is made of stainless steel and quartz transparent glass materials.

4. The interfacial photothermal steam-driven membrane filtration system according to claim 1, wherein: The filter membrane (2) includes a reverse osmosis membrane and a nanofiltration membrane.

5. The interfacial photothermal steam-driven membrane filtration system according to claim 1, wherein: The seawater chamber (6) is connected to a seawater tank (12).

6. The interfacial photothermal steam-driven membrane filtration system according to claim 1, wherein: The pressure boosting chamber (5) is connected to a condenser (13).

7. The interfacial photothermal steam-driven membrane filtration system according to claim 6, wherein: The pressure of the steam (8) rises to 8 - 12 atmospheres, reaching the starting pressure of the filter membrane (2). The piston (402) moves towards the fresh water chamber (3) for water filtration. After the water filtration ends, the remaining steam is discharged into the condenser (13). After the pressure in the pressure boosting chamber (5) returns to normal pressure, the water inlet stage begins.

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