CN101693559B - A vacuum or direct contact dual-purpose horizontal solar film distillation device - Google Patents

Abstract

The invention discloses a horizontal solar membrane distiller for vacuum and direct contact, which comprises a membrane module, a hot working medium heating system and a cold working medium cooling system, wherein the hot working medium heating system is a hot side loop composed of a solar thermal-collection water receiver, a membrane module hot-water inlet, a membrane module hot-water outlet and a hot-side recycle pump; the cold working medium cooling system is a cold side loop composed of a membrane module condensed-water outlet, a heat exchanger, a condensed water collector, a cold-side control valve, a cold-side recycle pump and a condensed water inlet; and the condensed water collector is communicated with a vacuum pump through a vacuum control valve. The distiller of the invention integrates the membrane distillation vacuum mode and the direct contact mode, and the two different modes for preparing drinking water can be converted flexibly and conveniently.

Description

A vacuum or direct contact dual-purpose horizontal solar film distillation device

technical field

The invention relates to a membrane distillation device, in particular to a horizontal membrane distillation drinking water device which utilizes low-grade energy solar energy as the driving force of membrane distillation in vacuum or direct contact.

Background technique

As we all know, China is a country with severe drought and water shortage. The total amount of fresh water resources is 2.8 trillion cubic meters, accounting for 6% of global water resources, ranking fourth in the world after Brazil, Russia and Canada, but the per capita is only 2,200 cubic meters, which is only 1/4 of the world average. 1/5 of the United States, ranking 121st in the world, is one of the 13 countries with the poorest per capita water resources in the world. According to statistics, more than half of the more than 600 cities in the country are short of water to varying degrees, and coastal cities are no exception, and even more serious. At present, the urban water supply in our country is dominated by surface water or groundwater, or mixed use of the two water sources. In some cities, due to excessive exploitation of groundwater, the groundwater level has dropped. . Due to the wanton discharge of industrial wastewater, more than 80% of the surface water and groundwater are polluted.

In some areas with inconvenient transportation and underdeveloped electricity, such as islands, deserts and remote areas where fresh water resources are scarce, and most of the drinking surface water in the central and western regions is brackish water with high minerals and high fluorine, it is completely possible to use the richness of these areas Advanced solar energy resources and membrane distillation technology are used to provide long-term continuous domestic water and drinking water for these areas. This use of renewable energy not only solves the problem of energy shortage, but also protects the environment, and is of great significance to the sustainable use of water resources.

Because there are huge reserves of seawater and salt water on the earth, accounting for about 97% of the total water storage on the earth. Therefore, desalination of seawater and brackish water is one of the effective solutions to the shortage of freshwater resources. At present, membrane distillation technology, especially solar membrane distillation technology, can be used in desalination of seawater, brackish water, and production of pure water. It is also due to the unique advantages of membrane distillation technology that can be separated under normal pressure and slightly higher than normal temperature, and the membrane distillation system is simple and easy to operate.

Among them, the mature seawater desalination technology can be mainly divided into distillation method and membrane method. Distillation mainly includes multi-effect evaporation, multi-stage flash evaporation, etc. They can use economic energy such as waste heat and nuclear energy, but the equipment is bulky and the operating cost is high.

Reverse osmosis (RO) is the most widely used membrane seawater desalination technology. High pressure is required in the process. Although the current optimal value has dropped below 5.0-5.5MPa, this means that a large amount of energy is still consumed, and the Equipment and membrane requirements are more stringent. At the same time, RO technology has high requirements on water quality. Seawater must be pretreated in various forms to remove oil, particles, bacteria and algae in seawater, making it close to the standard of pure salt water. Membrane materials are regularly cleaned to eliminate clogging, pollution, and scaling, which are complex tasks with strict requirements. Therefore, membrane desalination technology - membrane distillation (Membrane Distillation, MD) has attracted more and more researchers' attention.

Membrane distillation is a membrane process that uses a hydrophobic microporous membrane and uses the difference in vapor pressure on both sides of the membrane as the driving force for mass transfer. Compared with other membrane processes, membrane distillation has the unique advantage of being able to separate under normal pressure and slightly higher than normal temperature. It can make full use of economic energy such as solar energy, wind energy, geothermal energy, industrial waste heat and waste heat, and the equipment is simple and easy to operate. convenient.

So far, the low membrane flux is still the main factor hindering the large-scale application of membrane distillation. The analysis of its deep-seated reasons mainly includes the following aspects:

1. Traditional membrane distillation membranes have low flux and are prone to pollution. Therefore, research on the preparation of pollution-resistant high-flux membrane distillation membranes needs to be further deepened.

2. The mass transfer and heat transfer performance of the traditional membrane distillation module is poor, so the structural design of the membrane module needs to be further optimized.

In recent years, solar membrane distillation technology has developed rapidly, and our country's patents on solar membrane distillation have been continuously disclosed and authorized:

Zhang Xinrong; Ren Jianxun and others (patent name: membrane distillation water treatment device using solar energy or waste heat; publication number: CN1396120; publication date: 2003.02.12) invented a technology that belongs to the field of heat energy utilization, water treatment and environmental protection, including membrane Components, solar heat collectors or waste heat collectors, more than one circulating pump and its driving device, and pipelines connecting various components; respectively constitute the loop of the raw material liquid, the loop of the distillate side, and the supplementary pipeline of the raw material liquid . The invention can continuously process the raw material liquid and continuously obtain domestic and drinking water; it can also save electric heating without any power consumption; and it can use the heat exchanger to recover the latent heat of condensation, which greatly reduces the required solar collector scale.

Tian Rui; Yang Xiaohong et al. (patent name: a solar membrane distillation system; patent number: 200520005444; publication date: September 27, 2006) provided a utility model invention of a solar membrane distillation system, including: thermal fluid heating system , a membrane module, a cold working fluid cooling system, a drive system and pipelines connecting various components, wherein a thermal solar heating system is added to the hot working fluid heating system, the cold working fluid cooling system adopts a solar cooling system, and the driving system adopts solar energy Power system. In this way, solar energy can be used to heat and cool the working medium, drive the circulating pump to work, and save a lot of electric energy; solar energy is a kind of clean energy, which can protect the environment and make effective use of solar energy resources.

Tian Rui; Yang Xiaohong and others (patent name: a portable solar membrane distillation seawater desalination device; patent number: CN1827532; publication date: 2006.09.06) invented a portable solar membrane distillation seawater desalination device, which includes: seawater container , the bottom surface of the seawater container is a hydrophobic film, which is sealed and connected with the periphery of the seawater container. A cooling plate is arranged at a certain gap below the hydrophobic film. There is a fresh water outlet on the cooling plate, and the gap is an air gap. , the seawater container is provided with a water inlet pipe, and the seawater container is provided with a solar heating device. When it is used on the sea, it can also include a floating device, which floats obliquely on the sea to fully absorb solar energy. The device applies the principle of air-gap membrane distillation, making full use of the abundant solar energy resources and seawater resources in the island area; it is simple in structure, easy to carry, and low in cost, which brings great benefits to the work and life of the residents in the island area and the soldiers defending the island. convenient.

Zhou Xiantao; Pan Jiazhen (patent name: a membrane distilled water treatment device; publication number: CN201049894; publication date: 2008.04.23) invented a membrane distilled water treatment device, which is characterized in that it includes a raw material liquid inlet pipeline, a membrane side raw material liquid chamber, Raw material outlet pipeline, hydrophobic microporous membrane module, membrane side distillate chamber and distillate outlet pipeline; the outer side of the partition wall corresponding to the microporous membrane module in the membrane side raw material solution chamber is in contact with the environment Dry wall surface, the outer side of the partition wall corresponding to the microporous membrane module in the distillate chamber on the membrane side is the wet wall surface in contact with the environment. The device automatically obtains heat from the environment to heat the raw material liquid, automatically obtains a cold source from the environment to cool the distillate, and does not need to provide energy for the operation of the device artificially; the device can continuously process the raw material liquid and continuously obtain distillation liquid; the device can not only operate in the absence of the sun, but also at night; it can be implemented on a small scale or in an integrated manner.

At present, solar water heaters in economically developed areas have been widely used, but affected by the seasons, the utilization rate of solar energy is not high in summer, and the heat energy obtained in large quantities cannot be effectively utilized. The solar membrane module of the present invention can be used in large quantities. Photothermal collectors are used in conjunction, especially large-scale solar collectors such as hotels, restaurants, and schools are connected and matched for use in the preparation of pure water. It provides space for the preparation of pure water using solar energy.

Contents of the invention

The invention provides a horizontal dual-purpose solar hollow fiber membrane distillation device with high membrane flux, low water production cost, replaceable membrane and large-scale application.

A vacuum or direct contact dual-purpose horizontal solar membrane distillation device, including a membrane module, a thermal working fluid heating system and a cold working fluid cooling system, wherein the thermal working fluid heating system is a solar heat collection water storage, a membrane module hot water The hot side circuit composed of the inlet, the hot water outlet of the membrane module, and the hot side circulation pump; The cold side circuit formed by the water inlet, and the condensate collector communicates with the vacuum pump through the vacuum control valve.

The membrane module includes a number of single membrane elements, which are embedded in a flanged head with an embedded groove for sealing and fixing, and a separation plate is provided in the middle of the membrane module, and the isolation plate is used between the single membrane elements. The plates are separated, and the dispersion of the internal membrane modules helps the heat transfer and mass transfer of the membrane distillation process, and improves the efficiency of the membrane distillation; the role of the middle isolation plate can also keep the hollow fiber membrane in the middle section parallel to the fluid direction of the raw material liquid , not to be too curved to affect the efficiency of membrane distillation. The other end of the single membrane element is also inserted into the embedding groove of the flange head, put on the shell, and then put on the cover at both ends.

The single-branch membrane element is composed of porous hydrophobic hollow fiber membranes, and the porous hydrophobic hollow fiber membranes are dispersed with dispersed grids, so that during the membrane distillation process, the water vapor passing through the membrane pores does not diffuse to adjacent hollow fibers Go up the membrane wall.

The method of embedding a single membrane element into a flanged head with an embedding groove for sealing and fixing is as follows: embedding a rubber gasket in the embedding groove, and then pressing the head of the single membrane element into the embedding groove. The other end adopts the same method of pressing and fixing the rubber washer. This method of sealing and fixing a single membrane element into a flanged head with an embedded groove is detachable, that is, if a single membrane element has broken wires, leakage, or clogged membrane holes, etc., it can be removed. Remove and replace.

According to the above operations, several single membrane elements of the same specification can be embedded in the whole module, so that a good space gap is maintained between the single membrane elements, which is beneficial to the heat transfer and mass transfer process of membrane distillation, and improves the efficiency of membrane distillation. The membrane module can maintain good sealing performance when the device is running, the modules are well dispersed, the single module is small in size and light in weight, and the head and shell of the module are easy to disassemble, which improves the packaging efficiency and facilitates the maintenance and replacement of the modules.

The material of the porous hydrophobic hollow fiber membrane is some traditional hollow fiber membrane polymers, such as: polypropylene, polysulfone, polytetrafluoroethylene, polyvinylidene fluoride, etc., and polypropylene and polyvinylidene fluoride are preferred in the present invention. Porous and hydrophobic hollow fiber membranes have an inner diameter of 0.1-2mm, an outer diameter of 0.6-2.8mm, a wall thickness of 0.1-0.3mm, a hollow fiber membrane wall porosity of 50-85%, and a maximum pore diameter of 0.1-1.0μm. The length is 50-100cm.

The method of membrane bundle dispersion not only reduces the number of hollow fiber membranes packaged by a single membrane element, but also uses a special grid to disperse the hollow fiber membranes in a single membrane element, and uses a separator plate to separate the single membrane element from the single membrane element. Keep a good space gap between the membrane elements to ensure that the hollow fiber membrane does not sag and bend excessively, and has a good effect of dispersing the membrane bundle.

The device also includes control valves, flow meters, thermometers, etc. of some optimized devices, which can be set according to actual production design needs.

The process of preparing drinking water for this kind of solar membrane distillation horizontal dual-purpose mass transfer is as follows:

1. Raw water is provided as a source of water, and the raw water is heated into hot water at a certain temperature by the solar heat collector and then enters the membrane module. Under the action of the circulation pump, the water flows back into the solar heat collector water storage, forming a hot water circulation loop on the hot side; on the cold side, open the vacuum control valve and close the cold side control valve. At this time, use the vacuum pump to suck through the membrane The water vapor is quickly liquefied by the condenser and collected in the condensed water collector, through which water can be taken at any time to test the water quality. This cold side system provides low-pressure condensation to collect condensed water membrane distillation system (vacuum membrane distillation) for the cold side.

2. Raw water is provided as a source of water. The raw water is heated by hot water at a certain temperature after passing through the solar heat collector and enters the membrane module. The hot water conducts mass transfer and heat transfer along the membrane surface. The water flows back to the solar collector water storage under the action of the circulation pump, forming a hot side circuit; on the cold side, close the vacuum control valve, open the cold side control valve, and use the cold side circulation pump to form a cooling cycle on the cold side Water, the water vapor passing through the membrane quickly passes through the circulating cooling water and the condenser, and then enters the circulating water. The liquid level in the condensed water collector rises evenly to form a cold side circuit. Water can be taken from the collector at any time to test the water quality. This cold side system provides cold working medium circulation cooling film distillation system (direct contact film distillation) for the cold side.

The device of the invention adopts a specially designed horizontal membrane module, and water vapor can be released under vacuum conditions. And the cold side circuit can adopt two schemes, namely: one is to provide low pressure on the cold side and the condenser is cooled to collect condensed water; The working fluid is directly cooled to collect condensed water. This device integrates two methods of membrane distillation vacuum and direct contact. The conversion between the two different methods of preparing drinking water is very flexible and convenient.

Description of drawings

Fig. 1 is the structural representation of horizontal solar film distillation device of the present invention;

Among them, 1-solar heat collector, 2-flow meter, 3-membrane module, 4-hot side circulating pump, 5-heat exchanger, 6-condensed water collector, 7-cold side circulating pump, 8- Flow meter, 9-vacuum pump, 10-first valve, 11-second valve, 13-flow control valve

Fig. 2 is a schematic diagram of a membrane module;

Among them, 31-embedded groove, 32-membrane module shell, 33-flange head, 34-cover, 35 hot water inlet, 36-single membrane module sealant, 37-cooling water inlet, 38-cooling water Outlet, 39-porous hydrophobic hollow fiber membrane, 310-hot water outlet, 311-partition plate

Fig. 3 (a) is the schematic diagram of dividing plate;

Fig. 3 (b) is the coordinating diagram of the hexagonal hole of the membrane module embedding groove and the dividing plate;

Figure 3(c) is a schematic diagram of the dispersed grid of the hollow fiber membrane of a single membrane module;

Figure 4 is a cross-sectional view of the membrane assembly;

Fig. 5 is the variation diagram of the permeated water flux of the membrane module with the inlet hot water temperature in Example 1;

Fig. 6 is the change figure of embodiment 1 pure water conductivity with operating time;

Fig. 7 is the comparison diagram of the hot water display temperature of the solar collector and the hot water display temperature of the membrane module inlet and outlet on August 7th in embodiment 1;

Fig. 8 is the variation graph of embodiment 1 cumulative permeated water flux with operating time;

Fig. 9 is the relation figure of embodiment 1 solar collector hot water temperature and membrane distillation utilization heat;

Fig. 10 is embodiment 18.7; 8.11; 8.12 day solar energy with temperature time change figure;

Fig. 11 is a diagram showing the variation of permeate flux with outlet hot water temperature in Example 2;

Fig. 12 is a comparison diagram of the permeate flux of the membrane module of the direct contact type and the vacuum membrane distillation in Example 2.

Detailed ways

The horizontal solar membrane distillation device as shown in Figure 1 includes a membrane module 3, a thermal working medium heating system and a cold working medium cooling system, wherein the thermal working medium heating system is a solar thermal water storage device 1, a flow control valve 13, The hot side hot water circulation circuit composed of the membrane module hot water inlet 35, the membrane module hot water outlet 310, and the hot side circulation pump 4; the cold working medium cooling system is the membrane module condensate outlet 38, the heat exchanger 5, and the condensate collector 6. The cold-side condensed water circulation loop composed of the cold-side control valve (the first valve 10 and the second valve 11), the cold-side circulation pump 7, the flow meter 8, and the condensed water inlet 37, and the condensed water collector 6 is controlled by vacuum The valve 12 communicates with the vacuum pump 9 .

The structure of the membrane module is shown in Figure 2. A suitable amount of porous hydrophobic hollow fiber membranes are dispersed with a dispersed grid 9 and sealed with a single membrane element sealant 36 to form a single membrane element, and the single membrane element is embedded in a Embedded in the flanged head 33 of the groove 31, cover the membrane module shell 32, and then cover the cover 34; in the middle section of the membrane module 3, use the isolation plate 311 to further disperse the single dispersed single membrane elements, and the membrane The other end of the component is also inserted into the flanged head, and both ends are sealed and fixed.

The drinking water preparation process of the device is as follows:

1. Raw water is provided as a source of water. The raw water turns into hot water at a certain temperature after passing through the solar heat collector 1, and then flows through the flowmeter 2 into the membrane module 3. The water temperature can be observed through the inlet thermometer of the membrane module. Mass transfer and heat transfer are carried out on the surface of the membrane, and the partially vaporized steam passes through the membrane holes. There is also a thermometer at the outlet of the membrane module 3, which can read the temperature of the outlet water, and then the heated hot water flows down under the action of the circulation pump 4 on the hot side. Returning to the solar collector water storage 1, constitutes the hot water circulation circuit on the hot side; on the cold side, open the vacuum control valve 12, close the first valve 10 and the second valve 11, at this time, use the vacuum pump 9 to suck through the membrane The water vapor is rapidly cooled by the heat exchanger 5, and is collected in the condensed water collector 6 after being liquefied. Water can be taken at any time through the condensed water collector 6 to detect the water quality.

2. Raw water is provided as a source of water. The raw water is heated by the solar heat collector 1 and becomes hot water at a certain temperature, and then flows through the flow meter 2 into the membrane module 3. The water temperature can be observed through the module inlet thermometer. The hot water Mass transfer and heat transfer are carried out along the surface of the membrane, and part of the steam passes through the membrane holes. There is also a thermometer at the outlet of the membrane module 3, which can read the temperature of the outlet water, and then the hot water cooled by the circulating pump 4 on the hot side flows back. To the solar heat collector water storage 1, constitute the hot side hot water circulation circuit; on the cold side, close the vacuum control valve 12, open the first valve 10 and the second valve 11, at this time, use the cold side circulation pump 7, in the cold side Cooling circulating water is formed on the side, and the water vapor passing through the membrane quickly passes through the circulating cooling water and the condenser 5 and then enters the circulating water. The temperature and flow of the inlet and outlet of the cooling circulating water cycle, the temperature of the circulating water on the cold side is controlled at 15°C to 30°C, which constitutes the loop of the condensate water cycle on the cold side, and water can be taken at any time through the condensate collector 6 to test the water quality.

Example 1

Solar Vacuum Membrane Distillation

The pyrogen water is heated by the solar thermal water storage device 1 and becomes hot water at a certain temperature, and then flows through the flow meter 2 (the flow rate is controlled at 50L/h~200L/h) and enters the membrane module 3, and the water temperature can be imported through the module It can be seen from the thermometer that hot water conducts mass and heat transfer along the surface of the membrane, and part of the steam passes through the membrane holes. There is also a thermometer at the outlet of the membrane module, which can read the temperature of the outlet water, and then flows back under the action of the circulation pump 4 on the hot side. The solar collector water storage device 1 constitutes a hot side circulation; at the cold side, the vacuum control valve 12 is opened, the first valve 10 and the second valve 11 are closed, and a vacuum pump 9 is used at this moment (the degree of vacuum on the vacuum side remains at 0.1Mpa ) suction, the water vapor passing through the membrane is quickly liquefied in the condenser 5 and then collected in the condensed water collector 6. The condensed pure water at 20°C to 30°C constitutes a cold side circuit.

The porous hydrophobic hollow fiber membrane 9 has an average inner diameter of 1 mm, an outer diameter of 1.5 mm, a wall thickness of 0.25 mm, a porosity of 85%, and a maximum pore diameter of 0.84 μm.

According to the absorption of solar energy by the solar collector, the flux of the membrane is between 4 and 18L/m ² h. If the operating time is 5 to 8 hours a day, the total amount of water produced can reach 20 to 100L, and the effect of daily sunlight is better. Under normal circumstances, the membrane distillation system can maintain a good membrane flux between 10:00 am and 4:00 pm, and the water production efficiency will be relatively high, and the conductivity of the produced water will be lower than 8 μs/cm.

The vacuum membrane distillation data are shown in Fig. 5-11.

Example 2

Solar Direct Contact Membrane Distillation

The thermal raw water is heated by the solar thermal water storage device 1 and becomes hot water at a certain temperature, and then flows through the flow meter 2 (the flow rate is controlled at 50L/h~200L/h) and enters the membrane module 3. The water temperature can be passed through the module inlet thermometer. It can be observed that the hot water conducts mass transfer and heat transfer along the surface of the membrane, and part of the steam passes through the membrane holes. There is also a thermometer at the outlet of the membrane module, which can read the temperature of the outlet water, and then cool down under the action of the circulating pump 4 on the hot side. Part of the hot water flows back to the solar heat collector water storage to form a hot water circulation circuit on the hot side; on the cold side, close the vacuum control valve 12, open the first valve 10 and the second valve 11, and use the cold side circulating water pump 7 , forming cooling circulating water on the cold side, the water vapor passing through the membrane quickly passes through the circulating cooling water and the condenser 5 and then enters the circulating water, the liquid level in the condensed water collector 6 rises evenly, the inlet and outlet thermometers and flow meters 8. The temperature and flow rate of the inlet and outlet of the cooling circulating water can be detected separately. The temperature of the circulating water on the cold side is controlled at 15°C to 30°C, which constitutes the condensed water circulation loop on the cold side.

The membrane flux is 1.5-9L/m ² h. According to the weather conditions and the sunlight time is good, the daily operation time is 5-8 hours, and the total water production can reach 10-50L. Every day from 10:00 am to 4:00 pm The membrane distillation system between points can maintain a good membrane flux, the water production efficiency will be relatively high, and the conductivity of the produced water will be lower than 10μs/cm.

The direct contact membrane distillation data are shown in Figures 12-13.

Claims (5)

1. A vacuum or direct contact dual-purpose horizontal solar membrane distillation device, comprising a membrane module, a thermal fluid heating system and a cold fluid cooling system, characterized in that: the thermal fluid heating system is a solar thermal water storage device , hot water inlet of the membrane module, hot water outlet of the membrane module, and hot side circulating pump; the cooling system of the cold working medium is the outlet of the condensed water of the membrane module, heat exchanger, condensed water collector, cold side control valve, cold side A cold side circuit composed of a side circulation pump and a condensate inlet, and the condensate collector communicates with the vacuum pump through a vacuum control valve; The membrane module includes a single membrane element composed of several hollow fiber membranes, the two ends of the single membrane element are sealed by epoxy resin or polyurethane, and the single membrane element is embedded in a flanged head with an embedded groove for sealing and fixing , There is an isolation plate in the middle section of the membrane module, and the single membrane elements are separated by an isolation plate. 2. The horizontal solar membrane distillation device as claimed in claim 1, characterized in that: the single membrane element is composed of a plurality of porous hydrophobic hollow fiber membranes, and dispersed grids are used between the porous hydrophobic hollow fiber membranes dispersion. 3. The horizontal solar membrane distillation device according to claim 2, characterized in that: the material of the porous hydrophobic hollow fiber membrane is polypropylene, polyethylene or polyvinylidene fluoride. 4. The horizontal solar membrane distillation device according to claim 2 or 3, characterized in that: the inner diameter of the porous hydrophobic hollow fiber membrane is 0.1-2 mm, the outer diameter is 0.6-2.8 mm, and the wall thickness is 0.1-0.3 mm. mm, the porosity of the hollow fiber membrane wall is 50-85%, and the maximum pore diameter is 0.1-1.0 μm. 5. The horizontal solar film distillation device as claimed in claim 1, characterized in that: said single membrane element is embedded in a flanged head with an embedding groove, and the method of sealing and fixing is: embedding in the embedding groove Rubber gasket, and then squeeze the head of the single membrane element into the embedding groove.

Images