CN102205993B - Adverse current closed type multistage seawater desalination system and method - Google Patents

Abstract

The invention relates to a countercurrent closed multi-stage seawater desalination system and method, which is characterized in that it includes a multi-stage heat exchanger in which heat exchange tubes are connected in series step by step, and the inlet of the heat exchange tube of the first stage heat exchanger passes through a seawater pump Connect the seawater inlet pipe, and the heat exchange pipe of the last heat exchanger is connected to a seawater heating device; the seawater heating device is connected to a number of spray heads installed on the top of a spray tower, and the spray tower is provided with multiple sections of packing to form a connected multiple stage spray tower, the evaporation space above each section of packing is connected to the top of the corresponding heat exchanger cylinder through the other end of a steam pipe; the bottom of the cylinder of each heat exchanger is connected in parallel to a fresh water collector The bottom of the cylinder of each heat exchanger is also pierced with a ventilation pipe, the ventilation pipe at the bottom of the subsequent heat exchanger is respectively connected to the top of the cylinder of the previous heat exchanger, and the bottom of the first heat exchanger is connected to the top of the cylinder. The ventilation pipe is connected to the lower part of the last-stage spray tower through a return pipe, and the bottom of the last-stage spray tower is connected to a spray seawater discharge pipe. The invention effectively improves the water production volume and water production efficiency of seawater desalination.

Description

A countercurrent closed multi-stage seawater desalination system and method

technical field

The invention relates to a seawater desalination system and method, in particular to a countercurrent closed multistage seawater desalination system and method.

Background technique

At present, the main methods of seawater desalination include thermal separation method, membrane method and chemical method, among which thermal separation method has higher requirements on temperature; membrane method is to obtain fresh water by pressurizing water molecules through a semi-permeable membrane. The requirements are relatively high; the chemical method uses ion exchange or hydrate formation to separate fresh water from seawater, but the power consumption is relatively high. Similarly, using the heat and mass exchange process between air and seawater and the condensation process of humid air to precipitate fresh water is also a method of desalinating seawater. In this method, on the one hand, when the air is in direct contact with water (or salt solution), heat will be transferred due to the difference in temperature, and moisture will be transferred due to the difference in partial pressure of water vapor until the temperature and water vapor are in equilibrium. . On the other hand, when the temperature of the air reaches saturation and continues to be cooled, the water vapor in the air will undergo a phase change, and the water vapor will condense into liquid water and precipitate. Due to the transfer characteristics of the above two aspects between air and water (or saline solution), air can be used to realize the "transportation" of moisture - using direct contact between air and water (or saline solution) to take away moisture, and then Moisture is obtained by condensation of water vapor in humid air. Since seawater can be regarded as a salt solution with a relatively low concentration, the direct contact between air and seawater and the condensation of humid air can be used to "transport" the water in seawater, that is, the desalination of seawater can be realized.

Devices that use air to “carry” water to desalinate seawater have appeared. For example, the Chinese patent No. ZL94216279.X discloses a low-temperature seawater desalination device, which uses heated air to contact seawater to make The moisture content increases, and the humidified air is condensed to obtain fresh water. The device heats the air instead of the sea water, which will limit the heat and mass exchange process in which the air and sea water are in direct contact, and cannot achieve the optimal heat and mass exchange effect. The Chinese patent No. ZL200610111779.X discloses a temperature difference seawater desalinator, which is designed according to the difference in the partial pressure of saturated water vapor in the air at different temperatures, using air to obtain water from seawater at high temperatures and A device for separating out pure water. The limitation of this device is that the contact area of the atomization chamber where the air and sea water directly contact is limited, and the heat and mass exchange process between the air and sea water cannot be fully carried out. The Chinese patent No. ZL200310107193.2 discloses a spray heat exchange type seawater desalination machine, which uses a heat pump condenser to heat seawater, and the moisture content of the air increases after contacting with high-temperature seawater, and the humid air is then mixed with the side of the heat pump evaporator. Exposure to precipitation of fresh water. The limitation of this device is that the air is an open cycle, and the low-temperature saturated air after the moisture is separated is not used. The Chinese patent No. ZL200620078403.9 discloses a closed-type solar or low-temperature heat source seawater desalination device (as shown in Figure 4). The air and the heated seawater exchange heat and mass in the spraying device. The air enters the condensing device to precipitate fresh water, and the air is a closed cycle. In this device, the contact form between the air and the high-temperature seawater spraying process is a cross-flow flow pattern, which limits the effect of heat and mass exchange between the air and seawater.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a countercurrent closed multi-stage seawater desalination system and method that has high freshwater recovery efficiency and can realize heat mass exchange and heat exchange process matching between air and seawater to a large extent.

In order to achieve the above object, the present invention adopts the following technical solutions: a countercurrent closed multi-stage seawater desalination system, characterized in that it includes a multi-stage heat exchanger in which heat exchange tubes are connected in series step by step, and the heat exchanger in the first stage The inlet of the heat exchange tube is connected to the sea water inlet pipe through a sea water pump, and the heat exchange tube of the heat exchanger in the last stage is connected to a sea water heating device; Shower head, the spray tower is provided with multiple sections of packing to form a connected multi-stage spray tower, the evaporation space above the packing of each section is respectively connected to a steam pipe, and the other end of each of the steam pipes is respectively connected to a corresponding The top of the cylinder of the heat exchanger; the bottom of the cylinder of each stage of the heat exchanger is respectively connected to a fresh water collection pipe in parallel through pipelines, and the bottom of the cylinder of each stage of the heat exchanger is also respectively pierced A ventilation pipe, the air inlet end of each stage of the ventilation pipe is higher than the bottom of the cylinder body of the stage, and the ventilation pipe at the bottom of the heat exchanger of the next stage is respectively connected to the cylinder of the heat exchanger of the previous stage At the top of the body, the ventilation pipe at the bottom of the first-stage heat exchanger is connected to the lower part of the last-stage spray tower through a return pipe, and the bottom of the last-stage spray tower is connected to a spray seawater discharge pipe.

A regulating valve is arranged between the spray seawater discharge pipe and the seawater inlet pipe.

The seawater heating device is a solar heat collecting device.

The seawater heating device is a heat pump circulation system.

The condenser of the heat pump cycle system is arranged on the pipeline between the water outlet of the heat exchange tube of the last stage heat exchanger and the water inlet of the first stage spray tower, and the evaporator of the heat pump cycle system is passed through A throttle valve is arranged on the discharge pipe of the sprayed seawater, a compressor is arranged on the pipeline between the evaporator and the condenser, and an expansion valve is arranged on the pipeline between the condenser and the evaporator.

The condenser of the heat pump cycle system is set on the pipeline between the water outlet of the heat exchanger tube of the last stage and the water inlet of the first stage spray tower, and the evaporator of the heat pump cycle system is set on On the return air pipe, and the bottom of the evaporator is connected to the fresh water collection pipe through a pipeline; a compressor is arranged on the pipeline between the evaporator and the condenser, and the pipeline between the condenser and the evaporator An expansion valve is arranged on the pipeline.

A counter-current closed multi-stage seawater desalination method using the above-mentioned device, characterized in that: a spray tower for heat and mass exchange in direct contact between multi-stage seawater and air and a heat exchanger for non-direct contact between multi-stage seawater and air are provided, and the high temperature Seawater and low-temperature air flow countercurrently in the spray tower for heat and mass transfer. After the heat and mass exchange, the temperature and moisture content of the air increase, and then enter the heat exchanger for countercurrent heat exchange with seawater. Part of the water vapor in the air condenses Precipitate to obtain fresh water, and the air after heat exchange enters the spray tower again to complete the closed cycle process of air. After the seawater flows out of the heat exchanger, it is heated by the heating device and then enters the spray tower for spraying.

The part of the seawater flowing out from the spray tower flows into the heat exchanger again, and continues to participate in the circulation desalination process of seawater.

Use solar energy as a seawater heating device.

The condenser of the heat pump circulation system is used to heat the seawater, and the evaporator of the heat pump circulation system is used to cool the seawater flowing out of the spray tower or the low-temperature saturated air flowing out of the heat exchanger.

Because the present invention adopts the above technical scheme, it has the following advantages: 1. Since the air and sea water in the present invention adopt a countercurrent mode for heat and mass exchange and heat exchange in the spray tower and heat exchanger, and the air adopts a closed type in the system at the same time. Circulation process, so better heat and mass transfer effects can be achieved. 2. Since the present invention cleverly arranges multi-stage spray towers and heat exchangers in the circulation process, the heat capacity matching between humid air and seawater can be realized as much as possible by changing the air flow in different heat exchangers or spray towers , for example: when the humid air temperature in a spray tower or heat exchanger of a certain level is high, its equivalent specific heat capacity is large, and the flow rate of the air can be correspondingly small; when the humid air in a certain spray tower or heat exchanger When the temperature of the humid air is low, its equivalent specific heat capacity is small, and the flow rate of the air can be correspondingly large. 3. Due to the multi-stage air-sea water spray tower and heat exchanger setting of the present invention, which changes the air flow step by step, the heat capacity matching of the heat mass exchange process and the heat exchange process between air and sea water can be realized as much as possible, so The invention achieves better heat and mass transfer effect, and effectively improves the water production rate and water production efficiency of seawater desalination.

Description of drawings

Fig. 1 is the structural representation of embodiment 1 of the present invention

Fig. 2 is the structural representation of embodiment 2 of the present invention

Fig. 3 is the structural representation of embodiment 3 of the present invention

Fig. 4 is a schematic diagram of prior art structure

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The design principle of the present invention is embodied in: at first multi-stage independent air-sea water spray tower (hereinafter referred to as spray tower) and multi-stage air-sea water heat exchanger (hereinafter referred to as heat exchanger) are arranged, utilize sea water and air The countercurrent heat and mass exchange process in the spray tower and the countercurrent heat exchange process in the heat exchanger are used to prepare fresh water. Secondly, if the temperature of seawater is higher (such as 80°C) when it is sprayed from the spray tower inlet, and the temperature is lower (such as 20°C) when it reaches the heat exchanger inlet, that is, the water temperature changes greatly, then the temperature range of the air will also vary. When the air temperature changes greatly, the specific heat capacity of seawater does not change much, but the equivalent specific heat capacity of hot and humid air will change greatly. When the temperature is high, the equivalent specific heat capacity of hot and humid air is large, and when the temperature is low The equivalent specific heat capacity of the air is small; the present invention utilizes the principle that the seawater flow rate in the spray tower and heat exchanger is basically constant in the circulation process, but the air flow rate is different in different levels of spray towers and heat exchangers. Realize the matching of heat capacity between air and seawater in the process of heat and mass exchange and heat exchange process, so as to obtain better heat and mass exchange or heat exchange effect between air and seawater, and then improve the efficiency of seawater desalination. The following is only an example of a system with three-stage heat exchangers and three-stage spray towers. In an actual multi-stage seawater desalination system, the number of stages of heat exchangers and spray towers can be changed. .

Example 1:

As shown in Figure 1, this embodiment includes a first-stage heat exchanger 1, a second-stage heat exchanger 2 and a third-stage heat exchanger 3, as well as a first-stage spray tower 4 and a second-stage spray tower 5 And the third stage spray tower 6. The heat exchange tubes of the three-stage heat exchangers 1, 2, and 3 are connected in series, and the inlet of the heat exchange tubes of the first-stage heat exchanger 1 is connected to a seawater inlet pipe 7, and a seawater pump 8 is arranged on the seawater inlet pipe 7; The outlet of the heat exchange tube of the heater 3 is connected to a solar heat collector 9 through a pipeline, and the outlet of the solar heat collector 9 is connected to a plurality of spray heads 10 arranged on the top of the first-stage spray tower 4 through a pipeline. The three-stage spray towers 4, 5, and 6 are connected. Each stage of the spray tower is provided with a section of packing 11. There is an evaporation space above the three-stage packing 11. Each evaporation space is connected to a steam pipe 12. The other ends of the three steam pipes 12 of the three-stage spray towers 4, 5, 6 are respectively connected to the cylinder tops of the heat exchangers 3, 2, 1 arranged in corresponding positions. The cylinder bottoms of the three-stage heat exchangers 1, 2, and 3 are respectively connected in parallel with a fresh water collection pipe 13 through a pipeline, and the fresh water collection pipe 13 is connected with a fresh water collection container (not shown in the figure). The bottoms of the three-stage heat exchangers 1, 2, and 3 are respectively pierced with a ventilation pipe, and the inlet end of each ventilation pipe protrudes from the bottom of the cylinder at a certain height, so that only the gas can enter, and the desalinated water cannot. Enter. The ventilation pipes at the bottom of the third and second stage heat exchangers 3 and 2 are respectively connected to the cylinder tops of the next stage heat exchangers 2 and 1, and the ventilation pipes at the bottom of the first stage heat exchanger 1 are connected to the first stage through a return pipe 14. The bottom of the third-stage spray tower 6 is connected to a spray seawater discharge pipe 15 at the bottom of the third-stage spray tower 6 .

In the above-mentioned embodiment, since the seawater entering the system of the present invention requires some preliminary treatment, in order to save the cost of the preliminary treatment, a part of the seawater flowing out of the spray seawater discharge pipe 15 can be sent back to the seawater inlet pipe 7 through a regulating valve 16 Continue to participate in the circulation process of desalination and extraction, and the specific amount of seawater entering the system circulation can be adjusted according to needs. In addition, the fillers of the present invention are common structured fillers, which can be wetted by the high-temperature seawater sprayed from the sprinkler head 10, effectively increasing the heat and mass transfer area between the low-temperature saturated air and the high-temperature seawater.

When this embodiment is working, the low-temperature seawater entering the seawater inlet pipe 7 through the seawater pump 8 flows upward through the heat exchange tubes of the three-stage heat exchangers 1, 2, and 3 connected in series and enters the solar heat collector 9, and simultaneously enters each The hot and humid air moving downwards in the cylinders of stage heat exchangers 1, 2, and 3 performs countercurrent heat exchange; The shower head 10 sprays out, passes through the three-stage spray towers 4, 5, and 6 successively, and flows out from the spray sea discharge pipe 15 at the bottom of the third-stage spray tower 6. , 4 The low-temperature saturated air flowing upwards from the lower part performs counter-flow heat and mass transfer exchange; the hot steam enters the cylinders of the corresponding heat exchangers 3, 2, and 1 through the steam pipes 12, and condenses after exchanging heat with seawater in the heat exchange pipes Become fresh water, enter the fresh water collection pipe 13 by the loop and then flow into the fresh water collection container. The steam that is not condensed into water in the third and second stage heat exchangers 3 and 2 enters the next heat exchanger 2 and 1 successively through the vent pipe, and finally flows into the return pipe 14 from the bottom of the first stage heat exchanger 1 Get back in the third stage spray tower 6, continue to carry out closed circulation in the system. A part of the sprayed seawater flowing out from the sprayed seawater discharge pipe 15 can return to the seawater inlet pipe 7 through the regulating valve 16 and continue to circulate in the system.

Example 2:

As shown in FIG. 2 , the basic configuration of this embodiment is the same as that of Embodiment 1, except that the seawater heating device is different, and a conventional heat pump circulation system 20 is provided to replace the solar heating system 9 . The heat pump circulation system 20 includes: a condenser 21 arranged on the pipeline between the water outlet of the heat exchange tube of the third stage heat exchanger 3 and the water inlet of the first stage spray tower 4, and arranged on the spray seawater discharge pipe 15 An evaporator 22 on the top, a compressor 22 is arranged on the pipeline between the evaporator 21 and the condenser 23, and an expansion valve 24 is arranged on the pipeline between the condenser 21 and the evaporator 22.

When this embodiment is working, the two countercurrent heat exchange processes are the same as in Embodiment 1, the difference is that: the seawater flowing out from the water outlet of the third-stage heat exchanger 3 heat exchange tubes enters the condenser 21 and passes through the condenser 21 The refrigerating medium inside is heated by exothermic heat, and then enters the shower head 10 of the first-stage shower 4; at the same time, the spray water flowing out from the third-stage shower 6 passes through a throttle valve (not shown in the figure) part of the seawater is directly discharged through the pipeline, and the other part of seawater flows through the evaporator 22, and after being cooled by the refrigerant in the evaporator 22, it enters the seawater inlet pipe through the spray seawater discharge pipe 15 and the regulating valve 16 7 to participate in the system cycle.

Example 3:

As shown in Figure 3, this embodiment is basically the same as Embodiment 2, and a set of conventional heat pump circulation system 20 is also provided. It differs from Embodiment 2 in that: the evaporator 22 is not arranged on the spray seawater discharge pipe 15 Instead, it is arranged on the return pipe 14 between the bottom of the first-stage heat exchanger 1 and the lower part of the third-stage spray tower 6 , and is connected to the fresh water collection pipe 13 in parallel at the bottom of the evaporator 22 through a pipeline.

When this embodiment works, the difference from Embodiment 2 is that the evaporator 22 absorbs the heat from the low-temperature hot and humid air entering the third-stage spray tower 6 from the first-stage heat exchanger 1 .

It can be seen from the above three embodiments: Embodiment 1 uses solar energy as a seawater heating device, which is more suitable for occasions where the solar energy supply is sufficient. And embodiment 2,3 is to utilize the condenser in the conventional heat pump cycle system as seawater heating device, and it is more suitable for the solar energy supply not sufficient enough, and the occasion that industrial waste heat can be utilized, thus provides more for the implementation of the present invention Of course, the present invention does not exclude other possible ways, and the proposal of these ways should not be excluded from the protection scope of the present invention.

Above-mentioned each embodiment is only for illustrating the present invention, wherein the structure of each component, connection mode etc. all can be changed to some extent, every equivalent conversion and improvement carried out on the basis of the technical solution of the present invention, all should not be excluded from the present invention. outside the scope of protection of the invention.

Claims (9)

1. A countercurrent closed multistage seawater desalination system is characterized in that: it comprises a multistage heat exchanger in which heat exchange tubes are connected in series step by step, and the inlet of the heat exchanger heat exchange tubes of the first stage is connected by a seawater pump The seawater inlet pipe, the heat exchange pipe of the heat exchanger in the last stage is connected to a seawater heating device; the seawater heating device is connected to a number of spray heads installed on the top of a spray tower through pipelines, and the spray tower is installed There are multiple stages of packing forming a connected multi-stage spray tower, the evaporation space above the packing of each stage is respectively connected to a steam pipe, and the other end of each of the vapor pipes is respectively connected to the top of a corresponding cylinder of the heat exchanger The bottom of the cylinder of each stage of the heat exchanger is respectively connected to a fresh water collection pipe in parallel through pipelines, and the bottom of the cylinder of the heat exchanger of each stage is also respectively pierced with a ventilation pipe, and the ventilation pipe of each stage is The inlet ends of the cylinders are all higher than the bottom of the cylinder of this stage, and the ventilation pipes at the bottom of the heat exchanger in the latter stage are respectively connected to the top of the cylinder of the heat exchanger in the previous stage, and the bottom of the heat exchanger in the first stage The vent pipe of the last stage is connected to the lower part of the last-stage spray tower through a return pipe, and the bottom of the last-stage spray tower is connected to a spray seawater discharge pipe. 2. A countercurrent closed multi-stage seawater desalination system according to claim 1, characterized in that: a regulating valve is arranged between the spray seawater discharge pipe and the seawater inlet pipe. 3. A countercurrent closed multi-stage seawater desalination system according to claim 1 or 2, characterized in that the seawater heating device is a solar heat collection device. 4. A countercurrent closed multi-stage seawater desalination system according to claim 1 or 2, characterized in that the seawater heating device is a heat pump circulation system. 5. A countercurrent closed multi-stage seawater desalination system as claimed in claim 4, characterized in that: the condenser of the heat pump circulation system is arranged between the water outlet of the heat exchange tube of the heat exchanger in the last stage On the pipeline between the water inlets of the first-stage spray tower, the evaporator of the heat pump circulation system is arranged on the discharge pipe of the sprayed seawater through a throttle valve, and the evaporator to the condenser A compressor is arranged on the pipeline, and an expansion valve is arranged on the pipeline between the condenser and the evaporator. 6. A countercurrent closed multi-stage seawater desalination system as claimed in claim 4, characterized in that: the condenser of the heat pump circulation system is arranged between the water outlet of the heat exchange tube of the heat exchanger in the last stage On the pipeline between the water inlets of the first-stage spray tower, the evaporator of the heat pump circulation system is arranged on the return pipe, and the bottom of the evaporator is connected to the fresh water collection pipe through a pipeline; the evaporator A compressor is arranged on the pipeline between the condenser and the condenser, and an expansion valve is arranged on the pipeline between the condenser and the evaporator. 7. Adopt a kind of countercurrent closed multistage seawater desalination method of the device as claimed in claim 1 or 2, it is characterized in that: the spray tower and the multistage seawater and air that the direct contact of multistage seawater and air carry out heat and mass exchange are set In the heat exchanger without direct contact, high-temperature seawater and low-temperature air flow countercurrently in the spray tower for heat and mass transfer. After the air undergoes heat and mass exchange, the temperature and moisture content increase, and then enters the heat exchanger for countercurrent flow with seawater. Heat exchange, part of the water vapor in the air condenses and precipitates to obtain fresh water, and the air after heat exchange enters the spray tower again to complete the closed air circulation process. After the seawater flows out of the heat exchanger, it is heated by the heating device and then enters the spray tower spray. 8. A countercurrent closed multi-stage seawater desalination method according to claim 7, characterized in that: part of the seawater flowing out of the spray tower flows into the heat exchanger again to continue to participate in the seawater desalination process. 9. A countercurrent closed multi-stage seawater desalination method as claimed in claim 7, characterized in that: solar energy is used as seawater heating device.

Images