LNG freezing method seawater desalination system and process

Abstract

The invention relates to the technical field of seawater desalination, in particular to an LNG freezing method seawater desalination system and process, and the LNG freezing method seawater desalination system comprises a seawater storage tank, a filter, a precooling heat exchanger, a two-phase heat exchanger, a crystallizer, a separator and a fresh water generator, the filter is used for filtering and removing impurities such as large-particle suspended solids, silt and shell fragments in seawater, the precooling heat exchanger is used for carrying out heat exchange on the filtered seawater to obtain precooled seawater, and the two-phase heat exchanger is used for carrying out direct or indirect heat exchange on the precooled seawater and LNG (Liquefied Natural Gas) to obtain low-temperature seawater; the crystallizer stirs to promote formation of ice crystals of low-temperature seawater and high-concentration low-temperature seawater, the separator separates the ice crystals from the high-concentration low-temperature seawater, and the fresh water generator melts the ice crystals based on an external heat source to generate fresh water. According to the system, cold energy released during LNG gasification is used as energy for seawater freezing crystallization, LNG cold energy is effectively utilized, energy waste is reduced, and energy consumption and cost of fresh water production are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of seawater desalination, and particularly to an LNG freezing method seawater desalination system and process. Background Art

[0002] With the continuous optimization of the global energy structure and the deepening of the concept of sustainable development, liquefied natural gas (LNG), as a clean and efficient energy source, plays an increasingly important role in the energy supply system. However, during the process of LNG being stored in liquid form and used as gas, a large amount of valuable cold energy is released, and the effective utilization of this cold energy has become an area that urgently needs to be explored.

[0003] LNG is liquefied, stored, and gasified for use. During the gasification process of LNG, a large amount of cold energy is released. If this cold energy is not utilized, it will be directly discharged into the environment, causing energy waste. In fact, the cold energy released during the gasification of LNG is equivalent to about 80% of the energy consumed during its liquefaction process, and has high utilization value.

[0004] As the industry gradually migrates to the southern region, the demand for high-purity fresh water in the southern region has increased sharply. However, the seawater in this region requires a large amount of energy for pure water treatment, increasing production costs and energy consumption. Summary of the Invention

[0005] The purpose of the present invention is to provide an LNG freezing method seawater desalination system and process, aiming to solve the problem that seawater pure water treatment requires a large amount of energy and the production cost of enterprises is relatively high.

[0006] To achieve the above purpose, in the first aspect, the present invention provides an LNG freezing method seawater desalination system, including a seawater storage tank, a filter, a precooling heat exchanger, a two-phase heat exchanger, a crystallizer, a separator, and a fresh water generator. The seawater storage tank, the filter, the precooling heat exchanger, the two-phase heat exchanger, the crystallizer, the separator, and the fresh water generator are connected, and the separator is connected to the precooling heat exchanger;

[0007] The seawater storage tank is used for storing seawater to be cooled and desalinated;

[0008] The filter removes large particle suspended matter, sediment, and shell fragment impurities in seawater based on physical filtration;

[0009] The precooling heat exchanger performs heat exchange between the high-concentration low-temperature seawater discharged after subsequent seawater desalination separation and the filtered seawater based on a plate heat exchanger to initially reduce the seawater temperature and obtain precooled seawater;

[0010] The two-phase heat exchanger directly or indirectly exchanges heat between the precooled seawater and LNG to obtain low-temperature seawater;

[0011] The crystallizer promotes the formation of ice crystals and high-concentration low-temperature seawater in the low-temperature seawater based on the agitation of the agitation device;

[0012] The separator separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device;

[0013] The fresh water generator melts the ice crystals with an external heat source to produce fresh water.

[0014] In a second aspect, the present invention further provides an LNG freezing method for seawater desalination process, which is applied to the LNG freezing method for seawater desalination system and process as described in the first aspect above, and is characterized by including the following steps:

[0015] Introduce seawater into the seawater storage tank for storage, and draw out the seawater for pretreatment to obtain pre-cooled seawater;

[0016] The two-phase heat exchanger cools the pre-cooled seawater and promotes the formation of ice crystals and high-concentration low-temperature seawater based on the crystallizer;

[0017] The separator separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device, and the fresh water generator melts the ice crystals to generate fresh water.

[0018] Among them, the seawater storage tank has the characteristics of anti-corrosion and anti-biofouling, and is provided with a water level monitor and an automatic replenishment system.

[0019] Among them, the specific method of introducing seawater into the seawater storage tank for storage and drawing out the seawater for pretreatment to obtain pre-cooled seawater:

[0020] Introduce seawater into the seawater storage tank for storage through a pipeline or natural drainage;

[0021] Draw out the seawater, and remove large particle suspended matter, sediment and shell fragment impurities in the seawater based on physical filtration to obtain filtered seawater;

[0022] Perform water quality detection on the filtered seawater until the filtered seawater is qualified;

[0023] Based on a plate heat exchanger, perform heat exchange on the filtered seawater to initially reduce the seawater temperature to obtain pre-cooled seawater.

[0024] Among them, the specific method of the two-phase heat exchanger cooling the pre-cooled seawater and promoting the formation of ice crystals and high-concentration low-temperature seawater based on the crystallizer:

[0025] The pre-cooled seawater flows into the two-phase heat exchanger and performs direct or indirect heat exchange with LNG to obtain low-temperature seawater;

[0026] The crystallizer promotes the formation of ice crystals in low-temperature seawater and high-concentration low-temperature seawater based on the agitation of the stirring device.

[0027] Among them, the separator separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device. The specific method for the fresh water generator to melt the ice crystals to generate fresh water is as follows:

[0028] Feed the ice crystals and the high-concentration low-temperature seawater into the separator, and use centrifugation to separate the ice crystals and the high-concentration low-temperature seawater;

[0029] The fresh water generator melts the ice crystals to form fresh water based on an external heat source, and exports and collects the fresh water;

[0030] The separated high-concentration low-temperature seawater is introduced into the pre-cooling heat exchanger to pre-cool the newly incoming seawater together with the pre-cooling heat exchanger, forming a closed-loop circulation system.

[0031] A seawater desalination system using the LNG freezing method of the present invention. The seawater storage tank stores the seawater to be cooled and desalinated. The filter removes impurities such as large particulate suspensions, sediment, and shell fragments in the seawater based on physical filtration. The pre-cooling heat exchanger performs heat exchange between the high-concentration low-temperature seawater discharged from the subsequent seawater desalination separation and the filtered seawater based on a plate heat exchanger to initially reduce the seawater temperature and obtain pre-cooled seawater. The two-phase heat exchanger directly or indirectly exchanges heat between the pre-cooled seawater and LNG to obtain low-temperature seawater. The crystallizer promotes the formation of ice crystals in the low-temperature seawater and high-concentration low-temperature seawater based on the agitation of the stirring device. The separator separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device. The separated high-concentration low-temperature seawater undergoes re-heat exchange and is used to pre-cool the newly incoming seawater, forming a closed-loop circulation. The fresh water generator melts the ice crystals based on an external heat source to produce fresh water. This system uses the cold energy released during the vaporization of LNG as the energy source for seawater freezing crystallization, separates the salt from the seawater by physical methods, thereby obtaining high-purity fresh water, which can not only effectively utilize the cold energy of LNG, reduce energy waste, but also significantly reduce the energy consumption and cost of fresh water production. It solves the problem that a large amount of energy is consumed in the seawater purification process and the production cost of enterprises is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a connection schematic diagram of a seawater desalination system using the LNG freezing method provided by the present invention.

[0034] Figure 2 This is a process flow diagram of a seawater desalination process using the LNG freezing method provided by the present invention.

[0035] Figure 3 This is a specific process flow diagram for pre - treating the seawater to be cooled and desalinated in the seawater storage tank to obtain pre - cooled seawater.

[0036] Figure 4 This is a specific process flow diagram for the two - phase heat exchanger to cool the pre - cooled seawater and promote the formation of ice crystals and high - concentration low - temperature seawater based on the crystallizer.

[0037] Figure 5 This is a specific process flow diagram for the separator to separate the ice crystals and the high - concentration low - temperature seawater based on the centrifugal device, and for the fresh - water generator to melt the ice crystals to generate fresh water.

[0038] In the figure: 1 - seawater storage tank, 2 - filter, 3 - pre - cooling heat exchanger, 4 - two - phase heat exchanger, 5 - crystallizer, 6 - separator, 7 - fresh - water generator. Specific embodiments

[0039] The following details the embodiments of the present invention. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] Please refer to Figure 1 , in the first aspect, the present invention provides an LNG - freezing - method seawater desalination system, including a seawater storage tank 1, a filter 2, a pre - cooling heat exchanger 3, a two - phase heat exchanger 4, a crystallizer 5, a separator 6 and a fresh - water generator 7. The seawater storage tank 1, the filter 2, the pre - cooling heat exchanger 3, the two - phase heat exchanger 4, the crystallizer 5, the separator 6 and the fresh - water generator 7 are connected, and the separator 6 is connected to the pre - cooling heat exchanger 3;

[0041] The seawater storage tank 1 is used to store the seawater to be cooled and desalinated;

[0042] The filter 2 removes large - particle suspended solids, sediment and shell fragment impurities in the seawater based on physical filtration;

[0043] The pre - cooling heat exchanger 3 performs heat exchange between the high - concentration low - temperature seawater discharged from the subsequent seawater desalination separation and the filtered seawater based on a plate - type heat exchanger, initially reducing the seawater temperature to obtain pre - cooled seawater;

[0044] The two-phase heat exchanger 4 directly or indirectly exchanges heat between the precooled seawater and the LNG to obtain low-temperature seawater;

[0045] The crystallizer 5 promotes the formation of ice crystals and high-concentration low-temperature seawater in the low-temperature seawater based on the agitation of the stirring device;

[0046] The separator 6 separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device;

[0047] The fresh water generator 7 melts the ice crystals based on an external heat source to generate fresh water.

[0048] In an embodiment of the present invention, the seawater storage tank 1 stores seawater to be cooled and desalinated. The filter 2 removes impurities such as large particulate suspensions, sediment, and shell fragments in the seawater based on physical filtration. The precooling heat exchanger 3 exchanges heat between the high-concentration low-temperature seawater discharged after subsequent seawater desalination separation and the filtered seawater based on a plate heat exchanger to preliminarily reduce the seawater temperature and obtain precooled seawater. The two-phase heat exchanger 4 directly or indirectly exchanges heat between the precooled seawater and the LNG to obtain low-temperature seawater. The crystallizer 5 promotes the formation of ice crystals and high-concentration low-temperature seawater in the low-temperature seawater based on the agitation of the stirring device. The separator 6 separates the ice crystals and the high-concentration low-temperature seawater based on the centrifugal device. The separated high-concentration low-temperature seawater undergoes re-heat exchange and is used to precool newly incoming seawater to form a closed-loop cycle. The fresh water generator 7 melts the ice crystals based on an external heat source to generate fresh water. This system utilizes the cold energy released during the gasification of LNG as the energy source for seawater freezing and crystallization, separates the salt and water in the seawater through physical methods, thereby obtaining high-purity fresh water. It can not only effectively utilize the cold energy of LNG, reduce energy waste, but also significantly reduce the energy consumption and cost of fresh water production. It solves the problem that a large amount of energy is consumed in the seawater purification process and the production cost of enterprises is relatively high.

[0049] Please refer to Figures 2 to Figure 5 Second, the present invention also provides an LNG freezing method for seawater desalination process, which is applied to the LNG freezing method for seawater desalination system and process as described in the first aspect above, and is characterized in that it includes the following steps:

[0050] S1 Introduce seawater into the seawater storage tank 1 for storage, and draw out the seawater for pretreatment to obtain precooled seawater;

[0051] In an embodiment of the present invention, the seawater storage tank 1 has the characteristics of corrosion resistance and anti-biofouling, and is equipped with a water level monitor and an automatic replenishment system; a precise water level monitor is installed inside the seawater storage tank 1 to ensure that the seawater always remains at a safe and sufficient level, and at the same time, an automatic replenishment system is equipped to maintain a stable seawater supply.

[0052] Specific method:

[0053] S11 Introduce seawater into the seawater storage tank through a pipeline or natural drainage for storage;

[0054] In the embodiment of the present invention, seawater is introduced into the large-scale, corrosion-resistant and biofouling-resistant seawater storage tank 1 through a pipeline or natural drainage for storage.

[0055] S12 Draw out the seawater and remove large particle suspensions, sediment and shell fragment impurities in the seawater based on physical filtration to obtain filtered seawater;

[0056] In the embodiment of the present invention, the seawater in the seawater storage tank 1 is drawn out by a liquid pump or the like, and a multi-stage screen or a precision filter is used to remove impurities such as large particle suspensions, sediment and shell fragments in the seawater, preventing these impurities from damaging subsequent treatment equipment and improving the overall treatment efficiency at the same time.

[0057] S13 Perform water quality detection on the filtered seawater until the filtered seawater is qualified;

[0058] In the embodiment of the present invention, before the filtered seawater enters the next treatment stage, rapid water quality detection is carried out to ensure that the water quality meets the requirements of subsequent treatment. For example, key indicators such as pH value and turbidity need to reach the preset standards. If the detected filtered seawater does not meet the indicators, the filtration operation is continued.

[0059] S14 Perform heat exchange on the filtered seawater based on a plate heat exchanger to preliminarily reduce the seawater temperature and obtain pre-cooled seawater.

[0060] In the embodiment of the present invention, the filtered seawater is pumped to the plate heat exchanger to perform heat exchange with an external cold source (such as naturally cooled seawater, a refrigeration unit, etc.), preliminarily reducing the seawater temperature and preparing for subsequent heat exchange with LNG. This step aims to reduce energy loss in the subsequent heat exchange process and improve energy efficiency.

[0061] S2 The two-phase heat exchanger 4 cools the pre-cooled seawater and promotes the formation of ice crystals and high-concentration low-temperature seawater based on the crystallizer 5;

[0062] Specific method:

[0063] S21 The pre-cooled seawater flows into the two-phase heat exchanger 4 to perform direct or indirect heat exchange with LNG to obtain low-temperature seawater;

[0064] In the embodiment of the present invention, a large amount of cold energy released during the gasification process of LNG is used to further significantly reduce the seawater temperature to make it close to the freezing point. This process makes full use of the low-temperature resources of LNG and realizes the effective utilization of energy.

[0065] S22 crystallizer 5 promotes the formation of ice crystals and high-concentration low-temperature seawater by stirring based on the stirring device.

[0066] In the embodiment of the present invention, after the low-temperature seawater enters the crystallizer 5, the stirring device promotes the rapid formation of ice crystals from water molecules. As the number of ice crystals increases, the salt in the seawater is discharged into the remaining liquid seawater, thereby achieving the initial separation of fresh water and salt.

[0067] The S3 separator 6 separates the ice crystals and the high-concentration low-temperature seawater based on a centrifugal device, and the fresh water generator 7 melts the ice crystals to generate fresh water.

[0068] Specific method:

[0069] S31: sending the ice crystals and the high-concentration low-temperature seawater into a separator, and separating the ice crystals and the high-concentration low-temperature seawater by centrifugation;

[0070] In the embodiment of the present invention, the seawater mixture containing ice crystals enters the highly efficient centrifugal separator 6. The ice crystals with a relatively high density are effectively separated from the remaining liquid seawater by the centrifugal force.

[0071] S32 A fresh water generator melts the ice crystals based on an external heat source to form fresh water, and the fresh water is exported and collected;

[0072] In the embodiment of the present invention, the ice crystal enrichment area is sent to the fresh water generator 7 through a collection system, and in the fresh water generator 7, the ice crystals are melted by an external heat source (such as a solar heat collection system, a waste heat recovery device, etc.). As the ice crystals gradually melt, pure fresh water is collected for subsequent use.

[0073] The high-concentration, low-temperature seawater separated in S33 is introduced into the precooling heat exchanger, and precools the newly-incoming seawater together with the precooling heat exchanger to form a closed-loop circulation system.

[0074] In the embodiment of the present invention, the separated high-concentration low-temperature seawater can be used to precool the newly incoming seawater after being heat exchanged again in the precooling heat exchanger 3, forming a closed-loop circulation system, which not only reduces wastewater discharge, but also saves energy, and improves the environmental protection and economy of the entire system.

[0075] The above disclosure is only a preferred embodiment of an LNG refrigeration seawater desalination system and process of the present invention. Of course, this cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention are still within the scope of the invention.

Claims

1. An LNG freezing seawater desalination system, characterized in that it includes a seawater storage tank, a filter, a precooling heat exchanger, a two-phase heat exchanger, a crystallizer, a separator and a fresh water generator. The seawater storage tank, the filter, the precooling heat exchanger, the two-phase heat exchanger, the crystallizer, the separator and the fresh water generator are connected, and the separator is connected to the precooling heat exchanger; the seawater storage tank is used for storing seawater to be cooled and desalinated; the filter removes large particle suspended solids, sediment and shell fragment impurities in seawater based on physical filtration; the precooling heat exchanger performs heat exchange between the high-concentration low-temperature seawater discharged after subsequent seawater desalination separation and the filtered seawater based on a plate heat exchanger to preliminarily reduce the seawater temperature and obtain precooled seawater; the two-phase heat exchanger directly or indirectly exchanges heat between the precooled seawater and LNG to obtain low-temperature seawater; the crystallizer promotes the formation of ice crystals in the low-temperature seawater and high-concentration low-temperature seawater based on the stirring of a stirring device; the separator separates the ice crystals and the high-concentration low-temperature seawater based on a centrifugal device; the fresh water generator melts the ice crystals based on an external heat source to generate fresh water.

2. A seawater desalination process by LNG freezing method, applied to the LNG freezing method seawater desalination system and process as described in Claim 1, characterized in that, It includes the following steps: Import seawater into the seawater storage tank for storage, and draw out the seawater for pretreatment to obtain precooled seawater; The two-phase heat exchanger cools the precooled seawater and promotes the formation of ice crystals and high-concentration low-temperature seawater based on the crystallizer; The separator separates the ice crystals and the high-concentration low-temperature seawater based on a centrifugal device, and the fresh water generator melts the ice crystals to generate fresh water.

3. The LNG freezing seawater desalination process according to claim 2, characterized in that the seawater storage tank has the characteristics of anti-corrosion and anti-biological attachment, and is provided with a water level monitor and an automatic replenishment system.

4. The LNG freezing seawater desalination process according to claim 2, characterized in that the specific method of importing seawater into the seawater storage tank for storage and drawing out the seawater for pretreatment to obtain precooled seawater: Import seawater into the seawater storage tank for storage through a pipeline or natural drainage; Draw out the seawater, and remove large particle suspended solids, sediment and shell fragment impurities in the seawater based on physical filtration to obtain filtered seawater; Perform water quality detection on the filtered seawater until the filtered seawater is qualified; Perform heat exchange on the filtered seawater based on a plate heat exchanger to preliminarily reduce the seawater temperature and obtain precooled seawater.

5. The LNG freezing seawater desalination process according to claim 2, characterized in that the specific method of the two-phase heat exchanger cooling the precooled seawater and promoting the formation of ice crystals and high-concentration low-temperature seawater based on the crystallizer: The precooled seawater flows into the two-phase heat exchanger and directly or indirectly exchanges heat with LNG to obtain low-temperature seawater; The crystallizer promotes the formation of ice crystals in the low-temperature seawater and high-concentration low-temperature seawater based on the stirring of a stirring device.

6. The LNG freezing seawater desalination process according to claim 2, characterized in that The separator separates the ice crystals from the high-concentration low-temperature seawater based on a centrifugal device, and the fresh water generator melts the ice crystals to generate fresh water in the following specific manner: Sending the ice crystals and the high-concentration low-temperature seawater into a separator, and separating the ice crystals and the high-concentration low-temperature seawater by centrifugation; The fresh water generator melts the ice crystals to form fresh water based on an external heat source, and then conducts the fresh water for collection; The separated high-concentration and low-temperature seawater is introduced into the precooling heat exchanger, and precools the newly-incoming seawater together with the precooling heat exchanger to form a closed-loop circulation system.

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