阅读说明：本技术 一种海水淡化装置的清洗方法 (Cleaning method of seawater desalination device ) 是由 王丰 李会作 于 2021-01-15 设计创作，主要内容包括：本发明公开一种海水淡化装置的清洗方法,海水淡化装置包括n效蒸发器,盐水泵和海水增压泵,n效蒸发器中的各效蒸发器中均设置有海水喷淋管道以及与海水喷淋管道喷出的液体连通的浓盐水管道,清洗方法包括：向第二效蒸发器至第n效蒸发器中的两个相邻蒸发器之间的浓盐水管道中注入酸洗溶液,使酸洗溶液依次流经盐水泵和海水增压泵,然后分别通过海水喷淋管道被喷淋到第二效蒸发器至第n效蒸发器中,使酸洗溶液与第二效蒸发器至第n效蒸发器中的换热管外壁接触。海水淡化装置的清洗方法有可有效清除海水淡化装置中蒸发器盐水侧的换热管、换热管管板和蒸发器内壁上的水垢,取得了良好的清洗效果,大幅提高了海水淡化造水比。(The invention discloses a cleaning method of a seawater desalination device, the seawater desalination device comprises n-effect evaporators, a brine pump and a seawater booster pump, each effect evaporator in the n-effect evaporators is provided with a seawater spray pipeline and a strong brine pipeline communicated with liquid sprayed out from the seawater spray pipeline, and the cleaning method comprises the following steps: and injecting a pickling solution into a strong brine pipeline between two adjacent evaporators of the second-effect evaporator to the nth-effect evaporator, enabling the pickling solution to sequentially flow through a brine pump and a seawater booster pump, and then respectively spraying the pickling solution into the second-effect evaporator to the nth-effect evaporator through a seawater spraying pipeline, so that the pickling solution is in contact with the outer walls of the heat exchange tubes of the second-effect evaporator to the nth-effect evaporator. The cleaning method of the seawater desalination device can effectively remove scales on the heat exchange tube, the heat exchange tube plate and the inner wall of the evaporator on the brine side of the evaporator in the seawater desalination device, obtains good cleaning effect and greatly improves the seawater desalination and water production ratio.)

1. A cleaning method of a seawater desalination device is characterized in that the seawater desalination device comprises n-effect evaporators, a brine pump and a seawater booster pump, wherein each effect evaporator in the n-effect evaporators is provided with a seawater spray pipeline and is provided with a strong brine pipeline communicated with liquid sprayed out from the seawater spray pipeline, all strong brine pipelines are communicated in sequence, n is a natural number not less than 3, and the cleaning method comprises the following steps:

enabling a strong brine pipeline between the first effect evaporator and the second effect evaporator to be in a disconnected state, and enabling a seawater spraying pipeline of the first effect evaporator and a seawater spraying pipeline of the second effect evaporator to be in a disconnected state; simultaneously enabling the strong brine pipelines of all the evaporators from the second effect evaporator to the nth effect evaporator to be in a communicated state and the seawater spraying pipelines of all the evaporators from the second effect evaporator to the nth effect evaporator to be in a communicated state, so that the strong brine pipelines of all the effect evaporators from the second effect evaporator to the nth effect evaporator, the seawater spraying pipelines of all the effect evaporators from the second effect evaporator to the nth effect evaporator, the brine pump and the seawater booster pump form an acid washing loop;

and injecting a pickling solution into a strong brine pipeline between a first group of two adjacent evaporators in the second-effect evaporator to the nth-effect evaporator, enabling the pickling solution to sequentially flow through a brine pump and a seawater booster pump, and then respectively spraying the pickling solution into the second-effect evaporator to the nth-effect evaporator through a seawater spraying pipeline, so that the pickling solution is in contact with the outer walls of the heat exchange tubes in the second-effect evaporator to the nth-effect evaporator.

2. The cleaning method according to claim 1, wherein an acid pickling solution is injected into a concentrated brine pipe between a first group of two adjacent evaporators of the second-effect evaporator to the nth-effect evaporator by a first acid injection pump;

the first acid injection pump is arranged at the bottom of the concentrated brine pipeline between the first group of two adjacent evaporators.

3. The cleaning method according to claim 1, wherein when the calcium ion concentration in the pickling solution is less than or equal to a set value, the pickling solution is discharged through a first acid discharge pipe provided at the bottom of a concentrated brine pipe between a second group of two adjacent evaporators among a second to n-th effect evaporators; and is

And when the concentration of calcium ions in the pickling solution is greater than a set value, replacing the pickling solution in the pickling loop.

4. The cleaning method according to claim 1, further comprising:

injecting a pickling solution into a seawater spraying pipeline in the first effect evaporator through a second acid injection pump, so that the pickling solution is in contact with the outer wall of a heat exchange pipe in the first effect evaporator;

controlling the flow rate of the second acid injection pump to be 250-300m when injecting the acid washing solution³/h。

5. The cleaning method according to claim 4, wherein when the calcium ion concentration in the pickling solution is greater than a set value, a second acid injection pump is used for continuously injecting the pickling solution into the seawater spraying pipeline in the first effect evaporator, and the pickling solution is discharged from a second acid discharge pipeline after contacting with the outer wall of the heat exchange pipe in the first effect evaporator;

the second acid discharge pipeline is arranged at the bottom of the concentrated brine pipeline between the first effect evaporator and the second effect evaporator.

6. The cleaning method according to claim 1, wherein an overflowing device is further arranged between the seawater booster pump and the seawater spraying pipelines of all the second-effect evaporators to the nth-effect evaporators, and the pickling solution enters the seawater spraying pipelines of all the second-effect evaporators to the nth-effect evaporators through the overflowing device.

7. The cleaning method according to claim 6, wherein the overflowing device comprises a heater and/or a condenser;

the number of the heaters is 1-3,

the number of the condensers is 1-3.

8. The cleaning method according to claim 1, wherein a solution containing a corrosion inhibitor and an antifoaming agent is injected into a strong brine pipe between a first group of two adjacent evaporators of a second effect evaporator to an nth effect evaporator for pre-corrosion inhibition before injecting a pickling solution into the strong brine pipe between the first group of two adjacent evaporators;

wherein in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%.

9. The cleaning method according to claim 4, wherein before injecting the pickling solution into the seawater spray piping in the first effect evaporator, a solution containing a corrosion inhibitor and an antifoaming agent is injected into the seawater spray piping in the first effect evaporator to perform pre-corrosion inhibition;

wherein in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%.

10. The cleaning method according to claim 1, wherein the pickling solution comprises the following components in percentage by mass:

1-3% of a pickling agent;

0.05-0.15% of iso-VC sodium.

Technical Field

The application relates to the technical field of seawater desalination, in particular to a cleaning method of a seawater desalination device.

Background

The sea water desalting low temperature multiple effect distillation (LT-MED) technology is characterized by that under the condition of vacuum the highest evaporation temperature of salt water is lower than 70 deg.C, and is characterized by that a series of horizontal pipe spray falling-film evaporators are series-connected, and a certain quantity of steam is used to make it undergo the processes of several times of evaporation and condensation, and the evaporation temperature of the latter effect is lower than that of the former effect so as to obtain the desalting process [1] of distilled water whose quantity is several times of that of steam. Compared with the multistage flash distillation seawater desalination technology, the operation temperature is lower, the scaling tendency is slowed down to a certain extent, but scaling cannot be completely avoided. Because the heat conductivity coefficient of the dirt is extremely low, the heat transfer performance of the heat exchange tube of the seawater desalination evaporator can be seriously influenced by the scaling, the water production ratio is greatly reduced, and more seriously, the scaling can cause under-scale corrosion, perforation leakage of the heat exchange tube and influence the quality of the desalinated water.

After the low-temperature multi-effect distillation seawater desalination device operates for several years, the tube bundle in the evaporator can be scaled, and the heat exchange efficiency of the evaporator tends to be reduced. Because the surface of the heat exchange tube of the evaporator is scaled, the heat conductivity coefficient of the scale is far smaller than that of the metal copper, so that the heat exchange rate is reduced, the flow speed of the brine is reduced, the temperature of the brine is increased, the condition is more obvious at the middle part of the tube bundle, and when the temperature of the local brine exceeds 70 ℃, the scaling tendency of the calcium carbonate is greatly improved. The scale deposit still can cause the under-deposit of copper pipe to corrode, because there is chloride ion in the sea water, remains in the incrustation scale of salt solution side to have a small amount of chloride ion, when the heat exchange tube is full of the scale around after, the pipe wall is no longer heat transfer, and pipe wall temperature can greatly increased, and remaining chloride ion can local concentration under high temperature, and then induces the dezincification corruption of aluminium brass heat exchange tube.

Through the total analysis of the scale formation sample of the heat exchange tube at the bottom of the evaporator main body, the carbonate scale of calcium and magnesium formed by the aluminum brass tube accounts for more than 90%, the sulfate scale is less than 5%, and the silicate is also less than 5%, and from the dissolution condition of the scale, the silicate mainly exists in a dispersed sand grain form.

Acid washing is the most effective cleaning process for removing oxide layers and dirt on metal surfaces. However, the number of large-scale low-temperature multi-effect distillation seawater desalination devices in China is small, and the seawater desalination devices face a plurality of technical difficulties such as a plurality of metal types, complex scale components, thin heat exchange tube walls, large cleaning areas, special contact modes of acid washing solution and metal and the like in the chemical cleaning process of an evaporator, so that an effective cleaning method is not available at present for the difficulty in cleaning the scale on the heat exchange tube, the heat exchange tube plate and the inner wall of the evaporator on the brine side of the evaporator in the seawater desalination device.

Therefore, there is a need for a cleaning method that can effectively remove scale on the heat exchange tube plate of the evaporator and the inner wall of the evaporator in a seawater desalination plant.

Disclosure of Invention

The invention discloses a cleaning method of a seawater desalination device, which aims to solve the technical problem that in the prior art, scale on a heat exchange tube, a heat exchange tube plate and the inner wall of an evaporator on the brine side of the evaporator is difficult to clean.

In order to solve the problems, the invention adopts the following technical scheme:

according to an embodiment of the application, a cleaning method of a seawater desalination device is provided, the seawater desalination device comprises n-effect evaporators, a brine pump and a seawater booster pump, each effect evaporator in the n-effect evaporators is provided with a seawater spray pipeline and is provided with a strong brine pipeline communicated with liquid sprayed out from the seawater spray pipeline, all strong brine pipelines are communicated in sequence, wherein n is a natural number not less than 3, and the cleaning method comprises the following steps:

enabling a strong brine pipeline between the first effect evaporator and the second effect evaporator to be in a disconnected state, and enabling a seawater spraying pipeline of the first effect evaporator and a seawater spraying pipeline of the second effect evaporator to be in a disconnected state; simultaneously enabling the strong brine pipelines of all the evaporators from the second effect evaporator to the nth effect evaporator to be in a communicated state and the seawater spraying pipelines of all the evaporators from the second effect evaporator to the nth effect evaporator to be in a communicated state, so that the strong brine pipelines of all the effect evaporators from the second effect evaporator to the nth effect evaporator, the seawater spraying pipelines of all the effect evaporators from the second effect evaporator to the nth effect evaporator, the brine pump and the seawater booster pump form an acid washing loop;

and injecting a pickling solution into a strong brine pipeline between a first group of two adjacent evaporators in the second-effect evaporator to the nth-effect evaporator, enabling the pickling solution to sequentially flow through a brine pump and a seawater booster pump, and then respectively spraying the pickling solution into the second-effect evaporator to the nth-effect evaporator through a seawater spraying pipeline, so that the pickling solution is in contact with the outer walls of the heat exchange tubes in the second-effect evaporator to the nth-effect evaporator.

Optionally, injecting an acid washing solution into a concentrated brine pipeline between a first group of two adjacent evaporators in the second-effect evaporator to the nth-effect evaporator through a first acid injection pump; the first acid injection pump is arranged at the bottom of the concentrated brine pipeline between the first group of two adjacent evaporators.

Optionally, when the calcium ion concentration in the pickling solution is less than or equal to a set value, discharging the pickling solution through a first acid discharge pipeline, wherein the first acid discharge pipeline is arranged at the bottom of a concentrated brine pipeline between a second group of two adjacent evaporators in the second-effect evaporator to the nth-effect evaporator; and when the concentration of calcium ions in the pickling solution is greater than a set value, replacing the pickling solution in the pickling loop.

Optionally, the method further comprises: injecting a pickling solution into a seawater spraying pipeline in the first effect evaporator through a second acid injection pump, so that the pickling solution is in contact with the outer wall of a heat exchange pipe in the first effect evaporator; controlling the flow rate of the second acid injection pump to be 250-300m when injecting the acid washing solution³/h。

Optionally, when the concentration of calcium ions in the pickling solution is greater than a set value, continuously injecting the pickling solution into the seawater spraying pipeline in the first effect evaporator through a second acid injection pump, wherein the pickling solution is discharged from a second acid discharge pipeline after contacting with the outer wall of the heat exchange pipe in the first effect evaporator; the second acid discharge pipeline is arranged at the bottom of the concentrated brine pipeline between the first effect evaporator and the second effect evaporator.

Optionally, an overflowing device is further arranged between the seawater booster pump and the seawater spraying pipelines of all the evaporators from the second-effect evaporator to the nth-effect evaporator, and the pickling solution enters the seawater spraying pipelines of all the evaporators from the second-effect evaporator to the nth-effect evaporator through the overflowing device.

Optionally, the over-current device comprises a heater and/or a condenser; the number of the heaters is 1-3, and the number of the condensers is 1-3.

Optionally, injecting a solution containing a corrosion inhibitor and an antifoaming agent into a strong brine pipeline between a first group of two adjacent evaporators of the second-effect evaporator to the nth-effect evaporator for pre-corrosion inhibition before injecting a pickling solution into the strong brine pipeline between the first group of two adjacent evaporators; wherein in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%.

Optionally, before injecting a pickling solution into the seawater spraying pipeline in the first-effect evaporator, injecting a solution containing a corrosion inhibitor and an antifoaming agent into the seawater spraying pipeline in the first-effect evaporator to perform pre-corrosion inhibition; wherein in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%.

Optionally, the acid washing solution comprises the following components in percentage by mass: 1-3% of a pickling agent; 0.05-0.15% of iso-VC sodium.

Optionally, the corrosion inhibitor is a copper slow-release agent and/or a steel slow-release agent; the copper slow release agent is selected from benzotriazole or methyl benzotriazole; the steel corrosion inhibitor is selected from at least one of thiourea, cinnamaldehyde, triphenylphosphine or tetraphenylphosphine; the defoaming agent is at least one selected from ethanol, emulsified silicone oil, polyoxyethylene polyoxypropylene pentaerythritol ether and polyoxypropylene.

Optionally, the acid wash is sulfamic acid or hydrochloric acid.

The technical scheme adopted by the invention can achieve the following beneficial effects:

the cleaning method of the seawater desalination device provided by the invention can effectively remove scales on the heat exchange tube, the heat exchange tube plate and the inner wall of the evaporator on the brine side of the evaporator in the seawater desalination device, obtains good cleaning effect, greatly improves the seawater desalination and water production ratio, and provides an effective solution for the scaling problem of the heat exchange tube of the evaporator of the low-temperature multi-effect distillation seawater desalination device.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic structural diagram of a seawater desalination plant according to the present invention;

FIG. 2 is a comparison of the water generation ratio before and after chemical cleaning of the seawater desalination apparatus according to the present invention.

Description of reference numerals:

1 first acid injection pump

2 second acid injection pump

3 seawater booster pump

4-salt water pump

5 strong brine pipeline

6 seawater spray pipeline

7 nine-effect regenerative heater

8 seven-effect regenerative heater

9 four-effect regenerative heater

10 three-stage injection condenser

11 two-stage injection condenser

12 first-stage injection condenser

13 first exhaust pipeline

14 second acid discharge pipeline

15 condensed water cooler

16 first valve

17 second valve

18 third valve

19 fourth valve

20 second effect evaporator concentrated brine pipeline inlet side flange

21 material water to first effect evaporator flowmeter water inlet side flange

22 material water to condensate water cooler pipeline flange

23 brine pump inlet pipe

24 brine pump to material water bypass pipe

25 first aeration tank

26 second aeration tank

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The technical solutions disclosed in the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

As shown in fig. 1, according to an embodiment of the present application, a method for cleaning a seawater desalination apparatus is provided, the seawater desalination apparatus includes n-effect evaporators, a brine pump 4 and a seawater booster pump 3, each of the n-effect evaporators is provided with a seawater spray pipe 6 and has a concentrated brine pipe 5 connected to a liquid sprayed from the seawater spray pipe, and all the concentrated brine pipes 5 are connected in sequence, where n is a natural number greater than or equal to 3, for example, 3 is greater than or equal to n is less than or equal to 100. In order to more clearly explain the technical scheme of the present application, the present application is described in detail below by taking an example of a low-temperature multi-effect distilled seawater desalination device comprising a ten-effect evaporator, wherein n is 10.

In the present invention, the material water refers to water inside the seawater desalination plant during normal operation, and the pickling solution refers to a pickling agent composition diluted with a solvent, for example, a solution formed by mixing the material water with the pickling agent composition of the present invention is a pickling solution.

In the present application, the inventors realized that the first effect evaporator of the low temperature multi-effect distillation seawater desalination plant is different in the amount of fouling from the remaining second to tenth effect evaporators, thus dividing the entire acid wash into two parts: acid pickling of the heat exchange tubes of the first-effect evaporator and acid pickling of the heat exchange tubes of the second-effect evaporator to the tenth-effect evaporator. It should be understood by those skilled in the art that the acid washing sequence of the first effect evaporator heat exchange tube and the second to tenth effect evaporator heat exchange tubes can be flexibly determined according to actual needs, for example, the second to tenth effect evaporator heat exchange tubes can be acid washed while the first effect evaporator heat exchange tube is acid washed, or the first effect evaporator heat exchange tube can be acid washed first and then the second to tenth effect evaporator heat exchange tubes can be acid washed, and vice versa.

In one embodiment of the application, the cleaning method of the low-temperature multi-effect distillation seawater desalination device comprises the following steps: firstly, a strong brine pipeline 5 between a first effect evaporator and a second effect evaporator is in a disconnected state, and a seawater spraying pipeline 6 of the first effect evaporator and a seawater spraying pipeline 6 of the second effect evaporator are in a disconnected state; simultaneously, the strong brine pipelines 5 of all the evaporators from the second effect evaporator to the tenth effect evaporator are in a communicated state, and the seawater spraying pipelines 6 of all the evaporators from the second effect evaporator to the tenth effect evaporator are in a communicated state, so that the strong brine pipelines 5 of all the effect evaporators from the second effect evaporator to the tenth effect evaporator, the seawater spraying pipelines 6 of all the effect evaporators from the second effect evaporator to the tenth effect evaporator, the brine pump 4 and the seawater booster pump 3 form an acid washing loop; and then, injecting an acid pickling solution into a U-shaped strong brine pipeline between the fourth effect evaporator and the fifth effect evaporator, enabling the acid pickling solution to sequentially flow through a brine pump 4 and a seawater booster pump 3, and then respectively spraying the acid pickling solution into the second effect evaporator to the tenth effect evaporator through a seawater spraying pipeline 6, so that the acid pickling solution is in contact with the outer walls of the heat exchange tubes in the second effect evaporator to the tenth effect evaporator. Wherein, the acid washing solution can be injected into the bottom of the U-shaped strong brine pipeline between the fourth effect evaporator and the fifth effect evaporator through the first acid injection pump 1; the first acid injection pump 1 can be arranged at the bottom of the U-shaped concentrated brine pipeline between the fourth effect evaporator and the fifth effect evaporator.

And the pickling solution enters the seawater spraying pipelines of all the evaporators from the second effect evaporator to the tenth effect evaporator through the overflowing device. The over-current device can comprise 1-3 heaters and/or 1-3 condensers.

Specifically, a salt water pump 4 in a salt water discharge system of the seawater desalination device is used as a cleaning power pump for cold-state circulating cleaning. The material water is blocked to a condensate cooler pipeline flange 22 before pickling so as to break the communication state of the material water to a condensate cooler 15 pipeline, and a second-effect evaporator strong brine pipeline inlet side flange 20 of a U-shaped strong brine pipeline between a first-effect evaporator and a second-effect evaporator and a material water to first-effect evaporator flowmeter incoming water side flange 21 are blocked. Before pickling, the second valve 17 is opened, while the first valve 16, the third valve 18 and the fourth valve 19 are opened. The bottom of a U-shaped concentrated brine pipeline between the fourth effect evaporator and the fifth effect evaporator (hereinafter, the U-shaped concentrated brine pipeline at the bottom of the fourth effect evaporator is simply called as' 4/5 effect) is connected with a first acid injection pump 1; the bottom of a U-shaped concentrated brine pipeline between the second effect evaporator and the third effect evaporator is connected with a first acid discharge pipeline 13, and the first acid discharge pipeline 13 is communicated to a first aeration tank 25. The specific principle is that a mobile pickling solution injection device is adopted to inject pickling solution into a pickling loop, the existing pipeline of a seawater desalination device is utilized, so that the pickling solution always keeps spraying under pressure on the outer wall of an evaporator heat exchange pipe under the driving of a brine pump, and the pickling solution flows in a material water system in a circulating reciprocating manner continuously, and the path is as follows:

the first acid injection pump 1 → 4/5 effect bottom U type concentrated brine pipe 5 → brine pump inlet pipe 23 → brine pump 4 → brine pump to material water bypass pipe 24 → nine effect regenerative heater 7, the acid cleaning solution is divided into two paths at A point by the nine effect regenerative heater 7, one path enters the ninth and tenth effect evaporator through A1 pipe, the other path enters A2 pipe and is divided into two paths at B point, one path enters the seventh and eighth effect evaporator through B1 pipe, the other path enters the seven effect regenerative heater 8 through B2 pipe, the acid cleaning solution after passing the seven effect regenerative heater 8 is divided into two paths at C point, one path enters the fourth, fifth and sixth effect evaporator through C1 pipe, the other path enters the four effect regenerative heater 9 through C2 pipe, then is divided into two paths at D point, one path enters the first stage injection condenser 12 through D1 pipe, then enters the second, and third effect regenerative heater, And the other path of the three-effect evaporator sequentially enters a secondary spray condenser 11 and a tertiary spray condenser 10 through a D2 pipeline, then enters a second effect evaporator and a third effect evaporator, then the pickling solution entering the second effect evaporator to the tenth effect evaporator is sprayed to the outer wall of a heat exchange pipe of the evaporator through a seawater spraying pipeline 6 in each evaporator, then is collected to a brine pump inlet pipe 23 through a U-shaped brine pipeline at the bottom of each effect evaporator respectively, and through the path, the pickling solution can circularly flow in a pickling loop.

According to the analysis of scale samples on the outer wall of the heat exchange tube of the evaporator, the inner component of the device is mainly calcium carbonate. Considering that the tube wall of the copper-aluminum alloy heat exchange tube of the evaporator is thin and the thickness of the scale layer is uneven, in the application, sulfamic acid, which is a pickling agent with small metal corrosivity and better cleaning effect, is selected. Compared with inorganic acid cleaning agents such as hydrochloric acid and nitric acid, the sulfamic acid contains amino groups in molecules, the corrosivity to metals is much weaker than that of inorganic acids, if a corrosion inhibitor is added into the formula of the cleaning agent, the corrosivity can be further reduced, the sulfamic acid can react with various metal salts, metal oxides, oxygen oxides, carbonates and the like to generate soluble salts, a protective film can be formed on the surface of the metal, the corrosion of a metal matrix is reduced, and oxides and scales on the surface of the metal can be removed. In addition, no solid precipitate is formed after the sulfamic acid is cleaned, so that the cleaning process can be greatly shortened. In addition, as a solid strong acid which does not absorb moisture, burn and explode, the transportation and the storage are very safe and convenient. The basic reaction equations are shown in formula (1) and formula (2):

CaCO₃+2NH₂SO₃H→Ca(NH₂SO₃)₂+H₂O+CO₂↑ (1)

MgCO₃+2NH₂SO₃H→Mg(NH₂SO₃)₂+H₂O+CO₂↑ (2)

in the embodiment, when the calcium ion concentration in the pickling solution is less than or equal to the set value, the pickling solution is discharged through a first acid discharge pipe 13, and the first acid discharge pipe 13 is arranged at the bottom of the concentrated brine pipe between the second effect evaporator and the third effect evaporator; and when the concentration of calcium ions in the pickling solution is greater than a set value, replacing the pickling solution in the pickling loop.

The cleaning method of the heat exchange tube of the first-effect evaporator comprises the following steps: and injecting a pickling solution into a seawater spraying pipeline 6 in the first-effect evaporator through a second acid injection pump 2, so that the pickling solution is contacted with the outer wall of the heat exchange tube in the first-effect evaporator.

Specifically, a mobile acid washing solution injection device is adopted as a cold circulating cleaning power pump. Before acid cleaning, a flange 20 at the inlet side of a strong brine pipeline of the second-effect evaporator and a flange 21 at the water inlet side of a material water-to-first-effect evaporator flowmeter are blocked. A second acid injection pump 2 is connected to the water outlet side of the material water to 1-effect flow meter through a flange; the bottom of the U-shaped concentrated salt water pipe between the first effect evaporator and the second effect evaporator is connected with a second acid discharge pipeline 14, and the second acid discharge pipeline 14 is communicated to a second aeration tank 26. The flow rate of the acid injection pump is controlled to be 250-300m³And h, the acid washing solution keeps spraying under pressure on the outer wall of the heat exchange tube of the first evaporator under the driving of the second acid injection pump 2 and continuously flows in the material water system.

During cleaning of the heat exchange tube of the first-effect evaporator, when the concentration of calcium ions in the pickling solution is greater than a set value, the pickling solution is continuously injected into the seawater spraying pipeline 6 in the first-effect evaporator through the second acid injection pump 2, and the pickling solution is discharged from the second acid discharge pipeline 14 after contacting with the outer wall of the heat exchange tube in the first-effect evaporator; the second acid discharge pipeline 14 is arranged at the bottom of the concentrated brine pipeline between the first effect evaporator and the second effect evaporator.

In the embodiment, before the pickling solution is injected into the pickling loop through the first acid injection pump 1, a solution containing a corrosion inhibitor and an antifoaming agent is injected into the pickling loop through the first acid injection pump 1 to perform pre-corrosion inhibition; wherein, in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%. Similarly, before the second acid injection pump 2 injects the pickling solution into the seawater spraying pipeline in the first-effect evaporator, a solution containing a corrosion inhibitor and a defoaming agent can also be injected into the seawater spraying pipeline in the first-effect evaporator to perform pre-corrosion inhibition; wherein, in the solution containing the corrosion inhibitor and the defoaming agent, the mass concentration of the corrosion inhibitor is 0.3-0.35%, and the mass concentration of the defoaming agent is 0.01-0.03%. The corrosion inhibitor comprises a copper slow-release agent and a steel slow-release agent; for example, the copper slow release agent can be methylbenzotriazole, the steel corrosion inhibitor can be cinnamaldehyde, and the defoaming agent can be polyoxyethylene polyoxypropylene pentaerythritol ether.

The special structure of the seawater desalination device can not accurately calculate the original scale amount attached to the heat exchange tube, so that the pH value of the mixed pickling solution of sulfamic acid and material water is sampled and measured at any time in the acid inlet process, the addition amount of the sulfamic acid is timely adjusted according to the pH value of the pickling solution and the scale dissolution trend, the pH value of the pickling solution is maintained between 0.9 and 1.1 as much as possible in the whole process, and the metal over-washing is prevented while the scale removal effect is ensured. Static and dynamic corrosion inhibition performance tests prove that the titanium material can be prevented from absorbing hydrogen by maintaining the lower hydrochloric acid content of the pickling solution. The wash data was closely monitored during the chemical wash to ensure that: the concentration of sulfamic acid is controlled at 2%, the concentration of corrosion inhibitor is controlled at 0.3-0.35%, and the temperature of washing liquid is controlled at 38-42 ℃.

According to another embodiment of the application, a more specific cleaning method of the seawater desalination device is provided, sulfamic acid is used as a cleaning agent, a cleaning auxiliary agent and a corrosion inhibitor are added to independently spray and clean the first effect evaporator of the seawater desalination device, and the second effect evaporator to the tenth effect evaporator are simultaneously sprayed and cleaned. The cleaning liquid level is strictly controlled in the cleaning process, various cleaning parameters are tested, and the cleaning end point is determined, and the method comprises the following steps:

firstly, provide cleaning agent

(1) Sulfamic acid concentration: the concentration is 2%;

(2) concentration of corrosion inhibitor: 0.3-0.35%;

(3) 0.01-0.03% of defoaming agent (defoaming);

(4) IsoVC sodium (except Fe)³⁺)0.05～0.15％；

(5) 0.05-0.15% of disodium hydrogen phosphate (single-effect passivation).

Secondly, cleaning of the evaporator

1. Construction and early-stage preparation of chemical cleaning system of evaporator

Installing a temporary system according to a chemical cleaning model and having the following conditions

(1) Before cleaning operation, the evaporator is stopped to be in a cold circulating state, the spraying condition of seawater of each effect is checked, the blocking, deflection, damage and falling conditions of a water distribution nozzle are treated, and the uniform spraying of the seawater is ensured;

(2) checking that each heat exchange tube bundle has no leakage, and plugging treatment is required if leakage exists;

(3) the desalted water or the industrial water is supplied in sufficient quantity, and the supply quantity is more than 100 tons per hour (seawater desalination condensate water can be taken as a cleaning water source); the steam ensures sufficient supply, the supply amount is more than 5 tons per hour, and the pressure is more than 0.4 MPa;

(4) the seawater lift pump, the seawater booster pump and the brine pump have operation conditions;

(5) isolating pressure, flow measurement points and the like related to the system before chemical cleaning;

(6) before chemical cleaning, the equipment and the pipeline which are connected with the cleaning range are closed to be isolated from the cleaning system;

(7) the discharge pipeline is smooth, the wastewater pool is emptied for standby, and the wastewater pool can be guaranteed to contain the pickling solution and can be neutralized and discharged in time.

2. Water spray inspection

And (4) spraying water on the upper part of the heat exchange tube at the brine side of the evaporator, and observing whether water flows out under the corresponding water flow so as to judge whether the upper part is scaled to block the water flow.

3. System flushing

Mend water to the interim level gauge liquid level of strong brine side to the highest control liquid level of distance 0.3 meters, open the discharge gate, maintain strong brine side liquid level among the washing process. Samples were taken at the drain until the rinse water was clear and free of impurities.

4. Hanging test piece

Suspending a titanium tube, a copper-aluminum alloy tube and an SS316L test piece at the upper heat exchange tube of the first, fourth, seventh and tenth-effect evaporators, and measuring the test pieces by a weight loss method after acid pickling so as to evaluate the corrosion degree of the acid pickling on the internal components of the evaporators;

5. simulation test of system circulation

After the system is washed, circulation is established according to a chemical cleaning model, the circulation of the system is maintained for 0.5h, and the liquid level of the concentrated brine side of the first effect evaporator is observed to determine whether the system leaks.

6. System warm-up

After the system circulation simulation test is finished, a temperature rise circulation loop is established, the circulation flow is controlled to be 250-.

7. Pre-inhibition

Adding a corrosion inhibitor and a defoaming agent into the cleaning tank, adding the corrosion inhibitor and the defoaming agent into the system through a cleaning pump, maintaining the circulation of the system for 0.5-1h, and performing pre-corrosion inhibition.

8. Cleaning with acid

(1) According to the chemical cleaning model of the evaporator, a movable pickling solution injection device and a brine pump in a brine discharge system of a seawater desalination device are respectively adopted as a first effect and a second effect to a tenth effect of cleaning the evaporator by a cold-state circulation of a power pump.

(2) Maintaining the circulation of the cleaning loop, slowly adding sulfamic acid and iso-VC sodium into the system, and reducing Fe generated in acid cleaning³⁺To prevent corrosion of the copper.

(3) In the cleaning process, sampling every 1h to analyze and test the acid concentration, the pH value, the calcium ion content and the copper ion content of the system cleaning liquid, supplementing a cleaning medium according to actual conditions, and maintaining the acid concentration to be 2%; when Ca is present²⁺Discharging waste liquid when the concentration is more than 15000mg/L, and performing acid cleaning again;

(4) when Ca is present²⁺Keeping the balance for more than 4h when the concentration is less than 15000mg/L, and finishing the cleaning.

9. System flushing and passivation

Mend water to the interim level gauge liquid level of strong brine side to about 0.3 meters apart from the highest control liquid level, open the discharge gate, maintain strong brine side liquid level in the washing process. The passivation mode of the second to tenth effect evaporators is that fresh seawater is sprayed into the evaporators for water washing, and the metals are naturally passivated while the pickling solution is diluted; the first effective passivation mode is to pump a disodium hydrogen phosphate solution into the evaporator for passivation. Sampling is carried out at a discharge port, and sampling is carried out in the drainage process until washing water is clear and free of impurities, and the pH value is more than or equal to 4.0. Sediment may exist at the bottom of the strong brine side of the evaporator after cleaning, and manual cleaning is carried out after cleaning.

10. Plugging and cleaning of evaporator heat exchange tube

Checking the leakage condition of the heat exchange tube during cold running, evaluating the leakage quantity, plugging the heat exchange tube which is corroded under the scale, and ensuring that the conductivity value of fresh water is qualified;

11. waste liquid neutralization

Adding caustic soda flakes into the aeration tank to neutralize the cleaning waste liquid, wherein the pH value is neutralized to 6-9.

The scale amount of the heat exchange tube is visually observed and compared, the surface of the heat exchange tube is clean, the passive film is compact, the cleaning and descaling are thorough, and no residue is left on the metal surface. Water flows out from the position right below the water spraying test point, which indicates that the upper scale layer is cleaned.

And (3) testing the cleaning effect:

1. after the seawater desalination device is cleaned, the rated fresh water ratio is measured, and as shown in fig. 2, the rated fresh water ratio is recovered from 11.3 to 13.0, which shows that the water production efficiency of the seawater desalination device is greatly improved after the seawater desalination device is cleaned.

2. The average corrosion rate and the total corrosion amount of the corrosion indicator sheet and the test pipe section in the first-effect, four-effect, seven-effect and ten-effect evaporators are measured by a weight loss method and are shown in table 1. The average metal corrosion rate of all the corrosion indicator sheets and the test pipe sections is less than 1 g/(m)²H) total corrosion amounts of less than 10g/m²All corrosion inhibition data are superior to the relevant standards of the power industry. After the seawater desalination device is acid-washed, the temperature difference between the effects and the output of the equipment are within the design range.

TABLE 1 test results of corrosion coupon and pipe section

Scaling of the outer wall of the heat exchange tube of the low-temperature multi-effect distillation seawater desalination evaporator increases the energy consumption and cost of water production, and seriously affects the normal operation of the device, so that active prevention and periodic removal are required. The invention provides a cleaning method of a seawater desalination device, which prevents metal from being washed excessively while ensuring the descaling effect, and the fresh water ratio of the device is restored to the design level after cleaning, thereby providing an effective solution for the scaling problem of the heat exchange tube of an evaporator.

In the above embodiments of the present invention, the difference between the embodiments is mainly described, and different optimization features between the embodiments can be combined to form a better embodiment as long as they are not contradictory, and further description is omitted here in view of brevity of the text.

The above description is only an example of the present invention, and is not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.