Condenser cleaning method and application

Abstract

The invention discloses a condenser cleaning method and application, and the method comprises the following steps: injecting a descaling agent composed of water and acetic acid into a condenser, diluting the descaling agent in water to form a cleaning liquid mixture, and driving the cleaning liquid to circularly flow in a condenser tube bundle by using a pump, so that deposited scale is in full contact with the cleaning liquid; wherein the content of acetic acid in the descaling agent is 5-15%; the scale remover further comprises an additive composed of a corrosion inhibitor and a surfactant, and the content of the additive is 0.1%-5%. By means of the method, the calcium carbonate scale layer in the condenser can be effectively removed, the condenser vacuum degree and the steam condensation efficiency are recovered, stable and efficient operation of a unit is guaranteed, the problems that traditional strong acid cleaning corrodes metal parts and the cost is high are solved, and an effective and environment-friendly new way is provided for condenser cleaning.

Description

Technical Field

[0001] The invention relates to the technical field of condenser cleaning, and in particular to a condenser cleaning method and application. Background Art

[0002] In my country's electricity production, steam turbine generator sets account for more than 70% of electricity generation. Thermal power plants and nuclear power plants generate steam by heating water to drive steam turbine generator sets to generate electricity. After the steam is used by the steam turbine, it needs to be cooled into water for recycling.

[0003] Steam condensation mainly adopts the following cooling systems: Open cooling system: water is taken from natural water sources such as rivers, lakes or oceans, sent to the condenser through a circulating water pipe to absorb the exhaust heat of the turbine, and the heated cooling water is then discharged back to the original water source.

[0004] Closed cooling system: Cooling water is recycled, and the cooling tower is used to exchange heat between the cooling water that absorbs heat and heats up and the air. Part of the water evaporates, and the remaining cooling water is cooled and returned to the condenser, such as the common cooling tower closed circulation system.

[0005] Dry cooling system: Air is used to cool turbine exhaust in dry and water-scarce areas, but the operating cost is high and the efficiency is low.

[0006] Condensers of almost all types of cooling systems will scale. Because the circulating water source contains solid dissolved matter, it will precipitate on the inner surface of the condenser pipe to form scale. Scaling is not only not conducive to heat transfer, but also reduces the efficiency of steam condensation, reduces the vacuum degree of the condenser and the operating efficiency of the turbine, thereby increasing fuel consumption and costs, and even causing power plant shutdowns. Traditional chemical cleaning mostly uses strong acid solvents such as hydrochloric acid and hydrofluoric acid for pickling, but it will corrode metal parts such as stainless steel and brass, and the cost is relatively high. Summary of the invention

[0007] The present invention aims to provide a condenser cleaning method and application, which can effectively avoid the corrosion problem caused by strong acid cleaning while ensuring the descaling effect and efficiency.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: A condenser cleaning method comprises: injecting a descaling agent consisting of water and acetic acid into the condenser, diluting the descaling agent in water to form a cleaning liquid mixture, and using a pump to drive the cleaning liquid to circulate in the condenser tube bundle so that the deposited scale is fully in contact with the cleaning liquid; wherein the content of acetic acid in the descaling agent is 5% to 15%; the descaling agent also contains an additive consisting of a corrosion inhibitor and a surfactant, and the content of the additive is 0.1% to 5%.

[0009] A further improvement of the present invention is that the corrosion inhibitor is oxalic acid.

[0010] A further improvement of the present invention is that the surfactant is one or more of propylene polyoxyethylene ether block polymer, polyoxyethylene amine, and sulfonated polyoxyethylene ether.

[0011] A further improvement of the present invention is that it also includes: measuring the property parameters of the cleaning liquid when it passes through the condenser tube bundle, and stopping the cleaning process when the measured parameters meet a predetermined threshold change.

[0012] A further improvement of the present invention is that the measured property parameter is the pH value of the mixture.

[0013] A further improvement of the present invention is that the cleaning process is stopped when the pH value of the cleaning liquid flowing through the condenser tube bundle changes by less than 0.2 within 5 hours.

[0014] A further improvement of the present invention is that the measured property parameter is the total hardness of the cleaning liquid.

[0015] A further improvement of the present invention is that the cleaning process is stopped when the total hardness of the mixture flowing through the condenser tube bundle changes by less than 30 mmol / L within 5 hours.

[0016] A further improvement of the present invention is that the total hardness is based on CaCO 3 count.

[0017] The invention discloses an application of a condenser cleaning method in removing condenser scale.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects: The present invention provides a condenser cleaning method and application, which can effectively remove the calcium carbonate scale layer in the condenser, restore the vacuum degree of the condenser and the steam condensation efficiency, ensure the stable and efficient operation of the unit, solve the problems of corrosion of metal parts and high cost of traditional strong acid cleaning, and provide an effective and environmentally friendly new way for condenser cleaning. After use, it was checked that the calcium carbonate scale layer in the condenser tube bundle was effectively removed, the vacuum degree of the condenser was significantly improved, the operating efficiency of the steam turbine was also significantly improved, the normal working performance of the condenser was successfully restored, and the stable operation and efficient power generation of the thermal power generation equipment were ensured. In addition, the results show that low-concentration acetic acid can achieve efficient descaling, no heating tank is required, calcium solubility is high, environmentally friendly and can be supplied in batches, and calcium carbonate can be controlled to dissolve, meeting the descaling needs of large condensers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is the structural diagram of the condenser. DETAILED DESCRIPTION

[0021] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0022] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0023] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0024] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0025] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] The present invention provides a condenser cleaning method, comprising: injecting a descaling agent composed of water and acetic acid into the condenser, diluting the descaling agent in water to form a cleaning liquid mixture, and using a pump to drive the cleaning liquid to circulate in the condenser tube bundle so that the deposited scale is fully in contact with the cleaning liquid; wherein the content of acetic acid in the descaling agent is 5% to 15%; the descaling agent also contains an additive composed of a corrosion inhibitor and a surfactant, and the content of the additive is 0.1% to 5%.

[0028] Furthermore, the corrosion inhibitor is oxalic acid. The surfactant is one or more of propylene polyoxyethylene ether block polymer, polyoxyethylene amine, and sulfonated polyoxyethylene ether. Propylene polyoxyethylene ether block polymer is formed by connecting propylene groups and polyoxyethylene ether segments through block copolymerization. This special structure makes it have both the hydrophobicity of propylene groups and the hydrophilicity of polyoxyethylene ether segments. Polyoxyethylene amine is a compound formed by introducing polyoxyethylene segments on amine groups. The amine group gives it certain alkalinity and reactivity, while the polyoxyethylene segments provide hydrophilicity and flexibility. Sulfonated polyoxyethylene ether is a sulfonic acid group introduced on the basis of polyoxyethylene ether. The sulfonic acid group has strong hydrophilicity and acidity, which makes the surfactant have good water solubility and ionicity.

[0029] The present invention also includes: measuring the property parameter of the cleaning liquid when it passes through the condenser tube bundle, and stopping the cleaning process when the measured parameter meets a predetermined threshold change. The measured property parameter is the pH value of the mixture. When the pH value of the cleaning liquid flowing through the condenser tube bundle changes by less than 0.2 within 5 hours, the cleaning process is stopped. The measured property parameter is the total hardness of the cleaning liquid, and the total hardness is measured in terms of CaCO 3 When the total hardness of the mixture flowing through the condenser tube bundle changes by less than 30 mmol / L within 5 hours, the cleaning process is stopped.

[0030] Furthermore, a descaling agent composed of water, acetic acid and additives is mixed with water to form a cleaning liquid. A condenser cleaning method is to inject a cleaning liquid into the condenser, and drive it to circulate in the condenser tube bundle with the help of a pump, so as to promote the deposited scale (mainly calcium carbonate) to fully contact with acetic acid. Among them, the mass fraction of acetic acid is 1%~25%, preferably 7%~10%; the additive is oxalic acid and / or ethoxyamine, and its mass fraction is 0.01%~10%, preferably 0.5%~1%; the temperature of the mixture is in the range of 10~50℃, preferably 20~30℃.

[0031] In a thermal power plant equipped with a steam turbine generator set, the steam discharged from the steam turbine enters the condenser, flows outside the condenser tube bundle, and is cooled by the cooling water in the condenser tube to become condensed water. At the same time, the air extraction equipment continuously removes the air and non-condensable gases in the condenser to maintain a high vacuum. Usually, the circulating cooling water condenses the steam at about 30°C, and an absolute pressure of about 47kPa (about 95kPa lower than the atmospheric pressure) is generated in the condenser. This high vacuum helps to increase the effective enthalpy drop of steam in the steam turbine and improve the thermal efficiency of the unit.

[0032] The condenser tube bundle is mostly made of brass or stainless steel, which has good heat transfer and corrosion resistance. However, bacteria, algae, silt and scale in the circulating cooling water are easy to scale inside the tube bundle, hindering heat transfer and reducing the condenser vacuum and unit cycle thermal efficiency.

[0033] The descaling agent of the present invention can be introduced into the condenser water circuit to clean the condenser and reduce or eliminate scale deposition. The descaling compound in the descaling agent can be an organic acid. In the embodiment of the present invention, acetic acid (CH 3 COOH) accounts for at least 60%, 70%, 80%, 90% or 95% of the mass fraction of the descaling agent. The descaling agent can be entirely organic acid, or it can be mixed with water to form a solution, with water accounting for 10%~90%, 25%~80% or 45%~70% of its mass fraction. Descaling agents with acetic acid as the main active ingredient are highly effective in removing calcium carbonate scale, do not require other organic acid compounds, and are also effective in the absence of strong acids such as hydrochloric acid. Here, strong acid refers to an acid that can be completely ionized into ions (H + and anions) such as hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ).

[0034] When the condenser is offline for cleaning, the entire condenser system can be offline or partially offline. For example, when the steam turbine generator set is online, half of the condenser is used to condense steam, and the other half is soaked for cleaning; or for a split condenser, one side is cooled by the first circulating water pump and the other side is cooled by the second circulating water pump. The first circulating water pump is shut down to isolate one side for water injection and soaking cleaning, while the other side operates normally. This process is preferably carried out in winter, because the lower cooling water temperature in winter allows the unit to operate at full load or close to full load when half of the condenser is operating.

[0035] The reasons for the excellent descaling performance of acetic acid are as follows: First, the pKa value of acetic acid is 4.74. Although it contains only one acid group, the acid group concentration per unit molecular weight (1 / 60.05) is higher than that of most other organic acids. It can effectively reduce the pH value, destroy the calcium carbonate crystal matrix, form a hydration shell with water, and establish a bicarbonate balance at the same time, promoting the formation of highly soluble calcium bicarbonate; second, in circulating water with a pH value of 4.5 to 6.0, acetic acid can fix calcium. Compared with organic acids such as adipic acid, formic acid, and lactic acid, acetic acid has a stronger fixation ability, a lower molecular weight, and a faster diffusion rate. In addition, acetic acid can controllably dissolve calcium carbonate, which is crucial for ultra-large condensers, because the dissolution of calcium carbonate scale will release a large amount of CO 2 The gas needs to be discharged outside the turbine building in a safe and controllable manner to avoid excessive pressure in the condenser.

[0036] As a preferred embodiment, the descaling agent contains additives in addition to acetic acid. The additives may include corrosion inhibitors such as oxalic acid that can effectively prevent corrosion of carbon steel parts in the system, and may also include surfactants for dissolving and transporting low-charge substances such as clay and other silicates that may reduce the effect of acetic acid. Applicable surfactants include propylene polyoxyethylene ether block polymers, polyoxyethylene amines, sulfonated polyoxyethylene ethers, etc. Amines are more soluble at low pH values ​​and can be evenly dispersed in acetic acid. The total mass fraction of additives in the descaling agent can be 0.01%~10%, 0.1%~5% or 0.5%~1%.

[0037] Before adding the descaling agent to the condenser system, the descaling agent is often diluted in water. For example, the final concentration of acetic acid in the cleaning liquid passing through the condenser is about 1%~25%, 3%~20%, 5%~15% or 7%~10%. The descaling agent may contain other acids or chlorides, but the total amount is less than the acetic acid content. Other acids may include hydrochloric acid or DBA, etc. The final concentration of DBA, chlorides and / or strong acids in the condenser circulating water is less than 1%, less than 0.5%, less than 0.3% or less than 0.1%. Other acids in the descaling agent, such as α-hydroxy acids or aminosulfonic acid, can form more polar complexes with calcium acetate, enhance diffusion and increase the solubility limit, which can offset the poor diffusion of calcium acetate and accelerate cleaning.

[0038] The descaling agent can be circulated in the circulating water system according to the set pH value. The pH value of the descaling agent mixture pumped into the condenser is preferably maintained below 4, and can be further maintained at 3.7 or below, 3.5 or below, 3.2 or below, or even 3.0 or below. At a pH value of 3.2, the increase in acetic acid concentration can provide significant buffering capacity to prevent the pH value from rising, ensuring that the pH value of the cleaning solution (water and descaling agent) after being neutralized by scale when passing through the heat exchange tubes in the condenser is maintained below 4, thereby improving the cleaning rate. In order to maintain the ideal pH value of the cleaning solution, the acetic acid concentration in it needs to be monitored.

[0039] The descaling agent does not require a heating tank and can effectively remove scale at low temperatures such as below 50°C, 40°C, 30°C, 20°C and even 10°C. For example, the cooling system can be cleaned at room temperature (about 2022°C). The cleaning liquid containing the descaling agent circulates in the condenser for at least 1 hour, 5 hours, 10 hours, 24 hours or 48 hours. After a period of circulation, more descaling agent can be injected to continue the circulation. This process can be repeated multiple times according to the expected amount of scaling to completely remove scale. The descaling agent can be circulated for a preset time, or it can be circulated until the system measurement results show that descaling is fully completed, such as circulating until the pH value of the cleaning liquid in the system changes by less than 0.5, less than 0.2 or less than 0.1 within 5 hours, or circulating until the calcium hardness of the cleaning liquid (measured as CaCO 3 Stop cleaning when the change is less than 20mmol / L or less than 10mmol / L within 5 hours.

[0040] Example 1 In the maintenance work of a condenser in a medium-sized nuclear power plant, a condenser cleaning method of the present invention is used. The tube bundle of the condenser is made of stainless steel, and a calcium carbonate scale layer with a thickness of about 0.4 mm is formed inside the condenser after long-term operation.

[0041] When preparing the descaling agent, select a solution with a mass fraction of 8% acetic acid and add an additive with a mass fraction of 0.7%, wherein the corrosion inhibitor is oxalic acid and the surfactant is polyoxyethylene amine. The descaling agent is fully mixed with an appropriate amount of clean water in a specific container to form a cleaning liquid, which is then injected into the condenser to ensure that the cleaning liquid can completely cover the condenser tube bundle area.

[0042] Start the circulation pump to make the cleaning liquid circulate in the condenser tube bundle at a stable flow rate. During the circulation process, monitor the temperature of the mixture in real time and maintain it at around 25°C through cooling or heating devices to ensure the best cleaning effect.

[0043] The properties of the cleaning fluid were tested every 30 minutes, including pH value and total hardness (measured as CaCO 3 In the first 5 hours after the start of cleaning, the pH value gradually decreased from the initial about 5.5 to 4.2, and the total hardness gradually increased from the initial 15mmol / L to 35mmol / L. As the cleaning continued, when the cleaning time reached 12 hours, the pH value dropped to 3.8, and changed less than 0.15 in the next 5 hours, and the total hardness changed less than 15mmol / L in these 5 hours.

[0044] According to the predetermined stop conditions, it is judged that the descaling process has been basically completed at this time. Stop the circulation pump, drain the cleaning liquid in the condenser, and inject clean water for flushing several times until the pH value and hardness of the discharged clean water are close to normal levels. Subsequently, a comprehensive inspection of the condenser was carried out, and it was found that the calcium carbonate scale layer in the tube bundle had been basically removed, the vacuum degree of the condenser was restored to close to the initial design value, and the steam condensation efficiency was significantly improved, effectively ensuring the stable and efficient operation of the nuclear power plant unit.

[0045] This Example 1 further demonstrates the application effects and operation processes of the present invention in different scenarios, and provides more abundant practical references for condenser cleaning.

[0046] Example 2 In the routine maintenance of a thermal power plant, a condenser cleaning method of the present invention is implemented for a condenser that has been running for a certain period and has obvious scaling.

[0047] The condenser tube bundle is made of brass, and the thickness of the calcium carbonate scale layer accumulated inside is about 0.6mm. The mass fraction of acetic acid in the descaling agent configured this time is set to 12%, and the mass fraction of additives is 0.8%. The corrosion inhibitor is oxalic acid, and the surfactant is a mixture of propylene polyoxyethylene ether block polymer and sulfonated polyoxyethylene ether in a ratio of 1:1.

[0048] The descaling agent and water are fully mixed in a special mixing device according to the proportion to form a cleaning liquid, which is then injected into the condenser. The circulation pump is turned on to circulate the cleaning liquid in the condenser tube bundle. During the circulation process, the temperature of the cleaning liquid is stabilized at 28°C through the temperature control system.

[0049] During the cleaning process, the pH value and total hardness (in terms of CaCO 3 At first, the pH value of the mixture was about 5.8. As the cleaning progressed, the pH value gradually decreased and dropped to about 4.0 after 8 hours of cleaning. In terms of total hardness, the initial value was about 20mmol / L, which rose to 45mmol / L after 10 hours of cleaning, and then the growth rate gradually slowed down.

[0050] When the cleaning time reaches 20 hours, it is found that the pH value of the mixture changes less than 0.1 within 5 hours, and the total hardness changes less than 10mmol / L within 5 hours, meeting the predetermined threshold for stopping cleaning. At this time, stop the circulation pump, drain the cleaning liquid, and inject a large amount of clean water into the condenser for multiple flushing until the indicators of the discharged water return to normal.

[0051] After inspection, it was found that the calcium carbonate scale layer in the condenser tube bundle was effectively removed, the vacuum degree of the condenser was significantly improved, the operating efficiency of the steam turbine was also significantly improved, and the normal working performance of the condenser was successfully restored, ensuring the stable operation and efficient power generation of the thermal power generation equipment.

[0052] Example 3 To verify the effectiveness of the descaling agent in the cooling system, a descaling experiment was carried out on the condenser using a descaling agent containing acetic acid. A descaling agent containing about 56% acetic acid and no chloride or other acids was used to clean the 0.5mm calcium carbonate scale layer on the condenser. The descaling agent was mixed with clean water, and the diluted acetic acid concentration reached 10% to become a cleaning solution. The cleaning solution was injected into two condenser water tanks and circulated in the condenser tube bundle for more than 24 hours until chemical measurements showed that all calcium carbonate scale was dissolved. After cleaning, the water tanks were dehydrated and refilled with clean water twice for inspection and leakage testing. The pH value, hardness and conductivity were measured approximately every hour for the two water tank loops, and the descaling agent was regularly added to maintain their levels. The circulation lasted for more than 24 hours until the chemical values ​​(hardness was stable and pH value did not rise) showed that the calcium carbonate scale was completely dissolved. After that, the loop was emptied and refilled with water for circulation. The results show that low-concentration acetic acid can achieve efficient descaling without the need for heating tanks, has high calcium solubility, is environmentally friendly and can be supplied in batches, and can controllably dissolve calcium carbonate to meet the descaling needs of large condensers.

[0053] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0054] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A condenser cleaning method, characterized in that: include: A descaling agent consisting of water and acetic acid is injected into the condenser. The descaling agent is diluted in water to become a cleaning liquid mixture, and a pump is used to drive the cleaning liquid to circulate in the condenser tube bundle so that the deposited scale is fully in contact with the cleaning liquid; wherein the content of acetic acid in the descaling agent is 5% to 15%; the descaling agent also contains an additive consisting of a corrosion inhibitor and a surfactant, and the content of the additive is 0.1% to 5%.

2. A condenser cleaning method according to claim 1, characterized in that: The corrosion inhibitor is oxalic acid.

3. A condenser cleaning method according to claim 1, characterized in that: The surfactant is one or more of propylene polyoxyethylene ether block polymer, polyoxyethylene amine, and sulfonated polyoxyethylene ether.

4. A condenser cleaning method according to claim 1, characterized in that: Also includes: The property parameters of the cleaning liquid when passing through the condenser tube bundle are measured, and when the measured parameters meet a predetermined threshold change, the cleaning process is stopped.

5. A condenser cleaning method according to claim 4, characterized in that: The measured property parameter is the pH of the mixture.

6. A condenser cleaning method according to claim 5, characterized in that: When the pH value of the cleaning liquid flowing through the condenser tube bundle changes by less than 0.2 within 5 hours, the cleaning process is stopped.

7. A condenser cleaning method according to claim 4, characterized in that: The measured property parameter is the overall hardness of the cleaning fluid.

8. A condenser cleaning method according to claim 7, characterized in that: When the total hardness of the mixture flowing through the condenser tube bundle changes by less than 30 mmol / L within 5 hours, the cleaning process is stopped.

9. A condenser cleaning method according to claim 7, characterized in that: Total hardness is measured in terms of CaCO3.

10. Use of a condenser cleaning method according to any one of claims 1 to 9 in removing condenser scale.

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