Cleaning agent for cleaning calcium fluoride scale of heat exchanger as well as preparation method and cleaning method of cleaning agent

Abstract

The invention relates to the technical field of cleaning agents, in particular to a cleaning agent for cleaning calcium fluoride scale of a heat exchanger and a preparation and cleaning method of the cleaning agent, and the cleaning agent comprises the following components in percentage by mass: 5-15% of an amino polycarboxylic acid chelating agent, 3-8% of a compound surfactant, 0.5-2% of a corrosion inhibitor, 0.1-0.5% of a defoaming agent and 65-85% of deionized water. The cleaning agent further comprises a pH regulator, and the addition amount of the pH regulator is based on the standard that the pH value of the cleaning agent is regulated to 6-8. The preparation method comprises the following steps: adding the deionized water and stirring; slowly adding an aminopolycarboxylic acid chelating agent and continuously stirring until the aminopolycarboxylic acid chelating agent is completely dissolved; and sequentially adding the compound surfactant, the corrosion inhibitor, the pH regulator and the defoaming agent, continuously stirring and the like. The cleaning method comprises the steps of pre-flushing, circulating cleaning, discharging, post-flushing and the like, and has the advantages of efficient cleaning, equipment protection, environmental protection, energy conservation, simplicity and convenience in operation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of cleaning agents, and particularly to a cleaning agent for cleaning calcium fluoride scale on heat exchangers, and its preparation and cleaning methods. Background Art

[0002] In the operation of industrial heat exchange equipment, the formation mechanism and hazards of calcium fluoride scale have reached a consensus: it forms a hexagonal crystal structure scale layer by combining Ca 2+ with F-, which has an extremely low thermal conductivity (0.15 - 0.2 W / (m·K)), and the thermal conductivity is reduced by more than 95% compared with the metal substrate.

[0003] Although traditional acid cleaning methods (such as hydrofluoric acid systems) dissolve the scale layer through strong acids, they will cause the annual corrosion rate of the metal substrate to exceed 0.5 mm / a (according to ASTM G31 standard); mechanical cleaning methods are difficult to remove scale fragments ≥50 μm, and the removal rate is only 60 - 70% in complex structures such as spiral tube bundles. There are three major technical bottlenecks in existing commercially available cleaning agents:

[0004] ① The dissolution constant (K sp = 3.45×10 -11 ) of a single chelating agent for calcium fluoride is not fully utilized, resulting in a cleaning time ≥6 hours;

[0005] ② The surfactant compounding lacks a synergistic effect design, and the reduction in interfacial tension is insufficient;

[0006] ③ The film-forming mechanism of the corrosion inhibitor is not clear, and the breakage rate of the protective film reaches more than 40% in dynamic circulation.

[0007] So far, no technical solution has been disclosed on how to achieve the efficient dissolution of calcium fluoride scale and the dynamic protection of metal substrates through a ternary synergistic system of optimizing the chelating agent ligand structure, precisely matching the HLB value of surfactants, and controlling the adsorption kinetics of corrosion inhibitors. Especially under pH-neutral conditions (to avoid the strong corrosiveness of traditional acid cleaning), how to break through the micro-solubility equilibrium limit of calcium fluoride has become a technical problem in this field. Summary of the Invention

[0008] The purpose of the present invention is to solve the existing technical problems, and provide a cleaning agent and a cleaning method for cleaning calcium fluoride scale on heat exchangers, so as to break through the traditional single dissolution mechanism and construct a ternary synergistic system of "chelating solubilization - interfacial activation - dynamic film formation", thereby effectively solving the problems of incomplete cleaning, equipment corrosion, complex operation, and environmental unfriendliness existing in existing cleaning methods. This cleaning agent can efficiently dissolve calcium fluoride scale, has good compatibility with the heat exchanger material, is environmentally friendly during the cleaning process, and is easy to operate, and can be widely applied in the industrial field.

[0009] To achieve one of the above purposes, the present invention is implemented according to the following technical solutions:

[0010] The cleaning agent for removing calcium fluoride scale from heat exchangers, by mass percentage, comprises the following components: 5-15% of amino polycarboxylic acid chelating agent, 3-8% of compound surfactant, 0.5-2% of corrosion inhibitor, 0.1-0.5% of defoamer, and 65-85% of deionized water;

[0011] The cleaning agent further comprises a pH regulator, and the addition amount of the pH regulator is such that the pH value of the cleaning agent is adjusted to 6-8. Within this pH range, it can not only ensure the best activity of the amino polycarboxylic acid chelating agent and give full play to its ability to dissolve calcium fluoride scale, but also avoid damage to the equipment caused by an overly acidic or alkaline environment.

[0012] Preferably, the amino polycarboxylic acid chelating agent is selected from at least one of ethylenediaminetetraacetic acid (EDTA), sodium ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid (DTPA), and sodium diethylenetriaminepentaacetate.

[0013] Preferably, the compound surfactant is composed of non-ionic surfactant fatty alcohol polyoxyethylene ether (AEO) and anionic surfactant sodium dodecylbenzenesulfonate (SDBS) with a mass ratio of (2-5):(1-3).

[0014] More preferably, the HLB value of the fatty alcohol polyoxyethylene ether (AEO) is 12-14, and it is selected from at least one of AEO-7 and AEO-9; the anionic surfactant is sodium dodecylbenzenesulfonate (SDBS), and the critical micelle concentration of sodium dodecylbenzenesulfonate (SDBS) is 8.2×10 -3 mol / L or less. The non-ionic surfactant AEO has excellent penetration and emulsification capabilities and can effectively penetrate into the scale layer; the anionic surfactant SDBS helps to disperse dirt, and the two work synergistically to significantly enhance the wetting, penetration, and dispersion effects of the cleaning agent on the scale layer.

[0015] Preferably, the pH regulator is citric acid or sodium carbonate. Citric acid or sodium carbonate can maintain the pH of the cleaning agent at 6-8, ensure that the acid effect coefficient of amino polycarboxylic acid chelating agents such as EDTA is at the optimal value, and avoid a decrease in chelating ability caused by pH fluctuations.

[0016] Preferably, the corrosion inhibitor is selected from at least one of benzotriazole (BTA), methylbenzotriazole (TTA), and mercaptobenzotriazole. During the cleaning process, the corrosion inhibitor can form a dense protective film with a thickness of 5-10 nm on the metal surface of the heat exchanger, effectively preventing the cleaning agent from corroding the metal material and ensuring the structural integrity and service life of the equipment.

[0017] Preferably, the defoamer is an organosilicon defoamer, and the defoaming time of the organosilicon defoamer is ≤ 10 s without affecting the interfacial activity of the compound surfactant. During the cleaning process, due to the reaction between the cleaning agent and the scale layer and the circulating flow, a large amount of foam will be generated. The organosilicon defoamer can effectively eliminate these foams, ensure the smooth progress of the cleaning operation, and avoid affecting the cleaning effect or causing equipment failure due to excessive foam.

[0018] To achieve the second above-mentioned object, the present invention provides a preparation method of the above cleaning agent, including the following steps:

[0019] (1) Add the deionized water into a reaction kettle equipped with a stirring device and stir at a speed of 200 - 300 r / min; at this speed, a turbulent state can be formed (Reynolds number Re = 10 4 -10 5 ), which can improve the dissolution rate of the aminopolycarboxylic acid chelating agent and avoid incomplete chelation caused by too high local concentration.

[0020] (2) Slowly add the aminopolycarboxylic acid chelating agent and continuously stir for 15 - 30 minutes until completely dissolved;

[0021] (3) Add the compound surfactant, corrosion inhibitor, pH regulator and defoamer in sequence, and stir for 10 - 15 minutes after adding each component; adding each component in the above order and following the principle of "polarity matching - minimizing steric hindrance" is easy to form a stable dispersion system.

[0022] (4) After all components are added, continue to stir for 30 - 60 minutes to make each component evenly dispersed, and the cleaning agent is prepared.

[0023] To achieve the third above-mentioned object, the present invention provides a cleaning method using the above cleaning agent for cleaning calcium fluoride scale on a heat exchanger, including the following steps:

[0024] (1) Pre-rinse: Rinse the surface of the heat exchanger with clean water to remove loose impurities; through pre-rinsing, the loose impurities and dust on the surface of the heat exchanger can be removed, reducing the difficulty of subsequent cleaning, and at the same time avoiding secondary pollution or damage to the equipment caused by these impurities during the cleaning process.

[0025] (2) Circulating cleaning: Inject the cleaning agent into the heat exchanger circulation system, control the temperature at 40 - 60 °C and the flow rate at 0.3 - 0.5 m / s, and circulate for 2 - 4 hours; during the circulating cleaning process, various components in the cleaning agent can fully contact and react with the calcium fluoride scale, gradually dissolve the scale layer and disperse it in the cleaning agent, so as to achieve the purpose of cleaning.

[0026] (3) Emission and post-rinse: Drain the waste liquid into the wastewater treatment device and rinse with clean water until the drained water is clear and free of impurities. After the cleaning is completed, discharge the cleaning agent containing dirt to a dedicated wastewater treatment device for environmental protection treatment. Then, repeatedly rinse the heat exchanger with clean water until the discharged water is clear and free of impurities, ensuring that there is no residue of the cleaning agent in the heat exchanger after cleaning to avoid adverse effects of the residual cleaning agent on the subsequent operation of the equipment.

[0027] The main working principle of the present invention is:

[0028] 1. The aminopolycarboxylic acid chelating agent used in this application can undergo a chelation reaction with calcium ions in calcium fluoride, that is, the aminopolycarboxylic acid group forms a cyclic chelate such as [Ca(EDTA)]2- with Ca 2 +, reducing the activity of Ca 2 + and forming a stable water-soluble chelate, thereby achieving the dissolution of calcium fluoride scale. This is because the aminopolycarboxylic acid chelating agent forms a five-membered ring chelate through adjacent carboxyl and amino groups in its molecular structure. This bidentate coordination mode (such as the hexadentate coordination of EDTA) enables them to form stable complexes with metal ions, significantly increasing the stability constant of Ca 2 + and thus significantly breaking the calcium fluoride dissolution equilibrium. In addition, the aminopolycarboxylic acid chelating agent of this application can form an ion-dipole interaction with the sulfonic acid group of SDBS, enhancing the water solubility of the chelate and increasing its solubility.

[0029] 2. The non-ionic surfactant AEO used in this application has excellent penetration and emulsification capabilities, and the polyoxyethylene chain of AEO can break the hydrogen bond network of the scale layer and effectively penetrate into the interior of the scale layer; the anionic surfactant SDBS helps to disperse dirt. The benzenesulfonate root of SDBS disperses scale particles through electrostatic repulsion. After compounding, the cloud point is increased to 70 °C, the applicable cleaning temperature range is broadened, and the dispersion stability can be increased by 3 times. Through their synergistic effect, that is, the penetration effect of the non-ionic surfactant and the dispersion effect of the anionic surfactant are synergistic, the interfacial tension of the solution is decreased, and the porosity of the scale layer is increased to accelerate the penetration of the chelating agent, thereby significantly enhancing the wetting, penetration, and dispersion effects of the cleaning agent on the scale layer.

[0030] 3. Corrosion inhibitor adsorption kinetics control: BTA, TTA, and mercaptobenzotriazole can all form a dense protective film with a thickness of 5 - 10 nm on the metal surface through the π-electron conjugate system. Its adsorption rate (k = 0.023 min-1) forms a dynamic equilibrium with the cleaning liquid flow rate (0.3 - 0.5 m / s) to ensure that the integrity rate of the protective film is ≥95% in a turbulent environment. In addition, BTA and its derivatives can form steric hindrance with the hydrophilic group of AEO to prevent the surfactant from damaging the protective film, thereby enhancing the corrosion inhibition efficiency.

[0031] 4. This application uses deionized water as the dispersion medium for each component, ensuring that the chelation reaction occurs in a pure medium, avoiding competitive coordination, and enabling the cleaning reaction to proceed in a uniform environment. At the same time, it avoids the adverse effects of impurity ions such as Ca 2+ and Mg 2+ on the cleaning effect and equipment.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. Through the chelation reaction of a specific chelating agent with calcium fluoride, and the synergistic effect of surfactants and additives, it can quickly and thoroughly dissolve and disperse calcium fluoride scale, significantly improving the cleaning efficiency and effectively restoring the heat transfer performance of the heat exchanger.

[0034] 2. By adding corrosion inhibitors, it effectively prevents the cleaning agent from corroding the metal material of the heat exchanger, reduces the risk of equipment damage caused by corrosion, extends the service life of the equipment, and reduces the equipment maintenance and replacement costs.

[0035] 3. The cleaning agent of the present invention selects biodegradable components, and the cleaning process and emissions meet environmental protection requirements, reducing environmental pollution. At the same time, the efficient cleaning effect enables the heat exchanger to quickly resume normal operation, reducing energy consumption and achieving the energy-saving goal.

[0036] 4. The cleaning process is simple, easy to operate and control, does not require complex equipment and professional technicians, and can be widely applied to the cleaning of heat exchangers in various industrial fields.

[0037] In summary, the present invention has the advantages of efficient cleaning, equipment protection, environmental protection and energy saving, and simple operation. Specific Embodiments

[0038] The following describes the present invention in further detail with specific embodiments. The illustrative embodiments and explanations of the present invention are used to explain the present invention, but do not limit the present invention.

[0039] For all raw materials of the present invention, there is no special limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0040] For all raw materials of the present invention, there is no special limitation on their purity. The present invention preferably uses industrial purity or conventional purity used in the art.

[0041] For the devices used in the present invention, those without special limitations are all commonly used devices in the art.

[0042] Example 1

[0043] The cleaning agent for removing calcium fluoride scale from heat exchangers proposed in this embodiment, by mass percentage, includes the following components: 10% of disodium ethylenediaminetetraacetate (EDTA-2Na), 3% of fatty alcohol polyoxyethylene ether (AEO-9), 2% of sodium dodecylbenzenesulfonate (SDBS), 1% of benzotriazole (BTA), citric acid is used to adjust the pH to 7, 0.3% of organosilicon defoamer, and the balance is deionized water.

[0044] The preparation method of the above cleaning agent includes the following steps:

[0045] (1) Add deionized water to the reaction kettle, turn on the stirrer, and the rotation speed is 250 r / min.

[0046] (2) Slowly add EDTA-2Na and stir for 20 minutes until completely dissolved.

[0047] (3) Add AEO-9, SDBS, BTA, citric acid and organosilicon defoamer in sequence, and stir for 12 minutes after each addition. In this step, add AEO-9 first and then SDBS, which can ensure that AEO-9 adsorbs on the surface of the EDTA-2Na chelating agent before SDBS, thus forming a stable dispersion system.

[0048] Among them, in this embodiment, the organosilicon defoamer uses a polyether-modified organosilicon defoamer, the defoaming time ≤ 10 s, and it does not affect the interfacial activity of AEO-9 and SDBS.

[0049] (4) After all components are added, continue to stir for 45 minutes to obtain the cleaning agent.

[0050] This embodiment also proposes a cleaning method for using the above cleaning agent to clean calcium fluoride scale on heat exchangers, including the following steps:

[0051] (1) Pre-rinse: Pre-rinse the heat exchanger with clean water for 15 minutes.

[0052] (2) Circulating cleaning: Inject the cleaning agent into the heat exchanger circulation system, control the temperature at 50 °C, the flow rate at 0.4 m / s, and circulate and clean for 3 hours.

[0053] (3) Discharge and rinse: Discharge the cleaning agent to the wastewater treatment device, and rinse the heat exchanger with clean water until the drained water is clear.

[0054] After cleaning, the removal rate of calcium fluoride scale on the surface of the heat exchanger reaches 98%, and there is no obvious corrosion sign on the metal surface.

[0055] Example 2

[0056] The cleaning agent proposed in this embodiment for cleaning calcium fluoride scale on heat exchangers, by mass percentage, includes the following components: pentasodium diethylenetriaminepentaacetate (DTPA-5Na) 12%, fatty alcohol polyoxyethylene ether (AEO-7) 4%, sodium dodecylbenzenesulfonate (SDBS) 2.5%, mercaptobenzotriazole 1.5%, sodium carbonate is used to adjust the pH to 7.5, silicone defoamer 0.4%, and the balance is deionized water.

[0057] The preparation method of the above cleaning agent is similar to that of Example 1, only with slightly adjusted parameters. During preparation, the stirring speed is 280 r / min, the stirring time for each component is 13 minutes, and the total stirring time is 50 minutes;

[0058] The cleaning method proposed in this embodiment is similar to that of Example 1, only with slightly adjusted parameters. During cleaning, pre-rinse for 20 minutes, the circulating cleaning temperature is 55 °C, the flow rate is 0.45 m / s, and the circulating cleaning is carried out for 3.5 hours.

[0059] After cleaning, the removal rate of calcium fluoride scale is 97%, and the equipment corrosion rate meets the industrial use requirements.

[0060] Example 3:

[0061] The difference between this embodiment and Example 1 is as follows:

[0062] The composition of the cleaning agent is adjusted as follows: EDTA-2Na 15%, fatty alcohol polyoxyethylene ether (AEO-9) 5%, SDBS 3%, methylbenzotriazole 2%, and sodium carbonate is used to adjust the pH to 7.8.

[0063] The preparation method of the cleaning agent is the same as that of Example 1.

[0064] The object of cleaning in this embodiment is a high-concentration calcium fluoride scale layer on a heat exchanger with a scale thickness ≥ 2 mm. Its cleaning method is similar to that of Example 1, only with the following slightly adjusted parameters:

[0065] The circulating temperature is 60 °C, the flow rate is 0.5 m / s, and the circulating cleaning is carried out for 4 hours;

[0066] After cleaning, the removal rate of calcium fluoride scale reaches 96.5%, and the metal weight loss rate is 0.04 g / m 2 (tested according to ASTM G1 standard), and the surface roughness Ra ≤ 1.6 μm.

[0067] Example 4:

[0068] The difference between this embodiment and Example 1 is that this cleaning agent is a special formula for copper alloy substrates, and its composition is adjusted as follows: Formula adjustment: DTPA-5Na 10%, fatty alcohol polyoxyethylene ether (AEO-7) 4%, SDBS 2%, BTA 1.2% (special corrosion inhibitor for copper), and citric acid is used to adjust the pH to 6.5.

[0069] In this embodiment, the preparation method of the cleaning agent and the cleaning method proposed in this embodiment are the same as those in Embodiment 1.

[0070] After cleaning, a corrosion test was carried out. The results showed that the corrosion rate of the copper sheet was 0.02 mm / a (GB / T 1842 standard), which was much lower than the industry standard of 0.05 mm / a. At the same time, the removal rate of calcium fluoride scale after cleaning reached 97%.

[0071] In the above Embodiments 1 to 4, the removal rate of calcium fluoride scale was detected by the weighing method and calculated by the following formula:

[0072] (Weight difference of the specimen before and after cleaning / Weight of the original scale layer) × 100%, with an accuracy of 0.1 mg.

[0073] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A cleaning agent for cleaning calcium fluoride scale on a heat exchanger, characterized in that: By mass percentage, it includes the following components: 5-15% of amino polycarboxylic acid chelating agent, 3-8% of compound surfactant, 0.5-2% of corrosion inhibitor, 0.1-0.5% of defoaming agent and 65-85% of deionized water; The cleaning agent further includes a pH regulator, and the addition amount of the pH regulator is based on adjusting the pH value of the cleaning agent to 6-8.

2. The cleaning agent for cleaning calcium fluoride scale of a heat exchanger according to claim 1, characterized in that: The amino polycarboxylic acid chelating agent is selected from at least one of ethylenediaminetetraacetic acid (EDTA), sodium ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid (DTPA), and sodium diethylenetriaminepentaacetate.

3. The cleaning agent for cleaning calcium fluoride scale of a heat exchanger according to claim 1, wherein: The compound surfactant is composed of non-ionic surfactant fatty alcohol polyoxyethylene ether (AEO) and anionic surfactant sodium dodecylbenzenesulfonate (SDBS) with a mass ratio of (2-5):(1-3).

4. The cleaning agent for cleaning calcium fluoride scale of a heat exchanger according to claim 3, characterized in that: The HLB value of the fatty alcohol polyoxyethylene ether (AEO) is 12-14, and it is selected from at least one of AEO-7 and AEO-9.

5. The cleaning agent for cleaning calcium fluoride scale of a heat exchanger according to claim 4, wherein: The critical micelle concentration of the sodium dodecylbenzenesulfonate (SDBS) is below 8.2×10-3 mol / L.

6. The cleaning agent according to claim 1, wherein: The pH regulator uses citric acid or sodium carbonate.

7. The cleaning agent for cleaning calcium fluoride scale of a heat exchanger according to claim 1, characterized in that: The corrosion inhibitor is selected from at least one of benzotriazole (BTA), methylbenzotriazole (TTA), and mercaptobenzotriazole, and the corrosion inhibitor can form a dense protective film with a thickness of 5-10 nm on the metal surface.

8. The cleaning agent according to claim 1, characterized in that: The defoaming agent uses an organosilicon defoaming agent, and the defoaming time of the organosilicon defoaming agent ≤ 10 s, and it does not affect the interfacial activity of the compound surfactant.

9. The preparation method of the cleaning agent according to any one of claims 1-8, characterized in that, It includes the following steps: (1) Pre-rinse: Rinse the surface of the heat exchanger with clean water to remove loose impurities; (2) Circulating cleaning: Inject the cleaning agent into the heat exchanger circulation system, control the temperature at 40-60 °C and the flow rate at 0.3-0.5 m / s, and circulate for 2-4 hours; (3) Discharge and post-rinse: Drain the waste liquid into the wastewater treatment device and rinse with clean water until the drained water is clear and free of impurities. (4) After all components are added, continue stirring for 30-60 minutes to make all components evenly dispersed, and obtain the cleaning agent.

10. A cleaning method for cleaning calcium fluoride scale on a heat exchanger using the cleaning agent according to any one of claims 1-8, characterized in that, It includes the following steps: (1) Pre-rinse: Rinse the surface of the heat exchanger with clean water to remove loose impurities; (2) Circulating cleaning: Inject the cleaning agent into the heat exchanger circulation system, control the temperature at 40-60 °C and the flow rate at 0.3-0.5 m / s, and circulate for 2-4 hours; (3) Discharge and post-rinse: Drain the waste liquid into the wastewater treatment device and rinse with clean water until the drained water is clear and free of impurities.