A high-pressure boiler water treatment agent and a boiler cleaning method

Abstract

The application discloses a high-pressure boiler in-furnace water treatment agent and a boiler cleaning method. The high-pressure boiler in-furnace water treatment agent comprises scale treatment agent A, pickling treatment agent B and oxidation passivation treatment agent C used in steps; the scale treatment agent A comprises phosphate, dimethylglyoxime, ammonia water and deionized water; the pickling treatment agent B comprises EDTA, nitric acid, corrosion inhibitor and deionized water; the oxidation passivation treatment agent C comprises hydrogen peroxide, ammonia water and deionized water; the boiler cleaning method comprises steps of scale and rust cleaning, pickling, oxidation treatment, periodical treatment and drying. The application forms a comprehensive passivation effect on the inner wall of the boiler, which is firm, uniform, dense and covers an area of more than 98%, avoids the corrosion battery reaction caused by the unevenness of the existing rust removal and passivation treatment from the root, greatly reduces the possibility of corrosion, rust and scale formation on the inner wall of the boiler, greatly reduces the boiler cleaning frequency and reduces the boiler maintenance cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of boiler cleaning and rust prevention treatment, and particularly relates to a high-pressure boiler in-furnace water treatment agent and a boiler cleaning method. BACKGROUND

[0002] Boiler in-furnace water treatment is an important link to ensure the safe production of boilers. A small amount of impurities such as colloid, calcium and iron dissolved in water as an energy transfer medium in a high-temperature and high-pressure environment is easy to deposit and form dirt, which is deposited on the inner surface of the boiler pipeline and causes pipeline corrosion and damage. Especially in a high-temperature and high-pressure special working environment, the surface stress of the boiler pipeline is very large, and the corrosion damage will also bring certain safety hazards, so the boiler water needs to be dosed for treatment under normal circumstances to adjust the water quality and as far as possible to delay or reduce the dirt generated by the high-pressure boiler.

[0003] The boiler in-furnace water treatment agents used at present are divided into corrosion and scale inhibitors, oxygen scavengers, cleaning agents, sludge dispersants and the like, and there are many types, but most of the boiler in-furnace water treatment agents have a high operation and use cost, and therefore there is an urgent need to provide a boiler in-furnace water treatment agent which is economic and efficient and has low phosphorus and can remove dirt, prevent corrosion and remove oxygen.

[0004] More importantly, the existing water treatment agents for passivation often target rusted parts or scaled parts, that is, the passivation film produced has a small and uneven coverage area, causing the corrosion of iron to still exist in the form of a corrosion cell during the operation of the boiler, that is, a single water treatment can only ensure a short time of operation, and iron rust will be generated at other parts after a certain period of time. Objectively, this causes the boiler to need to be maintained and serviced including cleaning, pickling, passivation and the like, and various regular maintenance, which makes the maintenance downtime of the boiler too long, the equipment maintenance cost too high, the service life of the boiler too short and the actual utilization value of the boiler too low, and improvement is urgently needed. SUMMARY

[0005] In order to solve the problems of water treatment mentioned in the background in the above (the problems that can be solved by claim 1), the present application provides a high-pressure boiler in-furnace water treatment agent and a boiler cleaning method.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A high-pressure boiler in-furnace water treatment agent, comprising scale treatment agent A, pickling treatment agent B and oxidation passivation treatment agent C used in steps;

[0008] The scale treatment agent A comprises phosphate, dimethylglyoxime, ammonia water and deionized water;

[0009] The pickling treatment agent B comprises EDTA, nitric acid, corrosion inhibitor and deionized water;

[0010] The oxidizing passivation treatment agent C comprises hydrogen peroxide, ammonia and deionized water.

[0011] Preferably, the weight percentage of each component in the scale treatment agent A is as follows:

[0012] Phosphate: 0.03%-0.1%,

[0013] Dimethylglyoxime: 0.1%-0.5%,

[0014] Ammonia: 70%-80%,

[0015] The rest is deionized water.

[0016] Further, the ammonia concentration in the ammonia is 30-40%, the purity of the phosphate and dimethylglyoxime is greater than 98%, and the phosphate is any of sodium phosphate, organic phosphate or polymeric phosphate, wherein the organic phosphate is any of aminotri(methylene)phosphonate (ATMP), ethylenediamine tetra(methylene)phosphonate (EDTMP) and hydroxy(methylene)phosphonate (HEDP);

[0017] The phosphate produced by the phosphate forms a precipitate with Ca 2+ , Mg 2+ and Fe ions:

[0018] Fe 2+ + HPO4 2- → FeHPO4↓, Fe 3+ + PO4 3- → FePO4↓

[0019] The addition of appropriate organic phosphate or polymeric phosphate can form water-soluble chelates with Ca 2+ , Mg 2+ , Fe 2+ and Fe 3+ ions, which can avoid the precipitation of water scale due to supersaturation, keep the soft water scale and newly produced precipitate soft, and facilitate the impact discharge.

[0020] Dimethylglyoxime reacts with iron rust to produce a dense Fe3O4 passivation film:

[0021] 2(CH3)2C=NOH+6Fe2O3→2(CH3)2C=O+4Fe3O4+N2O+H2O

[0022] The pH is 9.5±0.5, and the ammonia also has complexing reactions with Ag + , Cu 2+ , Cr 3+ , Zn 2+ , etc., which can remove such heavy metals.

[0023] Further, the phosphate, dimethylglyoxime and ammonia in the scale treatment agent A are mixed with deionized water in certain proportions and stored in three different storage tanks, and the preparation method is as follows:

[0024] (1) The phosphate and deionized water are mixed in a weight ratio of 1:200-280 to obtain mixed agent one;

[0025] (2) The dimethylglyoxime and deionized water are mixed in a ratio of 1:90-120 to obtain mixed agent two;

[0026] (3) The ammonia is added to the remaining proportion of deionized water, and the mixture is stored separately;

[0027] (4) To achieve the predetermined amount of agent, the mixing ratio of mixed agent one, mixed agent two and ammonia when used is (6-10):(0.6-1):(0.8-1.2).

[0028] Preferably, the weight percentage of each component in the pickling agent B is:

[0029] EDTA: 5-7%,

[0030] Nitric acid: 8-10%,

[0031] Corrosion inhibitor: 5-7%,

[0032] and the rest is deionized water.

[0033] Further, the preparation process of the pickling agent B is as follows:

[0034] The nitric acid is added dropwise into the deionized water, and after cooling to room temperature, the EDTA and the corrosion inhibitor are added respectively, and stirred until uniform. The prepared pickling agent B has a HNO3 content of 4.8-6.8%, which allows the system to be cleaned in dilute nitric acid, has a dual effect of corrosion and passivation on carbon steel, and the EDTA can be dissolved in dilute nitric acid solution under the acidity condition, thereby improving the solubility of EDTA.

[0035] Preferably, the corrosion inhibitor is GL5004, the purity of EDTA is greater than 99%, and the nitric acid is a concentrated HNO3 solution with a concentration of 60-68%. Alternatively, a fuming nitric acid with a concentration of 90-97% can be used to prepare an equivalent amount of HNO3 component. The prepared pickling agent B has a HNO3 content of 4.8-6.8%, which allows the system to be cleaned in dilute nitric acid, has a dual effect of corrosion and passivation on carbon steel, and the EDTA can be dissolved in dilute nitric acid solution under the acidity condition, thereby improving the solubility of EDTA.

[0036] 3NO2+H2O→2HNO3+NO

[0037] When the carbon steel in the boiler reacts, more NO content is produced, which reacts with Fe2+ EDTA complex produces Fe 2+ EDTA(NO):

[0038]

[0039] The complex can adhere in situ to the steel surface, allowing the steel surface to carry the complex and to release it slowly: nitric acid pickling is highly corrosive to the carbon steel material of the inner wall of a boiler, and by producing iron complexing agents from EDTA and absorbing the generated NO, Fe 2+ EDTA(NO) has a different oxidation reaction with nitric acid, and Fe 2+ EDTA(NO) has a relatively mild reactivity with the carbon steel surface of the inner wall of a boiler and can adhere to the steel surface in situ, allowing the steel surface to react uniformly, and Fe 3+ EDTA reacts with the carbon steel surface of the inner wall of a boiler, allowing Fe 2+ EDTA regeneration:

[0040] 2Fe 2+ EDTA(NO) + Fe + 10H + + EDTA → 3Fe 2+ EDTA + Fe 2+ + 2NH4 + + 2H2O

[0041] 2Fe 3+ EDTA + Fe + EDTA → 3Fe 2+ EDTA

[0042] There is also a corrosion cell reaction in the system, which promotes Fe 2+ and Fe 3+ equilibrium:

[0043] 2Fe 3+ + Fe → 3Fe 2+

[0044] During the pickling process, the Fe3O4 passivation film and phosphating film produced in the previous production can be consumed by reaction:

[0045] 3Fe3O4 + 28HNO3 → 9Fe(NO3)3 + 14H2O + NO↑

[0046] Fe3O4 + 8HNO3 → 2Fe(NO3)3 + Fe(NO3)2 + 4H2O

[0047] There is also a corrosion reaction on the carbon steel surface of the uncoated area during the pickling process:

[0048] Fe + 4HNO3 → Fe(NO3)3 + NO↑ + 2H2O

[0049] 3Fe + 8HNO3→ 3Fe(NO3)2 + 2NO↑ + 4H2O

[0050] 3Fe(NO3)2 + 4HNO3→ 3Fe(NO3)3 + 2H2O + NO↑

[0051] In addition, under acidic conditions, the phosphating film produces (HPO4) 2- can form complex ions [Fe (HPO4) 2] - It is also an oxidizing agent, which can further promote the corrosion range of the steel surface, occupy the reaction site of HNO3, and further weaken the corrosion passivation rate of nitric acid on carbon steel;

[0052] By pickling, the uneven Fe3O4 passivation film and phosphating film surface is reacted and activated, and through impact, the film with low adhesion can be removed and settled. Again, through the oxidation of Fe 2+ EDTA (NO), [Fe (HPO4) 2] - In-situ oxidation and the balance of each complex produce and adsorb Fe 2+ and Fe 3+ Complex ions, slowly produce a more uniform and high coverage new Fe3O4 passivation film on the carbon steel surface of the inner wall of the boiler.

[0053] Preferably, the weight percentage of each component in the oxidizing passivation treatment agent C is:

[0054] Hydrogen peroxide: 15-20%,

[0055] Ammonia: 5-7%,

[0056] The rest is deionized water.

[0057] Further, the concentration of H2O2 in hydrogen peroxide is 15-20%, and it is prepared and used immediately; the concentration of ammonia in ammonia water is 30-40%;

[0058] Adjust the pH to 8-8.5, and after removing the acid, the pH drops to 7.8-8.2, and the system temperature in the boiler is raised to 110-130°C. Hydrogen peroxide oxidizes Fe 2+ EDTA (NO), Fe 3+ EDTA and [Fe (HPO4) 2] -

[0059] 2Fe 2+ + H2O2→ 2Fe 3+ + 2OH -

[0060] 2Fe 2+ EDTA + H2O2→ 2Fe​3+ EDTA+2OH -

[0061] After 15-20 min of reaction, the new Fe3O4 passivation film generated in the previous step is deposited again;

[0062] After the discharge, hot air at 250-300℃ is passed to dry and deammoniate and dehydrate, and the treatment is performed for 20-30 min. The coverage area of the Fe3O4 passivation film on the inner wall of the boiler is more than 98%, and the passivation film thickness uniformity of the original rust part, fouling part and clean part is good. A uniform and dense black oxide film is formed, which is similar to the "blackening" or "bluing" treatment of carbon steel. A chemical deposition passivation film forming process in the cleaning process is formed, which fundamentally avoids the corrosion cell reaction caused by the unevenness of the existing rust removal and passivation treatment, greatly reduces the possibility of rusting and fouling of the inner wall of the boiler, and maintains the cleanliness of the inner wall of the boiler for a long time, greatly reduces the cleaning frequency of the boiler, and reduces the maintenance cost of the boiler.

[0063] The residual nitrogen oxides NO x After oxidation by H2O2, NO3 - and H2O are generated, which can be normally discharged to reduce air pollution in the treatment workshop.

[0064] In addition, the present application is also suitable for the maintenance of water supply pipes, discharge pipes and other pipe fittings connected with the system in the boiler. When used, the water treatment agent is filled in the pipe to be treated, the valve is closed, and sufficient water treatment agent is added in the boiler to maintain sufficient reaction time. After batch treatment is completed, it can be discharged.

[0065] The present application also proposes a boiler cleaning method using the high-pressure boiler inner water treatment agent described above, which comprises the following steps:

[0066] S1, scale and rust cleaning:

[0067] The newly prepared scale treatment agent A is poured into the boiler, the inner wall of the boiler is washed and soaked for 10-15 min, and the treatment is performed for 3-4 times. Most of the rust and dirt on the inner wall of the boiler are cleaned, and a phosphating film, a Fe3O4 passivation film or a composite film of the two is generated on the original rust part;

[0068] S2, pickling:

[0069] The scale treatment agent A is discharged, the newly prepared pickling treatment agent B is poured into the boiler, the inner wall of the boiler is washed and soaked for 15-20 min, part of the phosphating film and Fe3O4 passivation film generated in the previous step is consumed, the remaining rust is removed, and a Fe3O4 passivation film is generated on the Fe 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] -Under the oxidation of the complex, the steel surface reaction of the original non-rust part is promoted to generate a new Fe3O4 passivation film with higher coverage and uniformity and compactness;

[0070] The pickling agent B is treated for 1-2 times, and the room temperature is ensured during pickling if the boiler material is low-carbon steel or medium-carbon steel, because the corrosion of dilute nitric acid aqueous solution to carbon steel is relatively strong, and the oxide passivation film is formed too fast due to the high-temperature corrosion, and the uniformity is poor; if the boiler material is gray cast iron or other alloy steel with very small carbon content, the system in the boiler can be appropriately heated to 50-60 DEG C to accelerate the passivation film forming reaction.

[0071] S3, oxidation treatment:

[0072] The pickling agent B is discharged, and the newly prepared oxidation passivation agent C is poured into the boiler, the inner wall of the boiler is washed and soaked for 5-8 min, ammonia water is added to adjust the pH to 8-8.5, the pH is reduced to 7.8-8.2 after acid removal, the system temperature in the boiler is increased to 110-130 DEG C, and the hydrogen peroxide is used to oxidize the Fe 2+ EDTA (NO), Fe 3+ EDTA and [Fe (HPO4) 2] - Oxidation, after 15-20 min of reaction, the newly generated Fe3O4 passivation film is secondarily deposited;

[0073] S4, periodic treatment:

[0074] According to the operation steps of S1, S2 and S3, the inner wall of the boiler is treated for 1-2 periods, and each period includes single scale and rust cleaning, single pickling and single oxidation treatment in turn.

[0075] S5, drying:

[0076] After the periodic treatment, the overheat water at 110-130 DEG C is used for washing for 2-3 times after complete discharge;

[0077] The hot air at 250-300 DEG C is introduced, and the ammonia and water are removed by drying for 20-30 min, and the boiler is returned to the factory for use.

[0078] Compared with the prior art, the beneficial effects of the present application are:

[0079] 1. The scale treatment agent A of the present application is a low-phosphorus environmentally friendly agent, which is low in price, excellent in corrosion and scale inhibition performance, and has oxygen removal effect, can adjust the PH value of circulating water, improve the PH value of condensate, and can also remove the scale formed in the boiler circulating water system, and can strip and decompose the scale layer formed on the inner wall of the boiler, so as to achieve remarkable scale removal effect; the boiler blowdown rate can be controlled to 2.0% or less.

[0080] 2. The present invention uses a compound of phosphate, dimethylglyoxime and ammonia to descale with phosphate and remove rust with dimethylglyoxime. The resulting scale treatment agent A not only has excellent descaling and rust removal functions, but also generates phosphating film and Fe3O4 passivation film on the original scale and rust sites.

[0081] 3. This invention utilizes a combination of nitric acid and EDTA. Nitric acid can react with and consume the previously produced Fe3O4 passivation and phosphating films, and can also corrode and passivate clean areas, generating NO. Furthermore, under the coordination effect of residual phosphate and EDTA from the previous step, NO reacts with Fe in the system. 2+ EDTA combines to form Fe 2+ EDTA(NO) further promotes the reaction on the steel surface, producing Fe in situ during corrosion. 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] - The oxidation of the complex promotes the reaction on the original unrusted steel surface, greatly weakens the direct corrosion passivation reaction of HNO3, and generates a new Fe3O4 passivation film with a relatively high coverage and uniform density.

[0082] 4. This invention uses an oxidation passivation agent C to perform a secondary deposition on the previously applied Fe3O4 passivation film, ultimately achieving a robust, uniform, and dense passivation effect with a coverage area of ​​over 98%. This avoids the defects of existing acid pickling passivation, which is too fast and uneven. It fundamentally avoids the corrosion cell reaction caused by the unevenness of existing rust removal and passivation treatments, greatly reducing the possibility of corrosion, rust, and scaling on the boiler inner wall. After treatment, the boiler inner wall can be kept clean for a longer period of time, significantly reducing the frequency of boiler cleaning and reducing boiler maintenance costs. Detailed Implementation

[0083] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0084] Comparative Example 1:

[0085] Existing boilers require at least the following procedures when in use:

[0086] 1) Use phosphate to descale the boiler approximately every month;

[0087] 2) Every 2-3 months of use, the boiler needs to be shut down and soaked in dimethylglyoxime for maintenance, with a soaking time of not less than 5 days;

[0088] 3) every use for about half a year, using pickling agent for pickling treatment of boiler, after treatment, in turn using ammonia neutralization, phosphate passivation treatment;

[0089] 4) in the warm season or production slack season, the boiler is maintained by dry or wet method, and there is also regular inspection;

[0090] The treatment cycle is long, the maintenance cost is high, and improvement is needed.

[0091] In order to solve the existing boiler maintenance problem as described in Comparative Example 1, the present application proposes a combined treatment high-pressure boiler in-furnace water treatment agent, which includes scale treatment agent A, pickling treatment agent B and oxidation passivation treatment agent C used in steps, the present application first verifies the scale removal effect of scale treatment agent A, as follows:

[0092] Scale treatment agent A test group:

[0093] Example 1:

[0094] The preparation method of scale treatment agent A is as follows: (1) phosphate and deionized water are mixed according to the weight ratio of 1:200 to obtain mixed agent one; (2) dimethyl glyoxime and deionized water are mixed according to the ratio of 1:90 to obtain mixed agent two; mixed agent one: mixed agent two: ammonia water = 6:0.6:1 (weight ratio).

[0095] After applying the above scale treatment agent A for multiple times, the boiler indicators are measured as follows:

[0096]

[0097] Example 2:

[0098] The preparation method of scale treatment agent A is as follows: (1) phosphate and deionized water are mixed according to the weight ratio of 1:240 to obtain mixed agent one; (2) dimethyl glyoxime and deionized water are mixed according to the ratio of 1:100 to obtain mixed agent two; mixed agent one: mixed agent two: ammonia water = 8:1:1 (weight ratio).

[0099] After applying the above scale treatment agent A for multiple times, the boiler indicators are measured as follows:

[0100]

[0101] Example 3:

[0102] The preparation method of the scale treatment agent A is as follows: (1) mixing the phosphate and deionized water according to the weight ratio of 1:280 to obtain mixed agent one; (2) mixing the dimethyl glyoxime and deionized water according to the ratio of 1:120 to obtain mixed agent two; the weight ratio of mixed agent one:mixed agent two:ammonia water is 10:1:1.2.

[0103] After the scale treatment agent A is applied for multiple times, the indexes of the boiler are measured as follows:

[0104]

[0105] The scale treatment agent A prepared in the examples 1, 2 and 3 has excellent scale and corrosion inhibition performance, and also has oxygen removal effect, and has good use effect. Through the effects of the above examples, it can be seen that the scale treatment agent A achieves the desired scale removal and rust removal purposes, and the detection indexes are better than the national standards. By adjusting the pH of the boiler water, the silicon entrainment phenomenon is prevented, and the generation of polymeric silicon is reduced; the scale treatment agent A can also remove the formed scale in the boiler circulating water system, and the scale layer formed on the inner wall of the boiler is stripped and decomposed, so that the remarkable scale removal effect is achieved.

[0106] The whole test group:

[0107] Example 4:

[0108] A novel boiler cleaning method, comprising the following steps:

[0109] S1, scale and rust cleaning:

[0110] The newly prepared scale treatment agent A of example 1 is poured into the boiler, the inner wall of the boiler is flushed and soaked for 10 minutes, and the process is repeated for 4 times, so that most of the rust and scale on the inner wall of the boiler are cleaned, and phosphating film, Fe3O4 passivation film or composite film of the two is generated on the original rust site;

[0111] S2, pickling:

[0112] The pickling agent B is prepared by adding the concentrated HNO3 solution with a concentration of 60% into deionized water dropwise, adding EDTA and corrosion inhibitor into the deionized water after the deionized water is cooled to room temperature, and stirring until uniform, wherein the weight ratio of EDTA:nitric acid:corrosion inhibitor is 5:10:7, and the corrosion inhibitor is GL5004;

[0113] The scale treatment agent A is discharged, the newly prepared pickling agent B is poured into the boiler, the inner wall of the boiler is flushed and soaked for 15 minutes, part of the phosphating film and Fe3O4 passivation film generated in the previous step is consumed, the remaining rust is removed through reaction, and Fe 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] -The oxidation of the complex promotes the reaction of the steel surface of the original non-rust part to generate a new Fe3O4 passivation film with higher coverage and uniformity and compactness;

[0114] The pickling agent B is treated once, and the temperature is room temperature (20-30℃) during pickling, because the dilute nitric acid aqueous solution has strong corrosion to carbon steel, and the oxide passivation film is formed too fast and is not uniform due to the fast high-temperature corrosion. If the boiler is made of gray cast iron or other alloy steel with very small carbon content, the system in the boiler can be appropriately heated to 50℃ to accelerate the passivation film forming reaction.

[0115] S3, oxidation treatment:

[0116] The oxidation passivation agent C is prepared by adding hydrogen peroxide into deionized water and then adding ammonia water and mixing, and the concentration of H2O2 in the hydrogen peroxide is 20%, and the concentration of ammonia in the ammonia water is 30%.

[0117] The pickling agent B is discharged, the newly prepared oxidation passivation agent C is put into the boiler, the inner wall of the boiler is rinsed and soaked for 5 min, ammonia water is added to adjust the pH to 8.3, the pH is reduced to 8.0 after acid removal, the temperature of the system in the boiler is increased to 110℃, the hydrogen peroxide reacts with the Fe 2+ EDTA (NO), Fe 3+ EDTA and [Fe (HPO4) 2] - Oxidation, after 20 min of reaction, the newly generated Fe3O4 passivation film is deposited again.

[0118] S4, periodic treatment:

[0119] According to the operation steps of S1, S2 and S3, the inner wall of the boiler is treated for one cycle, and each cycle includes single scale and rust cleaning, single pickling and single oxidation treatment.

[0120] S5, drying:

[0121] After the periodic treatment, the system is completely discharged, and superheated water at 110℃ is used for rinsing three times.

[0122] Hot air at 250℃ is introduced, and ammonia and water are removed by drying for 30 min, and the boiler is returned to the factory for use.

[0123] Example 5:

[0124] A new type of boiler cleaning method, comprising the following steps:

[0125] S1, scale and rust cleaning:

[0126] The newly prepared scale treatment agent A of Example 2 is put into the boiler, the inner wall of the boiler is flushed and soaked for 15 min, and the process is repeated for 3 times, most of the rust and dirt on the inner wall of the boiler are cleaned, and phosphating film, Fe3O4 passivation film or composite film of the two are generated on the original rust site;

[0127] S2, pickling:

[0128] Preparation of pickling agent B: a concentrated HNO3 solution with a concentration of 68% is added dropwise into deionized water, and after being cooled to room temperature, EDTA and corrosion inhibitor are added respectively, and stirred until uniform, and the prepared pickling agent B is used immediately, wherein EDTA: nitric acid: corrosion inhibitor = 7:8:6, and the corrosion inhibitor is Lan-826;

[0129] The scale treatment agent A is discharged, the newly prepared pickling agent B is put into the boiler, the inner wall of the boiler is flushed and soaked for 20 min, part of the phosphating film and Fe3O4 passivation film generated in the previous step are consumed, the remaining rust is removed by reaction, and a new Fe3O4 passivation film with high coverage and uniform density is generated on the Fe 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] - Under the oxidation of the complex, the steel surface at the original rust-free site is promoted to react, and a new Fe3O4 passivation film with high coverage and uniform density is generated;

[0130] The pickling agent B is treated for 1 time, and the temperature of the boiler system is appropriately increased to 60°C according to the material of the boiler, such as low carbon steel or medium carbon steel, so as to accelerate the passivation film forming reaction, because the corrosion of dilute nitric acid aqueous solution on carbon steel is strong, and the passivation film of oxides is formed too fast and is not uniform due to high temperature corrosion;

[0131] S3, oxidation treatment:

[0132] Preparation of oxidation passivation agent C: hydrogen peroxide is added to deionized water, and ammonia water is poured and mixed, and the prepared oxidation passivation agent C is used immediately, wherein the concentration of H2O2 in the hydrogen peroxide is 20%, and the concentration of ammonia in the ammonia water is 40%;

[0133] The pickling agent B is discharged, the newly prepared oxidation passivation agent C is put into the boiler, the inner wall of the boiler is flushed and soaked for 8 min, ammonia water is added to adjust the pH to 8.2, the pH is reduced to 7.9 after acid removal, the temperature of the boiler system is increased to 130°C, the Fe 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] - Oxidation, and the newly generated Fe3O4 passivation film in the previous step is deposited again after 15 min of reaction;

[0134] S4, periodic treatment:

[0135] According to the operation steps of S1, S2 and S3, the inner wall of the boiler is treated for 2 periods, each period sequentially including single scale and rust cleaning, single pickling and single oxidation treatment;

[0136] S5, drying:

[0137] After the periodic treatment, the water is completely discharged, and 130℃ superheated water is used for rinsing twice;

[0138] Hot air at 300℃ is introduced, and ammonia and water are removed by drying, and the treatment is performed for 20min, and the product is returned to the factory for use.

[0139] Example 6:

[0140] A new type of boiler cleaning method, comprising the following steps:

[0141] S1, scale and rust cleaning:

[0142] The newly prepared scale treatment agent A of Example 3 is poured into the boiler, the inner wall of the boiler is washed and soaked for 12min, a total of 4 times, most of the rust and dirt on the inner wall of the boiler are cleaned, and a phosphating film, Fe3O4 passivation film or a composite film of the two is generated on the original rust site;

[0143] S2, pickling:

[0144] Pickling agent B is prepared: a concentrated HNO3 solution with a concentration of 65% is added dropwise into deionized water, and after being cooled to room temperature, EDTA and corrosion inhibitor are added respectively, and stirred until uniform, and used immediately, wherein EDTA: nitric acid: corrosion inhibitor = 6:9:6, and the corrosion inhibitor is SGR-0405;

[0145] The scale treatment agent A is discharged, the newly prepared pickling agent B is poured into the boiler, the inner wall of the boiler is washed and soaked for 18min, part of the phosphating film and Fe3O4 passivation film generated in the previous reaction is consumed, the remaining rust is removed by reaction, and a new Fe3O4 passivation film with high coverage and uniform and dense is generated on the Fe 2+ EDTA(NO), Fe 3+ EDTA and [Fe(HPO4)2] - Under the oxidation of EDTA(NO) and [Fe(HPO4)2] complex, the steel surface of the original rust-free site is promoted to react, and a new Fe3O4 passivation film with high coverage and uniform and dense is generated;

[0146] The pickling agent B is treated for 2 times. Depending on the material of the boiler, if it is low carbon steel or medium carbon steel, the room temperature should be ensured during pickling, because the corrosion of dilute nitric acid aqueous solution to carbon steel is relatively strong. In order to avoid the non-uniformity caused by the rapid formation of oxide passivation film due to the rapid corrosion at high temperature, the system in the boiler can be appropriately heated to 55℃ to accelerate the passivation film forming reaction. If it is gray cast iron or other alloy steel with very small carbon content, the system in the boiler can be appropriately heated to 55℃ to accelerate the passivation film forming reaction.

[0147] S3, oxidation treatment:

[0148] The oxidation passivation agent C is prepared by pouring hydrogen peroxide into deionized water, pouring ammonia water and mixing. The prepared agent is used immediately. The ratio of hydrogen peroxide to ammonia water is 18:6. The concentration of H2O2 in hydrogen peroxide is 16%, and the concentration of ammonia in ammonia water is 35%.

[0149] The pickling agent B is discharged, and the newly prepared oxidation passivation agent C is poured into the boiler. The inner wall of the boiler is rinsed and soaked for 6 min. Ammonia water is added to adjust the pH to 8. After acid removal, the pH is reduced to 7.8. The temperature of the system in the boiler is increased to 120℃. The Fe 2+ EDTA (NO), Fe 3+ EDTA and [Fe (HPO4) 2] - Oxidation, after 16 min of reaction, the newly generated Fe3O4 passivation film is deposited again.

[0150] S4, periodic treatment:

[0151] According to the operation steps of S1, S2 and S3, the inner wall of the boiler is treated for 1 cycle. Each cycle includes single scale and rust cleaning, single pickling and single oxidation treatment.

[0152] S5, drying:

[0153] After the periodic treatment, the system is completely discharged, and then rinsed with 120℃ superheated water for 3 times.

[0154] Hot air at 280℃ is introduced, and the ammonia and water are removed by drying for 25 min. The treated boiler is returned to the factory for use.

[0155] The treated boiler products of examples 4-6 are compared with the original boiler of comparative example 1, which is pickled and passivated every half year (pickled with 3.5% dilute hydrochloric acid and passivated with sodium phosphate). The boilers treated in examples 4-6 are returned to the factory for use for more than 10-14 months without rusting.

[0156] Since the passivation film on the inner wall of the boiler is relatively uniform, the scale rate is also less. For continuous operation of 1.5-2 months, the scale rate at the boiler drain port is monitored, and compared with Comparative Example 1, the scale rate is reduced by 70% in the same period. Specifically: compared with the original boiler of Comparative Example 1 after descaling every month, the scale rate of the boiler of Example 4 is reduced by 95.1% in the first 5 days, 82.3% in 5-10 days, 65.9% in 10-20 days, and 53.3% in 20-30 days; the scale rate of the boiler of Example 5 is reduced by 96.7% in the first 5 days, 84.6% in 5-10 days, 70.1% in 10-20 days, and 59.4% in 20-30 days; the scale rate of the boiler of Example 6 is reduced by 94.3% in the first 5 days, 80.2% in 5-10 days, 64.7% in 10-20 days, and 50.0% in 20-30 days.

[0157] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solutions and the inventive concept of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method of boiler cleaning, characterized in that, The high-pressure boiler in-furnace water treatment agent comprises the following steps: S1, scale and rust cleaning: Pour the newly prepared scale treatment agent A into the boiler, flush the inner wall of the boiler and soak for 10-15 min, and treat for 3-4 times in total; S2, pickling: Pour the newly prepared pickling treatment agent B into the boiler, flush the inner wall of the boiler and soak for 15-20 min; Pickling treatment agent B is treated for 1-2 times, depending on the material of the boiler, if it is low carbon steel or medium carbon steel, the pickling temperature should be room temperature, if it is gray cast iron, the temperature of the boiler system can be appropriately increased to 50-60℃ to accelerate the passivation film forming reaction; S3, oxidation treatment: Pour the newly prepared oxidation passivation treatment agent C into the boiler, flush the inner wall of the boiler and soak for 5-8 min, add ammonia water to adjust the pH to 8-8.5, the pH after acid removal is 7.8-8.2, the temperature of the boiler system is increased to 110-130℃, and the reaction is carried out for 15-20 min; S4, periodic treatment: According to the operation steps of S1, S2 and S3, the inner wall of the boiler is treated for 1-2 periods, each period includes single scale and rust cleaning, single pickling and single oxidation treatment in turn; S5, drying: After the periodic treatment, completely discharge, and then use 110-130℃ superheated water for 2-3 times of rinsing; Pass in 250-300℃ hot air, dry and dehydrate, treat for 20-30 min, and the boiler is returned to the factory for use; The high-pressure boiler in-furnace water treatment agent comprises scale treatment agent A, pickling treatment agent B and oxidation passivation treatment agent C used in steps; The scale treatment agent A comprises phosphate, dimethyl glyoxime, ammonia water and deionized water; The pickling treatment agent B comprises EDTA, nitric acid, corrosion inhibitor and deionized water; The oxidation passivation treatment agent C comprises hydrogen peroxide, ammonia water and deionized water; The weight percentage of each component in the scale treatment agent A is: Phosphate: 0.03%-0.1%, Dimethyl glyoxime: 0.1%-0.5%, Ammonia water: 70%-80%, The rest is deionized water; The corrosion inhibitor is GL5004, and the nitric acid is a concentrated HNO3 solution with a concentration of 60-68%; The weight percentage of each component in the oxidation passivation treatment agent C is: Hydrogen peroxide: 15-20%, Ammonia water: 5-7%, The rest is deionized water.

2. A boiler cleaning method according to claim 1, characterized in that The ammonia concentration in the ammonia water is 30-40%, and the phosphate is any of sodium phosphate, organic phosphate or polyphosphate, wherein the organic phosphate is any one of aminotriethylene phosphonate (ATMP), ethylenediamine tetraethylene phosphonate (EDTMP) and hydroxy methylene phosphonate (HEDP).

3. A method of boiler cleaning according to claim 1, wherein The phosphate, dimethyl glyoxime and ammonia water in the scale treatment agent A are mixed with deionized water in a certain proportion and stored in three different storage tanks, and the preparation method is as follows: (1) Mix the phosphate and deionized water in a weight ratio of 1:200-280 to obtain mixed agent one; (2) Mix dimethyl glyoxime and deionized water in a ratio of 1:90-120 to obtain mixed agent two; (3) Ammonia water is added to the remaining deionized water, and the mixture is stored separately; (4) To achieve the predetermined amount of the mixed medicament, the mixing ratio of the mixed medicament I, the mixed medicament II and the ammonia water is (6-10):(0.6-1):(0.8-1.2) when used.

4. A method of boiler cleaning according to claim 1, wherein The weight percentage of each component in the pickling agent B is as follows: EDTA: 5-7%, Nitric acid: 8-10%, Corrosion inhibitor: 5-7%, The rest is deionized water.

5. A method of boiler cleaning according to claim 1, wherein The preparation process of the pickling agent B is as follows: Nitric acid is added dropwise into deionized water, and after cooling to room temperature, EDTA and corrosion inhibitor are added respectively, and stirred until uniform. The prepared pickling agent B is used immediately.

6. A method of boiler cleaning according to claim 1, wherein The concentration of H2O2 in the hydrogen peroxide is 15-20%, and the concentration of ammonia in the ammonia water is 30-40%.

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