Method for descaling of steam injection boiler for reuse of purified sewage water

Abstract

The present application relates to a descaling method for a steam injection boiler, and the method comprises the following steps: based on the water chemistry theory, a function relationship of the existing state of minerals is established, a dynamic model is established based on the hydrolysis reaction, the scale layer type of the water scale is determined by combining the process flow of the steam injection boiler and the dynamic model, and a relationship diagram at different types of scale layers is fitted based on the dynamic model, the hydrolysis reaction and the field operation parameters according to the scale layer type of the water scale. The present application is based on the dissolution theory of key factors such as the mineral dissolution equilibrium, the mixing parameters of the fluid, the separation of the gas due to the pressure drop or boiling, and the interaction between the organic matter and the inorganic matter. After the scale formation type of the boiler tube is predicted, the scale is eliminated by the flushing and soaking methods, the maintenance workload is reduced, the production cost is reduced, the operation rate is improved, and the present application has a good application prospect in the production.

Description

Technical Field

[0001] This invention relates to the field of descaling technology for oilfield steam injection boilers, and is a descaling method for reusing purified wastewater from steam injection boilers. Background Technology

[0002] With the deepening development of heavy oil thermal recovery, all produced wastewater from oilfields is now being recycled and reused. In this process, the treated wastewater is used as feedwater for thermal recovery boilers, fully utilizing the high temperature of the oily wastewater from thermally recovered heavy oil to achieve comprehensive utilization of thermal energy and recycling of water resources. The recycled wastewater has a complex composition, containing, besides, calcium... 2+ Mg 2+ Besides ions, compared with using clean water, the purification of wastewater with heavy oil showed a significant increase in other ionic components, with TDS increasing more than 10 times and Cl... - With an increase of more than 30 times and a silicate content increase of more than 6 times, scale and other problems inevitably occur in boilers after long-term operation.

[0003] During the process of heat exchange and temperature rise of feedwater on the boiler heating surfaces, certain salts dissolved in the boiler water have a certain solubility. If this solubility limit is exceeded, the boiler water becomes a supersaturated solution of that salt. The excess salt precipitates out of the boiler water and, under suitable conditions, adheres to the pipe walls, forming scale and crystals. Scale has a complex chemical composition; it is usually not a simple compound but rather composed primarily of certain chemical components. Scale has very poor thermal conductivity, which worsens heat transfer, leading to deterioration of heat transfer on the heating surfaces, wasting fuel, or causing accidents such as pipe ruptures. Therefore, necessary descaling methods should be adopted. In descaling, determining the type and composition of the scale is crucial for analyzing the causes of scale formation and for effective scale removal.

[0004] Therefore, it is necessary to study a safe and quick method for identifying and removing boiler scale, so as to ensure equipment safety and achieve energy saving and consumption reduction in production and improve equipment operating rate. Summary of the Invention

[0005] This invention provides a descaling method for reusing purified wastewater in steam injection boilers, overcoming the shortcomings of the prior art. It can effectively solve the problems of short boiler tube service life, high fuel consumption, scale corrosion of boilers, and high production costs in oilfield steam injection boilers.

[0006] The technical solution of the present invention is achieved through the following measures: a descaling method for reusing purified wastewater in steam injection boilers, comprising the following steps:

[0007] The first step, based on hydrochemistry theory, is to establish the functional relationship of the existence state of minerals:

[0008] ΔG diff=f(Q i K i α i )

[0009] Where Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and α is the ion activation degree;

[0010] The second step involves establishing a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, based on the hydrolysis reaction:

[0011] D=f(ΔG,P,T,v,g,t,β)

[0012] Where ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, and β is the correction parameter.

[0013] The third step is to determine the type of scale layer by combining the process flow and dynamic model of the steam injection boiler.

[0014] The fourth step involves fitting a schematic diagram of the relationship between the dissolution rate D and pressure P, temperature T, flow rate v, and soaking and rinsing time t for different types of scale, based on the dynamic model, hydrolysis reaction, and on-site operating parameters, according to the scale type. By adjusting the rinsing and soaking time of the boiler tube scale, the descaling of different types of scale is completed.

[0015] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0016] In the second step above, the functional relationship of the mineral's state of existence includes determining the mineral's state of existence when ΔG diff <0, mineral dissolution is unsaturated, minerals do not precipitate; ΔG diff When the value is greater than 0, the mineral is supersaturated and the precipitation condition is met, so the mineral precipitates.

[0017] In the third step above, when determining the type of scale layer, the specific operation is as follows: based on the composition of the feedwater, the heating intensity of the feedwater on each heating surface, and the change process of the working fluid in the process flow of the steam injection boiler, determine the type of scale layer.

[0018] The scale types mentioned above include: carbonate composite scale and sulfate composite scale deposited in the convection section of the steam injection boiler; silicate composite scale deposited in the radiant section of the steam injection boiler.

[0019] In the aforementioned carbonate composite scale, the mass content of calcium carbonate is 50% to 95%; in the sulfate composite scale, the mass content of calcium sulfate is 50% to 95%; and in the silicate composite scale, the mass content of silicon dioxide is 20% to 25%.

[0020] This invention is based on the dissolution theory, which is based on key factors such as mineral dissolution equilibrium, fluid mixing parameters, gas separation due to pressure drop or boiling, and the interaction between organic and inorganic matter. After predicting the type of scale buildup on boiler tubes, the invention uses flushing and soaking methods to remove the scale, reducing maintenance workload, lowering production costs, and increasing operating efficiency. It has good application prospects in production. Attached Figure Description

[0021] Appendix Figure 1 This is a schematic diagram showing the relationship between the dissolution rate D of carbonate composite scale and the key technical parameters P, T, v, and t, as fitted in this invention.

[0022] Appendix Figure 2 This is a schematic diagram showing the relationship between the sulfate composite scale dissolution rate D and key technical parameters P, T, v, and t, as fitted in this invention.

[0023] Appendix Figure 3 This is a schematic diagram showing the relationship between the silicate composite scale dissolution rate D and key technical parameters P, T, v, and t, as fitted in this invention. Detailed Implementation

[0024] This invention is not limited to the following embodiments; specific implementation methods can be determined based on the technical solution of this invention and actual circumstances. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art.

[0025] The present invention will be further described below with reference to embodiments:

[0026] Example 1: The descaling method for recycling purified wastewater in steam injection boilers is carried out according to the following steps:

[0027] The first step, based on hydrochemistry theory, is to establish the functional relationship of the existence state of minerals:

[0028] ΔG diff =f(Q i K i α i )

[0029] Where Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and α is the ion activation degree;

[0030] The second step involves establishing a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, based on the hydrolysis reaction:

[0031] D=f(ΔG,P,T,v,g,t,β)

[0032] Where ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, and β is the correction parameter.

[0033] The third step is to determine the type of scale layer by combining the process flow and dynamic model of the steam injection boiler.

[0034] The fourth step involves fitting a schematic diagram of the relationship between the dissolution rate D and pressure P, temperature T, flow rate v, and soaking and rinsing time t for different types of scale, based on the dynamic model, hydrolysis reaction, and on-site operating parameters, according to the scale type. By adjusting the rinsing and soaking time of the boiler tube scale, the descaling of different types of scale is completed.

[0035] In this invention, the formation of scale in boilers used for wastewater purification and reuse is related to the content of bicarbonate, sulfate, and silicate ions in the boiler feedwater, as well as the total dissolved solids (TDS) of the feedwater. During steam generation, water continuously evaporates and concentrates on the heated surface wall, resulting in localized drying or bubbling along the wall surface. Deposited salts remain on the metal surface. However, when the bubbles on the wall burst or leave, the dried salt comes into contact with the boiler water. Unsaturated salts re-dissolve in the water, while supersaturated, insoluble salts adhere to the heated surface. This process repeats continuously, accumulating more and more salt on the heated surface wall. If the metal surface of the heated surface is rough and uneven, it creates conditions conducive to deposit adhesion. When the scale layer is not formed due to high heat load intensity on the heated surface, a dynamic model based on hydrolysis reactions, establishing the dissolution rate D of the composite precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, can guide the descaling process.

[0036] Example 2: As an optimization of the above example, in the second step, the determination of the mineral's state of existence in the functional relationship of the mineral's state of existence includes: when ΔG diff <0, mineral dissolution is unsaturated, minerals do not precipitate; ΔG diff When the value is greater than 0, the mineral is supersaturated and the precipitation condition is met, so the mineral precipitates.

[0037] Example 3: As an optimization of the above example, in the third step, when determining the scale layer type, the specific operation is as follows: the scale layer type is determined based on the feedwater quality composition, the heating intensity of the feedwater on each heating surface, and the change process of the working fluid in the steam injection boiler process.

[0038] Example 4: As an optimization of the above examples, the scale layer types include: carbonate composite scale and sulfate composite scale deposited in the convection section of the steam injection boiler; silicate composite scale deposited in the radiant section of the steam injection boiler.

[0039] Due to HClO3 in the feedwater 2- Ion hydrolysis produces CO2 and CO3- 0H - When plasma combines with calcium and carbonate ions in the water supply, it forms carbonate scale, mainly CaCO3. As the water temperature rises, the solubility of certain calcium and magnesium salts, such as CaSO4, Mg(OH)2, and Ca(OH)2, decreases in water. Once they reach a supersaturated state, they gradually form scale.

[0040] As the temperature continues to rise, some calcium and magnesium salts decompose upon heating, forming insoluble precipitates.

[0041] Ca(HCO3)2 = CaSO4↓ + CO2↑ + H2O

[0042] Mg(HClO3)2 = MgSO4↓ + CO2↑ + H2O

[0043] When the pH value of the boiler water is high, it will further hydrolyze into insoluble hydroxide precipitates:

[0044] MgCO3 + H2O = Mg(OH)2↓ + CO2↑

[0045] Therefore, it can be determined that carbonate and sulfate composite scales are mainly deposited in the convection section of the steam injection boiler, while silicate composite scales are mainly deposited in the radiant section of the steam injection boiler.

[0046] Example 5: As an optimization of the above examples, in the carbonate composite scale, the mass content of calcium carbonate is 50% to 95%; in the sulfate composite scale, the mass content of calcium sulfate is greater than 50%; and in the silicate composite scale, the mass content of silicon dioxide is 20% to 25%.

[0047] In on-site operation of steam injection boilers, the system pressure difference (the value of the working fluid outlet pressure minus the working fluid inlet pressure) is used to determine the scaling condition. Because the steam injection boiler is affected by back pressure (oil well demand pressure) during on-site operation, the system pressure difference can vary significantly. In actual on-site operation, when the operating parameters do not change significantly, an increase in system pressure difference of 0.5 MPa or more is usually considered an indicator of scaling. When the system pressure difference increases by 2 MPa or more, flushing is necessary. Since steam injection boilers must be shut down for maintenance after a period of operation, flushing is generally performed during shutdown to reduce steam injection losses. An increase in system pressure difference of 2 MPa during operation is considered an abnormal situation, requiring load reduction and flushing. During flushing, different types of scale layers can be removed using the descaling method of this invention for reusing purified wastewater from steam injection boilers.

[0048] Example 6: The descaling method for recycling purified wastewater in steam injection boilers is carried out according to the following steps:

[0049] The first step, based on hydrochemistry theory, is to establish the functional relationship of the existence state of minerals:

[0050] ΔGdiff =f(Q i K i α i )

[0051] Where Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and α is the ion activation degree;

[0052] The second step involves establishing a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, based on the hydrolysis reaction:

[0053] D=f(ΔG,P,T,v,g,t,β)

[0054] Where ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, and β is the correction parameter.

[0055] The third step, based on the process flow and dynamic model of the steam injection boiler, is to determine the scale type as follows: carbonate composite scale and sulfate composite scale are deposited in the convection section of the steam injection boiler; silicate composite scale is deposited in the radiant section of the steam injection boiler.

[0056] The fourth step involves fitting a schematic diagram, based on the scale type, dynamic model, hydrolysis reaction, and on-site operating parameters, to illustrate the relationship between the dissolution rate D of carbonate composite scale and pressure P, temperature T, flow rate v, and soaking and rinsing time t. (See diagram below.) Figure 1 As shown, from Figure 1 It can be seen that temperature is the main influencing factor for carbonate composite scale. According to the dynamic model, the dissolution rate does not change much when the temperature is above 100℃, and the influence of pressure and other factors is relatively small. The longer the soaking time, the better. However, the dissolution rate does not change much over time and is prone to under-scale corrosion. Therefore, the soaking time should generally not exceed 3 days. Intermittent changes in flow rate can flush away the scale layer after soaking. The following should be considered in conjunction with the site conditions:

[0057] (1) When the boiler is under maintenance or during normal shutdown, after the automatic purging is completed, manually start the plunger pump to flush it. When the temperature at the outlet of the radiant section drops below 100°C, stop the pump and close the valves at the inlet of the convection section and the outlet of the radiant section to ensure that the boiler tubes are full of water. When the temperature drops to 40°C, the water can be discharged.

[0058] (2) Based on daily water quality monitoring data, the pressure difference of the boiler convection section, radiation section and superheated section system is statistically analyzed. When the pressure difference changes more than 0.5 MPa compared with the normal, flushing can be carried out during boiler maintenance and equipment repair shutdown. The temperature is controlled between 60℃ and 150℃ during flushing, and the flushing time is not less than 30 minutes. If the pressure difference is still large, the flushing time needs to be extended and the boiler tubes should be soaked for more than 8 hours after flushing before flushing.

[0059] (3) For boilers that have been shut down for a long time, if the scale is determined to be mainly composed of carbonates, the temperature should be controlled below 150℃ during soaking, and the higher the temperature, the better. The soaking time should be no less than 24 hours. Multiple soaking and rinsing methods can be used to reduce the system pressure difference.

[0060] Example 7: The descaling method for recycling purified wastewater in steam injection boilers is carried out according to the following steps:

[0061] The first step, based on hydrochemistry theory, is to establish the functional relationship of the existence state of minerals:

[0062] ΔG diff =f(Q i K i α i )

[0063] Where Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and α is the ion activation degree;

[0064] The second step involves establishing a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, based on the hydrolysis reaction:

[0065] D=f(ΔG,P,T,v,g,t,β)

[0066] Where ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, and β is the correction parameter.

[0067] The third step, based on the process flow and dynamic model of the steam injection boiler, is to determine the scale type as follows: carbonate composite scale and sulfate composite scale are deposited in the convection section of the steam injection boiler; silicate composite scale is deposited in the radiant section of the steam injection boiler.

[0068] The fourth step involves fitting a schematic diagram, based on the scale type, dynamic model, hydrolysis reaction, and on-site operating parameters, to illustrate the relationship between the dissolution rate D of sulfate composite scale and pressure P, temperature T, flow rate v, and soaking and rinsing time t. (See diagram below.) Figure 2 As shown, from Figure 2 It can be seen that the main influencing factor for sulfate composite scale is temperature. The lower the temperature, the less likely the sulfate scale layer will detach due to hydrolysis. According to dynamic model predictions, the dissolution rate does not change significantly after the temperature exceeds 80℃, and pressure and other factors have little impact. The longer the soaking time, the better. However, as time goes on, the dissolution rate does not change significantly and under-deposit corrosion is likely to occur. Therefore, the soaking time generally does not exceed 3 days. Intermittent changes in flow rate can flush away the scale layer after soaking. It needs to be implemented in conjunction with the following site conditions:

[0069] (1) When the boiler is under maintenance or during normal shutdown, after the automatic purging is completed, manually start the plunger pump to flush it. When the temperature at the outlet of the radiant section drops below 100°C, stop the pump and close the valves at the inlet of the convection section and the outlet of the radiant section to ensure that the boiler tubes are full of water. When the temperature drops to 40°C, the water can be discharged.

[0070] (2) Based on daily water quality monitoring data, the pressure difference of the boiler convection section, radiation section and superheated section system is statistically analyzed. When the pressure difference changes more than 0.5 MPa compared with the normal, flushing can be carried out during boiler maintenance and equipment repair shutdown. The temperature should be controlled at no more than 80℃ during flushing and the flushing time should be no less than 30 minutes. If the pressure difference is still large, the flushing time should be extended and the boiler tubes should be soaked for more than 8 hours after flushing before flushing.

[0071] (3) For boilers that have been shut down for a long time, if the scale is determined to be mainly sulfate, the temperature should be controlled below 80°C during soaking, the lower the temperature the better, and the soaking time should be no less than 24 hours. Multiple soaking and rinsing methods can be used to reduce the system pressure difference.

[0072] Example 8: The descaling method for recycling purified wastewater in steam injection boilers is carried out according to the following steps:

[0073] The first step, based on hydrochemistry theory, is to establish the functional relationship of the existence state of minerals:

[0074] ΔG diff =f(Q i K i α i )

[0075] Where Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and α is the ion activation degree;

[0076] The second step involves establishing a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates, and silicates, and its influencing factors, based on the hydrolysis reaction:

[0077] D=f(ΔG,P,T,v,g,t,β)

[0078] Where ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, and β is the correction parameter.

[0079] The third step, based on the process flow and dynamic model of the steam injection boiler, is to determine the scale type as follows: carbonate composite scale and sulfate composite scale are deposited in the convection section of the steam injection boiler; silicate composite scale is deposited in the radiant section of the steam injection boiler.

[0080] The fourth step involves fitting a schematic diagram of the relationship between the dissolution rate D of silicate composite scale and pressure P, temperature T, flow rate v, and soaking and rinsing time t, based on the dynamic model, hydrolysis reaction, and on-site operating parameters, according to the scale type. Figure 3 As shown, from Figure 3 It can be seen that the main influencing factors for silicate composite scale (silicate composite scale is generally composed of silicate and some soluble composite silicate scale layer; this invention mainly removes soluble composite silicates) are temperature and pressure. The solubility of soluble composite silicates is most affected by temperature; generally, the solubility is very low below 80℃, and increases sharply above 80℃. Pressure also has a significant impact on silicate scale; the dissolution rate increases sharply at 9MPa. Other factors have a relatively small impact. Longer soaking time is better, but the dissolution rate does not change much over time and is prone to under-deposit corrosion. Therefore, the soaking time generally does not exceed 3 days. Intermittent flow rate changes can flush away the scale layer after soaking. This should be implemented in conjunction with the following on-site conditions:

[0081] (1) Based on daily water quality monitoring data, the pressure difference of the boiler convection section, radiation section and superheated section system is statistically analyzed. When the pressure difference changes more than 0.5 MPa compared with the normal, flushing can be carried out during boiler maintenance and equipment repair shutdown. The temperature is controlled between 80℃ and 150℃ during flushing, and the flushing time is not less than 30 minutes. If the pressure difference is still large, the flushing time needs to be extended and the boiler tubes should be soaked for more than 8 hours after flushing before flushing.

[0082] (2) When the boiler is shut down for a long time, the temperature should be controlled above 80℃ during soaking. The higher the temperature, the better. The soaking time should be no less than 24 hours. Multiple soaking and rinsing methods can be used to reduce the system pressure difference.

[0083] (3) For boilers that have been shut down for a long time, if the scale is determined to be mainly silicate, the soaking temperature should be controlled above 100℃ and the soaking time should be no less than 24 hours. The pressure during rinsing should preferably be maintained between 9MPa and 12MPa. Multiple soaking and rinsing methods can be used to reduce the system pressure difference. If the pressure conditions are not available, pressure change pulsating rinsing can be used.

[0084] The beneficial effects of this invention are as follows:

[0085] (1) Cost savings

[0086] In China, acid washing is commonly used to remove scale from boiler tubes used for heavy oil purification water reuse in oilfields. However, by adopting this invention, the acid washing cycle can be extended from 2 to 3 years to 5 years.

[0087] The boiler acid cleaning cycle has been extended from 2 to 3 years to more than 5 years. Taking the annual cleaning of 20 boilers by a heavy oil company as an example, the acid cleaning cost for each boiler is 38,000 yuan, which can save 760,000 yuan per year. If Xinjiang Oilfield adopts this method to slow down the scaling trend of boilers, it can save more than 4 million yuan per year.

[0088] (2) Service life of furnace tubes

[0089] Pickling can thin the furnace tubes, and when they are no longer able to withstand pressure, the furnace tubes must be replaced. This invention can reduce the number of cleaning cycles and extend the service life of the furnace tubes by more than double.

[0090] (3) Fuel consumption

[0091] Timely removal of deposits from pipe walls can extend equipment lifespan and save fuel. By using soaking and flushing during equipment maintenance intervals, each boiler can save approximately 50,000 cubic meters of natural gas per year (based on equipment operation for 250 days per year).

[0092] In summary, this invention is based on the dissolution theory of key factors such as mineral dissolution equilibrium, fluid mixing parameters, gas separation due to pressure drop or boiling, and the interaction between organic and inorganic matter. By predicting the type of scale buildup on boiler tubes, the invention uses flushing and soaking methods to remove scale, reducing maintenance workload, lowering production costs, and increasing operating efficiency. It has good application prospects in production.

[0093] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for descaling for reusing purified sewage water in a steam injection boiler, characterized by The following steps are taken: First, based on the water chemistry theory, a functional relationship of the existence state of minerals is established: Delta G diff = f(Q i , K i , alpha i ) Wherein, wherein Q is the reaction entropy, K is the equilibrium constant at a specific temperature and pressure, and a is the ion activity degree; Second, based on the hydrolysis reaction, a dynamic model of the dissolution rate D of the complex precipitate formed by carbonates, sulfates and silicates and the influencing factors is established: D=f(ΔG, P, T, v, g, t, β) Wherein, ΔG is the mineral free energy, P is the pressure, T is the temperature, v is the flow rate, g is the gas content, t is the soaking time, β is the correction parameter, the function relation of the existence state of the mineral, the judgment of the existence state of the mineral includes: when ΔG diff <0, the mineral dissolution is unsaturated, and the mineral does not precipitate; diff >0, the mineral dissolution is supersaturated, the precipitation condition is met, and the mineral precipitates. Third, the process flow and dynamic model of the steam injection boiler are combined to determine the scale layer type of the scale, wherein when determining the scale layer type of the scale, the specific operation is: according to the water quality composition of the feed water, the heating intensity of the feed water on each heating surface, and the change process of the working medium in the process flow of the steam injection boiler, the scale layer type of the scale is determined, and the scale layer type of the scale includes: carbonate complex scale and sulfate complex scale deposited in the convection section of the steam injection boiler; silicate complex scale deposited in the radiation section of the steam injection boiler; Fourth, according to the scale layer type of the scale, based on the dynamic model, the hydrolysis reaction and the field operation parameters, a relationship diagram of the dissolution rate D and the pressure P, temperature T, flow rate v, soaking and flushing time t when the different types of scale layers are fitted, and by adjusting the flushing and soaking time of the boiler tube scale, the descaling of different types of scale layers is completed, Wherein, combined with the daily water quality monitoring data, the system pressure difference of the boiler convection section, radiation section and superheating section is counted, when the pressure difference is greater than 0.5 MPa than usual, flushing is carried out during boiler maintenance and equipment maintenance shutdown, the temperature is controlled between 80℃ and 150℃ during flushing, the flushing time is not less than 30 minutes, if the pressure difference is still greater than 0.5 MPa, the flushing time needs to be extended and the boiler tube needs to be soaked for more than 8 hours after flushing before being flushed again; For long-term idle boiler, the temperature is controlled at more than 80℃ during soaking, the higher the temperature, the better, and the soaking time is not less than 24 hours, multiple soaking and flushing methods are used to reduce the system pressure difference; For long-term idle boiler, for the silicate scale, the temperature is controlled at more than 100℃ during soaking, the soaking time is not less than 24 hours, the pressure is kept between 9MPa and 12MPa during flushing, multiple soaking and flushing methods are used to reduce the system pressure difference, and pressure change pulse flushing is used for those without pressure conditions.

2. The method for descaling according to claim 1, wherein In the carbonate complex scale, the mass content of calcium carbonate is 50% to 95%; in the sulfate complex scale, the mass content of calcium sulfate is 50% to 95%; in the silicate complex scale, the mass content of silicon dioxide is 20% to 25%.

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