Protection method for prolonging service life of converter gas holder

Abstract

The invention discloses a protection method for prolonging the service life of a converter gas holder. The protection method comprises the steps that (1) manufacturing materials are selected, specifically, a holder body, a bell jar, a piston and a side plate are made of Q235 steel plates, and a bottom arch plate and a water accumulation groove plate are made of Q345NS steel plates; (2) main body partition corrosion prevention: a cabinet body bottom plate is welded with a heat affected zone, an annular water accumulation groove plate and a cabinet body side plate are protected by thermal aluminum spraying, and a base material of the bottom plate is protected by sacrificial anodes; and (3) corrosion prevention of other parts: adopting epoxy coal pitch anti-corrosion paint with the thickness of 300 microns on the base materials of the dome, the side plate and the bottom plate of the gas chamber, which avoid the aluminum anode. The method has the advantages that the service life of the gas holder is prolonged, the maintenance interval time is prolonged, the later maintenance cost is reduced, the anti-corrosion effect is improved, and the converter gas holder is efficiently protected.

Description

Technical Field

[0001] The invention belongs to the technical field of gas tank corrosion and protection, and in particular relates to a protection method for increasing the service life of a converter gas tank. Background Art

[0002] The converter gas holder is composed of a dome, a cabinet, a bell piston, an annular water tank and an arched bottom plate. It is made of carbon steel, specifically Q235A, and is a steel container for storing converter gas produced by converter steelmaking. The working principle of the converter gas holder is to place the bell in the cabinet, and change the gas storage volume by freely lifting it under certain conditions to ensure the gas output pressure.

[0003] The main media in the converter gas tank include dust and gas condensation. The water in the gas condenses on most of the side walls of the gas tank to form water droplets, which flow down to the bottom plate. Water also condenses on the lower part of the piston plate and drips onto the bottom plate. Most of the ash in the gas falls to the bottom of the gas, and some is adsorbed on the side walls and the bottom of the piston. A large amount of ash is deposited on the bottom plate of the gas tank in a clay state, and the depth can reach 50mm in about a year. In addition, the depth of water on the bottom ring plate is about 100mm, and the water contains Cl - 、SO4 2- For anions, the gas temperature in the gas cabinet is generally between 20 and 70°C, and the condensed water temperature is generally between 20 and 70°C.

[0004] Normally, the corrosion of converter gas tanks occurs inside the cabinet, which is chemical and electrochemical corrosion under high temperature and high humidity. At present, most domestic companies use epoxy coal tar anti-corrosion paint to protect converter gas tanks, but the anti-corrosion layer usually falls off after about two years, exposing the parent material and starting to corrode. The parent material is mostly uniform surface corrosion, with dense pits and varying depths. Cracks and corrosion perforations appear after about three years of use. The perforations are mainly concentrated in the bottom arch plate welds and welding heat-affected zones, annular water trough plates and cabinet bottom side plates, about 300mm from the bottom.

[0005] In addition, the bottom plate can be lined with anti-corrosion material clay board + epoxy for anti-corrosion, but after a period of use, the clay board will fall off and corrode and perforate, which does not achieve the expected effect. In order to extend the anti-corrosion time, some companies will use concrete plus asphalt mortar layer plus polymer material multi-layer patching for anti-corrosion, but because the condensate of the gas tank contains Cl - , coupled with high temperature and high humidity environment, corrosion perforation will occur in about six years.

[0006] When the gas tank is corroded, the gas concentration in the space will increase due to gas leakage, which is prone to gas explosion, fire and other accidents. It will also cause serious consequences and huge losses to the gas tank operators, surrounding personnel and environment, as well as the safety production of the enterprise. At the same time, the corrosion of the gas tank will also cause the leakage of gas condensate, polluting the environment.

[0007] For this reason, the company needs to clean the converter gas holder once every two years on average, remove the ash and slag from the bottom and the annular water tank, check the corrosion condition, and repair and prevent corrosion of the corroded and perforated parts. The cleaning of the gas holder must go through several stages, including shutdown, valve closure, gas release, nitrogen-driven gas and steam cleaning. The downtime is long and the repair and anti-corrosion working environment is harsh. The average annual maintenance cost of an 80,000 cubic meter converter gas holder is about 100,000 yuan. Under the general anti-corrosion method, the bottom plate and side plate are severely corroded and perforated in an average of five to seven years and need to be replaced, with a one-time cost of more than 1.2 million yuan. Summary of the invention

[0008] The purpose of the present invention is to solve the problems of poor anti-corrosion effect, high maintenance cost, great difficulty, time-consuming and labor-intensive of existing gas holders, and to provide a protection method for increasing the service life of converter gas holders, extending the service life and maintenance interval of gas holders, reducing later maintenance costs, improving anti-corrosion effects, and efficiently protecting converter gas holders.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: A protection method for increasing the service life of a converter gas holder, specifically comprising: (1) Selection of manufacturing materials: The cabinet, bell, piston and side panels are made of Q235 steel plates, and the bottom arch plate and water tank plate are made of Q345NS steel plates; (2) Anti-corrosion of main body partitions: The heat-affected zone of the cabinet bottom plate welding, the annular water trough plate, and the cabinet side plate are protected by thermal spraying aluminum, and the base material of the bottom plate is protected by sacrificial anodes; (3) Anti-corrosion of other parts: Epoxy coal tar anti-corrosion paint with a thickness of 300 μm is used on the base materials of the gas tank dome, side panels and bottom panel, avoiding the aluminum anode.

[0010] Furthermore, in the step (1), the yield strength of the Q345NS steel plate is between 220 and 350 MPa, and it is in a passivation state in the converter gas condensate, and the passivation zone is not less than 300 mv.

[0011] Furthermore, in step (2), the aluminum spraying area includes the welding heat affected zone, i.e., an area 50 mm wide on the left and right sides of the weld as the center line; the annular water trough plate; and the cabinet body 300 mm upward from the bottom.

[0012] Furthermore, in the step (2), the thickness of the thermally sprayed aluminum is not less than 150 μm, and the thermally sprayed aluminum is performed by wire flame spraying.

[0013] Furthermore, in step (2), the oil and dust on the surface of the aluminum spray layer are removed and dried, and then a test paper soaked in 20g / 1000ml potassium chloride solution is used to cover the spray layer for 5-10 minutes. When the blue spots on the test paper are no more than 1-3 dots / cm 2 , it is considered qualified.

[0014] Furthermore, in step (2), the open circuit potential of the sacrificial anode is -1.09~-1.05V, the actual working potential is -1.05~-1.0V, the capacitance is ≥780Ah / kg, the consumption rate is ≤11.23 kg.(Aa)-1, the current efficiency is ≥70%, and the sacrificial anode is installed by welding.

[0015] Furthermore, in step (2), the sacrificial anode protection method is applicable to an environment with a working temperature of 60-80°C.

[0016] Furthermore, in step (3), for the dry film thickness, 15% of the readings are allowed to be lower than the design value, but each individual reading shall not be lower than 85% of the specified value; when the coating thickness does not meet the design requirements, the number of coating coats should be increased until it is qualified.

[0017] Furthermore, in the step (3), the maximum value of the paint film thickness measurement point cannot exceed twice the design thickness, the adhesion of the coating system is not less than 3 MPa, and the test method is the pull-off method.

[0018] Compared with the prior art, the advantages of the technical solution of the present invention are: (1) The present invention adopts Q345NS acid-resistant plate as the arched bottom plate and the annular water trough plate of the converter gas holder, which effectively resists the corrosion of the steel plate by the high-temperature corrosive condensed water in the gas holder, ensures good working strength, and can not only meet the mechanical performance requirements of the converter gas holder, but also effectively reduce the stress corrosion risk of the converter gas holder; (2) The present invention uses thermal aluminum spraying to cover the welding heat affected zone of the arched bottom plate, the annular water trough plate and the bottom side plate weld area. On the one hand, the welding heat affected zone is isolated from the corrosive medium, and on the other hand, electrochemical cathode protection is formed to ensure that the welding heat affected zone does not corrode; (3) The present invention adopts the method of installing an aluminum sacrificial anode to cathodically protect the base material in the aluminum spraying area of ​​the arched bottom plate, so that the base material is in the same electrolyte, the highly active aluminum loses electrons and is corroded, while the poorly active base material obtains electrons and is protected; (4) The present invention selects corrosion-resistant materials by precise zoning and adopts an anti-corrosion method combining anti-corrosion coating and electrochemical anti-corrosion to effectively protect the gas holder around the furnace, thereby doubling the service life of the converter gas holder and greatly reducing the cost of use. DETAILED DESCRIPTION Example

[0019] In order to make the present invention more clear, a protection method for increasing the service life of a converter gas holder according to the present invention is further described below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] In this embodiment, taking an 80,000 cubic meter gas tank as an example, the protection method for increasing its service life is as follows, which is characterized by: 1. Selection of manufacturing materials: (1) According to the results of the on-site hanging test as shown in the following table, the cabinet bell, piston and side plate are made of Q235 steel plate; (2) The bottom arch plate and water trough plate are made of 345NS steel plate.

[0021]

[0022] It can be seen from the table that in converter gas, the corrosion rate of 2.5-year Q235B steel is much greater than that of Q345NS steel.

[0023] (II) Cabinet anti-corrosion method: Since the heat affected zone of the bottom plate of the converter gas tank, the annular water trough plate, and the cabinet side plate 300mm above the bottom are the concentrated areas of corrosion and perforation, and the corrosion of other parts is relatively light, the anti-corrosion is carried out in different areas, specifically: (1) The heat-affected zone of the cabinet bottom plate welding, the annular water trough plate, and the cabinet side plate 300 mm upward from the bottom are protected by thermal spraying aluminum, specifically: (a) Thermal spraying aluminum parts: The welding heat affected zone is 50mm wide on each side with the weld as the center line; annular water trough plate; 300mm area upward from the bottom of the cabinet; (b) Thermal spray aluminum thickness: not less than 150 μm; (c) Thermal spraying method: wire flame spraying.

[0024] (2) The base plate base material is protected by sacrificial anode (aluminum block), specifically: (a) The sacrificial anode protection performance is as follows:

[0025] (b) Aluminum consumption of sacrificial anode for 15 years: 0.8kg / m 2 ; (c) Sacrificial anode installation method: welding.

[0026] (III) Anti-corrosion of other parts of the gas tank: The base materials of the gas tank dome, side panels and bottom panels are painted with epoxy coal tar anti-corrosion paint with a thickness of 300μm, avoiding the aluminum anode.

[0027] In this embodiment, the steel plate made of Q345NS material is selected, and the yield strength of the steel plate is 220-350MPa. It is in a passivation state in the converter gas condensate, and the passivation zone is not less than 300mv. The acid-resistant Q345NS steel plate is used to replace the ordinary Q235 used previously as the material for making the converter gas holder arched bottom plate, annular water trough plate and lower side plate to improve the acid resistance and stress corrosion resistance of the gas holder, and the yield strength requirement can ensure good working strength.

[0028] In this embodiment, the oil and dust on the surface of the aluminum spray layer are removed and dried, and then a test paper soaked in 20g / 1000ml potassium chloride solution is used to cover the spray layer for 5-10 minutes. The blue spots on the test paper should not exceed 1-3 dots / cm 2 To be qualified.

[0029] In the present invention, the open circuit potential of the sacrificial anode (aluminum anode) is about -1.05V, the current efficiency is greater than 70%, △E=0.25V, and it is suitable for an environment with a working temperature of 60~80℃.

[0030] Taking an 80,000 cubic meter converter gas holder as an example, the present invention can ensure that the converter gas holder has a service life of 15 years. According to the traditional anti-corrosion method, the bottom plate needs to be replaced twice within 15 years, and the cost each time is more than 1.2 million yuan; during the 15-year service life, in addition to replacing the bottom plate, a periodic overhaul is required every 3 years, and the overhaul cost is about 100,000 yuan.

[0031] After adopting the anti-corrosion method of the present invention, the one-time investment is about 255,000 yuan + the cost of changing the bottom plate material is 280,000 yuan, that is, 140 tons × 2,000 yuan / ton = 280,000 yuan.

[0032] In summary, saving the cost of replacing the base plate twice + reducing the maintenance cost 5 times within the cycle - the base plate anti-corrosion cost - the cost of changing the base plate material can yield the total cost reduction gain within 15 years = 120×2+10×5-26.5-28=2.355 million yuan / unit.

[0033] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A protection method for increasing the service life of a converter gas holder, characterized in that: (1) Selection of manufacturing materials: The cabinet, bell, piston and side panels are made of Q235 steel plates, and the bottom arch plate and water tank plate are made of Q345NS steel plates; (2) Anti-corrosion of main body partitions: The heat-affected zone of the cabinet bottom plate welding, the annular water trough plate, and the cabinet side plate are protected by thermal spraying aluminum, and the base material of the bottom plate is protected by sacrificial anodes; (3) Anti-corrosion of other parts: Epoxy coal tar anti-corrosion paint with a thickness of 300 μm is used on the base materials of the gas tank dome, side panels and bottom panel, avoiding the aluminum anode.

2. The protection method for increasing the service life of a converter gas holder according to claim 1, characterized in that: In the step (1), the yield strength of the Q345NS steel plate is between 220 and 350 MPa, and the steel plate is in a passivation state in the converter gas condensate, and the passivation zone is not less than 300 mv.

3. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In the step (2), the aluminum spraying area includes the welding heat affected zone, i.e., the area 50 mm wide on the left and right sides of the weld as the center line; the annular water trough plate; and the cabinet body 300 mm upward from the bottom.

4. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In the step (2), the thickness of the thermally sprayed aluminum is not less than 150 μm, and the thermally sprayed aluminum is performed by wire flame spraying.

5. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In step (2), the oil and dust on the surface of the aluminum spray layer are removed and dried, and then a test paper soaked in 20g / 1000ml potassium chloride solution is used to cover the spray layer for 5-10 minutes. When the blue spots on the test paper are no more than 1-3 dots / cm 2 , it is considered qualified.

6. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In the step (2), the open circuit potential of the sacrificial anode is -1.09~-1.05V, the actual working potential is -1.05~-1.0V, the capacitance is ≥780Ah / kg, the consumption rate is ≤11.23 kg.(Aa)-1, the current efficiency is ≥70%, and the sacrificial anode is installed by welding.

7. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In the step (2), the sacrificial anode protection method is applicable to an environment with a working temperature of 60-80°C.

8. The protection method for increasing the service life of a converter gas holder according to claim 1 or 2, characterized in that: In step (3), for the dry film thickness, 15% of the readings are allowed to be lower than the design value, but each individual reading shall not be lower than 85% of the specified value; when the coating thickness does not meet the design requirements, the number of coating coats should be increased until it is qualified.

9. The protection method for increasing the service life of a converter gas holder according to claim 8, characterized in that: In the step (3), the maximum value of the paint film thickness measurement point cannot exceed 2 times of the design thickness, the adhesion of the coating system is not less than 3 MPa, and the test method is the pull-off method.

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