Cleaning method for heat exchangers in sulfuric acid production facilities

Abstract

To provide a cleaning method for heat exchangers in sulfuric acid production facilities, capable of suppressing the corrosiveness of a deposit-dissolving solution generated during cleaning of the heat exchangers in the sulfuric acid production facilities, and also preventing the diffusion of harmful gases into the surroundings.SOLUTION: In a cleaning method for heat exchangers in sulfuric acid production facilities, a heat exchanger used in a sulfuric acid production process is cleaned by injecting water into the heat exchanger, where the cleaning water is water containing a corrosion inhibitor, and where gas generated during the cleaning is brought into contact with a gas absorption liquid containing an oxidizing agent and an alkali. After the corrosion inhibitor-containing water is supplied into the heat exchanger, the gas generated inside the heat exchanger by the contact between the corrosion inhibitor-containing water and scale is suctioned and brought into contact with the gas absorption liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for cleaning a heat exchanger in a sulfuric acid production facility. [Background technology]

[0002] In facilities that manufacture sulfuric acid, a process is carried out in which sulfur dioxide is oxidized to sulfur trioxide in a converter (Patent Document 1). In this conversion process, a contact process, particularly a two-stage contact process, is used. As an example, in a two-stage contact process using a converter with four catalyst layers, the converted gas is extracted from the second or third layer, cooled by a heat exchanger, and then the sulfur trioxide is absorbed in a first absorption tower. The gas after absorption is again heated to the reaction temperature by a heat exchanger and introduced into the remaining catalyst layer for conversion reaction. The gas after this reaction is cooled by a heat exchanger and then sent to a second absorption tower. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-26159 A Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, sulfuric acid production facilities are equipped with multiple heat exchangers attached to the converter. As these heat exchangers are used, scale consisting mainly of oxygen, sulfur, and iron will build up, so they are washed with water periodically or as needed to remove the deposits. Heat exchangers are also washed when sulfuric acid production facilities are updated or dismantled.

[0005] In this heat exchanger cleaning process, harmful gases such as sulfur oxides and nitrogen oxides are generated when the deposits dissolve in water.

[0006] Furthermore, the liquid in which the deposits are dissolved is highly acidic and highly corrosive, and is likely to corrode the heat exchanger body and piping.

[0007] An object of the present invention is to provide a method for cleaning a heat exchanger of a sulfuric acid production facility, which can suppress the corrosiveness of a deposit dissolving solution generated when cleaning the heat exchanger of the sulfuric acid production facility and can prevent the diffusion of harmful gases into the surrounding area. [Means for solving the problem]

[0008] The method for cleaning a heat exchanger of a sulfuric acid production facility of the present invention is a method for cleaning a heat exchanger used in a sulfuric acid production process by injecting water into the heat exchanger, the method being characterized in that water containing a corrosion inhibitor is used as the water, and gas generated during cleaning is brought into contact with a gas absorbing liquid containing an oxidant and an alkali.

[0009] In one embodiment of the invention, the oxidizing agent is at least one of potassium permanganate and hydrogen peroxide.

[0010] In one embodiment of the present invention, after the corrosion inhibitor-containing water is supplied into the heat exchanger, gas produced in the heat exchanger as the scale dissolves is sucked in and brought into contact with the gas absorbing liquid.

[0011] In one embodiment of the present invention, the gas sucked from the heat exchanger is brought into contact with a gas absorbing liquid in a gas absorption tank, and the gas flowing out from the gas absorption tank is passed through a gas absorption tower and brought into contact with the gas absorbing liquid.

[0012] In one aspect of the present invention, a plurality of gas absorption tower trains are provided, each having a plurality of the gas absorption towers connected in series, and the gas flowing out of the gas absorption tank is passed through some of the gas absorption tower trains, while the other gas absorption tower trains are kept in a standby state. Effect of the Invention

[0013] According to the method for cleaning a heat exchanger in a sulfuric acid production facility of the present invention, the heat exchanger in the sulfuric acid production facility is cleaned with water containing a corrosion inhibitor, so that corrosion of the heat exchanger is inhibited.

[0014] During this cleaning, SO X and NO XIn the present invention, this gas is contacted with a liquid containing an oxidizing agent and an alkali to produce a gas containing SO X and NO X In addition, SO X and NO X is absorbed by alkali. X Of these, NO is not easily absorbed by alkali, but it is oxidized by an oxidizing agent to become NO2, and is then absorbed by alkali.

[0015] In this way, the present invention can suppress the corrosiveness of the deposit dissolving solution generated when cleaning the heat exchanger of a sulfuric acid production facility, and can also prevent the diffusion of harmful gases into the surrounding area. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is an explanatory diagram of a method for cleaning a heat exchanger of a sulfuric acid production facility according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a method for cleaning a heat exchanger in a sulfuric acid production facility according to an embodiment will be described with reference to FIG.

[0018] In this method for cleaning a heat exchanger in a sulfuric acid manufacturing facility, when cleaning a heat exchanger 10, water is pumped toward the heat exchanger 10 through a water injection pipe 1 having a flow meter 2, and an aqueous solution of a corrosion inhibitor is added along the way through a pipe 3, a pump 4, and a check valve 5, and the water containing the corrosion inhibitor is injected into the heat exchanger 10 through a water injection seat 11 of the heat exchanger 10.

[0019] After a predetermined amount of corrosion inhibitor-containing water is injected into the heat exchanger 10, the cleaning water level is observed by level gauges (WLI) installed on a number of seats 12 at the bottom of the heat exchanger 10.

[0020] SO produced by contact of scale with water containing corrosion inhibitors X and NO XThe exhaust gas, which is waste air containing the above-mentioned, is sent from a plurality of exhaust gas seats 13 provided in the heat exchanger 10 through each pipe 14 and collecting pipes 15 and 16 toward the gas absorption tank 20. Air can be added to or sucked from the pipe 15 through a pipe 17. The water injection seat 11, the plurality of seats 12 provided at the bottom of the heat exchanger 10, and the plurality of exhaust gas seats 13 provided in the heat exchanger 10 may be added by processing the heat exchanger 10 depending on the installation orientation and structure of the heat exchanger.

[0021] An absorption liquid containing an oxidizing agent and an alkali is stored in the gas absorption tank 20. The absorption liquid in the gas absorption tank 20 is circulated via a pipe 21, a pump 22, a pipe 23, an ejector 24, and a pipe 25. The end of the pipe 16 is connected to the throat of the ejector 24. By operating the pump 22 to pass water through the ejector 24, the exhaust gas from the heat exchanger 10 is sucked out.

[0022] The mixed fluid of the exhaust gas and the gas absorbing liquid from the ejector 24 is introduced into the gas absorption tank 20 through a fluid dispersion nozzle 26 in the tank 20. X and NO X Most of the soluble components of react with the alkali and are absorbed into the liquid. NO is oxidized to NO2 by the oxidizing agent and is similarly absorbed into the liquid. The top of the tank 20 and the pipe 25 are connected by a circulation pipe 27. However, SO X and NO X Not all of the SO is absorbed in the gas absorption tank 20. X and NO X The gas containing the above-mentioned is sent from the gas absorption tank 20 to the gas absorption column train 40 or 50 via the pipe 31 and the branch pipe 32 or 33 together with the air component in the exhaust gas. X and NO X Absorption of the compound takes place.

[0023] The absorption tower trains 40, 50 each include absorption towers 41, 42 and absorption towers 51, 52 connected in series. While gas is being ventilated to one of the absorption tower trains 40, 50, the other is in a standby state. If necessary, the absorbing liquid is replaced during this standby state. Depending on the concentration of the generated gas, the absorption tank or the gas absorption tower may be operated alone.

[0024] The remaining SO X and NO X The treated gas from which SO has been absorbed is released into the atmosphere via the pipe 43 or 53 and the pipes 60 and 61. The joint between the pipes 60 and 61 is connected to the middle of the pipe 15 via the pipe 63. X and NO X When the concentration is high, it is possible to return the gas from the pipe 63 to the pipe 15 .

[0025] The joint of the pipes 15 and 16 is connected to the middle of the pipe 31 by a bypass pipe 70 having an open / close damper 71. The damper 71 is normally closed. The pH, ORP (oxidation-reduction potential), sulfate ions and NO ions of the liquid circulating from the gas absorption tank 20 through the pipes 21, 23, and 25 are measured. X The ion concentration of ions, etc. is measured, and if it exceeds a predetermined value, the pump 22 is stopped and the damper 71 is opened, and the exhaust gas from the heat exchanger 10 is sent from the pipe 70 to the pipe 31 and then sent to the spare absorption tower row 40 or 50 for gas absorption treatment, while the absorbing liquid in the gas absorption tank 20 is replaced with new liquid.

[0026] The absorption liquid for the gas absorption tank 20 and each of the absorption towers 41, 42, 51, and 52 is prepared in an absorption liquid preparation tank 80. Water is supplied to this absorption liquid preparation tank 80 via a pipe 81 branched off from the pipe 1. An oxidizing agent and an alkali are added to this water to prepare the absorption liquid. The prepared absorption liquid is sent to the absorption tank 20 and each of the absorption towers 41, 42, 51, and 52 by a pump 82.

[0027] Waste liquid used in the gas absorption tank 20 and each of the absorption towers 41, 42, 51, 52 is introduced into a recovery tank 90, where a pH adjuster and an oxidant decomposer are added to decompose the residual oxidant, and then the wastewater is sent to a wastewater treatment process 91.

[0028] After cleaning, the wastewater from the heat exchanger 10 is discharged into a wastewater receiving tank 95, and is then sent to a wastewater treatment process 97 via a neutralization process 96. If the seat 12 becomes clogged with sludge, the blockage is cleared by injecting air.

[0029] In this manner, according to this cleaning method, the heat exchanger 10 is cleaned with water containing a corrosion inhibitor, so that the corrosion of the heat exchanger 10 is suppressed. In addition, the SO X , NO X The above-mentioned substances are sufficiently removed by the gas absorption tank 20 and the absorption tower train 40 or 50 using an absorption liquid containing an oxidizing agent and an alkali.

[0030] As the oxidizing agent, potassium permanganate, hydrogen peroxide, etc. are preferable. Other general oxidizing agents such as persulfate and ozone may be used. As the alkali, sodium hydroxide is preferable. Other chemicals that show alkalinity when dissolved in an aqueous solution, such as calcium hydroxide and potassium hydroxide, may also be used.

[0031] As the corrosion inhibitor, a corrosion inhibitor containing an acid, particularly sulfuric acid, can be used. When the amount of deposits on the heat exchanger is small and the amount of gas generated is small, water containing a corrosion inhibitor is filled into the heat exchanger, and then a circulation treatment is carried out. During this circulation treatment, an alkaline agent and an oxidizing agent may be directly added to remove deposits in the heat exchanger and suppress the generation of gas at the same time. [Explanation of symbols]

[0032] 10 Heat exchanger 20 Gas absorption tank 22 Pump 24 Ejector 40,50 Absorber column 41, 42, 51, 52 Absorption tower 70 Bypass piping 71 Damper 80 Absorption liquid preparation tank 90 Recovery Tank 91 Wastewater treatment process 95 Wastewater receiving tank 96 Neutralization process 97 Wastewater treatment process

Claims

1. In a method for cleaning a heat exchanger used in a sulfuric acid manufacturing process by injecting water into the heat exchanger, The water used is a corrosion inhibitor-containing water, The gas generated during cleaning is brought into contact with a gas absorbing liquid containing an oxidizing agent and an alkali.

1. A method for cleaning a heat exchanger in a sulfuric acid production facility.

2. 2. The method for cleaning a heat exchanger in a sulfuric acid production facility according to claim 1, wherein the oxidizing agent is at least one of potassium permanganate and hydrogen peroxide.

3. 3. The method for cleaning a heat exchanger in a sulfuric acid production facility according to claim 1 or 2, wherein after the corrosion inhibitor-containing water is supplied into the heat exchanger, gas produced in the heat exchanger as scale dissolves is sucked in and brought into contact with the gas absorbing liquid.

4. The gas sucked from the heat exchanger is brought into contact with a gas absorbing liquid in a gas absorption tank, 4. The method for cleaning a heat exchanger in a sulfuric acid production facility according to claim 3, wherein the gas flowing out from said gas absorption tank is passed through a gas absorption tower to be contacted with a gas absorbing liquid.

5. A plurality of gas absorption tower rows are provided, each row including a plurality of the gas absorption towers connected in series, 5. A method for cleaning a heat exchanger in a sulfuric acid manufacturing facility according to claim 4, wherein the gas flowing out from said gas absorption tank is passed through a part of the gas absorption tower trains while the other gas absorption tower trains are kept in a standby state.

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