Method for cleaning sediment in gas cooler of phthalic anhydride device

Abstract

The invention discloses a method for cleaning sediments in a gas cooler of a phthalic anhydride device, the whole method is based on soda boiling, local physical flushing, slaked lime protection and thermal drying, soda boiling is independently carried out for three times and is effective for phthalic anhydride, maleic anhydride, benzoic acid and ferric salt, cutting and hoisting are not needed in the whole process, equipment is not damaged, flaw detection and reflow cost is saved, and the production cost is reduced. And internal sediment of the gas cooler is effectively and thoroughly cleaned.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of maintenance of phthalic anhydride production device, and particularly relates to a method for cleaning internal sediment of a phthalic anhydride device gas cooler. BACKGROUND

[0002] Phthalic anhydride is also known as phthalic anhydride. Phthalic anhydride is a white needle-like or white flaky crystal at room temperature. The solubility of phthalic anhydride in cold water is very low, and the solubility in hot water, ethanol and other organic solvents is very high. Phthalic anhydride is easy to burn and sublimate below the boiling point, and a slight irritating odor can be smelled. Phthalic anhydride has a strong irritating effect on the respiratory organs and can cause allergies. The dust and steam of phthalic anhydride have a strong irritating effect on the exposed skin tissue of the human body, especially the moist skin tissue. For the cleaning of the gas cooler, the current methods mainly include chemical cleaning and physical cleaning. The chemical cleaning mainly uses acidic substances to cook the gas cooler, dissolves the impurities, and then uses clean water to flush. The physical cleaning cuts the gas cooler, hoists out the internal finned tube, flushes it with a high-pressure water gun, and synchronously flushes the inside with a high-pressure water gun. Then, the finned tube is reassembled and re-welded. However, the chemical cleaning method cannot effectively clean the phthalic anhydride and other acid-soluble substances deposited in the internal gas cooler, the residual cleaning is not thorough, and the heat exchange effect of the gas cooler cannot be guaranteed. The cutting type physical cleaning needs to spend a lot of time on cutting, hoisting and re-welding due to the complex pipeline at the top of the gas cooler, and the operation time is long, the cost is high, and the equipment is damaged to a certain extent. SUMMARY

[0003] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application provides a method for cleaning internal sediment of a phthalic anhydride device gas cooler, which can effectively and completely clean the internal sediment of the gas cooler.

[0004] The method for cleaning internal sediment of a phthalic anhydride device gas cooler according to the embodiment of the present application comprises the following steps: Step 1: without cutting the shell and pipeline of the gas cooler, the manhole, handhole and top explosion-proof sheet are removed, and a blind plate is inserted into the inlet and outlet flanges; Step 2: NaOH lye with a mass concentration of 10-50 % is injected into the internal gas cooler, and desalted water is added, so that the liquid level submerges all the finned tubes, and the pH is controlled to be greater than 11; Step 3: nitrogen with a flow rate of greater than or equal to 300 Nm³ / h is introduced into the bottom, and S6 grade steam is synchronously introduced, and S6 grade steam is introduced into the top, so that the lye is bubbled and heated, and the temperature of the upper part, middle part and lower part of the cooler is kept greater than or equal to 90 ℃; Step 4: after continuous lye cooking for greater than or equal to 15 h, the waste liquid in step 3 is discharged; Step 5: steps 2 to 3 are repeated, and the process is continued for greater than or equal to 10 h. Step 6: drain the waste liquid in step 5; Step 7: inject desalted water into the gas cooler and repeat the bubble heating, keep the temperature ≥ 90 ℃, time ≥ 10 h, and then drain the waste water; Step 8: remove all hand holes, manholes and inlet blind plates, use high-pressure water gun to flush the finned tube, inner wall and bottom from the manhole, hand hole and inlet flange at multiple angles until no visible dregs; Step 9: evenly spray lime water solution on the finned tube, inner wall and bottom using a spray gun to form a corrosion protection layer; Step 10: dry by passing steam through the water section and the gas section synchronously for ≥ 10 h until there is no water dripping on the finned tube and no obvious water marks on the bottom; Step 11: reinstall the manhole, hand hole, explosion-proof piece and flange, use the hot air of the reactor to dry the inside of the cooler again for ≥ 10 min, close the bottom drain valve, and complete the cleaning.

[0005] The method for cleaning the internal dregs of the gas cooler of the phthalic anhydride device according to the embodiments of the present application has at least the following beneficial effects: the alkali boiling is effective for phthalic anhydride, maleic anhydride, benzoic acid and iron salt, the whole process does not cut and does not hoist, the equipment is not damaged, the cost of flaw detection and rewelding is saved, and the internal dregs of the gas cooler are effectively and completely cleaned.

[0006] According to some embodiments of the present application, in step 4, after steps 2 to 3 are completed, close the nitrogen, steam and blowdown valves, remove the bottom joint, and then open all the blowdown valves to drain the waste liquid.

[0007] According to some embodiments of the present application, in step 2, measure the pH every 2 h during the alkali boiling, and if the pH ≤ 11, add alkali to make the pH > 11.

[0008] According to some embodiments of the present application, in step 2, use a strip of cloth to surround the flange of the explosion-proof piece flange at the top outlet of the gas cooler to guide the foam in the alkali boiling process to the ground cofferdam.

[0009] According to some embodiments of the present application, in step 7, inject desalted water into the gas cooler until the finned tube is filled.

[0010] According to some embodiments of the present application, in step 7, use a hose to pass nitrogen and steam into the bottom of the gas cooler, use a hose to pass steam into the top of the gas cooler, and perform heating and bubbling.

[0011] According to some embodiments of the present application, in step 7, close the bottom nitrogen and steam, top steam valves, stop heating of the water preheater, close the gas section high-pressure package blowdown valve and stop the high-pressure filter feed water pump, and drain the waste water from the bottom of the gas cooler.

[0012] According to some embodiments of the present application, in step 8, the flanges are not reassembled with a gap.

[0013] According to some embodiments of the present application, in step 9, the lime water solution is prepared with a mass ratio of water:lime = 4:1.

[0014] According to some embodiments of the present application, in step 10, the temperature in the middle part of the cooler is controlled to be ≥90 ℃.

[0015] Additional aspects and advantages of the present application will be made apparent from the following description. DETAILED DESCRIPTION

[0016] In the description of the present application, the meaning of one or more is one or more, the meaning of multiple is two or more, greater than, less than, more than, etc. are understood as not including the number, above, below, etc. are understood as including the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0017] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0018] The method for cleaning the internal sediment of the gas cooler of the phthalic anhydride device according to the embodiment of the present application comprises the following steps: Step 1: under the premise of not cutting the shell and pipeline of the gas cooler, remove the manhole, handhole and top explosion-proof sheet, and insert a blind plate in the flange at the inlet and outlet; Step 2: inject NaOH lye with a mass concentration of 10-50 % into the internal part of the gas cooler and supplement with desalted water, until the liquid level submerges all the finned tubes, and control the pH>11; in step 2, the high-concentration lye is first mixed with desalted water, the liquid surface is pushed up from bottom to top, gradually immersing the gap and surface deposition layer of each finned tube, and the pH>11 provides sufficient OH⁻activity to make phthalic anhydride open ring, maleic anhydride saponify, and benzoic acid salt.

[0019] Step 3: introduce ≥300 Nm³ / h nitrogen gas into the bottom and simultaneously introduce S6 grade steam into the top, so as to bubble and heat the lye, and keep the temperature of the upper part, middle part and lower part of the cooler ≥90 ℃; in step 3, the nitrogen gas-steam two-phase flow is sprayed from the bottom to form violent bubbling; the steam at the top condenses downward to release heat and form a "top-down convection heating" double loop, and the reaction rate is exponentially increased above 90 ℃, while the nitrogen gas isolates oxygen.

[0020] Step 4: drain the waste liquid in step 3 after continuous alkaline boiling for ≥ 15 h; Step 5: repeat steps 2 to 3, and continue for ≥ 10 h; wherein, step 5 is a second alkaline boiling, the second alkaline boiling uses fresh alkaline liquid, rapidly penetrates into the interior of the first incompletely reacted slits and micro-cracks, continues saponification / dissolution, the residual acidic core is completely removed, and the metal surface reaches a "chemically clean" state; the second bubbling further peels off mechanically attached objects.

[0021] Step 6: drain the waste liquid in step 5; Step 7: inject desalted water into the gas cooler and repeat the bubbling heating, maintain the temperature ≥ 90 ℃, time ≥ 10 h, and then drain the waste water; in step 7, the desalted water performs a "hot rinsing" on the metal-alkali interface at 90 ℃, the bubbling rolls up and transports the residual alkali and fine particles upwards, the hot desalted water reduces the ionic strength, and the OH⁻ adsorbed on the pipe wall is desorbed; the bubbling provides mechanical scouring, and completes the "third level purification".

[0022] Step 8: remove all handholes, manholes and inlet blind plates, and use a high-pressure water gun to perform multi-angle flushing on the finned tubes, inner wall and bottom from the manholes, handholes and inlet flanges until no visible scum is present; in step 8, the high-pressure jet impacts the surface at a speed of 30-40 m / s to peel off the undissolved residual coke; and a clean surface is provided for the subsequent lime mud layer.

[0023] Step 9: uniformly spray lime water solution on the finned tubes, inner wall and bottom using a spray gun to form a corrosion protection layer; the film layer is uniform and has no cracks, the surface pH is raised to 11-12, can neutralize subsequent trace amounts of acidic gas, and inhibits the rooting of newly deposited substances.

[0024] Step 10: pass steam through the water section and the gas section synchronously, and dry for ≥ 10 h until there is no water dripping on the finned tubes and no obvious water marks on the bottom; the double-path steam heat flow dries the cooler.

[0025] Step 11: reinstall the manholes, handholes, explosion-proof sheets and flanges, use the hot air of the reactor to dry the interior of the cooler again for ≥ 10 min, close the bottom drain valve, and complete the cleaning.

[0026] In actual application, the alkaline boiling is effective on phthalic anhydride, maleic anhydride, benzoic acid and iron salts, the whole process does not cut or hoist, the equipment is not damaged, the cost of flaw detection and rewelding is saved, and the internal sediment of the gas cooler is effectively and completely cleaned.

[0027] In some embodiments, in step 4, after steps 2 to 3 are completed, the nitrogen, steam and blowdown valves are closed, the bottom joint is disassembled, and then all the blowdown valves are opened to drain the waste liquid. First, the gas source is closed to stop bubbling, the static pressure is instantaneously reduced, the waste liquid is quickly drained, and splashing caused by draining under pressure is avoided.

[0028] In some embodiments, in step 2, the pH is measured every 2 h during the alkali boiling, and if the pH≤11, alkali is added to make the pH>11. The high OH⁻ activity is always maintained, and the reaction rate remains constant.

[0029] In some embodiments, in step 2, the gas cooler top outlet explosion-proof flange is surrounded by a strip cloth to guide the foam during the alkali boiling process to the ground cofferdam. The foam rises with the gas flow, and after being blocked by the strip cloth, it flows down along the cloth surface, concentrates into the cofferdam, and avoids the accumulation of liquid on the tower top platform.

[0030] In some embodiments, in step 7, desalted water is injected into the gas cooler to fill the finned tube.

[0031] In some embodiments, in step 7, nitrogen and steam are introduced into the bottom of the gas cooler using a skin tube, steam is introduced into the top of the gas cooler using a skin tube, and heating and bubbling are performed.

[0032] In some embodiments, in step 7, the bottom nitrogen and steam, top steam valves are closed, the water preheating stops heating, the gas section high-pressure package blowdown valve is closed and the high-pressure filter feed water pump is stopped, and the waste water is discharged from the bottom of the gas cooler.

[0033] In some embodiments, in step 8, the flange is left with a gap and is not reassembled.

[0034] In some embodiments, in step 9, the slaked lime aqueous solution is prepared according to the mass ratio of water:slaked lime=4:1. This ratio is near the saturation solubility of Ca(OH)2, the particle surface has the same charge, the dispersion is good, the settling speed is low, and it is suitable for spraying.

[0035] In some embodiments, in step 10, the temperature in the middle of the cooler is controlled to be≥90 ℃.

[0036] The embodiments of the present application are described in detail above, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A method of cleaning the interior of a phthalic anhydride plant gas cooler of sludge, characterized in that, The method comprises the following steps: Step 1: remove manholes, handholes and top explosion-proof sheets without cutting the shell and pipelines of the gas cooler, and insert blind plates into the inlet and outlet flanges; Step 2: inject NaOH lye with a mass concentration of 10-50 % into the gas cooler and supplement desalted water until the liquid level submerges all finned tubes, and control pH>11; Step 3: introduce nitrogen with a flow rate of ≥300 Nm³ / h into the bottom and simultaneously introduce S6 grade steam, and introduce S6 grade steam into the top, so that the lye is bubbled and heated, and the temperature of the upper, middle and lower parts of the cooler is kept ≥90 ℃; Step 4: after continuous lye boiling for ≥15 h, the waste liquid in step 3 is discharged; Step 5: repeat steps 2 to 3, and continue for ≥10 h; Step 6: discharge the waste liquid in step 5; Step 7: inject desalted water into the gas cooler and repeat the bubbling and heating, and keep the temperature ≥90 ℃ for ≥10 h, and then discharge the waste water; Step 8: remove all handholes, manholes and inlet blind plates, and use a high-pressure water gun to flush the finned tubes, inner wall and bottom from the manholes, handholes and inlet flanges at multiple angles until no visible scum is present; Step 9: evenly spray a lime water solution on the finned tubes, inner wall and bottom by using a spray gun to form a corrosion protection layer; Step 10: introduce steam through the water section and the gas section synchronously, and dry for ≥10 h until there is no water dripping from the finned tubes and no obvious water marks on the bottom; Step 11: reinstall the manholes, handholes, explosion-proof sheets and flanges, use the hot air of the reactor to dry the inside of the cooler again for ≥10 min, close the bottom blowdown valve, and complete the cleaning.

2. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 4, after steps 2 to 3 are completed, close the nitrogen, steam and blowdown valves, remove the bottom joint, and then open all the blowdown valves to discharge the waste liquid.

3. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 2, measure the pH every 2 h during the lye boiling, and if the pH≤11, supplement lye until the pH>11.

4. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 2, use a strip of cloth to surround the flange of the top outlet explosion-proof sheet of the gas cooler to guide the foam in the lye boiling process to the ground cofferdam.

5. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 7, inject desalted water into the gas cooler until the finned tubes are filled.

6. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 5, characterized in that, In step 7, use a hose to introduce nitrogen and steam into the bottom of the gas cooler, use a hose to introduce steam into the top of the gas cooler, and perform heating and bubbling.

7. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 5, characterized in that, In step 7, close the bottom nitrogen and steam, top steam valves, stop water preheating, close the gas section high-pressure package blowdown valve and stop the high-pressure filtration feedwater pump, and discharge the waste water from the bottom of the gas cooler.

8. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 8, the flange is left with a gap and is not reinstalled.

9. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 9, prepare the lime water solution according to a mass ratio of water: lime = 4:

1.

10. The method of cleaning the interior of a gas cooler of a phthalic anhydride plant of settled sediments according to claim 1, characterized in that, In step 10, control the temperature of the middle part of the cooler to be ≥90 ℃.