CN112626528B

CN112626528B - Cleaning solution and cleaning method for renewable coke on inner surface of pipeline

Info

Publication number: CN112626528B
Application number: CN202011359659.8A
Authority: CN
Inventors: 马大衍; 卢丙迎
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2020-11-27
Filing date: 2020-11-27
Publication date: 2022-06-07
Anticipated expiration: 2040-11-27
Also published as: CN112626528A

Abstract

The invention discloses a cleaning solution and a cleaning method for renewable coke on the inner surface of a pipeline. The cleaning liquid which takes sodium hydroxide and potassium permanganate as main components is adopted to ultrasonically clean the interior of the pipeline for 8 hours at the temperature of 80 ℃, coke on the inner surface of the pipeline can be removed, and the pipeline cannot be corroded and damaged in the cleaning process. The cleaning liquid is suitable for cleaning coke formed on the inner wall of the metal pipeline by various endothermic hydrocarbon fuels.

Description

Cleaning solution and cleaning method for renewable coke on inner surface of pipeline

Technical Field

The present invention relates to surface treatment of renewable pipelines, and more particularly to cleaning of coke from the inner surface of metal tubing, such as cooling pipelines, without damaging or damaging the pipelines.

Background

At present, hydrocarbon fuel is widely applied to industrial production and daily life, however, carbon deposition is inevitably generated in the cracking process of the hydrocarbon fuel, and the hydrocarbon fuel is further heated and coked, so that coke is formed on the wall surface. The coke thus formed reduces the heat exchange efficiency of the metal surface, reduces the corrosion resistance of the metal material, and blocks valves and filters, even oil passages, which can cause engine stall, with serious adverse consequences.

The coke on the inner surface of the renewable pipeline made of the metal material is removed by low-temperature (less than 100 ℃) cleaning, so that the potential safety hazard can be reduced, and the service life of the pipeline can be prolonged. However, cryogenic cleaning of the inner surface of a regenerable pipeline presents several technical challenges:

1) the cleaning of the inner surface of the pipe is limited by the shape and size of the inner cavity, and the traditional physical cleaning method (such as brushing) is difficult to apply, and the cleaning quality cannot be guaranteed.

2) The chemical cleaning agent has strong corrosivity, and can corrode a pipeline while dissolving coke, so that the pipeline cannot meet the use requirement.

3) The coke has stronger inertia at low temperature (less than 100 ℃), is not easy to generate chemical reaction, and causes the difficulty in removing the coke.

Chinese patent CN108150288A discloses a chemical carbon deposition removing method, which adopts the steps of potassium permanganate oxidative decomposition, citrate pre-pickling, cold hydrochloric acid pickling and the like, and is suitable for removing the carbon deposition of parts with plating layers of the guide pipe with complicated shape and structure. However, for metal pipes, pipes without surface coatings (more in number and more in recycling value) still face the problem of corrosion damage of the pipes caused by chemical cleaning. Meanwhile, the cleaning process takes soaking as a main means, and the problem of incomplete cleaning of pipelines with small sizes exists.

Disclosure of Invention

The invention aims to provide a cleaning solution and a cleaning method for renewable pipeline inner surface coke, which can effectively remove coke, can not corrode a metal pipeline, and is suitable for cleaning a coke coating layer which is solidified on a pipeline matrix and is generated by pyrolysis and autoxidation of heat-absorbing hydrocarbon fuel.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for cleaning coke on the inner surface of a pipeline comprises the following steps:

1) pre-washing coke formed on the inner wall of a metal pipe (e.g., an alloy steel pipe), and then drying;

2) after the step 1), ultrasonically cleaning the inner surface of the metal pipeline by using a cleaning solution containing sodium hydroxide and potassium permanganate, so that coke is stripped from the inner wall of the metal pipeline and is dispersed in the cleaning solution; the cleaning solution takes water as a solvent, wherein the weight ratio of sodium hydroxide to potassium permanganate is 1 (1-2).

3) After the step 2), removing cleaning residues (including metal oxides formed by the reaction of the cleaning solution in the cleaning and attached to the inner wall of the pipeline and also including the alkaline components of the residual cleaning solution) on the inner wall of the metal pipeline by acid washing and then drying.

Preferably, in the step 1), the pre-cleaning specifically comprises the following steps: respectively carrying out ultrasonic cleaning on the inner surface of the metal pipeline for 10-15 minutes by using acetone, absolute ethyl alcohol and deionized water, wherein the ultrasonic cleaning temperature is 20-30 ℃; in the step 2), the ultrasonic cleaning temperature is 70-80 ℃, and the ultrasonic cleaning time is 8-10 hours.

Preferably, in the step 2), the cleaning solution is composed of, by weight, 85% -90% of mixed alkali solution, 3% -5% of surfactant, 3% -5% of solubilizer and 1% -5% of chelating agent; the mixed alkali solution consists of a sodium hydroxide solution with the mass fraction of 17% -20% and a potassium permanganate solution with the mass fraction of 17% -20%, wherein the weight ratio of the sodium hydroxide solution to the potassium permanganate solution is 1: 1-2.

Preferably, the surfactant consists of a nonionic surfactant (such as fatty alcohol-polyoxyethylene ether) and an anionic surfactant (such as sodium dodecyl benzene sulfonate), and the molar ratio of the nonionic surfactant to the anionic surfactant is 1: 2-3; the solubilizer is selected from isopropanol; the chelating agent consists of sodium tripolyphosphate and triethanolamine, and the weight ratio of the sodium tripolyphosphate to the triethanolamine is 5: 1-2.

Preferably, the step 3) specifically comprises the following steps:

3.1) carrying out ultrasonic cleaning on the inner surface of the metal pipeline subjected to ultrasonic cleaning by the cleaning solution (namely cleaning in the step 2) by using 0.1-0.2 mol/L oxalic acid solution;

3.2) carrying out ultrasonic cleaning on the inner surface of the metal pipeline subjected to the ultrasonic cleaning by the oxalic acid solution (namely the cleaning in the step 3.1) by using a 65-85% ethanol solution, and then drying.

Preferably, in the step 3.1), the ultrasonic cleaning temperature is 70-80 ℃, and the ultrasonic cleaning time is 4-6 hours; in the step 3.2), the ultrasonic cleaning temperature is 20-30 ℃, and the ultrasonic cleaning time is 15-30 minutes.

Preferably, the ultrasonic cleaning in each step is performed by circulating a cleaning reagent (e.g., a cleaning solution) of the corresponding step through a metal pipe under ultrasonic conditions.

A pipeline cleaning fluid comprises sodium hydroxide, potassium permanganate, water and a cleaning auxiliary agent, wherein the cleaning auxiliary agent comprises the surfactant, a solubilizer and a chelating agent, and the weight ratio of the sodium hydroxide to the potassium permanganate to the water is 1 (1-2) to 8-10.

Preferably, the cleaning solution consists of 85 to 90 weight percent of mixed alkali solution, 3 to 5 weight percent of surfactant, 3 to 5 weight percent of solubilizer and 1 to 5 weight percent of chelating agent; the mixed alkali solution consists of a sodium hydroxide solution with the mass fraction of 17% -20% and a potassium permanganate solution with the mass fraction of 17% -20%, wherein the weight ratio of the sodium hydroxide solution to the potassium permanganate solution is 1: 1-2.

The surfactant is composed of a nonionic surfactant (such as fatty alcohol-polyoxyethylene ether) and an anionic surfactant (such as sodium dodecyl benzene sulfonate), and the molar ratio of the nonionic surfactant to the anionic surfactant is 1: 2-3; the solubilizer is selected from isopropanol; the chelating agent consists of sodium tripolyphosphate and triethanolamine, and the weight ratio of the sodium tripolyphosphate to the triethanolamine is 5: 1-2.

The application of the pipeline cleaning liquid in cleaning coke formed by cracking and/or autoxidation of endothermic hydrocarbon fuel on the inner wall of a metal pipeline and a pipe fitting.

The invention has the beneficial effects that:

the method utilizes pre-cleaning and solution chemical cleaning (cleaning solution with sodium hydroxide and potassium permanganate as main components) and combines ultrasonic action to remove coke generated by pyrolysis and autoxidation of heat-absorbing hydrocarbon fuel on the inner surface of the metal pipeline under mild conditions (the cleaning temperature is lower, strong-acid cleaning solution is not needed), and ensures that the cleaning solution and the cleaning method can meet the process requirements of practical use (the conditions are mild, the process is simple, and the operation safety is high).

Furthermore, by using the surfactant, the solubilizer and the chelating agent, the invention can improve the cleaning effect of the main components (sodium hydroxide and potassium permanganate) on the coke in the chemical cleaning of the solution and solve the problem of corrosion and damage of the pipeline caused by the chemical cleaning. The invention is suitable for cleaning coke formed by various endothermic hydrocarbon fuels on the inner wall of a metal pipeline (especially a pipeline without surface coating).

Drawings

FIG. 1 is a macroscopic view of a cross section of a pipe before a cleaning process.

FIG. 2 is a macroscopic view of the cross section of the pipe after the cleaning process.

FIG. 3 is a typical microscopic morphology and elemental analysis of the inner wall of a pipe prior to a cleaning process; wherein: b) is a) the result of elemental analysis of the location corresponding to the spectral marker 19 in the shown micro topography, d) is the result of elemental analysis of the location corresponding to the spectral marker 20 in the shown micro topography, f) is the result of elemental analysis of the location corresponding to the spectral marker 21 in the shown micro topography.

FIG. 4 is a typical microscopic morphology and major element (not less than 2%) analysis of the inner wall of the pipeline after the cleaning process; wherein: b) is a) an elemental analysis result of a position corresponding to a spectrogram marker 7 in the shown micro topography, d) is a result of an elemental analysis of a position corresponding to a spectrogram marker 8 in the shown micro topography, f) is a result of an elemental analysis of a position corresponding to a spectrogram marker 9 in the shown micro topography.

FIG. 5 is a comparison before and after pre-wash, wherein: a) the microstructure of the inner surface of the pipeline before pre-cleaning, b) the scanning result of the element C of a), and C) the microstructure of the inner surface of the pipeline after pre-cleaning.

FIG. 6 is a comparison of the effects of different cleaning agents after cleaning; wherein, a) cleaning cases; b) the control group was washed.

Detailed Description

The present invention will be described in further detail with reference to the following drawings and examples. The examples are given solely for the purpose of illustration and are not intended to limit the scope of the invention.

Cleaning liquid capable of regenerating coke on inner surface of cooling pipeline

Preparing a cleaning solution according to the weight percentage: 87% of mixed alkali solution, 3% of surfactant, 5% of solubilizer and 5% of chelating agent.

The mixed alkali solution consists of a sodium hydroxide aqueous solution with the mass fraction of 20% and a potassium permanganate aqueous solution with the mass fraction of 20% (the weight ratio of the sodium hydroxide aqueous solution to the potassium permanganate aqueous solution is 1: 1). The surfactant is prepared by compounding fatty alcohol-polyoxyethylene ether and sodium dodecyl benzene sulfonate according to the molar ratio of 1: 2. The solubilizer is isopropanol. The chelating agent is prepared by compounding sodium tripolyphosphate and triethanolamine according to the weight ratio of 5: 1.

When the cleaning solution is prepared, the mixed alkali solution, the surfactant, the solubilizer and the chelating agent are mixed by using magnetons and then continuously stirred to obtain a mixed solution for 10 minutes, and then an ultrasonic cleaner is used for carrying out ultrasonic treatment for 10-15 minutes to uniformly mix the solution.

Cleaning process for coke on inner surface of renewable cooling pipeline

In order to clean coke on the inner surface of the renewable cooling pipeline and ensure that cleaning liquid can fully contact and react with the coke on the inner wall of the pipeline, the cleaning process of the invention utilizes a circulating pump and a heat preservation container to realize the circulating flow of cleaning reagents such as the cleaning liquid and the like in the pipeline, so that the cleaning process is not limited by the shape and the size of the inner cavity of the pipeline (for example, the cleaning liquid is difficult to reach the center of the slender pipeline only by soaking).

The cleaning process comprises the steps of preparation of cleaning reagents such as cleaning liquid and the like, heating, ultrasonic cleaning and removal of cleaning residues on the inner wall of the pipeline after cleaning, and comprises the following specific steps:

and step one, removing dust attached to the inner wall of the pipeline and organic matters such as alkane and alkene which are not completely decomposed by precleaning.

The specific steps of the pre-cleaning are as follows: acetone, absolute ethyl alcohol and deionized water are sequentially used for carrying out ultrasonic cleaning on the inner surface of the pipeline, the whole pipeline is placed in an ultrasonic treatment container (the ultrasonic power is 300-400W), the cleaning time is 10 minutes, and the cleaning temperature is normal temperature (the acetone and the ethyl alcohol are prevented from being volatilized too fast). If the length-diameter ratio of the pipeline is overlarge, acetone, absolute ethyl alcohol and deionized water respectively flow in the pipeline in a circulating mode by using a circulating pump and a heat-insulating container, and the whole pipeline is placed in an ultrasonic treatment container (normal-temperature water is used as an ultrasonic action medium), so that the pre-cleaning efficiency is improved. After cleaning, the pipes were blow-dried using compressed air.

And step two, heating the cleaning solution prepared in the step one, enabling the cleaning solution heated to 80 ℃ to circularly flow in the pre-cleaned pipeline by using a circulating pump and a heat preservation container, cleaning the inner surface of the pipeline by using ultrasonic for 8 hours, putting the whole pipeline in an ultrasonic treatment container (containing water at 80 ℃ as an ultrasonic medium) in the cleaning process, and enabling the ultrasonic power to be 300-400W.

And step three, taking out the pipeline, emptying the liquid in the pipeline, removing the cleaning liquid (at the moment, some metal oxide residues are generated after the cleaning liquid is cleaned, and the inner surface of the pipeline is yellow), using a circulating pump and a heat preservation container to enable 0.1mol/L oxalic acid solution heated to 80 ℃ to circularly flow in the pipeline, cleaning the inner surface of the pipeline for 4 hours by using ultrasonic, putting the whole pipeline in an ultrasonic treatment container (containing water at 80 ℃ as an ultrasonic medium) in the cleaning process, and enabling the ultrasonic power to be 300-400W.

And step four, taking out the pipeline, emptying the liquid in the pipeline, removing the oxalic acid solution, enabling alcohol with the volume fraction of 75% (normal temperature) to circularly flow in the pipeline by using a circulating pump and a heat preservation container, and cleaning the inner surface of the pipeline for 15 minutes by using ultrasonic waves, wherein the whole pipeline is placed in an ultrasonic treatment container (containing normal temperature water as an ultrasonic medium) in the cleaning process, and the ultrasonic power is 300-400W.

And step five, flushing the inner surface of the pipeline by using compressed air until the residual alcohol is dried.

The heat preservation container is formed by coating a container for containing a cleaning solution or an oxalic acid solution by using an LDPE film, and can prevent the change of solution components and the precipitation of partial solute caused by the evaporation of water in the ultrasonic process.

(III) cleaning case and Effect

A316 stainless steel pipe with the inner diameter of 2mm, the outer diameter of 4mm and the length of 1.5m is taken as a cooling pipeline, coke produced by cracking kerosene with the trademark of 851-2 on the inner surface of the cooling pipeline is cleaned as an example, and an ultrasonic cleaning instrument is taken as an ultrasonic treatment container.

A plurality of 2-10 cm long pipe sections are cut before a cleaning experiment. One of the tube sections is cut open, the appearance of coke on the inner wall of the stainless steel tube is observed (figure 1), and the inner wall of the stainless steel tube is covered by black coke, so that the surface of the stainless steel tube is seriously coked. And (3) after the rest pipe sections are cleaned according to the cleaning process in the step (II), cutting open one pipe section, observing the inner surface appearance (figure 2) of the pipe section, and removing most coke to expose the color of the inner wall of the stainless steel pipe.

In order to verify the cleaning efficiency of the cleaning process, the micro-morphology and the components of the pipeline before and after the cleaning process are further analyzed. Referring to fig. 3, the composition analysis of several typical regions found that the carbon content of the rest of the inner surface of the tube was above 90% except for a part of the regions of metal carbide, indicating that the coking of the inner wall of the tube was severe. Referring to fig. 4, the carbon content in the typical area after the cleaning process is reduced to below 15%, and the content of the tube components such as Fe, Cr, Ni, etc. is increased significantly, which proves that most of the coke is removed and the stainless steel matrix (inner wall of the tube) is fully exposed.

Referring to FIG. 5, coking products of hydrocarbon fuels can be separated into two layers: the surface layer is a colloidal layer which is easy to clean, and the asphalt layer which is tightly combined with the matrix and is difficult to remove is positioned below the surface layer. In a whole view, the inner wall of the pipeline is seriously coked before the cleaning process, and the inner wall of the pipeline is covered by the coke. After the pre-cleaning is completed, the colloidal layer components in the coke are almost cleaned, but the cleaning effect on the asphaltene layer is very limited, most of the asphaltene layer still adheres to the surface of the stainless steel substrate, and only a few areas of the substrate are exposed. Thus, the use of a precleaning process effectively removes the colloidal layer from the coke, providing an advantage in further cleaning the asphaltene layer (and thus completely stripping the coke coating from the substrate).

(IV) control experiment of cleaning solution formula

Washing the control group: the cleaning solution is different from the cleaning solution, and the rest is the same as the cleaning process in the second step. The cleaning solution of the control group adopts the mixed alkali solution in the step one.

Referring to fig. 6, experiments show that coke in a partial area of the inner wall of the pipeline is not completely removed after the cleaning is performed by using the mixed alkali solution, and a channel and a pot hole (fig. 6b) generated due to corrosion appear in a partial area, which indicates that the cleaning effect of the mixed alkali solution is unstable and has a certain corrosion damage to the stainless steel substrate, and proves that the cleaning effect of the cleaning solution (in which the surfactant, the solubilizer and the chelating agent are added in the mixed alkali solution) in the step (ii) is better, and the cleaning process does not corrode the stainless steel substrate.

In a word, the invention takes the cleaning of coke on the inner surface of a stainless steel cooling pipeline without a coating on the surface as an example, and provides a cleaning solution and a cleaning method which are suitable for efficiently cleaning coke formed on the inner wall of the pipeline after pyrolysis and autoxidation of heat-absorbing hydrocarbon fuel, thereby providing a simple, convenient, economic and efficient inner surface coke cleaning scheme for a renewable pipeline.

Claims

1. A method for cleaning coke on the inner surface of a pipe without surface coating alloy is characterized by comprising the following steps: the method comprises the following steps:

1) pre-washing coke formed on the inner wall of the pipeline;

2) after the step 1), ultrasonically cleaning the inner surface of the pipeline by using a cleaning solution containing sodium hydroxide and potassium permanganate, so that coke is stripped from the inner wall of the pipeline and is dispersed in the cleaning solution;

3) after the step 2), removing cleaning residues on the inner wall of the pipeline by acid cleaning, and then drying;

the cleaning solution consists of 85 to 90 weight percent of mixed alkali solution, 3 to 5 weight percent of surfactant, 3 to 5 weight percent of solubilizer and 1 to 5 weight percent of chelating agent; the mixed alkali solution consists of a sodium hydroxide solution with the mass fraction of 17% -20% and a potassium permanganate solution with the mass fraction of 17% -20%, wherein the weight ratio of the sodium hydroxide solution to the potassium permanganate solution is 1: 1-2; the chelating agent consists of sodium tripolyphosphate and triethanolamine, and the weight ratio of the sodium tripolyphosphate to the triethanolamine is 5: 1-2; the surfactant is composed of a nonionic surfactant and an anionic surfactant, and the molar ratio of the nonionic surfactant to the anionic surfactant is 1: 2-3; the solubilizer is selected from isopropanol.

2. The method for cleaning coke on the inner surface of the pipe without the surface coating alloy as claimed in claim 1, wherein the method comprises the following steps: the pre-cleaning specifically comprises the following steps: respectively carrying out ultrasonic cleaning on the inner surfaces of the pipelines for 10-15 minutes by using acetone, absolute ethyl alcohol and deionized water, wherein the ultrasonic cleaning temperature is 20-30 ℃; in the step 2), the ultrasonic cleaning temperature is 70-80 ℃, and the ultrasonic cleaning time is 8-10 hours.

3. The method for cleaning coke on the inner surface of the pipe without the surface coating alloy as claimed in claim 1, wherein the method comprises the following steps: the step 3) specifically comprises the following steps:

3.1) ultrasonically cleaning the inner surface of the pipeline subjected to ultrasonic cleaning by using 0.1-0.2 mol/L oxalic acid solution;

3.2) carrying out ultrasonic cleaning on the inner surface of the pipeline subjected to the ultrasonic cleaning by using 65-85% ethanol solution, and then drying.

4. The method for cleaning coke on the inner surface of the pipe without the surface coating alloy as claimed in claim 3, wherein the method comprises the following steps: in the step 3.1), the ultrasonic cleaning temperature is 70-80 ℃, and the ultrasonic cleaning time is 4-6 hours; in the step 3.2), the ultrasonic cleaning temperature is 20-30 ℃, and the ultrasonic cleaning time is 15-30 minutes.

5. A surface-coating-free alloy pipeline cleaning fluid is characterized in that: the cleaning solution comprises sodium hydroxide and potassium permanganate, wherein the weight ratio of the sodium hydroxide to the potassium permanganate is 1: 1-2;

the cleaning solution consists of 85 to 90 weight percent of mixed alkali solution, 3 to 5 weight percent of surfactant, 3 to 5 weight percent of solubilizer and 1 to 5 weight percent of chelating agent; the mixed alkali solution consists of a sodium hydroxide solution with the mass fraction of 17% -20% and a potassium permanganate solution with the mass fraction of 17% -20%, wherein the weight ratio of the sodium hydroxide solution to the potassium permanganate solution is 1: 1-2; the chelating agent consists of sodium tripolyphosphate and triethanolamine, and the weight ratio of the sodium tripolyphosphate to the triethanolamine is 5: 1-2;

the surfactant is composed of a nonionic surfactant and an anionic surfactant, and the molar ratio of the nonionic surfactant to the anionic surfactant is 1: 2-3; the solubilizer is selected from isopropanol.

6. Use of the alloy pipe cleaning solution without surface coating according to claim 5 for cleaning coke formed by cracking and/or autoxidation of endothermic hydrocarbon fuel on the inner wall of metal pipes and pipe fittings.