CN108914135B - Pickling solution and pickling method - Google Patents
Pickling solution and pickling method Download PDFInfo
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- CN108914135B CN108914135B CN201810645621.3A CN201810645621A CN108914135B CN 108914135 B CN108914135 B CN 108914135B CN 201810645621 A CN201810645621 A CN 201810645621A CN 108914135 B CN108914135 B CN 108914135B
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/04—Cleaning or pickling metallic material with solutions or molten salts with acid solutions using inhibitors
- C23G1/06—Cleaning or pickling metallic material with solutions or molten salts with acid solutions using inhibitors organic inhibitors
- C23G1/066—Cleaning or pickling metallic material with solutions or molten salts with acid solutions using inhibitors organic inhibitors phosphorus-containing compounds
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/085—Iron or steel solutions containing HNO3
Abstract
The invention provides a pickling solution and a pickling method, wherein the pickling solution comprises nitric acid; and the scale and corrosion inhibitor comprises diethylenetriamine penta (methylene phosphonic acid). According to the invention, the concentration of nitric acid in the pickling solution is reduced to 2% -3%, and the scale and corrosion inhibitor is added into the pickling solution, so that the corrosion effect of the pickling solution on the wet oxidation regeneration device of the powdered activated carbon is reduced, the pickling efficiency is improved, and the pickling time is shortened.
Description
Technical Field
The invention relates to the field of acid washing, in particular to acid washing liquid and an acid washing method for a wet oxidation regeneration device of powdered activated carbon.
Background
In the treatment of high-concentration organic wastewater difficult to degrade, powdered activated carbon is commonly used for adsorbing organic matters in the wastewater. In order to reduce the treatment cost, it is necessary to perform wet oxidation regeneration on the powdered activated carbon which has been saturated by adsorption, thereby realizing the reuse thereof. Under the conditions of high temperature (about 250 ℃) and high pressure (about 5MPa) provided by a wet oxidation regeneration device, organic matters adsorbed by the powdered activated carbon and oxygen are subjected to oxidation reaction and decomposed into micromolecular organic matters or inorganic matters, and after the reaction is finished, the activated carbon is regenerated. Meanwhile, organic matters and inorganic salts in the materials can be scaled under the conditions of high temperature and high pressure and are attached to a heat exchanger and a reactor of a regeneration system, so that the problems of system blockage, substandard treatment effect, incapability of long-period stable operation of a regeneration device and the like are caused. In order to solve the above problems, the wet oxidation regeneration apparatus for powdered activated carbon needs to be cleaned by acid washing periodically.
Scale (calcium, magnesium) and rust (Fe) caused by nitric acid2O3And Fe3O4) Has good dissolving capacity and can not generate on stainless steel substrate equipmentPitting corrosion, and therefore nitric acid is commonly used in the industry as an acid wash. The conventional pickling method for the wet oxidation regeneration device of powdered activated carbon is generally referred to the above industrial pickling method. Specifically, nitric acid with a temperature of 80 to 85 ℃ and a concentration of 5 to 10% is usually used as a pickling solution, and the pickling solution is injected into a regeneration system (heat exchange system + reactor) and then internally circulated, and when the acidity of the pickling solution does not change any more, the pickling is considered to be finished.
However, the acid washing method has the following disadvantages:
1. the nitric acid pickling solution with the concentration of 5-10% has a corrosion effect on the powdered activated carbon wet oxidation device. When using the conventional wet oxidation regenerator pickling method, i.e. with nitric acid at a concentration of 5-10% as pickling liquid, it was found that the regeneration system had suffered corrosion.
2. The pickling solution has too single component and low descaling efficiency. The traditional wet oxidation regeneration device acid washing solution only comprises nitric acid, and scale components in the wet oxidation regeneration device are complex, so that the working efficiency of the method is low, and the acid washing time is more than 70 hours.
3. The judgment of the pickling end point is unreasonable. In the traditional wet oxidation device pickling method, the pickling termination standard is used when the acidity value of the pickling solution is constant and does not fluctuate any more. The method cannot accurately reflect the pickling effect of the wet oxidation regenerator due to sulfate scales (such as CaSO) in the regenerator4) The content change has no obvious mathematical logic relation with the acidity of the pickling solution.
Therefore, it is urgently needed to provide a new pickling method for the wet oxidation regeneration device of the activated carbon.
Disclosure of Invention
In view of the above problems, the present invention provides a pickling solution, comprising:
nitric acid; and the scale and corrosion inhibitor comprises diethylenetriamine pentamethylene phosphoric acid.
In the pickling solution, the concentration of the nitric acid is 2% -3%.
In the pickling solution, the addition amount of the scale and corrosion inhibitor is 80ppm-120 ppm.
The invention also provides an acid washing method of the activated carbon wet oxidation regeneration device, which comprises the following steps:
heating the pickling solution to a temperature T;
flowing the pickling solution through a heat exchanger into a reactor; and
after the reactor is filled with the pickling solution, circulating the pickling solution in the reactor for a certain time H between the heat exchanger and the reactor,
wherein the pickling solution comprises nitric acid and a scale and corrosion inhibitor, and the scale and corrosion inhibitor comprises diethylenetriamine pentamethylene phosphoric acid.
In the above pickling method, after the pickling solution in the reactor was circulated between the heat exchanger and the reactor for a certain time H, the calcium hardness value of the pickling solution after circulation was measured.
In the above acid washing method, the certain time H is 5 to 9 hours.
In the above pickling method, when the calcium hardness value of the pickling solution after the circulation is higher than 5% of the calcium hardness value at the calcium ion saturation concentration (i.e., the calcium hardness value of the pickling solution > 5% of the calcium hardness value at the calcium ion saturation concentration), pickling is performed again; and when the calcium hardness value of the acid washing solution after the circulation is lower than 5% of the calcium hardness value of the calcium ion saturated concentration (namely, the calcium hardness value of the acid washing solution is less than 5% of the calcium hardness value of the calcium ion saturated concentration), completing the acid washing.
In the above pickling method, the heating rate of heating is 2 ℃/min or less.
In the above pickling method, the temperature T is 80 to 85 ℃.
Compared with the prior art, the invention has the following advantages:
1. the concentration of nitric acid in the pickling solution is reduced from 5-10% to 2-3%, and the scale and corrosion inhibitor is added into the pickling solution, so that the corrosion effect of the pickling solution on an active carbon wet oxidation regeneration device is reduced;
2. by changing the composition of the pickling solution, namely adding the scale and corrosion inhibitor on the basis of taking nitric acid as a pickling agent, the solubility of inorganic salt scales is improved and the pickling efficiency of the pickling solution is improved by utilizing the synergistic effect of the scale and corrosion inhibitor.
3. According to the invention, the calcium hardness value of calcium ions (inorganic salt scales) in the pickling solution is taken as the judgment basis of pickling, so that the accuracy of the judgment of the pickling end point is improved; that is, the calcium hardness value (in terms of calcium carbonate) of the pickling solution is compared with 5% of the calcium hardness value at the time of calcium ion saturation concentration, and when the former is lower than the latter, it is determined that the pickling end point is reached.
Drawings
FIG. 1 is a schematic diagram of the acid washing of a wet oxidation regeneration device for powdered activated carbon (wherein, 1-reactor, 2-heat exchanger 2, 3-heat exchanger 1, 4-acid washing pump, 5-acid washing tank, 6-sampling port, 7-low pressure steam, 8-acid washing liquid, 9-shell side, 10-tube side, 11-reactor outlet, 12-reactor inlet).
Detailed Description
The following examples are presented to enable those skilled in the art to more fully understand the present invention and are not intended to limit the invention in any way.
The invention provides a pickling agent which is prepared from 2-3% nitric acid and 80-120 ppm scale and corrosion inhibitors (including diethylenetriamine pentamethylene phosphoric acid),
the concentration of the nitric acid is 2% -3%, because the scale and corrosion inhibitor can generate a synergistic effect with the nitric acid to improve the solubility of inorganic salt scales, the concentration of the nitric acid can be reduced, and the corrosion of the pickling solution on the activated carbon wet oxidation regeneration device is further reduced.
The adding amount of the scale and corrosion inhibitor is 80ppm-120ppm, because when the adding amount of the scale and corrosion inhibitor is too much (namely more than 120ppm), the content of nitric acid is low, and the pickling is not facilitated; when the adding amount of the scale and corrosion inhibitor is too small (namely less than 80ppm), the dissolution of inorganic salt scale is not facilitated, so when the adding amount of the scale and corrosion inhibitor is 80ppm-120ppm, the pickling can be better carried out.
The invention also provides an acid washing method of the activated carbon wet oxidation regeneration device, which comprises the following steps:
heating the pickling solution to a temperature T; enabling the pickling solution to flow through a heat exchanger and enter a reactor; and after the reactor is filled with the pickling solution, circulating the pickling solution in the reactor between the heat exchanger and the reactor for 5-9 hours,
wherein the pickling solution comprises nitric acid and a scale and corrosion inhibitor, and the scale and corrosion inhibitor comprises diethylenetriamine pentamethylene phosphoric acid.
In the pickling method, after the pickling solution in the reactor is circulated between the heat exchanger and the reactor for 5-9 hours, the calcium hardness value of the circulating pickling solution is tested and compared with 5% of the calcium hardness value at the calcium ion saturation concentration, so as to detect whether the pickling end point is reached;
calcium hardness value of pickling solution after circulation (calcium hardness value is CaCO3Calculated) is higher than 5 percent of the calcium hardness value when the calcium ion saturation concentration is reached, the pickling waste liquid is emptied, the pickling liquid is prepared again, the acid cleaning is carried out on the activated carbon wet oxidation regeneration device again,
when the calcium hardness value of the acid washing solution after circulation is lower than 5% of the calcium hardness value when the calcium ion saturation concentration is reached, acid washing is completed;
the judging method can accurately judge whether the acid washing of the active carbon wet oxidation regeneration device reaches the end point, and improves the judging accuracy.
In the pickling method, the heating rate of the pickling solution does not exceed 2 ℃/min, because when the heating rate of the pickling solution is too high, it is not easy to control the temperature of the pickling solution, and the mixing of nitric acid and the scale and corrosion inhibitor is liable to be uneven.
In the acid washing method, the acid washing temperature of the acid washing solution is 80-85 ℃, and at the temperature, the activity of nitric acid and a scale and corrosion inhibitor (comprising diethylenetriamine pentamethylene phosphoric acid) is stronger, so that the acid washing can be effectively carried out on the activated carbon wet oxidation regeneration device.
In the pickling method, the composition of the pickling solution is changed, namely, the scale and corrosion inhibitor is added on the basis of taking nitric acid as a pickling agent, the synergistic effect of the nitric acid and the pickling solution is utilized, the dissolution and dispersion of inorganic salt scale substances are improved, the pickling efficiency of the pickling solution is improved, and the pickling time of an activated carbon wet oxidation regeneration device is reduced to be within 50h from more than 70 h.
In the acid washing method, acid washing liquid in the reactor is circulated between the heat exchanger and the reactor for 5-9 hours, so that the acid washing is ensured to be fully carried out.
Example 1
Referring to fig. 1, fig. 1 shows a schematic acid wash of a powdered activated carbon wet oxidation regeneration unit; in fig. 1, the powdered activated carbon wet oxidation regeneration device is composed of a heat exchanger 1, a heat exchanger 2 and a reactor, wherein the heat exchanger is used for increasing the temperature of the material to be regenerated from room temperature to about 250 ℃ (the heat exchange medium is low-pressure steam and regenerated material from the outlet of the reactor), and the reactor is a main place for the oxidation reaction of the powdered activated carbon and oxygen.
The pickling process specifically comprises the following steps:
injecting a nitric acid solution with the concentration of 2-3% into a pickling tank, adding a scale and corrosion inhibitor, wherein the adding amount of the scale and corrosion inhibitor is 80-120 ppm and comprises diethylenetriamine pentamethylene phosphoric acid, the volume of the pickling solution is 1.5 times of the total volume of a heat exchanger and a reactor, low-pressure steam is used for heating the pickling solution, and the heating rate is not more than 2 ℃/min;
when the temperature of the pickling solution reaches 80-85 ℃, starting a pickling pump to carry out circulating pickling, wherein the pickling solution firstly passes through a heat exchanger 1 and a heat exchanger 2 in sequence in a tube pass mode (inner tubes) as shown in figure 1; then, pickling solution enters the reactor from the bottom and is gradually filled into the reactor, when the level of the pickling solution in the reactor is higher than the outlet of the reactor (namely, when the reactor is filled), the pickling solution sequentially flows through the heat exchanger 2 and the heat exchanger 1 again in a shell pass mode (outer tube), the pickling solution circulates between the heat exchangers 1 and 2 and the reactor for 5-9 hours, and finally, the pickling solution returns to a pickling tank along with dirt substances;
sampling from the sampling port of the pickling tank at intervals of 8h, and testing the calcium hardness value (as CaCO) in the pickling solution3Measured), when the acid wash solution has a calcium hardness value greater than 5% of the calcium hardness value at the calcium ion saturation concentration (analyzed, calcium ion saturation in this test)And the calcium hardness value at concentration is 8000mg/L, so that 5% of the calcium hardness value at calcium ion saturation concentration is 400mg/L), emptying the pickling waste liquid, preparing the pickling liquid again, and carrying out the circulating pickling of the powdered activated carbon wet oxidation regeneration device again; after the steps of repeated sampling and analysis, waste liquid emptying and pickling solution reconfiguration are carried out for a plurality of times, the calcium hardness value in the pickling solution is gradually reduced, and when the calcium hardness value of the pickling solution is lower than 5% of the calcium hardness value when the calcium ion saturation concentration is reached (namely the calcium hardness value of the pickling solution is less than 400mg/L), and the value is not changed after the secondary measurement, the pickling end point is reached.
When the pickling end point is reached, emptying the pickling waste liquid, washing the heat exchanger 1, the heat exchanger 2 and the reactor by using industrial water, and after the residual pickling waste liquid and the residual slag are discharged, finishing the pickling process of the powder activated carbon wet oxidation regeneration device, wherein the pickling time of the whole pickling process is about 48 hours;
wherein, the temperature of the pickling solution is kept between 80 and 85 ℃ in the whole pickling process.
In this embodiment, the change of the hardness value of the pickling solution calcium in the pickling process of the wet oxidation regeneration device for powdered activated carbon and the pickling consumption time are shown in table 1 below:
TABLE 1
The invention has the advantages that:
1. the corrosion of the pickling solution on the activated carbon wet oxidation regeneration device is reduced; the concentration of nitric acid in the pickling solution is reduced from 5-10% to 2-3%, and a scale and corrosion inhibitor is added into the pickling solution, so that the corrosion of the pickling solution on an active carbon wet oxidation regeneration device is reduced;
2. the pickling efficiency of the pickling solution is improved; by changing the composition of the pickling solution, namely adding the scale and corrosion inhibitor on the basis of taking nitric acid as a pickling agent, improving the solubility of inorganic salt scales and the pickling efficiency of the pickling solution by utilizing the synergistic effect of the nitric acid and the corrosion inhibitor, and reducing the pickling time of the wet oxidation regeneration device for the powdered activated carbon from more than 70 hours to within 50 hours.
3. The accuracy of the acid washing end point judgment is improved; according to the invention, the calcium hardness value of calcium ions (inorganic salt scales) in the pickling solution is taken as the judgment basis of pickling, so that the accuracy of the judgment of the pickling end point is improved; namely, the calcium hardness value (calculated by calcium carbonate) of the pickling solution is compared with 5% of the calcium hardness value at the calcium ion saturation concentration, and when the former is lower than the latter, the pickling end point is judged to be reached.
Those skilled in the art will appreciate that the above embodiments are merely exemplary embodiments and that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention.
Claims (6)
1. An acid washing method of an active carbon wet oxidation regeneration device comprises the following steps:
heating the pickling solution to a temperature T;
flowing the pickling solution through a heat exchanger into a reactor; and
after the reactor is filled with the pickling solution, circulating the pickling solution in the reactor for a certain time H between the heat exchanger and the reactor,
the pickling solution is composed of nitric acid and a scale and corrosion inhibitor, the concentration of the nitric acid is 2% -3%, the scale and corrosion inhibitor is diethylenetriamine penta (methylene phosphonic acid), and the addition amount of the scale and corrosion inhibitor is 80-120 ppm.
2. The acid wash process of claim 1 wherein after the acid wash in the reactor is circulated between the heat exchanger and the reactor for a period of time H, the calcium hardness value of the acid wash after circulation is tested.
3. The pickling method according to claim 2, wherein the predetermined time H is 5 to 9 hours.
4. The pickling method as claimed in claim 2, wherein when the calcium hardness value of the pickling solution after the circulation is higher than 5% of the calcium hardness value at the calcium ion saturation concentration, pickling is performed again; and when the calcium hardness value of the acid washing solution after the circulation is lower than 5% of the calcium hardness value of the calcium ion saturated concentration, finishing the acid washing.
5. The pickling method according to claim 1, wherein the heating rate of heating is 2 ℃/min or less.
6. The pickling process of claim 1, wherein the temperature T is 80-85 ℃.
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