Patent Application
20250034738
The disclosure relates to the field of aluminum electrolysis, and in particular to a method for reducing perfluorocarbon emissions from an aluminum electrolysis.
The aluminum industry includes industrial chains such as the production of primary aluminum (the mining of bauxite, the production of aluminum oxide, the production of anode, the production of electrolytic aluminum), processing and product manufacturing of recycled aluminum and aluminum, among which CO2 emissions from the production of primary aluminum account for approximately 94.85% of that from the aluminum industry. During the operation of an electrolytic cell of aluminum, in addition to carbon dioxide, gases of perfluorocarbons (PFCs) such as a carbon tetrafluoride and a carbon hexafluoride are also produced, and these gases are the main products of an anode effect in a process of an aluminum electrolysis. The greenhouse effect coefficient of PFCs is much higher than that of CO2. Contributions of 1 kilogram of CF4 to global warming and the contribution of 1 kilogram of C2F6 to global warming are equivalent to that of 6,630 kilograms and 11,100 kilograms of CO2 respectively. According to the statistics, the carbon dioxide emissions equivalent to the PFCs in the aluminum electrolysis in China is averagely about 0.6 t/t-Al (that is, the PFCs emissions generated from Al per ton in the electrolysis process is equivalent to CO2 of 0.6 ton), which is still far behind the current recommended value of 0.260 t/t-Al for the carbon dioxide emissions equivalent to the PFCs in the aluminum electrolysis proposed by the International Aluminum Institute.
At present, aluminum electrolytic companies and cells types have different technical routes, i.e., developing directions, and there are regional differences in aluminum oxide raw materials and electrolyte systems, and there are also great differences in the perfluorocarbon emissions during the process of aluminum electrolysis. In some enterprises, a composition of the electrolyte is appropriately controlled, processing parameters for the aluminum electrolysis are reasonably configured, and concentration parameters of aluminum oxide are reasonably set. Therefore, the carbon dioxide emissions equivalent to the PFCs in the aluminum electrolysis in some enterprises is lower than the recommended value proposed by the International Aluminum Institute. On the contrary, in some other enterprises, the composition of the electrolyte does not match the performance of aluminum oxide, the processing parameters of the aluminum electrolysis are not set reasonably, a concentration of aluminum oxide in an electrolyte is low, and therefore the perfluorocarbon emissions of the aluminum electrolysis are high which are several times the recommended value proposed by the International Aluminum Institute.
Some embodiments of the disclosure provide a method for reducing perfluorocarbon emissions from an aluminum electrolysis to solve a technical problem that the perfluorocarbon emissions from the aluminum electrolysis are high in some implementations.
According to the disclosure, a method for reducing perfluorocarbon emissions from an aluminum electrolysis is provided, which includes: placing an aluminum oxide in an electrolytic cell with set parameters for proceeding the aluminum electrolysis, and regulating feeding parameters of the aluminum oxide to obtain an electrolyte; adding a set amount of LiF, KF, MgF2 and CaF2 into the electrolyte, and regulating a molar ratio of NaF and AlF3 in the electrolyte to reduce the perfluorocarbon emissions from the aluminum electrolysis.
To illustrate technical solutions more clearly in embodiments of the disclosure, a brief introduction will be given below to accompanying drawings needed to be used in the description of the embodiments. Obviously, the accompanying drawings described in the following show some embodiments of the disclosure. For those of ordinary skill in the art, other accompanying drawings can also be obtained based on these accompanying drawings without creative efforts.
In order to make the purposes, technical solutions and advantages of the embodiments of the disclosure clearer, the technical solutions in the disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the disclosure. Obviously, the described embodiments are some embodiments of the disclosure, but not all embodiments. Based on the embodiments in the disclosure, all other embodiments obtained by those skilled in the art without any creative efforts shall fall within the scope of protection sought by the disclosure.
Various embodiments of the present disclosure may exist in the form of a range. It should be understood that the description in the form of a range is only for convenience and simplicity and should not be understood as a hard limit to the scope of the disclosure. Therefore, the described range should be considered to have specifically disclosed all possible subranges as well as the single values within such range. For example, a description of a range from 1 to 6 should be considered to have specifically disclosed subranges, such as ranges from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, and from 3 to 6, and a single number within the stated range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it is intended to include any cited number (fractional or whole) within the indicated range. Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in the disclosure are commercially available or obtained through existing methods.
In the disclosure, unless otherwise specified, the directional words used such as “upper” and “lower” refer specifically to the direction of the figure in the drawing. In addition, in the description of the disclosure, the terms “including”, “comprising” and the like refer to “including but not limited to”. In the disclosure, relational terms such as “first” and “second” are merely used to distinguish one entity or operation from another and do not necessarily require or imply any such actual relationship or sequence between these entities or operations. In the disclosure, “and/or” describes the relationship between associated objects, indicating that there may be three relationships. For example, A and/or B may refer to A alone, both A and B, and B alone. In which, A and B can be singular or plural. In the disclosure, “at least one” refers to one or more, and “plurality” refers to two or more. “At least one”, “at least one of the following” or similar expressions thereof refer to any combination of these items, including single items or any combination of plural items. For example, “at least one of a, b, or c”, or “at least one of a, b, and c” may represent a, b, c, a-b (that is, a and b), a-c, b-c, or a-b-c, in which a, b, and c can each be single or multiple.
In a first aspect, the disclosure provides a method for reducing perfluorocarbon emissions from an aluminum electrolysis, which includes: placing an aluminum oxide in an electrolytic cell with set parameters for the aluminum electrolysis, and regulating feeding parameters of the aluminum oxide to obtain an electrolyte; adding a set amount of LiF, KF, MgF2 and CaF2 into the electrolyte, and regulating a molar ratio of NaF and AlF3 in the electrolyte to reduce the perfluorocarbon emissions from the aluminum electrolysis.
A suitable primary crystallization temperature of the electrolyte is obtained by regulating a composition of the electrolyte for dissolving aluminum oxide. Parameters of the electrolytic cell are regulated, and therefore an energy distribution in the electrolytic cell is optimized, thereby improving a solubility of the aluminum oxide in the electrolyte. A lowest concentration of the aluminum oxide in the electrolyte is increased and the perfluorocarbon emissions are effectively reduced by regulating the feeding parameters of the aluminum oxide with assistance of the above-mentioned regulating ways.
In some embodiments, the composition of the electrolyte satisfies the following relation formula: CR=3.334-0.0446×w(KF)eletrolyte+0.0942×w(LiF)electrolyte+0.0098×w(MgF2)eletrolyte−0.0070×ΔT−0.0895×AO−0.0452×t+r, where: CR represents a molar ratio of NaF and AlF3; w(KF) electrolyte, w(LiF)electrolyte and w(MgF2)eletrolyte represent mass fractions of KF, LiF, and MgF2 in the electrolyte respectively; ΔT represents a superheat degree of the electrolyte, a unit of ΔT being° C.; AO represents a type of an aluminum oxide, and when the aluminum oxide is a flour aluminum oxide: AO=1, when the aluminum oxide is an intermediate aluminum oxide: AO=2, and when the aluminum oxide is a sandy aluminum oxide: AO=3; t represents a time for 1% aluminum oxide (that is, a mass of the aluminum oxide accounts for one percent of the mass of the electrolyte) to be completely dissolved in a molten electrolyte, and t≤20, a unit of t being min; and r represents an adjustment constant, and r=0−0.1.
A reason for providing the above relation formula is that the electrolyte having compositions whose ranges are limited by the above relation formula can have sufficient dissolution speed and dissolution ability for the above-mentioned aluminum oxide.
In some embodiments, regulating parameters of the electrolytic cell include at least one of the following: regulating an average superheat degree of the electrolytic cell to 8−15° C.; and regulating an electrolyte height of the electrolytic cell≥19 cm.
The reason for regulating the average superheat degree is that a relatively high current efficiency can be maintained. A too low or too high superheat degree is detrimental to the current efficiency and may affect overall indicators of economy and technology of an electrolysis process. The reason for regulating the electrolyte height is that the aluminum oxide can be dissolved as the aluminum oxide settles in the electrolyte, in order to keep the aluminum oxide in the electrolyte for sufficient time to be completely dissolved.
In some embodiments, the regulating the feeding parameters of the aluminum oxide includes at least one of the following: regulating a break through rate of a feeding hole; regulating a coverage rate by carbon residue of the feeding hole. The break through rate of a feeding hole≥90%, the coverage rate of the feeding hole by carbon residue≤80%, a deviation of a feeding amount of the aluminum oxide from a theoretical value≤10%, and the lowest concentration of the aluminum oxide≥1.2%.
If the break through rate of a feeding hole is less than 90%, a portion of the aluminum oxide will not be able to enter the electrolyte, which may ultimately affect a concentration of the aluminum oxide in the electrolyte. If the coverage rate of the feeding hole by carbon residue is greater than 80%, a portion of the aluminum oxide will be mixed with a carbon residue, thereby affecting a dissolution of the aluminum oxide, and ultimately affecting the concentration of the aluminum oxide in the electrolyte. If the concentration of the aluminum oxide is lower than 1.2%, an anode effect coefficient of the electrolysis process is increased, thereby increasing the perfluorocarbon emissions.
Technical solutions of the disclosure will be described in detail below with reference to examples, comparative examples and experimental data.
Example 1: with a method for reducing perfluorocarbon emissions from an aluminum electrolysis, an intermediate aluminum oxide is used as a raw material; compositions of an electrolyte are LiF 4.3−4.5%, KF 2.3−2.5%, CaF2 3.8−4.0%, MgF2 0.7−0.8%; a molar ratio of (NaF/AlF3) is 2.50±0.05; an electrolytic cell temperature is 935±5° C.; and an average superheat degree is 12° C. The electrolyte height during a production process is 19 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 96%. The coverage rate of the feeding hole by carbon residue during feeding is 80%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 12 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 30 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.3%.
Example 2: with a method for reducing perfluorocarbon emissions from an aluminum electrolysis, an intermediate aluminum oxide is used as a raw material; compositions of an electrolyte are LiF 4.3−4.5%, KF 2.3−2.5%, CaF2 3.8−4.0%, MgF2 0.7−0.8%; a molar ratio of (NaF/AlF3) is 2.40+0.05; a temperature of an electrolytic cell is 935±5° C.; and an average superheat degree is 15° C. The electrolyte height during a production process is 19 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 90%. The coverage rate of the feeding hole by carbon residue during feeding is 50%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 12 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 30 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.2%.
Example 3: with a method for reducing perfluorocarbon emissions from an aluminum electrolysis, a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 5.6−6.0%, KF 2.8−3.0%, CaF2 3.2−3.7%, MgF2 1.3−1.5%; a molar ratio of (NaF/AlF3) is 2.80±0.05; a temperature of an electrolytic cell is 925±5° C.; and an average superheat degree is 10° C. The electrolyte height during a production process is 20 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 97%. The coverage rate of the feeding hole by carbon residue during feeding is 36%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.4%.
Example 4: with a method for reducing perfluorocarbon emissions from an aluminum electrolysis, a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 3.6−4.0%, KF 2.8−3.0%, CaF2 3.2−3.7%, MgF2 1.3−1.5%; a molar ratio of (NaF/AlF3) is 2.50±0.05; a temperature of an electrolytic cell is 930±5° C.; and an average superheat degree is 8° C. The electrolyte height during a production process is 20 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 96%. The coverage rate of the feeding hole by carbon residue during feeding is 30%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.4%.
Example 5: with a method for reducing perfluorocarbon emissions from an aluminum electrolysis, a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 1.9−2.1%, KF 1.9−2.1%, CaF2 4.8−5.2%, MgF2 0.9−1.1%; a molar ratio of (NaF/AlF3) is 2.40+0.05; a temperature of an electrolytic cell is 945±5° C.; and an average superheat degree is 12° C. The electrolyte height during a production process is 19 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 98%. The coverage rate of the feeding hole by carbon residue during feeding is 20%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.5%.
Comparative Example 1: an intermediate aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 4.3−4.5%, KF 2.3−2.5%, CaF2 3.8−4.0%, MgF2 0.7−0.8%; a molar ratio of (NaF/AlF3) is 2.40±0.05; a temperature of an electrolytic cell is 930±5° C.; and an average superheat degree is 10° C. The electrolyte height during a production process is 17 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 85%. The coverage rate of the feeding hole by carbon residue during feeding is 90%. A deviation of a feeding amount of the aluminum oxide from a designed value is 20%-30%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.0%.
Comparative Example 2: an intermediate aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 4.3−4.5%, KF 2.3−2.5%, CaF2 3.8−4.0%, MgF2 0.7−0.8%; a molar ratio of (NaF/AlF3) is 2.40±0.05; a temperature of an electrolytic cell is 925±5° C.; and an average superheat degree is 5° C. The electrolyte height during a production process is 18 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 80%. The coverage rate of the feeding hole by carbon residue during feeding is 85%. A deviation of a feeding amount of the aluminum oxide from a designed value is 20% 30%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.0%.
Comparative Example 3: a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 5.6−6.0%, KF 2.8−3.0%, CaF2 3.2−3.7%, MgF2 1.3−1.5%; a molar ratio of (NaF/AlF3) is 2.50±0.05; a temperature of an electrolytic cell is 915±5° C.; and an average superheat degree is 8° C. The electrolyte height during a production process is 18 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 85%. The coverage rate of the feeding hole t by carbon residue during feeding is 72%. A deviation of a feeding amount of the aluminum oxide from a designed value is 20%-30%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.1%.
Comparative Example 4: a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 5.6−6.0%, KF 2.8−3.0%, CaF2 3.2−3.7%, MgF2 1.3−1.5%; a molar ratio of (NaF/AlF3) is 2.50±0.05; a temperature of an electrolytic cell is 915±5° C.; and an average superheat degree is 8° C. The electrolyte height during a production process is 17 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 72%. The coverage rate of the feeding hole by carbon residue during feeding is 55%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.1%.
Comparative Example 5: a flour aluminum oxide is used as a raw material; compositions of the electrolyte are LiF 1.9−2.1%, KF 1.9−2.1%, CaF2 4.8−5.2%, MgF2 0.9−1.1%; a molar ratio of (NaF/AlF3) is 2.30+0.05; a temperature of an electrolytic cell is 940±5° C.; and an average superheat degree is 12° C. The electrolyte height during a production process is 17 cm. During the crust breaking and aluminum oxide feeding process, the break through rate of the feeding hole is 80%. The coverage rate of the feeding hole by carbon residue during feeding is 80%. A deviation of a feeding amount of the aluminum oxide from a designed value is 10%. Regulating parameters of the concentration of the aluminum oxide are set as the switching cycle coefficient of the aluminum oxide concentration 11 μΩ, an increment rate of 1.2, a decrement rate of 1.2, a maximum time of excess amount period 25 minutes, and a maximum time of normal amount period 3 minutes. A lowest concentration of the aluminum oxide in the electrolyte is 1.10.
The perfluorocarbon emissions of Example 1—Example 5 and Comparative Example 1—Comparative Example 5 are detected, and the detected results are shown in Table 1.
Referring to Table 1, according to a comparison between Example 1 and Comparative Example 1, a comparison between Example 2 and Comparative Example 2, a comparison between Example 3 and Comparative Example 3, a comparison between Example 4 and Comparative Example 4, and a comparison between the Example 5 and the Comparative Example 5, it can be seen that the method for reducing the perfluorocarbon emissions in the aluminum electrolysis provided by Example 1—Example 5 of the disclosure can effectively reduce the perfluorocarbon emissions compared with that of Comparative Example 1-Comparative Example 5. The perfluorocarbon emissions of Example 1—Example 5 is ≤800 kg/t-Al, while the perfluorocarbon emissions of Comparative Example 1—Comparative Example 5 is ≥1760 kg/t-Al.
The above descriptions are only specific embodiments of the disclosure, enabling those skilled in the art to understand or implement the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principle defined in the disclosure may be practiced in other embodiments without departing from the spirit or scope of the disclosure. Therefore, the disclosure is not to be limited to the embodiments shown in the disclosure but is to be accorded the widest scope consistent with the principles and novel features claimed in the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210713148.4 | Jun 2022 | CN | national |
This is a continuation of International application No. PCT/CN2023/098543 filed on Jun. 6, 2023, which claims priority to Chinese patent application No. 202210713148.4 filed on Jun. 22, 2022. The disclosures of the above-referenced applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2023/098543 | Jun 2023 | WO |
| Child | 18912423 | US |
