CN113980699B - Method for improving lignite pyrolysis tar yield - Google Patents
Method for improving lignite pyrolysis tar yield Download PDFInfo
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Abstract
The invention provides a method for improving the yield of lignite pyrolysis tar, wherein lignite upgrading is studied for years in China, but cannot be applied in a large scale all the time, the root cause of the lignite upgrading is poor in profitability and difficult to adapt to markets, and the method realizes the removal of moisture of lignite in a non-evaporative mode by treating raw lignite through a combined process of 'hydro-thermal' + 'swelling', saves a large amount of latent heat of evaporation, saves more energy and is lower in carbonization; the hydrothermal modification process realizes the transfer of hydrogen ions in water to a lignite macromolecular structure through an ion channel, increases the H/C atomic ratio of upgraded coal, increases the content of hydrogen free radicals in the pyrolysis process, and generates an amplifying effect on the increase of the H/C atomic ratio in the swelling process, thereby improving the yield of the pyrolysis coal tar; the invention realizes the dehydration, deoxidation and quality improvement of the lignite, and can effectively improve the yield of the lignite pyrolysis coal tar, further increase the added value of the quality improvement and improve the market applicability of the lignite in the clean coal field.
Description
Technical Field
The invention belongs to the field of lignite upgrading in coal chemical industry, and particularly relates to a method for improving the yield of lignite pyrolysis tar.
Background
Lignite is rich in reserves in China, and is an important energy reserve for ensuring that the economy of China maintains long-period stable development. However, the high water content, high oxygen content, easy spontaneous combustion and other adverse factors of lignite severely restrict the efficient application of the lignite. With the continuous consumption and exhaustion of high-order coal, the development and utilization of lignite resources are urgent. It is therefore necessary to develop clean and efficient application ways to achieve their high value-added applications.
Lignite upgrading is studied in China for many years, and is not applicable on a large scale all the time, and the essential reason is that the lignite upgrading cannot adapt to market rules and enterprises are difficult to profit. In particular, the yield of the pyrolysis coal tar with high added value is low, and the coal tar is widely used as a raw material for producing a plurality of high-end chemical raw materials. However, for lignite, the low temperature crosslinking reaction causes the tar precursor to be crosslinked to the lignite macromolecular structure before the lignite escapes during pyrolysis, which is the main reason for low yield of lignite pyrolysis tar.
Disclosure of Invention
Based on a plurality of adverse factors existing in the lignite large-scale development and utilization process and combined with the proposition and construction of the free radical control and crosslinking inhibition theory, the invention provides a method for improving the yield of lignite pyrolysis tar, which is used for improving the added value and market competitiveness of lignite upgrading industry products.
The technical scheme adopted for solving the technical problems is as follows: a method for improving the yield of lignite pyrolysis tar, comprising the following steps:
step 1, crushing lignite raw coal, uniformly mixing the lignite raw coal with deionized water, and then placing the lignite raw coal in a hydrothermal reaction kettle for reaction;
step 2, carrying out solid-liquid separation on the solid-liquid mixture after the reaction in the step 1, and drying the separated solid product in a vacuum drying oven;
step 3, mixing the solid product dried in the step 2 with tetralin, and placing the mixture in a water bath thermostat for swelling treatment;
step 4, washing the swelling product obtained in the step 3 until the color of the washing liquid is not changed any more;
step 5, carrying out solid-liquid separation on the washed swelling product obtained in the step 4, and drying the separated swelling product in a vacuum drying oven;
and 6, placing the dried swelling product obtained in the step 5 into a fixed bed pyrolysis system for pyrolysis, collecting coal tar, and quantifying the yield.
Further, in the step 1, raw coal is crushed to 0.2-0.5 mm, and the mass ratio of raw coal to deionized water is 0.5-1: 1.
Further, in the step 1, the process conditions of the hydrothermal reaction kettle are as follows: the final temperature of the reaction is 100-350 ℃, the initial pressure of the reaction is normal pressure, and N is introduced before the reaction 2 The flow is 150-200 ml/min, the time is 3-10 min, then the sealing is carried out, the temperature is raised to the final temperature at the temperature raising rate of 3-15 ℃/min, and the mixture stays30～60min。
Further, in the step 2, the vacuum drying temperature is 100-110 ℃ and the drying time is 8-12 h.
Further, in the step 3, the dried solid product is mixed with tetralin according to a mass ratio of 1:1-2, the swelling treatment temperature is 30-50 ℃ and the time is 24-48 h (the swelling height is not changed).
Further, the washing liquid in the step 4 is acetone.
Further, in the step 5, the vacuum drying temperature is 100-110 ℃ and the drying time is 8-15 h.
Further, in the step 6, the pyrolysis process conditions are as follows: the final pyrolysis temperature is 600-870 ℃, and the temperature is raised to the final pyrolysis temperature according to the temperature-raising rate of 10-15 ℃/min and stays for 30-60 min; before pyrolysis, introducing N at a flow rate of 150-200 ml/min 2 Heating after 5-10 min, and maintaining N 2 The reaction was terminated by passing through the reaction vessel.
Further, in the step 6, coal tar is collected and separated through acetone washing and anhydrous magnesium sulfate is separated, and the quality of the coal tar is determined.
Further, in the step 6, after the pyrolysis reaction is finished, the mass of the pyrolysis system before and after the reaction with a cooler is weighed to obtain the yield of a liquid product, the liquid product contains pyrolysis water and coal tar, and the flow of oil-water separation is as follows: washing and collecting the pipe wall of a cooler by using acetone, uniformly mixing, adding anhydrous magnesium sulfate accounting for 10-20% of the total mass of a liquid product, placing the anhydrous magnesium sulfate in a vacuum drying oven at 30-50 ℃ for 48-60 hours, wherein the mass difference of the anhydrous magnesium sulfate before and after the anhydrous magnesium sulfate is the pyrolysis water yield, obtaining the pyrolysis coal tar yield by a difference method, and the ratio of the coal tar yield to the mass of a swelled product after the drying in the step 5 is the coal tar yield.
Further, the coal tar yield is required to remove the residual tetralin after pyrolysis, namely the final coal tar yield=the coal tar yield obtained by subtraction-the residual amount of tetralin.
Further, in the step 6, in the calculation of the yield of coal tar, the residual tetrahydronaphthalene is calculated according to the following method, so that the yield of coal tar is more accurately quantified, and the principle is that the mass fraction of tetrahydronaphthalene remained in the swelled product is calculated by the mass balance of elements before and after swelling:
wherein C is HD And H HD Respectively representing the mass of carbon element and hydrogen element in the coal sample before swelling, namely the solid product after drying in the step 2; 0.91 and 0.09 represent mass fractions of carbon element and hydrogen element in tetrahydronaphthalene, respectively; the swelling product in the step 6 is a swelling coal sample with tetrahydronaphthalene residues; x is x 1 And x 3 Representing the residual amount (g/100-dry ashless basis) of tetrahydronaphthalene in the swelled product calculated by carbon element and hydrogen element, respectively; c (C) HDS And H HDS Respectively representing the mass fractions of carbon element and hydrogen element in the swelling product; x is x 2 And x 4 Representing the mass fraction of residual tetrahydronaphthalene in the swollen product calculated by the carbon element and the hydrogen element, respectively.
Further, the final coal tar yield was calculated, and the tetrahydronaphthalene residue used was the residue calculated on the basis of carbon element.
The invention is based on the deep structural transformation of dehydration and deoxidation of lignite by hydrothermal modification, effectively reduces the moisture content and oxygen content of lignite, and avoids the problems of ineffective transportation and easy spontaneous combustion of lignite in the transportation process. And the reduction of the oxygen content in the hydrothermal modification process can effectively reduce the occurrence of crosslinking reaction in the pyrolysis process, so that the yield of coal tar is improved. In addition, the transfer of hydrogen in water to a lignite macromolecular structure is realized based on an ion channel, the H/C atomic ratio of upgraded coal is improved, the concentration of hydrogen free radicals in the pyrolysis process can be effectively improved, and then the collision between hydrocarbon free radicals and the hydrogen free radicals is improved, so that coal tar is formed. Because not only the cleavage reaction of alkyl fat side chains but also the radical reaction are carried out in the pyrolysis process.
The invention is also characterized in that the swelling treatment is carried out on the hydrothermally upgraded coal, and the reason for the swelling treatment is selected from the following points: (1) The hydrothermal treatment promotes the increase of H/C atomic ratio in lignite, and the swelling treatment can remarkably improve the fluidity and transfer efficiency of hydrogen radicals of the pyrolysis coal sample. The fluidity of free hydrogen after swelling treatment is increased by 4-5 times, so that the increase of H/C atomic ratio in the hydrothermal treatment produces an amplifying effect after swelling treatment, and hydrocarbon free radical fragments are easier to capture hydrogen free radicals in the pyrolysis process, so that the hydrocarbon free radical fragments are stable and coal tar is formed; (2) Although hydrothermal modification leads to more stable and compact macromolecular structure of lignite and reduces pyrolysis activity, the development of pore structure and volume expansion of lignite are promoted by swelling treatment, so that the structure of a swelled coal sample is relatively loose, the residence time of tar precursor is shortened, and effective escape of tar precursor is promoted; (3) The crosslinking reaction of the low-temperature section of the lignite is a main reason for low tar yield, the tar yield can be improved by effectively inhibiting the occurrence of pyrolysis crosslinking reaction, and the occurrence of pyrolysis crosslinking reaction can be effectively reduced by pretreatment of the organic solvent. Based on the method, a mechanism of improving lignite pyrolysis tar by a combined process is reasonably explained by providing and constructing a free radical control theory and a crosslinking inhibition theory, which are important theoretical components of the invention. Under the combined process condition, the moisture content and the oxygen content of the lignite are greatly reduced, the yield of the pyrolysis coal tar is greatly increased, and the market competitiveness of the lignite upgrading industry is improved.
Compared with the prior art, the invention has the following beneficial effects:
the invention realizes the removal of the moisture of the lignite in a non-evaporation mode, saves a great amount of latent heat of evaporation, saves more energy and is lower in carbonization; the hydrothermal modification process realizes the transfer of hydrogen ions in water to a lignite macromolecular structure through an ion channel, increases the H/C atomic ratio of upgraded coal, increases the content of hydrogen free radicals in the pyrolysis process, and generates an amplifying effect on the increase of the H/C atomic ratio in the swelling process, thereby improving the yield of the pyrolysis coal tar; the occurrence of cross-linking reaction of pyrolysis reaction of lignite is effectively inhibited by both the hydrothermally modified deoxidization and the swelling of the organic solvent, so that the tar precursor is effectively prevented from being cross-linked to a macromolecular structure of lignite before escaping; the proposal and construction of the free radical control theory and the crosslinking inhibition theory provide rich and detailed theoretical mechanism explanation for the combined process of 'hydro-thermal modification' and 'swelling treatment', and the theory is used as a core to provide more guidance for improving the quality research and production of lignite.
Drawings
FIG. 1 is a flow chart of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
As shown in fig. 1, a method for improving the yield of lignite pyrolysis tar specifically comprises the following steps:
(1) Crushing raw coal of lignite 1 to 0.2mm, storing into a self-sealing bag, and carrying out industrial analysis and element analysis on the lignite 1 according to GB/T212-2008 and GB476-91 methods, wherein the results are shown in Table 1;
(2) Mixing the crushed raw coal sample and deionized water in a beaker according to the mass ratio of 0.5:1, uniformly stirring through a glass rod, placing the mixture in a hydrothermal reaction kettle, sealing the reaction kettle, and introducing N at a flow rate of 150ml/min by utilizing a pore canal reserved in the reaction kettle 2 The air in the reaction kettle is replaced after the air is introduced for 5min, and then the device is sealed and is ready for starting the reaction; heating according to the programmed temperature, starting heating at 4deg.C/min, and reacting at 150deg.C until the reaction reaches the endMaintaining the final temperature for 30min, and ending the reaction;
(3) Cooling the reaction kettle to room temperature, taking out reactants, using a vacuum suction filtration device and a Buchner funnel, and using qualitative filter paper to realize solid-liquid separation; the separated solid was dried for 12 hours at 30℃in a vacuum drying oven, and after drying was completed as a sample for test industrial analysis and elemental analysis, measured by referring to GB/T212-2008 and GB476-91 methods, the results are shown in Table 1, the remaining part was dried for 12 hours at 100℃in an additional vacuum drying oven,
(4) Mixing the dried upgraded coal sample with tetralin and other substances, placing the mixture in a flat bottom pipe with scales, uniformly stirring the mixture, and placing the mixture in a constant-temperature water bath kettle at 50 ℃ for 48 hours for swelling treatment;
(5) After the swelling treatment of the hydrothermal upgrading coal sample is finished, flushing the swelling coal sample by using a benzene organic solvent, performing solid-liquid separation by using a vacuum filter device, continuously flushing again by using a benzene solution, and repeating the steps for more than 3 times until the color of the benzene solution is not changed;
(6) Drying the separated solid coal sample for 8 hours at the temperature of 100 ℃ in a vacuum drying oven, taking part of test element analysis, and determining by referring to a GB476-91 method, wherein the result is shown in Table 2;
(7) The dried coal sample is used as pyrolysis raw material to carry out pyrolysis experiment in a fixed bed pyrolysis system so as to verify the redistribution influence of the combined process technology of 'hydro-thermal' + 'swelling' on the pyrolysis coal tar of the lignite, wherein the pyrolysis flow is as follows: introducing N at a flow rate of 150ml/min before the experiment starts 2 After 5min, the temperature is raised and N is always maintained 2 Introducing until the experiment is finished, heating at a rate of 10 ℃/min, keeping the final temperature at 600 ℃ for 30min;
after the pyrolysis experiment is finished, the mass of the cooler before and after the reaction is weighed to determine the yield of pyrolysis liquid products (comprising pyrolysis water and tar), and the flow of oil-water separation is as follows: washing and collecting the pipe wall of a cooler by using an acetone solution, uniformly mixing, adding anhydrous magnesium sulfate accounting for 10% of the total mass of the product, placing the anhydrous magnesium sulfate in a vacuum drying oven at 50 ℃ for 48 hours, wherein the mass difference before and after the anhydrous magnesium sulfate is the pyrolysis water yield, obtaining pyrolysis coal tar yield (containing tetrahydronaphthalene) by a subtraction method, subtracting residual tetrahydronaphthalene on the basis, and calculating the residual tetrahydronaphthalene according to the following method, wherein the coal tar yield is more accurately quantified, and the principle is that the mass fraction of the residual tetrahydronaphthalene is calculated by balancing the mass of elements before and after swelling:
wherein C is HD And H HD The mass of the carbon element and the hydrogen element in the coal sample before swelling can be calculated by the table 1; 0.91 and 0.09 represent mass fractions of carbon element and hydrogen element in tetrahydronaphthalene, respectively; x is x 1 And x 3 Representing the residual amounts of tetrahydronaphthalene calculated from the carbon element and the hydrogen element (g/100-dry ashless basis), respectively; c (C) HDS And H HDS The mass fractions of carbon element and hydrogen element in the swelled coal sample (containing tetralin) are respectively represented and can be obtained by table 2; x is x 2 And x 4 Representing the mass fractions of residual tetrahydronaphthalene calculated from the carbon element and the hydrogen element, respectively. X is x 1 、x 2 、x 3 、x 4 The calculation results of (2) are shown in Table 2;
the quality of hydrogen is light, the error is larger, therefore, the tetrahydronaphthalene residue calculated based on carbon is selected as the basis, the accurate yield of the pyrolytic coal tar is finally determined, and the accurate yield is divided by the quality of the coal sample before and after the pyrolysis in the step (7), namely the yield of the pyrolytic coal tar, and the result is shown in the table 3.
Example 2
In the step (2), the mass ratio of the raw coal sample to the deionized water is 0.6:1, N 2 The flow is 200ml/min, the charging time is 6min, the heating rate is 7 ℃/min, the reaction final temperature is 200 ℃, and the final temperature is maintained for 35min when the reaction final temperature is reached.
In the step (4), the dried upgraded coal sample and tetralin are mixed according to the mass ratio of 1:1.2 and placed in a flat bottom pipe with scales, and the mixture is stirred uniformly and placed in a 40 ℃ constant temperature water bath kettle for 30 hours for swelling treatment;
in this embodiment, the operation is the same as that of embodiment (1) except for the above operation setting.
Example 3
In the step (2), the mass ratio of the raw coal sample to the deionized water is 0.7:1, N 2 The flow is 180ml/min, the charging time is 8min, the heating rate is 10 ℃/min, the reaction final temperature is 250 ℃, and the final temperature is maintained for 50min when the reaction final temperature is reached.
In the step (4), the dried upgraded coal sample and tetralin are mixed according to the mass ratio of 1:1.5 and placed in a flat bottom pipe with scales, and the mixture is stirred uniformly and placed in a constant temperature water bath kettle at 50 ℃ for 35 hours for swelling treatment;
in this embodiment, the operation is the same as that of embodiment (1) except for the above operation setting.
Example 4
In the step (2), the mass ratio of the raw coal sample to the deionized water is 0.5:1, N 2 The flow is 200ml/min, the charging time is 10min, the heating rate is 8 ℃/min, the reaction final temperature is 310 ℃, and the final temperature is maintained for 60min when the reaction final temperature is reached.
In the step (4), the dried upgraded coal sample and tetralin are mixed according to the mass ratio of 1:2 and placed in a flat bottom pipe with scales, and the mixture is stirred uniformly and placed in a constant-temperature water bath kettle at 35 ℃ for 48 hours for swelling treatment;
in this embodiment, the operation is the same as that of embodiment (1) except for the above operation setting.
Table 1 lignite 1 hydrothermal upgraded coal quality analysis
* Performing subtraction calculation; the temperature of 150 ℃,200 ℃,250 ℃ and 310 ℃ respectively represent the hydrothermal quality-improving coal sample of the lignite 1 at each temperature
TABLE 2 elemental analysis of lignite 1 swollen coal sample and residual tetrahydronaphthalene content
TABLE 3 pyrolysis product yield under Brown coal 1 combination treatment Process
The temperature of 150 ℃,200 ℃,250 ℃ and 310 ℃ respectively represent the hydrothermal quality-improving coal samples of the lignite 1 at different temperatures; 150 ℃ +RZ,200 ℃ +RZ,250 ℃ +RZ and 310 ℃ +RZ respectively represent lignite 1 hydrothermal upgrading and swelling treatment coal samples
As can be seen from table 1, as the hydrothermal upgrading temperature increases, the moisture content and the oxygen content are continuously reduced, and the carbon content is continuously increased, which indicates that the hydrothermal upgrading is an effective method for improving the quality of lignite; as can be seen from the data in Table 3, after the combination treatment of 'hydro-thermal' + 'swelling', the yield of lignite pyrolysis tar reaches 10.89%, and the yield of tar is increased by 47.56% relative to raw coal, which is mainly due to the increase of H/C atomic ratio in the hydro-thermal modification process and the inhibition of crosslinking reaction in the pyrolysis process.
Example 5
In this example, lignite 2 was used as a raw material, and industrial analysis and elemental analysis of lignite 2 were performed according to methods GB/T212-2008 and GB476-91, and the results are shown in Table 4; the remaining operation procedure was the same as in example 1. The analysis of the coal quality after the hydrothermal upgrading in the step (3) is shown in table 4, the elemental analysis of the swelled coal sample and the results of the residual amount of tetrahydronaphthalene in the swelled coal sample are shown in table 5, and the yield of the pyrolyzed coal tar is shown in table 6.
Example 6
In this example, lignite 2 was used as a raw material, and industrial analysis and elemental analysis of lignite 2 were performed according to methods GB/T212-2008 and GB476-91, and the results are shown in Table 4; the remaining operation procedure was the same as in example 2. The analysis of the coal quality after the hydrothermal upgrading in the step (3) is shown in table 4, the elemental analysis of the swelled coal sample and the results of the residual amount of tetrahydronaphthalene in the swelled coal sample are shown in table 5, and the yield of the pyrolyzed coal tar is shown in table 6.
Example 7
In this example, lignite 2 was used as a raw material, and industrial analysis and elemental analysis of lignite 2 were performed according to methods GB/T212-2008 and GB476-91, and the results are shown in Table 4; the remaining procedure was the same as in example 3. The analysis of the coal quality after the hydrothermal upgrading in the step (3) is shown in table 4, the elemental analysis of the swelled coal sample and the results of the residual amount of tetrahydronaphthalene in the swelled coal sample are shown in table 5, and the yield of the pyrolyzed coal tar is shown in table 6.
Example 8
In this example, lignite 2 was used as a raw material, and industrial analysis and elemental analysis of lignite 2 were performed according to methods GB/T212-2008 and GB476-91, and the results are shown in Table 4; the remaining procedure was the same as in example 4. The analysis of the coal quality after the hydrothermal upgrading in the step (3) is shown in table 4, the elemental analysis of the swelled coal sample and the results of the residual amount of tetrahydronaphthalene in the swelled coal sample are shown in table 5, and the yield of the pyrolyzed coal tar is shown in table 6.
Table 4 lignite 2 hydrothermal upgraded coal quality analysis
* Performing subtraction calculation; the temperature of 150 ℃,200 ℃,250 ℃ and 310 ℃ respectively represent the hydrothermal quality-improving coal sample of the lignite 2 at different temperatures
TABLE 5 elemental analysis of lignite 2 swollen coal sample and residual tetrahydronaphthalene content
TABLE 6 pyrolysis product yields for Brown coal 2 at various treatments
The temperature of 150 ℃,200 ℃ and 250 ℃ respectively represent the hydrothermal quality-improving coal samples of the lignite 2 at different temperatures; 150 ℃ +RZ,200 ℃ +RZ,250 ℃ +RZ,310 ℃ +RZ respectively represent lignite 2 hydrothermal upgrading and swelling treatment coal samples
The pyrolysis tar yield of the coal sample subjected to the combined treatment of 'hydro-thermal' + 'swelling' of lignite is shown in table 6, and the data in the table indicate that the yield of the pyrolysis tar is up to 10.09% after the coal sample is subjected to the hydrothermal modification treatment and the swelling treatment, and the tar yield is increased by 38.79% relative to the raw coal.
The invention provides a combined process technology aiming at improving the yield of lignite pyrolysis tar, which greatly improves the yield of lignite pyrolysis tar on the basis of realizing dehydration of lignite in a more energy-saving mode, has remarkable amplification, greatly increases the market competitiveness of lignite upgrading industry and has huge potential market application prospect in the future.
The technical scheme of the invention is explained in the technical scheme, the protection scope of the invention cannot be limited by the technical scheme, and any changes and modifications to the technical scheme according to the technical substance of the invention belong to the protection scope of the technical scheme of the invention.
Claims (7)
1. A method for increasing the yield of lignite pyrolysis tar, comprising the steps of:
step 1, crushing lignite raw coal, uniformly mixing the lignite raw coal with deionized water, and then placing the lignite raw coal in a hydrothermal reaction kettle for reaction;
step 2, carrying out solid-liquid separation on the solid-liquid mixture after the reaction in the step 1, and drying the separated solid product in a vacuum drying oven;
step 3, mixing the solid product dried in the step 2 with tetralin according to the mass ratio of 1:1-2, and placing the mixture in a water bath thermostat for swelling treatment; the swelling treatment temperature is 30-50 ℃ and the time is 24-48 h;
step 4, washing the swelling product obtained in the step 3 until the color of the washing liquid is not changed any more;
step 5, carrying out solid-liquid separation on the washed swelling product obtained in the step 4, and drying the separated swelling product in a vacuum drying oven;
step 6, placing the dried swelling product obtained in the step 5 into a fixed bed pyrolysis system for pyrolysis, collecting coal tar, and quantifying the yield, wherein the ratio of the coal tar yield to the mass of the swelling product obtained in the step 5 after drying is the yield of the coal tar;
the coal tar yield is required to remove the quality of the product after pyrolysis of the residual tetrahydronaphthalene, namely the final coal tar yield = the residual quantity of the tetrahydronaphthalene which is the coal tar yield obtained by the subtraction method; the residual quantity of the tetrahydronaphthalene is calculated according to the following method, so that the yield of the coal tar is more accurately quantified, and the principle is that the mass fraction of the tetrahydronaphthalene remained in a swelling product is calculated through the mass balance of elements before and after swelling:
wherein C is HD And H HD Respectively representing the mass of carbon element and hydrogen element in the coal sample before swelling, namely the solid product after drying in the step 2; 0.91 and 0.09 represent mass fractions of carbon element and hydrogen element in tetrahydronaphthalene, respectively; the swelling product in the step 6 is a swelling coal sample with tetrahydronaphthalene residues; x is x 1 And x 3 Representing the residual amount (g/100-dry ashless basis) of tetrahydronaphthalene in the swelled product calculated by carbon element and hydrogen element, respectively; c (C) HDS And H HDS Respectively representing the mass fractions of carbon element and hydrogen element in the swelling product; x is x 2 And x 4 Representing the mass fraction of residual tetrahydronaphthalene in the swollen product calculated by the carbon element and the hydrogen element, respectively.
2. The method for improving the yield of lignite pyrolysis tar according to claim 1, wherein in the step 1, raw coal is crushed to 0.2-0.5 mm, and the mass ratio of raw coal to deionized water is 0.5-1: 1.
3. The method for increasing the yield of lignite pyrolysis tar according to claim 1, wherein in the step 1, the hydrothermal reaction kettle is under the process conditions of: the final temperature of the reaction is 100-350 ℃, the initial pressure of the reaction is normal pressure, and N is introduced before the reaction 2 The flow is 150-200 ml/min, the time is 3-10 min, then the sealing is carried out, the temperature is raised to the final temperature at the temperature raising rate of 3-15 ℃/min, and the residence time is 30-60 min.
4. The method for improving the tar yield of lignite pyrolysis according to claim 1, wherein in the step 2, the vacuum drying temperature is 100-110 ℃ and the drying time is 8-12 h.
5. The method for improving the tar yield of lignite pyrolysis according to claim 1, wherein in the step 5, the vacuum drying temperature is 100-110 ℃ and the drying time is 8-15 h.
6. The method according to claim 1A method for improving the yield of lignite pyrolysis tar, which is characterized in that in the step 6, pyrolysis process conditions are as follows: the final pyrolysis temperature is 600-870 ℃, and the temperature is raised to the final pyrolysis temperature according to the temperature-raising rate of 10-15 ℃/min and stays for 30-60 min; before pyrolysis, introducing N at a flow rate of 150-200 ml/min 2 Heating after 5-10 min, and maintaining N 2 The reaction was terminated by passing through the reaction vessel.
7. The method for increasing the yield of lignite pyrolysis tar according to claim 1, wherein in the step 6, after the pyrolysis reaction is finished, the mass of the pyrolysis system before and after the reaction with a cooler is weighed to obtain the yield of a liquid product, the liquid product contains pyrolysis water and coal tar, and the flow of oil-water separation is as follows: and (3) washing and collecting the pipe wall of the cooler by using acetone, uniformly mixing, adding anhydrous magnesium sulfate accounting for 10-20% of the total mass of the liquid product, placing the anhydrous magnesium sulfate in a vacuum drying oven at 30-50 ℃ for 48-60 hours, wherein the quality difference before and after the anhydrous magnesium sulfate is the pyrolysis water yield, and obtaining the pyrolysis coal tar yield through a difference method.
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