System and method for co-producing fulvic acid and humic acid

Abstract

The system comprises a first reaction unit and a second reaction unit which are connected in series, and the second reaction unit comprises an alkali dissolution device and an acid extraction device which are connected in series; in the first reaction unit, nitric acid oxidizes lignite to generate fulvic acid, and a separated solid phase sequentially passes through an alkali dissolution device and an acid extraction device to obtain humic acid; the system further comprises a tail gas buffering device, the tail gas buffering device is connected with the first reaction unit and the acid extraction device, and NOx generated by the first reaction unit enters the acid extraction device through the tail gas buffering device. According to the system for co-producing the fulvic acid and the humic acid, the fulvic acid and the humic acid are obtained through one-step activation reaction, and co-production is achieved by separating reaction products; nOx generated by activation reaction is introduced into the acid extraction device, so that the pH value in the acid extraction device is 1-2, ulmic acid and humic acid are extracted, and the product precision is improved.

Description

Technical Field

[0001] The invention relates to the field of coal chemical industry, and in particular to a system and method for co-producing fulvic acid and humic acid from lignite. Background Art

[0002] Lignite is rich in fulvic acid and humic acid. Fulvic acid can be used as a drought-resistant agent and anti-transpiration agent for crops, while humic acid can be used to promote the agglomeration and aggregation of soil particles, improve the structural stability of the soil, and improve the permeability and water retention of the soil. Therefore, extracting these two substances from lignite can improve the utilization rate of lignite and improve economic benefits. Fulvic acid is easily soluble in water, while humic acid is insoluble in water. Compared with humic acid, the extraction process of fulvic acid is relatively simple, but the concentration of fulvic acid in lignite is often lower than that of humic acid, and the economic benefits of extracting fulvic acid and humic acid alone are poor. How to achieve the co-production of fulvic acid and humic acid is the key to improving the utilization rate and economic value of lignite.

[0003] Currently, there are few studies on the co-production of fulvic acid and humic acid, and the studies are often based on the extraction of one substance of fulvic acid or humic acid.

[0004] For example, patent CN1304463C discloses a method for extracting humic acid from coal. First, nitric acid is added. After the reaction is completed, the supernatant is removed by precipitation. The precipitate and water are added to a reactor. After stirring evenly, sulfuric acid is added. The residue is removed to obtain a filtrate. The residue is rinsed with clean water and filtered to obtain a rinse liquid. The filtrate and the rinse liquid are mixed to obtain a combined liquid. The combined liquid is concentrated and dried to obtain humic acid.

[0005] Patent CN102515885B discloses a method for extracting and preparing humic acid from weathered coal, comprising: (1) preparing an ammonium humic acid solution: pickling the weathered coal with a mass concentration phosphoric acid solution, filtering after pickling, adding water and ammonia water to the filter residue, and reacting the mixture in a flask under reflux for 2-6 hours, adjusting the end point pH to 9-10 with a phosphoric acid solution or ammonia water, and maintaining normal pressure. After the reaction, filtering the mixture to obtain the ammonium humic acid solution; (2) oxidizing hydrogen peroxide to increase the phenolic hydroxyl content: dripping a defoaming agent, adding a copper-iron composite catalyst and ethylenediaminetetraacetic acid or citric acid, and then adding an aqueous hydrogen peroxide solution, adjusting the pH to greater than 8 with a phosphoric acid solution or ammonia water, and reacting for 4-10 hours to obtain a humic acid solution with a high phenolic hydroxyl content.

[0006] There are the following problems with fulvic acid and humic acid extraction:

[0007] ① A large amount of NOx will be produced during the reaction of fulvic acid or humic acid. NOx in the form of foam in the reaction liquid limits the oxidation reaction;

[0008] ② The gas isolation of the reaction unit is not complete, and the NOx produced by the extraction of fulvic acid and humic acid will enter the humic acid alkali dissolution device, resulting in a low humic acid extraction rate;

[0009] ③ The humic acid product is a mixture of multiple substances, and the product precision is low;

[0010] ④ Extracting fulvic acid alone has low economic benefits.

[0011] In view of the above technical problems, the present invention is specially introduced. Summary of the invention

[0012] The main purpose of the present invention is to provide a system and method for co-producing fulvic acid and humic acid.

[0013] In order to achieve the above object, the present invention provides a system for co-producing fulvic acid and humic acid, comprising a first reaction unit and a second reaction unit connected in series, wherein the second reaction unit comprises an alkali dissolution device and an acid extraction device connected in series;

[0014] In the first reaction unit, nitric acid oxidizes lignite to generate fulvic acid, and the separated solid phase is sequentially reacted through an alkali dissolution device and an acid extraction device to obtain humic acid;

[0015] It also includes an exhaust gas buffer device, which is connected to the first reaction unit and the acid extraction device respectively. The NOx generated by the first reaction unit enters the acid extraction device through the exhaust gas buffer device.

[0016] Preferably, a valve is provided between the exhaust gas buffer device and the acid extraction device, and the opening of the valve is adjusted to control the NOx air intake flow rate from the exhaust gas buffer device into the acid extraction device.

[0017] Preferably, a tail gas absorption device is provided between the first reaction unit and the alkaline dissolution device, and the tail gas absorption device adsorbs NOx before entering the alkaline dissolution device.

[0018] Preferably, both the alkaline dissolution device and the acid extraction device are provided with a pH value detection device.

[0019] In addition, the present application also proposes a method for co-producing fulvic acid and humic acid, using the above-mentioned system for co-producing fulvic acid and humic acid, comprising the following steps:

[0020] Step S1: lignite and nitric acid solution are mixed in the first reaction unit, and fulvic acid is separated after a period of reaction, and the tail gas enters the tail gas buffer device.

[0021] Step S2, the solid phase obtained by separation in the first reaction unit enters the alkali dissolution device and the acid extraction device in sequence for reaction to obtain humic acid;

[0022] Step S3, NOx in the exhaust gas buffer device enters the acid extraction device, and the pH value in the acid extraction device is adjusted.

[0023] Preferably, step S3 includes controlling the NOx intake amount of the exhaust gas buffer device entering the acid extraction device so that the pH value of the reaction liquid in the acid extraction device is in the range of 1-2.

[0024] Preferably, step S2 further comprises: adsorbing NOx entering the alkaline dissolution device by a tail gas absorption device.

[0025] Preferably, the concentration of nitric acid in the first reaction unit is 8-15 wt %, the reaction temperature is 60-90° C., and the pressure ranges from 0.05-0.1 MPa.

[0026] Preferably, the acid extraction device uses 10-20 wt % HNO 3 solution.

[0027] Preferably, the molar concentration of the alkali dissolution device is 20 to 40 mol·L -1 The amount of NaOH added is 2% to 7% of the solid content in the alkali dissolution device, and the reaction temperature is 50 to 90°C.

[0028] The system and method for co-producing fulvic acid and humic acid proposed in the present invention achieve the following technical effects:

[0029] 1. Fulvic acid and humic acid are obtained through a one-step activation reaction, and co-production is achieved by separating the reaction products. The process is simple and the product yield is high.

[0030] 2. By reducing the activation reaction pressure and concentration and prolonging the reaction time, the NOx produced by the activation reaction can be fully released, the yield of fulvic acid and humic acid can be increased, and excessive oxidation of humic acid and fulvic acid can be avoided.

[0031] 3. The NOx produced by the activation reaction is passed into the acid extraction device to make the pH in the acid extraction device between 1 and 2, and humic acid and black humic acid are extracted to improve the product accuracy.

[0032] 4. By inhibiting the NOx generated in the activation reaction from entering the alkaline dissolution device, the extraction amount of humic acid can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] In the attached picture:

[0035] Figure 1 The schematic diagram of the system structure for co-producing fulvic acid and humic acid in the present application is shown;

[0036] Figure 2 The process steps of the method for co-producing fulvic acid and humic acid of the present application are shown;

[0037] Figure 3 The infrared spectrum of the final solid product obtained in Example 2 of the present application is shown;

[0038] Figure 4 The infrared spectrum of the final solid product obtained in Example 4 of the present application is shown.

[0039] The above drawings include the following reference numerals:

[0040] 100. First reaction unit; 200. Second reaction unit; 300. Tail gas buffer device; 220. Alkaline dissolution device; 240. Acid extraction device; 400. Tail gas absorption device; 340. Valve. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] The present invention is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be understood as limiting the scope of protection claimed by the present invention. The term "including" when used indicates the existence of a feature, but does not exclude the existence or addition of one or more other features; the orientation or position relationship indicated by the terms "lateral", "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention; in addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0043] In the description, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0044] This application proposes a system for co-producing fulvic acid and humic acid, such as Figure 1As shown, it includes a first reaction unit 100 and a second reaction unit 200 connected in series, and the second reaction unit 200 includes an alkali dissolution device 220 and an acid extraction device 240 connected in series. In addition, the system is also equipped with other auxiliary equipment, such as vacuum equipment, etc., which will not be described in detail here.

[0045] like Figure 2 As shown, the overall process flow is that lignite and nitric acid solution are mixed in the first reaction unit 100, humic acid is separated after a period of reaction, and the exhaust gas enters the exhaust gas buffer device 300; the solid phase separated in the first reaction unit 100 enters the alkaline dissolution device 220 and the acid extraction device 240 in turn to obtain humic acid; NOx in the exhaust gas buffer device 300 enters the acid extraction device 240 to adjust the pH value in the acid extraction device 240.

[0046] In the application, the concentration of nitric acid in the first reaction unit is 8-15 wt %, the reaction temperature is 60-90° C., the pressure range is 0.05-0.1 MPa, and the reaction time is 5-8 hours.

[0047] Different from the conventional reaction process, the inventors found that by reducing the concentration of nitric acid and the internal pressure in the reaction unit, the excessive degradation of fulvic acid is avoided, thereby improving the extraction rate of fulvic acid; and reducing the excessive oxidation and nitrification of humic acid, which is beneficial to improving the quality of humic acid. In addition, by controlling the pressure in a slightly negative pressure state, the NOx produced by nitric acid can be separated from the nitric acid solution, avoiding the dissolution of NOx gas in the reaction solution, and inhibiting the oxidation process. In order to ensure the yield, the present application adjusted the reaction time and appropriately extended the reaction time.

[0048] The solid phase obtained after solid-liquid separation enters the alkaline dissolution device 220 and the acid extraction device 240 in sequence, and humic acid is obtained by alkaline dissolution and acid precipitation. The alkaline dissolution device 220 uses a molar concentration of 20 to 40 mol·L -1 The amount of NaOH added is 2% to 7% of the solid content in the alkaline dissolution device 220, and the reaction temperature is in the range of 50 to 90° C. In the alkaline dissolution device, the humic acid in the lignite is dissolved in the alkaline solution to generate soluble sodium humate.

[0049] The product in the alkaline dissolution device is separated into solid and liquid, and the upper liquid phase is taken and sent to the acid extraction device 240 for precipitation reaction to obtain humic acid. In the initial state, the acid extraction device 240 adds 15-25wt% HNO3 solution, and the volume ratio of the HNO3 solution to the liquid phase entering the acid extraction device is in the range of 1:0.5 to 1:1.2.

[0050] In order to prevent the NOx gas generated by the first reaction unit 100 from entering the alkaline dissolution device and causing adverse effects on the reaction, the present application adds a tail gas buffer device 300 to the cogeneration system, and the tail gas buffer device 300 is connected to the middle and top of the reactor in the first reaction unit. As mentioned above, by controlling the pressure of the first reaction unit 100, the NOx gas is forced to separate from the reaction liquid, and the tail gas generated by the first reaction unit 100 is absorbed by the tail gas buffer device 300 to prevent the NOx gas from mixing into the alkaline dissolution device.

[0051] In addition to setting up an exhaust gas buffer device, the present application also needs to add an absorption device between the first reaction unit 100 and the alkaline dissolution device to adsorb the NOx gas that has not entered the exhaust gas buffer device, thereby minimizing the impact of NOx on the pH value in the alkaline dissolution device, so that the pH value in the alkaline dissolution device is maintained at ≥13, promoting the alkaline dissolution reaction, thereby improving the humic acid extraction rate.

[0052] In addition, in the cogeneration system proposed in the present application, the tail gas buffer device 300 is connected to the humic acid extraction device 240, and the NOx generated by the first reaction unit 100 enters the acid extraction device 240 through the tail gas buffer device 300, so as to realize the utilization of waste NOx, reduce the amount of nitric acid in the acid extraction device 240, reduce the initial concentration of nitric acid, and thus reduce the cost of raw materials. In the present application, the tail gas buffer device 300 uses carbon nanotubes as a physical adsorbent to realize the adsorption and release of NOx.

[0053] A valve 340 is provided between the exhaust gas buffer device 300 and the acid extraction device 240 , and the NOx intake flow rate from the exhaust gas buffer device 300 to the acid extraction device 240 is adjusted by controlling the valve opening, thereby controlling the pH value of the reaction liquid in the acid extraction device 240 .

[0054] In addition, the present application has found that by strictly controlling the pH value of the reaction solution in the acid extraction device 240, an ideal humic acid product can be extracted, thereby improving the accuracy of the humic acid product. Among the numerous humic acids, palmitic acid and black humic acid have relatively high economic value and relatively high content. By controlling the pH value in the acid extraction device 240 to be between 1 and 2, palmitic acid and black humic acid can be preferentially precipitated, thereby preventing precipitation of other humic acid products.

[0055] In the initial state, the pH value of the nitric acid solution in the acid extraction device is 1-2. As the acid precipitation reaction proceeds, the pH value in the acid extraction device increases. The pH value in the acid extraction device is monitored online. When the pH value is greater than 2, the valve 340 is opened, and the exhaust gas buffer device 300 delivers NOx intake air to the acid extraction device 240, so that the pH of the acid extraction device 240 is maintained at 1-2.

[0056] The experiment in this application uses Baoqing lignite, in which fulvic acid accounts for 6-10% by weight and humic acid accounts for 30-50% by weight. The method and system for co-producing fulvic acid and humic acid proposed in this application are not only applicable to Baoqing lignite, but also to other lignites with similar component proportions, which are not specifically limited here.

[0057] The technical solution will be further described below in conjunction with specific implementation examples.

[0058] Example 1

[0059] Baoqing lignite is used as a raw material. First, the lignite raw material is crushed to a particle size range of 50 to 90 meshes. 100g of nitric acid solution and 100g of lignite particles are added to the reactor of the first reaction unit. The concentration of nitric acid is 20wt%, the reaction temperature is controlled to be 80°C, the pressure range is 0.3Mpa, the reaction is carried out for 5 hours, and after the reaction is completed, the reaction is allowed to stand for 10 minutes to separate and extract solid phase substances and liquid phase substances. The liquid phase substances are concentrated and dried to obtain fulvic acid, and the fulvic acid is weighed.

[0060] Take 80g of the solid phase obtained in the first reaction unit and send it to an alkali dissolution device. Add 80g of NaOH into the alkali dissolution device. The concentration of NaOH is 30mol·L -1 The reaction temperature was controlled at 60°C and the reaction time was 2 hours. After the reaction was completed, the mixture was allowed to stand for separation, and the supernatant and the residual solid matter were extracted. The residual solid matter P1 was concentrated and dried, and then weighed.

[0061] 100 g of the supernatant was sent to an acid extraction device, 60 g of nitric acid solution was added to the acid extraction device, the concentration of the nitric acid solution was 20 wt %, the reaction temperature was 60° C., the reaction time was 1 hour, and after the reaction was completed, the final solid product L1 was extracted, the final solid product was concentrated and dried, and then weighed. In addition, the pH in the acid extraction device was tested after the reaction was completed.

[0062] Example 2

[0063] Baoqing lignite is used as a raw material. First, the lignite raw material is crushed to a particle size range of 50 to 90 meshes. 100 g of nitric acid and 100 g of lignite particles are added to the reactor of the first reaction unit. The concentration of nitric acid is 10 wt %. The reaction temperature is controlled to be 80° C. and the pressure range is 0.08 MPa. The reaction is carried out for 5 hours. After the reaction is completed, the reaction is allowed to stand for 10 minutes to separate and extract the solid phase and the liquid phase. The liquid phase is concentrated and dried to obtain fulvic acid, and the fulvic acid is weighed.

[0064] Take 80g of the solid phase obtained in the first reaction unit and send it to an alkali dissolution device. Add 80g of NaOH into the alkali dissolution device. The concentration of NaOH is 30mol·L-1 The reaction temperature was controlled at 60°C and the reaction time was 2 hours. After the reaction was completed, the mixture was allowed to stand for separation, and the supernatant and the residual solid matter were extracted. The residual solid matter P1 was concentrated and dried, and then weighed.

[0065] 100 g of the supernatant was sent to an acid extraction device, 60 g of nitric acid solution was added to the acid extraction device, the concentration of the nitric acid solution was 20 wt %, the reaction temperature was 60° C., the reaction time was 1 hour, and after the reaction was completed, the final solid product L1 was extracted, the final solid product was concentrated and dried, and then weighed. In addition, the pH in the acid extraction device was tested after the reaction was completed.

[0066] Example 3

[0067] Baoqing lignite is used as a raw material. First, the lignite raw material is crushed to a particle size range of 50 to 90 meshes. 100g of nitric acid and 100g of lignite particles are added to the reactor of the first reaction unit. The concentration of nitric acid is 15wt%, the reaction temperature is controlled to be 80°C, the pressure range is 0.06Mpa, the reaction is carried out for 5 hours, and the reaction is allowed to stand for 10 minutes after the reaction is completed. The solid phase and the liquid phase are separated and extracted. The liquid phase is concentrated and dried to obtain fulvic acid, and the fulvic acid is weighed.

[0068] Take 80g of the solid phase obtained in the first reaction unit and send it to an alkali dissolution device. Add 80g of NaOH into the alkali dissolution device. The concentration of NaOH is 30mol·L -1 . The reaction temperature was controlled at 60°C and the reaction time was 2 hours. After the reaction was completed, the mixture was allowed to stand for separation, and the supernatant and residual solid matter were extracted. The residual solid matter P1 was concentrated and dried, and then weighed.

[0069] In this embodiment, the situation of NOx entering the alkaline dissolution device is simulated, and 2 mL of NOx gas is introduced into the alkaline dissolution device. In the actual process, the reactor in the first reaction unit is connected to the alkaline dissolution device, and the separation of the product is completed in the reactor in the reaction unit.

[0070] 100 g of the supernatant was sent to an acid extraction device, into which 60 g of nitric acid solution was added, the concentration of the nitric acid solution was 20 wt %, the reaction temperature was 60° C., the reaction time was 1 hour, and after the reaction was completed, the solution was allowed to stand for separation, and the final solid product L1 was extracted. The final solid product was concentrated and dried, and then weighed.

[0071] Example 4

[0072] Baoqing lignite is used as a raw material. First, the lignite raw material is crushed to a particle size range of 50 to 90 meshes. 100g of nitric acid and 100g of lignite particles are added to the reactor of the first reaction unit. The concentration of nitric acid is 12wt%, the reaction temperature is controlled to be 80°C, the pressure range is 0.07Mpa, the reaction is carried out for 5 hours, and after the reaction is completed, the reaction is allowed to stand for 10 minutes to separate and extract the solid phase and the liquid phase. The liquid phase is concentrated and dried to obtain fulvic acid, and the fulvic acid is weighed.

[0073] Take 80g of the solid phase obtained in the first reaction unit and send it to an alkali dissolution device. Add 80g of NaOH into the alkali dissolution device. The concentration of NaOH is 30mol·L -1 . The reaction temperature was controlled at 60°C and the reaction time was 2 hours. After the reaction was completed, the mixture was allowed to stand for separation, and the supernatant and residual solid matter were extracted. The residual solid matter P1 was concentrated and dried, and then weighed.

[0074] 100 g of the supernatant was sent to an acid extraction device, into which 60 g of nitric acid solution was added, the concentration of the nitric acid solution was 20 wt %, the reaction temperature was 60° C., the reaction time was 1 hour, and after the reaction was completed, the solution was allowed to stand for separation, and the final solid product L1 was extracted. The final solid product was concentrated and dried, and then weighed.

[0075] This embodiment simulates the situation of introducing NOx into the acid extraction device, and the pH value of the solution in the acid extraction device is adjusted to between 1 and 2 by introducing NOx gas.

[0076] Example Fulvic acid weight / g Residual solid matter P1 weight / g Final solid product L1 weight / g Example 1 2.12 60 1.73 Example 2 6.89 45.3 36 Example 3 6.54 48.1 33.1 Example 4 6.77 46.8 32.6

[0077] By comparing the weight of fulvic acid in Example 1 and Examples 2, 3, and 4, it can be seen that the formation of a slight negative pressure can promote the precipitation of the generated NOx gas, thereby improving the conversion rate of fulvic acid.

[0078] By comparing the weights of the final solid product L1 and the residual solid matter P1 of Examples 2 and 3, it can be seen that the extraction rate of humic acid can be improved by limiting the entry of NOx into the alkaline dissolution device.

[0079] In addition, the final solid product L1 obtained in Example 2 and Example 4 was characterized by infrared spectrum. In Example 2, the pH value in the acid extraction device was not regulated, and the pH value measured after the reaction was between 4 and 6; while in Example 4, the pH value in the acid extraction device was controlled to be between 1 and 2 by adding NOx gas. Figure 3 and Figure 4 It can be seen that the infrared spectra of the substances extracted at pH 4-6 and 1-2 are quite different. The substance obtained when the pH is 1-2 has a peak at 3400 cm -1There is a broad absorption peak near 1700 cm -1 There is an obvious C=O stretching vibration peak near 1500cm -1 Aromatic C=C bond absorption peaks can be observed in the vicinity; ester or ether group absorption peaks appear in the range of 1000-1300cm-1. These absorption peaks are consistent with the absorption peaks of humic acid and palmitic acid. Therefore, by controlling the precipitation acidity at 1-2, humic acid and palmitic acid with higher purity can be extracted. In comparison, the substance obtained when the precipitation pH is 4-6 has more impurity peaks, and the peak at 1500cm-1 is not as bright as the peak at 1500cm-1. -1 The absorption peak is not obvious.

[0080] The system and method for co-producing fulvic acid and humic acid proposed in the present invention achieve the following technical effects:

[0081] 1. Fulvic acid and humic acid are obtained through a one-step activation reaction, and co-production is achieved by separating the reaction products. The process is simple and the product yield is high.

[0082] 2. By reducing the activation reaction pressure and concentration and prolonging the reaction time, the NOx produced by the activation reaction can be fully released, the yield of fulvic acid and humic acid can be increased, and excessive oxidation of humic acid and fulvic acid can be avoided.

[0083] 3. The NOx produced by the activation reaction is passed into the acid extraction device to make the pH in the acid extraction device between 1 and 2, and humic acid and black humic acid are extracted to improve the product accuracy.

[0084] 4. By inhibiting the NOx generated in the activation reaction from entering the alkaline dissolution device, the extraction amount of humic acid can be increased.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for co-producing fulvic acid and humic acid, characterized in that: It comprises a first reaction unit (100) and a second reaction unit (200) connected in series, wherein the second reaction unit (200) comprises an alkali dissolution device (220) and an acid extraction device (240) connected in series; In the first reaction unit (100), nitric acid oxidizes lignite to generate fulvic acid, and the separated solid phase is sequentially reacted through the alkaline dissolution device (220) and the acid extraction device (240) to obtain humic acid; The invention also comprises an exhaust gas buffer device (300), wherein the exhaust gas buffer device (300) is respectively connected to the first reaction unit (100) and the acid extraction device (240), and NOx generated by the first reaction unit (100) enters the acid extraction device (240) through the exhaust gas buffer device (300).

2. A system for co-producing fulvic acid and humic acid according to claim 1, characterized in that: A valve (340) is provided between the exhaust gas buffer device (300) and the acid extraction device (240), and the opening of the valve (340) is adjusted to control the NOx intake flow rate of the exhaust gas buffer device (300) entering the acid extraction device (240).

3. A system for co-producing fulvic acid and humic acid according to claim 1 or 2, characterized in that: A tail gas absorption device (400) is provided between the first reaction unit (100) and the alkaline dissolution device (220), and the tail gas absorption device (400) adsorbs NOx before entering the alkaline dissolution device (220).

4. A system for co-producing fulvic acid and humic acid according to claim 1 or 2, characterized in that: The alkali dissolution device (220) and the acid extraction device (240) are both provided with a pH value detection device.

5. A method for co-producing fulvic acid and humic acid, using the system for co-producing fulvic acid and humic acid according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1: brown coal and nitric acid solution are mixed in the first reaction unit (100), and fulvic acid is separated after a period of reaction, and the tail gas enters the tail gas buffer device (300). Step S2, the solid phase separated by the first reaction unit (100) enters the alkaline dissolution device (220) and the acid extraction device (240) in sequence to react and obtain humic acid; Step S3, NOx in the exhaust gas buffer device (300) enters the acid extraction device (240), and the pH value in the acid extraction device (240) is adjusted.

6. The method for co-producing fulvic acid and humic acid according to claim 5, characterized in that: Step S3 includes controlling the NOx intake amount of the exhaust gas buffer device (300) entering the acid extraction device (240) so that the pH value of the reaction liquid in the acid extraction device (240) is in the range of 1 to 2.

7. The method for co-producing fulvic acid and humic acid according to claim 5 or 6, characterized in that: Step S2 also includes: adsorbing NOx entering the alkaline dissolution device (220) by a tail gas absorption device (400).

8. The method for co-producing fulvic acid and humic acid according to claim 5 or 6, characterized in that: The concentration of nitric acid in the first reaction unit (100) is 8-15 wt%, the reaction temperature is 60-90° C., and the pressure ranges from 0.05-0.1 MPa.

9. The method for co-producing fulvic acid and humic acid according to claim 5 or 6, characterized in that: The acid extraction device (240) uses 10-20 wt% HNO3 solution.

10. The method for co-producing fulvic acid and humic acid according to claim 5 or 6, characterized in that: The alkali dissolution device (220) uses a molar concentration of 20 to 40 mol·L -1 The amount of NaOH added is 2% to 7% of the solid content in the alkaline dissolving device (220), and the reaction temperature is 50 to 90°C.

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