Method for sludge-low rank coal co-forming and pyrolyzing

Abstract

This invention discloses a method for co-forming and pyrolysis of sludge and low-rank coal, belonging to the field of pyrolysis technology. The method involves mixing sludge and quicklime to obtain pretreated sludge; crushing low-rank coal and asphalt; kneading and stirring the pretreated sludge with the crushed low-rank coal and asphalt; continuously extruding and granulating the resulting mixture to obtain briquettes; pyrolyzing the obtained briquettes to obtain pyrolytic char; and using the pyrolytic char as a pyrolysis catalyst to catalytically pyrolyze the pyrolysis gas generated during the pyrolysis process to obtain high-grade pyrolysis gas. This invention solves the problems of difficulty in utilizing sludge alone and low utilization efficiency of low-rank coal, realizing the harmless and resource-based utilization of sludge; simultaneously, the co-pyrolysis conversion of sludge and low-rank coal not only yields high-strength pyrolytic char but also allows for further catalytic pyrolysis to obtain high-grade pyrolysis gas.

Description

Technical Field

[0001] This invention belongs to the field of pyrolysis technology, and specifically relates to a method for sludge-low-rank coal co-forming and pyrolysis. Background Technology

[0002] Sludge is characterized by high moisture content, high levels of sulfur, nitrogen, and heavy metals, and contains a significant portion of biomass with utilization value. It is difficult to dispose of due to its high degree of dispersion, significant property variations, and difficulty in independent conversion and utilization. How to utilize sludge is a broad and complex issue.

[0003] Low-rank coal has high moisture content, low calorific value, and some is high in sulfur, resulting in low utilization efficiency.

[0004] Dried sludge, as a raw material with a calorific value comparable to fossil fuels such as coal, can be coupled with coal to form briquettes through molding technology. This is an effective way to utilize sludge and coal resources and turn waste into treasure. Generally, sludge drying methods include high-temperature drying or sun drying. High-temperature drying is energy-intensive, while sun drying is time-consuming and unstable, varying with weather and region.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] This invention aims to provide a method for the co-forming and pyrolysis of sludge and low-rank coal, solving the problems of difficulty in utilizing sludge alone and low utilization efficiency of low-rank coal, thus realizing the harmless and resource-based utilization of sludge. Simultaneously, the co-pyrolysis conversion of sludge and low-rank coal not only yields high-strength pyrolytic char, but also allows for further catalytic cracking to obtain high-grade pyrolysis gas, thereby improving product quality and added value, synergistically regulating nitrogen and sulfur and solidifying heavy metals, achieving energy conservation, emission reduction, and consumption reduction, and enhancing the recycling value of low-quality carbon-containing resources.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0008] This invention provides a method for co-forming and pyrolyzing sludge and low-rank coal, comprising the following steps:

[0009] S1: Mix sludge and quicklime to obtain pretreated sludge.

[0010] Furthermore, the quicklime accounts for 10-30% of the mass of the obtained pretreated sludge.

[0011] The addition of quicklime has the following multiple functions: (1) It destroys the biological water-containing cytoplasm of sludge after calcium addition, which can better dehydrate it and also solve the problem of high energy consumption in heating dehydration. (2) Quicklime can also regulate the nitrogen in sludge, so that it is released in the form of ammonia. (3) The addition of quicklime can form a calcium-sulfur complex, which can play a role in sulfur fixation. (4) More importantly, the carbon-calcium complex acts as a catalyst, which can play a good catalytic role in the decomposition of volatiles.

[0012] S2: Crush low-rank coal and bitumen.

[0013] Furthermore, the particle size of the low-rank coal and bitumen after crushing is 150-200 mesh.

[0014] S3: The pretreated sludge is kneaded and mixed with crushed low-rank coal and bitumen to obtain a mixture.

[0015] Further, according to the mass fractions, the pretreated sludge, low-rank coal, and bitumen are 40-60 parts, 40-60 parts, and 1-30 parts, respectively.

[0016] Preferably, the raw materials for kneading and mixing also include starch; the starch is 1-5 parts by weight. The simultaneous addition of asphalt and starch can synergistically improve the strength of the briquettes. The starch binder mainly improves the strength during the briquetting stage, while the asphalt mainly improves the strength during the briquette-forming stage, ensuring overall strength improvement throughout the process and optimizing the raw material ratio.

[0017] Furthermore, the kneading and mixing power is 30-50 Hz, and the kneading and mixing time is 5-30 min.

[0018] S4: The mixture is fed into a molding machine for continuous extrusion molding and granulation to obtain coal briquettes.

[0019] Furthermore, the power of the continuous extrusion granulation is 30-50 Hz.

[0020] Preferably, the diameter of the extrusion die is 5-10 mm.

[0021] S5: The obtained coal briquettes are transported to a rotary kiln for co-pyrolysis to obtain high-strength pyrolytic char.

[0022] Furthermore, the strength of the obtained pyrolytic char is 190-500 N / piece.

[0023] Furthermore, the pyrolysis temperature is 500-800℃, and the pyrolysis time is 30-60 min.

[0024] S6: The pyrolytic carbon is fed into a pyrolysis furnace as a pyrolysis catalyst to catalytically pyrolyze the pyrolysis gas generated in the pyrolysis process, thereby obtaining high-grade pyrolysis gas.

[0025] Furthermore, the temperature for the catalytic cracking is 600-900℃;

[0026] Furthermore, the amount of the cracking catalyst used per unit time is 50-100% of the amount of pyrolysis gas feedstock used.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) By adding quicklime, not only can it play a dehydration role, but it can also synergistically regulate nitrogen and sulfur, and play a good catalytic role in the cracking of volatiles.

[0029] (2) The main raw material of this application is sludge, which is readily available and low in cost; and this application does not require energy consumption for sludge drying treatment, which further reduces operating costs.

[0030] (3) The preparation method of this application is simple and the proportioning is flexible; the product has high added value, including high-strength pyrolysis char and high-grade pyrolysis gas.

[0031] (4) The sludge-low-rank coal co-forming pyrolysis technology of this application is a clean and efficient sludge harmless resource utilization technology, in which biomass can also be pyrolyzed and utilized, which has good social, ecological and economic benefits. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a photograph of the briquettes prepared in Example 1 of this application;

[0034] Figure 2 This is a photograph of the pyrolytic carbon prepared in Example 1 of this application;

[0035] Figure 3 The results are the cold compressive strength of the pyrolytic carbons prepared in Examples 1-15 and Comparative Examples 1-4;

[0036] Figure 4 The results are the composition of high-grade pyrolysis gas obtained in Examples 1-15 and Comparative Examples 1-4. Detailed Implementation

[0037] The terminology used in the implementation section of this application is for the purpose of explaining specific embodiments of this application only, and is not intended to limit this application.

[0038] The cold compressive strength test method in the examples and comparative examples is: "Method for Determining the Cold Compressive Strength of Industrial Briquettes" (MT / T748) The method specified in (2007).

[0039] The test method for the composition of pyrolysis gas was as follows: the composition of pyrolysis gas was analyzed using a gas chromatograph (GC-2014C, SHIMADZU, Japan).

[0040] The low-rank coal used in the examples and comparative examples is Xiaosizhuang coal from Huanglong County, Shaanxi Province. It is a high-sulfur, low-rank coal, and the existing technology has low utilization efficiency.

[0041] Example 1

[0042] A method for co-forming and pyrolysis of sludge and low-rank coal:

[0043] (1) Add 20% quicklime powder to the sludge and mix evenly to obtain pretreated sludge;

[0044] (2) Grind low-rank coal and bitumen to 200 mesh using a coal mill;

[0045] (3) According to the mass parts, take 60 parts of pretreated sludge, 40 parts of low-rank coal, 3.2 parts of asphalt and 3 parts of starch and mix them. Knead and stir at 50Hz for 20 min to obtain the mixture.

[0046] (4) The mixture is fed into a molding machine and continuously extruded using a 10 mm die at a power of 50 Hz to obtain coal briquettes, such as... Figure 1 As shown;

[0047] (5) In a closed, low-oxygen environment (oxygen content below 5%), briquettes are pyrolyzed in a rotary kiln at 600 °C for 30 min to obtain high-strength pyrolyzed charcoal, such as... Figure 2 As shown, its cold compressive strength was measured to be 260.3 N / piece.

[0048] (6) 50% of the hourly pyrolysis gas feedstock amount of pyrolysis carbon is added to the cracking furnace as a catalyst. The pyrolysis gas is cracked at 700 °C for 30 min to obtain high-grade pyrolysis gas, of which the hydrogen production is 64.95 mL / g.

[0049] Example 2

[0050] Compared with Example 1, Example 2 differs in that in step (1), the 20% quicklime is replaced with 10% quicklime. The cold compressive strength of the pyrolytic char was measured to be 198.2 N / piece; the hydrogen production was 58.46 mL / g.

[0051] Example 3

[0052] Compared with Example 1, Example 3 differs in that: in step (3), the mixture is prepared in the following proportions: 50 parts sludge, 50 parts low-rank coal, 3.2 parts asphalt, and 3 parts starch. The cold compressive strength of the pyrolytic char was measured to be 302.4 N / piece; the hydrogen production was 68.20 mL / g.

[0053] Example 4

[0054] Compared with Example 1, Example 4 differs in that: in step (3), the mixture is prepared in the following proportions: 40 parts sludge, 60 parts low-rank coal, 3.2 parts asphalt, and 3 parts starch. The cold compressive strength of the pyrolytic char was measured to be 366.8 N / piece; the hydrogen production was 72.75 mL / g.

[0055] Example 5

[0056] Compared with Example 1, Example 5 differs in that: in step (3), the mixture is prepared in the following proportions: 60 parts sludge, 40 parts low-rank coal, 8 parts asphalt, and 3 parts starch. The cold compressive strength of the pyrolytic char was measured to be 370.8 N / piece; the hydrogen production was 71.45 mL / g.

[0057] Example 6

[0058] Compared with Example 1, Example 6 differs in that: in step (3), the mixture is prepared in the following proportions: 60 parts sludge, 40 parts low-rank coal, 13 parts asphalt, and 3 parts starch. The cold compressive strength of the pyrolytic char was measured to be 428.3 N / piece; the hydrogen production was 77.94 mL / g.

[0059] Example 7

[0060] Compared with Example 1, Example 7 differs in that: in step (3), the mixture is prepared in the following proportions: 60 parts sludge, 40 parts low-rank coal, 23 parts asphalt, and 3 parts starch. The cold compressive strength of the pyrolytic char was measured to be 459.1 N / piece; the hydrogen production was 82.49 mL / g.

[0061] Example 8

[0062] Compared with Example 1, Example 8 differs in that: in step (4), the 10 mm extrusion die is replaced with an 8 mm die. The cold compressive strength of the pyrolytic char was measured to be 226.2 N / piece; the hydrogen production was 59.76 mL / g.

[0063] Example 9

[0064] Compared with Example 1, Example 9 differs in that the pyrolysis temperature of 600 ℃ in step (5) is replaced with 500 ℃. The cold compressive strength of the pyrolytic char was measured to be 237.8 N / piece; the hydrogen production was 53.96 mL / g.

[0065] Example 10

[0066] Compared with Example 1, Example 10 differs in that the pyrolysis temperature of 600 ℃ in step (5) is replaced with 700 ℃. The cold compressive strength of the pyrolytic char was measured to be 307.9 N / piece; the hydrogen production was 70.94 mL / g.

[0067] Example 11

[0068] Compared with Example 1, Example 11 differs in that the pyrolysis temperature of 600 ℃ in step (5) is replaced with 800 ℃. The cold compressive strength of the pyrolytic char was measured to be 334.0 N / piece; the hydrogen production was 84.44 mL / g.

[0069] Example 12

[0070] Compared with Example 1, Example 12 differs in that the pyrolysis time of 30 min is replaced with 60 min in step (5). The cold compressive strength of the pyrolytic char was measured to be 247.5 N / piece; the hydrogen production was 79.89 mL / g.

[0071] Example 13

[0072] Compared with Example 1, Example 13 differs in that the pyrolysis temperature of 700 ℃ is replaced with 600 ℃ in step (6). The cold compressive strength of the pyrolytic carbon was measured to be 260.3 N / piece; the hydrogen production was 52.59 mL / g.

[0073] Example 14

[0074] Compared with Example 1, Example 14 differs in that the pyrolysis temperature of 700 ℃ is replaced with 500 ℃ in step (6). The cold compressive strength of the pyrolytic carbon was measured to be 260.3 N / piece; the hydrogen production was 41.66 mL / g.

[0075] Example 15

[0076] Compared with Example 1, Example 15 differs in that: in step (6), the amount of pyrolysis catalyst (pyrolytic carbon) used is replaced by 100% instead of 50% of the feed amount per unit time. The cold compressive strength of the pyrolytic carbon was measured to be 260.3 N / piece; the hydrogen production was 102.85 mL / g.

[0077] Comparative Example 1

[0078] Compared with Example 1, Comparative Example 1 differs in that: in step (3), the mixture was prepared in a ratio of 60 parts sludge to 40 parts low-rank coal, without the addition of asphalt and starch, and without the addition of quicklime to the sludge. The cold compressive strength of the pyrolytic char was measured to be 60.1 N / piece; the hydrogen production was 38.97 mL / g.

[0079] Comparative Example 2

[0080] Compared with Example 1, Comparative Example 2 differs in that pyrolytic carbon was not added as a catalyst in step (6). The cold compressive strength of the pyrolytic carbon was measured to be 260.3 N / piece; the hydrogen production was 13.95 mL / g.

[0081] Comparative Example 3

[0082] Compared with Example 1, Comparative Example 3 differs in that quicklime was not added in step (1). The cold compressive strength of the pyrolytic char was measured to be 102.4 N / piece; the hydrogen production was 46.12 mL / g.

[0083] Comparative Example 4

[0084] Compared with Example 1, Comparative Example 4 differs in that starch was not added in step (3). The cold compressive strength of the pyrolytic char was measured to be 216.8 N / piece; the hydrogen production was 61.05 mL / g.

[0085] The pyrolytic char prepared in Examples 1-15 and Comparative Examples 1-4 were subjected to cold compressive strength tests, and the test results are as follows: Figure 3 As shown.

[0086] The high-grade pyrolysis gases obtained in Examples 1-15 and Comparative Examples 1-4 were subjected to compositional analysis and testing, and the test results are as follows: Figure 4 As shown.

[0087] from Figure 3 and Figure 4 Test results show that the sludge-low-rank coal co-forming pyrolysis technology described in this application can obtain high-strength pyrolysis char and high-grade hydrogen-rich pyrolysis gas.

[0088] As can be seen from the comparison between Example 1 and Comparative Example 1, Comparative Example 1 did not add asphalt and starch, and the molding strength of the charcoal was extremely low; and since no quicklime was added to the sludge, the hydrogen content in the pyrolysis gas decreased significantly.

[0089] As can be seen from the comparison between Example 1 and Comparative Example 2, Comparative Example 2 did not add pyrolytic carbon as a cracking catalyst, and the hydrogen content in the pyrolysis gas was extremely low.

[0090] A comparison of Example 1 and Comparative Example 3 shows that Comparative Example 3, which did not add quicklime and sludge for pretreatment, exhibited a decrease in char strength and a significant decrease in hydrogen content in the pyrolysis gas. This is because, during the pyrolysis stage in step (5), the calcium hydroxide generated from the quicklime partially decomposes at high temperature, resulting in a decrease in Ca²⁺ content. + Calcium diffuses onto the carbon matrix surface to form highly dispersed active sites. Calcium reacts with oxygen-containing functional groups (-OH) on the carbon surface to form a Ca-OC bond structure. This interfacial bonding firmly anchors calcium to the carbon surface, preventing sintering deactivation. Thus, the acidic sites on the carbon surface promote pyrolysis, while calcium provides basic sites to promote dehydrogenation, forming a bifunctional acid-base catalysis. During the pyrolysis of macromolecules, the C-C bonds break, generating small molecule gases.

[0091] Adding quicklime in step (1) and then pyrolyzing calcium hydroxide in step (5) creates the conditions for the formation of a calcium-carbon composite catalyst. Calcium catalysts alone have a small specific surface area and are easily sintered; carbon catalysts alone have a large specific surface area but a limited density of active sites. After calcium-carbon composite formation, calcium is highly dispersed on the carbon surface, maintaining a high specific surface area while increasing the density of active sites, and the carbon matrix inhibits the sintering of calcium species.

[0092] At the same time, the pyrolysis temperature in step (5) is also crucial. Excessively high pyrolysis temperatures can cause calcium to form CaCO3, CaS, etc., thereby losing its activity.

[0093] As can be seen from the comparison between Example 1 and Comparative Example 4, Comparative Example 4 did not add starch, and the strength of the char was significantly reduced, and the quality of the pyrolysis gas was also slightly reduced.

[0094] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for co-forming and pyrolyzing sludge and low-rank coal, characterized in that, Includes the following steps: S1: Mix sludge and quicklime to obtain pretreated sludge; S2: Crushing low-rank coal and bitumen; S3: Knead and mix the pretreated sludge with crushed low-rank coal and pitch to obtain a mixture; S4: The mixture is continuously extruded and granulated to obtain coal briquettes; S5: Pyrolyze the obtained coal briquettes to obtain pyrolytic char. S6: Using the pyrolytic carbon as a cracking catalyst, the pyrolysis gas generated in the pyrolysis process is catalytically cracked to obtain high-grade pyrolysis gas. In step S3, the pretreated sludge, low-rank coal, and bitumen are in the following proportions by weight: 40-60 parts, 40-60 parts, and 1-30 parts, respectively. The raw materials for kneading and mixing also include starch; the starch is 1-5 parts by weight. The kneading and mixing time is 5-30 minutes; In step S5, the pyrolysis temperature is 500-800℃ and the pyrolysis time is 30-60 min.

2. The sludge-low-rank coal co-forming and pyrolysis method according to claim 1, characterized in that, In step S1, the quicklime accounts for 10-30% of the mass of the obtained pretreated sludge.

3. The sludge-low-rank coal co-forming and pyrolysis method according to claim 1, characterized in that, In step S2, the particle size of the low-rank coal and bitumen after crushing is 150-200 mesh.

4. The sludge-low-rank coal co-forming and pyrolysis method according to claim 1, characterized in that, In step S4, the diameter of the extrusion die for continuous extrusion granulation is 5-10 mm.

5. The sludge-low-rank coal co-forming and pyrolysis method according to claim 1 or 4, characterized in that, In step S5, the strength of the pyrolytic char is 190-500 N / piece.

6. The sludge-low-rank coal co-forming and pyrolysis method according to claim 1, characterized in that, In step S6, the temperature of the catalytic cracking is 600-900℃.

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