Method for preparing porous semicoke from Nanzuo Lake coal

Abstract

The invention relates to a method for preparing porous semicoke from Nanhao Lake coal, and belongs to the technical field of coal resource utilization and clean energy. The method comprises the following steps: firstly, quickly pyrolyzing Nuyi Lake coal in a dropper furnace at 800-1000 DEG C to prepare semi-coke with relatively complete active bridging fracture as a skeleton of a pore structure; and then carrying out secondary pyrolysis for a long residence time by using a carbonization furnace at a temperature above the polycondensation temperature of the Pan Mao Lake coal and below the rapid pyrolysis temperature to eliminate most of non-aromatic organic structures in the semicoke so as to form porous semicoke. The obtained semicoke is subjected to N2 physical adsorption and desorption analysis, and the result shows that compared with rapid pyrolysis semicoke, the pore structure specific surface area of the semicoke obtained through the two-step pyrolysis method is remarkably increased. The porous semi-coke can be widely applied to the fields of adsorption and catalysis, can also improve the burn-off rate of combustion and gasification processes, and provides a new way for resource utilization of low-rank coal.

Description

Technical Field

[0001] The present invention provides a method for preparing porous semicoke from Naomaohu coal through two-step pyrolysis, which relates to the fields of coal resource utilization and clean energy, and more specifically, relates to a method for preparing porous semicoke from low-rank coal. Background Art

[0002] Energy is the material basis for human survival and development and the core driving force for the development of human society. In the global fossil energy system, coal is the earliest energy source used on a large scale by humans.

[0003] Coal pyrolysis is a common means of clean and efficient utilization of coal and also the initial stage of gasification and combustion. Studying the coal pyrolysis process can provide guidance and assistance for the clean and efficient utilization of coal. Coal pyrolysis is a process in which coal undergoes thermal decomposition under anaerobic or anoxic conditions, triggering a series of physical and chemical changes, and finally generating gas products (coal gas), liquid products (tar), and solid products (semicoke). By controlling the pyrolysis temperature, pressure, heating rate, etc., the yields and properties of the three-phase products of pyrolysis can be controlled. The semicoke yield of low-rank coal pyrolysis is usually 40%-50%, and the carbon content in the semicoke is greater than 70%, and the calorific value is close to that of raw coal, having great application potential. However, in the actual process, due to the collapse of the pyrolysis pore structure of the semicoke at high temperature, the specific surface area is usually lower than 50 m 2 / g, seriously affecting the application of the semicoke. Summary of the Invention

[0004] Aiming at the problem of small specific surface area caused by the collapse of the pore structure of semicoke in traditional pyrolysis products, the present invention proposes a method for obtaining high-specific-surface-area semicoke from low-rank coal by two-step pyrolysis. The low-rank coal is first rapidly pyrolyzed in a dropping tube furnace to prepare semicoke with relatively complete fracture of active bridge chains. At the same time, taking advantage of the concentrated cross-linking reaction during the rapid pyrolysis process, more stable cross-linking structures are formed, maintaining a relatively low degree of order in the arrangement of aromatic nuclei, which serves as the framework of the pore structure. Then, using a carbonization furnace reactor, at a temperature above the condensation temperature of the low-rank coal and below the rapid pyrolysis temperature, the rapidly pyrolyzed semicoke is subjected to secondary pyrolysis for a sufficient long residence time to eliminate most of the non-aromatic organic structures in the semicoke and form pores. After measuring the pore specific surface area of the semicoke by N 2 physical adsorption and desorption, it is found that the specific surface area of the semicoke obtained by this pyrolysis method is significantly increased compared with that of the semicoke obtained by single rapid pyrolysis, which is beneficial for the application of the semicoke in adsorption, catalysis, and improving the burnout rate.

[0005] The technical solution adopted by the present invention is: a method for preparing porous semicoke from coal, comprising the following steps: S1. Grind and dry the coal to obtain coal powder; S2. The dried pulverized coal is rapidly pyrolyzed in an inert atmosphere in a drop tube furnace at a temperature of 800 - 1000 °C to obtain rapidly pyrolyzed semicoke. S3. The rapidly pyrolyzed semicoke is heated to a temperature between the coal condensation temperature and the rapid pyrolysis temperature in an inert atmosphere in a carbonization furnace device and held for 30 - 120 min for secondary pyrolysis to obtain porous semicoke.

[0006] Further, the coal used is low - rank coal, selected from one or more of Naomaohu coal, lignite, and long - flame coal.

[0007] Further, in step S1, the coal is ground to less than 180 mesh.

[0008] Further, the inert atmosphere used is N 2 or an inert gas.

[0009] Further, the temperature between the coal condensation temperature and the rapid pyrolysis temperature is 700 °C - 750 °C.

[0010] Further, the pyrolysis reaction is carried out in an N 2 atmosphere, and the rapid pyrolysis temperature in the drop tube furnace is 800, 900, 1000 °C.

[0011] Further, the temperature between the coal condensation temperature and the rapid pyrolysis temperature is selected as 750 °C.

[0012] Further, the heating rate of the carbonization furnace is 3 - 5 K / min.

[0013] Preferably, the final heating temperature is 750 °C, and the residence time is 30 min - 120 min, such as 30 min, 60 min, and 120 min. Preferably, the residence time of the carbonization furnace at 750 °C is 30 - 60 min. It is found that the two - step pyrolysis method can significantly increase the specific surface area of the semicoke.

[0014] The beneficial effects that can be significantly achieved by the solution of the present invention compared with the prior art are as follows: (1) The drop tube furnace has the advantages of fast heating and rapid pyrolysis reaction of the sample, and the carbonization furnace has the advantages of simple operation and sufficient pyrolysis. Combining the advantages of both, Naomaohu coal is first used to prepare rapidly pyrolyzed semicoke in a drop tube furnace, and then the rapidly pyrolyzed semicoke is secondarily pyrolyzed in a carbonization furnace to obtain porous semicoke. Compared with the semicoke obtained only by rapid pyrolysis, the semicoke obtained by two - step pyrolysis; N 2 The specific surface area obtained by adsorption - desorption is more than 20 times that of the rapidly pyrolyzed semicoke, and the specific surface area is significantly increased. The porous semicoke can be widely used in the fields of adsorption and catalysis, increasing the added value of the semicoke.

[0015] (2) The rapid pyrolysis temperature of the dropping tube furnace and the residence time of the carbonization furnace at 750 °C will both have a certain impact on the pore structure of semicoke. When the rapid pyrolysis temperature is 800-1000 °C, the two-step pyrolysis method will significantly increase the specific surface area of semicoke. The residence time of the carbonization furnace at 750 °C should not be too long, and 30-60 min is appropriate. Too long residence time will cause the collapse of the pore structure of semicoke, and a moderate residence time can reduce energy consumption and is conducive to the sustainable development of energy. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the device of the dropping tube furnace reactor; Figure 2 It is a schematic diagram of the carbonization furnace device; Figure 3 It is a graph of the specific surface area of semicoke at different residence times of the carbonization furnace at 750 °C under rapid pyrolysis temperatures of 800, 900, and 1000 °C. Detailed Embodiments

[0017] The following further illustrates the method through specific embodiments, but does not limit the present invention thereby. The following non-limiting embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0018] In the test methods described in the following embodiments, unless otherwise specified, they are all conventional methods; the reagents and materials, unless otherwise specified, can all be obtained from commercial channels.

[0019] The low-rank coal is ground to a certain mesh number and then dried, and rapid pyrolysis experiments are carried out in a dropping tube furnace under the condition of 800 °C in an N 2 atmosphere. In the following embodiments, the N 2 flow rate is set to 800 mL / min, and the feeding rate of the low-rank coal is 0.9-1.0 g / min. The rapid pyrolysis semicoke obtained is placed in the heating center section of the carbonization furnace, and the N 2 flow rate is 200 mL / min. It is heated from room temperature to 750 °C at a heating rate of 5 K / min, and the residence time is 30, 60, 120 min. After the temperature of the carbonization furnace drops to room temperature, the semicoke is taken out for N 2 physical adsorption and desorption analysis.

[0020] In the preferred embodiment of the above method, Naomaohu coal is selected as the pyrolysis raw material, ground to 180 mesh, and placed in a vacuum oven for drying. The Naomaohu coal is loaded into the hopper of the dropping tube furnace. After the dropping tube furnace is heated to the specified temperature, N with a flow rate of 800 mL / min is introduced 2, the reaction tube in the dropping tube furnace is a quartz reaction tube with a diameter of 40 mm and a reaction zone length of 80 cm. Fast pyrolysis semicoke is collected by the lower solid collection device. The fast pyrolysis semicoke is placed in the middle of the carbonization furnace reactor, and N with a flow rate of 200 mL / min is first introduced 2 for 30 min to remove the influence of the remaining gases in the tube on the reaction. Then, it is heated from room temperature to 750 °C at a heating rate of 5 K / min, and the residence time of the carbonization furnace at 750 °C is changed. After the carbonization furnace is cooled to room temperature, the obtained semicoke is taken out for N 2 physical adsorption and desorption analysis.

[0021] N 2 For physical adsorption and desorption, the semicoke is first weighed and treated under vacuum conditions at 150 °C for 3 hours in a precise G-Praxis JW-BK200A specific surface area and pore size analyzer to remove the adsorbed molecules and water on the semicoke. Then, the N 2 adsorption / desorption test of the sample is completed at -196 °C. The Brunauer-Emmett-Teller (BET) method is used to determine the mesoporous specific surface area, and the pore volume and pore size distribution are determined by the Barrett-Joyner-Halenda (BJH) method.

[0022] Examples 1-3 The method for preparing porous semicoke from Naomaohu coal provided in this example includes the following steps: (1) Grind Naomaohu coal to less than 180 mesh, and then place it in a vacuum oven for drying; (2) Place the dried Naomaohu sample in the hopper of the dropping tube furnace. After the dropping tube furnace is heated to 800 °C, introduce N with a flow rate of 800 mL / min 2 and purge for 10 min to remove the influence of the residual gases in the reaction tube on the reaction. Then start the screw feeder and feed the material evenly at a feeding rate of 0.9 - 1.0 g / min. The Naomaohu coal is pyrolyzed in the reaction tube of the dropping tube furnace and collected in the bottom collection device.

[0023] (3) Place the obtained fast pyrolysis semicoke in a porcelain boat, and place the porcelain boat in the pyrolysis center area of the carbonization furnace. First, introduce 200 mL / min of N 2 to remove the influence of the gas in the device on the reaction, and then heat it from room temperature to 750 °C at a heating rate of 5 K / min. After holding for 30 min (Example 1), 60 min (Example 2), and 120 min (Example 3), it is cooled to room temperature in an N 2 atmosphere and then taken out.

[0024] (4) Treat the semicoke obtained in step (3) in a precise G-Praxis JW-BK200A specific surface area and pore size analyzer at 150 °C for 3 hours, and then perform N under the condition of liquid nitrogen -196 °C2 Physical adsorption and desorption, analyzing the pore shape according to the adsorption and desorption curves, the Brunauer-Emmett-Teller (BET) method was used to determine the specific surface area of mesopores, and the pore volume and pore size distribution were determined by the Barrett-Joyner-Halenda (BJH) method. The results show that the specific surface area of the semicoke obtained by the method of this invention is greater than 200 m 2 / g. The specific surface area of the semicoke obtained at different residence times in the carbonization furnace is different. The specific surface area of the semicoke is the largest when the residence time is 60 min, which is 281.2 m 2 / g.

[0025] Examples 4-6 The pyrolysis process is the same as that of Example 1, except that the rapid pyrolysis temperature of the dropping furnace is 900 °C. After heating to 750 °C in step (3), keep the temperature constant for 30 min (Example 4), 60 min (Example 5), and 120 min (Example 6).

[0026] The obtained semicoke was subjected to N 2 physical adsorption and desorption analysis. The results show that the specific surface area of the semicoke obtained by this method is greater than 200 m 2 / g, and the specific surface area of the semicoke with a residence time of 30 min in the carbonization furnace at 750 °C is the largest, which is 315.4 m 2 / g. Comparing with the semicoke obtained at 800 °C in the dropping furnace, under the same residence time, the specific surface area of the semicoke obtained at 900 °C in the dropping furnace is larger.

[0027] Examples 7-9 The difference from Example 1 is that the rapid pyrolysis temperature of the dropping furnace is 1000 °C. And after heating to 750 °C in step (3), keep the temperature constant for 30 min (Example 7), 60 min (Example 8), and 120 min (Example 9).

[0028] The obtained semicoke was subjected to N 2 physical adsorption and desorption analysis. The results show that the specific surface area of the semicoke obtained by this method is greater than 300 m 2 / g, and when the residence time in the carbonization furnace is 30 min, the specific surface area of the semicoke is the largest, which is 324.8 m 2 / g. Compared with other temperatures, the specific surface area of the rapid pyrolysis semicoke obtained at 1000 °C after secondary pyrolysis in the carbonization furnace is the largest.

[0029] The specific surface areas of the rapid pyrolysis semicokes obtained at 800, 900, and 1000 °C in the dropping furnace in Examples 1-3 and the semicokes obtained after staying at 750 °C in the carbonization furnace for 30, 60, and 120 min were plotted on Figure 3It can be seen from the figure that porous semicoke can be obtained by two-step pyrolysis, and the specific surface area of the semicoke is greater than 200 m 2 / g. Under the same residence time of 750 °C in the carbonization furnace, the higher the rapid pyrolysis temperature, the larger the specific surface area of the semicoke. At the same rapid pyrolysis temperature in the dropping tube furnace, when the residence time in the carbonization furnace at 750 °C is 30 - 60 min, the specific surface area of the semicoke is relatively large. When the residence time is 120 min, the pore specific surface area of the semicoke will decrease due to the collapse of the pore structure.

[0030] Comparative Example 1 The Naomaohu coal was ground to 180 mesh, placed in a vacuum oven for drying, and then placed in the hopper of the dropping tube furnace. After the dropping tube furnace was heated to 800 °C, N with a flow rate of 800 mL / min was introduced 2 to purge the gas in the reaction tube. Then, the screw feeder was opened, and the feeding rate was 0.9 - 1.0 g / min. The Naomaohu coal was pyrolyzed under an N atmosphere of 800 mL / min 2 to obtain rapid pyrolysis semicoke. The rapid pyrolysis semicoke in the solid collection device was subjected to N 2 physical adsorption and desorption analysis to obtain the specific surface area of the pore structure of the semicoke. The specific surface area of the semicoke was 4.2 m 2 / g. Combining with the specific surface area of Example 1, it was found that the two-step pyrolysis method could significantly increase the specific surface area of the semicoke.

[0031] Comparative Example 2 The Naomaohu coal was ground to 180 mesh, placed in a vacuum oven for drying, and then placed in the hopper of the dropping tube furnace. After the dropping tube furnace was heated to 900 °C, N with a flow rate of 800 mL / min was introduced 2 to purge the gas in the reaction tube. Then, the screw feeder was opened, and the feeding rate was 0.9 - 1.0 g / min. The Naomaohu coal was pyrolyzed under an N atmosphere of 900 mL / min 2 to obtain rapid pyrolysis semicoke. The rapid pyrolysis semicoke in the solid collection device was subjected to N 2 physical adsorption and desorption analysis to obtain the specific surface area of the pore structure of the semicoke. The specific surface area of the semicoke was 9.2 m 2 / g.

[0032] Comparative Example 3 The Naomaohu coal was ground to 180 mesh, placed in a vacuum oven for drying, and then placed in the hopper of the dropping tube furnace. After the dropping tube furnace was heated to 1000 °C, N with a flow rate of 800 mL / min was introduced 2 to purge the gas in the reaction tube. Then, the screw feeder was opened, and the feeding rate was 0.9 - 1.0 g / min. The Naomaohu coal was pyrolyzed under an N atmosphere of 1000 mL / min 2 to obtain rapid pyrolysis semicoke. The rapid pyrolysis semicoke in the solid collection device was subjected to N2 Physical adsorption and desorption analysis was carried out to obtain the specific surface area of the char pore structure. The specific surface area of the char was 12.8 m 2 / g.

[0033] The pore structure characteristic parameters of the chars obtained in Examples 1-9 and Comparative Examples 1-3 are shown in Table 1. It can be seen from Table 1 that compared with direct pyrolysis in a dropping tube furnace, the two-step pyrolysis method can significantly increase the specific surface area of the char. The residence time in the carbonization furnace at 750 °C will significantly affect the pore structure of the char. When the residence time is 30-60 min, the specific surface area of the char is relatively large. From the perspective of clean and efficient utilization of coal, the two-step pyrolysis method can significantly increase the pore specific surface area of the char, which has great application potential in adsorption and catalysis, and is also beneficial to subsequent combustion and gasification treatment.

[0034] Table 1 Pore structure characteristic parameters of chars in Examples 1-9 and Comparative Examples 1-3

[0035] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for preparing porous semi-coke from coal, characterized in that: The following steps are involved: S1, grinding and drying coal to obtain coal powder; S2, the dried coal powder is rapidly pyrolyzed in an inert atmosphere in a drop tube furnace at a temperature of 800-1000°C to obtain rapid pyrolysis semi-coke; S3. The rapid pyrolysis semi-coke is heated to a temperature above the coal polycondensation temperature and below the rapid pyrolysis temperature in a carbonization furnace under an inert atmosphere and kept for 30-120 minutes for secondary pyrolysis to obtain porous semi-coke.

2. The method according to claim 1, characterized in that The coal is low-rank coal, selected from one or more of Naomaohu coal, lignite, and long bituminous coal.

3. The method according to claim 2, characterized in that In the step S1, the coal is ground to a size below 180 mesh.

4. The method according to claim 1, characterized in that: The inert atmosphere is N2 or an inert gas.

5. The method according to claim 1, characterized in that: The temperature above the coal polycondensation temperature and below the rapid pyrolysis temperature is 700°C-750°C.

6. The method according to claim 4, characterized in that: The temperature above the coal polycondensation temperature and below the rapid pyrolysis temperature is 750°C.

7. The method according to claim 1, characterized in that The carbonization furnace has a heating rate of 3-5 K / min.

8. The method according to claim 1, characterized in that The residence time at the secondary pyrolysis temperature of the carbonization furnace is 30-60 min.

Images