CN101613617B - Method for preparing biological oil through vacuum pyrolysis of biomasses - Google Patents

Abstract

The method for preparing bio-oil by vacuum pyrolysis of biomass includes the following processes: (1) Vacuum pyrolysis: the pretreated raw materials are put into a reaction kettle, and the temperature is raised and cracked under the heating of a peripheral tube furnace. The reaction kettle is equipped with a heat conducting device. (2) Condensation: The volatile matter at low temperature (mainly water vapor) is introduced into the drying tower, and the volatile matter at high temperature is led into the coil condenser for condensation, and online sampling can be realized during the cracking process. (3) Absorption: The water vapor in the non-condensable gas is absorbed by the drying tower, and the nitrides and sulfides are absorbed by the bubbling absorption bottle, which effectively reduces the pollution of vacuum pump oil. The method of the invention partially solves the problems of temperature rise lag caused by low biomass heat transfer efficiency, low condensation efficiency and on-line sampling during the temperature rise process, and at the same time preliminarily reduces the water content in the bio-oil.

Description

A method for preparing bio-oil by vacuum cracking of biomass

technical field

The invention discloses a method for recovering biomass solid waste, in particular to a method for producing bio-oil by pyrolysis under a certain degree of vacuum.

Background technique

With the increasing scarcity of fossil energy, biomass energy has begun to attract attention due to its low toxicity, low pollution and abundant reserves.

Biomass thermochemical conversion technology is a kind of biomass energy utilization technology, in which vacuum cracking is a technology with liquid phase bio-oil as the main target product, which converts biomass raw materials into non-condensable gas under a certain degree of vacuum and temperature , three energy forms of bio-oil and coke. Biomass is first converted into volatile matter at high temperature, and the volatile matter is converted into bio-oil and non-condensable gas after passing through the condensing device. The composition of volatile matter is similar to flue gas, and the commonly used condensation method is rapid condensation. Patent CN101343547A discloses a method for preparing bio-oil by vacuum cracking and classification, but the limitation of the design of the condensing device restricts the yield of bio-oil, and because the whole system is under negative pressure, it is difficult to realize online sampling of samples. The cracking oil condensation method disclosed in CN1030252A adopts the second-stage condensate to condense the previous stage, which may cause polymerization or even coking of low-boiling heat-sensitive substances. Condensed bio-oil contains a large amount of water, and is highly miscible with polar components in bio-oil, making it difficult to separate. Conventional separation methods, such as vacuum distillation, are difficult to achieve ideal results due to the poor thermal stability of bio-oil. Although methods such as column chromatography and molecular distillation can separate water well, their cost is too high and they are only suitable for the separation and production of high value-added products. The moisture in bio-oil comes from two parts, one part comes from the free water adsorbed by the biomass itself, and the other part comes from the water produced by cracking. The free water can be removed after the biomass raw material is dried, but it still remains in the process of transferring and sealing. Will absorb moisture from the air. In addition, in the initial stage of cracking, due to the low pressure in the kettle, the gas content is small, and the biomass itself is a poor conductor of heat, so there is a hysteresis in its heat transfer, which increases the heating time of the biomass.

Contents of the invention

Technical problem: The purpose of the method of the present invention is to provide a method for preparing bio-oil by vacuum cracking of biomass, which can improve the condensation effect of volatile components and realize online sampling of samples. At the same time, it can increase the heat transfer efficiency in the reactor and properly reduce the oil phase The content of water in the medium partly solves the problem of difficult subsequent separation of pyrolysis oil.

Technical solution: The method for preparing bio-oil by vacuum cracking of biomass according to the present invention is as follows:

1) Place the enhanced heat transfer device in the reactor first, then add the processed biomass sample, seal the flange surface, start the vacuum pump, check the air tightness of the system, and close the first three-way after confirming that the air tightness is good Valve, open the nitrogen valve and fill with nitrogen, wait for the pressure in the reactor to rise to normal pressure, close the nitrogen valve;

2) Close the second stop valve, open the first three-way valve to switch to the third branch, and empty the gas in the reactor;

3) When the vacuum degree of the system reaches about 5-10kpa, start the temperature controller, control the furnace temperature to rise to 105-140°C in the first stage, and stay at this temperature for 15-35 minutes to remove the residual free water in the biomass;

4) The first three-way valve is switched to the fourth branch, the second three-way valve is switched to the first collector, the fourth stop valve is opened, and the fifth stop valve on the absorber is adjusted to obtain a suitable Bubble rate; adjust the temperature controller to control the furnace temperature to rise to the final temperature of 400-600°C at a rate of 10-30°C/min in the second stage, and the condensed products are collected in the first collector, the second collector, and the third collector The non-condensable gas is collected in the gas collection tank by the compression pump;

5) When sampling online, close the fourth shut-off valve, switch the second three-way valve to the fifth branch, and collect liquid samples from the collector; open the seventh shut-off valve to collect gas samples from the gas collection tank;

6) After the reaction is finished, close the first three-way valve, open the sixth shut-off valve to prevent the pump oil from being sucked back, close the vacuum pump, close the eighth shut-off valve, open the nitrogen valve and fill it with nitrogen, until the pressure in the kettle rises to normal pressure, Close the nitrogen valve;

7) Open the first stop valve and the third stop valve to collect bio-oil, wait until the temperature of the reactor drops to room temperature, collect coke, and clean the reactor.

Beneficial effect:

1. The method of the present invention can increase the heat transfer efficiency of the reaction system, reduce the reaction time, reduce energy consumption, and relieve energy shortage to a certain extent;

2, the inventive method passes into nitrogen before and after reaction, effectively reduces the oxygen content of whole reaction system, has reduced the oxygen content of cracking component, has increased product calorific value;

3. The method of the present invention adopts a stainless steel elbow to immerse in the condensation medium, which increases the contact area, improves the condensation effect, and increases the yield of pyrolysis oil;

4. The method of the present invention is provided with branches L3 and L4 after the reactor lead-out line L2, and reduces the mixing amount of water vapor in the bio-oil at low temperature and high temperature by switching the branches;

5. The method of the present invention can realize online sampling of samples without affecting the vacuum degree of the whole reaction system;

6. The method of the present invention has an absorption bottle in front of the vacuum pump, which can adjust the degree of bubbling by adjusting the intake valve to improve the absorption efficiency, and at the same time effectively reduce the pollution of the nitrogen and sulfide in the uncondensed gas to the pump oil.

Description of drawings

Fig. 1 is the structural representation of the method device of the present invention;

Fig. 2 is the bottom schematic diagram of the enhanced heat transfer device in the method device of the present invention;

Fig. 3 is a cross-sectional view of an enhanced heat transfer device in the method device of the present invention;

Figure 4 is the heating curve.

The above figures include: 1. Nitrogen cylinder, 2. Nitrogen valve, 3. Reactor, 4. Tube furnace, 5. Dead tube, 6. Thermocouple, 7. Vacuum gauge, 8. The first three-way valve, 9. Coil condenser, 10. Second three-way valve, 11. First stop valve, 12. Second stop valve, 13. Third stop valve, 14. Fourth stop valve, 15. Third collector, 16. Fifth stop valve, 17. Absorber, 18. Drying tower, 19. Sixth stop valve, 20. Vacuum pump, 21. Buffer bottle, 22. Compression pump, 23. Seventh stop valve, 24. Gas collection tank , 25. The eighth stop valve, 26. The temperature controller, 27. The first collector, 28. The second collector, L1, the first branch, L2, the second branch, L3, the third branch, L4 , the fourth branch, L5, the fifth branch.

Detailed ways

The method of the present invention will be further described below in conjunction with the accompanying drawings.

Example:

As shown in Fig. 1, the plant diagram of the inventive method includes a reaction system, a condensation system and a pump system connected to each other. The reaction system includes a stainless steel reaction kettle 3, a tube furnace 4, and a temperature controller 26. There are interfaces on the flange surface of the reaction kettle, which are respectively connected to the vacuum gauge 7, the blind pipe 5, the first branch L1 and the second branch L2 , The reaction kettle condensation system includes three-stage condensation. The first two-stage condensation tanks are respectively equipped with water and ice-water mixtures. The condensation tank and the stainless steel elbow are welded as one. 9. A collector is connected to the outlet of the stainless steel elbow. The third-stage condensation The tank is ice-salt mixture. The pump system includes an absorber 17 , a drying tower 18 , a buffer bottle 21 , a vacuum pump 20 and a compression pump 22 . A three-way valve and a stop valve are respectively provided at the joints of the pipe fittings.

Combining the above devices, the steps of producing bio-oil by vacuum pyrolysis of biomass in this example are as follows:

Wheat straw is used as raw material, crushed to a particle size range of 3-5mm, and baked at 80-105°C for 12 hours. Put the heat conduction device—a circular steel plate welded with heat conduction rods (as shown in Figures 2 and 3) in the reaction kettle, then add raw materials, and seal the flange surface. Start the vacuum pump 20, check the airtightness of the system, and after confirming that the airtightness is good, close the first three-way valve 8, open the nitrogen valve 2 to fill with nitrogen, wait for the pressure in the reactor to rise to normal pressure, and close the nitrogen valve 2. Close the second cut-off valve 12, open the first three-way valve 8 to switch to the third branch L3, and empty the gas in the reactor. When the vacuum degree of the system reaches 5-10kpa, start the temperature controller 26, control the furnace temperature to rise to 105-140°C in the first stage, and stay at this temperature for 10-30 minutes to remove residual free water in the biomass. The first three-way valve 8 is switched to the fourth branch L4, the second three-way valve 10 is switched to the first collector 27, the fourth cut-off valve 14 is opened, and the fifth cut-off valve 16 on the absorber 17 is adjusted to pass the adjustment valve Switch size to obtain proper bubble rate. Adjust the temperature controller 26 to control the furnace temperature to rise to a final temperature of 400-600°C at a rate of 10-30°C/min in the second stage, and the condensed products are collected in the first collector 27, the second collector 28, and the third collector 15 The non-condensable gas is pressed into the gas collection tank 24 by the compression pump 22 to collect. During online sampling, the fourth cut-off valve 14 is closed, the second three-way valve 10 is switched to the fifth branch L5, and the liquid sample is collected from the collector 11 . Open the seventh shut-off valve 23 to collect gas samples from the gas collection tank 24; after the reaction finishes, close the first three-way valve 8, open the sixth shut-off valve 19 to prevent pump oil from sucking back, close the vacuum pump 20, and close the eighth shut-off valve 25. Open the nitrogen valve 2 and fill it with nitrogen. After the pressure in the kettle rises to normal pressure, close the nitrogen valve 2. Open the first shut-off valve 11, and the third shut-off valve 13 collects the bio-oil, waits for the temperature of the reactor to drop to room temperature, collects the coke, and cleans up the reactor.

Figure 4 shows the temperature rise curve. When the furnace temperature is raised from room temperature to 500°C, curves 1, 2, and 3 are the temperature rise curves of the furnace body, the reactor with and without heat conduction devices, respectively. The heat conduction device improves the hysteresis of biomass heating up, thereby reducing the heating time and saving energy.

Table 1 is the experimental comparison data, data 1 is common straight tube condensation, and cracked gas directly enters condensation system, does not go through the step 3 low-temperature dehydration described in the method of the present invention; Data 2 is the coil condensation described in the method of the present invention, after Low temperature water removal step.

Table 1 Bio-oil yield and water content

Claims (1)

1. A method for preparing bio-oil by vacuum cracking of biomass, is characterized in that the method may further comprise the steps: 1) Place the enhanced heat transfer device in the reaction kettle (3) first, then add the treated biomass sample, seal the flange surface, start the vacuum pump (20), check the air tightness of the system, and confirm that the air tightness is good , close the first three-way valve (8), open the nitrogen valve (2) and fill with nitrogen, wait for the pressure in the reactor to rise to normal pressure, close the nitrogen valve (2); 2) Close the second stop valve (12), open the first three-way valve (8) to switch to the third branch (L3), and empty the gas in the reactor; 3) When the vacuum degree of the system reaches about 5-10kPa, start the temperature controller (26), control the furnace temperature to rise to 105-140°C in the first stage, and stay at this temperature for 15-35 minutes to remove the residues in the biomass. of free water; 4) The first three-way valve (8) is switched to the fourth branch (L4), the second three-way valve (10) is switched to the first collector (27), the fourth cut-off valve (14) is opened, and the absorber is adjusted The fifth cut-off valve (16) on (17) obtains a suitable bubbling rate by adjusting the size of the valve switch; adjust the temperature controller (26), and control the temperature of the furnace to rise to 10-30°C/min rate in the second stage The final temperature is 400-600°C, the condensed product is collected in the first collector (27), the second collector (28), and the third collector (15), and the non-condensable gas is pressed into the gas collection tank by the compression pump (22) Collected in (24); 5) When sampling online, close the fourth shut-off valve (14), switch the second three-way valve (10) to the fifth branch (L5), and collect liquid samples from the collector; open the seventh shut-off valve (23) from Gas samples are collected in the gas collection tank (24); 6) After the reaction is finished, close the first three-way valve (8), open the sixth shut-off valve (19) to prevent the pump oil from sucking back, close the vacuum pump (20), close the eighth shut-off valve (25), and open the nitrogen valve ( 2) Charge nitrogen, wait for the pressure in the kettle to rise to normal pressure, close the nitrogen valve (2); 7) Open the first shut-off valve (11) and the third shut-off valve (13) to collect bio-oil, wait for the temperature of the reactor to drop to room temperature, collect coke, and clean the reactor. the

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