CN109943353B - System and method for preparing levoglucosan by utilizing concentrating solar energy dual-temperature-zone effect - Google Patents
System and method for preparing levoglucosan by utilizing concentrating solar energy dual-temperature-zone effect Download PDFInfo
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Abstract
The invention belongs to the field of biomass pyrolysis, and particularly discloses a system and a method for preparing levoglucosan by utilizing a concentrating solar dual-temperature-zone effect. The invention efficiently utilizes the heat energy generated by solar radiation, so that the cellulose is pyrolyzed in a high-temperature area of the reactor to generate primary tar, quickly enters a low-temperature area to avoid secondary reaction, and is condensed and collected in time, thereby obtaining the biological oil rich in the levoglucosan.
Description
Technical Field
The invention belongs to the field of biomass pyrolysis, and particularly relates to a system and a method for preparing levoglucosan by utilizing a concentrating solar dual-temperature-zone effect.
Background
Cellulose is used as a pure and single substance with wide distribution in biomass, is very suitable for preparing chemical products from the biomass, and the components of the products after pyrolysis are mainly levoglucosan. Levoglucosan, a derivative of glucose, has unique structure and chemical properties, is widely applied in industry, is expensive, is about 378 yuan/g, and has high commercial potential. Levoglucosan has been receiving much attention from people, and various very valuable compounds can be synthesized by levoglucosan and used in various industries. For example, the polysaccharide is used as a new sugar source in the fields of bio-based platform compound preparation and biotechnology fermentation, and can also be used for synthesizing plant growth regulators, pesticides and the like.
At present, a cellulose pyrolysis model widely applied is shown in fig. 1, wherein cellulose is subjected to a fast pyrolysis reaction in an inert gas atmosphere at 400-550 ℃ to generate the biological oil rich in the levoglucosan. However, levoglucosan is unstable at 380 deg.C or higher, and can be easily decomposed into H2O、CO2Low-molecular-weight products with low utilization values such as furan, furfural and acetic acid, so that the preparation efficiency of the levoglucosan is low, the prepared biological oil has low levoglucosan content, and a great part of utilization values are lost. On the other hand, the temperature required by pyrolysis is above 400 ℃, and the energy consumption for maintaining the pyrolysis to be continuously carried out is large.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a system and a method for preparing levoglucosan by utilizing the concentrating solar dual-temperature-zone effect, which efficiently utilize heat energy generated by solar radiation to ensure that cellulose is pyrolyzed in a high-temperature zone of a reactor to generate primary tar, quickly enters a low-temperature zone to avoid secondary reaction, and then is condensed and collected in time, thereby obtaining the biological oil rich in the levoglucosan.
To achieve the above object, according to one aspect of the present invention, there is provided a system for preparing levoglucosan by using a concentrated solar dual-temperature-zone effect, which comprises a heliostat field, a hyperboloid reflector, a screw feeder, a solar fluidized bed pyrolysis reactor, a bio-oil fractional condensation collection device, and a tail gas recycling device, wherein:
the heliostat field is used for receiving solar radiation and converging the received solar radiation to a high-temperature region of the solar fluidized bed pyrolysis reactor through the hyperboloid reflector so as to obtain heat energy to provide heat required by the reaction;
the screw feeder is connected with the upper port of the solar fluidized bed pyrolysis reactor and is used for feeding cellulose into the solar fluidized bed pyrolysis reactor;
the solar fluidized bed pyrolysis reactor is divided into a high-temperature area directly irradiated by solar radiation and a low-temperature area, wherein the high-temperature area is positioned below the high-temperature area, the low-temperature area is positioned above the high-temperature area, the bottom of the high-temperature area is a cone with a certain inclination angle, the high-temperature area is connected with a capillary tube which is coaxially arranged with the cone, and a branch port for exhausting is also arranged on the side surface above the high-temperature area; the cellulose entering the solar fluidized bed pyrolysis reactor from the upper port is cracked into gas-phase primary tar rich in levoglucosan by falling into a high-temperature area of the reactor under the action of gravity, unreacted cellulose repeatedly passes through the high-temperature area to be fully reacted under the action of fluidizing gas of a capillary at the bottom of the reactor, and the gas-phase primary tar generated by cracking the cellulose is conveyed to the low-temperature area of the reactor by the fluidizing gas below before secondary reaction and enters a bio-oil fractional condensation and collection device through a branch port to be condensed and collected;
the bio-oil fractional condensation and collection device is connected with a branch port on the upper side surface of the solar fluidized bed pyrolysis reactor, gas-phase primary tar discharged from the solar fluidized bed pyrolysis reactor is condensed by adopting a three-stage condensation mode to obtain the required bio-oil rich in levoglucosan, and the residual condensed tail gas is discharged from a gas outlet of the bio-oil fractional condensation and collection device;
the tail gas recycling device comprises a three-way valve which connects the gas outlet of the bio-oil fractional condensation collecting device, a nitrogen source and a capillary tube at the bottom of the solar fluidized bed pyrolysis reactor together, and nitrogen provided by the nitrogen source and tail gas discharged from the gas outlet of the bio-oil fractional condensation collecting device are mixed at the three-way valve to provide fluidized gas for the reactor.
As a further preferred mode, the three-stage condensation mode of the bio-oil fractional condensation collection device is specifically as follows: the first-stage condenser uses oil as a condensing medium, the temperature is controlled to be 270-280 ℃, preferably 275 ℃, and is used for condensing most of levoglucosan in gas, the second-stage condenser uses oil as a condensing medium, the temperature is controlled to be 250-260 ℃, preferably 255 ℃, and is used for condensing residual levoglucosan, the third-stage condenser uses dry ice as a condensing medium, the temperature is controlled to be-25-15 ℃, preferably-20 ℃, and is used for condensing residual liquid products.
Preferably, the radiation flux per unit area of the high-temperature region of the solar fluidized bed pyrolysis reactor is 180-220W/cm2More preferably 200W/cm2The speed of feeding the cellulose into the solar fluidized bed pyrolysis reactor is 0.5-1.5 g/min, and more preferably 1 g/min.
Preferably, the bio-oil fractional condensation collection device is connected with a first inlet end of a three-way valve of the tail gas recycling device, a second inlet end of the three-way valve is connected with a nitrogen cylinder, and an outlet end of the three-way valve is connected with a capillary tube at the bottom of the solar fluidized bed pyrolysis reactor.
As a further preference, the solar fluidized bed pyrolysis reactor is a cylinder made of quartz tube, the inclination angle of the bottom cone of the solar fluidized bed pyrolysis reactor is preferably 20 degrees, and the branch port is preferably opened at a quarter position close to the upper port of the reactor.
According to another aspect of the invention, a method for preparing levoglucosan by utilizing the concentrating solar dual-temperature zone effect is provided, which adopts the system for preparation, and comprises the following steps:
s1 feeding cellulose into the solar fluidized bed pyrolysis reactor at a constant speed through a screw feeder;
s2, the solar radiation is collected by the heliostat field and reflected to the hyperboloid reflector, and the hyperboloid reflector reflects and converges the solar radiation to the high-temperature region on the solar fluidized bed pyrolysis reactor;
s3 cellulose enters the solar fluidized bed pyrolysis reactor from the upper port of the solar fluidized bed pyrolysis reactor, the cellulose falls into the high-temperature area of the reactor under the action of gravity and is cracked into primary tar rich in levoglucosan, unreacted cellulose repeatedly passes through the high-temperature area of the reactor under the action of fluidizing gas in capillaries at the bottom of the reactor and fully reacts, and the primary tar generated by cracking the cellulose is conveyed to the low-temperature area of the reactor by the lower fluidizing gas before secondary reaction, and is condensed and collected by a bio-oil fractional condensation and collection device;
s4, carrying out three-stage condensation on the primary tar gas in a biological oil fractional condensation and collection device to obtain biological oil rich in levoglucosan and tail gas;
and (3) introducing the tail gas S5 into a tail gas recycling device, mixing the tail gas with nitrogen provided by a nitrogen source, and then sending the mixture into the solar fluidized bed pyrolysis reactor through a bottom capillary tube of the solar fluidized bed pyrolysis reactor to realize recycling of the fluidized gas.
As a further preferred, the tertiary condensation in step S3 is specifically: oil is used as a condensing medium of a first-stage condenser, the temperature is controlled to be 270-280 ℃, preferably 275 ℃, the oil is used for condensing most of levoglucosan in gas, the temperature is controlled to be 250-260 ℃, preferably 255 ℃, the oil is used for condensing residual levoglucosan, dry ice is used as a condensing medium of a third-stage condenser, the temperature is controlled to be-25-15 ℃, preferably-20 ℃, and the oil is used for condensing residual liquid products.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. the preparation system adopts the double-temperature-zone solar fluidized bed pyrolysis reactor, the cellulose is pyrolyzed in the high-temperature zone to generate primary tar, the primary tar rapidly enters the low-temperature zone to avoid secondary reaction, and then condensation and collection are carried out in time, so that the bio-oil rich in the levoglucosan is obtained, the preparation process is simple and convenient, and the yield is high.
2. The invention can make the cellulose without reaction repeatedly pass through the high temperature area of the reactor to fully react and can be used as carrier gas to convey the primary tar gas to the bio-oil fractional condensation collection device by arranging the capillary at the bottom of the reactor to jet the fluidizing gas.
3. The method adopts a three-stage condensation mode for condensation, wherein the first stage uses oil as a condensation medium, the temperature is controlled to be 270-280 ℃, preferably 275 ℃, and is used for condensing most of levoglucosan in gas, the second stage uses oil as a condensation medium, the temperature is controlled to be 250-260 ℃, preferably 255 ℃, and is used for condensing residual levoglucosan, the third stage uses dry ice as a condensation medium, the temperature is controlled to be-25-15 ℃, preferably-20 ℃, and is used for condensing residual liquid products, and levoglucosan can be effectively condensed and collected under the condensation process.
4. The invention also researches and designs the radiation flux per unit area and the supply speed of the cellulose at the high-temperature area of the reactor, and obtains the optimal process, namely the radiation flux per unit area is 200W/cm through continuous exploration and research2The cellulose supply rate was 1g/min, so that the L-glucan yield was as high as 31.2%
5. The reactor main body adopts the quartz tube which is almost transparent to infrared, a large amount of solar radiation penetrates through the quartz tube and directly irradiates on materials, and the characteristic of high temperature rise rate of concentrated solar energy is utilized to meet the requirement of high temperature rise rate required by the preparation of the biological oil rich in the levoglucosan.
6. The invention fully utilizes the solar energy to condense and collect heat so as to radiate flux of 200W/cm in proper unit area2The heat energy of 400-550 ℃ is obtained to drive the cellulose to carry out the pyrolysis reaction, and compared with the prior art, the method has the advantages of reducing the cost, saving the energy, realizing zero emission and the like.
7. The system is also provided with a tail gas recycling device, so that the tail gas is recycled and used as the fluidizing gas, and the cost is saved.
Drawings
FIG. 1 is a diagram of a model of cellulose pyrolysis which is currently widely used;
FIG. 2 is a schematic structural diagram of a system for preparing levoglucosan by using the concentrating solar dual-temperature zone effect, which is constructed according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 2, the system for preparing levoglucosan by using the concentrated solar dual-temperature-zone effect, which prepares levoglucosan-rich bio-oil by using the concentrated solar reactor dual-temperature-zone effect, according to an embodiment of the present invention, includes a heliostat field 1, a hyperboloid reflector 2, a screw feeder 3, a solar fluidized bed pyrolysis reactor 4, a bio-oil fractional condensation collection device 5, and an exhaust gas recycling device 6, wherein the heliostat field 1 is configured to receive solar radiation and condense the received solar radiation to a focal point, i.e., a high-temperature zone b of the solar fluidized bed pyrolysis reactor 4, through the hyperboloid reflector 2 to obtain heat energy required for providing reaction; the screw feeder 3 is connected with the upper port of the solar fluidized bed pyrolysis reactor 4 and is used for feeding reaction raw material cellulose into the solar fluidized bed pyrolysis reactor 4; the solar fluidized bed pyrolysis reactor 4 is divided into two parts, the area which is directly irradiated by solar radiation and is positioned below is called a high-temperature area b, the rest part which is positioned above the high-temperature area except the high-temperature area is a low-temperature area a, the bottom of the solar fluidized bed pyrolysis reactor 4 is a cone with a certain inclination angle and is connected with a capillary tube, the capillary tube and the solar fluidized bed pyrolysis reactor 4 are coaxially arranged, a branch opening for exhausting gas is also arranged on the side surface above the solar fluidized bed pyrolysis reactor 4, cellulose entering the solar fluidized bed pyrolysis reactor 4 from an upper port during preparation starts to crack into gas-phase primary tar rich in levoglucosan when entering the high-temperature area b of the reactor under the action of gravity, unreacted cellulose repeatedly passes through the high-temperature area b to be fully reacted and cracked under the action of fluidizing gas in the capillary tube at the bottom of the reactor, and the gas-phase primary tar generated by cracking of the cellulose is conveyed to a reverse fluidized gas before the secondary reaction of the gas-phase primary tar The low-temperature area a of the reactor is discharged to a bio-oil fractional condensation collection device 5 through a branch port for condensation and collection; the bio-oil fractional condensation collection device 5 is connected with a branch port on the upper side surface of the solar fluidized bed pyrolysis reactor 4, and is used for condensing gas-phase primary tar discharged from the solar fluidized bed pyrolysis reactor 4 to obtain required bio-oil rich in levoglucosan, and the residual tail gas after condensation is discharged from a gas outlet of the bio-oil fractional condensation collection device 5; the tail gas recycling device 6 comprises a three-way valve which connects the gas outlet of the bio-oil fractional condensation collecting device 5, a nitrogen source and a capillary tube at the bottom of the solar fluidized bed pyrolysis reactor 4 together, and nitrogen provided by the nitrogen source and tail gas discharged from the gas outlet of the bio-oil fractional condensation collecting device 5 are mixed at the three-way valve to provide fluidized gas for the reactor.
Specifically, the solar fluidized bed pyrolysis reactor 4 is a cylinder made of a quartz tube, the inclination angle of a cone at the bottom of the reactor is preferably 20 degrees, and a branch port is preferably arranged near one quarter of an upper port of the reactor.
Further, the biological oil fractional condensation collection device 5 is used for carrying out condensation treatment on the gas-phase primary tar discharged from the solar fluidized bed pyrolysis reactor 4 in a three-stage condensation mode, wherein the first-stage condenser c takes oil as a condensation medium, the temperature is controlled to be 270-280 ℃, preferably 275 ℃, the first-stage condenser c is used for condensing most of levoglucosan in the gas-phase primary tar, the second-stage condenser d takes oil as a condensation medium, the temperature is controlled to be 250-260 ℃, preferably 255 ℃, the second-stage condenser d is used for condensing the levoglucosan remained in the gas-phase primary tar, the third-stage condenser e takes dry ice as a condensation medium, the temperature is controlled to be-25 ℃ to-15 ℃, preferably-20 ℃, and the third-stage condenser c is used for condensing the remained liquid product in the. By the above condensation process, particularly preferred condensation processes: the first-stage condenser is used for condensing by taking oil as a condensing medium at 275 ℃, the second-stage condenser is used for condensing by taking oil as a condensing medium at 255 ℃, the third-stage condenser is used for condensing by taking dry ice as a condensing medium at-20 ℃ so that levoglucosan is separated as far as possible, and finally, the mixture of the levoglucosan and a liquid product collected by the third-stage condenser is the prepared biological oil rich in levoglucosan.
Furthermore, the three-way valve comprises a first inlet end, a second inlet end and an outlet end, the first inlet end of the three-way valve is connected with the gas outlet of the bio-oil fractional condensation collecting device 5, the second inlet end of the three-way valve is connected with the nitrogen cylinder k, and the outlet end of the three-way valve is connected with the capillary tube at the bottom of the solar fluidized bed pyrolysis reactor 4. Wherein, a first flowmeter g, a valve j and a pipe orifice i are arranged on a connecting pipeline between the first inlet end of the three-way valve and the air outlet of the biological oil fractional condensation collecting device 5, a second flowmeter h is arranged on a connecting pipeline between the second inlet end of the three-way valve and the nitrogen gas bottle k, and a third flowmeter f is arranged on a connecting pipeline between the outlet end of the three-way valve and the capillary tube.
More specifically, the inventor finds that the radiation flux per unit area and the cellulose supply speed are two very important parameters in the invention through research, the combination of the two parameters influences the yield of the levoglucosan, and the inventor obtains better parameters through continuous research and test, so that the radiation flux per unit area of the high-temperature region is 180-220W/cm2The raw material supply speed is 0.5-1.5 g/min, and the optimal parameter of the unit area radiation flux is 200W/cm2The raw material feed rate was 1g/min, so that the yield of levoglucosan was as high as 31.2% (i.e., the mass ratio of levoglucosan to cellulose raw material).
The method for preparing the biological oil rich in the levoglucosan by adopting the system comprises the following steps:
s1 cellulose is fed into the solar fluidized bed pyrolysis reactor 4 at a constant speed by a screw feeder 3;
s2, the solar radiation is collected by the heliostat field and reflected to the hyperboloid reflector, and the hyperboloid reflector reflects and converges the solar radiation to the high-temperature region on the solar fluidized bed pyrolysis reactor;
s3 cellulose enters the solar fluidized bed pyrolysis reactor 4 from the upper port of the solar fluidized bed pyrolysis reactor 4 and falls into the high-temperature area b of the solar fluidized bed pyrolysis reactor 4 under the action of gravity, pyrolysis reaction starts to occur, the pyrolysis temperature is above 400 ℃, the cellulose is subjected to pyrolysis reaction to generate primary tar, the primary tar is in a gas phase due to the higher temperature of the reactor, the primary tar rapidly flows through the low-temperature area b of the solar fluidized bed pyrolysis reactor 4 under the action of fluidizing gas in a capillary at the bottom of the reactor and enters the bio-oil fractional condensation collection device 5 through a branch port to be collected, secondary reaction is avoided, and byproduct gas (comprising nitrogen used for fluidization and low-molecular-weight organic gas such as carbon monoxide and methane generated by the reaction) enters the tail gas recycling system 6 to be mixed with the nitrogen to serve as fluidizing gas of the reactor;
s4, carrying out three-stage condensation on the primary tar gas in a biological oil fractional condensation collection device 5 to obtain biological oil rich in levoglucosan and tail gas, specifically, taking the oil as a condensation medium of a first-stage condenser, controlling the temperature to be 270-280 ℃, preferably 275 ℃, for condensing most of levoglucosan in the gas, taking the oil as a condensation medium of a second-stage condenser, controlling the temperature to be 250-260 ℃, preferably 255 ℃, for condensing residual levoglucosan, taking dry ice as a condensation medium of a third-stage condenser, controlling the temperature to be-25-15 ℃, preferably-20 ℃, for condensing residual liquid products;
the tail gas S5 enters the tail gas recycling device 6 to be mixed with nitrogen provided by a nitrogen source and then is sent into the solar fluidized bed pyrolysis reactor 4 through a bottom capillary tube of the solar fluidized bed pyrolysis reactor 4 to realize recycling of the fluidized gas.
Specifically, before materials are added, inert gas purging is firstly carried out to remove air in the whole system, the whole system is in a strict inert environment, a valve of a nitrogen cylinder k is opened, a second flowmeter h is adjusted, a valve j in a tail gas recycling device is closed, whether the flow is consistent with that of the second flowmeter h is detected at an air tightness detection pipe orifice i, and good air tightness is guaranteed (if the air tightness is good, j is closed, nitrogen passes through h-6-f-4-5-i, and the detection at i is consistent with h); and opening a valve j, closing the air tightness detection pipe opening i, setting a third flow meter f as a fixed value, and strictly calculating and determining the gas flow at the third flow meter f to ensure that the cellulose is well fluidized, wherein the optimal fluidizing gas flow is 50ml/min by considering economic factors according to the density and the particle size of the adopted cellulose, the internal pressure of the reactor and the size of the reactor. After the reaction is started, the flow rate of the reaction by-product gas may be read from the first flow meter g, at which time the gas flow rate of the nitrogen gas cylinder is made equal to the difference between the third flow meter f and the first flow meter g, so that the third flow meter f is kept stable.
The following are specific examples of the present invention:
example 1
The selected raw material is cellulose with the particle size of 25 microns, a heliostat field is composed of a 24-surface 30 × cm plane glass mirror, the diameter of the hyperboloid mirror is 1.5m, the capacity of a screw feeder is about 50g, the feeding speed is 1g/min, the solar fluidized bed pyrolysis reactor is a cylinder with the inner diameter of 22mm and the wall thickness of 1.5mm, the diameter of a capillary tube is 1mm, a branch port is 24cm above the quartz tube, and the incident radiation flux range of unit area is 180-class 220W/cm2The reaction is carried out, a plurality of groups of experiments are respectively carried out, the primary tar gas generated by pyrolysis is condensed and collected by a bio-oil fractional condensation and collection device, the yield of the levoglucosan is shown in table 1, and the residual byproduct gas is mixed with nitrogen to provide fluidizing gas for the reactor.
TABLE 1 levoglucosan yield results
| Incident radiation flux per unit area | L-glucan yield |
| 180W/cm2 | 27.6％ |
| 190W/cm2 | 29.3％ |
| 200W/cm2 | 31.2％ |
| 210W/cm2 | 32.1％ |
| 220W/cm2 | 32.5％ |
According to the above data, considering the economic factor, at 200W/cm2The method is most economical and reasonable, and the yield of the levoglucosan is 31.2 percent
Example 2
The incident radiation flux per unit area is 200W/cm2Under conditions of (a), experiments were carried out with several different sets of feed rates: 0.2g/min, 0.5g/min, 1g/min, 1.5g/min, 2g/min, the other conditions were the same as example 1, and the levoglucosan yield was as shown in Table 2.
TABLE 2 levoglucosan yield results
| Feed rate | Levoglucosan yield. |
| 0.2g/min | 29.8％ |
| 0.5g/min | 30.6％ |
| 1g/min | 31.2％ |
| 1.5g/min | 29.2％ |
| 2g/min | 27.8％ |
According to the above data, the incident radiation flux per unit area was 200W/cm2The levoglucosan yield reached 31.2% at a feed rate of 1 g/min.
In conclusion, the invention utilizes the double-temperature-zone effect of the concentrated solar energy to ensure that the primary tar of the pyrolysis product of the cellulose is immediately transferred from the high-temperature zone of the reactor to the low-temperature zone of the reactor once being generated, thereby avoiding the secondary reaction of the primary tar to reduce the content of the levoglucosan in the bio-oil. The optimal parameters are obtained by researching the incident radiation flux, so that the yield of the levoglucosan reaches 31.2%, and meanwhile, the heat supply of the reaction is from solar energy, and the energy consumption is reduced to a certain extent. The system has the characteristics of compact structure, simple operation process, low equipment maintenance cost, high solar energy utilization rate, high purity and good quality of the levoglucosan in the prepared bio-oil and the like.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. Utilize system of two temperature zone effect preparation levoglucosan of spotlight solar energy, its characterized in that, including heliostat field (1), hyperboloid speculum (2), screw feeder (3), solar fluidized bed pyrolytic reaction ware (4), fractional condensation collection device of bio-oil (5) and tail gas cyclic utilization device (6), wherein:
the heliostat field (1) is used for receiving solar radiation and converging the received solar radiation to a high-temperature area (b) of the solar fluidized bed pyrolysis reactor (4) through the hyperboloid reflector (2) to obtain heat energy to provide heat required by reaction;
the screw feeder (3) is connected with the upper port of the solar fluidized bed pyrolysis reactor (4) and is used for feeding cellulose into the solar fluidized bed pyrolysis reactor (4);
the solar fluidized bed pyrolysis reactor (4) is divided into a high-temperature area which is positioned below and directly irradiated by solar radiation and a low-temperature area which is positioned above the high-temperature area, the bottom of the reactor is a cone with a certain inclination angle and is connected with a capillary tube which is coaxially arranged with the reactor, and the side surface above the reactor is also provided with a branch port for exhausting; the cellulose entering the solar fluidized bed pyrolysis reactor (4) from the upper port is cracked into gas-phase primary tar rich in levoglucosan by falling into the high-temperature zone of the reactor under the action of gravity, the unreacted cellulose repeatedly passes through the high-temperature zone to be fully reacted under the action of the fluidizing gas of the capillary at the bottom of the reactor, and the gas-phase primary tar generated by cracking the cellulose is conveyed to the low-temperature zone of the reactor from the fluidizing gas below before the secondary reaction of the gas-phase primary tar, and enters the bio-oil fractional condensation and collection device (5) through the branch port to be condensed and collected;
the bio-oil fractional condensation collection device (5) is connected with a branch opening on the upper side surface of the solar fluidized bed pyrolysis reactor (4), gas-phase primary tar discharged from the solar fluidized bed pyrolysis reactor (4) is condensed by adopting a three-stage condensation mode to obtain the required bio-oil rich in levoglucosan, and the residual tail gas after condensation is discharged from a gas outlet of the bio-oil fractional condensation collection device (5);
the tail gas cyclic utilization device (6) include with bio-oil fractional condensation collection device (5) gas outlet, nitrogen gas source and solar fluidized bed pyrolytic reaction ware (4) bottom capillary are connected together's three way valve, and the nitrogen gas that the nitrogen gas source provided mixes with the tail gas of following bio-oil fractional condensation collection device (5) gas outlet and provide fluidization gas for the reactor at three way valve department.
2. The system for preparing levoglucosan by utilizing concentrating solar energy dual-temperature zone effect according to claim 1, wherein the three-stage condensation mode of the bio-oil fractional condensation collection device (5) is specifically: the first-stage condenser takes oil as a condensing medium, the temperature is controlled to be 270-280 ℃ and is used for condensing most of levoglucosan in gas, the second-stage condenser takes oil as a condensing medium, the temperature is controlled to be 250-260 ℃ and is used for condensing residual levoglucosan, the third-stage condenser takes dry ice as a condensing medium, the temperature is controlled to be-25-15 ℃ and is used for condensing residual liquid products.
3. The system for preparing levoglucosan by utilizing concentrating solar dual-temperature zone effect as claimed in claim 1, wherein the radiation flux per unit area of the high-temperature zone of the solar fluidized bed pyrolysis reactor is 180-220W/cm2The speed of feeding the cellulose into the solar fluidized bed pyrolysis reactor is 0.5-1.5 g/min.
4. The system for preparing levoglucosan by utilizing concentrating solar dual-temperature zone effect according to claim 1, wherein the bio-oil fractional condensation collection device (5) is connected with the first inlet end of the three-way valve of the tail gas recycling device (6), the second inlet end of the three-way valve is connected with the nitrogen bottle, and the outlet end is connected with the capillary tube at the bottom of the solar fluidized bed pyrolysis reactor (4).
5. The system for preparing levoglucosan by utilizing concentrating solar dual-temperature zone effect according to any one of claims 1-4, wherein the solar fluidized bed pyrolysis reactor (4) is a cylinder made of quartz tube, the inclination angle of the bottom cone is 20 °, and the branch opening is opened at the quarter of the position near the upper end opening of the reactor.
6. Method for preparing levoglucosan by concentrating solar two-temperature zone effect, which is prepared by the system of any one of claims 1-5, characterized in that it comprises the following steps:
s1 cellulose is fed into a solar fluidized bed pyrolysis reactor (4) at a constant speed through a screw feeder (3);
s2, solar radiation is collected and reflected to the hyperboloid reflector (2) through the heliostat field (1), and the hyperboloid reflector (2) reflects and converges the solar radiation to the high-temperature area (b) on the solar fluidized bed pyrolysis reactor (4);
s3 cellulose enters a solar fluidized bed pyrolysis reactor (4) from the upper port of the solar fluidized bed pyrolysis reactor (4), the cellulose falls into a high-temperature region (b) of the reactor under the action of gravity to start to be cracked into primary tar rich in levoglucosan, unreacted cellulose repeatedly passes through the high-temperature region of the reactor under the action of fluidizing gas in a capillary tube at the bottom of the reactor to be fully reacted, the primary tar generated by cracking the cellulose is conveyed to the low-temperature region of the reactor by the lower fluidizing gas before secondary reaction, and then is condensed and collected by a biological oil fractional condensation and collection device (5);
s4, carrying out three-stage condensation on the primary tar gas in a biological oil fractional condensation collection device (5) to obtain biological oil rich in levoglucosan and tail gas;
and (3) introducing the tail gas S5 into a tail gas recycling device (6), mixing the tail gas with nitrogen provided by a nitrogen source, and then sending the mixture into a solar fluidized bed pyrolysis reactor (4) from a bottom capillary of the solar fluidized bed pyrolysis reactor (4) to realize recycling of the fluidized gas.
7. The method for preparing levoglucosan by utilizing concentrating solar energy dual-temperature zone effect as claimed in claim 6, wherein the third condensation in step S3 is specifically: oil is used as a condensing medium of a first-stage condenser, the temperature is controlled to be 270-280 ℃, the oil is used for condensing most of levoglucosan in gas, the oil is used as a condensing medium of a second-stage condenser, the temperature is controlled to be 250-260 ℃, the oil is used for condensing residual levoglucosan, dry ice is used as a condensing medium of a third-stage condenser, the temperature is controlled to be-25-15 ℃, and the oil is used for condensing residual liquid products.
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