Horizontal type two-section pyrolysis tobacco stem circulating system capable of resisting alkali metal slagging and process of horizontal type two-section pyrolysis tobacco stem circulating system

Abstract

The invention discloses a horizontal two-stage pyrolysis tobacco stem circulating system capable of resisting alkali metal slagging and a process thereof. The system comprises a horizontal two-section pyrolyzing furnace formed by sequentially connecting a pyrolyzing chamber, an alkali metal adsorption plate and a combustion chamber, a continuous feeding device externally connected to an inlet of the pyrolyzing chamber, a continuous deslagging device externally connected to an outlet of the pyrolyzing chamber, and a heat circulating device for exchanging heat of the combustion chamber to the pyrolyzing chamber through a heat exchanger and a tail gas fan. The process based on the system comprises the steps that tobacco stems enter the pyrolysis chamber for pyrolysis through the continuous feeding device, obtained volatile gas enters the combustion chamber for combustion through the alkali metal adsorption plate, tail gas obtained through combustion enters the heat exchanger through tail gas air to exchange heat with external cold air and then enters the pyrolysis chamber, and hot air obtained through heat exchange enters the combustion chamber. By means of the system and the process, tar volatile matter can be effectively eliminated, the alkali metal content in the biochar can be greatly reduced, and therefore the fertilizer efficiency of the biochar is ensured, and resource utilization of tobacco stems is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to a tobacco stem pyrolysis system, in particular to an anti-alkali metal slagging horizontal two-stage pyrolysis tobacco stem circulating system and process thereof, belonging to the technical field of biomass pyrolysis. BACKGROUND

[0002] Waste tobacco leaves are usually used to extract flavor ingredients and nicotine, while tobacco stems, although the concentration of these ingredients is relatively low, still need to be treated to avoid the leakage of proprietary products. In order to solve this problem, tobacco companies use pyrolysis technology to convert tobacco stems into biochar, gas and tar. Biochar can be used as a fertilizer to return to the field, not only helping to improve the soil environment, but also promoting carbon sequestration. However, the treatment of tar is still a challenge due to its high viscosity, irritating odor and the presence of harmful ingredients such as nicotine and polycyclic aromatic hydrocarbons, which can cause equipment blockage, pollution and damage. Another problem is the high ash content of tobacco stems (21.3 wt.%), mainly composed of K2O (51.6 wt.%) and CaO (12.4 wt.%). At high temperatures, the melting and volatilization of alkali metals can cause corrosion and slagging of equipment. Therefore, the key to solving these problems is to find a way to effectively eliminate tar volatiles while retaining or intercepting alkali metals in biochar, thereby ensuring the fertility of biochar and preventing alkali metal slagging. SUMMARY

[0003] In view of the problems existing in the prior art, the first object of the present application is to provide an anti-alkali metal slagging horizontal two-stage pyrolysis tobacco stem circulating system. The circulating system significantly reduces the release of alkali metals while significantly reducing the tar content of tobacco stems through a two-stage pyrolysis furnace. On the one hand, the heat required for tobacco stem pyrolysis is completely covered by the heat released by tar combustion, eliminating the need for external energy input. On the other hand, the alkali metal content of the biochar obtained by pyrolysis of tobacco stems can be significantly reduced by the alkali metal adsorption plate, and the slagging phenomenon of alkali metals in the equipment can be inhibited, thereby realizing the environmental protection and continuous circulation of tobacco stem pyrolysis.

[0004] The second object of the present application is to provide an anti-alkali metal slagging horizontal two-stage pyrolysis tobacco stem circulating process, which is executed by the above-mentioned circulating system. The process is based on the system provided by the present application, which uses low-temperature pyrolysis and high-temperature combustion in two temperature zones, and then uses the high-temperature tail gas obtained by tar combustion as the only heat source for the low-temperature pyrolysis process through the heat recycling device. The alkali metal adsorption plate intercepts the alkali metals, effectively eliminating the tar volatiles while retaining or intercepting the alkali metals in the biochar, thereby ensuring the fertility of the biochar.

[0005] To achieve the above technical purposes, the application provides a horizontal two-stage pyrolysis tobacco stem circulating system resistant to alkali metal slagging, characterized in that it comprises: a horizontal two-stage pyrolysis furnace composed of a pyrolysis chamber, an alkali metal adsorption plate and a combustion chamber connected in sequence, a continuous feeding device externally connected to the inlet of the pyrolysis chamber, a continuous slagging device externally connected to the outlet of the pyrolysis chamber and a heat circulation device for heat exchange from the combustion chamber to the pyrolysis chamber through a heat exchanger and an exhaust gas fan.

[0006] The circulating system provided by the application has two-stage temperature zones with temperature gradients arranged in the same reactor, the first stage is used for low-temperature pyrolysis of tobacco stems, and the second stage is used for high-temperature combustion of volatile matters, thereby significantly reducing the volatilization of alkali metals in the tobacco stems and achieving complete combustion of tar. Through heat balance calculation, the heat released by the combustion of volatile matters in the tobacco stems is much greater than the energy required for pyrolysis of the tobacco stems, therefore, the application uses the heat generated in the high-temperature combustion process as the only heat source in the low-temperature pyrolysis process, and further, the alkali metal adsorption plate arranged between the pyrolysis zone and the combustion zone can effectively intercept the release of alkali metals, so that the system realizes heat circulation and effectively avoids the problem of slagging of the pyrolysis equipment.

[0007] As a preferred scheme, the continuous feeding device is composed of a hopper and an inlet spiral connected in sequence.

[0008] As a preferred scheme, the continuous slagging device is composed of a cooling conveying spiral and a carbon box connected in sequence.

[0009] As a preferred scheme, the cooling conveying spiral is further provided with a water cooling circulation device for cooling.

[0010] As a preferred scheme, the exhaust gas inlet of the heat circulation device is connected to the outlet of the combustion chamber, enters the heat exchanger through the exhaust gas fan, enters the pyrolysis chamber after heat exchange with cold air, and the hot air obtained by heat exchange enters the combustion chamber.

[0011] As a preferred scheme, the alkali metal adsorption plate has replaceable hollow cavities filled with heat-insulating adsorption materials.

[0012] As a preferred scheme, the heat-insulating adsorption materials are at least one of quartz wool, biochar, cordierite and bentonite.

[0013] The application further provides a horizontal two-stage pyrolysis tobacco stem circulating process resistant to alkali metal slagging, which is executed by the system according to any one of the above.

[0014] As a preferred scheme, the process of the circulating system is that the tobacco stems enter a pyrolysis chamber through a continuous feeding device for pyrolysis, the obtained volatile gas enters a combustion chamber through an alkali metal adsorption plate for combustion, the combustion tail gas enters a heat exchanger through a tail gas air fan after heat exchange with external cold air, and then enters the pyrolysis chamber, and the hot air obtained by heat exchange enters the combustion chamber.

[0015] As a preferred scheme, the pyrolysis process is under the conditions of a pyrolysis temperature of 300-500 DEG C and a residence time of 1-5 min.

[0016] As a preferred scheme, the combustion process is under the conditions of a combustion temperature of 600-800 DEG C and a residence time of 1-5 min.

[0017] As a preferred scheme, the biochar obtained after pyrolysis of the tobacco stems is cooled and transported by a cooling conveying screw, and then is sent into a carbon box for recovery.

[0018] As a preferred scheme, the mass ratio of the tobacco stems to the adsorption material in the alkali metal adsorption plate is 35-45:1.

[0019] As a preferred scheme, the combustion tail gas is heat-exchanged with cold air to a temperature close to the pyrolysis temperature, and then enters the pyrolysis chamber to provide all the heat required by the pyrolysis process.

[0020] Compared with the prior art, the technical scheme of the present application has the beneficial technical effects that:

[0021] 1) The circulating system provided by the present application can significantly reduce the release of alkali metal while significantly reducing the tar content of tobacco stems through a two-stage pyrolysis furnace, on the one hand, the heat required for pyrolysis of tobacco stems is completely covered by the heat released by tar combustion, without the need for external energy input, on the other hand, the alkali metal content of the biochar obtained by pyrolysis of tobacco stems can be greatly reduced through the alkali metal adsorption plate, and the slagging phenomenon of alkali metal in the equipment is inhibited, thereby realizing the environmental protection and continuous circulation of pyrolysis of tobacco stems.

[0022] 2) The circulating pyrolysis process provided by the present application uses low-temperature pyrolysis and high-temperature combustion in two temperature zones based on the system provided by the present application, and then uses the high-temperature tail gas obtained by tar combustion as the only heat source for the low-temperature pyrolysis process through a heat recycling device, and intercepts alkali metal through an alkali metal adsorption plate, thereby effectively eliminating tar volatiles while retaining or intercepting alkali metal in biochar, thereby ensuring the fertility of biochar.

[0023] 3) In the technical scheme provided by the present application, the main functions of the alkali metal adsorption plate are two, one is to intercept alkali metal in the volatile gas atmosphere of tobacco stem pyrolysis, and the other is to separate the low-temperature pyrolysis zone and the high-temperature combustion zone, avoiding direct mixing of heat in the two zones to cause incomplete combustion, and avoiding too high pyrolysis temperature to cause coking of flue gas. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a horizontal two-stage pyrolysis furnace and a method for preventing alkali metal slagging in tobacco stem pyrolysis according to the present application. DETAILED DESCRIPTION

[0025] Embodiments of the present application will be described in detail with reference to the accompanying drawings and examples. The examples are intended to illustrate the present application and should not be construed as limiting the scope of the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The instruments used are not specified by the manufacturer, but are conventional products that can be obtained by commercial purchase.

[0026] The present application does not have a special limitation on the amount of tobacco stem added, which can be adjusted according to the processing scale and reactor size.

[0027] The anti-alkali metal slagging horizontal two-stage pyrolysis tobacco stem circulation system and process used in the embodiments of the present application are carried out in the following manner: a horizontal two-stage pyrolysis furnace includes a continuous feeding system, a first-stage pyrolysis chamber, a continuous slagging system, an alkali metal adsorption plate, a second-stage combustion chamber, and a heat circulation system. The continuous feeding system is composed of a tobacco stem bin and a feeding screw device; the first-stage pyrolysis chamber is connected to the feeding system at the left end, connected to the alkali metal adsorption plate at the right end, and connected to the slagging system at the lower end; the continuous slagging system uses a conveying screw to transport the pyrolysis biochar residue to a carbon box, and the conveying screw is cooled by cooling water; the alkali metal adsorption plate has two hollow cavities on both sides, filled with a layer of replaceable heat-insulating adsorption material, connected to the first-stage pyrolysis chamber at the left end, and connected to the second-stage combustion chamber at the right side; the second-stage combustion chamber is connected to the preheated air at the upper end and outputs the combustion gas at the right side; the heat circulation system transports the combustion gas to a heat exchanger through a combustion gas fan, and then cools the combustion gas to a certain temperature (pyrolysis temperature) through air, while the preheated air is transported to the second-stage combustion chamber, and the cooled combustion gas hot air is transported to the first-stage pyrolysis chamber to maintain the pyrolysis temperature.

[0028] Example 1

[0029] In this embodiment, the heat required for the pyrolysis of each kilogram of tobacco stem is 3602.8 kJ, and the heat released by the complete combustion of the volatiles produced by the pyrolysis is 5963.6 kJ, which meets the prerequisite condition for heat circulation.

[0030] In the embodiment, the tobacco stem is used as raw material, and a layer of alkali metal adsorption plate filled with quartz wool is added between the pyrolysis chamber and the combustion chamber of the horizontal two-stage pyrolysis furnace. The pyrolysis temperature of the pyrolysis chamber is 500 DEG C, and the combustion temperature of the combustion chamber is 800 DEG C. In the embodiment, the tail gas obtained from the combustion chamber is carbon dioxide and water, which is heated by a heat exchanger to 300 DEG C and then enters the pyrolysis chamber as the only heat source of the pyrolysis process. The tobacco stem is continuously fed into the pyrolysis furnace, and the biochar is continuously discharged from the pyrolysis furnace. The alkali metal release rate is 4.1%, which is reduced by 71.3% compared with the case without the alkali metal adsorption plate.

[0031] Example 2

[0032] In the embodiment, the heat required for pyrolysis of each kilogram of tobacco stem is 2846.1 kJ, and the heat released by combustion of the generated volatiles is 5926.7 kJ, which meets the prerequisite condition of heat circulation.

[0033] In the embodiment, the tobacco stem is used as raw material, and a layer of alkali metal adsorption plate filled with quartz wool is added between the pyrolysis chamber and the combustion chamber of the horizontal two-stage pyrolysis furnace. The pyrolysis temperature of the pyrolysis chamber is 400 DEG C, and the combustion temperature of the combustion chamber is 600 DEG C. In the embodiment, the tail gas obtained from the combustion chamber is carbon dioxide and water, which is heated by a heat exchanger to 400 DEG C and then enters the pyrolysis chamber as the only heat source of the pyrolysis process. The tobacco stem is continuously fed into the pyrolysis furnace, and the biochar is continuously discharged from the pyrolysis furnace. The alkali metal release rate is 3.1%, which is reduced by 78.2% compared with the case without the alkali metal adsorption plate.

[0034] Example 3

[0035] In the embodiment, the heat required for pyrolysis of each kilogram of tobacco stem is 2991.1 kJ, and the heat released by combustion of the generated volatiles is 5924.1 kJ, which meets the prerequisite condition of heat circulation.

[0036] In the embodiment, the tobacco stem is used as raw material, and a layer of alkali metal adsorption plate filled with quartz wool is added between the pyrolysis chamber and the combustion chamber of the horizontal two-stage pyrolysis furnace. The pyrolysis temperature of the pyrolysis chamber is 400 DEG C, and the combustion temperature of the combustion chamber is 600 DEG C. In the embodiment, the tail gas obtained from the combustion chamber is carbon dioxide and water, which is heated by a heat exchanger to 400 DEG C and then enters the pyrolysis chamber as the only heat source of the pyrolysis process. The tobacco stem is continuously fed into the pyrolysis furnace, and the biochar is continuously discharged from the pyrolysis furnace. The alkali metal release rate is 3.1%, which is reduced by 78.2% compared with the case without the alkali metal adsorption plate.

[0037] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the original application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A horizontal two-stage pyrolysis tobacco stem circulation system resistant to alkali metal slagging, characterized in that, include: The horizontal two-stage pyrolysis furnace consists of a pyrolysis chamber, an alkali metal adsorption plate, and a combustion chamber connected in sequence; a continuous feeding device externally connected to the inlet of the pyrolysis chamber; a continuous slag discharge device externally connected to the outlet of the pyrolysis chamber; and a heat circulation device that transfers heat from the combustion chamber to the pyrolysis chamber through a heat exchanger and a tail gas fan.

2. The horizontal two-stage pyrolysis tobacco stem circulation system for resisting alkali metal slagging according to claim 1, characterized in that: The continuous feeding device consists of a hopper and an infeed screw connected in sequence; the continuous slag discharge device consists of a cooling conveying screw and a carbon box connected in sequence; the cooling conveying screw is also equipped with a water cooling circulation device for cooling and temperature reduction.

3. The horizontal two-stage pyrolysis tobacco stem circulation system for resisting alkali metal slagging according to claim 1, characterized in that: The exhaust gas inlet of the heat circulation device is connected to the combustion chamber outlet. The exhaust gas enters the heat exchanger via the exhaust gas fan, exchanges heat with cold air, and then enters the pyrolysis chamber. The hot air obtained from the heat exchange then enters the combustion chamber.

4. The horizontal two-stage pyrolysis tobacco stem circulation system for resisting alkali metal slagging according to claim 1, characterized in that: The alkali metal adsorption plate has replaceable hollow cavities filled with heat-insulating adsorption material; the heat-insulating adsorption material is at least one of quartz wool, biochar, cordierite and bentonite.

5. A horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging, characterized in that: Performed by the system according to any one of claims 1 to 4.

6. The horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging according to claim 5, characterized in that: The process of the cycle is as follows: tobacco stems are fed into the pyrolysis chamber via a continuous feeding device for pyrolysis. The resulting volatile gases are fed into the combustion chamber via an alkali metal adsorption plate for combustion. The exhaust gas from the combustion is fed into a heat exchanger via exhaust gas air and exchanges heat with external cold air before entering the pyrolysis chamber. The hot air obtained from the heat exchange enters the combustion chamber.

7. The horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging according to claim 6, characterized in that: The conditions for the pyrolysis process are: pyrolysis temperature of 300-500℃ and residence time of 1-5 min.

8. The horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging according to claim 6, characterized in that: The conditions for the combustion process are: combustion temperature of 600-800℃ and residence time of 1-5 minutes.

9. The horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging according to claim 6, characterized in that: The biochar obtained after the pyrolysis of the tobacco stems is cooled by a conveying spiral and then sent to a charcoal box for recycling; the mass ratio of the tobacco stems to the adsorbent material in the alkali metal adsorption plate is 35-45:

1.

10. The horizontal two-stage pyrolysis tobacco stem recycling process for resisting alkali metal slagging according to claim 6, characterized in that: The exhaust gas from the combustion is heated by exchanging heat with cold air until its temperature reaches the pyrolysis temperature, and then enters the pyrolysis chamber to provide all the heat required for the pyrolysis process.

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