A method for biomass fixed-bed pressurized gasification

Abstract

The present invention relates to a method for biomass fixed-bed pressurized gasification, the method comprising: S1, mixing and pretreating woody biomass with a pretreatment agent to obtain a first mixture; wherein the content of lignin in the woody biomass is 20-35% by weight; the pretreatment agent is selected from sodium alcoholate with a carbon number of 1-4 and / or potassium alcoholate with a carbon number of 1-4; S2, mixing and granulating the first mixture with high-silicon biomass to obtain a first solid product; wherein the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (2-10):1; the silicon content in the high-silicon biomass ash is greater than 20% by weight, and the silicon content is measured in terms of the content of silicon element; S3, subjecting the first solid product to a fixed-bed pressurized gasification reaction to obtain synthesis gas and liquid ash. The method of the present invention can improve the stability of biomass fixed-bed pressurized gasification.

Description

Technical Field

[0001] The present application relates to the field of biomass energy, and in particular to a method for biomass fixed-bed pressurized gasification. Background Art

[0002] The production of combustible gas / synthesis gas by high-temperature cracking of biomass can be used for heating, power generation and chemical synthesis, and has received extensive attention and research in recent years. However, biomass varieties are diverse, and the physical and chemical properties of different biomasses vary greatly. Several problems have brought many limitations to the biomass gasification industry: (1) Rice husks, bamboo and other materials are representative agricultural processing residues and fast-growing plants. They are widely available and have abundant reserves, making them ideal biomass raw materials. However, their silicon content is very high, and the mass content of silicon dioxide in rice husk ash is even as high as 90% or more. Therefore, their slag removal method is usually solid slag removal, which has many defects, such as a large amount of fly ash in the flue gas. Although it is possible to learn from the coal chemical process and adopt the method of adding metal oxides such as calcium oxide, or using materials rich in such oxides to reduce the ash melting point, this method will not only increase the cost of biomass granulation, but also bring other effects. For example, currently biomass is mostly transported and fed by granulation or briquetting technology. The addition of metal oxides will affect the interaction between biomass powders and reduce the compressive strength of granulation. (2) After biomass combustion or gasification, a large amount of ash solid waste is generated, and the lack of disposal channels leads to additional landfill disposal costs. (3) The current biomass gasification process mainly draws on traditional coal chemical technology. However, applying advanced coal gasification technology to biomass gasification will encounter certain difficulties during the scale-up process. For example, when using fixed-bed pressurized gasification, biomass particles are very easy to break under high pressure and water vapor conditions, making it difficult to ensure bed stability. Summary of the Invention

[0003] The object of the present invention is to provide a method for biomass fixed bed pressurized gasification, which can improve the stability of biomass fixed bed pressurized gasification.

[0004] In order to achieve the above object, the present invention provides a method for biomass fixed-bed pressurized gasification, the method comprising:

[0005] S1. Mixing and pretreating woody biomass with a pretreatment agent to obtain a first mixture; wherein the woody biomass has a lignin content of 20-35% by weight; and the pretreatment agent is selected from sodium alcoholate having 1-4 carbon atoms and / or potassium alcoholate having 1-4 carbon atoms;

[0006] S2. Mixing the first mixture with high-silicon biomass and granulating the mixture to obtain a first solid product; wherein the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (2-10):1; and the silicon content in the ash of the high-silicon biomass is greater than 20% by weight, and the silicon content is calculated as the content of elemental silicon;

[0007] S3. Subjecting the first solid product to a fixed-bed pressurized gasification reaction to obtain synthesis gas and liquid ash.

[0008] Optionally, the lignin content in the woody biomass is 20-35% by weight, and the silicon content in the high-silicon biomass ash is greater than 30% by weight;

[0009] Preferably, the woody biomass is selected from one or more of cedar, eucalyptus branches, camphor branches, pine branches and poplar branches, and the high-silicon biomass is selected from one or more of rice husks, bamboo and reeds.

[0010] Optionally, in step S1, mixing the woody biomass with the pretreatment agent and pretreating the mixture comprises: mixing the woody biomass with the pretreatment agent at 10-50°C for 5-60 minutes, and reacting the mixture under closed conditions at 50-150°C for 5-60 minutes.

[0011] Optionally, in step S1, the weight ratio of the woody biomass to the pretreatment agent is 10:(1-10);

[0012] The pretreatment agent is selected from sodium alcoholate with 1-3 carbon atoms and / or potassium alcoholate with 1-3 carbon atoms; preferably, the pretreatment agent is selected from one or more of sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide.

[0013] Optionally, in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (4-6):1.

[0014] Optionally, in step S3, the pressure of the pressurized gasification reaction is 0.1-5 MPa.

[0015] Optionally, the method further comprises step S4, cooling, crushing, shaping and high-temperature solidifying the liquid ash to obtain a calcium silicate hydrate solidified body; the calcium silicate hydrate solidified body has a flexural strength of 5-22 MPa.

[0016] Optionally, the molding method includes: mixing the crushed ash with water and then molding; the weight ratio of the crushed ash to the water is (2-10):1.

[0017] Optionally, the high-temperature curing conditions include: a temperature of 120-250° C. and a time of 1-12 hours.

[0018] Optionally, the maximum radial compressive strength of the first solid product is 1000-2000N, and the contact angle of the first solid product is 0-120°.

[0019] Through the above technical solution, the method of the present invention pre-treats woody biomass and then mixes it with high-silicon biomass to carry out a fixed-bed pressurized gasification reaction, which can effectively improve the pressurized gasification stability.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 This is a process flow chart of the biomass fixed bed pressurized gasification method according to Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0024] The present invention provides a method for biomass fixed-bed pressurized gasification, which comprises:

[0025] S1. Mixing and pretreating woody biomass with a pretreatment agent to obtain a first mixture; wherein the woody biomass has a lignin content of 20-35% by weight; and the pretreatment agent is selected from sodium alcoholate having 1-4 carbon atoms and / or potassium alcoholate having 1-4 carbon atoms;

[0026] S2. Mixing the first mixture with high-silicon biomass and granulating the mixture to obtain a first solid product; wherein the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (2-10):1; and the silicon content in the ash of the high-silicon biomass is greater than 20% by weight, and the silicon content is calculated as the content of elemental silicon;

[0027] S3. Subjecting the first solid product to a fixed-bed pressurized gasification reaction to obtain synthesis gas and liquid ash.

[0028] The method of the present invention uses woody biomass to assist in the granulation of high-silicon biomass, which can improve its pressurized gasification stability. Specifically, the woody biomass is treated with a pretreatment agent, and the water in the woody biomass reacts with the pretreatment agent (sodium alcoholate and / or potassium alcoholate) to generate alcohol and sodium hydroxide or potassium hydroxide in situ. Under the action of sodium hydroxide and / or potassium hydroxide, the lignin in the woody biomass undergoes peeling and dissolution. When subsequently mixed with high-silicon biomass for granulation, the two can be brought into closer contact, thereby increasing the radial maximum compressive strength of the resulting particles. In addition, some of the surface hydrophilic hydroxyl groups in the lignin undergo an etherification reaction with ethanol, which also enhances the hydrophobicity of the biomass particles as a whole, improving the bed stability in a gasification environment using water vapor as a gasifying agent, thereby effectively improving pressurized gasification stability.

[0029] According to the present invention, alcohol is produced during the pretreatment process in step S1. In a specific embodiment of the present invention, when the alcohol is an alcohol with a relatively low carbon number, such as methanol and ethanol, negative pressure operation can be used to achieve separation and recovery.

[0030] In one embodiment of the present invention, in step S1, mixing and pretreating the woody biomass with a pretreatment agent includes mixing the woody biomass and the pretreatment agent at 10-50°C for 5-60 minutes, and reacting the resulting mixture under closed conditions at 50-150°C for 5-60 minutes. These reaction conditions allow for the complete exfoliation and dissolution of lignin in the woody biomass, and allow some hydroxyl groups to undergo etherification with alcohol, further improving the radial compressive strength and hydrophobicity of the subsequently produced particles, thereby effectively enhancing the stability of the fixed-bed pressurized gasification process.

[0031] According to the present invention, the content of lignin in the woody biomass and the silicon oxide content of the high-silicon biomass can vary over a wide range. In a specific embodiment of the present invention, the content of lignin in the woody biomass is 20-35% by weight, preferably 25-35% by weight, and the silicon content in the ash of the high-silicon biomass is greater than 20% by weight, preferably greater than 30% by weight. More preferably, the woody biomass is selected from one or more of cedar, eucalyptus branches, camphor branches, pine branches and poplar branches, and the high-silicon biomass is selected from one or more of rice husks, bamboo and reeds. The synergistic effect between the above-mentioned types of high-silicon biomass and pretreated woody biomass is better, which can make the method of the present invention have better pressurized gasification stability.

[0032] According to the present invention, in step S1, the weight ratio of the woody biomass to the pretreatment agent can vary within a wide range, for example, 10:(1-10), preferably 10:(3-5). Within this range, the biomass can fully exfoliate and dissolve the lignin in the woody biomass, and allow some hydroxyl groups to undergo etherification reaction with alcohol, further improving the radial compressive strength and hydrophobicity of the subsequently produced particles, thereby effectively enhancing the stability of the fixed-bed pressurized gasification process.

[0033] In a specific embodiment of the present invention, the pretreatment agent is selected from sodium alcoholate with a carbon number of 1-3 and / or potassium alcoholate with a carbon number of 1-3; preferably, the pretreatment agent is selected from one or more of sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide, more preferably sodium methoxide.

[0034] According to the present invention, in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product can vary within a wide range, for example, it can be (4-6):1. A silicon-calcium ratio within the above range is more suitable, which is more conducive to lowering the ash melting point of the first solid product, promoting the formation of liquid ash, and facilitating the subsequent processing of the liquid ash to co-produce a calcium silicate hydrate solidified body. This eliminates fly ash and other problems, and is more environmentally friendly.

[0035] In one embodiment of the present invention, in step S3, the pressure of the pressurized gasification reaction is 0.1-5 MPa. The gasifying agent is well known to those skilled in the art and can be, for example, a mixture of water vapor and air, or a mixture of water vapor and oxygen. Those skilled in the art can select the gasifying agent based on actual needs, and the details will not be repeated here.

[0036] In a specific embodiment of the present invention, the method further includes step S4, wherein the liquid ash is cooled, crushed, formed and cured at high temperature to obtain a calcium silicate hydrate solidified body. The flexural strength of the calcium silicate hydrate solidified body obtained by the method of the present invention is 5-22 MPa. The method of the present invention adjusts the ratio of silicon oxide and calcium oxide in the ash of the first solid product to reduce the ash melting point to produce liquid ash, and the silicon-calcium ratio of the liquid ash meets the formation ratio requirements of the calcium silicate hydrate product, so the liquid ash can be directly processed to obtain the calcium silicate hydrate solidified body. This step includes a liquid eutectic process at high temperature, and elements such as silicon and calcium in the ash can achieve highly uniform mixing at the ionic level. Therefore, compared with the existing method of directly mixing calcium oxide and silicon dioxide powder at the particle level and then preparing the solidified body, in addition to reducing the input of stirring pretreatment, the compressive strength of the final calcium silicate hydrate solidified body can also be improved.

[0037] In one embodiment, the liquid ash is directly discharged into a quenching tank for cooling. During the heat exchange between the liquid ash and the cooling water, water vapor is generated, thereby cooling the ash. The cooled liquid ash can be crushed and ground into a powder using a crusher and a grinder, and preferably sieved for later use.

[0038] In a specific embodiment of the present invention, the molding method includes: mixing the ash obtained by crushing with water and then molding; the weight ratio of the ash obtained by crushing to the water is (2-10):1, preferably (3-5):1, and preferably, the water is the remaining water from the liquid slag quenching tank.

[0039] In a specific embodiment of the present invention, the high-temperature curing conditions include: a temperature of 120-250° C. and a time of 1-12 hours; preferably, a temperature of 190-220° C. and a time of 8-10 hours.

[0040] In a specific embodiment of the present invention, the maximum radial compressive strength of the first solid product is 1000-2000 N, and the contact angle of the first solid product is 0-120°. The maximum radial compressive strength can be measured using a radial extrusion crushing point test method, and the contact angle of the first solid product can be measured using a contact angle meter.

[0041] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0042] In the following examples and comparative examples, the radial maximum compressive strength of the first solid product was measured using a radial extrusion crushing point test method, and the contact angle of the first solid product was measured using a contact angle meter.

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment uses the method of the present invention to perform fixed-bed pressurized gasification on biomass, and the specific steps are as follows.

[0045] S1. Cut and crush the cedar wood into 8 mm lengths, then mix the cedar wood and sodium ethoxide in a weight ratio of 10:5 and stir at 25°C for 30 minutes. Then, heat the mixture to 80°C and seal the mixture for 10 minutes to obtain a first mixture. After the pretreatment, ethanol is separated and recovered using negative pressure.

[0046] S2. Mix the first mixture and rice husks and then extrude and granulate them to obtain a first solid product; wherein the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is 5:1, the maximum radial compressive strength of the first solid product is 1921N, and the contact angle of the first solid product is 101°.

[0047] S3. The first solid product is subjected to a pressurized gasification reaction in a fixed-bed pressurized gasifier to produce synthesis gas. The fixed-bed gasification temperature is approximately 1300°C and the pressure is 3 MPa. The ash is discharged in liquid form. As shown in Table 1, ash melting point testing revealed that the ash melting point of the rice husk and cedar wood mixed pellets was reduced to 1259°C, significantly lower than the ash melting point of 1580°C for rice husk alone. The syngas discharge during the reaction is shown in Table 2.

[0048] S4. The liquid ash is directly discharged into the liquid slag quenching pool. Water vapor is generated during the heat exchange process, and the ash is cooled. The cooled ash is prepared into powder using a crusher and a grinder, and the powder is sieved through a 100-mesh sieve for later use. The moisture content of the ash is tested, and the remaining water in the liquid slag quenching pool is used as the water source (part of the ash is dissolved, and the water in the quenching pool is alkaline). Water is added to control the weight ratio of ash and water to 5:1. After stirring for 60 minutes, it is formed in a mold. The demoulded ash is placed in a high-temperature resistant container, and steam is introduced to high-temperature wet-heat cure at 190°C for 10 hours to obtain a hydrated calcium silicate solid body.

[0049] Example 2

[0050] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S1, the weight ratio of the cedar wood to the sodium ethoxide was 10:15.

[0051] In step S2 , the maximum radial compressive strength of the first solid product is 1923 N, and the contact angle of the first solid product is 103°.

[0052] Example 3

[0053] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S1, the weight ratio of the cedar wood to the sodium ethoxide was 10:0.5.

[0054] In step S2 , the maximum radial compressive strength of the first solid product is 1462 N, and the contact angle of the first solid product is 68°.

[0055] Example 4

[0056] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product was 8:1, the maximum radial compressive strength of the first solid product was 1289 N, and the contact angle of the first solid product was 55°.

[0057] Example 5

[0058] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product was 2:1, the maximum radial compressive strength of the first solid product was 1892 N, and the contact angle of the first solid product was 96°.

[0059] Example 6

[0060] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product was 1:1, the maximum radial compressive strength of the first solid product was 1899 N, and the contact angle of the first solid product was 97°.

[0061] Example 7

[0062] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S1, sodium ethoxide was replaced with sodium methoxide, and the cedar wood was replaced with eucalyptus branches. In step S2, the rice husk was replaced with bamboo. The weight ratio of silicon oxide to calcium oxide in the ash of the first solid product was 3:1. The maximum radial compressive strength of the first solid product was 1816 N, and the contact angle of the first solid product was 93°.

[0063] Comparative Example 1

[0064] Biomass was pressurized and gasified using the same method as in Example 1, except that the cedar wood was cut and crushed to 8 mm in length. The cut cedar wood was then mixed with rice husks and directly extruded into pellets without the use of a pretreatment agent, yielding a first solid product. The first solid product had a maximum radial compressive strength of 1421 N and a contact angle of 46°. The ash was discharged in liquid form.

[0065] Comparative Example 2

[0066] The biomass was pressurized and gasified using the same method as in Example 1, except that in step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product was 15:1, and the ash was discharged in a solid form.

[0067] Table 1

[0068]

[0069]

[0070] Table 2

[0071]

[0072]

[0073] It can be seen from the above that the method of the present invention can effectively improve the stability of biomass fixed-bed pressurized gasification.

[0074] Furthermore, when the weight ratio of woody biomass to the pretreatment agent is within the preferred range of 10:(1-10) of the present invention, the biomass gasification gasification rate has better stability and lower production costs. Example 3 demonstrates that when too little pretreatment agent is added, the biomass gasification gasification rate becomes unstable. Example 2 demonstrates that when too much pretreatment agent is added, the gasification stability is similar to that of Example 1, but excessive additives increase costs.

[0075] In addition, it can be seen from the examples that the biomass fixed bed pressurized gasification method of the present invention not only improves the ash melting point so that the ash is discharged in liquid form, but also examines the performance of the calcium silicate hydrate solid body obtained after the ash is treated. The fixed bed pressurized gasification conditions can be selected and adjusted according to the performance requirements of the calcium silicate hydrate solid body or the slag discharge requirements. Preferably, when the weight ratio of silicon oxide and calcium oxide in the ash of the first solid product is within the preferred range of the present invention (4-6): 1, the calcium silicate hydrate solid body has a higher flexural strength. Examples 4-6 demonstrate that as the material ratio conditions change, the flexural strength of the solid body finally obtained decreases to varying degrees compared to that of Example 1. In addition, when the material ratio exceeds a certain range (Comparative Example 2), the fixed bed cannot achieve liquid slag discharge, and the final ash is in solid form.

[0076] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0077] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0078] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for biomass fixed bed pressurized gasification, characterized in that: The method includes: S1. Mixing woody biomass with a pretreatment agent and pretreating the mixture to obtain a first mixture; wherein the woody biomass has a lignin content of 20-35% by weight; and the pretreatment agent is selected from sodium alcoholate having 1-4 carbon atoms and / or potassium alcoholate having 1-4 carbon atoms; S2. Mixing the first mixture with high-silicon biomass and granulating the mixture to obtain a first solid product; wherein the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (2-10):1; the silicon content in the ash of the high-silicon biomass is greater than 20% by weight, and the silicon content is calculated as the content of elemental silicon; S3. Subjecting the first solid product to a fixed-bed pressurized gasification reaction to obtain synthesis gas and liquid ash.

2. The method according to claim 1, wherein The content of lignin in the woody biomass is 25-35% by weight, and the content of silicon in the ash of the high-silicon biomass is greater than 30% by weight.

3. The method according to claim 2, wherein the woody biomass is selected from one or more of cedar, eucalyptus branches, camphor branches, pine branches and poplar branches, and the high-silicon content biomass is selected from one or more of rice husks, bamboo and reeds.

4. The method according to claim 1, wherein In step S1, mixing the woody biomass with the pretreatment agent and pretreating the mixture comprises: mixing the woody biomass with the pretreatment agent at 10-50° C. for 5-60 minutes, and reacting the mixture at 50-150° C. under closed conditions for 5-60 minutes.

5. The method according to claim 1, wherein In step S1, the weight ratio of the woody biomass to the pretreatment agent is 10:(1-10); The pretreatment agent is selected from sodium alcoholate with 1-3 carbon atoms and / or potassium alcoholate with 1-3 carbon atoms.

6. The method according to claim 4, wherein: The pretreatment agent is selected from one or more of sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide.

7. The method according to claim 1, wherein In step S2, the weight ratio of silicon oxide to calcium oxide in the ash of the first solid product is (4-6):

1.

8. The method according to claim 1, wherein In step S3, the pressure of the pressurized gasification reaction is 0.1-5 MPa.

9. The method according to claim 1, wherein The method further includes step S4, cooling, crushing, shaping and high-temperature solidifying the liquid ash to obtain a calcium silicate hydrate solidified body; the calcium silicate hydrate solidified body has a flexural strength of 5-22 MPa.

10. The method according to claim 9, wherein: The molding method includes: mixing the ash obtained by crushing with water and then molding; the weight ratio of the ash obtained by crushing to the water is (2-10):

1.

11. The method according to claim 9, wherein The high-temperature curing conditions include: a temperature of 120-250° C. and a time of 1-12 hours.

12. The method according to claim 1, wherein The maximum radial compressive strength of the first solid product is 1000-2000N, and the contact angle of the first solid product is 0-120°.

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