阅读说明：本技术 一种燃烧中超细颗粒排放低的生物质燃料及制备方法 (Biomass fuel with low emission of ultrafine particles in combustion and preparation method thereof ) 是由 邵敬爱 成伟 朱有健 王贤华 杨鹏 吴贵豪 蒋好 杨海平 张世红 陈汉平 于 2019-11-29 设计创作，主要内容包括：本发明属于生物质燃料领域,并公开了一种燃烧中超细颗粒排放低的生物质燃料及制备方法。该方法包括下列步骤：(a)选取高岭土和生物质作为原料,将高岭土采用磷酸进行改性,以此获得改性的高岭土,该改性过程中,高岭土中的比表面积和活性位点增加,使得其对碱金属的吸附效率提高；(b)将改性的高岭土与生物质按照质量比(5～7)：100的比例混合,将混合后的混合物用于制备生物质燃料,以此获得所需的燃烧中超细颗粒排放低的生物质燃料。本发明相应还公开了该制备方法获得的产品。通过本发明,显著增强了高岭土反应活性,可降低超过一半的成型生物质燃烧生成的超细颗粒物,同时提高生物质成型燃料的品质。(The invention belongs to the field of biomass fuels, and discloses a biomass fuel with low emission of ultrafine particles during combustion and a preparation method thereof. The method comprises the following steps: (a) kaolin and biomass are selected as raw materials, and the kaolin is modified by phosphoric acid to obtain modified kaolin, wherein in the modification process, the specific surface area and active sites in the kaolin are increased, so that the adsorption efficiency of the kaolin to alkali metals is improved; (b) the modified kaolin and the biomass are mixed according to the mass ratio of (5-7): 100, and the mixed mixture is used for preparing the biomass fuel, so that the required biomass fuel with low emission of ultrafine particles in combustion is obtained. The invention also discloses a product obtained by the preparation method. The invention obviously enhances the reaction activity of the kaolin, can reduce more than half of ultrafine particles generated by combustion of the formed biomass, and simultaneously improves the quality of the biomass formed fuel.)

1. A method for preparing biomass fuel with low emission of ultrafine particles in combustion is characterized by comprising the following steps:

(a) selecting kaolin and biomass as raw materials, and modifying the kaolin by adopting phosphoric acid to obtain modified kaolin, wherein in the modification process, the specific surface area and active sites in the kaolin are increased, so that the adsorption efficiency of the kaolin to alkali metals is improved;

(b) mixing the modified kaolin and the biomass according to the mass ratio (5-7): 100, and the mixed mixture is used for preparing the biomass fuel, so that the required biomass fuel with low emission of ultrafine particles in combustion is obtained.

2. The method of claim 1, wherein in step (a), the kaolin is modified with phosphoric acid, preferably according to the following steps:

(a1) calcining the kaolin at the temperature of 600-800 ℃ for 5-10 h to convert the kaolin into metakaolin with higher reaction activity;

(a2) adding a phosphoric acid solution with the concentration of 6-10 mol/L into the higher territory, and uniformly mixing;

(a3) and (b) stirring the solution uniformly mixed in the step (a2) under the condition of constant-temperature water bath for reaction, and then performing centrifugal separation and drying to obtain the required modified kaolin.

3. The method for preparing biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 2, wherein in step (a2), the adding ratio of the higher territory to the phosphoric acid solution is: adding 15 ml-25 ml phosphoric acid solution into 1g metakaolin.

4. The method for preparing biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 1, wherein the temperature of the constant-temperature water bath is preferably 100 ℃ to 120 ℃ in the step (a 3).

5. The method for preparing biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 1, wherein the stirring reaction time in step (a3) is 6-10 h.

6. The method for preparing a biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 1, wherein the particle size of the modified kaolin is less than 0.2mm in step (b).

7. The method for preparing a biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 1, wherein in step (b), water is added to the mixture in an amount of 10-20% by mass of the total mass of the mixture during the preparation of the biomass fuel, and the water can be used as a pollution-free binder to ensure the stability of the biomass briquette fuel.

8. The method for preparing biomass fuel with low emission of ultrafine particles during combustion as claimed in claim 1, wherein in step (a), the biomass raw material is obtained from agricultural straw waste, the particle size of the biomass raw material is not more than 3mm, and the moisture content of the biomass raw material is less than 5% after drying treatment.

9. A biomass fuel obtained by the production method according to any one of claims 1 to 8.

Technical Field

The invention belongs to the field of biomass fuels, and particularly relates to a biomass fuel with low emission of ultrafine particles in combustion and a preparation method thereof.

Background

As a renewable energy source, the biomass has the advantages of environmental friendliness, zero emission of carbon dioxide, wide distribution, large reserve and the like, and is the fourth largest energy source next to coal, petroleum and natural gas. The annual output of Chinese agricultural wastes is about 9 hundred million tons, wherein 75.7 percent of the Chinese agricultural wastes are composed of corn, rice and wheat straws and are mainly used for fuels, feeds and papermaking raw materials. The biomass fuel has the defects of large stacking volume, low energy density, poor hydrophobicity, high transportation cost and the like, so the biomass fuel is usually processed into the biomass briquette fuel by adopting a solidification molding technology, the energy density of the biomass fuel can be greatly improved, the storage and the transportation are facilitated, and the popularization of the biomass fuel is also facilitated. The biomass can generate pollutants such as particles in the combustion process, and the pollutants are harmful to the environment and human bodies. Particles with aerodynamic diameters less than 1 micron (PM1) are generally defined as ultrafine particles, which are inhaled by people and easily enter alveoli, blood and nervous systems, and are greatly related to the occurrence of leukemia, cardiovascular diseases and lung cancer.

Research shows that the biomass has high volatile content, and particles are mainly generated in the volatile combustion stage, formed by evaporation-condensation of alkali metal compounds and mainly ultrafine particles. The electrostatic dust collection and cloth bag dust collection systems used in the existing power plants mainly collect large particle pollutants such as fly ash and bottom ash, and have low collection efficiency of ultrafine particles. In the coal burning process, kaolin is usually used as an additive in the furnace, and reacts with an alkali metal compound under a high temperature condition to form silicate or aluminosilicate, so that the generation of ultrafine particles can be effectively inhibited. The kaolin is mainly composed of silicon-aluminum oxide and bound water, is a 1:1 type dioctahedral lamellar structure and is connected by Si-O tetrahedron and Al-OH pseudo-octahedron through oxygen atoms, and has low capture efficiency on ultrafine particles due to the defects of small interlayer spacing, weak interlayer binding force and the like of the kaolin, and particularly has about 9.9 percent when being applied to biomass fuel. In addition, kaolin is an odorless and white powder, has a small particle size, is combined with water to generate an electron exchange reaction to form a gel-like mucous membrane, adsorbs cellulose in biomass to enhance intermolecular force, and can be used as a binder for preparing biomass briquette fuel.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a biomass fuel with low emission of ultrafine particles in combustion and a preparation method thereof, wherein the kaolin is modified by selecting phosphoric acid, so that the binder performance of the kaolin and the adsorption efficiency of alkali metals are improved, the modified kaolin is mixed with biomass, phosphorus ions loaded on the surface or in pores of the modified kaolin have a competitive reaction with chloride ions and sulfate ions in the biomass at high temperature to generate alkali metal phosphate with higher melting point, coarse particles are formed through a melting and coalescence process, and even part of alkali metals can be remained in fly ash or bottom ash, so that the capture efficiency of the ultrafine particles in the combustion process is greatly improved, and the ultrafine particles generated by biomass combustion are reduced.

To achieve the above objects, according to one aspect of the present invention, there is provided a method for preparing a biomass fuel having low emission of ultra fine particles during combustion, the method comprising the steps of:

(a) selecting kaolin and biomass as raw materials, and modifying the kaolin by adopting phosphoric acid to obtain modified kaolin, wherein in the modification process, the specific surface area and active sites in the kaolin are increased, so that the kaolin has better binder performance and the adsorption efficiency on alkali metals is improved;

(b) mixing the modified kaolin and the biomass according to the mass ratio (5-7): 100, the mixture is used for preparing the biomass fuel, and the modified kaolin plays the role of a binder, so that the biomass fuel with low emission of ultrafine particles in combustion is obtained.

Further preferably, in step (a), the modifying the kaolin with phosphoric acid is preferably performed according to the following steps:

(a1) calcining the kaolin at the temperature of 600-800 ℃ for 5-10 h to convert the kaolin into metakaolin with higher reaction activity;

(a2) adding a phosphoric acid solution with the concentration of 6-10 mol/L into the higher territory, and uniformly mixing;

(a3) and (b) stirring the solution uniformly mixed in the step (a2) under the condition of constant-temperature water bath for reaction, and then performing centrifugal separation and drying to obtain the required modified kaolin.

Further preferably, in the step (a2), the adding ratio of the higher territory to the phosphoric acid solution is: adding 15 ml-25 ml phosphoric acid solution into 1g metakaolin.

Further preferably, in the step (a3), the temperature of the constant-temperature water bath is preferably 100 ℃ to 120 ℃.

Further preferably, in the step (a3), the stirring reaction time is 6 to 10 hours.

Further preferably, in step (b), the particle size of the modified kaolin is less than 0.2 mm.

Further preferably, in the step (b), when the biomass fuel is prepared, water which is 10-20% of the total mass of the mixture is added into the mixture, and the water can be used as a pollution-free binder to ensure the stability of the biomass briquette fuel.

Further preferably, in the step (a), the biomass raw material is obtained from agricultural straw waste, the particle size of the biomass raw material is not more than 3mm, and the moisture content of the biomass raw material after drying treatment is lower than 5%.

According to another aspect of the invention, the biomass fuel obtained by the preparation method is provided.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. according to the invention, the kaolin is modified, and the modified kaolin adsorbs ultrafine particles through two ways: firstly, after phosphoric acid modification, partial aluminum ions are dissolved out, the free silicon dioxide is increased, active sites on the surface of kaolin are increased, chemical reaction with alkali metal vapor is easier to occur at high temperature, and alkali metals are captured by chemical adsorption, so that the alkali metals are prevented from generating ultrafine particles through evaporation-condensation process and homogeneous nucleation or heterogeneous condensation; secondly, phosphorus ions loaded on the surface or in pores of the kaolin after phosphoric acid modification have a competitive reaction with chloride ions and sulfate ions in biomass at high temperature, preferentially react with alkali metals to generate alkali metal phosphates with higher melting points, coarse particles are formed through a melting and coalescence process, even part of the alkali metals can be fixedly retained in fly ash or bottom ash, and finally the fly ash or the bottom ash is removed by an electrostatic dust removal system or a bag dust removal system;

2. compared with other modification methods, such as hydrochloric acid modification, the method for modifying kaolin provided by the invention has the advantage that the leaching process after centrifugal separation is reduced in the preparation process. The hydrochloric acid modification can bring a large amount of chloride ions, and the chloride ions can be combined with alkali metal to generate alkali metal chloride, which is an important component of the ultrafine particles, so that the chloride ions are removed through the leaching process, and a large amount of water resources are consumed in the leaching process, the research shows that at least 5L of water is consumed for leaching 10g of modified kaolin samples, phosphorus ions brought in during the phosphoric acid modification can react with the alkali metal to generate phosphate with a higher melting point, and the alkali metal phosphate can convert the ultrafine particles into large particles through the melting and coalescence processes, so that leaching is not needed, and the economy of the preparation process is improved;

3. the modified kaolin provided by the invention can be used as a binder to improve the quality of biomass briquette fuel, including improving the compressive strength and durability and reducing the molding energy consumption, wherein the improvement of the compressive strength is because the modified kaolin is combined with water to generate an electron exchange reaction to form a gel-like mucous membrane, so that the binding power among biomass particles can be effectively enhanced, and the breaking force caused by molding resilience after compression can be effectively resisted; the change of the compressive strength is consistent with that of the durability, and the improvement of the compressive strength leads the performance of the biomass briquette to be more stable and the durability to be better; the gel-like sticky membrane formed by combining part of the modified kaolin and water is extruded to the surface of the formed fuel, so that a certain lubricating effect is achieved, the friction force among biomass particles and between the raw material and the die is reduced, and the total energy consumption of the biomass formed fuel is reduced;

4. the mixed biomass briquette fuel belongs to clean renewable energy sources, the annual output of selected agricultural wastes is large, the transportation cost of the briquette fuel is low, the storage time is long, the briquette fuel is suitable for household stoves, industrial boilers, power station boilers and the like, the combustion efficiency is high, and the popularization of the biomass briquette fuel is facilitated;

5. the modified kaolin powder provided by the invention is convenient to prepare, has sufficient raw materials, and can be produced and applied on a large scale.

Drawings

FIG. 1 is a flow chart of a method of manufacture constructed in accordance with a preferred embodiment of 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. 1, a method for preparing biomass fuel with low emission of ultrafine particles during combustion comprises the following steps:

1) calcining kaolin at 600-800 ℃ for 5-10 h, and converting the kaolin into metakaolin with higher reaction activity, which is beneficial to subsequent phosphoric acid modification; the calcination temperature and the calcination time are not too high, otherwise mullite and cristobalite are formed, the modification effect is influenced, and the risk of particle sintering is avoided;

2) adding 15-25 ml of phosphoric acid solution into every 1g of kaolin, adding 6-10 mol/L of phosphoric acid solution into the calcined kaolin, stirring and reacting for 6-10 h under the condition of a constant-temperature water bath at the temperature of 100-120 ℃, performing centrifugal separation, and centrifuging to obtain phosphoric acid modified kaolin; if the adding ratio of the phosphoric acid is too low, the phosphoric acid cannot completely react with the surface active sites of the kaolin, if the adding ratio is too high, the pH value of a reaction system is too low, aluminum ions in a liquid phase are difficult to adsorb on the surface of a solid phase, and the subsequent alkali metal trapping efficiency is influenced; the concentration of phosphoric acid is not too low, otherwise, a proper acidic environment cannot be provided, but not too high, otherwise, the solid content of the reaction system is high, and the mass transfer process is not facilitated; the high-temperature water bath reaction is helpful for promoting the modification process of phosphoric acid, and the overlong reaction time can cause excessive damage of the Si-Al structure in kaolin, so that the displayed acid sites are reduced;

3) drying the phosphoric acid modified kaolin at 105 ℃, crushing and grinding the dried phosphoric acid modified kaolin, and collecting powder with the particle size of less than 0.2mm to obtain the phosphoric acid modified kaolin powder.

4) Uniformly mixing modified kaolin powder and biomass according to a certain mass ratio;

5) preparing biomass briquette fuel from the mixture of the modified kaolin powder and the biomass through a molding process;

6) the biomass briquette fuel mixed with the phosphoric acid modified kaolin is sent into a hearth for combustion, the modified kaolin, the loaded phosphoric acid and the alkali metal compound react in the hearth to form silicate, aluminosilicate and phosphate with higher melting points, large-particle fly ash and bottom ash are formed through melting and coalescence processes, and the fly ash and the bottom ash can be captured by a dust removal device.

Preferably, the preparation method of the shaped biomass added with the modified kaolin comprises the following steps:

1) uniformly mixing the biomass powder and the modified kaolin powder according to the mass ratio of 5: 100-7: 100; too low mixing ratio can cause the modified kaolin to be incapable of fully adsorbing alkali metals, while too high mixing ratio can cause the redundant kaolin to become one of the sources of coarse particles, thus affecting the overall emission reduction effect of the particles;

2) adding water which accounts for 10-20% of the total mass of the mixture into the mixed biomass in the step (1), wherein the water can be used as a pollution-free binder to ensure the stability of the biomass briquette;

3) and (3) standing the mixed biomass in the step (2) to ensure the sufficient diffusion of moisture, and then preparing the biomass briquette fuel by a forming process, wherein the suitable forming process comprises ring die compression, roll forming and the like.

4) Drying the biomass briquette fuel in the step (3) at 55-75 ℃; low-temperature drying is enough, and the economic efficiency is reduced due to the overhigh drying temperature.

The present invention will be further illustrated with reference to specific examples.