High ash melting point composite biomass fuel and method for preparing the same

Abstract

The present application relates to high ash melting point composite biomass fuel and its preparation method. The composite biomass fuel is composed of 25-35% herbaceous biomass, 55-70% woody biomass, 2-8% anthracite and 1-5% zirconium-based anti-slagging agent by weight percentage. The preparation method comprises: (1) slurry: according to the formula of zirconium-based anti-slagging agent, add 0.1% sodium carboxymethyl cellulose, 0.4% sodium tripolyphosphate and 50% water, ball mill, release slurry, and obtain anti-slagging agent slurry; mix the anti-slagging agent slurry and coal water slurry according to the ratio of 5:3, and add water to adjust the slurry concentration of the mixture to 50%; (2) spray slurry: mix the herbaceous biomass and woody biomass according to the weight percentage of 31:61, use high-pressure nozzles to uniformly spray the mixture slurry in the slurry step on the biomass at a ratio of 8%, and obtain the composite biomass material with a moisture content of 9-11%; (3) granulation: use the compression roller hot pressing forming method to granulate the composite biomass material in the spray slurry, and the forming pressure is 15-20 MPa, to obtain the high ash melting point composite biomass fuel with compact texture and smooth surface.

Description

Technical Field

[0001] This invention belongs to the field of composite biomass fuel technology, and specifically relates to a high ash melting point composite biomass fuel and its preparation method. Background Technology

[0002] Biomass energy, as the fourth largest energy source after coal, oil, and natural gas, is a clean energy source that is both environmentally friendly and renewable, and is also known as "green coal." Global energy is accelerating its evolution towards low-carbon and zero-carbon goals, and renewable energy will gradually become the main energy source supporting economic and social development.

[0003] According to relevant statistics, in 2021, the natural gas consumed by building ceramics accounted for 5% of the total natural gas consumption in China. In the ceramic brick production process, the kiln firing process has the highest energy consumption, accounting for about 60% of the total production energy consumption, followed by the raw material spray drying process, which accounts for 20% of the total energy consumption. To promote the efficient and sustainable development of the construction industry, some building ceramics companies are currently trying to use biomass fuel as a heat source for spray towers to reduce the use of non-renewable coal and natural gas. However, due to the high content of inorganic elements such as silicon, potassium, and calcium in biomass, low-melting-point alkali metal salts are easily formed during the combustion of biomass fuel in biomass furnaces. The flue gas formed during combustion carries these low-ash-melting-point alkali metal salts, which condense when they come into contact with the heating surfaces of the biomass furnace, continuously growing and accumulating to form slag. This reduces the operating cycle of the biomass furnace and also corrodes the equipment, severely reducing its service life. CN113430027B discloses a biomass fuel, which involves crushing and drying crop straw residue to obtain residue powder; mixing the residue powder with functional additives, and then processing it to obtain biomass fuel. This biomass fuel is improved by adding dolomite and nepheline minerals to reduce the biomass slagging rate. However, in practical applications, the added dolomite and nepheline easily react with calcium silicate or potassium silicate salts in the ash residue to form low-melting-point eutectic compounds, leading to unstable slagging. Summary of the Invention

[0004] The purpose of this invention is to provide a high ash melting point composite biomass fuel with good anti-slagging properties, which not only provides good protection for biomass furnace equipment and flue gas pipes, but also makes the resulting ash suitable for use in building ceramics production and its preparation method.

[0005] The technical solution of the present invention is the high ash melting point composite biomass fuel, which is characterized by being composed of the following components by weight percentage: 25-35% herbaceous biomass, 55-70% woody biomass, 2-8% anthracite, and 1-5% zirconium-based anti-slagging agent.

[0006] As a preferred embodiment, the high ash melting point composite biomass fuel is composed of the following components by weight percentage: 31% herbaceous biomass, 61% woody biomass, 5% anthracite, and 3% zirconium-based anti-slagging agent.

[0007] Preferably, the herbaceous biomass consists of herbaceous or fleshy stems with underdeveloped xylem, the above-ground parts of which are derived from the biomass material of plants that withered in the current year. Straw-type biomass is preferred, and the mixture is prepared by mixing corn straw, wheat straw, and rice straw in a ratio of 2:2:1. The industrial analysis of the mixed herbaceous biomass shows that the composition by weight percentage is as follows: moisture 0-5%, ash 3-8%, volatile matter 65-78%, and fixed carbon 14-25%. The lower heating value of the herbaceous biomass is >15000 kJ / kg, and the particle size is <1 mm.

[0008] Preferably, the woody biomass is from sturdy plants whose roots and stems have grown to form a large amount of xylem and whose cell walls are mostly lignified. Pinus family biomass is the best choice. The combination is a mixture of red pine, Scots pine, larch wood chips and scraps from furniture processing plants in a ratio of red pine: Scots pine: larch = 1:1:1. The industrial analysis of the mixed woody biomass composition by weight percentage is as follows: moisture 0-5%, ash 0-2%, volatile matter 75-83%, fixed carbon 11-20%, lower heating value >18000kJ / kg, and particle size <2mm.

[0009] As a preferred option, the anthracite has a carbon content of 95% and a lower heating value of about 23,000 kJ / kg. When used in composite biomass, the introduction of anthracite increases the unit calorific value of the biomass.

[0010] Preferably, the zircon-based anti-slagging agent is composed of the following components by weight percentage: 54% zircon sand, 5% bauxite, 25% high-alumina gangue, 15% potassium feldspar, and 1% montmorillonite.

[0011] Preferably, the high-alumina gangue is a low-iron, high-alumina gangue with an Fe2O3 content of <1% and a lower heating value of 6000–8000 kJ / kg. The chemical composition of the high-alumina gangue by weight percentage consists of the following components: SiO2 41.48%; Al2O3 33.58%; Fe2O3 0.48%; CaO 0.40%; MgO 1.34%; TiO2 0.81%; K2O 2.52%; and loss on ignition 19.39%. The zircon sand has a softening point of 1700℃ and a melting point of 2310℃. The fineness of the zircon sand, bauxite, high-alumina gangue, potassium feldspar, and montmorillonite is required to be 300-500 mesh.

[0012] Preferably, the high ash melting point composite biomass fuel pellets have a diameter of 3–6 mm and a pellet density of 0.96–1.20 g·cm³. -3 The lower heating value is >17000kJ / kg, the total moisture content is ≤8%, and the ash content is ≤5%. From its combustion thermogravimetric curve, it can be seen that the moisture drying stage is before 200℃, the main combustion stage is in the range of 200~400℃, the fixed carbon combustion stage is in the range of 400~560℃, and the burnout process of the residue is after 560℃. The ash content of the high ash melting point composite biomass fuel after combustion is >1500℃ according to the ash melting point Ts measured by GB / T219-1996.

[0013] Another technical solution of the present invention is a method for preparing the high ash melting point composite biomass fuel, characterized by comprising the following steps:

[0014] (1) Pulping:

[0015] (1.1) The formula of zircon anti-slagging agent by weight percentage is as follows: 54% zircon sand, 5% bauxite, 25% high alumina gangue, 15% potassium feldspar, and 1% montmorillonite are added, along with 0.1% sodium carboxymethyl cellulose, 0.4% sodium tripolyphosphate, and 50% water by weight. The mixture is ball-milled for 30 minutes until the material is uniform. After the slurry in the ball mill stabilizes, the slurry is discharged to obtain the anti-slagging agent slurry for later use.

[0016] (1.2) The anthracite is made into a coal-water slurry with a concentration of 55% and the content of the coal-water slurry after passing through a 200-mesh sieve is >90%;

[0017] (1.3) Mix the anti-slagging agent slurry with coal-water slurry at a ratio of 5:3, and add water to adjust the slurry concentration to 50%.

[0018] (2) Spraying: Herbaceous biomass and woody biomass are mixed in a weight ratio of 31:61. During the mixing process, the mixed slurry obtained in the pulping step is evenly sprayed onto the biomass at a ratio of 8% using a high-pressure nozzle. The resulting composite biomass has a moisture content of 9-11%, which meets the requirements for biomass granulation.

[0019] (3) Granulation: The composite biomass material obtained in the spraying step is granulated by a roller hot pressing molding method with a molding pressure of 15-20 MPa to obtain a high ash melting point composite biomass fuel with a dense texture and smooth surface.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The composite biomass fuel prepared by this invention generates high ash melting point ash when burned in a biomass furnace. It has good anti-slagging properties during high-temperature burning, avoids slagging on the inner wall of the combustion furnace, prevents corrosion of the flue gas pipe, and extends the operating cycle and service life of the biomass furnace.

[0022] (2) The anthracite contained in the composite biomass fuel of this invention has a high calorific value, a short flame and little smoke when burning, is not easy to coke, and has no thick plastic layer, which greatly improves the unit calorific value of the composite biomass fuel. The zirconium-based anti-slagging agent used contains low-iron and high-alumina gangue, which has a certain calorific value and high ash content. Its ash is mainly composed of alumina and silicon dioxide, and has a high ash melting point.

[0023] (3) The composite biomass fuel of the present invention has good combustibility and can achieve good combustion efficiency at a combustion temperature of 700-850℃. Its ash is mainly composed of zirconium oxide and alumina, which has a high ash melting point. The ash in the furnace / biomass furnace combustion pipe is not easy to stick and has good anti-slagging performance.

[0024] (4) The zirconium-based ash from the combustion of biomass fuel of the present invention can be used as the main raw material for ceramic blanks and glazes. It can be applied in high-volume production of building ceramics, which broadens the application field of traditional biomass ash and slag, completes the recycling of inorganic elements in biomass, and achieves zero waste discharge. Attached Figure Description

[0025] Figure 1 This is the TG curve of the high ash melting point composite biomass fuel combustion of the present invention;

[0026] Figure 2 This is the DTG curve of the high ash melting point composite biomass fuel combustion of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments:

[0028] This high ash melting point composite biomass fuel is composed of the following components by weight percentage: 31% herbaceous biomass, 61% woody biomass, 5% anthracite, and 3% zirconium-based anti-slagging agent.

[0029] The herbaceous biomass is composed of herbaceous or fleshy stems with underdeveloped xylem, the above-ground parts of which are biomass materials from plants that withered that year, with straw being the best choice. The combination is made up of corn straw: wheat straw: rice straw in a ratio of 2:2:1. The industrial analysis of the mixed herbaceous biomass shows that, by weight percentage, it consists of the following components: moisture 4.5%, ash 7.8%, volatile matter 71.5%, and fixed carbon 16.2%. The lower heating value of the herbaceous biomass is 17850 kJ / kg, and the particle size is <1 mm.

[0030] The woody biomass refers to sturdy plants whose roots and stems have grown to form a large amount of xylem and whose cell walls are mostly lignified. Pinus family biomass is the best choice. The combination is a mixture of red pine, Scots pine, larch wood chips and scraps from furniture processing plants in a ratio of red pine: Scots pine: larch = 1:1:1. The industrial analysis of the mixed woody biomass composition, by weight percentage, consists of the following components: moisture 4.8%, ash 0.4%, volatile matter 79.6%, fixed carbon 15.2%, lower heating value 19484 kJ / kg, and particle size <2 mm.

[0031] The anthracite has a carbon content of 95% and a lower heating value of about 23,000 kJ / kg. It is used in composite biomass to increase the unit calorific value of biomass.

[0032] The zircon-based anti-slagging agent is composed of the following components by weight percentage: 54% zircon sand, 5% bauxite, 25% high-alumina gangue, 15% potassium feldspar, and 1% montmorillonite.

[0033] The high-alumina gangue is a low-iron, high-alumina gangue with an Fe2O3 content of 0.48% and a lower heating value of 7850 kJ / kg. Its chemical composition by weight percentage consists of the following components: SiO2 41.48%; Al2O3 33.58%; Fe2O3 0.48%; CaO 0.40%; MgO 1.34%; TiO2 0.81%; K2O 2.52%; and a loss on ignition of 19.39%. The zircon sand has a softening point of 1700℃ and a melting point of 2310℃. The fineness of the zircon sand, bauxite, high-alumina gangue, potassium feldspar, and montmorillonite is required to be 300-500 mesh.

[0034] A method for preparing high ash melting point composite biomass fuel includes the following steps:

[0035] (1) Pulping:

[0036] (1.1) The formula of zircon anti-slagging agent by weight percentage is as follows: 54% zircon sand, 5% bauxite, 25% high alumina gangue, 15% potassium feldspar, and 1% montmorillonite are added, along with 0.1% sodium carboxymethyl cellulose, 0.4% sodium tripolyphosphate, and 50% water by weight. The mixture is ball-milled for 30 minutes until the material is uniform. After the slurry in the ball mill stabilizes, the slurry is discharged to obtain the anti-slagging agent slurry for later use.

[0037] (1.2) The anthracite is made into a coal-water slurry with a concentration of 55% and the content of the coal-water slurry after passing through a 200-mesh sieve is >90%;

[0038] (1.3) Mix the anti-slagging agent slurry with coal-water slurry at a ratio of 5:3, and add water to adjust the slurry concentration to 50%.

[0039] (2) Spraying: Herbaceous biomass and woody biomass are mixed in a weight ratio of 31:61. During the mixing process, the mixed slurry obtained in the pulping step is evenly sprayed onto the biomass at a ratio of 8% using a high-pressure nozzle. The resulting composite biomass has a moisture content of 10.5%, which meets the requirements for biomass granulation.

[0040] (3) Granulation: The composite biomass material obtained in the spraying step is granulated by roller hot pressing with a molding pressure of 15-17 MPa to obtain a high ash melting point composite biomass fuel with a dense texture and smooth surface.

[0041] The resulting high ash melting point composite biomass fuel pellets had a diameter of 4–5 mm and a pellet density of 1.12 g·cm³. -3 The lower heating value is 18783 kJ / kg, the total moisture content is 5.23%, and the ash content is 4.58%. Its combustion thermogravimetric curve shows that the moisture drying stage is before 200℃, the main combustion stage is in the range of 200-400℃, the fixed carbon combustion stage is in the range of 400-560℃, and the burnout process of the residue is after 560℃. The ash content of the high ash melting point composite biomass fuel after combustion is 1580℃ according to the ash melting point Ts measured by GB / T219-1996.

[0042] Please see Figure 1 , Figure 2 As shown, the biomass combustion process is divided into four stages: moisture drying, volatile matter release and combustion, fixed carbon combustion, and residue burnout. Figure 1 , Figure 2 The thermogravimetric curves (TG) of biomass combustion show that the drying stage of the high ash melting point composite biomass fuel of this invention is from room temperature to about 200°C. During this stage, the TG curve changes gradually, and the weight loss of the sample is mainly due to the evaporation of free water and bound water. The DTG curve also shows a small weight loss peak at about 100°C. In the TG curve, the weight loss of the high ash melting point composite biomass fuel in the 200-400°C range accounts for 50%-70% of the total weight loss, which is the main combustion stage. The DTG curve also shows a shouldered single peak in this stage. The 400-560°C range can be identified as the fixed carbon combustion stage. In this range, the products of the previous stage are further devolatilized and carbonized, releasing gaseous products such as CH4, CO2, and CO. The gas phase combustion reaction is gradually completed, and the solid phase combustion process begins. At this time, oxygen enters the interior of the material through the porous structure, leading to the combustion of fixed carbon. Finally, the burnout process of the residue is not obvious in the TG curve due to the slow reaction rate.

[0043] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. A high ash melting point composite biomass fuel, characterized in that, The compound biomass is composed of the following components by weight percentage: 25-35% herbaceous biomass, 55-70% woody biomass, 2-8% anthracite, and 1-5% zirconium-based anti-slagging agent. The anthracite contains 95% carbon and has a lower heating value of 23,000 kJ / kg. It is used in composite biomass to increase the unit calorific value of the biomass. The zirconium-based anti-slagging agent is composed of the following components by weight percentage: 54% zircon sand, 5% bauxite, 25% high-alumina gangue, 15% potassium feldspar, and 1% montmorillonite. The high-alumina gangue is low-iron, high-alumina gangue with an Fe2O3 content of <1%. The lower heating value is 6000-8000 kJ / kg. The chemical composition of the high-alumina gangue is as follows by weight percentage: SiO2 41.48%; Al2O3 33.58%; Fe2O3 0.48%; CaO 0.40%; MgO 1.34%; TiO2 0.81%; K2O 2.52%; loss on ignition 19.39%; the softening point of the zircon sand is 1700℃ and the melting point is 2310℃; the fineness of the zircon sand, bauxite, high-alumina gangue, potassium feldspar, and montmorillonite is required to be 300-500 mesh.

2. The high ash melting point composite biomass fuel according to claim 1, characterized in that, It is composed of the following components by weight percentage: 31% herbaceous biomass, 61% woody biomass, 5% anthracite, and 3% zirconium-based anti-slagging agent.

3. The high ash melting point composite biomass fuel according to claim 1 or 2, characterized in that, The herbaceous biomass refers to herbaceous or fleshy stems with underdeveloped xylem, the above-ground parts of which are derived from the biomass material of plants that withered in the current year.

4. The high ash melting point composite biomass fuel according to claim 3, characterized in that, The herbal biomass is selected from straw-based biomass, and is mixed in a ratio of corn straw: wheat straw: rice straw = 2:2:

1. The industrial analysis of the mixed herbal biomass consists of the following components by weight percentage: moisture 0-5%, ash 3-8%, volatile matter 65-78%, and fixed carbon 14-25%; the lower heating value of the herbal biomass is >15000kJ / kg, and the particle size is <1mm.

5. The high ash melting point composite biomass fuel according to claim 1 or 2, characterized in that, The woody biomass refers to sturdy plants whose roots and stems have grown to form a large amount of xylem and whose cell walls are mostly lignified.

6. The high ash melting point composite biomass fuel according to claim 5, characterized in that, The woody biomass is selected from pine family biomass, and the mixture consists of red pine, Scots pine, larch, and wood chips and scraps from furniture processing plants in a ratio of red pine: Scots pine: larch = 1:1:

1. The industrial analysis of the mixed woody biomass composition by weight percentage consists of the following components: moisture 0-5%, ash 0-2%, volatile matter 75-83%, fixed carbon 11-20%, lower heating value >18000kJ / kg, and particle size <2mm.

7. The high ash melting point composite biomass fuel according to claim 1 or 2, characterized in that, The high ash melting point composite biomass fuel pellets have a diameter of 3–6 mm and a particle density of 0.96–1.20 g·cm³. -3 The lower heating value is >17000kJ / kg, the total moisture content is ≤8%, and the ash content is ≤5%. From its combustion thermogravimetric curve, it can be seen that the moisture drying stage is before 200℃, the main combustion stage is in the range of 200~400℃, the fixed carbon combustion stage is in the range of 400~560℃, and the burnout process of the residue is after 560℃. The ash content of the high ash melting point composite biomass fuel after combustion is >1500℃ according to the ash melting point Ts measured by GB / T219-1996.

8. A method for preparing a high ash melting point composite biomass fuel according to claim 1, characterized in that, Includes the following steps: (1) Pulping: (1.1) The formula of zircon anti-slagging agent by weight percentage is: 54% zircon sand, 5% bauxite, 25% high alumina gangue, 15% potassium feldspar, and 1% montmorillonite. In addition, add 0.1% sodium carboxymethyl cellulose, 0.4% sodium tripolyphosphate, and 50% water by weight. Ball mill the mixture for 30 minutes until the material is uniform. After the slurry in the ball mill stabilizes, discharge the slurry to obtain the anti-caking agent slurry for later use. (1.2) The anthracite is made into a coal-water slurry with a concentration of 55%. The content of the coal-water slurry after passing through a 200-mesh sieve is >90%. (1.3) Mix the anti-slagging agent slurry with coal-water slurry at a ratio of 5:3, and add water to adjust the slurry concentration to 50%; (2) Spraying: Herbaceous biomass and woody biomass are mixed in a weight percentage ratio of 31:

61. During the mixing process, the mixed slurry obtained in the pulping step is evenly sprayed onto the biomass at a ratio of 8% using a high-pressure nozzle. The resulting composite biomass material has a moisture content of 9-11%, which meets the requirements for biomass granulation. (3) Granulation: The composite biomass material obtained in the spraying step is granulated by a roller hot pressing molding method with a molding pressure of 15-20 MPa to obtain a high ash melting point composite biomass fuel with a dense texture and smooth surface.

9. The method for preparing high ash melting point composite biomass fuel according to claim 8, characterized in that, The resulting high ash melting point composite biomass fuel pellets had a diameter of 4–5 mm and a pellet density of 1.12 g·cm³. -3 The lower heating value is 18783 kJ / kg, the total moisture content is 5.23%, and the ash content is 4.58%. Its combustion thermogravimetric curve shows that the moisture drying stage is before 200℃, the main combustion stage is in the range of 200-400℃, the fixed carbon combustion stage is in the range of 400-560℃, and the burnout process of the residue is after 560℃. The ash content of the high ash melting point composite biomass fuel after combustion is 1580℃ according to the ash melting point Ts measured by GB / T219-1996.

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