Biomass pellet fuel and preparation method thereof

Abstract

The invention relates to the technical field of fuels, and provides a biomass pellet fuel and a preparation method thereof. The biomass pellet fuel comprises the following materials in parts by weight: 40-50 parts of wood chips, 20-25 parts of rice husks, 6-8 parts of a modified starch binder, 3-4 parts of a waste paper pulp sludge binder, 2-3 parts of calcium carbonate and 30-34 parts of water. According to the biomass pellet fuel and the preparation method thereof provided by the invention, secondary pollution hazards such as waste gas are reduced, the stability of the bonding effect of various raw materials is ensured, and the combustion performance of the pellet fuel is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel, in particular to a kind of biomass pellet fuel and preparation method thereof. BACKGROUND

[0002] As a renewable carbon source, biomass energy has the advantages of abundant resources, wide distribution, clean and environmental protection, etc., and is considered as an important part of future energy structure. Biomass pellet fuel, as an important form of biomass energy, is receiving more and more attention. Biomass pellet fuel has high combustion efficiency, its density is large, the contact area with air is relatively small, the combustion process is more complete, and more heat can be released. Secondly, the pollution emission is low, the content of sulfur and nitrogen in biomass is low, and the pollutants such as sulfur dioxide and nitrogen oxides produced during combustion are much lower than coal. Thirdly, biomass pellet fuel is easy to store and transport, its shape is regular and its volume is small, which can effectively reduce the storage and transportation cost. Therefore, biomass pellet fuel has broad application prospects in industrial boilers, civilian heating and other fields, and has important significance for relieving energy pressure and improving environmental quality.

[0003] Some traditional binders may cause certain pollution to the environment during production and use. For example, asphalt is a petrochemical product, and a large amount of waste gas, wastewater and waste residue will be generated during its production, causing serious pollution to the environment. Moreover, harmful substances in asphalt may be released during the combustion of biomass pellet fuel, causing secondary pollution and harm to human health and the environment. In addition, existing binders often have difficulty in ensuring the stability of the binding effect when binding different biomass raw materials. For example, some binders work well when binding wood fiber raw materials, but when binding straw raw materials, the binder is difficult to adhere due to the smooth surface and high wax content of the straw, resulting in poor binding effect, easy breaking of the pellet fuel, and affecting its combustion performance and storage stability. Based on this, the present application provides a kind of biomass pellet fuel and preparation method thereof. SUMMARY

[0004] The present application provides a kind of biomass pellet fuel and preparation method thereof, which reduces the secondary pollution hazards such as waste gas, ensures the stability of the binding effect of various raw materials, and improves the combustion performance of pellet fuel.

[0005] The technical scheme of the present application is as follows: In a first aspect, the present application provides a kind of biomass pellet fuel, which comprises the following materials by weight: sawdust 40-50 parts, rice husk 20-25 parts, modified starch binder 6-8 parts, waste paper pulp sludge binder 3-4 parts, calcium carbonate 2-3 parts, and water 30-34 parts.

[0006] As a further technical solution, the preparation method of the modified starch binder comprises: mixing corn starch and water to obtain a suspension, adding alpha-amylase and reacting at 60-70 DEG C for 30-40 min, adding hydrogen peroxide, adjusting the pH to 10.5±0.1, and reacting at 50-60 DEG C for 90-100 min, adjusting the pH to 6.5-7.0 to terminate the reaction, and spray drying at 80-85 DEG C to obtain a powder with a water content of ≤8% to obtain the modified starch binder.

[0007] In the present application, the modified starch binder is prepared by a specific preparation process, corn starch is treated by alpha-amylase and hydrogen peroxide, the molecular structure of the starch is changed, and the modified starch binder has good film forming property. In the preparation process of biomass pellet fuel, the modified starch can form a uniform and dense film on the surface of the pellet, enhance the bonding force between the pellets, and improve the compactness of the pellets.

[0008] As a further technical solution, the mass concentration of hydrogen peroxide is 30%; the corn starch, water, alpha-amylase, and hydrogen peroxide are used in a ratio of 100g:300-340g:0.1-0.2g:1.5-2mL.

[0009] As a further technical solution, the corn starch has a water content of ≤12%, and is passed through a 100 mesh sieve.

[0010] As a further technical solution, the alpha-amylase has an enzyme activity of ≥5000U / g.

[0011] As a further technical solution, the preparation method of the waste paper pulp sludge binder comprises: mixing paper mill wastewater sludge with a solid content of ≥20% and magnesium oxide, stirring at 200-240 rpm and 40-50 DEG C for 50-60 min, adding calcium lignosulfonate and stirring at 2500-3000 rpm for 15-20 min, and homogenizing at 20-22 MPa and 40-45 DEG C for at least 3 times until D90≤40μm to obtain the waste paper pulp sludge binder.

[0012] In the present application, the waste paper pulp sludge binder is prepared by mixing paper mill wastewater sludge with magnesium oxide and calcium lignosulfonate. Magnesium oxide plays a role in sulfur fixation in the subsequent combustion process, and calcium lignosulfonate is uniformly dispersed in the sludge system after specific stirring and homogenization treatment.

[0013] The magnesium oxide in the waste paper pulp sludge binder in the application plays an indirect sulfur fixation role. In the early stage of combustion, the magnesium oxide can react with part of the sulfur elements in the fuel to generate magnesium sulfide and other compounds; at the same time, the magnesium oxide can also act as a catalyst to promote the oxidation reaction of other sulfur-containing substances in the fuel, so that they are more easily captured and fixed by calcium carbonate. In addition, the calcium lignosulfonate plays a coating role in the sludge-magnesium oxide system, which can uniformly coat the magnesium oxide and other components in the sludge, so that the magnesium oxide can more fully play a role in sulfur fixation in the combustion process, and at the same time, it can also improve the combustion performance of the sludge and reduce the generation of ash. The direct sulfur fixation of calcium carbonate and the indirect sulfur fixation of magnesium oxide cooperate with each other to form an efficient sulfur fixation system, which effectively reduces the emission of SO2 in the combustion process of biomass pellet fuel, and realizes the unity of environmental protection and efficient combustion.

[0014] As a further technical solution, the use amount ratio of the waste water sludge, magnesium oxide and calcium lignosulfonate is 100:3-5:1-2.

[0015] As a further technical solution, the sawdust is wood processing waste, including at least one of pine sawdust, fir sawdust, poplar sawdust and fruit wood sawdust.

[0016] As a further technical solution, the rice husk is treated by 5%-10% NaOH aqueous solution at 70-80 DEG C for 30-40 min, washed to neutral, dried and crushed to 1-3 mm.

[0017] The rice husk in the raw material is subjected to special alkali treatment in the application. The rice husk originally contains a large amount of silicon dioxide and waxes, which will hinder the combustion process, cause incomplete combustion, increase ash residue and reduce fuel quality. Through pretreatment, chemical reaction with the silicon dioxide and waxes on the surface of the rice husk can be carried out to destroy their structure and make them fall off from the surface of the rice husk. Subsequently, through the steps of washing to neutral, drying and crushing, the treated rice husk is obtained. After alkali treatment, the content of silicon dioxide and waxes on the surface of the rice husk is greatly reduced, the hindering factors during combustion are reduced, and the rice husk can more fully participate in the combustion reaction. This not only reduces the ash content after combustion, but also improves the combustion efficiency of the fuel, so that the biomass pellet fuel can release more energy during the combustion process, thereby ensuring the high calorific value of the fuel, which is a key pretreatment step for controlling the quality of biomass pellet fuel.

[0018] In a second aspect, the present application provides a method for preparing biomass pellet fuel, comprising the following steps: weighing raw materials according to a formula, crushing sawdust to ≤2mm particles, and pyrolyzing the sawdust at 280-300°C under oxygen deficiency for 10-15min; increasing the fixed carbon content to ≥35% to obtain pre-carbonized sawdust; mixing the pre-carbonized sawdust with rice husk and calcium carbonate at 200-250rpm for 5-7min to obtain a mixture; adding a modified starch binder configured into an aqueous solution and a waste paper pulp sludge binder to the mixture, and mixing the mixture at 50-60°C and 100-150rpm for 13-15min to obtain the biomass pellet fuel.

[0019] In the pre-carbonization process, the volatile components in the sawdust gradually separate out under certain temperature and atmosphere conditions, and the fixed carbon is relatively enriched. After the pre-carbonization treatment, the fixed carbon content of the sawdust can be increased by about 35%. The fixed carbon is the main component that can provide heat in the fuel, and the increase in the content means that the fuel can release more heat during the combustion process.

[0020] The working principle and beneficial effects of the present application are as follows: The biomass pellet fuel of the present application constructs a unique synergistic binding system, in which the modified starch binder and the waste paper pulp sludge binder jointly act. When used together with the modified starch binder, the two complement each other and are indispensable. The film-forming property of the modified starch provides basic structural support and binding strength for the pellets, while the effective components in the waste paper pulp sludge binder fill the inside and surface of the pellets, further enhancing the binding effect and providing a material basis for subsequent environmental protection functions such as sulfur fixation. This synergistic effect enables the biomass pellet fuel to effectively control pollutant emissions during the combustion process while ensuring the stability of the binding effect.

[0021] The biomass pellet fuel of the present application adopts a double sulfur fixation mechanism, in which calcium carbonate and magnesium oxide in the waste paper pulp sludge binder jointly achieve low SO2 emission. As a common sulfur fixation agent, calcium carbonate can chemically react with sulfur elements in the fuel during the combustion process to generate stable compounds such as calcium sulfate, thereby fixing sulfur in the ash and reducing SO2 emission.

[0022] In the present application, sawdust is one of the important raw materials for biomass pellet fuel. The present application increases the fixed carbon content of the sawdust through a pre-carbonization process. Mixing the pre-carbonized sawdust with other raw materials in a certain proportion to prepare biomass pellet fuel can effectively increase the overall calorific value of the fuel, maintain the calorific value of the biomass pellet fuel at a high level (>18.5MJ / kg), meet the market demand for high-efficiency biomass fuel, and is the core process for ensuring the high calorific value of biomass pellet fuel. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work, are within the scope of protection of the present application.

[0024] Embodiment 1 The biomass pellet fuel provided in the embodiment includes the following materials by weight: pine sawdust 45 parts, rice husk 22 parts, modified starch binder 7 parts, waste paper pulp sludge binder 3.5 parts, calcium carbonate 2.5 parts, and water 32 parts. The rice husk needs to be pretreated, and the steps include: the rice husk is treated with a 7% NaOH aqueous solution at 75℃ for 35 min, washed with water until neutral, dried, and then crushed to 2 mm; The preparation method of the modified starch binder includes: 100 g of corn starch with a water content of 12% is sieved through a 100-mesh sieve and mixed with 320 g of water to obtain a suspension, 0.15 g of α-amylase with an enzyme activity of 5000 U / g is added and reacted at 65℃ for 35 min, 1.8 mL of hydrogen peroxide with a mass concentration of 30% is added, the pH is adjusted to 10.5 by using 10 wt% sodium hydroxide aqueous solution, and the reaction is carried out at 55℃ for 95 min, the pH is adjusted to 6.8 by using 10 wt% dilute sulfuric acid aqueous solution to terminate the reaction, and 82℃ is used for spray drying to obtain a powder with a water content of 8%, thereby obtaining the modified starch binder. The preparation method of the waste paper pulp sludge binder includes: 100 g of paper mill wastewater sludge with a solid content of 20% and 4 g of magnesium oxide are mixed, stirred at 220 rpm and 45℃ for 55 min, 1.5 g of calcium lignosulfonate is added and stirred at 2700 rpm for 18 min, and then homogenized at 21 MPa and 42℃ for 3 times until the D90 is 40 μm, thereby obtaining the waste paper pulp sludge binder. The preparation method of the biomass pellet fuel includes the following steps: the raw materials are weighed according to the formula, the sawdust is crushed to 2 mm particles, and pyrolysis is carried out at 290℃ under anaerobic conditions for 12 min; the fixed carbon content is increased to 35% to obtain pre-carbonized sawdust; the rice husk and calcium carbonate are mixed in the mixture at 220 rpm for 6 min to obtain a mixture; the modified starch binder is configured into an aqueous solution and added to the mixture with the waste paper pulp sludge binder, and then mixed at 55℃ and 120 rpm for 14 min, and then discharged, thereby obtaining the biomass pellet fuel.

[0025] Embodiment 2 The biomass pellet fuel provided in the embodiment includes the following materials by weight: pine sawdust 45 parts, rice husk 22 parts, modified starch binder 7 parts, waste paper pulp sludge binder 3.5 parts, calcium carbonate 2.5 parts, and water 32 parts. The rice husk needs to be pretreated, and the steps include: the rice husk is treated with a 5% NaOH aqueous solution at 70°C for 30 min, washed with water to neutral, dried, and then crushed to 1 mm; The preparation method of the modified starch binder includes: 100 g of corn starch with a water content of 12% is mixed with 300 g of water after being sieved through a 100-mesh sieve to obtain a suspension, 0.1 g of α-amylase with an enzyme activity of 5000 U / g is added and reacted at 60°C for 30 min, 1.5 mL of hydrogen peroxide with a mass concentration of 30% is added, 10 wt% sodium hydroxide aqueous solution is used to adjust the pH to 10.5, and reaction is carried out at 50°C for 90 min, 10 wt% dilute sulfuric acid aqueous solution is used to adjust the pH to 6.5 to terminate the reaction, and spray drying is carried out at 80°C to obtain a powder with a water content of 8%, thereby obtaining the modified starch binder; The preparation method of the waste paper pulp sludge binder includes: 100 g of paper mill wastewater sludge with a solid content of 20% is mixed with 3 g of magnesium oxide, stirred at 200 rpm and 40°C for 50 min, 1 g of calcium lignosulfonate is added and stirred at 2500 rpm for 15 min, and homogenization treatment is carried out at 20 MPa and 40°C for three times until the D90 is 40 μm, thereby obtaining the waste paper pulp sludge binder; The preparation method of the biomass pellet fuel includes: the raw materials are weighed according to the formula, the sawdust is crushed to 2 mm particles, and pyrolysis is carried out at 280°C under anoxic conditions for 10 min; the fixed carbon content is increased to 35% to obtain pre-carbonized sawdust; the pre-carbonized sawdust is mixed with the rice husk and calcium carbonate at 200 rpm for 5 min to obtain a mixture; the modified starch binder is configured into an aqueous solution, and the waste paper pulp sludge binder is added into the mixture, and the mixture is mixed at 50°C and 100 rpm for 13 min, and then the mixture is discharged, thereby obtaining the biomass pellet fuel.

[0026] Example 3 The biomass pellet fuel provided in this example includes the following materials in parts by weight: 50 parts of pine sawdust, 25 parts of rice husk, 8 parts of modified starch binder, 4 parts of waste paper pulp sludge binder, 3 parts of calcium carbonate, and 34 parts of water; The rice husk needs to be pretreated, and the steps include: the rice husk is treated with a 10% NaOH aqueous solution at 80°C for 40 min, washed with water to neutral, dried, and then crushed to 3 mm; The preparation method of the modified starch binder includes: 100 g of corn starch with a water content of 12% is mixed with 340 g of water after being sieved through a 100-mesh sieve to obtain a suspension, 0.2 g of α-amylase with an enzyme activity of 5000 U / g is added and reacted at 70°C for 40 min, 2 mL of hydrogen peroxide with a mass concentration of 30% is added, 10 wt% sodium hydroxide aqueous solution is used to adjust the pH to 10.5, and reaction is carried out at 60°C for 100 min, 10 wt% dilute sulfuric acid aqueous solution is used to adjust the pH to 7.0 to terminate the reaction, and spray drying is carried out at 85°C to obtain a powder with a water content of 8%, thereby obtaining the modified starch binder; The preparation method of the waste paper pulp sludge binder comprises the following steps: 100 g of paper mill wastewater sludge with a solid content of ≥20% and 5 g of magnesium oxide are mixed, stirring is performed at 240 rpm and 50°C for 60 min, 2 g of calcium lignosulfonate is added, stirring is performed at 3000 rpm for 20 min, and homogenization treatment is performed 4 times at 22 MPa and 45°C until the D90 is 40 μm. The preparation method of the biomass pellet fuel comprises the following steps: raw materials are weighed according to a formula, sawdust is crushed to 2 mm particles, and pyrolysis is performed at 300°C under anoxic conditions for 15 min; the fixed carbon content is increased to 35% to obtain pre-carbonized sawdust; the pre-carbonized sawdust is mixed with rice husks and calcium carbonate at 250 rpm for 7 min to obtain a mixture; the modified starch binder is configured into an aqueous solution, and the aqueous solution and the waste paper pulp sludge binder are added into the mixture; and the mixture is mixed at 60°C and 150 rpm for 15 min, and then the mixture is discharged to obtain the biomass pellet fuel.

[0027] Example 4 In example 4, the rice husks are not pretreated; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0028] Comparative Example 1 In comparative example 1, the modified starch binder is replaced by corn starch of the same mass, and the corn starch is not modified; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0029] Comparative Example 2 In comparative example 2, the modified starch binder is replaced by waste paper pulp sludge binder of the same mass; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0030] Comparative Example 3 In comparative example 3, the waste paper pulp sludge binder is replaced by calcium lignosulfonate of the same mass, and the calcium lignosulfonate is not coated with an oxide; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0031] Comparative Example 4 In comparative example 4, the waste paper pulp sludge binder is replaced by modified starch binder of the same mass; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0032] Comparative Example 5 In comparative example 5, calcium carbonate is not added; the rest is the same as in example 1, and the preparation steps are the same as in example 1.

[0033] Test Example 1: The biomass pellet fuels prepared in the foregoing examples 1-4 and comparative examples 1-5 are tested as follows: Calorific value: tested in accordance with the standard GB / T 30727-2014; high calorific value (HHV) is measured by an oxygen bomb calorimeter; Ash content: tested in accordance with the standard GB / T 28731-2012; a muffle furnace calcination method is used at 815°C for 2 h; Pollutant emission test: the flue gas analyzer (Testo 350) was used to monitor the CO emission concentration (ppm), NO x emission concentration (ppm), SO2 emission concentration (ppm) in the combustion tail gas online.

[0034] The results are shown in Table 1 as follows: Table 1

[0035] In combination with the foregoing, the present application realizes low sulfur dioxide emission by the synergistic bonding system of modified starch and sludge binder, rice husk alkali treatment, and the sulfur fixation mechanism of calcium carbonate and magnesium oxide, while realizing high calorific value of fuel.

[0036] The calorific value of Comparative Example 1 decreased, the ash content increased, and the CO emission increased. The unmodified starch had poor bonding properties, resulting in low particle density, incomplete combustion, and increased ash residue. The ash content of Comparative Example 2 increased, and the SO2 emission increased. The lack of film-forming effect of modified starch resulted in increased pollutant release due to high sludge ash content and insufficient coating of sulfur-containing impurities. The SO2 emission of Comparative Example 3 increased, and the ash content increased. The calcium lignosulfonate not coated with sludge-magnesium oxide had weak sulfur fixation capacity, and the uneven dispersion of impurities increased the ash content. The calorific value of Comparative Example 4 decreased, and the SO2 emission increased. The lack of magnesium oxide sulfur fixation component in the sludge binder, and the low calorific value of excessive starch. The ash content of Example 4 increased, and the calorific value decreased. The unalkali-treated rice husk contained a large amount of silicon dioxide and waxes, which hindered combustion and significantly increased ash residue. The SO2 emission of Comparative Example 5 increased, and the other indicators were close to the implementation. The lack of calcium carbonate resulted in the loss of sulfur fixation capacity, confirming its core role as a sulfur fixation agent.

[0037] The above is only a preferred embodiment of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A biomass pellet fuel, characterized in that, The following materials are included by weight: 40-50 parts sawdust, 20-25 parts rice husks, 6-8 parts modified starch binder, 3-4 parts waste paper pulp sludge binder, 2-3 parts calcium carbonate, and 30-34 parts water.

2. The biomass pellet fuel according to claim 1, characterized in that, The preparation method of the modified starch binder includes: mixing corn starch and water to obtain a suspension, adding α-amylase and reacting at 60-70℃ for 30-40 min, adding hydrogen peroxide and adjusting the pH to 10.5±0.1, reacting at 50-60℃ for 90-100 min, adjusting the pH to 6.5-7.0 to terminate the reaction, and spray drying at 80-85℃ to obtain a powder with a moisture content ≤8%.

3. The biomass pellet fuel according to claim 2, characterized in that, The mass concentration of the hydrogen peroxide is 30%; the ratio of corn starch, water, α-amylase, and hydrogen peroxide is 100g:300-340g:0.1-0.2g:1.5-2mL.

4. The biomass pellet fuel according to claim 2, characterized in that, The corn starch has a moisture content of ≤12% and passes through a 100-mesh sieve.

5. A biomass pellet fuel according to claim 2, characterized in that, The α-amylase activity is ≥5000 U / g.

6. The biomass pellet fuel according to claim 1, characterized in that, The preparation method of the waste pulp sludge binder includes: mixing paper mill wastewater sludge with a solid content ≥20% and magnesium oxide, stirring at 200-240 rpm and 40-50℃ for 50-60 min, adding calcium lignosulfonate and stirring at 2500-3000 rpm for 15-20 min, and homogenizing at 20-22 MPa and 40-45℃ at least 3 times until D90≤40μm is obtained.

7. A biomass pellet fuel according to claim 6, characterized in that, The ratio of wastewater sludge, magnesium oxide, and calcium lignosulfonate is 100:3-5:1-2.

8. The biomass pellet fuel according to claim 1, characterized in that, The wood chips are wood processing waste, including at least one of pine wood chips, fir wood chips, poplar wood chips, and fruit wood chips.

9. A biomass pellet fuel according to claim 1, characterized in that, The rice husks are treated with a 5%-10% NaOH aqueous solution at 70-80℃ for 30-40 minutes, washed with water until neutral, dried, and then pulverized to 1-3 mm.

10. A method for preparing biomass pellet fuel as described in any one of claims 1-9, characterized in that, step include: Weigh the raw materials according to the formula, crush the wood chips to ≤2mm particles, and pyrolyze them at 280-300℃ in anoxic conditions for 10-15 minutes; increase the fixed carbon content to ≥35% to obtain pre-carbonized wood chips; mix them with rice husks and calcium carbonate at 200-250rpm for 5-7 minutes to obtain a mixture; prepare the modified starch binder into an aqueous solution and add it to the mixture along with the waste pulp sludge binder; mix at 50-60℃ and 100-150rpm for 13-15 minutes and then discharge the material to obtain the final product.

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