Biomass fuel and preparation method thereof

Abstract

A biomass fuel is composed of 20-40% straw, 20-40% miscanthus, 10-20% combustion aid, and 10-20% agave biowaste. This design uses agave biowaste to replace traditional calcium additives. Through the synergistic combustion of the various components in the formula, it improves combustion efficiency and reduces ignition temperature. It also mitigates the impact of alkali metals in the biomass fuel on boiler operation, reducing issues such as bed material agglomeration, contamination, slagging, and corrosion after biomass combustion. It also addresses environmental issues associated with agave waste disposal. Compared to conventional biomass fuel pellets, this biomass fuel offers improved economic efficiency and a higher combustion value, as it does not require the addition of additional chemical additives.

Description

Technical Field

[0001] The present invention belongs to the technical field of bioenergy, and in particular relates to a biomass fuel and a preparation method thereof. Background Art

[0002] Decarbonizing the energy system is a crucial measure to address today's global climate change. While the utilization of photovoltaic and wind energy is still in its early stages of development, the research and utilization of carbon-neutral biomass energy is relatively mature and has been widely adopted in countries like Europe and the United States. However, research in China on the production, processing, and direct combustion of biomass fuel pellets is still in its early stages, and the promotion and application of biomass energy pellets in China is relatively limited. As a major coal-burning country, the transition from coal-fired power plants to biomass energy is imperative in the new round of energy reform.

[0003] Biomass fuel pelletization increases the calorific value of the raw material per unit density. At the same time, the higher ignition point of pelletized fuel places higher demands on existing boiler technology. Fluidized bed boilers, with their excellent fuel adaptability, are currently the preferred choice for biomass energy pellet combustion. However, the alkali metals in the ash after biomass combustion can cause problems such as bed agglomeration, contamination, slagging, and corrosion within the furnace, significantly impacting energy efficiency. Therefore, conventional biomass fuel pelletization uses combustion aids to enhance the combustibility of biomass fuel pellets, and calcium-based additives to mitigate the effects of alkali metals in the ash.

[0004] Existing conventional calcium-based additives, such as calcium carbonate and calcium oxide, can effectively increase the melting temperature of ash after biomass fuel combustion, thereby reducing the process of ash agglomeration with bed material after melting, extending the service life of bed material, reducing the number of shutdowns, and improving combustion efficiency. However, at the same time, they will also reduce the economy and green environmental protection characteristics of biomass fuel, reduce the calorific value of the fuel to a certain extent, and there are problems such as alkali metal and alkaline earth metal emissions, contamination and slagging, and corrosion erosion.

[0005] Chinese patent: The invention with application number CN110684579A discloses a biomass pellet fuel, comprising the following components in parts by weight: 30-35 parts of corn straw, 15-20 parts of poplar wood chips, 20-30 parts of cassava stems, 3-5 parts of coffee grounds, 0.3-0.5 parts of leveling agent, 0.5-1 parts of sulfur-fixing agent, 4-6 parts of combustion promoter, and 1-3 parts of additives. This method requires more additives and has a high cost. Chinese patent: The invention with application number CN113430027A discloses a biomass fuel prepared by the following method: first, the crop straw residue is crushed and dried to obtain residue powder, and then the residue powder, anti-slagging agent, and functional additive are mixed, and then pressed and cut to obtain biomass fuel. Although the biomass fuel of this method can be fully burned, has high calorific value, and has a low flue gas slagging rate, this method still requires additional functional additives during the preparation process, which increases the cost and reduces the calorific value of the fuel. Therefore, there is a problem in the prior art that calcium-based additives need to be used to reduce the impact of alkali metals in the ash and reduce the economy and calorific value of biomass fuel. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and provide a biomass fuel and its preparation method that utilizes agave biowaste to replace traditional calcium-based additives, thereby controlling potassium emissions during biomass combustion and reducing problems such as bed material agglomeration, contamination, slagging, and corrosion erosion after late biomass combustion.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] A biomass fuel, the raw materials of which include straw, miscanthus, combustion aid and agave biological waste.

[0009] The raw material composition and mass percentage of the biomass fuel are: 20-40% straw, 20-40% miscanthus, 10-20% combustion aid, and 10-20% agave biological waste.

[0010] The raw material composition and mass percentage of the biomass fuel are: 30-40% of straw, 25-38% of miscanthus, 13-20% of combustion aid, and 13-17% of agave biological waste.

[0011] The raw material composition and mass percentage of the biomass fuel are: 35% straw, 35% miscanthus, 15% combustion aid, and 15% agave biological waste.

[0012] The combustion aid is coffee grounds.

[0013] A method for preparing biomass fuel comprises the following steps: fully mixing straw, miscanthus, a combustion aid, and agave biowaste in a desired proportion and then granulating the mixture to obtain the biomass fuel, wherein the mass percentages of straw, miscanthus, a combustion aid, and agave biowaste in the biomass fuel are 20-40%, 20-40%, 10-20%, and 10-20%, respectively.

[0014] The biomass fuel has a diameter of 6-8 mm and a length of 12-25 mm.

[0015] The granulation temperature is 120-175°C.

[0016] The combustion aid is coffee grounds, and the particle size of the coffee grounds is 30-40 meshes.

[0017] The water content of the straw and the Miscanthus is less than 10 wt %, and the water content of the coffee grounds and the agave biowaste is less than 15 wt %.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The raw materials of a biomass fuel of the present invention include straw, Miscanthus, combustion aid, and agave biowaste; since ash accounts for about 7% after combustion of agave biowaste, and its main components are calcium carbonate and calcium oxide, the design uses agave biowaste to replace traditional calcium additives, and through the synergistic combustion effect of each component in the formula, the ignition temperature is reduced, and at the same time, the influence of alkali metals present in the biomass fuel on boiler operation is alleviated, and the generation of problems such as bed material agglomeration, contamination and slagging, and corrosion erosion after late biomass combustion is reduced, combustion efficiency is improved, and the environmental problems caused by the treatment and disposal of agave waste are solved. Compared with conventional biomass fuel particles, since no other chemical additives are added, the economic efficiency of the design is better and the combustion value is higher. Therefore, the biomass fuel in the present invention can not only avoid the generation of problems such as bed material agglomeration, contamination and slagging, and corrosion erosion after late biomass combustion, but also has high combustion efficiency, better economy and higher combustion value, and can solve the environmental problems caused by the treatment and disposal of agave waste.

[0020] 2. The raw material composition and mass percentage of a biomass fuel of the present invention are: 20-40% straw, 20-40% miscanthus, 10-20% combustion aid, and 10-20% agave biowaste. Since the proportion of agave biowaste should not be too high or too low, if the proportion is too high, a large amount of calcium carbonate and calcium oxide will be formed. Although it will not have much impact on the combustion process, it will cause a certain amount of waste in the treatment and disposal of straw and miscanthus. If the proportion is too low, the calcium carbonate and calcium oxide in the ash of agave biowaste are not enough to prevent the potassium in the straw and miscanthus ash from forming a eutectic with the silicon in the bed material, thereby failing to delay the agglomeration of the bed material. By controlling the distribution ratio of each component within the above-mentioned specific ratio, the design can maintain the mass ratio of calcium in the ash of agave biowaste to potassium in the ashes of the other three raw materials at about 1:1, thereby achieving the best combustion efficiency and reducing the combustion time. Therefore, the present invention can further improve the combustion efficiency of the fuel and reduce the combustion time through a reasonable distribution ratio of the components.

[0021] 3. In a biomass fuel of the present invention, oil-rich coffee grounds are used instead of traditional combustion aids to improve the flammability and durability of biomass pellets. Therefore, the present invention can improve the flammability and durability of biomass pellets.

[0022] 4. In a biomass fuel production method according to the present invention, the moisture content of straw and Miscanthus is controlled to below 10 wt%, and the moisture content of coffee grounds and agave biowaste is controlled to below 15 wt%. This design ensures the necessary moisture content during the production process while also increasing the calorific value of the resulting biomass fuel. Therefore, the present invention ensures the necessary moisture content during the production process while also increasing the calorific value of the resulting biomass fuel. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with specific embodiments.

[0024] A biomass fuel, the raw materials of which include straw, miscanthus, combustion aid and agave biological waste.

[0025] The raw material composition and mass percentage of the biomass fuel are: 20-40% straw, 20-40% miscanthus, 10-20% combustion aid, and 10-20% agave biological waste.

[0026] The raw material composition and mass percentage of the biomass fuel are: 30-40% of straw, 25-38% of miscanthus, 13-20% of combustion aid, and 13-17% of agave biological waste.

[0027] The raw material composition and mass percentage of the biomass fuel are: 35% straw, 35% miscanthus, 15% combustion aid, and 15% agave biological waste.

[0028] The combustion aid is coffee grounds.

[0029] A method for preparing biomass fuel comprises the following steps: fully mixing straw, miscanthus, a combustion aid, and agave biowaste in a desired proportion and then granulating the mixture to obtain the biomass fuel, wherein the mass percentages of straw, miscanthus, a combustion aid, and agave biowaste in the biomass fuel are 20-40%, 20-40%, 10-20%, and 10-20%, respectively.

[0030] The biomass fuel has a diameter of 6-8 mm and a length of 12-25 mm.

[0031] The granulation temperature is 120-175°C.

[0032] The combustion aid is coffee grounds, and the particle size of the coffee grounds is 30-40 meshes.

[0033] The water content of the straw and the Miscanthus is less than 10 wt %, and the water content of the coffee grounds and the agave biowaste is less than 15 wt %.

[0034] The principle of the present invention is described as follows:

[0035] In a conventional biomass fuel 20 kW fluidized bed burner with an oxygen excess rate of 5%, the combustion time of a single straw is about 60 minutes, i.e., bed material agglomeration and collapse occur. However, the biomass fuel provided by the present invention, by adding agave biowaste, can stably burn straw pellets for over 1000 minutes, which is comparable to the combustion time of straw pellets containing calcium carbonate additives.

[0036] Example 1:

[0037] A method for preparing biomass fuel, wherein the preparation method is specifically carried out according to the following steps:

[0038] S1, cutting straw into small pieces, filtering through a filter screen, and then crushing in a grinder, drying in a drying drum, and collecting for later use after drying, wherein the moisture content of the straw is about 10wt%;

[0039] S2, cutting the Miscanthus into small pieces, filtering through a filter screen, and then crushing the pieces into pieces in a grinder. After the crushing is completed, the pieces are placed in a drying drum for drying. After the drying is completed, the pieces are collected for later use. The moisture content of the Miscanthus is about 10 wt%;

[0040] S3, taking coffee grounds and putting them into a grinder for grinding, sieving them with a 35-mesh sieve, and collecting them for later use. The moisture content of the coffee grounds is about 15 wt%;

[0041] S4, taking agave biological waste and putting it into a grinder for crushing, sieving it after the crushing, the sieve aperture is 18 mesh, and collecting it for later use after the completion, wherein the water content of the agave biological waste is about 10wt%;

[0042] S5. Add straw, miscanthus, coffee grounds, and agave biowaste into a mixer according to the required proportions and mix them thoroughly, controlling the mass percentages of straw, miscanthus, coffee grounds, and agave biowaste to be 35%, 35%, 15%, and 15%, respectively;

[0043] S6. The mixed materials are conveyed to a pelletizer for pelletizing. The pelletizer operates at a temperature of 150° C. The obtained biomass fuel pellets have a diameter of 7 mm and a length of 20 mm.

[0044] Example 2:

[0045] It is basically the same as Example 1, except that:

[0046] In step S5, the mass percentages of the straw, Miscanthus, coffee grounds, and Agave biowaste are 30%, 30%, 20%, and 20%, respectively;

[0047] In step S6, the pelletizer operates at a temperature of 175° C., and the biomass fuel particles produced have a diameter of 6 mm and a length of 20 mm.

[0048] Example 3:

[0049] It is basically the same as Example 1, except that:

[0050] In step S5, the mass percentages of the straw, miscanthus, coffee grounds, and agave biowaste are 40%, 40%, 10%, and 10%, respectively;

[0051] In step S6, the pelletizer operates at a temperature of 120° C., and the biomass fuel particles produced have a diameter of 12 mm and a length of 25 mm.

[0052] Example 4:

[0053] It is basically the same as Example 1, except that:

[0054] In step S5, the mass percentage ratios of the straw, Miscanthus, coffee grounds and Agave biowaste are 40%, 30%, 20% and 10% respectively.

[0055] Example 5:

[0056] It is basically the same as Example 1, except that:

[0057] In step S5, the mass percentage ratios of the straw, Miscanthus, coffee grounds and Agave biowaste are 20%, 40%, 20% and 20% respectively.

[0058] Example 6:

[0059] It is basically the same as Example 1, except that:

[0060] In step S5, the mass percentage ratios of the straw, Miscanthus, coffee grounds and Agave biowaste are 30%, 38%, 13% and 19% respectively.

[0061] Example 7:

[0062] It is basically the same as Example 1, except that:

[0063] In step S5, the mass percentage ratios of the straw, Miscanthus, coffee grounds and Agave biowaste are 40%, 25%, 18% and 17% respectively.

[0064] Example 8:

[0065] It is basically the same as Example 1, except that:

[0066] In step S5, the mass percentage ratios of the straw, Miscanthus, coffee grounds and Agave biowaste are 40%, 27%, 20% and 13% respectively.

[0067] Performance testing:

[0068] 1. Comparative Example Preparation

[0069] Comparative Example 1:

[0070] This embodiment is basically the same as embodiment 1, except that the mass percentage ratios of the straw, Miscanthus, coffee grounds, and Agave biowaste are 37.5%, 37.5%, 20%, and 5%, respectively.

[0071] Comparative Example 2:

[0072] This embodiment is basically the same as embodiment 1, except that the mass percentage ratios of the straw, Miscanthus, coffee grounds, and Agave biowaste are 20%, 20%, 20%, and 40%, respectively.

[0073] Comparative Example 3:

[0074] This embodiment is basically the same as embodiment 1, except that the mass percentage ratios of the straw, Miscanthus, coffee grounds, and calcium-based additive (calcium carbonate) are 48%, 35%, 15%, and 2%, respectively.

[0075] Comparative Example 4:

[0076] This embodiment is basically the same as embodiment 1, except that the mass percentage ratios of the straw, miscanthus, and coffee grounds are 40%, 40%, and 20%, respectively.

[0077] 2. Performance comparison

[0078] The biomass fuels prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests. The main test was to determine the stable combustion temperature and duration of the biomass fuels when the oxygen excess rate was maintained at 5% in a 20 kW fluidized bed combustor. The performance test results are shown in Table 1:

[0079] Table 1 Performance test results

[0080] sample Combustion temperature (℃) Duration (min) Example 1 900 780 Example 2 900 >1000 Example 3 890 320 Example 4 890 330 Comparative Example 1 860 120 Comparative Example 2 900 >1000 Comparative Example 3 900 >1000 Comparative Example 4 850 60

[0081] As can be seen from Table 1, the biomass fuel provided by Examples 1 and 2 has a combustion temperature of 900°C, and can ensure a long combustion duration, and has a good combustion effect. The effects of Examples 3 and 4 are poor. The reason is that the content of agave biowaste is reduced, and the calcium in its ash cannot fully counteract the potassium in the fuel ash to form a low-temperature melt, thereby significantly reducing the combustion time; in Comparative Example 1, the amount of agave biowaste added is small, and the combustion duration of the biomass fuel is lower than that of Examples 3 and 4. In Comparative Example 2, the amount of agave biowaste added is high. At this time, the biomass fuel can maintain a good effect, but it is impossible to process more straw and miscanthus at this time. In Comparative Example 3, ordinary calcium-based additives are used. Although the combustion temperature and duration can still maintain good effects, there are problems such as alkali metal and alkaline earth metal emissions, contamination and slagging, and corrosion erosion during the combustion process of the fuel. In Comparative Example 4, due to the lack of agave biowaste, the combustion effect of the biomass fuel is poor.

[0082] In summary, the present invention uses agave biowaste to replace traditional calcium additives, which not only has a good combustion effect and a long combustion time, but also can avoid the problems of bed material agglomeration, contamination, slagging and corrosion erosion after the late biomass combustion. It can meet the combustion requirements of most fluidized bed boilers, so that biomass fuel can be widely used in the industrial energy field.

Claims

1. A biomass fuel, characterized by: The raw materials of the biomass fuel include straw, Miscanthus, combustion aid, and Agave biowaste; The raw material composition and mass percentage of the biomass fuel are: 30-35% straw, 30-35% miscanthus, 15-20% combustion aid, and 15-20% agave biowaste; The combustion aid is coffee grounds.

2. The biomass fuel according to claim 1, characterized in that: The raw material composition and mass percentage of the biomass fuel are: 35% straw, 35% miscanthus, 15% combustion aid, and 15% agave biowaste.

3. A method for preparing biomass fuel according to claim 1, characterized in that: The preparation method comprises the following steps: fully mixing straw, miscanthus, a combustion aid, and agave biowaste in a desired proportion and then granulating the mixture to obtain biomass fuel, wherein the mass percentages of straw, miscanthus, combustion aid, and agave biowaste in the biomass fuel are 30-35% for straw, 30-35% for miscanthus, 15-20% for combustion aid, and 15-20% for agave biowaste, respectively; and the combustion aid is coffee grounds.

4. The method for preparing a biomass fuel according to claim 3, wherein: The biomass fuel has a diameter of 6-8 mm and a length of 12-25 mm.

5. A method for preparing biomass fuel according to claim 3 or 4, characterized in that: The granulation temperature is 120-175°C.

6. The method for preparing a biomass fuel according to claim 3 or 4, characterized in that: The particle size of the coffee grounds is 30-40 meshes.

7. The method for preparing biomass fuel according to claim 6, characterized in that: The water content of the straw and the Miscanthus is less than 10 wt %, and the water content of the coffee grounds and the agave biowaste is less than 15 wt %.