Preparation method of cow dung biomass pellet fuel

Abstract

The invention relates to a preparation method of cow dung biomass granular fuel, and belongs to the technical field of livestock and poultry manure treatment and biomass fuel. The method specifically comprises the following steps that fresh cow dung and wood chips serve as raw materials, the fresh cow dung and the wood chips are pretreated respectively, the water content of the fresh cow dung is 20%-32%, and the water content of the wood chips is smaller than or equal to 32%; the method comprises the following steps: proportioning the pretreated cow dung and wood chips by dry weight, with the wood chip mass fraction of 0-40wt% and the water content of 20%-32%, and then mechanically stirring to obtain a uniform mixture; and extruding and forming the mixture into the cow dung biomass granular fuel at a proper feeding rate by adopting a biomass granulator. The forming rate of the obtained cow dung pellet fuel is 99.2% or above, the mechanical durability is as high as 99.3% or above, the low calorific value can reach 16 MJ / kg or above, and the water content of a finished product is small and lower than 10%. The technological process is short and easy to operate, and the cow dung pellet fuel has the advantages of no peculiar smell, moisture resistance, mildew resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing cattle manure biomass pellet fuel, belonging to the technical field of biomass fuel and environmental protection, in particular to the comprehensive treatment and resource utilization technology of livestock and poultry breeding manure. BACKGROUND

[0002] Biomass solid formed fuel is usually made of agricultural and forestry waste, kitchen waste (plants) and other waste biomass through drying, crushing, forming or further carbonization, etc. It is a fuel that can replace coal and traditional charcoal, with the characteristics of low ash content, high calorific value, good durability, clean and environmental protection, etc. At present, due to the increasing global energy demand and the increasing awareness of environmental protection, the use of biomass formed fuel can reduce the destruction of natural forest resources and the dependence on traditional fossil fuels, and optimize the energy structure.

[0003] The large-scale, intensive and regional development of cattle breeding industry has produced a large amount of cattle manure, and the ecological environmental problems caused by it have become increasingly prominent. Because the organic fertilizer made of cattle manure has poor fertilizer effect, it is not as good as chicken manure, pig manure and sheep manure, and is usually mixed with other livestock and poultry manure organic fertilizer for use and digestion, resulting in a large amount of cattle manure surplus, far exceeding the soil assimilation capacity of the surrounding area, and seriously affecting the surrounding ecological environment. As we all know, cattle manure contains rich organic matter and can be used as fuel directly. However, fresh cattle manure has a high water content, usually 80%-85%, and needs to be dried before use, and the structure of cattle manure is relatively loose, so it is not convenient to transport and store. Therefore, the end-of-pipe manure treatment and resource utilization has become a problem and a bottleneck for the development of cattle farms.

[0004] There are some documents reported that cattle manure can be prepared into biomass formed fuel. In order to remove the odor of cattle manure, more studies on fermentation treatment of cattle manure are carried out. Invention patent (CN107267244A) discloses a method for making high-density fuel from cattle manure, which mixes the fermented mature cattle manure with crop straw and sawdust powder uniformly, and then presses and forms it, and then the product is naturally dried for 3-5 days, and then dried at 100℃ by using a drying machine until the water content is less than 10%. The fermentation of cattle manure needs at least 10-15 days, which makes the process cycle long, and the product needs to be further dried after forming. The invention patent with publication number CN106244279A discloses a method for preparing biomass fuel from fresh cattle manure as the main raw material, which mixes fresh cattle manure, mushroom rod material and calcined shell powder to obtain a mixture, and then inoculates the mixture with nitrogen-fixing and desulfurization composite microorganisms for 2-3 days to remove the odor and toxic and harmful gases. The fermented mixture is naturally dried to reduce the moisture content to below 18%, and then the naturally dried tea stem material is added to it, and then extruded and granulated into cattle manure biomass fuel. The calcination of shell powder needs to be calcined at a high temperature of 900-1100℃ for 3-5h.

[0005] In order to improve the performance of biomass fuel forming, antibacterial and mildewproof, usually add binder, bacteriostatic agent and other additives to the raw materials. For example, the invention patent with publication number CN108865314A discloses a new type of environmental protection and fuel resistant biomass pellet and its preparation method, which is composed of cow dung, bamboo chips, wood chips, straw, coal powder, combustion improver, limestone, bentonite and the like. The biomass pellet with particle size of 0.7-0.8mm is obtained by extrusion granulation. Diatomite is added to the raw material composition to prevent the mildew of biomass pellet, and adhesive is used for pellet forming. The disadvantage is that the raw material composition is complex and the process is complex. In order to reduce the chlorine corrosion weight gain in cow dung, the invention patent with publication number CN116574546A discloses a preparation method of cow dung biomass fuel. The cow dung is treated by twice water washing combined with adding kaolin, and the water content of the mixture is controlled to be 8%. The forming rate of cow dung pellet fuel is 97.3%, and the mechanical durability is 96.2%. The low heat value is 15.8MJ / kg.

[0006] Due to the difference of inherent physicochemical properties of raw materials, the forming effect and performance of biomass fuel prepared by physical method are greatly affected by factors such as raw material type, composition, water content, operating conditions and forming equipment. For example, single wood chip is not easy to form due to poor adhesion, and rice husk is also not easy to form due to less fiber. Therefore, it is of great significance to develop a kind of cow dung biomass pellet fuel with simple process, low cost and good forming effect for the green and sustainable development of cattle breeding industry. SUMMARY

[0007] The present application provides a preparation method of cow dung biomass pellet fuel aiming at the problems and deficiencies in the process of end-of-life manure treatment and resource utilization in cattle breeding industry. By drying, crushing and screening fresh cow dung, adding wood chips and mixing, the cow dung pellet fuel is obtained by extrusion molding. It has the advantages of high forming rate, high mechanical strength, no odor, easy transportation and storage. This method solves the problem of effective treatment of cow dung and realizes the harmless, reduction and energy utilization of livestock and poultry manure.

[0008] To achieve the above purpose, the technical scheme of the present application is:

[0009] A preparation method of cow dung biomass pellet fuel, the cow dung biomass pellet fuel is composed of 60wt%-100wt% fresh cow dung and 0wt%-40wt% wood chips in terms of dry weight, and is prepared according to the following steps:

[0010] (1) Cow dung pretreatment: collect fresh cow dung (water content 80%-83%) from cattle farm, dry the fresh cow dung naturally to remove part of the water, then dry at 105℃, further reduce the water content to 20%-32%, and then crush and pass through a 6 mesh screen;

[0011] (2) Wood chip pretreatment: some common trees are broken into wood chips or sawdust is directly used, then the wood chips or sawdust is sieved through a 6-mesh sieve, and the sieved wood chips or sawdust is dried at a temperature of 105℃ to make the moisture content ≤32%;

[0012] (3) Uniform mixing: the pretreated cow dung and wood chips are mixed according to the above composition, the moisture content of the mixture is controlled to be 20%-32%, and then the mixture is mechanically stirred for 10-15 min to obtain a uniform mixture;

[0013] (4) Biomass pellet forming: the mixture is added to the working chamber of a biomass pellet machine at a suitable feeding rate, and is extruded to form cow dung biomass pellet fuel;

[0014] (5) Finished product screening: the formed cow dung biomass pellet fuel is naturally cooled to room temperature, then sieved through a 6-mesh sieve, and the sieve residue is the qualified cow dung biomass pellet fuel finished product.

[0015] The common trees in step (2) are white bark pine, Chinese fir, cypress or Chinese pine, etc., the broken wood chips are one or more of these common trees, and the sawdust is the broken wood chips generated by a wood processing plant, which can be directly used after sieving without drying if the moisture content meets the requirements.

[0016] The biomass pellet machine used in step (4) is a flat mode (or called roller disc type), and the working part mainly consists of a compression roller and a flat die. The number of compression rollers is 2 or 3, and the surface of the compression roller is gear-shaped. The surface of the flat die is flat, and a large number of through holes are uniformly distributed in the interior, and the diameter of the through holes determines the diameter of the product. During pellet forming, the compression roller revolves around the rotation axis and contacts the material to generate pressure to form rotation, and at the same time, the material is extruded into the through holes of the flat die. After the extruded material is extruded into a cylindrical shape, it is cut into cylindrical pellets of a certain length when it contacts the rotating disc at the bottom of the discharge chamber. If the strength of the extruded pellet fuel is not enough, it may break before contacting the bottom rotating disc.

[0017] The feeding rate in step (4) is 3.8-5.0 kg / min. The model of the biomass pellet machine selected in the present application is 200, the power is 7.5 kw, the diameter of the working chamber is 24.5 cm, and the height is 18 cm. When the biomass pellet machine of the present application is used, the suitable feeding rate is 3.8-5.0 kg / min. When other models and parameters of biomass pellet machines are selected, other suitable feeding rates need to be selected.

[0018] The prepared cow dung biomass pellet fuel is in a cylindrical shape, with a diameter of 8-10 mm and a length of 5-76 mm.

[0019] The forming rate of the cattle dung biomass pellet fuel product prepared by the method is more than 99.2%, the mechanical durability is more than 99.3%, the dry base low heat value can reach more than 16 MJ / kg, the moisture is less than 10%, the nitrogen content is 1.1-1.7%, the sulfur content is 0.1-0.3%, and the burning resistance is good.

[0020] The present application has the following advantages:

[0021] (1) The preparation process of the present application is short and simple. In the prior art, cattle dung is usually treated by fermentation. The fermentation time is several days, dozens of days, or even several months, which greatly reduces the existing large amount of cattle dung disposal capacity of the farm. Moreover, a large fermentation site is required, the process parameters are harsh, and the fermentation process easily produces odor and pollutes the environment. The present application directly uses fresh cattle dung, and does not need fermentation treatment. The fresh cattle dung is naturally dried and controlled to a high moisture content. After simple crushing and passing through a 6-mesh sieve, the pretreatment of the fresh cattle dung is completed. The operation is easy to implement, the cattle dung treatment time is saved, and the cost of drying and crushing the cattle dung is reduced. The moisture content of the formed product is less than 10%, and further drying and drying are not required, which can well meet the use requirements.

[0022] (2) The preparation process of the present application does not use any additives, thereby reducing the production cost. The cattle dung itself has a high ash content, and the heat value is lower than that of pig dung and sheep dung. If some mineral type binders or bacteriostatic agents for promoting pellet formation or bacteriostatic and mildew prevention are added, the heat value of the cattle dung biomass fuel will be reduced and the ash content will be further increased. The present application utilizes the inherent sticky substances in the cattle dung, such as fat and starch, to promote pellet formation. Moreover, the moisture content of the cattle dung and wood chip mixture is high. When the mixture is formed by a biomass pellet machine, the particle size is reduced, the specific surface area is increased, and the temperature of the material is rapidly increased due to friction, which causes a large amount of internal water to evaporate into water vapor, softens the abundant cellulose and lignin in the cattle dung and wood chips, and is beneficial to the formation of pellet fuel.

[0023] (3) The cattle dung biomass fuel obtained by the present application has the advantages of no odor, moisture resistance, and mildew resistance. The cattle dung is the residue of the feces of herbivorous animals, and the odor is not as heavy as that of chicken and pig feces. On the one hand, part of the odor can be removed during the drying process, and the odor gas emitted is light, which also indicates that the odor of the cattle dung itself is light. On the other hand, the high-temperature water vapor emitted during the formation of the cattle dung biomass pellets has a good sterilization effect on the cattle dung, and further removes the odor. The odor gas generated during the preparation process can be extracted by an indoor exhaust fan or discharged after further treatment. The surface of the cattle dung biomass pellet fuel is smooth and dense, environmentally friendly, odorless, and does not absorb moisture and mildew even after one year, which is convenient for transportation and storage.

[0024] (4) The cow manure biomass pellet fuel product obtained by this invention has a high forming rate and high output. It has the characteristics of high calorific value, low moisture content, good mechanical strength, good fire resistance and good combustion efficiency. It effectively solves the end-of-life treatment problem of cattle breeding industry, provides a direction for the energy utilization of cow manure, and has significant economic and social value. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the method for preparing cow dung biomass pellet fuel according to the present invention;

[0026] Figure 2 This is the finished product of cow dung biomass pellet fuel prepared in Example 3 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] like Figure 1 As shown, the preparation method of this cow dung biomass pellet fuel is specifically carried out according to the following steps:

[0030] (1) Pretreatment of cow manure: Collect fresh cow manure (80% moisture content) from the cattle farm, air dry the fresh cow manure to remove moisture to 50%, then dry it at 105℃ to further reduce the moisture content to 20%, and then crush and pass the dried cow manure through a 6-mesh sieve.

[0031] (2) Wood chip pretreatment: Use cedar sawdust with a moisture content of 20%, and pass it through a 6-mesh sieve for later use;

[0032] (3) Uniform mixing: 5 kg of pretreated cow manure and 0, 0.556, 1.250, 2.143 and 3.333 kg of wood chips were mixed separately. The wood chip mass fraction was 0 wt%, 10 wt%, 20 wt%, 30 wt% and 40 wt% of the total dry weight, respectively. The moisture content of the mixture was 20%. Then, the mixture was mechanically stirred for 15 min to obtain a uniform mixture.

[0033] (4) Biomass pellet forming: Pure cow dung or mixed material is added to the working chamber of the flat-mode biomass pellet mill at a feeding rate of 4.6-5.0 kg / min and extruded to obtain cow dung biomass pellet fuel.

[0034] (5) Finished product screening: After the formed cow dung biomass pellet fuel is naturally cooled to room temperature, it is then passed through a 6-mesh sieve. The material on the sieve is the qualified finished cow dung biomass pellet fuel.

[0035] The prepared cattle manure biomass pellet fuel is cylindrical, with a diameter of 8-9 mm and a length of 5-76 mm. The physical and chemical properties such as molding rate and calorific value are shown in Table 1. The molding rate refers to the ratio of the mass of the finished product on the screen to the total mass of the material on the screen and under the screen (mainly fine powder) after the extruded pellet fuel is screened through a 6-mesh screen (pore size 3.35 mm). The small particle ratio refers to the ratio of the mass of small particles with a length of 5-8 mm in the finished pellet fuel to the total mass of the finished product. The mechanical durability, also known as mechanical strength, reflects the ability of the biomass fuel to maintain its integrity and strength during transportation and storage.

[0036] As can be seen from Table 1, when the moisture content of the mixture is 20%, the cattle manure biomass pellet fuel with different amounts of sawdust maintains a high molding rate of more than 99.20%, but the molding rate of the pellet fuel containing 40wt% of sawdust decreases to 97.45%, and the proportion of small pellet fuel increases significantly to 5.93%. The relevant indicators of cattle manure pellet fuel with different amounts of sawdust, such as received basis low calorific value, moisture, mechanical durability, etc., meet the corresponding grade requirements of non-wood biomass pellet fuel in the agricultural industry standard NY / T 2909-2016 "Biomass Solid Molding Fuel Quality Classification" (see Table 2), for example, the moisture of cattle manure pellet fuel is less than 10%, the mechanical durability is more than 99% (except for pellet fuel containing 40wt% of sawdust), and there is no amount of fine particles less than 3.15 mm because the finished product is screened through a 6-mesh screen. The received basis low calorific value of pure cattle manure pellet fuel is 13.19 MJ / kg, which meets the B3 grade requirement; the received basis low calorific value of cattle manure pellet fuel containing 10wt% and 20wt% of sawdust is 13.52 MJ / kg and 14.00 MJ / kg, respectively, which meets the B2 grade requirement; and the received basis low calorific value of cattle manure pellet fuel containing 30wt% and 40wt% of sawdust is 14.77 MJ / kg and 15.30 MJ / kg, respectively, which meets the B1 grade requirement. With the increase of the amount of sawdust added, the ash content, nitrogen content and sulfur content of the cattle manure pellet fuel gradually decrease, and the sulfur content is significantly lower than that of coal.

[0037] Table 1 Performance of cattle manure biomass pellet fuel with different amounts of sawdust

[0038] Sawdust addition amount (wt%) 0 10 20 30 40 Molding rate (%) 99.57 99.28 99.26 99.46 97.45 Small particle ratio (%) 0.54 0.31 0.99 0.29 5.93 Low heat value (received basis, MJ / kg) 13.19 13.52 14.00 14.77 15.30 Low heat value (dry basis, MJ / kg) 14.27 14.71 15.20 15.85 16.31 Moisture (received basis, %) 6.56 7.00 6.86 5.98 5.44 Ash content (dry basis, %) 24.66 22.61 20.37 17.36 15.06 Mechanical durability (received basis, %) 99.4 99.5 99.7 99.7 96.2 Nitrogen content (air-dry basis, %) 1.69 1.50 1.36 1.22 1.12 Sulfur content (air-dry basis, %) 0.27 0.26 0.24 0.19 0.16

[0039] Table 2 Relevant grade requirements of non-wood biomass pellet fuel in NY / T 2909-2016 agricultural industry standard

[0040] Fuel properties B1 grade B2 grade B3 grade Total moisture (received basis, %) ≤10 ≤12 ≤16 Mechanical durability (received basis, %) ≥97.5 ≥95 ≥95 Amount of fine particles less than 3.15 mm (%) ≤1.0 ≤1.0 ≤1.0 Low heat value / (received basis, MJ / kg) ≥14.6 ≥13.4 ≥12.6

[0041] As can be seen from Table 1, when the sawdust addition amount is 0, that is, the composition of the cow dung biomass pellet fuel is completely cow dung, after the preparation by the treatment of the application, the non-wood biomass pellet fuel B3 related grade requirements in the agricultural industry standard NY / T 2909-2016 "Biomass Solid Shaped Fuel Quality Grading" can still be prepared. And after adding appropriate sawdust (addition amount is 10-40%), cow dung biomass pellet fuel with better B1, B2 grade requirements and better performance can be obtained.

[0042] Example 2

[0043] As Figure 1 shown, the preparation method of the cow dung biomass pellet fuel is prepared according to the following steps:

[0044] (1) Cow dung pretreatment: fresh cow dung (moisture content is 83%) is collected from a cattle farm, the fresh cow dung is naturally dried to 52% moisture content, and then dried at 105°C to further reduce the moisture content to 16.17%, 20%, 24%, 28%, and 32%, respectively. The dried cow dung is crushed and passed through a 6-mesh sieve in sequence;

[0045] (2) Sawdust pretreatment: pine sawdust is used, and the moisture content can be 16.17%, 20%, 24%, 28%, and 32%. The pine sawdust with different moisture contents is passed through a 6-mesh sieve for standby;

[0046] (3) Uniform mixing: 5 kg of pretreated cow dung with different moisture contents and 2.143 kg of sawdust with corresponding moisture content are respectively prepared, and the sawdust mass fraction is 30wt% of the total dry weight. The moisture content of the mixed material is 16.17%, 20%, 24%, 28%, and 32%, respectively. Then, the mixed material is mechanically stirred for 15 min to obtain a uniform mixture;

[0047] (4) Biomass pellet forming: the mixed material is added to the working chamber of the flat mode biomass pellet machine at a feeding rate of 3.8-4.3 kg / min, and extruded to form cow dung biomass pellet fuel;

[0048] (5) Finished product screening: the formed cow dung biomass pellet fuel is naturally cooled to room temperature, and then passed through a 6-mesh sieve. The sieve residue is the qualified cow dung biomass pellet fuel finished product.

[0049] The prepared cattle dung biomass pellet fuel is cylindrical, with a diameter of 8-9 mm and a length of 5-76 mm. The physical and chemical properties such as molding rate and calorific value are shown in Table 3. As can be seen from Table 3, as the moisture content of the mixture increases, the molding rate of the cattle dung pellet fuel increases slightly, but when the moisture content of the mixture is 16.17%, the proportion of small particles in the finished product increases significantly, and the mechanical durability is not as good as that of the cattle dung pellet fuel prepared from the mixture with high moisture content. In addition, if the moisture content of the mixture is low, more energy is required for drying the raw materials. When the moisture content of the mixture is 32%, the moisture content of the cattle dung pellet fuel is 9.57%. If the moisture content of the mixture continues to increase, the moisture content of the product will exceed 10%. Therefore, the moisture content of the mixture used for the cattle dung pellet fuel is preferably controlled at 20%-32%. When the moisture content of the mixture increases, the received low calorific value of the cattle dung pellet fuel decreases. When the moisture content is 28%-32%, the received low calorific value of the pellet fuel meets the B2 level requirement in the agricultural industry standard NY / T 2909-2016.

[0050] Table 3 Performance of cattle dung biomass pellet fuel with different moisture contents of the mixture

[0051] Mixture moisture (%) 16.17 20 24 28 32 Molding rate (%) 98.82 99.45 99.38 99.61 99.65 Small particle ratio (%) 4.29 0.16 0.21 0.10 0.15 Low heat value (received basis, MJ / kg) 14.65 14.65 14.55 13.75 13.57 Low heat value (dry basis, MJ / kg) 15.51 15.58 15.86 15.32 15.25 Moisture (received basis, %) 4.82 5.88 7.08 8.92 9.57 Ash content (dry basis, %) 19.02 18.91 19.09 18.96 19.27 Mechanical durability (received basis, %) 97.6 99.7 99.7 99.3 99.4 Nitrogen content (air-dry basis, %) 1.12 1.24 1.07 1.11 1.07 Sulfur content (air-dry basis, %) 0.20 0.19 0.19 0.20 0.20

[0052] Example 3

[0053] As Figure 1 shown, the preparation method of the cattle dung biomass pellet fuel is prepared according to the following steps:

[0054] (1) Cattle dung pretreatment: Fresh cattle dung (moisture content 81%) is collected from a cattle farm, and the fresh cattle dung is naturally dried to 60% moisture content, and then dried at 105°C to further reduce the moisture content to 28%. The dried cattle dung is crushed and then passed through a 6-mesh sieve. The particle size distribution of the sieved cattle dung is shown in Table 4.

[0055] (2) Wood chip pretreatment: White pine tree is crushed into wood chips, and then passed through a 6-mesh sieve. The sieved wood chips are dried at 105°C to a moisture content of 12.59%.

[0056] (3) Uniform mixing: 5 kg of pretreated cattle dung and 1.765 kg of wood chips are mixed, with the wood chip mass fraction being 30 wt% of the total dry weight. The moisture content of the mixture is 23.98%, and then the mixture is mechanically stirred for 10 min to obtain a uniform mixture;

[0057] (4) Biomass pellet molding: The mixture is added to the working chamber of the flat mode biomass pellet machine at a feeding rate of 4.0-4.5 kg / min, and extruded to obtain cattle dung biomass pellet fuel;

[0058] (5) Product screening: After the molding of the cow dung biomass pellet fuel, the product is naturally cooled to room temperature, and then screened through a 6-mesh sieve. The sieve residue is the qualified cow dung biomass pellet fuel product.

[0059] The prepared cow dung biomass pellet fuel is cylindrical, with a diameter of 8-9 mm and a length of 5-76 mm. The proportion of pellet fuel with a length of 50-76 mm is more than 85%, indicating that the extruded length of the pellet fuel during molding is good and the pellet fuel is not easy to break and has high mechanical strength. The density of the cow dung biomass pellet fuel is about 1.38 g / cm 3 The molding rate, heat value, and other physical and chemical properties of the cow dung biomass pellet fuel are shown in Table 5. The actual product photo of the cow dung biomass pellet fuel prepared in this embodiment is shown in Figure 2 From Figure 2 it can be seen that the cow dung biomass pellet fuel has a smooth surface, dense texture, no odor, good moisture and mildew resistance, and will not deteriorate after being placed for more than one year.

[0060] Table 4 Particle size distribution of pretreated cow dung and sawdust (unit: %)

[0061] Note: The particle size of the cow dung in Example 3 and the sawdust in Example 4 is 6-10 mesh or more.

[0062] Table 5 Properties of the cow dung biomass pellet fuel prepared in Examples 3-5 and Comparative Examples 1-3 of the present application

[0063]

[0064] Example 4

[0065] As shown in Figure 1 , the preparation method of the cow dung biomass pellet fuel is prepared according to the following steps:

[0066] (1) Cow dung pretreatment: Fresh cow dung (moisture content of 82%) is collected from a cattle farm, and the fresh cow dung is naturally dried to a moisture content of 58%, and then dried at a temperature of 105°C to further reduce the moisture content to 22%. The dried cow dung is crushed and then screened through a 6-mesh sieve;

[0067] (2) Sawdust pretreatment: Chinese pine sawdust with a moisture content of 20% is used, and the sawdust is screened through a 6-mesh sieve (the particle size distribution of the screened sawdust is shown in Table 4). The screened sawdust is dried at a temperature of 105°C to a moisture content of 19.08%;

[0068] (3) Uniform mixing: 5 kg of pretreated cow dung and 2.595 kg of sawdust are mixed, with the mass fraction of sawdust being 35 wt% of the total dry weight. The moisture content of the mixture is 21%, and then the mixture is mechanically stirred for 10 minutes to obtain a uniform mixture;

[0069] (4) Biomass pellet forming: the mixed material is added to the working chamber of the flat mode biomass pellet machine at a feeding rate of 4.4-4.8 kg / min, and extrusion forming is performed to obtain the cow dung biomass pellet fuel;

[0070] (5) Product screening: the formed cow dung biomass pellet fuel is naturally cooled to room temperature, and then passed through a 6-mesh sieve, and the sieve residue is the qualified cow dung biomass pellet fuel product.

[0071] The prepared cow dung biomass pellet fuel is cylindrical, with a diameter of 9-10 mm and a length of 5-76 mm, wherein the length of the pellet fuel is 50-76 mm, accounting for more than 85%. The density of the cow dung biomass pellet fuel is about 1.36 g / cm 3 , and the forming rate, calorific value and other physical and chemical properties are shown in Table 5.

[0072] Example 5

[0073] As Figure 1 shown, the preparation method of the cow dung biomass pellet fuel is prepared according to the following steps:

[0074] (1) Cow dung pretreatment: fresh cow dung (moisture content of 81%) is collected from a cattle farm, and the fresh cow dung is naturally dried to 62% moisture content, and then dried at 105°C to further reduce the moisture content to 27%. The dried cow dung is crushed and then passed through a 6-mesh sieve;

[0075] (2) Wood chip pretreatment: the Platycladus orientalis is crushed to a certain extent, and then passed through a 6-mesh sieve. The sieved wood chips are dried at 105°C to a moisture content of 19.01%;

[0076] (3) Uniform mixing: 5 kg of pretreated cow dung and 3.004 kg of wood chips are mixed, with the wood chip mass fraction being 40 wt% of the total dry weight. The moisture content of the mixed material is 24%, and then mechanical stirring is performed for 15 min to obtain a uniform mixture;

[0077] (4) Biomass pellet forming: the mixed material is added to the working chamber of the flat mode biomass pellet machine at a feeding rate of 4.2-4.6 kg / min, and extrusion forming is performed to obtain the cow dung biomass pellet fuel;

[0078] (5) Product screening: the formed cow dung biomass pellet fuel is naturally cooled to room temperature, and then passed through a 6-mesh sieve, and the sieve residue is the qualified cow dung biomass pellet fuel product.

[0079] The prepared cow dung biomass pellet fuel is cylindrical, with a diameter of 9-10 mm and a length of 5-76 mm, wherein the pellet fuel with a length of 50-76 mm accounts for more than 85%. The density of the cow dung biomass pellet fuel is about 1.33 g / cm 3 The physical and chemical properties such as molding rate, calorific value, etc. of the prepared cow dung biomass pellet fuel are shown in Table 5.

[0080] Comparative Example 1

[0081] The raw material composition and preparation process used in Comparative Example 1 are the same as those in Example 3, and the only difference is that the particle size of the dried cow dung in step (1) is relatively coarse, and it is not passed through a 6-mesh sieve. The particle size distribution of the broken cow dung is shown in Table 4. As can be seen from Table 4, the cow dung raw material with a particle size of more than 10 mesh accounts for 13.72%, and the particle size of 10-20 mesh accounts for 25.73% in the present comparative example. The content of these coarse particles of cow dung is significantly higher than the corresponding particle size in Example 3, while the content of the fine and fine particle size of the cow dung raw material below 20 mesh in the present comparative example is less than the corresponding particle size in Example 3, especially the particle size below 60 mesh. Therefore, the particle size of the raw material cow dung in the present comparative example is relatively coarse. The physical and chemical properties such as molding rate, calorific value, etc. of the prepared cow dung biomass pellet fuel are shown in Table 5.

[0082] Comparative Example 2

[0083] The raw material composition and preparation process used in Comparative Example 2 are the same as those in Example 4, and the only difference is that the sawdust used in step (2) is the broken sawdust of Chinese pine, which is relatively coarse and is not passed through a 6-mesh sieve. The broken sawdust is dried at a temperature of 105°C to make the moisture content 19.08%. The particle size distribution of the broken sawdust is shown in Table 4. As can be seen from Table 4, the sawdust with a particle size of more than 10 mesh accounts for 47.72%, and the particle size of 10-20 mesh accounts for 44.00% in the present comparative example. The content of coarse particle size is significantly higher than the corresponding particle size in Example 4, while the content of the fine and fine particle size of the sawdust raw material below 20 mesh in the present comparative example is significantly less than the corresponding particle size in Example 3. Therefore, the particle size of the sawdust in the present comparative example is relatively coarse. The physical and chemical properties such as molding rate, calorific value, etc. of the prepared cow dung biomass pellet fuel are shown in Table 5.

[0084] Comparative Example 3

[0085] The raw material composition and preparation process used in Comparative Example 3 are the same as those in Example 5, and the only difference is that the feeding rate of the mixed material into the working chamber of the flat mode biomass pellet machine during the molding of the cow dung pellet fuel in step (4) is relatively slow, which is 2.4-2.9 kg / min. The physical and chemical properties such as molding rate, calorific value, etc. of the prepared cow dung biomass pellet fuel are shown in Table 5.

[0086] In combination with Table 4 and Table 5, the raw material particle size and feeding rate mainly affect the forming effect and mechanical strength of the cow dung pellet fuel, and other physicochemical properties have no obvious effect. Compared with Example 3, the cow dung particle size used in Comparative Example 1 is relatively coarse, the forming rate of the cow dung biomass pellet fuel obtained is reduced, the proportion of small pellet fuel in the finished product is obviously increased, and the mechanical durability is reduced. Compared with Example 4, the sawdust particle size used in Comparative Example 2 is relatively coarse, the forming rate of the cow dung biomass pellet fuel obtained is reduced, the proportion of small pellet fuel in the finished product is obviously increased, and the mechanical durability is reduced more obviously. Compared with Example 5, the feeding rate of the pellet fuel in Comparative Example 3 is slow, although the material can fill part of the chamber space of the pellet machine, due to the loose structure of the cow dung and sawdust, when the material filling amount is insufficient, the contact between the materials is not close enough, so that the extruded pellet fuel is not dense enough and the strength is poor, resulting in that the forming rate of the cow dung biomass pellet fuel obtained is significantly reduced, only 78.76%, and the proportion of small pellet fuel in the finished product reaches 23.94%, and the mechanical durability is obviously reduced, only 84.16%, which shows that the feeding rate of the mixed material added to the pellet machine has a great effect on the forming effect and mechanical strength of the pellet fuel. When the biomass pellet is formed, under the synergistic effect of water content, forming temperature, forming pressure and material filling amount in the material, the adhesion, elastic-plasticity and density of the material will evolve, and comprehensive control of factors such as raw material properties, composition, water content and operating conditions can prepare biomass pellet fuel with good forming effect and excellent performance.

[0087] Comparative Example 4

[0088] Directly using cow dung to prepare cow dung biomass pellet fuel in a biomass pellet machine: fresh cow dung (water content of 80%) was collected from a cattle farm, and the fresh cow dung was naturally dried to 50% water content, then dried at 105°C to further reduce the water content to 10%, and then crushed and passed through a 6-mesh sieve. The treated cow dung was added to the working chamber of the flat-mode biomass pellet machine at a feeding rate of 4.6-5.0 kg / min, and was extruded to form cow dung biomass pellet fuel. The formed cow dung biomass pellet fuel was naturally cooled to room temperature, then passed through a 6-mesh sieve, and the sieve residue was the qualified cow dung biomass pellet fuel product. The performance of the cow dung biomass pellet fuel in this comparative example and the cow dung biomass pellet fuel in Example 1 with no sawdust added is shown in Table 6.

[0089] Table 6

[0090]

[0091] As can be seen from Table 6, when fresh cow dung biomass pellet fuel is prepared directly by using fresh cow dung with moisture of 10%, the forming rate of the fresh cow dung biomass pellet fuel is only 50.24%, the small particle amount accounts for as high as 21.25%, and the mechanical durability is only 64.16%, which is far from meeting the requirements of the agricultural industry standard NY / T 2909-2016. However, according to the embodiment 1 of the present application, after the treatment, fresh cow dung can be directly used to prepare cow dung biomass pellet fuel with relevant indexes meeting the requirements of the agricultural industry standard NY / T 2909-2016 B3 grade.

[0092] By the preparation method of the present application, the industry technical prejudice that cow dung usually needs to be fermented or other binders are added to prepare cow dung biomass pellet fuel with traditional biomass such as wood chips is overcome, the process is simplified, and even without adding traditional biomass such as wood chips, cow dung biomass pellet fuel with relevant indexes meeting the requirements of the agricultural industry standard NY / T 2909-2016 can be prepared. In the preparation process of the present application, the wood chip raw material can completely use agricultural and forestry waste and waste materials generated in wood processing. Therefore, the cow dung biomass pellet fuel obtained by the present application has good application prospect in national economy and life, such as industrial boiler fuel and new type of biomass fuel for civilian use.

[0093] The specific embodiments of the present application are described in detail above with reference to the accompanying drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.

Claims

1. A method of producing a cattle dung biomass pellet fuel, characterized by: The cattle manure biomass pellet fuel is composed of 60wt%-100wt% fresh cattle manure and 0wt%-40wt% sawdust in terms of dry weight, and is prepared according to the following steps: (1) Cattle manure pretreatment: fresh cattle manure is collected from a cattle farm, and a part of water is removed by natural airing, and then the dried cattle manure is further dried at 105℃ to reduce the water content to 20%-32%, and then the dried cattle manure is crushed and sieved through a 6-mesh sieve; (2) Sawdust pretreatment: some common trees are crushed into sawdust or sawdust is directly used, and then sieved through a 6-mesh sieve, and then the sieved sawdust or sawdust is dried at 105℃ to reduce the water content to ≤32%; (3) Uniform mixing: the pretreated cattle manure and sawdust are mixed according to the above composition, the water content of the mixture is controlled to be 20%-32%, and then the mixture is mechanically stirred for 10-15 min to obtain a uniform mixture; (4) Biomass pellet forming: the mixture is added to the working chamber of a biomass pellet machine at a suitable feeding rate, and then extruded to form cattle manure biomass pellet fuel; (5) Finished product screening: the formed cattle manure biomass pellet fuel is naturally cooled to room temperature, and then sieved through a 6-mesh sieve, and the sieve residue is the qualified cattle manure biomass pellet fuel product.

2. The process for the preparation of cattle dung biomass pellets fuel as claimed in claim 1 wherein: The common trees in step (2) are white bark pine, Chinese fir, Chinese arborvitae or Pinus massoniana, and the crushed sawdust is one or more of these common trees, and the sawdust is the sawdust produced by a wood processing plant, which can be directly used after sieving without drying if the water content meets the requirements.

3. The process for the preparation of cattle dung biomass pellets fuel as claimed in claim 1 wherein: The biomass pellet machine used in step (4) is a flat mode.

4. The process for the preparation of cattle dung biomass pellets fuel as claimed in claim 1 wherein: The feeding rate in step (4) is 3.8-5.0 kg / min.

5. The process for the preparation of cattle dung biomass pellets fuel as claimed in claim 1 wherein: The prepared cattle manure biomass pellet fuel is cylindrical, with a diameter of 8-10 mm and a length of 5-76 mm.

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