China is a big energy consumer. The total consumption is growing at a rate of 6% to 7% per year. The consumption structure is mainly non-renewable resources such as coal (72%) and oil (15%). The energy reserves are severely consumed, and S02 is generated. By-products such as NOx, polluting the atmosphere China is a big energy consumer. The total consumption is increasing at a rate of 6% to 7% per year. The consumption structure is mainly based on non-renewable resources such as coal (72%) and petroleum (15%). The reserves are severely consumed and produce by-products such as S02 and NOx, which pollute the atmosphere. Agroforestry residues (eg straw, wood-based sanding powder) are excellent biomass pellet fuels that are clean and renewable, although calorific (eg straw 15 000 kj/kg, poplar 17 000 kj/kg) than coal ( There is a gap between 21 000 and 30 000 kj/kg), but it can completely replace some coal and oil to meet the needs of urban and rural life and even industrial energy and environmental protection. Based on the previous studies, this paper discusses the process and performance of mixed fuels for rice and wood, and focuses on the effects of particle form and rice mixture ratio on product performance.
1. Materials and methods
1.1 Materials
Three kinds of scraps were selected as raw materials for fuel rods: 1) straw scrap (water content 9.6%); 2) straw bale (hereinafter referred to as “straw flourâ€, moisture content 7.5%), taken from Dingyuan, Jiangsu Science and Technology Development Co., Ltd.; 3) Wood-based wood sanding powder (hereinafter referred to as "wood powder", Yi Yang, moisture content 9.9%), taken from Xuzhou Changqing Oriented Structural Board Co., Ltd. The particle size distribution of the scrap is shown in Figure 1. It can be seen from the figure that all three kinds of scraps contain more fine powder (less than 80 mesh: 45.61% of straw scrap, 80.99% of straw board sanding powder, 67.39% of wood-based sanding powder), but straw crushed grain The diameter distribution is larger (more than 80 mesh 46.61%). The effects of the form of the raw materials on the process and properties of the forming fuel will be examined later.
Granulator straw briquetting machine
1.2 Fuel rod production process and preparation
The screw extrusion molding machine has a fuel rod with a regular hexagon and a 20 mm exhaust hole. Studies have shown that the key process factors for dense forming include: particle form, molding temperature, molding pressure (or screw speed) and particle moisture content. The basic process is: straw scrap and sanding powder preparation → pellet machine straw briquetting machine and other extruder heating - charging → extrusion finished product → residual fuel rod burning. Based on the research results of the predecessors, the process conditions of this study were determined as follows: the molding temperature was 300 ° C, the extrusion speed was 1 m / min, the water content was 8% to 10%, and the raw material ratio is shown in Table 1.
1.3 performance test
In order to reveal the compactness and combustion performance of the fuel rod, the density, burning rate, moisture, ash, volatile matter and fixed carbon content of the product were tested in accordance with CB/T 212-2001 "Industrial Analysis Method for Coal". In addition, since the fuel rod is formed by rubber-free extrusion, long-term moisture absorption (water) in the air may cause swelling or even collapse, and the concept of "Time-related Moisture Content" is proposed, and the water content of the reaction fuel rod is The relationship of time changes. The specific test method is as follows: the fuel rod sample is placed in a closed environment with a relative humidity of 100%, and the mass of the sample is weighed every 24 hours until the sample exhibits a collapse phenomenon, and then taken out and dried to obtain a dry mass. Based on this, the water content at each time point is obtained, and the correlation between the water content and the fuel rod collapse time is explored, which can provide reference for the storage and transportation of fuel rods (not carbonized).
2, results and analysis
2.1 density
Biomass compact molding technology is to compact loose biomass (such as sawdust, shavings, sanding powder, rice husk, etc.) by mechanical pressure and heating without external adhesive. Density and strength to improve the combustion properties of biomass. Density is one of the key factors in determining fuel formation, strength, durability, and combustion performance due to the lack of additional adhesives. It can be seen from Table 1 that the density of the rice wood powder fuel rod is generally higher than 1.0 g/cm3.
Fragment morphology and material properties have a significant impact on density levels. It can be seen from Table 1 that under the same extrusion process conditions, 100% straw scrap fuel rods can be well formed at a density of 1.0 g/cm3, while 100% straw board sanding powder and 100% wood wood-based panels. The sanding powder can reach 1.34 g/cm3 and 1.27 g/cm3 respectively. Obviously, the larger the shape, the stronger the interweaving ability of the scrap material, which is more conducive to molding. Relatively speaking, straw powder is weaker than “self-adhesive†of wood flour, which is mainly due to the barrier effect of inorganic minerals (such as silica), which are relatively high in straw flour. The mixed scrap (mixing ratio: 20%, 50%, 80%) also shows the above trend. The higher the content of straw scrap, the lower the required forming density; the mixed raw material of "wood flour-straw straw" The molding fuel density is lower than the "straw flour-tobacco scrap".
Jiang Yang et al. (2004) pointed out that the material suitable for biomass forming fuel should have a reasonable particle size of 5 mm and a length of 25 mm or less. This test further shows that within the above optimization range, the density of the molding fuel can be flexibly controlled by changing the particle form and material type to achieve the desired combustion performance.
2.2 Burning rate
Fuel form is an important factor affecting combustion performance. For scrap type fuels (such as sanding powder), the traditional chain type boiler must be modified by means of combustion or fluidized combustion; even then, the burning rate is affected by the uniformity of feeding, which is difficult to control; Forming, the above difficulties can be effectively improved. The test tested the burning rate of different proportions of fuel rods. At the initial stage of combustion (0~10 min), the concentration of volatile matter is large, the burning rate is generally fast, reaching 0.60~1.18 g/min; in the middle and late period (1~30 min), the gray shell is gradually thickened, which hinders the outward spillage of volatiles. , causing the burning rate to slow down and tend to be stable, reaching 0.03 to 0.09 g/min. As can be seen from Table 1, the change in the raw material has no significant effect on the burning rate.
2.3 Industrial Analysis
Industrial analysis covers water, ash, volatiles and fixed carbon
The standard test values ​​of the four indicators satisfy the following mathematical relationship: moisture content (%) + ash content (%) + volatile content (%) + fixed carbon content (%) = 100%. This test analyzes the fuel rods of different raw materials. The results are shown in Table 1 and Figure 2. The results show that the volatile matter content of all fuel rod products (test pieces 1 to 9) is similar (64.62%~69.27%), but the ash content (6.22%~20.85%) and the fixed carbon content (7.54%~22.37%) There was a significant difference in the change in the shape of the powder and the ratio of the raw materials. 1) Effect of the shape of the powder: The sample of No.1 and No.2 is representative. Although it is the same straw, the ash content of the crushed material (20.85%) is obviously higher than that of the sanding powder (13.41010). This can be analyzed from the manufacturing process of the straw board: straw cut-off (including sorting) → crushing → sorting - → straw crushing → straw board → sanding → sanding powder. It can be seen that from straw to sanding powder, it has undergone two sorting processes, resulting in a decrease in inorganic mineral (ash) content. 2) Influence of raw material ratio: With the increase of the proportion of straw and straw (20%→80%), the ash content of the mixed fuel rods increased significantly (“straw straw powderâ€: 6.62%→16.72%; “Straw straw → rice flourâ€: 14.90% → 19.36%).
Granulator straw briquetting machine
The above analysis further shows that by adjusting the shape of the powder and compounding different raw materials, the combustion performance of the fuel rod can be effectively improved.
2.4 aging water content
The shape and dimensional stability of the fuel rod is related to the storage time of the product. In the test, the accelerated wet change method (relative humidity 100010) was adopted to reveal the durability of the fuel rod. The results show that under the condition of initial moisture content of 0.32%-2.73%, the fuel rods of the nine raw materials have a moisture absorption of 4.89%~16.59% after 9-10 days of forced moisture absorption, which is generally characterized by collapse. The higher the initial moisture content, the higher the water content after 10 days. It is worth noting that in this test, the heating temperature condition of 300 °C is adopted, and there is no obvious carbonization on the surface of the product; if the carbonization protective layer on the surface of the fuel rod is given by adjusting the extrusion process, it is expected to prolong the storage period of the product. .
Granulator straw briquetting machine
Figure 3 shows the moisture content of the fuel rod as a function of time, taking the sample No. 1-3 as an example (other specimens show the same trend). It can be seen from the figure that under the condition of 100% relative humidity for 10 days, the moisture content MC(t) of the test piece has a strong linear relationship with the time t (regression coefficient R2 is shown in Table 2), namely: MC(t)=MCo +Kt. In the formula, MCo and K are the initial moisture content (%) and the hourly rate of change (%), respectively. The linear analysis parameters (hourly rate of change K, regression coefficient R2) of the nine test pieces are summarized in Table 2.
From Table 2, the moisture absorption rate of the fuel rod can be compared under different raw material ratio conditions. Among the three raw materials, the hourly rate of change of straw sanding powder was the largest (2,59%), followed by straw (2.34%) and wood powder (2.18%). This trend is also reflected in the blend of raw fuel rods. In the “straw straw-wood flour†mixed fuel rod, the K value showed a significant increasing trend with the increase of straw content (20%-80%). This indicates that the moisture variability of the mixed fuel rod can be controlled to some extent by utilizing the moisture absorbing difference of the scrap, wood powder and straw powder.
3. Conclusion
Biomass compact molding technology makes straw dust as an industrial fuel. Under the conditions of extrusion speed (pressure) and temperature determination, the material type, scrap form and finished product density are the key factors determining the performance of the molded fuel product. The method of coarse matching and material mixing can make straw and wood raw materials. Complementary advantages in terms of extrusion and hygroscopicity, giving the product excellent overall performance.
Sanmenxia Futong New Energy produces biomass fuel feed molding machinery such as pellet machine, straw briquetting machine and feed pellet machine.
Information from: Research on the manufacturing process and product performance of rice dust fuel rods http://
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