Mixed fuel composed of corn straw and salix psammophila and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of biomass fuels, and particularly relates to a mixed fuel prepared from corn straws and salix mongolica and a preparation method of the mixed fuel. The invention relates to a mixed fuel composed of corn straw and salix mongolica. The mixed fuel is obtained by mixing crushed corn straw and crushed salix mongolica according to a mass ratio of (1-3): 1 and then performing compression molding, the water content of the mixed fuel is 12%-18%; the unit density of the mixed fuel is 0.917 to 1.003 g / m < 3 >; the thickness of the interface transition layer of the mixed fuel reaches 8-15 microns; the pore size of the mixed fuel is smaller than 50 micrometers, and the mixed fuel meets the requirement of third-level fuel and is good in combustion performance.

Description

A blended fuel composed of corn stalks and willow branches and its preparation method Technical Field

[0001] This invention belongs to the field of biomass fuel preparation technology, specifically relating to a mixed fuel composed of corn stalks and sand willow and its preparation method. Background Technology

[0002] Depending on the composition of the raw materials, the preparation of biomass briquettes mainly falls into two technical paths: single-raw-material briquetting and mixed-raw-material briquetting. During the compression molding process of single biomass raw materials (such as straw, sawdust, etc.), due to insufficient lignin content or damage to the fiber structure, additional binders (such as starch, lignin sulfonates, or polyacrylamide) are usually added to improve the bonding strength and molding stability of the pellets. However, the introduction of binders is often a double-edged sword: on the one hand, it increases the cost of raw material pretreatment and additive procurement, directly raising the overall economic burden of fuel production; on the other hand, some binders may release volatile organic compounds or alter ash melting characteristics during combustion, adversely affecting the fuel's ignition temperature, combustion rate, and pollutant emissions, and even increasing the risk of slagging and corrosion in combustion equipment. Therefore, improving molding characteristics and combustion performance through the synergistic formulation of multiple biomass raw materials without relying on external binders has become an important research direction in the field of biomass energy utilization.

[0003] Against this backdrop, corn stalks, as a highly representative agricultural residue, are extremely abundant in resources and have a huge annual output, making them an important reserve source for biomass energy development. However, due to the imperfect collection, storage, and transportation system and the extensive traditional utilization methods, the open burning of corn stalks in the fields still occurs frequently. To alleviate this problem, converting corn stalks into solid briquettes has been considered an effective alternative. Existing research mostly uses binders to mix and mold corn stalks with sawdust or other agricultural and forestry wastes to reduce incineration pollution and achieve resource utilization. However, it is worth noting that while the introduction of binders improves the molding effect, it often negatively interferes with the pyrolysis behavior of the fuel—for example, reducing the volatile matter release rate, changing the pyrolysis reaction pathway, or increasing coke yield, thereby affecting the subsequent thermal conversion efficiency and energy recovery quality of the fuel.

[0004] In summary, the combustion feedstocks prepared by existing technologies have poor pyrolysis performance. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a mixed fuel composed of corn stalks and willow branches and its preparation method, which can solve the technical problem of poor combustion performance of mixed fuels formed by modifying corn stalks.

[0006] This invention is achieved by adopting the following technical solution: a mixed fuel composed of corn stalks and sand willow, which is obtained by mixing corn stalk fragments and sand willow fragments in a mass ratio of (1~3):1 and then compressing them; the moisture content of the mixed fuel is 12%~18%; the unit density of the mixed fuel is 0.917~1.003 g / m³. 3 The pore size of the mixed fuel is less than 50 μm.

[0007] Furthermore, the corn stalk fragments and sand willow fragments have a mesh size of 90 to 110 mesh.

[0008] Furthermore, the corn stalk fragments and sand willow fragments have a mesh size of 100.

[0009] Furthermore, the moisture content of both the corn stalk raw material used to make corn stalk shreds and the sand willow raw material used to make sand willow shreds is 14%.

[0010] A method for preparing a mixed fuel composed of corn stalks and sand willow includes the following steps: mixing 100-mesh corn stalks and 100-mesh sand willow at a mass ratio of (1~3):1, compressing and molding to obtain the mixed fuel; the compression speed is 8mm / min~12mm / min, the final compression pressure is 45kN~55kN, and the final compression pressure holding time is 50s~60s. This process effectively avoids the "explosion" phenomenon by controlling the compression speed and temperature, ensuring stable molding quality. "Explosion" refers to the abnormal phenomenon in which the internal moisture of the material is instantly vaporized by heating due to excessively fast compression speed or insufficient holding time, and the internal stress is rapidly released, thereby causing the molded particles to be suddenly ejected with a popping sound.

[0011] Furthermore, the compression speed is 10 mm / min.

[0012] Furthermore, the final pressure of the compression is 50 kN.

[0013] Furthermore, the final pressure of the compression is maintained for 60 seconds.

[0014] Furthermore, the compression temperature is 55℃~115℃.

[0015] Furthermore, the compression temperature is 100°C.

[0016] The claims will be amended after confirmation.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a mixed fuel composed of corn stalks and sand willow, which is obtained by mixing corn stalk fragments and sand willow fragments in a mass ratio of (1~3):1 and then compressing them; the moisture content of the mixed fuel is 12%~18%; the unit density of the mixed fuel is 0.917~1.003g / m³. 3 The interfacial transition layer thickness of the mixed fuel reaches 8μm~15μm; the pore size of the mixed fuel is less than 50μm, enabling it to be formed into smooth and dense particles. A suitable amount of moisture can be fully absorbed by the raw materials, reducing evaporation energy consumption, and also provides good lubrication and adhesion between particles, promoting the formation of solid bridges and resulting in good combustion performance. Especially when the moisture content is 12%, the ratio is 3:1, and the heating temperature is 100℃, the unit density of the mixed fuel is 1.003g / cm³. 3 1. It meets the requirements of Class 3 fuel. 2. The preparation process of this invention compresses the mixed raw materials into shape. Through the physicochemical complementarity of different raw materials, the overall performance is improved while reducing or avoiding the use of binders. This combination of raw materials not only makes full use of local resources and reduces collection and transportation costs, but also provides a feasible solution for the resource utilization of agricultural and forestry waste.

[0018] 3. The preparation method of the present invention achieves clean and efficient utilization through thermochemical conversion technology. The lignin content of sand willow is high, and it can play a binding role when heated; while the fiber structure of corn stalk is loose and easy to compress. The combination of the two can not only utilize the binding properties of sand willow to improve molding strength, but also take advantage of the easy compression of corn stalk to reduce energy consumption.

[0019] 4. This invention optimizes the mixed combustion of sand willow and corn stalks, and improves combustion efficiency and suppresses pollution emissions through ratio control, providing theoretical support for the large-scale application of biomass energy. Attached Figure Description

[0020] Figure 1 is a diagram of the morphology of the mixed fuel; where 1, 2, 3, 4, and 5 represent the mixed fuels obtained in Comparative Example 1, Example 2, Example 3, Example 4, and Comparative Example 2, respectively.

[0021] Figure 2 shows the effect of moisture content on the unit density and crush resistance of the shaped particles; where Shatterresistance represents crush resistance, Density represents unit density, and Moisture content represents moisture content.

[0022] Figure 3 shows the effect of the ratio on the morphology of the formed pellets; where 1, 2, 3, 4, and 5 represent the mixed fuels of Comparative Example 3, Comparative Example 4, Example 5, Example 3, and Example 6, respectively.

[0023] Figure 4 shows the analysis of the effect of proportion on the unit density and shatter resistance of the shaped particles; where shatter resistance represents shatter resistance, density represents unit density, and proportion represents proportion.

[0024] Figure 5 shows the effect of heating temperature on the morphology of the formed pellets; where 1, 2, 3, 4, and 5 represent the mixed fuels obtained in Comparative Example 5, Comparative Example 6, Example 7, Example 3, and Example 8, respectively.

[0025] Figure 6 shows the effect of deheating temperature on the unit density and crush resistance of the molded particles; where Shatterresistance represents crush resistance, Density represents unit density, and Temperature represents temperature.

[0026] Figure 7 shows the displacement-force curve; where Pressure represents pressure and Displacement represents displacement.

[0027] Figure 8 shows the microstructure of the best-formed particles; where (a) is a cross-section and (b) is a side view.

[0028] Figure 9 shows the microstructure of the combustion particles in Example 3; where (a) is a 50x magnified view of the cross-section of the combustion particles, (b) is a 150x magnified view of the cross-section, (c) is a 50x magnified view of the side view, and (d) is a 150x magnified view of the side view.

[0029] Figure 10 shows the microstructure of the combustion particles in Example 6; where (a) is a 50x magnified view of the cross-section of the combustion particles, (b) is a 150x magnified view of the cross-section, (c) is a 50x magnified view of the side view, and (d) is a 150x magnified view of the side view.

[0030] Figure 11 shows the microscopic morphology of the combustion particles in Comparative Example 7; where (a) is a 50x magnified view of the cross-section of the combustion particle, (b) is a 50x magnified view of the side view, (c) is a 150x magnified view of the cross-section, and (d) is a 150x magnified view of the side view. Detailed Implementation

[0031] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods. Specific explanations are needed as follows:

[0032] Both corn stalk and sand willow raw materials are from Inner Mongolia, China. The basic moisture content of both corn stalk and sand willow raw materials is 14%. High heating value is abbreviated as HHV; Scanning electron microscope is abbreviated as SEM; Micro-thermogravimetric curve is abbreviated as DTG; Thermogravimetric curve is abbreviated as TG.

[0033] To obtain the moisture content gradient for subsequent experiments, the required water volume is calculated using the following formula: In the formula: m w The water content is expressed in g; m0 is the raw material mass before preparation in g; k0 is the base moisture content in %; k1 is the set moisture content in %; subsequently, the raw materials are moistened and uniformly mixed, packaged in 100g / bags, and sealed for storage to prevent moisture evaporation. In this specific embodiment, all moisture content data are based on wet basis moisture content.

[0034] Example 1: A method for preparing a mixed fuel composed of corn stalks and sand willow, the specific steps of which are as follows: S1, crush the corn stalks and sand willow, and use a combination of sieves to screen them to remove excessively large or small raw material particles, because uneven material morphology will affect the quality of the shaped fuel. Take the crushed corn stalks and sand willow, and pass them through a 100-mesh sieve to obtain corn stalk fragments and sand willow fragments.

[0035] S2. Mix corn stalk fragments and sand willow fragments at a mass ratio of 1:1 to obtain 6.0g of mixture material with a moisture content of 12%.

[0036] S3. Load 6.0g of the mixture into the molding cavity for pre-pressurization and degassing, heat to 85℃, then compress to 50kN at a speed of 10mm / min and hold for 60s. After molding, the pellets are slowly ejected and sealed and stored in an environment of 25℃ to obtain the mixed fuel.

[0037] Example 2: A method for preparing a mixed fuel composed of corn stalks and willow branches, the specific steps of which are as follows: S1, crush the corn stalks and willow branches, and use a combination of sieves to sieve them to remove excessively large or small raw material particles, because uneven material morphology will affect the quality of the shaped fuel. Take the crushed corn stalks and willow branches, and pass them through a 90-mesh sieve to obtain corn stalk fragments and willow branch fragments, as shown in Figure 1.

[0038] S2. Mix corn stalk fragments and sand willow fragments at a mass ratio of 2:1 to obtain 6.0g of mixture material with a moisture content of 12%.

[0039] S3. Load 6.0g of the mixture into the molding cavity for pre-pressurization and degassing, heat to 85℃, then compress to 45kN at a speed of 8mm / min and hold for 60s. After molding, the pellets are slowly ejected and sealed and stored in an environment of 25℃ to obtain the mixed fuel.

[0040] Example 3S1: Corn stalks and sand willow are crushed and sieved using a combination of screens to remove excessively large or small raw material particles, as uneven material morphology will affect the quality of the molten fuel. The crushed corn stalks and sand willow are then passed through a 110-mesh sieve to obtain corn stalk fragments and sand willow fragments, as shown in Figure 1.

[0041] S2. Mix corn stalk fragments and sand willow fragments at a mass ratio of 2:1 to obtain 6.0g of mixture material with a moisture content of 15%.

[0042] S3. Load 6.0g of the mixture into the molding cavity for pre-pressurization and degassing, heat to 85℃, then compress to 55kN at a speed of 12mm / min and hold for 50s. After molding, the pellets are slowly ejected and sealed and stored in an environment of 25℃ to obtain the mixed fuel.

[0043] Example 4 is based on Example 2, but the water content is changed from 12% to 18%, while the rest remain unchanged, to obtain a mixed fuel.

[0044] Example 5 is based on Example 3, but instead of mixing corn stalk fragments and sand willow fragments in a 2:1 mass ratio, it is mixed with corn stalk fragments and sand willow fragments in a 1:1 mass ratio, with the rest remaining unchanged, to obtain a mixed fuel.

[0045] Example 6 is based on Example 3, but instead of mixing corn stalk fragments and sand willow fragments in a 2:1 mass ratio, it is mixed in a 3:1 mass ratio, with the rest remaining unchanged, to obtain a mixed fuel.

[0046] Example 7 is based on Example 3, but the heating temperature is changed from 85°C to 55°C, while the rest remains the same, to obtain a mixed fuel.

[0047] Example 8 is based on Example 3, but the heating temperature is changed from 85°C to 115°C, while the rest remains the same, to obtain a mixed fuel.

[0048] Example 9 is based on Example 2, but the heating temperature is changed from 85°C to 100°C, and the mass ratio of corn stalk fragments and sand willow fragments is changed from 2:1 to 3:1, with the rest remaining unchanged, to obtain a mixed fuel.

[0049] Comparative Example 1 was based on Example 2, but the water content was changed from 12% to 9%, while the rest remained the same, resulting in a mixed fuel.

[0050] Comparative Example 2 was based on Example 2, but the water content was changed from 12% to 21%, while the rest remained the same, resulting in a mixed fuel.

[0051] Comparative Example 3, based on Example 3, changed the mass ratio of corn stalk fragments and sand willow fragments from 2:1 to 1:0, with the rest remaining unchanged, to obtain a mixed fuel.

[0052] Comparative Example 4, based on Example 3, changed the mass ratio of corn stalk fragments and sand willow fragments from 2:1 to 0:1, while keeping the rest unchanged, to obtain a mixed fuel.

[0053] Comparative Example 5, based on Example 3, changed the heating temperature from 85°C to 25°C, while keeping the rest unchanged, to obtain a mixed fuel.

[0054] Comparative Example 6, based on Example 3, changed the heating temperature from 85°C to 145°C, while keeping the rest unchanged, to obtain a mixed fuel.

[0055] Comparative Example 7S1: Corn stalks and sand willow were crushed and sieved using a combination of screens to remove excessively large or small raw material particles, as uneven material morphology can affect the quality of the molten fuel. The crushed corn stalks and sand willow were then passed through a 100-mesh sieve to obtain corn stalk fragments and sand willow fragments.

[0056] S2. Mix corn stalk fragments and sand willow fragments at a mass ratio of 5:2 to obtain 6.0g of mixture. The initial moisture content of both corn stalk fragments and sand willow fragments is 14%.

[0057] S3. Load 6.0g of the mixture into the molding cavity for pre-pressurization and degassing, heat to 85℃, then compress to 50kN at a speed of 10mm / min and hold for 60s. After molding, the pellets are slowly ejected and sealed and stored in an environment of 25℃ to obtain the mixed fuel.

[0058] Experiment 1: Moisture Content Molding Test. Appropriate moisture content facilitates starch gelatinization, protein denaturation, and fiber dissolution during granulation, lubricating the raw material particles and improving bonding. When the moisture content is too low, the friction between raw material particles increases, leading to a decrease in bonding strength; when the moisture content is too high, the water vapor generated during compression accumulates, creating high pressure. If this pressure exceeds the structural strength of the raw material, the instantaneous release of steam upon demolding can cause fuel expansion or cracking. Therefore, by analyzing the effects of moisture content on the unit density, crush resistance, and appearance quality of the shaped granules, the optimal moisture content range was determined.

[0059] The morphology of the mixed fuels obtained from Comparative Example 1, Example 2, Example 3, Example 4, and Comparative Example 2 was observed, as shown in Figure 1. The mixed fuels obtained from Comparative Example 1 and Comparative Example 2 showed cracks, while the mixed fuels obtained from the Examples were intact. Specific data are shown in Table 1.

[0060] Table 1. Experimental data on the effect of moisture content on the unit density, crush resistance, and appearance of molded granules. Figure 2 shows the effect of moisture content on the molding effect. Under a fixed heating temperature and mixing ratio, the unit density and crush resistance of the mixed molding particles show the same trend, both increasing first and then decreasing with increasing moisture content. When the moisture content is 15%, both the unit density and crush resistance of the molding particles reach their maximum values.

[0061] Experimental results show that when the moisture content is 9%, insufficient moisture reduces the contact area between raw material particles, weakens intermolecular forces, and leads to a small number of cracks on the surface of the molded particles. Within the suitable moisture content range of 12% to 18%, the molding quality is significantly improved, and the particle surface becomes smooth and dense. This is mainly due to the fact that appropriate moisture can be fully absorbed by the raw material, reducing evaporation energy consumption, and also plays a good lubricating and binding role between particles, promoting the formation of solid bridges. However, when the moisture content increases to 21%, excessive moisture exceeds the raw material's absorption capacity. The resulting water film increases the interparticle gaps, and under pressure, water vapor that cannot escape from the closed mold is squeezed to the bottom, making it difficult to compact the particles, ultimately leading to loose and crumbling particles at the bottom.

[0062] In summary, the molding effect of the granules was good when the moisture content was between 12% and 18%, which determined the optimal moisture content range for subsequent orthogonal experiments.

[0063] Experiment 2: The morphology of the mixed fuels obtained from Comparative Examples 3, 4, 5, 3, and 6 was observed in Figure 3. The mixed fuels obtained from Comparative Examples 3 and 4 were irregular, while the mixed fuels obtained from the Examples were regular. Specific data are shown in Table 2.

[0064] Table 2. Experimental data on the effect of proportion on the unit density, crush resistance, and appearance of the molded pellets. Note: " / " indicates that the shape cannot be formed.

[0065] The effects of different proportions on the molding effect are shown in Figure 4. Under fixed moisture content and heating temperature, the molding density and crush resistance of the mixed pellets show the same trend, both increasing first and then decreasing with the increase of corn stalk proportion. When the proportion is 2:1, the unit density and crush resistance of the molded pellets reach their maximum values.

[0066] The molding density and crush resistance initially increased and then decreased with increasing corn stalk proportion. On the one hand, willow bark is more difficult to compress due to its higher lignin content, so reducing its proportion is beneficial for molding; at the same time, corn stalk particles can effectively fill the gaps between willow bark particles, increasing density. On the other hand, when the corn stalk proportion is too high, the amount of lignin that acts as a binder decreases, leading to a decrease in particle bonding strength.

[0067] Taking all factors into consideration, when the mixing mass ratio is (1~3):1, the forming effect of the shaped particles is better, which determines the optimal mixing ratio range for subsequent orthogonal experiments.

[0068] Experiment 3: The effect of heating temperature on the morphology of the mixed fuels obtained in Comparative Examples 5, 6, 7, 3, and 8 was observed, as shown in Figure 5. All the obtained mixed fuels were intact. Specific data are shown in Table 3.

[0069] Table 3. Experimental data on the effects of temperature on the unit density, crush resistance, and appearance of molded granules. Figure 6 shows the effect of heating temperature on the molding effect. Under fixed moisture content and ratio, the molding density and crush resistance of the mixed molding particles show the same trend, both gradually increasing with the increase of heating temperature.

[0070] At 25℃, the insufficient temperature prevents lignin from softening and exerting its binding effect, resulting in the lowest molding density and strength. Between 55℃ and 115℃, as the temperature increases, lignin softens and promotes particle plastic deformation, gradually improving molding quality. At 145℃, the synergistic effect of starch gelatinization, lignin softening, and protein denaturation optimizes molding performance; however, excessively high temperatures can cause lignin to melt, leading to difficulties in demolding and mold adhesion problems.

[0071] Taking all factors into consideration, the granulation effect was good when the heating temperature was between 55℃ and 115℃, which determined the optimal heating temperature range for subsequent orthogonal experiments. From an energy-saving perspective, the room temperature of 25℃ was retained for subsequent orthogonal experiments.

[0072] Experiment 4. Orthogonal Experiment: Based on the optimal parameter range determined by the single-factor experiments, a three-factor, five-level orthogonal experiment was conducted. The factors and levels are shown in Table 4. The single-factor experiments revealed that within the experimental range, unit density and shatter resistance exhibited similar trends. Therefore, the orthogonal experiment investigated the effects of moisture content (factor A), proportioning (factor B), and heating temperature (factor C) on the unit density of the formed particles to find the optimal combination of forming parameters and thus obtain the best forming effect. The orthogonal experimental design table is a standardized table created based on practical experience and theoretical understanding. This experiment used the L25 / 56 type Taguchi orthogonal experimental table, and 25 sets of experiments were planned. The experimental results are shown in Table 5.

[0073] Table 4. Factors and Levels of Orthogonal Experiment Table 5. Experimental data and results analysis of orthogonal experiments By performing range analysis on the unit density of the shaped pellets, as shown in Table 6, it can be seen from the range R value that the order of importance of the molding parameters affecting the unit density of the shaped pellets made from corn stalks and willow is C > A > B. Based on the mean value k, it is known that the unit density of the shaped pellets made from the corn stalks and willow reaches its maximum when using the mixed fuel B5 in Example 6 (C4). Specifically, the optimal combination of molding parameters for densely shaped pellets made from the corn stalks and willow is: a moisture content of 12%, a corn stalk to willow ratio of 3:1, and a heating temperature of 100℃.

[0074] Table 6. Extreme Value Analysis of Orthogonal Experiments SPSS software was used to perform analysis of variance and significance tests on the orthogonal experimental data to quantitatively evaluate the influence of each experimental factor on the unit density of the molded particles. As shown in Table 7, factor A had a significant effect on the unit density of the molded particles (P < 0.05); factor B had no significant effect on the unit density of the molded particles; and factor C had a highly significant effect on the unit density of the molded particles (P < 0.0001). The model coefficient of determination R0 was calculated. 2 =0.904, adjusted coefficient of determination R 2 =0.809, the difference is less than 0.2, indicating that the fitting accuracy is high and the model can fully represent the orthogonal experimental process.

[0075] Table 7 Results of orthogonal experiment variance analysis Note: " / " indicates that the item does not exist.

[0076] The optimal combination of molding parameters was not found in the orthogonal experiment. Verification experiments were conducted to prove the correctness of the theoretical analysis. When using the mixed fuel B5 from Example 6 (C4), the unit density of the molded particles in Example 9 was 1.003 g / cm³. 3 This is better than the maximum value of 0.976 g / cm³ observed in the orthogonal experiment. 3 This confirms that the obtained optimal molding parameter combination is relatively accurate. The density meets the requirements of NY / T1878-2010 Technical Conditions for Biomass Solid Molded Fuel, which specifies a density of ≥1.00 g / cm³ for Class III fuel. 3 The standard is met; the drop resistance is 97.6%, which is greater than the standard requirement of 97%.

[0077] Energy consumption is a crucial indicator to consider in actual production, and reducing energy consumption is essential while ensuring the quality of the shaped fuel. The optimal molding parameters are compared with those of the 10th group in the orthogonal experiment at room temperature (25℃), differing only in heating temperature. The compression energy consumption is then compared. Based on data collected by the pressure sensor, a displacement-force curve was plotted using Origin 2024, as shown in Figure 7. The compression energy consumption of the shaped pellets can be calculated by integration using the following formula:

[0078] In the formula, W is the compression energy consumption in J; F is the extrusion pressure in KN; X is the compression displacement in mm; the compression energy consumption is 100.33J and 131.79J respectively. Heating facilitates compression, increases molding density and reduces compression energy consumption.

[0079] Experiment 5: Physicochemical Properties of Raw Materials. Elemental analysis, industrial analysis, and calorific value analysis were performed on the raw materials according to GB / T 31391-2015 and GB / T 212-2008. The results are shown in Table 8. Physicochemical property analysis of the raw materials shows that corn stalks and sand willow have complementary advantages in elemental composition and combustion characteristics. Elemental analysis shows that the sulfur content of both raw materials is low, with corn stalks at 0.07% and sand willow at 0.05%, meaning the maximum sulfur content of the mixed raw material does not exceed 0.10%. Industrial analysis shows that the ash content of sand willow is 6.78%, higher than that of corn stalks (4.02%). The ash content of herbaceous biomass is often significantly higher than that of woody biomass, which is inconsistent with this test result. This is because the sand willow raw material used has a high bark content; a reasonable ratio can effectively balance the ash content and improve combustion performance. Calorific value determination results show that the HHV of both raw materials is superior compared to other biomass. These characteristics indicate that the mixture of corn stalks and sand willow to prepare briquettes has good performance in terms of both environmental protection and energy efficiency.

[0080] Table 8 Physicochemical Properties of Raw Materials Note: S is sulfur, Aad is ash, ar is as received, all others are air-dried, LHVar is lower heating value, and Mtar is total moisture.

[0081] Experiment 6: Energy Density Test of Molded Particles in Example 9. Energy density represents the energy storage capacity of a sample. The overall combustion performance of the mixed molded particles was further analyzed by calculating the energy density. The formula is as follows: ED = HHV × ρ / 1000, where ED is the energy density; the unit is GJ / m³. 3 ρ represents the unit density of the formed particles, in kg / m³. 3 .

[0082] Testing revealed that the HHV of the molded particles from Example 9 was 19.42 MJ / kg, higher than that of the two raw materials. This is because under high pressure, the distance between raw material particles decreases, the intermolecular forces increase, and new hydrogen bonds are formed between different functional groups, leading to increased heat of reaction during combustion and thus higher calorific value. Calculations showed that the ED of the molded particles from Example 9 was 19.48 GJ / m³. 3 It is 1.66 times that of corn stalk raw material and 1.82 times that of sand willow raw material, and its combustion performance is significantly improved.

[0083] Experiment 7 Scanning Electron Microscopy Analysis of Molded Particles from Example 9 The microstructure of the molded particles from Example 9 is shown in Figure 8. Observing the cross-section of the sample, as shown in Figure 8(a), it was found that heating softened the lignin, and the presence of moisture caused it to partially dissolve in water. After molding, as the temperature decreased, the dissolved lignin recrystallized, exhibiting crystal filling, marked by green circles. Both corn stalks and willow branches are composed of fibers. During the compression molding process, longer fibers broke into sheets, while intact fibers intertwined and entangled, forming a "woven" interlocking structure, marked by yellow circles. The willow fiber network structure, acting as a "skeleton," could encapsulate small-diameter corn stalk particles. When the small-diameter particles were not completely filled, pores appeared, marked by red circles; this phenomenon was less common in the figure. Heating gradually softened the lignin, allowing it to penetrate the fiber surface and interparticle gaps, forming "glue-like" bridges, marked by blue circles. The thin-walled tissue of corn stalks has a natural layered structure. Under pressure, the raw material particles slide and form layered stacks, marked by white circles, similar to the effect of "folding paper". The more uniform the particle size of the crushed material, the smoother the stacking. Observing the side view, as shown in Figure 8(b), it can be seen that there are no obvious boundaries between particles, the side is smooth, and slight carbonization occurs near the inner wall of the mold when heated.

[0084] Using SEM with energy-dispersive X-ray spectroscopy to determine the elemental distribution, it was found that the sulfur content in the cross section was 0.08%, and no sulfur was detected in the side section. This meets the requirements of Grade 1 mixed biomass pellet fuel in the "NB / T34024-2015 Biomass Pellet Fuel Quality Classification" standard, where the sulfur content in the cross section of Grade 1 mixed biomass pellet fuel is less than or equal to 0.10%.

[0085] In summary, experiments 1-7 show that the unit density of the molded granules is mainly affected by the heating temperature and moisture content, while the ratio is a marginal factor. The experiments determined that a moisture content of 12%, a ratio of 3:1, and a heating temperature of 100℃ are the optimal combination of molding parameters, under which the unit density is 1.003 g / cm³. 3It meets the requirements for Class 3 fuel. With the same moisture content and proportions, compared to a room temperature of 25℃, heating at 100℃ increases the unit density by 16.1% and reduces compression energy consumption by 23.9%. Heating facilitates compression, reducing energy consumption while ensuring molding effect. Elemental analysis, industrial analysis, and calorific value testing revealed that the complementary physicochemical properties of the two raw materials improve combustion performance. Microscopic analysis of the molded particles shows that the tight bonding between the fiber skeleton and the filler particles is key to molding, and the sulfur content meets the requirements for Class 1 fuel.

[0086] Experiment 8 Thermogravimetric Analysis (TGA) Samples: Pure corn stalks, pure sand willow, and the mixed fuels of Example 3, Example 6, and Comparative Example 7 were all tested three times, and the average value was taken. The standard deviation of the DTG peak temperature was controlled within ±2.5℃ / min, and the deviation of the TG weight loss rate was ≤±1.5%.

[0087] A Netzsch STA449F3 Jupiter simultaneous thermal analyzer (Germany) was used to accurately observe and record the dynamic curves of continuous weight loss of the samples over time and with increasing temperature. Three different heating rates—5℃ / min, 10℃ / min, and 15℃ / min—were selected. This design of three heating rates meets the needs of basic research for elucidating the reaction mechanism while also considering parameter calibration for engineering applications, providing a multi-scale research framework for the clean utilization of biomass blended fuels. The temperature range was set from 30℃ to 800℃ to ensure complete sample reaction. High-purity 99% nitrogen was used as the carrier gas as a protective gas. Combustion experiments were conducted when the temperature reached 30℃, with the gas flow rate maintained at 20 mL / min.

[0088] The TG and DTG curves of biomass fuels are core tools for studying their thermochemical properties, enabling systematic analysis of the fuel's pyrolysis, combustion characteristics, and energy release patterns. The TG curve visually presents the weight loss process of fuel at different temperature ranges through the change in mass with temperature, mainly divided into three stages (see Table 9). The drying stage (100–200℃) reflects moisture evaporation; the volatile matter release stage (200–500℃) reflects the rapid release of volatiles and the decomposition of solid carbon; and the fixed carbon combustion stage (>500℃) characterizes the oxidation of fixed carbon and ash residue. The DTG curve, as the derivative of the TG curve, further reveals the peak temperature of the mass loss rate and reaction kinetic parameters, clarifying the dominant temperature ranges for volatile matter release and fixed carbon combustion.

[0089] Table 9 Characteristics of each stage of combustion Based on the thermogravimetric-derivative thermogravimetric curve (TG-DTG) obtained by referring to thermogravimetric analysis, the T value of the sample is obtained. i The ignition temperature of biomass fuel, ν max For the maximum combustion rate, T Pν is the temperature corresponding to the maximum combustion rate. α T represents the average combustion rate. f S is the burnout temperature. N This is a comprehensive combustion characteristic index.

[0090] Based on the above parameters, the following formula is used: ; β is the heating rate; ε i ε p The average combustion rate ν and the comprehensive combustion characteristic index S can be derived from the remaining mass fraction of the sample corresponding to the ignition temperature and burnout temperature. N .

[0091] Thermogravimetric curves (TG / DTG) were used to assess the thermal stability of biomass based on reactivity. Overall, the reactivity index plays a crucial role in understanding the pyrolysis and combustion processes of biomass materials.

[0092] The reactivity index is analogous to a thermometer for biomass materials. A higher value indicates a stronger tendency to burn, making the material more ideal for controlled combustion or efficient clean energy. This index is used to examine how it fluctuates with factors such as heating rate or biomass composition during the production process of converting biomass materials into biomass fuel. The reactivity index at peak temperature is used to characterize pyrolysis using the following formula combined with a thermogravimetric curve reflecting the thermal stability of biomass:

[0093] DTG max The maximum weight loss rate due to volatilization is expressed as % / min; Tp is the temperature corresponding to the maximum combustion rate, expressed as °C.

[0094] The results are shown below: The TG curve visually presents the weight loss process of fuel at different temperature ranges through the change in mass with temperature, mainly divided into three stages. As the heating rate increases from 5℃ / min to 15℃ / min, the temperature range for the volatilization stage and the fixed carbon combustion stage of corn stalks shifts to the right from 432℃ to 636℃. When the heating rate is too fast, the heat transfer inside the material lags behind, requiring a higher temperature to complete the process. max It doubles with increasing heating rate: 4.705% / min at 5℃ / min to 10.502% / min at 15℃ / min. α The rate increased synchronously, from 1.91% / min to 2.91% / min. The increased heat input per unit time accelerated the release of volatiles and the oxidation of fixed carbon. iThe temperature dropped from 247℃ to 208℃, indicating that heat accumulates rapidly on the material surface at high heating rates, making it easier to reach the ignition critical conditions and reducing the difficulty of ignition. Both the comprehensive combustion index and the reactivity index increase with the increase of the heating rate.

[0095] The thermal decomposition trend of *Salix psammophila* is consistent with that of corn stalks, but due to its dense microstructure, SEM shows that *Salix psammophila* particles are dense with few pores; its carbon content is high, 52.19% vs. 46.3% for corn stalks; exhibiting obvious uniqueness; under the same heating rate, the thermal decomposition temperature (Tc) of *Salix psammophila* is higher. P The significantly higher temperature than corn stalks indicates that *Salix psammophila* requires a higher temperature to reach its maximum combustion rate, suggesting stronger thermal stability. At a low heating rate of 5℃ / min, the *ν* of *Salix psammophila*... max The heat transfer rate was 3.247% / min, lower than that of corn stalks (4.705% / min), because the dense structure of *Salix psammophila* hinders heat and mass transfer; at a high heating rate of 15℃ / min, the *ν* of *Salix psammophila*... max The rate of heating (11.285% / min) surpassed that of corn stalks (10.502% / min) because the concentrated heat at the high heating rate accelerated the reaction. (Salix matsudana T) f The temperature of sand willow is consistently higher than that of corn stalks, requiring a higher temperature to burn completely. This is because sand willow has a higher ash content, and the residual ash hinders heat transfer. At the same heating rate, the overall combustion performance of sand willow is lower than that of corn stalks, due to the lower proportion of fixed carbon and slightly poorer combustion stability.

[0096] Using corn stalks as the main fuel, a low-to-medium heating rate of 5℃ / min to 10℃ / min is sufficient to ensure good combustion performance. If sand willow is used as the main fuel, a medium-to-high heating rate of 10℃ / min to 15℃ / min is needed to overcome the resistance of its dense structure. The high calorific value of sand willow and the high combustion stability of corn stalks can complement each other.

[0097] At a low heating rate of 5℃ / min, the total weight loss of the other three groups of samples from 180℃ to 680℃ was approximately 67%. However, the TG curves showed that the mixed fuel of Example 6 exhibited a steeper weight loss slope, indicating that it maintained a relatively high decomposition rate even at low temperatures. Correspondingly, the maximum combustion rate νmax of the mixed fuel of Example 6 reached 4.671% / min, higher than the 3.062% / min of the mixed fuel of Example 3 and the 4.068% / min of the mixed fuel of Comparative Example 7. Furthermore, the peak position was close to that of corn stalks, indicating its easy ignition and high reactivity. In contrast, the mixed fuel of Example 3 had a lower DTG peak due to the weak interfacial bonding caused by the excessive proportion of corn stalks, while the mixed fuel of Comparative Example 7 had a reactivity index RM of only 0.0268%·min due to the local aggregation of sand willow. -1 ·℃ -1 The concentration was lower than 0.0307% per min of the mixed fuel in Example 6. -1 ·℃ -1The overall combustion index of the mixed fuel in Example 6 (0.953) was higher than that of the mixed fuel in Example 3 (0.842) and the mixed fuel in Comparative Example 7 (0.859). At a heating rate of 10°C / min, the burnout temperature Tf of the three TG curves was... f All values ​​increased significantly from 5℃ / min, with the mixed fuel in Example 6 increasing from 482℃ to 569℃. However, the mixed fuel in Example 6 showed more complete weight loss and less residual ash during the burnout stage of its TG curve. This is attributed to its uniform pore structure, which provides channels for oxygen diffusion and promotes the full oxidation of fixed carbon. The DTG curve shows that the mixed fuel in Example 3 exhibits significantly higher ν0.05. max The combustion rate of the mixed fuel in Example 6 was 8.594% / min, slightly higher than the 8.045% / min of the mixed fuel in Example 6. However, the peak value of the mixed fuel in Example 6 was wider and more concentrated at 331.35°C, which is lower and avoids local overheating and coking. The overall combustion coefficient of the mixed fuel in Example 6 reached 1.65, an increase of 21.3% compared to 1.36 of the mixed fuel in Example 2, and an increase of 11.5% compared to 1.48 of the mixed fuel in Comparative Example 7. The average combustion rate ν... α The ignition temperature Ti of the three groups was 2.16% / min, the highest among the three groups, indicating the best combustion stability. When the heating rate reached 15℃ / min, at a high rate, the ignition temperature Ti of the three TG curves was... i All were reduced to the lowest values. The mixed fuel of Example 6, at 209°C, was the easiest to ignite because its uniform microstructure allowed heat to be quickly transferred to the whole, avoiding localized cold spots. Although the peak value of the DTG curve of the mixed fuel of Comparative Example 7 was the highest among the three groups at 12.519% / min, the TG curve showed that its T f The initial temperature was only 583℃, resulting in premature burnout. This was due to the accumulation of sand willow, leading to intense localized reactions and rapid burnout, resulting in low overall heat utilization. While the peak DTG of the mixed fuel in Example 6 (10.249% / min) was lower than that of the mixed fuel in Comparative Example 7, it exhibited the highest peak symmetry and no significant tailing, indicating a smooth transition between the volatile matter removal and fixed carbon combustion stages. Ultimately, the overall combustion coefficient of the mixed fuel in Example 6 reached 3.01, a 16.2% improvement over the 2.59 of the mixed fuel in Example 2 and a 13.2% improvement over the 2.66 of the mixed fuel in Comparative Example 7. The reactivity index R... M 0.0565%·min -1 ·℃ -1 It also has the highest value among the three groups, achieving a balance between reactivity and stability.

[0098] In summary, the three groups of samples showed a common trend as the heating rate increased: T i The temperature continues to decrease, for example, the mixed fuel in Example 6 decreased from 256°C to 209°C; max With ν α Significantly elevated, T P With T f Move right, SN With R M The simultaneous improvement confirms the uniformity of the thermal decomposition mechanism. The mixed fuel of Example 6 performed optimally at all heating rates. Essentially, the 3:1 ratio achieved the complementary properties of corn stalks ("high volatile matter, easy to ignite") and willow ("high calorific value, anti-coking"), combined with a uniform microstructure and a low activation energy of 49.13 kJ / mol at 5℃ / min, which is lower than the 51.58 of the mixed fuel of Example 2 and the 56.53 of the mixed fuel of Comparative Example 7. This makes it the optimal ratio that balances combustion efficiency, stability, and anti-coking properties, providing a clear basis for the selection of mixed fuel ratios and the control of heating rates in industrial applications.

[0099] Experiment 9: Microscopic Morphology Analysis of Individual Samples. The morphology of corn stalks, willow branches, and mixed fuels was characterized using SEM, focusing on the surface morphology and pore structure distribution. The samples were cut longitudinally and transversely; then, the cut surfaces were finely polished with sandpaper (0.015mm–0.025mm), and surface dust was removed with a blower. Finally, the microstructure of the cut surfaces was observed and analyzed under an inverted metallographic microscope.

[0100] SEM images of corn stalks reveal typical plant fiber structural features. At 50x magnification, the stalk surface exhibits a rough, porous morphology, with fibers arranged in a directional pattern. Numerous micropores exist between the fibers, with uneven pore size distribution. This porous structure is a typical microscopic feature of corn stalks, reflecting their natural fibrous tissue structure. At higher magnification, the stalk fiber surface appears relatively smooth, lacking effective bonding structures. This microscopic morphological characteristic may lead to insufficient molding strength when using stalks alone. Side views at 50x and 150x magnification show a relatively smooth surface, a lack of tight bonding between fibers, and noticeable fiber separation gaps.

[0101] SEM images of the *Salix psammophila* samples revealed a microstructure significantly different from that of corn straw. The *Salix psammophila* particles exhibited a denser morphology, a smoother surface, and fewer, unevenly distributed pores. At 50x magnification, distinct bright areas were observed on the surface of the *Salix psammophila* particles, which may be a unique microstructural feature. At 150x magnification, the microstructural features of the *Salix psammophila* particle surface were more clearly observed, including a denser structure and irregular surface morphology. This dense structure is typical of *Salix psammophila* materials and may contribute to the formation of a stable granular structure. Side views at 50x and 150x magnification showed a few fine cracks on the surface, but no obvious large pores, and the interfiber bonding was higher than that of corn straw.

[0102] SEM images of the blended fuel sample from Example 3 show that, at a 2:1 ratio, corn stalk fibers dominate, forming a continuous matrix structure. Willow granules are distributed as a dispersed phase within the stalk fiber network, but their distribution is not uniform, and aggregation of willow granules can be observed in some areas. In a 150x magnified image, the interface structure between the stalk fibers and willow granules is visible, with a narrow transition region of 8-10 μm. This microstructural characteristic indicates limited physical cross-linking between the two materials and insufficient interfacial bonding. Side views show a continuous fiber bonding layer on the surface, reduced crack numbers, and a small number of "honeycomb" micropores, balancing structural stability and oxygen diffusion channels, as shown in Figures 9(c) and (d).

[0103] SEM images of the blended fuel sample from Example 6 reveal the microstructural features under optimal proportions. In the 50x magnified image, light gray willow particles are clearly visible, uniformly dispersed within a continuous matrix of dark gray corn stalk fibers, forming an ideal "continuous phase-dispersed phase" composite structure. As shown in Figures 10(c) and (d), the side SEM images of the blended fuel sample from Example 6 show that under a molding pressure of 52.5 ± 2.5 MPa, the willow particles are deeply embedded in the stalk fiber network, forming a highly dense composite. This densification process results in a sample surface pore size generally less than 50 μm, forming a relatively uniform microstructure. As shown in Figures 10(a) and (b), the cross-sectional SEM images of the blended fuel sample from Example 6 reveal a more complex microstructure. A distinct transition layer, 11 μm to 15 μm thick, is formed at the interface between the willow particles and the stalk fibers. This relatively thick interfacial transition layer indicates better physical cross-linking of the two materials at the microscale. In the 150x magnified image, it can be observed that the pores in the blended fuel sample of Example 6 are uniformly distributed, forming an interconnected network structure. This microscopic pore structure is a unique microscopic morphological feature of the blended fuel of Example 6.

[0104] SEM images of the mixed fuel sample of Comparative Example 7, as shown in Figure 11, reveal that at a 5:2 ratio, the content of *Salix matsudana* (a type of sand willow) increased relatively, leading to significant changes in the microstructure. In the 50x magnified image, an increased proportion of *Salix matsudana* particles was observed, with particle aggregation appearing in some areas, disrupting the ideal "continuous phase-dispersed phase" structure. In the 150x magnified image, the interfacial transition layer of the mixed fuel sample of Comparative Example 7 was observed to be thinner, ranging from 7 μm to 9 μm, and the interfacial structure was less clear than that of the mixed fuel sample of Example 6. Furthermore, the pore distribution in the mixed fuel sample of Comparative Example 7 was less uniform than that of the mixed fuel sample of Example 6, with larger pores appearing in some areas, indicating poor uniformity of the microstructure.

[0105] Based on the TG / DTG curves, combustion characteristic parameters, Table 10, and SEM microstructures of the three mixed fuels (Example 3, Example 6, 3:1, and Comparative Example 7, 5:2), the thermogravimetric behavior of the three samples under different heating rates (5℃ / min, 10℃ / min, and 15℃ / min) was analyzed. First, the core differences among the three samples need to be clarified: the differences in microstructure and component complementarity caused by different ratios. The mixed fuel of Example 3 exhibits corn-like characteristics due to its high corn stalk proportion. The mixed fuel in Example 6, with a 3:1 ratio, forms an ideal "continuous phase-dispersed phase" structure where the corn straw fiber is dominant, the willow bark is unevenly dispersed, and the interfacial transition layer is narrow (8-10 μm). The mixed fuel has a 3:1 ratio, resulting in willow bark particles uniformly embedded in the corn straw fiber network, an interfacial transition layer thickness of 11-15 μm, and uniform pore distribution with a pore size of less than 50 μm. In contrast, the mixed fuel in Comparative Example 7 exhibits problems such as local particle aggregation, a thin interfacial transition layer (7-9 μm), and poor pore uniformity due to the increased proportion of willow bark. This structural difference is directly reflected in the TG / DTG curve characteristics and combustion parameters.

[0106] Table 10 Combustion characteristic parameters of different samples Experiment 10 Combustion kinetics analysis used the Coats-Redfern integral method, the Flynn-Wall-Ozawa method, and the Kissinger-Akahira-Sunose method to determine the activation energy E and the pre-exponential factor A from thermogravimetric experimental data.

[0107] Verification using the Coats-Redfern, FWO, and KAS methods showed that the mixed fuel in Example 6 exhibited significant kinetic advantages. In the Coats-Redfern method, the activation energy of the mixed fuel in Example 6 during the volatilization stage was lower, with an activation energy of 49.13 kJ / mol at 5 °C / min, compared to a higher pre-exponential factor for the mixed fuel in Example 7. Under the FWO and KAS methods, the average activation energy of the mixed fuel in Example 6 (138.39 and 139.88 kJ / mol) was similar to that of the mixed fuel in Example 7, indicating that the mixed fuel in Example 6 was easier to initiate and had a higher probability of reaction.

[0108] Verification using the Coats-Redfern, FWO, and KAS methods showed that the blended fuel in Example 6 exhibited significant kinetic advantages. In the Coats-Redfern method, the activation energy of the blended fuel in Example 6 during the volatilization stage was lower (E = 49.13 kJ / mol at 5 °C / min), lower than that of the blended fuel in Comparative Example 7, with a higher pre-exponential factor. Under the FWO and KAS methods, the average activation energy of the blended fuel in Example 6 (138.39 and 139.88 kJ / mol, respectively) was lower than that of the blended fuel in Comparative Example 7, with minimal difference between the two methods, confirming that the blended fuel in Example 6 was easier to initiate and had a higher probability of reaction.

[0109] The blended fuel in Example 6 achieves component complementarity by combining the "high volatile matter and easy ignition" of corn stalks with the "high calorific value and anti-coking" properties of sand willow. Combined with optimal microstructure and kinetic characteristics, it achieves a multi-dimensional performance balance: an ignition temperature of 209°C at 15°C / min, high burnout efficiency, and the localized coking problem of the blended fuel in Example 7. It meets the requirements of "easy ignition, high combustion efficiency, strong stability, and low coking risk," and it is recommended that industrial applications adopt this ratio with a heating rate of 10°C / min to 15°C / min to maximize energy utilization value.

[0110] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A mixed fuel composed of corn stalks and sand willow, characterized in that, The mixture is made by compressing a mixture of corn stalk fragments and willow stalk fragments at a mass ratio of (1~3):1; the moisture content of the mixture is 12%~18%; and the unit density of the mixture is 0.917~1.003 g / m³. 3 The pore size of the mixed fuel is less than 50 μm.

2. The blended fuel according to claim 1, characterized in that, The corn stalk fragments and sand willow fragments have a mesh size of 90-110 mesh.

3. The blended fuel according to claim 2, characterized in that, The corn stalk fragments and sand willow fragments have a mesh size of 100.

4. The blended fuel according to claim 1, characterized in that, The moisture content of both the corn stalk raw material used to make corn stalk shreds and the sand willow raw material used to make sand willow shreds is 14%.

5. The method for preparing the blended fuel according to claim 1, characterized in that, The process includes the following steps: mixing corn stalk fragments and sand willow fragments at a mass ratio of (1~3):1, compressing them into a mixed fuel; the compression speed is 8mm / min~12mm / min, the final compression pressure is 45kN~55kN, and the final compression pressure is maintained for 50s~60s.

6. The method for preparing the blended fuel according to claim 5, characterized in that, The compression speed is 10 mm / min.

7. The method for preparing the blended fuel according to claim 5, characterized in that, The final pressure of the compression is 50 kN.

8. The method for preparing the blended fuel according to claim 5, characterized in that, The final pressure of the compression is maintained for 60 seconds.

9. The method for preparing the blended fuel according to claim 5, characterized in that, The compression temperature is 55℃~115℃.

10. The method for preparing the blended fuel according to claim 9, characterized in that, The compression temperature is 100°C.

Images