Briquette Production and Characterization

The residues obtained before briquetting were dried in natural environment (In summer, outdoor temperature: 28ºC, outdoor humidity: 42%). In addition, in order to accelerate the drying time of the residues, the drying process was accelerated by taking the residues into the glass greenhouse (outdoor temperature: 36ºC, outdoor humidity: 35%). For the briquetting experiments, the moisture content of the residues was determined in the range of 8-10% in accordance with the standards [15]. Agricultural residues, which were dried, were ground in a hammer mill and 2-5 mm particle size determined for the study and in accordance with the standards for the briquetting process.

A specially designed hydraulic type briquetting machine was developed and briquetting of the residues was carried out. In the developed hydraulic type briquetting machine, the compression pressures can be adjusted between 0-240 MPa. The specified working pressures have been set on the machine with the help of a pressure gauge. The hydraulic press carries out the compression process with a horizontal positioning of its cylinder and piston. Here’s the optimized content: Fig. 1 shows the hydraulic briquetting machine used for agricultural residue briquetting, while Fig. 2 displays the mold features. In the experiments, the briquettes were obtained as full. The cylindrical mold has a length of 135 mm, an inner diameter of 50 mm and a wall thickness of 25 mm.

The new design briquetting machine was tested at five different working pressures to determine its optimal performance. These three instances, Krizan P. [17], et al., Zhang J. and Guo Y. [18] and Sun B. [19] et al. demonstrate similarities with their respective studies. The agricultural residues were ground in a hammer mill after being dried, and then brought to an appropriate particle size for the briquetting process. The compaction process was carried out without the use of any additional material. No extra materials were added during the process. The residue was transferred to the material tank and then pushed into the cylindrical mold using a piston. In each trial, approximately 150-250 g residue was poured into the mold gradually, depending on the filling state of the mold. Afterward, the compaction process was performed. The compacted material was pressed for an extra 20 seconds to avoid any expansion after the compaction process was completed. Briquettes measuring 50 mm in diameter and 80-110 mm in length were produced as a result of the briquetting process.

Fig. 1.

General view and main structural elements and mold used of the specially designed hydraulic type briquetting machine (A: 1280 mm; B: 1155 mm; C: 740 mm) [16].

Fig. 2.

PCA graph of operating characteristics P: pressure P1: 80 MPa, P2: 100 MPa, P3: 120 MPa, P4: 140, MPa, P5: 160 MPa.

Briquetting Process

Huang Q.B. [20] et al. and Saeed A.A.H. [21] et al. reported that moisture content is very important in both material strength and compaction. With these studies in parallel with EU standards, the moisture content has been determined as 8-10% for apricot pruning residues depending on these standards [22]. The dried material was ground using an electric hammer mill equipped with 8 hammers rotating at a speed of 2850 rpm and powered by 3 kW. The ground particles had a size range of 2-5 mm, and the moisture content was measured again. Subsequently, the particles were compacted into briquettes using a briquetting machine [23]. Table 1 provides the properties of the apricot pruning residues utilized in the briquetting experiments.

Briquette Tests

The tests made for the briquettes obtained from the residues released after the pruning of the apricot tree are given in the Table 2 together with the standards.

Work Capacity and Energy Consumption

After the briquetting machine entered the regime, a specific amount of material was added to the material warehouse to determine the machine’s capacity and energy consumption. The machine’s work capacity was determined by measuring the briquetting time of the material poured into the warehouse and was calculated as kg.h^-1. The machine’s energy consumption was determined by reading the electricity meter it is connected to, measured in kWh. The processes were conducted thrice in order to ascertain the mean machine work capacity and energy consumption.

Specific Energy Consumption

The machine’s briquetting capacity was determined by dividing the mass of produced briquettes by the time taken to complete the briquetting process. The specific electrical energy consumption of the machine was determined by calculating the ratio of consumed electrical energy to machine capacity (kWh. kg^-1) during a certain amount of briquette production while the machine was operating under regular conditions.

Statistical Analysis

The use of the SPSS statistical package program was employed to analyze the alterations in briquette parameters based on pressure and size. The article contains the relationship between significant variables was subjected to Duncan multiple comparison test. The XLSTAT package program was utilized to perform principal component analysis (PCA) on the variables.

Density of Raw Materials and Briquettes, Compaction Rate and Moisture of the Material

Density is an important parameter that determines physical quality of briquettes. According to Davies R.M. and Davies O.A. [35] and Ikubanni P.P. [36] et al. the higher the density, the better and higher is the energy/volume ratio. When the moisture level of particles is high, fine materials are unable to bind and instead only grind and become dirty, whereas coarse materials turn into pulp. Smaller particles have a greater capacity to absorb moisture compared to larger particles, resulting in a more intense grinding process. However, when it comes to high density briquetting, the size of the particles does not greatly affect the quality of the briquettes. This is due to the high pressure applied during compaction, which, combined with the heat applied, causes the lignin to melt and bind the material particles together. The densities of the materials used in the experiment before and after briquette were determined and given in Table 3. Acceptable briquette density should be 900 kg.m^-3 and above [27]. In the study by [37], higher density briquettes were obtained with more small particles in the particle size distribution [38,39]. However, in hydraulic briquette machines, the power of the machine also determines the density of the briquette. It has been seen that the different compaction pressures used in the briquette machine used are sufficient to obtain the desired density briquette. In these new designed hydraulic type of briquette machines, it is recommended that the moisture content of the material be in the range of 8-10%. The compaction ratio of the material is important for the storage, storage and transportation of the raw material [40]. As the compression ratio increases, it is better understood that briquetting of the material is necessary for storage and transportation. In this respect, the apricot branch is close to the tree dust. The particle sizes of the materials are important for compaction, but they do not need to be crushed too small. Particle sizes vary according to the type of material.

Tumbler and Shatter Test, Deformation Resistances

These are the tests carried out to determine the strength of the briquettes and the losses that may occur as a result of the vibrations that may occur during storage and transportation [41]. These tests are performed on special devices and are expressed as %. The generally acceptable value should be 95% and above [27]. According to [42], the gravitational resistance to drop should attain a value higher than 90%. According to the test results, apricot pruning residues gave values below 95%. It has been observed that the relevant standards are met at pressures other than 80 MPa compression pressure in the shatter test (Table 5). Apricot pruning residue is above the standard in this respect. Another measure of the strength of the briquette (Briquette firmness) is its good deformation resistance. This value is calculated by the pressure applied on the product with a special device. It is desirable that the value be high (at least 2000 N). Table 3 shows the values obtained as a result of the analysis.

According to Table 3, it can be observed that the particle size has a more significant impact on the quality parameters of the produced briquettes, specifically when considering their interactions, at a significance level of 1%. As a result of the tests, it was observed that there was not much fragmentation in the briquettes and did not break into pieces for all the durability tests examined. According to the literature, the maximum value for gravitational resistance during a drop is 93.09%, while the minimum value is 89.55%. This aligns with the findings in reference [42], which state that the gravitational resistance during a drop should exceed 90%. For the specified briquette combinations compacted at different pressures, it was observed that the maximum loading power of the samples was 5 kN diametrically to the briquettes in the universal testing device and the samples were broken at the allowable values. A similar briquette compaction method was performed by [43] and it was observed that similar results were obtained. Considering the capacity values for this new designed hydraulic press, it is seen that the capacity and specific energy consumption values are at a significant level compared to different compression pressures depending on the design. However, considering the enterprises that will produce more in rural areas in this type of designed machines, it can be said that this press is suitable for both capacity and specific energy consumption.

Principal Components (PCs) Analysis

Principal Component Analysis (PCA) was conducted to determine the effects of briquette materials at different pressures on the investigated briquette density, briquette firmness, shatter test, capacity, specific energy consumption and tumbler test parameters. According to the PCA analysis, PC1 and PC2 variables explained 96.25% of the total variance. The share of PC1 value in the total variance was determined as 86.48%, PC2, on the other hand was determined to explain only 9.55% of the total variance as a result of the analysis (Fig. 2).

As a result of the PCA analysis, when the eigenvalues of the PC values were examined, the eigenvalues were calculated as 6.058 in PC1, On the other hand, in PC2. The eigenvalue was measured as 0.675 and was determined below the value of 1. PC in the other group had eigenvalues below 1 and explained only 4.69% of the total variance (Table 4).

Heating Value, ADL-Lignin and Elemental Analysis Values

The calorific value, lignin and elemental analysis values of the obtained briquettes are given in Table 5. In order for a briquette to be of acceptable quality, it must have a calorific value over 3800 kcal.kg^-1 [27]. The heating value of the studied material apricot pruning residue was calculated as 4605 kcal.kg^-1 as seen in the table and it is well above the accepted value. When the timber industry is considered in terms of fuel, wood dust are mostly used because it is easy and accessible. The heating value of wood dust is 4522 kcal.kg^-1. Heating value of apricot pruning residue is very close to wood dust and is at a value that can be used easily. Briquettes of materials with high lignin content are expected to be more solid. Because lignin has a natural adhesive property. In this study, this effect of lignin was investigated without using any heating system or additives. Depending on the compression pressure, there was an increase in the level of this lignin with the pressure in the material. The lignin content of the apricot branch is as high as 18.08% and is more than wood dust (16.24%). It was observed that more durable briquettes were obtained with the release of this amount of lignin with the temperature depending on the pressure. Elemental analysis results of apricot branch and tree dust are also shown in Table 5. It is seen that the material is low in nitrogen and rich in carbon. The reason for its high calorific value is its high carbon content. The briquettes obtained in the experiment were burned in the briquette stove and the flue gas emission values were measured. The data obtained are shown in Table 5. As can be seen in Table 5, apricot branch is a cleaner fuel than wood dust in terms of flue gases. The obtained values were found to be within acceptable limits.