Design and Implementation of a Low-Pressure Briquetting Machine for the Use of Pinus spp. Wood Residues: An Approach to Appropriate Rural Technology

Abstract

This research analyzes the technical feasibility and implementation of an appropriate technology for the production of briquettes from Pinus spp. waste (sawdust and shavings) in a rural community in Michoacán, Mexico. The results indicate that local small-scale briquette production in the Pichátaro community has the potential to boost a local economy based on the manufacturing and marketing of densified solid biofuels. The design of the manual briquetting machine was developed through a participatory approach with community users. Structural simplicity and locally accessible maintenance were prioritized, the aspects that were addressed little in previous studies. The machine allows for the production of briquettes using a low-cost mixture composed of sawdust and Pinus spp. shavings, corn starch, and water. Based on local conditions and production needs, parameters such as reduced processing times and simplified manufacturing methods were identified as essential to establishing an efficient regional production and supply chain. Furthermore, the valorization of solid waste through the production of alternative biofuels contributes to the diversification of the energy matrix in rural residential sectors and small industries in communities in Mexico. The estimated cost of the machine is USD 75.44, and most of its components are easily replaceable, which favors its sustainability and prolonged use. This study demonstrates that the implementation of a low-pressure briquette system based on appropriate rural technologies represents a viable strategy for the use of wood waste and the promotion of sustainable energy solutions in rural communities.

1. Introduction

Currently, there is a global need to transition to renewable energies, which will allow us to avoid an energy crisis due to dependence on finite fossil fuels, which are increasingly expensive and have greater environmental impacts due to extraction and refining processes [1]. At the same time, there is an increase in the world population and the expansion of industrialization, which increases the need for more energy consumption and production, as well as the generation of waste. These wastes often have a potential for use that has not been used, such as solid biofuels [2,3], which, among their advantages, they contribute to the mitigation of greenhouse gases (GHG), to maintaining the carbon cycle, and to promoting energy alternatives to fossil fuel [4,5]. This is why biomass sources are an attractive option for generating heat and electricity with applications in various economic sectors [6,7,8,9].

However, it is imperative to raise awareness about the limitations of biofuels since it is not possible for them to fully replace fossil fuels; there must be a radical change in consumption patterns and there must be awareness of energy consumption [10]. The use of biomass, mainly traditional fuels such as firewood, is estimated at 10% globally, higher than solar and wind energy, and in various scenarios, it is expected to contribute up to 30% to the energy matrix with the incorporation of emerging fuels such as pellets and briquettes [11,12]. The use of biofuels reduces the contribution of atmospheric pollutants due to the reduction in CO₂ and short-lived pollutants such as methane and black carbon [13]. Furthermore, biomass energy has the potential to generate significant impacts on current and urgent challenges, such as reducing energy poverty, contributing to curbing climate change, and achieving access to clean and appropriate technologies [14]. In this sense, in generation of bioenergy, Mexico has great potential for the generation of biofuels derived from wood residues with high lignocellulosic content of Pinus spp. [15]. Recent studies show that the basic chemical composition and calorific value of pine sawdust samples from different forestry industries in Mexico are suitable for obtaining densified solid biofuels [16]. Specifically, the biomass waste from the Purépecha Plateau, which is an important forest area of the country, has no use and is seen as a local problem due to the space required for the storage of large volumes and the uncontrolled burning to free up the spaces where they are dumped [17].

The manufacture of briquettes produced non-industrially at low pressures is a moderately acceptable energy alternative compared to the conventional industrial method at high pressures [18,19]. A common problem in briquette production is the implementation of production technology, as it is currently related to high acquisition costs of a high-pressure briquetting press, high voltage and energy consumption requirements in operation, as well as the need for highly trained personnel [20]. These modern briquetting devices are expensive and manufactured abroad, which makes them difficult to import for most developing countries, much more so for rural populations. Industrial briquetting machines require very specific and strict operating parameters, such as high-quality raw materials, imported binders, and complex operating parameters [21]. Additionally, they are focused on a very select sector without prioritizing the local area or the appropriate economic sectors [22]. Therefore, there is a need to generate regional innovation with inputs and designs appropriate to the locality [23]. For example, low-pressure mechanical designs, such as manual briquetting presses, are suitable for rural areas with high availability of biomass resources and developing economies [24,25]. These low-pressure briquetting presses can use commonly used binders to ensure the compaction of the briquettes; they require human energy for operation, and there is no need for the consumption of electric power, which is often lacking in rural areas [26]. In this type of technology, the use of a screw or piston as a pressing unit becomes the key accessory in this type of low-cost eco-technologies [27].

The design and feasibility of the briquetting machine are based on three basic operating principles: compaction, binder use, and production time, including the generation of a hole in the center of the briquette for better combustion [28].

In the present study, the design of the machine focuses on reusing the waste of Pinus spp. (sawdust and shavings) and the use of a low-cost natural binder for compaction, which allows for its use in rural communities with limited access to industrial inputs, as is the case of the study community. Unlike traditional briquetting machines, which usually require high pressures and more complex processes, the proposed low-pressure manual design allows for efficient compaction of biomass without the need for electrical energy, facilitating its local manufacturing and maintenance with accessible materials. This strategy responds to the specific conditions of the Pichátaro community and its productive capacity, ensuring that the briquetting process is viable and sustainable in a rural environment.

2. Materials and Methods

The methodology proposed for this research is based on the implementation of appropriate technology through a participatory design [29], with the identification of priority energy needs, eco-technological development, and implementation processes [30,31]. The integration of the described socio-techno-environmental aspects is crucial to contribute to the successful functionality and operation of the proposed technology. Figure 1 shows a flow chart describing the stages of the methodology used, integrating the development, evaluation, and redesign of the technology. This methodology consists of 3 stages, with interactions between them. The first stage captures the idea of the device through Computer Aided Design (CAD). This stage comes from the previous participation of the users; the second stage is related to the operation and redesign of the machine, and finally, the last stage is related to the production and evaluation of the briquettes.

2.1. Area of Study

The Purépecha Plateau, in the state of Michoacán, Mexico, is a region with a high rate of forest use, especially of species of the Pinus genus, used in various economic activities [32]. The community of San Francisco Pichátaro (Latitude 19.55°, Longitude 101.8°) has an economy based on the timber industry, specifically on the manufacture of furniture (see Figure 2). In this community, in addition to the extraction of firewood for personal consumption or sale, there are numerous carpentry shops that constantly generate quantities of wood waste (approximately 1376 to 2110 kg/week), mainly sawdust and shavings, with poor use and commercial value, which causes storage problems [33].

2.2. Briquetting Machine Design

The design of the briquetting machine will be for non-industrial purposes [34] and with a focus on use in rural communities (commercial, residential, and small-scale industry sectors) [35]. This design integrates the following components: structure, shaft for compaction, device to activate manual compaction, and mold to generate solid biofuel (briquette). Each of these components helps to guarantee a quality product during the production process [36]. For this study, the non-industrial design of the manual briquetting machine was performed in the CAD design program SolidWorks^® 2023. This design is based on the use of recycled materials from the locality in order to achieve a sustainable product, and this study complies with the integration of the three components of sustainable design: (1) Environmental aspect: focused on the mitigation of GHG; (2) Social aspect: integrates the user through participatory design, understands their needs and provides appropriate technology for the conditions of the community; and (3) Economic aspect: encourages the generation of local markets, which promotes a value chain and supply of inputs and accessories related to the production of biofuels in the community [37].

2.3. Model for Computational Simulation of the Briquetting Machine

To complement the analysis of briquettes made from biomass mixtures, computational models were developed to simulate production conditions and predict optimal device performance. These models allow for determining the compression applied to the mixture during batch production, with a total of 4 briquettes per batch. Simulations were performed using SolidWorks^® software, considering the properties of the materials involved in the manufacture of the briquettes. Under controlled conditions, key variables were defined, such as the type of biomass (sawdust), the material of the impact surface (cement), and the drop height (2 m). In addition, the mesh of the model was adjusted through a convergence process to ensure the independence of the results obtained.

2.4. Technology Used

The design of the machine, specifically the molding tubes for producing the briquettes, is one of the main components used in the production of biomass briquettes. The proposed briquette molding unit can produce 4 cylindrical pieces in one pressing. Each briquette has an approximate diameter of 7.2 cm with a length of 9 to 10 cm. The internal perforation of the briquettes is performed after drying, generating an internal diameter of 1 cm at the center of the circular surface, which allows for improving the different stages of combustion (drying, pyrolysis, gasification, and combustion) [38]. The machine consists of three main parts: mold, cover, and mechanical jack.

2.5. Preparation of the Mixture for Densification and Economic Cost of the Materials

The generation of wood waste from the Pichátaro community consists of sawdust and shavings; corn starch is used as a binding material, which is commonly used in the locality due to a region with the greatest diversity of native corn in the country [39]; sawdust (250 g), shavings (250 g), corn starch (310 g), and water (1 L) were used [40].

This analysis of the cost of making the briquettes was based on the following

Table 1. Production cost per briquette in dollars (USD).

Average Amount of Material Used	Cost Per Briquette (USD)
0.25 L	0.053
75 g Shavings of sawdust	0.0050
77.5 g Cornstarch	0.0075
Cost per briquette	(USD) 0.065

.

Table 1 presents the unit production cost for the manufacture of briquettes, estimated and reported in previous research [40]. In this analysis, the information has been updated with the prices corresponding to the year 2025. It is important to highlight that the calculation of the production cost considers only the value of the raw material, without including the costs associated with labor individually, but it is reported in the results section from a prospective working day.

2.6. Production of Briquettes

Random productions were performed with 7 male individuals from the community with similar physical characteristics, who were trained to operate the machine and handle the briquettes produced. The parameters of interest in the process were the number of briquettes manufactured during 7 days, as well as wear and tear from handling the briquettes. Homogeneous working conditions were simulated among the participants and were consistent with the conditions of the locality, with 6-hour work schedules. The activities include conditioning the equipment, preparing the mixture, and producing and drying the briquettes (drying is performed in the sun, similar to the drying tasks of the wood industry in the community). Working conditions were ensured, and financial compensation was made based on the number of briquettes produced.

The level of compaction of the mixture for the generation of briquettes was calculated using Equation (1) [36].

$$s=H_P/(H_P-x)$$

(1)

where

• s = is the level of compaction;
• Hp = is the initial height of the compacted material;
• x = is the displacement of the axis.

2.7. Final Use of Briquettes

In rural communities in the state of Michoacán, Mexico, cooking typical dishes is a daily practice. To evaluate the briquettes produced, cooking tests were performed on a three-stone stove, simulating traditional culinary activities in the region. The cooked foods included cauliflower, egg, chicken broth, quelites, and fish broth cooking. The tests were performed in a controlled environment within a room with four brick walls. The type and volume of the stove evaluated are representative of previous studies (average volume of 41 m³ ± 20) [41]. Briquettes were made from pine wood residue with average dimensions of 7.2 cm in diameter and 9 to 10 cm in length, with a humidity range of 11 to 13%. All cooking tests of the different foods were started with 10 g of “ocote”, which is a piece of Pinus leiophylla resin used as a fire starter. The cooking cycle allows us to evaluate both energy and emission parameters [42].

2.8. Identification of Polluting Gases

Emission factor analyses were performed in accordance with protocols established in the scientific literature [43]. Emission factors per dry fuel consumed were evaluated for the following compounds: carbon dioxide (gCO₂/kg), carbon monoxide (gCO/kg), methane (mgCH₄/kg), and particulate matter 2.5 microns in diameter (mgPM_2.5/kg). The methods used were consistent with those described by several authors in previous studies [44], ensuring the rigor and comparability of the results obtained with the existing database on the subject. The calculation of the CO₂ equivalent (CO_2eq) was performed following the protocols reported in the scientific literature [45]; the calculation of CO_2e was as follows: CO₂ = 1 [45], CO = 1.9 [46], CH₄ = 28 [45], NMHC = 12 [47], EC = 680 [48], and OC = −79 [48]. The first scenario is based on the protocol established by the Intergovernmental Panel on Climate Change (IPCC), while the second scenario integrates all gases with global warming potential reported in the scientific literature. To determine CO emissions, the fraction of non-renewable biomass (fNRB) was 0.25 for Southern Mexico [49].

As part of the analysis, the emission factors of briquettes were compared with pine firewood, oak firewood, eucalyptus, and charcoal. For this analysis, the fuels used were white oak (Quercus bicolor), with an average moisture content on a wet basis of 11% (±1.4), as well as briquettes of pine wood residues (Pinus spp.) [43], with a base moisture content of 12% (±2); both fuels were measured using a wood moisture meter (Protimeter Timbermaster GE, Billerica, MA, USA) [42]. These measurements were based on ISO 19867-1 [43], and are representative of the performance of griddle stoves with chimneys and open fires [43]. A comparative analysis of emissions was also performed with studies that evaluated other types of fuels. All the analyses mentioned were performed in a laboratory and using water for heating and calculating the emissions.

3. Results and Discussion

3.1. Briquetting Machine Design

The design of the briquetting machine was developed according to the needs and technical possibilities of the target community. The device was designed primarily from steel components (mostly recycled), with labor requirements for the operation of the briquetting machine. The design of the machine is described in Figure 3 and Figure 4.

Figure 4 shows the number of parts and their function. The most important elements are described below: one steel plate where the pressure for the briquettes is generated, four briquettes (representative images), four steel tubes that help generate the cylindrical briquettes, four recycled rubber bands to prevent friction inside the tubes, four steel tubes that form the axis for compaction, one mechanical device that serves to generate the pressure for compacting the mixture, and a metal structure (½ inch by 1/8 inch angle) that makes up the entire structure of the machine.

3.2. Construction of the Briquetting Machine

The second stage of this design involves the construction of the machine, fully integrating the technical part and low impact on the environment due to the construction materials. The machine was built using the eco-design method, which reflects the energy needs of the users [40,50]. The machine was constructed primarily from recycled steel components; the machine only requires manpower to manipulate the mechanical system. Figure 5 presents the development process of the briquetting machine, from its conceptual, functional design to its operation. Figure 5a shows the complete design of the equipment modeled in computer-aided design (CAD) software, where the structural and mechanical components of the machine are defined. Subsequently, Figure 5b shows the physical construction of the prototype, evidencing the transition from the digital model to a tangible structure through the manufacturing and integration of its elements. Finally, Figure 5c illustrates the machine in operation carrying out the production process of solid biofuels (briquettes).

The cost of the machine was USD 75.44, including materials, supplies, and labor. For other similar designs, costs are reported between USD 220 [39] and USD 57.02 [51]. In another study, briquettes of 27.43 mm in length by 41.66 mm in diameter were produced, similar to the briquettes in our study [52]. The briquetting machine designed in this study is used in rural communities and has the potential to be used in small associations, rural implementation projects, or private investment by community members. Its cost represents an acceptable investment and is related to similar costs of existing eco-technologies in the community, for example, improved wood stoves with costs between USD 100 and USD 200. An advantage of this innovation is the use of local materials for its construction and easy operation, which promotes sustainable innovation.

3.3. Analysis of the Compaction Process and Simulation of the Briquetting Machine

Figure 6 shows the operating concepts for briquette production. The compaction process of the mixture for briquette generation is shown in the same figure. For the mechanical analysis of the sawdust densification model, the Computer Aided Design (CAD SolidWorks^®) program was used. This program allowed the real conditions of sawdust mixture compression to be replicated, facilitating the manufacture of briquettes. The analysis included the displacement of the shaft and the obtaining of briquettes, as well as the wear of the device in each processing cycle. The simulation of different movements is illustrated in Figure 7.

The compaction analysis was performed considering a time of 10 s, corresponding to the period during which the mixture of sawdust and components remains inside the tube for compaction. This analysis shows different mechanical stresses for different phases. Figure 7a shows the Von Mises strain stress, where the minimum strain found was 2.265 × 10⁻⁶ N/m², and the maximum strain was 2.866 × 10² N/m². The equivalent unit strain (ESTRN) showed a minimum strain of 9.692 × 10⁻¹⁸ and a maximum of 1.177 × 10⁻⁹. Figure 7b also shows the Von Mises strain stress, with a calculated minimum strain of 1.600 × 10⁻⁶ N/m² and a calculated maximum strain of 2.500 × 10⁸ N/m². Regarding the ESTRN, the minimum calculated strain was 1150 × 10⁻¹⁵, and the maximum calculated strain was 1279 × 10⁻⁹. For the case shown in Figure 7c, the minimum Von Mises strain was 2628 × 10⁻³ N/m², and the maximum strain was 2500 × 10⁸ N/m². The ESTRN showed a minimum calculated strain of 1019 × 10⁻¹⁴ and a maximum strain of 1845 × 10⁻⁸. Finally, a model was implemented to analyze the fall of the briquettes, considering conditions such as height (2 m), impact surface (cement), briquette material (sawdust), and gravity (9.81 m/s²) [53]. The model mesh was adjusted by convergence to achieve independence of the results with respect to the mesh size. The appropriate size for the simulations was determined to correspond to a mesh of 11,733 elements with 12,613 nodes, as shown in Figure 8.

For a height of two meters, it is observed that in the four briquettes, there is a decrease in the stress, where the greatest stress occurs when the briquette hits one of the base faces of the briquette on the rigid ground. The analysis of the graph of maximum equivalent stresses (Figure 9) shows that there is a multivariate interaction in the model since the general behavior of the equivalent stresses depends on the launch height, associated with a greater impact on the briquette and greater deformation energy, on the angle of impact, associated with the direction of application of the impact force and the direction and distribution of the stresses, which, in turn, will depend on the orthotropic properties of the briquette material and the type of briquette. The latter could indicate a correlation with the apparent density, elastic modulus, or Poisson’s coefficient, which, for the briquette material model, have orthotropic values and affect the response of the material.

Figure 9 shows the result of the Von Mises Stress (VON) deformation: for this analysis, a minimum stress of 1.362 × 10⁵ N/m² and a maximum stress of 4.426 × 10⁶ N/m² were obtained.

The simulation presented in Figure 10a shows the distribution of equivalent stresses as a function of the impact angle. This distribution maintains an approximately constant shape in the four briquettes, regardless of the launching height (2 m). Figure 10b shows the stresses decomposed into the radial, tangential, and longitudinal directions within the simulation reference frame, resulting in stresses distributed along these orientations. The resulting displacements (URES) associated with this effort present values that vary between a minimum of 7.392 × 10⁻¹ mm and a maximum of 7.857 × 10⁻¹ mm. The stresses during the 90° impact also depend on the impact force review, with the radial and tangential directions being the main ones. The tangential component favors the distribution of the total impact stresses along the curved surface of the briquette, generating a lower equivalent stress similar to the behavior of an arch. The effect of orthotropic properties, which modify the resulting stresses, is relevant.

Figure 11 shows the deformation on the base face of the four briquettes; the ESTRN (Equivalent Unit Strain) shows a minimum deformation of 2.178 × 10⁻⁵ and a maximum distribution of 1.224 × 10⁻³. Finally, a complete mesh (see Figure 12) of the four briquettes is shown with a section cut out to know the greater impact of deformation inside the briquettes.

Each of the analyses shows the deformation represented in a color bar, in which the blue color results in a minimum effort, and the red color results in a maximum effort that occurs in the internal part at the time of a fall. Figure 12b shows the VON analysis that resulted in a minimum internal stress of 8.458 × 10⁴ N/m² and a maximum of 2.168 × 10⁶ N/m². Figure 12c shows the URES analysis, which resulted in a minimum of 8.076 × 10⁻¹ mm and a maximum of 8.425 × 10⁻¹ mm. Finally, Figure 12d shows the ESTRN analysis, which resulted in a minimum internal stress of 1.840 × 10⁻⁵ and a maximum of 6.110 × 10⁻⁴. Finally, according to these analyses, the greatest compaction of the four briquettes is found in the center. This result may be due to factors such as porosity effects not considered since the simulation considers a mainly linear elastic model. This analysis provides us with information to know the impact that the briquettes may have with a fall, especially in the transport stage, once these briquettes begin to be marketed.

3.4. Production of Briquettes

Field production tests are presented in

Table 2. Production of briquettes.

Participant	Height (m)	Briquettes Produced (Quantity)
1	1.75	108
2	1.70	92
3	1.70	84
4	1.65	98
5	1.85	96
6	1.70	102
7	1.78	80

. No statistical analysis was performed in this test. The main objective was to observe and record the performance of various users in briquette production during a production simulation.

The data presented in Table 2 refer to a 6 h workday. However, this work period can be extended to 8 h per day, in line with the usual work practices of the community, with the option of organizing two shifts to increase the production day. Participants in this test were asked to formulate the mixture for briquetting, carry out the pouring into the compaction tubes, and carry out the densification. The operators rated the machine as an easy-to-use technology. A homogeneous mixture facilitates its handling in the molders, as well as the production of briquettes. Pilot and formal tests demonstrated the operational stability of the machine. The parts with the greatest wear on the machine are the hinge welded on the cover and the steel bar, where the mechanical device for carrying out the compression is attached. Finally, the production varied between 80 and 108 briquettes per operator per day; for a period of 7 days, the total number of briquettes produced ranged between 560 and 756 units. This variability in production is mainly attributed to technical problems in the operation of the briquetting machine. On average, production was 16 ± 4 briquettes per hour.

3.5. Cost Analysis of Briquettes

The price of briquettes produced using the proposed eco-technological innovation is USD 0.065 per piece and USD 0.325 per kilogram (equivalent to five pieces per kilogram) [40]. Considering production costs, such as operator labor, which averages MXN 300, equivalent to USD 16 per workday, it can be seen that the briquettes generated in this study are competitively positioned in the market. Previous studies have reported pine sawdust-based briquettes with a cost per briquette of USD 0.003 [24], although these pieces are smaller in size and have lower calorific value. Other studies have recorded costs of USD 0.14/kg [54] and USD 10.16 /kg [55] for different types of briquettes, while similar biomass has shown a price per briquette of USD 0.39 [56]. The briquettes produced in this study are within market prices, and in some communities, they are even considered the cheapest option. It is important to mention that this type of briquette is aimed at a local market, so the comparison costs are with firewood, which is the dominant energy source in rural communities. In 2024, the cost of firewood in the study community is set at MXN 2.00 (USD 0.11) per piece of pine and MXN 3.00 (USD 0.16) per piece of oak. In comparison, the briquettes proposed in this research have a cost of USD 0.065 per piece for a cheaper option and USD 0.325 for a higher-quality option. At first glance, it is clear that there is a significant difference in price between briquettes and traditional firewood, with the most expensive briquettes being approximately 2.4 times more expensive than pine firewood and up to 1.66 times more expensive than oak firewood.

However, it is important to note that the use of briquettes should not be seen as a direct competition against traditional firewood but rather as an energy complement that offers several advantages to users. The integration of briquettes into the household energy matrix allows for the diversification of fuel use, offering a more efficient and sustainable option for daily domestic activities. In addition, the use of briquettes can contribute to a reduction in the dependence on firewood, alleviating pressure on local forest resources and promoting more sustainable practices in the long term.

3.6. Operation of the Device for Generating Briquettes

The mixtures used for the production of briquettes were cited by Vera-Velásquez [57], who reported the use of 230 g of starch, 500 mL of water, and 1 kg of cassava for the manufacture of a briquette with a diameter of 5.08 cm and a length of 5 cm, generated by manual pressure. In this research, cassava was replaced by local wood waste and starch by corn starch, using 1 L of water. For the manufacture of briquettes using the proposed machine design, which has the capacity to produce four briquettes in a single operation cycle, a specific mixture of materials is used. The formulation consists of 1 L of water, 300 g of wood waste, which can be sawdust, shavings, or a combination of both in equivalent proportions, and approximately 310 g of corn starch as a binder. These components are mixed until a homogeneous mass is obtained, as shown in Figure 12a. Considering that the total mixture is distributed equally among the four briquettes, it is estimated that the amount of material used per unit is approximately 0.25 L of water, 75 g of wood residue, and 77.5 g of corn starch. This is the mixture necessary for the production of a briquette of 7.2 cm in diameter and an average length of 9 to 10.5 cm. This method not only corroborated the data of Vera-Velázquez [57] but also increased the amount of briquettes manufactured. After making and drying the briquette, a hole was made in the center of the briquette. Figure 12 presents the complete briquette production process, from the preparation of the base mixture to the final drilling to optimize its combustion. Figure 12a shows the mixing process of the materials necessary to obtain a homogeneous composition suitable for the manufacture of briquettes. Subsequently, Figure 12b shows the placement of the prepared mixture at the bottom of the tubes of the briquetting machine, ensuring that the material completely fills the conduits to their limit before compaction. Figure 12c illustrates the machine in operation, showing the production of four briquettes simultaneously. Finally, Figure 12d shows the drilling stage in the center of the briquettes using a drill, with the purpose of improving combustion efficiency by allowing for greater airflow during its use as biofuel (the drilling is additional)

The briquetting process is technically feasible and produces densified solid biofuels of cylindrical shape (7 to 9.3 cm in height and 7.2 cm in diameter). Briquette production, as previously reported, was a maximum of 108 briquettes with the device designed, as shown in Figure 13.

Several recent studies have explored the production of briquettes without additives at low pressures, obtaining variable results in terms of dimensions and structural characteristics. In one study, the production of briquettes with a diameter of 25 mm was reported without specifying their length and without central perforation. Other authors reported the manufacture of briquettes with an external diameter of 56.6 mm, a height of 74 mm, and a central perforation with an internal diameter of 14.4 mm [58]. Likewise, briquettes have been developed from poplar wood, obtaining products with an approximate diameter of 60 mm and a height of 50 mm [20]. Furthermore, research that used greenhouse plant waste as raw material reported obtaining bio-briquettes with a diameter of 55 mm and lengths between 45 and 50 mm [59]. These results show the variability in the dimensions of the briquettes depending on the source material and the conditions of the compaction process.

Figure 13 represents different aspects of large-scale briquetting production using the briquetting machine. Figure 13a shows the preparation of the material in large volumes to guarantee continuous and efficient production, as well as its subsequent processing in the briquetting machine. Figure 13b shows the production capacity achievable with the use of the machine when it operates constantly, evidencing its potential for the sustained manufacturing of solid biofuels. Finally, Figure 13c presents the sizing of the briquettes obtained, which have a height that varies between 7 and 8.3 cm with a diameter of 7.2 cm, which allows their size to be standardized for efficient storage and use.

The previously formulated biomass waste was placed in the cylindrical molders until they were completely filled. The molder lid was then closed and locked with the machine bolt to perform the densification. The mechanical device was then operated again without the lid to extract the produced briquettes. The estimate of a fixed production rate of 80 to 108 pieces per day was based on the average number of briquettes produced during previous manufacturing tests.

During low-pressure or manual briquetting, a pressure of 2.40 MPa was reached. In comparison, other devices can reach pressures of up to 5 MPa using a mechanical mechanism designed by the author, which operates by mechanical force exerted by the device operator [25]. Other briquetting machines report low compaction pressures for sawdust and rubber samples of 40 kg/cm² (3.92 Mpa) [60], while lever-based devices have pressures of 4.2 Mpa [61]. Studies that prioritize particle size report pressures from 13.8 to 48.3 Mpa [62] and 5 Mpa [63]. Finally, there are devices that operate at compressions of 9, 12, and 15 MPa, where the pressure time is 15 min to generate a single briquette [64].

3.7. Evaluation of Food Cooking on a Three-Stone Stove

The operation of the devices used to cook food in the study community is characterized by low thermal efficiency and incomplete combustion (open fires). Much of the energy is lost to the environment, and there are no chimneys for ventilation of pollutants. In many cases, there is a lack of good practices in the use of biofuels (firewood), and they are used in inadequate dimensions and humidity.

Table 3. Cooking of the most common dishes in the study community.

Food (1 kg)	Cooking Time with Briquettes (min)	Number of Briquettes Used
Cauliflower cooking	48	17
Cooking eggs	55	21
Chicken broth cooking	67	25
Quelites cooking	50	19
Fish broth cooking	62	22

Note: For the “egg” cooking, this task was performed at two events because these are the typical quantities used in the community. The rest of the food was cooked at one event.

below shows the list of foods (most common dishes in the study community) cooked with the briquettes produced in this study and prepared in the field.

Table 2 shows the cooking times of the foods cooked in the rural study community. The dish with the longest cooking time was chicken broth, which required 67 min and used 25 briquettes. On the other hand, the dish with the shortest cooking time was cauliflower, which was cooked in 48 min using 17 briquettes. These cooking times are comparable to those obtained using wood (firewood), suggesting that the final device performs efficiently.

3.8. Greenhouse Gas Emissions

To perform this analysis, water must be heated, and the procedure must be performed in a laboratory in order to control the different variables that may influence the results and, thus, accurately detect emissions.

Table 4. GHG emission factors.

Emission Factors per Dry Fuel Consumed
Parameters	Briquette	Pine Firewood	Oak Firewood	Eucalyptus	Coal
gCO2/kg	309 ± 75	1129 ± 118	1632 ± 315 [65]	1726 ± 28 [66]	264 ± 69 [67]
gCO/kg	12 ± 5	39 ± 12	1.12 ± 0.09 [68]	63.33 ± 6.18 [69]	17.746 ± 0.01 [70]
mg CH4/kg	233 ± 124	852 ± 324	101± 9 [71]	16 ± 0.05 [72]	40.3361 ± 0.03 [70]
mg PM2.5/kg	1204 ± 579	3375 1293	5.8 ± 3.9 [73]	10 ± 6.7 [73]	543.2 ± ND [74]
g CO2e/kg	77 ± 19	285 ± 31	4.62 ± ND [75]	0.74 ± ND [76]	80.62 ± ND [77]

Note: ND = Not detected.

presents a detailed comparative analysis of the average emissions of gases and particles per kilogram of various materials, including briquettes, pine, oak, eucalyptus, and charcoal. This analysis covers both the evaluations carried out in the laboratory and those reported in the scientific literature. This comparative approach allows us to identify and compare the differences and similarities in the emissions of each material, providing a comprehensive view of the environmental impact of briquettes in relation to other fuels, supported by experimental data and bibliographical references.

In the comparative analysis of emissions from different fuels, briquettes stand out for their low environmental impact in relation to the other fuels studied. Table 4 shows that briquettes have an average emission of 309 gCO₂/kg, compared to pine wood at 1129 gCO₂/kg, oak wood at 1632 gCO₂/kg, eucalyptus at 1726 gCO₂/kg and slightly higher than coal at 264 gCO₂/kg.

In terms of CO emissions, briquettes generate 12 gCO/kg, which is lower than that of pine wood at 39 gCO/kg, eucalyptus at 63.33 gCO/kg, and charcoal at 17.746 gCO/kg. Although oak wood shows a lower CO emission of 1.12 gCO/kg, it is essential to consider the overall balance of emissions for a comprehensive assessment.

As for emissions of methane (CH₄), a gas with a high global warming potential, briquettes emit 233 mgCH₄/kg. This value is lower compared to pine wood 852 mgCH₄/kg, oak wood 101 mgCH₄/kg, and charcoal 40.3361 mgCH₄/kg, but higher than the emissions of eucalyptus 16 mgCH₄/kg.

Particulate matter (PM_2.5) is a critical pollutant for human health. Briquettes emit 1204 mgPM_2.5/kg, while pine and oak firewood have higher emissions of 3375 mgPM_2.5/kg and 5.8 mgPM_2.5/kg, respectively. Emissions from eucalyptus 10 mgPM_2.5/kg and charcoal 543.2 mgPM_2.5/kg are also higher compared to briquettes.

Finally, regarding carbon dioxide equivalent emissions (g CO_2e/kg), briquettes show a value of 77 g CO_2e/kg, compared to pine wood 285 g CO_2e/kg, oak wood 4.62 g CO_2e/kg, eucalyptus 0.74 g CO_2e/kg and coal 80.62 g CO_2e/kg.

The comparison of the results shows that briquettes are a greener alternative compared to other traditional fuels, with lower emissions of CO₂, CO, CH₄, PM_2.5, and CO_2e, which contributes to the mitigation of climate change and the reduction in negative impacts on public health.

3.9. Application of Technology

The machine designed in this study is a participatory innovation to use woody biomass waste in local conditions (see Figure 14). This machine demonstrates efficient biomass management, transforming waste into products with added value to promote national energy alternatives. It also contributes to the creation of a sustainable production cycle for the community.

Figure 14 shows the summarized process in this case study of how the rural community uses its biomass waste to make solid biofuels. The process begins with the available biomass waste, in this case Pinus spp. sawdust. The technology for densification is then designed and manufactured. The process continues with the production of briquettes until their final use for thermal purposes.

4. Conclusions

The main conclusions are as follows:

• The machine is suitable for local production of briquettes. It uses low-cost materials for its construction; the cost of the machine is USD 75.44, three times less than a conventional machine purchased abroad;
• In the simulation performed with SolidWorks, the Von Mises stress presented a deformation range that varied between a minimum value of 2.628 × 10⁻³ N/m² and a maximum of 2.500 × 10⁸ N/m². On the other hand, the calculated equivalent unitary strain (ESTRN) showed minimum values of 1.019 × 10⁻¹⁴ and maximum values of 1.845 × 10⁻⁸;
• A briquette machine operator generates, on average, 94 briquettes in a 6-hour workday, with a maximum operating pressure of 2.40 MPa;
• Briquettes, with carbon dioxide equivalent emissions of 77 g CO_2e/kg, are presented as a viable and balanced alternative among traditional fuels. Although their emissions are higher than those of oak and eucalyptus firewood, they are significantly lower than those of pine firewood and comparable to those of coal. This combination of moderate environmental impact and energy efficiency positions briquettes as a sustainable option, especially in contexts where CO_2e emissions are sought to be reduced without compromising energy performance.

Documented perceptions show the following:

• Environmental: There is a positive perception among users when using community biomass waste to reduce firewood consumption and, thus, reduce the pressure of firewood extraction from forests.
• Social: Participatory processes promoted local innovation focused on solving the energy needs of the region. These processes included the active participation of women;
• Economic: The design of a local machine encourages the beginning of a densified biofuel market in the region, with supply chains served by members of the same community of this study.