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Coffee tree trunks are a low-demand biomass resource with potential to be converted into higher-value products, such as charcoal briquettes. This study investigates the effect of drying temperature and particle size (Mesh 30 and Mesh 250) on the performance of coffee wood charcoal briquettes using starch as a binder. Drying was conducted at temperatures of 60°C, 80°C, and 100°C. The briquettes were tested through combustion by heating 50 ml of water, while temperature changes were recorded every minute using a thermocouple until boiling point was reached. Additional analyses included moisture content, ash content, combustion rate, and calorific value.The results show that higher drying temperatures improve briquette performance. The highest combustion rate for Mesh 30 was 0.20 g/min at 100°C, while Mesh 250 reached 0.16 g/min at the same temperature. The calorific value increased with temperature, with Mesh 30 reaching 7178.02 cal/g and Mesh 250 achieving 7498.80 cal/g at 100°C. Although Mesh 30 briquettes exhibited competitive calorific values, their combustion stability was lower compared to Mesh 250.These findings indicate that drying temperature and particle size significantly influence the quality and performance of coffee wood charcoal briquettes

Through this study, there are two variables of concern, namely the effect of the initial comparison of the combustion of raw materials of pine wood charcoal & coffee wood charcoal (70%: 30%, 30%: 70% and 50%: 50%) with mesh sizes of 100 and 250. The initial process of the study is the manufacture of charcoal in pine wood and coffee wood briquettes, pine wood and coffee wood are processed by carbonization at a temperature of 500°C, crushed, sieved using mesh 100 and 250, variations of 70%: 30%, 30%: 70% and 50%: 50% mixed with adhesive, given a pressure of 4 kg, and dried at a temperature of 80°C for 3 hours. The purpose of this study is to determine the comparative value of the combustion rate and calorific value of each briquette sample. The methodology used in this study is to conduct experiments on pine wood charcoal briquettes and coffee wood charcoal in testing the calorific value and combustion rate. From the research that has been done, it was found that the burning rate of briquette samples with variations of pine and coffee wood charcoal with variations of 70%: 30% mesh 100, the burning time is 189 minutes, while at mesh 250 the burning time is 215 minutes. The variation of briquette samples 30%: 70% at mesh 100 the burning time is 192 minutes and mesh 250 is 194 minutes. The variation of briquette samples 50%: 50% mesh 100 has a burning time value of 19 minutes and mesh 250 is 155 minutes. For coffee wood charcoal briquettes and pine wood charcoal at mesh 250 it can be said to meet the SNI 01-6235-2000 standard because the calorific value produced is ≥5000 cal / gram.

One of the promising renewable energy sources is biomass, particularly underutilized candlenut shells, which can be processed into briquettes as a superior alternative to charcoal. This study aimed to utilize candlenut shell waste for briquette production, evaluating hardness and calorific value under varying carbonization temperatures (400°C, 500°C, 600°C) and mesh sizes (30 and 100). Briquettes were produced via carbonization and compression. Hardness was measured using a durometer, yielding the highest value of 76.33 HA at 600°C and 100 mesh, and the lowest of 43.58 HA at 400°C and 30 mesh. Calorific value, determined by bomb calorimetry, peaked at 7834.70 cal/g for 500°C and 30 mesh, while the lowest was 5085.24 cal/g at 500°C and 100 mesh. These results demonstrate that optimized carbonization and particle size enhance briquette quality, promoting sustainable biomass utilization for energy applications.

This study aims to analyze the development of studies on the use of biomass as a renewable energy source to support national energy security using a bibliometric approach. Research data were obtained from the Scopus, Web of Science, and Google Scholar databases with a publication range of 2015-2025. The analysis was conducted using VOSviewer and Biblioshiny. The results show a significant increase in publication trends in the last decade, especially in the period 2016-2024, reflecting the increasing academic attention to biomass as a solution in the energy transition. Keyword visualization shows that biomass is closely related to concepts such as combustion, thermal efficiency, calorific value, and pelletizing. China is the country with the highest publication contribution, while Indonesia is strategically positioned due to its abundant biomass waste potential. Overall, biomass has great potential to support energy diversification, reduce dependence on fossil fuels, and strengthen national energy security in a sustainable manner.

Low-rank coal generally has a high moisture content, which results in a low calorific value and suboptimal quality for utilization as an energy source. One method that can be applied to improve coal quality is the Upgrading Brown Coal (UBC) process, which functions to reduce moisture content and increase fixed carbon value. This study aims to analyze the effect of heating time and the ratio of used oil composition on improving coal quality based on proximate parameters. The research method includes collecting coal samples from four locations in Samarinda and its surrounding areas, namely SMAN 1 Samarinda, Bhineka Street, Palaran Stadium, and Tani Bakti Village. The samples were analyzed using proximate analysis, including inherent moisture (IM), ash content (AC), volatile matter (VM), and fixed carbon (FC), both before and after the UBC process. The upgrading process was carried out with variations in heating time and used oil composition as a coating medium to enhance coal stability and prevent moisture reabsorption. The final results of the upgrading process showed the best values of inherent moisture at 13.64%, ash content at 4.66%, volatile matter at 55.06%, and fixed carbon at 44.94%. The results indicate that the UBC process is capable of reducing inherent moisture and increasing fixed carbon, thereby improving coal quality. Variations in heating time and used oil composition have a significant effect on changes in proximate parameters. Longer heating time and an appropriate ratio of used oil composition result in a more optimal improvement in coal quality.

This study aims to estimate coal resources using the kriging method at PT. Inti Bara Perdana, Taba Penanjung, Bengkulu. Geostatistical analysis was applied to evaluate spatial variability of coal quality parameters, including total moisture (TM), inherent moisture (IM), ash content (ASH), volatile matter (VM), fixed carbon (FC), and calorific value (CV). The research utilized drilling data with an average spacing of 80 meters. Variogram modeling was conducted using SGeMS software, employing spherical models to determine nugget, sill, and range parameters. The results show a low nugget effect (0%) indicating strong spatial continuity. The obtained ranges vary between 180–1296 meters depending on the parameter. Blo./ck kriging estimation was performed using block dimensions of 25 × 25 × 8 meters and a coal density of 1.3 ton/m³. The total estimated coal resource up to an elevation of 230 m is 253,500 tons. These findings demonstrate that kriging provides reliable resource estimation and supports mine planning optimization. This research contributes to improving coal resource evaluation accuracy and operational decision-making in open-pit mining.

This study comprehensively evaluates the quality of biomass briquettes produced from blends of coconut shell charcoal and sengon sawdust, using both carbonized and non-carbonized materials. Composite briquettes were fabricated with varying compositions and characterized through proximate analysis, calorific value, density, and burning rate measurements to determine their suitability as solid fuel. The results indicate that adding non-carbonized sawdust increases volatile matter content and burning rate but reduces the calorific value of the briquettes. In contrast, incorporating up to 10% carbonized sawdust significantly improves the calorific value to 6119.2 cal/g, approaching that of pure coconut shell charcoal (6352.2 cal/g), while maintaining a relatively high burning rate. Briquettes containing carbonized sawdust also exhibit low ash content, below 3%, and moisture content under 8%, meeting standard solid fuel quality requirements. These findings demonstrate that a strategic combination of carbonized and non-carbonized materials can produce hybrid biomass briquettes with optimized thermal performance, providing a promising, sustainable, and environmentally friendly alternative fuel for domestic and industrial applications.

Increasing in energy demand and limited fossil fuel reserves have driven the use of environmentally friendly alternative energy sources. This study aims to analyze the effect of pyrolysis temperature variations on the quality of biopellets made from bagasse and coffee husks. The materials were prepared in a 50:50 ratio with the addition of 15% tapioca flour as a binder. The pyrolysis process was carried out at temperatures of 450°C, 500°C, and 550°C for 120 minutes in oxygen-free conditions. The biochar resulting from pyrolysis was formed into biopellets, which were then tested for proximate composition, calorific value, and combustion rate. The results showed that an increase in pyrolysis temperature had a significant effect on the characteristics of the biopellets. A temperature of 550°C produced the lowest moisture content (8.436%), the highest fixed carbon content (62.191%), the highest calorific value (6293 cal/g), and the highest combustion rate (0.05789 g/sec). Conversely, ash content increased with rising temperature, while volatile matter content decreased. Thus, the best biopellets were obtained at a temperature of 550°C. This study confirms the potential of bagasse and coffee husks as raw materials for biopellets through pyrolysis temperature optimization to support the development of sustainable biomass energy.

During the coal stockpiling process, the quality of coal may increase or decrease due to direct exposure to open environmental conditions, which can lead to changes in its characteristics. The longer the coal is stored in an open area, the more it undergoes changes caused by rainfall, heat, and air exposure, resulting in an increase in moisture content and ash content, while the calorific value decreases. Therefore, this research was conducted to determine the optimal coal stockpiling duration at the ROM coal stockpile to ensure that the calorific value does not significantly decrease. Coal sampling was carried out every two days from the initial time of stockpiling. After a two-month stockpiling period, the final coal quality results showed a total moisture of 13.89% (ar), inherent moisture of 15.95% (ad), ash content of 4.59% (ad), volatile matter of 40.3% (ad), and fixed carbon of 39.16% (ad). Based on these results, it can be concluded that the recommended storage duration for MCV-HS type coal at the ROM coal stockpile is 154 days. The laboratory analysis results obtained during the research indicate that the longer the coal is stored, the higher the moisture content and ash content become, while the calorific value continues to decrease. This occurs due to water absorption and oxidation reactions that take place during the coal storage period in the ROM coal stockpile.

This study aims to analyze the quality of coal from the AR_10 borehole in Muara Enim Regency, South Sumatra, based on proximate analysis. The AR_10 borehole has three coal seams (A, B, and C) that were analyzed using the standard ASTM method to determine the coal quality characteristics. The parameters analyzed include total moisture (TM), volatile matter (VM), fixed carbon (FC), ash content (Ash), calorific value (CV), and total sulfur (TS) on an as-received (AR) basis. The analysis results show that seam A has the highest moisture content (19%), seam B exhibits the optimal calorific value (6045 kcal/kg), and seam C has the highest fixed carbon content (42.63%) with the highest sulfur content (0.83%). The correlation between parameters indicates that increases in moisture and ash content negatively affect the calorific value, while an increase in fixed carbon is positively correlated with the calorific value. All three seams fall into the category of low to medium rank coal (subbituminous to high volatile bituminous) with adequate quality for power generation and industrial purposes. This research provides an important contribution to the characterization of Muara Enim Formation coal in South Sumatra for the optimization of local coal resource utilization.

Coal is an important energy source that is still widely used in industry, especially the power generation industry, because of its high energy content. However, in the process of handling and storage, coal has the characteristic of being easily oxidized, This oxidation process, if it occurs continuously, can cause internal heat accumulation which eventually triggers spontaneous combustion. This study aims to analyze changes in coal quality before and after spontaneous combustionto find out how spontaneous combustionaffects coal quality in stockpiles. The research method used is a quantitative method where the data from laboratory tests on coal quality before and after spontaneous combustionis analyzed, the comparison of coal quality in stockpile 10 before and after spontaneous combustionis then graphed to see changes in the quality of each parameter. Based on the results of the analysis of changes in coal quality before and after spontaneous combustion, there were significant changes to several coal quality parameters, namely Total Moisture which was originally from 7.06% to 5.50% (down by 1.56%), Moisture which was originally 3.91% to 3.22% (down by 0.69%), Ash Content which was originally 8.84% to 14.67% (up by 5.83%), Volatile Matter which was originally 39.77% to 35.10% (down by 4.67%),  Fixed Carbon from 47.48% to 47.01% (down by 0.47%), Sulphur from 0.55% to 0.46% (down by 0.9%), and Calorific value decreased from 6,921 to 6,289 kcal/kg (down by 632 kcal/kg). This decrease in quality has a direct effect on the selling value and efficiency of coal combustion. The existence of an analysis of changes in coal quality due to spontaneous combustioncan help companies to find out how much of an impact losses can be caused by the occurrence of spontaneous combustion. By considering the potential losses due to spontaneous combustion, the company will make efforts to prevent the occurrence of spontaneous combustion in the future to minimize the losses caused.

Biomass is one of the materials that can be utilized as fuel. To ensure optimal quality, effective management of biomass is required to maximize its potential. One possible approach is the application of a biomass stove fueled by rubber wood pellets. By integrating a thermoelectric generator, data can be obtained to determine whether all aspects meet the established standards. This system is designed to generate electrical energy from combustion heat, supported by components such as a buck-boost converter and a 3V DC lamp. Testing was carried out using proximate and ultimate analyses on the fuel as well as the Water Boiling Test (WBT) on the stove, referring to SNI 8021:2020 and SNI 8021:2014 standards. The results showed that rubber wood pellets contained 7.64% moisture and had a calorific value of 4050 kcal/kg. The stove demonstrated an efficiency of 23.53%–37.28% and a fuel consumption rate of 0.61–0.77 kg/hour, both of which meet the requirements. In addition, the thermoelectric generator produced a voltage of 3.6 V and an electric current of 0.05 A, which are higher than those reported in previous studies (2.06 V and 0.01 A, respectively). Therefore, this thermoelectric biomass stove system is considered successful and feasible for further development as an alternative energy application.

The coal blending process conducted by PT. Bukit Baiduri Energi (PT. BBE) aims to achieve coal quality specifications that align with customer requirements. PT. BBE possesses multiple coal seams with varying quality characteristics, necessitating a carefully planned blending system with precise proportions to produce coal products that meet market demands. The objectives of this study are: to plan the quantity and quality parameters for coal blending, to evaluate the actual outcomes of coal blending in terms of quantity and quality, and to identify the factors contributing to discrepancies between the planned and actual coal quality following the blending process. To determine the optimal quantity and quality of each coal product in the blending plan, the simplex method was employed with the assistance of POM-QM for Windows version 5 software, alongside the weighting factor method. The final coal blending plan resulted in a total of 55,000 MT with the following quality specifications total moisture of 20.00% (ar), ash content of 6.10% (ad), total sulfur of 1.65% (ad), and a calorific value of 5,350 kcal/kg (ad). The actual blending outcome yielded the same quantity of 55,000 MT, with quality parameters as follows: total moisture of 20.18% (ad), ash content of 5.60% (ad), total sulfur of 1.35% (ad), and a calorific value of 5,340 kcal/kg (ad). The analysis of quality discrepancies revealed several contributing factors the presence of water accumulation in the ROM Stockpile following rainfall, which increased total moisture, the inadvertent inclusion of foreign materials into the feeder, resulting in elevated ash content, the unintentional mixing of coal from different product types, which led to inconsistencies in total moisture, ash content, total sulfur, and calorific value, and the rise in total moisture, which adversely affected the calorific value.

The use of palm oil waste as boiler fuel is one of the innovative solutions in supporting the use of renewable energy while reducing the environmental impact of palm oil industry waste. Waste such as palm shells, mesocarp fibers, and empty oil palm bunches have high energy potential through direct combustion and other thermal technologies. This study aims to evaluate the potential use of palm oil waste as boiler fuel based on its calorific value, combustion efficiency, and environmental impact. The methods used include analysis of the physical and chemical characteristics of waste, boiler performance tests, and exhaust gas emission evaluation. The results show that palm oil waste has a high calorific value (15–20 MJ/kg), which makes it an efficient alternative fuel. In addition, the use of this waste is able to reduce dependence on fossil fuels while minimizing carbon emissions, thereby supporting the greenhouse gas emission reduction target. From an operational perspective, the use of palm oil waste in industrial boilers can increase combustion efficiency by up to 75–85%, depending on fuel conditions and boiler design. This makes palm oil waste not only economically valuable, but also strategic in supporting the transition to clean energy. Another advantage is that waste management becomes more targeted, because solid waste that is usually only an environmental burden can be reused as an energy source. However, some of the challenges that need to be considered include relatively high ash levels, the potential for corrosion in boiler equipment, and the need for emission control technology to comply with environmental standards. With the right mitigation strategy, palm oil waste can be processed into sustainable and environmentally friendly energy.

Dependence on fossil fuels, such as gasoline and diesel, has become a global issue that affects environmental sustainability and energy security. Increasing greenhouse gas emissions, decreasing natural resource reserves, and instability of global energy prices encourage the need for innovation in motor vehicle fuel systems. This study aims to assess fuel efficiency and engine performance on a 110 CC motorcycle with a standard compression of 10.7:1, by utilizing a mixture of RON 90 gasoline and alcohol. The main focus of the study is to compare the effect of varying alcohol content on engine power output, with mixtures of E12.5, E17.5, and E22.5. The method used is an experimental method with three variables, namely the independent variable (type and content of fuel mixture), the dependent variable (engine power), and the control variables (engine condition, temperature, and testing method). Testing was carried out using a combination of iridium spark plugs and standard spark plugs, as well as variations in Pilot Jet sizes 34 and 35 on aftermarket carburetors. Each combination was tested to determine its effect on the maximum engine power. The results showed that a blend of E12.5 fuel with Pilot Jet 35 and iridium spark plugs produced the highest power output compared to other tested combinations. This combination was proven to optimize combustion in the combustion chamber, thereby improving engine efficiency and performance. Conversely, increasing the alcohol content above E12.5 did not provide a significant increase and even tended to decrease power due to alcohol's lower calorific value than gasoline. The conclusion of this study is that the use of an aftermarket carburetor with Pilot Jet 35 and iridium spark plugs, combined with an E12.5 fuel blend, can be an effective alternative for improving the performance of a 110cc motorcycle. These findings are expected to serve as a reference for the development of more efficient and environmentally friendly blended fuel technology.

Candlenut shell is an organic waste that has a hard texture and has a high carbon element. The amount of candlenut shell produced from each processing of candlenut seeds is very large but has not been optimally utilized. For this reason, an effort is needed to utilize candlenut shells so that they do not become waste. In the manufacture of hazelnut shell briquettes, hazelnut shells are carbonized at 500 °, sifted with mesh 30 and 100 sieves, given a compressive load of 3 kg, 4 kg, 5 kg and 5.5 kg, the adhesive on hazelnut shell briquettes is starch and drying is carried out with a drying oven for 3 hours at a temperature of 80 °. The purpose of this study was to determine the effect of variations in pressure and particle size on the quality of hazelnut shell briquettes when viewed from the combustion rate and calorific value. The methodology used in this research is experimentation on hazelnut shell briquettes, testing hazelnut shell briquettes including testing water content, testing ash content, burning rate and calorific value of briquettes. From the results of the research on hazelnut shell briquettes with variations in pressure and mesh, the highest calorific value in hazelnut shell raw material briquettes is in the 5.5 Kg pressure specimen on mesh 30, namely 9855.18 Cal/gram and the bomb calorimeter test results are 7008.03 Cal/gram with an error rate of 24.40%, the higher the pressure will produce a higher calorific value as well. The highest combustion rate value is in hazelnut shell briquettes at a pressure specimen of 3 Kg mesh 100 with a value of 1.2 grams/minute the smaller the particle size, the higher or faster the combustion rate.

The selection of coffee wood in this study is based on the fact that coffee wood is waste and has not been utilized optimally and the availability of coffee wood is large and easy to obtain in the East Java region. Coffee wood is a type of wood that is not in demand by many people because this wood is relatively small and not straight. To reduce waste, researchers made briquettes made from coffee wood using mesh 30 and 250 with variations in drying temperatures (60 °C, 80 ° C and 100 ° C). After that was carried out Calorimeter Bomb Testing, and hardness. The highest calorific value resulting from temperature variations of 60°C, 80°C, and 100°C mesh 30 and 250 drying coffee wood briquettes is mesh 30 temperature 100°C of 6972.23 cal/g, and mesh 250 temperature 100°C of 6763.19 cal/g. The effect of the ratio of temperature variations (60°C, 80°C and 100°C) mesh 30 and 250 Drying coffee wood briquettes is: Grain and adhesive size. The smaller the grain size on the briquettes, namely mesh 250, it produces a high hardness value of 60 °C of 26.6 HA, a temperature of 80 °C of 27.7 HA, and a temperature of 100 ° C of 27.4 HA, the larger the grain size in the briquette, namely mesh 30, the low hardness value of 60 ° C of 25.6 HA, temperature of 80 ° C of 26.4 HA, and a temperature of 100°C of 26.2 HA.  The effect of the adhesive is that when drying the oven for 3 hours with temperature variations (60 ° C, 80 ° C and 100 ° C) makes the adhesive react so that the adhesive evaporates and coagulates which causes the hardness value to rise and fall.

Through this research there are two variables observed, namely the effect of variations in briquette charcoal pressure and specific heat value on the composition of carbonisation of hazelnut shell charcoal with tapioca adhesive on specific heat value. The initial process of research in the form of making charcoal on hazelnut shell briquettes, hazelnut shells are carbonised at 500 °, sieved with mesh 30 and 100 sieves, given a compressive load of 3 kg, 4 kg, 5 kg and 5.5 kg, the adhesive on hazelnut shell briquettes is starch and drying is carried out with a drying oven for 3 hours at a temperature of 80 °. The purpose of this study was to determine the effect of variations in pressure and particle size on the quality of hazelnut shell briquettes when viewed from the combustion rate and calorific value. The methodology used in the research is by using hazelnut shell briquette experiments, hazelnut shell briquette testing includes testing through hardness and briquette calorimeter bomb value. Through the research, it was found that the highest calorific value was in the 4 kg pressure specimen on mesh 30, namely 9221.09 cal/gram while the lowest combustion rate was produced by the hazelnut shell briquette specimen with a pressure of 5 kg and 5.5 kg, which was 4076.17 g/min. Giving different compressive loads and mesh sieves can provide advantages to briquettes including increasing specific calorific value, reducing water content and slowing the combustion rate

Along with the times, the availability of fossil energy is decreasing, especially natural gas and coal, before using fossil energy, humans have used biomass as an energy source. Indonesia has many plantation commodities, one of which is coffee which is the fourth largest coffee producer in the world. Coffee grounds are the main waste produced by coffee shops and are usually only thrown away. The main ingredients in this study were arabica coffee grounds and robusta. By using robusta composition 60% arabica 40%, robusta 50% arabica 50% robusta 40% arabica 60%. In addition, briquettes are tested for hardness by making points on the surface of the briquettes using a durometer shore A tool of 30 points, then a calorimeter bomb test is carried out to obtain the calorific value content. The result obtained from the highest hardness value is briquettes with a robusta mixture of 50% arabica 50% with a value of 23.7 HA, while the highest calorific value is found in a robusta mixture of 60% arabica 40% with a value of 4526.85 cal / gram.

The purpose of this research is to get the optimum condition of temperature and ideal ratio biopellet made from shell and kernel of rubber seed by using screw oil press machine according to Indonesian National Standards (SNI 8021-2014) which include heating value, ash content, moisture content, volatile matter, and density of biopellet. Comparison of the basic ingredients shell and kernel of rubber seed in this research include 80:20, 70:30, 60:40, 50:50, and 40:60 with varying temperature 200ᵒC and 150ᵒC. The results of the research it is known that the best composition of biopellet is a sample at temperature 200ᵒC, and ratio of shell and kernel of rubber seed 80:20 with calorific value of 5,083.4919 cal/g, moisture content of 4,00%, density 1.6322 gr/ cm3, ash content 1.9802%, volatile matter 77.1881%, and fixed carbon 16.8317%. The calorific value and the proximate analysis have fulfilled the SNI 8021:2014.