Formulation and Characterization of Bio-Briquettes and Bio-Pellets from Ramie (Boehmeria nivea) Biomass as Renewable Fuel

Abstract

This study evaluates bio-briquettes and bio-pellets made from ramie (Boehmeria nivea), sacha inchi (Plukenetia volubilis), and palm kernel shell (Elaeis guineensis) as renewable fuel sources. Proximate analysis was conducted to measure moisture, ash, volatile matter, fixed carbon, and calorific values, while combustion tests assessed boiling efficiency and burn time. Results reveal that bio-briquettes generally outperform bio-pellets in calorific value, with sample B-S8R2 achieving the highest at 6455 kcal/kg and the fastest boiling time of 14 min at 88 °C. This enhanced performance is attributed to its high fixed carbon (71.81%) and low volatile matter, optimizing combustion and energy yield. In contrast, bio-pellets like sample P-PO7R3, with a calorific value of 4212 kcal/kg, offer moderate heat and durability, making them suitable for household use. The high density and low moisture content across all samples support efficient combustion, while the bio-briquettes’ low ash production indicates a more environmentally friendly fuel. The findings suggest that bio-briquettes are optimal for high-energy applications due to their superior combustion efficiency and environmental benefits, whereas bio-pellets provide a viable option for moderate-energy needs. This research supports the development of sustainable biofuel from biomass waste, providing a promising alternative to traditional fossil fuels.

1. Introduction

Energy based on fossil fuels such as coal, oil, and gas is a major energy source in the world, including in Indonesia, where it is used for power generation, transportation, and more [1]. This non-renewable energy has limited availability and has a negative impact on the surrounding environment, such as increased carbon emissions [2]. Renewable energy can be an alternative to address these issues. One of the renewable energies with potential for development in Indonesia is fuel from plant biomass waste, such as briquettes and bio-pellets [3].

Bio-pellets and bio-briquettes are forms of renewable energy produced from biomass, such as plants and organic waste, through densification or thermophysical processes. This energy is considered an alternative source that is environmentally friendly, carbon-neutral, and renewable, and can replace charcoal, firewood, and coal [4,5]. Bio-pellets and bio-briquettes can be produced from various types of biomass, including agricultural plant residues, wood waste, and industrial organic waste, which can then be used as a sustainable and environmentally friendly alternative energy source [6,7].

The biomass of the ramie plant (Boehmeria nivea L. Goud) has significant potential as a raw material for bio-pellets and bio-briquettes due to its availability. Ramie, a plant known for its fiber production, generates waste during fiber extraction, primarily from its stems. This waste, rich in lignin and cellulose, can be utilized for producing bio-briquettes and bio-pellets, as it serves as a source of carbon [8]. This opportunity could support the development of a bio-briquette industry as an extension of the existing ramie fiber industry. With lignin content of 30% and cellulose content of 44.82%, ramie wood chips are a promising fuel source, as the lignin content in lignocellulose contributes to a higher calorific value, making it an attractive option for alternative fuel production [9]. According to research by Lestari and Priambodo (2020), the ash content of ramie wood chips is relatively high, reaching 40%, whereas for producing quality briquettes, the maximum ash content should be 8% [10]. One of the solutions that can be applied is to combine ramie wood chips with other biomass such as sacha inchi shells and palm kernel shells, which are known to have high calorific values and lower ash content. This combination can potentially improve the quality of alternative fuels by utilizing biomass waste more effectively.

The sacha inchi (Plukenetia volubilis) shell contains a high lignin content of 36.44% and a cellulose content of 6.17%. The biomass of sacha inchi seed shells has significant potential as a biomass fuel due to its chemical properties, including its carbon, nitrogen, hydrogen, and oxygen content [11]. Based on the preliminary test results, the biomass of sacha inchi seed shells has a calorific value of 4610 cal/g. The advantage of sacha inchi seed shells is their ability to reduce the ash content of the mixed biomass for briquette production due to their low ash content; the seed shells (husk) have an ash content of 1.44%.

Oil palm (Elaeis guineensis) is a plant primarily cultivated for palm oil production. The waste generated during palm oil processing is substantial, and palm kernel shells are a promising byproduct for utilization. Approximately 7–9% of processed fresh fruit bunches (FFBs) yield palm kernel shells, which are rich in lignin (50%) and cellulose (29.7%) [12,13]. The use of palm kernel shell waste is well established, particularly in the fuel sector, such as for making charcoal briquettes. Palm kernel shells are known for their high calorific value and low ash content [14], making them a potentially effective material to enhance the fuel quality of ramie wood chips.

The price of TKKS raw materials is IDR 120/kg [12]. Meanwhile, plant-based raw materials derived from industrial waste, such as ramie and sacha inchi, have no established market value in Indonesia due to their low production volumes. As a result, utilizing this biomass is significantly cheaper than fossil fuels in the local market, making it a more economical alternative.

This research evaluated the influence of ramie wood chip formulations involving palm kernel shells and sacha inchi shells on two main fuel parameters: the proximate test and the combustion test. The primary objective is to determine the optimal formulation that combines both materials to produce efficient and sustainable fuel. This research uses an experimental approach to obtain accurate and meaningful data and determine the best formulation ratio to achieve the desired results.

2. Materials and Methods

2.1. Materials

The study utilized pellets and briquettes derived from various biomass sources, including ramie wood chips (Boehmeria nivea L. Goud) and sacha inchi husk and shell biomass (Plukenetia volubilis) from PT Haramai Jaya Nusantara, Bandung, Indonesia, as well as palm kernel shell (Elaeis guineensis) obtained from the Sari Echo Tanjung Sari tofu factory. These raw materials were selected based on their availability, chemical composition, and potential for biofuel production.

The different types of biomass raw materials used in this study, all derived from industrial waste, can be seen in Figure 1. Figure 1a displays ramie chips, which are bark chips obtained from decorticated ramie stems during fiber processing. These chips measure 1–2 cm in size and are light brown, indicating partial carbonization. Their high lignin (30%) and cellulose (44.82%) content contribute to efficient combustion, making them a promising biofuel material. Ramie chips are lightweight and readily combustible, offering advantages in blending formulations for briquettes and pellets. Figure 1b presents palm kernel shells (PKS), a by-product of palm oil production. These shells are coarse-textured particles, ranging in size from 1–3 cm, and are dark brown. PKS is an excellent biomass material due to its high lignin content (50%), low ash content, and substantial calorific value, which enhance the overall energy density and combustion performance of biofuels. Their durability and resistance to moisture make them suitable for long-term storage and transportation.

Figure 1c features the husk of sacha inchi (Plukenetia volubilis), with particle dimensions of 2–3 cm. The husk has a dark brown color and contains 36.44% lignin, which imparts natural adhesive properties, reducing the need for additional binders in briquette production. These properties make the husk ideal for creating a denser and more compact biofuel product, improving burn efficiency and reducing emissions. Figure 1d showcases the shells of sacha inchi seeds, which share similar dimensions (2–3 cm) with the husk but is distinguished by its harder texture and higher carbon content. This shell significantly contributes to the calorific value of biofuels, providing longer burning durations and greater thermal efficiency. Due to these properties, the shell is often included in biofuel formulations in higher proportions, enhancing the overall energy output and sustainability of the fuel. By leveraging these biomass materials, the study aims to optimize biofuel formulations that combine their unique characteristics to produce efficient, sustainable, and environmentally friendly fuel sources. The use of these industrial waste products not only reduces the reliance on fossil fuels but also addresses waste management challenges, contributing to a circular economy.

2.2. Formulation and Production of Bio-Briquettes and Bio-Pellets

2.2.1. Formulation

In this study, the formulation of Ramie biomass (code R) was carried out with variations in the percentage composition of palm kernel shell (Palm oil/PO), sacha inchi (S) with the same formula (

Table 1. The material composition of bio-pellets and bio-briquettes.

	Samples	Ramie (R) %	Palm Oil (PO) %	Husk of SI (H) %	Shell of SI (S) %
Bio-Briquettes	B-PO5R5	50	50	-	-
	B-PO7R3	70	30	-	-
	B-S5R5	50	-	-	50
	B-S6R4	40	-	-	60
	B-S7R3	30	-	-	70
	B-S8R2	20	-	-	80
Bio-Pellets	P-PO5R5	50	50	-	-
	P-PO7R3	30	70	-	-
	P-S7R3	30	-	-	70
	P-S5R5	50	-	-	50
	P-H7R3	30	-	70	-
	P-H5R5	50	-	50	-

) for both bio-briqettes (code B) and bio-pellets. (P). The formula was established by considering the chemical composition and physical properties, as well as how these combinations affected the combustion results. The high cellulose content in ramie, which is 44.82% [9], allows it to be easily combustible and contributes to increasing the ignition rate, which is beneficial for rapid heating. To enhance higher thermal stability, a combination of biomass with high lignin content from kernel shell and sacha inchi, 53.4% and 36.44% respectively, is required [11,13,14]. The use of these two biomasses is expected to reduce the ash residue from the content produced by the ramie.

2.2.2. Production of Bio-Briquettes

The bio-briquette production stage follows the modified [15] procedure, where the stages of bio-briquette production include chopping, carbonization, mixing, pressing, and drying. The dried material is ground using a disk mill until it forms a fine powder. Wood chips and palm kernel shells that have been powdered are then carbonized at a temperature of 400 °C for 1.5 h [16]. In the pyrolysis process, volatile matter will evaporate, flowing out through the pipe openings. The result of the carbonization is separated from the ash, so what is used for the next process is charcoal. Then, the fine charcoal is mixed with tapioca flour in a ratio of ramie wood chips, palm kernel shells, and sacha inchi. The mixed materials are then pressed into briquettes using a briquette press machine with a pressure of 200 MPa, cooled at room temperature for 14 days, and then oven-dried at 70 °C for 24 h.

2.2.3. Production of Bio-Pellets

The bio-pellet production stage follows the modified [17] procedure, where the dried raw material is ground using a disk mill until it forms a fine powder. The powdered materials are then sifted with a 40 mesh sieve and mixed with 5% tapioca flour as a binder (Table 1). The mixed materials are then molded with a pelletizer and cooled at room temperature.

2.3. Proximate Test

The proximate test is the stage for testing the quality of bio-pellets based on SNI 8021-2018 and bio-briquettes based on SNI 1/6235/2000. The pellets and briquettes that have been produced are then subjected to calorific value tests, moisture content tests, volatile matter tests, and ash content tests. The proximate analysis is conducted at the Balai Besar Pengujian Mineral dan Batubara tekMIRA, Jl. Jend. Sudirman No. 623, Bandung City, West Java.

2.3.1. Moisture (MC)

The moisture content (MC) was determined by calculating the loss in weight of material using the oven drying method at 105–110 °C for 1 h until a constant weight loss was reached [18].

$$Moisture \left(\%\right)={\displaystyle \frac{wg2-wg3}{wg2-wg1}}\times 100\%$$

(1)

• wg1 = weight of the empty crucible (g)
• wg2 = weight of empty crucible + sample (g)
• wg3 = weight of the crucible + sample after heating (g)

2.3.2. Ash (A)

The sample residue was heated in an uncovered crucible in a muffle furnace at 815 ± 15 °C to measure the ash content for three hours. After heating, the crucible was removed and cooled first in the air and then in a desiccator before being weighed. The remaining material was recorded as the ash content, expressed as a percentage [18].

$$Ash \left(\%\right)={\displaystyle \frac{wg9-wg7}{wg8-wg7}}\times 100\%$$

(2)

• wg7 = weight of the empty crucible (g)
• wg8 = weight of empty crucible + sample (g)
• wg9 = weight of the crucible + ash (g)

2.3.3. Volatile Matter (VM)

For volatile matter determination, the dried sample was placed in a covered crucible, heated in an electric furnace at 900 ± 15 °C for seven minutes, and then cooled first in air and subsequently in a desiccator. The weight loss was measured and reported as the volatile matter on a percentage basis [18].

$$Volatile Matter \left(\%\right)={\displaystyle \frac{wg5-wg6}{wg5-wg4}}\times 100\%$$

(3)

• wg4 = weight of the empty crucible (g)
• wg5 = weight of empty crucible + sample (g)
• wg6 = weight of the crucible + ash (g)

2.3.4. Fixed Carbon

The fixed carbon (FC) followed [18], where the percentage was calculated using the following equation:

Fixed carbon (%) = 100 − % of (M + VM + A)

(4)

2.3.5. Gross Calorific Value

The calorific value is known as the energy content and can be measured using a bomb calorimeter or calculated using thermodynamical values. It can be expressed in kcal/m³ or MJ/kg⁻¹.

$$Gross Calorific Value \left(MJ/kg\right)={\displaystyle \frac{\left(Wg+wg\right)\times (T1-T2)}{wf}}$$

(5)

• Wg = weight of water in calorimeter (kg)
• wg = weight equivalent of apparatus
• T1 = initial temperature of water (°C)
• T2 = final temperature of water (°C)
• wf = weight of fuel sample taken (kg)

2.4. Combustion Test

The combustion test followed the procedure of [19] with modification, conducted by burning bio-briquettes and bio-pellets to observe the physical appearance and the color of the flame produced. A water boiling test was conducted on 500 mL of water in the combustion test. The temperature of the water was measured when the water had boiled, and the time taken to boil the water was recorded. The analysis was conducted by comparing each sample in the combustion test.

2.5. Statistical Analysis

All experimental results are presented as mean ± standard deviation. Data analysis was conducted using Statistical Package for the Social Sciences (SPSS) version 26 for Windows (IBM Corp., Armonk, NY, USA) and Microsoft Excel 2021 MSO (Version 2410) (Microsoft, Washington, DC, USA). Pearson’s correlation and statistical computing was used for the correlation analysis.

3. Results

3.1. Production of Bio-Pellets and Bio-Briquettes

Bio-Briquette Production Results

The bio-briquettes produced in this study are uniform in size, with a diameter of 5 cm and an average weight of 70 g. These briquettes have a dark gray to black appearance and a smooth surface, as shown in Figure 2, achieved through a high-pressure compaction process at 200 MPa. This process enhances their density, solidity, and non-porous characteristics, resulting in efficient combustion. The formulations differ based on the proportions of raw materials, such as palm kernel shells, ramie chips, and sacha inchi shells, each chosen for their specific contributions to fuel quality. The formulations include the B-PO5R5 with 50% palm kernel shell and 50% ramie chips (Figure 2a), as well as the B-PO7R3 with 70% palm kernel shell and 30% ramie chips (Figure 2b). Additionally, sacha inchi shell-based formulations are included, with ratios ranging from 50% to 80% (Figure 2c–f). These compositions aim to optimize calorific value and combustion stability.)

Bio-pellets were produced with uniform dimensions, averaging 2–4 cm in length. Their color and texture vary depending on the raw material formulation (Figure 3). Palm kernel shell-based pellets are darker and denser, indicating higher energy content, while sacha inchi shell and husk-based pellets are lighter in color and more brittle, reflecting their lower fixed carbon content. The formulations include P-PO5R5, made from 50% palm kernel shell and 50% ramie chips (Figure 3a), and P-PO7R3, consisting of 70% palm kernel shell and 30% ramie chips (Figure 3b). The bio-pellet formulation P-S7R3, consisting of 70% sacha inchi shells, is characterized by its darker color and uniform length (Figure 3c), indicating consistent compaction and material distribution. Other formulations with sacha inchi husks are also shown in Figure 3d–f, with a lighter color reflecting a lower fixed carbon content, with a brittle structure and non-uniform size.

3.2. Proximate Analysis

3.2.1. Bio-Briquettes

The proximate analysis of the bio-briquettes showed varied results (

Table 2. Proximate test results of bio-briquettes.

	Sample	Moisture in Air-Dried	Ash	Volatile Matter	Fixed Carbon	Gross Calorific Value
SNI Briquette		Max 10%	Max 8%	Max 15%	Min 70%	Min 5000 kcal/kg
Bio-Briquette	B-PO5R5	6.91 ± 0.01	10.8 ± 0.01	15.48 ± 0.11	66.81 ± 0.10	6190 ± 3.54
	B-PO7R3	6.88 ± 0.08	10.6 ± 0.01	15.58 ± 0.05	66.94 ± 0.12	6194 ± 18.38
	B-S5R5	8.17 ± 0.03	9.78 ± 0.14	14.11 ± 0.13	67.94 ± 0.04	6114 ± 20.15
	B-S6R4	8.02 ± 0.05	8.57 ± 0.03	14.45 ± 0.07	68.96 ± 0.05	6216 ± 8.49
	B-S7R3	8.16 ± 0.04	6.5 ± 0.04	16.37 ± 0.16	68.97 ± 0.08	6350 ± 12.02
	B-S8R2	8.19 ± 0.04	6.24 ± 0.01	13.76 ± 0.02	71.81 ± 0.03	6455 ± 15.56

). All samples have a moisture content below the maximum SNI (Indonesian National Standard) limit of 10%, ranging from 6.88% to 8.19%, which reflects efficiency in the combustion process. However, some samples, such as B-PO5R5 and B-PO7R3, have an ash content that exceeded the SNI maximum limit of 8%, which can increase combustion residue. In formulations using palm kernel shell (PKS), the ash content exceeds the SNI standard due to high mineral levels. According to [20], elevated ash content is attributed to various ash-forming elements, including Cl, K, Na, P, and S. Potassium (K), in particular, is prone to oxidation, forming ash residues; PKS contains a high K level of 67.08 ± 0.72 mg/100 g [21], which increases ash content in briquette formulations.

Some samples, such as B-S7R3, also exhibited volatile matter content exceeding the SNI standard limit of 15%, with a recorded value of 16.37%. While higher volatile matter can enhance ignition and accelerate the combustion process, it can also lead to faster but less stable burning, reducing the overall efficiency. Lignin, a major contributor to volatile matter, releases phenolic compounds such as volatile phenolic structural monomers during combustion [22]. PKS is rich in lignin, approximately 50% [14], while ramie wood chips have a lignin content ranging from 15–30% [23]. The higher lignin content in PKS increases the volatile matter, thereby enhancing the combustion reactivity compared to other formulations.

In terms of fixed carbon, only sample B-S8R2 meets the SNI standard with a content of 71.81%, indicating good combustion resistance. In addition, all samples have a high calorific value, ranging from 6114 to 6455 kcal/kg, far above the SNI standard of 5000 kcal/kg, indicating high energy potential. Overall, the B-S8R2 sample excels in combustion efficiency, stability, and calorific value, making it the best potential alternative fuel.

3.2.2. Bio-Pellets

Based on the proximate test results of the bio-pellets (

Table 3. Proximate test result of bio-pellets.

	Sample	Moisture in Air-Dried	Ash	Volatile Matter	Fixed Carbon	Gross Calorific Value
SNI Biopellet		Max 12%	Max 1.5%	Max 80%	Min 14%	Min 4000 kcal/kg
Bio-Pellets	P-PO5R5	9.02 ± 0.1	5.2 ± 0.01	68.32 ± 0.11	17.46 ± 0.11	4164 ± 7.78
	P-PO7R3	8.61 ± 0.08	4.4 ± 0.01	68.59 ± 0.07	18.4 ± 0.16	4212 ± 15.56
	P-S7R3	10.22 ± 0.01	4 ± 0.01	60.24 ± 0.06	25.54 ± 0.08	4232 ± 9.19
	P-S5R5	9.94 ± 0.01	4.7 ± 0.01	61.95 ± 0.07	23.41 ± 0.09	4158 ± 17.68
	P-H7R3	8.93 ± 0.07	5.23 ± 0.01	67.5 ± 0.14	18.34 ± 0.08	3918 ± 9.19
	P-H5R5	9.75 ± 0.10	5.62 ± 0.02	67.27 ± 0.00	17.36 ± 0.08	3891 ± 4.24

), all samples showed moisture content below the SNI (Indonesian National Standard) maximum limit of 12%, ranging from 8.61% to 10.22%. This indicates that the drying process was quite efficient for all samples. However, most samples have an ash content far above the SNI standard, which sets a maximum of 1.5%. For instance, the P-PO5R5 sample recorded an ash content of 5.2%, while P-H7R3 had 5.23%. Such high ash content can negatively impact the quality of the bio-pellets by producing more residue after combustion. According to Vassilev et al. [20], elevated ash content is attributed to various ash-forming elements, including Cl, K, Na, P, and S. The volatile matter content in all samples is below the maximum limit of 80%, with the highest value in P-PO5R5 at 68.32%, indicating good combustion potential. On the other hand, the fixed carbon content in most samples is below the SNI minimum limit of 14%, except for the P-S7R3 (25.54%) and P-S5R5 (23.41%) samples, which show better combustion resistance in these two samples. The calorific value of all samples varied, with P-S7R3 showing the highest value of 4232 kcal/kg, exceeding the minimum SNI standard of 4000 kcal/kg, thus having greater potential as an energy source. Although there is an excess in ash content, the P-S7R3 sample showed the best performance in the proximate analysis with a high carbon content and calorific value.

The bio-pellets produced from the formulated mixtures also exhibited good density. This was proven when the bio-pellets were pressed and thrown onto the floor, and the bio-pellets remained intact and did not break. This indicates that the density and strength of the bio-pellets are quite good, since the density of the bio-pellets affects the combustion quality, including burn time and thermal efficiency. Denser pellets tend to burn more slowly and in a more controlled manner [24]. In general, the surface texture and color of the bio-pellets do not affect the quality of the bio-pellet fuel. However, it can enhance consumer appeal and influence user preference.

3.3. Combustion Test

The combustion test for bio-briquettes (Figure 4a), revealed that the B-S8R2 sample has the shortest time to reach 88 °C, requiring only 14 min. This performance is attributed to its high calorific value, substantial fixed carbon content, and lower volatile matter, all of which contribute to optimized combustion. However, the B-S5R5 sample has the longest time to heat water because it has the smallest calorific value among all samples because the calorific value affects the energy at the time of combustion [25,26].

In the bio-pellet test (Figure 4b), P-PO5R5 has a high temperature and fast time because it has a high volatile value. A higher volatile matter content accelerates the combustion process, resulting in quicker heating [27,28]. However, the P-S7R3 sample, which has the highest calorific value and fixed carbon content, exhibits a lower temperature of 88 °C and the longest heating time of approximately 24 min. This result is likely influenced by its higher moisture content, which disrupts ignition despite its high calorific and carbon values, leading to prolonged combustion once ignited. However, it will be more challenging to ignite compared to P-PO5R5. Then P-H7R3 has a lower calorific value, resulting in a lower maximum temperature of 84 °C. Its high volatile matter content causes the fire to ignite quickly and burn intensely but extinguish just as rapidly.

Based on this analysis, for bio-briquettes, sample B-S8R2 shows the best performance as it reaches a temperature of 88 °C in the shortest time 14 min, indicating high combustion efficiency. Meanwhile, sample P-PO5R5 is superior for bio-pellets, as it can reach a temperature of 90 °C in 8 min, demonstrating good heat efficiency even though its temperature is slightly lower than the others.

3.4. Statistical Analysis

Based on the Pearson correlation analysis (Figure 5) of biofuel parameters (bio-briquettes and bio-pellets), the fixed carbon content shows a very strong positive correlation with the gross calorific value of 0.841, indicating that an increase in fixed carbon content can enhance the energy value of biofuel. Conversely, ash content has a very strong negative correlation with gross calorific value (−0.874) and fixed carbon content (−0.888), indicating that biofuels with high ash contents tend to have lower energy and less fixed carbon content. A moderately strong negative correlation is also observed between the moisture content ) and ash content (−0.77), indicating that ash content tends to decrease as moisture content increases. Moreover, although the volatile matter content shows a negative correlation with fixed carbon content (−0.527), its influence on the gross calorific value is very weak (−0.053), making it not very significant in determining the energy quality of biofuel. Overall, the composition of biofuel with a high fixed carbon content and low ash content will produce biofuel with better energy quality, so these two parameters can be the main reference in optimizing biofuel production [29].

4. Discussion

In this study, the calorific value, bound carbon content, and volatile matter content of bio-briquette and bio-pellet samples are directly related to combustion efficiency. The high calorific value in bio-briquettes (e.g., sample B-S8R2 with 6455 kcal/kg) and bio-pellet (e.g., sample P-PO7R3 with 4212 kcal/kg) highlights greater heat potential, which is ideal for both household and industrial energy needs [30]. Specifically, the high bound carbon content (71.81% in B-S8R2) contributes to stable combustion and sustained heat output. It is supported by literature stating that biofuels with high bound carbon will have more efficient combustion and reduce ash and exhaust gas formation [31].

Previous studies, such as those conducted by Sharma et al. [32], have shown that low moisture content and high fuel density contribute to better combustion efficiency. For example, the P-PO7R3 sample with a volatile matter content of 68.59% can produce a quick flame because the high volatile matter value makes the combustion reaction easier to initiate. This aligns with findings that fuels with higher volatile matter tend to have faster initial combustion, although their durability may be slightly reduced [27].

Several previous studies, such as Lestari and Priambodo [9] on ramie biomass, identified high ash content as a factor that negatively impacts fuel quality, as it increases combustion residue and the frequency of cleaning. In contrast, this study’s formulation for the B-S8R2 bio-briquette successfully reduced the ash content to 6.24%, which shows a significant improvement compared to Lestari and Priambodo’s findings of up to 40% ash content in ramie. Additionally, research by Rueda-Ordóñez et al. [11] on the combustion characteristics of sacha inchi observed that the high lignin and cellulose content in this material contributes to the optimal calorific value, supporting the results of the P-PO7R3 sample in this study.

A positive correlation between carbon content and calorific value, as observed in this research, is consistent with findings from Anshariah et al. [33]. Fixed carbon plays a key role in the oxidation process during combustion, directly contributing to energy release [34]. Higher levels of fixed carbon result in greater energy output, with lignin, rich in carbon, providing high thermal stability and prolonged combustion [35,36]. This enhances thermal efficiency and extends burn duration [37]. However, volatile matter content generally shows a negative correlation with calorific value and fixed carbon, as higher volatility can lead to rapid but less efficient combustion. Balancing carbon, lignin, and volatile matter content is essential to optimizing biofuel quality and energy output [38].

The significant difference in the increase of bound carbon content in the B-S8R2 bio-briquette also reinforces the new findings of this study. Previous research reported that the bound carbon content in biomass fuel derived from sacha inchi was relatively low, at around 7.8% [11], whereas, in this study, the carbon content was enhanced significantly, reaching 71.81%. This substantial improvement enables more efficient combustion and higher heat output, making it suitable for industrial applications. These results suggest that the combination of ramie and sacha inchi in the newly developed formulation effectively enhances the overall quality of the fuel.

The use of bio-briquette and bio-pellet formulations based on local raw materials, such as ramie and sacha inchi, offers great potential for large-scale biofuel development. These formulations address energy demands in households and light industrial sectors, particularly in regions abundant in such biomass resources. The production of energy-efficient bio-briquette B-S8R2 and bio-pellet P-PO7R3 can reduce dependence on fossil fuels. From an economic perspective, diversifying the use of ramie and sacha inchi waste into biofuel can add value for local farmers and create jobs in biomass processing.

On a large scale, the production of bio-briquettes and bio-pellets based on ramie and sacha inchi also offers long-term economic benefits. Lower production costs, compared to conventional fuels, as well as the abundant availability of raw materials in Indonesia, indicate the potential to create an affordable and more environmentally friendly sustainable energy source. Further studies involving supply chain analysis, large-scale economic utilization, and life cycle analysis to predict the environmental and economic impacts of biofuel production will clarify the practical benefits that may be achieved.

5. Conclusions

This research shows that among the tested bio-briquette formulations, sample B-S8R2 produced the best performance with the highest calorific value(6455 ± 15.56 kcal/kg), a bound carbon content of 71.81%, and a low ash content (6.24%). This contributes to high combustion efficiency, producing stable heat, and a short burning time (14 min to reach 88 °C), making this bio-briquette optimal for applications requiring high and sustainable energy in the industrial sector. Meanwhile, for bio-pellets, sample P-PO7R3 shows optimal performance with a calorific value of 4212 ± 15.56 kcal/kg, a bound carbon content of 18.4%, and a volatile matter content of 68.59%. This sample is suitable for household or small-scale use that requires moderate heat and a longer but stable burning time, as its composition allows for efficient combustion and relatively low ash residue (4.4%).

In summary, these results highlight that bio-briquette with the B-S8R2 formulation excels as an alternative fuel for high energy needs. At the same time, bio-pellet P-PO7R3 is ideal for applications with lower energy intensity. This study offers a solid basis for the creation of sustainable biofuels derived from the biomass waste of ramie and sacha inchi. Future research should focus on comparing theoretical and measured heating values to enhance the accuracy of calorimetric assessments and optimize biofuel formulations. Additionally, to more accurately assess their environmental impact, it is essential to evaluate the CO₂ equivalent mitigated per kilogram of pellets during combustion, which will help classify these biofuels as low-emission alternatives.