F1000Research F1000Research 2046-1402 F1000 Research Limited London, UK 10.12688/f1000research.147958.2 Review Articles Enhancing sustainable energy production through biomass gasification gas technology: a review

[version 2; peer review: 2 approved with reservations, 2 not approved]

 Alabi Oluwaseyi O. Writing – Original Draft Preparation https://orcid.org/0009-0005-0027-5930 1 Gbadeyan Oluwatoyin Joseph Conceptualization Supervision Writing – Review & Editing https://orcid.org/0000-0002-7906-3965 a 2 Towoju Olumide A. Writing – Original Draft Preparation https://orcid.org/0000-0001-8504-2952 1 Deenadayalu Nirmala Supervision 2 Department of Mechanical Engineering, Lead City University, Ibadan, Oyo, Nigeria Department of Chemistry, Durban University of Technology, Durban, KwaZulu-Natal, South Africa oluwatoyinG@dut.ac.za

No competing interests were disclosed.

 2 9 2024 2024 13 511 28 8 2024 Copyright: © 2024 Alabi OO et al. 2024 This is an open access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This proposed research investigates the sustainable and innovative use of biomass gasification for generating electricity. Biomass gasification is a versatile and eco-friendly technology that converts organic materials, such as agricultural residues, forestry waste, and even municipal solid waste, into a valuable source of clean energy. This research delves into the various aspects of this technology, including its processes, efficiency, environmental impact, and potential applications in power generation. Biomass gasification gas, often referred to as syngas, presents a promising avenue for addressing the rising energy demand while lowering greenhouse gas emissions and preventing climate change. This research seeks to offer a thorough insight into the principles and practices behind biomass gasification, highlighting its role in the transition towards a sustainable and renewable energy future. The research will investigate the technical and economic feasibility of utilizing biomass gasification gas for electricity generation, examining the benefits, challenges, and opportunities associated with this alternative energy source. By addressing critical issues such as feedstock availability, gasifier technology, gas cleaning processes, and power plant integration, this study seeks to offer valuable insights into the potential of biomass gasification gas as a clean and renewable energy solution.

 Biomass Gasification Renewable Energy Solid Waste Technology The author(s) declared that no grants were involved in supporting this work. Amendments from Version 1

The increasing global demand for energy has led to a significant focus on sustainable energy production. Biomass gasification technology has emerged as a promising solution, offering a cleaner and more efficient alternative to traditional fossil fuels. This review aims to provide a comprehensive overview of the current state of biomass gasification gas technology, highlighting its potential to enhance sustainable energy production. This work explores various biomass feedstocks, gasification processes, and syngas applications, including power generation, biofuel production, and chemical synthesis. Additionally, this work discusses the environmental benefits, economic advantages, and challenges associated with biomass gasification gas technology. The analysis reveals that this technology has the potential to significantly reduce greenhouse gas emissions, support energy security, and promote sustainable development. However, further research and development are needed to address the technical, economic, and policy barriers to its widespread adoption. This review provides a foundation for future research and development in biomass gasification gas technology, supporting the transition to a more sustainable energy future.

 1. Introduction

Electricity stands as the prevailing source of energy consumption worldwide, notably in industrialized nations, and several developing countries find themselves in a similar predicament. The pivotal role of electricity in the industrial sector cannot be overstated. As society advances into the future, emerging concepts such as Industry 4.0 and the digital age gain prominence, underscoring the mounting significance of a reliable electrical supply. According to an analysis by British Petroleum (BP) within the Evolving Transition scenario, approximately 70% of the increased demand for energy production will go toward electricity production. This projection stems from the anticipation that the need for electricity will surge at a rate threefold greater than that of other energy forms ( Situmorang et al., 2020).

At present, the primary sources of power generation are fossil fuels, including coal, natural gas, and oil, along with nuclear energy. Coal, in particular, is the most prevalent fuel for power production, constituting approximately 39.3 percent of global energy consumption, as illustrated in Figure 1 ( Wnetrzak et al., 2013). The world is actively exploring new, more sustainable, environmentally friendly, and safer alternatives to address the challenges of diminishing fossil fuel reserves, increasing sustainability, and the dangers of nuclear power ( Alabi et al., 2023b). An increasingly widespread consensus suggests that renewable energy sources, including biomass, solar, wind, and geothermal energy as illustrated in Figure 1 ( Wnetrzak et al., 2013), are poised to progressively supplant the future of nuclear energy in conjunction with fossil fuels. According to projections, the use of renewable energy is expected to increase steadily over the next two decades, while the use of coal and nuclear energy may either stabilize or decline. This suggests that biomass gasification may become an increasingly important part of the energy mix ( You et al., 2015; Li et al., 2018). The anticipated future expansion of renewable energy technology is therefore likely to be significant. The transition to renewable energy sources is becoming progressively vital in reshaping the global energy landscape ( Huggins et al., 2014; Güleç et al., 2022). These sources are characterized by their ability to be consistently replenished over short timeframes and include biomass, solar energy, wind power, hydropower, geothermal energy, and ocean tides ( Boldrin et al., 2016). Notably, the utilization of various renewable energy sources varies and departs from traditional energy sources. This transition holds significant promise, especially in rural areas where conventional electricity access is challenging ( Madanayake et al., 2017).

Percentage utilization resources for power generation globally.

Source: Wnetrzak et al. (2013).

Hydro energy, also known as hydroelectric power, is a renewable energy source. Hydro energy harnesses the power of moving water, such as water flowing in rivers, oceans, and tidal currents, to generate electricity. It is a clean and renewable energy source, constituting approximately 50% of the total renewable energy resources, as illustrated in Figure 2 ( Watson et al., 2020). Biomass, derived from organic materials such as plants, animals, and algae that do not fossilize and can decompose, comprises lignin, cellulose, hemicellulose, along with trace quantities of substances like proteins, lipids, simple sugars, and starches ( Li et al., 2018; Azeta et al., 2021). In the case of biomass from wood and grass, cellulose typically constitutes around 38 to 50 percent of its total weight ( Huggins et al., 2014; Mondal et al., 2018). Biomass is characterized by its key attributes as an energy source, which include ease of availability, widespread utilization, renewability, sustainability, and versatility. Nevertheless, it should be noted that biomass possesses a lower heating value compared to coal and faces transportation challenges due to its solid state ( Situmorang et al., 2020).

The global percentage of available renewable energy resources.

Source: Watson et al. (2020).

The wide range of available biomass resources, and the diversity of their sources, present a promising opportunity for future energy generation ( Li et al., 2018; Siddiki et al., 2022). Non-woody biomass includes household refuse and processed waste, while woody biomass encompasses a range of forestry resources, including trees, shrubs, scrub, bushes, palms, and bamboos ( Subramaniam and Masron, 2021). Household refuse stand as the most abundant biomass resources, contributing 27% and 30% of the total production, respectively, as delineated in Figure 3 ( Situmorang et al., 2020; Abdulyekeen et al., 2021). Forestry accounts for only around 23% of total biomass production, but it represents the most significant resource for future expansion, with significant potential for growth in the years to come ( Al-Rumaihi et al., 2022). The global primary energy supply harnessed from forests is estimated at approximately 56 exajoules (EJ), and woody biomass, in particular, is anticipated to supply nearly All bio fuels provide 90% of the annual electricity usage ( Lee et al., 2020b).

Biomass resources and different types of Biomasses.

Source: Abdulyekeen et al. (2021).

Biomass is widely recognized as a significant and sustainable alternative to fossil fuels in the long term, ranking among the primary energy sources with the most potential for the future. As such, it is a key focus of research and development in the energy sector ( Situmorang et al., 2020; Ge et al., 2021). In 2014, it contributed to 14% of global final energy consumption ( Picchio et al., 2020). Notably, reports indicate that while biomass constitutes 3% of energy consumption in industrialized nations, it makes up a striking 33% in developing nations ( Picchio et al., 2020). Biomass energy has the dual benefits of being cost-effective and more efficient in energy production than other renewable sources. With an annual production estimated at, much of it from organic growth, biomass is the largest renewable energy source, surpassing the combined energy consumption of other renewable sources by around 8% ( Ge et al., 2021; Mostafa et al., 2021). Biomass has a wide range of applications across industries, particularly for the production of biofuels. It is currently the only renewable resource capable of effectively replacing liquid fossil fuels ( Djatkov, Martinov and Kaltschmitt, 2018).

The most efficient biochemical process for energy generation is anaerobic digestion, which effectively converts wet biomass into biogas. This biogas typically comprises methane (50–75%), carbon dioxide (20–35%), and traces of contaminants like hydrogen sulfide and moisture ( Larsson and Samuelsson, 2017). Over the past two decades, this technology has seen widespread use in Europe, Asia, and North America, leading to the establishment of numerous biogas facilities. Biogas is typically combusted in internal combustion engines to generate electricity or used as a fuel. European countries have implemented regulations that encourage the utilization of biomass as a renewable energy source. In contrast, Asian countries commonly use biomass for cooking and local electricity generation. Most countries in Europe have developed biomass-based technology for domestic energy production ( Puig-Arnavat et al., 2016; Fogarasi and Cormos, 2015). Pig, cow, and chicken manures, as well as industrial wastes like palm oil mill effluent (POME) from the palm oil industry, are common sources of biomass for anaerobic digestion, resulting to the production of biogas ( Ong et al., 2020; Chyuan et al., 2020). A product of various biological processes, bioethanol is often blended with gasoline for automotive fuel. Many modern vehicles can run on a mixture of 10% bioethanol and 90% gasoline without needing engine modifications. Notably, in Brazil, gas stations frequently offer bioethanol-gasoline blends ranging from 18 to 27.5 percent, whereas in Europe, a common practice involves adding 5 percent bioethanol to gasoline ( Digman, Joo and Kim, 2009). Recent advancements have shown that dark fermentation and photo-fermentation are potential methods for producing biohydrogen from biomass, although production is currently limited and further research is needed ( Larsson and Samuelsson, 2017).

Presently, the most widely employed thermochemical method for biomass conversion is direct combustion, which accounts for over 97 percent of global biomass energy production ( Güleç et al., 2022). Worldwide, direct combustion facilities with a combined capacity of 40 gigawatts of electricity generation have been established ( Huggins et al., 2014). In recent years, co-firing biomass with coal during the combustion process has become a widely accepted method for co-generating electricity. During combustion, biomass is ignited with excess oxygen to produce heat and operates in an oxygen-free environment. This process breaks down biomass into three distinct byproducts: non-condensable gases, char, and bio-oil ( Uddin et al., 2018). There are various heating rates used in this process, with pyrolysis being the most commonly used method for extracting bio-oil from biomass. This bio-oil can subsequently be further processed into valuable chemicals or used as automotive fuel ( Zhang et al., 2018). While direct combustion is straightforward and commonly used, it suffers from relatively poor thermal efficiency. In response, gasification has emerged as a more attractive and highly efficient thermochemical process, versatile enough to produce heat, power, fuels, and chemicals ( Zhang and Zhang, 2019). Gasification offers several advantages, including reduced NOx and SOx emissions, lower reaction temperatures, and decreased oxygen requirements ( Ong et al., 2020). Importantly, it boasts significantly higher overall electrical efficiency for power generation ( Zhang and Zhang, 2019). As a result, gasification may be a more viable option for smaller-scale applications, as it can be economically feasible for capacities as low as 5 kilowatts electric and higher ( Ong et al., 2020; Chyuan et al., 2020). As such, gasification is poised for widespread adoption in the large-scale conversion of biomass into energy in the future. An overview of various primary pathways for converting biomass into energy is provided in Figure 4 ( Situmorang et al., 2020; Chyuan et al., 2020).

Conversion of biomass to energy.

Source: Situmorang et al. (2020).

The feasibility of gasification systems, especially in terms of their procurement and large-scale energy generation, is significantly hindered by the limited availability of biomass feedstock. Insufficient feedstock can frequently disrupt the operation of large-scale gasification systems. Consequently, the preference leans toward smaller-scale biomass gasification systems, particularly those with a capacity below 200 kW. These smaller systems can efficiently leverage locally sourced biomass, offering a practical solution to the challenges associated with biomass collection. In this analysis, we delve into the latest advancements in the study of “Enhancing Sustainable Energy Production through Biomass Gasification Gas Technology” to explore the opportunities and obstacles in this specific domain. This examination aims to shed light on the current state, development prospects, and practical implementation of such systems.

 2. Biomass Gasification Technology

Biomass gasification is a transformative energy conversion process that has gained significant attention in recent years due to its potential to provide sustainable and renewable energy sources. It involves the thermal conversion of biomass feedstock, such as wood, agricultural residues, or organic waste, into a gaseous fuel called syngas (synthesis gas). Syngas is composed primarily of carbon monoxide (CO), hydrogen (H 2), carbon dioxide (CO 2), and traces of methane (CH 4). This gas can be utilized for various energy applications, including electricity generation, heat production, and biofuel synthesis. Syngas predominantly consists of components like CO, H 2, CO 2, and CH 4 ( Roncancio and Gore, 2021). Gasification has been around for over 180 years, with the first systems developed in France in the 1840s. It has since become widely used in the United States, with many commercial-scale gasification systems in operation since the 1920s. Notably, during World War II, gasification played a pivotal role in generating syngas for the Fischer-Tropsch-based synthesis of liquid fuels. The United States has seen the construction of many gasification systems over the past 30 years since the 1973 oil crisis ( Situmorang et al., 2020; Pradhan, Mahajani and Arora, 2018b).

The gasification process comprises four primary stages: drying, pyrolysis, combustion, and reduction. During the initial stage of drying, the moisture content of biomass, which typically ranges from 30% to 60%, is vaporized or evaporated. This phase continues until the moisture content drops to the ideal gasification range of below 15%, occurring at temperatures up to approximately 200°C ( Pradhan, Arora and Mahajani, 2018a). The second phase, pyrolysis, involves breaking down the biomass’s hemicellulose, cellulose, and lignin into volatile compounds and solid residues. This phase occurs at around 220°C and yields tar-like liquid products and small gas molecules as volatile compounds, alongside solid char containing non-degradable carbonaceous materials ( Frodeson, Henriksson and Berghel, 2019). During the combustion phase, volatile compounds and char undergo conversion by reacting with oxygen gasifying agents to produce CO, CO 2, and H 2O. This highly exothermic reaction generates heat, with temperatures surpassing 700°C. During reduction, the syngas is converted into a high-quality fuel gas through reactions with carbon dioxide, water, and other compounds. Gasification processes typically take place at temperatures above 800°C, resulting in the formation of ash as a residual substance in the gasifier. It’s important to note that gasification often involves multiple simultaneous processes, with exothermic reactions providing heat for endothermic ones as needed. The effectiveness of the gasification process can be influenced by various factors, including the type of gasifier, the choice of gasifying agents, the biomass composition, and the size of the biomass particles.

2.1 Biomass composition

Figure 4 demonstrates how various components of the same biomass have different physical and chemical properties. This diversity is even more pronounced when considering different biomass sources ( Figure 4: Illustration of the various properties of biomass components). The inherent heterogeneity of biomass poses a challenge in accurately predicting the optimal operating conditions and final product qualities, representing a notable drawback in biomass gasification ( Mostafa et al., 2019). Fundamental analyses of biomass characteristics typically encompass the measurement of heating value, proximate analysis, and ultimate analysis. Key components of biomass composition, such as moisture content, volatile matter, fixed carbon, and ash concentrations, are identified using proximate analysis. Importantly, the moisture content notably affects the progression and phases of the process ( Gilvari, de Jong and Schott, 2019; Alabi, Adeyi and Ekun, 2023a). Fixed carbon represents the carbonaceous solid material, whereas volatile matter comprises the gases released during this phase. It’s worth noting that the presence of tar from volatile biomass materials can pose challenges during the gasification process. The final examination makes it possible to identify the biomass’s components for carbon, oxygen, hydrogen, nitrogen, and sulfur. Both fixed and volatile carbon contribute to the carbon content in char and volatile substances ( Siyal et al., 2021). Biomass further comprises components like lignin, hemicellulose, and cellulose, each decomposing differently during gasification. Higher lignin content slows down the rate of biomass decomposition, necessitating elevated gasification temperatures at the expense of reduced gas output ( Du et al., 2019).

 2.2 Gasification processes and reactors

Gasification is a thermochemical conversion process that transforms carbon-containing feedstock, such as biomass, coal, or waste materials, into a gaseous mixture known as syngas (synthesis gas). This versatile and energy-efficient technology is employed in various applications, including power generation, heat production, and the synthesis of valuable chemicals and fuels. Gasification processes and reactors play a crucial role in the efficient conversion of solid, liquid, or gaseous fuels into syngas. Several gasification technologies and reactor designs are available, each with its own characteristics and advantages. Gasifying agents play a crucial role in various thermochemical processes, such as gasification and combustion, where solid, liquid, or gaseous fuels are converted into valuable products like syngas (synthesis gas), heat, or electricity. The choice of a gasifying agent has a significant impact on the efficiency, product composition, and environmental performance of these processes.

The selection of gasifying agents plays a central role in every gasification reaction, influencing reactivity and gas composition. Different gasifying agents, whether individually or in combination, lead to diverse outcomes in terms of the intended results ( Frodeson, Henriksson and Berghel, 2019; Singh et al., 2014). Because of its affordability and widespread availability, air stands as the most commonly employed gasifying agent among these options. For the production of syngas with an elevated heating value, it is recommended to utilize pure oxygen or oxygen-enriched air. This is because the high nitrogen concentration in regular air can diminish the heating value of the resulting syngas. It’s essential to keep in mind that this choice may lead to increased operational expenses since extracting oxygen and nitrogen from the air requires energy. The air-to-fuel ratio, also known as the equivalency ratio (ER), employed in the gasification process governs the extent of partial oxidation within the gasifier when air is used as the gasifying agent. To prevent full combustion, the ER value is usually kept below 1. The ER ratio is also thought to impact the ultimate heating value of the syngas, typically falling within the range of 0.2 to 0.4 for optimal formation. Utilizing pure oxygen from the air is a cost-effective approach compared to partial oxidation, offering a feasible means to attain higher gas content and reduce undesirable byproducts. However, this choice necessitates additional energy due to the endothermic reactions involved in primary and secondary steam processes, as well as the water gas shift reaction ( Gilvari, de Jong and Schott, 2019; Singh et al., 2014). Moreover, steam is frequently employed to expedite the sluggish reaction rate, obtaining energy for endothermic processes from exothermic partial oxidations. It has been proposed that for gasifiers, a combination of air and 40–70 mol% steam is advisable ( Frodeson, Henriksson and Berghel, 2019; Lee et al., 2020a).

 2.3 Gasification byproducts and applications

The outcome of the gasification process is directly influenced by the size of biomass particles. Smaller particles offer a larger specific surface area for gasification reactions, typically resulting in higher gas production and lower energy consumption. They also enable faster heat transfer and reaction rates ( Roncancio and Gore, 2021). Consequently, gasifying smaller biomass particles yields increased syngas production and reduced tar and char formation. In contrast, larger biomass particles, due to their greater heat resistance and incomplete decomposition, tend to generate more char ( Skorupskaitė et al., 2015).

While smaller biomass particle sizes offer advantages, it’s important to consider that the energy required for size reduction may lead to a decrease in overall energy efficiency. Various gasifier types have been developed to accommodate a range of biomass particle sizes. For example, gasification requires biomass particles with a diameter less than 0.15 mm. Thus, pre-processing of biomass before it enters the gasifier remains an important consideration, despite some studies suggesting otherwise ( Singh et al., 2014).

 2.4 Operating conditions

In gasification, the two main working conditions are temperature and pressure. Among them, temperature is crucial to the gasification process since it has a direct impact on a number of factors, such as gas yield, composition, heating value, formation of tar and char, carbon conversion, and cold gas efficiency. Higher gasification temperatures result in gas products with elevated heating values, characterized by increased CO and H 2 content and reduced tar. Moreover, as temperature increases, both carbon conversion and cold gas efficiency improve ( Yao et al., 2023). However, it’s important to keep in mind that other elements, such as the biomass mixture’s composition and particle size, can affect the necessary combustion rate. For instance, higher temperatures are required to produce more gas from waste with a higher fiber content. In addition, the breakdown of the biomass structure requires greater temperatures for larger catalyst particles ( Sekar et al., 2021). Normally, gasification is kept going at temperatures above 700°C since this is the point at which the spontaneous steam reforming reaction starts to happen. In the case of steam gasification, temperatures should exceed 750°C.

Gasification primarily takes place under atmospheric conditions, although pressurized approaches are now being extensively researched and employed. Due to its low initial investment costs, atmospheric gasification is more prevalent for small-scale gasifiers. Pressurized gasification, on the other hand, is a more effective technique that results in enhanced gasification efficiency and reduced tar production. Conversely, pressurized gasification is a more efficient method, leading to improved gasification efficiency and reduced tar production ( Gilvari, de Jong and Schott, 2019). It’s important to bear in mind that gasification typically operates at low pressure and high temperature, in the context of chemical equilibrium ( Skorupskaitė et al., 2015).

The schematic procedure for this particular type of gasifier is shown in Figure 5(a). The updraft gasifier stands out as an efficient gasification method with a high thermal efficiency. It achieves this by utilizing the sensible heat of the hot gas to preheat and dehumidify the internal components of the system before the lower-temperature gas exits from the top of the gasifier, typically falling within the range of 200°C to 400°C. Remarkably, it demonstrates an impressive performance, capable of accommodating biomass with moisture content as high as it also effectively processes particles ranging from 5 to 100 mm in size ( Sarker et al., 2023). Despite its efficiency, the air gasification process tends to produce a greater amount of tar compared to other methods. The tar generated in the pyrolysis zone flows upward to the cooler region, preventing it from reaching the high-temperature zone where it could be cracked ( Zhang and Zhang, 2019; Razi and Dincer, 2022).

(a) Updraft gasifier and (b) Downdraft gasifier designs.

Source: Roncancio and Gore (2021).

The gasifier in Figure 5(b) uses a unique method for introducing the gasifying agent. Biomass is introduced from the top or sides of the reactor, while the gasifying agent is introduced from the top or sides. This results in a co-current flow between the biomass and the gasifying agent ( Roncancio and Gore, 2021). This suggests that the biomass and gasifying agent come into touch during the gasification operations, improving the quality of the generated gas that leaves the reactor’s bottom. Due to the ability of devolatilization products to enter the high-temperature oxidation zone, despite their brief residence duration in that zone, the tar production in this setup is minimal ( Lee, Balu and Chung, 2013). However, there is relatively limited heat transfer between the hot and cold zones of the reactor in this design, which reduces its tolerance for moisture content. Therefore, only biomass with a moisture level below 30% is suitable for processing. Additionally, due to the alignment of the drag force with gravity, biomass travels downward more swiftly during its residence time in the reactor. Consequently, the carbon conversion efficiency is lower in comparison to an updraft gasifier. This type of gasifier is also susceptible to issues like blocking, channeling, and bridging, requiring consistent particle size to stop these occurrences. Typically, the permissible particle size range is between 40 and 100 mm. With a typical capacity ranging from 10 kW to 1 MW, the downdraft gasifier is well-suited for small-scale power plant applications ( Pavkov et al., 2022).

 3. Utilization of syngas

The primary product of the gasification process is known as synthesis gas or syngas. The term “synthesis gas” is used because these gases mainly consist of CO and H 2, which serve as fundamental building blocks for the production of a wide range of complex chemicals used in various applications. These applications encompass the manufacture of hydrogen, the production of synthetic liquid fuels through the Fischer-Tropsch process, the creation of synthetic natural gas (S-NG), and the synthesis of chemicals such as ammonia, methanol, its derivatives, and dimethyl ether. Syngas is also a popular alternative energy source for electricity generation ( Sarker et al., 2023). Traditionally, syngas has been employed in two main ways for large-scale power generation. In comparison to direct combustion, these techniques have better advantages, such as high thermodynamic performance, and reduced emissions of NOx and SOx. IGCC systems, in particular, have achieved an electrical efficiency exceeding 42% ( Branco, Serafim and Xavier, 2019). Another approach for power generation using syngas is through Internal Combustion Engines (ICE), which are versatile for variable power outputs. ICE technology is cost-effective, reliable, operationally efficient, and adaptable for both stationary and mobile applications. It also exhibits better cost-competitiveness compared to gas turbines, as it is less sensitive to gas impurities. There are two operating methods within ICE technology: Spark Ignition (SI) and Compression Ignition (CI). SI engines utilize air and a spark to ignite syngas in a combustion chamber, resembling the operation of an Otto/gasoline engine. In the CI approach, similar to a diesel engine, compression is used to automatically ignite syngas, often with a small amount of diesel fuel serving as a pilot. Syngas can replace between 60 and 90 percent of the diesel fuel required to run CI engines at the same power level. SI engines are better suited for syngas engines than the CI approach ( Carter et al., 2018).

Syngas generated through the gasification of biomass holds great potential as a source of electricity for rural and peri-urban areas. For this application, there are significant obstacles in developing a small-scale gasification system with an inexpensive initial investment cost, outfitted with effective clean gas technology to support the appropriate operation of gas engines, and built to accommodate different types of biomass ( Situmorang et al., 2020). Even though there are many large-scale facilities for producing power from biomass around the world, some of them are having trouble finding enough biomass supplies. In contrast to fossil fuels, biomass is generally available worldwide and is only constrained by elements like temperature, location, and season. It might be expensive to harvest biomass from isolated farming and mountainous regions. Therefore, the direct utilization of biomass energy in communities and rural regions abundant in biomass resources is a more practical approach. It is imperative to make small-scale gasification power plants available, with capacities ranging from 10 to 200 kW, to enable the effective and cost-efficient utilization of local biomass energy. Successful future initiatives in this field will depend on the successful implementation of such strategies. One potential source of electricity for rural and peri-urban areas is syngas produced from biomass.

 4. Emerging biomass gasification trends 4.1 Technology economic viability

Biomass technology, which harnesses energy from organic materials like wood, agricultural residues, and waste, has garnered significant attention due to its potential as a renewable and sustainable energy source. The economic viability of biomass technology is a critical aspect that influences its adoption and sustainability. Large- and medium-scale gasification systems of over 1 MW capacity are becoming increasingly popular worldwide, particularly in developed nations, for generating electricity ( Situmorang et al., 2020). These systems are not only cost-effective in terms of per unit of electricity produced, but also have a significant impact on the electricity distribution landscape within a country or region. To fully utilize the potential, however, biomass gasification system development and acceptance are essential, particularly in developing and emerging nations ( Sarker et al., 2023). At present, most commercially available gasifiers exhibit relatively low gasification efficiency, including updraft and downdraft gasifiers. There is a critical need to create next-generation gasifiers that offer both high efficiency and cost-effectiveness in order to increase the application of small-scale biomass gasification systems in the power generation sector.

4.1.1 Development of new gasifier

Larger-scale power generation systems often employ fluidized-bed gasifiers, especially circulating fluidized bed gasifiers like dual-bed gasifiers known for their high efficiency. However, scaling down and effectively adapting these systems for small-scale use is a challenging task. Notably, small-scale biomass gasification systems need to be versatile and capable of handling various types of biomass ( Carter et al., 2018). The small gasifiers currently on the market are more suitable for high-quality biomass sources, like woody biomass. When lower-quality feedstocks are used, these gasifiers tend to produce notable quantities of tar and ash, which can present challenges for their operation ( Perera et al., 2021). As a result, the development of these systems must address challenges related to their production. One approach to mitigating tar issues is to implement a two-stage gasification system that includes an initial pyrolysis process, which can reduce tar production. However, this design typically results in a larger gasifier size, making operation more complex and costly. Alternatively, tar in the gas can be post-treated using syngas cleaning systems or catalysts. Furthermore, notable enhancements in gasification efficiency can be attained through the design and incorporation of a distinct setup. As depicted in Figure 6, this biomass gasification system operates similarly to a large-scale triple-bed gasification system, performing biomass pyrolysis, charcoal gasification, and tar reforming as separate, independent processes ( Situmorang et al., 2020; Evaristo et al., 2022).

A three-bed gasification system.

Source: Situmorang et al. (2020).

4.1.2 Economic evaluation and policy

The cost of building the power generating system and the revenue from selling the energy produced are two crucial considerations in the economic assessment of a biomass gasification system used for power generation ( Arslan et al., 2022). The investment costs for the project are an accurate representation of the costs paid, and a crucial metric is the minimum power price based on the levelized cost of electricity (LCOE). According to this split ( Arslan et al., 2022), the gasification unit receives around 24% of the investment, the gas engine and electrical supporting systems receive 54%, and the remaining expenses, such as the purchase of raw materials and transportation, are covered by the remaining funds. Another study on small-scale biomass gasification power plants in Brazil found that the power plant’s capital cost was approximately 1267 USD/kW, resulting in an LCOE of 0.53 USD/kWh ( Bacenetti et al., 2013). According to Carrara’s theory, the investment cost for a gasification system coupled with a 100kW internal gas engine combustion would be between 1200-3300 €/kW (or 906-2491 USD/kW based on 2010 exchange rates) ( Bacenetti et al., 2013). In comparison, 1 MW and 5 MW systems were estimated to have costs of 900-1800 €/kW and 700-1300 €/kW, respectively. According to the International Renewable Energy Agency (IRENA), the typical LCOE for small-scale fixed-bed biomass gasification power plants (up to 600 kW) with internal combustion engines falls within the range of 0.065 to 0.24 USD/kWh. It’s worth noting that costs can vary depending on the country, and despite such variations, large-scale deployments of biomass gasification power systems continue to involve substantial expenses ( Asadullah, 2014).

 4.2 Environmental benefits of biomass gasification

There are two main environmental issues with the use of a biomass gasification plant: the impact of biomass cultivation and the consequences of biomass gasification itself. Perennial energy crops, as indicated by numerous life cycle assessments (LCAs), have been found to reduce greenhouse gas (GHG) emissions by approximately 5 mg/ha of fossil carbon and decrease NO 2 emissions by 40–50% compared to burning fossil fuels. One specific LCA study suggests that cultivating perennial grasses on marginal land for electricity generation can lead to saving approximately 13% of CO 2 equivalent per hectare per year ( Shamsul, Kamarudin and Rahman, 2020). In the context of small-scale biomass gasification systems, their relatively modest biomass resource requirements imply a minimal impact on land use. Moreover, the release of hazardous compounds and GHG emissions is more manageable in such systems, allowing them to efficiently utilize locally generated biomass or agricultural residues.

While biomass gasification has the potential to be a more sustainable alternative to fossil fuels, its environmental impacts must be considered in their entirety. A holistic approach, taking into account the entire life cycle of the technology, is necessary to fully understand the environmental implications. This includes considering the impacts of feedstock procurement, such as the use of resources and land use change, the energy and emissions associated with processing the biomass, the effectiveness of emissions control technologies, and the disposal of any waste products ( Tripathi, Sahu and Ganesan, 2016). Only by considering all of these factors can the true environmental impact of biomass gasification be assessed. Also, there are some negative environmental impacts associated with biomass gasification, the technology also offers some significant environmental benefits that can be optimized through the use of best practices and advanced technologies. For example, by using low-impact feedstock sources, such as agricultural waste or dedicated energy crops, and implementing efficient processing techniques, the environmental impacts can be minimized. In addition, the use of advanced emissions control technologies can help to reduce the release of pollutants into the atmosphere. Finally, the utilization of byproducts from biomass gasification, such as biochar, can further offset the environmental impact of the technology. In the end, the particular feedstock used, the technology used, and the operational procedures all have a significant impact on the environmental impact of biomass gasification. Biomass gasification has the potential to significantly contribute to the mitigation of climate change and the shift to a more sustainable energy future when it is developed and used responsibly ( Alper et al., 2020).

Biomass gasification can have both positive and negative environmental impacts. On the positive side, biomass gasification is a renewable energy source that can reduce the need for fossil fuels. It can also help reduce greenhouse gas emissions by converting biomass into usable energy, and it can help reduce waste by using biomass that would otherwise be discarded ( Güleç et al., 2022; Alper et al., 2020). However, there are also some potential negative environmental impacts of biomass gasification. For example, it can produce air pollutants like nitrogen oxides and volatile organic compounds. It can also release carbon dioxide and methane, which are greenhouse gases. In addition, the process of harvesting biomass for gasification can have a negative impact. The environmental impacts of biomass gasification can vary depending on the specific biomass source and the technology used. For example, using agricultural residues as a biomass source can have a positive environmental impact by reducing the amount of agricultural waste that would otherwise be burned or left to decompose. On the other hand, harvesting biomass from forests can have negative impacts on biodiversity and habitat loss ( Abdulyekeen et al., 2021; Bacenetti et al., 2013). In addition, the type of technology used for gasification can have an impact on the overall environmental impact. For example, gasification systems that use inefficient combustion or have a high energy input can have a higher carbon footprint than other technologies ( Bacenetti et al., 2013; Asadullah, 2014).

 4.3 Practical implication

While there is a plethora of technology vendors capable of providing suitable solutions for small-scale biomass gasification technology, and gasification technologies are now well-established, the number of actual implementations remains limited ( Ong et al., 2020; Chyuan et al., 2020; Roncancio and Gore, 2021). The substantial construction expenses remain a notable obstacle, particularly for developing and less economically developed nations. Therefore, research and development efforts aimed at producing high-efficiency technology are anticipated to involve foreign capital in the creation of a few prototype projects. Local governments in developing and less economically developed nations are likely to lend support by instituting appropriate feed-in tariffs. Collaborative efforts between technology and equipment providers can enhance the reliability of commercializing and industrializing biomass gasification power generation systems.

 5. Conclusions

The gasification process exhibits significant potential for the efficient transformation of biomass into electricity, providing numerous economic and environmental benefits compared to fossil fuels. It plays a crucial role in delivering local electricity, especially in regions with limited electrification and underdeveloped electricity distribution infrastructure. Biomass energy is particularly well-suited for decentralized and localized applications, presenting substantial market potential in many nations and regions. The deployment of power production systems demands substantial engagement from all stakeholders, and proactive policy initiatives by local governments can expedite the commercialization and industrialization of these systems. Furthermore, active participation of local communities, particularly those in agricultural and plantation areas, is expected in the acquisition of biomass feedstock. In conclusion, “Enhancing Sustainable Energy Production through Biomass Gasification Gas Technology” sheds light on the vast potential of biomass gasification, illustrating how this technology can play a crucial role in advancing sustainable energy production globally. By addressing challenges and promoting collaboration, the extensive adoption of these technologies can make a significant contribution to meeting our energy requirements while efficiently harnessing biomass resources. Biomass gasification technology offers a valuable avenue for advancing sustainable energy production, but its path forward necessitates careful consideration of environmental impacts and responsible implementation. Optimizing technology, adopting best practices, and prioritizing the use of sustainable feedstocks are essential to maximize the benefits of this technology while minimizing its potential drawbacks. By navigating these challenges with foresight and responsible planning, biomass gasification can play a significant role in shaping a cleaner and more sustainable energy future.

 Data availability

No data are associated with this article.

 References Abdulyekeen KA : Torrefaction of biomass: Production of enhanced solid biofuel from municipal solid waste and other types of biomass. Renew. Sust. Energ. Rev. 2021;150(June):111436. 10.1016/j.rser.2021.111436 Al-Rumaihi A : A review of pyrolysis technologies and feedstock: A blending approach for plastic and biomass towards optimum biochar yield. Renew. Sust. Energ. Rev. 2022;167(June):112715. 10.1016/j.rser.2022.112715 Alabi OO : Study of Combustion Characteristics of Diesel-Vegetable Oil Blends Utilizing an Industrial Fuel Burner. Fuel Communications. 2023b;18:100104. (Elsevier) [Preprint]. 10.1016/j.jfueco.2023.100104 Alabi OO Adeyi TA Ekun SK : Analyzing Energy Performance and Assessing Dry Moisture Content of Briquettes through Numerical Investigations. 2023a. (October). Alper K : Sustainable energy and fuels from biomass: A review focusing on hydrothermal biomass processing. Sustain. Energy Fuels. 2020;4(9):4390–4414. 10.1039/d0se00784f Arslan A : An experimental study of the combustion and emissions of a syngas diesel dual- fuel generator under a constant An experimental study of the combustion and emissions of a syngas- diesel dual-fuel generator under a constant load condition. 2022. (September). Asadullah M : Barriers of commercial power generation using biomass gasification gas: A review. Renew. Sust. Energ. Rev. 2014;29:201–215. 10.1016/j.rser.2013.08.074 Azeta O : A review on the sustainable energy generation from the pyrolysis of coconut biomass. Sci. Afr. 2021;13:e00909. 10.1016/j.sciaf.2021.e00909 Bacenetti J : Anaerobic digestion of different feedstocks: Impact on energetic and environmental balances of biogas process. Sci. Total Environ. 2013;463-464:541–551. 23831800 10.1016/j.scitotenv.2013.06.058 Boldrin A : Optimised biogas production from the co-digestion of sugar beet with pig slurry: Integrating energy, GHG and economic accounting. Energy. 2016;112(2016):606–617. 10.1016/j.energy.2016.06.068 Branco RHR Serafim LS Xavier AMRB : Second generation bioethanol production: On the use of pulp and paper industry wastes as feedstock. Fermentation. 2019;5(1):1–30. 10.3390/fermentation5010004 Carter E : Development of renewable, densified biomass for household energy in China. Energy Sustain. Dev. 2018;46:42–52. 32863650 10.1016/j.esd.2018.06.004 PMC7453936 Chyuan H : A state-of-the-art review on thermochemical conversion of biomass for biofuel production: A TG-FTIR approach. Energy Convers. Manag. 2020;209(February):112634. 10.1016/j.enconman.2020.112634 Digman B Joo S Kim D : Recent Progress in Gasification/Pyrolysis Technologies for Biomass Conversion to Energy. 2009;28(1):47–51. 10.1002/ep Djatkov D Martinov M Kaltschmitt M : Influencing parameters on mechanical–physical properties of pellet fuel made from corn harvest residues. Biomass Bioenergy. 2018;119(October):418–428. 10.1016/j.biombioe.2018.10.009 Du J : Research on thermal disposal of phytoremediation plant waste: Stability of potentially toxic metals (PTMs) and oxidation resistance of biochars. Process Saf. Environ. Prot. 2019;125:260–268. 10.1016/j.psep.2019.03.035 Evaristo RBW : Evaluation of waste biomass gasification for local community development in central region of Brazil. Biomass Convers. Biorefinery. 2022;12(7):2823–2834. 10.1007/s13399-020-00821-y Fogarasi S Cormos CC : Technico-economic assessment of coal and sawdust co-firing power generation with CO2 capture. J. Clean. Prod. 2015;103:140–148. 10.1016/j.jclepro.2014.07.044 Frodeson S Henriksson G Berghel J : Effects of moisture content during densification of biomass pellets, focusing on polysaccharide substances. Biomass Bioenergy. 2019;122(November 2018):322–330. 10.1016/j.biombioe.2019.01.048 Ge S : Progress in microwave pyrolysis conversion of agricultural waste to value-added biofuels: A batch to continuous approach. Renew. Sust. Energ. Rev. 2021;135(January 2020):110148. 10.1016/j.rser.2020.110148 Gilvari H Jong W de Schott DL : Quality parameters relevant for densification of bio-materials: Measuring methods and affecting factors - A review. Biomass Bioenergy. 2019;120(October 2018):117–134. 10.1016/j.biombioe.2018.11.013 Güleç F : A comprehensive comparative study on the energy application of chars produced from different biomass feedstocks via hydrothermal conversion, pyrolysis, and torrefaction. Energy Convers. Manag. 2022;270(July):116260. 10.1016/j.enconman.2022.116260 Huggins T : Biochar as a sustainable electrode material for electricity production in microbial fuel cells. Bioresour. Technol. 2014;157:114–119. 24534792 10.1016/j.biortech.2014.01.058 Larsson SH Samuelsson R : Prediction of ISO 17831-1:2015 mechanical biofuel pellet durability from single pellet characterization. Fuel Process. Technol. 2017;163(August):8–15. 10.1016/j.fuproc.2017.04.004 Lee MC : Conversion of Microalgae Biomass to Biofuels, Microalgae Cultivation for Biofuels Production. Elsevier Inc.;2020a. 10.1016/B978-0-12-817536-1.00010-2 Lee U Balu E Chung JN : An experimental evaluation of an integrated biomass gasification and power generation system for distributed power applications. Appl. Energy. 2013;101:699–708. 10.1016/j.apenergy.2012.07.036 Lee XJ : State of art review on conventional and advanced pyrolysis of macroalgae and microalgae for biochar, bio-oil and bio-syngas production. Energy Convers. Manag. 2020b;210(December 2019):112707. 10.1016/j.enconman.2020.112707 Li SX : Torrefaction of corncob to produce charcoal under nitrogen and carbon dioxide atmospheres. Bioresour. Technol. 2018;249(October 2017):348–353. 29054066 10.1016/j.biortech.2017.10.026 Madanayake BN : Biomass as an energy source in coal co-firing and its feasibility enhancement via pre-treatment techniques. Fuel Process. Technol. 2017;159:287–305. 10.1016/j.fuproc.2017.01.029 Mondal S : Thermochemical pyrolysis of biomass using solar energy for efficient biofuel production: a review. 2018;12(May):125–134. 10.1080/17597269.2018.1461512 Mostafa ME : The significance of pelletization operating conditions: An analysis of physical and mechanical characteristics as well as energy consumption of biomass pellets. Renew. Sust. Energ. Rev. 2019;105(June 2018):332–348. 10.1016/j.rser.2019.01.053 Mostafa ME : Experimental and numerical modelling of solid and hollow biomass pellets high-temperature rapid oxy-steam combustion: The effect of integrated CO2/H2O concentration. Fuel. 2021;303(March):121249. 10.1016/j.fuel.2021.121249 Ong HC : A state-of-the-art review on thermochemical conversion of biomass for biofuel production: A TG-FTIR approach. Energy Convers. Manag. 2020;209(December 2019):112634. 10.1016/j.enconman.2020.112634 Pavkov I : Hydrothermal Carbonization of Agricultural Biomass: Characterization of Hydrochar for Energy Production. Solid Fuel Chem. 2022;56(3):225–235. 10.3103/S0361521922030077 Perera SMHD : Modeling of thermochemical conversion of waste biomass – a comprehensive review. Biofuel Res. J. 2021;8(4):1481–1528. 10.18331/BRJ2021.8.4.3 Picchio : Pellet production from woody and non-woody feedstocks: A review on biomass quality evaluation. Energies. 2020;13:1–20. 10.3390/en13112937 Pradhan P Arora A Mahajani SM : Pilot scale evaluation of fuel pellets production from garden waste biomass. Energy Sustain. Dev. 2018a;43:1–14. 10.1016/j.esd.2017.11.005 Pradhan P Mahajani SM Arora A : Production and utilization of fuel pellets from biomass: A review. Fuel Process. Technol. 2018b;181(August):215–232. 10.1016/j.fuproc.2018.09.021 Puig-Arnavat M : From a single pellet press to a bench scale pellet mill - Pelletizing six different biomass feedstocks. Fuel Process. Technol. 2016;142:27–33. 10.1016/j.fuproc.2015.09.022 Razi F Dincer I : Challenges, opportunities and future directions in hydrogen sector development in Canada. Int. J. Hydrog. Energy. 2022;47(15):9083–9102. 10.1016/j.ijhydene.2022.01.014 Roncancio R Gore JP : CO2 char gasification: A systematic review from 2014 to 2020. Energy Convers. Manag.: X. 2021;10(December 2020):100060. 10.1016/j.ecmx.2020.100060 Sarker TR : Densification of waste biomass for manufacturing solid biofuel pellets: a review, Environmental Chemistry Letters. Springer International Publishing;2023. 10.1007/s10311-022-01510-0 Sekar M : A review on the pyrolysis of algal biomass for biochar and bio-oil – Bottlenecks and scope. Fuel. 2021;283(September 2020):119190. 10.1016/j.fuel.2020.119190 Shamsul NS Kamarudin SK Rahman NA : Conversion of bio-oil to bio gasoline via pyrolysis and hydrothermal: A review. Renew. Sustain. Energy Rev. 2020;80(May 2017):538–549. 10.1016/j.rser.2017.05.245 Siddiki SYA : Microalgae biomass as a sustainable source for biofuel, biochemical and biobased value-added products: An integrated biorefinery concept. Fuel. 2022;307(August 2021):121782. 10.1016/j.fuel.2021.121782 Singh B : Towards a sustainable approach for development of biodiesel from plant and microalgae. Renew. Sust. Energ. Rev. 2014;29:216–245. 10.1016/j.rser.2013.08.067 Situmorang YA : Small-scale biomass gasification systems for power generation (<200 kW class): A review. Renew. Sust. Energ. Rev. 2020;117(October 2019):109486. 10.1016/j.rser.2019.109486 Siyal AA : Characterization and quality analysis of wood pellets: effect of pelletization and torrefaction process variables on quality of pellets. Biomass Convers. Biorefinery. 2021;11(5):2201–2217. 10.1007/s13399-020-01235-6 Skorupskaitė V : Green energy from different feedstock processed under anaerobic conditions. Agron. Res. 2015;13(2):420–429. Subramaniam Y Masron TA : The impact of economic globalization on biofuel in developing countries. Energy Convers. Manag.: X. 2021;10:100064. 10.1016/j.ecmx.2020.100064 Tripathi M Sahu JN Ganesan P : Effect of process parameters on production of biochar from biomass waste through pyrolysis: A review. Renew. Sust. Energ. Rev. 2016;55:467–481. 10.1016/j.rser.2015.10.122 Uddin MN : An overview of recent developments in biomass pyrolysis technologies. Energies. 2018;11(11). 10.3390/en11113115 Watson J : Valorization of hydrothermal liquefaction aqueous phase: pathways towards commercial viability. Prog. Energy Combust. Sci. 2020;77:100819. 10.1016/j.pecs.2019.100819 Wnetrzak R : The influence of the pig manure separation system on the energy production potentials. Bioresour. Technol. 2013;136:502–508. 23567723 10.1016/j.biortech.2013.03.001 Yao Y : Potential for Thermo-Chemical Conversion of Solid Waste in Canada to Fuel, Heat, and Electricity. 2023;689–710. You J : Stability and reliability of anodic biofilms under different feedstock conditions: Towards microbial fuel cell sensors. Sensing and Bio-Sensing Research. 2015;6:43–50. 10.1016/j.sbsr.2015.11.007 Zhang J Zhang X : 15. The thermochemical conversion of biomass into biofuels, Biomass, Biopolymer-Based Materials, and Bioenergy. Elsevier Ltd.;2019. 10.1016/B978-0-08-102426-3.00015-1 Zhang W : Progress and Perspective of Electrocatalytic CO2 Reduction for Renewable Carbonaceous Fuels and Chemicals. Adv. Sci. 2018;5(1). 10.1002/advs.201700275 10.5256/f1000research.171104.r392616 Reviewer response for version 2 Chianese Simeone 1 Referee https://orcid.org/0000-0002-9356-845X University of Campania “Luigi Vanvitelli”, Roma, Italy

Competing interests: No competing interests were disclosed.

 28 8 2025 Copyright: © 2025 Chianese S 2025 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation approve-with-reservations

Comment on the paper: “Enhancing sustainable energy production through biomass gasification gas technology: a review” by Oluwaseyi O. Alabi et al.

General comment:

The manuscript deals with an overview of the use of biomass gasification for generating electricity. Processes, efficiency, environmental impact, and potential applications in power generation were discussed.

The manuscript is suitable for publication in this journal; however, some points should be addressed before publication.

Some minor language mistakes are present that should be corrected.

2. Biomass Gasification Technology

Please summarize the main findings in tables in order to be more systematic and support the readability of the review.

Please improve the description of this section with a critical point of view.

Please include quantitative data (not limited to being descriptive).

3. Utilization of syngas

Please summarize the main findings in tables in order to be more systematic and support the readability of the review.

Please improve the description of this section with a critical point of view.

Please include quantitative data (not limited to being descriptive).

4. Emerging biomass gasification trends

Please summarize the main findings in tables in order to be more systematic and support the readability of the review.

Please improve the description of this section with a critical point of view.

Please include quantitative data (not limited to being descriptive).

Is the review written in accessible language?

Yes

Are all factual statements correct and adequately supported by citations?

Yes

Are the conclusions drawn appropriate in the context of the current research literature?

Yes

Is the topic of the review discussed comprehensively in the context of the current literature?

Yes

Reviewer Expertise:

Biomass gasification; advanced energy vector production

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

 10.5256/f1000research.171104.r390465 Reviewer response for version 2 Narnaware Sunil L. 1 2 Referee https://orcid.org/0000-0002-1208-0787 Department of Renewable Energy Engineering, College of Agricultural Engineering & Post Harvest Technology, Central Agricultural University Imphal, Ranipool, Sikkim, India Pratap University Agriculture and Technology,, Udaipur, Rajasthan, India

Competing interests: No competing interests were disclosed.

 2 7 2025 Copyright: © 2025 Narnaware SL 2025 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation reject

I have reviewed the manuscript thoroughly and think that, in the present state, it is difficult to recommend the manuscript for acceptance. Please take a look at the following comments.  

Title: Gasification itself indicates the gas production process, so using “gasification technology” instead of “gasification gas technology” will be sufficient

I suggest using simply producer gas or syngas instead of using biomass gasification gas throughout the draft

Abstract: The intention and objectives of the review are repeated several times in the abstract, which must be rewritten with proper summarisation of the review presented  

Keywords: My suggestion is to use another keyword in place of Technology, as it is a very generic term. eg. Power generation

Introduction:

The analysis by British Petroleum (BP) is cited, but the reference is missing.  Please add the reference.

The sentence- Coal, in particular, is the most prevalent fuel for power production, constituting approximately 39.3 per cent of global energy consumption, as illustrated in Figure 1. Still, in Figure 1, but there is no representation of the per cent share of coal or other fossil fuels. This needs correction either in the sentence or the figure.  

The sentence “During combustion, biomass is ignited with excess oxygen to produce heat and operates in an oxygen-free environment” contradicts itself, as it is stated that combustion requires excess air, and later it says it operates in an oxygen-free environment. Needs real correction. Also, subsequent sentences are not clear about which exact process is being explained. This lacks clarity for the readers.  

Ideally, Figure 4 should be included in the Introduction section.

Section 2 Biomass gasification technology:  Biomass Gasification Technology, the composition of syngas is mentioned twice, which is not necessary.

Section 2.1 Biomass composition: The description of Figure 4 is different from Figure 4 itself. It says Figure 4 represents biomass composition, while it depicts the different biomass conversion processes.  Huge blunder in the presentation of the figure and its description, as no proper care was taken in editing.

Section 2.2 Gasification processes and reactors: There is no need to define the gasification process when it is already defined in section 2. The repetition is occurring several times for other sentences also, and needs to be avoided

Section 2.3 Gasification byproducts and applications: The section is named as Gasification byproducts and applications; however, the content in the section does not discuss the byproduct, but rather it provides information about the effect of particle size on gasification. It is not clear which type of gasifier requires this small particle size of 0.15 mm because fixed bed gasifiers and fluidised bed gasifiers require different particle sizes.

4 .1 Technology economic viability: No sufficient relevant data has been provided to support the section, such as which parameters are more important in deciding the economic viability, and what would be the best possible ways to make the technology economically viable.

Overall review:

The manuscript has major scope for improvement. It has missed several basic things, like it nowhere mentions the heating value of syngas.  The types of gasification agents, their effect on the heating value of syngas, etc.

The flow in writing the manuscript is missing at large. Suddenly, the discussion jumps to a different topic, so readers may find it difficult to keep track.

The supporting data is missing throughout the draft. For example, a tabular data table on different biomasses with physical and chemical properties used for gasification would have provided a better understanding of the suitability of biomass for gasification. Similar data for the other important section is also missing.

Is the review written in accessible language?

Yes

Are all factual statements correct and adequately supported by citations?

Partly

Are the conclusions drawn appropriate in the context of the current research literature?

Partly

Is the topic of the review discussed comprehensively in the context of the current literature?

No

Reviewer Expertise:

Renewable Energy, Biomass and Bioenergy, Biomass gasification, thermochemical conversion of biomass, Gasification-based Power generation

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

 10.5256/f1000research.162211.r312249 Reviewer response for version 1 Njoka Francis 1 Referee https://orcid.org/0000-0002-0544-6824 Kenyatta University, Nairobi, Nairobi County, Kenya

Competing interests: No competing interests were disclosed.

 27 8 2024 Copyright: © 2024 Njoka F 2024 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation reject

Thank you for giving me the opportunity to look at the article.

I however wish not to conclude the review.

To start with, the abstract is simply a series of recurring statements giving no direction. The study objective is repeated five time in almost every statement. Figures 1 and 2 present totally different statistics from what is quoted in the text. Key statements are not complete but rather jump to explaining different concepts which makes it a bit unclear. For example on page 5 line 2, 'In particular, has developed its own biomass.....' Line 4 in the same paragraph reads, 'Another significant

outcome of diverse biological processes, it is frequently mixed...….' Such statements and many more are unacceptable.

In chapter 2, the authors say gasification has 4 stages, pyrolysis, combustion, reduction and gas separation. This is incorrect. In the explanation of the each stage, they start with stage one, and then say stage 2 is pyrolysis converse to their earlier statement.

As such, this article can easily and greatly confuse young readers who seek clarity on issues.

Is the review written in accessible language?

Yes

Are all factual statements correct and adequately supported by citations?

No

Are the conclusions drawn appropriate in the context of the current research literature?

Partly

Is the topic of the review discussed comprehensively in the context of the current literature?

No

Reviewer Expertise:

Renwables; Solar energy, biomass, hydrogen and fuels cells, etc.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

Gbadeyan Oluwatoyin Joseph Durban University of Technology, Durban, KwaZulu-Natal, South Africa

Competing interests: No competing interests were disclosed.

 27 8 2024

Response:  Thank you for your feedback on our abstract. We appreciate your input and are revising the abstract to better reflect our research findings and align with our findings.  We have revised the captions for Figures 1 and 2 in the revised manuscript, as quoted in the text. As you suggested, we have reviewed and corrected some grammatical errors in the manuscript. We have carefully examined and modified the relevant sections to ensure accuracy and clarity.

Thank you for your insightful feedback on the gasification process. We have revised the manuscript as highlighted, incorporating your valuable observations

 10.5256/f1000research.162211.r298699 Reviewer response for version 1 Saravanakumar Dr. Ayyadurai 1 2 Referee https://orcid.org/0000-0003-0936-2107 M R Dr. Sudha 3 Co-referee Centre for Research In Environment, Sustainability Advocacy and Climate Change (REACH), SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu, India SRM Institute of Science and Technology, Kattankulathu, Tamilnadu, India Computer Applications, SRM Institute of Science and Technology (Deemed to be University) (Ringgold ID: 93104), Kattankulathur, Tamil Nadu, India

Competing interests: No competing interests were disclosed.

 12 7 2024 Copyright: © 2024 Saravanakumar DA and M R DS 2024 This is an open access peer review report distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. recommendation approve-with-reservations

1. What are the key technological advancements in biomass gasification that contribute to increased efficiency and sustainability in energy production?

2. How do different types of biomass feedstocks affect the performance and environmental impact of gasification processes?

3. What are the major challenges and potential solutions in scaling up biomass gasification technology for widespread sustainable energy production?

4. Quote the below references in the manuscript : (Saravanakumar A, et al., 2024 [Ref-1]), (Saravanakumar A, et al., 2023 [Ref-2]), (Saravanakumar A, et al., 2022 [Ref-3]), (Ayyadurai S, et al., 2020 [Ref-4]), (Ayyadurai S, et al., 20217 [Ref-5]), (Ayyadurai S, et al., 2017 [Ref-6]), (Kang J, et al., 2016 [Ref-7]), (Ivanov. I, et al., 2011 [Ref-8])

5. What are the primary types of reactors used in biomass gasification, and how do they differ in terms of design and operation?

6. How do the temperature and pressure conditions within a gasification reactor impact the quality and composition of the produced syngas?

7. What role do catalysts play in gasification processes, and what are the most effective catalysts currently used in gasification reactors?

8. How do different gasification processes (such as fixed-bed, fluidized-bed, and entrained-flow) compare in terms of efficiency, scalability, and environmental impact?

9. What are the key challenges in maintaining reactor performance and longevity, and what maintenance or technological improvements can address these challenges?

Section 4

10. What recent technological innovations in biomass gasification have shown the most promise for improving efficiency and reducing costs?

11. How is the integration of artificial intelligence and machine learning being utilized to optimize biomass gasification processes?

12. What advancements have been made in feedstock preprocessing techniques to enhance the gasification process and improve syngas quality?

13. How are emerging gasification technologies addressing the challenges of tar formation and removal in syngas production?

14. What are the latest developments in reactor design that are contributing to more effective and scalable biomass gasification systems?

15. How are policy and regulatory changes influencing the adoption and innovation of biomass gasification technologies in different regions?

Is the review written in accessible language?

Yes

Are all factual statements correct and adequately supported by citations?

Partly

Are the conclusions drawn appropriate in the context of the current research literature?

Partly

Is the topic of the review discussed comprehensively in the context of the current literature?

Yes

Reviewer Expertise:

1.    Biomass Gasification Technologies. [Design and experimental investigation of gasification plants, Comparative experimentation focusing on different types of modes, temperature profile and different fuel materials as feedstock for gas production – long stick wood gasification for hilly and rural regions] 2.    Biomass to Charcoal conversion technologies [Design, fabrication and installation of charcoal conversion kiln, temperature profile and different feed materials as feedstock for charcoal conversion] 3.    Computational modelling of long stick wood gasifier 4.     Rural village development of charcoal production technologies. 5.     Fuel Characteristics

We confirm that we have read this submission and believe that we have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however we have significant reservations, as outlined above.

References : Green circular economy of co-gasification with municipal solid waste and wood waste in a novel downdraft gasifier with rotating grate. Chemical Engineering Journal .2024;479: 10.1016/j.cej.2023.147987 10.1016/j.cej.2023.147987 : Thermochemical conversion of large-size woody biomass for carbon neutrality: Principles, applications, and issues. Bioresour Technol .2023;370: 10.1016/j.biortech.2022.128562 128562 36587772 10.1016/j.biortech.2022.128562 : Pilot-scale study on downdraft gasification of municipal solid waste with mass and energy balance analysis. Fuel .2022;315: 10.1016/j.fuel.2022.123287 10.1016/j.fuel.2022.123287 : Experimental analysis of municipal solid waste blended with wood in a downdraft gasifier. Journal of Environmental Engineering and Science .2020;15(4) : 10.1680/jenes.20.00007 180-188 10.1680/jenes.20.00007 : Mass and energy analysis of a 60 kW th updraft gasifier using large size biomass. Fuel .2017;187: 10.1016/j.fuel.2016.09.080 356-366 10.1016/j.fuel.2016.09.080 : Performance Investigation of an Advanced Robust Biomass Gasifier Operation for Drying Process at Hilly Region in India. Journal of Electrical & Electronic Systems .2017;06(01) : 10.4172/2332-0796.1000212 10.4172/2332-0796.1000212 : A Study on Environmental Assessment of Residue from Gasification of Polyurethane Waste in E-Waste Recycling Process. Procedia Environmental Sciences .2016;35: 10.1016/j.proenv.2016.07.056 639-642 10.1016/j.proenv.2016.07.056 : Initial results of studies and possibilities for biomass gasification in Bulgaria and India, Ecological Engineering and Environment Protection. Ecological Engineering and Environment Protection .2011;1:72--82 Gbadeyan Oluwatoyin Joseph Durban University of Technology, Durban, KwaZulu-Natal, South Africa

Competing interests: No competing interests were disclosed.

 16 7 2024

RESPONSE TO REVIEWER COMMENTS

1. What are the key technological advancements in biomass gasification that contribute to

increased efficiency and sustainability in energy production?

Response: Thank you for your feedback. Some key technological advancements in biomass

gasification that contributes to increased efficiency and sustainability in energy production

include, Advanced Gasification Systems, Gas Cleaning and Upgrading, Innovative gas cleaning and upgrading technologies to remove impurities, and producing high-quality biofuels and biochemicals. These advancements contribute to increased efficiency, sustainability, and cost-effectiveness. Effectiveness in biomass gasification, enabling the production of renewable energy and biofuels while minimizing environmental impacts.

2. How do different types of biomass feedstocks affect the performance and environmental

impact of gasification processes?

Response: Thank you for your feedback. By understanding the characteristics and effects of

different biomass feedstocks, gasification processes can be optimized to improve performance,

reduce environmental impacts, and increase the production of renewable energy and biofuels.

3. What are the major challenges and potential solutions in scaling up biomass gasification

technology for widespread sustainable energy production?

Response: Thank you for your comments. Addressing these challenges and implementing

solutions will help scale up biomass gasification technology, enabling widespread sustainable

energy production and contributing to a low-carbon future.

5. What are the primary types of reactors used in biomass gasification, and how do they differ in terms of design and operation?

Response: Thank you for your comments. The primary types of reactors used in biomass gasification are, fixed Bed Reactors, Fluidized Bed Reactors. Each reactor type has its advantages and disadvantages, and the choice of reactor depends on the specific application, biomass feedstock, and desired gas composition.

6. How do the temperature and pressure conditions within a gasification reactor impact the

quality and composition of the produced syngas?

Response: Thank you for your comments. Gasification temperature: Entrained flow reactors operate at higher temperatures (1000-1500°C), while fixed bed and fluidized bed reactors operate at lower temperatures (700-1000°C).

8. How do different gasification processes (such as fixed-bed, fluidized-bed, and entrained-flow) compare in terms of efficiency, scalability, and environmental impact?

Response: Thank you for your comments. Different reactors produce varying gas compositions, with entrained flow reactors producing more syngas (CO and H2) and fixed bed reactors producing more methane (CH4).

9. What are the key challenges in maintaining reactor performance and longevity, and what

maintenance or technological improvements can address these challenges?

Response: Thank you for your comments. Tar formation and deposition on reactor walls and

surfaces, reducing efficiency and increasing maintenance needs. Ash and slag formation: Ash

and slag accumulation, potentially causing reactor damage, corrosion, and operational issues.

Section 4

11. How is the integration of artificial intelligence and machine learning being utilized to optimize biomass gasification processes?

Response: Thank you for your feedback. However, I'd like to clarify that the focus of this project is not on machine learning or artificial intelligence

12. What advancements have been made in feedstock preprocessing techniques to enhance

the gasification process and improve syngas quality?

Response: Thank you for your response: Advancements in feedstock preprocessing techniques to enhance the gasification process and improve syngas quality include the Densification of biomass into pellets increases the bulk density of biomass, which increases the net calorific content per unit volume. This makes storage, transport, and handling of the material easier and cheaper

13. How are emerging gasification technologies addressing the challenges of tar formation and removal in syngas production?

Response: Thank you for your response. Tar formation in fixed bed reactors tend to produce more tar, while entrained flow reactors produce less tar due to higher temperatures and residence times

14. What are the latest developments in reactor design that are contributing to more effective

and scalable biomass gasification systems?

Response: Thank you for your response. The latest developments in reactor design that contribute to more effective and scalable biomass gasification systems include dual-bed catalyst gasification.