Torrefaction Technology Research Articles

Evolution of chemical functional groups during torrefaction of rice straw

The evolution of CHON functional groups during torrefaction of rice straw at 200–300 °C were investigated. The results showed that 300 °C was more suitable for rice straw torrefaction due to the ideal fuel ratio, energy densification, energy-mass co-benefit index and the significantly improved HHV of the torrefied products. The functional groups such as O–H, N–H, C–H, C = O in the solids decreased with rising temperature accompanied by the releases of H2O, CH4, CO2, CO and NH3, et al. At 300 °C, 40.04% of fuel-N was released in the form of NH3, HCN, HNCO et al. due to the decomposition of N-A which was the overall N-functionality in the raw rice straw. It is worth noting that the absorbance of NH3 and HCN has the same order of magnitude as CO. Therefore, the releases of N-containing gases should be highly concerned for the application of torrefaction technology from the environmental perspective.

Energy trilemma based prioritization of waste-to-energy technologies: Implications for post-COVID-19 green economic recovery in Pakistan

As lockdown eases, economic activities resume in Pakistan. If the country continues to follow business-as-usual (BAU) then it is anticipated that carbon output could surge past pre-COVID-19 levels – that means more disasters in future. Thus, it is an unprecedented opportunity to shift from BAU and achieve carbon-neutral and nature-positive economic recovery – green economic recovery (GER). To fuel the GER, access to modern, equitable, affordable and sustainable energy is paramount. This study explores waste-to-energy (WtE) as an alternative green fuel for GER. Seven WtE technologies are prioritized based on the concept of energy trilemma – energy security, energy equity, and environmental sustainability. For the evaluation, an energy trilemma based decision support framework is developed using most prominent multi-criteria decision-making (MCDM) methods. The fuzzy set theory is integrated with MCDM methods to minimize uncertainty in results. Sixteen experts are engaged to score each WtE technology with respect to every energy trilemma dimension and sub-dimension. Gasification technology is found to be the most feasible option for WtE generation in Pakistan whereas Torrefaction technology is least favorable. It is concluded that the need to shift towards sustainable energy is more than ever to limit the carbon emission and prevent future crisis.

Inclusion of innovative technology in integrated waste management of a city: case of Bogura, Bangladesh

Abstract Bogura is the largest municipality in Bangladesh by population. Its huge population and agri-industry produces a great deal of solid, faecal and industrial waste which has been a matter of concern for the municipality. IRC started working for a solution and completed a pre-feasibility and feasibility study to find innovative technologies and an operation model. The feasibility study has produced an integrated solution of faecal sludge, municipal solid waste, agri-waste and aerosol can recycling model which also helps to reduce surface and ground water contamination. The solution integrates conventional anaerobic digestion with new torrefaction and aerosol-propellant capture technologies which treats the municipality solid waste and aerosol cans to produce biofuel and liquid petroleum gas, respectively.

Impact of post-torrefaction process on biochar formation from wood pellets and self-heating phenomena for production safety

Abstract The advancement of torrefaction in the industry raises safety issues lately. This work aims to investigate the impact of post-torrefaction upon biochar formation and the self-heating phenomena of torrefied wood pellets. Three operating scenarios are taken into account. Specifically, dried wood pellets are first torrefied in nitrogen at various temperatures (200–300 °C) followed by immediate exposure to N2 or air with/without keeping temperature, namely, the post-torrefaction, to examine the self-heating behavior. Meanwhile, the influences of torrefaction temperature, duration, and self-heating on biochar’s characteristics are analyzed. It is found that self-heating with the highest temperature rise of 61 °C is triggered when the biochars are in an oxidative post-torrefaction process with keeping temperature. Alternatively, oxidative post-torrefaction without keeping temperature can efficiently intensify the pellets’ calorific value up to 42%. The X-ray photoelectron spectroscopy analysis reveals the depletion of the CO functional group. It is concluded that uncontrolled self-heating in large scale production will lead to combustion and make biochar unsafe. Alternatively, if heat accumulation inside the biochar piles can be prevented, the oxidative environment that causes self-heating can open a lot of research opportunities that can help in the advancement of torrefaction technologies for biomass as an alternative source of energy.

Torrefaction: a sustainable method for transforming of agri-wastes to high energy density solids (biocoal)

The depletion of fossil fuel reserves and greenhouse gas emissions led to limit the use of fossil fuels, including natural gas, coal, or petroleum, and demand a clean and sustainable source of energy. Many efforts are being made by the researchers to address these issues through the use of natural renewable resources (or lignocellulosic biomass), such as agricultural wastes and forest residues as a cleaner source of energy. But its poor properties like low energy density, high moisture content, irregular shape and size, and heterogeneity make it difficult to use in its natural form. Torrefaction, a simple heat treatment procedure, is widely employed to the natural bioresources to improve its thermal properties to be used as an energy source in the domestic power plants. The quality of the resultant torrefied solids (the so-called biocoal) is depending on the settings of heating conditions under the absence of oxygen, which can be improved by selecting and adjusting the processing conditions precisely. Typically, the process brings down the moisture content up to < 3 wt%, and increases the grinding energy up to 90%. Mainly, the calorific value and fixed carbon content of torrefied biomass increase by roughly 15–25 wt%, which makes it more appealing than non-torrefied biomass. The review emphasizes the available biomass torrefaction technologies, and it’s potential in the field of bioenergy generations. It also covers few case studies of biomass torrefaction and its application in the power generation sectors.

The Effects of Torrefaction on Lignocellulose Composition and Moisture Absorption Ability of Cocoa Pod Husk

The weakness of biomass as a fuel can be minimized by torrefaction technology. Mass yield and enhancement factor are two of the parameters that can be used to evaluate the torrefaction process. Some of the important changes in the biomass properties after being torrefied are a reduction of moisture content and moisture absorption ability. This study was performed to determine the change of lignocel-lulose composition and moisture absorption ability of the cocoa pod husk (CPH) which was torrefied at 200, 250, and 300 oC and holding times of 0, 30, 60, and 90 min. The mass yield and enhancement factor of torrefied cocoa pod husk ranged from 54.6 % to 86.7 % and 1.09 to 1.34, respectively, depending on tem-perature and holding time. Hemicellulose fraction of torrefied CPH at 200 oC was 28.99 % then decreased to 8.39 % when torrefied at 300 oC. Amount of cellulose in CPH was in the range of 13.14 % (200 oC, 60 min) to 1.43 % (300 oC, 60 min). The lignin content increased from 28.99 % to 72.4 % with the temperature increased from 200 to 300 oC. Amount of hemicellulose in torrefied CPH tended to decrease along with the increasing of temperature and holding time, while lig-nin had the opposite trend. The moisture absorption was 11.5 % for raw CPH down to 5.5 % for torrefied CPH at 300 oC. The ability of CPH to absorb mois-ture decrease as increasing torrefaction temperature and holding time.

Property Upgrades of Some Raw Nigerian Biomass through Torrefaction Pre-Treatment- A Review

Today, agricultural waste is one of the most common resources in Nigeria that could solve environmental, fuel and energy issues. However, it has some limitations such as low bulk densities, loose and irregular sizes, handling and storage problems, low energy density, reduced fixed carbon, low calorific value, high volatile matter and high moisture content etc. making it difficult to be utilized for fuel. One of the viable and promising technologies to upgrade the properties of raw biomass is through torrefaction technique which is capable of upgrading the combustion and fuel characteristics of biomass, demonstrated from behaviours that are similar to coal during combustion. During this process, about 70% of the initial biomass weight and about 90% of the original biomass energy is obtained as torrefied biomass while the remaining 30% biomass weight and 10% biomass energy is given off. In addition, the presence of moisture content in raw biomass that could aid biological degradation is reduced (< 3% w.b.) while combustion efficiency is being enhanced through upgraded fixed carbon and calorific value (15-25% wt) and reduced volatiles. These upgraded properties makes torrefied Nigerian biomass suitable to be used independently or co-fired in power plants and as an upgraded feedstock for domestic and industrial applications in a developing country like Nigeria. Unfortunately, there is scarce research materials on biomass torrefaction in Nigeria which could be attributed to the cost of acquiring torrefaction plant and other resources for torrefaction characterization which are on the high side. This paper therefore explores and reviews the property upgrades of raw biomass through torrefaction technique. The challenges of biomass energy in Nigeria, torrefaction effects on some Nigerian biomass, equipment used for the analysis of torrefied samples, alongside the torrefaction properties, combustibility indices and their products were examined. The review study concluded that torrefaction technology is a promising technique in Nigeria which is capable of improving and upgrading the quality, energy value and other properties of raw Nigerian biomass and could at the same time serve as an alternative source of energy asides hydropower energy if embraced by the concerned bodies.

Improving the Efficiency of Biowaste Torrefaction

Russia faces an important environmental challenge associated with the accumulation of a large amount of biowaste due to the lack of technologies for their efficient processing. In particular, the intensive development of aviculture in Russia, including poultry farming, in the coming years will lead to the need of processing significant amounts of poultry manure and poultry litter. One of the options for litter disposal is its processing into biofuel suitable for the production of heat energy for the needs of poultry farms themselves and for outside consumers. However, with this option, the disposal of litter requires its disinfection, for example, by the method of torrefaction. However, the existing torrefaction technologies are characterized by a considerable process duration. A new method of torrefaction has been proposed and comparative studies have been carried out on the process of poultry litter torrefaction in a fixed bed under a nitrogen blanket (dry torrefaction) and in a fluidized manure bed pretreated in superheated steam (wet torrefaction). After both methods following heat treatment, manure samples are obtained, the mass of which is decreased twice due to an almost threefold decrease in the oxygen content, which, along with an increase in the carbon content and a decrease in the amount of moisture, causes the fuel efficiency of the manure. The manure torrefaction in a fluidized bed also makes it possible to significantly (four times) speed up the process. Technical solutions are proposed to solve the issues of full or partial recovery of energy costs related to the production of superheated steam due to the processing of gaseous torrefaction products into syngas using hot biochar thermal cracking.

Torrefaction of Sewage Sludge: Kinetics and Fuel Properties of Biochars

We propose a ‘Waste to Carbon’ thermal transformation of sewage sludge (SS) via torrefaction to a valuable product (fuel) with a high content of carbon. One important, technological aspect to develop this concept is the determination of activation energy needed for torrefaction. Thus, this research aimed to evaluate the kinetics of SS torrefaction and determine the effects of process temperature on fuel properties of torrefied products (biochars). Torrefaction was performed using high ash content SS at six (200~300 °C) temperatures and 60 min residence (process) time. Mass loss during torrefaction ranged from 10~20%. The resulting activation energy for SS torrefaction was ~12.007 kJ·mol−1. Initial (unprocessed) SS higher heating value (HHV) was 13.5 MJ·kg−1. However, the increase of torrefaction temperature decreased HHV from 13.4 to 3.8 MJ·kg−1. Elemental analysis showed a significant decrease of the H/C ratio that occurred during torrefaction, while the O/C ratio fluctuated with much smaller differences. Although the activation energy was significantly lower compared with lignocellulosic materials, low-temperature SS torrefaction technology could be explored for further SS stabilization and utilization (e.g., dewatering and hygienization).

PERSPECTIVES FOR DEVELOPING AND USING THE TORREFACTION TECHNOLOGY IN UKRAINE

Ukraine refers to countries that only partially provide themselves with traditional types of energy resources, and it is forced to import about 65% of fossil fuels. This article shows the possibility of increasing the biomass energy using through introduction of torrefaction technology as a relatively new process that allows converting raw material to highly efficient fuels with properties close to fossil fuels increasing amount of processing of raw materials geography of its delivery, reducing the cost of transportation, storage what will be enable to save traditional fuel and energy resources, diversify sources of energy supplies, strengthen energy independence of the state and improve the environment. There are a number of applications for torrefaction products, the most promising of which are: combustion in pellet boilers, cofiring with coal, gasification of raw biomass for fuel production, and the production of composite wood-based materials. Estimation of the efficiency of considered technologies is carried out.

Recent Advancements in Torrefaction of Solid Biomass

The study focuses on the recent advancements on the torrefaction of solid biomass feedstock. A literature review has been conducted and the most important findings of selected studies which have been published the last 5 years are presented. According to the published research, solid biomass torrefaction gains significant interest with more than 500 studies since 2002. Based on the existing literature, a focus on the torrefaction woody biomass is observed. However, investigation of torrefaction of herbaceous and other types of biomass such as aquatic is increasing. The integration of pelletization with torrefaction is also widely investigated. Finally, significant effort is given for the development, scaling up, and introduction to market of various torrefaction technologies. Future research should address the improvement and commercialization of existing torrefaction technologies. Integrated torrefaction and pelletization shall be further investigated especially using non-woody biomass feedstock.

Biomass torrefaction: A promising pretreatment technology for biomass utilization

Torrefaction is an emerging technology also called mild pyrolysis, which has been explored for the pretreatment of biomass to make the biomass more favorable for further utilization. Dry torrefaction (DT) is a pretreatment of biomass in the absence of oxygen under atmospheric pressure and in a temperature range of 200-300 degrees C, while wet torrrefaction (WT) is a method in hydrothermal or hot and high pressure water at the tempertures within 180-260 degrees C. Torrrefied biomass is hydrophobic, with lower moisture contents, increased energy density and higher heating value, which are more comparable to the characteristics of coal. With the improvement in the properties, torrefied biomass mainly has three potential applications: combustion or co-firing, pelletization and gasification. Generally, the torrefaction technology can accelerate the development of biomass utilization technology and finally realize the maximum applications of biomass energy.

Modelling of heat transfer during torrefaction of large lignocellulosic biomass

Preparation of feedstock is a major energy intensive process for the thermochemical conversion of biomass into fuel. By eliminating the need to grind biomass prior to the torrefaction process, there would be a potential gain in the energy requirements as the entire step would be eliminated. In regards to a commercialization of torrefaction technology, this study has examined heat transfer inside large cylindrical biomass both numerically and experimentally during torrefaction. A numerical axis-symmetrical 2-D model for heat transfer during torrefaction at 270°C for 1 h was created in COMSOL Multiphysics 5.1 considering heat generation evaluated from the experiment. The model analyzed the temperature distribution within the core and on the surface of biomass during torrefaction for various sizes. The model results showed similarities with experimental results. The effect of L/D ratio on temperature distribution within biomass was observed by varying length and diameter and compared with experiments in literature to find out an optimal range of cylindrical biomass size suitable for torrefaction. The research demonstrated that a cylindrical biomass sample of 50 mm length with L/D ratio of 2 can be torrefied with a core-surface temperature difference of less than 30 °C. The research also demonstrated that sample length has a negligible effect on core-surface temperature difference during torrefaction when the diameter is fixed at 25 mm. This information will help to design a torrefaction processing system and develop a value chain for biomass supply without using an energy-intensive grinding process.

Torrefaction of wood pellets: New solutions

The current state of the market of conventional and torrefied wood pellets and the trends of its development have been analyzed. The advantages and disadvantages of pellets of both types have been compared with other alternative fuels. The consumer segment in which wood pellets are the most competitive has been determined. The original torrefaction technology using exhaust gas heat from a standard gas engine that was developed at the Joint Institute for High Technologies and the scheme of an experimental unit for the elaboration of the technology have been presented. The scheme of the combined operation of a torrefaction unit and a standard hot water boiler, which makes it possible to utilize the heat of exhaust steam-and-gas products of torrefaction with the simultaneous prevention of emissions of harmful substances into the environment, has been proposed. The required correlation between the capacity of the torrefaction unit and the heating boiler house has been estimated for optimal operation under the conditions of the isolated urban village in a region that is distant from the areas of extraction of traditional fuels and, at the same time, has quite sufficient resources of raw materials for the production of wood pellets.

Integrating Torrefaction in the Wood Pellet Industry: A Critical Review

As an established bioenergy industry, the global wood pellet sector is ideally positioned to adopt biomass torrefaction technologies. In this review, potential benefits and challenges of integrating torrefaction within the pellet industry are reviewed and the required technological interventions to enable this integration are analyzed. It is apparent that integration would accelerate the commercialization of biomass torrefaction and benefit the wood pellet industry, torrefaction developers, as well as coal-based utilities. Torrefied pellets are expected to have distinct applications in power generation and help coal-based utilities to reduce their emission levels and comply with increasingly stringent regulations. Co-firing coal with black pellets requires little-to-no retrofit of the existing power plant and, therefore, can offer a low-cost solution. Two potential pathways, in either an upstream or downstream configuration, for retrofitting torrefaction within a white pellet facility are assessed. A succ...

Challenges and opportunities of torrefaction technology

Since the active exploitation and usage of classical non-renewable energy resources the most promising direction is the development of technologies of heat and electricity production from renewable sources—biomass. This is important in terms of reducing the harmful man-made influence of fuel-and-energy sector on the ecological balance. One of the most important aims when using biomass is its pre-treatment. The paper describes the fuel preliminary preparation for combustion with such technological process as torrefaction. Torrefaction allows bringing the biomass fuel as close as it possible to fossil coals for the main thermotechnical parameters. During torrefaction moisture is removed from initial material and the partial thermal decomposition of its components appears. The final torrefied product can be recommended for utilization in existing coal-fired boilers without their major reconstruction. Thus torrefaction technology enables the partial or complete replacement of fossil coal. At JIHT RAS, a torrefaction pilot plant is developed. As heat transfer medium the gas-piston engine exhaust gases were used. Results of researching and proposals for further development are showed in this paper.

Energy efficiency analysis of reactor for torrefaction of biomass with direct heating

Paper presents energy analysis of reactor for torrefaction with direct heating of granulated biomass by exhaust gases. Various schemes of gas flow through the reactor zones are presented. Performed is a comparative evaluation of the specific energy consumption for the considered schemes. It has been shown that one of the most expensive processes of torrefaction technology is recycling of pyrolysis gases.

Detailed mapping of the mass and energy balance of a continuous biomass torrefaction plant

Biomass torrefaction was tested on pilot scale (50 kg h−1 throughput) for 3 types of wood: spruce, ash and willow at torrefaction temperatures of 250 °C–265 °C. Quantitative analysis of process streams was accomplished by utilising on- and off-line analytical methods.The data obtained from the pilot tests could be very well translated into large-scale operations. A theoretical overall thermal efficiency of 88–89% was calculated for a large-scale heat-integrated torrefaction process that uses wet woody feedstock containing a mass fraction of 45% moisture.These results show that a pilot plant is most suitable not only for exploration of (new) feedstocks but also for generating experimental data that provide valuable information for the design of full-scale plants. The detailed mapping of the mass and energy balances presented in this work can be used further as input for process optimisation, evaluation of commercial viability and techno-economic analyses which can further help in up-scaling and commercialisation of the torrefaction technology.

Current Trends in the Production and Applications of Torrefied Wood/Biomass - A Review

Trends in the production and applications of torrefied wood/biomass are reviewed in this article. The thermochemical conversion of biomass is a promising technology because biomass is an environmentally friendly fuel that produces substantially lower CO2 emissions compared to fossil fuel. Torrefaction is the thermal treatment of biomass at temperatures from 200 to 300 oC in the absence of air or oxygen to liberate water and release volatile organic compounds, primarily through the decomposition of the hemicelluloses. Torrefied biomass has a higher heating value, is more hydrophobic, resists rotting, and has a prolonged storage time. The different torrefaction technologies and reactors are described. An overview of the applications of torrefied biomass, the economic status, and future prospects of torrefaction technology are presented and discussed. Currently, torrefaction demonstration plants have technical problems that have delayed their commercial operation. Torrefaction reactors still require optimization to economically meet end-use requirements and attain product standardization for the market. Several characteristics of torrefaction need to be demonstrated or scaled up for successful commercialization.

Torrefaction of Pinus radiata and Eucalyptus globulus: A combined experimental and modeling approach to process synthesis

The use of wood as feedstock for the production of energy and chemicals is a strategy used by both developing and developed countries because it increases the sustainability of their energy infrastructure. Torrefaction of forest resources for co-firing and densification of biomass energy is among the most prominent alternatives. This study is focused on technical aspects of torrefaction technology by analyzing both energy and exergy changes through a comprehensive physico-chemical model (Aspen One v8.6 software) of a plant operating in mild (250°C) and severe (280°C) regimes. The main wood species in Chilean plantations, Eucalyptus globulus and Pinus radiata, were processed in a lab-scale apparatus to obtain the data for model calibration. We found that xylan composition in hemicelluloses has a considerable effect on global thermal efficiency, volatiles energy content, energy density, and exergy yield of torrefied product. The highest efficiency (96%) is obtained for Eucalyptus at 250°C when moisture in the feedstock is ≤20%. Combustion of volatile products (torgas) for drying does not result in substantial technical benefits for the overall process; however, their post-combustion does lead to lower exergy losses.