The potential use of torrefied Nigerian biomass for combustion applications

Many countries are seeking to expand their use of solid biomass for electricity and heat generation. Nigeria, too, is exploring its own potential energy crops and indigenous residues. The use of this biomass for energy production is, however, limited by factors such as high moisture content, low bulk and low energy density. This study examines the torrefaction and combustion properties of four readily available Nigerian woody biomass, Gmelina arborea, Terminalia superba, Nauclea diderrichii, Lophira alata and a residue, palm kernel expeller (PKE). They are considered for their suitability for use in large scale power stations, especially as pulverized fuels.The Fuels were torrefied at 270 and 290 °C for either 30 or 60 min, and assessed for pyrolysis and combustion characteristics in comparison to their untreated counterparts. Energy densities of the woods improved from 19.2 to 21.2 MJ/kg for the raw fuels to 21.5–24.6 MJ/kg for the torrefied fuels. The milling behaviour of the torrefied fuels improved upon torrefaction, especially for Nauclea; however, torrefaction had very little effect on the grindability of PKE. The apparent first order kinetics for pyrolysis were determined by thermogravimetric analysis (TGA). After torrefaction, the fuels become less reactive; Nauclea and Gmelina were the most reactive fuels, whilst PKE was the least reactive. The combustion behavior of selected fuels was visually examined in a methane air flame. This showed that torrefaction resulted in shorter ignition delay, shorter duration of volatile combustion and longer duration of char burn out.     

Conditions for the sustainability of biomass based fuel use

Sustainability of biomass based fuel use requires that in biomass production erosion and water usage do not exceed addition to stocks of soil and water and that levels of nutrients and organic matter in soils do not decrease. Levels of volatile carbon compounds and N₂O in the atmosphere should remain unaffected. To maintain ecosystems services of nature useful to mankind, restriction of biomass production to degraded and currently fallow land is to be preferred. Also sustainability of biomass-for-energy use requires a high efficiency recycling of nutrients present in ashes and low emissions of persistent organics, acidifying compounds and heavy metals due to biomass combustion. Meeting such conditions requires major efforts.     

生物质热裂解制取液体燃料技术的发展

对生物质热裂解技术进行了系统的研究，阐述了其基本技术要求和发展现状，并将现有的生物质热裂解反应器进行分类，分析了相应的优势与不足。最后评估了生物质热裂解制取液体燃料技术的经济和社会效益，结果表明它具有广泛的应用前景。     

Assessment of the fuel wood of India: A case study based on fuel characteristics of some indigenous species of Arunachal Pradesh

Biomass in the form of fuelwood has been a source of energy for many centuries all over the world. In rural India, fuelwood remains the first choice of energy source. Arunachal Pradesh is home to many different tree species; so far most of the fuelwoods of Arunachal Pradesh have never been studied for their fuel characteristics. This study is carried out with the following objectives: (i) Identification and selection of indigenous fuelwood species, which are widely distributed throughout Arunachal Pradesh, North East India; (ii) quantitative and qualitative analysis of these fuelwoods; and (iii) to rank these fuelwoods according to their fuel value index.     

Experimental study on oxygen-enriched combustion of biomass micro fuel

The oxygen-enriched combustion of biomass micro fuel (BMF) was carried out respectively in the thermogravimetric analyzer and cyclone furnace to evaluate the effects of oxygen concentration on combustion performance. The experimental results show that with the increasing oxygen concentration, the volatile releasing temperature, ignition temperature and burnout temperature were decreasing. Oxygen-enriched atmosphere subtracts burning time and improves combustion activity of biomass micro fuel. Oxygen-enriched atmosphere improves the combustion temperature of BMF in cyclone furnace; while the improvement is weaken as oxygen concentration is above 40%.     

The introduction and expansion of biomass use in Swedish district heating systems

District heating satisfies about 60% of the heat demand in Swedish buildings. Today, more than two thirds of the heat supply to the district heating systems is based on biomass and waste, and biomass alone accounts for about half of the heat supply. The purpose of this paper is to present the Swedish experiences of introducing and expanding the use of biomass in the district heating systems and to identify the main drivers behind this development. Our five research questions and the corresponding conclusions consider the driving forces from energy policy tools and local initiatives, the biomass prices, the established infrastructures in forestry and district heating, the technology paths for biomass conversion, and finally the future challenge of competing uses of biomass.     

Effect of gasification agent on the performance of solid oxide fuel cell and biomass gasification systems

In this paper, an integrated solid oxide fuel cell (SOFC) and biomass gasification system is modeled to study the effect of gasification agent (air, enriched oxygen and steam) on its performance. In the present modeling, a heat transfer model for SOFC and thermodynamic models for the rest of the components are used. In addition, exergy balances are written for the system components. The results show that using steam as the gasification agent yields the highest electrical efficiency (41.8%), power-to-heat ratio (4.649), and exergetic efficiency (39.1%), but the lowest fuel utilization efficiency (50.8%). In addition, the exergy destruction is found to be the highest at the gasifier for the air and enriched oxygen gasification cases and the heat exchanger that supplies heat to the air entering the SOFC for the steam gasification case.     

Industrial processes for biomass drying and their effects on the quality properties of wood pellets

This paper contributes to the discussion of how different kinds of industrial scale dryers for biomass influence the quality properties of wood pellets. It also discusses how the drying technique can affect the environment. The most common biomass drying processes in use, i.e., convection dryers are discussed. The discussion of drying techniques is based on advantages and disadvantages with a focus on the drying medium, temperature and residence time. The choice of drying technique is particularly important if the end-user’s choice of pellets is made due to the specific requirements for the heating system used. Some specific parameters were tested in order to investigate how the choice of drying technique affects the pellet quality. The parameters tested were moisture content and the emissions of volatile hydrocarbons. Pellets available on the market were chosen for the tests. The amount of volatile hydrocarbons left in sawdust after drying vary with drying technique, as emissions of terpenes are larger in dryers with long residence times. Low emissions of volatile hydrocarbons would improve the energy content of the sawdust, and by decreasing air pollution improve the work environment and the environment in the surroundings of the dryers.     

Gasification of torrefied oil palm biomass in a fixed-bed reactor: Effects of gasifying agents on product characteristics

Gasification represents an attractive pathway to generate fuel gas (i.e., syngas (H₂ and CO) and hydrocarbons) from oil palm biomass in Malaysia. Torrefaction is introduced here to enhance the oil palm biomass properties prior to gasification. In this work, the effect of torrefaction on the gasification of three oil palm biomass, i.e., empty fruit bunches (EFB), mesocarp fibres (MF), and palm kernel shells (PKS) are evaluated. Two gasifying agents were used, i.e., CO₂ and steam. The syngas lower heating values (LHV_syngas) for CO₂ gasification and steam gasification were in the range of 0.35–1.67 MJ m⁻³ and 1.61–2.22 MJ m⁻³, respectively. Compared with EFB and MF, PKS is more effective for fuel gas production as indicated by the more dominant emission of light hydrocarbons (CH₄, C₂H₄, and C₂H₆) in PKS case. Gasification efficiency was examined using carbon conversion efficiency (CCE) and cold gas efficiency (CGE). CCE ranges between 4% and 55.1% for CO₂ gasification while CGE varies between 4.8% and 46.2% and 27.6% and 62.9% for CO₂ gasification and steam gasification, respectively. Our results showed that higher concentration of gasifying agent promotes higher carbon conversion and that steam gasification provides higher thermal efficiency (CGE) compared to CO₂ gasification.     

Experimental study on biomass steam gasification for hydrogen-rich gas in double-bed reactor

Based on Response Surface Methodology, the experiments of biomass catalytic gasification designed by Design-Expert software were carried out in steam atmosphere and double-bed reactor. The response surface was set up with three parameters (gasification temperature, the content of K-based catalyst in gasification bed and the content of Ni-based catalyst in reforming bed) for biomass gasification performance of carbon conversion efficiency and hydrogen yield to make analysis and optimization about the reaction characteristics and gasification conditions. Results showed that gasification temperature and the content of K-based catalyst in gasification bed had significant influence on carbon conversion efficiency and hydrogen yield, whilst the content of Ni-based catalyst in reforming bed affected the gasification reactions to a large extent. Furthermore, appropriate conditions of biomass steam gasification were 800 °C for gasification temperature, 82% for the content of K-based catalyst in gasification bed and 74% for the content of Ni-based catalyst in reforming bed by the optimization model. In these conditions, the steam gasification experiments using wheat straw showed that carbon conversion efficiency was 96.9% while hydrogen yield reached 64.5 mol/kg, which was in good agreement with the model prediction. The role of the reforming bed was also analyzed and evaluated, which provided important insight that the employment of reforming bed made carbon conversion efficiency raised by 4.8%, while hydrogen yield achieved a relative growth of 50.5%.     

High-temperature gasification of woody biomass in a drop tube reactor: A special focus on the particle size and axial temperature gradient

Pine sawdust (PS) was gasified in a drop-tube reactor (DTR) using air as a gasifying agent. An almost complete mass balance was achieved by establishing a burning operation after gasification to determine the carbon deposits (CD) inside the reactor tube, providing an authentic depiction of the feedstock conversion. The results indicated that particle size reduction led to a significant improvement in the gasification performance. When the particle size of PS was below 0.25 mm, almost complete char gasification was achieved at 1300 °C, while soot remained a major particulate in the syngas. An experimental approach is proposed to simulate the axial temperature gradient (ATG) inside an auto-thermal entrained-flow gasifier by setting two different temperature zones in the DTR. The results revealed that char was rapidly and almost completely exhausted in the high-temperature zone (1300 °C). When the ATG between the upper and lower heater zones was above 300 °C, both homogeneous reforming and heterogeneous gasification proceeded slowly or almost stagnated in the lower temperature zone. An evident enhancement of soot formation was observed at ATG = 200 °C. After that, the soot yield monotonously decreased with decreasing ATG due to the substantial enhancement of the heterogeneous gasification kinetics, contributing more to carbon conversion and CGE than char gasification.     

A study on torrefaction of various biomass materials and its impact on lignocellulosic structure simulated by a thermogravimetry

Torrefaction processes of four kinds of biomass materials, including bamboo, willow, coconut shell and wood (Ficus benjamina L.), were investigated using the thermogravimetric analysis (TGA). Particular emphasis is placed on the impact of torrefaction on hemicellulose, cellulose and lignin contained in the biomass. Two different torrefaction processes, consisting of a light torrefaction process at 240 °C and a severe torrefaction process at 275 °C, were considered. From the torrefaction processes, the biomass could be divided into two groups; one was the relatively active biomass such as bamboo and willow, and the other was the relatively inactive biomass composed of coconut shell and wood. When the light torrefaction was performed, the results indicated that the hemicellulose contained in the biomass was destroyed in a significant way, whereas cellulose and lignin were affected only slightly. Once the severe torrefaction was carried out, it further had a noticeable effect on cellulose, especially in the bamboo and willow. The light torrefaction and severe torrefaction were followed by a chemically frozen zone, regardless of what the biomass was. From the viewpoint of torrefaction application, the investigated biomass torrefied in less than 1 h with light torrefaction is an appropriate operation for producing fuels with higher energy density.     

Investigation of forestry wastes: Torrefaction and their thermal properties for use in energy recovery schemes

Three biomasses like Eucalyptus, Azadirachata, and Ficus religiosa were torrefied to investigate the effect of temperature and residence time was investigated on torrefied biomasses for yield, volatile matter, fixed carbon, ash, and Gross calorific value (GCV). Thermogravimetric analysis and Hardgrove grindability index (HGI) of three torrefied samples were studied at optimum conditions of temperature and residence time. According to the results, an optimum temperature was found to be 260°C at 45 min residence time. A maximum GCV of torrefied biomasses of Eucalyptus, Azadirachata, and F. religiosa were found to be 4,301, 3,190, and 3,278 kcal/kg, respectively. According to thermogravimetric analyzer results, the Azadirachata has shown higher weight loss compared to Eucalyptus and F. religiosa during thermogravimetirc study. The weight loss rate for Azadirachata was maximum to nearly 12.8%/min compared to 6.11 and 5.12%/min for Eucalyptus and F. religiosa, respectively. The order of reactivity based on mean reactivity and combustion characterization factor was found to be Azadirachata indica > Eucalyptus > F. religiosa. According to HGI results, Eucalyptus, Azadirachata, and F. religiosa have shown HGI values of 71, 60.7, and 81.7, respectively. The results of this study could be useful for the energy recovery schemes in the country.     

Plate reactor as an analysis tool for rapid pyrolysis of biomass

This work presents a study of the performance of the modified plate reactor by rapid pyrolysis experiments with different biomass samples (MDF, bark pine and Avicel cellulose). The use of the plate instead of a grid allowed us to achieve a more homogeneous temperature distribution across the plate and, therefore, biomass sample. The mass yields of the major pyrolysis products CO, CO₂, C₂H₂, CH₄, C₂H₄ and C₂H₆ are measured as a function of the holding time (from 0 to 50 s) for a number of the final temperatures (from 435 to 1100 C) using the novel approach to quantitative FTIR analysis of biomass pyrolysis spectra. Special care was taken to demonstrate the influence of the secondary tar cracking on the yields of the permanent gases. Yields of major permanent gases plotted versus each other on a logarithmic scale show two distinctive regions reflecting primary and secondary kinetic processes. The experiments show that the modified plate reactor can be used for studying the kinetics of the primary decomposition of the biomass at temperatures ≤600 C.     

Influence of temperature and residence time in the pyrolysis of woody biomass waste in a continuous screw reactor

The aim of this paper is to study the influence of temperature and residence time in the quality of the charcoal obtained in the pyrolysis of biomass waste, in order to be used as a reducing agent in metallurgical applications. Woody biomass waste (pinus pinaster) coming from forest activities carried out in the north of Spain has been pyrolyzed in a laboratory scale screw continuous reactor connected to a second reactor where the pyrolysis vapors have been thermally treated to promote further cracking, with the aim of diminishing tars and improving the composition of the gas phase.Both the peak temperature and the exposition time at peak temperature have an impact in the pyrolysis fractions yields and composition, however it is at 1173 K where the bigger changes occur both in pyrolysis products yield and composition. In all cases the solids obtained (charcoal) fulfill the requirements to perform as metallurgical reducers. The higher the peak temperature the greater the charcoal quality but the lower the pyrolysis solid yield since secondary pyrolysis reactions consume charcoal. The pyrolysis gases obtained are valuable products rich in CO (22–35 vol%) and hydrogen (35–50 vol%); on the contrary, the pyrolysis liquids obtained are mainly worthless products composed of water and some aromatic compounds (e.g. naphthalene, fluorene & antrhacene).     

GA-ANFIS modeling of higher heating value of wastes: Application to fuel upgrading

Combustion of wastes is a promising source for energy recovery because of having appropriate higher heating value (HHV) in order to use as fuel. The present study was aimed to estimate HHV value using a hybrid adaptive neuro-fuzzy inference system and genetic algorithm called GA-ANFIS. This model can predict HHV as a function of carbon (%C), hydrogen (%H), oxygen (%O), nitrogen (%N), and sulfur (%S) mass percentages. This suggested model has been also compared with other published correlations, and based on obtained results, great accuracy of our model was confirmed. The obtained values of Mean Squared Error (MSE) and R-squared were 0.236 and 0.9983, respectively. Consequently, this model can be very valuable to have accurate prediction of waste HHV value.     

Investigating the effects of methanol-water vapor mixture on a PBI-based high temperature PEM fuel cell

This paper investigates the effects of methanol and water vapor on the performance of a high temperature proton exchange membrane fuel cell (HT-PEMFC). A H₃PO₄-doped polybenzimidazole (PBI) membrane electrode assembly (MEA), Celtec P2100 of 45 cm² of active surface area from BASF was employed. A long-term durability test of around 1250 h was performed, in which the concentrations of methanol-water vapor mixture in the anode feed gas were varied. The fuel cell showed a continuous performance decay in the presence of vapor mixtures of methanol and water of 5% and 8% by volume in anode feed. Impedance measurements followed by equivalent circuit fitting revealed that the effects were most significant for intermediate-high frequency resistances, implying that charge transfer losses were the most significant losses. Vapor mixture of 3% in feed, however, when introduced after operation at 8%, showed positive or no effect on the cell's performance in these tests.     

Higher heating value prediction of torrefaction char produced from non-woody biomass

The higher heating value of five types of non-woody biomass and their torrefaction char was predicted and compared with the experimental data obtained in this paper. The correlation proposed in this paper and the ones suggested by previous researches were used for prediction. For prediction using proximate analysis data, the mass fraction of fixed carbon and volatile matter had a strong effect on the higher heating value prediction of torrefaction char of non-woody biomass. The high ash fraction found in torrefied char resulted in a decrease in prediction accuracy. However, the prediction could be improved by taking into account the effect of ash fraction. The correlation developed in this paper gave a better prediction than the ones suggested by previous researches, and had an absolute average error (AAE) of 2.74% and an absolute bias error (ABE) of 0.52%. For prediction using elemental analysis data, the mass fraction of carbon, hydrogen, and oxygen had a strong effect on the higher heating value, while no relationship between the higher heating value and mass fractions of nitrogen and sulfur was discovered. The best correlation gave an AAE of 2.28% and an ABE of 1.36%.     

Cogeneration of power and substitute of natural gas using electrolytic hydrogen,biomass and high temperature fuel cells

Energy storage from renewable sources is one of the main current goals for the energy sector, and the production of a substitute of natural gas could be a good solution to solve the problem in the short term, helping the transition to hydrogen in the long term.Renewable energy sources usually generate variable electric power or medium/low energy content gas. This paper proposes a way to upgrade these products through the use of electrolytic hydrogen. By using electrolytic oxygen as an oxidant for biomass partial oxidation and for high temperature fuel cells, the exhaust gas after post-combustion is an almost pure mixture of water and carbon dioxide. Once such a gas is dehydrated, the carbon dioxide can be mixed with electrolytic hydrogen to obtain methane through the Sabatier process.Four layouts based on molten carbonate fuel cells and solid oxide fuel cells has been investigated. The results obtained are very similar: the conversion efficiency is close to 60% and the mix of energy output consist of fuel for about 75% and electric power for about 25%.