Evaluation of usher wood and karkadeh stem for charcoal in Sudan

Two unusual biomass materials Hibiscus sabdarifja var. sabdariffa (karkadeh) stem and Calotropis procera (usher) wood were investigated in the laboratory as potential raw materials for charcoal making in Sudan. The materials were characterized physically and chemically and despite the low density and high bark-to-wood ratio by volume, good yields and quality of charcoal were predicted. The carbonization trials with a laboratory retort at conditions close to those of field metal kiln gave very good charcoal yields (35% for karkadeh and 38% for usher) with high energy transformation (58% and 62%, respectively). The karkadeh charcoal, except for a somewhat high ash content, was good for domestic uses (79% fixed carbon and 30.3 MJ kg⁻¹ heat value). The usher charcoal was better with respect to fixed carbon (86.5%) and gross heat value (32.4 MJ kg⁻¹ ). Both charcoals were of low density (140–160 kg m⁻³) and further assessment of their economic suitability should be carried out under field conditions. The carbonization by-products were also collected and characterized by means of gas chromatography.     

Effects of carbonisation conditions on the yield and chemical composition of Acacia and Eucalyptus wood chars

Acacia and Eucalyptus woods were carbonised in the temperature range 400–1200°C using two different heating-cooling cycles, viz. slow and rapid. The yield of chars and their chemical composition was found to be dependent on the carbonisation temperature, heating rate, soaking time and wood species. The char yield gradually decreased with increase in carbonisation temperature and the majority of volatilisation occurred up to 800°C. Slow carbonisation resulted in higher char yield than rapid carbonisation. The char yield from Eucalyptus wood samples was greater than from Acacia wood. The carbon content of Eucalyptus wood char was found to be a little higher than Acacia wood char produced under similar carbonisation conditions, possibly due to relatively higher lignin content of Eucalyptus wood.     

Charcoal made in the pit-tumulus type of earth-kiln

Charcoal can be made in the pit-tumulus, a type of earth-kiln introduced into Guyana over a century ago, of a quality and with an efficiency not far short of those obtained using a metal kiln, as judged mainly by the levels and the distribution of volatile matter throughout the bed at the end of a good burn. Low average volatile matter, taken together with other criteria of quality, serves to explain why this charcoal found a place for many years in discriminating, overseas, industrial markets. Upgrading the efficiency of production and the quality of charcoal from earth kilns in non-industrialized countries deserves a high priority, especially in view of thier present economic circumstances and the importance of this fuel in development. Advancement in the science and technology of wood carbonization in these countries depends on increased co-operative research and development, best effected within a South-South framework.     

Improved and more environmentally friendly charcoal production system using a low-cost retort–kiln (Eco-charcoal)

Research into a low-cost retort–kiln, used to produce charcoal from sustainably managed forests in a more environmentally friendly way (Eco-Charcoal), has been completed and pilot units have been built in India and East Africa. The unit is called ICPS (Improved Charcoal Production System). Importantly, it has a much higher efficiency rating than traditional earth-mound kilns, which have until now been the main means of domestic charcoal production in developing nations. The efficiency of traditional charcoal production methods is about 10%–22% (calculated on using oven-dry wood with 0% water content) while the efficiency of the ICPS is approximately 30%–42%. As compared with traditional carbonisation processes, the ICPS reduces emissions to the atmosphere by up to 75%. The ICPS works in two different phases. During the first phase the ICPS works like a traditional kiln; however, waste wood is burned in a separate fire box to dry the wood. During the second phase of operation the harmful volatiles are burned in a hot ‘fire chamber’ meaning all resulting emissions are cleaner, minus these already reduced volatiles. The heat gained by flaring the wood gazes, is used and recycled to accelerate the carbonisation process. Unlike traditional methods the ICPS can complete a carbonisation cycle within 12 h.     

Sustainable charcoal production from biomass

Charcoal products can be produced from biomass sources such as charcoal from wood, woody agricultural products, the biogenic fraction of municipal wastes, nut shells, etc. The liquid and gaseous fractions obtained from biomass are a valuable fuel source; however, the solid fraction (charcoal) has the recovery potential of carbon black or as carbon adsorbent after applying an activation step. Charcoal is produced by slow heating wood (carbonization) in airtight ovens or retorts, in chambers with various gases, or in kilns supplied with limited and controlled amounts of air. Charcoal has the potential to improve soil properties, crop productivity, and carbon sequestration in soil. The most interesting temperature range for the production of the pyrolysis products is between 625 and 775 K. The charcoal yield decreased gradually from 43.5 to 31.0% for the walnut shell and from 38.3 to 25.4% for the spruce wood with an increase of temperature from 550 to 1150 K. The charcoal yield decreases as the temperature increases. The ignition temperature of charcoal increases as the carbonization temperature increases. The charcoal briquettes that are sold on the commercial market are typically made from a binder and a filler.     

水热处理对生物质成型炭理化性质的影响

棉秆(CS)及木屑(WS)经高压反应釜水热预处理后压制成型,并于固定床热解炉内进行炭化实验,利用电子万能材料试验机、热重分析仪等分析手段分析水热预处理对生物质成型炭的产率、物理性能(机械强度和表观密度)、热值及燃烧性能的影响。研究表明:随着水热温度的升高,生物质成型炭的产率增加且热值稳定,但燃烧性能变差;经水热预处理制得的生物质成型炭灰分产率均小于18%,固定碳产率均大于60%,满足欧标要求;随着水热温度的升高,生物质成型炭的表观密度及抗压强度均先增加后减小;对比所有实验样品,经230℃水热预处理制得的生物质成型炭(CS/WS-HT230-CB)物理性能及燃烧性能最佳,且均优于商用烧烤炭性能。     

A new technology for the combined production of charcoal and electricity through cogeneration

This paper presents an historical approach on the development of the existing biomass carbonization technologies in industrial operation in Brazil, the biggest charcoal producing country in the world. The gravimetric yield of charcoal from wood does not usually surpass 25%; the time of each operation cycle is more than seven days; and less than 50% of the energy contained in the feedstock is transformed into charcoal – the rest is discharged into the environment. The electricity generation associated with charcoal production is nowadays inexistent in Brazil. This paper presents the development of an industrial technology of semi-continuous pyrolysis process, characterized by using metallic kilns with forced exhaust system: the Rima Container Kiln (RCK). The results of the test runs are related to 5 m³ and 40 m³ kilns, with a thermal power of 200 kW (pilot scale: 5 m³) and 3000 kW (industrial scale: 40 m³). The low heating value of the pyrolysis gases is 670 and 1470 kJ/m³, respectively.The main results are: a 3 h carbonization time; an average productivity per kiln of 1 ton of charcoal per hour; and a gravimetric yield of 35%. In this paper, four scenarios for the conversion of exhaust gases and tar into electricity were evaluated: the Conventional Rankine Cycle (CRC) and the Organic Rankine Cycle (ORC), each one with and without forest residues utilization. It is shown that the best economic indicators correspond to the scenario where ORC technology is used. The electricity generation cost is around U$30/MWhe for ORC and US$40/MWhe for CRC.     

Catalytic conversion of particle board over microporous catalysts

Catalytic pyrolysis of particle board, a type of waste wood that is increasingly produced all over the world, was carried out over three types of zeolite catalysts: HBETA, HZSM-5, and Ga-impregnated HZSM-5 (Ga/HZSM-5). Experiments conducted using a batch reactor showed that the bio-oil yield and gas yield in catalytic pyrolysis were lower and higher than those in non-catalytic pyrolysis, respectively. Analysis of the bio-oil using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) showed that the yields of high-value-added species such as aromatics and phenolics were increased to a large extent by catalytic upgrading, thus increasing the value of the product bio-oil. In particular, HZSM-5 exhibited high selectivity for aromatic compounds, and impregnation of Ga further increased the selectivity. HBETA could cause levoglucosans to decompose completely owing to its large pore size, resulting in increased yields of low-molecular-mass species.     

Biomass productivity and wood energy of Salix species after 2 years growth in SRIC fertilized with wastewater sludge

The energy equivalent of willows in short-rotation intensive culture (SRIC) varies in terms of yield and woody biomass characteristics. Three willow species (Salix discolor Mühl., Salix petiolaris Smith and Salix viminalis L.) were planted on two sites, well-drained and poorly drained, in two different densities (20 000 and 30 000 plants per ha). Four doses of dried and granulated sludge were applied: the equivalents of 0, 100, 200 and 300 kg “available” N per ha. At the end of the second season, above-ground biomass was similar for S. discolor and S. viminalis, and greater than that of S. petiolaris on both sites and for all sludge treatments. On the well-drained site, each increment in the sludge dose significantly increased the performance of the species, regardless of plant density. Fertilized with a sludge dose equivalent to 300 kg N per ha, S. viminalis and S. discolor yielded 30.17 and 24.97 t/ha of dry matter respectively. On the poorly drained site, differences in performance were also observed between fertilized and unfertilized plots, but not among the various treatments. The calorific value of the wood of the three species being similar (19.21–19.59 kJ/g), the energy equivalent of a hectare of willows is proportional to the yield of each species. Thus the energy equivalent of S. viminalis and S. discolor is two to three times that of S. petiolaris. S. viminalis had the highest woody biomass quality, with an FVI (fuelwood value index) of 1030.58 (100%), followed by S. petiolaris with 954.25 (92.6%) and S. discolor with 849.08 (82.4%).     

Wood and bark of some poplar and willow clones as fuelwood

Poplars and willows are widely used to produce biomass for energy. Calorific values of wood and bark, as well as for whole tree of Populus × euramericana (cl. I-214), Populus deltoides (cl.PE 19/66) and white willow Salix alba (cl.378) of different ages were determined. one- and 2-year-old rooted cuttings were grown in plantations with high planting density, in order to produce a high biomass yield per hectare. Mature trees in both species (poplar and willow) originated from the corresponding plantations; willow 14-year old, and poplar 12 years (cl.I-214) and 8 years (cl.PE 19/66). As the share of bark depends on the age of wood, calorific values were determined separately for bark and for wood. The share of bark (proportion of total weight) in 1- and 2-year-old rooted cuttings ranged between 18% and 27%, and in older trees it was from 10% to 15%. The higher heating values of oven dry poplar wood (calculated for the whole tree, based on the proportion of bark) were from 15,787 (cl. I-214 1-year old) to 24,275 kJ/kg (cl.I-214 2-year old). The average calorific values of willow wood (whole tree with bark) were from 16,169 (14-year old) to 22,572 kJ/kg (2-year old). It should be pointed out that the calorific value of wood is more favorable than that of bark, and the highest calorific values refer to 2-year-old trees.     

Modelling and measurements of heat transfer in charcoal from pyrolysis of large wood particles

The pyrolysis rate limiting heat transfer properties of charcoal from large wood particles are studied by comparing experiments and simulations of transient heat conduction in large charcoal samples. The interior temperatures in cylindrical charcoal samples of 20±2 mm radius were measured during heating from room temperature to 700°C in an inert atmosphere. Simulations are performed for two cases of constant material properties and for two cases of temperature dependent specific heat and/or effective thermal conductivity. The material properties of charcoal used in the simulations are found in literature related to modelling of wood pyrolysis. The simulations show that a constant thermal diffusivity of approximately 0.7 mm²/s agrees better with measured data than the assumption of temperature dependent material properties. Constant material properties are preferred due to simplicity, although the correct interpretation is that the increase in specific heat and effective thermal conductivity with temperature cancel each other.     

Solar gasification of carbonaceous materials

Charcoal, wood and paper have been gasified in a packed-bed reactor using steam and solar energy. The steam was generated by spraying water directly on to the surface of the fuel and, at the same time, heating the fuel at the focus of a solar furnace. Half of the steam reacted with carbon and 30 per cent of the incident solar energy was stored as chemical enthalpy.

The performance of a fluidized-bed reactor was compared to that of a packed-bed reactor using charcoal and CO₂. The fraction of the incident solar energy utilized to produce CO (stored) was 10 per cent in the case of the fluidized-bed reactor and 40 per cent for the packed-bed reactor.

The fuel value of the gas produced from the steam-gasification of wood and paper was 65 kcal/mole (320 Btu/lb). On an ash free basis the volume yield of the gas was 1 ± 0.1 m³/kg.     

Performance evaluation of natural draft based agricultural residues charcoal system

A natural draft based agricultural residues charcoal reactor has been described herein along with its performance details. Instead of releasing pyrogases into the atmosphere, these gases are burnt inside the charcoal reactor, offering better energy efficiency and environmental acceptability.Agricultural residues like arhar stalks (Cajanus cajan), saw mill woody waste, Ipomoea (Ipomoea fistulasa, Syn. Ipomoea Carnea) and babul wood (Acacia nilotica), all sun dried, were used as the feedstocks for charcoal making.Saleable charcoal (SC) yield was in the range of 28 to 47% dry basis (db) with the maximum from saw mill woody waste and the minimum from Ipomoea. Fixed carbon (FC) content in the SC varies from 69 to 77% (db) in the agricultural residues based charcoal.Babul wood charring gave the highest SC yield (50%, db) and the best quality charcoal in terms of FC (80%, db).Economic analysis revealed that if the system developed was operated annually for 4000 h, the user could have a net profit of around Rs.1,00,000/– (US $2500).     

Emission factors of wood and charcoal-fired cookstoves

In the developing countries, energy required for cooking often has the biggest share in the total national energy demand and is normally met mostly by biomass. This paper presents the results of experimental studies on emission conducted on a number of traditional and improved cookstoves collected from different Asian countries using wood and charcoal as fuel. The emission factors from this study are comparable to those reported in the literature. In the case of wood combustion, CO₂ emission factor is in the range of 1560–1620 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC and NO_x were in the ranges 19–136, 6–10, 6–9 and 0.05–0.2 g kg⁻¹, respectively. In the case of charcoal combustion, CO₂ emission factor is in the range of 2155–2567 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC were in the ranges 35–198, 6.7–7.8, 6–10 g kg⁻¹, respectively.

Comparison between wood and charcoal fired stoves shows that, CO₂ and CO emission factor values for wood are lower as compared to charcoal. CH₄ and TNMOC emission factors for wood are with the same range as compared to charcoal. Emission factors for NO_x using wood is slightly lower than charcoal. The emission of all the pollutants per unit of useful heat was found to decrease with increasing stove efficiency for both wood and charcoal fired stoves.     

Comparative economic analysis of perennial, annual, and intercrops for biomass production

Herbaceous crops may be an important source of renewable energy. Production costs can be more competitive by increasing yields so that overhead costs are applied to more biomass. Most previous economic studies of energy crops have concentrated on the production of switchgrass (Panicum virgatum L.). This study analyzes the biomass yield and economic potential of several high-yielding annual and perennial crops on prime and marginal, sloping land. Crops evaluated were reed canarygrass (Phalaris arundinacea L.) harvested twice per year; switchgrass and big bluestem (Andropogon gerardii Vitman var. gerardii); alfalfa (Medicago sativa L.); and sweet sorghum, forage sorghum [both Sorghum bicolor (L.) Moench], and maize (Zea mays L.). The intercropping of the two sorghum species into reed canarygrass and alfalfa was also analyzed. All crops but alfalfa were fertilized with 0, 70, 140, or 280 kgNha⁻¹, with economic analysis performed assuming 140 kgNha⁻¹. Sorghums were most productive, with more than 16 t of dry matter ha⁻¹. Switchgrass was the highest-yielding perennial crop. Costs per ton of biomass produced were lowest for sorghum, somewhat higher for switchgrass, higher still for big bluestem, and highest for alfalfa and reed canarygrass. Yields per ton for intercropped species were higher than for perennial species but lower than for monocrop sorghum. Costs per ton for intercropped species were less than for either alfalfa or reed canarygrass, but were higher than costs per ton of monocrop sorghum. Although the sorghums had the highest yields, high potential for erosion on sloping soils may preclude their use on these soils.     

Alternative energy sources from plants of Western Ghats (Tamil Nadu, India)

Twenty-two taxa of Western Ghats plants were screened as potential alternative crops for renewable energy, oil, hydrocarbon and phytochemicals. The highest hydrocarbon yields were observed in Carissa carandas (1.7%), and Jatropha gossypifolia (1.7%). The highest polyphenol fraction was observed in Dodonaea viscosa (17.1%), Carissa carandas (7.7%), Swietenia mahagoni (6.6%), and Jatropha glandulifera (6.2%). The highest oil content was observed in Aganosma cymosa (10.3%), Carissa carandas (5.8%), and Argemone mexicana (5.0%). Swietenia mahagoni yielded the highest protein content with 8.1%. The gross heat value of 4175.0 cal/g(17.5 MJ/kg) for Lochnera rosea (pink flowered var.), and 4112.0 cal/g for Dalbergia sissoo were the highest among the species analysed. NMR spectra of the hydrocarbon fractions of Alstonia scholaris, Carissa carandas, Ichnocarpus frutescens, Plumeria rubra, Thevetia neriifolia (white flowered var.), Vallaris solanacea, Lochnera rosea (pink flowered var.), Euphorbia hirta, E. splendens, Artocarpus integrifolia and Ficus religiosa revealed the presence of cis-polyisoprene (natural rubber), whereas Argemone mexicana showed the presence of trans-polyisoprene (gutta). Several new crop species were identified with potentially useful compounds. The potential exists for growing these alternate crops in areas of underutilized lands, subsequently stimulating industrial and economic growth.     

Growth patterns and biomass productivity of two Salix species grown under short-rotation intensive culture in southern Quebec

Samples of two species of Salix, Salix discolor, which grows naturally in the northern half of North America and S. viminalis, which originated from central Europe, were studied to compare their productivity and their growth patterns under the short-rotation, intensive-culture system (SRIC). The study was conducted in the nursery of the Montreal Botanical Garden on former agricultural land. The plantation was established at a density of 27,000 trees per hectare from unrooted cuttings without any fertilizer or irrigation. Growth parameters were measured at regular intervals during summer of the two first years following planting. At the end of each growing season, after leaf drop, a part of each plot was cut down and the stems and branches were harvested and weighed to evaluate their annual growth rates and their biomass yields. For the first growing season, height growth in both species was greater than 2 m. Although S. viminalis grew more rapidly early in summer, S. discolor grew about three weeks longer and its total height at the end of the growing season was greater than the former. Meanwhile the stem-branch dry weight of S. discolor was similar to the one produced by S. viminalis. Two growing seasons after establishment, the total tree height was about 3.5 m for both species, while the biomass of stems and branches of S. viminalis was weakly superior in comparison to S. discolor and reached very high values-about 27 Mg ha⁻¹ for S. viminalis. The growth patterns and yields of the one-year-old coppice (one-year-cycle) were similar to those recorded at the end of the first year for trees developed directly from cuttings. Both species produced a comparable quantity of sprout biomass. The yield of the trees harvested two years after planting was about twice the total biomass harvested two times, at the end of each growing season, suggesting that a two-year cycle is more productive than a one-year cycle.     

生物质气化焦油在高温木炭床上的裂解试验研究

在高温木炭床裂解炉上,对以木粉为原料的120Kw鼓泡流化床气化炉产生的气化气中的焦油进行了裂解研究,采用溶剂冷态捕集焦油和称重分析相结合的方法对裂解前、后的焦油含量进行了测量.结果表明,在高温木炭床上发生的木炭吸附焦油、焦油的高温裂解和木炭灰催化裂解焦油等一系列的物理化学过程,可有效降低燃气中的焦油含量,同时可以获得热值为5MJ/m^3的可燃气.     

Pyrolytic behavior and products of some wood varieties

Thick wood cylinders have been pyrolyzed with applied radiation intensities in the range 28–80 kW/m², to investigate the role of wood variety on the degradation characteristics (temperature and weight loss dynamics), product (char, gas, and liquid) yields, and gas composition. Two hardwoods (beech, chestnut) and three softwoods (Douglas fir, redwood, and pine) have been examined. Apart from the higher minimum heat flux needed for softwood pyrolysis, all the varieties present the same qualitative behavior, and the process dynamics tend to become the same for applied heat fluxes above 40 kW/m², when internal heat transfer is the controlling mechanism. However, quantitative differences remain large in terms of pyrolysis temperature (maximum values of 600–650 K), product yields (minimum char yields of 21–33%, maximum liquid yields of 47–57%), and average devolatilization rate, as a consequence of variations in the chemical composition.