Carbonisation of bagasse in a fixed bed reactor: influence of process variables on char yield and characteristics

Carbonisation experiments on samples of sugar cane bagasse were conducted in a static fixed bed reactor to determine the effect of process variables such as temperature, heating rate, inert sweep gas flow rate and particle size on the yield and composition of solid product char. Experiments were performed to the final temperatures of 250–700°C with heating rates from 5 to 30°C/min with nitrogen sweep gas flow rate of 350 cc/min. Additional tests were aimed at studying the effect of different flow rates of nitrogen sweep gas from 0 to 700 cc/min during carbonization and different particle size fractions of bagasse. The results showed that as the carbonisation temperature was increased, the yield of char decreased. The reduction in yield was rapid up to a final temperature of 500°C and was slower thereafter. The yield of char was relatively insensitive to the changes in heating rate and particle size. Increasing the sweep gas flow rate to 350 cc/min reduced the yield of char. It appears the presence of inert sweep gas reduced secondary reactions which promoted char formation. The proximate analysis of the char suggests that fixed carbon and ash content increased with temperature. The char obtained at temperatures higher than 500°C have high carbon content and is suitable as renewable fuel and for other applications. The carbonization of bagasse has the potential to produce environmental friendly fuels and can assist in reducing deforestation for the production of charcoal.     

Bio-oils from arid land plants: Flash pyrolysis of Euphorbia characias bagasse

The devolatilization of the bagasse obtained by solvent extraction of dried Euphorbia characias, a bushy plant growing in arid land of the Mediterranean area, was investigated under rapid heating conditions at atmospheric pressure using a bench-scale fluidized bed pyrolyser. Particle heating rates exceeded 10⁴°C s⁻¹. Bagasse was fed continuously at the rate of 6 g h⁻¹ directly into a sand bed fluidized by nitrogen operating in the temperature range of 400°–750°C. The yields of oils, gases and chars are reported. A maximum oil yield of 44% (wt/wt) (moisture free bagasse) was obtained at 500°C. Yields of gases, CO, CO₂, C₁–C₄ hydrocarbons increased with the rise in temperature, reaching a maximum at 750°C. Elemental analyses showed that the composition of oils and chars was dependent on pyrolysis temperature. The nitrogen content is fairly high; an upgrading process could be necessary for its remotion before the use of the bio-oil as combustible. The other characteristics of oils fall in the range of oils derived from other biomass feedstocks. Chars have a high HHV (15.36 MJ kg⁻¹ at 500°C), representing a valuable fuel.     

Probing the reaction pathway of dehydrogenation of the LiNH2 + LiH mixture using in situ H NMR spectroscopy

Using variable temperature in situ ¹H NMR spectroscopy on a mixture of LiNH₂ + LiH that was mechanically activated using high-energy ball milling, the dehydrogenation of the LiNH₂ + LiH to Li₂NH + H₂ was investigated. The analysis indicates NH₃ release at a temperature as low as 30 °C and rapid reaction between NH₃ and LiH at 150 °C. The transition from NH₃ release to H₂ appearance accompanied by disappearance of NH₃ confirms unambiguously the two-step elementary reaction pathway proposed by other workers.     

Fermentative biohydrogen production by a new chemoheterotrophic bacterium Citrobacter sp. Y19

A newly isolated Citrobacter sp. Y19 for CO-dependent H₂ production was studied for its capability of fermentative H₂ production in batch cultivation. When glucose was used as carbon source, the pH of the culture medium significantly decreased as fermentation proceeded and H₂ production was seriously inhibited. The use of fortified phosphate at 60–180 mM alleviated this inhibition. By increasing culture temperatures (25–36°C), faster cell growth and higher initial H₂ production rates were observed but final H₂ production and yield were almost constant irrespective of temperature. Optimal specific H₂ production activity was observed at 36°C and pH 6–7. The increase of glucose concentration (1–20 g/l) in the culture medium resulted in higher H₂ production, but the yield of H₂ production (mol H₂/mol glucose) gradually decreased with increasing glucose concentration. Carbon mass balance showed that, in addition to cell mass, ethanol, acetate and CO₂ were the major fermentation products and comprised more than 70% of the carbon consumed. The maximal H₂ yield and H₂ production rate were estimated to be 2.49 molH₂/mol glucose and 32.3 mmolH₂/gcellh, respectively. The overall performance of Y19 in fermentative H₂ production is quite similar to that of most H₂-producing bacteria previously studied, especially to that of Rhodopseudomonas palustris P4, and this indicates that the attempt to find an outstanding bacterial strain for fermentative H₂ production might be very difficult if not impossible.     

Thermogravimetric kinetic analysis of Nannochloropsis oculata combustion in air atmosphere

The thermal behavior of Nannochloropsis oculata combustion in air atmosphere were investigated by performing experiments on STA PT1600 Thermal Analyzer at heating rates of 10°C/min, 40°C/min and 70°C/min and range of temperatures from room temperature to 1200°C. The kinetic parameters were evaluated by using Kissinger and Ozawa methods. The result showed that Nannochloropsis oculata combustion occurred in five stages. Started with initial devolatilization, the main thermal decomposition and combustion process, transition stage, the combustion of char and the last stage was the slow burning reaction of residual char. In line with increasing heating rate, the mass loss rate increased as well, but it delayed the thermal decomposition processes toward higher temperatures. The average activation energy at the main thermal decomposition stage and the stage of char combustion were approximately 251 kJ/mol and 178 kJ/mol, respectively.     

Preparation of activated carbon from rockrose char. influence of activation temperature

The influence of the activation temperature on textural characteristics of activated carbon prepared by partial gasification of a carbonized product (C-600) from rockrose wood (Cistus ladaniferus L.) was studied. Activations were effected in air, CO₂, and steam. The temperature ranged between 450° and 750°C in air and between 750° and 950°C in CO₂ or steam. Burnoff was 40%. Techniques used in the characterization study of the samples were gas adsorption (N₂, 77K; CO₂, 298K), mercury porosimetry, and density measurements. As temperature was increased, the microporosity increased for activations of C-600 in air, whereas the macroporosity decreased in CO₂ and in steam. The development of mesoporosity was greater when activating in steam at the lowest temperature. The product of steam activation at 750°C had the best textural characteristics.     

Static model of coal pyrolysis in a circulating fluidised-bed reactor

Four different coals were investigated: two sub-bituminous, one bituminous and lignite, which were processed in the temperature range 750–950 °C. The heat for pyrolysis was generated by partial gasification of the char produced. Air was used as the gasifying medium with amounts of 0.6–1.5 m³/kg of coal, depending on the required gasification-temperature. Two sequential phenomena were taken into account: char gasification and coal devolatilisation in respect of temperature. The experimental data on carbon dioxide and monoxide concentrations in a LCV gas produced were used for the correlation of Boudouard's equilibrium and the data on carbon burn-off and final volatile matter content in char were used for the solid-products yield. The equations for the quasi-equilibrium state were developed and calculated values were compared with the measurements. The model takes into account the equations developed and the total energy-balance assuming the heat losses of the experimental system. The investigated coal throughput amounted to 200–300 kg/h depending on the coal properties. Process characteristics were discussed, namely: the effect of air/coal ratio on the pyrolysis temperature; char and gas yield, volatile matter and ash content in a char; as well as the gas calorific value.     

Catalytic conversion of fast pyrolysis oil to hydrocarbon fuels over HZSM-5 in a dual reactor system

The catalytic conversion of fast pyrolysis bio-oil to hydrocarbon fuels was studied over HZSM-5 at atmospheric pressure. Experiments were conducted in a dual reactor system having two reactors in series. The temperatures in these reactors were in the range 340–400°C (first reactor) and 350–450°C (second reactor). The bio-oil was co-processed with tetralin in all the runs. The objective was to maximize the organic distillate product with a high concentration of aromatic hydrocarbons. The maximum amount of organic distillate in the effluent from the second reactor was 21 wt% of the bio-oil feed and the highest concentration of aromatic hydrocarbons was 76 wt% of the distillate. The dual reactor system was particularly beneficial when the temperature in the first reactor was low. Thus, with the first reactor at 340°C, the yields of organic distillate and aromatic hydrocarbons were 15–16 wt% and 8–11 wt% of wood, respectively, which are nearly two-fold compared to those from a single reactor system operated at 340°C (7.8 wt% and 4.8 wt%). Under the above conditions, the coke plus char yields were 25–26 wt% of wood which are up to 10 wt% lower than from the single reactor system at 340°C (29 wt%).     

Kinetics of rice husk char gasification

The gasification of rice husk char in carbon dioxide and steam was investigated for determining the kinetic parameters. Experiments were conducted with rice husk char in its original grain form in a silica tube reactor with steam at temperatures of 750°C, 800°C, 850°C and 900°C and experiments were conducted with rice husk char powder in a thermogravimetric balance in a carbon dioxide medium at temperatures of 750°C, 800°C, 850°C and 900°C. The data was analysed based on the volume reaction and shrinking core models. The activation energies obtained for the rice husk grain sample were 200 kJ/mol and for the rice husk powder, about 180 kJ/mol respectively. The results obtained are in good agreement with literature values of different char gasification reactions.     

Experimental study of effects of prior overload on fracture toughness of A533B steel

This paper presents the results of an extensive study carried out to examine the effects of prior overloading over the entire fracture transition regime for 50-mm thick A533B steel. The main variables examined are temperature, crack orientation with respect to the rolling direction, level of prior overload, the initial crack length, and the statistical variation of prior overload effects. It is found that the effect of prior overload on fracture toughness at lower temperatures is dependent on orientation, so that in the L-T orientation for short and medium cracks (0·2 and 0·5 a/W) there is a benefit throughout the transition regime of 50-mm thick A533B steel. In the T-L orientation no benefit is obtained for temperatures greater than the initiation of tearing temperatures. Above these temperatures the prior overload sequence lowers the fracture toughness. For L-T orientation long cracks (a/W = 0·7) it is found for temperatures lower than −140°C that prior overload apparently increases the toughness. At higher temperatures there is a loss of toughness even though failure is cleavage dominated up to −80°C.

On the lower shelf at −170°C in the L-T orientation the fracture toughness variability after preloading is found (based on a sample of 14 specimens) to exhibit a bimodal distribution. This distribution is similar to that exhibited by non-preloaded material.     

More efficient biomass gasification via torrefaction

Wood torrefaction is a mild pyrolysis process that improves the fuel properties of wood. At temperatures between 230 and 300 °C, the hemicellulose fraction of the wood decomposes, so that torrefied wood and volatiles are formed. Mass and energy balances for torrefaction experiments at 250 and 300 °C are presented. Advantages of torrefaction as a pre-treatment prior to gasification are demonstrated. Three concepts are compared: air-blown gasification of wood, air-blown gasification of torrefied wood (both at a temperature of 950 °C in a circulating fluidized bed) and oxygen-blown gasification of torrefied wood (at a temperature of 1200 °C in an entrained flow gasifier), all at atmospheric pressure. The overall exergetic efficiency of air-blown gasification of torrefied wood was found to be lower than that of wood, because the volatiles produced in the torrefaction step are not utilized. For the entrained flow gasifier, the volatiles can be introduced into the hot product gas stream as a ‘chemical quench’. The overall efficiency of such a process scheme is comparable to direct gasification of wood, but more exergy is conserved in as chemical exergy in the product gas (72.6% versus 68.6%). This novel method to improve the efficiency of biomass gasification is promising; therefore, practical demonstration is recommended.     

Charge–discharge and high temperature reaction of LiCoO2 in ionic liquid electrolytes based on cyano-substituted quaternary ammonium cation

The charge–discharge performance of LiCoO₂ positive electrode was observed in a mixed electrolyte system consisting of two ionic liquids: cyano-substituted quaternary ammonium bis(trifluoromethane)sulfoneimide (TFSI) and a same-anion salt of 1-ethyl-3-methyl imidazolium (EMI). The positive electrode exhibited a discharge capacity rather close to the theoretical one when N,N,N,N-cyanoethyl trimethyl ammonium salt was applied. Differential scanning calorimetry (DSC) studies revealed that these electrolytes exhibited exotherm only around 260 °C, 50 °C higher than conventional carbonate-based electrolytes. This is the first attempt to reveal the thermal stability of ionic liquid electrolyte under a practical situation.     

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.     

Isothermal aging test results (up to 100 000 h) of NiCrMoV steels for low-pressure steam turbine

Isothermal aging test of NiCrMoV rotor steel was carried out up to 100 000 h and change in the Charpy transition behavior was investigated. The test result revealed considerable embrittlement of the steels tested. Even at 343°C, the embrittlement of around 100°C was observed and higher temperature enhanced the embrittlement significantly. This embrittlement behavior strongly depends on the impurity contents of the materials and temper embrittlement parameter J factor or X well characterize the temper embrittlement susceptibility. Based on these test results, the amount of the temper embrittlement can be estimated from the information of chemistry. A correlation between the step cooling embrittlement and 100 000 h embrittlement was also found.     

PMMA-assisted synthesis of Li1−xNi0.5Mn1.5O4−δ for high-voltage lithium batteries with expanded rate capability at high cycling temperatures

In this work, poly(methyl methacrylate) (PMMA), a non-surfactant polymer was used to synthesize nonstoichiometric Li_0.82Ni_0.52Mn_1.52O_4−δ (0 ≤ δ ≤ 0.25) spinels. The presence of the polymer was found to be beneficial with a view to facilitating the use of the spinel in electrodes for lithium batteries. Thus, PMMA allowed spinel particles of a high crystallinity and uniform size and shape to be obtained, and particle size to be tailored by using an appropriate calcining temperature and time. By controlling these variables, spinels in nanometric, submicrometric and micrometric particle sizes were prepared and characterized by chemical analysis, X-ray diffraction, electron microscopy, thermogravimetry and nitrogen adsorptions measurements. The spinels were obtained as highly crystalline phases with lithium and oxygen deficiency and some cation disorder as revealed by chemical analysis, thermogravimetric and XRD data. Their electrochemical performance in two-electrode cells was tested at room temperature and 50 °C over a wide range of charge/discharge rates (from C/4 to 4C). Cell performance was found to depend on particle size rather than on structural properties. Thus, the spinel best performing at 50 °C was that consisting of submicrometric particles, which delivered a high capacity and exhibited the best capacity retention and rate capability. Particles of submicronic size share the advantages of nanometric particles (viz. the ability to withstand high charge/discharge rates) and micrometric particles (a high capacity and stability at low rates).     

Preliminary irradiation test results from the Yankee Atomic Electric Company reactor vessel test irradiation program

The Yankee Atomic Electric Company test irradiation program was implemented to characterize the irradiation response of representative Yankee Rowe reactor vessel beltline plate materials and to remove uncertainties in the analysis of existing irradiation data on the Yankee Rowe reactor vessel steel. Plate materials each containing 0·24 w/o copper, but different nickel contents at 0·63 w/o and 0·19 w/o, were heat treated to simulate the Yankee vessel heat treatment (austenitized at 982°C (1800°F)) and to simulate Regulatory Guide 1·99 database materials (austenitized at 871°C (1600°F)). These heat treatments produced different microstructures so the effect of microstructure on irradiation damage sensitivity could be tested. Because the nickel content of the test plates varied and the copper level was constant, the effect of nickel on irradiation embrittlement was also tested. Correlation monitor material, HSST-02, was included in the program to benchmark the Ford Nuclear Reactor (University of Michigan Test Reactor) which had never been used before for this type of irradiation program. Materials taken from plate surface locations (versus 1/4T) were included to test whether or not the improved toughness properties of the plate surface layer, resulting from the rapid quench, are maintained after irradiation. If the improved properties are maintained, pressurized thermal shock calculations could utilize this margin. Finally, for one experiment, irradiations were conducted at two irradiation temperatures (260°C and 288°C) to determine the effect of irradiation temperature on embrittlement. The preliminary results of the irradiation program show an average temperature effect of 38°C for a 28°C difference in irradiation temperature. The results suggest that for nickel bearing steels, the superior toughness of plate surface material is maintained after irradiation and for the copper content tested, nickel has little effect on irradiation response. No apparent microstructure effect on irradiation response was noted and the HSST-02 material's response to irradiation was similar to results from power reactor and other test reactor tests, thus qualifying the Ford Test Reactor for irradiation experiments such as those conducted for the Yankee Atomic program.     

Syngas yield during pyrolysis and steam gasification of paper

Main characteristics of gaseous yield from steam gasification have been investigated experimentally. Results of steam gasification have been compared to that of pyrolysis. The temperature range investigated were 600–1000 °C in steps of 100 °C. Results have been obtained under pyrolysis conditions at same temperatures. For steam gasification runs, steam flow rate was kept constant at 8.0 g/min. Investigated characteristics were evolution of syngas flow rate with time, hydrogen flow rate and chemical composition of syngas, energy yield and apparent thermal efficiency. Residuals from both processes were quantified and compared as well. Material destruction, hydrogen yield and energy yield is better with gasification as compared to pyrolysis. This advantage of the gasification process is attributed mainly to char gasification process. Char gasification is found to be more sensitive to the reactor temperature than pyrolysis. Pyrolysis can start at low temperatures of 400 °C; however char gasification starts at 700 °C. A partial overlap between gasification and pyrolysis exists and is presented here. This partial overlap increases with increase in temperature. As an example, at reactor temperature 800 °C this overlap represents around 27% of the char gasification process and almost 95% at reactor temperature 1000 °C.     

Waste pyrolysis and generation of storable char

Sustainable cities require the generation of energy from waste that cannot be economically reused or recycled. This study focuses on slow pyrolysis that can generate a high yield of char along with liquid and gas products from waste. Char is high in energy content, storable and transportable with low cost so that it can be used as an intermediate medium for high efficiency energy conversion. Pre‐processed municipal waste pellets, wood and grass were pyrolysed in a batch type reactor for a final temperature ranging from 350 to 700°C, and the char products were characterized. The mass yields of char ranged from 55 to 20% for the tested temperature range, recovering 70–30% of energy and 62–30% of carbon in the raw material. The gross calorific value of char was 30–35 MJ kg^?1 on a dry ash free basis. The ash content of raw materials was a key parameter for the quality of char, since its proportion increased by 2–4 times in char depending on the mass yield. A significant amount of volatile metals such as Hg, As and Pb in the waste sample was evaporated at 500°C. Therefore, evaporation of volatile metals was another important parameter in determining the pyrolysis temperature and fuel residence time. The char did not show significant morphological change in the tested range of temperatures. It was concluded that slow pyrolysis of waste for char production should be performed below 500°C in order to increase the energy yield and also to reduce the evaporation of heavy metals. Copyright © 2006 John Wiley & Sons, Ltd.     

Heat exchanger design: Optimal thickness (under natural convective conditions) of vertical rectangular fins protruding upwards from a horizontal rectangular base

Steady-state rates of heat transfer from an array of vertical, rectangular polished duralumin fins under natural convective conditions have been measured. The horizontal base, which was manufactured of the same material, was kept at the uniform temperature of either 20·0 (±0·2)°C or 40·0 (±0·2)°C above the local air temperature of 20 (±0·2)°C.

The optimal thickness of the fins in this array, corresponding to a maximum rate of heat dissipation, was deduced. For a base of width 190 mm and length 500 mm, the optimal thickness for fins of 60 mm protrusion rose from 2·0 mm to 4·5 mm when the fin separation was increased from 20 mm to 60 mm. This optimal fin thickness was almost invariant with respect to the change of the considered base temperature.     

Effect of particle size on pyrolysis of single-component municipal solid waste in fixed bed reactor

According to the differences in components, three representative components (plastic, kitchen garbage and wood) in municipal solid waste (MSW) were pyrolyzed in a fixed bed reactor to evaluate the influence of particle size on pyrolysis performance of single-component municipal solid waste (MSW). The bed temperature was set at 800°C and each sample was separated into three different size fractions (0–5 mm, 5–10 mm and 10–20 mm). The results show for all the samples particle size has an effect on pyrolysis product yields and composition: smaller particle size results in higher gas yield with less tar and char; the decrease of particle size can increase H₂ and CO contents of gas, as well as the ash and carbon element contents in the char. And the influence is the much more significant for sample with higher fixed carbon and ash contents, such as kitchen garbage, and less for sample with higher volatile content, plastic in the test.