Fuel Processing Technology (v.158, #C)
Editorial Board (IFC).
Environmentally benign halloysite clay nanotubes as alternative catalyst to metal nanoparticles in H2 production from methanolysis of sodium borohydride by Nurettin Sahiner; Sultan Butun Sengel (1-8).
Here, for the first time a natural clay, halloysite nanotubes (HNTs) was used as catalyst in H2 generation from methanolysis of sodium borohydride (NaBH4). The natural HTNs were modified with (3-aminopropyl)triethoxysilane (APTES) and then threated with HCl to obtain mod-HNTs (HNTs-NH2·HCl) as natural catalysts. The catalytic activity of mod-HNTs was found to be comparable for the very well-known metal nanoparticle catalysts used for the same purpose in the literature. Moreover, the activation energy, enthalpy and entropy are calculated 30.41 kJ·mol− 1, 27.93 kJ·mol− 1, and − 163.27 J·mol− 1·K− 1, respectively and are also comparable with metal nanoparticle catalysts that are used in H2 generation reactions. Interestingly, the mod-HNT catalysts showed greater reusability with catalytic activity (91%) after 10th usage having 100% conversion at each time. Additionally, H2 generation rate of about 220.5 mLmin− 1 g− 1 catalyst which is comparable to most of the reported good catalyst up to date.Display Omitted
Keywords: Natural clay catalyst; Halloysite nanotubes catalyst; Environmentally benign catalyst; H2 production; NaBH4 methanolysis;
Characterization of cold densified rice straw briquettes and the potential use of sawdust as binder by Sheikh Aminur Rahaman; P. Abdul Salam (9-19).
This study investigated the effect of particle size, pressure and mold diameter on the physical characteristics of rice straw briquettes. The briquettes were prepared utilizing a manually operated piston-press cold densification system and analyzed in terms of initial density, stable density, density ratio, compaction ratio, percentage of volume change, shatter index and energy consumption. Reduction of mold diameter significantly (p < 0.05) improved briquettes stable density and reduced compaction pressure requirement. Particles of < 2.5 mm or 0.1–150 mm, pressure ≥ 27.6 MPa and mold diameter of ≤ 51 mm should be used to prepare cold densified rice straw briquettes of higher stable density and durability. Interestingly, the briquettes of 0.1–150 mm particles showed significantly (p < 0.05) higher shatter index of > 0.90 even at lower pressure at a cost of stable density. The use of sawdust as binding material at 3:1 and 1:1 mixing ratios increased briquettes stable density > 600 kg/m3, improved shatter index significantly (p < 0.05), increased heating value by 6–7.2%, and reduced ash content from 13.61% to 10.3% and 6.93%, respectively. The energy consumed for briquette preparation accounted 5.6–7.5% and 11.1–13% of the energy which was stored in rice straw briquettes for large and small mold respectively.
Keywords: Rice straw; Sawdust; Piston-press cold densification; Compaction pressure; Mold diameter; Shatter index;
Polyethylene glycol oligomers as green and efficient extractant for extractive catalytic oxidative desulfurization of diesel by Yong Chen; Hongyan Song; Hong Meng; Yingzhou Lu; Chunxi Li; Zhigang Lei; Biaohua Chen (20-25).
An efficient and green extractive catalytic oxidative desulfurization (ECODS) process is developed for diesel by using polyethylene glycol (PEG) oligomers, H2O2 and a phosphotungstate based poly ionic liquid (HPW-PIL) as extractant, oxidant and catalyst, respectively. The PEG oligomers with repeating glycol units of 0, 4 and 8 are determined as the best extractants among acetonitrile, methanol, DMF, [BMIM]BF4, and PEG-2000 with comprehensive characteristics like non-toxicity, non-volatility, low cost, easy recycling, and good desulfurization performance. Benzothiophene (BT) and dibenzothiophene (DBT) in model oil can be removed completely within 2 h at the following conditions: PEG oligomer/oil = 0.2 (mass ratio), H2O2 usage of O/S = 20 (mole ratio), HPW-PIL catalyst/oil = 1/100 (mass ratio), at the temperature of 353 K. And the desulfurization ability of the present process can be retained as 99% even after six successive reuses without regeneration. Further, the S-content in real diesel can also be reduced from 110 to 9.3 ppm-S by the ECODS process followed by AlCl3 adsorption for the oxidized diesel. Meanwhile, the PEG extractant and the HPW-PIL catalyst can be facilely regenerated and recycled.
Keywords: Oxidation; Desulfurization; Diesel; Poly ionic liquid; Polyethylene glycol oligomers;
Mass loss rates for wood chips at isothermal pyrolysis conditions: A comparison with low heating rate powder data by Lina N. Samuelsson; Kentaro Umeki; Matthaus U. Babler (26-34).
Spruce chips of three different thicknesses were pyrolyzed isothermally in a vertical furnace macro-TGA at 574 to 676K, which is the temperature range relevant for char production. The measured mass loss data was analyzed in terms of mass loss rate, thermal lag and char yield as a function of chip size and pyrolysis temperature. The char yield decreased with increasing temperature and there was no significant difference in char yield as a function of sample thickness, ranging from 1mm to 7mm. Thermal lag was present for all chip sizes above 600K. At 574K the data suggests that chips below 1mm in thickness are decomposing at rates governed by reaction kinetics. An isoconversional kinetic model based on low heating rate data of spruce powder was adopted to analyze the data. The model predicted lower mass loss rates than those measured for the chips, suggesting that the pyrolysis process of wood proceeds through a network of parallel reactions. Despite this, the model could predict the final char yield of the wood chips with an accuracy above 80%. The predictive capability of the isoconversional reaction rate expression is promising since the procedure to derive such a rate expression is straight-forward, compared to the conventional model-fitting methods. The data and modeling approach presented in this work is important to the field of biomass pyrolysis as it covers the temperature range and chip sizes relevant for pyrolysis in multi-staged gasification plants which has been given little attention.
Keywords: Pyrolysis; Biomass; Isoconversional; Spruce; Char;
Review on chemical upgrading of coal: Production processes, potential applications and recent developments by Moshfiqur Rahman; Deepak Pudasainee; Rajender Gupta (35-56).
Coal is a major source of energy. In order to overcome the operational problems and environmental issues related to direct utilization of coal, coal upgrading research and development works are in progress in terms of moisture removal, demineralization, removal of harmful constituents such as sulfur, mercury etc. There have been two major approaches to achieve this: dissolving minerals out of coal – the product is termed as ultra clean coal (UCC) and solvent extraction of coaly matter – the product termed as ash-free coal (AFC). In this paper, current knowledge regarding chemical upgrading of coal has been reviewed. In particular, production process and effects of various parameters on yield and product quality have been discussed. The potential applications of the demineralized coals and the economic assessment with respect to commercialization of this process have also been presented.Chemical treatment processes have been demonstrated as the most effective techniques for removal of ash forming minerals from coal to produce coal with minimal or almost no ash. In general, the ash content of UCC is reported within the range of 0.15 to 0.6% either by treating bituminous coal with HF followed by HCl or HNO3. Most effective treatment available in literature is HF followed by HNO3, achieving ash content as low as 0.15%. Organic solvents like polar, non-polar and mixed solvent have been used to extract the organic matters from coal to produce AFC. In general, extraction yield has been found higher at high treatment temperature with polar solvents.The advantages of using UCC and AFC are that they emit lesser pollutants and cause less or no abrasion/erosion and fouling/slagging in the boilers. However, the literature on economic evaluation of AFC applications is scarce and needs to be carried out in future.Conceptual diagram of producing A) clean coal, B) UCC and C) AFC, and their characteristics.Display Omitted
Keywords: Chemical upgrading of coal; Ultra-clean coal; Ash-free coal; Applications of UCC/AFC; Clean energy;
Numerical study of methane steam reforming and methane combustion over the segmented and continuously coated layers of catalysts in a plate reactor by Mayur Mundhwa; Christopher P. Thurgood (57-72).
Four separate 2D steady state numerical models are developed for a catalytic plate reactor (CPR), designed with the four different configurations between segmented and continuously coated layers of combustion and reforming catalysts for hydrogen production by combustion assisted methane steam reforming (MSR). MSR is simulated on one side of a plate by implementing experimentally validated surface microkinetic model for nickel/alumina catalyst. Required heat to an endothermic MSR is provided by simulating catalytic methane combustion (CMC) on an opposed-side of the plate by implementing reduced surface microkinetic model for platinum/alumina catalyst. Four different combinations of coating configurations between reforming and combustion catalysts are studied in terms of reaction heat flux and reactor plate temperature distributions as well as in terms of methane and hydrogen mole fraction distributions. These combinations are: (1) continuous combustion-catalyst and continuous reforming-catalyst (conventional CPR design), (2) continuous combustion-catalyst and segmented reforming-catalyst, (3) segmented combustion-catalyst and continuous reforming-catalyst, and (4) segmented combustion-catalyst and segmented reforming-catalyst. For the same reforming-side gas hourly space velocity, the study has shown that the CPR designed with the segmented catalysts requires 66% less combustion-catalyst to achieve similar methane conversion and hydrogen yield in MSR compared to the conventional CPR design. The study has also shown that maximum reactor plate temperature, thermal hot spots and axial thermal-gradients are reduced significantly in the CPR designed with the segmented catalysts than the CPR designed with the conventional continuous catalysts configuration.Display Omitted
Keywords: Methane steam reforming; Methane combustion; Surface microkinetic; Catalytic plate reactor; Segmented reforming catalyst; Segmented combustion catalyst;
Modelling and experimental studies on oxy-fuel combustion of coarse size coal char by Shyamal Bhunia; Anup Kumar Sadhukhan; Parthapratim Gupta (73-84).
Oxy-fuel combustion of single coarse sub-bituminous coal char particle is investigated in an isothermal mass loss apparatus. Experimental studies are performed at the reactor temperature of 1100 K and in varying O2 concentrations of 42–60% in both O2-CO2 and O2-N2 environments. A fully transient model is developed for the combustion and gasification reactions including the transport of heat and mass in the porous char particle and the gas film. The model is validated with experimental findings of the present authors as well as that reported in literature over a wide range of O2 concentrations. Simulation study is carried out to assess the effect of the particle size, the reactor temperature and the gas composition. The simulation shows that low diffusivity of O2 within the reactor in CO2 environment and the endothermic gasification reaction are mainly responsible for lowering the peak temperature and the rate of combustion of char than that in O2-N2 environment. It is also observed that though the effect of CO2 on the combustion rate at low temperatures is insignificant, it is considerable at the reactor temperature of 1273 K and above in O2-CO2 environment. The model is expected to provide vital information for reactor design under oxy-fuel combustion and its integration with CFD analysis for identifying the optimum particle size, reactor temperature and oxygen concentration.
Keywords: Oxy-fuel combustion; Coal char; Isothermal mass loss apparatus; Modelling; Simulation;
Catalytic ethylene production from ethanol dehydration over non-modified and phosphoric acid modified Zeolite H-Y (80) catalysts by Jiah Chee Soh; Soo Ling Chong; Sk Safdar Hossain; Chin Kui Cheng (85-95).
The present work reports on the effects of phosphoric acid-modified Zeolite-Y towards ethylene formation from ethanol dehydration. The catalyst was impregnated with different H3PO4 loadings from 10 to 30 wt%. All the catalysts were characterized using N2-physisorption, thermogravimetric analysis, NH3-TPD, FTIR, SEM-EDX, X-ray diffraction and XPS techniques. The non-modified Zeolite-Y with Si/Al 80:1, H-Y (80) was found to exhibit excellent catalytic activity owing to the presence of weak acid sites that was able to protonate the hydroxyl group of ethanol. Although ethanol conversion dropped with phosphorus modified catalysts, it was found that the modified Zeolite-Y with 10 wt% H3PO4 can achieve 99% selectivity to ethylene at 723 K and ethanol partial pressure of 16 kPa. Overall, ethanol conversion and ethylene selectivity decreased in the order of H-Y (80) > 10P/H-Y (80) > 20P/H-Y (80) > 30P/H-Y (80). The decrease in ethanol dehydration activity of phosphorus modified catalysts can be ascribed to the reduced BET specific surface area and pore volume due to the surface coverage by layers of H3PO4, consequently, hindering ethanol access to the active site. However, the spent phosphorus modified Zeolite-Y catalyst consistently showed less carbon formation compared to the undoped catalyst. This could be due to the reduction in strong acid sites and also hindering of C2H5OH from travelling deep into the pore networks of H-Y (80), therefore reducing the residence time with the consequence of minimizing the carbon laydown.
Keywords: Dehydration; Ethanol; Ethylene; Phosphoric acid; Zeolite-Y;
Low-temperature dry reforming of methane to produce syngas in an electric field over La-doped Ni/ZrO2 catalysts by Tomohiro Yabe; Kenta Mitarai; Kazumasa Oshima; Shuhei Ogo; Yasushi Sekine (96-103).
Dry reforming of methane (DRM) was conducted over various transition metal supported ZrO2 catalysts in an electric field. Catalyst of 1wt%Ni/10 mol%La-ZrO2 showed high DRM activity even at 423 K of external temperature, at which no DRM proceeds in the conventional catalytic systems. By virtue of the low reaction temperature, low amounts of carbon deposition were confirmed even in conditions of high CH4 conversion in the electric field. The imposed electric power was correlated to with the catalytic activities in the electric field. Syngas is producible at low temperature with high energy efficiency.Graphical abstractDisplay Omitted
Keywords: Dry reforming of methane; Carbon dioxide utilization; Electric field; Low temperature catalytic reaction; Low carbon deposition;
Development of semi-parallel reaction model of devolatilization and heterogeneous reaction for pulverized coal particles by Shota Akaotsu; Junichi Tanimoto; Tatsuya Soma; Yasuhiro Saito; Yohsuke Matsushita; Hideyuki Aoki; Akinori Murao (104-114).
A semi-parallel reaction model for the devolatilization and heterogeneous reaction of coal particles during pulverized coal combustion was developed. The quasi-steady mass transfer around a single coal particle with devolatilization and the oxidation of char were analyzed to investigate the effect of the convective flow generated by devolatilization on the mass transfer of the oxidant to the particle surface at various reaction temperatures and particle diameters. The oxidation rates of char with devolatilization were lower than those without devolatilization. This tendency became pronounced with increasing reaction temperature and particle diameter. This indicated that the convective flow generated by devolatilization inhibits the mass transfer of the oxidant to the particle surface and that the influence of the devolatilization depends on the reaction temperature and particle diameter. In addition, the oxidation rates estimated by the semi-parallel reaction model were compared with those obtained from the conventional sequential reaction model and parallel reaction model. In contrast to the other models, the semi-parallel reaction model more accurately represented the decrease in char oxidation rates with increasing devolatilization rate.
Keywords: Pulverized coal combustion; Devolatilization; Mass transfer rate; Semi-parallel reaction;
Viscosity fluctuation behaviors of coal ash slags with high content of calcium and low content of silicon by Xia Liu; Guangsuo Yu; Jianliang Xu; Qinfeng Liang; Haifeng Liu (115-122).
This work aims to study the ash slagging behaviors of two specific coals, on account of a blocking problem of the slag discharge encountered when these coals were used in an industrial entrained-flow gasifier. Through the measurements of the ash fusion temperatures (AFTs) and the slag viscosities of the two coal samples, it was found that while the coal ashes had sufficiently low AFTs, they exhibited a strong viscosity fluctuation as well as a slag foaming and expansion. By comparing to the slagging behaviors of some artificial ash mixtures, it was ascertained that while the enrichment of sulfate in the coals ashes was responsible for the slag foaming and expansion, the viscosity fluctuation was attributed to a high content of calcium together with a low content of silicon in the coal ashes. With the help of X-ray diffraction (XRD) analysis and FactSage thermochemical modeling, it was found that the presence of a crystalline gehlenite phase during the slagging process for the two coal ashes was closely related to the slag viscosity fluctuation. The addition of silica to the coal ashes could virtually eliminate the slag viscosity fluctuation. The sand (a silica rich mineral) addition method had also been successfully used in the industrial gasifier.
Keywords: Entrained-flow gasification; Coal; Slagging; Viscosity;
Experimental study of kukersite oil shale pyrolysis by solid heat carrier by Gennady Gerasimov; Vladimir Khaskhachikh; Oleg Potapov (123-129).
The investigation of oil shale pyrolysis in the experimental retorting system by solid heat carrier (silica sand) was conducted. Modeling of the heat and mass transfer processes in the retorting system was performed with use of simplified mathematical model. It was shown that the radiation heat exchange plays the main role in the heat transfer between oil shale particles and solid heat carrier under the conditions of volatiles release. The maximum yield of the shale oil amounts to 73% at temperature of experiment of 560 °C, which exceeds the data obtained in the Fisher assay on 20%. The conditions that lead to increase in maximum yield of shale oil in the industrial UTT units with the rotary drum reactor were ascertained. They are mainly associated with a decrease in the solid heat carrier (ash) temperature, which leads to the inhibition of secondary reactions between ash and the acidic compounds of the shale oil.
Keywords: Oil shale pyrolysis; Solid heat carrier; Shale oil yield; Heat and mass transfer; Decomposition kinetics; Rotary drum reactor;
Ni supported on γ-Al2O3 promoted by Ru for the dry reforming of methane in packed and monolithic reactors by Igor Luisetto; Caterina Sarno; Daniele De Felicis; Francesco Basoli; Chiara Battocchio; Simonetta Tuti; Silvia Licoccia; Elisabetta Di Bartolomeo (130-140).
Dry reforming (DRM) is as an efficient way for CH4 and CO2 valorisation because the produced syn-gas has an H2/CO ratio equal to that suitable for the synthesis of oxygenated hydrocarbons and synthetic fuels. The development of Ni (10 wt%) based structured and unstructured catalysts promoted by a small amount of Ru (0.5 wt%) for DRM has been investigated. Unstructured catalysts were prepared by wet impregnation method and a combination of wash coating-wet impregnation methods was used for cordierite monoliths. Samples were characterized by XRD, BET, H2-TPR, TEM, FE-SEM, XPS techniques and the catalytic activity for DRM was evaluated in the temperature range 600–800 °C. The catalyst stability was followed at 800 °C during time on stream. Ru promoted catalyst (Ni-Ru) was remarkable active and stable whereas Ni catalyst deactivated due to the formation of Ni2 +-containing inactive phases. Ni-Ru monolith was initially much more active than monometallic Ni stating the positive effect of Ru on maintaining Ni reduced. Reaching steady state condition, Ni rapidly deactivated due to carbon formation, whereas Ni-Ru monolith remained stable confirming that Ru behaves as an efficient and cheap promoter of Ni for DRM.Display Omitted
Keywords: Ni/Al2O3; NiRu/Al2O3; Structured catalyst; Dry reforming of methane; Carbon deposition;
An approach for on-line analysis of multi-component volatiles from coal pyrolysis with Li+-attachment ionization mass spectrometry by Lu Zhang; Shi-Chao Qi; Keita Iwanaga; Kazuhiro Uemura; Li-Xin Zhang; Shinji Kudo; Jun-ichiro Hayashi; Kenji Furuya; Koyo Norinaga (141-145).
Ion-attachment mass spectrometry (IAMS) is a technique used for measuring easily ionized organic compounds in a non-fragmenting mode by softly attaching a Li+ or another type of alkaline ion to the gaseous molecule. In this study, a prototype device for Li+ IAMS is developed for real-time quantitative monitoring of the vapor produced from thermochemical conversion of coal. Simulated tar vapor containing a suite of aromatics and the real vapor produced from the pyrolysis of coal are monitored by IAMS with a Li+ source. It is confirmed that both the simulated and real vapors are ionized without undergoing fragmentation and the sensitivities of these detected aromatic molecules are similar to one another. In addition, when the feeding rate of the coal sample is changed from 0.5 to 1.0 g/min, the peak intensities increase nearly twice as much. These results show the possibility of applying IAMS to the quantitatively monitoring of coal-derived volatiles.
Keywords: Coal tar monitoring; On-line analysis; Aromatic carbons;
Thermal properties of lignocellulosic precipitates from neutral sulfite semichemical pulping process by Dmitry Tarasov; Mathew Leitch; Pedram Fatehi (146-153).
In a neutral sulfite semichemical (NSSC) pulping process, wood chips are pretreated with sodium sulfite and sodium carbonate solution. This pretreatment dissolves a part of hemicellulose and lignin from wood chips. The spent liquor (SL) that is produced in the pretreatment process contains a considerable amount of lignosulfonate and hemicelluloses, but SL is generally treated in the wastewater effluent system of the mills (i.e. lignocelluloses are wasted). In this paper, these lignocelluloses were separated from SL with organic solvents, and their thermal properties were determined. The results showed that the precipitates isolated from SL/acetone, SL/ethanol or SL/isopropyl mixtures with the weight ratio of 67/33 had the highest heating values of 18.61, 17.59 and 17.05 MJ/kg, respectively. The precipitates made from mixing acidified SL and solvents had lower heating values than those made from mixing untreated SL and solvents, which is likely due to the relatively high ash content of the precipitates made from mixing acidified SL and solvent. The theoretical and experimental heating values of precipitates were compared in this work. The precipitates displayed lower ignition temperatures compared with other biomass-based solid fuels, implying that the combustion of precipitates would require lower activation energies.
Keywords: Lignosulfonate; Heating value; Biofuel; TGA; DSC; Spent liquor;
Methane hydrate combustion by using different granules composition by S.Y. Misyura; I.G. Donskoy (154-162).
Dissociations of methane gas hydrate during gas combustion were investigated. The anomalous behavior of a sample was revealed after termination of combustion and long stay of powder at the ice melting temperature (“secondary self-preservation of methane”). Increasing storage temperature and transport of natural gas hydrate are the important scientific and technical problems. The effect of combustion on decay of gas methane clathrate is considered using the important key parameters: powder layer height, external heat flux, granules composition. Existing methods of combustion modeling use a simplified one-dimensional case of kinetic combustion without taking into account the granule size and thickness of the hydrate layer. In the present research, the boundary dissociation conditions at non-stationary combustion were determined from the experiment data. The heat flux before combustion was constant and it was controlled by the ambient air temperature. During combustion, the heat flux increased by an order, and its value was determined experimentally. Currently, when simulating non-stationary combustion of СH4 gas hydrate, constant flows of combustible gasses were used. In reality, magnitudes of mass gas flows vary by several orders in time. As a result, CH4 combustion occurs under the non-stationary and non-isothermal regime in violation of stoichiometric ratio. The proposed model allowed us to connect the non-stationary gas flows with decomposition kinetics of gas clathrate. Thus, chemical reaction kinetics is controlled by means of the internal transfer processes. The existing predictions for describing the decomposition at negative temperatures did not take into account the structural parameters of particle surface as well. As a result, these simplified models incorrectly described the decomposition process. It is shown that non-uniform distribution of particle sizes and thick powder layer will result in unsteady dissociation and hydrate burning and this will lead to a decrease in combustion efficiency.Display Omitted
Keywords: Hydrate combustion; Energy storage and transportation; Hydrate dissociation; Granule composition; Kinetics;
Pyrolysis of large mallee wood particles: Temperature gradients within a pyrolysing particle and effects of moisture content by MD Mahmudul Hasan; Xun Hu; Richard Gunawan; Chun-Zhu Li (163-171).
Temperature profiles inside a large pyrolysing particle were studied and are reported in this paper. Mallee trunks of similar diameter from the same tree were used to prepare cylindrical samples with 40 mm length. A fluidised-bed reactor was used to pyrolyse the large particles. The temperature profiles inside the particles were recorded during pyrolysis to allow the calculation of corresponding heating rate profiles inside the particle. The effects of moisture were studied by pyrolysing some particles with 15 to 20% moisture content. The temperature profiles obtained from the pyrolysis of dry and wet samples have been compared to identify the possible effects of moisture on the temperature profiles. A possible change in the thermal conductivity of the wood was identified around 100 °C, which caused a peak in the heating rate profile. Some possible exothermic peaks were observed at around 325 °C and 425 °C. A peak in the heating rate profile at around 200 °C in the case of the pyrolysis of wet particles was believed to be related to the changed 3-D macromolecular structure of the biomass in the presence of moisture. Some yields of tar and char along with other analytical results were presented to support our observations on the temperature profiles. Our results indicate that moisture can potentially alter the overall pyrolysis reactions and product distribution, in particular through changes in the 3-D macromolecular structure of biomass.Display Omitted
Keywords: Pyrolysis; Large particles; Mallee wood; Temperature profile; Heating rate; Moisture;
Performance of the primary air concentrators on anthracite ignition and combustion in a 600 MW supercritical arch-fired boiler by Pengyuan Liu; Jiajia Gao; Hai Zhang; Dalong Zhang; Yuxin Wu; Man Zhang; Junfu Lu (172-179).
A set of comprehensive on-site experiments was conducted to assess the performance of the louver-type primary air (PA) concentrators on anthracite ignition and combustion in a 600 MW supercritical arch-fired boiler (AFB) equipped with slot burners. The temperature profiles along the PA stream from fuel-rich and fuel-lean streams were measured under various conditions. The separation efficiency of the PA concentrators of two selected burners was also measured and its effect on the ignition of the PA streams was studied. Experimental results revealed that separation performance of some louver concentrators was even opposite to design setting. The ignitability of PA stream, however, was more profoundly depended on the configuration of burner, the position of the nozzle and the SA distribution than the separation performance of the louver concentrators. On the other hand, confirmed by numerical simulation, the unsatisfied separation performance of the louver-type concentrators could result in overall poor ignition of PA, causing over-shooting of the flame penetration length, and high loss of ignition and difficulties for combustion organization. Some suggestions are given to the retrofit and new design of combustion system.Display Omitted
Keywords: Arch-fired boiler; Primary air concentrator; Combustion; Ignition; Louver concentrator;
Evolution of structure and activity of char-supported iron catalysts prepared for steam reforming of bio-oil by Yi Wang; Long Jiang; Song Hu; Sheng Su; Yingbiao Zhou; Jun Xiang; Shu Zhang; Chun-Zhu Li (180-190).
The aim of this study is to investigate the changes in iron phase, crystal size, surface area, and char structure/reactivity of the char-supported iron catalysts after them being used for bio-oil reforming. The catalysts were prepared under different conditions (varying in temperatures, gasification agents and iron concentrations) and then used to reform bio-oil under a fixed experimental condition at 800 °C. The results show that the catalysts prepared from the steam gasification of Fe-loaded coal were preferred in terms of catalytic performance. The X-ray diffraction analysis indicates that the iron phases in the fresh catalysts varied while the used catalysts nearly showed identical iron phase of magnetite (Fe3O4). The crystal iron particle in the catalysts would apparently increase after reforming when the initial iron phase was carbides (γ-Fe and/or α-Fe). The char structure of the catalysts was significantly affected by the ‘volatile-char interactions’ during reforming process. And the catalysts' surface area and reactivity in air were both reduced mainly due to the coke formation.
Keywords: Bio-oil; Catalytic reforming; Char-supported iron catalyst; Char structure; Volatile-char interaction;
Characterization of oil shale pyrolysis by solid heat carrier in moving bed with internals by Dengguo Lai; Guangyi Zhang; Guangwen Xu (191-198).
Oil shale pyrolysis by solid heat carrier in moving bed with internals (MBI) was investigated with the aim to identify the effect of oil shale properties (moisture content and particle size) and heat carrier types on the physicochemical properties and distributions of pyrolysis products. Pyrolysis of oil shale with high moisture content of 10 wt% caused obvious increase in shale oil yield due to the protective effect of steam atmosphere by its reducing secondary reactions and also catalysis action of shale ash. The obtained highest shale oil yield was close to the yield of Fischer Assay. Pyrolyzing dried oil shale produced shale oil containing more light oils (gasoline and diesel) and allowed higher gas yield. Pyrolysis of large size (i.e. > 10 mm) oil shale reduced oil yield but increased light oil content due to the required long time for heat transfer and intra-particle volatile diffusion. Comparing with ceramic balls, shale ash as the heat carrier presented a favorably catalytic effect on cracking and upgrading of shale oil. With increasing pyrolysis temperature from 465 to 525 °C, using shale ash greatly raised light oil content by 10.24% (relatively), considerably reduced the content of heteroatomic compounds, and promoted the conversion of aliphatics to aromatics. Shale ash carrier particles enabled better dust removal than ceramic balls did to attain oil product with a dust content below 0.2 wt%. Generally, oil shale pyrolysis using shale ash heat carrier in MBI process has obvious effects of in-situ shale oil upgrading and in-bed dust removal to allow good pyrolysis performance.
Keywords: Pyrolysis; Oil shale; Internals; Steam atmosphere; Shale ash; Ceramic balls;
A plasma-assisted catalytic system for NO removal over CuCe/ZSM-5 catalysts at ambient temperature by Tao Wang; Hanzi Liu; Xinyu Zhang; Yonghong Guo; Yongsheng Zhang; Yang Wang; Baomin Sun (199-205).
A series of CuCe catalysts were prepared by an incipient-wetness impregnation method for selective catalytic reduction of NO in combination with dielectric barrier discharge plasma. The effect of the Cu/Ce mass ratio on NO and NOx (NO + NO2) removal efficiency has been studied as a function of energy density at ambient temperature. The catalyst samples were characterised by BET, XRD, XPS, H2-TPR and NH3-TPD. The results indicated that catalyst addition enhances NO and NOx removal based on only the plasma process. The CuCe catalysts exhibited higher reduction performance compared with the 4 wt.% Cu or 4 wt.% Ce catalysts, and the catalyst with 4 wt.% Cu and 4 wt.% Ce showed the best reduction performance with the highest NO and NOx removal efficiencies of 90.7% and 80.1%, respectively, at an energy density of 367 J/L. The interactions between Cu and Ce increase oxygen migration to form oxygen vacancies, which facilitates the oxidation of NO to NO2, and NO2 favours NO removal via a fast selective catalytic reduction reaction at low temperature. In addition, the CuCe catalysts exhibited low thermal stability, thereby facilitating the catalytic reduction of NO at ambient temperature.Display Omitted
Keywords: Dielectric barrier discharge; NO; CuCe/ZSM5; Catalyst;
Relationship between chemical components and coal ash deposition through the DTF experiments using real-time weight measurement system by Hueon Namkung; Li-Hua Xu; Kuangfei Lin; Guangsuo Yu; Hyung-Taek Kim (206-217).
The chemical components of ash in coal are important factors affecting the ash deposition in the entrained-flow gasification process. Most previous research aimed at investigating pertinent chemical components affecting ash deposition has focused on the deposited sample after experiments without consideration of the time frame to verify the relationship between ash chemical components and deposition. However, this study examined the relation of the chemical components to the ash deposition by using the drop tube furnace (DTF), in which a real-time weight measurement (RWM) system had been installed. The RWM system, capable of recording the amount of deposited ash per second, was specifically developed for this work. Three pulverized coal samples, in the range of bituminous and sub-bituminous coal, were employed in the DTF experiments to compare the relationship between the ash chemical components and deposition. It was found that the ash deposition behavior in a real-time was related to the presence of Fe and Ca components, and high concentrations of these components tended to increase the deposition rate. The ash deposition could be diverse by maintaining or decreasing the Fe and Ca components, which are responsible for fouling growth.
Keywords: Entrained-flow coal gasification; Real-time measurement; Fouling; Chemical component;
Facile preparation of PtSn-La/Al2O3 catalyst with large pore size and its improved catalytic performance for isobutane dehydrogenation by An-hua Dong; Kang Wang; Shi-zhen Zhu; Gong-bing Yang; Xi-tao Wang (218-225).
Al2O3 beads with various pore sizes were successfully synthesized by combining ammonium alginate assisted sol-gel and emulsion template methods using liquid paraffin as pore-enlarging agent and polysorbate 80 as dispersant. The great influences of textural structure of Al2O3 beads on the activity and stability of PtSn-La/Al2O3 catalyst for isobutane dehydrogenation were investigated by N2 adsorption-desorption, XRD, NH3-TPD, SEM, HRTEM, H2-TPR, XPS, isobutene transient response experiment and TG analysis. The results showed that Al2O3 beads with tunable pore sizes (7.4–13.3 nm), surface areas (294-322 m2/g) and pore volumes (0.56–1.1cm3/g) could be obtained by changing the addition amount of liquid oil. Moreover, the transient response experiment stated that the PtSn-La/Al2O3 catalysts with large pore sizes could enhance the diffusion speed of the gas molecule in the channels. With increasing the amount of liquid oil from 0 to 20%wt, the particle sizes of platinum decreased from 2.86 nm to 1.45 nm, the amount of carbon deposit declined by 30.6% and the final yield of isobutene increased from 42% to 48%. The enhancement of catalytic performance of PtSn-La/Al catalyst with larger pore size was related to its smaller Pt particles, lower surface acidity and diffusion resistance of reaction products in the pore.
Keywords: Al2O3 bead; Ammonium alginate; Emulsion template; PtSn-La/Al2O3 catalyst; Isobutane dehydrogenation; Large pore size;
Comprehensive CFD modelling of solar fast pyrolysis of beech wood pellets by José Soria; Kuo Zeng; Daniela Asensio; Daniel Gauthier; Gilles Flamant; Germán Mazza (226-237).
The present work focuses on the study of the solar pyrolysis of beech wood pellets. The biomass degradation process was modelled in the CFD (Computational Fluid Dynamics) platform ANSYS FLUENT 14.0. The results of simulations were compared to experimental tests conducted in a lab-scale solar reactor in order to validate the CFD model. The biomass pyrolysis was carried out at temperatures ranging from 600 to 2000 °C, at two heating rates: 10 and 50 °C/s.This new 2D single particle model represents a significant improvement of previous simpler version, not only because it allows monitoring the evolution of gas speciation but also because its formulation enables to deal with different types of biomass feedstock. The model structure comprises a multi-step complex kinetic framework that involves competitive reactions –including secondary tar reaction- along with rigorous heat and mass (species) transport inside the particle.On this basis, char, tar and gas predicted yields are compared with experimental data. In addition, the gas composition (CH4, CO, CO2, H2 and CxHy) is also compared. CFD results are in good agreement with the experimental values, validating this approach as a useful tool to predict the products yields and their composition when pyrolyzing biomass particles. Furthermore, the model can be used when modelling any process where pyrolysis occurs and it can even be easily coupled to any reactor scale model.
Keywords: CFD; Solar pyrolysis; Beech wood; High temperature; High heating rate; Single particle model;
Stepwise structural characterization of hydrocarbon compounds and polar components during atmospheric residue hydrotreatment by Mei Liu; De-Zhi Zhao; Lin-Zhou Zhang; Suo-Qi Zhao (238-246).
A continuous fixed-bed micro-reactor was adopted to conduct a hydrotreatment experiment on the atmospheric residue obtained from Saudi Arabia. The feedstock and hydrotreated liquid products were subjected to high-temperature gas chromatography to undertake simulated distillation analysis, and to gel permeation chromatography to carry out molecular size investigations. 1H NMR and element analysis were carried out to derive structural parameters. Positive- and negative-ion electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry was combined with other analytical means to explore the stepwise structural characterization of polar components (especially the nitrogen (N)-containing compounds) when passing through beds filled with different catalysts during the hydrotreatment process. According to the different numbers of nitrogen, oxygen, and sulfur atoms, N-containing compounds could be divided into Nx, NxOy, and NxSy class species. The results indicated that hydrotreatment process led to more concentrated distribution of hydrocarbon molecules in the products. The heteroatoms, which accounted for the largest proportion in the feedstock and liquid products, were N1 class species. During the hydrotreatment process, the relative abundance of N1, N2, N1O1, N1O2, and N1S1 class species changed significantly with the progress of hydrotreatment process, however the conversion regularity varied among heteroatomic compounds.
Keywords: Hydrotreatment; Atmospheric residue; Polar components; Characterization;
Syngas production from steam reforming of acetic acid over Ni- and Co-based catalysts supported on La2O3 and AlLaOx by Saioa Goicoechea; Elka Kraleva; Heike Ehrich (247-254).
Ni and Co promoted catalysts supported on single La2O3 and mixed AlLaOx were tested in a fixed bed reactor for the steam reforming of acetic acid. Their performance in AcOH conversion and syngas production was evaluated for its application in solid oxide fuel cells for electricity generation. The samples were prepared with an active metal loading of 10% by wetness impregnation method. The catalytic tests were performed at atmospheric pressure, starting from a steam to acetic acid molar ratio of 2/1, and in the temperature range of 600–800 °C. The catalyst composition was analyzed by in-situ XRD analysis in order to see the phase transformations inside the catalyst from room until reactor temperature. Perovskite structures were observed on both single and mixed oxide supported catalysts. All catalysts were active and showed high selectivity to syngas during the screening tests. The obtained selectivities were close to the thermodynamic equilibrium values. Ni/La2O3 catalyst showed a stable performance up to 33 h.
Evolution of chars during slow pyrolysis of citrus waste by Roberto Volpe; José Miguel Bermudez Menendez; Tomas Ramirez Reina; Antonio Messineo; Marcos Millan (255-263).
Conversion of agro-wastes into energy can be key to a circular-driven economy that could lead to models for sustainable production. Thermochemical processing is an interesting alternative for the upgrading of agro-wastes to energy. However, owing to the complex and largely unknown set of reactions occurring during thermal breakdown, to ensuring consistent quality of the final products is still a goal to achieve at industrial level. The present study investigates the evolution of solid products of pyrolysis, to gain some insights in these complexities. Chars derived from slow pyrolysis (200–650 °C) of citrus pulp in a horizontal reactor have been characterized by means of Fourier Transform Infrared spectroscopy (FT-IR), X-Ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). Results are discussed also in light of similarities with coal thermal breakdown.At temperatures below 300 °C, changes in solid matrix are mainly due to breaking of aliphatic compounds. Significant changes in char structure and behavior then occur between 300 °C and 500 °C mainly related to secondary char-tar reactions. Above 500 °C, changes appear to occur mainly due to recombination reactions within matrix, which thereby becomes progressively less reactive.
Keywords: Citrus waste; Pyrolysis; Char reactivity; Downdraft gasification;
Investigation of reducing ultrafine particulate matter formation by adding modified montmorillonite during coal combustion by Yu Zhang; Xiao-Wei Liu; Yi-Shu Xu; Wei Sun; Ming-Hou Xu (264-271).
Up to now, nearly all sorbents used to reduce the formation of particulate matter (PM) during coal combustion are raw minerals in nature. In this work, a new idea is proposed to improve the control ability by modifying the natural minerals. First, hydrochloric acid (HCl) and hydroxyl polymeric aluminum were selected to modify raw montmorillonite, respectively. Then combustion experiment of pulverized coal alone and that mixed with the raw/modified montmorillonite was performed under O2/N2 atmosphere in a lab-scale drop tube furnace (DTF). The produced PM was collected via a low pressure impactor system (LPI). The results show that the raw montmorillonite reduced the PM0.2 yield by 17.99%. Compared with raw montmorillonite, PM0.2 yield further decreased by 29.00% and 13.11% when acid-treated montmorillonite and aluminum-treated aluminum were added. Further characterization show that the formation of ultrafine PM was reduced mainly because of the chemical reaction between the sorbent and the vaporized alkali metal. More importantly, the modification treatment optimized the surface characteristics of montmorillonite. Moreover, modification treatment increased the number of free oxygen active sites in montmorillonite due to the breakage or formation of certain metallic bonds. These changes promoted the process of capturing alkali metal and thereby the modified montmorillonite showed better performance in reducing PM0.2 formation.
Keywords: Particulate matter; Reduction; Montmorillonite; Modification; Sodium;
Migration and emission characteristics of Hg in coal-fired power plant of China with ultra low emission air pollution control devices by Yi Zhang; Jianping Yang; Xuehai Yu; Ping Sun; Yongchun Zhao; Junying Zhang; Gang Chen; Hong Yao; Chuguang Zheng (272-280).
The emission and migration characteristics of Hg from an ultra low emission (ULE) coal-fired power plant in China was investigated. During the tests, the flue gas was sampled simultaneously at the inlet and outlet of selective catalytic reduction (SCR) system, low temperature economizer (LTE), electrostatic precipitators (ESP), wet flue gas desulfurization (WFGD), and wet electrostatic precipitators (WESP) by EPA 30B method. The feed coal, lime, limestone slurry, process water, fly ash, bottom ash, gypsum, FGD effluent, and WESP effluent were also sampled. The results showed that Hg concentration in flue gas at the outlet of boilers and stacks was in the range of 4.46–5.17 μg/m3 and 0.51–1.22 μg/m3, respectively. The overall gaseous Hg removal efficiencies of SCR + LTE + ESP + WFGD + WESP equipped in the ULE power plant were about 88.5%–89.6%. Mass distribution of Hg in the whole system showed that about 70% of Hg present in solid and liquid combustion products and 30% of Hg emitted into atmosphere. After ULE reformation, the atmospheric emission factor of the power plant is in the range of 0.39–0.81 g/TJ, which is much lower that of power plants before ULE reformation (2.18–2.34 g/TJ). Thus, the ULE reformation for coal-fired plants is beneficial for the reduction of Hg emission to atmosphere.
Keywords: Hg emission; Air pollution control devices; Ultra low emission; Power plants;