1,720,988 research outputs found
Effects of oxygen and steam equivalence ratios on updraft gasification of biomass
No full textSeveral experimental datasets available on the gasification of different lignocellulosic feedstocks were used to correlate the flow of gasifying agents with the performance of updraft gasification in an autothermic 200 kWth pilot plant. The feedstocks used included eucalyptus wood chips, torrefied eucalyptus and spruce chips, lignin rich residues from biorefined straw and reed, shells of almond and hazelnut, which were gasified in flows of air, air and steam, oxygen, oxygen and steam. Thermal profiles inside the gasifier and gas quality in terms of incondensable gas and tar content were recorded and used to calculate the energy efficiency of converting solid feedstock into gaseous and liquid carriers. Common behaviors and parametric functionalities were identified to better understand the process and the most efficient tools to achieve the desired products. In analyzing data, the ratio steam to biomass was reported in terms of the equivalence ratio, ER(H2 O) i.e., the fraction of the stoichiometric quantity required to convert the feedstock into H2 and CO2 . The use of steam was useful to stabilize the process and to tune the H2 /CO ratio in the syngas which reached the value of 2.08 in the case of oxy-steam gasification of lignin rich residues at ER(H2 O) of 0.25. Larger use of steam depressed the process by lowering the average temperature of the bed, which instead increased steadily with ER(O2 ). The production of tar depends on the biomass type and a substantial reduction can be achieved with the torrefaction pretreatment. The same effect was observed increasing the residence time of the syngas in the reactor, typically achieved using oxygen instead of air as main gasification flow or reducing the ER(H2 O). Oxy-steam gasification of torrefied wood led to the best results in terms of cold gas efficiency and low heating value when carried out in the ranger 0.23–0.27 of both the ERs
Steam gasification of agro-industrial lignocellulosic residues from bioethanol industry
No full textBioethanol produced from lignocellulosic biomass is a promising alternative for fossil fuel substitution. Hydrolytic lignin rich residues could be exploited through gasification for more efficient bioethanol production processes. The char gasification is generally one of the slowest thermal steps and a fundamental understanding of the heterogeneous reaction kinetics is needed forreactors design. The aim of this work was to investigate the kinetic behavior of chars from byproducts of 2nd generation bioethanol production. Two chars were studied: hydrolytic reed lignin and hydrolytic wheat straw lignin.Isothermal experiments, using temperatures from 725°C to 825°C were conducted in a thermobalance. The atmosphere was 50%(volmol%)steam and 50%(vol%)N2. Additional tests at 10% and 20% of steam (N2as complement) were performed in order to determine the effect of steam partial pressure. Additional sample characterizations, such as the proximate and ultimate analyses of the two residues, as well as the metals content in chars, and morphological characterization were also performed. The apparent activation energy, Ea, of steam-char reaction was determined at different degrees of char conversion. The results showed that the Eaincreases with conversion for both samples, ranging from 135 to 188 kJ/mol. © 2016 ETA-Florence Renewable Energies
Combustion characteristics of biodiesel saturated with pyrolysis oil for power generation in gas turbines
No full textThere is a perceived need for multi-fuel burner geometries capable of operating with variable composition fuels from diverse sources to achieve fuel flexibility in gas turbines. The objective of the research covered herein is a comparison study between two liquid fuels, a biodiesel (in a pure form) and the biodiesel as a saturated mixture with a pyrolysis by-product; these two fuels were compared against a standard kerosene as a baseline. The research methodology involved two stages: firstly atomization patterns and injection regimes were obtained using a high speed imaging method, secondly a combustion test campaign was undertaken using a swirl burner to quantify the operational behaviour, species production and exhaust gas compositions of the fuels. Emissions, flame stability trends and power outputs were measured at gas turbine relevant equivalence ratios. Excess oxygen and atomization trends in the biodiesel seem to be playing a major role in the production of emissions and flame stability when compared to kerosene. Also, heavy organics seem to be acting as catalytic substances for OH production close to the burner mouth. In terms of stability and combustion, it is proposed that the saturated blend would be a viable candidate for power generation. © 201
Pilot plant air-steam gasification of nut shells for syngas production
No full textAutothermal gasification of hazelnut and almond was carried out and the performances of a pilot plant with a feeding rate of 20-30 kg/h were evaluated. Air, mixes of air with steam and oxygen with steam were used as gasification medium; the gas flows corresponded to different equivalence ratios of combustion, ER(O2), and water reaction, ER(H2O). The recording of the thermal profile inside the reactive bed during the runs made it possible to highlight a sequence of exothermic and endothermic reactions. In the plant tests, the residues were completely converted in gaseous and liquid energy carriers with a cold gas efficiency (CGE) ranging from 61% to 75% while the production of biooil ranged from 90-250 g/kg of fed nutshell (dry basis). The molar ratio H2/CO in syngas increased by using steam as co-gasification agent. Steam was necessary to stabilize the process in the case of using oxygen as main gasification agent. Oxy-steam gasification also provided the best results in terms of syngas heating value and thermal power output of the plant. The tar yield was inversely correlated to the residence time of the gas in the bed, in according with a zero order reaction for tar cracking into incondensable hydrocarbons. © 2017, ETA-Florence Renewable Energies. All rights reserved
Ultrapure hydrogen from biomass syngas by PD/AG membrane reactor
No full textThe work dealt with the enrichment of hydrogen by Water Gas Shift (WGS) reaction in a catalytic Membrane Reactor (MR) starting from a syngas having the typical composition obtained in updraft gasification of lignocellulosics. The used MRs were externally made of Pd-Ag membranes, which exhibit high hydrogen selectivity, and contain a Pt on ZrO2 catalyst. The permeate flow of hydrogen is of ultrapure quality and positively affected the WGS yields that, in optimized conditions, overcame the theoretically expected values in closed system. The experiments were performed in a recently built rig designed to treat up to 0.25 Nm3/h of syngas and explored the operative ranges 300-350°C, 2 -8 bar; H2O/CO molar ratio 2-4. © 2018 ETA-Florence Renewable Energies
Fractionation of olive woody waste (OWW) obtained after milling by hydrothermal pretreatments - Steam explosion and hot water
No full textThe olive woody waste (OWWis a promising feedstock for biorefineries in the Mediterranean region. In order to valorize this lignocellulosic residue, a pretreatment is necessary to fractionate its components and to improve the cellulose enzymatic hydrolyzability. The work target was to compare the efficiency of two physicochemical pretreatments, viz.: Steam Explosion (SE) and Hot Water/OrganoSolv (OS) towards acid fractionation of OWW and enzymatic digestibility of the cellulosic residue. The SE pretreatment was performed with a batch reactor of 10 L, coupled with a 125 kW boiler. The biphasic Hot Water/OrganoSolv (OS) pretreatment was carried out with a high pressure and temperature batch reactor of a 0.5 l vessel with adjustable internal stirrer and heat control. After SE and Hot Water/OrganoSolv (OS) pretreatments the materials were extracted by water to remove and quantify the soluble hemicellulose as monomers and oligomers as well as the inhibitors; the solid residue was saccharified. The digestibility of cellulose was very good in both cases, OS was slightly more effective in terms of sugars recovery. © 2018 ETA-Florence Renewable Energies
Life cycle assessment of hydrogen production from biorefinery residues
No full textGasification of biomass can be used for obtaining hydrogen so reducing the greenhouse gases emissions due the fixation of CO2 during photosynthetic processes. The hydrolytic lignin residue is an appropriate raw material since it does not compete directly with the food chain and can be exploited for producing additional chemicals, power, combined heat and power. Indeed, the optimal use of this residue is a key factor for the economic and environmental sustainability of a bio-refinery, not only disposal costs can be avoided but also additional incomes can be provided. The work dealt the environmental potentials impacts of the production of hydrogen through gasification of this residue and to identify the hotspots of the process. An LCA study was developed for a 200 kWth gasification pilot plant using experimental data. Model was constructed using GaBi software in accordance with LCA leading Standards and ILCD Handbook recommendations. A gate-to-gate analysis of the gasification process was carried out and compared to a reference scenario consisting of hydrogen production by steam reforming of methane. LCA methodology was applied using global warming potential, acidification, eutrophication and the gross energy necessary for the production of 1 kg of hydrogen as impact categories
Thermal conversion of lignin-rich residues from lignocellulose biorefining: From thermogravimetry to updraft gasification
No full textThe reported work deals with the use of lignin rich solid, which is available as residue from enzymatic hydrolysis of lignocellulosic biomass, to produce syngas. The tested process was an updraft gasification carried out at pilot scale of about 20 kg/h as dry feed. The thermal conversion of the residue was investigated by TGA in air, carbon dioxide and nitrogen atmospheres pointing out the relative contribute of pyrolysis, combustion and gasification at different temperatures. In the plant tests, the residue was completely converted in gaseous and liquid energy carriers with overall energy efficiency near 90%. Several process conditions were examined corresponding to different flows of O2 and steam. The molar ratio H2/CO in syngas increased by using steam as co-gasification agent. Steam was necessary to stabilize the process in the case of using oxygen as main gasification agent. Oxy-steam gasification provided the best results in terms of syngas heating value and highest thermal power output of the plant. © 2017, ETA-Florence Renewable Energies. All rights reserved
Gasification of Wood and Torrefied Wood with Air, Oxygen, and Steam in a Fixed-Bed Pilot Plant
No full textIn this work, the efficiency of the updraft gasification of different biomass was analyzed using a 20 kg/h pilot facility. Eucalyptus wood chips, torrefied Eucalyptus wood chips, and torrefied Spruce chips were investigated. Absolute air, mixes of air with steam, and mixes of pure oxygen with steam were used as gasification media. The direct comparison between the parental and torrefied biomass emphasizes the positive effect of this pretreatment on syngas properties and plant performances. Typically, the use of torrefied feedstock resulted in a reduction to about 1/5 of the tar load in the syngas and in 44% increment of the thermal power of the plant when compared to the performances obtained with the parental wood. The introduction of steam as co-gasifying stream was effective to avoid hot spots inside the reactive bed and to stabilize the process. Moreover, the use of steam positively affected the molar ratio of H2/CO that reached the value of 1.17 with the H2 concentration in the syngas of 39 vol %. The cold gas efficiency was 0.85 with torrefied biomass and pure oxygen with steam (0.82 when taking into account the energy for steam production), whereas the use of parental wood in similar conditions gave a value of 0.67 (net of 0.65). The treatment capacity of the plant was directly proportional to the reactivity of the feedstock as assessed by thermogravimetric analysis when the feed was reported as volumetric flow. © 2016 American Chemical Society
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