[Show abstract][Hide abstract] ABSTRACT: The behavior of Cynara cardunculus L. was studied during fluidized-bed (FB) combustion and gasification. The Cynara had a low moisture content and considerable lower heating value (LHV). Cynara presented significant quantities of S, Cl, and ash, which contained high levels of Na, K, P, Ca, and Si. The fuel N conversion to NO x was high because of the large release of NH 3 and HCN during pyrolysis. The conversion of the fuel S to SO 2 was low because of S retention mainly as alkali sulfates. HCl emissions were higher than the usual legal limits imposed in European Union (EU) countries, although retentions of 40− 55% fuel Cl could be estimated. The co-combustion of Cynara with eucalyptus was tested with benefits regarding process conditions, pollutant emissions, and ash behavior, but still, the HCl concentration surpassed the legal limit. The tendency for bed agglomeration was also observed during the gasification of cardoon. Two strategies were carried out to minimize this adverse effect: (1) co-gasification of cardoon with eucalyptus and (2) addition of natural minerals to the gasification bed. The results of the first strategy caused a decrease in H 2 levels, while tar, hydrocarbon, and CO amounts were found to increase. On the other hand, the addition of natural minerals did not lead to any significant change in the major gas components, although some tar and hydrocarbon abatements were observed, with olivine being the most effective. Dolomite and ZnO gave rise to a greater reduction in HCl and sulfur compounds in the gas phase, respectively.
[Show abstract][Hide abstract] ABSTRACT: Hydrogen separation from a syngas mixture with different compositions was studied by using a Pd–Ag membrane. The effect of temperature (from 300 °C to 600 °C) and of relative pressure (from 0.2 MPa to 0.5 MPa) was studied. In general, rises of both these parameters allowed increasing H2 permeate flux. The Pd–Ag membrane showed to have a great selectivity, as when inlet gas mixture contained different compositions of CO2, CO or CH4, these gases were never detected in membrane permeate side. However, when hydrogen content in inlet gas decreased, a significant reduction in H2 permeate flux was observed, especially when CO was present, probably due to the deposition of solid carbon in membrane surface by Boudouard reaction. It was also observed the formation of hydrocarbons, due to CO and H2 reactions. H2 permeances were calculated by application of Sieverts’ law and values between 4.9 × 10−4 and 1.5 × 10−3 mol m−2 s−1 Pa−0.5 were obtained. The highest value was obtained at 600 °C. H2 permeances at different temperature followed Arrhenius’ equation. Thus, activation energies values between 11.5 kJ mol−1 and 14.0 kJ mol−1 were calculated.
[Show abstract][Hide abstract] ABSTRACT: The release of H2S and NH3 into syngas during co-gasification of two coals (German and Polish) mixed with wastes (pine, olive bagasse and polyethylene) was studied. Sulphur and nitrogen contents in feedstock were found to have a great influence on H2S and NH3 concentrations in syngas, as the highest contents of these elements led to the highest releases. Air/steam or oxygen/steam mixtures were used in the gasification medium, keeping constant experimental conditions, including equivalent ratio. However, when air was added instead of oxygen, higher flow rates were used, due to the introduction of nitrogen and thus lower residence times were used. Different H2S and NH3 contents were obtained by changing the gasification medium. In presence of oxygen and steam higher H2S contents and lower NH3 concentrations were obtained than those produced in presence of air and steam. However, after syngas hot treatment in two fixed bed reactors, the first one with dolomite and the second one with a Ni-based catalyst (G-90 B 5) these differences lost significance. On the other hand, different final compositions of H2S and NH3 were obtained for different feedstocks. Those with highest sulphur and nitrogen contents led to the highest final H2S and NH3 contents in syngas.
[Show abstract][Hide abstract] ABSTRACT: Syngas obtained by co-gasification of coal and wastes was hot cleaned in two catalytic reactors, which allowed destroying tar and gaseous hydrocarbons with more than one carbon atom. H2S and NH3 contents were also significantly reduced, but CH4 concentrations varying between 2% and 10% and small amounts of H2S (below 100ppmv) were still found in syngas, depending on coal type and waste composition. This paper studies the effect of experimental conditions on CH4 destruction by reforming reactions in absence and in presence of catalysts. The effect of experimental conditions (temperature, steam flow rate and syngas composition) on CH4 destruction and on CO conversion into CO2 in the absence of catalyst was studied first, using the Equilibrium Reactor model from CHEMKIN modelling software. The selected experimental conditions were then tested in a fixed bed reactor with and without catalyst and the results obtained were consistent with CHEMKIN Equilibrium Reactor model predictions. Commercial Ni-based catalysts were tested (G-90 B5 and G 56B from C&CS). These catalysts were capable of significantly reducing CH4 content, by promoting reforming reactions. At the experimental conditions used and in absence of steam, G 56B seems to be more effective in CH4 conversion, as lower CH4 contents were obtained. In presence of steam both catalysts were capable of completely destroying CH4. Both catalysts also promoted WGS (water gas shift) reaction to some extent, though they are not specific catalysts for this reaction. Thus, a high increase in H2 content was observed, due to its formation by both reforming and WGS reactions. For a complete conversion of CO into CO2 and H2 a specific catalyst for WGS reaction is still needed.
[Show abstract][Hide abstract] ABSTRACT: It is predictable that in the near future fossil fuels will continue to have the greatest contribution to energy production. Thus, it is necessary to develop and improve technologies that ensure low CO2 emissions. Oxy-gasification is one of such technologies, as the use of oxygen instead of air will allow solving the problem of nitrogen dilution effect in syngas and consequently will simplify the process of CO2 capture. On the other hand, the use of oxygen will increase investment costs, as an oxygen production unit will have to be added to the overall installation, and operation costs will also rise, due to the extra energy necessary for oxygen production. Apart from this, it is important to check the performance of installations initially designed to operate with air, when retrofitted to use oxygen and to analyse the effect that this change may have on syngas composition. In this work the effect of gasification agent on syngas composition, including tar content was determined during co-gasification of two types of coals (German and Polish) mixed with several wastes, like pine, olive bagasse and polyethylene (PE). Air and steam or oxygen and steam mixtures were used as gasification agent, keeping constant ER (equivalent ratio), that is to say, for each coal and wastes blend the oxygen flow was the same for both gasification agents. However, when oxygen was used, gas flows fed into the gasifier were lower than those used in presence of air, which means that residence times were higher than when air was used. Therefore, syngas presented lower hydrocarbons contents and higher CO2 concentrations, probably because there was more time for reactions to occur in presence of oxygen.
[Show abstract][Hide abstract] ABSTRACT: Coal mixed with different types of wastes was co-gasified in a pilot-scale installation. The syngas produced was hot treated in two catalytic fixed-bed reactors. In the first one, dolomite was used and in the second reactor, a nickel-based catalyst was employed. Two different grade coals were tested, Puertollano and Colombian. Puertollano coal had high ash and sulphur contents, 42.5% and 2.4%, respectively, while ash and sulphur contents of Colombian coal were, respectively, 12.7% and 0.9%. Pine, bagasse, RDF and PE were the wastes mixed with both coals. After dolomite fixed-bed reactor, H2S and NH3 contents in syngas were much lower than those of the gas leaving the gasifier. For most coal and waste blends, NH3 reductions changed between 30% and 50% depending on feedstock nitrogen content, while H2S reductions achieved values from 68% to 74%, also depending on H2S concentration in syngas. After syngas had gone through the nickel-based catalyst, it presented H2S and NH3 contents that allowed its use in boilers and gas engines for most coal and waste blends. The overall syngas treatment led to H2S and NH3 reductions higher than 97%. For most experiments, final H2S and NH3 concentration in syngas were below 20ppmv and 30ppmv, respectively.
[Show abstract][Hide abstract] ABSTRACT: The use of biomass fuels for energy production through combustion has a growing application worldwide mainly for two reasons:
first, the utilization of biomass for energy contributes to mitigate emission of green house gases; second, its use decreases
the dependence of imported fossil fuels in Europe. The objective of this work was to study the combustion behaviour of two
endogenous biomass species: cardoon (cynara cardunculus) and arundo (arundo donax), which were specially produced in energy
crops plantations. Mixtures of cardoon and a forestry biomass specie (eucalyptus) were also studied to evaluate potential
benefits from synergies between both biomass fuel types. The results showed that the utilization of cardoon, in pelletized
form, and loose arundo as feedstock, did not give rise to any operational problems related with the feeding system. It was
verified that the mono combustion of cardoon could pose problems at industrial scale in fluidised bed systems, considering
the high levels of HCl and NOx emissions obtained and tendency to sinter the bed sand material. The addition of the forestry biomass to cardoon appeared
to prevent the bed agglomeration problem. Furthermore, both the NOx and SO2 emissions were found to decrease at the same time suggesting potential synergy of blending different types of biomass regarding
pollutant emissions and in bed agglomeration problems.
[Show abstract][Hide abstract] ABSTRACT: Co-gasification of poor quality coals mixed with wastes has the advantage of diversifying energy resources and of decreasing the dependency on imported fossil fuels. However, the use of wastes like plastics increased the production of tar and gaseous hydrocarbons. Although, the correct adjustment of gasification experimental conditions, like temperature and air flow, may lead to some reduction of undesirable compounds, this procedure is not usually enough to accomplish effective reductions of tar and hydrocarbons, thus obliging to the use of further gas treatment. Co-gasification studies were undertaken in a pilot-scale installation. The syngas produced, after going through a cyclone to decrease particulates content, was further treated in two catalytic fixed bed reactors. In the first fixed bed reactor was used a low cost catalyst, like dolomite, to reduce H2S content in the gas and also to promote some tar destruction. In the second fixed bed reactor, Ni based catalysts were employed to achieve effective reduction of tar and other undesirable compounds. After the second fixed bed reactor, H2 content was much higher than that of the gas leaving the gasifier, values higher than 50% were obtained, while gaseous hydrocarbons contents were much lower, particularly CnHm contents were quite low, usually below the detection limit of the method used. The presence of tar was never detected after the second fixed bed reactor.
[Show abstract][Hide abstract] ABSTRACT: Environmental regulations concerning emission limitations from the use of fossil fuels in large combustion plants have stimulated interest in biomass for electricity generation.The main objective of the present study was to examine the technical and economic viability of using combustion and gasification of coal mixed with biomass and plastic wastes, with the aim of developing an environmentally acceptable process to decrease their amounts in the waste stream through energy recovery. Mixtures of a high ash coal with biomass and/or plastic using fluidised bed technologies (combustion and gasification) were considered. Experiments were carried out in laboratory and pilot plant fluidised bed systems on the combustion and air/catalyst and air/steam gasification of these feedstocks and the data obtained were used in the techno-economic analyses.The experimental results were used in simulations of medium to large-scale circulating fluidised bed (CFB) power generation plants. Techno-economic analysis of the modelled CFB combustion systems showed efficiencies of around 40.5% (and around 46.5% for the modelled CFB gasification systems) when fuelled solely by coal, which were only minimally affected by co-firing with up to 20% biomass and/or wastes. Specific investments were found to be around $2150/kWe to $2400/kWe ($1350/kWe to $1450/kWe) and break-even electricity selling prices to be around $68/MWh to $78/MWh ($49/MWh to $54/MWh). Their emissions were found to be within the emission limit values of the large combustion plant directive.Fluidised bed technologies were found to be very suitable for co-firing coal and biomass and/or plastic waste and to offer good options for the replacement of obsolete or polluting power plants.
[Show abstract][Hide abstract] ABSTRACT: Edible oil wastes (EOW) are generally used in the production of soap and/or disposed in waste water treatment stations. In Europe, their use for energy is almost exclusively for the production of biodiesel. However, the nature and quality of EOW may turn their use for biodiesel not always suitable. Therefore, for environmental reasons, it is important to investigate other options like co-gasification with coal. Gasification is generally considered more environmentally friendly and its impact is considerably less polluting than other thermochemical processes. Co-gasification requires that synergy exists between coal and EOW to take profit of their complementary advantages. Co-gasification runs were undertaken on a bench-scale atmospheric fluidised bed gasifier, using both steam and air-steam mixtures as gasification medium. Operating conditions like gasification temperature, steam/air ratio and oil content in feedstock blends were varied to check their effect with the aim of optimising the gasification process. Some difficulties in feeding the blend of coal with EOW were observed when the oil content increased, which also raised hydrocarbons content in the gas produced. Both the rise of temperature and of air flow rate allowed lower tars and gaseous hydrocarbons concentrations. Higher gas yields were obtained at higher gasification temperatures, the gas being richer in hydrogen content at the expense of hydrocarbons. Solid residues (ashes and char) produced by gasification of blends of coal and EOW were also analysed to understand their nature and to evaluate their impact on the environment.
[Show abstract][Hide abstract] ABSTRACT: Co-gasification of bagasse wastes mixed with coal is technically feasible, without major installation changes. The effect of experimental conditions on co-gasification process was analysed, to enhance gas production and improve its composition and energetic content. The rise of bagasse content increased tars and gaseous hydrocarbons contents, which can be reduced by increasing gasification temperature and/or air flow rate. The rise of temperature till 890 °C favoured hydrocarbons further reactions and allowed an increase of 45% in hydrogen release and a decrease in gaseous hydrocarbons of 55%. A reduction of around 30% in gaseous hydrocarbons was also achieved by rising O2/fuel ratio till 0.6 g/g daf, which decreased gas heating value, due to nitrogen diluting effect. Though no significant changes in gaseous hydrocarbons composition were obtained, the presence of dolomite in the fluidised bed had the benefit of decreasing tars content and rising gas yield, being the gas richer in hydrogen content.
[Show abstract][Hide abstract] ABSTRACT: The effect of temperature and of gasification medium was studied, using only air, only steam and mixtures of both as gasification medium, with the aim of optimising co-gasification of coal and wastes. The rise in gasification temperature promoted hydrocarbons further reactions, leading to a decrease in tars and hydrocarbons contents and an increase in H2 release. Increasing temperature, from 750 to 890 °C, during gasification of a mixture with 60% (w/w) of coal, 20% of pine and 20% of PE wastes, led to a decrease in methane and other hydrocarbons concentration of about 30 and 63%, respectively, whilst hydrogen concentration increased around 70%. Hydrocarbons contents decrease was also achieved by increasing air flow rate, because partial combustion caused by oxygen decreased tars and gaseous hydrocarbons, with even a decrease in heating requirements. However, the presence of air is disadvantageous, because it decreases the higher heating value of the gasification gas, due to nitrogen diluting effect. The rise of steam flow rate has proven to be advantageous, because reforming reactions were favoured, thus hydrocarbons concentrations decreased and hydrogen release increased.
[Show abstract][Hide abstract] ABSTRACT: Biomass gasification was used to produce activated carbon on a pilot-scale fluidised-bed gasifier. The feedstock included both biomass alone and biomass mixed with coal and coal/granulated plastic wastes. This paper reports the results obtained from four different runs undertaken under various conditions of fuel supply, different ratios of steam/air for the gasification and temperature. These conditions were selected because they led to a significant amount of unconverted chars produced during gasification (from 0.72 to 1.4 kg) which then served as raw material for the production of activated carbon whilst the amount of gas obtained was also high enough for its potential use for different end-use applications. From the analysis of the results obtained, it can be concluded that a reasonable porosity development (mainly in the area of narrow micropores) was obtained by gasifying unblended pine wastes with steam for 4 h, producing about 1.4 kg of good-quality activated carbon (micropore volume of 0.263 cm(3)/g). In other runs, chars with a reduced microporosity development (i.e. 0.180 cm(3)/g) were obtained, however, they could be used as a proper starting material for the chemically activated carbon production.
No preview · Article · Jun 2003 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: Steam gasification studies were carried out in an atmospheric fluidised bed. The gasifier was operated over a temperature range of 700–900 °C whilst varying a steam/biomass ratio from 0.4 to 0.85 w/w. Three types of forestry biomass were studied: Pinus pinaster (softwood), Eucalyptus globulus and holm-oak (hardwood). The energy conversion, gas composition, higher heating value and gas yields were determined and correlated with temperature, steam/biomass ratio, and species of biomass used. The results obtained seemed to suggest that the operating conditions were optimised for a gasification temperature around 830 °C and a steam/biomass ratio of 0.6–0.7 w/w, because a gas richer in hydrogen and poorer in hydrocarbons and tars was produced. These conditions also favoured greater energy and carbon conversions, as well the gas yield. The main objective of the present work was to determine what reactions were dominant within the operation limits of experimental parameters studied and what was the effect of biomass type on the gasification process. As biomass wastes usually have a problem of availability because of seasonal variations, this work analysed the possibility of replacing one biomass species by another, without altering the gas quality obtained.
[Show abstract][Hide abstract] ABSTRACT: Fluidised bed steam gasification has proven to be a possible way of converting biomass and plastic undesirable wastes into fuel gases. The addition of plastics to pine wastes decreased CO content, but increased H2 released, up to values of 50% (v/v). The highest gas yield obtained was 1.96 Nl/g daf for 98% of energy conversion, when 60% (w/w) of plastic was in the feedstock. The steam/waste mixture ratio seems to have a small effect on gas composition. Temperature is the parameter that most influenced gases composition. The rise of temperature favoured the formation of H2 and decreased the formation of hydrocarbons, tars and char. At 885°C and in presence of 40% (w/w) of plastic, conversion to char was around 2%, whilst feedstock conversion to gas was around 90%. In this paper, the effect of experimental conditions on gasification process, with the aim of enhancing the gas production and improving its composition and energetic content was analysed.
[Show abstract][Hide abstract] ABSTRACT: The increase in energy demand and at the same time the generation of more and more wastes both caused by the growth of world population and higher standards of people's life puts several problems that need to be faced. The development of our society in a sustainable way demands, not only an effort to reduce and recycle the wastes generated, but also the application of new energy technologies to process in a useful manner, with lower environmental impact, the combustible wastes resulting from the industry, forestry and agricultural activities. The application of gasification technology to mixtures of coal and wastes relies on this perspective. In the present work, co-gasification of coal, biomass and plastic wastes mixtures was studied. Experimental fluidised bed gasification tests were done in two facilities, a bench and a pilot scale, using air and steam mixtures. It was studied the effect of temperature and feedstock composition on different gasification parameters, such as, gas composition, gas yield, heating value and energy conversion. The results obtained so far are encouraging, as they have shown that it is possible to co-gasify coal mixed with either pine and polyethylene wastes to values up to 40% (w/w) of wastes, being even possible to substitute one waste type by the other, whenever their availability is seasonally affected. However, the presence of pine led to the production of higher amounts of CO, while the presence of PE wastes favoured the release of hydrocarbons, which may be reduced by either an increase in gasification temperature or in air flow.