Desenvolvimento de processos de co-gasificação de carvão com resíduos

Doutoramento em Ciências Aplicadas ao AmbientePortugal e a maioria dos países da União Europeia são altamente dependentes da importação de fontes de energia que permitam manter os níveis de conforto e de qualidade de vida a que a sua população se habituou. Em virtude do tempo de vida limitado das reservas de petróleo, principal combustível fóssil utilizado, e face aos problemas políticos, sociais e económicos dos principais países produtores deste combustível, é urgente diversificar os processos de produção de energia, bem como encontrar fontes energéticas alternativas. Uma delas poderá ser a co-gasificação aplicada ao processamento de carvão misturado com resíduos com potencial energético, sendo este um dos aspectos inovadores deste trabalho, de forma a valorizar esses resíduos e simultaneamente reduzir a carga poluente a eles associada. Este trabalho teve como principal objectivo estudar o efeito das condições experimentais, de modo a seleccionar as variáveis que permitissem maximizar o rendimento e a qualidade do gás produzido por co-gasificação em leito fluidizado usando misturas de ar e vapor. Os resultados obtidos mostraram que a composição das misturas a co-gasificar, assim como o tipo e características dos resíduos a utilizar afectavam bastante a composição e o rendimento do gás obtido. No presente trabalho foi estudada a co-gasificação de um carvão, proveniente das minas de Puertollano, em Espanha, misturado com diferentes teores de resíduos, tendo sido utilizados resíduos de polietileno e de biomassa. Foi utilizada biomassa florestal, pinho, e bagaço de azeitona, proveniente da indústria de produção de azeite. De um modo geral, o aumento da quantidade de resíduos a co-gasificar aumentava o teor em hidrocarbonetos no gás e consequentemente o seu poder calorifico, o que seria vantajoso se esse gás se destinasse a ser utilizado como combustível, próximo da unidade de produção. Caso contrário e devido ao teor elevado em alcatrões, que poderia causar problemas mesmo no transporte do gás, seria preferível reduzir o teor em hidrocarbonetos, especialmente se o gás se destinasse à produção de energia, a partir da utilização em motores, turbinas ou pilhas de combustível, que exigem um controlo apertado de determinados constituintes, tais como: partículas, alcatrões, ou compostos de enxofre. A redução do teor em alcatrões mostrou-se particularmente necessária quando foram utilizados resíduos de polietileno. O trabalho desenvolvido mostrou que a partir da selecção de condições operatórias adequadas era possível atingir este objectivo, nomeadamente através da utilização de temperaturas de ensaio mais elevadas e de maiores caudais de ar. O aumento da temperatura permitiu reduzir consideravelmente os teores de hidrocarbonetos gasosos, de alcatrões e de carbonizado, aumentando o rendimento do gás e a produção de hidrogénio. As evoluções das concentrações de hidrogénio e de hidrocarbonetos foram opostas, pois um aumento da temperatura de 765 para 885ºC, durante a co-gasificação de carvão misturado com 20 % (m/m) de PE, permitiu aumentar a concentração de hidrogénio em 56% e diminuir a de hidrocarbonetos gasosos de 47%. Os resultados obtidos mostraram que em termos técnicos a temperatura a seleccionar deveria ser relativamente elevada, entre 850 e 900ºC. O aumento do caudal de ar e consequentemente da razão de equivalência também permitiu diminuir apreciavelmente os teores de alcatrões e de carbonizado, conduzindo a um gás com menores concentrações de hidrocarbonetos e de hidrogénio e com maiores teores de CO e sobretudo de CO2, devido à oxidação parcial do gás formado, apresentando este consequentemente, um menor poder calorífico. Com tal, os resultados obtidos mostraram que embora a razão de equivalência dependesse da composição da mistura a co-gasificar e da aplicação do gás produzido, não deveriam ser seleccionados valores superiores a 0,20 para este parâmetro, uma vez que tal correspondia a inverter as concentrações relativas de H2 e de CO2, tornando-se o gás mais rico neste último componente. Reduções adicionais dos teores de alcatrões e de carbonizado e consequentemente o aumento do rendimento do gás foram conseguidos com a introdução de catalisadores no meio reaccional sendo estre também outro aspecto inivado do trabalho desenvolvido. Dos vários catalisadores testados deve salientar-se a dolomite, pela sua acção moderada e o seu baixo custo e também um catalisador de óxido de níquel suportado em alumina (Ni-Al) que revelou ser o mais eficaz, embora apresentasse um custo mais elevado. A presença de 25% (m/m) de dolomite no leito durante a co-gasificação de carvão Puertollano misturado com 20 % (m/m) de PE e 20 % (m/m) de pinho a 845ºC, permitiu aumentar o rendimento do gás em 35% e reduzir em 55 % e em 47%, respectivamente os teores em alcatrões e em carbonizado. A utilização de óxido de níquel durante a co-gasificação da mesma mistura de carvão e resíduos, permitiu aumentar o rendimento do gás em 75% e diminuir em 79 % e 66% respectivamente os teores em alcatrões e em carbonizado. Os resultados obtidos demonstraram que seria interessante combinar a acção destes dois catalisadores, utilizando a dolomite dentro do reactor de gasificação, podendo o catalisador de óxido de níquel ser utilizado num segundo reactor sempre que o aperfeiçoamento das características do gás produzido assim o exigisse. O trabalho desenvolvido de co-gasificação de carvão misturado com resíduos demonstrou a viabilidade técnica deste tipo de tecnologia para o processamento de resíduos com aproveitamento do seu teor energético, quer à escala laboratorial, quer à escala piloto. O estudo do efeito das condições experimentais conduziu em ambos os casos ao mesmo tipo de tendências e a composições gasosas muito semelhantes, embora as razões de caudais entre o reactor piloto e laboratorial tivessem aumentado 16,7 vezes. Estes resultados promissores encorajam a continuação do estudo do efeito do aumento da escala e a demonstração desta tecnologia a uma escala semi-industrial. Outro dos aspectos inovadores do trabalho realizado foi o desenvolvimento de um processo de modelação com o programa CHEMKIN, modificando um modelo cinético (GRI-mech) desenvolvido para simulação de oxidação. para o adaptar à descrição dos fenómenos e das reacções químicas que ocorrem durante a co-gasificação, permitiu melhorar o conhecimento sobre o tipo de sistemas estudado. O modelo desenvolvido permitiu conhecer quais as reacções químicas que apresentam uma velocidade mais elevada e os correspondentes parâmetros cinéticos, sendo portanto possível prever a composição final do gás produzido a partir da constituição da mistura de carvão e diferentes resíduos a co-gasificar, desde que estes apresentem composições químicas não muito diversas das utilizadas no presente estudo.Portugal, like most European Union countries is highly dependent on energy import to assure its population requirements for achieving high comfort levels and high living standards. The known viable resources of oil that is the most used fossil fuel, petroleum, have a limited lifetime, and the social, political and economical problems of the main oil producing countries put at risk petroleum supplies at acceptable prices. Therefore, it is urgent to find more efficient processes to obtain energy and also alternative energy sources. The application of co-gasification technology to process coal blended with wastes with energetic content is one to the innovative aspects of the work done, which showed that this is a very promising technology both for its energy output and for the reduction of the environmental impact currently associated with these residues. This work main objective was to study the effect of experimental conditions, in order to select the variables that could maximize syngas yield and quality, produced through fluidized bed gasification in presence of steam and air. The results have shown that both the fuel composition and the residues characteristics had a high impact on gas yield and composition. A low volatile coal from Puertollano mines, in Spain, was co-gasified with different amounts of residues like biomass and polyethylene. Biomass tested was forestry pine and bagasse residues from the olive oil industry. Increasing the residue amount in the initial fuel mixtures led to a syngas with higher hydrocarbon contents and also with a higher calorific value, especially useful if the gas is to be burnt as a gaseous fuel near the main energy installation. However, the gas high tar contents may have a negative impact on its transportation and is also unsuitable if the gas is to be used on different energy production units like engines, turbines or fuel cells. These units are very exigent regarding tar and hydrocarbon contents and also other gas contaminants like particles or sulphur oxides. Tars release was particularly high when polyethylene was present in the initial fuel mixture. The use of higher temperatures and higher air flow rates was shown to have a major impact on tar reduction. Higher temperatures decreased gaseous hydrocarbons contents, tar and char formation, with higher gas yields and hydrogen selectivity. The rise of temperature favoured hydrogen release, probably at the expenses of tars and hydrocarbons decomposition mainly through cracking and reforming reactions. The increase of temperature from 765 to 885ºC during co-gasification of coal blended with 20 % (w/w) of PE, led to a decrease in gaseous hydrocarbons concentration, of about 47%, whilst hydrogen content increase around 56%. The results obtained have shown that a high temperature, around 850 to 900ºC should be selected. The rise of air flow rate and consequently of equivalent ratio, also allowed decreasing tars, char, gaseous hydrocarbons and hydrogen contents, whilst CO and CO2 concentrations increased, due to partial oxidation reactions. Therefore, the syngas produced presented lower energy contents. The results obtained have shown that the selection of the right air flow rate depended on the waste type and amount to be co-gasified and also on the syngas end-use, however, equivalent ratios higher than 0.20 should be avoided as they led to an inversion in relative concentrations of H2 and CO2, being the gas poorer in the former component. Further reductions in tars and char and consequently increases in gas yields were achieved with the addition of catalysts to the reactional medium which was one of the innovative aspects of this work. Of the several catalysts studied, dolomite and Ni-Al catalyst (nickel oxide supported in alumina) should be focused. The former one due to its low cost and moderate action and the latter because, despite being more expensive, it was the most active. The addition of 25% (w/w) of dolomite to the gasification bed during co-gasification of coal mixed with 20% (w/w) of PE and of 20% (w/w) of pine at 845ºC, allowed decreasing tars and char contents of about 55% and 47%, respectively, whilst increasing gas yield of around 35%. The presence of the same amount of Ni-Al increased gas yield of about 75%, whilst reduced tars and char contents of about 79% and 66%, respectively. These results have shown that it would be useful the combination of both catalysts, using dolomite inside the gasification reactor, while Ni-Al catalyst could be used in a second reactor to further treat the syngas produced in the first one, by this way the life cycle of the latter catalyst could be increased. Co-gasification studies of coal mixed with wastes showed that this technology was technical viable to process wastes with valuable energetic content, both at lab and pilot scales. The study of the experimental conditions effect led to the same tendencies and to similar gas compositions in both installations, even being pilot feeding ratios 16.7 higher than lab ones. These promising results encourage further increasing of scale and the demonstration of this technology at semi-industrial scale. CHEMKIN software and an existing kinetic model (GRI-mech) were used to simulate the chemical reactions and the phenomena that occur during cogasification of coal and wastes. However, as this model had been developed for combustions systems, it had to be modified and adapted for a better description of gasification phenomena, which was another of the innovative aspects of the research work. The modified model allowed the assessment of the reactions with higher rates, that is to say those that most contribute to syngas final composition, and the respective kinetic parameters. Through this model it is also possible to predict the composition of the syngas produced by cogasification of other coal and wastes mixtures, providing the wastes to be used present a chemical composition similar to the ones used in this study

Study of the experimental conditions of the co-pyrolysis of rice husk and plastic wastes

The main objective of this study is to access the technical and economical viability of using pyrolysis technology applied to the rice production main wastes to produce bio-fuels to substitute fossil fuels and electricity consumption during rice milling processes. Therefore, it was studied the effect of operating conditions (reaction temperature, initial pressure and reaction time) on products yields and quality, as well as the possible synergetic effects that may occur during the pyrolysis of these wastes. The pyrolysis experiments were performed in 1 L capacity batch reactor made of Hastelloy C276 and built by Parr Instruments. According to previous studies, the range of operational conditions studied was: 350-430 ºC for reaction temperature, 2-10 bar for initial pressure and 10-60 min for reaction time. So far, the results obtained showed that these two wastes can be processed together. The presence of PE seems to favour the biomass conversion, as PE is easily converted into liquids by pyrolysis, which increases heat and mass transfer in the reaction medium

Hot treatment and upgrading of syngas obtained by co-gasification of coal and wastes

Nowadays there is a great interest in producing energy through co-gasification of low grade coals and waste blends to increase the use of alternative feedstocks with low prices. The experimental results showed that the viability of co-gasification to process such blends and that by the right manipulation of coal and biomass or waste blends, syngas treatment and upgrading may be simplified and the cost of the overall process may be reduced. Blends of three different coal grades (sub-bituminous coal from Puertollano mines, South African bituminous coal and German brown coal) with two different types of biomass (pine and olive oil bagasse) or polyethylene (PE) were co-gasified. Blend co-gasification showed to be beneficial to reduce the negative characteristics of some coals, such as the high ash and sulphur contents, especially of Puertollano coal. Syngas obtained by these blends was hot cleaned and undesirable syngas components (tar, NH3 and H2S) were measured along the hot treatment tested, which proved to be suitable to treat syngas produced by a wide range of feedstocks. Different routes for syngas cleaning were analysed to reduce unsuitable components to values required by most common end-uses. The results obtained showed that the type of feedstock to be gasified is a key outcome on initial syngas composition, affecting greatly syngas cleaning needs, its application and the economic viability of the overall process

Co-gasification of rice production wastes

Rice production is one of the major food sources in the world and unavoidably generates large amounts of wastes, mainly husk and straw that must be dealt in an environmentally sound and sustainable way. Traditional solutions, like burning in open fields or soil incorporation, may contribute for local pollution. Even the use of these wastes as animal food is not an appropriate solution. Plastics are also an additional waste arising from the life cycle of rice production, manufacturing and distribution. The co-gasification of these wastes was easily accomplished in a fluidized bed installation using steam mixed with air or oxygen as gasifying and fluidisation agents. By changing the gasifying agent composition it is possible to select the best conditions to co-gasify rice husks and PE wastes blends. For rice husks gasification, highest H2/hydrocarbons molar ratios were obtained using a mixture of air and steam and an equivalent ratio of 0.2. These conditions correspond to low tar emissions and very good gas yields and gas higher heating values (HHV). Co-gasification of rice husk mixed with PE enables to increase gas HHV, but also generates more tar. Nevertheless using up to 20 % of PE can be considered a promising solution to deal with this kind of wastes. Pollutants like H2S and NH3 were formed in the gasification process in acceptable amounts. Co-gasification with PE enables to decrease these pollutants. Depending on the gas end-use, the installation of a hot gas conditioning system could be needed to further decrease the contents of tar, H2S and NH3, while also promoting the conversion of hydrocarbons into H2 and CO

Prediction of H2S and HCl formation during RDF and co-gasification in fluidized bed

Most solid fuels contain S and Cl and during their gasification, the formation of pollutants such as H2S and HCl becomes inevitable, however, a better understanding of the mechanism involved in their formation and subsequent destruction during the process could help to define operating conditions and to achieve synergy during co-gasification to minimize their emissions. The formation of these pollutants along with the partitioning of S and Cl in the gas and solid phases can be predicted using theoretical models in software packages like FactSage. If the tendency of H2S and HCl emissions predicted by the model corresponds to what has been observed, then an overall mechanism could be derived at using the thermochemical stability data. In this paper a comparison between numerical and experimental results is presented. The results obtained seem to suggest a relationship between the levels of sulphur in the fuels and the concentration of H2S in the gas phase, although the presence of K, Na and Ca may minimize the release of H2S. The formation of HCl seemed to be greatly affected by the inorganic matter of the fuels

Biocatalytic performance of Butyribacterium methylotrophicum in the long-term conversion of synthesis gas produced from low-grade lignin gasification by Butyribacterium methylotrophicum [Resumo]

ABSTRACT: Second-generation biorefineries produce large streams of low-grade lignin. Its thermochemical conversion, through gasification, enables the carbon recovery from an otherwise recalcitrant by-product. The main product of gasification is producer synthesis gas (PS), which is mainly composed by carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), methane (CH4) and minor impurities. Carboxydotrophic acetogenic bacteria can utilize CO and CO2 as carbon and energy source, and convert them into biomass, biofuels and biochemicals through the Wood-Ljungdahl pathway.N/

Production of bio-hydrocarbons by hydrotreating of pomace oil

Olive pomace oil is a by-product from the olive oil industry that is still being used in the food industry as a low value vegetable oil. Crude olive pomace oil needs to be refined and is blended with virgin olive oils before being used as edible oil. The detection of toxic compounds led to more restricted legislation and to the search of alternative valorisation processes, such as hydrotreating to obtain bio-hydrocarbons. Hydrotreating of olive pomace oil at moderate temperatures (from 300 to 430 C) and in presence of initial hydrogen pressure of 1.1 MPa led to triglycerides destruction and to their conversion into a large range of organic compounds with predominance to hydrocarbons. Even without any catalyst, conversions into hydrocarbons were always higher than 90% (v/v). Catalyst presence, such as: CoMo/Al2O3, FCC (fluid catalytic cracking) or HZSM-5 changed hydrogenated liquids composition. The highest content of alkanes was obtained with CoMo catalyst, while FCC and HZSM-5 led to the highest contents of aromatic compounds. The results obtained showed that olive pomace oil can be efficiently converted into bio-hydrocarbons with a wide range of applications. It was also studied the effect of pyrolysing olive pomace oil prior to its hydrotreating. Pyrolysis pre-treatment seems to have favoured hydrotreating process by promoting initial cracking reactions. Thus, it was possible to increase the production of liquid compounds with a higher content of light molecules. However, the advantages of using a more complex two steps process still need to be proven

Co-pyrolysis of pre-treated biomass and wastes to produce added value liquid compounds

ABSTRACT: It is imperative to find novel environmental friendly liquid fuels to be used in the long distance transportation sector. Pyrolysis of wastes may have an important role in the near future to attain this goal. Biomass pyrolysis has also been widely studied by several researchers, but besides the potentialities of such technology, the bio-oil obtained still has to overcome some challenges related to its unsuitable properties to be used in conventional combustion devices. On the contrary, plastics pyrolysis produces oils, whose main compounds are hydrocarbons, thus they can be used in conventional engines without complex and high cost upgrading processes. Thus, co-pyrolysis of plastics blended with biomass may be a suitable option to produce alternative liquid fuels from wastes. The biomass selected for this study was Eucalyptus globulus wastes, because it has been mostly used in the pulp and paper industry in Iberian Peninsula, which has produced high amounts of wastes. On the other hand, PE (polyethylene) was the plastic chosen, because of the huge wastes amounts generated per year. With the aim of facilitating biomass pyrolysis and to increase the production of liquid compounds with suitable properties to be used as fuels, an alternative to the conventional biomass pyrolysis was studied. First eucalyptus wastes were pre-treated by diluted acid hydrolysis, which removed the hemicellulose fraction, produced added value sugar-based compounds and upgraded the remaining solids to better conditions for pyrolysis. Several pathways were studied, including untreated and pre-treated eucalyptus, blended with different contents of PE wastes. The best technical option is the co-pyrolysis of pre-treated eucalyptus mixed with PE, as the highest liquids yields were produced. However, this process needs to be further studied and the economic viability of the overall process still needs to be proven.info:eu-repo/semantics/publishedVersio

Effect of experimental conditions on co-pyrolysis of pre-treated eucalyptus blended with plastic wastes

ABSTRACT: Eucalyptus has been largely used in the pulp and paper industry in Iberian Peninsula, due to its fast growth and high productivity. This eucalyptus utilisation has generated high amounts of wastes, including leaves, branches and stumps. Hence, these wastes were selected for the co-pyrolysis studies to produce liquid fuels or raw materials. As an alternative to the conventional biomass pyrolysis, biomass was pre-treated under mild acidic conditions to obtain valuable sugar-rich stream to be used in fermentation and the solids rich in lignin were mixed with PE (polyethylene) wastes to be used in co-pyrolysis. The pre-treatment process seems to have weakened initial macromolecular structure of eucalyptus wastes and thus might have helped chemical bonds breakdown during co-pyrolysis. The results obtained so far have shown that PE presence seems to have favoured the biomass conversion. The effect of experimental conditions using Response Surface Methodology (RSM) was studied. There was a good agreement between theoretical and experimental data. The highest liquid yield (78 % wt) was obtained at 380 ºC and for the reaction time of 20 min. These conditions led to the lowest gases yield (7 % wt) and also to the lowest solids yield (14 % wt).info:eu-repo/semantics/publishedVersio