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Woodroll® is a gasification technology developed by Cortus that produces synthetic gas (syngas) from biomass. Syngas can be used in several different applications. One interesting option is to convert it further into biomethane, which can be used as automotive fuel or replace natural gas in gas grids. The revenues and profitability of biomethane production is heavily dependent on policy instruments and support schemes. These subsidies can be either direct, where the producer receives a feed-in tariff for biomethane production, or indirect, where consumption rather than production is stimulated. This work has investigated which revenues that can be expected from biomethane production via Woodrooll® in Sweden, the Netherlands, Germany, the UK, France and Italy, both in terms of amounts and risks. A profitability analysis have also been carried out to preliminary compare the returns in the different countries, where two different scenarios for different revenues have been analyzed for two different feedstock prices. The results showed that the Netherlands and Italy provides the potentially highest revenues. However, there are uncertainty factors associated with all cases. Sweden and Germany offers indirect support and negative market trends. The Netherlands and the UK are the only options that provide a feed-in tariff for biomethane production via gasification. In the Netherlands the tariff can be secured before making investment decision but is only disbursed for 12 years. The UK offers a fixed feed-in tariff for 20 years but the tariff is secured first after plant start-up and the tariff may be reduced on a quarterly basis. In fact, the tariff has been reduced with 40 % over the last 24 months, but there are discussions on introducing a separate tariff for gasification. Italy has the support schemes that potentially offer the highest revenues, but gasification is currently not eligible for support. The latter also holds for France, which may be an interesting case in the future. If risk is to be minimized, Cortus may either focus on the Netherlands or await the discussions in the UK and France on introducing a gasification tariff. The work on standardization of biomethane use should also be followed since Italy offers the potentially highest return of the investigated countries. It is also recommended to look further for other cases. The best-case scenario for the risk averse is the one that provides a fixed tariff for 20 years and in which the tariff can be secured before an investment decision is taken. / Woodroll® är en förgasningateknik som utvecklats av Cortus som producerar syntesgas (syngas) från biomassa. Det finns en rad olika användningsområden för gasen. Ett intressant sådant är att omvandla den till biometan, vilket kan användas som drivmedel eller ersätta naturgas i gasnät. Dock så är intäktern och lönsamheten starkt beroende av stödsystem. Dessa subventioner kan antingen vara i form av en inmatningstariff, där biometanproducenten får en fast peng för biometanproduktion, eller i form av indirekt stöd där konsumtion snarare än produktion stimuleras. I detta arbete har det utretts vilka intäkter som kan förväntas för biometan-produktion genom Woodroll® i Sverige, Nederländerna, Tyskland, Storbritanninen, Frankrike och Italien, både i termer av belopp och risk. En lönsamhetsanalys har också gjorts för att preliminärt jämföra avkastningen för de olika länderna. Två olika scenarier för olika intäkter har analyserats för två olika råvarupriser. Resultatet visade att samtliga länder kan erbjuda attraktiv avkastning. Dock är samtliga fall förknippade med osäkerhetsfaktorer. Sverige och Tyskland erbjuder indirekt stöd och negativa marknadstrender. Nederländerna och Storbritannien är de enda alternativen som ger en feed-in-tariff för biometanproduktion. I Nederländerna kan tariffen säkras innan investeringsbeslut fattats men betalas endast i 12 år. Storbritannien ger en fast tariff i 20 år men kan justeras kvarstalsvis och nivån säkras först efter uppstart av anläggningen. Tariffen har reducerats med 40 % de senaste 24 månaderna, men det pågår diskussioner om att introducera en särskild tariff för förgasning. Italien erbjuder stödsystemet som ger högst potentiella intäkter men biometan från förgasning är inte berättigat för stödet. Det senare gäller också för Frankrike som kan bli ett intressant fall i framtiden. Om det önskas att minimera risken så bör Cortus fokusera antingen på Nederländerna eller invänta diskussionerna om förgasningstariffen i Storbritannien och Frankrike. Arbetet kring standardisering av biometan-användning bör också följas eftersom Italien erbjuder de potentiellt högsta intäkterna. Det rekommenderas också att Cortus tittar vidare på andra alternativ. Det bästa fallet för den risk-aversiva är fallet som ger en fast tariff i 20 år och där stödet kan säkras innan investeringsbeslut fattas.

Thesis (MBA)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: The goal of this study was to investigate the feasibility of a small-scale biomass gasification system within the context of a cooperative wine cellar operation in the Western Cape of South Africa. Central to this goal was the questions whether the time for the implementation of such small-scale renewable energy technologies in South Africa has arrived, in light of the status quo which has changed drastically from the days of abundant and cheap coal-based electricity, and whether the new opportunities afforded by the CDM can help foster financial feasibility. There are various macro-drivers contributing to the current-day emphasis on renewable energy and cogeneration projects. The first and most pressing driver is the global climate change imperative, while the others include the increased aspiration of countries towards energy security, the realization of the importance of sustainable development and the subsequent renewable energy policies that falls within the ambit of sustainable development. Small-scale biomass gasification technology still poses some challenges, particularly when it comes to the gasification of agricultural residues, as with grape residues in the case of this project. The most important technical feasibility problem to overcome is the low ash agglomeration temperature of grape residues reported in the literature. Although the local equipment manufacturer foresees no problem in this regard with their system design - since they have conducted tests on sunflower seed residues, which have similar ash properties, without experiencing any agglomeration problems - the seriousness of this aspect will be confirmed during pilot trials. In order to be eligible for emissions reduction trading under the CDM, the project must adequately demonstrate that the emissions reductions are additional to the business-as-usual scenario, in both the environmental and financial sense. The project will satisfy the environmental additionality requirement, since in its absence the wine cellar will continue its full reliance on coal-based electricity from the grid. Financial additionality, in its strictest sense, requires for the project to be infeasible if it does not pursue CDM participation, which the financial feasibility modeling results indicated to be true in this case. A feasibility model was developed to - subject to the input parameter values assumed and basic assumptions made - be able to assess the financial viability of the project. The main assumptions were that the private feed-in into the national electricity grid was available to all IPPs, in spite of the fact that in its Medium Term Power Purchase Program me (MTPPP) of May 2008 Eskom had only requested expressions of interest from IPPs that had a generating capacity of 5MW and higher to install private base load capacity. This assumption is commensurate with the country's renewable energy targets and the official government aim of achieving a 30% contribution from IPPs to the national electricity mix. The second assumption was that the 65 to lOOclkWh offered by Eskom in its MTPPP will be applicable to sub-SMWe IPPs as well (Creamer, 2008), and that this lower bound electricity price of 65clkWh can be applied over the whole project lifetime. Inherent to this assumption is the further supposition that the progressive decline of electricity prices to an eventual level of 35clkWh by 2018 foreseen by Eskom will not materialize, due both to the sustained pressure an expanding South African economy will put on the considerable but time-consuming supply-side initiatives launched by Eskom, and the likelihood for price premiums to be introduced for clean electricity in order to meet the country's renewable energy targets. From the assumed input parameter values the initial capital and COM expenditures, operating revenues and costs over the project lifetime were determined, and then used to calculate the net cash flows, where after the NPV was computed to serve as the deciding criterion on financial feasibility. A discount rate of 18% was assumed, corresponding with the subjectively judged risks that the project posed as a small-scale renewable energy system within the wine cellar operations. In the case where the project excluded all CDM aspects, the NPV was negative at - ZAR342 573, but this improved to ZAR325 193 if the project participated in the CDM. Thus it was concluded that the project will only be financially feasible if it includes CDM participation, and that this positive contribution can be leveraged by pursuing a programmatic CDM approach. This entails the development of this project as part of a larger program in which similar projects are implemented as they arise, up to the official UN limit of 15MWe in total to still qualify as a small-scale program. The nature of the assumptions that form the backbone of this study indicate that the positive financial feasibility result in the case where the project includes COM participation will become practically relevant only over the short- to medium-term as these assumptions become reality in South Africa. Therefore, although the time for such small-scale renewable energy projects has clearly not arrived as yet, it would seem that it is indeed around the corner. / AFRIKAANSE OPSOMMING: Die mikpunt van die navorsing was om die lewensvatbaarheid van 'n klein-skaal biomassa vergassing sisteem binne die konteks van 'n kooperatiewe wynkelder in die Wes-Kaap van Suid-Afrika te ondersoek. 'n Sentrale aspek was die vrae of die tyd aangebreek het om klein-skaal volhouhare energie projekte in Suid-Afrika tot uitvoering te bring, gesien in die lig van 'n status quo wat drasties weg beweeg het van die tydperk toe elektrisiteit volop en goedkoop was, en of die geleentheid wat die CDM bied sulke projekte finansieel lewensvatbaar kan maak. Daar is verskeie eksterne makro-drywers wat bydrae tot die huidige fokus op sulke volhoubare energie projekte. Hieronder tel globale klimaatsverandering as die dringendste drywer, terwyl die res onder andere die hernuwe strewe van lande tot verbeterde energie-sekuriteit, die besef van die belangrikheid van volhoubare ontwikkeling en die daaropvolgende volhoubare energie beleid stappe insluit. Daar bestaan nog etlike tegniese uitdagings tot die toepassing van klein-skaal biomassa vergassing tegnologie, spesifiek met betrekking tot die vergassing van afval landbou byprodukte, soos wat die geval is met druiwe afval in hierdie projek. Die belangrikste tegniese uitvoerbaarheids-aspek wat aandag verg is die lae smeltpunt van druifafval-as wat in die literatuur rapporteer word. Alhoewel die plaaslike toerustings-vervaardiger nie enige probleme in hierdie verhand voorsien nie, aangesien toetse met sonneblom afval - met as-eienskappe rofweg identies aan die van druiwe-afval - geen smelting van die as getoon het nie, sal dit tog nogsteeds aan verdere toetse onderwerp word. Vir die projek om te kwalifiseer as geskik vir verhandeling in kweekhuisgas vermindering deur middel van die COM, moet dit voldoende bewys kan word dat alle uitlaatgas vermindering addisioneel is tot wat die geval sou wees in die gewone gang van besigheid. Hierdie addisionaliteit is relevant in beide 'n omgewings- en finansiele sin. Hierdie projek sal orngewings-addisionaliteit bevredig deurdat die wynkelder in sy afwesigheid volkome afhanklik van die steenkool-gebaseerde elektrisiteit vanaf die nasionale netwerk sou bly, terwyl finansiele addisionaliteit bewys is deur die finansiele lewensvatbaarheids-model wat getoon het dat die projek slegs ekonomies uitvoerbaar sal wees indien dit CDM deelname insluit. Die lewensvatbaarheids-model is ontwikkel om die ekonomiese uitvoerbaarheid van die projek te evalueer, onderworpe aan die aangenome inset parameter waardes en basiese aannames in die studie. Die hoof-aanname was naamlik dat privaat terugvoer in die nasionale elektrisiteits-netwerk vir alle grootte IPPs moontlik is, ten spyte van die feit dat Eskom se MTPPP van Mei 2008 slegs kapasiteite van 5MW en groter aanvaar bet. Hierdie aanname is gebaseer op Suid-Afrika se volhoubare energie teikens en die regering se offisiele mikpunt om 30% van alle krag-voorsiening vanaf IPPs te bekom. Die tweede hoof-aanname was dat die 65 tot 100clkWh wat Eskom in sy MTPPP aangebied het, ook van toepassing sal wees op sub-SMW IPPs (Creamer, 2008), en dat die laer prys-limiet van 65c/kWb oor die hele projek-leeftyd toegepas kon word. Inherent tot hierdie aanname is die verdere veronderstelling dat die progressiewe daling in elektrisiteits-pryse tot 'n eventuele vlak van 35clkWh voorsien deur Eskom nie sal realiseer nie, beide as gevolg van die volgehoue druk wat die groeiende Suid-Afrikaanse ekonomie op die aansieniike, maar tydrowende, opwekkings-kapasiteit uitbreidings van Eskom behoort te plaas, en ook die hoe waarskynlikheid dat prys premiums vir skoon elektrisiteit ingestel word sodat Suid-Afrika sy volboubare energie telkens kan bereik. Die aanvanklike kapitaal en CDM uitgawes, en bedryfsuitgawes en - inkomstes oor die projekleeftyd is vanaf die aangenome inset parameter waardes afgelei, waarop die NPV van die projek uitgewerk is om te dien as die beslissende maatstaf van ekonomiese haalbaarheid. 'n Diskontokoers van 18% is gebruik, ooreenstemmend met die subjektief beraamde risikos wat die projek inhou as 'n klein-skaal volhoubare energie sisteem. Die resultate van die finansiele lewensvatbaarheids-model het getoon dat in die geval waar die projek geen CDM aspekte bevat nie, die NPV hoogs negatief sou wees met 'n waarde van -ZAR342 573, terwyl dit verbeter na ZAR325 193 as die projek CDM deelname insluit. Die gevolgtrekking is dus gemaak dat die spesifieke projek slegs ekonomies haalbaar sal wees indien dit wel CDM deelname insluit, en dat hierdie positiewe finansiele bydrae van die CDM geoptimaliseer kan word deur 'n programmatiese CDM benadering te volg. Dit behels die ontwikkeling van die projek as deel van 'n groter program waarin soortgelyke projekte mettertyd geimplementeer word soos hulle ontstaan, tot by die offisiele VN limiet van 15MWe om sodoende nog te kwalifiseer as 'n algehele klein-skaalse program. Die aard van die hoof-aannames in hierdie studie is indikatief dat die positiewe finansiele lewensvatbaarheid in die geval waar die projek CDM deelname insluit, eers oor die kort- tot medium-termyn prakties relevant sal word soos die aannames bevredig word. Dus, alhoewel die era van klein-skaalse volhoubare energie projekte nog nie aangebreek het in Suid-Afrika nie, lyk dit tog asof dit om die draai is.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Although more than a hundred papers dealing with the agglomeration problem in combustion and gasification of biomass can be found in the literature, very few studies focusing on the bed particle layer formation process in fluidized bed combustion (FBC) and fluidized bed gasification (FBG) can be found. With increased knowledge of the bed particle layer formation process — i.e. the main route behind bed agglomeration and bed material deposition in wood combustion/gasification — suitable combinations of fuel/bed material and/or bed material management measures can be suggested. This would not only aim to reduce the risk of ash related operational problems but also to enhance the catalytic activity of the bed material (e.g. for tar removal in gasification). The present investigation was therefore undertaken to determine the layer formation process on and within typical bed materials (i.e. quartz and olivine) and for a potentially interesting new bed material, K-feldspar. Bed material samples were collected from four different combustion and two different gasification appliances: two bubbling fluidized beds (BFB) (5 kWth/30 MWth), two full-scale circulating fluidized beds (CFB) (90/122 MWth), and two dual fluidized bed gasifiers (DFB) (8/15 MWth). Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were used to explore layer morphology and elemental composition and to gain information about crystalline phases of the layers. Phase diagrams and thermodynamic equilibrium calculations (TECs) were used to interpret the melting behavior of the layers and the melt fragments in deposits. In addition, a diffusion model was used to interpret the layer growth process. For quartz bed particles taken from BFB, the younger particles (< around 1 day) had only one thin layer, but for particles older than 3 days, the layer consisted of inner and outer layers. In addition to the inner and outer layers, a K-rich inner-inner layer was found for bed particles taken from CFB and DFB. No outer layers were found for quartz bed particles taken from DFB. The thin/absence of an outer layer could have resulted from the more significant attrition between particles in CFB and DFB. Reduced availability of Ca and a risk of layer breakage from the particle lead to the formation of the inner-inner layer. Similar elemental compositions of the layers upon the quartz bed particles taken from different fluidized bed techniques were found. The inner-inner layers are dominated by Si, K and Ca (excluding O), and the outer layers are rich in Ca, Si and Mg, which seem to resemble more closely the fuel ash composition. The inner layers, mainly consisted of Si and Ca, were found to have higher concentrations of Ca for older particles. The layer thickness increases with particle age, but the growth rate decreases. Melt was estimated to exist in the inner layer for younger particles (< around 1 day) and in the inner-inner layer. The existence of partially melted inner-inner layers, in particles from CFB and DFB, points towards higher risk of bed agglomeration in these techniques compared to BFB. Based on the experimental results, thermodynamic equilibrium calculations, and diffusion model analyses, a layer formation process on quartz bed particle was suggested: the layer formation is initiated by reaction of gaseous K compounds with quartz to form K-rich silicate melt, which prompts the diffusion of Ca2+. The gradual incorporation of Ca into the melt followed by the precipitation of Ca-silicates, e.g. Ca2SiO4, will result in the continuous inner layer growth. However, because of increasing concentration of Ca and release of K from the inner layer, the melt disappears in the inner layer and the layer formation process gradually becomes Ca diffusion controlled. The diffusion resistance increases with increasing thickness of a more Ca-rich layer, resulting in a decreasing layer growth rate. Crack layers with similar compositions dominated by Si, K and Ca were observed in relatively old quartz bed particles. A melt was predicted to exist in the crack layer according to thermodynamic equilibrium calculations. The crack layers found in quartz particles from BFB and CFB connect with the cracks in the inner layer, whereas for bed samples collected from DFB, the crack layers were found along existing cracks in the quartz particle. The different morphologies may indicate different routes of formation for crack layers in bed particles from different fluidized bed technologies. For quartz particles from BFB and CFB, crack formation through the inner layer down to the interface between the inner layer and the core of quartz bed particle initiates the cracks in the quartz bed particle. This allows for diffusion of gaseous alkali compounds to react with quartz in the bed particle core, thereby forming crack layers. The reaction is accelerated with bridge formation between crack layers. This may later lead to the breakdown of the bed particle into smaller alkali-silicate-rich fragments. For K-feldspar bed particles from BFB and CFB, only one layer was found for particles with an age of 1 day. For bed particles with ages older than 3 days, two layers including a homogenous inner layer containing cracks and a more particle-rich outer layer can be distinguished. Compared to bed particles from BFB with similar ages, the outer layer is thinner for bed particles from CFB. The inner layer is dominated by Ca, Si and Al (excluding O), whereas the outer layer is dominated by Ca, Si and Mg. The average concentration of Ca in the inner layer increases with bed particle age. Increasing layer thickness with decreasing growth rate was found, similar to that on quartz particles. For particles from DFB, the inner layer is also mainly consisted of Ca and Si, but cracks in the inner layer were not found. For all the particles, the Ca/Si molar ratio in the layer decreases towards the bed particle core and the change of concentration is more significant at the bed particle core/layer interface. The overall inner layer growth is resultant from the gradual incorporation of Ca into the layer. For olivine bed particles from DFB, the younger bed particles (< around 24 h) have only one layer, but after 24 h, an inner layer and an outer layer appear. Furthermore, for bed particles older than 180 h, the inner layer is separated into a distinguishable Ca-rich and Mg-rich zone. Two kinds of cracks in the inner layer either perpendicular or parallel to the particle surface were observed. Compared to the younger bed particles, the Ca concentration in the layer of older particles is much higher. A detailed mechanism for layer formation on olivine particles in fluidized bed gasification (most likely also applicable to combustion) based on the interaction between woody biomass ash and olivine has been proposed. The proposed mechanism is based on a solid-solid substitution reaction. However, a possible enabling step in the form of a Ca2+ transport via melts may occur. Ca2+ is incorporated into the crystal structure of olivine by replacing either Fe2+ or Mg2+. This substitution occurs via intermediate states where Ca-Mg silicates, such as CaMgSiO4, are formed. Mg2+ released from the crystal structure most likely forms MgO, which can be found in a distinguishable zone between the main particle layers. Due to a difference in the bond lengths between Mg/Fe and incorporated Ca2+ with their respective neighboring oxygen atoms, the crystal structure shifts, resulting in formation of cracks. The dominating elements in the inner layers are similar for each kind of bed material from BFB, CFB, and DFB, indicating limited effects of atmosphere on the inner layer formation. The initiation of layer formation differs depending on the bed material, but increasing Ca concentration in the inner layer with time for all bed materials indicates that the layer growth resulted from the incorporation of Ca into the layer. Compared to quartz, K-feldspar and olivine are more promising bed materials in wood combustion/gasification, especially in CFB and DFB techniques, from the perspective of mitigating bed agglomeration and bed material deposit build-up.

L'objectif de ce travail est d'étudier une stratégie catalytique originale, consistant à insérer par imprégnation, au sein de la matrice lignocellulosique du bois, un sel métallique de Ni ou Fe, dont les phases catalytiquement actives pour la conversion des goudrons sont générées in-situ au cours de l'étape de pyrolyse. La caractérisation des échantillons de bois imprégné révèle que l'insertion des cations métalliques fait intervenir des mécanismes d'adsorption électrostatique, d'échange ionique et de complexation au sein des hémicelluloses, de la lignine et des microfibrilles de cellulose, assurant un état élevé de dispersion du métal dans la matrice lignocellulosique. L'étude de l'évolution des espèces de Ni au cours de la pyrolyse du bois met en évidence la formation de nanoparticules (NPs) de Ni0 quasi-monocristallines dans la gamme de température 400-500°C, les atomes de carbone jouant le rôle d'agent réducteur. Dans la même gamme de température, les espèces de Fe sont transformées en NPs de FeOx amorphes. Les tests de pyrolyse à 700°C révèlent que le nickel est plus efficace pour augmenter la production de H2 et réduire la formation d'hydrocarbures aromatiques, tandis que le fer est plus performant pour réduire la production totale de goudrons. D'un point de vue mécanistique, la présence des espèces métalliques, très dispersées dans la matrice lignocellulosique, impacte considérablement les mécanismes primaires de pyrolyse. De plus, les réactions secondaires de pyrolyse sont fortement modifiées par la génération in-situ des NPs de Ni0 et de FeOx, considérées comme les phases actives pour les réactions de conversion des goudrons et la réaction du gaz à l'eau. / This exploratory research work aimed at studying an original catalytic strategy for biomass gasification which consists in inserting into the lignocellulosic matrix of wood, by impregnation, a salt of Ni or Fe whose catalytically active phases for tar conversion reactions are generated in-situ during the pyrolysis stage. The characterization of the metal impregnated wood samples reveals that electrostatic adsorption, ion-exchange and metal complexation within hemicelluloses, lignin and cellulose microfibrills are involved in the mechanisms of metal cations insertion, resulting in a very high metal dispersion into the lignocellulosic matrix. The study of the nickel species evolution during wood pyrolysis demonstrates the formation of quasi-monocristalline Ni0 nanoparticles (NPs) in the temperature range 400-500°C, the carbon atoms acting as the reducing agent. In the same temperature range, the Fe species are transformed into amorphous FeOx NPs. The pyrolysis tests performed at 700°C reveal that the nickel catalyst is more efficient for enhancing H2 production and reducing the formation of aromatic hydrocarbons, whereas the iron catalyst exhibits better performances for reducing total tar production. From a mechanistic standpoint, it is suggested that the presence of highly dispersed metal species into the lignocellulosic matrix strongly impacts the mechanisms of primary pyrolysis. Moreover, the secondary pyrolysis reactions are strongly modified by the in-situ generation of Ni0 and FeOx NPs considered as the active phases for tar conversion and water gas shift reactions. Potential interests of the new nanocomposite materials Ni0/C and FeOx/C as obtained are discussed.

Over the past few decades, a growing interest in the thermal conversion of alternative fuels such as biomass and waste-derived fuels has been observed among the energy-producing companies. Apart from meeting the increasing demand for sustainable heat and power production, other advantages such as reducing global warming and ameliorating landfilling issues have been identified. Among the available thermal conversion technologies, combustion in grate-fired furnaces is by far the most common mode of fuel conversion. In recent years, Fluidized-Bed (FB) technologies have grown to become one of the most suitable technologies for combustion and gasification of biomass and waste-derived fuels.In spite of the benefits, however, some difficulties are attributed to the thermal conversion of the alternative fuels. Ash-related issues could be a potential problem, as low-grade fuels may include considerable concentrations of ash-forming elements such as K, Na, S, Ca, Mg, P, Si and Cl. These elements undergo many undesirable chemical and physical transformations during the thermal conversion, and often cause operational problems such as deposition-related issues, slag formation in furnaces, corrosion of the heat transfer surfaces, and bed agglomeration of the fluidized-beds. Ash-related problems in the utility boilers are a major concern that may result in decreased efficiency, unscheduled outages, equipment failures, increased cleaning and high maintenance costs.This thesis investigated the ash behavior and ash-related problems in two different FB conversion systems: a Bubbling Fluidized-Bed (BFB) boiler combusting solid waste, and a Dual Fluidized-Bed (DFB) gasifier using biomass as feedstock. Full-scale measurements, chemical analysis of fuel and ash, as well as thermodynamic equilibrium modeling have been carried out for the BFB boiler (Papers I-IV), to investigate the impact of reduced-bed temperature (RBT) and also co-combustion of animal waste (AW) on the ash transformation behavior and the extent of ash-related issues in the boiler. For the DFB gasifier (Paper V), a thermodynamic equilibrium model was developed to assess the risk of bed agglomeration when forest residues are used as feedstock.The experimental results showed that the RBT and AW co-combustion could decrease or even resolve the ash-related issues in the BFB boiler, resulting in a lower deposit-growth rate in the superheater region, eliminating agglomerates, and a less corrosive deposit (in RBT case). Thermodynamic equilibrium modeling of the BFB boiler gave a better understanding of the ash transformation behavior, and also proved to be a reliable tool for predicting the risk of bed agglomeration and fouling. The modeling of the DFB gasifier indicated a low risk of bed agglomeration using the forest residues as feedstock and olivine as bed material, which was in good agreement following the observations in a full-scale DFB gasifier.

Des nouveaux procédés éco-efficients basés sur une meilleure utilisation des ressources renouvelables sont nécessaires pour assurer la continuité du développement énergétique. La thèse étudie le procédé de gazéification en eau supercritique (T>374°C et P>22,1 MPa) de la biomasse très humide pour l’obtention de l’hydrogène, molécule ayant un potentiel énergétique très intéressant à valoriser avec un impact environnemental très favorable. L’étude porte sur l’application du procédé à la biomasse modèle (solutions de glucose, glycérol et leur mélange) ainsi qu’au bioglycérol, résidu de la fabrication du biodiesel. Les propriétés du solvant et les mécanismes prépondérants développés par l’eau en phase souset supercritique peuvent être contrôlés par les paramètres opératoires imposés au processus : température, pression, concentration en molécules organiques et catalyseur alcalin, temps de réaction... Les études paramétriques des systèmes réactionnels ont été menées dans des réacteurs batch à deux échelles différentes, les phases résultantes étant caractérisées par des protocoles analytiques élaborés et validés dans le cadre de l’étude. Le suivi du milieu réactionnel en batch lors de son déplacement vers l’état supercritique a mis en évidence une conversion avancée des molécules organiques et une identification de certains intermédiaires générés. Parmi les paramètres étudiés, la température et le temps de réaction influent le plus le rendement à l’obtention d’hydrogène en présence de catalyseur (K2CO3) dans les réacteurs batch, rendements de 1,5 et 2 mol d’H2 respectivement par mol de glycérol et de glucose introduites. Les gaz obtenus contiennent des proportions variables d’hydrocarbures légers et du CO2. Environ 75% du carbone est converti en phase gaz et liquide (sous forme de carbone organique et inorganique), le restant étant déposé sous forme solide ou huileuse. L’analyse du solide généré (plus de 90% de C) laisse apparaître différentes phases, y compris la formation de nanoparticules sphériques. Enfin, la gazéification en réacteur continu du glycérol préchauffé a montré de meilleurs rendements en hydrogène que le procédé batch, pendant que celle du bioglycérol demande une évolution du procédé à cause de la précipitation en phase supercritique des sels contenus dans le réactant. En conclusion, la gazéification en eau supercritique de la biomasse peut être considérée comme une alternative intéressante à d’autres procédés physico-chimiques de production de l’hydrogène. L’amélioration du procédé sera possible par son intensification menée en parallèle avec l’utilisation de matériaux plus performants et le contrôle de la salinité de la phase réactante. / Supercritical water (T > 374 ° C and P > 22.1 MPa) gasification of wet biomass for hydrogen production is investigated. This process converts a renewable resource into a gas, which is mainly composed of hydrogen and hydrocarbons with interesting energy potential, and which can be separated at high pressure. In addition, the greenhouse gas effect of the process is zero or negative. Model biomasses (glucose, glycerol and their mixture) and bio-glycerol, residue from bio-diesel production, have been gasified by different processes: two-scale batch reactors (5 mL and 500 mL) and a continuous gasification system. Supercritical water acts as a reactive solvent, its properties can be adjusted by the choice of the experimental (P, T) couple. The operating parameters, e.g. temperature, pressure, concentration of biomass and alkaline catalysts, reaction time… allow favoring certain reaction mechanisms. In order to characterize the processes, specific analytical protocols have been developed and validated. The intermediates, formed during the heating time in the batch reactors, have been identified. Among the investigated operating parameters, temperature and reaction time have the greatest influence on the hydrogen production in batch reactors. In the presence of catalyst (K2CO3), H2 yields of 1.5 mol/mol glucose and 2 mol/mol glycerol have been respectively observed. The obtained gas contains different proportions of light hydrocarbons and CO2. About 75% of the carbon is converted into gas and liquid (in form of organic and inorganic carbon). The conversion leads also to a solid or oily residue. In the generated solid phase (composed over 90% of C), spherical nanoparticles are observed via electronic microscopy. The hydrogen production from glycerol is improved in the continuous process compared to batch reactors, however, bio-glycerol supercritical water gasification requests process improvement due to the precipitation of the salt contained in the reactant. In conclusion, supercritical water gasification of biomass can be considered as an promising alternative process for hydrogen production. The process should be improved by more performing equipments and by the control of the salinity content of the crude biomass.

La gazéification étagée de biomasse permet la production d'un gaz de synthèse propre, facilement valorisable en énergie électrique et/ou thermique. Néanmoins, l'optimisation de ces procédés en termes de rendement de conversion et de souplesse vis-à-vis de la nature de la biomasse constitue un enjeu industriel fort. Dans cette thèse, nous avons étudié spécifiquement une étape clef du procédé : la gazéification du charbon en lit fixe continu. La granulation est la solution proposée pour valoriser des biomasses de faible granulométrie ou densité. Ainsi les comportements de deux charbons de bois - issus de plaquettes forestières et de granulés - ont été étudiés en parallèle à partir d'outils expérimentaux et numériques.Dans un premier temps des expérimentations ont été menées sur un réacteur pilote, très largement instrumenté, reproduisant cette zone du procédé. Les profils mesurés de température, de composition des gaz, de densité du lit et de vitesse des particules constituent une base de données unique, révélatrice du comportement du réacteur. Nous avons ainsi pu localiser en haut du lit une zone très réactive d’épaisseur inférieure à 5 cm, ou encore un tassement significatif du lit entrainant une chute de la vitesse des particules dans un rapport de 8. La gazéification de charbons de granulés conduit aux mêmes taux de conversion finale et compositions du gaz de synthèse que celle de charbons issus de plaquettes forestières. Dans un deuxième temps, nous avons développé un modèle numérique de la zone d'étude, basé sur la résolution des équations de conservation couplées aux cinétiques des réactions, à l'aide du logiciel COMSOL. La prise en compte du tassement du lit, et de la cinétique apparente des réactions hétérogènes à l'échelle particule dans les termes sources réactionnels, sont les deux spécificités du modèle. Ce dernier permet de reproduire de manière satisfaisante les profils des grandeurs physiques mesurés pour diverses conditions opératoires et pour les deux charbons de l'étude. L'exploitation de ce modèle apporte des informations nouvelles et complémentaires de l’expérience ; il permettra à terme d'optimiser le procédé industriel / Multi-stage gasification of biomass leads to the production of a clean synthetic gas that can easily be used for electrical and/or thermal energy. However, optimization of these processes in terms of conversion yield and flexibility regarding the type of biomass is a major industrial challenge. To that end, a key stage of the process was specifically studied in this thesis: char gasification in a continuous fixed bed reactor. Granulation is the solution proposed for making use of low density or small particle-size biomasses. The performance of two wood chars – made from wood chips and pellets – was studied at the same time using experimental and numerical tools. Experiments were first conducted in a very highly instrumented pilot reactor, reproducing this zone of the process. The profiles measured, namely temperature, gas composition, bed density and particle velocity formed a unique database revealing reactor performance. A very reactive zone under 5 cm thick was thus located at the top of the bed, or even significant compaction leading to a drop in particle velocity, in a ratio of 8. Granular char gasification led to the same final conversion rates and synthetic gas compositions as for the chars derived from wood chips. A numerical model of the study zone was then developed, based on solving conversion equations combined with reaction kinetics, using COMSOL software. Taking into account bed compaction and the apparent kinetics of the heterogeneous reactions on a particle scale in the reaction source terms were two specificities of the model. It enabled satisfactory reproduction of the profiles of the physical magnitudes measured, for various operating conditions and for the two charsstudied. Use of this model is already providing new and complementary experimental information; it will eventually make it possible to optimize the industrial process