The simultaneous combined heat and power (CHP) production via biomass gasification is considered as one of the main alternatives to fossil energy. Yet, a major obstacle in the development of this advanced technology lies in the presence of tars in syngas that are responsible for clogging downstream process equipment. Mathematical modelling and simulation studies are powerful tools to predict the performance of new processes. Baratieri et al. (2009), Perez-Fortes et al. (2011) or Damartzis et al. (2012) develop comprehensive models of integrated biomass gasification plant, but based on thermochemical equilibrium approach that do not take into account the formation of tars. Recently, extensive models of Dual Fluidised Bed (DFB) gasifier demonstrate the possibility of accurately predict the formation of tars in syngas (Abdelouahed et al., 2012). The work presented in this paper consists in integrating a rigorous model of a DFB gasifier capable of predicting tar and contaminants in a global biomass CHP process. Our model includes the steps of wood drying, wood gasification, syngas cleaning, and power production in gas engine. Heat integration is considered all over the process for intern consumption and extern district heating. The model is set in Aspen Plus® and external Fortran user-subroutines are used to precisely describe complex phenomena in gasification reactor and gas engine. The energey efficiency of the CHP plant is evaluated. Simulation results highlight the strong impact of the syngas cleaning step in the overall performance of the CHP plant.
Nowadays many types of biomass are studied to satisfy the increased demand of renewable energy based on pellet combustion. However, only a few biomasses fulfil the high quality standard required for pellet used in domestic appliances. European and International standards in force define this quality of non-industrial use of pellets in term of the origin of biomass, physical, mechanical and chemical parameters. Vineyard residues are a worldwide potential source of energy but their compliance to be used in domestic pellet stoves has not been yet proven according to the new standards in force. In order to meet this need, this study makes an exhaustive characterisation of vineyard based pellets manufactured from residues of Prosecco (Glera variety) vineyards, assessing both the quality of biofuel and its behaviour during combustion in a domestic pellet stove. The quality of biofuel has been evaluated according to the in force standards for wood and non-woody pellets. The results show that vineyard pellets do not meet the type B quality standards required for non-industrial use of wood pellet mainly because of the high amount of ash content (>2%) and the high amount of copper (>10 ppm) but they fulfil the specifications of the type B non-woody pellets. Furthermore, during combustion test of vineyard-based pellet the high emission of CO indicates incomplete combustion; and vineyard- based pellet NOx emissions are more than double compared to those obtained during the control tests, confirming that the analysed vineyard-based pellets are unsuitable, as they are, for use in traditional pellet stoves.
Le bois-énergie, majoritairement utilisé sous forme de chauffage individuel et de chaufferies industrielles et collectives bénéficie de forts potentiels inexploités en termes de ressources et de consommateurs. C'est dans cette optique de développement que s'inscrit ce travail basé sur l'étude de 18 chaudières au bois dont la puissance varie de 20 kW à 4 MW et de plusieurs appareils indépendants d'une puissance de l'ordre de 10 kW. Le monoxyde de carbone étant un très bon indicateur de la qualité de combustion, nous avons utilisé cette mesure pour qualifier les appareils et voir l'influence de paramètres tels que la nature du foyer, le système de régulation ou la qualité du combustible sur les résultats de combustion. En effet, l'utilisation du bois comme source d'énergie ne peut être considérée comme renouvelable et participant pleinement au développement durable que si les rejets émis sont faibles et maîtrisés. A l'heure actuelle, toutes les installations satisfont aux normes de rejets en vigueur, mais il est maintenant nécessaire d'aller plus loin et d'atteindre des performances thermiques et environnementales proches de celles obtenues avec les combustibles fossiles.
L’objectif de cette etude est de mettre en evidence l’influence sur les emissions et les performances d’un appareil de differents parametres, comme l’humidite du bois, la presence d’ecorce ou non, le calibre utilise ainsi que le mode d’allumage. De nombreux resultats ressortent de cette etude. Tout d’abord, tous ces parametres influent de maniere considerable sur les emissions des appareils, notamment les emissions de particules, et ce, meme a regime nominal. La presence d’ecorce modifie la composition en carbone total des particules totales et implique l’emission d’un nouveau type de particule : les nano-cristaux. Une humidite elevee induit des niveaux de temperatures plus faibles. Ainsi, les emissions d’imbrules gazeux tels que les Composes Organiques Volatils vont augmenter de maniere importante. Les emissions de particules, en quantite et en composition chimique, sont aussi significativement impactees par l’humidite du combustible. Deux modes d’allumage ont aussi ete etudies. Il s’avere qu’un allumage inverse permet de reduire de maniere significative la globalite des emissions par rapport a un allumage classique. En effet, seules les emissions de Carbone Elementaire sont plus importantes avec un allumage inverse.
This paper presents a theoretical assessment of energy, exergy, and syngas cleaning performances in a biomass gasification combined heat and power (CHP) plant with varying operating parameters. The analysis is carried out using a detailed model of a biomass gasification CHP plant developed with Aspen Plus. The model describes: wood drying and gasification in a dual fluidized bed (DFB) reactor, syngas cleaning, as well as combustion in a gas engine for electricity production. Heat is recovered from the CHP system for internal needs and for district and domestic water heating. An accurate prediction of tar and inorganic contaminants is developed for proper modeling of syngas cleaning efficiency. The influence of wood moisture content, drying conditions, flow rate of the sand circulating in the DFB reactor, catalyst and scrubbing agent efficiencies, as well as additional electricity production through steam turbine on the overall process performances is studied. On the basis of the comparative analysis of nine case studies, it is found that the highest energetic efficiencies are obtained when forced drying is not implemented in the CHP system. Lowering the inlet wood moisture content with natural drying (energy-free) prior to the CHP plant improves the electrical efficiency. An overall energetic efficiency of 74% (23% electric, 51% thermal; based on the lower heating value of wood on anhydrous basis) is then reached with wood fed at 30% moisture content. The best exergetic efficiency is reached when wood (naturally dried to 30%) is dried further to 15% by forced drying in the CHP plant and when some of the high-temperature heat is recovered for electricity production via steam turbine instead of district heating. In this case, the overall energetic efficiency is 63% (32% electric, 31% thermal). This model is a useful tool to assess process design improvements and life cycle inventory.
The simultaneous combined heat and power (CHP) production via biomass gasification is considered as one of the main alternatives to fossil energy. The possibility of significantly decrease greenhouse gas emissions as well as higher electrical performance compared to conventional wood combustion system have led to a growing interest in the gasification process. In the past decades several gasification units at lab- and pilot-scale have been developed but despite promising results (Hofbauer, 2003) none of them reached commercial scale due to unresolved technical issues.Mathematical modeling and simulation studies are then necessary to predict and evaluate the overall performance of new processes, especially at large scale. Numerous simulations have been reported regarding gasification technology (Spath, 2005; Gomez-Barea, 2010; Kaushal, 2010; Radmanesh, 2005) however in most studies gasification reactions are essentially modeled by chemical equilibriums that do not take into account the formation of tars, and the presence of inorganics in the biomass is generally not considered. Besides syngas cleaning and power generation steps are only rarely integrated (Damartzis, 2012).The aim of our work is to provide a rigorous model of an integrated CHP plant consisting of a wood gasification unit including a drying step, a syngas cleaning and cooling unit and a syngas combustion engine. The simulation is implemented in Aspen Plus where the combination of various modules coupled with Fortran user-subroutines gives a comprehensive representation of the system.The gasification unit is an indirect heated gasifier based on the TNEE technology (Deglise, 1985). The raw syngas exiting the gasifier consists of H2, CO, CO2, H2O, CH4, C2H4, C2H6, C6H6, C7H8, C8H8, C9H8, C10H8, C12H8, C14H10, C16H10, NH3, H2S, HCl and solid particles. All of these compounds are modeled for the first time under a biomass gasification process simulation. In order to burn the syngas in a gas engine, strict gas quality requirements have to be achieved (Jenbacher Documentation). As suggested in the literatures (Zwart, 2009; Goransson, 2011), the syngas cleaning unit consists of the following successive steps: cyclone, catalytic tar cracking, syngas cooling up to 120°C, bag filter, water scrubber for tars, NH3 and HCl removal, amine unit for H2S removal and a compressor. The syngas enters the engine at 40 °C and 1 bar with a LHV of 14.5 MJ/kg. The engine produces 10 MWe and 3.3.105 kg/hr of hot water (90/105°C) for district heating.The heat integration of the overall system will be detailed in the communication. A part of the heat contained in the flue gas is used to preheat the air combustion, while the remaining heat added to the recovered heat from the syngas cooling is used to dry the biomass. The energetic assessment of the CHP plant will be discussed and a complete mass balance of the whole process will be depicted. Later in the study, the accurate quantification of the input and output of the CHP plant will be used to evaluate the environmental impact of the technology.
Increase the part of renewable energy in the primary energy consumption is an interesting resolution to lower CO2 emissions of human activities. Utilization of wood for combustion represents an important contribution for this objective: in France the potential of 9,5MTep for energy is growing with the expansion of forest on the territory. To improve the environmental impact of wood combustion, some advance need to be achieved in term of undesirable emissions of carbon monoxide (CO), volatile organic compounds (VOC), polycyclic aromatic compounds (PAC), and particles. Emissions measurement on an old technology wood stove confirms no negligible emissions rates for CO, VOC and particles. The goal of this project is to create a new technology efficient for both gaseous and solid emissions abatement. This technology will also have to be affordable, compact and self generated to be of interest for consumers. Catalysis science can help to treat gaseous emissions. Some tests on catalyst with high redox properties showed promising results for CO and methane CH4 total oxidation. Experiences on a very simple filtration technique indicate 50% abatement for particles smaller than 2.5µm (PM2.5). Regeneration and optimization of these different techniques are ongoing.
