Tar formation is one of the major problems to deal with during biomass gasification. Tar condenses at reduced temperature, thus blocking and fouling process equipments such as engines and turbines. Considerable efforts have been directed on tar removal from fuel gas. Tar removal technologies can broadly be divided into two approaches; hot gas cleaning after the gasifier (secondary methods), and treatments inside the gasifier (primary methods). Although secondary methods are proven to be effective, treatments inside the gasifier are gaining much attention as these may eliminate the need for downstream cleanup. In primary treatment, the gasifier is optimized to produce a fuel gas with minimum tar concentration. The different approaches of primary treatment are (a) proper selection of operating parameters, (b) use of bed additive/catalyst, and (c) gasifier modifications. The operating parameters such as temperature, gasifying agent, equivalence ratio, residence time, etc. play an important role in formation and decomposition of tar. There is a potential of using some active bed additives such as dolomite, olivine, char, etc. inside the gasifier. Ni-based catalyst are reported to be very effective not only for tar reduction, but also for decreasing the amount of nitrogenous compounds such as ammonia. Also, reactor modification can improve the quality of the product gas. The concepts of two-stage gasification and secondary air injection in the gasifier are of prime importance. Some aspects of primary methods and the research and development in this area are reviewed and cited in the present paper.

A review of the primary measures for tar elimination in biomass gasification processes

A study is conducted to demonstrate catalytic dehydrogenation of light alkanes on metals and metal oxides. The study provides a complete overview of the materials used to catalyze this reaction, as dehydrogenation for the production of light olefins has become extremely relevant. Relevant factors, such as the specific nature of the active sites, as well as the effect of support, promoters, and reaction feed on catalyst performance and lifetime, are discussed for each catalytic Material. The study compares different catalysts in terms of the reaction mechanism and deactivation pathways and catalytic performance. The duration of the dehydrogenation step depends on the heat content of the catalyst bed, which decreases rapidly due to the endothermic nature of the reaction. Part of the heat required for the reaction is introduced to the reactors by preheating the reaction feed, additional heat being provided by adjacent reactors that are regenerating the coked catalysts.

Catalytic dehydrogenation of light alkanes on metals and metal oxides.

This book offers comprehensive coverage of the design, analysis, and operational aspects of biomass gasification, the key technology enabling the production of biofuels from all viable sources--some examples being sugar cane and switchgrass. This versatile resource not only explains the basic principles of energy conversion systems, but also provides valuable insight into the design of biomass gasifiers. The author provides many worked out design problems, step-by-step design procedures and real data on commercially operating systems. After fossil fuels, biomass is the most widely used fuel in the world. Biomass resources show a considerable potential in the long term if residues are properly handled and dedicated energy crops are grown. 5 years of the author's research in the area Biomass fuel production First book devoted to Biomass Gasification Includes step-by-design procedures, cases studies and worked out numerical examples

Biomass Gasification and Pyrolysis: Practical Design and Theory

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.

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Recent Advances in the Catalytic Oxidation of Volatile Organic Compounds: A Review Based on Pollutant Sorts and Sources.

Catalytic oxidation of volatile organic compounds (VOCs) – A review

This paper discusses different biomass materials such as pine sawdust, pine wood chips, cereal straw, and thistles (Cynara cardunculus) from energetic crops gasified with steam in a 15-cm-i.d. fluidized bed reactor. The gas, tar, and char yields, the composition and heating value of the gas produced, and the conversion of carbon have been determined at temperatures between 650 and 780{degrees}C (923-1053 K) for each material. The product distribution varies with the biomass used and the gasification temperature. The differences are very marked for the H{sub 2}, CO, and CO{sub 2} contents in the gas product at low gasification temperatures. These differences decrease when the temperature increases to 780{degrees}C at which point a gas composition similar for all types of biomass tested is obtained by the achievement of equilibrium in the water-gas shift reaction.

Steam gasification of lignocellulosic residues in a fluidized bed at a small pilot scale. Effect of the type of feedstock

The kinetics of propane dehydrogenation to produce propene over a Cr 2 O 3 /Al 2 O 3 catalyst has been investigated over the temperature range of 525–575 °C at atmospheric pressure. The reaction rate of coke formation and its influence over catalyst deactivation has been studied. A Langmuir–Hinshelwood mechanism provides the best fit for the reaction, while a monolayer–multilayer mechanism is proposed to model the coke growth. Furthermore, this model was able to predict coke formation under conditions far from those employed in the experiments used to obtain the kinetics.

Propane dehydrogenation over a Cr2O3/Al2O3 catalyst: transient kinetic modeling of propene and coke formation

A complete kinetic model of propane dehydrogenation to produce propene over a Pt–Sn–K/Al2O3 catalyst was obtained. This has been investigated over the temperature range of 460–540 °C at atmospheric pressure. A Langmuir–Hinshelwood mechanism provides the best fit for propane dehydrogenation, while a monolayer–multilayer mechanism is proposed for modelling the coke formation. In addition, the reaction rate of coke formation and its influence on catalyst deactivation and subsequent regeneration have been studied. Finally, a suitable mathematical model is developed for simulating the process behaviour in a two-zone fluidized bed reactor (TZFBR).

Javier Herguido

Papers

Steam gasification of lignocellulosic residues in a fluidized bed at a small pilot scale. Effect of the type of feedstock

Propane dehydrogenation over a Cr2O3/Al2O3 catalyst: transient kinetic modeling of propene and coke formation

Transient kinetic modelling of propane dehydrogenation over a Pt–Sn–K/Al2O3 catalyst

Preparation and characterization of Ce-Zr and Ce-Mn based oxides for n-hexane combustion: Application to catalytic membrane reactors

Hydrogenation of Acetylene over Ni/NiAl2O4Catalyst: Characterization, Coking, and Reaction Studies