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Biomasses with relatively high N contents generate a gasification gas with a NH3 content between 500 and 6000 ppm, with 2000 ppm of NH3 as the value that can be selected as a reference. This NH3 would generate NOx contents above the legally accepted limits; this is the reason why very often NH3 has to be removed from a gasification gas that also contains tar and particulates. The present paper only focuses on the performance of Ni-based monoliths for NH3 elimination from a realistic gasification gas coming from a bubbling-fluidized-bed biomass gasifier, at small pilot-plant scale. Besides using NH3 conversions, analysis of the results was also made using effective kinetic constants (keff) not only for NH3 but also for the simultaneous and competitive tar removal reaction. Correlations were found between the keff,NH3 and keff,tar values, included in effective Sherwood numbers, and the Reynolds and Schmidt numbers, the pitch of the channels of the monolith, and the temperature. The effect of the temperature is of the potential type, not Arrhenius, with an exponent of 2.75 ± 1.75, because of the control by the external mass transfer. keff,NH3 is also somewhat smaller (0.8 ± 0.3) than the equivalent one for tar elimination (keff,tar). Data on the deactivation of the monoliths, their causes, and their possible solutions are also provided. A final discussion on the poor performance of these monoliths in biomass gasification in a fluidized bed is also included in this paper.

Nickel-containing monoliths can be used to eliminate tar and ammonia in a real biomass gasification gas. They can work with a fuel gas containing important amounts of particulates, as in the case of the fuel gas produced in fluidized-bed gasifiers. The use of monoliths is a very recent and promising technology that has not yet reached a commercial level and requires experimental studies at pilot scale. Those studies indicate that tar and ammonia conversions (eliminations) with these monoliths depend on so many experimental variables that a model is needed to understand and correlate the results obtained with these monolithic reactors. A model is developed in this paper for the monolithic reactor that has two very different zones:  the gas reheating zone and the monolith itself. The model is developed according to the basic rules of chemical reaction engineering, and it includes two microkinetic models for the tar and NH3 elimination reactions, mass balances for tar and NH3, and a heat balance in the monolith. Several important facts appear and are confirmed in this study, such as the control of the external mass transfer in the channels of the monolith, which generates a dependence of the overall kinetic constants on the temperature of potential, not Arrhenius, type. The ΔT across the monolith is also analyzed in detail. The equations developed for the model are easy to handle, allow a correct analysis of experimental data, and may be used to design new monolithic reactors for this application.

The deactivation of a solid catalyst may affect in different ways each reaction taking place in a complex network. This creates a variation with time on stream of the product distribution at the reactor exit. To handle data from this common situation, a selective deactivation kinetic model fits the data much better than a nonselective one. Selective deactivation kinetic models are scarcely used because they are often complex and difficult to handle. They also introduce more deactivation kinetic parameters than the nonselective models. Nevertheless, selective deactivation kinetic models are a refinement and are a step forward in the modeling of deactivation kinetics. They might also improve the existing macrokinetic models for commercial reactors. In this paper, several new concepts and ideas are given relating to selective deactivation kinetic models. These concepts are applied to the kinetics of the deactivation of commercial fluidized catalytic cracking catalysts with commercial feedstocks. It is also proven how the kinetics of cracking of the feedstock (heavy oils) is much more affected by the catalyst deactivation than the cracking of the gasoline. A discussion of the results is included.

Full-size 15 × 15 × 30 cm nickel-based monoliths are tested for tar elimination in fuel gas produced by biomass gasification in a fluidized bed at a small pilot-plant scale. The feedstocks used were mixtures of pine wood chips and “orujillo”, the residue from olive oil production. Temperatures at the front or face of the monolith ranged from 820 to 956 °C, gas hourly space velocities in the monolith ranged from 1280 to 4550 h^-1 (normal conditions, nc), area velocities ranged from 2.7 to 7.1 m/h, and superficial or face gas velocities at the inlet of the monolith ranged from 0.34 to 1.3 m/s. Samples of gas and tar were taken before and after the monolith reactor, and variations in gas composition and tar content were determined. Using a macrokinetic model presented elsewhere, some key kinetic constants for the tar-removal reaction are calculated for the monolith and used as indexes of its activity. The effects of some important operating conditions on the activity and sometimes on the deactivation of the monolith are presented here. The intrinsic activity of the monolith for tar abatement is finally compared with those of other competing catalysts such as dolomites and commercial steam-reforming catalysts. It is concluded that these monoliths are not very high in activity, but they can operate with a fuel gas containing particulates, thereby avoiding the use of hot filters, which are problematic when used in biomass gasification.

Biomass gasification in fluidized beds generates tar that can be effectively eliminated with catalysts located downstream from the biomass gasifier. Some previously obtained results from such catalytic tar elimination were hard to be understood because the tar was considered as only one or two lumps. For this reason, in this work, tar is considered in two ways:  (i) as being composed of six different lumps and (ii) as a continuous mixture. For these studies, tar was sampled before and after two catalytic beds located in a slip-flow downstream from a fluidized-bed gasifier (pilot scale). Such tar samples were then completely characterized, and the tar composition was thus determined before and after the catalytic bed. The conversion of each of the species present in tar, and thus of the lumps, was calculated at different temperatures and space-times in the catalytic reactor. The two most advanced reaction networks and their corresponding kinetic models are presented here. The first one provides the evolution with gas residence time of the mean molecular weight of the tar and of the variance of the tar molecular weight distribution. The second kinetic model is based on a set of six kinetic equations and eleven kinetic constants, which are calculated here. This second model allows the species present in tar to be ranked according to their reactivity or resistance to being destroyed. Predictions from these models are consistent with all existing data on this matter.

A single one-lump first-order reaction for the catalytic elimination of tar present in the flue gas from biomass-fluidized bed gasifiers is not good enough for some applications. A new and more advanced reacting network and microkinetic model has been generated and is here presented. It is based on two lumps, the more and the less reactive tar species, and has four kinetic constants. Each lump reacts (disappears) by both catalytic and thermal reactions. The microkinetic model is applied to results obtained at around 840 °C and at small pilot plant level with two very different solids:  silica sand and a commercial (ICI 46-1) nickel-based steam-reforming catalyst. The values found for the four kinetic constants are self-consistent, fit well the results, and mean a clear step forward in the modeling of the catalytic tar abatement.

Seven different total oxidation catalysts (PRO*CLEAN*500; EF 258 H/D; Siemens A; ZERONOX; and Ru, Pd, and V2O5 on a TiO2 support) have been tested for abatement of principal organic hazardous compounds (POHCs) in the flue gas from a waste incinerator of the fluidized-bed type. These catalysts were placed in a slip flow downstream from the waste incinerator. The catalytic reactors used were both metallic and glass, made for monoliths and for particulates. The temperatures used in the catalytic reactors ranged from 240 to 510 °C, and the volumetric gas hourly space velocities (GHSVs) ranged from 1200 to 5700 [(mgas,normal conditions³/h)/mcatalyst³]. The catalysts operated under a realistic flue gas, which was sampled before and after the catalytic reactor at different times on stream. Condensates after the catalytic reactor were also analyzed for organics and for compounds sometimes lost from the catalyst. Gas sampling and analysis were carried out using standarized methods. Conversions (destructions) of most of the POHCs were 99.99%, but small GHSV values were required. Experimental conditions for an even more refined catalyst comparison are also provided.

Three selected commercial, full-size steam-reforming catalysts for naphthas, BASF G1-50, ICI 46-1, and Topsøe R-67, are tested at pilot-scale level for hot gas cleanup in biomass gasification in a fluidized bed. Gas composition and tar content in the flue gas are measured before and after the catalytic bed. Variations of the catalytic bed in H2, CO, CO2, CH4, and H2O contents are reported for different operating conditions. Tar conversions and an apparent first-order kinetics constant for the overall tar removal reaction are calculated. Tar contents at the exit of the catalytic reactor as low as 10 mg/mn³ are obtained in a test of 50 h-on-stream without noticeable catalyst deactivation. Important variations in tar conversion with space time in the catalytic bed, with H2O/C* in the flue gas, and with the equivalence ratio in the upstream gasifier are observed. These results obtained at the pilot-scale level and with the use of full-sized commercial catalysts are an important forward step in demonstrating the technical feasibility of the overall biomass gasification process.

Four commercial catalysts for steam reforming of higher hydrocarbons (naphthas) and three for steam reforming of light hydrocarbons are tested for hot gas clean up and upgrading in biomass gasification with air in fluidized bed. The catalysts used originate from four manufacturers:  BASF AG, ICI-Katalco, Haldor Topsoe a/s, and United Catalysts Inc. The work is performed in a small pilot plant (1−2 kg of biomass fed/h) with three reactors in series:  gasifier, guard bed of dolomite, and full flow catalytic bed. Samples of gas are taken before and after the catalytic bed at different times-on-stream. It is shown how the H2, CO, CO2, CH4 and steam contents in the flue gas change because of the catalytic bed approaching contents near to the ones corresponding to the equilibrium state. Variations in the heating value of the gas and gas yield as a result of the catalytic bed are also reported.

The performance of a biomass gasifier, fluidized-bed type, is improved by in-bed use of calcined dolomite. Tar contents in the raw flue gas below 1 g/mn³ are obtained by using a bed with a percentage between 15 and 30 wt % of dolomite (the rest being silica sand). The work is carried out at small pilot-plant scale (10 kg of biomass/h) with equivalence ratios (ER) between 0.20 and 0.35 and temperatures of 800−840 °C in the gasifier bed. To replace the eroded and elutriated dolomite (from the gasifier bed), an amount of dolomite (0.40−0.63 mm) is continuously fed, mixed with the biomass at 3 wt %. When the results obtained with in-bed dolomite are compared to the ones gained in a gasifier bed without dolomite, change of the following variables is reported:  gas composition and its corresponding heating value, gas and char yields, apparent thermal efficiency, and tar contents. Once the usefulness of the in-bed use of dolomite is established, three main operation variables (ER and temperatures of the gasifier bed and freeboard) are studied in the improved gasifier. Carryover of solids from the gasifier also increases when calcined dolomite is used because of its softness. Elutriation rate constants are calculated for several operational parameters.

The upgrading of the raw gas from a biomass gasifier is studied with the commercial steam-reforming BASF G1-25 S nickel-based catalyst. It is located downstream of the gasifier, a bubbling fluidized bed type in which air is used as gasifying agent. To increase the catalyst lifetime, a guard bed of a calcined dolomite at 800−850 °C is used. It decreases the throughput of tar entering the catalytic bed to amounts below 2 g tar/m³(NC). This work is focused only on the catalytic bed which easily decreases the tar content in the gas to only 1−2 mg/m³(NC). Variables studied include the particle diameter of the catalyst, time-on-stream, temperature of the catalytic bed, and gas and tar compositions. Both tar and gas compositions in the catalytic (Ni) reactor depend on the equivalence and H/C ratios existing in the gasifier and on the operating conditions of the guard bed of dolomite. A simple kinetic model is used to describe the overall tar elimination network. Its overall kinetic constant is used as index of the catalyst activity for tar elimination. Values of this overall kinetic constant are given for very different operating conditions.

Calcined dolomites, limestones, and magnesites are active and inexpensive solids for cleaning raw hot gas from biomass gasifiers with steam. The variations of their activities with time-on-stream are studied here. Simultaneous coke formation and coke elimination by steam gasification increases the life of these “naturally occurring” catalysts under some circumstances. The lives of these solids are studied at different temperatures (800−880 °C), space times (0.08−0.32 kg of dolomite·h/nm³), particle diameters (1−4 mm), and types of solid. Not much deactivation was observed for tar concentration in the raw gas below 48 g/nm³, particle diameters of less than 1.9 mm, temperatures above 800 °C, and space times above 0.13 kg·h/nm³. The effectiveness of these calcined minerals is compared with that of an inert material (silica sand) and with a commercial steam reforming catalyst (R-67 from Haldor Topsøe).

Biomass gasification with air in a bubbling fluidized bed is studied in a small pilot plant. Variables analyzed are equivalence ratio (from 0.20 to 0.45), temperatures of the gasifier bed (750−850 °C) and of its freeboard (500−600 °C), H/C ratio in the feed, use of secondary air (10% of the overall) in the freeboard, and addition (2−5 wt %) of a calcined dolomite mixed with the biomass used as the feedstock. Using advanced tar and gas sampling and analysis methods, the gas composition and tar content in the gas are determined and their variation with the operation parameters is given. A statistical analysis of the effects of the gasification variables is also here presented.

Eight different commercial catalysts, nickel based, for steam reforming of naphthas and of natural gas are tested in biomass gasification for hot gas cleanup and conditioning. They were manufactured by BASF AG, ICI−Katalco, UCI, and Haldor Topsøe a/s. The catalysts were tested in a slip flow after a biomass gasifier of fluidized bed type at small pilot-plant scale (10−20 kg of biomass/h). The gasifying agent used is steam-oxygen mixtures. A guard bed containing a calcined dolomite is used to decrease the tar content in the gas at the inlet of the catalytic bed. Main variables studied are catalyst type, bed temperature, H2O + O2 to biomass feed ratio, and time-on-stream. All catalysts for reforming of naphthas show to be very active and useful for tar removal and gas conditioning (in biomass gasification). 98% tar removal is easily obtained with space velocities of 14 000 h^-1 (n.c.). No catalysts deactivation is found in 48 h-on-stream tests when the catalyst temperature is relatively high (780−830 °C). Using a simple first-order kinetic model for the overall tar removal reaction, apparent energies of activation (of around 58 kJ/mol) and preexponential factors are obtained for the most active catalysts.

Commercial steam reforming (nickel-based) catalysts are used for hot gas cleaning and upgrading in biomass gasification with steam−oxygen mixtures. The gasifier used was an atmospheric and bubbling fluidized bed with an internal diameter of 15 cm and a total height of 3.2 m and was continuously fed with 5−20 kg of biomass/h. Eight different catalysts from four different manufacturers (BASF AG, TOPSOE A/S, ICI, and UCI) have been tested. They were located in a downflow fixed-bed reactor of 4 cm i.d. placed in a slip flow after the gasifier. A guard bed with a calcined dolomite was also used before the catalytic bed to decrease the tar content in the raw gas below the limit of 2 g of tar/m³n, thus avoiding the catalyst deactivation by coke formation. The main variables studied were the temperature of the catalytic bed and the gas composition in the bed. Effects concerning tar elimination will be reported in part 2 of this work. This paper is mainly devoted to characterization of catalysts and to upgrading of the flue gas. H2 and CO contents increased by 4−14 and 1−8 vol %, dry basis, respectively. CO2, CH4, and steam contents decreased by 0−14, 87−99, and 2−6 vol %, dry basis, respectively. Other parameters varied in the following ways:  the lower heating value decreased by 0.3−1.7 MJ/m³n, gas yield increased by 0.1−0.4 m³n/kg of biomass daf, and apparent thermal efficiency increased by 1−20%. The results presented allow screening of the best catalysts to get an upgraded and useful gas in biomass gasification with steam−oxygen mixtures.

When some calcined dolomite (OCa·OMg) is used in the bed of a biomass gasifier of fluidized bed type the raw gas produced is cleaner than when only silica sand is used in it as fluidizing medium. In-bed dolomite changes the product distribution at the gasifier exit because of in-situ catalytic reactions promoted by the calcined dolomite. Gasifying with steam−O2 mixtures causes the tar content in the exit gas to decrease from 12 to 2−3 g tar/m³n, the H2 content to increase from 25−28 to 43 vol %, and the CO content to decrease from 45 to 27 vol % when the gas and char yields, heating value of the gas, and other main variables also undergo important changes because of the in-bed dolomite. The experimental work here reported is carried out at small pilot plant scale in a 15 cm i.d. atmospheric and bubbling fluidized bed gasifier fed by 10 kg biomass/h. Dolomite is continuously fed to the gasifier, mixed with the biomass in percentages of 2−3 wt % of the total mass flow fed. A 10 wt % of calcined dolomite in the gasifier bed is enough to significantly improve the product distribution and gas quality.

Calcined dolomites (CaO−MgO) from four different quarries have been tested for the upgrading of the hot raw gas from a fluidized bed gasifier of biomass with air. These calcined dolomites have big macropores (900−4000 Å) and low (3.8−12 m²/g) BET surface areas. They have been tested in a fixed bed of 6 cm i.d. downstream from the air-blown biomass gasifier. The change in gas composition (contents in H2, CO, CO2, CH4, ...), tar content, gas heating value, etc., has been studied at different temperatures (780−920 °C) as well as space-times for the gas in the bed (0.03−0.10 kg·h/m³) and the type of dolomite. Increasing the equivalence ratio used in the gasifier and decreasing the H/C ratio of the gas increases the refractoriness of the tars to be eliminated by the calcined dolomite. Activation energies (100 ± 20 kJ/mol) and preexponential factors for the overall tar elimination reaction have been calculated for the different dolomites under realistic conditions. The activity of the dolomite for tar elimination can increase by 20% on increasing its pore diameter or its Fe2O3 content. Comparison of results with similar ones obtained in biomass gasification with steam is also presented.

The upgrading of the raw hot gas from a bubbling fluidized bed biomass gasifier is studied using cheap calcined minerals or rocks downstream from the gasifier. Biomass gasification is made with steam (not air) at 750−780 °C and about 0.5−1.0 kg of biomass/h. Calcined solids used are dolomite (MgO−CaO), pure calcite (CaO), and pure magnesite (MgO). Variables studied have been temperature of the secondary bed (780−910 °C), time of contact or space-time of the gas (0.08−0.32 kg·h/m³n), and particle diameter (1−4 mm) and type of mineral. Their effects on tar conversion, tar amount in the exit gas, product distribution, and gas composition are presented. Using a macrokinetic model for the tar disappearance network, the activities of the stones are expressed by their apparent kinetic constant. Apparent energies of activation for tar elimination (42−47 kJ/mol) and preexponential and effectiveness factors are given for all tested solids of which the most active is the calcined dolomite.

The pyrolysis of pine sawdust has been carried out in a High-Temperature Fluid-Wall Reactor. This unit has been specially designed to withstand working temperatures of up to 2200° C. The biomass is fed to the top of the reactor after sieving to the appropriate size, at a rate of 1.0 to 1.8 kg/min. The feed falls and, at the same time is very quickly heated by radiation to the reaction temperature. The estimated heating rate is on the order of 106° C/s for reactant surfaces. The fluid-wall, produced by a nitrogen flow through the 30 cm diameter porous reactor core, prevents both reactants and products from reaching the reactor wall. The product distribution at the reactor exit has been determined for different operating conditions. The influence of reactor temperature, biomass feed rate, and biomass particle size on the product distribution and on the heating value of the exit gas has been investigated.

The benzene ligand in the complex (I) can be activated toward electrophiles by potassium naphthalenide reduction to the dianionic η4‐benzene complex (II).