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Combustion of residual forest biomass (RFB) derived from eucalypt (Eucalyptus globulus), pine (Pinus pinaster) and golden wattle (Acacia longifolia) was evaluated in a pilot-scale bubbling fluidised bed reactor (BFBR). During the combustion experiments, monitoring of temperature, pressure and exhaust gas composition has been made. Ash samples were collected at several locations along the furnace and flue gas treatment devices (cyclone and bag filter) after each combustion experiment and were analysed for their unburnt carbon content and chemical composition. Total suspended particles (TSP) in the combustion flue gas were evaluated at the inlet and outlet of cyclone and baghouse filter and further analysed for organic and elemental carbon, carbonates and 57 chemical elements. High particulate matter collection efficiencies in the range of 94-99% were observed for the baghouse, while removal rates of only 1.4-17% were registered for the cyclone. Due to the sand bed, Si was the major element in bottom ashes. Fly ashes, in particular those from eucalypt combustion, were especially rich in CaO, followed by relevant amounts of SiO 2 , MgO and K 2 O. Ash characteristics varied among experiments, showing that their inorganic composition strongly depends on both the biomass composition and combustion conditions. Inorganic constituents accounted for TSP mass fractions up to 40 wt%. Elemental carbon, organic matter and carbonates contributed to TSP mass fractions in the ranges 0.58-44%, 0.79-78% and 0.01-1.7%, respectively.

In this study, a binary fluidised bed made out of quartz sand and cenospheres for the biomass combustion process was created. Materials were fluidised with air to achieve a vertical density profile (from 0.5 g/cm³ to 1.1 g/cm³) resulting from grains segregation. The density profile was selected to ensure optimal control over the location of the combusted fuel particle. This involved positioning the process as close to the bottom sieve as possible. Fluidised bed combustion was carried out at temperatures of 600 °C, 700 °C, 820 °C and 870 °C using straw, willow and sawmill pellets as fuels. Qualitative and quantitative analysis of flue gases was performed using an FTIR spectrometer. Over 90 % carbon conversion from the biomass to carbon dioxide was achieved at 700 °C. At 820 °C and 870 °C, 100 % of biomass carbon left the reactor as CO2. The composition of organic compounds in the process products remained low, reaching a maximum of 3.0 % wt. at 600 °C. To gain further insights into the processes occurring in the immediate vicinity of biomass samples, a complementary TGA/FTIR analysis was conducted. This aimed to clarify the impact of the biomass particle decomposition stage in the fluidised bed combustion process. The proposed mechanism for biomass combustion in the binary fluidised bed contains the particle decomposition stage and the subsequent stage resulting from the coalescence of bubbles containing flammable components and bubbles containing oxidiser. [ABSTRACT FROM AUTHOR]

The sustainable fulfilment of world energy demand should be based on the diversification of the energetic portfolio and, at the same time, on the decrease of the use of fossil fuels in favour of renewable energy sources. This perspective review article focuses its attention on a particular source of renewable energy, i.e. biomass. As non‐fossil materials of natural origin, biomasses are formed by storing, in the noble and stable form of chemical bonds, solar energy. Gasification has been here chosen as biomass thermoconversion route: general concepts and history, chemical reactions and uses of syn‐gas, and the role of tar, are addressed. Fluidised beds are discussed as reactors to carry out biomass gasification, also considering that a new approach based on dual interconnected fluidised bed schemes can realise the concept of sorption‐enhanced gasification (to increase H2 productivity). Syn‐gas and tar characteristics are presented and, finally, an original case study concerning the fluidised bed gasification of civil and industrial sludges is presented. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Production of syngas from the gasification of a biomass is attracting attention with an eye to the concepts of circularity, sustainability, and recent needs, triggered by socio-political events, to increase the level of self-sufficiency of energy sources for a given community. This manuscript reports on the gasification of spruce wood chips in a demonstration fluidised bed gasifier (1.5 MWth, height of 5.40 m, internal diameter of 1.2 m), with 0.2–0.4 mm olivine inventory (1000 kg). Gasification was carried out in air, at four different values of equivalence ratio (from 27% to 36%). The bed was fluidised at about 0.6 m/s, and the bed temperature resulted in the range of about 960–1030 °C as a function of the different tests. A mass flow rate of biomass in the range of about 360–480 kg/h (as a function of the different tests) was fed to the fluidised bed gasifier. Syngas lower heating value, specific mass and energetic yield, and chemical composition, were reported along with data on the production of elutriated fines. Moreover, tar compounds were collected, quantified and chemically speciated. The effect of the equivalence ratio on the main process parameter was critically discussed, proposing useful analytical relationships for the prediction of syngas lower heating value, tar mass flow rate and chemical composition. [ABSTRACT FROM AUTHOR]

Production of syngas from the gasification of a biomass is attracting attention with an eye to the concepts of circularity, sustainability, and recent needs, triggered by socio-political events, to increase the level of self-sufficiency of energy sources for a given community. This manuscript reports on the gasification of spruce wood chips in a demonstration fluidised bed gasifier (1.5 MWth, height of 5.40 m, internal diameter of 1.2 m), with 0.2–0.4 mm olivine inventory (1000 kg). Gasification was carried out in air, at four different values of equivalence ratio (from 27% to 36%). The bed was fluidised at about 0.6 m/s, and the bed temperature resulted in the range of about 960–1030 °C as a function of the different tests. A mass flow rate of biomass in the range of about 360–480 kg/h (as a function of the different tests) was fed to the fluidised bed gasifier. Syngas lower heating value, specific mass and energetic yield, and chemical composition, were reported along with data on the production of elutriated fines. Moreover, tar compounds were collected, quantified and chemically speciated. The effect of the equivalence ratio on the main process parameter was critically discussed, proposing useful analytical relationships for the prediction of syngas lower heating value, tar mass flow rate and chemical composition.

Graphical abstract Highlights • Lime added to biomass as a countermeasure to agglomeration in BFB combustion. • Defluidisation time extensively prolonged for biomass fuels with lime addition. • Reduced K/Ca ratio in ash leads to smaller agglomerates & less sand cracking. • Fe precipitates from sand & reacts with molten ash, accelerating agglomeration. • Lime addition to fuels hinders the acceleration caused by Fe precipitation. Abstract The unique fuel flexibility of fluidised bed system facilitates the combustion of low quality solid fuels such as agricultural residues, but may suffer from serious bed agglomeration problems especially when operating at the high end of the typical fluidised bed combustion temperature range (800–900 °C). In this study, a 1.5 wt% lime addition to biomass fuels was investigated as a countermeasure to agglomeration for the combustion of pelletised wheat straw and miscanthus in a 20 kW bubbling fluidised bed (BFB) combustor using quartz sand as the bed material. Comparing to the widely studied agglomeration countermeasures such as bed additives and alternatives, the lime addition to fuel can provide a continuous on-site agglomeration counter action. Without lime addition, defluidisation as a result of bed agglomeration occurred once the bed temperature reached 860 °C and 877 °C for miscanthus and wheat straw respectively. However, with the lime addition, stable combustion could be achieved at 900 °C for both fuels with a substantially prolonged operation time. The obtained agglomerates were characterised using CAMSIZER, XRD and SEM/EDX and the results showed that the presence of lime in the fuel could significantly reduce the agglomerates size by forming high melting point calcium silicates/phosphates which hinder the K-rich molten substance attachment and result in heterogeneous coating layers in the agglomerates. The results of this study clearly indicate that using lime as fuel additive can realise the combustion of the problematic non-woody biomass fuels by considerably reducing the bed agglomeration propensity in practical fluidised bed combustion plants. [ABSTRACT FROM AUTHOR]

The use of thermogravimetric analysis to describe biomass kinetics often uses bench top thermogravimetric analyser (TGA) analysers which are only capable of low heating rates. The aim of this research was to compare experimental fast pyrolysis of Olive kernels in a bespoke laboratory thermogravimetric fluidised bed reactor (TGFBR) characterised by rapid heating rates at high flow rates, compared to a smaller bench scale fixed bed TGA system. The pyrolysis in the TGFBR was analysed by using the isothermal kinetic approach and it was theorised that the pyrolysis decomposition reactions occurred by two mechanisms depending on the temperature, resulting in an activation energy of 67.4 kJ/mol at temperatures below <500 °C and 60.8 kJ/mol at temperatures >500 °C. For comparison, a bench scale TGA was used to look at the thermal behaviour in different fixed bed thermal conditions giving a higher activation energy of 74.4 kJ/mol due to the effect of external particle gas diffusion. The effect of biomass particle size (0.3-4.0 mm) on the conversion of biomass at different temperatures, was investigated between 300 and 660 °C in the TGFBR. The results suggested inhibition of internal gas diffusion was more important at lower temperatures, but in comparison had no significant effect when measured in the fixed bed TGA at lower heating rates. Bench top TGA analysis of pyrolysis is a rapid and valuable method, but is limited by smaller sample sizes and lower heating rates. In comparison, the conditions encountered with the laboratory scale TGFBR are more likely to be relevant to larger scale systems where heat distribution, heat transfer and mass diffusion effects play major roles in the reactivity of biomass. [ABSTRACT FROM AUTHOR]

[Display omitted] • New analytical and numerical models for char conversion in CLOU were developed. • Predicted burnout time from models agreed with CLOU combustion experiments. • Using the models, the effect of operating parameters on CLOU is explored. • Char temperature is similar to that of the bed material when operating at T < 1173 K. This research concerns the combustion of a biomass char in a fluidised bed of either inert silica particles or particles of a material capable of supporting combustion using chemical looping oxygen uncoupling (CLOU). An analytical solution for combustion using CLOU was developed, accounting for the chemical reactions occurring within a mass-transfer boundary layer of a finite thickness, surrounding a char particle. The reactions considered were: (1) combustion of char with oxygen to CO and CO 2 , (2) homogenous reaction of CO with O 2 , and (3) oxygen release from CLOU particles. The thickness of the boundary layer, γ, was evaluated using correlation in the literature and the combustion of the char particle was modelled as a shrinking particle. Results from the model were compared with experiments performed by combusting char from birch-wood and activated carbon in a fluidised bed (i.d. 30 mm) of either particles capable of CLOU (CuO supported on mayenite) or inert silica sand. Both types of experiments were undertaken with a partial pressure of oxygen, p O 2 , close to the equilibrium pressure of O 2 over CuO at 1173 K, i.e. ∼0.016 bar of O 2. The results from the analytical model agreed with the experimental observations from both beds. In addition to the analytical solution, fuller, numerical models were developed, in which a char particle and its surroundings were discretised in 1D to solve the mass balance equations and to assess the validity of the assumptions made in the analytical solution. To establish the range of conditions in which the analytical solution is valid, various cases were simulated. For example, char combustion and gasification in a bed of CuO-particles fluidised by CO 2 -rich gas. Hence, besides the validation of the analytical solution, the results of the numerical solutions provided insight into the importance of char gasification with CO 2 on the overall particle conversion in CLOU at the industrial scale. [ABSTRACT FROM AUTHOR]

This paper reports the diagnosis of bed agglomeration during biomass fast pyrolysis in a fluidized-bed reactor at a wide range of temperatures (200–700 °C). The results show that under all conditions, bed agglomeration can be modelled using sand loading ( S L ), which is the mass of sand that directly interacts with the incoming biomass feed normalised to the total mass of biomass fed into the reactor. The values of sand loading S L during pyrolysis is greatly influenced by the ethanol-soluble extractive contained within the raw biomass. For the pyrolysis of the raw biomass, at temperatures <310 °C, S L follows an endothermic reaction pathway ( E a = 28 kJ/mole) during which its values increases with increasing temperature. However, at higher temperatures >350 °C, S L follows an exothermic reaction pathway ( E a = –45 kJ/mole) during which its values decrease with increasing temperature. [ABSTRACT FROM AUTHOR]

The present work concerns with CFD modelling of biomass fast pyrolysis in a fluidised bed reactor. Initially, a study was conducted to understand the hydrodynamics of the fluidised bed reactor by investigating the particle density and size, and gas velocity effect. With the basic understanding of hydrodynamics, the study was further extended to investigate the different kinetic schemes for biomass fast pyrolysis process. The Eulerian–Eulerian approach was used to model the complex multiphase flows in the reactor. The yield of the products from the simulation was compared with the experimental data. A good comparison was obtained between the literature results and CFD simulation. It is also found that CFD prediction with the advanced kinetic scheme is better when compared to other schemes. With the confidence obtained from the CFD models, a parametric study was carried out to study the effect of biomass particle type and size and temperature on the yield of the products. [ABSTRACT FROM AUTHOR]

Fast pyrolysis of biomass in a fluidised-bed reactor incorporated with a moving-bed granular filter is carried out to investigate the effects of pyrolysis and filter temperatures on product yields and bio-oil properties. The results showed that increasing the pyrolysis temperature reduced organic bio-oil and increased reaction water. When the temperature was increased from 400 to 500 °C, the char decomposed to permanent gas and reaction water. Further increase to 550 °C caused the organics to transform to gas. The proportion of CO2 reduced with pyrolysis temperature, while other gases increased. The increase of the filter media temperature from 350 to 380 °C resulted in the decomposition of char to reaction water. Bio-oil water content increased with both pyrolysis and filter temperatures, whereas opposite trend was found with the viscosity. Increasing the filter temperature could lower the bio-oil solids content. Both temperatures did not affect the bio-oil pH and density. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics analysis of a fluidised bed combustor fuelled by coal and biomass is performed. A discrete phase modelling approach is used to track fuel particles. Combustion is modelled using a two-mixture fraction probability density function approach. The standard k-ɛ two-phase turbulence model is used to describe the gas-solids flow. The residence time of coal particles is found to be greater than that of biomass particles. Contours of char burnout and devolatilisation are obtained and combustion is found to be quantitatively complete, and thus no significant change in combustion efficiency is found under full-load conditions. Velocity vectors are obtained and it is found that the velocity increases from the notch region towards the exit of the furnace, owing to the reduction in cross-sectional area. Heat exchange from in-bed superheater tubes to flue gases is greatest at the highest-temperature regions of the tubes. [ABSTRACT FROM AUTHOR]

In this study, vinasse, a by-product of sugar industry, was analysed for its behaviour during combustion in a fluidised bed combustor. Due to potential agglomeration problems owing to its high potassium content, the vinasse was first pre-assessed using agglomeration indices and muffle furnace tests. Subsequently it was co-fired with Thoresby singles coal in a bubbling fluidised bed of 25 kW thermal capacity. It is found that the agglomeration indices are good indicators of agglomeration tendency of biomass fuels and should be used to pre-analyse the material before firing in a fluidised bed. It was observed during cofiring in fluidised bed that agglomeration occurred very quickly due to high alkali content of vinasse. It is found that not only the alkali content of the material but its feed rate and combustion temperature are also controlling parameters for agglomeration. Vinasse can be used as potential fuel source by carefully controlling operational parameters or by adding alkali getters such as kaoline. [ABSTRACT FROM AUTHOR]

Thermo–chemical gasification of sawdust refuse-derived fuel was performed on a bench-scale fluidised bed gasifier with enriched air and steam as fluidising and oxidising agents. Dolomite as a natural mineral catalyst was used as bed material to reform tars and hydrocarbons. A series of experiments were carried out under typical operating conditions for gasification, as reported in the article. A modified equilibrium model, based on equilibrium constants, was developed to predict the gasification process. The sensitivity analysis of operating parameters, such as the fluidisation velocity, oxygen percentage of the enriched air and steam to biomass ratios on the produced gas composition, lower heating value, carbon conversion and cold gas efficiency was investigated. The results showed that the predicted syngas composition was in better agreement with the experimental data compared with the original equilibrium model. The higher fluidisation velocity enhanced gas–solid mixing, heat and mass transfers, and carbon fines elutriation, simultaneously. With the increase of oxygen percentage from 21% to 45%, the lower heating value of syngas increased from 5.52 MJ m−3 to 7.75 MJ m−3 and cold gas efficiency from 49.09% to 61.39%. The introduction of steam improved gas quality, but a higher steam to biomass ratio could decrease carbon conversion and gasification efficiency owing to a low steam temperature. The optimal value of steam to biomass ratio in this work was 1.0. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Co-gasification of biomass and petroleum coke in an atmospheric bubbling fluidised bed and thermogravimetric analyzer. [•] Synergetic effect between biomass and petroleum coke was observed. [•] The activation energy for pure petcoke is 121.5kJ/mol, for the 50/50 blend it is 96.3, and for the 20/80 blend – 83.5kJ/mol. [•] Biomass ash has a catalytic effect on the reactivity of petcoke due to the alkali and alkaline earth metals present in ash. [Copyright &y& Elsevier]

Highlights: [•] Measuring the CHON composition of a raw gas by current methods is challenging. [•] An alternative method is to burn the raw gas before measuring the CHON composition. [•] The CHON contents of the raw gas can be accurately measured by the alternative method. [•] Measuring the CHON contents of the raw gas is now performed in a “one-step” analysis. [•] The new method is used to evaluate the operation of a dual fluidised bed gasifier. [ABSTRACT FROM AUTHOR]

In the present study, particulate emissions from the co-combustion of forest biomass residues with sewage sludge in a pilot-scale bubbling fluidised bed combustor were characterised. The combustion flue gas was exhausted to the atmosphere after passing through a cyclone separator. Physical–chemical characteristics of the particles were studied: i) morphology and aerosol size, surface and volume distributions before the cyclone and ii) chemical composition (carbonates, water soluble-inorganic ions, organic and elemental carbon) before and after the cyclone. Chemical composition data were used to calculate aerosol density and refractive index. Aerosols showed a unimodal size distribution with a geometric mean diameter of 2.25±0.02μm and a geometric standard deviation of 1.27±0.01. The surface and volume mean diameters were 2.64±0.02μm and 2.91±0.05μm, respectively. Water-soluble inorganic ions were predominant in the fine particle fraction (PM2.5). The filters were loaded of crystallised mineral particles. The analysis revealed a dominance of calcium carbonate/oxide and halide (NaCl or KCl), sulphate and aluminosilicate nanocrystals forming larger mixed aggregates. [ABSTRACT FROM AUTHOR]

Abstract: The fast pyrolysis of spruce (Picea abies), short rotation willow coppice (Salix alba), Miscanthus (Miscanthus x giganteus), and wheat straw (Triticum aestivum) was compared on a laboratory scale bubbling fluidized bed reactor at 460–475°C. The presence of ash, ranging from 0.26wt.% for spruce to 3.76wt.% for wheat straw (moisture free basis) favoured decomposition of cell-wall constituents to char (spruce [11.4wt.%]Salix [45.4wt.%]>Miscanthus [37.3wt.%]>wheat straw [37.2wt.%]). Bio-oils from Miscanthus and wheat straw were inhomogeneous. Differences between absolute masses of compounds determined by GC/MS-FID of the bio-oils compared with Py-GC/MS-FID suggested a greater role of secondary reactions at the fluidised bed scale, with reduced concentrations of certain lignin-derived, furan and pyran compounds. [Copyright &y& Elsevier]

Pressed sugar beet pulp with a moisture content of 71% and wood chips with moisture contents of 15 and 55% were cofired with Thoresby coal in a 25 kW thermal capacity bubbling fluidised bed combustor over a wide range of operating conditions. The wood chips were blended with the coal in 50/50 (wt/wt) ratio. The overall moisture content of the blends was 10·3 and 30·3%. The pulp was blended with the coal in 70/30, 60/40 and 50/50 (coal/pulp, wt/wt) ratios. The overall moisture content of the blends was 25·2, 31·8 and 38·3% respectively. Emissions of NOx for the tests are compared with those from coal only firing. The emissions of NOx are found to be lower during cofiring as compared to coal only firing due to lower nitrogen content of biomass fuels. The emissions increased with increase in bed temperature when only coal was fired but decreasde with increase in bed temperature when coal pulp blends were cofired. Moreover, the emissions increase with increase in the amount of excess air. The effect of moisture on the emissions is found to be negligible. The effect of individual fuel characteristics on NOx emissions could not be quantified due to interference of other operating parameters. [ABSTRACT FROM AUTHOR]

Highlights: [•] No significant carbon deposition in fluidised bed methanation containing C2H4. [•] C2H4 is dominantly hydrogenated to C2H6 and further to CH4. [•] At lower methanation temperature, the SNG heating value increases due to C2H6. [Copyright &y& Elsevier]

Abstract: This biomass gasification process study compares the energetic and economic efficiencies of a dual fluidised bed and an oxygen-blown entrained flow gasifier from 10MWth to 500MWth. While fluidised bed gasification became the most applied technology for biomass in small and medium scale facilities, entrained flow gasification technology is still used exclusively for industrial scale coal gasification. Therefore, it is analysed whether and for which capacity the entrained flow technology is an energetically and economically efficient option for the thermo-chemical conversion of biomass. Special attention is given to the pre-conditioning methods for biomass to enable the application in an entrained flow gasifier. Process chains are selected for the two gasifier types and subsequently transformed to simulation models. The simulation results show that the performance of both gasifier types is similar for the production of a pressurised product gas (2.5MPa). The cold gas efficiency of the fluidised bed is 76–79% and about 0.5–2 percentage points higher than for the entrained flow reactor. The net efficiencies of both technologies are similar and between 64% and 71% depending on scale. The auxiliary power consumption of the entrained flow reactor is caused mainly by the air separation unit, the oxygen compression, and the fuel pulverisation, whereas the fluidised bed requires additional power mainly for gas compression. The costs for the product gas are determined as between €4.2cent/kWh (500MWth) and €7.4cent/kWh (10MWth) in the economic analysis of both technologies. The study indicates that the entrained flow reactor is competitive technology for biomass gasification also on a smaller scale. [Copyright &y& Elsevier]

Abstract: A 3D Eulerian/Lagrangian simulation incorporating multi-step reaction mechanisms has been used to study fast pyrolysis of biomass in a 100g/h fluidised bed reactor. The overall goal to optimise the production of bio-oil from fast pyrolysis is largely dependent on the thermochemical degradation process inside fluidised bed reactors. The discrete representation of biomass and sand particles in the simulation bridges accurate numerical modelling with reproducing realistic phenomena seen experimentally. Herein, the hydrodynamic bed behaviour causes temperature variations among batches of biomass particles injected at different times. It is found that such disparity affects the instantaneous tar release, causing relatively large differences in tar quantity and quality. [Copyright &y& Elsevier]

Abstract: Five Chinese fuels (one AlSi rich coal with low S content (LSC), one sulphur rich coal with low AlSi content (HSC), two straws and one sawdust) were thoroughly analysed and burned alone and blended in a bench-scale fluidised bed reactor. Flue gases and mass flows of the elements in the fine fly ash (<10μm, including condensed vapours) were analysed. In addition, chemical equilibrium calculations were carried out. When burnt alone, both straws produced significant concentrations of alkali chlorides, which cause corrosive deposits on superheaters. Both coals were capable of destroying alkali chlorides during co-firing. The destruction was based mostly on sulphation with HSC, and alkali aluminium silicate formation dominated with LSC. Bed agglomeration occurred in most of the experiments, but it will be discussed elsewhere. [Copyright &y& Elsevier]

The effects of particle size, fuel blending ratio, moisture content and excess air ratio on combustion efficiency and air emissions (CO2, CO, SO2 and NO x) from the co-combustion of white pine or peat with a Canadian lignite coal, were examined in a pilot-scale bubbling fluidised bed combustor. Pelletising was important for the efficient combustion of wood due to its high volatile content. Co-firing lignite and pine pellets gave a proportional reduction in SO2 and NO x emissions with blending ratio, while co-firing of peat and lignite resulted in increased SO2 emissions, but decreased NO x emissions. Moisture promotes combustion but with increased CO emissions, and results in increased NO x emissions, and decreased SO2 emissions. High excess air decreased CO, but moderately increased SO2 and NO x emissions. © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]

Abstract: Steam gasification of Miscanthus X Giganteus (MXG) at high heating rate in a fluidised bed reactor with the use of olivine as catalyst was investigated. The effects of temperature (815–880 °C) on the yields and the compositions of syngas and tars were determined. The experimental results show that the gas yields and the content of H2 increase with the temperature, while the yields of tar, char and the content of CO, CO2 and CH4 in the product gas decrease. Noteworthy is that about 1.1 m3 of dry gas (at ambient conditions) per kg of dry ash free biomass were obtained with about 46% of H2 and 24% of CO by volume at 880 °C. The tars composition was determined by FTIR, NMR and GC/MS. The identification of different compounds shows mainly the presence of simple molecules. This may be facilitating the possibility of complete tar reforming process (hot gas cleaning), to improvement of the syngas yield and the decrease of the formation of pollutants. [Copyright &y& Elsevier]

Energy from renewable sources is expected to contribute increasingly to the future energy supply. Particularly, the utilisation of biomass via gasification features a high potential for local energy supply. In addition to the conventional heat and power supply, the biomass-derived product gas is utilisable for further conversion, e.g. into liquid fuels, synthetic natural gas or even chemicals. In the field of biomass gasification systems, fluidised bed gasification has achieved notable relevance. Biomass gasification by fluidised bed processing produces high-quality product gas. However, the technical and economical effectiveness is not yet competitive. A major issue is the purity of the product gas, which is mainly focused on the gasification originating tar. A promising option to yield tar-free product gas is the application of a catalyst directly in the fluidised bed process. The present paper outlines catalysts for biomass gasification in fluidised bed processing. Recent activities in the development of gasifier catalysts are highlighted. Different catalysts are described depending on their performance and capability regarding tar conversion. The scope of catalysts ranges from naturally occurring materials to synthetic materials. [ABSTRACT FROM AUTHOR]

Abstract: Combustion experiments of forest biomass waste in a pilot-scale bubbling fluidised bed combustor were performed under the following conditions: i) bed temperature in the range 750–800 °C, ii) excess air in the range 10–100%, and iii) air staging (80% primary air and 20% secondary air). Longitudinal pressure, temperature and gas composition profiles along the reactor were obtained. The combustion progress along the reactor, here defined as the biomass carbon conversion to CO2, was calculated based on the measured CO2 concentration at several locations. It was found that 75–80% of the biomass carbon was converted to CO2 in the region located below the freeboard first centimetres, that is, the region that includes the bed and the splash zone. Based on the CO2 and NO concentrations in the exit flue gas, it was found that the overall biomass carbon conversion to CO2 was in the range 97.2–99.3%, indicating high combustion efficiency, whereas the biomass nitrogen conversion to NO was lower than 8%. Concerning the Portuguese regulation about gaseous emissions from industrial biomass combustion, namely, the accomplishment of CO, NO and volatile organic compounds (VOC) (expressed as carbon) emission limits, the set of adequate operating conditions includes bed temperatures in the range 750°C–800 °C, excess air levels in the range 20%–60%, and air staging with secondary air accounting for 20% of total combustion air. [Copyright &y& Elsevier]

Abstract: Using sustainably-grown biomass as the sole fuel, or co-fired with coal, is an effective way of reducing the net CO2 emissions from a combustion power plant. There may be a reduction in efficiency from the use of biomass, mainly as a result of its relatively high moisture content, and the system economics may also be adversely affected. The economic cost of reducing CO2 emissions through the replacement of coal with biomass can be identified by analysing the system when fuelled solely by biomass, solely by coal and when a coal-biomass mixture is used. The technical feasibility of burning biomass or certain wastes with pulverised coal in utility boilers has been well established. Cofiring had also been found to have little effect on efficiency or flame stability, and pilot plant studies had shown that cofiring could reduce NOx and SOx emissions. Several technologies could be applied to the co-combustion of biomass or waste and coal. The assessment studies here examine the potential for co-combustion of (a) a 600MWe pulverised fuel (PF) power plant, (i) cofiring coal with straw and sewage sludge and (ii) using straw derived fuel gas as return fuel; (b) a 350MWe pressurised fluidised bed combustion (PFBC) system cofiring coal with sewage sludge; (c) 250 and 125MWe circulating fluidised bed combustion (CFBC) plants cofiring coal with straw and sewage sludge; (d) 25MWe CFBC systems cofiring low and high sulphur content coal with straw, wood and woody matter pressed from olive stones (WPOS); and (e) 12MWe CFBC cofiring low and high sulphur content coal with straw. The technical, environmental and economic analysis of such technologies, using the ECLIPSE suite of process simulation software, is the subject of this study. System efficiencies for generating electricity are evaluated and compared for the different technologies and system scales. The capital costs of systems are estimated for coal-firing and also any additional costs introduced when biomass is used. The Break-even electricity selling price is calculated for each technology, taking into account the system scale and fuel used. Since net CO2 emissions are reduced when biomass is used, the effect of the use of biomass on the electricity selling price can be found and the premium required for emissions reduction assessed. Consideration is also given to the level of subvention required, either as a Carbon dioxide Credit or as a Renewable Credit, to make the systems using biomass competitive with those fuelled only with coal. It would appear that a Renewable Credit (RC) is a more transparent and cost-effective mechanism to support the use of biomass in such power plants than a Carbon dioxide Credit (CC). [Copyright &y& Elsevier]