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• Simultaneous production of hydrogen and separable solid carbon from CH 4 was demonstrated in a fluidised bed. • Carbon types including CNTs, CNOs, carbon sheets, and amorphous carbon were observed. • Multiple carbon formation mechanisms were responsible for carbon growth. • High U/U mf allowed better separation of carbon from the main catalytic particles. • Lattice oxygen in the NiO/Ca 2 Fe 2 O 5 /CaO particles promoted the production of hydrogen and carbon growth. This work investigated the possibility of simultaneous production of hydrogen/syngas and separable solid carbon in a fluidised bed by using CH 4 -CO 2 cycles and exploring the carbon growth over solid catalytic particles of NiO/Ca 2 Fe 2 O 5 /CaO. This two-stage process included i) stage I: H 2 -rich gas and carbon were simultaneously generated from the interaction between CH 4 and NiO/Ca 2 Fe 2 O 5 /CaO particles; and ii) stage II: the reduced/carbon-deposited particles were regenerated in CO 2. Following our previous successful demonstration of the process for stable hydrogen production over cycles, this study focused on the formation of solid carbon and aimed at understanding its growth mechanism as well as demonstrating the potential of using fluidisation as a means of automatic carbon separation. By tracking the carbon growth history and the change in phases of the reacted NiO/Ca 2 Fe 2 O 5 /CaO particles at temperatures from 700 to 900 °C, we discovered the formation of various forms of nano-structured carbon from CH 4 conversion (e.g. partial oxidation, pyrolysis). These include carbon nanotubes (CNTs), carbon graphite sheets, carbon onions (CNOs), and carbon fibres. Amorphous carbon was also observed, particularly in the initial stage of CH 4 conversion. Higher temperatures like 800 °C and 900 °C gave faster kinetics of CH 4 conversion and more formation of solid carbon. Fe 3 C phase was observed on the reduced catalytic particles and could act as an intermediate phase or carbon sink for carbon growth. The results suggested that other mechanisms for carbon deposition, such as directly over Fe sites, may also exist. Fluidisation with a higher U/U mf ratio separated more carbon-rich fines from the bulk catalytic particles in the fluidised bed. Fluidising with air at 700 °C effectively removed amorphous carbon on the reacted catalytic particles, whilst structured carbon remained. Full separation and purification to obtain pure carbon require furthers optimisation of e.g. fluidisation parameters and material design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cable plastic, a mix of PE, XLPE and PVC, cannot be mechanically recycled. • Cable plastic steam cracking was evaluated as recycling option in an industrial scale. • Steam cracking of cable plastic shows the production of olefins and benzene. The use of plastic materials in a circular way requires a technology that can treat any plastic waste and produce the same quality of product as the original. Cable plastic residue from metal recycling of electric wires is composed of cross-linked polyethene (XLPE) and PVC, which is a mixture that cannot be mechanically recycled today. Through thermochemical processes, polymer chains are broken into syngas and monomers, which can be further used in the chemical industry. However, feedstock recycling of such a mixture (XLPE, PVC) has been scarcely studied on an industrial scale. Here, the steam cracking of cable plastic was studied in an industrial fluidised bed, aiming to convert cable plastics into valuable products. Two process temperatures were tested: 730 °C and 800 °C. The results show that the products consist of 27–31 wt% ethylene and propylene, 5–16% wt.% other linear hydrocarbons, and more than 10 wt% benzene. Therefore, 40%–60% of the products are high-value chemicals that could be recovered via steam cracking of cable plastic. [ABSTRACT FROM AUTHOR]

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]

Steam can be fully or partially substituted by CO 2 as a gasification agent. This substitution affects producer gas composition, char conversion and in-situ tar reforming. Here, wood chips were gasified in a spouting fluidised bed using silica sand and catalytic dolomitic lime as the bed material at 850 °C. The use of a gasifying agent composed of CO 2 and H 2 O was compared to the use of CO 2 or H 2 O alone. It was found that mixtures of CO 2 and H 2 O as the gasifying agent improve char conversion, and that the combined gasification agents are very effective in ensuring the decomposition/destruction of tars when lime based materials are used in the fluidised bed. [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]

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]

The reversible reaction of CaO with CO 2 can be used for post- and pre-combustion capture of CO 2 ; however, the reactivity of CaO particles is found to reduce upon repeated use. Hydration has been shown to be an effective method of increasing the reactivity of (or reactivating) CaO to CO 2 for CO 2 capture. Here, a lab-scale fluidised bed reactor was used to investigate reactivation of sorbent using steam at two different hydration temperatures of 473 and 673 K. Prior to hydration, the sorbent was cycled at three different calcination temperatures of 1123, 1173 and 1223 K; the carbonation temperature was kept constant at 973 K. Following hydration, the sorbent was either carbonated directly or carbonated indirectly via a CaO intermediate. The hydration extent was found to decrease with increasing calcination temperature before hydration and with increasing hydration temperature. The carbonation extent following hydration was found to increase linearly with hydration extent – depending on the method of carbonation – with direct carbonation resulting in higher conversions. Mass loss from the fluidised bed was found to be higher for lower hydration temperatures and increased calcination temperatures before cycling. The hydration behaviour of sorbent was subsequently investigated using a TGA at three different steam hydration temperatures of 483, 578 and 678 K. Material for the TGA tests was prepared using the lab-scale fluidised bed reactor, with a calcination temperature of 1173 K and a carbonation temperature of 973 K. In this case, the number of cycles was varied from 0 to 13, in order to provide a wider range of sorbent properties. Data from the TGA were used to project subsequent carbonation conversions and relative increases in carrying capacity across hydration. The TGA hydration tests emphasise the importance of hydration temperature and prior cycling conditions and length on the increase in carrying capacity following hydration. [ABSTRACT FROM AUTHOR]

To accelerate progress in the industrial use of RDF as an alternative fuel in gasification plants, the problems associated with hazardous solid residues and ash deposition must be resolved. The practical approach to reduce these problems must be aimed at preventing the accumulation of fly ash/condensable vapours on heat transfer surface areas while minimising the amount of residual materials that have to be treated before the disposal. One such approach is adopted in an advanced two-stage thermal process which incorporates a plasma processing stage for conditioning the gas generated from a primary waste gasification unit, primarily for the treatment of household and industrial wastes. This paper presents a comprehensive examination of ashes sampled under different operational conditions and in different locations of a two-stage fluid bed-plasma demonstration plant. A demonstration test miming the normal commercial operation was conducted over 44 h of operation with RDF from a standard UK municipal solid waste. The results are presented according to solid samples composition, gas composition, and further specific data (e.g., enrichment factor, XRD analysis, leaching test, etc.). An investigation on pollutant removal from the hot syngas, focusing on the partitioning and chemistry of sulphur and chlorine along with other relevant components, is also carried out. Experimental trials revealed a reduced extent of alkali and metals availability in the gas phase, i.e. a minor deposit forming potential into downstream equipment. From 85% to 91% of the fly ash was captured and vitrified within the plasma converter and made non-leachable with respect to non-volatile heavy metals, allowing for near complete landfill diversion. [ABSTRACT FROM AUTHOR]

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: [•] Steady state results of a two dimensional Euler–Lagrangian model for wood gasification are shown. [•] A complex reactive Euler–Lagrangian model in the dense particle regime is used for long time simulations. [•] Comparison with experimental results indicate reasonable agreement. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion is one of the leading options for power generation with CO2 capture. The process consists of burning the fuel with a mixture of nearly pure oxygen and a CO2-rich recycled flue gas, resulting in a product flue gas from the boiler containing mainly CO2 and H2O. Among the possible boiler types, fluidised bed combustors are very appropriate for the oxy-fuel process because they allow the in situ desulphurisation by feeding Ca-based sorbents into the combustor. In this work, the effect of the temperature of the combustor on the retention of the SO2 generated in the combustion of two coals with very different sulphur content (a lignite and an anthracite) has been studied. The experimental facility used was a bubbling fluidised bed (BFB) combustor of ∼3kWth. Tests were conducted under oxy-fuel combustion mode and also under enriched-air combustion mode for comparison reasons. A Spanish limestone “Granicarb” was used as Ca-based sorbent for sulphur retention. The temperatures tested were between 800 and 970°C using Ca/S molar ratios between 0 and 3. It was found that in BFB combustors operating under oxy-fuel combustion conditions the optimum temperature to achieve the highest sulphur retention was 900–925°C, whereas operating with enriched air the optimum combustion temperature was 850–870°C. Working at the optimum temperature, the SO2 retentions were lower in oxy-fuel combustion than in enriched air combustion conditions. It was also observed that working with lignite there was 10–15% of sulphur retention by coal ashes, however, working with anthracite the sulphur retention by coal ashes was negligible. This finding was independent of the combustion mode used, oxy-fuel or enriched air. [ABSTRACT FROM AUTHOR]

Abstract: After the Bovine Spongiform Encephalopathy illness appeared, the meat and bone meat (MBM) produced from animal residues became an important waste. In spite of being a possible fuel due to its heating value (around 21.4MJ/kg), an important fraction of the meat and bone meal is being sent to landfills. The aim of this work is to evaluate the co-gasification of low percentages of meat and bone meal with coal in a fluidised bed reactor as a potential waste management alternative. The effect of the bed temperature (800–900°C), the equivalence ratio (0.25–0.35) and the percentage of MBM in the solid fed (0–1wt.%) on the co-gasification product yields and properties is evaluated. The results show the addition of 1wt.% of MBM in a coal gasification process increases the gas and the liquid yield and decreases the solid yield at 900°C and 0.35 of temperature and equivalence ratio operational conditions. At operational conditions of 900°C and equivalence ratio of 0.35, the specific yield to gas (ygas ) increases from 3.18m3(STP)/kg to 4.47m3(STP)/kg. The gas energy yield decreased 24.1% and the lower heating value of the gas decreases from 3.36MJ/m3(STP) to 2.16MJ/m3(STP). The concentration of the main gas components (H2, CO and CO2) hardly varies with the addition of MBM, however the light hydrocarbon concentrations decrease and the H2S concentration increases at the higher temperature (900°C). [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]

Abstract: SNG production from coal or biomass is considered again due to rising prices for natural gas, the wish for less dependency from natural gas imports and the opportunity of reducing green house gases by CO2 capture and sequestration. Coal and solid dry biomass (e.g., wood and straw) have to be converted to SNG by thermo-chemical processes (gasification followed by gas cleaning, conditioning, methanation of the producer gas and subsequent gas upgrading). During the 1970s, a number of methanation processes have been developed comprising both fixed bed and fluidised bed methanation. Meanwhile several new processes are under development, especially with a focus on the conversion of biomass. While coal based systems usually involve high pressure cold gas cleaning steps, biomass based systems require, due to the smaller unit size, different gas cleaning strategies. Moreover, the ethylene content of a few percent, typical for methane-rich producer gas from biomass gasifiers, is a challenge for the long-term catalyst stability in adiabatic fixed bed methanation due to the inherent high temperatures. This paper reviews the processes developed for the production of SNG from coal during the sixties and seventies and the recent developments for SNG production from coal and from dry biomass. [Copyright &y& Elsevier]

Abstract: In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed to consist of a fast gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The developed model is employed to predict the dynamic response of the bed combustion to fluctuations in sludge feeding-rate. Calculation results indicate that the bed combustion is sensitive to fluctuations with response times greater than 30min, but severe delays exist for both outlet oxygen level and bed temperatures; from 6 to 13min for O2 and 22–45min for temperatures. Depending on the fluctuation frequency, the corresponding phase shifts are 39–96° for outlet O2, 138–336° for bed temperature and 80–336° for freeboard temperature. [Copyright &y& Elsevier]

Abstract: Firing or co-firing of biomass in efficient power plants can lead to high-temperature corrosion of superheaters due to condensation of alkali chlorides into superheater deposits. Corrosion can be prevented if a significant portion of the alkali chlorides present in the flue gases is destroyed before reaching the superheaters. The alkali capturing power of aluminium and ferric sulphates was determined in a pilot-scale fluidised bed (FB) reactor. The reagents were added in solution, through a spraying nozzle, to the upper part of the freeboard. Both reagents, at economical dosages, fast and effectively destroyed the alkali chlorides by producing sufficient SO3 for the sulphation. Both the mass flow rate and type of sulphate affected the sulphation ability. Thus, the cation, too, plays a role in the reaction. The required chemical dosage is not directly proportional to the Sreagent/Cl2fuel ratio because alkali chlorides must compete with calcium and magnesium oxides and probably also with alkali oxides for the available SO3. [Copyright &y& Elsevier]

Abstract: Costs of biofuel production from energy crops can be reduced by applying the crop residues in heat and power production. Perennial herbaceous crops like Cynara cardunculus L. are challenging fuels because they tend to have high ash and chlorine contents. Coals, however, are often rich in aluminium silicates and sulphur, and co-firing of these biofuels with coal could be expected to reduce operational problems. In addition, CO2 emissions are lower than during coal firing alone. Blends of Cynara and two coals, South African bituminous and Spanish sub-bituminous coal, were combusted in a 20kW bubbling bed pilot reactor to ascertain the ability of the coals to reduce operational problems by alkali capture. The Cynara fuel sample contained almost 2wt% chlorine. The South African coal was rich in kaolinite capable of capturing alkalies from chlorides to produce alkali aluminium silicate and HCl. The Spanish coal was rich in sulphur (mostly present as FeS2), and produced high concentrations of SO2 that partially oxidised to SO3. The SO3 can capture alkalies from chlorides by sulphation. Up to 30% Cynara, on energy basis, could be co-fired with Spanish coal without operational problems, whereas the same percentage of Cynara with South African coal led to strong Cl deposition. Co-firing of Cynara with both coals resulted in high HCl emissions (up to 1500mg/Nm3 in 6% O2). In addition, co-firing of the Spanish coal led to very high SO2 emissions (up to about 16,000mg/Nm3 in 6% O2). Thus, a power plant capable of firing such blends must be equipped with flue gas cleaning equipment for effective SO2 and HCl capture in the flue gas channel after the superheaters, or else the quality of the Cynara must be markedly improved by changing the harvesting technology and fertilisers, which could be major sources of high ash and chlorine content in the fuel. [Copyright &y& Elsevier]

Abstract: Because little information is available about sewage sludge gasification in a bubbling fluidised bed (BFB), further experiments are required to quantify the power generation potential of dried sewage sludge (DSS) as well as to evaluate the optimum conditions for its gasification. In this work, the influence of the bed height on the process was experimentally determined using a laboratory-scale BFB reactor. The gasification tests were performed at different values of equivalence ratio (λ) and at two values of constant bed height (150 and 300mm). Attention was focused on the effect of increasing bed height on the gas composition, average cold gas efficiency, and product distribution. Results obtained in this study show that a bed height increase improves the efficiency of the DSS gasification process. This fact could be explained because the high ash content of DSS represents an obstacle to the gas diffusion. [Copyright &y& Elsevier]

Abstract: Atmospheric bubbling fluidised bed coal combustion (ABFBCC) of a bituminous coal and an anthracite with particle diameters in the range 500–4000μm was investigated in a pilot-plant facility, with and without limestone addition. The experiments were conducted at steady-state conditions using three excess air levels (10, 25 and 50%) and bed temperatures in the range 750–900°C. Combustion air was staged, with primary air accounting for 100, 80 and 60% of total combustion air. During limestone addition, in general, the NO emission decreases with the decrease in excess air and the increase in air staging, for both coals (as also observed without limestone). The bed temperature does not influence the NO emission significantly (as also observed without limestone); however, it was observed that during bituminous coal combustion there is a slight trend for a decrease on the NO emission with temperature increase in the range 825–900°C, whereas for anthracite coal the trend is the opposite. On the other hand, the N2O emission increases with: the decrease in excess air, the increase in air staging (as opposed to what was observed without limestone), and the decrease in bed temperature (as also observed without limestone). Taking the coal combustion without limestone as reference, it was observed that the effect of limestone addition on the NO and N2O emission depends on the first stage stoichiometry: (1) under first stage fuel lean conditions the NO emission increases, while that of N2O decreases, (2) under first stage fuel rich conditions (for example, high air staging) the opposite trend is observed. [Copyright &y& Elsevier]

Abstract: Atmospheric Bubbling Fluidised Bed Combustion (ABFBC) of a bituminous coal and anthracite with particle diameters in the range 500–4000μm was investigated in a pilot-plant facility (circular section with 0.25m internal diameter and 3m height). The experiments were conducted at steady-state conditions using three excess air levels (10, 25 and 50%) and bed temperatures in the 750–900°C range. Combustion air was staged, with primary air accounting for 100, 80 and 60% of total combustion air. The effect of limestone addition was also tested. Large CO concentrations were observed inside the bed, up to 8 and 6% (v/v) in the cases of anthracite and bituminous coals, respectively. These concentrations decreased sharply as the gases emerged from the bed, and the CO flue gas concentration observed was in general less than 2000 and 4000ppm, respectively. The CO flue gas concentration increased with air staging and with limestone addition, but decreased with either excess air or temperature increase. The observed results confirm the influence of sand particles (and probably of SO2) in the ‘quenching’ of the oxygenated free radicals (HO and HO2) reactions responsible for the CO oxidation inside the bed. [Copyright &y& Elsevier]

Biomass fuels often contain higher concentrations of easily vaporisable alkalis and chlorine than do coal and peat. The more vaporisable the alkalis or chlorine compounds the higher is the risk for ash-related problems. The presence of certain elements may reduce or remove these problems. This work shows how co-combusting of different biomass fuels in a fluidised bed boiler can result in useful interactions that decrease or totally inhibit Cl deposition and bed agglomeration. In a first set of experiments, fuel 1 contained easily vaporised chlorine that produces Cl-rich deposits on superheaters. Fuel 2 was enriched in aluminium silicate, but contained much ash, resulting in low heating value and high load of fly ash. In a second set of experiments, fuel 1 was enriched in Cl and alkalis, which lead to corrosive deposits, bed agglomeration and fouling. As a result of protecting reactions, the mixtures were free from the problems observed during their separate combustion. [Copyright &y& Elsevier]

Recently new environmental regulations of fossil fuels have further increased interest in the use of waste and biomass for energy generation. Co-combustion is generally viewed as the most cost-effective approach to biomass and wastes utilisation by the electric utility industry.The aim of this paper is to assess the feasibility of co-firing coal and a very specific biomass waste from the olive oil industry: foot cake, in a fluidised bed. This waste is quite difficult material to be used in combustion process, due to its high moisture content and alkaline content in ashes.Two different Spanish coals were selected for this study: a lignite and an anthracite. The combustion tests were carried out in the CIEMAT bubbling fluidised bed pilot plant. In order to study the effect of different parameters on the emissions and combustion efficiency, the tests were done using different operating conditions: furnace temperature, share of foot cake in the mixtures and coal type.The pilot plant tests show that the combustion of foot cake/lignite or anthracite mixtures in bubbling fluidised bed is one way to utilise this biomass residue in energy generation. The presence of foot cake in the mixtures has not any significant effect on the combustion efficiency. SO2 and NOx emissions decrease when the amount of foot cake in the mixtures increases, while N2O emission increases. [Copyright &y& Elsevier]

Steam gasification studies were carried out in an atmospheric fluidised bed. The gasifier was operated over a temperature range of 700–900 °C whilst varying a steam/biomass ratio from 0.4 to 0.85 w/w. Three types of forestry biomass were studied: Pinus pinaster (softwood), Eucalyptus globulus and holm-oak (hardwood). The energy conversion, gas composition, higher heating value and gas yields were determined and correlated with temperature, steam/biomass ratio, and species of biomass used. The results obtained seemed to suggest that the operating conditions were optimised for a gasification temperature around 830 °C and a steam/biomass ratio of 0.6–0.7 w/w, because a gas richer in hydrogen and poorer in hydrocarbons and tars was produced. These conditions also favoured greater energy and carbon conversions, as well the gas yield. The main objective of the present work was to determine what reactions were dominant within the operation limits of experimental parameters studied and what was the effect of biomass type on the gasification process. As biomass wastes usually have a problem of availability because of seasonal variations, this work analysed the possibility of replacing one biomass species by another, without altering the gas quality obtained. [Copyright &y& Elsevier]

The main results of an experimental work on gasification of Colombian coal in a fluidised bed are reported in this paper. Experiments were carried out at different steam/coal (Fs/Fc) and air/coal (Fa/Fc) ratios and temperatures of gasifying agent. In addition, the influence of bed temperature on coal conversion was analysed. Results show a maximum value in the curve of high heating value versus Fa/Fc. From the environmental standpoint, low concentrations of sulphur compounds were obtained but more work should be done in order to decrease particulate matter. [Copyright &y& Elsevier]

A probe-based technique for measurement of gas phase metal species in flue gas at high temperatures has been developed. This paper deals with work carried out to test and evaluate the technique through field measurements of cadmium species during co-combustion of sewage sludge and other solid fuels in a circulating fluidised bed combustion boiler. During the measurements of vaporous cadmium forms, solid fly ash samples were also collected at the measurement positions. Chemical composition data from these fly ash samples were used to discuss the influence that the fly ash filter cake built up on the probe tip can have on the measurements. Additionally, the solid samples were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to have a better insight into the problem. Using the data from the field measurements and/or from the integrated measurements and weighing devices of the boiler the mass balance of cadmium from the combustion process was calculated by different methods. The calculation results were fairly consistent. In one method, data from the field measurements was used. This method gave the mass balance for cadmium in the process Cdout/Cdin=113.6%, which was a very good result considering that it involved the analysis of trace amount of metals in full-scale measurements. [Copyright &y& Elsevier]

• Very low concentrations of tar measured under conditions of oxy-fuel gasification. • Effects of oxy-fuel conditions on fuel-S released as H 2 S measured. • S retention influenced by the high partial pressure of CO 2. • Raising the T and P increased the proportion of fuel-N released as NH 3. • Up to 40% of fuel-N released as NH 3 in CO 2 /steam at 950 °C. The release of species of environmental concern during simulated oxy-fuel gasification in a laboratory scale fluidised bed have been investigated. Fluidising gases containing a high partial pressure of CO 2 and in some tests, steam, were used. The species considered are tars, H 2 S and NH 3 and the aim has been to gain an understanding of the impact of the gasifer operating conditions on their release. This is part of a programme of work on the potential of oxy-fuel gasification as a means of enabling the use of coal to continue as a source of energy, whilst capturing the CO 2 for sequestration to minimise the impact on climate change. It has been shown that the tars released during pyrolysis are efficiently destroyed during their passage through the hot, char containing bed. The measured emission of tar was very low, particularly when compared to a conventional fixed bed gasifier. The extent of S release as H 2 S depends on the fuel-S and ash-Ca contents, and on the operating conditions. Increasing the partial pressure of CO 2 , steam and raising the temperature increased the proportion of S released. Adding dolomite, to retain S, decreased the emission level at atmospheric pressure, provided the temperature was above 950 °C. The use of this method to reduce S emissions at elevated pressure would require careful consideration, as the high partial pressure of CO 2 in the fluidising gas can prevent the calcination of the dolomite and therefore reduce its effectiveness. Steam was found to increase the proportion of fuel-N converted to NH 3 and the concentration also depended on the bed temperature. A peak in the concentration was noted at 850 °C, due to the opposing impacts on increased release as the temperature was raised and increasing equilibration of NH 3 to N 2 and H 2. [ABSTRACT FROM AUTHOR]