•A recent review on biomass gasification in fluidized bed is presented.•LHV of the product gas increases with decreasing ER.•Gas quality hardly varies with steam to fuel ratio.•Measurements agree ...with previous studies.•Walnut shell and pistachio shell give close gas concentrations.
The present study investigates gasification of biomass in a laboratory scale set-up to obtain product gas. The gasifier is a bubbling fluidized bed (BFB) type. The bed material in the reactor is silica sand. Walnut shell and pistachio shell are gasified in the reactor under air and steam atmospheres. A gas analyzer is used to measure the CO, CO2, CH4, H2 and O2 concentrations of the product gas. The effects of equivalence ratio (ER) and steam to fuel ratio on the components of the product gas are studied for air and steam gasification cases, respectively. The lower heating value (LHV) of the product gas is calculated by using the measurement of concentrations. In the case of air gasification, the components and LHV of the product gas linearly change with varying ER. The LHV of pistachio shell is higher than that of walnut shell by 8–12% for the ER range of 0.2–0.4. The LHV increases from 3.2 to 5.4MJ/Nm3 with the decrease in ER from 0.4 to 0.2 for pistachio shell. In the case of steam gasification, the LHV is nearly constant with changing steam to fuel ratio. A product gas with a calorific value of 9.9MJ/Nm3 is generated. A recent review on biomass gasification in both pilot and laboratory scale bubbling fluidized bed gasifiers is presented. The operating conditions of the gasifiers and the components of the product gas are provided for air and steam gasification cases.
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•Addition of CaCO3 was efficient for SO2 removal in fluidized bed combustion.•Emissions of PM1 and heavy metals were also stimulated.•Reaction between Ca-Si-Al caused agglomeration ...and fragment and PM formation.•Reaction between Ca-Si-Al also led to heavy metal released from ash field.
Incineration of sludge can be an effective method to minimise waste whilst producing useful heat. However, incineration can cause secondary pollution issues due to the emission of SO2, therefore a set of experiments of sludge incineration in a bubble bed furnace were conducted with limestone addition to study desulfurization of sludge incineration flue gas. As expected, over 93% emission of SO2 was reduced with limestone addition, and that of CO and NOx were increased and decreased respectively when the fuel feeding rate raised. The distribution of fly ash was also increased by raising the fuel feeding rate due to increasing fragmentation of the ash. However, distributions of PM2.5 and heavy metals in submicron particles have dramatically increased with limestone desulfurization. The mechanism was revealed by SEM and EDS statistical analysis, indicating that the reaction between aluminosilicate and calcium made particles agglomerate and eutectic mixtures form, these larger ash particles were found to divide between collection as cyclone ash and fragmentation into finer particles that bypassed the cyclone. Those fine particles provided more surface area for heavy metal condensation. Furthermore, it was found that the reaction mechanism for semi-volatile metals involved them being released from the sludge and forming PM1 particles due to the vaporization-condensation mechanism, leading to higher emission of PM1 and distribution of heavy metals in PM1. Thus, it should be considered that there may actually be higher emission risks of PM and heavy metal emissions when aiming to desulfurize a flue gas using Ca-based minerals in certain circumstances.
Steam gasification enables the thermochemical conversion of solid fuels into a medium calorific gas that can be utilized for the synthesis of advanced biofuels, chemicals or for heat and power ...production. Dual fluidized bed (DFB) gasification is at present the technology applied to realize gasification of biomass in steam environment at large scale. Few large-scale DFB gasifiers exist, and this work presents a compilation and analysis of the data and operational strategies from the six DFB gasifiers in Europe. It is shown that the technology is robust, as similar gas quality can be achieved despite the differences in reactor design and operation strategies. Reference concentrations of both gas components and tar components are provided, and correlations in the data are investigated. In all plants, adjusting the availability and accessibility to the active ash components (K and Ca) was the key to control the gas quality. The gas quality, and in particular the tar content of the gas, can conveniently be assessed by monitored the concentration of CH4 in the produced gas. The data and experience acquired from these plants provide important knowledge for the future development of the steam gasification of biomass.
•Reference concentrations of gas and tar components for industrial steam gasifiers.•Similar gas qualities are obtained despite differences in design and operation strategies.•Availability of active compounds (K and Ca) have the strongest impact on gas quality.•Additions of Ca and K, fuel feeding position, and operating conditions are discussed.•Plant- and fuel-specific CH4-tar correlations are convenient to monitor activation.
This paper investigates the thermochemical and physical conversion processes of coal gasification numerically with particular interest on calcination in a bubbling fluidized bed furnace. A ...comprehensive Eulerian-Eulerian three-dimensional model is developed for studying the gasification process. Three calcination cases are carried out under different operating conditions while one inert case is conducted to evaluate the effect of calcination. The presented numerical results aim at determining the mechanism of coal gasification in an air-steam environment with different flowrates. Evidence of particle segregation is found in the bed of coal and limestone due to density reduction and diameter shrinkage. Char conversion is investigated for different air-coal and steam-coal ratios, also the effect of bed temperature, fluid flowrate and fuel feeding rate on the carbon conversion is studied comprehensively. The highest char conversion rate is observed in the airflow rate of 17.0 kg/h where the bed temperature is found to be maximum. A noticeable impact of calcination is found in the gaseous emission while increasing CO2 concentration. Time averaged solid and gas temperature and species concentration profiles indicate the steady-state condition of numerical simulation.
•A 3D CFD model is used for coal gasification in a bubbling fluidized bed furnace.•Influence of calcination on overall gasification is investigated.•Gaseous emission is analysed for both limestone and inert beds.•The rate of carbon conversion is analysed under different operating conditions.•Predicted results are compared with experimental analysis.
The plasma catalytic valorization of gases, particularly CH4 and CO2, has gained increasing attention. Value‐added chemicals, such as syngas and ethene, can be formed under mild conditions when ...temperature‐decoupled plasma activation and multistep feasible catalytic conversion are combined. In this sense, efficient plasma–catalyst interaction is of key importance, for which, however, plasma catalysis, as an emerging technology, is still poorly studied, where new catalyst design and investigation took up the most effort. In this perspective work, the challenging but equally important plasma–catalyst interaction is discussed, comparatively analyzing which type of plasma, catalyst bed, is the most promising. Representative plasma catalytic systems with their characteristic features are summarized, where the intrinsic capability of fluidized‐bed dielectric barrier discharge (FB‐DBD) reactor to maximize the plasma–catalyst interaction is highlighted. Furthermore, ongoing research on FB plasma catalysis is reviewed, based on which the superiority of FB‐DBD to other candidates, especially the most widely used packed‐bed DBD reactor, is critically evaluated. In addition, the perspectives of FB‐DBD, including challenges and development potential, are discussed.
Herein, we focused on the challenging but critically important plasma–catalyst interaction, comparatively analyzing the candidate plasma catalytic technologies in terms of both catalyst bed and plasma characteristics, by which, the intrinsic superiority of fluidized‐bed dielectric barrier discharge (FB‐DBD) reactor was clearly confirmed: the FB with extended powdered catalyst surface area, efficient plasma generation and high transfer of heat, combined with DBD with direct catalyst‐oriented coupling, highly nonthermal properties and appropriate ionization, can cooperatively contribute to a maximized plasma–catalyst interaction.
In the context of climate change, efficiency and energy security, biomass gasification is likely to play an important role. Circulating fluidised bed (CFB) technology was selected for the current ...study. The objective of this research is to develop a computer model of a CFB biomass gasifier that can predict gasifier performance under various operating conditions. An original model was developed using ASPEN Plus. The model is based on Gibbs free energy minimisation. The restricted equilibrium method was used to calibrate it against experimental data. This was achieved by specifying the temperature approach for the gasification reactions. The model predicts syn-gas composition, conversion efficiency and heating values in good agreement with experimental data. Operating parameters were varied over a wide range. Parameters such as equivalence ratio (ER), temperature, air preheating, biomass moisture and steam injection were found to influence syn-gas composition, heating value, and conversion efficiency. The results indicate an ER and temperature range over which hydrogen (H
2) and carbon monoxide (CO) are maximised, which in turn ensures a high heating value and cold gas efficiency (CGE). Gas heating value was found to decrease with ER. Air preheating increases H
2 and CO production, which increases gas heating value and CGE. Air preheating is more effective at low ERs. A critical air temperature exists after which additional preheating has little influence. Steam has better reactivity than fuel bound moisture. Increasing moisture degrades performance therefore the input fuel should be pre-dried. Steam injection should be employed if a H
2 rich syn-gas is desired.
As the largest coal consumer in China, the coal-fired power plants have come under increasing public concern in regard to atmospheric mercury pollution. This study developed an up-to-date and ...high-resolution mercury emission inventory of Chinese coal-fired power plants using a unit-based method that combined data from individual power plants, provincial coal characteristics, and industry removal efficiencies. National mercury emissions in 2015 were estimated at 73 tons, including 54 tons of elemental mercury, 18 tons of gaseous oxidized mercury and 1 ton of particle-bound mercury. Pulverized coal boilers emitted 65 tons, mainly in the coastal provinces and coal-electricity bases. Circulating fluidized bed boilers emitted 8 tons, mainly in Inner Mongolia and Shanxi Province. The average mercury emission intensity over the Chinese mainland was 18.3 g/GWh, which was similar to the limit for low-rank coal-fired units in the United States. The overall uncertainty of national mercury emission was estimated to be −19% to 20%, with the mercury content in coal being the major contributor. In most provinces, monthly mercury emissions generally peaked in December and August. However, monthly partition coefficients of southwest China were obviously lower than other regions from June to October due to the high proportion of hydropower generation.
•Limitations of Fenton oxidation and approaches to address them are discussed.•Heterogeneous Fenton and fluidized bed Fenton can reduce sludge generation.•Chelating agents extend the application of ...homogeneous Fenton to circumneutral pH.•Electro-Fenton & bioelectro-Fenton can reduce cost associated with Fenton’s reagent.•Perspectives on future research are offered.
Fenton oxidation is an effective technology for the degradation of recalcitrant organic pollutants. However, conventional Fenton oxidation possesses some drawbacks such as the requirement of acidic pH condition, production of iron sludge and requirement of high chemical inputs. Strategies such as heterogeneous Fenton, fluidized bed Fenton, use of chelating agents and in-situ production of Fenton’s reagent have been studied as possible solutions to these limitations. Although there have been reviews on the fundamentals and applications of Fenton oxidation, a review with focus on the limitations of Fenton oxidation and their possible solutions is lacking. Here, we review the limitations of Fenton oxidation and the recent strategies toward addressing them. For each approach, fundamentals and applications in the removal of recalcitrant pollutants are reviewed. Heterogeneous Fenton process is the most widely investigated due to the progress in catalysis. Fluidized bed Fenton process could lower sludge generation and enhance process performance. Chelating agents are used to conduct homogeneous Fenton at circumneutral pH, though the potential detrimental effect of some chelating agents remains a source of concern. In situ production of Fenton’s reagent through bioelectrochemical technology (bioelectro-Fenton) is emerging as a possible strategy to reduce the cost associated with Fenton’s reagent.
•Steam gasification via fluidized-bed is an interesting technology for hydrogen rich gas production.•The increase of steam/biomass ratio plays a major role on the hydrogen yield.•Hydrogen yield ...slightly increases as the biomass particle size decreases.•Tar yield strongly depends on reaction temperature.
A research scale fluidized-bed reactor has been built and used to study the effect of steam/biomass ratio, time duration of experiments, reactor temperature, and biomass particle size on hydrogen yield and tar content in produced syngas during steam gasification of biomass. Batch experiments were performed with wood residue crushed into three different sizes of 0.5–1mm (small), 1–2.5mm (medium), and 2.5–5mm (large), at reactor temperatures of 700, 800, and 900°C. As the steam/biomass ratio increases, a decrease in formation of CO, accompanied by an increase in the hydrogen concentration, is observed. As expected, an increase in reactor temperature leads to a significant increase of H2 output and tar reforming. The obtained results show that hydrogen yield increases as time duration of the experiment is increased. It is also found that a reduction in particle diameter leads to a significant improvement in hydrogen yield.
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