Laboratory-scale Fluidized Bed Reactor Research Articles

Investigating combustion efficiency and NOx emission reduction in fluidized bed ammonia-coal co-firing

Ammonia, a carbon-free fuel, can significantly reduce CO2 emissions when co-fired with coal in power plants. Fluidized bed combustion, known for its excellent gas-solid mixing and low NOx emissions, is a promising method for ammonia-coal co-firing. However, challenges remain in optimizing ammonia injection and controlling nitrogen oxide emissions. This study investigates these aspects using a lab-scale fluidized bed reactor with flexible ammonia injection points. Key variables, such as ammonia co-firing ratios, injection location, temperature, and outlet oxygen concentration, are examined. The results show that with ammonia injection ratios up to 70 %, NO and N2O emissions slightly increase, while ammonia escape is maintained below 5 ppm. Air staging effectively controls NOx emissions, and higher temperatures promote N2O decomposition, but increase NOx levels. Ammonia injection does not raise unburned carbon content. Rate of production and sensitivity analyses highlight the role of OH radicals in ammonia conversion and identify the critical reactions affecting NO generation. This study highlights the feasibility of fluidized bed ammonia-coal co-firing technology.

Fluidized-bed OCM reaction: A promising Mn2O3-Na2WO4/TiO2 catalyst and a numerical study

The fluidized-bed reactor with excellent heat and mass transfer features has great appeal for application in the oxidative coupling of methane (FB-OCM), whereas qualified fluid catalysts represent a grand challenge. Herein, we report a high-performance Mn2O3-Na2WO4/TiO2 fluid catalyst (5.4 wt% Mn2O3 and 2 wt% Na2WO4), which was obtained by the incipient-wetness impregnation method and examined in the OCM reaction in an electric-heating quartz fluidized-bed reactor (i.d., 2 cm). The standard normalization method on the basis of carbon atom was used for calculating the CH4 conversion and C2-C3 selectivity. This catalyst achieves 35.5 % CH4 conversion, 66 % C2-C3 selectivity and particularly 15.1 % single-pass yield of C2H4 for a feed of CH4/O2/H2O=3/1/1 with a catalyst dosage of 20 mL at 700 °C and a total GHSV of 7200 h−1. Such catalyst is stable for at least 50 h without signs of deactivation and agglomeration/defluidization. The catalyst particle size is crucial for the FB-OCM reaction with respect to the reaction light-off and catalyst fluidization. The catalyst with preferable particle size of 450–600 μm can not only trigger the OCM reaction at a relatively low temperature of 630 °C but also warrant active bubbling fluidization. Furthermore, thanks to the low amount of Na2WO4 and interpenetrating structure of TiO2-nanorod, such catalyst achieves good anti-aggregation and robust mechanical strength (with a low attrition index of 1.9 %). The effects of water-adding amount in feedstock and catalyst particle size distribution on the hydrodynamics behaviour were investigated in a laboratory-scale fluidized-bed OCM reactor by using numerical simulation method.

Adsorptive and oxidative removal of phenolphthalein by sono-assisted synthesized FeAcC in advanced oxidation-integrated fluidized bed reactor

ABSTRACT Environmental water sources are under increasing threat due to the addition of harmful chemicals not addressed by conventional water treatment processes. To work on this concern, the current study aimed to synthesize sono-assisted Fe-modified activated carbon-chitosan (FeAcC) composite and construct a laboratory-scale ozone-integrated fluidized bed reactor (FBR) to eliminate phenolphthalein (php). Following 120 min of incubation, the adsorbent demonstrated a 27.28 mg g−1 of php adsorption capacity at pH 4 with 0.5 g L−1 of adsorbent dosage. The adsorption efficacy and mechanism were defined using isotherm and kinetic models. The study investigated the impact of different factors including, initial concentration, reuse of FeAcC, recirculation flow rate, and hydraulic retention time (HRT), on the efficiency of php removal. The optimum removal efficiency was observed at approximately 95% after 20 min of operation at 1.5 L min−1 recirculation flow rate (batch FBR) and 70 min of HRT (continuous FBR) under 400 mg h−1 ozonation rate. Experimental parameters were optimized using response surface methodology (RSM) with central composite design (CCD) to improve php removal. The large-scale implementation of the findings in the future can be a step for adding new technology for clean water treatment processes for emerging toxic pollutants.

Effect of CaO addition on the migration behavior of nitrogen and sulfur during Beipiao oil shale combustion

Adding CaO during the combustion of oil shale (OS) reduces sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions, but it is challenging to synergistically control SO2 and NOx during fluidized combustion. This study utilized a lab-scale fluidized-bed reactor to explore the transformations of nitrogen and sulfur during the combustion of Chinese Beipiao oil shale (BOS) under different temperatures and Ca/S molar ratios. CaO significantly changed the combustion characteristics of OS by slowing the combustion rate of organic matter and altering the transformation mechanisms of nitrogen and sulfur. As the combustion temperature increased, the NO emissions initially rose and then decreased, while SO2 showed the opposite trend. The addition of CaO promoted the conversion of NH3 and HCN into NO and facilitated the reduction of NO to N2 through reactions with CO and char, which helped control NOx. Moreover, when the Ca/S molar ratio was 4.53, CaO reacted with released SO2 to form CaSO4, which significantly increased the sulfur fixation rate to 90.82 %. This research provides guidance for optimizing large-scale clean combustion technologies for OS and reducing pollutant emissions.

Performance evaluation of red mud-based oxygen carriers in the chemical looping gasification of wet sludge rich in iron

A high-performance and low-cost oxygen carrier (OC) is the key for industrialization of chemical looping gasification (CLG) technology for sludge treatment. In this work, four OCs (RM_15 %CuO, RM_10 %CuO, RM, RM_POC) were prepared in an industrial-scale granulation equipment. The red mud was composited by mixing with different amounts of CuO and MnO2, then subjecting to different calcination temperatures. Firstly, the oxygen decoupling and oxygen carrying capacities of the OCs were compared using 5% H2 as the reducing agent. RM_15%CuO and RM_POC showed excellent oxygen release capabilities, with oxygen release loss of −1.99 % for RM_15%CuO. The catalytic gasification performances of RM_15%CuO and RM_POC were evaluated in a lab-scale fluidized bed reactor with wet sludge as the feedstock. Both OCs were able to maintain the H2 concentration of over 44.6% and no less than 79.2% sludge gasification efficiency after 30 cycles. However, the H2 content was clearly higher in case of RM_POC. SEM-EDS was used to analyze the influence of sludge ash, rich in Fe, on the performance of two OCs after the fluidized bed operation. The results showed that the sludge ash sample with more than 20% Fe2O3 could transfer its lattice oxygen to assist OC and prevent the in-situ segregation of Fe phase in the POC surface. However, the inhibitory effect of RM_15%CuO was much lower. The degradation performance of RM_POC carrier was slower and thus the H2 content was higher. This performance evaluation provides a theoretical guide for chemical looping gasification of sludge in future with an idea of mixed ratio of recycling sludge ash to the RM_POC.

Desulfurization characteristics of slaked lime and regulation optimization of CFB-FGD (circulating fluidized bed flue gas desulfurization) process—A combined experimental and numerical simulation study

Circulating fluidized bed flue gas desulfurization (CFB-FGD) process has been widely applied in recent years. However, high cost caused by the use of high-quality slaked lime and difficult operation due to the complex flow field are two issues which have received great attention. Accordingly, a laboratory-scale fluidized bed reactor was constructed to investigate the effects of physical properties and external conditions on desulfurization performance of slaked lime, and the conclusions were tried out in an industrial-scale CFB-FGD tower. After that, a numerical model of the tower was established based on computational particle fluid dynamics (CPFD) and two-film theory. After comparison and validation with actual operation data, the effects of operating parameters on gas–solid distribution and desulfurization characteristics were investigated. The results of experiments and industrial trials showed that the use of slaked lime with a calcium hydroxide content of approximately 80% and particle size greater than 40 μm could significantly reduce the cost of desulfurizer. Simulation results showed that the flow field in the desulfurization tower was skewed under the influence of circulating ash. We obtained optimal operating conditions of 7.5 kg·s−1 for the atomized water flow, 70 kg·s−1 for circulating ash flow, and 0.56 kg·s−1 for slaked lime flow, with desulfurization efficiency reaching 98.19% and the exit flue gas meeting the ultraclean emission and safety requirements. All parameters selected in the simulation were based on engineering examples and had certain application reference significance.

The Influence of Solid Heat Carrier Load of Char on Pyrolysis Characteristics of Pulverized Coal in a Fluidized Bed Reactor

Pulverized coal pyrolysis based on solid heat carrier has a huge advantage in high tar yield. In this study, pyrolysis experiments on pulverized coal were conducted in a lab-scale fluidized bed reactor at 650 °C, utilizing char as the solid heat carrier. The influence of mass ratio of char to coal (RATIO) was investigated. Results show that the incorporation of solid heat carrier of char significantly enhanced the primary pyrolysis reaction in coal pyrolysis, resulting in increasing yields of tar and gas but reducing one of char. The yield of tar maximally reached 148.80–262.22% of the Gray–King analysis value at the RATIO of 14.52 g/g. As the RATIO increased, the tar contained more light component content, indicating that incorporating solid heat carriers improved the tar quality. These findings offer significant insights for the design of fluidized bed pyrolysis unit utilizing char as solid heat carrier.

Process performance and precipitate quality of phosphorus recovery by struvite precipitation in a fluidized bed reactor using a MgO industrial by-product

Phosphorus recovery through struvite precipitation has gained interest due to the potential use of struvite as a fertiliser, with fluidised bed reactors being a popular technology for carrying out the process. Struvite precipitation requires a magnesium source and an alkaline reagent. This research uses a low-grade magnesium oxide (LG-MgO) industrial by-product with a 56 wt% of MgO as magnesium source and an alkaline reagent to lower operating costs and value-add an industrial by-product. LG-MgO is poorly soluble in water, but its solubility increases significantly when dissolved in anaerobic digestion supernatants due to its circumneutral pH and high buffer capacity. Phosphorus precipitation was carried out in a laboratory-scale fluidised bed reactor where three operating variables (i.e. P:Mg molar ratio, feed inlet position, and recirculation flow rate) were studied to determine the LG-MgO impact on precipitate struvite content. Experimental results showed a high struvite content in all precipitates, close to the values reported for pure magnesium sources. The P:Mg molar ratio influenced precipitate composition. The percentage of struvite in the precipitate were 75–82 wt%, 85–88 wt%, and 75–76 wt% for the P:Mg ratio of 1:0.5, 1:1 and 1:3, respectively. The feed inlet position (side or bottom) also had an impact on precipitate struvite content when the P:Mg molar ratio was 1:3, but not for the other molar ratios. The recirculation flow rate did not have a significant impact on precipitate struvite content.

Co-Gasification of Polyethylene and Biomass in Catalytic Bed Material

In this work, a simplified comprehensive three-dimensional numerical model is developed to study the effect of hydrogen production on co-gasification of biomass and low-density polyethylene (LDPE). CFD software AVL Fire 2020 inbuilt algorithms were employed to develop the gas phase while the solid phase was developed by user-defined FORTRAN subroutines. Solid hydrodynamics, fuel conversion, homogenous and non-homogenous chemical reactions, and heat transfer, including radiation, subroutines were defined and incorporated into AVL FIRE explicitly. Species concentrations of the syngas were analyzed for co-gasification of Beechwood and LDPE for three distinct types of bed materials (silica sand, Na-Y zeolite, and ZSM-5 zeolite). Then, the model is validated with experiment results available in the literature for a lab-scale fluidized bed reactor. The highest hydrogen production was observed in Na-Y zeolite followed by ZSM-5 zeolite and silica in both numerical and experimental analysis for the co-gasification of Beechwood and LDPE, providing a reasonable agreement between the numerical and the experimental results. Therefore, the current model predicts the enhancement of the quality of hydrogen-rich syngas through the application of co-pyrolysis within a fluidized bed reactor, incorporating a catalytic bed material.

Coupled kinetic and hydrodynamic model for a carbonator reactor of calcium looping process: Sulfur dioxide effect

The application of the calcium looping (CaL) process for CO2 capture has gained recognition as a highly efficient technology in mitigating greenhouse gases emission. In this study, by considering the characteristics of the adsorbent and the hydrodynamics of the fluidized bed in the fast fluidization regime, a fractal-like random pore kinetic model and a 1D hydrodynamic model were combined together. In order to validate the kinetic model, experimental carbonation data obtained from a lab-scale fluidized bed reactor under realistic operational condition and in the absence/presence of SO2 gas were used. The results demonstrated a satisfactory agreement between the model and experimental data, as indicated by the maximum absolute error of 1.23% and 1.78% in the absence and presence of SO2, respectively. Based on sensitivity analysis, the efficiency of the carbonator reactor was found to be predominantly affected by the solid inventory in the bed and the gas inlet velocity. Also, the results of this analysis indicate that in the presence of SO2, a higher make-up flow rate leads to a more pronounced enhancement in the efficiency of the carbonator reactor, as compared to the absence of SO2 in the reaction environment. Results of modelling indicated that the presence of SO2 necessitated a 36.5-fold increase in the minimum-required make-up flow to attain comparable efficiency obtained in the condition of the absence of SO2. Furthermore, the results of modelling as a function of number of cycles demonstrated a substantial decline in the efficiency of the carbonator reactor, which in the absence of SO2, the efficiency decreased from 68.13% to 18.81%, while in the presence of SO2, it decreased from 45.53% to 4.75% over 100 sequential cycles.

Scaling a Gas Phase Residual Lithium Conversion Process on Ni-Rich NMC Cathode Materials in Commercial Fluidized Bed Reactors

‘Residual lithium’, the LiOH and Li2CO3 surface contamination that is ubiquitous to Ni-rich NMC manufacturing, is a significant obstacle in the large-scale production and handling of high-nickel layered oxides. These hydroxide and carbonate surface phases influence reproducibility and shelf stability of the NMC powder and cause gelation and particle aggregation during electrode casting. There is ample evidence in the literature that atomic layer deposition (ALD) possesses a two-fold solution to this problem.1-3 First, reactive organometallic species such as trimethylaluminum (TMA) can convert insulating residual lithium to a Li-rich LixAlyO conducting layer. Customizable ALD layers can then be added to inhibit the re-formation of the carbonate layer and to deter negative side reactions of the CAM surface with the liquid electrolyte. While highly impactful, these studies have mostly been relegated to small, lab-scale demonstrations of <50 g. As such, there remains a need to enable this ALD-assisted-technology for high-throughput commercial applications.In this talk, we will explore the progression of a residual lithium conversion process from lab (10 – 1000 mL) to industrial-scale (10 L – 100 L) fluidized bed equipment and how scale and material-dependent parameters can impact performance. Using a commercial NMC 811 cathode as a case study, we first applied aluminum phosphate ALD coatings on a lab-scale fluidized bed reactor to examine the interfacial and electrochemical changes of the CAM material under various process conditions. ICP-OES measurements confirmed linear and reproducible deposition versus ALD cycle number between 200- 300°C. XPS analysis showed the ALD coated NMC 811 powder had an 80% reduction in Li2CO3 versus the pristine material and that a reduction persisted even after 10 days of storage in atmospheric conditions. At standard (0.5C/1C) cycling to 4.4V, AlPO4 coatings increased cycle life by 44% versus the uncoated powder. Under optimized conditions, the process was scaled first to 1 kg and finally to 10 kg in a pilot-scale reactor. In-situ mass spectrometry indicated that residual lithium conversion byproducts such as CO2 could be used to monitor reaction progress and optimize chemical usage efficiency. Fluidization aids including vibration and mechanical stirring were used to inhibit and break up powder agglomerates. ICP-OES and electrochemical cycling data confirmed reproducible deposition and cycle life benefits versus the small scale runs and pristine materials, demonstrating a pathway for these ALD-enhanced materials to transition from lab-scale demonstration to viable product. We will discuss strategies for continuing the scaling process to 100 kg batches for commercial applications.[1] M. Young et al., The Journal of Physical Chemistry C 2019 123 (39), 23783-23790[2] P. Darapaneni et al., ACS Applied Energy Materials 2022, 5, 8, 9870–9876[3] J. Li et al., Coatings 2022, 12(1), 84

Numerical modelling of biomass gasification with steam injection for catalytic bed materials

Biomass gasification with steam injection in a fluidized bed reactor has emerged as a promising method to improve syngas quality by increasing hydrogen production. In this work, a simplified yet comprehensive three-dimensional multiphase model incorporating combustion chemistry and heat transfer was integrated into AVL FIRE CFD software through the implementation of user-defined subroutines. Biomass combustion and gasification for four different bed materials acting as catalysts to the biomass pyrolysis process with steam injection were investigated for this work. Beechwood was consistently used as the biofuel for all the experiments while varying the bed material. Four various types of bed materials (Silica sand, Olivine, Na–Y Zeolite, and ZSM-5 Zeolite) were used in the study and a constant steam injection was maintained. ZSM-5 Zeolite exhibited the highest hydrogen production under steady-state condition. The present model was validated against experimental results available in the literature for a lab-scale fluidized bed reactor. The model's results of species concentrations of the syngas were analyzed and compared with the experimental results and found reasonable similarity.

Design and first application of a novel laboratory reactor for alkali studies in chemical looping applications

Alkali compounds are readily released during biomass conversion and their complex interactions with reactor walls and sampling equipment makes detailed investigations challenging. This study evaluates a novel laboratory-scale fluidized bed reactor for chemical looping combustion (CLC) studies. The reactor design is based on detailed consideration of the behavior of alkali-containing molecules and aerosol particles and is guided by computational fluid dynamic simulations. The design allows for interactions between gaseous alkali and a fluidized bed, while minimizing alkali interactions with walls before and after the fluidized bed. The function of the laboratory reactor is demonstrated in experiments using online gas and alkali analysis. Alkali is continuously fed to the reactor as KOH or KCl aerosol with and without a fluidized bed of the oxygen carrier CaMn0.775Ti0.125Mg0.1O3-δ present in inert, reducing and oxidizing conditions at temperatures up to 900 °C. Alkali uptake by the OC is characterized in all conditions, and observed to sensitively depend on gas composition, reactor temperature and type of alkali compound. The experimental setup is concluded to have a significantly improved functionality compared to a previously used reactor, which opens up for detailed studies of interactions between alkali compounds and oxygen carriers used in CLC.

Characterization and gasification of end-of-life banknotes rich in cotton content

Many central banks are reviewing their environmentally sustainable activities, including the disposal of end-of-life banknotes, within the scope of green finance policies aimed at reducing environmental impacts. The total amount of banknote production waste and end-of-life (non-reusable) banknotes is estimated to exceed 185.000 tons per year worldwide. End-of-life banknotes are commonly disposed of as combustion, incineration for energy recovery, and landfill. In this study, the characterization and gasification of end-of-life banknotes rich in cotton content, which are classified as lignocellulosic waste, were investigated to bring them into the economy more effectively. The proximate, calorific value, lignocellulosic, elemental, and metal analyses were performed as characterization tests. Thermogravimetric analysis was performed at six different heating rates from 5 to 30 °C. The gasification experiments were carried out in a laboratory-scale fluidized bed reactor. With the gas analyzer, CO, CO2, CH4, H2, and O2 compositions as the mole fraction were determined simultaneously. The effects of temperature, particle size, and H2O/O2 ratio at the inlet intake on the experimental mole fractions were examined. The gasification main reactions that could be effective in gas composition were examined. The cotton-based banknote sample presented high levels of calorific value, C, O, H, cellulose, and lignin concentrations. The sample contained various transition metals such as Fe, Cu, Co, and Cr, which can be used as catalysts in gasification. The activation energy was calculated as 171.13 kJ/mol according to Kissinger method. In gasification experiments, the production of CO (12.11 %) and H2 (8.77 %) in a high composition was carried out.

Influence of Fluidised Bed Inventory on the Performance of Limestone Sorbent in Calcium Looping for Thermochemical Energy Storage

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the “closed-loop” scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration).

Improvement of coal and Petroleum coke combustion in a fluidized bed by using ilmenite ore as bed material

Oxygen carrier-aided combustion (OCAC) is an innovative technology that adopts the reactive oxygen carrier (OC) particles as bed materials instead of inert ones, which improves the uniformity of temporal and spatial oxygen distribution in the fluidized bed combustor. However, the existing research of OCAC mainly focuses on high-volatile fuels, less attention has been paid to high-ash and low-volatile fuels (such as coal), which are widely used in the world. In this work, three kinds of solid fuels have been comprehensively evaluated in a lab-scale fluidized bed reactor. Results show that compared to quartz sands as bed material, the OC as bed material shows an apparent “oxygen buffering capacity”, improving combustion stability and reducing the unburnt gas. The promotion effect of OCAC increases with the increase of volatile content in fuel, which indicates that OCAC mainly improves combustion through the redox reaction between volatile and OC particles. The solid-solid reaction between OC and char was negligible. The OCAC experiment was carried out for more than 20 h and found that due to the abrasion of the OC surface, the generated fly ash has a significantly higher Fe content than that using quartz sand as bed material at the initial stage of the experiment, and the abrasion of OC decreases with the increase of experimental time. Interestingly, during a 20-h continuous operation, the reactivity of ilmenite ore increased gradually, which was attributed to the development of pore structure and Fe diffusion of ilmenite ore. In addition, the content of unburnt carbon in the fly ash is similar regardless of the bed materials.

Prediction and optimization of syngas production from Napier grass air gasification via kinetic modelling and response surface methodology

In this research, a kinetic model was developed for Napier grass air gasification using Aspen Plus software and thereafter collated and validated with experimental results obtained from a lab-scale fluidized bed reactor. Herein, the model was further employed to investigate the effect of gasification operating parameters, including temperature (650–850) °C, equivalence ratio (0.2–0.4), and moisture content (0–18) wt.% on products’ yields and syngas quality. The model was segregated into four sections: the drying, devolatilization, combustion, and reduction sections. The outputs of tar, gas, and char from the devolatilization section were defined by external Microsoft Excel subroutine. Kinetic parameters were incorporated in the combustion and reduction sections to simulate tar cracking, oxidation, and reduction reactions. A good agreement was observed between the predicted and experimental results. Furthermore, response surface methodology (RSM) was employed to analyze the mutual effects of process variables and perform multi-objective optimization to maximize producer gas yield, higher heating value, carbon conversion efficiency, and cold gas efficiency by incorporating the predicted results from the developed kinetic model. The optimized syngas yield and HHV were 69.42 wt% and 8.14 MJ/Nm3 at 850 °C, 0.3021, and 15.69 wt% for temperature, ER, and moisture content, respectively.

A combined experimental and multiscale modeling approach for the investigation of lab-scale fluidized bed reactors

We show the potential of coupling numerical and experimental approaches in the fundamental understanding of catalytic reactors, and in particular fluidized bed ones.

Tannery Sludge Gasification in a Fluidized Bed for Its Energetic Valorization

The present article deals with the valorization of the organic content of tannery sludges to produce energy vectors. In this scenario, gasification is a viable option to obtain a flexible gaseous stream (syngas) of interesting energetic value, under operating conditions that do not favor the oxidation of Cr(III) (typically found in tannery sludges) to the more harmful Cr(VI) state. To this end, an industrial tannery sludge was characterized through proximate/ultimate analyses and determination of the heating value, showing its capability to act as a solid fuel in a gasification process, and metal analyses, showing that its Cr(VI) content was below the detection limit (2 ppm). The material was subjected to gasification tests in a lab-scale fluidized bed (FB) reactor. The reactor, with a 41 mm inside diameter and a 1 m height, was electrically kept at an operating temperature of 850 °C. The fluidization velocity was 0.30 m/s at 850 °C, i.e., 7.5 times the value of the minimum fluidization velocity. The gasifying stream was composed by O2 (3% vol.) diluted in N2. The adopted oxidant equivalence ratio (ER) levels were 0.15 and 0.24, to ensure substoichiometric (i.e., reducing) conditions in the FB atmosphere. Under the most reducing operating conditions, it was possible to produce syngas with a lower heating value of 12.0 MJ/N m3 (dry and N2-free basis). It contained, under these conditions, about 42% H2, 36% CO, and 4% CH4, plus 16% CO2 and other components. The tar produced from the process, fully characterized by gas chromatography–mass spectrometry, showed a favorably low concentration of about 25 g/N m3. FB bottom and fly ashes were analyzed for their carbon and metal contents. In bottom ash, the total Cr concentration resulted in the range of 8–12 g/kg, with a Cr(VI) concentration between 8 and 10 ppm. In the elutriated stream, the total Cr concentration was about 55 g/kg, with a Cr(VI) concentration between 4 and 7 ppm. The Cr(VI) concentration was higher when higher values of the ER were used, but it resulted in 3–4 orders of magnitude lower than the total Cr concentration, showing the appropriateness of the process to produce syngas with very limited oxidation of chromium in the solid residues.

Investigation on self-sustained combustion, NOx emissions, and ash characteristics of coal slime in a lab-scale fluidized bed

Incineration of coal slime in the fluidized bed boiler is an efficient means of energy recovery and environmental protection. In this study, combustion behaviors and NOx emissions of coal slime were studied using a lab-scale fluidized bed reactor. Besides, the fundamental characteristics of coal slime and its ash were explored coupled with a particle size analyzer, X-Ray Diffraction (XRD), thermogravimetric analysis (TGA), automatic specific surface, porosity analyzer, etc. It revealed that the range of 350–640 °C was the main mass loss stage with more than 92% of the total loss during combustion through the thermogravimetric analysis, guaranteeing good burnout performance. The challenges of fluidization and burnout of C-type particles accounting for 36.59% of coal slime were solved by mixing the water with coal slime to enhance its agglomeration and thermal explosion. Through the coupling of multiple operating parameters such as primary and secondary air rate, secondary air height, the oxygen content of flue gas, etc., reasonable furnace temperature and reduction zone distribution can be achieved. In addition, it was found that the migrations of most heavy metals are correlated with the proportion of fine particles in coal slime during combustion. The high content of alkaline substances of coal slime leads to a slightly slagging propensity below 900 °C due to the prevention of eutectics formation. Pore analysis implies that bottom ash and fly ash show different trends in the specific surface area and pore volume compared to the coal slime during combustion.