•As release and recovery have been clearly elaborated during pyrolysis and gasification of P. vittata in this study.•The As concentration and speciation are determined by HPLC-ICP-MS.•The As solubility in solid residue shows significant difference between low and high temperatures.•The soluble As in solid residue mainly presents as As5+.Thermal treatment of P. vittata, an arsenic hyperaccumulator harvested from contaminated land is a promising method of achieving volume reduction, energy production and arsenic (As) recovery simultaneously. In this paper, the arsenic transformation characteristics of field-harvested P. vittata were investigated during its pyrolysis and gasification process. The produced solid residue and flue gas were analysed by a high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) to determine both the arsenic concentration and speciation. Moreover, the occurrence of arsenic in the solid residues was further identified as soluble and insoluble, which can feed information to the next arsenic recovery step. Results show that the fuel arsenic into gas phase increases firstly from 400 °C to 600 °C, but then drops from 600 °C to 800 °C, probably due to the self-retention of arsenic by CaO enriched in this P. vittata. Further increasing temperature to 900 °C will result in fast arsenic release. Gasification results in slightly higher arsenic release into the gas phase compared with pyrolysis.

Combustion and gasification for biomass to energy conversion is often suggested for the management of residual Pteris vittata from phytoremediation. In this study, the thermal behaviour of P. vittata was studied on a thermogravimetric analyser, and the kinetic triplet of biomass sample was further determined for different stages of the thermochemical processes using the Ozawa and KAS methods, subsequently modified by an iterative procedure. Results show that thermal decomposition under combustion condition was complete at a lower temperature of ~500 °C compared to ~700 °C for gasification, indicating the both easily complete conversion of P. vittata by combustion and gasification. Kinetic study shows that although activation energy for each stage under combustion condition is mostly larger than that under gasification, the reaction rate of thermal decomposition of P. vittata under combustion condition is still great larger than that under gasification condition. These findings strongly suggest that thermochemical processes offer suitable methods for the volume reduction and energy production of P. vittata.

•Evaluation of Arsenic (As) emission from circulating fluidized bed (CFB) boilers co-firing petroleum coke and coal•Mass balance ratio and distribution of As in the entire system•Partitioning and abatement of Arsenic across air pollution control devices•Arsenic speciation analysis in combustion by-products and atmospheric emissionThe emission of Arsenic from coal-fired power plants has generated widespread environmental and human health concerns. This paper discusses Arsenic partitioning from three 440 t/h circulating fluidized bed (CFB) boilers co-firing petroleum coke and coal. All the boilers were equipped with electrostatic precipitator (ESP) or fabric filter (FF), and wet flue gas desulfurization (WFGD). Flue gas was sampled simultaneously both up- and down-stream of the ESP/FF and at the outlet of the WFGD based on EPA Method 29. Concurrent with flue gas sampling, feed fuel, bottom ash, ESP/FF ash, WFGD gypsum, WFGD wastewater, limestone slurry and flush water were also collected. The results show that, for three tested CFB boilers, the overall mass balance ratios of As ranged from 80.0%–114.2%, which can be considered to be acceptable and reliable. Most of the As was distributed in the bottom ash and ESP/FF ash with the values of 17.4%–37.5% and 55.6%–77.5%, respectively. Speciation analysis suggests that As5 + was the major water-soluble species in the feed fuel, bottom ash and fly ash, while As3 + was found to be the dominant species in WFGD wastewater. For three CFB boilers, the concentrations of total As in the stack emission were 0.97, 0.32 and 0.31 μg/m3, respectively. The CFB boiler equipped with ESP/FF + WFGD was shown to be able to provide good control of the emission of As emitted into the atmosphere.

•Multi-stage solid management of a CFBC Pilot Plant has been explored for bituminous and anthracite coal;•Volatile elements are depleted in bottom ash for anthracite and volatile elements are enriched in fine particles;•As, Cd and Pb are likely to escape to the atmosphere, but CaO (if present) helps to retain As in the bottom ash;•CFBC combustion shows significantly better capture of trace elements than PC combustionCoal combustion introduces large amounts of pollutants into the atmosphere, including trace elements originally bonded in the coal matrix. The emission of these elements raises considerable environmental and human health concerns. To optimise process parameters and reduce gaseous trace element emissions, it is of significant importance to investigate the solid–gas partitioning behaviour of trace elements during combustion processes. To date, limited numbers of experimental studies have been carried out, especially using pilot circulating fluidised bed (CFB) combustion plants. This paper discusses the partitioning behaviour of seven elements (As, Ba, Cd, Cr, Cu, Mn and Pb) in different product streams during combustion tests on anthracite and bituminous coal. The combustion tests were carried out in a 2.5 MWth CFB unit equipped with multi-stage control of solids, which is well suited for trace element partitioning studies. The mass balance ratio of the elements studied ranged from 56%–137%, which is, considering their concentrations, both satisfactory and reasonable. Most of the elements were found in the bottom ash and fly ash during CFB combustion, while small amounts of As, Cd and Pb were emitted to the atmosphere along with fine particulates. The trace elements are more likely to be retained in the bottom ash from the bituminous coal but not in the case of anthracite. For the volatile elements, the enrichment in solid streams follows the trend of: bag filter ash > cyclone ash > IBHX (in-bed heat exchanger) solids > bottom ash, indicating that the volatile elements tend to be enriched in fine particles. Anthracite, when compared to bituminous coal, shows lower emission factors for all monitored elements, except for Pb. This study can serve as a good reference for trace element control strategies in coal-fired CFB boilers.

An enhanced CO2 capacity was reported recently for biomass-modified Ca-based sorbent, but undesired attrition resistance was also observed. In this study, cement was used as a support for biomass-activated calcium sorbent during the granulation process to improve the poor mechanical resistance. Attrition tests were carried out in an apparatus focused on impact breakage to evaluate how the biomass addition and cement support influence the particle strength during Ca looping. The results showed that biomass addition impairs the mechanical strength and that a cement support can improve it, as reflected in the breakage probability and size change after impact of pellets that had experienced calcination and multiple calcination/carbonation cycles. Larger-sized particles suffered more intense attrition. The mechanical strength of the sorbents declined significantly after higher-temperature calcination but increased after carbonation. After multiple cycles, the mechanical strength of particles was greatly enhanced, but more cracks emerged. A semiempirical formula for calculating the average diameter after attrition based on Rittinger’s surface theory was developed. Observations of the morphology of the particles indicated that particles with more porosity and more cracks were more prone to breakage.

Synthetic biomass-templated cement-supported CaO-based sorbents were produced by the granulation process for high-temperature postcombustion CO2 capture. Commercial flour was used as the biomass and served as a templating agent. The investigation of porosity showed that the pellets with biomass or cement resulted in an enhancement of porosity. Four types of sorbents containing varying proportions of biomass and cement were subjected to 20 cycles in a thermogravimetric analyzer under different calcination conditions. After the first series of tests calcined below 850 °C in 100% N2, all composite sorbents clearly exhibited higher CO2 capture activity than untreated limestone with the exception of sorbents doped by seawater. The biomass-templated cement-supported pellets exhibited the highest CO2 capture level of 46.5% relative to 20.8% for raw limestone after 20 cycles. However, the enhancement in performance was substantially reduced under 950 °C calcination condition. Considering the fact that both sorbents supported by cement exhibited relatively high conversion with a maximum value of 19.5%, cement-promoted sorbents appear to be better at resisting harsh calcination conditions. Although flour as biomass-templated material generated a significant enhancement in CO2 capture capacity, further exploration must be carried out to find ways of maintaining outstanding performance for CaO-based sorbents under severe reaction conditions.

Water vapor in the furnace can be raised up to 45% during oxy-fuel combustion with wet flue gas recycle and will significantly affect the limestone sulfation process. In this paper, two limestone sorbents were used to investigate the effect of water vapor on indirect sulfation. Nitrogen adsorption analysis, scanning electron microscope, and X-ray diffraction (XRD) techniques were employed to analyze the products and investigate the sulfation mechanism in the presence of water vapor. Results indicate that the difference of calcium conversion in the atmosphere containing H2O(g) or not is indistinctive during the kinetic-controlled regime. However, the degradation of sulfation rate is delayed in the presence of H2O(g) and the calcium conversion is enhanced in the later stage. Solid-state diffusion is intensified in the presence of water vapor, and recrystallization and sintering are promoted. Pore size distribution obtained by nitrogen adsorption analysis indicates that the activity of gas–solid diffusion in the presence of H2O(g) diminishes, and the enhancement is mainly caused by solid-state diffusion. The maps of XRD analysis further validate the experiment results.

Oxy-fuel Circulating Fluidized Bed (CFB) combustion technology, a very promising technology for CO2 capture, combines many advantages of oxy-fuel and CFB technologies. Experiments were carried out in a 50 kWth CFB facility to investigate how operation parameters influence the NO emission in O2/CO2 atmospheres. The simulated O2/CO2 atmospheres were used without recycling the flue gas. Results show that NO emission in 21% O2/79% CO2 atmosphere is lower than that in air atmosphere because of lower temperature and higher char and CO concentrations in the dense bed. Elevating O2 concentration from 21% to 40% in O2/CO2 atmosphere enhances fuel-N conversion to NO. Increasing bed temperature or oxygen/fuel stoichiometric ratio brings higher NO emission in O2/CO2 atmosphere, which is consistent with the results in air-fired CFB combustion. As primary stream fraction increases, NO emission increases more rapidly in O2/CO2 atmosphere than that in air atmosphere. Stream staging is more efficient for controlling NO emission in oxy-CFB combustion than that in air combustion. Oxygen staging provides an efficient way to reduce NO emission in oxy-CFB combustion without influencing the hydrodynamic characteristic in the riser.

The pyrolysis/gasification experiments of Xuzhou bituminous coal (XZ) and Longyan anthracite (LY) were carried out in a tube furnace under Ar or CO2 atmosphere, and the effect of CO2 on the evolution of NOx precursors, NH3 and HCN, was studied using a Fourier transform infrared (FTIR) spectrometer. Results show that CO2 influences NH3 and HCN evolution process in two main ways: one is blocking the contact of the N-sites and the H-radicals by absorbed on the coal matrix surface at low temperature, and the other is opening the N-sites from the coal matrix by gasification at high temperature. For both XZ and LY coals, CO2 atmosphere suppresses NH3 yield and enhances HCN yield due to the gasification effect compared with that in Ar atmosphere. But the impact is not the same. The HCN/NH3 ratio is elevated in CO2 atmosphere compared with that in Ar atmosphere.

To clarify the sulfur transformation behavior during oxy-fired circulating fluidized bed (CFB) combustion, experiments on SO2 emission characteristics were carried out in a 50 kWth CFB combustor. Results show that SO2 emission is quite dependent on the bed temperature in different atmospheres without limestone injection. With Ca/S=2.5, SO2 emission in 21%O2/79%CO2 atmosphere is smaller than that in air atmosphere, but SO2 emission decreases with the increase of O2 concentration. The calcium forms in the ash prove the combination of calcination/carbonation and direct sulfation mechanism of limestone under oxy-combustion conditions. And the desulfurization efficiency of limestone (as deducting the self-retention efficiency from the total sulfur removal efficiency) increases from 40% to 52% as the O2 concentration increases from 21% to 40%.