• Energy Research

The devolatilisation step of coal is a vital stage in both air–coal and oxy-coal combustion and there is interest in whether methods of estimating the reaction parameters are similar for both cases. A network pyrolysis model, the FG-DVC (Functional Group-Depolymerisation Vaporisation Cross-linking) code was employed to evaluate the effect of temperature (1273–1773 K) and heating rate (104–106 K/s) on the devolatilisation parameters of two coals of different rank. The products distribution between char and volatiles, and volatiles and NH3/HCN release kinetics were also determined. In order to assess the accuracy of the FG-DVC predictions, the values for nitrogen distribution and devolatilisation kinetics obtained for a temperature of 1273 K and a heating rate of 105 K/s were included as inputs in a Computational Fluid Dynamics (CFD) model for oxy-coal combustion in an entrained flow reactor (EFR). CFD simulations with the programme default devolatilisation kinetics were performed. The oxygen content in oxy-firing conditions ranged between 21% and 35%, and air-firing conditions were also employed as a reference. The experimental coals burnouts and oxygen concentrations from the EFR experiments were employed to test the accuracy of the CFD model. The temperature profiles, burning rates, char burnout and NO emissions during coal combustion in both air and O2/CO2 atmospheres were predicted. The predictions obtained when using the CFD model with FG-DVC coal devolatilisation kinetics were much closer to the experimental values than the predictions obtained with the ANSYS Fluent (version 12) program default kinetics. The predicted NO emissions under oxy-firing conditions were in good agreement with the experimental values. The present study was carried out with financial support from the Spanish MICINN (Project PS-120000-2005-2) co-financed by the European Regional Development Fund. L.A. and J.R. acknowledge funding from the CSIC JAE program, which was cofinanced by the European Social Fund, and the Asturias Regional Government (PCTI program), respectively. MG acknowledges financial support from E.ON UK, and for an EPSRC Dorothy Hodgkin Postgraduate Award. We also thank Dr L Ma for helpful discussions. Peer reviewed

The thermal reactivity and kinetics of five coal chars, a biomass char, and two coal/biomass char blends in an oxy-fuel combustion atmosphere (30%O2–70%CO2) were studied using the non-isothermal thermogravimetric method at three heating rates. Fuel chars were obtained by devolatilization in an entrained flow reactor at 1273 K under N2 and CO2 atmospheres. Three nth-order representative gas–solid models – the volumetric model (VM), the grain model (GM) and the random pore model (RPM) – were employed to describe the reactive behaviour of the chars. The RPM model was found to be the best for describing the reactivity of the high rank coal chars, while VM was the model that best described the reactivity of the bituminous coal chars, the biomass char and the coal-biomass blend char. The kinetic parameters of the chars obtained in N2 and CO2 in an oxy-fuel combustion atmosphere with 30% of oxygen were compared, but no relevant differences were observed. The behaviour of the blend of the bituminous coal (90%wt.) and the biomass (10%wt.) chars resembled that of the individual coal concealing the effect of the biomass. Likewise, no interaction was detected between the high rank coal and the biomass chars during oxy-fuel combustion of the blend. This work was carried out with financial support from the Spanish MICINN (Project PS-120000-2005-2) co-financed by the European Regional Development Fund (ERDF). M.V.G. and L.A. acknowledge funding from the CSIC JAE-Pre and CSIC JAE-Doc programs, respectively, co-financed by the European Social Fund. J.R. acknowledges funding from the Government of the Principado de Asturias (Severo Ochoa program). Peer reviewed

The effect of co-firing coal and biomass on the ignition behaviour and NO emissions was evaluated under both air and O2/CO2 (21-35% O2) atmospheres. The results showed a worsening of the ignition properties in the 21%O2/79%CO2 atmosphere in comparison with air. Furthermore, in order to obtain similar or better ignition properties, the oxygen concentration in the O2/CO2 mixture must be 30% or higher. A decrease of the ignition temperature was observed with the addition of biomass in air and oxy-fuel conditions. The results also indicate that NO emissions in the 21%O2/79%CO2 atmosphere were lower than under air-firing conditions, although they increased in the 30%O2/70%CO2 and 35%O2/65%CO2 atmospheres. The addition of biomass resulted in lower NO emissions in all cases. This work was carried out with financial support from the Spanish MICINN (Project PS-120000-2005-2) co-financed by the European Regional Development Fund. L.A. and M.V.G. acknowledge funding from the CSIC JAE program, co-financed by the European Social Fund. J.R. acknowledges funding from the Government of the Principado de Asturias (Severo Ochoa program) Peer reviewed

The ignition temperature and burnout of a semi-anthracite and a high-volatile bituminous coal were studied under oxy-fuel combustion conditions in an entrained flow reactor (EFR). The results obtained under oxy-fuel atmospheres (21%O2–79%CO2, 30%O2–70% O2 and 35%O2–65%CO2) were compared with those attained in air. The replacement of CO2 by 5, 10 and 20% of steam in the oxy-fuel combustion atmospheres was also evaluated in order to study the wet recirculation of flue gas. For the 21%O2–79%CO2 atmosphere, the results indicated that the ignition temperature was higher and the coal burnout was lower than in air. However, when the O2 concentration was increased to 30 and 35% in the oxy-fuel combustion atmosphere, the ignition temperature was lower and coal burnout was improved in comparison with air conditions. On the other hand, an increase in ignition temperature and a worsening of the coal burnout was observed when steam was added to the oxy-fuel combustion atmospheres though no relevant differences between the different steam concentrations were detected. This work was carried out with financial support from the Spanish MICINN (Project PS- 120000-2005-2) co-financed by the European Regional Development Fund. L.A. and J.R. acknowledge funding from the CSIC JAE program, co-financed by the European Social Fund, and the Government of the Principado de Asturias (Severo Ochoa program), respectively. Peer reviewed

he present study investigates the air-steam gasification of ten commercial and alternative lignocellulosic biomass fuels (pine sawdust, chestnut sawdust, torrefied pine sawdust, torrefied chestnut sawdust, almond shells, cocoa shells, grape pomace, olive stones, pine kernel shells and pine cone leafs) in order to evaluate the product gas composition and the process performance in a bubbling fluidized bed gasifier with focus on the different biomass properties. Accordingly, an effort to correlate the biomass characteristics with the gasification results has been done. Pine kernel shell (PKS) was used to test the effect of the gasification temperature (700, 800 and 900 °C), steam to air ratio in the gasifying agent (S/A = 10/90, 25/75, 50/50 and 70/30) and stoichiometric ratio (SR = 0.13 and 0.25) on the product gas composition, combustible gas (H2 + CO + CH4) production, H2/CO ratio, heating value, energy yield and cold gas efficiency of the obtained gas. Results showed that higher temperature and S/A ratio favored H2 production and gasification performance. A higher value of SR slightly affected the gas composition, but led to a higher process efficiency as a consequence of a higher biomass conversion into gaseous combustible products. All the biomass samples of different origin and characteristics were then gasified at the best experimental conditions found (900 °C, S/A = 70/30, SR = 0.25). Gasification of all the biomasses was feasible and H2 and combustible gas concentrations of 30–39 vol% and 59–78 vol% (inert gas-free basis), respectively, were obtained for the biomasses studied, with energy yields of 8–18 MJ/kgbiomass. Torrefied biomass showed similar combustible gas production than the corresponding raw biomass under the conditions studied, but it gave slightly higher H2 production and efficiency results. Possible correlations of the gasification performance parameters with biomass properties were also analyzed. The results showed positive effects of biomass volatile matter content, C content and high heating value (HHV) on the CO and combustible gas contents, calorific value of the product gas, as well as gas and energy yields. This work has received financial support from the Spanish MINECO (ENE2014-53515-P), cofinanced by the European Regional Development Fund (ERDF). M.P. González-Vázquez acknowledges a fellowship awarded by the Spanish MINECO (FPI program), cofinanced by the European Social Fund. Peer reviewed

12th International Conference on Greenhouse Gas Control Technologies, GHGT-12 Water vapor is the third component of flue gases after N2 and CO2. The permanent dipole moment of the water molecule makes it strongly adsorbable on many adsorbents, which can negatively affect the adsorption capacity of carbon dioxide (even causing an irreversible loss in certain cases). Carbon materials have high stability in moist conditions and present a hydrophobic nature that makes these materials appealing adsorbents for post-combustion CO2 capture. Furthermore, these adsorbents present the added advantage that can be obtained from a globally available, cheap and renewable source of carbon: biomass. In the present work the effect of water vapor on the adsorption performance of CO2 using a microporous biochar developed from olive stones by single- step oxidation is evaluated. The equilibrium of adsorption of water vapor on the selected biochar was studied in a wide temperature range that is considered of interest for the post-combustion case (12.5-85 °C). This biochar presents a moderate water adsorption capacity and type V adsorption isotherms, which will facilitate the desorption of water vapor during cyclic operation. Breakthrough curves were obtained using a gas mixture which composition resembled flue gas in the presence and absence of water vapor. The breakthrough curves of CO2 obtained under dry and humid conditions overlap each other, which indicates that the presence of water vapor does not hinder CO2 adsorption in the short time scale. Moreover, the adsorbent recovered its full adsorption capacity after regeneration. These findings point out that this material could be used to separate CO2 from humid flue gas using cyclic adsorption processes. Work carried out with financial support from the Spanish MINECO (Project ENE2011-23467), co-financed by the European Regional Development Fund (ERDF). M.G.P. acknowledges funding from the CSIC (JAE-Doc program) and A.S.G. acknowledges a contract from the Spanish MINECO (FPI program), both programs are co-financed by the European Social Fund Peer reviewed

The non-isothermal thermogravimetric method (TGA) was applied to a bituminous coal (PT), two types of biomass, chestnut residues (CH) and olive stones (OS), and coal–biomass blends in order to investigate their thermal reactivity under steam. Fuel chars were obtained by pyrolysis in a fixed-bed reactor at a final temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis from room temperature to 1373 K at heating rates of 5, 10 and 15 K min−1. After blending, no significant interactions were detected between PT and CH during co-gasification, whereas deviations from the additive behaviour were observed in the PT–OS blend. However, for the two coal–biomass blends, the gasification behaviour resembled that of the individual coal, as this component constituted the larger proportion of the blend. The temperature-programmed reaction (TPR) technique was employed at three different heating rates to analyze noncatalytic gas–solid reactions. Three nth-order representative gas–solid models, the volumetric model (VM), the grain model (GM) and the random pore model (RPM) were applied in order to describe the reactive behaviour of the chars during steam gasification. From these models, the kinetic parameters were determined. The best model for describing the reactivity of the PT, PT–CH and PT–OS samples was the RPM model. VM was the model that best fitted the CH sample, whereas none of the models were suitable for the OS sample. This work was carried out with financial support from the Spanish MICINN (Project PS- 120000-2006-3, ECOCOMBOS), and co-financed by the European Regional Development Fund, ERDF. Peer reviewed