• Energy Research

The results presented in this work are part of a more extensive research programme aimed at assessing the impact of coal porous structure on density-based process evaluation and modelling. The coal samples used were obtained from two different density-based cleaning processes, a Vorsyl dense medium separator for treating an anthracite (TW) with a size fraction of 0.5–8.0 mm and a spiral concentrator for treating a bituminous coal (DH) with a size of less than 2 mm. Textural characterisation of the samples was carried out by measuring true (helium) and apparent (mercury) densities and mercury porosimetry up to a maximum pressure of 200 MPa. Adsorption isotherms in CO2 at 273 K were also determined for both coal series. In the case of the bituminous coal series a linear relationship between porosity and ash level was found. This may have important implications if coal porosity and/or textural parameters need to be incorporated into new density-based simulation models. Work carried out with a financial grant from the European Coal and Steel Community (ECSC Project 7220 – EA/132). Peer reviewed

Traditional methods to develop biomass-based carbon adsorbents generally involve carbonization followed by chemical or physical activation. However, routes involving the hydrothermal treatment of biomass are receiving growing interest. In this work, two different strategies for the synthesis of sustainable CO2 adsorbents are compared, i.e., in situ ionic activation and hydrothermal treatment followed by activation with CO2. The latter is a green and simple procedure that does not require the addition of chemicals or acid-washing stages, and which leads to carbon adsorbents with relatively high CO2 adsorption capacity at low pressures, up to 0.64 mmol g−1 at 15 kPa and 50 °C, conditions relevant for postcombustion CO2 capture applications. On the other hand, in situ ionic activation can lead to carbon adsorbents with superior CO2 adsorption capacity in the aforementioned conditions, 0.78 mmol g−1, and with reduced cost and environmental impact compared to conventional chemical activation.

Oxy-fuel combustion is usually performed in pf reactors under an enriched O2 atmosphere of CO2 to obtain a high CO2 content in the flue gases. The effect of the differences in thermal properties of N2 (conventional air combustion) and CO2 (oxy-fuel combustion) on the devolatilization process needs to be evaluated. The morphology and reactivity of biomass chars obtained by devolatilization in an EFR (entrained flow reactor) at 1300 °C under N2 and CO2, simulating air and oxy-fuel combustion atmospheres, were studied. Four biomasses were selected: PIN (pine sawdust), OW (olive waste), OS (olive stones) and CW (coffee waste). The apparent volatile yield under CO2 was greater than under N2. The morphology of the chars was assessed using SEM (scanning electron microscopy). The higher mass loss and the lower char particle size obtained during CO2 devolatilization indicate that a char-CO2 reaction occurred. The reactivity indices indicate a lower reactivity of the CO2-chars than the N2-chars. The devolatilization atmosphere had a significant effect on the biomass chars, suggesting that gasification had occurred during CO2 devolatilization. The OW, OS and CW chars showed a very high reactivity up to intermediate conversion levels, probably due to the catalytic effect of inherent alkali metals. This work was carried out with financial support from the Principado de Asturias (PCTI 2013-2017, GRUPIN14-079), co-financed by the European Regional Development Fund (ERDF). Financial support from the CSIC (Project PIE 201380E064) is also gratefully acknowledged Peer reviewed

The biological production of H2 by dark fermentation is being extensively investigated due to the great potential of the two-phase hydrogen/methane fermentation process for recovering energy from carbohydrate-rich wastes. However, the purification of the bio-hydrogen and biogas obtained is needed to produce high-purity H2 and CH4 streams appropriate for industrial application. In this study, the performance of three activated carbons (No1KCla-600, No1KClb-1000 and No2OS-1000), synthesized from phenol–formaldehyde resins, as potential adsorbents for CO2 capture from bio-hydrogen and biogas streams has been evaluated under dynamic conditions. Adsorption–desorption cycles by means of temperature swings were conducted at ambient temperature and atmospheric pressure with CO2/H2 (40/60 and 70/30 vol.%) and CO2/CH4 (50/50 vol.%) binary gas mixtures in a purpose-built fixed-bed set-up. The performance of the resin-derived carbons to separate CO2 was superior to that of reference commercial carbons in terms of CO2 uptake, breakthrough time and column efficiency. These adsorbents presented high CO2/H2 and CO2/CH4 selectivity values, were easily completely regenerated and did not show capacity decay after multiple cycling. Breakthrough capacities reached 2.11 and 2.03 mmol g−1 at 25 °C for 70/30 CO2/H2 and 50/50 CO2/CH4, respectively. The No2OS-1000 adsorbent, produced from phenol–formaldehyde resin and olive stones (20:80 wt.), gave the greatest values of CO2 capture capacity on a volumetric basis and CO2/CH4 selectivity, which may be advantageous to biogas purification applications because it reduces the size of the necessary equipment. This work was carried out with financial support from the Spanish MINECO (Project ENE2011-23467), co-financed by the European Regional Development Fund (ERDF). N.A.-G. acknowledges a FPI Predoctoral fellowship from the Spanish MINECO, co-financed by the European Social Fund. Peer reviewed

Coal as a fossil fuel has long been used for a variety of industrial and domestic purposes. The worldwide distribution and widespread availability of coal resources have been a major contributor to the economic growth of many countries, either directly through their own resources or indirectly through access to the international coal trade. Alhough coal usage has continued to increase, environmental concerns and changes in the political climate have begun to give coal an unfavorable public image. Increasing concerns about coal utilization as a contributor to greenhouse gas emissions, particularly CO2, have led to more intense questioning of the role of coal and a renewed search for alternative energy sources. Despite this coal will remain the second largest energy source worldwide in the next years and a key feedstock for other industrial usages. Coal has been thoroughly researched over the years to the point where all its characteristics and properties that make it such a versatile product are known. This chapter describes and summarizes the general knowledge acquired about coal in relation to its formation, worldwide resources and reserves, composition and properties, and all the characteristics relevant for describing the quality of a coal when it is used in the main conversion processes: combustion, gasification, and cokemaking.

Woody biomass pellets' demand for primary energy production is increasing. To guarantee sustainable and cost-efficient pellet production the diversification of biomass feedstock is mandatory. In this work it is proposed to re-use the solid biochar obtained from pyrolysis of eucalyptus (PEc) at 700 °C as an additive to produce enhanced pine sawdust (PIN) pellets. The process required the addition of glycerol as a lubricant in a percentage of 1 and 2 wt% per 5 and 10 wt% of pyrolyzed eucalyptus in the blend, respectively. Small additions of PEc enhanced PIN pellets’ grindability and water-resistance, providing products with remarkable values of durability (up to 99%), net calorific value (up to 20 MJ/kg), energy density (up to 13.3 GJ/m3), and particle density (up to 1.24 g/cm3). N, S, chlorine, and heavy metals contents were also analyzed. The proposed pellets fulfill the A1/A2 and the I1/I2 quality classes for domestic and industrial wood pellets, respectively. A preliminary economic evaluation indicated that pellets made up from a mixture of 90% PIN and 10% PEc are competitive compared to raw PIN pellets, with expected savings in the costs of production, energy, transport, and construction of a storage site of 4, 13, 10 and 7%, respectively. This work was carried out with financial support from the Gobierno del Principado de Asturias (PCTI, Ref. IDI/2018/000115), co-financed by the European Regional Development Fund (ERDF). M.V. Gil acknowledges support from a Ramón y Cajal grant (RYC-2017-21937) of the Spanish Government and the Spanish State Research Agency, co-financed by the European Social Fund (ESF). Peer reviewed

The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 °C) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process.