• Energy Research

Abstract During oxy-fuel combustion, the gas composition inside the boiler differs from that of conventional combustion in air, which affects to different aspects in combustion processes. Besides, the need to increase the efficiency in energy production in a sustainable way leads to increasingly extreme conditions imposing more demanding performances on materials such as higher temperatures and pressures in more corrosive environments. The scope of this work is to understand the thermal behaviour and the kinetic of an energetic crop with high chlorine content blended with a Spanish coal at different atmospheres with special attention to oxyfuel combustion conditions and to determine the formation of those compounds which may induce corrosion, by means of mass spectrometry analysis. The addition of biomass to the fuel mixture seems to increase the reactivity of the samples. The rate maximum of mass change increases with the oxygen content reaching values from 13.6, 16 and 17.7%/min with N2, air and oxyfuel atmosphere respectively using 100% of cynara as fuel. The greater reactivity of the oxygen decreases the peak temperature being about 325 °C with N2, 309 °C with air and 304 °C at oxyfuel conditions. The activation energy increased when the biomass share in the blend independently of the atmosphere and the heating rate. The activation energy is similar to combustion and oxyfuel combustion conditions but about 5–7 kJ/mol higher than pyrolysis atmosphere for all biomass mixture studied. The optimal blend based on the lowest activation energy is 20:80% of cynara/coal. HCl presence is higher when the percentage of biomass increased. However, SO2 presence is more related with coal presence. It is important to stand out that any percentage of cynara in the mixture shift to lower temperatures the SO2 emission profile, from 500 °C to 300 °C. This fact is also observed in the curves of the weight loss derivative.

Mercury is a high-priority regulatory concern because of its persistence and bioaccumulation in the environment and evidence of its having serious adverse effects on the neurological development of children.Mercury is released into the atmosphere from both natural and anthropogenic sources. Coal-fired utilities are considered to be one of the largest anthropogenic mercury emission sources. The period since the late 1990s has been marked by increasing concern over mercury emissions from combustion systems to the extent that a number of national governments have either already implemented or are in the process of implementing, legislation aimed at enforcing tighter control over mercury emissions and a reduction in mercury consumption.This review examines the most important national and international policies and agreements for controlling mercury emissions from coal-fired combustion systems. To provide a global perspective, this study lists the countries with the largest estimated mercury emissions and regulatory efforts to reduce them.

During oxy-fuel combustion, the gas composition inside the boiler differs greatly from that of conventional combustion with air, involving consequences for different aspects in fuel combustion. Research on oxy-fuel combustion is needed to understand which factors influence the process, especially for coal and biomass co-firing. In this study, the combustion behaviour of coal/biomass blends was determined by thermogravimetric studies (TG) with different CO2/O2 mixtures and compared with similar results for conventional combustion. This approach determines the appropriate conditions for the oxy-fuel combustion for future studies that will be carried out in lab- and bench-scale combustors. One sub-bituminous coal (Puertollano coal) and two Spanish biomasses (olive grove and thistle) were the fuels selected for the study. The combustion behaviour of each pure fuel and several coal/biomass blends, under air and oxy-fuel conditions (70 %CO2–30 %O2, 60 %CO2–40 %O2), was studied. Results obtained for the pure fuels have shown that the temperatures of maximum reaction rate, T max, determined under oxy-fuel combustion were lower than those found during conventional combustion. Similar pattern was encountered for the different coal/biomass blends studied (varying from 80 % coal/20 % biomass to 20 % coal/80 % biomass), with a more reactive behaviour in oxy-fuel conditions than in conventional air combustion. The values of temperatures at maximum mass loss, T m, obtained for these blends in an oxy-fuel atmosphere were 100–200 °C lower than the values found for the air atmosphere. T m values determined for the blends were also dependent on the oxy-fuel conditions, with larger differences observed with the 60 %CO2–40 %O2 mixture than with the 70 %CO2–30 %O2 atmosphere with respect to air combustion. However, the greatest decreasing effect compared to air of biomass addition on T m values was found for the blend with the lowest biomass content (20 % biomass w/w).

Abstract Arsenic emissions are currently considered to be one of foremost importance. Arsenic volatility is higher than most of trace elements, but its vaporization behaviour is strongly dependent on the atmosphere composition. In this sense, thermodynamic equilibrium calculations, using HSC-Chemistry 5.0 software, were performed to evaluate the influence of different compounds in the distribution and mode of occurrence of arsenic in co-combustion processes. The influence of different parameters influencing arsenic behaviour, such as temperature, pressure, trace element concentration and flue gas composition on equilibrium composition were also evaluated. Predicting arsenic species, based on combustion conditions and fuel composition, will be useful to choose the best available control technology to reduce arsenic emissions. Finally, the possible interactions between arsenic and different trace elements (TE), mercury, cadmium and antimony, relevant from an environmental point of view, have also been studied; these interactions are not usually considered in thermodynamic studies; however, TE’s interactions affects the behaviour of a single TE, not only as a result of the formation of new species, but also, because of the different reactivity of TEs towards different elements which may affect TE’s volatilization behaviours. From results obtained in this study it may be concluded that in most cases, arsenic is mainly captured in ashes as a result of the formation of thermally stable species both from interactions with bulk ash and TE’s interactions. Nevertheless, the presence of some compounds (silicon, chlorine and sulphur) may enhance arsenic volatilization.