High temperature behavior of NiO-based oxygen carriers for Chemical Looping Combustion

AbstractHigh temperature behavior of spray-dried NiO-based oxygen carrier samples for Chemical Looping Combustion (CLC) under oxidizing and reducing conditions was studied using a ceramic fluidized bed furnace. Differently from the common CLC process, high enough temperatures were obtained by burning air and methane mixture directly in the bed of carriers, changing the stoichiometric air to fuel ratio in the range of 0.70 to 1.30 and using external electric heating.None of the five particle samples tested showed any sign of defluidization in oxidizing atmosphere at any of the temperatures tested, i.e. up to 1175–1185 ∘C. However, under reducing conditions or in the oxidizing-reducing sequences, shortly after changing the atmosphere from oxidative to reducing, some of the spray-dried samples agglomerated causing defluidization. To study the structure of the carrier particles and to clarify the agglomeration phenomena, SEM and EDX analysis of the initial and treated samples was carried out. It was shown that agglomerates are formed through small bridges between the particles which consist of pure Ni phase. Three samples which were produced using MgO as an additive were tested. For these no defluidization was observed at any of the temperatures tested, i.e. up to 1175–1185 ∘C, neither in oxidizing, nor in reducing atmosphere. So, addition of proper components to the carrier particles can significantly improve reliability of the CLC process at higher temperatures

Characterization of Ash Melting of Reed and Wheat Straw Blend

This work was supported by the European Regional Development Fund and the programme Mobilitas Pluss grant MOBTP112, Estonian Ministry of Education and Research (IUT19-4), as well as the European Regional Development Fund through the project TK141 “Advanced materials and high-technology devices for energy recuperation systems.” Peter Backman, Linus Silvander, and Arvo Mere are acknowledged for their help on the characterization of materials and for valuable comments and discussionsAsh melting could cause severe problems in boiler operation, such as agglomeration of the fluidized bed. Our previous work has shown that the ash melting behavior of the blend of reed and wheat straw is complex and needs further investigation. The ash melting behavior was studied using different laboratory methods such as simultaneous thermal analysis, heating microscope, scanning electron microscopy with energy dispersive X-ray (SEM/EDX) analysis, and X-ray diffraction (XRD). In the thermodynamic modeling, we used FactSage software, which supplements well the results obtained by other methods and vice versa. The results indicated that melting started at 660-680 °C when Na and K salts were melted and molten K2SO4 covered the ash material; the content of liquid mass fraction was 13.8%, revealing that the studied ash blend could already be sticky at 680 °C. Intensive melting took place in the temperature range of 800-980 °C. The rapid melting between 950 and 980 °C was caused by the melting of SiO2 and K2MgSi5O12; the ash material became glassy and amorphous. We propose an alternative distribution of ash melting stages for the studied blend.Peer reviewe

Dependence of the interaction mechanisms between l-serine and O-phospho-l-serine with calcium hydroxyapatite and copper modified hydroxyapatite in relation with the acidity of aqueous medium

International audienceMotivated by the role of copper ions in biological processes the aim of this study was to elucidate the impact of copper ions bound to hydroxyapatite on l-serine (l-Ser) and O-phospho-l-serine (O-Ph-l-Ser) adsorption at different acidity of aqueous solutions. The adsorption phenomenon was studied by FTIR, UV, and AA spectroscopy, XRD and thermal analysis methods together with the evolved gases analysis taking into consideration the ionic state of the amino acids as well as the apatite surface state, which are tightly correlated with the solution pH. In acidic solution, the main process involves apatite dissolution releasing calcium and copper ions. At pH > 5 the complexation of amino acids with Ca2+ or Cu2+ ions is more important leading also to the release of cations. The ability of copper ions to form water soluble complexes with l-Ser and O-Ph-l-Ser leads to an important loss of these ions, while calcium release is very low at this pH. Therefore, the use of copper ions substituting calcium in the apatite structure to enhance the ability of amino acids adsorption on the apatite surface seems problematic even at pH > 5

Thermal Behavior of Estonian Graptolite–Argillite from Different Deposits

Graptolite–argillites (black shales) are studied as potential source of different metals. In the processing technologies of graptolite–argillites, a preceding thermal treatment is often applied. In this study, the thermal behavior of Estonian graptolite–argillite (GA) samples from Toolse, Sillamäe and Pakri areas were studied using a Setaram Labsys Evo 1600 thermoanalyzer coupled with the Pfeiffer OmniStar Mass Spectrometer. The products of thermal treatment were studied by XRD, FTIR, and SEM analytical methods. The experiments were carried out under non-isothermal conditions of up to 1200 °C at different heating rates in the atmosphere containing 79% Ar and 21% O2. The differential isoconversional Friedman method was applied for calculating the kinetic parameters. All studied GA samples are characterized with high content of orthoclase (between 38.0 and 57.3%) and quartz (between 23.8 and 35.5%), and with lower content of muscovite, jarosite, pyrite, etc. The content of organic carbon in GA samples studied varied between 7.3 and 14.2%. The results indicated that, up to 200 °C, the emission of hygroscopic and physically bound water takes place. Between 200 °C and 500–550 °C, this is followed by thermo-oxidative decomposition of organic matter. The first step of thermo-oxidation of pyrite with the emission of water, carbon and sulphur dioxide, nitrogen oxides, and different hydrocarbon fragments indicated the complicated composition of organic matter. At higher temperatures, between 550 °C and 900 °C, the transformations continued by dehydroxylation processes in clay minerals, and the decomposition of jarosite and carbonates took place. At temperatures above 1000–1050 °C, a slow increase in the emission of sulphur dioxide followed, indicating the beginning of the second step of thermo-oxidative decomposition of pyrite, which was not completed for temperatures of up to 1000 °C. Kinetic calculations prove the complicated mechanism of thermal decomposition of GA samples: for Pakri GA samples, it occurs in two steps, and for Silllamäe and Toolse GA samples, it occurs in three steps. Preliminary tests for the estimation of the influence of pre-roasting of GA samples on the solubility of different elements contained in GA at the following leaching in sulphuric acid is based on Toolse GA sample

Effect of Flotation Time and Collector Dosage on Estonian Phosphorite Beneficiation

Phosphorus is an essential and non-substitutable element for the cellular processes of all living organisms. The main source of phosphorus in the biosphere is phosphate rock. With more than 700 Mt phosphate rock, Estonia holds the largest sedimentary phosphate rock deposits in the European Union. Estonian phosphate rock is particularly outstanding due to its remarkably low content of hazardous heavy metals such as Cadmium (2O5 that can be added to the final product. Moreover, it was found that, with the lower dosage of the collector, the extended flotation time does not influence the phosphate grade and a high amount of quartz remains in the concentrates. It was also shown that, by raising the collector dosage and setting the flotation time, an adequate grade (>32 wt% P2O5) and recovery (up to 98%) can be gained. The results showed that Estonian phosphate rock can be beneficiated to produce a high-quality concentrate at high recovery levels by modifying the main flotation parameters depending on the properties of the ore

Chemical-looping combustion with natural gas using spray-dried NiO-based oxygen carriers

The work presented in this chapter demonstrates the economical feasibility of making a good oxygen carrier from commercial raw materials using a commercial production method, i.e. spray-drying. A batch fluidized-bed reactor was used for an extensive screening of many NiO-based oxygen carriers. This screening process led to the production of two major particle batches, which were used in continuous chemical-looping experiments. High-temperature experiments in a batch-fluidized bed verified the thermal durability of the particles. The most important result presented here concerns long-term operation (> 1000 h) of a 10-kWth chemical-looping combustor using spray-dried NiO-based oxygen carriers. Conversion of the fuel was good, and increased with (a) decreased circulation, and (b) increased fuel-reactor temperature. Combustion efficiency close to 99% was accomplished using these spray-dried particles. At the end of the test series, the continuous loss of fine material was 0.003%/h, which corresponds to a particle life time of 33000 h. No decrease in reactivity was seen during these long-term tests. The fuel used in the experiments was natural gas and methane

Study of Thermooxidation of Oil Shale Samples and Basics of Processes for Utilization of Oil Shale Ashes

A circular economy becomes an object of actual discussions as a real alternative to the existing linear economy system. The problem is actually in Estonia also, first of all in the sector of heat and power production which based mainly on the combustion of local solid fossil fuel—Estonian oil shale (OS) resulting in the formation of ~5–6 million tons of OS ashes annually. The thermooxidative decomposition of OS samples from different deposits and estimation of the possibilities of utilization of OS ashes formed at both—pulverized firing (PF) and circulating fluidized bed combustion (CFBC) of Estonian OS were studied. The thermal analysis combined with evolved gas analysis (EGA) methods like Fourier transform infrared (FTIR) and mass-spectroscopy (MS) was exploited. It was established that the differences in the thermal behaviour of different OS samples are caused by the differences in the chemical matrix of organic matter, chemical and mineralogical composition of the inorganic part of OS, and morphology of samples. It was also found that moderate grinding of OS ashes with simultaneous moderate water treatment notably improved the SO2 binding efficiency of cyclone ash, and that the strength and leachability characteristics of granulated OS ashes strongly depend on the post-granulation treatment conditions allowing to increase the soil neutralizing ability of the granulated products. This overview was based on our investigations carried out during the last fifteen years