Effect Of Oxygen Carriers Research Articles

Syngas production from chemical looping gasification of rice husk-derived biochar using BaFe2O4 as an oxygen carrier

Chemical Looping Gasification (CLG) is a promising technology for producing syngas with several merits. In this work, BaFe2O4 has been prepared via a sol-gel method as an iron-based composite oxygen carrier, and it was used to produce syngas from CLG of rice husk-derived biochar. At first, the effect of oxygen carrier (OC) content in the mixture sample of biochar and OC has investigated by a thermogravimetric analyzer (TGA). The results revealed that the highest weight loss rate was obtained when the OC content attained 60%, indicating it achieved the highest gasification reactivity. The effect of different conditions (temperature, reaction time, N2 carrier flow rate, and OC content) on syngas production from CLG of biochar was evaluated using a fixed bed reactor as the main objective of this study. The maximum syngas yield was 0.0182 mol/g with H2/CO ratio of 0.39, which has obtained at a temperature of 900 °C, N2 flow rate of 50 ml/min, a reaction time of 60 min, and OC content of 60%. Adding steam for CLG of biochar has significantly enhanced syngas yield and H2/CO ratio to 0.0778 mol/g and 3.2, respectively (at a steam flow of 0.055 ml/min). This indicates that the H2/CO ratio can be flexibly set to meet the requirement of syngas applications by controlling the steam addition rate. Moreover, the characterization of BaFe2O4 was investigated using XRD, SEM, H2-TPR, and BET, as the results have obviously confirmed the sintering of regenerated OC.

CO2-gasification kinetics of biomass char with a red mud oxygen carrier for chemical looping combustion

Experiments and modelling of CO2-gasification of rice husk char which was derived from its pellet pyrolysis, were performed in a bed of red mud oxygen-carrier with respect to chemical looping combustion. Effects of oxygen carrier, temperature, CO2 concentration were evaluated and modeled. An experimentally-fitted function was used for expressing the char characteristics evolution. The red mud remarkably enhanced char gasification due to the fast consumption of CO. Thus, a simplified Langmuir-Hinshelwood equation by neglecting the influence of CO was applied for evaluating the intrinsic kinetics. A model coupling the kinetics of char gasification and mass transfers throughout and surrounding the whole char were established. A good agreement between modelling and experimental results was obtained. With the reaction progressing, the dynamic of concentration gradients suggested the mass transfer resistance within the char particle. The gradients increased until the carbon conversion was about 0.3, which was corresponding to the pore structure change.

Gasification Kinetics of Victorian Brown Coal-Derived Char in Fluidized Bed Reactor

Abstract In a chemical looping combustion (CLC) system, gasification kinetics of char holds immense importance being the rate-limiting reaction in the fuel reactor. This paper studied the gasification kinetics of char derived from Victorian brown coal (VBC) in a fluidized bed reactor which mimics the fuel reactor conditions of a chemical looping combustion process. Mass of char, char particle size, and gas flow conditions were optimized to ensure the gasification reaction free from mass transfer limitations. Effect of oxygen carrier (OC), hematite, being the bed material was also studied. The experiments were conducted in the temperature range of 800 °C–950 °C, which is a typical range for fuel reactor. The experimental results were modeled with the help of grain model (GM) and random pore model (RPM) to analyze the kinetic parameters. Activation energy was found to be around 177 kJ/mol in sand bed and 175.5 kJ/mol in the hematite bed. Reaction in hematite bed was found to be 42% faster on average compared with the reaction in a sand bed. Fastest total conversion of char took as low as 4.1 min in hematite bed at 950 °C. While catalytic effect of hematite was ruled out due to insignificant change in activation energy, it was concluded that increase in CO2 partial pressure at the vicinity of char particle enhanced the reaction rate in the case of hematite bed. This study has generated relevant information for the CLC of Victorian brown coal with hematite as the oxygen carrier.

Cement/CaO-modified iron ore as oxygen carrier for chemical looping combustion of coal

Chemical looping combustion (CLC) of solid fuels is considered as a potential technology to reduce the energy penalty and the cost for CO2 capture. However, the low efficiency of carbon conversion and gasification products conversion is a big concern for the in-situ gasification chemical looping combustion (IG-CLC) process with the low-cost natural iron ore as an oxygen carrier. This paper evaluates the enhanced fuel conversion with a new CaO-modified iron ore as oxygen carrier during the continuous coal CLC in a 1kWth reactor. Both CaO-mixed iron ore and cement/CaO-combined iron ore were tested. The effect of oxygen carrier on the gaseous products was evaluated in the fuel reactor temperature range of 880–980°C. The samples of oxygen carrier were characterized using BET, SEM–EDX and XRD. The results indicate that compared with the pure iron ore oxygen carrier, the utilization of both CaO-mixed iron ore and the cement/CaO-combined iron ore could efficiently enhance coal conversion and gaseous conversion in the fuel reactor. However, when the CaO-mixed iron ore was used, some CaO powder due to the attrition during continuous operation adhered to the particle surface of iron ore. The Ca-containing compounds, i.e., potential eutectic of a low melting point caused sintering on the particle surface of iron ore. As a result, it caused the reactivity deterioration of oxygen carrier at a high fuel reactor temperature. To avoid the occurrence of sintering on the particle surface of the oxygen carrier, an improvement of cement/CaO-combined iron ore as oxygen carrier was proposed. A stable structure of Ca2Al2SiO7 was formed during the calcination process of the cement/CaO-combined iron ore. The sintering resistance of the iron ore was improved and the oxygen carrier after experiments maintained the porous structure. Reactivity deterioration of the combined oxygen carrier did not occur during the 5h continuous operation even at the fuel reactor temperature of 980°C. Overall, the Cement/CaO-combined iron ore is a competitive oxygen carrier in the coal CLC process.

Effect of Oxygen Carriers on Performance of Power Plants with Chemical Looping Combustion

Abstract The paper pursues process based analyses on power plants employing multi-stage chemical looping combustion (CLC) technology for carbon capture using different oxygen carrying materials and fuels. The aim is to determine any specific process based advantages offered by different oxygen carriers. CLC is an innovative combustion concept, which offers a potentially attractive option to capture CO2 with a significantly lower energy penalty than other existing carbon-capture technologies. In the CLC process, the combustion of fuel is split into two separate reactions carried out in two separate reactors: an oxidation reaction and a reduction reaction, by introducing a suitable metal oxide as an oxygen-carrier that circulates between the two reactors. This study investigates the viability of nickel, copper and iron as oxygen carriers using them with natural and synthesis gas fuels. It was conducted by developing an Aspen Plus based model, which employed the conservative principles of mass and energy. Equilibrium based reactor models with no oxygen-carrier (OC) deactivation were assumed. The choice of oxygen carrier and its effect on key operating parameters such as air, fuel and oxygen carrier mass flow rates, operating pressure, and the waste heat recovery were investigated for each fuel. For all OCs, the maximum temperatures were observed at stoichiometric OC mass flow rates for the given fuel supply. The peak reduction reactor temperatures were obtained with copper OC, which may require inerts or other temperature reduction strategies to avoid thermal deterioration. Maximum thermal efficiencies were observed for iron and nickel OCs. However, iron requires considerably larger OC mass flow rates compared to nickel and copper.

Oxygen transport to renal tissue: effect of oxygen carriers.

The isolated perfused rat kidney introduced by Weiss and colleagues in 1959 has become a commonly used tool in the field of renal physiology and pharmacology (Weiss, Passow and Rothstein, 1959; Little and Cohen, 1974; Ross, 1978; Maack, 1986). In view of technical complications such as blood clotting and the release of vasoactive factors most authors preferred a hyperoxygenated (PO2~660 mmHg) balanced salt solution instead of blood as a perfusate. However, recent experiments with the isolated Ringer-perfused rat kidney indicate that oxygen transport to renal tissue has become a central question: due to a steep gradient of oxygen partial pressure in the outer medullary region of mammalian kidneys (Leichtweiss et al., 1969; Baumgartl et al., 1972) the poor oxygen binding capacity of hyperoxygenated salt solutions induced functional and morphological lesions in distinct renal tissue zones (Alcorn et al., 1981; Brezis et al., 1984; Schurek and Kriz, 1985). The aim of the present experiments was to compare the effects of three different oxygen carriers on function and tissue integrity of the isolated perfused rat kidney. The following served as oxygen carriers: a) coupled haemoglobin, b) washed erythrocytes, and c) perfluorocarbons. Perfusions performed with hyperoxygenated Ringer solutions (PO2~660 mmHg) served as a control. Our data indicate that renal function (perfusion flow rate, glomerular filtration rate, absolute and fractional Na+ reabsorption) as well as parameters of tissue integrity (i.e. the loss of enzymes, and tissue water content) are maintained best with an erythrocyte suspension and, for a limited time period, with coupled haemoglobin in the perfusate. They are reasonably maintained during Ringer perfusion, but are severely impaired in the presence of a perfluorocarbon emulsion.