Monolithic Ceramic Redox Materials for Thermochemical Heat Storage Applications in CSP Plants

AbstractThe present work relates to the investigation of cobalt and manganese oxide based compositions as candidate materials for the storage of surplus energy, available in the form of heat, generated from high temperature concentrated solar power plants (e.g. solar tower, solar dish) via a two-step thermochemical cyclic redox process under air flow. Emphasis is given on the utilization of small structured monolithic bodies (flow-through pellets) made entirely from the two aforementioned oxides. As compared to the respective powders, and in addition to the natural advantage of substantially lower pressure drop that monolithic structures can offer, this study demonstrated that structured bodies can also improve redox kinetics to a measurable extent. Cobalt oxide was found to be superior to manganese oxide both from an estimated energy density and from a redox reactions kinetics point-of-view. Among the redox conditions studied, the optimum reduction-oxidation operating window for the former oxide was determined to be in the range of 1000-800°C, while for the latter material no clear conclusion was drawn with reduction reaching its maximum extent at 1000°C and oxidation occurring in the range of 500-650°C. In both cases, no significant degradation of redox performance was observed upon cyclic operation (up to 10 cycles), however manganese oxide showed notably slower oxidation kinetics

On-Line / In-Line Measurements of Particle Emissions by a Combustion Aerosol Standard

A system for the on-line/in-line measurement of soot particle sizes and concentrations in the undiluted exhaust gas of diesel engines was developed and successfully tested. The unit uses the individual attenuations of three different laser wavelengths and is combined with an optical cell (white principle) with adjustable path lengths from 2.5 to 15 meters

Particle Model Investigation For The Thermochemical Steps Of The Sulfur–Ammonia Water Splitting Cycle

Solar-driven hybrid sulfur–ammonia water splitting cycle (HySA) is a promising technology for energy and environment applications. The advantage of the proposed cycle is the utilization of both solar photon and thermal radiation in a series of reaction steps from ambient temperature to less than 900 °C. It uses molten salts as reagents to control products of each step and as potential thermochemical energy storage. The use of a solar aerosol based reactor for the thermochemical steps of the cycle appears promising, therefore a particle model is required. Reliable thermodynamic data are necessary to develop an efficient conceptual particle model. Therefore, in this present study, we perform thermal analysis experiments and thermodynamic calculations for the related compounds and their reciprocal mixtures. Based on the experimental and numerical findings, we discuss the conceptual particle model according to the thermochemical steps of the hybrid sulfur–ammonia water splitting cycle

Hybrid Photo-Thermal Sulfur-Ammonia Water Splitting Cycle: Thermodynamic Analysis Of The Thermochemical Steps

Solar driven hybrid sulfur-ammonia water splitting cycle (HySA) integrates a solar-photocatalytic hydrogen, H2, production step (H2 sub-cycle) with a high-temperature solar thermochemical oxygen, O2, evolution step (O2 sub-cycle), implementing efficient thermal energy storage as part of the cycle operation. Previous studies of the cycle omitted intermediate products, such as ammonium bisulfate, from the O2 sub-cycle and, thus, neglected their potential impact on the cycle\u27s chemistry. Also, there are discrepancies in reported literature for the thermodynamic properties of ammonium sulfate, (NH4)2SO4 and ammonium bisulfate, NH4HSO4. In this study, thermal analysis experiments were conducted in order to determine the phase transition temperatures and enthalpies, and the heat capacity temperature dependence of the ammonium sulfate, (NH4)2SO4 and ammonium bisulfate, NH4HSO4. Our experimentally determined values for these parameters agree well with the data reported in DIPPR Project 801 database. Moreover, an exploratory thermodynamic analyses was performed using AspenPlus© and FactSage©, that included all potential reaction products, in order to identify critical parameters for an optimum O2 sub-cycle. A methodology is proposed and evaluated to mitigate AspenPlus©\u27s deficiency to handle solid phase changes. The thermodynamic analyses demonstrate that the NH4HSO4 inclusion in the O2 sub-cycle reduces the overall process energy requirements, and allows its use as an energy storage medium. Finally, we show that the use of molten salts, in combination with their interactions, significantly affects the efficiency and the operating conditions of the process, as well as the state of the mixtures