Daniel Wuillemin

A solar chemical reactor for co-production of zinc and synthesis gas

A novel solar chemical reactor has been designed to perform the combined ZnO-reduction and CH4-reforming processes. It consists of a gas-particle vortex flow confined to a solar cavity-receiver that is exposed to concentrated solar irradiation. A 5-kW reactor was fabricated and tested in a high-flux solar furnace. The design methodology and experimental program are described. Tests were conducted from 1000 to 1600K and yielded up to 90% chemical conversion of zinc in a single pass.

A Novel 50kW 11,000 suns High-Flux Solar Simulator Based on an Array of Xenon Arc Lamps

A novel high-flux solar simulator, capable of delivering over 50 kW of radiative power at peak radiative fluxes exceeding 11,000 suns, is operational at the Paul Scherner Institute. It comprises an array of ten Xe arcs, each close-coupled with ellipsoidal specular reflectors of common focus. Its optical design, main engineering features, and operating performance are described. The Monte Carlo ray-tracing technique is applied to optimize the geometrical configuration for maximum source-to-target transfer efficiency of radiative power. Calorimeter measurements indicated an average flux of 6800 kW/m2 over a 60-mm-diameter circular target, which corresponds to stagnation temperatures above 3300 K. This research facility simulates the radiation characteristics of highly concentrating solar systems and serves as an experimental platform for investigating the thermochemical processing of solar fuels and for testing advanced high-temperature materials.

A receiver-reactor for the solar thermal dissociation of zinc oxide

A propelling drive control apparatus for a working vehicle comprising hydraulically operable friction clutches, a first clutch control valve for selecting between the friction clutches, and a second clutch control valve connected in series to the first clutch control valve. The second clutch control valve is manually switchable to a declutching position for disengaging the friction clutches, a first clutch engaging position for engaging one of the friction clutches, and a second clutch engaging position intermediate between the declutching position the first clutch engaging position. In this second clutch engaging position one of the friction clutches is operable under a lower hydraulic pressure than in the first clutch engaging position.

Solar thermal production of zinc and syngas via combined ZnO-reduction and CH4-reforming processes

Abstract The combined thermal reduction of ZnO and reforming of CH4 has been thermodynamically and kinetically examined. The chemical equilibrium composition of the system ZnO + CH4 at 1200 K and 1 atm consists of a single gas phase containing Zn (vapor) and a 2:1 mixture of H2 and CO. The overall reaction can be represented as: ZnO(s) + CH4 = Zn(g) + 2H2 + CO. Thermogravimetric measurements on ZnO powder were conducted at various temperatures and CH4 concentrations of the reducing gas. The apparent activation energy obtained was 146 kJ mol−1. By aplying a shrinking-particle model, the reaction mechanism was found to be controlled by gas film diffusion in the Stokes regime. The reaction was also studied in a solar furnace using concentrated radiation as the energy source of high-temperature process heat (ΔH∘1200K = 440 kJ mol−1). Its technical feasibility was demonstrated. The solar receiver consisted of a fluidized-bed tubular quartz reactor coupled to a compound parabolic concentrator. Directly irradiated ZnO particles, fluidized in CH4, acted as heat absorbers and chemical reactants, while the Zn vapor produced was trapped in a cold-finger condenser. The proposed solar combined thermochemical process offers the possibility of simultaneous production of zinc and synthesis gas from zinc oxide and natural gas, without discharging greenhouse gases and other pollutants to the atmosphere. Furthermore, it provides an environmentally clean path for either recycling Zn-air batteries or producing H2 in a water-splitting scheme.

Design and experimental investigation of a horizontal rotary reactor for the solar thermal production of lime

We designed and tested a 10-kW solar rotary kiln reactor to effect the calcination reaction: CaCO3 → CaO+CO2. The reactor processes 1–5 mm limestone particles, producing 95% or higher purity lime with a t60 reactivity ranging from 14 s to 38 min. The degree of calcination and the reactivity both depend on the reactant’s decomposition temperature (1323–1423 K), residence time (3–7 min), and feed rate (10–50 g/min). The reactor’s efficiency, defined as the enthalpy of the calcination reaction at a specified temperature divided by the solar energy input, reached 20% for solar flux inputs of about 1200 kW m−2 and for quicklime production rates of about 1.3 kg/h. The solar lime reactor operated reliably for more than 100 h for a total of 24 sunny days, withstanding the thermal shocks that occur in solar applications.

Experiment for modelling high temperature rock bed storage

Abstract High temperature thermal storage in rock beds using air as a heat transfer medium was repeatedly proposed for large solar power plants. Subsequently, a mathematical model describing the thermal behavior of such a storage system was developed. This one-phase dynamic model solves analytically the one-dimensional linear nonhomogeneous boundary-value problem for the heat transfer between air and particles, leading to a computer code called PACKBEDA. Recently, this program has been improved and modified in order to include the temperature dependent thermophysical properties of air (density, viscosity, and thermal conductivity), as well as the heat losses through the insulated walls. Moreover, the program keeps track of the amount of pressure drop across the solid bed. To validate this model, an experimental store called ARIANE was built. Measurements of the transient behavior of the rock bed during the charging process show a fairly well stratified temperature distribution. Due to the somewhat unfavorable shape of the storage vessel with its high surface-to-volume ratio, the heat losses through the wall are considerable. These features are well reproduced by the modified computer program PACKBEDA which seems to be a reliable and useful tool for the analysis of large scale air/rock bed storage systems.

Pilot Scale Demonstration of a 100-kWth Solar Thermochemical Plant for the Thermal Dissociation of ZnO

A solar-driven thermochemical pilot plant for the high-temperature thermal dissociation of ZnO has been designed, fabricated, and experimentally demonstrated. Tests were conducted at the large-scale solar concentrating facility of PROMES-CNRS by subjecting the solar reactor to concentrated radiative fluxes of up to 4477 suns and peak solar radiative power input of 140 kWth. The solar reactor was operated at temperatures up to 1936 K, yielding a Zn molar fraction of the condensed products in the range 12–49% that was largely dependent on the flow rate of Ar injected to quench the evolving gaseous products.

1kW imaging furnace with in situ measurement of surface temperature

This article describes the development and characterization of a 1kW imaging furnace that allows to investigate materials such as sulfides at ultrahigh temperatures under controlled atmosphere. Peak flux densities up to (15.37±0.66)×106Wm−2 corresponding to a maximum stagnation temperature of 3090K can be reached in the center of the heating zone of 3mm diameter (full width at half height). Individual sample holders can be mounted on a generic sample stage that is aligned in three axes. Together they define an experiment. Experiments can thus be easily interchanged without requiring any realignment. The use of a specific sample holder is reported where the sample rests on a water-cooled tip to avoid contamination by crucible material and where a protective glass dome can be mounted to allow the study of samples releasing condensable or corrosive gases. With the dome in place the peak flux density decreases to a value of (13.59±0.45)×106Wm−2 (Tstag=2980K). The surface temperature of the sample and the aver...

A compact setup to study homogeneous nucleation and condensation.

An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

Experimental Setup of a Laser Diagnostics System for a High-Temperature Solar Receiver/Reactor

A solar receiver/reactor has been designed specifically to study high-temperature gas phase chemical reactions using a laser based metrology. It is a cavity-type receiver, lined with stabilized ZrO[sub 2], and operated at temperatures up to 2,000 K. The gas temperature is measured in situ using the coherent anti-Stokes Raman spectroscopy (CARS) of N[sub 2]. Optical access for the CARS measurement is accomplished via two side windows, each subtending a 118-mrad cone angle at the center of the cavity, providing enough clearance for the input laser beams and the output signal carrying the temperature information. Two endothermic processes were used for the initial evaluation of this method: the NH[sub 3] dissociation into N[sub 2] and H[sub 2], and the CO[sub 2]-reforming of CH[sub 4] into synthesis gas. The process flow was directly exposed to high solar fluxes in addition to infrared radiation emitted by the hot reactor walls. The laser-based metrology performed satisfactorily in spite of the presence of the intense radiation field. This paper describes in detail the technical aspects of the experimental setup, presents examples of spectra and temperature measurements, and discusses practical problems encountered during experimentation.