V. Goetz

Optimal design of an activated carbon for an adsorbed natural gas storage system

Abstract The Dubinin–Astakhov equation was used to determine the influence of the microporous characteristics of activated carbon on the performances of both charge and discharge of an ANG system. From the dynamic performance criterion as a function of total microporous volume (Wo), average micropore width (Lo), and micropore size dispersion (n), it is possible to identify the optimal activated carbon for methane storage under dynamic conditions by way of the heat and mass transfer limitations. This study shows that the activated carbon must be conductive (with an average micropore width of 1.5 nm) for the charge step only, permeable and sufficiently conductive for the discharge process (with an average micropore width of 2.5 nm). The well-known Maxsorb activated carbon shows the better performance. This theoretical investigation has been validated by experimental results.

A model for reversible solid-gas reactions submitted to temperature and pressure constraints: simulation of the rate of reaction in solid-gas reactor used as chemical heat pump

An unreacted-core model is formulated in the case of a reversible solid-gas reaction and applied to intrepretation of the experimental results obtained by microcalorimetry for the MnCl2NH3 couple. The model gives a close correlation with experimental data and is able to predict the effects of temperature and pressure on grain kinetics. The solution of the thermal balance equation applied to a reactive mixture used in a chemical heat pump, which is composed of reactive salt and an inert binder, is then developed. The thermal parameters are fitted from experimental results obtained from a laboratory reactor. The composition and temperature profiles allow the main rate-limiting phenomena between heat transfer in the reactive mixture and grain kinetics to be determined.

Characterization of adsorbent composite blocks for methane storage

Abstract Adsorbent composite blocks for natural gas adsorption have been produced by mixing PX-21 and expanded natural graphite (ENG), followed by consolidation in a mould. These composite blocks of 10–30% weight ratio of expanded natural graphite and 430–480 kg m−3 apparent density have shown good methane adsorption capacities and good heat and mass transfer properties. Volumetric methane adsorption capacity (V/V) of adsorbent composite blocks produced is in the range of 110–125 V/V. Permeability increases with weight ratio of ENG, and thermal conductivity, in the range of 2–10 W m−1K−1, is much higher than activated carbon packed bed. These good transfer properties of the adsorbent composite blocks will enhance performances of on-board natural gas vehicles in terms of delivered methane volume under realistic dynamic conditions.

A solid-gas thermochemical cooling system using BaCl2 and NiCl2

The feasibility of effective cooling using two solid-gas reactors has been tested experimentally with a low-power machine. The ambient temperature was 313 K. The power output of the reactors has been determined as a function of cooling temperature for air conditioning and refrigeration. Refrigeration requires a heat-transfer fluid temperature of 273 K, while air conditioning of buildings requires 285–288 K. For personal air-conditioning units, the desired temperature is between 310 and 313 K. We have used a model to validate charts for the power produced per unit of reactive volume with proper consideration of desired temperatures for both reactors.

The structure and performance of single effect solid-gas chemical heat pumps

Among sorption machines, those involving solid-gas reactions have at their disposal a particularly plentiful supply of reactive agents, whether they be ammoniates or hydrides. The possibilities of refrigeration down to −40°C or thermo-transformation up to 350°C are analysed in the case of chlorides reacting with NH3. The performance of these single effect machines is presented and analysed in terms of exergetic efficiency and the coefficient of performance (COP).

Energy storage comparison of sorption systems for cooling and refrigeration

A comparison between different sorption systems (binary mix only) such as absorption, adsorption and solid/gas reaction is presented with relation to their storage capacity for cooling. So as to be complete, phase change material (PCM) storage capacity has been added. The results are presented in kWh per kilogram of the total mass of the species involved in the cycle: the refrigerant fluid and the sorbent. In order to make a real condition comparison, two simple case studies have been made using temperatures that are compatible with a solar heat source. It appears that for negative temperatures, solid/gas reaction with ammonia has the best capacity. Storage with phase change material appears to be quite competitive even if a little less efficient. For positive temperatures, the best storage capacity is for water (working fluid) in absorption with NaOH as absorbent and in reaction with CaCl2, MgCl2 and Na2S as salt.

Solar photo-Fenton using peroxymonosulfate for organic micropollutants removal from domestic wastewater: Comparison with heterogeneous TiO2 photocatalysis

This work aims at decontaminating biologically treated domestic wastewater effluents from organic micropollutants by sulfate radical based (SO4(-)) homogeneous photo-Fenton involving peroxymonosulfate as an oxidant, ferrous iron (Fe(II)) as a catalyst and simulated solar irradiation as a light source. This oxidative system was evaluated by using several probe compounds belonging to pesticides (bifenthrin, mesotrione and clothianidin) and pharmaceuticals (diclofenac, sulfamethoxazole and carbamazepine) classes and its kinetic efficiency was compared to that to the well known UV-Vis/TiO2 heterogeneous photocatalysis. Except for carbamazepine, apparent kinetic rate constants were always 10 times higher in PMS/Fe(II)/UV-Vis than in TiO2/UV-Vis system and more than 70% of total organic carbon abatement was reached in less than one hour treatment. Hydroxyl radical (OH) and SO4(-) reactivity was investigated using mesotrione as a probe compound through by-products identification by liquid chromatography-high resolution-mass spectrometry and transformation pathways elucidation. In addition to two OH based transformation pathways, a specific SO4(-) transformation pathway which first involved degradation through one electron transfer oxidation processes followed by decarboxylation were probably responsible for mesotrione degradation kinetic improvement upon UV-Vis/PMS/Fe(II) system in comparison to UVVis/TiO2 system.

Cooling storage with a resorption process. Application to a box temperature control

Abstract The resorption process is based on the use of two solid–gas reactors. It is an efficient system for cold production, in any application where the presence of a liquid phase is not desirable. Experimental results show that this system is adapted to an effective production of cold at a temperature of the order of 273 K. This result is also supported by simulation from a dynamic and simplified model. The application presented here, consists in cooling and to maintain in temperature a box. It makes it possible to propose a very simple control of cold production by control of the working pressure of one of solid–gas reactors.

A new analytical model for solid-gas thermochemical reactors based on thermophysical properties of the reactive medium

Abstract In the following study, a basis has been developed for a pseudo-permanent model, taking into account the average functioning characteristics of a solid-gas reactor during an interval of time. This model is of interest thanks to its analytical form and allows simple calculations to be made concerning the dimensioning, and thereby helps in the decision-making process. The industrial development of thermochemical reactors requires the design and construction of demonstration machines and thus calls for dimensioning models. The already existing models are based on dynamic simulation linked to the discontinuous and transient functioning mode of such processes. Hence, these dynamic models require initially arbitrary choices, which are tested successively to achieve a correct sizing of the machine. The comparison of the analytical model developed in this study with a dynamic model, and with the results of experiments, demonstrates the limits of the analytical model, as well as its reliability compared to the dynamic model. Elsewhere, the flexibility linked to its analytical form shows the scale of the field of application.

Modelling and experimental investigation of a new type of thermochemical transformer based on the coupling of two solid-gas reactions

Abstract The feasibility of thermochemical transformer based on the coupling of two solid-gas reactions has been demonstrated by a 1 kW experimental laboratory plant. A model has been built taking into account the dynamic coupling of the two reactors by the gaseous phase and the consumption of the reactive medium in each reactor. The model has been validated by experimental results and is capable of simulating the running mode of the process for a series of working cycles.