Devolatilization of organo-sulfur compounds in coal gasification

Coal gasification is a thermo-chemical process aiming at the production of high heating value syngas. The coal charges present, typically, a low quantity of sulfur compounds for prevent the formation of a large amount of sulfuric acid (H2S), that is a pollutant and a poison for catalysts, in syngas stream. However, in the world there are a lot of coals that cannot be used for gasification because of their high sulfur content (e.g. Sulcis Italian coal or Inner Mongolia Chinese coal). The interest on these types of coal is increasing due to a novel technology that allows to convert H2S and CO2into syngas (AG2S\u2122). The aim of this work is to propose a predictive kinetic model of the release of sulfur compounds (e.g H2S) from coal. This kinetic scheme is implement into GASDS, a package that includes a gasifier mathematical model, which accurately describes the inter-phase mass and heat transfer. The first complexity relies in the characterization of the coal, in particular the relative amount of the different forms of sulfur components (e.g. inorganic such as pyritic and sulfates, and organic sulfur such as aliphatic, aromatic and thiophenic) and their pyrolysis and devolatilization process. The kinetic model, with the related rate parameters, is validated through comparison with experimental data from the literature and obtained during several experimental campaigns at the Sotacarbo S.p.A. pilot platform. Finally, different operating conditions of gasification are analyzed in order to obtain the best yield in the downstream process, with special reference to the novel Acid Gas to Syngas (AG2STM) process

Ex-LDH-based catalysts for CO2 conversion to methanol and dimethyl ether

CO2-derived methanol and dimethyl ether can play a very important role as fuels, energy carriers, and bulk chemicals. Methanol production from CO2 and renewable hydrogen is considered to be one of the most promising pathways to alleviate global warming. In turn, methanol could be subsequently dehydrated into DME; alternatively, one-step CO2 conversion to DME can be obtained by hydrogenation on bifunctional catalysts. In this light, four oxide catalysts with the same Cu and Zn content (Cu/Zn molar ratio = 2) were synthesized by calcining the corresponding CuZnAl LDH systems modified with Zr and/or Ce. The fresh ex-LDH catalysts were characterized in terms of composition, texture, structure, surface acidity and basicity, and reducibility. Structural and acid– base properties were also studied on H2-treated samples, on which specific metal surface area and dispersion of metallic Cu were determined as well. After in situ H2 treatment, the ex-LDH systems were tested as catalysts for the hydrogenation of CO2 to methanol at 250 °C and 3.0 MPa. In the same experimental conditions, CO2 conversion into dimethyl ether was studied on bifunctional catalysts obtained by physically mixing the ex-LDH hydrogenation catalysts with acid ferrierite or ZSM-5 zeolites. For both processes, the effect of the Al/Zr/Ce ratio on the products distribution was investigated

CO2 hydrogenation to methanol with an innovative Cu/Zn/Al/Zr catalyst: Experimental tests and process modeling

In this study, an innovative Cu/Zn/Al/Zr catalyst for the conversion of CO2 and H2 into methanol is tested at laboratory scale (0.5 g of catalyst into a cylindrical fixed bed reactor, with 9.1 mm internal diameter). Fourteen experimental tests are performed under isothermal conditions (T = 250 °C), covering a range of pressure (3.0–7.0 MPa), Gas Hourly Space Velocity (4000–13,000 h-1) and H2/CO2 molar ratio (between 3 and 6) relevant to industrial applications, with or without CO in the feed mixture, with flow-rates ranging between 200 and 650 NmL min-1. Based on the established Graaf’s kinetic model, new kinetic parameters are calibrated and a plug-flow model of the isothermal reactor is implemented and simulated in Aspen Plus. A reasonable agreement between experimental data and calibrated model is achieved, with deviations lower than 10% of the measured flow rates for each species in the product stream. CO2 conversion up to 26% and methanol yields up to 13% are obtained during the test campaign (test run #12). The model represents a valid tool for future research or engineering studies targeting the design and performance assessment of demo/full-scale CO2-to-methanol synthesis processes based on the Cu/Zn/Al/Zr catalyst introduced in this paper

Enhancing the separation performance of glassy PPO with the addition of a molecular sieve (ZIF-8): Gas transport at various temperatures

In this study, we prepared and characterized composite films formed by amorphous poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and particles of the size-selective Zeolitic Imidazolate Framework 8 (ZIF-8). The aim was to increase the permselectivity properties of pure PPO using readily available materials to enable the possibility to scale-up the technology developed in this work. The preparation protocol established allowed robust membranes with filler loadings as high as 45 wt% to be obtained. The thermal, morphological, and structural properties of the membranes were analyzed via DSC, SEM, TGA, and densitometry. The gas permeability and diffusivity of He, CO2, CH4, and N2 were measured at 35, 50, and 65 \ub0C. The inclusion of ZIF-8 led to a remarkable increase of the gas permeability for all gases, and to a significant decrease of the activation energy of diffusion and permeation. The permeability increased up to +800% at 45 wt% of filler, reaching values of 621 Barrer for He and 449 for CO2 at 35 \ub0C. The ideal size selectivity of the PPO membrane also increased, albeit to a lower extent, and the maximum was reached at a filler loading of 35 wt% (1.5 for He/CO2, 18 for CO2/N2, 17 for CO2/CH4, 27 for He/N2, and 24 for He/CH4). The density of the composite materials followed an additive behavior based on the pure values of PPO and ZIF-8, which indicates good adhesion between the two phases. The permeability and He/CO2 selectivity increased with temperature, which indicates that applications at higher temperatures than those inspected should be encouraged

Detailed petrophysical and geophysical characterization of core samples from the potential caprock-reservoir system in the Sulcis Coal Basin (Southwestern Sardinia - Italy)

In this work we present a methodology suitable to identify a caprock-reservoir system for the CO2 storage in the Sulcis Coal Basin (SW Sardinia - Italy). The petrophysical and geophysical characterizations indicate that the potential carbonate reservoir ("Miliolitico" Fm. Auct.) located at the base of the Eocene stratigraphic sequence in the mining district of the Sulcis Coal Basin, southwestern Sardinia, is heterogeneous but presents suitable reservoir zones for the storage of the CO2. The GPS data analysis indicates that the study area is stable, since it is characterized by a surface crustal deformation smaller than 1 mm/y

Syngas production, clean-up and wastewater management in a demo-scale fixed-bed updraft biomass gasification unit

This paper presents the experimental development at demonstration scale of an integrated gasification system fed with wood chips. The unit is based on a fixed-bed, updraft and air-blown gasifier-with a nominal capacity of 5 MWth-equipped with a wet scrubber for syngas clean-up and an integrated chemical and physical wastewater management system. Gasification performance, syngas composition and temperature profile are presented for the optimal operating conditions and with reference to two kinds of biomass used as primary fuels, i.e., stone pine and eucalyptus from local forests (combined heat and power generation from this kind of fuel represents a good opportunity to exploit distributed generation systems that can be part of a new energy paradigm in the framework of the circular economy). The gasification unit is characterised by a high efficiency (about 79-80%) and an operation stability during each test. Particular attention has been paid to the optimisation of an integrated double stage wastewater management system-which includes an oil skimmer and an activated carbon adsorption filter-designed to minimise both liquid residues and water make-up. The possibility to recycle part of the separated oil and used activated carbon to the gasifier has been also evaluated

Performance Evaluation of a Direct Absorption Collector for Solar Thermal Energy Conversion

The solar absorption efficiency of water as a base-fluid can be significantly improved by suspending nanoparticles of various materials in it. This experimental work presents the photo thermal performance of water-based nano-fluids of graphene oxide (GO), zinc oxide (ZnO), copper oxide (CuO), and their hybrids under natural solar flux for the first time. Nanofluid samples were prepared by the two-step method and the photothermal performance of these nanofluid samples was conducted under natural solar flux in a particle concentration range from 0.0004 wt % to 0.0012 wt %. The photothermal efficiency of water-based 0.0012 wt % GO nanofluid was 46.6% greater than that of the other nanofluids used. This increased photothermal performance of GO nanofluid was associated with its good stability, high absorptivity, and high thermal conductivity. Thus, pure graphene oxide (GO) based nanofluid is a potential candidate for direct absorption solar collection to be used in different solar thermal energy conversion applications

Hydrogen production from coal gasification in updraft gasifier with syngas treating line

Hydrogen production through coal gasification is becoming one of the most attractive options for energy production due to its remarkable advantages in pollution control and greenhouse gases-emissions monitoring. With this aim, Sotacarbo, Ansaldo Ricerche, ENEA and the University of Cagliari, are developing a research project to design, construct and test a pilot plant for hydrogen production from coal gasification (in particular from high-sulphur Sulcis coal). The project has been funded by the Italian Ministry of Education, University and Research (MIUR) and by the European Commission and the total cost has been estimated in about 12 million euros. The pilot plant, which has been recently constructed in the Sotacarbo Research Centre located in Sardinia (Italy), includes two updraft fixed-bed Wellman-Galusha gasifiers (a 700 kg/h pilot gasifier and a 35 kg/h laboratory-scale gasifier) and an overall syngas treating process for hydrogen production. In particular, the raw gas cleaning sections is composed by both hot and cold gas desulphurization processes, which can operate in parallel in order to compare their performances. This paper reports the main results of the process analysis and performance evaluation, in particular the analysis of the updraft moving bed gasifiers has been carried out under the assumption of chemical equilibrium by using two different simulation models, developed using the Aspen Plus and the ChemCAD commercial software. The results obtained with the two gasification models are very similar and compare favourably with the expected performances specified by the gasifier manufacturer