Selecting Technologies for Sour and Ultra-Sour Gas Treating

As the cleanest fossil fuel, natural gas plays a key role in the path towards renewables. Considering the increasing gas demand, rich CO2 and H2S gas reserves, in the past considered economically unviable, are becoming fruitful. However, the non-conventional nature of this kind of gases, in addition to the potentially higher production cost, raises the need of new strategies for their monetization, bypassing the conventional approaches. Starting from the huge number of novel large-scale projects for the exploitation of rich-H2S gas fields, this paper overviews the current tendencies in sour and ultra-sour natural gas production, focusing on the removal of sulfur-based compounds, together with H2S and CO2. At first, available technologies for ultra-sour gas treatment are discussed. Then, simulations of the absorption processes based on a real case-study are carried out, in order to verify the effectiveness of the proposed alternatives for the removal of mercaptans, as well as CO2 and H2S. Results are critically analyzed, in view of providing a practical guide of industrial interest for the selection of the most suitable method

Ammonia as a Carbon-Free Energy Carrier: NH3 Cracking to H2

In the energy transition from fossil fuels to renewables,hydrogenis a realistic alternative to achieving the decarbonization target.However, its chemical and physical properties make its storage andtransport expensive. To ensure the cost-effective H-2 usageas an energy vector, other chemicals are getting attention as H-2 carriers. Among them, ammonia is the most promising candidate.The value chain of NH3 as a H-2 carrier, consideringthe long-distance ship transport, includes NH3 synthesisand storage at the loading terminal, NH3 storage at theunloading terminal, and its cracking to release H-2. NH3 synthesis and cracking are the cost drivers of the valuechain. Also, the NH3 cracking at large scale is not a maturetechnology, and a significant effort has to be made in intensifyingthe process as much as possible. In this respect, this work reviewsthe available technologies for NH3 cracking, criticallyanalyzing them in view of the scale up to the industrial level

Assessing opportunities and weaknesses of green hydrogen transport via LOHC through a detailed techno-economic analysis

In the transition towards a more sustainable energy system, hydrogen is seen as the key low-emission energy source. However, the limited H2 volumetric density hinders its transportation. To overcome this issue, liquid organic hydrogen carriers (LOHCs), molecules that can be hydrogenated and, upon arrival, dehydrogenated for H2 release, have been proposed as hydrogen transport media. Considering toluene and dibenzyltoluene as representative carriers, this work offers a systematic methodology for the analysis and the comparison of LOHCs, in view of identifying cost-drivers of the overall value-chain. A detailed Aspen Plus process simulation is provided for hydrogenation and dehydrogenation sections. Simulation results are used as input data for the economic assessment. The process economics reveals that dehydrogenation is the most impactful cost-item, together with the carrier initial loading, the latter related to the LOHC transport distance. The choice of the most suitable molecule as H2 carrier, ultimately, is a trade-off between its hydrogenation enthalpy and cost.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/)

Liquefied hydrogen value chain: A detailed techno-economic evaluation for its application in the industrial and mobility sectors

Green hydrogen can be efficiently produced in regions rich in renewable sources, far from the European large-production sites, and delivered to the continent for utilization in the industrial and mobility sectors. In this work, the transportation of hydrogen from North Africa to North Italy in its liquefied form is considered. A techno-economic assessment is performed on its value chain, which includes liquefaction, storage, maritime trans-port, distribution, regasification and compression. The calculated transport cost for the industrial application (delivery to a hydrogen valley) ranges from 6.14 to 9.16 euro/kg, while for the mobility application (delivery to refueling stations) the range is 10.96-17.71 euro/kg. In the latter case, the most cost-effective configuration involves the distribution of liquefied hydrogen and regasification at the refueling stations. The liquefaction process is the cost driver of the value chain in all the investigated cases, suggesting the importance of its optimization to minimize the overall transport cost

On the Effect of the Reaction Medium on the HydroClaus Process: A Novel Sustainable H2S Valorization Strategy

Hydrogen sulfide (H2S) is becoming a critical issue to manage, due to the increasing sulfur content in the processed gas together with the stricter environmental regulations. Novel alternatives are being developed for the H2S abatement and conversion to valuable chemicals. Among them, the HydroClaus process, patented by Eni S.p.A., deserves attention. This technology aims at converting H2S and SO2 into a hydrophilic mixture of sulfur and sulfur-rich compounds, polythionates, to be used as a fertilizer. An improved configuration for an efficient water management is proposed in this work. The process operability has been demonstrated at the bench scale, through an ad hoc experimental campaign. For the technology scale-up, a flowsheet has been set up and its performances have been assessed in terms of heat and material balances and CO2 emissions. Results reveal that the modified HydroClaus process can be a valid solution for an effective H2S valorization, also considering that no direct CO2 emissions are released. Moreover, since only electric power is required, a further reduction of the indirect CO2 emissions is expected, if renewable sources can be exploited for this purpose

Solid-Liquid-Vapor Equilibrium Prediction for Typical Helium-Bearing Natural Gas Mixtures

Industrial, large-scale helium recovery from natural gas is typically performed though cryogenic distillation. These technologies need a deep knowledge of the thermodynamics of the treated mixture: in the case of natural gas to a pipeline, CO2 present in the feed stream might freeze at the process operating temperatures. The aim of this work is to analyze the thermodynamic behavior of the four-component mixture CH4-N2-He-CO2 to predict its triphasic solid-liquid-vapor equilibrium (SLVE). Through a developed computational method based on the classical approach, the nitrogen and helium effect on CO2 solidification has been assessed. The investigated conditions are consistent with typical cryogenic procesthesing temperatures (i.e., 100-200 K) and natural gas compositions. Pressure-temperature and temperature-composition equilibrium loci are provided for each analyzed case, varying the N2 and He content in mixture. Helium behavior as a quantum gas has been considered by introducing temperature-dependent critical parameters, as suggested by Prausnitz and co-workers, valid for an acentric factor equal to zero. Referring to the proposed thermodynamic modeling, the risk of CO2 freezing within a cryogenic helium recovery plant can be avoided by carefully managing the process operating conditions

Simultaneous Multiphase Flash and Stability Analysis Calculations Including Solid CO2 for CO2−CH4, CO2−CH4−N2, and CO2−CH4−N2− O2 Mixtures

This work deals with solid–vapor equilibria and solid–liquid–vapor equilibria of carbon dioxide in mixtures of interest for natural gas purification and biogas upgrading. Experimental data available in the literature are reviewed and an algorithm for solving an isobaric–isothermal flash coupled to a phase stability analysis is presented, which does not require a-priori knowledge of the number and type of phases existing at equilibrium. The good agreement between calculation results, also performed with a tool that makes use of Gibbs free energy minimization, and experimental data suggests that the proposed approach can be used for determining suitable operating conditions for processes aimed at separating CO2 out of a gas by freezing it. This work points out that more experimental studies should be performed on phase equilibria in the presence of solid CO2 for multicomponent mixtures containing species other than methane (e.g., nitrogen and oxygen), which are representative of gaseous streams from which CO2 needs to be removed, such as natural gas, biogas, and flue gas from power plants. Such data are important for a proper calibration of thermodynamic models that must be selected for reliable process simulations