Simplified correlation models for CO/H2 chemical reaction times

This paper provides simplified correlation models for CO/H₂ chemical reaction times. The procedure used for the CO/H₂ simplified modeling utilized the full chemical kinetics mechanism run over a range of temperatures from 700 to 1800 K, pressures from 0.5 to 50 atm, mixtures from 0% to 95% CO, and equivalence ratios from 0.2 to 2.0 to determine ignition (or reaction) time. The correlations for ignition times are given in formulas as functions of equivalence ratio, temperature, and pressure. Two different forms of correlations were obtained, one being a single, overall correlation and the other a two-stage correlation representing regions of high and low temperatures. These correlations are shown to work well over a range of chemical time scales spanning ten orders of magnitude. The correlations are also compared with measured data from the literature.     

An evaluation of detailed reaction mechanisms for hydrogen combustion under gas turbine conditions

Chemical kinetics in hydrogen combustion for elevated pressures have recently become more relevant because of the implementation of hydrogen as a fuel in future gas turbine combustion applications, such as IGCC or IRCC systems. The aim of this study is to identify a reaction mechanism that accurately represents H₂/O₂ kinetics over a large range of conditions, particularly at elevated pressures as present in a gas turbine combustor. Based on a literature review, six mechanisms of different research groups have been selected for further comparisons within this study. Reactor calculations of ignition delay times show that the mechanisms of Li et al. and Ó Conaire et al. yield the best agreement with data from shock tube experiments at pressures up to 33 bar. The investigation of one-dimensional laminar hydrogen flames indicate that these two mechanisms also yield the best agreement with experimental data of laminar flame speed, particularly for elevated pressures. The present study suggests that the Li mechanism is best suited for the prediction of H₂/O₂ chemistry since it includes more up-to date data for the range of interest.     

Laminar flame speed correlations for pure-hydrogen and high-hydrogen content syngas blends with various diluents

Hydrogen is an attractive fuel for large-scale combustion systems due to its high flame speeds and clean burning characteristics. This paper presents a new set of correlations for the laminar flame speeds of hydrogen-oxygen mixtures with nitrogen (air) and helium as diluents, using a recently updated chemical kinetics mechanism. A wide excursion of equivalence ratios (φ = 0.5–5.0), pressures (1–30 atm) and temperatures (270–620 K) was performed. Flame speed correlations were developed at five pressures, namely 1, 5, 10, 20, and 30 atm for the pure-hydrogen case. The disparities between the kinetic model predictions and the correlation estimates, commonly associated with existing correlations, were significantly reduced, and the correlation estimates are within ±13 cm/s of the model predictions. Also, a correlation for lean and high-hydrogen content (HHC) syngas blends of H₂ + CO + H₂O was developed from the pure-hydrogen correlations. A wide range of pressures (1–30 atm), initial temperatures (323–550 K), steam contaminant levels (5–15%), and hydrogen content in the fuel blend (15–100%) were simulated. A design of experiments approach was adopted to determine the critical mixtures necessary to develop the correlation. The developed HHC correlation agrees within ±12% of the model predictions.     

Role of methane as a cushion gas for hydrogen storage in depleted gas reservoirs

Depleted natural gas reservoirs play an important role as a viable option for large-scale hydrogen storage and production. However, its deployment depends on the accurate knowledge of the cushion gas (such as CH₄, CO₂, and N₂) compositions, which are key components affecting the rock-fluid interfacial phenomenon. In addition, there are currently few reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension representing this type of reservoir. Hence, we report the feasibility of using CH₄ as a cushion gas (in the presence of CO₂ and N₂) for H₂ storage at various pressures (500 up to 3000 psi), temperatures (30 up to 70) ^oC, and salinities (2 up to 20) wt.% using drop shape analyzer equipment. Contact angle (CA) and surface tension (ST) experiments were extensively conducted for the different gas mixtures (H₂–CH₄–CO₂–N₂) to establish relevant data for H₂ storage in depleted gas reservoirs.Our result indicates that unless when the rock's initial wetting state is altered, the studied gas-mixture compositions (Test case 1: 80% H₂ – 10% CH₄ – 5% CO₂ – 5% N₂; case 2: 70% H₂ – 20% CH₄ – 5% CO₂ – 5% N₂; case 3: 60% H₂ – 30% CH₄ – 5% CO₂ – 5% N₂; case 4: 50% H₂ – 40% CH₄ – 5% CO₂ – 5% N₂; case 5: 40% H₂ – 50% CH₄ – 5% CO₂ – 5% N₂; case 6: 30% H₂ – 60% CH₄ – 5% CO₂ – 5% N₂; and case 7: 20% H₂ – 70% CH₄ – 5% CO₂ – 5% N₂) will exhibit comparable wettability behavior as the CAs ranged between [20 to 41°] irrespective of the reservoir pressure, temperature, and salinity. ST decreases with increasing temperature and linearly with increasing pressure. ST for each gas mixture increased with salinity. ST decreases systematically with increasing CH₄ fraction (at any given salinity, temperature, and pressure) with the highest observed in Test case 1 and the lowest in Test case 7 compositions. Test cases 3 and 4 with H₂ (50–60%) and CH₄ (30–40%) fractions was selected as the optimal gas mixture based on CA and ST for H₂ storage and withdrawal. The study's findings offer precise and useful input data for the reservoir-scale simulation used in geo-storage optimization in depleted natural gas reservoirs.     

Evaluation of premature failure of a gas turbine component

A case study of certain gas turbine stator vanes which fail prematurely is presented, with a view to determining whether operational procedure might have caused the failures. The engines had been operated from a ‘hot-and-high’ environment, and this could have contributed to the failures.

Computational fluid dynamics (CFD) techniques were employed in order to obtain an accurate design point thermal history. The resulting convection boundary conditions were then interpolated over a finite element mesh. Transient thermal and stress analyses were performed. At the same time, microstructural analyses of the service-exposed material were carried out to estimate the maximum temperature seen by the component. These showed that higher than expected vane metal temperatures were experienced. Emphasis was placed on the procedures outlined in the USAF Engine Structural Integrity Program¹, since little detail was known about the actual engine operating histories.     

CO2 separation from the mixture of CO2/H2 using gas hydrates: Experimental and modeling

Hydrate formation is a new technique to separate hydrogen from carbon dioxide. In this way, modeling and prediction of gas hydrate kinetics is very important. Several experiments have been conducted to study the hydrate formation from pure carbon dioxide and mixture of hydrogen and carbon dioxide in a stirred reactor in different temperatures, pressures and compositions. The mass transfer approach model was used to predict the mass transfer coefficient for each experiment, and the dependency of temperature and pressure has been studied. It was observed that the mass transfer coefficient of CO₂ in the mixture is close to the pure system. The result of this work shows that the pure data on the kinetics for CO₂ hydrate formation is applicable for the case of CO₂ separation from the mixture of carbon dioxide and hydrogen.     

Mechanism of liquid unloading by single flowing plunger lift in gas wells

The plunger lift is one of the main methods to release liquid loading in gas wells. Due to the leakage in the process of moving for plunger, the efficiency of liquid unloading is decreased. In recent years, the single flowing plunger was invented and has been used in many gas fields. However, the mechanism of enhanced liquid unloading is still unclear. In this paper, a full-size visible plunger lift equipment was built to study the process of single flowing plunger lift (SFPL) and normal plunger lift (NPL). Moreover, a transient model was built to simulate SFPL and NPL in different situation. Results show that the SFPL can prevent the liquid from dropping, decrease the bottom-hole pressure, and enhance gas production. The SFPL performs well in a certain range, and the SFPL would be out of operation first. A plate has been built to help engineers optimize the SFPL. The paper helps clear the situation of SFPL and provides the theoretical basis for researchers.     

Numerical analysis of accidental hydrogen releases from high pressure storage at low temperatures

Evaluations of the performance of simplified engineering and CFD models are important to improve risk assessment tools e.g. to predict accurately releases from various types of hydrogen storages. These tools have to predict releases from a wide range of storage pressures (up to 80 MPa) and temperatures (down to 20 K), e.g. cryogenic compressed gas storage covers pressures up to 35 MPa and temperatures between 33 K and 338 K. Accurate calculations of high pressure releases require real gas EOS. This paper compares a number of EOS to predict hydrogen properties typical in different storage types. The vessel dynamics are modeled using a simplified engineering and a CFD model to evaluate the performance of various EOS to predict vessel pressures, temperatures mass flow rates and jet flame lengths. It is shown that the chosen EOS and the chosen specific heat capacity correlation are important to model accurately hydrogen releases at low temperatures.     

Derivation and validation of a reference data-based real gas model for hydrogen

Hydrogen plays an important role for the decarbonization of the energy sector. In its gaseous form, it is stored at pressures of up to 1000 bar at which real gas effects become relevant. To capture these effects in numerical simulations, accurate real gas models are required. In this work, new correlation equations for relevant hydrogen properties are developed based on the Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). Within the regarded temperature (150–400 K) and pressure (0.1–1000 bar) range, this approach yields a substantially improved accuracy compared to other data-based correlations. Furthermore, the developed equations are validated in a numerical simulation of a critical flow Venturi nozzle. The results are in much better accordance with experimental data compared to a cubic equation of state model. In addition, the simulation is even slightly faster.     

Preliminary report on the commercial viability of gas production from natural gas hydrates

Economic studies on simulated gas hydrate reservoirs have been compiled to estimate the price of natural gas that may lead to economically viable production from the most promising gas hydrate accumulations. As a first estimate, $CDN₂₀₀₅ 12/Mscf is the lowest gas price that would allow economically viable production from gas hydrates in the absence of associated free gas, while an underlying gas deposit will reduce the viability price estimate to $CDN₂₀₀₅ 7.50/Mscf. Results from a recent analysis of the simulated production of natural gas from marine hydrate deposits are also considered in this report; on an IROR basis, it is $US₂₀₀₈ 3.50–4.00/Mscf more expensive to produce marine hydrates than conventional marine gas assuming the existence of sufficiently large marine hydrate accumulations. While these prices represent the best available estimates, the economic evaluation of a specific project is highly dependent on the producibility of the target zone, the amount of gas in place, the associated geologic and depositional environment, existing pipeline infrastructure, and local tariffs and taxes.     

Prediction of some performance characteristics of shale oil in the gas turbine combustor

Measurements of radiation, smoke and temperature in a developed experimental combustor at various air pressures, inlet temperatures and air-fuel ratios have shown the effects of such fuel properties as volatility, boiling range and H percentage mass content on ignition, lean blow-out, liner temperature and exhaust smoke. This study has been extended to cover some of these performance characteristics for shale oil.     

Factors influencing future oil and gas prospects in the Arctic

The article explores oil and natural gas development in the Arctic. While several commentators have argued that an increase in Arctic petroleum production in the years to come will follow directly from an increased demand for energy, our study finds that oil and natural gas production in the Arctic is dependent on a range of variables. By using climate-driven changes as a baseline, we examine spill-over effects and conditions that are important for further Arctic hydrocarbon production. Using the available literature from different scientific fields, this article provides a broad and nuanced perspective on the much debated question of whether or not the Arctic will become a region driven by oil and gas production.     

Reduction of a detailed reaction mechanism for hydrogen combustion under gas turbine conditions

The aim of this study is to find a reduced mechanism that accurately represents chemical kinetics for lean hydrogen combustion at elevated pressures, as present in a typical gas turbine combustor. Calculations of autoignition, extinction, and laminar premixed flames are used to identify the most relevant species and reactions and to compare the results of several reduced mechanisms with those of a detailed reaction mechanism. The investigations show that the species OH and H are generally the radicals with the highest concentrations, followed by the O radical. However, the accumulation of the radical pool in autoignition is dominated by HO₂ for temperatures above, and by H₂O₂ below the crossover temperature. The influence of H₂O₂ reactions is negligible for laminar flames and extinction, but becomes significant for autoignition. At least 11 elementary reactions are necessary for a satisfactory prediction of the processes of ignition, extinction, and laminar flame propagation under gas turbine conditions. A 4-step reduced mechanism using steady-state approximations for HO₂ and H₂O₂ yields good results for laminar flame speed and extinction limits, but fails to predict ignition delay at low temperatures. A further reduction to three steps using a steady-state approximation for O leads to significant errors in the prediction of the laminar flame speed and extinction limit.     

Assessment of resistance to fatigue crack growth of natural gas line pipe steels carrying gas mixed with hydrogen

Hydrogen embrittlement of line pipe steels in the natural gas transmission and distribution network is investigated. The objective is to assess whether the existing network can be used to safely transport a mixture of hydrogen and natural gas. The surveyed literature indicates that the hydrogen-induced acceleration of fatigue crack growth induced by natural gas pressure fluctuations can be the most probable type of failure. We analyzed the fatigue crack growth in line pipe steels containing a long axial crack in the inner diameter (ID) surface by accounting for random cyclic loading due to random and realistic pressure fluctuations, crack closure, and accurate calculation of the stress intensity factor. Using the available experimental data for the crack growth rate vs. stress intensity factor range in the presence of hydrogen, we simulated crack growth over a period of 100 years. The results show that under typical pressure fluctuations in the natural gas network, cracks with depths less than 40% of the wall thickness will never reach depths equal to 75% of the wall thickness. This is a conservative estimate that results from i) the nature of the geometry of the initial flaw in the ID surface that we used in the analysis, ii) the fact that the existing experimental data for the effect of hydrogen on the Paris law are for pressures that are orders of magnitude larger than the partial pressures intended for the hydrogen gas in the mixture, and iii) the experimental data are for fatigue crack growth in pure hydrogen gas without impurities normally present in natural gas, such as oxygen or methane, that can inhibit hydrogen uptake.     

Sensitivity analysis on sampling from affected wells by gas coning

Only representative samples could represent original reservoir conditions and have prevented overdesigning surface facilities and have been requirements of reservoir management programs. Representative samples cannot be collected in unsteady state situations. In some cases, samples must be collected in this state, so non-representative samples are obtained. Gas coning is one of the parameters that makes unsteady state flows. There is no standard method to determine accurate original compositions from non-representative samples. In this article, an attempt is made to introduce an accurate method for obtaining original in situ compositions from gas coning wells. Four Iranian oil reservoir samples obtained from the pressure volume temperature laboratory are used for evaluating methods of obtaining original fluids in unsteady state situations for the first time. For this purpose a synthetic model is formed by compositional simulation, and fluid properties of each reservoir are imported to it. Separator sampling is performed in the model. Methods of synthesizing original compositions (recombination and equilibrium contact mixing) are modeled by detailed equation of state characterization in the new scheme. Then collected samples are imported to them. Comparisons are made on obtained results of recombination and equilibrium contact mixing methods to find the most accurate method. It is concluded that equilibrium contact mixing, which was uncertain for companies, is definitely the most accurate method. Also, the authors conclude that after more than 2 years production performing an equilibrium contact mixing method is impossible in volatile oil models with gas coning but recombination with low accuracy can be used; however, equilibrium contact mixing has no limitation in black oil systems with gas coning and has minimum errors.     

Temperature traverse quality in the gas turbine combustor using heavy fuels

One of the most important performance requirements and most difficult to achieve is a uniform distribution of temperature in the exhaust gases of the gas turbine combustor. This is expected to be impaired by the trend of using heavier fuel oils. Measurements in a developed experimental combustor at various air pressures, inlet temperatures, air fuel ratios and fuel blends showed the importance of these operating parameters in optimizing the combustor design.     

Comparing through-plane diffusibility correlations in PEFC gas diffusion layers using the lattice Boltzmann method

One of the key elements in a polymer electrolyte fuel cell (PEFC) is the gas diffusion layer (GDL). The GDL offers mechanical support to the cell and provides the medium for diffusing the reactant gases from the flow plates to the electrolyte enabling the electrochemical reactions, and therefore the energy conversion. At the same time, it has the task of transporting the electrons from the active sites, near to the electrolyte, towards the flow plates.Describing the fluid flow and mass transport phenomena through the GDLs is not an easy task not only because of their complex geometries, but also because of these phenomena occur at microscale levels. Most of the PEFC models at cell scale make assumptions about certain microscale transport parameters, assumptions that can make a model less close to the reality. The purpose of this study is to analyze five different proposed correlations to estimate the through-plane (TP) diffusibility of digitally created GDLs and using lattice Boltzmann (LB) models. The correlations are ranked depending on their precision, accuracy and symmetry. The results show that the best estimation is given when the porosity and gas-phase tortuosity are taken into account in the correlation.     

Enhanced hydrogen-rich gas production from steam gasification of coal in a pressurized fluidized bed with CaO as a CO2 sorbent

Steam gasification of a typical Chinese bituminous coal for hydrogen production in a lab-scale pressurized bubbling fluidized bed with CaO as CO₂ sorbent was performed over a pressure range of ambient pressure to 4 bar. The compositions of the product gases were analyzed and correlated to the gasification operating variables that affecting H₂ production, such as pressure (P), mole ratio of steam to carbon ([H₂O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H₂ concentration was enhanced by raising the temperature, pressure and [H₂O]/[C] under the circumstances we observed. With the presence of CaO sorbent, CO₂ in the production gas was absorbed and converted to solid CaCO₃, thus shifting the steam reforming of hydrocarbons and water gas shift reaction beyond the equilibrium restrictions and enhancing the H₂ concentration. H₂ concentration was up to 78 vol% (dry basis) under a condition of 750 °C, 4 bar, [Ca]/[C] = 1 and [H₂O]/[C] = 2, while CO₂ (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be used as a substantially excellent CO₂ sorbent for the pressurized steam gasification of bituminous coal. For the gasification process with the presence of CaO, H₂-rich syngas was yielded at far lower temperatures and pressures in comparison to the commercialized coal gasification technologies. SEM/EDX and gas sorption analyses of solid residues sampled after the gasification showed that the pore structure of the sorbent was recovered after the steam gasification process, which was attributed to the formation of Ca(OH)₂. Additionally, a coal-CaO–H₂O system was simulated with using Aspen Plus software. Calculation results showed that higher temperatures and pressures favor the H₂ production within a certain range.     

Modelling of gas network transient flows with multiple hydrogen injections and gas composition tracking

Blending hydrogen into the natural gas (NG) network could provide an efficient pathway for decarbonising the NG system through power-to-gas technologies. However, due to the presence of potentially multiple and intermittent hydrogen injection sources, the gas blended throughout the network would be neither homogenous nor at a constant mole fraction. The above features are not captured by the current transient modelling techniques. To bridge this gap, this work presents a transient analysis model that enables the tracking of gas compositions and particularly hydrogen fractions in real-world meshed networks with multiple NG sources, non-pipe elements, and multiple and intermittent hydrogen injection sources. A time-varying compressibility factor is also introduced to account for the variable gas composition across the network. Moreover, numerical techniques are adopted for improving the stability of the Eulerian numerical calculation, and a specific grid size threshold Δx_max is introduced for selecting the stable mesh grid to alleviate convection-dominated oscillations caused by the hydrogen fraction tracking. The case study based on the well-known 20-node Belgian gas network validates the effectiveness of the method in solving practical-scale problems, whereas the unsuitability of steady-state models is also discussed and highlighted. The results clearly demonstrate the effect and importance of introducing variable compressibility factor, hydrogen fraction tracking, and variable gas demand. The impacts of hydrogen blending on pressures and linepack of the network are further investigated.     

Permeability,solubility and diffusivity of hydrogen isotopes in stainless steels at high gas pressures

In this report, we provide a framework for describing the permeability, solubility and diffusivity of hydrogen and its isotopes in austenitic stainless steels at temperatures and high gas pressures of engineering interest for hydrogen storage and distribution infrastructure. We demonstrate the importance of using the real gas behavior for modeling permeation and dissolution of hydrogen under these conditions. A simple one-parameter equation of state (the Abel–Noble equation of state) is shown to capture the real gas behavior of hydrogen and its isotopes for pressures less than 200 MPa and temperatures between 223 and 423 K. We use the literature on hydrogen transport in austenitic stainless steels to provide general guidance on and clarification of test procedures, and to provide recommendations for appropriate permeability, diffusivity and solubility relationships for austenitic stainless steels. Hydrogen precharging and concentration measurements for a variety of austenitic stainless steels are described and used to generate more accurate solubility and diffusivity relationships.