Oxidation Of Natural Gas Research Articles

The engine reformer: Syngas production in an engine for compact gas‐to‐liquids synthesis

Methane (CH4) reforming was carried out in an internal combustion engine (an “engine reformer”). We successfully produced syngas from the partial oxidation of natural gas in the cylinder of a diesel engine that was reconfigured to perform spark ignition. Performing the reaction in an engine cylinder allows some of the exothermicity to be captured as useful work. Intake conditions of 110 kPa and up to 480 °C allowed low cycle‐to‐cycle variability (COVnimep < 20 %) at methane‐air equivalence ratios (ϕM) of 2.0, producing syngas with an H2‐to‐CO ratio of 1.4. Spark ignition timing was varied between 45–30° before top‐dead‐center (BTDC) piston position, showing significant improvement with delayed timing. Hydrogen (H2) and ethane (C2H6) were added to simulate recycle from a downstream synthesis reactor and realistic natural gas compositions, respectively. Adding these gases yielded a stable combustion up to hydrocarbon‐air equivalence ratios (ϕHC) of 2.8 with COVnimep < 5 %. Ethane concentrations (with respect to methane) of up to 0.2 L/L (20 vol%) (with and without H2) produced robust and stable combustions, demonstrating that the engine can be operated across a range of natural gas compositions. Engine exhaust soot concentrations demonstrated elevated values at ϕHC > 2.4, but < 1 mg/L below these equivalence ratios. These results demonstrate that the engine reformer could be a key component of a compact gas‐to‐liquids synthesis plant by highlighting the operating conditions under which high gas conversion, high H2‐to‐CO ratios close to 2.0, and low soot production are possible.

Nickel-Containing Systems in Reaction of Partial Oxidation of Hydrocarbons

Nickel dispersion, which provides total catalytically active metal surface, is significant for partial catalytic oxidation of natural gas to obtain high purpose products yield and productivity in syngas. The interaction of reaction medium under high reaction temperatures during 20-25 hours promotes the increase of total square of active Ni component for block catalysts obtained with self-propagating high-temperature synthesis, which allows achieving productivity in syngas 7.1·103cm3(syngas)/cm3(catalyst)·hour. It is observed that for catalyst systems obtained with precipitation, chemical composition of oxide phase influences the particles size of metal nickel. For granular catalysts obtained through precipitation after 25-hour exploitation, average particle size (according to CSR) metal nickel is 3-4.5 times smaller than Ni in catalysts obtained with self-propagating high-temperature synthesis. This allows achieving productivity in syngas 8.1·103cm3/сm3·hour, when there is average temperature decrease over the catalytic layer by ~100°С in comparison with blocks acquired through self-propagating high-temperature synthesis.

Experimental and kinetic modeling study of the oxy-fuel oxidation of natural gas, CH4 and C2H6

The oxidation of simulated natural gas mixtures, methane and ethane under oxy-fuel conditions has been studied experimentally in a flow reactor, at atmospheric pressure and in the 773–1673K temperature range. The influence of the stoichiometry has been analyzed by varying the excess air coefficient (λ) from fuel-rich (λ=0.2) to fuel-lean (λ=2) conditions.The results are interpreted in terms of a chemical kinetic model for the oxidation of small hydrocarbons. The updated kinetic mechanism in relation to the CH4 and C2H6 subsets, together with the interactions between CO2 and C1–C2 hydrocarbon radicals, is able to reproduce satisfactorily the experimental trends. Concerning C1 radicals, only CH2 is able to consume significant quantities of CO2, whereas the reactions with C2 radicals are insignificant under the present conditions.The effect of CO2 as collision partner on important third-body reactions is evaluated and the major pathways of the oxidation of natural gas, methane and ethane are identified. The reaction paths for all fuels tested are found to be similar to those in air combustion, except for the interactions of CO2 with H and CH2 radicals and the lower importance of reactions between H radicals and hydrocarbons in oxy-fuel combustion.

Numerical optimization and reaction flow analysis of syngas production via partial oxidation of natural gas in internal combustion engines

The production of hydrogen is studied numerically under uncatalyzed partial oxidation and homogeneous charge compression ignition (HCCI) conditions in an internal combustion engine fueled by natural gas. The HCCI process is modeled by a single-zone variable volume reactor using a global heat transfer model and elementary-step reaction mechanisms. Numerical optimization is applied to maximize the hydrogen yield at the end of the expansion stroke by varying the equivalence ratio, engine speed and initial pressure for a fixed initial temperature. Suitable constraints were defined, including peak pressure and bounds to the optimization variables. From these results, maximum hydrogen yield profiles and the associated operating parameter profiles as functions of initial temperature were obtained. The profiles exhibit strong linear dependency with initial temperature. Reaction flow analysis was performed to gain detailed insight into the chemical processes involved when the engine is run under optimal conditions for a maximum hydrogen yield. The integral reaction flow analysis shows that substantial amounts of hydrogen are produced from precursors, which are also valuable products, such as methanol, formaldehyde and ethylene.

Numerical Investigation of the Flameless Oxidation of Natural Gas in the IFRF Furnace Using Large Eddy Simulation

In this paper, in order to investigate the effect of working parameters on 3D non-premixed Flameless oxidation occurring in the IFRF furnace, large eddy simulation model is applied on OpenFOAM environment. The radiation and combustion are modeled by applying the finite volume discrete ordinate model and partially stirred reactor, respectively. Furthermore the detailed mechanism GRI-2.11 is undertaken represent chemistry reactions. The obtained results are compared with the published experimental measurements. After ensuring the accuracy of the LES method, the combustion characteristics are examined with different fuel injection angles, adding H2O, H2, and the inlet Reynolds number. The results indicated significant changes in the characteristics of the Flameless oxidation process.

Kinetic analysis of co formation under oxy-combustion conditions

The paper reports the results of numerical computations concerning the formation of CO in the kinetic flame during natural gas oxy-combustion. The effect of temperature, reagent residence time and the composition of an atmosphere containing CO2 with 21 and 29 vol % O2 on the variation of CO concentration in the flame was examined. The oxy-combustion process was conducted with a 25 % excess oxygen. The analysis of reactions in flames at temperatures of 1500 K and 1800 K was performed within the Chemked II program using the combustion mechanism proposed by Mendiara & Glarborg, which includes 779 reactions. The computation results have confirmed that the rate of the key reactions responsible for the production of CO in the flame depends on the flame temperature and the oxy-combustion temperature. The peak CO concentrations are higher for the oxidizing mixture containing 29 vol % O2. After attaining a maximum, the CO flame concentration drops faster for an atmosphere richer in oxygen. The longer the time of reagent residence in the flame region, the lower the CO concentration. In different atmospheres and at different combustion temperatures, an identical CO level can be achieved in wet combustion gas. Irrespective of the temperature and atmosphere of oxy-combustion, most CO is produced as a result of the reaction OH + CO HCO2. The reduction of oxygen in the oxidizing atmosphere at flame temperatures of 1500 and 1800 K lowers the CO production in the dominant reactions responsible for CO formation. The contribution of individual reactions in the CO production for the identical atmospheres is different with varying temperature. In the case of the reaction HCO + O2 HO2 +CO, the temperature increase reduces the CO production. A reverse dependence of CO production on temperature characterizes the reaction H2 + CO + M CH2O + M. In addition, change in temperature changes the order in which the dominant reactions occur. Within the residence time equal to 100 ms, two periods of intensified CO production and consumption can be identified. The peak concentrations of H, OH and O radicals in the flame attain a maximum within the same time; as time goes by, the highest concentration is achieved by OH radicals. The presence of considerable levels of CO2 in the combustion substrates has an inhibiting effect on the natural gas oxidation process.

Oxidative conversion of hydrocarbon gases in the surface combustion mode

An increase in the natural gas fraction produced from low-debit unconventional resources requires new small-scale technologies for its transportation, conversion to chemicals, and ecologically safe use in power production. A technology of flameless combustion and partial oxidation of natural gas in combustors or converters with permeable volumetric matrix is proposed as an efficient method for the solution of these problems.

Catalytic oxidation of natural gas using flameless burners of a new design

Various aspects of operating burners traditionally used for oxidizing gaseous hydrocarbons and heat exchangers used for heat recovery are considered. A method developed by FAST ENGINEERING LTD. for the efficient burning of fuel with deep heat recovery of waste gases while maintaining a given adiabatic temperature is described. The method is based on using a flameless burner and heat exchangers of a new design. Burner operation is tested on an experimental stand with determination of the dependences for the aerodynamic drag of a granular layer and the content of unburned hydrocarbons, CO, and NOx in combustion products on the consumption of the fuel-air mixture and the adiabatic temperature of fuel combustion. The described method for burning fuel is shown to provide the desired temperature of combustion products for a consumer of heat energy and to reduce the consumption of fuel by 5–20%. Burning fuel at an adiabatic combustion temperature of no more than 1200°C virtually eliminates the CO and NOx content in the combustion products. Designed flameless burner, new generation of heat exchangers, and technology for the efficient burning of fuel can be applied to vapor and water-heating boilers, gas turbines, and catalytic reactors to produce synthesis gas from natural gas for processing into hydrogen, ammonia, methanol, synthetic liquid hydrocarbons, and so on.

A shock tube study of the rate constants of HO2 and CH3 reactions

HO2 and CH3 are major intermediate species presented during the oxidation of natural gas at intermediate temperatures and high pressures. Previous theoretical calculations have identified several product channels for HO2 and CH3 reactions, with CH3+HO2→CH3O+OH and CH3+HO2→CH4+O2 being the dominant reaction pathways. Both reaction pathways play an important role in the kinetics of CH4 oxidation as CH3+HO2→CH3O+OH is a chain-branching reaction whereas CH3+HO2→CH4+O2 a chain termination reaction.H2O2/CH4/Ar mixtures were shock-heated to a temperature between 1054 and 1249K near 3.5atm to initiate the reaction. OH radicals yielded from H2O2 thermal decomposition react with H2O2 and CH4 respectively to produce HO2 and CH3 in the reacting system. Using laser absorption spectroscopy, time-histories of H2O, OH and HO2 were measured behind reflected shock waves. The rate constant of reaction CH3+HO2→CH3O+OH was determined to be 6.8×1012cm3mol−1s−1 with an uncertainty factor of 1.4. The rate constant of the competing CH3+HO2→CH4+O2 reaction was determined to be 4.4×1012cm3mol−1s−1, with an uncertainty factor of 2.1. In addition, the rate constants of two other major reactions of the reacting system, H2O2 (+M)→2OH (+M) and OH+CH4→CH3O+OH, were found to have excellent agreement with values recommended in literature.

Study on a Coupling Reactor for Catalytic Partial Oxidation of Natural Gas to Syngas

In the current paper, engineering issues for catalytic partial oxidation of natural gas to syngas have been investigated in a pilot plant. In contrast to the microreactor for catalyst evaluation, for a large scale fixed bed reactor operated under high temperature and pressure, attentions should be paid to: introduction method of feeding gases, preheat temperature of feeds, and the coupling of exothermic oxidation reactions with endothermic reforming reactions. As indicated by thermodynamic calculations at a pressure of 2.0 MPa, the reaction temperature should reach at least 1273 K in order to obtain a yield of CO higher than 80 percent. To reach such a high reaction temperature under adiabatic conditions, the feeding gases need to be preheated to a temperature within the range of 773-923 K. With safety considerations of explosion potential, a newly designed nozzle that can premix reactant gases well and thus is suitable for natural gas catalytic partial oxidation process, has been adopted in this pilot unit. A thermally coupled fixed bed reactor is then proposed and proved to be feasible based on thermodynamic calculations and experimental validations.

Study on a Coupling Reactor for Catalytic Partial Oxidation of Natural Gas to Syngas

In the current paper, engineering issues for catalytic partial oxidation of natural gas to syngas have been investigated in a pilot plant. In contrast to the microreactor for catalyst evaluation, for a large scale fixed bed reactor operated under high temperature and pressure, attentions should be paid to: introduction method of feeding gases, preheat temperature of feeds, and the coupling of exothermic oxidation reactions with endothermic reforming reactions. As indicated by thermodynamic calculations at a pressure of 2.0 MPa, the reaction temperature should reach at least 1273 K in order to obtain a yield of CO higher than 80 percent. To reach such a high reaction temperature under adiabatic conditions, the feeding gases need to be preheated to a temperature within the range of 773-923 K. With safety considerations of explosion potential, a newly designed nozzle that can premix reactant gases well and thus is suitable for natural gas catalytic partial oxidation process, has been adopted in this pilot unit. A thermally coupled fixed bed reactor is then proposed and proved to be feasible based on thermodynamic calculations and experimental validations.

Thermochemical reduction of magnesium sulfate by natural gas: Insights from an experimental study

Thermochemical reduction of MgSO 4 by natural gas was carried out in the presence of water. Chemical and carbon isotopic variations were characterized with microcoulometry, gas chromatography, FT-IR, XRD and GC-C-IRMS. It was found that natural gas reacted with MgSO4 to produce H2S, CO2, MgO and solid bitumen as the main products of thermochemical sulfate reduction (TSR). Gas dryness, gas souring index and the extent of reaction parameter positively correlated with temperature. The extent of acidulation and oxidation of natural gas were intensified as TSR proceeded. TSR has induced an evident carbon isotope fractionation in natural gas. Based on the experimental results, the reaction mechanism was tentatively investigated. It was found that the catalytic role of a metallic ion in the TSR process may be controlled by at least three factors: the charges and the radius of a metallic ion and the number of Lewis acid centers scatted on the surface of the sulfates. The last factor is largely determined by the amount of water in a TSR system. A small amount of water and metallic ions with more charges and short radius may effectively initiate the TSR.

Multi-dimensional modeling of non-catalytic partial oxidation of natural gas in a high pressure reformer

A three-dimensional simulation model for non-catalytic partial oxidation of natural gas in a high pressure reformer has been developed. In the model, the numerical methods and submodels conventionally used in turbulent reacting flows are used. The GRI-Mech 3.0 mechanism and a tabulated chemistry approach are applied to model the non-catalytic oxidation of natural gases under high pressures and temperatures. The reactions are assumed to be fast, hence only the equilibrium states of the multi-step reactions are read in an off-line generated chemistry table. This chemistry table has been created using the equilibrium solver EQUIL from the CHEMKIN II package, and the equilibrium values are functions of the initial mixture compositions and the temperatures at a constant pressure. A presumed PDF model is applied to simulate the interactions between turbulent mixing and the multi-step chemical reactions. Simulations have been performed for a commercial natural gas reformer at various O 2/CH 4 and O 2/H 2O ratios and pressures in order to investigate the effect of these parameters on the syngas yields. The results have provided some insights into the strategies of solving the hot-spot problem in industrial reformers.

Simulation of partial oxidation of natural gas with detailed chemistry: Influence of addition of H2, C2H6 and C3H8

The partial oxidation (POX) of natural gas to produce acetylene was studied using detailed chemistry simulation to determine the influences of adding H2, C2H6 and C3H8 to the CH4 feed. Four detailed chemistry mechanisms, codenamed GRI 3.0, GRI 486, Petersen, and Curran, for describing the POX of natural gas under fuel-rich conditions were evaluated by comparing calculated results with ignition delay time and homogeneous oxidation data. The Curran mechanism gave the best performance, and was further used to examine the influences brought about by changes in the natural gas composition due to the addition of H2, C2H6 and C3H8. The addition of H2, C2H6 and C3H8 reduced the consumption of natural gas per ton of acetylene produced, and would enhance the economy of the POX process and help use up excess H2, C2H6 and C3H8 from other processes in chemical plants. For natural gases that contain small amounts of higher hydrocarbons, the adding of H2, C2H6 and C3H8 significantly decreased the ignition delay time, and the residence time of the feed in the mixing zone has to be reduced when adding these species to avoid uncontrolled combustion.

Influence of Temperature and Pressure on the Non-Catalytic Partial Oxidation of Natural Gas

The influence of temperature and pressure on the non-catalytic partial oxidation and reforming of natural gas in an entrained-flow reactor under non-equilibrium conditions has been investigated experimentally in pilot scale.As thermochemical equilibrium suggests, the methane conversion increases drastically with temperature, but does not reach equilibrium in the investigated range of parameters (Tmax = 1450 °C; 30 bar (3 MPa) < p(g) < 100 bar (10 MPa), 5 s < ? < 20 s). A practical method to describe the non-equilibrium state of a partial oxidation product gas at high temperatures due to kinetic limitations and/or mixing conditions within a reactor is by calculating apparent equilibrium temperatures Teq,ap for the main global kinetic reactions from the measured concentrations of the gas. The temperature difference between Teq,ap and the measured reactor outlet temperature Tex results in the temperature differental approach (?TApp = Teq,ap - Tex).In this paper, typical parameters influencing ?TApp for the methane reforming reaction (temperature T, pressure p, residence time ?) were examined. ?TApp was found in the range between -300 K and -50 K in non-catalytic partial oxidation. Its absolute value decreases with increasing pressure and decreasing ratio of steam to fuel carbon H2O : Cf , but is just weakly dependent on the reactor temperature Tex in a range from 1100-1450 °C. The results were used for the evaluation and further development of a model combining kinetics and residence time behaviour of the non-catalytic partial oxidation and reforming of natural gas.For comparison, results from catalytic autothermal reforming of natural gas and non-catalytic partial oxidation of liquid hydrocarbons are also presented.

CO 2 capture from combined cycles integrated with Molten Carbonate Fuel Cells

In this paper Molten Carbonate Fuel Cells (MCFCs) are considered for their potential application in carbon dioxide separation when integrated into natural gas fired combined cycles. The MCFC performs on the anode side an electrochemical oxidation of natural gas by means of CO 3 2− ions which, as far as carbon capture is concerned, results in a twofold advantage: the cell removes CO 2 fed at the cathode to promote carbonate ion transport across the electrolyte and any dilution of the oxidized products is avoided. The MCFC can be “retrofitted” into a combined cycle, giving the opportunity to remove most of the CO 2 contained in the gas turbine exhaust gases before they enter the heat recovery steam generator (HRSG), and allowing to exploit the heat recovery steam cycle in an efficient “hybrid” fuel cell + steam turbine configuration. The carbon dioxide can be easily recovered from the cell anode exhaust after combustion with pure oxygen (supplied by an air separation unit) of the residual fuel, cooling of the combustion products in the HRSG and water separation. The resulting power cycle has the potential to keep the overall cycle electrical efficiency approximately unchanged with respect to the original combined cycle, while separating 80% of the CO 2 otherwise vented and limiting the size of the fuel cell, which contributes to about 17% of the total power output so that most of the power capacity relies on conventional low cost turbo-machinery. The calculated specific energy for CO 2 avoided is about 4 times lower than average values for conventional post-combustion capture technology. A sensitivity analysis shows that positive results hold also changing significantly a number of MCFC and plant design parameters.

Modeling of non-catalytic partial oxidation of natural gas under conditions found in industrial reformers

Non-catalytic partial oxidation of natural gas/O 2/H 2O mixture at elevated pressures was simulated kinetically using Chemkin package incorporating detailed reaction mechanisms of methane oxidation. The dependence of reaction time was investigated as a function of inlet temperature, system pressure, and O 2/CH 4 ratio. The conversion to products was predicted to complete within a residence time of less than 0.1 ms at pressures greater than 30 atm and temperatures higher than 1450 K. A minimum O 2/CH 4 ratio of 0.64 was found necessary for a complete methane conversion at the conditions typical for the industrial reformer. The effect of O 2/H 2O in the feed gas was examined computationally, and the results suggested that adding H 2O in the feed gas could be a viable tool for adjusting the H 2/CO ratio in the products and for controlling the flame temperature. Formations of higher order hydrocarbons and soot, which may play important roles in the actual fuel-rich conversion environment, are not considered in the present study.

2-3-3 混合セラミック担体を用いたフォーム触媒による天然ガスの部分酸化反応(2-3 科学1,Session 2 天然ガス・メタンハイドレート等,研究発表)

2-3-3 混合セラミック担体を用いたフォーム触媒による天然ガスの部分酸化反応(2-3 科学1,Session 2 天然ガス・メタンハイドレート等,研究発表)

Synthesis and study of tetraamminecobalt hydrogen hexamolybdometalates(III)

Tetraamminecobalt hydrogen hexamolybdoferrate [Co(NH3)4] · H[FeMo6O18(OH)6] · 6H2O (I) and tetraamminecobalt hydrogen hexamolybdogallate(III) [Co(NH3)4] · H[GaMo6O18(OH)6] · 6H2O (II) were synthesized and studied by mass spectrometry, thermogravimetry, IR spectroscopy, and X-ray diffraction. Crystals of I and II are monoclinic; a = 16.21 A, b = 5.43 A, c = 12.32 A, β = 119.63°, V = 1092.11 A3, ρcalcd = 2.21 g/cm3, and Z = 1 for I; a = 16.24 A, b = 5.59 A, c = 12.29 A, β = 119.79°, V = 1064.05 A3, ρcalcd = 2.15 g/cm3, and Z = 1 for II. Compounds I and II were used as catalysts for soft oxidation of natural gas.

High-temperature transport and stability of SrFe 1− xNb xO 3 − δ

The conductivity is measured in the series of solid solutions SrFe 1 − x Nb x O 3 − δ , where x = 0.05, 0.1, 0.2, 0.3, 0.4, within the oxygen partial pressure limits 10 −18–0.5 atm and temperature range 650–950 °C. The contributions to the total conductivity from oxygen ions, electrons and electron holes are obtained based on their different pressure dependences. The doped derivative with x = 0.1 is found to be a singular composition where ion conductivity attains a maximal value while activation energy for ion transport is minimal. This peculiar behavior is attributed to formation of favorable microstructure in the oxide. The deeper doping results in deterioration of ion transport, which is explained by oxygen vacancy filling. It is shown that replacement of iron for niobium favors enhanced thermodynamic stability towards reduction. The oxygen permeability is evaluated from the conductivity data, and it achieves rather high values in the doped derivatives. These oxides can, therefore, be recommended for further evaluation as oxygen separating membrane materials for partial oxidation of natural gas.