Development of membrane reformer system for highly efficient hydrogen production from natural gas

A membrane reformer is composed of a steam reformer equipped with palladium-based alloy membrane modules and can perform steam reforming reaction of natural gas and hydrogen separation processes simultaneously, without shift converters and purification systems. We have developed a membrane reformer system with nominal hydrogen production capacity of 40 Nm³/h. The system has demonstrated the potential advantages of the membrane reformer: simple system configuration as benefited by single-step production of high-purity hydrogen (99.999% level), compactness, and high-energy efficiency of 70–76%. We are promoting development towards commercialization of the membrane reformer technology, focusing on further improvement of energy efficiency, proof of long-term durability and reliability, and establishment of system engineering technologies. The target of our current project is to develop a membrane reformer system that can produce 99.99% or higher-purity hydrogen from natural gas at a rate of 40 Nm³/h with hydrogen production energy efficiency of over 80%.     

Impact of choice of CO2 separation technology on thermo‐economic performance of Bio‐SNG production processes

Three different CO₂ separation technologies for production of synthetic natural gas (SNG) from biomass gasification – amine‐based absorption, membrane‐based separation and pressure swing adsorption – are investigated for their thermo‐economic performance against the background of different possible future energy market scenarios. The studied scale of the SNG plant is a thermal input of 100 MW_th,LHV to the gasifier at a moisture content of 20 wt‐% with a preceding drying step reducing the biomass' natural moisture content of 50 wt‐%. Preparation of the CO₂‐rich stream for carbon capture and storage is investigated for the amine‐based absorption and the membrane‐based separation technology alternatives. The resulting cold gas efficiency η_cg for the investigated process alternatives ranges between 0.65 and 0.695. The overall system efficiency η_sys ranges from 0.744 to 0.793, depending on both the separation technology and the background energy system. Amine‐based absorption gives the highest cold gas efficiency whereas the potential for cogeneration of electricity from the process' excess heat is higher for membrane‐based separation and pressure swing adsorption. The estimated specific production costs for SNG c_SNG for a process input of 90.3 MW_th,LHV at 50 wt‐% moisture vary between 103–127 €₂₀₁₀/MWh_SNG. The corresponding production subsidy level c_subsidy needed to achieve end‐user purchase price‐parity with fossil natural gas is in the range of 56–78 €₂₀₁₀/MWh_SNG depending on both the energy market scenario and the CO₂ separation technology. Sensitivity analysis on the influence of changes in the total capital cost for the SNG plant on the production cost indicates a decrease of about 12% assuming a 30% reduction in total capital investment. Capture and storage of biogenic CO₂ – if included in the emission trading system – only becomes an option at higher CO₂ charges. This is due to increased investment costs but, in particular, due to the rather high costs for CO₂ transport and storage that have been assumed in this study. Copyright © 2013 John Wiley & Sons, Ltd.     

A Large Potential Methane Source—Natural Gas Hydrates

Abstract

Natural gas, essentially methane, can be obtained from natural gas hydrate (NGH). NGH reserves are difficult to pinpoint in the subsurface, but large sources have been identified by seismic reflection. This is particularly so below the sea floor near continental shelf plates in the oceans deeper than 300 m as NGH is stable at 4°C and 50 bar pressure. When extracted, 1 m³ of NGH can contain 160 sm³ of gas. Currently, estimates of this gas resource are very uncertain, but recent estimates suggest perhaps 2,500 trillion sm³, but how much gas can actually be produced from these accumulations is totally unclear at present. NGH could possibly solve much of the energy needs after 2020, but safe ways of extraction still have to be designed. Possible methods include the injection of hot water or inhibitor or reduction of reservoir pressure, but none have yet been commercially tested. Great caution will be needed because catastrophic environmental damage is likely if the methane is carelessly released from the sediments. This article reviews the ‘state of the art’ of NGH.     

Synthetic natural gas (SNG) liquefaction processes with hydrogen separation

The fact that synthetic natural gas (SNG) contains hydrogen has a great impact on its liquefaction process. Aiming to produce liquefied natural gas (LNG) from SNG, hydrogen separation from SNG through cryogenic processes is studied. A new separation method combining distillation and flash is developed, resulting in higher liquefaction rate than that of distillation under same operating parameters. Process simulations are performed by combining one liquefaction part (a nitrogen expansion process or a mixed refrigerant one) and one distillation part (direct flash, atmospheric distillation, pressurized distillation or the new separation method). Compared to direct flash, distillation can reduce the hydrogen content of products to a very low level, increasing the temperature of products by 8 °C and reducing the unit power consumption by 3%; and, compared to the other three separation ways, the new separation method reduces the unit power consumption by 7–10%. Both nitrogen expansion and SMR liquefaction processes can be integrated with hydrogen separation, but power consumptions for SMR processes are less than those for nitrogen expansion ones.     

Optimal dispatch of HCNG penetrated integrated energy system based on modelling of HCNG process

Hydrogen is injected into the existing natural gas network to form hydrogen-rich compressed natural gas (HCNG), effectively addressing the high cost of hydrogen transmission. However, the traditional IES model cannot be used due to the hydrogen injection's effect on gas properties and the vague characteristics of the transport and separation processes. Therefore, this paper proposes an HCNG penetrated integrated energy system (HPIES) optimal dispatching method by comprehensively modelling the injection, transmission, and separation processes of HCNG. An HCNG mass flow rate model considering variable mixing ratio and unknown beginning flow direction is developed to describe the effect of hydrogen injection. Furthermore, the hydrogen separation model is established by introducing a combined membrane and pressure swing adsorption separation process. The tightening McCormick algorithm is proposed to solve quickly HPIES optimal dispatch problem with an acceptable feasibility check. Finally, case studies on the HPIES consisting of IEEE 39-bus power system and 20-node natural gas system validate the effectiveness of the algorithm and model. The results show that the average error is 0.031% for the bilinear term constraint.     

Techno-economic analysis of adiabatic four-stage CO2 methanation process for optimization and evaluation of power-to-gas technology

Owing to increasing demands for clean energy, caused by global warming, renewable energy sources have attracted significant attention. However, these sources can affect the reliability of electrical grids owing to their intermittency. Power-to-gas technology is expected to help address this issue. In this study, the CO₂ methanation process, which yields synthetic natural gas (SNG) via the synthesis of CO₂ and H₂ through proton exchange membrane (PEM) water electrolysis using surplus electricity generated from renewable energy, was evaluated and optimized based on techno-economic analyses. Requirements for the introduction of SNG produced through CO₂ methanation in domestic natural gas markets are presented by considering various scenarios. Results indicate that, even if the electricity costs, including system marginal price and renewable energy costs, are minimal, the costs for PEM water electrolysis and CO₂ methanation must be reduced by ~$550/kW and 25%, respectively, relative to current levels for the viable introduction of SNG in domestic markets.     

China’s natural gas reform: why and how

Natural gas is playing an extremely significant role in implementing green and low-carbon economy in China, while its share in energy mix only accounted for 6.4% of China’s total energy consumption in 2016. The Chinese government began to make a series of policies and measures to catalyze natural gas production and consumption for dealing with severe air pollution and optimizing energy structure. Some key issues such as highly regulated natural gas pricing system, the monopoly of natural gas pipelines, and the dominance of state-owned oil companies are substantially existing to be addressed in the forthcoming natural gas reforms. The dilemma of reforms is analyzed in this article and the related reform solutions are to be explored in the deregulation of Chinese natural gas pricing mechanism, separation of state-owned companies’ pipeline, and nondiscriminatory third-party access. The results show that Chinese natural gas reform is destined to be a long-lasting war.     

Thermodynamic analyses of hydrogen production from sub-quality natural gas: Part I: Pyrolysis and autothermal pyrolysis

Sub-quality natural gas (SQNG) is defined as natural gas whose composition exceeds pipeline specifications of nitrogen, carbon dioxide (CO₂) and/or hydrogen sulfide (H₂S). Approximately one-third of the U.S. natural gas resource is sub-quality gas [1]. Due to the high cost of removing H₂S from hydrocarbons using current processing technologies, SQNG wells are often capped and the gas remains in the ground. We propose and analyze a two-step hydrogen production scheme using SQNG as feedstock. The first step of the process involves hydrocarbon processing (via steam–methane reformation, autothermal steam–methane reformation, pyrolysis and autothermal pyrolysis) in the presence of H₂S. Our analyses reveal that H₂S existing in SQNG is stable and can be considered as an inert gas. No sulfur dioxide (SO₂) and/or sulfur trioxide (SO₃) is formed from the introduction of oxygen to SQNG. In the second step, after the separation of hydrogen from the main stream, un-reacted H₂S is used to reform the remaining methane, generating more hydrogen and carbon disulfide (CS₂). Thermodynamic analyses on SQNG feedstock containing up to 10% (v/v) H₂S have shown that no H₂S separation is required in this process. The Part I of this paper includes only thermodynamic analyses for SQNG pyrolysis and autothermal pyrolysis.     

Development of an integrated membrane condenser system with LNG cold energy for water recovery from humid flue gases in power plants

This paper investigates a detailed thermodynamic analysis of a modular-type membrane condenser system where a cooler or condenser is connected in series upstream of the membrane condenser module. A coolant circulates inside the cooler/condenser to cool down the industrial flue gas up to saturation conditions. The analysis covers water recovery rate and energy requirement for different combinations of flue gas humidity, flow rate, and temperature. Additionally, a case study is included which considers a practical industrial exhaust flue gas where the constituents of the flue gas with volumetric ratio and the feed parameters are referred from the literature. The case study investigated the utilization of cold energy obtained by LNG regasification facility as a cooling power source for the water vapor recovery process. A detailed heat transfer analysis based on the heat exchanger model is performed to determine the required mass flow rate of cooling water and natural gas. It is concluded that, the water self-sufficiency of a power plant can be achieved if the mass flow rate of the −50 °C natural gas which is entering the membrane condenser is kept around 0.3 kg s⁻¹ for every 1  kg s⁻¹ flow rate of the 168 °C flue gas.     

Monthly natural gas demand forecasting by adjusted seasonal grey forecasting model

ABSTRACT

Natural gas stands out among fossil fuels because it is relatively cleaner. It is also an important energy source type for several fields such as electricity production, industry, and heating, etc. Due to the poor capacity of Turkey in terms of natural gas sources, the demand is supplied by producer countries. Hence, accurate forecasting for the demand is of critical importance for Turkey, which imports 99% of its natural gas consumption. In the current literature about demand forecasting, most studies were conducted on an annual basis. However, the seasonal effect on the demand for natural gas cannot be foreseen through annual studies. Besides, to deal with some situations such as seasonal balancing, peak shaving, and gas supply shortage in monthly demand, forecasting models that capture the seasonal trend are needed. Therefore, in this study, a new grey seasonal forecast model has been presented and Turkey’s monthly natural gas demand was predicted via the proposed model. Performance of that model was compared with SGM(1,1) and SARIMA (p,d,q) x (P,D,Q)^s. The obtained results show the superiority of the proposed model. By using this model, Turkey’s monthly natural gas demand was forecasted up until the year 2025. The proposed model allows us to capture seasonal patterns more successfully. In case this seasonal behavior continues, Turkey’s natural gas demand is expected to increase by %20 until 2025. At this point, the outcomes of the study provide important information to decision-makers to be able to determine reliable and stable energy policies.     

ANFIS modeling of CO2 separation from natural gas using hollow fiber polymeric membrane

The present study is proposed to develop the Adaptive Neuro-Fuzzy Inference System optimized by genetic algorithm to estimate CO₂ value in permeate stream using a hollow fiber polymeric membrane for separation of binary gas containing CO₂ and CH₄ in natural gas. To that end, a number of 65 samples was gathered from the literature. Results indicated that the proposed ANFIS model has great potential with high correlation (R² = 0.9993) and less error (RMSE = 0.0064) for estimation of aforementioned parameter.     

Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C₃H₈, CH₄, CO₂, and H₂ were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H₂/CH₄ and H₂ permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H₂/CH₄ separation.     

Thermo‐economic investigation: an insight tool to analyze NGCC with calcium‐looping process and with chemical‐looping combustion for CO2 capture

In this work, three kinds of natural gas‐based power generation processes for CO₂ capture and storage, that is, natural gas‐combined cycle with pre‐combustion decarburization (NGCC‐PRE), NGCC‐PRE with calcium‐looping process, and NGCC‐PRE with chemical‐looping combustion (NGCC‐CLC), are analyzed by Aspen Plus. The effects of two decisive variables (i.e., steam‐to‐natural gas (S/NG) ratio and oxygen‐to‐natural gas (O/NG) ratio) on the thermodynamic performances of individual process, such as energy and exergy efficiencies, are investigated systematically. Based on simulation outcomes, all the three processes are favored by operating at S/NG = 2.0 and O/NG = 0.65. Furthermore, comparisons of individual system efficiencies and exergy destruction contributor are herein involved. The results show that the highest system efficiencies and lowest exergy destruction are achieved in the NGCC‐CLC process. In addition, capital investment, dynamic payback period, net present value, and internal rate of return are used for deciding the economic feasibility and surely are involved in this work for comparison purpose. Copyright © 2016 John Wiley & Sons, Ltd.     

An experimental investigation into the effects of zeolites on the formation of methane hydrates

Methane hydrate is an ice‐like nonstoichiometric compound that forms when methane reacts with water at high pressures and low temperatures. It has a lot of practical applications such as separation processes, natural gas storage transportation, and carbon dioxide sequestration. Especially, the industrial use of hydrates requires large amounts of gas to be formed quickly into hydrates. Porous media significantly influence the rate of hydrate formation by reducing the chemical barrier, where zeolites are microporous minerals. This paper deals with natural and synthetic (5A and 13A) zeolites for hydrate formation and gas storage capacity. The results show that methane hydrates are formed much faster in the three zeolite solutions tested compared with their formation in distilled water at low subcooling temperatures (<7 K). It was also observed that the gas consumption was the greatest in the 0.01 wt.% zeolite 13X solution of distilled water. Its gas consumption was 5.1 times that of distilled water at 0.5 K subcooling. Zeolite 13X demonstrated its effectiveness in enhancing and expediting methane hydrate formation. Copyright © 2014 John Wiley & Sons, Ltd.     

天然气的发展前景及政策建议

发展天然气工业已成为世界各国改善人类生存环境和维持经济可持续发展的最佳选择。本文论述了我国城市燃气市场目前在发展中存在的天然气定价、天然气冷热电联供的发展、燃气管网的建设与经营等问题,建议在政府尽快出台关于天然气开发、利用与监管的法律框架的同时,加快城市燃气市场的市场化进程,鼓励民营企业与外资企业参与城市燃气市场的开发和建设,并建立加快城市气化的激励机制。     

A liquefied energy chain for transport and utilization of natural gas for power production with CO2 capture and storage – Part 1

A novel transport chain for stranded natural gas utilized for power production with CO₂ capture and storage is developed. It includes an offshore section, a combined gas carrier, and an onshore integrated receiving terminal. Due to utilization of the cold exergy both in the offshore and onshore processes, and combined use of the gas carrier, the transport chain is both energy and cost effective. In this paper, the liquefied energy chain (LEC) is explained, including novel processes for both the offshore field site and onshore market site. In the offshore section, natural gas (NG) is liquefied to LNG by liquid carbon dioxide (LCO₂) and liquid inert nitrogen (LIN), which are used as cold carriers. The LNG is transported in a combined gas carrier to the receiving terminal where it is used as a cooling agent to liquefy CO₂ and nitrogen. The LCO₂ and LIN are transported offshore using the same combined carrier. Pinch and Exergy Analyses are used to determine the optimal offshore and onshore processes and the best transport conditions. The exergy efficiency for a thermodynamically optimized process is 87% and 71% for the offshore and onshore processes, respectively, yielding a total efficiency of 52%. The offshore process is self-supported with power and can operate with few units of rotating equipment and without flammable refrigerants. The loss of natural gas due to power generation for the energy requirements in the LEC processes is roughly one third of the loss in a conventional transport chain for stranded natural gas with CO₂ sequestration. The LEC has several configurations and can be used for small scale (<0.25 MTPA LNG) to large-scale (>5 MTPA LNG) transport. In the example in this paper, the total costs for the simple LEC including transport of natural gas to a 400 MW_net power plant and return of 85% of the corresponding carbon as CO₂ for a total sailing distance of 24 h are 58.1 EUR/tonne LNG excluding or including the cost of power. The total power requirements are 319 kWh/tonne, hence the energy costs are 31.9 EUR/tonne LNG adding up to 90.0 EUR/tonne LNG. The exergy efficiency for this energy chain including power production and CO₂ capture is 46.4% with a total cost of 20.4 EUR/MWh for the produced electricity. The total emissions (in CO₂ equivalents) in the chain are 1–1.5% of the transported CO₂.     

Sustainability assessment of hydrogen production by steam reforming

A specific methodology was applied to investigate the expected impact on sustainability of processes for hydrogen production by steam reforming of natural gas. Reference process schemes based on the current industrial state-of-the-art and on innovative steam reforming technologies were defined and assessed. The methodology allowed the calculation of a sustainability “fingerprint” of the reference schemes, based on sustainability key performance indicators. The results obtained evidenced the potential advantages of innovative processes, based on integrated conversion and internal membrane separation reactors. However, the valorization of the by-product streams is an essential requirement to reduce the impact on sustainability of these processes. Besides the improvement of the reaction section, the optimization of the overall separation efficiency and of energy requirement emerged as the key elements that control the overall sustainability performance of these processes.     

燃机电厂天然气调压站配置探讨

天然气用于燃气轮机发电在我国越来越多,但燃气轮机对天然气的压力、温度等都有一定的要求。天然气调压站是天然气的主要处理系统,直接影响到燃气轮机的安全稳定运行。根据已投产燃气轮机的运行经验,对天然气调压站的系统设备配置作了分析探讨,对设备提出了经济合理地配置的建议。     

Corrosion behaviour of ceramic filter candle materials for hot gas filtration under biomass gasification conditions at 850°C

Abstract

A compact version of a gasifier realised by integrating the fluidised bed steam gasification of biomass and the hot gas cleaning and conditioning system into one reactor vessel was the aim of the ‘UNIQUE’ project. Hot gas filtration systems are designed to protect the gas turbine or fuel cell from erosion and particle contamination, clean the process gases for production of synthetic fuels and indirectly improve efficiency and decrease maintenance. Knowledge of critical points of the porous ceramic filter elements is essential for the successful operation of the hot gas filtration. The corrosion behaviour of ceramic filter materials in contact with different biomass ashes under simulated gasification conditions was investigated for aluminium oxide, based SiC with mullite filter layer and mullite based filter candles. Analyses by energy dispersive X-ray spectroscopy show the influence of potassium on filter candle materials.     

Lab-scale bioreactor integrated with active membrane system for hydrogen production: experience and prospects

The development of new, low-energy consuming and clean technologies can include the utilization of organic wastes with the production of high-quality fuel gases (methane, hydrogen). This paper presents the results of organic wastes’ bioconversion into hydrogen and of the respective H₂/CO₂ gas mixtures’ separation by using active membrane systems (membrane contactors) with moving liquid carriers. Rhodobacter capsulatus was used for lactate or low organic decomposition to H₂-containing gas mixture and Thermohydrogenium kirishi was used for hydrogen production from glucose. Active membrane system was used for the separation of H₂/CO₂ gas mixtures with the production of high-purity hydrogen. The possibility of integration of gas separating membrane systems with aerobic or anaerobic bioreactors are considered as well.