Thermodynamic and environmental study on synthetic natural gas production in power to gas approaches involving biomass gasification and anaerobic digestion

The main goal of this paper is to assess and compare three hybrid systems for the production of synthetic natural gas (biomethane) from biogas or process gas. Mathematical models were built to determine the main performance indicators and plant efficiency of the proposed solutions, such as mass and energy flows and gas composition in characteristic points of the systems, as well as the efficiencies of the full chains. The carbon footprint of the three approaches was calculated using a streamlined life cycle assessment. The results show that both methanation cases may be an interesting option for SNG production and energy storage. The energy efficiency of the solutions reaches a value of 84% for Case 1 (methanation from syngas) and 90% for Case 2 (methanation of biogas) and 3 (biogas upgrading), respectively. If the manure credit is accounted for emissions, the carbon footprint of biomethane from Case 3 is the lowest.     

Analysis of rationality of coal-based synthetic natural gas (SNG) production in China

To alleviate the problem of the insufficient reserves of natural gas in China, coal-based synthetic natural gas (SNG) is considered to be a promising option as a source of clean energy, especially for urban use. However, recent study showed that SNG will not accomplish the task of simultaneous energy conservation and CO₂ reduction. In this paper, life cycle costing is made for SNG use in three main applications in residential sector: heating, household use, and public transport. Comparisons are conducted between SNG and coal, natural gas, liquefied petroleum gas (LPG), diesel, and methanol. The results show that SNG is a competitive option only for household use. The use of SNG for heating boilers or city buses is not as cost-effective as expected. The biggest shortcoming of SNG is the large amount of pollutants generated in the production stage. At the moment, the use of SNG is promoted by the government. However, as shown in this paper, one can expect a transfer of pollution from the urban areas to the regions where SNG is produced. Therefore, it is suggested that well-balanced set of environmental damage-compensating policies should be introduced to compensate the environmental losses in the SNG-producing regions.     

Thermodynamic analysis and techno-economic assessment of synthetic natural gas production via ash agglomerating fluidized bed gasification using coal as fuel

Implementing coal to synthetic natural gas (SNG) is a key way to deal with the conflict between supply and demand of natural gas in China. For the coal to SNG process, gasification is a crucial unit, which determines the syngas composition and influences cost of coal to SNG system. In this current study, a coal to SNG system using ash agglomerating fluidized bed gasification is designed and modeled. According to the above results, the thermal performance and technoeconomic assessment of the coal to SNG system are performed. The research demonstrates that exergy efficiency and energy efficiency of the whole system are 55.37% and 61.50%, respectively. Additionally, the results of the economic evaluation show that the SNG production cost is 1.87 CNY/Nm³ with a coal price of 250 CNY/t and an electricity price of 0.65 CNY/kWh. Sensitivities to variables such as water price, electricity price, total equipment cost and coal price are performed. Coal price represents the most important sensitivity, but the sensitivity to water price is relatively small.     

Renewable energy storage system via coal hydrogasification with co-production of electricity and synthetic natural gas

In this paper a novel integrated plant, designed for the co-production of electricity and synthetic natural gas (SNG), has been proposed as suitable strategy for renewable energy storage and CO₂ emission control.     

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.     

Small‐scale production of synthetic natural gas by allothermal biomass gasification

The gasification of biomass can be coupled to a downstream methanation process that produces synthetic natural gas (SNG). This enables the distribution of bioenergy in the existing natural gas grid. A process model is developed for the small‐scale production of SNG with the use of the software package Aspen Plus (Aspen Technology, Inc., Burlington, MA, USA). The gasification is based on an indirect gasifier with a thermal input of 500 kW. The gasification system consists of a fluidized bed reformer and a fluidized bed combustor that are interconnected via heat pipes. The subsequent methanation is modeled by a fluidized bed reactor. Different stages of process integration between the endothermic gasification and exothermic combustion and methanation are considered. With increasing process integration, the conversion efficiency from biomass to SNG increases. A conversion efficiency from biomass to SNG of 73.9% on a lower heating value basis is feasible with the best integrated system. The SNG produced in the simulation meets the quality requirements for injection into the natural gas grid. Copyright © 2012 John Wiley & Sons, Ltd.     

The future of natural gas consumption in Beijing,Guangdong and Shanghai: An assessment utilizing MARKAL

Natural gas could possibly become a si0gnificant portion of the future fuel mix in China. However, there is still great uncertainty surrounding the size of this potential market and therefore its impact on the global gas trade. In order to identify some of the important factors that might drive natural gas consumption in key demand areas in China, we focus on three regions: Beijing, Guangdong, and Shanghai. Using the economic optimization model MARKAL, we initially assume that the drivers are government mandates of emissions standards, reform of the Chinese financial structure, the price and available supply of natural gas, and the rate of penetration of advanced power generating and end-use. The results from the model show that the level of natural gas consumption is most sensitive to policy scenarios, which strictly limit SO₂ emissions from power plants. The model also revealed that the low cost of capital for power plants in China boosts the economic viability of capital-intensive coal-fired plants. This suggests that reform within the financial sector could be a lever for encouraging increased natural gas use.     

A complementarity model for the European natural gas market

In this paper, we present a detailed and comprehensive complementarity model for computing market equilibrium values in the European natural gas system. Market players include producers and their marketing arms which we call “traders”, pipeline and storage operators, marketers, LNG liquefiers, regasifiers, tankers, and three end-use consumption sectors. The economic behavior of producers, traders, pipeline and storage operators, liquefiers and regasifiers is modeled via optimization problems whose Karush–Kuhn–Tucker (KKT) optimality conditions in combination with market-clearing conditions form the complementarity system. The LNG tankers, marketers and consumption sectors are modeled implicitly via appropriate cost functions, aggregate demand curves, and ex post calculations, respectively. The model is run on several case studies that highlight its capabilities, including a simulation of a disruption of Russian supplies via Ukraine.     

Thermo-economic optimisation of the integration of electrolysis in synthetic natural gas production from wood

Converting wood to grid quality methane allows to distribute a CO₂ free, renewable energy resource in a conventional energy distribution system and use it in transportation applications. Applying a multi-objective optimisation algorithm to a previously developed thermo-economic process model for the thermochemical production of synthetic natural gas from wood, the present paper assesses the prospect of integrating an electrolyser in conversion systems based on directly and indirectly heated gasification. Due to an inherent lack of hydrogen for complete conversion of wood into methane and the possibility for rational use of oxygen, it is shown that electrolysis is an efficient and economically interesting option for increasing the gas output of the process while storing electricity and producing fuel that mitigates CO₂ emissions.     

低压煤气储气罐采用可变喉部截面引射器引射利用研究

为结合上海市重大工程项目建设,进一步改善天然气引射调峰装置性能,围绕低压煤气储气罐在天然气榆配调峰中的应用问题开展低压煤气储气罐配套可变喉部截面引射器系统用于天然气储气调峰的模拟研究,为低压煤气储气罐的改造利用提供技术支撑。     

Extending existing combined heat and power plants for synthetic natural gas production

In this work, integration of a synthetic natural gas (SNG) production process with an existing biomass CHP steam power cycle is investigated. The paper assesses two different biomass feedstock drying technologies—steam drying and low‐temperature air drying—for the SNG process. Using pinch technology, different levels of thermal integration between the steam power cycle and the SNG process are evaluated. The base case cold gas efficiency for the SNG process is 69.4% based on the lower heating value of wet fuel. The isolated SNG‐related electricity production is increased by a factor of 2.5 for the steam dryer alternative, and tenfold for the low‐temperature air dryer when increasing the thermal integration. The cold gas efficiency is not affected by the changes. Based on an analysis of changes to turbine steam flow, the integration of SNG production with an existing steam power cycle is deemed technically feasible. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of conceptual electrolysis-based energy storage systems using gas expanders

In this study, four energy storage systems (Power-to-Gas-to-Power) were analysed that allow electrolysis products to be fully utilized immediately after they are produced. For each option, the electrolysis process was supplied with electricity from a wind farm during the off-peak demand periods. In the first two variants, the produced hydrogen was directed to a natural gas pipeline, while the third and fourth options assumed the use of hydrogen for synthetic natural gas production. All four variants assumed the use of a gas expander powered by high-temperature exhaust gases generated during gas combustion. In the first two options, gas was supplied from a natural gas network, while synthetic natural gas produced during methanation was used in the other two options. A characteristic feature of all systems was the combustion of gaseous fuels within a ballast-free oxidant atmosphere without nitrogen, which is the fundamental component of air in conventional systems. The fifth variant was a reference for the systems equipped with gas expanders and assumed the use of fuel cells for power generation. To evaluate the individual variants, the energy storage efficiency was defined and determined, and the calculated overall efficiency ranged from 17.08 to 23.79%, which may be comparable to fuel cells.     

天然气汽车的储气技术

推广和应用天然气汽车是降低汽车排放污染的有效途径，天然气作为汽车燃料的一个技术关键是天然气贮气技术。文章介绍了目前车用天然气贮存方法的现状及研究中的贮气技术。     

Exergy analysis of biomass-to-synthetic natural gas (SNG) process via indirect gasification of various biomass feedstock

This paper presents an exergy analysis of SNG production via indirect gasification of various biomass feedstock, including virgin (woody) biomass as well as waste biomass (municipal solid waste and sludge). In indirect gasification heat needed for endothermic gasification reactions is produced by burning char in a separate combustion section of the gasifier and subsequently the heat is transferred to the gasification section. The advantages of indirect gasification are no syngas dilution with nitrogen and no external heat source required. The production process involves several process units, including biomass gasification, syngas cooler, cleaning and compression, methanation reactors and SNG conditioning. The process is simulated with a computer model using the flow-sheeting program Aspen Plus. The exergy analysis is performed for various operating conditions such as gasifier pressure, methanation pressure and temperature. The largest internal exergy losses occur in the gasifier followed by methanation and SNG conditioning. It is shown that exergetic efficiency of biomass-to-SNG process for woody biomass is higher than that for waste biomass. The exergetic efficiency for all biomass feedstock increases with gasification pressure, whereas the effects of methanation pressure and temperature are opposite for treated wood and waste biomass.     

天然气利用技术及其应用

天然气作为一种清洁的能源，开发和利用能够改善我国的能源结构。文章介绍了天然气利用的几种典型技术及其应用现状，如发电、燃料电池、天然气汽车、化工、城市燃气。文章还对国内的天然气利用动向和浙江省天然气利用途径进行了简单分析并对加快浙江省天然气利用提出了一些建议。     

Long term forecasting of natural gas production

Natural gas is an important energy source for power generation, a chemical feedstock and residential usage. It is important to analyse the future production of conventional and unconventional natural gas. Analysis of the literature determined conventional URR estimates of 10,700–18,300 EJ, and the unconventional gas URR estimates were determined to be 4250–11,000 EJ. Six scenarios were assumed, with three static where demand and supply do not interact and three dynamic where it does. The projections indicate that world natural gas production will peak between 2025 and 2066 at 140–217 EJ/y (133–206 tcf/y). Natural gas resources are more abundant than some of the literature indicates.     

Technical assessment of synthetic natural gas （SNG） production from agricul- ture residuals

This paper presents thermodynamic evaluations of the agriculture residual-to-SNG process by thermochemical conversion, which mainly consists of the interconnected fluidized beds, hot gas cleaning, fluidized bed methanation reactor and Selexol absorption unit. The process was modeled using Aspen Plus software. The process performances, i.e., CH 4 content in SNG, higher heating value and yield of SNG, exergy efficiencies with and without heat recovery, unit power consumption, were evaluated firstly. The results indicate that when the other parameters remain unchanged, the steam-to-biomass ratio at carbon boundary point is the optimal value for the process. Improving the preheating temperatures of air and gasifying agent is beneficial for the SNG yield and exergy efficiencies. Due to the effects of CO 2 removal efficiency, there are two optimization objectives for the SNG production process: (I) to maximize CH 4 content in SNG, or (II) to maximize SNG yield. Further, the comparison among different feedstocks indicates that the decreasing order of SNG yield is: corn stalk > wheat straw > rice straw. The evaluation on the potential of agriculture-based SNG shows that the potential annual production of agriculture residual-based SNG could be between 555×10 8～611×10 8 m 3 with utilization of 100% of the available unexplored resources. The agriculture residual-based SNG could play a significant role on solving the big shortfall of China’s natural gas supply in future.     

Demand for natural gas in Kuwait: An empirical analysis using two econometric models

This paper estimates the demand for natural gas in Kuwait for the period 1975–93 using two models. A partial flow-adjustment model and a co-integration and error correction model. It is found that natural gas demand is inelastic with respect to price and income in the short and long run. Furthermore, natural gas consumption adjusts towards its long-run level with about 61% of the adjustment occurring in the first year.     

上海市天然气资源的利用

“西气东输”是我国实施西部大开发的重要举措之一。作为“西气东输”工程下游最大的用气城市，加上东海天然气，进口液化石油天然气（LPG），东西伯利亚天然气等气源的引入，上海市能否在大量天然气输入时对其进行充分的利用，是关系到天然气能否产生最大效益的重要因素。介绍了上海市天然气资源状况，分析了上海市天然气利用的主要方向，以使这种优质资源能得到高效利用。指出在21世纪的中国，特别是上海，天然气将扮演越来越重要的角色。在天然气利用方面，除了可作为工业和民用燃料外，还要加快天然气发电，天然气汽车，天然气化工等方面的利用，努力开发天然气利用新技术，为实施可持续发展战略和能源结构调整做出贡献。     

Downstream natural gas in Europe—High hopes dashed for upstream oil and gas companies

Access for independents to retail gas markets was a central concern in European policy reform efforts in the 1990s. Upstream oil and gas companies reacted with strategic intentions of forward integration. By late 2004, forward integration was still weak, however. An important explanation of the gap between announced strategic re-orientation and actual strategy implementation lies in the political failure of EU member states to dismantle market barriers to entry for independents. Variations between companies in downstream strategy implementation are explained by variations in business opportunities and internal company factors.