Substitute Natural Gas Research Articles

Using MCFC for capturing CO2 from flue gases and delivering to Sabatier reactor for SNG synthesis

In contemporary power generation, enhancing efficiency and mitigating environmental contamination are of paramount importance. The imperative to curtail greenhouse gas emissions stands as a preeminent challenge within this sector. Concurrently, there is a marked surge in the exploitation of renewable energy sources, which, due to their intermittent nature, precipitates the imperative for advanced energy storage solutions. This paper introduces an integrated system designed to address both the reduction of CO2 emissions and the storage of energy. The advocated system integrates a Molten Carbonate Fuel Cell (MCFC), Solid Oxide Electrolysis Cell (SOEC), and a Sabatier reactor. The MCFC is employed for its proficient CO2 capture capabilities at the cathode, exhibiting remarkable efficiency, operational flexibility, and a high CO2 separation quotient. The SOEC is recognized for its effective hydrogen production, leveraging high operational temperatures to augment hydrogen output while diminishing electrical energy consumption through thermal energy substitution. The Sabatier reactor is utilized for catalytic methanation, transforming CO2 into Substitute Natural Gas—a compound predominantly comprising methane and hydrogen with minimal CO2 and water traces. This system facilitates the capture and utilization of over 80% of CO2 from exhaust fumes, achieving an overall energy efficiency of 71%. The system's design and off-design operational parameters were meticulously modeled and analyzed.

Production of Substitute Natural Gas Integrated with Allam Cycle for Power Generation

The accumulation of energy from non-programmable renewable sources is a crucial aspect for the energy transition. Using surplus electricity from renewable energy sources, power-to-gas plants allow to produce a substitute natural gas (SNG) that can be injected in the existing infrastructure for large-scale and long-term energy storage, contributing to gas grid decarbonisation. The plant layout, the method used for carbon dioxide capture and the possible cogeneration of electricity can increase the efficiency and convenience of SNG synthesis plants. In this work, a system for the simultaneous production of SNG and electricity starting from biomass and fluctuating electricity from renewables is proposed, using a plant based on the Allam thermodynamic cycle as the power unit. The Allam power cycle uses supercritical CO2 as evolving fluid and is based on the oxycombustion of gaseous fuels, thus greatly simplifying CO2 capture. In the proposed system, oxycombustion is performed using biomass syngas and electrolytic oxygen. The CO2 generated by means of oxycombustion is captured, and it is subsequently used together with renewable hydrogen for the production of SNG through thermochemical methanation. The system is also coupled with a solid oxide electrolyser and a biomass gasifier. The whole plant was analysed from an energy-related point of view. The results show overall plant efficiency of 67.6% on an LHV basis (71.6% on an HHV basis) and the simultaneous production of significant amounts of electricity and of high-calorific-value SNG, whose composition could be compatible with the existing natural gas network.

Modelling and validation of energy systems with dynamically operated Power to Gas plants for gas-based sector coupling in de-central energy hubs

Participants of the COP 26 summit have agreed to limit global temperature rise to 1.5 K by 2050. Out of the many strategies envisaged to meet the targets of COP 26, the ‘Sector Coupling’ process aims to use renewable electricity in residential heating, chemical industry, and transportation sectors. Several studies predict that de-central energy systems will play a significant role in the future. Among the proposed sector coupling strategies in de-central energy systems, the Power to Gas (PtG) process producing chemical energy carriers like Substitute Natural Gas (SNG) from renewable power is gaining acceptance. Numerical models of de-central energy systems are needed to analyse sector coupling under fluctuating renewable energy generation and changing gas demand. This study introduces a numerical model of a decentral energy system that includes a novel methanation concept developed at the Engler Bunte Institut of KIT called 3 Phase Methanation. Here, H2 from electrolysis and CO2 from DAC or other biomass-based sources are passed through a slurry bubble column reactor. The slurry is a suspension of the catalyst in a liquid heat transfer medium where the heat of the reaction is dissipated. The 3-Phase methanation process is modelled in this study using the axial dispersion method. Earlier studies describing experimental campaigns conducted on the pilot plant in KIT have proven that the reactor core is nearly isothermal with stable product gas compositions even if the load changes are instantaneous. In this study, it is shown that the numerical model can replicate the experimental results. Following modelling and validation, the numerical model of the PtG plant is integrated with the other components to simulate the de-central energy system. The simulation results demonstrate the dynamic output of all the components and, in particular, the response provided by the PtG plant. This model can be adapted to simulate sector coupling in future de-central energy systems and analyse aspects like long-term energy storage, GHG minimisation and cost-optimal operation.

Upcycling of CO2 into sustainable hydrocarbon fuels via the integration of Fe-based Fischer-Tropsch synthesis and olefin oligomerization: A comparative case study

Power-to-X (PtX) technologies, especially for the Power-to-Liquids (PtL) and Power-to-Gas (PtG) have attracted extensive attention recently, as promising pathways for carbon upcycling via converting CO2 into high-value products including liquid fuels and substitute natural gas (SNG). Herein, aiming at further improving the PtX process efficiency, we proposed two novel PtL/PtG hybrid processes, namely an indirect process (with RWGS unit) and a direct process (without RWGS unit) by integrating Fe-based Fischer-Tropsch synthesis (FTS) and olefin oligomerization technologies, which co-produce syncrude and SNG. Both process simulation and techno-economic analysis were implemented to evaluate the overall process performances, through various indicators involving technical indicators (e.g., syncrude production, energy efficiency, and net CO2 reduction), and economic indicators such as total capital investment, net CO2 reduction costs together with total product costs. Both proposed PtL/PtG processes are efficient in converting CO2 into valuable hydrocarbon fuels, and the syncrude production and total product revenues of indirect process are 2.35–14.58% and 7.55–8.51% higher than those of the direct process, respectively. Whereas, the direct process has lower net CO2 reduction cost of 206.09 $/tonne CO2. Moreover, the present PtL/PtG processes have higher syncrude production and total product revenues than those of our previous studies including a direct PtL/PtG process coupled with Fe-based FTS and two indirect PTL/PTG processes combined with RWGS and Fe/Co-based FTS reaction, with rates of 30.95 and 12.73% at most.

Evaluation of alternative processes of CO2 methanation: Design, optimization, control, techno-economic and environmental analysis

Converting carbon dioxide (CO2) into substitute natural gas (SNG) has received renewed interests recently. It not only realizes large scale CO2 conversion, but also provides a synthetic source for those countries lacking natural gas. This study firstly attempts to explore and evaluate alternative processes for CO2 methanation, in which four schemes (six processes overall) based on adiabatic and/or non-adiabatic fixed-bed reactors are focused. Rigorous process design, optimization, waste heat recovery, economic and environmental evaluation, and control are covered. From this work, the most promising configuration (i.e. Scheme 4B) uses only two reactors. A counter-current cooling, non-adiabatic reactor equipped with internal recycle goes first, and an adiabatic reactor follows. This process reveals great CO2 reduction potential (i.e. CO2-e: −3.338 kg/kg), as compared with other previously developed processes converting CO2 to value-added chemicals (i.e. CO2-e: −0.154 to 2.242 kg/kg). More importantly, better operability of the first reactor is indicated by the generated temperature profile. Finally, a suitable control strategy is developed for this scheme, which results in satisfactory closed-loop responses under throughput and composition disturbances. For future work, clarifying how the feed impurities influence the reaction kinetics, and developing a less expensive hydrogen source, will be recommended.

The First In-Depth Assessment Of Carbon Capture Utilization And Sequestration (Ccus) For Co2 Management Of South Sumatera Sng Plant

A commercial low-rank coal SNG (substitute natural gas) plant is being planned to build in Pendopo, South Sumatra. However, the CO2 produced is not allowed to be vented and should be managed properly. One approach to manage this anthropogenic CO2 emission is through the utilization for CO2 EOR (enhanced oil recovery) or CO2 sequestration. This workaims to investigate the possibility of application and the readiness carbon capture utilization and sequestration (CCUS) for CO2 management of South Sumatera SNG Plant. It presents technical ranking of suitable reservoirs, injection profiles determination, cluster principle of oil fields that can accommodate the amount of CO2 supplied for a number of years, and planning and realization of trunk pipelines and the possibility to reuse the major part of the present infrastructure. The results show the A1 oil field has the highest rank in the sink scoring indicating that this field has highest suitability for CO2 EOR application and CO2 sequestration. Three clusters are formed, north, southeast and west cluster as the basis to establish pipelines network development. The largest CO2 storage potential is in southeast cluster, 27 MtCO2 and the injection strategy developed is successful to manage CO2 supply from SNG Plant.

Power-to-gas: CO2 methanation in a catalytic fluidized bed reactor at demonstration scale, experimental results and simulation

CO2 methanation tests were carried out in a demonstration scale fluidized bed reactor (400 kWSNG capacity) to investigate its efficiency and flexibility towards operating conditions fluctuations associated with Power-to-Methane (PtM) production units. A wide range of operating conditions were explored: pressure (2–4 bara), reaction temperature (260−375 °C), H2/CO2 inlet ratio (1.5–4.8), heat released by the reaction exothermicity (13.4–32.7 kWth), and U/Umf (2.2–7.2). Whatever the operating conditions, this technology (reactor and catalyst) reached the maximum possible conversion, i.e. the thermodynamic equilibrium, in only one step. These excellent performances resulted from efficient management of methanation exothermicity (temperature gradient in the fluidized bed is lower than 20 °C) and optimized catalyst activity (even at low temperature: 280 °C). In addition to its high flexibility towards operating conditions, short stabilization time (<30 min) was required for the process to reach permanent and stable regime when the operating condition setpoints were changed. Simulations were performed to investigate different process chains efficiency for producing SNG (Substitute Natural Gas) compliant with natural gas grid standards. A process chain composed of the fluidized bed reactor studied in this article followed by a condensation step, a partial recirculation stream to the reactor inlet, and a polishing reactor was proved to be an interesting solution to produce high quality SNG with reduced equipment and compression cost. The present reactor together with the specific metal-based catalyst developed in this study appear as a very efficient and flexible solution for PtM application.

Life Cycle Assessment of Substitute Natural Gas production from biomass and electrolytic hydrogen

The synthesis of a Substitute Natural Gas (SNG) that is compatible with the gas grid composition requirements by using surplus electricity from renewable energy sources looks a favourable solution to store large quantities of electricity and to decarbonise the gas grid network while maintaining the same infrastructure. The most promising layouts for SNG production and the conditions under which SNG synthesis reduces the environmental impacts if compared to its fossil alternative is still largely untapped. In this work, six different layouts for the production of SNG and electricity from biomass and fluctuating electricity are compared from the environmental point of view by means of Life Cycle Assessment (LCA) methodology. Global Warming Potential (GWP), Cumulative Energy Demand (CED) and Acidification Potential (AP) are selected as impact indicators for this analysis. The influence of key LCA methodological aspects on the conclusions is also explored. In particular, two different functional units are chosen: 1 kg of SNG produced and 1 MJ of output energy (SNG and electricity). Furthermore, different approaches dealing with co-production of electricity are also applied. The results show that the layout based on hydrogasification has the lowest impacts on all the considered cases apart from the GWP and the CED with SNG mass as the functional unit and the avoided burden approach. Finally, the selection of the multifunctionality approach is found to have a significant influence on technology ranking.

Steady-state Simulation of Cryogenic Distillation on UniSim Design to Refine Substitute Natural Gas

Steady-state Simulation of Cryogenic Distillation on UniSim Design to Refine Substitute Natural Gas

Highly Nickel-Loaded γ-Alumina Composites for a Radiofrequency-Heated, Low-Temperature CO2 Methanation Scheme.

In this work, we joined highly Ni-loaded γ-Al2 O3 composites, straightforwardly prepared by impregnation methods, with an induction heating setup suited to control, almost in real-time, any temperature swing at the catalyst sites (i. e., "hot spots" ignition) caused by an exothermic reaction at the heart of the power-to-gas (P2G) chain: CO2 methanation. We have shown how the combination of a poor thermal conductor (γ-Al2 O3 ) as support for large and highly interconnected nickel aggregates together with a fast heat control of the temperature at the catalytic bed allow part of the extra-heat generated by the reaction exothermicity to be reused for maintaining the catalyst under virtual isothermal conditions, hence reducing the reactor power supply. Most importantly, a highly efficient methanation scheme for substitute natural gas (SNG) production (X up 98 % with >99 % S ) under operative temperatures (150-230 °C) much lower than those commonly required with traditional heating setup has been proposed. As far as sustainable and environmental issues are concerned, this approach re-evaluates industrially attractive composites (and their large-scale preparation methods) for application to key processes at the heart of P2G chain while providing robust catalysts for which risks associated to nano-objects leaching phenomena are markedly reduced if not definitively suppressed.

Power‐to‐Gas: CO2 Methanation Concepts for SNG Production at the Engler‐Bunte‐Institut

AbstractPower‐to‐Gas approaches comprise different activities to store electric power in form of gaseous energy carriers like hydrogen or methane. The synthesis of SNG (substitute natural gas) and its injection into the natural gas grid allows the utilization of the well‐established infrastructure for natural gas storage, distribution and utilization without the need for further changes to the energy system. At the Engler‐Bunte‐Institut research focuses on catalytic methanation in catalytically coated metallic honeycomb reactors and in slurry bubble column reactors with the aim of evaluating alternative reactor concepts offering optimized heat transfer characteristics as well as maximizing the possibility of dynamic operation. Both concepts are attractive for small to medium scale power‐to‐gas applications. Hence, a scale‐up was performed for bothreactor concepts with the aim of implementation on commercial scale.

Can bioenergy carbon capture and storage aggravate global water crisis?

Bioenergy carbon capture and storage (BECCS) is an effective option for mitigation of greenhouse gas (GHG) emissions. Nevertheless, there is barely serious debate about whether its implementation can possibly jeopardize the global water resources security. Here, we provided an assessment of biomass-based Substitute Natural Gas (BioSNG) production combined with CCS, a promising BECCS technology, in terms of global water resources security, with a focus on the growth of two typical second-generation bioenergy crops: switchgrass and miscanthus. A bottom-up analysis approach was applied in this paper to calculating water consumption for BECCS and estimating water quality deterioration caused by increasing fertilizer and pesticide application. The results indicated that water usage of BECCS was equal to adding 12.86%–16.64% (switchgrass) and 17.59%–26.06% (miscanthus) additional water stress on global available water resources at 2100. Additional N fertilizer application in 2100 would be equal to over 84%, 55% and 42% for both switchgrass and miscanthus under three CCS capture efficiency scenarios, respectively, comparing to such global scale in 2012. Additional phosphate fertilizer adding to global annual available water at 2100 were 0.004–0.008 mg L−1 (switchgrass) and 0.003–0.006 mg L−1 (miscanthus), respectively. The secondary environmental hazards, such as N2O emission, would offset GHG emission mitigation by BECCS. Meanwhile, the enrichment and leaching of pesticide residues increased the risk of groundwater contamination. This study revealed water consumption and contamination issues caused by BECCS cannot be neglected. Thus, additional studies of accurate land-use models in global scale and advanced technology for biofuel extraction are needed in the future.

Cost optimisation and life cycle analysis of SOEC based Power to Gas systems used for seasonal energy storage in decentral systems

Abstract Chemical energy carriers and storage mechanisms will play a significant role in future energy systems. Apart from stabilising network fluctuations caused by renewable energy supply, chemical energy carriers also serve multiple sectors like electricity generation, chemical industry, transportation and shipping. Power to Gas (PtG) is a method that can be adapted for energy storage using chemical energy carriers produced from reserve electricity. This study contains the evaluation of long term energy storage in a decentral energy hub using a high temperature Power to Gas (PtG) plant. The Power to Gas process in this study uses surplus electricity for high temperature SOEC electrolysis. The resulting H2 undergoes methanation to generate Substitute Natural Gas (SNG) which has the same properties of natural gas and can be distributed using existing infrastructure. Compared to PtG processes using PEM or alkaline electrolysis, better overall process efficiencies up to 85% have been estimated for the high temperature PtG process. A pilot plant with thermally coupled SOEC-Electrolysis and Methanation was constructed as a part of the HELMETH project and is used in this study. Based on the experiments conducted in the pilot plant, the technical feasibility of long term energy storage and transient operations were evaluated. It was observed that short term energy storage with transient plant operation resulted in more operational costs when compared to long term storage with continuous plant operation. Novel methods to minimise the operational costs of the plant were also investigated using a dynamic pricing model and numerical optimisation of PtG plant. The numerical optimisation shows that if the duration of plant operation is adapted to target surplus renewable energy production, the concept could also be economically viable. Further, a life cycle analysis (LCA) of the PtG process was performed to evaluate the global warming potential (GWP) of the PtG plant configured with various input feeds. From the LCA, it was determined that if the input electricity is generated from sources with a global warming potential of less than 150 g CO2-eq/kWh, and carbon dioxide used for methanation is derived from biogenic sources, the PtG plant could act as a carbon sink.

From biomass and electrolytic hydrogen to substitute natural gas and power: The issue of intermediate gas storages

The possibility to upgrade biomass and intermittent power from renewable energy sources generating stable power and substitute natural gas (SNG) has been discussed in previous papers. Such papers focussed mainly on the choice and design of the most suitable power units to generate power and a high purity carbon dioxide stream to feed the methanation section; moreover, heat recovery strategies to improve the plant efficiency were investigated and implemented. In the proposed plant, power for electrolysis potentially comes from renewable energy sources (RES), thus arises the need to introduce gas storages in order to fully decouple the outputs (SNG flow and stable electric power) from the input intermittency. This paper analyses some different possible layouts for intermediate gas storages and compares them from an energy consumption point of view.

Coal to substitute natural gas based on combined coal-steam gasification and one-step methanation

In the face of the requirement of clean coal utilization and greenhouse gas emission reduction, coal to substitute natural gas (SNG) production attracts increasing attention worldwide. This work proposed a coal-to-SNG process, which combines a high-efficiency coal-steam gasification and one-step methanation. Through regenerative unit, the sensible heat of the syngas can be recovered via the oxidant steam and then finally converted into chemical energy of syngas, and thereby the cold gas efficiency can be 8.8 percentage points higher than the traditional GE gasification. The H2/CO mole ratio of syngas leaving the gasifier is about 1.2 which can be used for one-step methanation directly and the traditional water gas shift process can be eliminated. Simulation and thermodynamic analysis of the whole plant are presented, and the experimental study of coke-steam gasification is carried out in a fixed bed reactor. Preliminary experiments show that when gasification temperature is higher than 1000 °C, the H2/CO ratio of the syngas is approximately 1.3–1.4. Thermodynamic analysis shows that the SNG conversion efficiency of the proposed process increases from 61.3% to 71.7% and the energy consumption for SNG product has been reduced from 84 GJ/t to 60.5 GJ/t, mainly due to the cold gas efficiency enhancement of gasification and elimination of water gas shift process. Besides, through the one-step methanation, the concentration of CO2 before CO2 separation unit increases from 31.1% to 43.2%, and the unit energy consumption in the CO2 capture decreases from 15.3 kJ/mol to 11.7 kJ/mol.

Modelling of Substitute Natural Gas production via combined gasification and power to fuel

The combination of water electrolysis and solid fuel gasification offers the substitution of Air Separation Unit, the reduction or elimination of water gas shift catalytic system and acid gas removal technology. Subsequently, the direct utilisation of CO2, which otherwise would be emitted during production and its conversion to valuable fuels in combination with energy storage are achieved. Steam gasification and steam-oxygen gasification in different operating conditions and scales are combined with electrolysers with the aim to define optimum efficiencies towards SNG production and reduction of direct CO2 emissions. Modelling and comparison of 6 different cases for steam and steam-oxygen gasification process, gas cleaning and conditioning technologies focusing on tar removal, activated carbon, water gas shift, and acid gas removal technologies with potassium carbonate and MDEA are investigated. Capture ratios are balanced with and without water gas shift reactor according to the requirements of SNG synthesis. The efficiency of gasification and power to SNG ranges between 57.67% and 63.43% for the optimum cases with low pressure steam/oxygen gasification and electrolysers sized according to oxygen demand and according to the oversized electrolysers case respectively. The overall energy conversion resulted in an energy conversion efficiency of 72.83% and 73.51% with the production of steam.

Experimental evaluation of a heat pipe cooled structured reactor as part of a two-stage catalytic methanation process in power-to-gas applications

Establishing the power-to-gas process as a suitable energy storage in future energy systems requires process simplification in order to make it competitive. An intensified methanation reactor concept could contribute to this overall goal. The present work suggests a new catalytic methanation reactor with heat pipe integration into a structured reactor. This approach benefits from the highly industrial maturity of the methanation process and simultaneously addresses the requirements of new applications in power-to-gas processes. The concept comprises a metallic body, which is perforated by channels for internal gas preheating, reaction channels and spaces for the incorporation of heat pipes. Calculation of the radial temperature profiles provided the limits for the channel geometry. Three layers of internal manifolds at different heights distribute, collect and divert the gas. Heating cartridges integrated at the bottom of the reactor enable rapid start up from cold conditions. The metallic block structure facilitates the sealing of the pressurized reaction space and the scaling. First experiments with a 5 kW prototype prove that the maximum temperature is kept more than 100 K below calculated adiabatic synthesis temperatures. Furthermore, the integration in a lab-scale two-stage test rig with intermediate water removal demonstrates the Substitute Natural Gas (SNG) production with grid-injectable quality.

Equilibrium and kinetic aspects for catalytic methanation focusing on CO2 derived Substitute Natural Gas (SNG)

The production of Substitute Natural Gas (SNG) can be a key component of indigenous energy supply towards a low carbon future. In the present work, state of the art catalytic processes for SNG production based on CO and CO2 methanation are presented. Equilibrium based simulations are performed for both CO and CO2 methanation in order to define the optimum process parameters. A special focus is given on SNG derived from CO2 and hydrogen via power to gas process, which combines energy storage, Carbon Capture and Utilisation (CCU) with SNG production. Three kinetic models for CO2 methanation at 10 atm, 17 atm and 20 atm from the literature are compared. The quality of SNG produced is evaluated depending on the different operating pressure and temperature of CO2 derived SNG process. Low pressure bulk methanation (< 20 atm) cannot meet today's grid specifications without any additional measures taken such as blending with fossil natural gas or additional process equipment. Although heating value and Wobbe Index can be fulfilled, the maximum allowed hydrogen content remains a critical issue. Optimum process scheme and conditions for a dry hydrogen mole fraction lower than 2%vol in the final SNG are presented.

Polygeneration system integrated with small non-wood pulp mills for substitute natural gas production

This study aims to examine the potential substitute natural gas (SNG) production by integrating black liquor gasification (BLG) island with a small wheat straw-based non-wood pulp mills (NPM), which do not employ the black liquor recovery cycle. For such integration, it is important to first build knowledge on expected improvements in an overall integrated non-wood pulp mill energy system using the key performance indicators. O2-blown circulating fluidized bed (CFB) gasification with direct causticization is integrated with a reference small NPM to evaluate the overall performance. A detailed economic analysis is performed together with a sensitivity analysis based on variations in the rate of return due to varying biomass price, total capital investment, and natural gas prices. The quantitive results showed considerable SNG production but significantly reduced electricity production. There is a substantial CO2 abatement potential combining CO2 capture and CO2 mitigation from SNG use replacing compressed natural gas (CNG) or gasoline. The economic performance through sensitivity analysis reflects significant dependency on both substitute natural gas production and natural gas market price. Furthermore, the solutions to address the challenges and barriers for the successful commercial implementation of BLG based polygeneration system at small NPMs are discussed. The system performance and discussion on the real application of integrated system presented in this article form a vital literature source for future use by large number of small non-wood pulp industries.

Relative Greenhouse Gas Abatement Cost Competitiveness of Biofuels in Germany

Transport biofuels derived from biogenic material are used for substituting fossil fuels, thereby abating greenhouse gas (GHG) emissions. Numerous competing conversion options exist to produce biofuels, with differing GHG emissions and costs. In this paper, the analysis and modeling of the long-term development of GHG abatement and relative GHG abatement cost competitiveness between crop-based biofuels in Germany are carried out. Presently dominant conventional biofuels and advanced liquid biofuels were found not to be competitive compared to the substantially higher yielding options available: sugar beet-based ethanol for the short- to medium-term least-cost option and substitute natural gas (SNG) for the medium to long term. The competitiveness of SNG was found to depend highly on the emissions development of the power mix. Silage maize-based biomethane was found competitive on a land area basis, but not on an energetic basis. Due to land limitations, as well as cost and GHG uncertainty, a stronger focus on the land use of crop-based biofuels should be laid out in policy.