Synthetic natural gas (SNG) can be obtained via methanation of synthesis gas (syngas). Many thermodynamic reaction details involved in this process are not yet fully understood. In this paper, a comprehensive thermodynamic analysis of reactions occurring in the methanation of carbon oxides (CO and CO2) is conducted using the Gibbs free energy minimization method. The equilibrium constants of eight reactions involved in the methanation reactions were calculated at different temperatures. The effects of temperature, pressure, ratio of H-2/CO (and H-2/CO2), and the addition of other compounds (H2O, O-2, CH4, and C2H4) in the feed gas (syngas) on the conversion of CO and CO2, CH4 selectivity and yield, as well as carbon deposition, were carefully investigated. In addition, experimental data obtained on commercial Ni-based catalysts for CO methanation and three cases adopted from the literature were compared with the thermodynamic calculations. It is found that low temperature, high pressure, and a large H-2/CO (and H-2/CO2) ratio are favourable for the methanation reactions. Adding steam into the feed gas could alleviate the carbon deposition to a large extent. Trace amounts of O-2 in syngas is unfavourable for SNG generation although it can lower carbon deposition. Additional CH4 in the feed gas almost has no influence on the CO conversion and CH4 yield, but it leads to the increase of carbon formed. Introduction of a small amount of C2H4, a representative of hydrocarbons in syngas, results in low CH4 yield and serious carbon deposition although it does not affect CO conversion. CO is relatively easy to hydrogenated compared to CO2 at the same reaction conditions. The comparison of thermodynamic calculations with experimental results demonstrated that the Gibbs free energy minimization method is significantly effective for understanding the reactions occurring in methanation and helpful for the development of catalysts and processes for the production of SNG.

A thermodynamic analysis of methanation reactions of carbon oxides for the production of synthetic natural gas

Progress in biofuel production from gasification

https://backend.orbit.dtu.dk/ws/files/141912942/Ahrenfeldt_2013_Biomass_gasification_cogeneration_pre_press_version.pdf

Biomass gasification cogeneration – A review of state of the art technology and near future perspectives

Microwave pyrolysis of lignocellulosic biomass: heating performance and reaction kinetics.

Conventional fossil fuel-based energy technologies can achieve efficiency in energy conversion but they are usually completely inefficient in carbon conversion because they generate significant CO2 emissions to the atmosphere per unit energy converted. In contrast, some renewable energy technologies characterized by negative carbon intensity can simultaneously achieve efficiency in the conversion of energy and in the conversion of carbon. These carbon negative renewable energy technologies can generate useful energy and remove CO2 from the atmosphere, either by direct capture and recycling of atmospheric CO2 or indirectly, by involving biofuels. Interestingly, the deployment of carbon negative renewable energy technologies can offset carbon emissions from conventional fossil fuel-based energy technologies and thus reduce the overall carbon intensity of energy systems. The current review analyzes two groups of renewable energy technologies involving biomass or CO2 as inputs. The discussions focus on useful techniques which enable to achieve negative carbon intensity of energy while being technologically promising in near-term as well as cost-effective. These analyzes include advanced carbon sequestration concepts such as soil carbon sequestration and CO2 recycling to useful C-rich products such as fuels and fertilizers. The 'drop-in' of renewable energy is achieved by allowing bioenergy and renewable energies in the form of renewable electricity, renewable thermal energy, solar energy, renewable hydrogen, etc. The carbon negative renewable energy technologies are analyzed and perspectives and constraints of each technology are expounded.

Negative carbon intensity of renewable energy technologies involving biomass or carbon dioxide as inputs

Exergy analysis of synthetic natural gas production method from biomass

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

Synthetic natural gas (SNG) is suggested as an important future energy carrier. The conventional route for SNG production is based on gasification of biomass to synthetic gas and the subsequent methanation of synthetic gas to SNG. This study is aimed to analyze the process units using the concept of exergy. Exergy analysis is a promising method, based on the 2nd law of thermodynamics, to analyze and improve chemical processes. In this work a detailed exergy analysis is performed for the SNG process based on woody biomass gasification. The main elements of the system are gasifier, gas cleaning, synthetic gas compression, methanation and final SNG condition. The above-mentioned process was simulated with a computer model using the flow-sheeting program Aspen Plus. Optimal values of the process conditions, particularly for the methanation reactors, are found. The internal exergy losses of different system units are evaluated. The largest internal exergy losses take place in the gasifier, methanation section and CO2 capture unit. The highest overall exergetic efficiency of 72.6% was found applying the following operating conditions: gasifier 700 °C and 1 bar; 1st methanation reactor 580 °C and 2nd methanation reactor 405 °C.

/pdf/exergetic-evaluation-and-improvement-of-biomass-to-synthetic-21cywzbxtd.pdf

Exergetic evaluation and improvement of biomass-to-synthetic natural gas conversion

Nowadays, biomass has a well-known potential for producing energy calTiers, such as electricity, heat (steam) and transport biofuels. However, biomass availability is rather limited and stochastically distributed. This could be a major problem in demographically dense regions where land is scarce and biomass may compete with other applications, notably agriculture for food production. In fact, this is the case for the first-generation biofuels (e.g. bioethanol and biodiesel) that are mainly produced from biochemical conversion of food crops such as sugar cane, com or wheat, and vegetable oils from feedstock like rapeseed or palm oil. Moreover, when taking into account emissions from transport and conversion treatments, life-cycle analyses reveal that first-generation biofuels frequently exceed the emission thresholds of fossil fuels . Second generation biofuels are now being developed as a possible better alternative to the first generation, as they can use non-food crops (e.g. switch grass) or biowastes from different origins (e.g., forest, agriculture, industry, municipalities). Second generation biofuels can also be produced via either biochemical or thennochemical conversion. Among all the existing thermochemical conversion technologies, gasification is gaining interest due to its higher efficiency, larger scales, and reliable operation. However, biowastes-to-biofuels conversion involves several challenges. Firstly, the existing technology must be fe-designed and optimized to become cost and efficiency competitive with fossil fuels. Moreover, due to the wide diversity of biowastes and biofuels that can be obtained, the most sustainable conversion routes must be properly selected. Hence, an inherent challenge is to develop a reliable model to evaluate the sustainabililY of any process. In this chapter we present the evaluation of second generation biofuels (SNG, methanol, Fischer-lropsch fuels, hydrogen) as well as heat and electricity, from different biowastes via gasification with subsequent catalytic conversion of syngas. Pre-treatment steps are also considered in order to enhance the low energy density of biomass prior to gasification. However, since pre-treatment is directly affected by local conditions, the Dutch province of Friesland is taken as a case study. The biowaste-to-biofuels routes are modeled in Aspen Plus, and mass and energy balances obtained from simulations are later used for efficiency evaluation. Results are presented in terms of mass conversion yield, energy and exergetic efficiency. The last part of the paper is devoted to explain how those results will be integrated for combined economic and environmental impact analysis.

A Anna Sues

Papers

Exergy analysis of synthetic natural gas production method from biomass

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

Exergetic evaluation and improvement of biomass-to-synthetic natural gas conversion

Biowastes-to-biofuels routes via gasification