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SUMMARY 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.

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Due to the high conversion rates and the low tar amounts in the product gas, entrained flow gasification of biomass can be an alternative process to state of the art gasification technologies, e.g., fluidized-bed gasifiers. Feedstock treatment is mandatory for entrained flow gasification (EFG). However, it has the potential of making residuals available for energetic use. In this study, the feasibility of EFG of solid biomass in an industrial-like test rig with a state of the art pneumatic dense-phase coal feeding system is shown. Four biomassestorrefied wood (TW), beech wood (B), hydrothermal carbonized green waste (HCG), and corn cobs (CoC)were used and compared to Rhenish lignite (RL). Especially, the gasification behavior of hydrothermal carbonized biomass is rarely known from the literature. The study includes a comparison of the fuels regarding feeding behavior, conversion rate, achievable gas composition, and cold gas efficiency (CGE) as well as tar formation. The oxygen stoichiometric ratio λ was varied from 0.35 to 0.55. Investigations have shown that B is not appropriate for the stable, long-term operation of a pneumatic dense-phase feeding system. B and CoC exhibited higher conversion rates at low λ values due to their higher volatile matter compared to the other fuels. The highest CGE of all trials was achieved with CoC (66.3%). B, CoC, and TW exhibited high amounts of CH 4 in the product gas, even at high temperatures. With regard to fuel conversion, HCG and TW generally behaved more like RL. Although EFG is often referred to be a tar-free technology, tar formationinvestigated by solidphase adsorptionwas observed for all fuels especially at low λ values. Due to the high temperatures, mainly tertiary tars (e.g., naphthalene) were detected. A significant higher amount of tar was observed only for B (3.5 g/m 3 ). For all of the other fuels, the total amount of tar was <1 g/m 3 in all of the trials. Regarding feeding behavior, conversion rates and gas composition TW and HCG seem to be suitable as substitutes in coal fed gasification plants.

The production of synthetic natural gas (SNG) to store renewable energy in a chemical energy carrier can be accomplished basically through three main production pathways: the biochemical (biogas upgrade), thermochemical (gasification and synthesis gas upgrade) and electrochemical ('Power-to-Gas') pathway. The technologies applied in these concepts are described and the three pathways are compared in terms of their state of development, efficiencies, and economics. While the biochemical pathway is already established on a commercial scale, the thermochemical and electrochemical routes are still in the pilot-plant phase. Biochemical production of SNG reaches efficiencies in the range of 55-57% but with a potential of above 80%. In comparison, higher efficiencies of up to 70% for the thermochemical pathway are currently expected, with future improvement up to 75%. Electrochemical production achieves efficiencies in the range of 54-60% with expected potential up to 78%. Therefore at the moment the highest efficiencies are given for the thermochemical pathway followed by the electrochemical and biochemical pathways. Economic evaluation is done by comparing specific production costs as well as mean specific investment costs for SNG. Generally speaking, specific production and investment costs decrease with time horizon and increasing scale of the plant. Specific production cost levels in €ct/kWh SNG vary between 5.9 and 13.7 (biochemical), 5.6 and 37 (thermochemical), and 8.2 and 93 (electrochemical). Thus, none of the concepts can compete with today's natural gas prices, but all options are able to provide valuable assistance for a sustainable transition of the energy system.

The substitution of fossil resources by renewable alternatives is a major challenge for our society. Kolbe electrolysis converts carboxylic acids to hydrocarbons, which can be used as base chemicals, specialty chemicals, or fuels. Carboxylic acids may be retrieved from biomass or residues and, in consequence, can be a sustainable feedstock. Since the Kolbe electrolysis has only been investigated in lab scale, this work proposes the first basic engineering design study on process development for a continuously working process. Thermophysical data, including solubility and boiling point, are used to gain insight into requirements on process equipment such as separation processes or process parameters such as operating temperature. Furthermore, Aspen Plus was used to retrieve information on acid base equilibria and azeotropes. The process development for three different feedstocks (acetic acid, valeric acid and lauric acid) was performed. The process design shows that most of the process units are rather straightforward and rely on state of the art technologies. The addition of an alkaline catalyst improves the solubility and deprotonation of the carboxylic acid but on the cost of a possibly lower product selectivity. Elevation of the operating temperature above the Krafft point is necessary for long-chain fatty acids. Kolbe electrolysis can be an interesting technology for future production processes based on carboxylic acids and electricity from sustainable sources.