I/O-Gas: Integration and optimization of the production of renewable gas from biogenic residues

As part of the Green Deal, greenhouse gas emissions in the EU are to be reduced by at least 55% by 2030 compared to 1990 levels. The Renewable Gas Act (EGG) is proposed in Austria as a key contribution to achieving these targets. According to the resolution passed by the Council of Ministers on February 21, 2024, 9.75% or at least 7.5 TWh of fossil natural gas is to be replaced annually by nationally produced renewable gas by 2030 - in comparison, consumption in 2022 was around 85 TWh. From 2024, annually increasing green gas quotas are to be implemented, which must be guaranteed by the suppliers - in the event of non-compliance, a compensation payment of €150/MWh is planned.

Gasification in dual fluidized bed (DFB) is a state-of-the-art process for converting woody biomass into product gas and using it to generate electricity and heat. The product gas from DFB gasification is considered very suitable for the production of synthetic natural gas (SNG) due to the comparatively high H₂/CO ratio, the high CH₄ content and the absence of N₂ dilution. Projects for SNG production from woody biomass in Güssing, AT (1 MW_SNG), Gothenburg, SE (20 MW_SNG) and Lyon, FR (500 kW_SNG) have demonstrated the technical feasibility.

Despite this, the technology has not yet been successfully implemented. The biggest issues to be resolved in the course of the I/O-Gas project using experimental, analytical and simulative approaches, can be divided into the following sub-processes:

1. Gasification: The use of biogenic residues with low ash melting temperatures and high volatile content and the long-term behavior on downstream process steps with regard to deposits of tar and inorganic components has not been sufficiently researched. Suitable pre-treatment processes and specific concepts for feedstocks with high moisture content as well as seasonal and decentralized biomass are lacking.

2. Gas cleaning: For the use of biogenic residues, it is unclear what concentrations of impurities are to be separated and how usually hardly relevant elements (e.g. halides) are separated with gas cleaning. It is also unclear how the existing chain can deal with the higher concentrations of certain impurities. Significant increases in efficiency are also possible in the regeneration of these gas cleaning stages.

3. SNG production: The methanation (multi-stage adiabatic fixed-bed cascade) and treatment technologies (especially CO₂ capture) used in refinery technology are too complex and cost-intensive for the operation of comparatively small biomass plants. The potential for increasing efficiency through suitable integration into the energy system is very high.

By coupling gasification with pre-treatment processes such as hydrothermal carbonization, the fuel potential can also be extended to low-melting biogenic residues. The use of straw-like biomass alone in DFB gasification could lead to an increase in SNG production of around 11 TWh/a in Austria - other input materials are possible. Through suitable sector coupling with the energy system using e.g. electrolysis H₂, the carbon utilization rate can be roughly doubled compared to the current state of the art. The SNG product generation costs can be significantly reduced with the proposed solutions and, according to the current state of knowledge, are then less than half of the penalty payments as mentioned in the Renewable Gas Act (EGG) of €150/MWh.