Carbon recovery from biogas through upgrading and methanation: A techno-economic and environmental assessment

Reducing the use of fossil fuels is an essential measure to counteract the rise in greenhouse gas emissions. In this context, biofuels and e-fuels make an important contribution to achieving climate neutrality targets, especially if their distribution can take place within existing infrastructure, as in the case of methane. The aim of this work is to carry out a techno-economic and environmental assessment of the combined production of biological and synthetic methane in a wastewater treatment plant (WWTP). Methane yield from biogas, usually associated only with biogas upgrading, is enhanced by recovering CO2 to produce additional synthetic natural gas (SNG) through a methanation process. The analysis is applied to a medium-sized WWTP in Italy, whose biogas production profile is known throughout the year. In the current scenario, SNG is not competitive on the gas market. The investment costs of the technologies and the electricity price are then varied in order to better investigate the profitability of SNG production. The results show that, considering long-term cost projections and an electricity price of about 50 €/MWh, SNG can become competitive, with a production cost of 1.4 €/Sm3. Finally, the environmental competitiveness of SNG (direct and indirect CO2 emissions) with respect to fossil natural gas is investigated: results are shown as a function of the carbon intensity of grid electricity and the share of local renewable energy. To make SNG environmentally sustainable, the renewable share must increase to 46% or, alternatively, the carbon intensity of grid electricity must decrease to 187 gCO2eq/kWh

Technologies for Deep Biogas Purification and Use in Zero-Emission Fuel Cells Systems

A proper exploitation of biogas is key to recovering energy from biowaste in the framework of a circular economy and environmental sustainability of the energy sector. The main obstacle to widespread and efficient utilization of biogas is posed by some trace compounds (mainly sulfides and siloxanes), which can have a detrimental effect on downstream gas users (e.g., combustion engines, fuel cells, upgrading, and grid injection). Several purification technologies have been designed throughout the years. The following work reviews the main commercially available technologies along with the new concepts of cryogenic separation. This analysis aims to define a summary of the main technological aspects of the clean-up and upgrading technologies. Therefore, the work highlights which benefits and criticalities can emerge according to the intended final biogas application, and how they can be mitigated according to boundary conditions specific to the plant site (e.g., freshwater availability in WWTPs or energy recovery)

Fuel cell cogeneration for building sector: European status

The advantages of fuel cell based micro-cogeneration systems are the high electrical and total efficiency coupled with zero pollutants emission, which makes them good candidates for distributed generation in the building sector. The status of installations, worldwide and European initiatives and the available supporting schemes in Europe are presented

H2-based energy storage systems in remote areas: the REMOTE project

The REMOTE project has the objective to demonstrate the techno-economic feasibility of hydrogen-based energy storage solutions in isolated micro-grids and off-grid remote areas. Four DEMOs will be installed in four different location across Europe: Ginostra (South of Italy), Agkistro (Greece), Ambornetti (North of Italy) and Froan Island (Norway). The four sites will be characterized by different types of renewable sources (i.e., solar, wind, biomass and water fall) and user loads (i.e., residential and/or industrial), which will affect differently the design and management of the hybrid storage solution. The variety of the DEMO cases can thus provide a robust demonstration of the benefits derived from these innovative storage systems paving way for their deployment at large. According to the ‘Power-to-Power (P2P)’ solution, renewable energy exceeding the electric demand, rather than being curtailed, is supplied to an electrolyzer for hydrogen production. In the four cases under consideration, the alkaline and PEM technology are considered for the electrolysis section. In case of renewable power shortages, PEM fuel cell stacks are then employed for hydrogen conversion into electricity. A battery bank is also coupled with the hydrogen section because of its short-term and quick response capability. Local Renewable Energy Sources (RES) can be therefore better used allowing to reduce or even eliminate the intervention of traditional diesel generators and avoid unstable connections to the grid, if present. The aim of the presented work is to demonstrate the effectiveness of the H2-based P2P solution in reducing the usage of external sources (e.g., diesel genset) by maximizing the exploitation of local RES. Operation strategy models have been developed in order to perform energy balance simulations on a yearly basis. Results showed the usefulness of the P2P operation: in Ginostra, for example, the intervention of diesel generators can be reduced to less than 5% of the total load. Hydrogen was found to be particularly effective as a longer term energy storage solution. Economic considerations are also provided to outline the economic viability of the suggested RES and H2-based scenario

Biogas composition from agricultural sources and organic fraction of municipal solid waste

s paper presents an overview of biogas compositions originating from agriculture and the organicfraction of municipal solid waste. An intensive data compilation was performed from literature, plantdata from an EU project (Waste2Watts) and from sampling campaigns at 5 different anaerobic digestersin Switzerland. Besides reporting the major components of biogas i.e. methane and carbon dioxide, theconcentration of minor components such as nitrogen and oxygen, as well as trace amounts of sulfurcompounds (H2S, mercaptans, sulfides, etc.), silicon compounds (siloxanes, silanes), ammonia, haloge-nated compounds, and other volatile organic compounds (VOCs) are reported. These trace compoundscan present a significant challenge to the energetic use of biogas, specifically in the use of novel, high-efficient processes such as high temperature fuel cells or catalytic fuel upgrading units. H2S and othersulfur compounds are the major concern, as they are abundantly found in agriculture biogas; unlikesilicon compounds, which are generally exist in low or undetectable levels

Design and Performance of an Adsorption Bed with Activated Carbons for Biogas Purification

Organic waste can be efficiently converted into energy using highly efficient energy systems, such as SOFCs coupled to the anaerobic digestion process. SOFC systems fed by biogenous fuels, such as biogas or syngas, suffer long-term stability due to trace compound impacts. It follows that, a mandatory gas cleaning section is needed to remove these pollutants at lower concentrations. This work investigates the adsorption mechanism for micro-contaminant removal through experimental results achieved using solid sorbents. Samples of different sorbent materials were analyzed in the laboratory to determine their performances in terms of sulfur (mainly hydrogen sulfide) and siloxanes (mainly D4-Octamethylcyclotetrasiloxane) adsorption capacities. The analysis shows that the chemical composition of the samples influences the adsorption of H2S (i.e., presence of calcium, iron, copper), while the effect of their textural properties mainly influences the adsorption of siloxane compounds, such as D4. A quantitative analysis was performed considering the influence of gas velocity on adsorption capacity. By increasing the biogas velocity (+45% and +89%), there was an indirect correlation with the H2S adsorption capacity (−27% and −44%). This identified an aspect related to the residence time required to be able to remove and retain the trace compound. The results obtained and summarized were used to develop a strategy for the removal of trace compounds in large-scale plants, e.g., for water purification

Efficiency analysis of 50 kWe SOFC systems fueled with biogas from waste water

Solid oxide fuel cell systems (SOFCs) are able to convert biogas from e.g. waste water plants highly efficiently into electricity and heat. An efficiency study of industrial sized solid oxide fuel cell systems installed at a waste water treatment plant is presented. The site consist of a biogas cleaning unit, two Convion C50 SOFC systems and a heat recovery section. The electric and total efficiencies of the systems are analyzed as a function of the electric net power output. The two systems achieved consistently high electric (50–55%) and total (80–90%) efficiencies in an electric net power output range between 25 kW and 55 kW. The study also shows that the high system efficiencies are independent of the CH4 content in the biogas. The results indicate that fuel cell systems are able to perform power modulation according to the power demand, while achieving constant high efficiencies. This is a clear benefit in comparison to micro turbines and combustion engines which are normally used for converting biogas into electricity and heat

Study of H2S Removal Capability from Simulated Biogas by Using Waste-Derived Adsorbent Materials

Funding: This work was part of the research activities carried out in the framework of the “European Biofuels Research Infrastructure for Sharing Knowledge 2 (BRISK2)” project under grant agreement 731101 (https://brisk2.eu/) and the European Commission is acknowledged for co-funding the work.Peer reviewedPublisher PD