Kristina Holmgren

Heat Recovery Aspects of Importance for the Product Mix and GHG Emission Reductions in a Bio-SNG System

This paper presents the impact of adjusted operating parameters (superheating temperature and backpressure or condensing mode) for the heat recovery steam cycle (HRSC) by external conditions on the product mix (SNG; power and heat) in a commercial scale gasification-based bio-SNG (biomass derived synthetic natural gas) production system. The GHG reduction potentials for a case with a condensing HRSC and for a case with the HRSC in backpressure mode producing heat for CO2 separation of the flue gases are evaluated. Pinch technology was used to identify the potential for heat recovery and process integration. Small changes in the operational parameters of the HRSC can result in significant changes of the conversion efficiencies of heat and power. With an HRSC in back-pressure mode, reducing the power production by 4 MW compared to the condensing case, it is possible to produce ~60 MW of heat for district heating. This study shows that approximately one third of the carbon input to the gasifier ends up in the SNG, whereas one third is separated prior to methanation and one third is emitted as CO2 in the flue gases from the combustor of the indirect gasifier. If infrastructure for CO2 storage is available, and CO2 separated from the process and from the flue gases is stored, the GHG emission reductions from the bio-SNG system can be doubled compared to a case without CO2 storage possibility.

Assessing the aggregated environmental benefits from by-product and utility synergies in the Swedish biofuel industry

ABSTRACT The production of biofuels in Sweden has increased significantly in the past years in order to reduce fossil fuel dependence and mitigate climate impacts. Nonetheless, current methodological guidelines for assessing the GHG savings from the use of biofuels do not fully account for benefits from by-products and other utilities (e.g. waste heat and electricity) from biofuel production. This study therefore reviews the aggregated environmental performance of these multi-functional biofuel systems by assessing impacts and benefits from relevant production processes in Sweden in order to improve the decision base for biofuel producers and policymakers in the transition to a bio-based and circular economy. This was done by (1) conducting a mapping of the Swedish biofuel production portfolio, (2) developing future production scenarios, and (3) application of life cycle assessment methodology to assess the environmental performance of the production processes. Special focus was provided to review the potential benefits from replacing conventional products and services with by-products and utilities. The results provide evidence that failure to account for non-fuel-related benefits from biofuel production leads to an underestimation of the contribution of biofuels to reduce greenhouse gas emissions and other environmental impacts when replacing fossil fuels, showing the importance of their multi-functionality.