(336d) Renewable Energy Integration and Waste Heat Recovery for the Production of Sustainable Jet Fuel and Decarbonization of Industrial Heating Applications

Heat use in industry is responsible for a significant portion of global greenhouse gas emissions, mainly due to the intensive use of natural gas and petroleum derivatives to drive different chemical and industrial processes. However, by transitioning to renewable resources, such as biomass and electricity, the industry can significantly reduce its carbon footprint.

For the steel industry, the use of electric arc furnaces that rely on electricity to melt scrap steel (instead of blast furnaces, which rely on coke) can reduce carbon emissions by up to 80%, (RMI, 2022). In the cement industry, alternative fuels derived from biomass along with carbon capture and utilization (CCU) can be an option to upgrade the biogenic emissions and store them to produce synthetic fuels when cheap electricity from prosumers is available in the summer. As for the aluminium industry, aluminum produced with renewable electricity can reduce emissions by up to 90% compared to conventional aluminum production, according to the report by the International Energy Agency (IEA) and the Aluminium Stewardship Initiative (ASI, 2021). Also, the aviation sector is a significant contributor to greenhouse gas emissions, thus the production of sustainable aviation fuel (SAF) is one approach to reducing emissions. SAF is a drop-in replacement for conventional jet fuel that can be produced from renewable resources such as biomass and electricity. Since the heating requirements of the Fischer Tropsch process can be also supplied by electrification or via implementation of biomass thermal gasification, SAF produced from biomass and electricity could reduce the lifecycle greenhouse gas emissions up to 85%, compared to conventional jet fuel (ICCT, 2022).

According to a study by Jacobson et al. (2018), electrification of industry and transportation sectors together can reduce global carbon emissions by 68%. Furthermore, IEA estimates that by 2050, electrification could reduce industrial sector emissions by 50% (IEA, 2021). Depending on the source of electricity, electrification of industrial heating applications may not only reduce emissions, but also improve the energy conversion efficiency. Moreover, whenever electrification may be considered inapplicable, biomass can also be used to defossilize the heating applications, reduce the emissions and promote the use of sustainable energy resources. Biomass reportedly has the potential to meet up to 40% of global energy demand by 2050 (Hoogwijk et al. 2005). Additionally, using biomass in combination with carbon capture and storage (CCS) may lead to negative emissions, helping to mitigate climate change (Smith et al., 2016; Florez-Orrego, et al. 2019).

The advantages of the use of the biomass gasification for decarbonizing the industrial applications are multiple. First, the waste heat available at about 800 °C-1000°C in the gasifier outlet stream suitably matches the high-grade heat temperature required for preheating or even melting some substances, leading to a reduction of combustion of natural gas. Moreover, the syngas produced is a staple feedstock to produce either synthetic natural gas and hydrogen, which can be stored and consumed to balance the heating requirements of the industrial applications. Methanation reaction for synthetic natural gas production also shows temperatures levels (300°C to 500°C) that fit the range of temperature found in biomass pretreatment processes of even metal preheating, such as sow dryers in aluminium remelting plants. In this regard, both the waste heat and, in less extent, the produced gas, can be a source of heat for decarbonizing the energy systems and also provide anergy heat to the surrounding populations.

On the other hand, if syngas produced is more than the amount required due to the seasonal operation or maintenance stops, syngas can still be used to produce Fischer-Tropsch liquids, which can minimize or even avoid the dependence of fossil fuels of hard-to-defossilize sectors, such as air transport. The temperature levels at the Fisher Tropsch process (including the offgas consumption) may lead to a surplus power generation in organic Rankine cycles and supercritical CO2 cycles, further increasing the overall energy efficiency of the energy conversion systems. This electricity can be in turn consumed in a co-electrolysis system that convert CO2 derived from the gasification process into more CO and H2, which are the feedstock to produce Fischer Tropsch liquids. The higher efficiency of these advanced energy systems can help mitigating the foreseen increment in the biomass- and electricity-derived fuels production, considering that, in 2021, United Airlines announced that it would purchase up to 10 million gallons of SAF from World Energy, making it the largest airline purchaser of SAF in the world. Other airlines, including Delta Air Lines, Lufthansa, and KLM, have also committed to using SAF (Reuters, 2021).

The process synthesis and optimization methods used in this work include simulation of biomass gasification, hydrogen and synthetic natural gas production, and jet fuel production via a Fisher Tropsch unit. Aspen Plus software has been used to calculate the properties of the conventional and non-conventional components, along with the heating, cooling and electricity demands of the energy systems. An energy integration approach, carried out by the OSMOSE platform, allowed minimizing the energy requirement of the integrated systems and prioritizing the use of waste heat at high temperature for industrial applications. In this way, the low grade waste heat can be reutilized to supply a nearby district heating network or a supercritical CO2 cycle to generate surplus power. In addition, the implementation of a seasonal power-to-gas approach, including electrolysis, methanation, and carbon abatement technologies, required the management of the time-varying demand and supply. To this end, a multi-time approach, using seasonal profiles of energy demands and prices, has been used to minimize the capital investment of the seasonal energy storage systems (e.g. liquids tanks). In the attached Figure, an industrial plant is represented as the main energy system to be heated by the use of renewable energy resources, whereas the city operates as the heat sink thereof. Accordingly, the goal was to reduce the valuable waste heat released to environment during the summer period and store it, so that it can be used to supply the energy needs in the winter, along with biomass, to the SAF production plant.

The time-varying demands, along with the number of decision variables required the application of the OSMOSE platform, which solved the MILP problem that worked out the best operating conditions and sizes of the equipment, maximizing the benefits while reducing the wastes. This platform is capable of integrating Aspen Plus and AMPL software in order to automatize the calculations and provide solutions to several scenarios of operation under different market conditions. Thanks to its versatility, the combination of different energy technologies has been applied to defossilize industrial heating applications, whereas producing value-added fuels. Typical energy demands of metal (aluminium remelting process), beverages (brewery process) and food (dairy process) industrial process were used to exemplify the application of this approach. A typical central European zone city is considered for the assumption of the thermal loads of district heating network, including domestic hot water, space heating, air conditioning and refrigeration. The integration with the surrounding population has been achieved implementing a novel CO2 district heating network, which can be used to distribute heat and upgrade the low-grade waste heat released by the industrial production processes making use of heat pumps. As a result, the fossil emissions could be virtually avoided and a production of up to 100000 barrel of synthetic aviation fuel per day has been achieved. Also, the installation of a CO2 management system, composed of liquefaction, storage and recompression units allowed injecting biogenic CO2 (120EUR/t), which translated to higher economic benefits of the integrated energy system.

References

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