Modelling and Optimization of a Process from Biomass to Liquid Fuels via Fischer-Tropsch Synthesis
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The global energy demand is expected to increase by almost 50% by 2040. Simultaneously, fossil energy reserves are threatened to disappear. Thus it is imperative to development renewable technologies such as Biomass-To-Liquid process. This work investigates the performances of a Biomass-To-Liquid process involving a Fischer-Tropsch synthesis and the performances of a hybrid hydrogen-carbon process including hydrogen supply for a biomass feedstock of 20 000 tonnes per day. The processes have been simulated using the software Aspen Hysys and Aspen Properties. The impact of several parameters such as the water and oxygen content in the gasifier as well as the influence of the recycle rate on the Biomass-To-Liquid-Fischer-Tropsch process has been explored. The syngas production reaches a maximum for an oxygen supply into the gasifier of 42.4 tonnes per hour. It has been found that the addition of steam into the gasifier is not beneficial when having a fixed gasifier temperature and that recycling 90% of the tail gas into the Fischer-Tropsch gives the best performances. An optimal configuration of the BTL process which maximizes the carbon and energy efficiencies has been determined. It gives an energy efficiency of 56.55% and a carbon efficiency of 40.23% with a production of 4 257 barrel per day. Results are improved when using the hybrid hydrogen-carbon process and when the gasifier inlets are pre-heated. The highest performances have been found when the feedstock is pre-heated at 100°C and the oxygen supply at 1600°C. It gives an energy efficiency of 63.09% and a carbon efficiency of 79.4%. Greenhouse emissions have been divided by 12 and the production of hydrocarbons has doubled when using the hybrid process. The simulation for the hybrid process requires an important amount of hydrogen which compensates the economic benefit generated by the production rise. An increase in the pre-heating of the gasifier inlet must enhance this aspect.