| Abstract: | The sustainability of biomass use as a primary energy source depends on the efficiency of its conversion processes. The key contributing factors are well understood, owing to extensive experimental and theoretical modeling efforts in literature. In this manuscript, we present a systematic study of the thermochemical conversion route that allows us to target desirable outcomes when converting biomass to other fuels and products. Using process synthesis techniques that include material, energy and work balances, we identify the best targets to consider for highly efficient processes given specific constraints. Our analysis shows that by supplying the right amount of oxygen, a 100% carbon conversion efficiency can be achieved for certain applications that require gas as product. If the objective is to obtain a cleaner fuel from biomass, converting it to char is most efficient in terms of carbon and energy conversion. According to our analysis, an energy neutral biomass gasification process is theoretically possible over a wide range of H2 and CO production rates. We demonstrate its feasibility by simulating the process on Aspen Plus®. The simulation reveals that with heat integration, we can achieve the energy neutral target at a hydrogen production rate of 0.9 mol/mol biomass. We further show that even at zero energy requirement, biomass gasification processes can have excess chemical potential, which can be recovered as useful work or conserved by producing more H2. Adding low temperature heat in the form of steam at 102 C gives an 8% gain in chemical potential conservation and increases the hydrogen production rate by 60%. The insights revealed in this work allow for better decision making in early stages of process design, and consequently, more efficient biomass gasification processes. |
