Production of synthetic natural gas from biomass - Process integrated drying

Paper in proceeding, 2009

Opportunities for process integrated feedstock drying in connection with the production of synthetic natural gas (SNG) from wet biomass via indirect gasification are investigated in this study. Drying is a very energy-intensive process step – corresponding to about 10% of the dry fuel lower heating value for woody biomass. Process integrated drying offers opportunities for reducing the external energy supply necessary for drying, thereby improving the overall process efficiency. Simulation models for three drying technology options – air, steam and flue gas drying – have been developed using the flowsheeting software tool ASPEN Plus. The influence of basic operation parameters on the performance of the different drying configurations is investigated using sensitivity analysis. Based on a proposed SNG production process that is built as an extension of a fluidized bed boiler for a combined heat and power plant, the potential for heat integrated drying is assessed using pinch analysis in combination with the developed drying models. The biomass – 100 MWth input for both combustion and gasification, respectively - needs to be dried from 50 to 10 weight-% moisture content prior to combustion/gasification. It is shown that it is not possible to cover all feedstock drying needs for the process by internal heat recovery. Steam drying offers the highest potential for heat integration with the proposed SNG process, making it possible to cover 47.7 % of the necessary total dry fuel supply to both combustion and gasification. However, not all process heat used in the steam dryer can be recovered, increasing the external heat need to the SNG process at a lower temperature level. Nevertheless, substantial savings are possible making use of integrated drying within the SNG production process compared to stand-alone drying.