Biomass Gasification-Based Syngas Production for a Conventional Oxo Synthesis Plant-Process Modeling, Integration Opportunities, and Thermodynamic Performance

Artikel i vetenskaplig tidskrift, 2014

This work investigates the energy performance consequences of replacing conventional natural gas-based syngas production with biomass gasification-based production as a supply of feedstock for a conventional oxo synthesis plant. The investigation is conducted for a plant currently processing 175 MW [higher heating value (HHV) basis] of natural gas (NG) annually. Two concepts based on the same gasification technology are considered: (i) replacing the NG feedstock with biomass-derived synthetic NG (bio-SNG); (ii) replacing syngas with biomass-derived syngas. The work is based upon process models established in Aspen Plus in order to obtain mass and energy balances. Heat recovery opportunities by means of production of useful thermal heat and integration of a steam network for combined heat and power production are investigated using pinch analysis tools. Two different ways of harnessing the high-temperature excess heat are investigated: (i) maximization of the power production; (ii) low-pressure (LP) steam (co)production for process heating to reduce or entirely cover the steam demand of the oxo synthesis plant, which is currently produced by firing of purchased fuel gas. The different process alternatives are compared in terms of energy efficiency (eta(en)) and exergy efficiency (eta(ex)). The results show that around 262 MW (HHV basis) of lignocellulosic biomass is required to fully substitute for the NG feedstock with bio-SNG. The biomass input can be reduced to 216 MW (HHV basis) if the required syngas is produced directly from gasified biomass, thus avoiding the intermediate SNG synthesis step. The direct syngas route achieves the highest thermodynamic performance of the biorefinery concepts investigated, especially if LP steam is exported to the oxo synthesis plant (eta(en) = 75% and eta(ex) = 57%, i.e., 9.1 and 7.2 efficiency points higher than for the route via bio-SNG, respectively).