Bio-CH4 from palm empty fruit bunch via pyrolysis-direct methanation: Full plant model and experiments with bio-oil surrogate

Abstract

A promising, cleaner alternative process of thermochemical conversion of lignocellulosic biomass to biomethane is proposed and rigorously investigated via modelling and experiments for the first time. Using a conventional nickel on calcium aluminate catalyst, operated in bench scale at 1 atm, 400 °C, and with a feed molar steam to carbon ratio of 2, the Low Temperature Steam Reforming of acetic acid, representing a single compound bio-oil surrogate, achieves a promising 81.9% fuel carbon conversion to gases with a methane yield of 15.7 wt% of the feed. This compares to 21 wt% methane yield at equilibrium, thus demonstrating encouraging first time performance and scope for future catalyst optimisation. A comprehensive Aspen Plus model is developed for the first time for an industrial plant producing biomethane from palm empty fruit bunch (50 wt% initial moisture), an under-used agro-industrial waste produced in vast amounts in South-East Asia and Sub-Saharan Africa. Dependency on external heating is completely eliminated by heat recovered from combusting 25% of the gas product. Based on the simulation results of the autothermal plant, a final gas product consisting of 99.2 wt% of CH4 and 0.8 wt% of H2 is predicted with a plant thermal efficiency of 80.6%, i.e., comparable to modelled efficiencies found in the literature for wood gasification to biomethane plants that generate syngas as a necessary intermediate.