A detailed thermo-economic model considering different technological alternatives for thermochemical production of Synthetic Natural Gas (SNG) from lignocellulosic biomass is presented. First, candidate technology for processes based on biomass gasification and subsequent methanation is discussed and assembled in a general superstructure. Both energetic and economic models for biomass drying with air or steam, thermal pretreatment by torrefaction or pyrolysis, indirectly and directly heated gasification, methane synthesis and carbon dioxide removal by physical absorption, pressure swing adsorption and polymeric membranes are then developed. Performance computations for the different process steps and some exemplary technology scenarios of integrated plants are carried out, and overall energy and exergy efficiencies in the range of 69-76% and 63-69%, respectively, are assessed. For these scenarios, the production cost of SNG including the investment depreciation is estimated to 76-107 EUR/MWh SNG for a plant capacity of 20 MWth biomass, whereas 59-97 EUR/MWh SNG might be reached at scales of 150 MWth biomass and above. Based on this work, a future thermo-economic optimisation will allow for determining the most promising options for the polygeneration of fuel, power and heat.