P2G movable modular plant operation on synthetic methane production from CO2 and hydrogen from renewables sources

Abstract

Renewables are steadily growing becoming a significant part of the global energy mix, in particular in the power sector. An attractive solution could be represented by Power to Gas (PtG), an energy storage strategy. In the PtG process renewable or excess electric energy is used for water electrolysis to produce hydrogen that is then combined with CO2 and converted into methane (synthetic or substitute natural gas, SNG) through the Sabatier reaction. SNG is particularly interesting because leads to an easily transportable (in the existing infrastructures) fuel with a wide proven market for power, thermal and mobility final use applications. The key issue consist on putting together green hydrogen produced by electrolysis fed by renewables with high content CO2 gases supplied from different sources (e.g. syngas from gasification, biogas, geothermic fields, soil gas and gas wells). In this work the CO2 hydrogenation process, coupled with renewables, has been study in a modular, moveable, skidable plant, in the scale of 0.2–1 Nm3/h of produced SNG. The pilot plant is equipped with a methanation unit constituted by a multi-tubular fixed bed reactor able to work in cooled or adiabatic conditions; water produced is separated by a plate&shell condenser. Several sensors, an online gas analysis system and a data acquisition system allow monitoring continuous experimental tests. The methanation facility is able to work in the range of 1–5 bars. The paper reports the results of first experimental activities related to SNG production with Ru based supported catalyst. The experimental activity was carried out in order to check the operability of all components and to improve the knowledge on methanation process in different conditions relevant to Power-to-Gas applications. Different weighted hourly space velocity (WHSV), gas inlet composition, reagent mixture, H2/CO2 ratio, temperature and pressure conditions have been investigated. Increasing pressure drives CH4 production as CO2 conversion is kinetically boosted by raising pressure. Results show that a decreasing trend of XCO2 is observed by increasing WHSV. Results indicate high CO2 per pass conversion with CO2/H2 concentrate feed using Ru based catalyst. Finally the effect of CH4 in the feed was studied emulating two reactors in series. Biogas representative CO2/H2/CH4 mixtures were tested in order to study direct methanation as a biogas upgrading technology.