ECN SYSTEM FOR METHANATION (ESME)

摘要

The Energy research Centre of the Netherlands (ECN) has developed and patented a novel concept for the methanation of gas from biomass gasification. The ECN System for Methanation (ESME) is especially designed for gas from fluidized bed gasifiers such as Bubbling Fluidized Beds, Circulating Fluidized Beds and allothermal gasifiers such as the ECN MILENA process or the FICFB process developed by the Technical University of Vienna. Producer gas from the gasifier must be first compressed to approximately 6 bar (in case of atmospheric gasification) after tar and water removal. The ESME concept is unique because of the smart sequence and the operating conditions of the different units. ESME allows the efficient conversion of producer gas to SNG because the hydrocarbons contained in the producer gas (e.g. benzene, toluene) are not removed but converted, thus being available to be converted to methane. The prereformer catalyst simultaneously reforms aromatic hydrocarbons (e.g. benzene) and produces methane, which has a positive consequence on the heat balance of the prereformer, since the heat released in the exothermic methanation reactions is supplied to the endothermic reforming of aromatic hydrocarbons. Other advantages of ESME include reduced compression cost and no need for gas recycling in the methanation units. The main parts of the ESME system have been extensively tested under realistic conditions. In October 2014 a duration test of 500 hours was successfully performed with producer gas generated in the ECN MILENA gasifier and cleaned in the OLGA tar removal system. The availability of MILENA during the test was close to 90%, and the availability of the whole methanation system (MILENA + OLGA + ESME) was approximately 85%. The “raw bio-SNG” produced contains (in dry basis) 52% vol. CO_2, 39% vol. CH_4, 2% vol. H_2, and traces of CO (~130 ppmv) and C2H6. The gas composition after the methanation section was found to be at chemical equilibrium. Gas composition remains nearly constant after several hundred hours operation despite variations in the inlet producer gas composition. Catalyst degradation was not observed or near detection limits. The produced bio-SNG should further undergo CO_2 removal (e.g. by amine scrubbing or ECN regenerative dry adsorption), water removal and a last high-pressure methanation step to remove the remaining H_2 and CO prior to injection to the grid. This milestone paves the way for the scale-up of bioSNG production. In particular, a consortium formed by ECN and a number of partners intends to build a 300 m~3/h SNG pilot-scale facility in the Netherlands.