Abstract: A process and a system treat a synthesis gas originating from a biomass gasification, which contains the following steps: a) performing a first quenching of the synthesis gas at a first temperature and a first pressure; b) performing a second quenching of the quenched synthesis gas at a second temperature and a second pressure, wherein the second temperature is lower than the first temperature; c) scrubbing the twice-quenched synthesis gas in an oil scrubber at a scrubbing temperature which is in the range of the second temperature; d) purifying the quenched and scrubbed synthesis gas in a catalyst-doped adsorption stage; and e) feeding the thus-purified synthesis gas into a refining process. The thus-described multistage prepurification by quenching and also an absorption/desorption stage and if appropriate reactive adsorption and also if appropriate HDS catalysis and/or chemisorption fulfils this object in an excellent manner.