Abstract: A method, system and use for heat exchange in super-critical or near-critical water gasification process of biomass. The method comprising steps of: heating a biomass in a first heat exchanger (6) by thermal energy of a heat transfer medium, reacting the biomass in said super-critical or near-critical water gasification process and producing reaction products, cooling the reaction products of the biomass in a second heat exchanger (12) by absorbing the thermal energy of the reaction products to said heat transfer medium, and circulating said heat transfer medium between the first heat exchanger (6) and the second heat exchanger (12), wherein molten salt is used as the heat transfer medium.