Filtration system for providing clean fuel

The present disclosure refers to filtration system configured to provide clean fuel to a running combustion engine, even if a filter exchange is necessary. The filtration system (5) may be configured to be connected to a main fuel tank (10) for storing contaminated fuel and to be connected to a fuel supply of a combustion engine of an electric power plant or a large vessel. A filtration circuit (16) may include at least one filter (30, 35), a first auxiliary fuel tank (15) for containing fuel, and a first fuel pump (40) configured to pump the fuel from the first auxiliary fuel tank (15) through the filtration circuit (16) back to the first auxiliary fuel tank (15). A second auxiliary fuel tank (20) may be connectable to said first auxiliary fuel tank (15) for receiving fuel from first auxiliary fuel tank (15) via a transfer valve (135), A control unit (132) may be configured to control the transfer valve (135) such that the first auxiliary tank (15) is fluidly connected to the second auxiliary fuel tank (16) only if fuel of a desired contamination level is contained in the first auxiliary tank (20).