A method of removing, at least partly, mercury from a process gas by means of a mercury absorbing sorbent and a filter having at least one filtering surface, the method comprising: applying said sorbent to said at least one filtering surface by mixing it with process gas upstream of the filter -, measuring upstream of the filter at least one first parameter (HGIN), which is indicative of the amount of mercury that needs to be removed in said filter, measuring at least one second parameter, which is indicative of the amount of material that has been collected on said filtering surface and which is utilized for determining when the filtering surface should be cleaned, comparing a measured value of said first parameter (HGIN) to a mercury set point (HGMEAN), and cleaning said filtering surface at a first cleaning intensity when said measured value of said first parameter (HGIN) is indicating an amount of mercury which is higher than the amount of mercury indicated by said mercury set point (HGMEAN) and at the same time said measured value of said second parameter is indicating a pressure drop which is higher than a pressure drop indicated by a second pressure drop set point (DPHighHigh), and at a second cleaning intensity, being higher in cleaning efficiency than said first cleaning intensity, when said measured value of said first parameter (HGIN) is indicating an amount of mercury which is equal to, or lower than, the amount of mercury indicated by said mercury set point (HGMEAN) and at the same time said measured value of said second parameter is indicating a pressure drop which is higher than a pressure drop indicated by a first pressure drop set point (DPHigh), wherein the second pressure drop set point (DPHighHigh) is higher than the first pressure drop set point (DPHigh) and no cleaning is effected if the above conditions are not fulfilled. applying said sorbent to said at least one filtering surface by mixing it with process gas upstream of the filter -, measuring upstream of the filter at least one first parameter (HGIN), which is indicative of the amount of mercury that needs to be removed in said filter, measuring at least one second parameter, which is indicative of the amount of material that has been collected on said filtering surface and which is utilized for determining when the filtering surface should be cleaned, comparing a measured value of said first parameter (HGIN) to a mercury set point (HGMEAN), and cleaning said filtering surface at a first cleaning intensity when said measured value of said first parameter (HGIN) is indicating an amount of mercury which is higher than the amount of mercury indicated by said mercury set point (HGMEAN) and at the same time said measured value of said second parameter is indicating a pressure drop which is higher than a pressure drop indicated by a second pressure drop set point (DPHighHigh), and at a second cleaning intensity, being higher in cleaning efficiency than said first cleaning intensity, when said measured value of said first parameter (HGIN) is indicating an amount of mercury which is equal to, or lower than, the amount of mercury indicated by said mercury set point (HGMEAN) and at the same time said measured value of said second parameter is indicating a pressure drop which is higher than a pressure drop indicated by a first pressure drop set point (DPHigh), wherein the second pressure drop set point (DPHighHigh) is higher than the first pressure drop set point (DPHigh) and no cleaning is effected if the above conditions are not fulfilled.