A plant (100) for the gasification of biomass comprises a gasifier (10) and an apparatus (23) for the filtration of the gas. The apparatus comprises a scrubber (31), a tank (41), and a wet electrostatic precipitator (51). The scrubber is in fluid communication with the gasifier and with the tank, and is adapted for the injection of a washing liquid in the gas flow. The tank comprises a bottom area for collecting the liquid and a top area for holding the gas. The wet electrostatic precipitator is in fluid communication with the top area of the tank. In some examples, a gasifier comprises a gasification reactor (12), a grate (125) for the support of the biomass in the reactor (12) and a plug (126). The plug is vertically movable so as to close and/or open the middle part of the grate.