In a blast furnace plant (10), at least three regenerative heaters (14.1, 14.2, 14.3) are cyclically operated on blast and on gas: while a regenerative heater is operated on gas, hot flue gas is produced and caused to flow through the regenerative heater so as to heat the heat storage elements (46); and while a regenerative heater is operated on blast, process gas (32), i.e. a CO-rich fraction of the top gas (16), is blown through the regenerative heater so that the process gas takes up heat from the heat storage elements. During a changeover of a regenerative heater from on-blast to on-gas operation, the regenerative heater is purged from process gas using flue gas collected after having flown through at least one of the regenerative heaters.