Method of operating regenerative heaters in blast furnace plant
In a blast furnace plant, at least three regenerative heaters 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; and while a regenerative heater is operated on blast, process gas, i.e. a CO-rich fraction of the top gas, is blown through the regenerative heater so that the process gas takes up heat from the heat storage elements, such that 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.
1. A method of operating regenerative heaters, in particular hot-blast stoves, in a blast furnace plant, said plant comprising:
a blast furnace,
a gas separation unit configured for separating top gas from said blast furnace into a stream of CO-enriched process gas and a stream of CO-depleted tail gas;
at least three regenerative heaters, each having internal heat storage elements, a cold blast inlet for receiving CO-enriched process gas from said gas separation unit and a hot blast outlet for feeding CO-enriched process gas to said blast furnace;
said method comprising
cyclically operating said regenerative heaters on blast and on gas, said cyclic operation including
while operating a regenerative heater on gas, producing hot flue gas with a burner and causing said hot flue gas to flow through said regenerative heater so as to heat said heat storage elements; and
while operating a regenerative heater on blast, blowing CO-enriched process gas through said regenerative heater for the CO-enriched process gas to take up heat from said heat storage elements;
said method further comprising
during a changeover of a regenerative heater from on-blast to on-gas operation, purging said regenerative heater from CO-enriched process gas with flue gas collected after having passed through at least one of said regenerative heaters.
2. Method as claimed in claim 1 , wherein said cyclic operations of said regenerative heaters are dephased amongst each other such that, at a time, at least one of said regenerative heaters is operated on blast while at least one of the others of said regenerative heaters is operated on gas, and wherein said purging of said regenerative heater undergoing said changeover is effected with flue gas from another one of said regenerative heaters that is operated on gas at the time of said changeover.
3. Method as claimed in claim 1 , wherein said purging of said regenerative heater undergoing said changeover is effected with flue gas previously stored in a gas storage.
4. Method as claimed in claim 1 , wherein a regenerative heater operated on blast is at an on-blast pressure, wherein a regenerative heater operated on gas is at an on-gas pressure lower than said on-blast pressure, and wherein, during a changeover of a regenerative heater from on-blast to on-gas operation, CO-enriched process gas is released from said regenerative heater undergoing said changeover so as to depressurize it prior to purging with flue gas.
5. Method as claimed in claim 4 , wherein said release of CO-enriched process gas is at least partly effected into a top gas recovery installation provided for leading top gas from said blast furnace to said gas separation unit.
6. Method as claimed in claim 4 , wherein said release of CO-enriched process gas is at least partly effected into a gas holder provided for storing CO-depleted tail gas.
7. Method as claimed in claim 4 , wherein CO-enriched process gas left over in said regenerative heater undergoing said changeover after said depressurization is expelled by said flue gas and burnt off.
8. Method as claimed in claim 6 , wherein CO-enriched process gas left over in said regenerative heater undergoing said changeover after said depressurization is expelled by said flue gas into said gas holder.
9. Method as claimed in claim 6 , wherein CO-enriched process gas is conveyed into said gas holder at most as long as CO concentration in said expelled CO-enriched process gas amounts to a predetermined percentage of CO concentration in said CO-depleted tail gas.
10. Method as claimed in claim 9 , wherein any expelled CO-enriched process gas not conveyed to said gas holder is burnt off.
11. A blast furnace plant comprising:
a blast furnace,
a gas separation unit configured for separating top gas from said blast furnace into a stream of CO-enriched process gas and a stream of CO-depleted tail gas;
at least three regenerative heaters, each having internal heat storage elements, a cold blast inlet for receiving CO-enriched process gas from said gas separation unit and a hot blast outlet for feeding CO-enriched process gas to said blast furnace;
wherein the blast furnace plant is structured to carry out a method comprising:
cyclically operating said regenerative heaters on blast and on gas, said cyclic operation including
while operating a regenerative heater on gas, producing hot flue gas with a burner and causing said hot flue gas to flow through said regenerative heater so as to heat said heat storage elements; and
while operating a regenerative heater on blast, blowing CO-enriched process gas through said regenerative heater for the CO-enriched process gas to take up heat from said heat storage elements; and
wherein the blast furnace plant is further structured to carry out the step of
purging said regenerative heater from CO-enriched process gas with flue gas collected after having passed through at least one of said regenerative heaters during a changeover of a regenerative heater from on-blast to on-gas operation.