BLAST FURNACE PLANT AND SHUTDOWN PROCESS

Abstract

Blast furnace plant (1) and shutdown process for such a blast furnace plant (1). The blast furnace plant comprises a blast furnace (2) and a gas cleaning section (6) for cleaning gas from the blast furnace. Clean gas is released via a clean gas vent line (11) downstream of the gas cleaning section.

Claims

1. A process of shutting down a blast furnace plant comprising a blast furnace and a gas cleaning section for cleaning gas from the blast furnace, said method comprising: releasing clean gas via a clean gas vent line downstream of the gas cleaning section; reducing hot blast pressure and/or flow to a set value; and subsequently generating a flow from tuyeres of the blast furnace to the clean gas vent line.

2. The process of claim 1, wherein the flow is generated by injecting a gas into the blast furnace.

3. The process of claim 1, wherein the flow is generated by suction in the clean gas vent line.

4. The process of claim 1, wherein the flow is maintained for a set period and further comprising a step of subsequently opening at least one bleeder valve of the blast furnace and closing the clean gas vent line.

5. A blast furnace plant comprising a blast furnace, a gas cleaning section, and a clean gas transport line to a gas grid for further transport of cleaned gas, wherein the clean gas transport line to the gas grid is provided with a clean gas vent line, and the blast furnace comprises tuyeres and means for generating a flow from the tuyeres of the blast furnace to the clean gas vent line.

6. The blast furnace plant of claim 5, wherein the means for generating a flow includes a source for a gas.

7. The blast furnace plant of claim 5, wherein the means for generating a flow includes a pressure reduction device downstream of the gas cleaning section.

8. The blast furnace plant of claim 7, wherein the pressure reduction device comprises an ejector and/or one or more pumps and/or one or more fans.

9. The blast furnace plant of claim 5, wherein the clean gas vent line extends above a level of the clean gas transport line to the gas grid.

10. The blast furnace plant of claim 5, wherein the clean gas vent line is connected to a flare.

11. The blast furnace plant of claim 5, wherein the clean gas vent line is connected to one or more further vent lines.

12. The process of claim 3, wherein the flow is generated by a pressure reducer.

13. The process of claim 12, wherein the pressure reducer is selected from the group consisting of an ejector, one or more gas pumps and one or more fans.

14. The process of claim 1, wherein the flow is generated by injecting a gas into the blast furnace or by suction in the clean gas vent line and wherein the flow is maintained for a set period and further comprising a step of subsequently opening at least one bleeder valve of the blast furnace and closing the clean gas vent line.

15. The blast furnace plant of claim 9, wherein the level of the clean gas transport line is up to a top level of the blast furnace or higher.

16. The blast furnace plant of claim 11, wherein the one or more further vent lines are selected from the group consisting of a semi-clean gas vent line and a chimney.

17. The blast furnace plant of claim 5, wherein the means for generating a flow includes a source for a gas and a pressure reduction device downstream of the gas cleaning section.

18. The blast furnace plant of claim 17, wherein the pressure reduction device comprises an ejector and/or one or more pumps and/or one or more fans.

19. The blast furnace plant of claim 18, wherein the clean gas vent line extends above a level of the clean gas transport line to the gas grid.

20. The blast furnace plant of claim 19, wherein the clean gas vent line is connected to one or more further vent lines.

Description

[0022] The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing a number of embodiments by way of example.

[0023] FIG. 1: shows a first embodiment of a blast furnace plant according to the invention;

[0024] FIG. 2: shows a second embodiment of a blast furnace plant according to the invention;

[0025] FIG. 3: shows a third embodiment of a blast furnace plant according to the invention.

[0026] FIG. 1 shows schematically an exemplary embodiment of a blast furnace plant 1 of the present invention. The blast furnace plant 1 comprises a blast furnace 2 and an off-gas system, in this particular embodiment embodied as an uptake 3 on top of the blast furnace 2. The shown embodiment has multiple uptakes 3, schematically represented in the drawing by a single line, but blast furnaces without an uptake or having only one uptake can also be used. Present-day blast furnaces mostly comprise a configuration of multiple uptakes joining each other at their top ends.

[0027] On top of the uptake 3 is a bleeder valve 4. Most blast furnaces have multiple bleeder valves on a bleeder platform above the junction of multiple uptakes.

[0028] A downcomer 5 transports raw gas from the top of the uptake 3 down to a gas cleaning section 6. The gas cleaning section 6 can have any suitable arrangement of dust removal systems, but typically comprises a gravity or cyclone dust catcher 7, usually followed by a wet scrubber 8 or a filter bag station or an electrostatic precipitator. If a wet scrubber is used, the blast furnace plant will usually also be provided with a demister 9 downstream of the gas cleaning section for separating the scrubber liquid. All gas cleaning equipment 7, 8 and the demister 9 can have associated purging gas supplies, for example at positions 7A, 8A, 9A.

[0029] A clean gas transport line 10 transports clean gas from the gas cleaning section, for example to the gas grid. A clean gas vent line 11 branches off from the clean gas transport line 10. The clean gas vent line 11 is closable by a vent valve 12. A clean gas isolation valve 13 is located downstream of the clean gas vent line 11.

[0030] At the inlet side the blast furnace 2 comprises tuyeres 14 forming a hot blast inlet to the blast furnace. The tuyeres 14 are evenly distributed around the circumference of the blast furnace, usually via a bustle main.

[0031] A blower 15 blows compressed air via a supply line 16 which, at a distance downstream of the blower 15, is split into a first branch 16A with hot blast stoves 17 for heating the air, and a second branch 16B without such stoves. Each one of the stoves 17 comprises its own valve 19. The two branches 16A, 16B join each other at a downstream point to form a blast mixing circuit. The valves 18, 19 can be used to meter and mix the flows of the two branches 16A, 16B to produce a blast of a desired temperature entering the blast furnace 2 at a given hot blast pressure. Additional oxygen and/or moisture and/or fuels like pulverized coal, natural gas, hydrogen or oil and/or other components can be added to the hot blast air, if so desired.

[0032] The supplied air flows via a line 20 to the tuyeres 14 of the blast furnace 2. In the shown exemplary embodiment, this line 20 can be provided with a backdraft stack 21 closable by a valve 22. Opening the valve 22 facilitates venting of gaseous products from the blast furnace 2 after a shutdown. Alternatively, the blast furnace plant 1 can be without such a back draft stack 21.

[0033] Some blast furnace plants may have a hot blast main isolation valve 34 just upstream of the bustle main of the tuyeres 14 or, if a back draft stack 21 is present, just upstream of the back draft stack 21.

[0034] The blast furnace 2 is provided with purging gas supplies 24. Typical purging gases are nitrogen and/or steam.

[0035] On top of the wet scrubber 8 is a line to a semi-clean gas bleeder valve 25.

[0036] During normal operation of the blast furnace plant 1, ferrous burden and coke are charged in discrete layers up to the top section of the blast furnace 2. Hot blast air of about 1200° C. is supplied to the blast furnace 2 via the tuyeres 14, optionally with additional oxygen and/or moisture and/or fuels like pulverized charcoal, natural gas, hydrogen or oil. The hot blast gasifies the coke and injected fuels, heating, reducing and melting the ferrous burden to form liquid hot metal, slag and raw gas. During normal operation the pressure in the blast furnace is typically about 2-5 bar. The raw gas is collected in the uptake section 3 and transported via the downcomer 5 to the gas cleaning section 6, where most of the dust content is removed and the pressure is reduced to the pressure of the gas grid, typically about 40-100 mbar. After passing the gas cleaning section 6 the clean gas is transported via the clean gas transport line 10 to the gas grid. The collected clean gas can be used as a fuel for heating, for example for the hot blast stoves or the production of steam.

[0037] Occasionally, it is required to shut down the blast furnace plant 1 by means of a blow down. In a first step of such a blow down procedure the blast furnace is operated without further charging the blast furnace. The charge level in the blast furnace 2 gradually decreases. In this stage, the clean gas vent line 11 is closed and the clean gas is transported via the clean gas transport line 10 to the gas grid.

[0038] When the carbon monoxide level is below a threshold value, for example below 7 vol. % by dry volume of the raw gas, the clean gas vent line is opened and subsequently the clean gas isolation valve 13 of the clean gas transport line 10 to the gas grid is closed off, so the clean gas flows via the clean gas vent line 11. When the oxygen content of the raw gas in the blast furnace 2 exceeds a threshold value, for example about 2 vol % of the total volume of the raw gas within the blast furnace, and the burden is at about the level of the tuyeres 14, the pressure of the hot blast at the tuyeres 14 is reduced to a lower value, e.g. about 0.1 bar. The valve 18 of the cold blast line 16B is then opened while the hot blast valve 19 is closed off. The valve 18 of the cold blast line 16B is controlled to maintain a pressure difference of about 10-30 mbar between the pressure in the blast furnace 2 and the pressure in the clean gas vent line 11. Subsequentially the bleeder valves 4 are opened and the vent line 11 is closed off.

[0039] FIG. 2 shows an alternative embodiment of a blast furnace plant 1′. All components of the plant are the same as in FIG. 1, except that a nitrogen supply line 23 is connected downstream of the valve 18 for closing off the second branch 16B of the blast mixing circuit, and upstream of the optional valve 34. Alternatively, the nitrogen supply 23 can be connected at any position on the supply line 20 upstream from the tuyeres 14.

[0040] When the blast furnace plant 1′ of FIG. 2 is shut down, the hot blast pressure in the blast furnace 2 is first reduced to about 0.2-0.3 bar by reducing the hot blast inlet flow via the tuyeres 14. In a next step, the purging gas supplies 24 for the blast furnace 2 are opened. Then the clean gas vent line valve 12 of the clean gas vent line 11 is opened and the valve 13 of the clean gas transport line to the gas grid is closed. Mostly, the hot blast pressure is then further reduced to about 0.1 bar. Optionally, the vented clean gas can be flared.

[0041] In a next step, the nitrogen supply 23 is opened and the valves 18 and 19 of the blast air branches 16A, 16B are closed. The nitrogen supply creates a flow between the blast furnace 2 and the clean gas vent line 11 maintaining the upward flow through the blast furnace 2. Since the supply of oxygen containing hot blast air is stopped, the production of carbon monoxide and dust will gradually be reduced, although for a while iron oxide (FeO) will react with the coke to produce carbon monoxide and dust. In this stage the raw gas has a low dust content and the clean gas vent line 11 can be closed after the bleeder valves 4 on top of the uptakes 3 are opened.

[0042] Subsequently, existing procedures for finalization of the shutdown can be followed accounting for the fact that residual nitrogen could be present in the hot blast main.

[0043] FIG. 3 shows an alternative embodiment of a blast furnace plant 1″ according to the invention. In this embodiment, there is no nitrogen supply line 23 in the configuration of the hot blast supply circuit 16A, 16B. Instead, the clean gas vent line 11″ is provided with an ejector 30 for increasing the pressure drop and promote the flow by suction. The clean gas vent line 11″ splits into a first branch 11A without the ejector 30 and a second branch 11B with the ejector 30. Downstream of the ejector 30 the two lines 11A, 11B join again as a single exhaust. Valves 12, 32 are used to close off one of the lines after opening the other line, so the clean gas vent line 11″ can selectively be used with or without the ejector 30. The ejector 30 is connected to a supply 33 of an inert motive gas, such as steam or nitrogen.

[0044] When the blast furnace plant 1″ is shut down, the hot blast pressure is first reduced to 0.2-0.3 bar by reducing the hot blast inlet flow. In a next step, the purging gas supplies 24 for the blast furnace 2 are opened. Then the valve 12 of the clean gas vent line 11A bypassing the ejector 30 is opened and the clean gas isolation valve 13 of the clean gas transport line 10 to the gas grid is closed. The hot blast pressure is then further reduced to about 0.1 bar.

[0045] In a next step the ejector 30 is opened while the line 11A bypassing the ejector 30 is closed. The pressure in the system is controlled by the suction generated by the ejector 30. After a set period the bleeder valves 4 on top of the uptakes 3 are opened and subsequently the ejector 30 and the clean gas vent line 11′ are closed off.

[0046] Further embodiments can for example comprise both the ejector 30 as well as the nitrogen supply 23 and/or comprise further means to promote the gas flow from the blast furnace to the clean gas vent line.