DIRECT REDUCTION SYSTEM AND PROCESS UTILIZING A PROCESS GAS DIRECT RECYCLE LINE

Abstract

A direct reduction system and process for reducing a metal oxide to a metal, including and utilizing: a process gas line configured to deliver a portion of a process gas to a reformer operable for reforming the process gas to form a reformed gas; a bustle gas line configured to deliver the reformed gas to a shaft furnace as a bustle gas, wherein the shaft furnace is operable for reducing the metal oxide to the metal; and a direct recycle line including a direct recycle cooler configured to selectively deliver a portion of the process gas to the bustle gas line while circumventing the reformer, thereby selectively cooling and lowering the moisture content of the bustle gas delivered to the shaft furnace. Optionally, the direct reduction system further includes a reheat line configured to deliver a portion of the bustle gas to the shaft furnace as reheat gas.

Claims

1. A direct reduction system for reducing a metal oxide to a metal, comprising: a process gas line configured to deliver a portion of a process gas to a reformer operable for reforming the process gas to form a reformed gas; a bustle gas line configured to deliver the reformed gas to a shaft furnace as a bustle gas, wherein the shaft furnace is operable for reducing the metal oxide to the metal; and a direct recycle line comprising a direct recycle cooler configured to selectively deliver a portion of the process gas to the bustle gas line while circumventing the reformer, thereby selectively cooling and lowering a moisture content of the bustle gas delivered to the shaft furnace.

2. The direct reduction system of claim 1, wherein the process gas line comprises a process gas compressor operable for compressing the process gas prior to the delivery of the process gas to the direct recycle cooler and/or the reformer.

3. The direct reduction system of claim 1, wherein the process gas line comprises a process gas preheater operable for preheating the portion of the process gas prior to the delivery of the portion of the process gas to the reformer.

4. The direct reduction system of claim 1, wherein the process gas line comprises a flow control valve operable for selectively enabling/disabling a flow of the portion of the process gas to the direct recycle cooler.

5. The direct reduction system of claim 1, wherein the direct recycle line comprises a duct assembly that is disposed at an elevation high enough to maintain a water seal length using a U-leg design without an underground seal leg.

6. The direct reduction system of claim 1, wherein the direct recycle cooler comprises one or more of a packed bed cooler and a shell-and-tube heat exchanger.

7. The direct reduction system of claim 1, further comprising a reheat line configured to deliver a portion of the bustle gas to the shaft furnace as reheat gas, wherein the reheat line is coupled to the bustle gas line between the direct recycle line and the shaft furnace.

8. The direct reduction system of claim 7, wherein the bustle gas line comprises a flow restrictor operable for selectively directing the portion of the bustle gas into the reheat line.

9. The direct reduction system of claim 1, wherein the direct recycle line and the direct recycle cooler are collectively operable for delivering the portion of the process gas to the bustle gas line and selectively cooling the bustle gas delivered to the shaft furnace from 950980 C. to 700950 C.

10. The direct reduction system of claim 1, wherein the direct recycle line and the direct recycle cooler are collectively operable for delivering the portion of the process gas to the bustle gas line and selectively drying the bustle gas delivered to the shaft furnace from 515% H.sub.2O to 46% H.sub.2O.

11. A direct reduction process for reducing a metal oxide to a metal, comprising: via a process gas line, delivering a portion of a process gas to a reformer operable for reforming the process gas to form a reformed gas; via a bustle gas line, delivering the reformed gas to a shaft furnace as a bustle gas, wherein the shaft furnace is operable for reducing the metal oxide to the metal; and via a direct recycle line comprising a direct recycle cooler, selectively delivering a portion of the process gas to the bustle gas line while circumventing the reformer, thereby selectively cooling and lowering a moisture content of the bustle gas delivered to the shaft furnace.

12. The direct reduction process of claim 11, wherein the process gas line comprises a process gas compressor operable for compressing the process gas prior to the delivery of the process gas to the direct recycle cooler and/or the reformer.

13. The direct reduction process of claim 11, wherein the process gas line comprises a process gas preheater operable for preheating the portion of the process gas prior to the delivery of the portion of the process gas to the reformer.

14. The direct reduction process of claim 11, wherein the process gas line comprises a flow control valve operable for selectively enabling/disabling a flow of the portion of the process gas to the direct recycle cooler.

15. The direct reduction process of claim 11, wherein the direct recycle line comprises a duct assembly that is disposed at an elevation high enough to maintain a water seal length using a U-leg design without an underground seal leg.

16. The direct reduction process of claim 11, wherein the direct recycle cooler comprises one or more of a packed bed cooler and a shell-and-tube heat exchanger.

17. The direct reduction process of claim 11, further comprising, via a reheat line, delivering a portion of the bustle gas to the shaft furnace as reheat gas, wherein the reheat line is coupled to the bustle gas line between the direct recycle line and the shaft furnace.

18. The direct reduction process of claim 17, wherein the bustle gas line comprises a flow restrictor operable for selectively directing the portion of the bustle gas into the reheat line.

19. The direct reduction process of claim 11, wherein the direct recycle line and the direct recycle cooler are collectively operable for delivering the portion of the process gas to the bustle gas line and selectively cooling the bustle gas delivered to the shaft furnace from 950980 C. to 700950 C.

20. The direct reduction process of claim 11, wherein the direct recycle line and the direct recycle cooler are collectively operable for delivering the portion of the process gas to the bustle gas line and selectively drying the bustle gas delivered to the shaft furnace from 515% H.sub.2O to 46% H.sub.2O.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components/process steps, as appropriate, and in which:

[0021] FIG. 1 is a schematic diagram illustrating a conventional DR process, utilizing a RGC 18 and a reheat line 26;

[0022] FIG. 2 is a schematic diagram illustrating one exemplary embodiment of the DR process of the present invention, utilizing a direct recycle line 28, a DRC 30, and a reheat line 26; and

[0023] FIG. 3 is a schematic diagram illustrating another exemplary embodiment of the DR process of the present invention, utilizing a direct recycle line 28 and a DRC 30.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring now specifically to FIGS. 2 and 3, related generally to tempering the bustle gas 16 during a start-up period, when starting-up with the SF entirely filled with cold iron oxide or the like, the temperature of the bustle gas 16 introduced into the SF must be controlled at typically 700750 C. and the lower moisture content of the bustle gas 16 must be maintained to avoid the melting or oxidation of the material, as mentioned herein above. A part of the process gas 32 from the process gas compressor 34 bypasses the reformer 14 to be mixed with the hot reformed gas 12. This bypass is again called the direct recycle line 28. The packed bed cooler (DRC) 30 is installed in the direct recycle line 28 to lower the temperature and the moisture content of the process gas 32, typically from 180 C. and 1015% H.sub.2O to less than 40 C. and 1.52% H.sub.2O. During the start-up period, the flow rate introduced to the DRC 30 is regulated by the flow control valve 24 to maintain the target bustle gas temperature. During normal plant operation, when no tempering of the bustle gas 16 is required, no process gas 32 is introduced to the DRC 30 or mixed with the reformed gas 12. The flow control valve or shut-off valve 24 is closed completely. Advantageously, no cooling water is supplied while the DRC 30 is idled. Due to the lower temperature and higher pressure of the direct recycle line 28, the diameter of the control valve 24 is smaller, such as 400 mm or less. Better sealing performance is thus expected when the valve 24 is closed. Even if a small leakage does occur with the valve 24, it will not influence the overall process 10.

[0025] The direct recycle line 28 is made of a carbon steel duct or the like. Advantageously, the DRC 30 has no refractory parts and a smaller diameter than the RGC 18 (FIG. 1). The location of the DRC 30 is flexible without the refractory-lined duct or the restriction of the reformer location. It can be somewhere between the process gas compressor 34 and the bustle gas line 16 to the SF. By locating the DRC 30 at an elevation high enough to maintain the water seal length using a U-leg design, for example, no underground seal leg is required. The DRC 30 has the seal leg to discharge the water and seal the pressure, typically 1.52 barg.

[0026] FIG. 2 illustrates the flowsheet with direct recycle in the case where a reheat line 26 is applied to heat up the material in the SF. The reheat line 26 can be branched from the bustle gas line 16 at a point close to the SF, which makes the duct shorter for the reheat line 26. This reduces the capital cost and the heat loss. The flow restriction brick orifice 22 is placed at the bustle gas line 16 between the SF and the branch to maintain the flow rate of the reheat line 26, but it does not have as much pressure drop as that with the current RGC 18. Direct recycle gas 28 cooled by the DRC 30 can be introduced into the bustle gas 16 downstream of the reformer 14 and/or downstream of the reheat line branch.

[0027] FIG. 3 illustrates the flowsheet with direct recycle in the case where a reheat line 26 (FIGS. 1 and 2) is not applied. No flow restriction 22 (FIGS. 1 and 2) is installed in the bustle gas line 16 accordingly. Thus, the corresponding electricity consumption for the process gas compressor 34 is saved.

[0028] Again, referring now to all FIGS. 1-3, the RGC 18 and the flow restriction 22, such as the brick orifice, are replaced by a direct recycle line 28 with another packed bed cooler, the DRC 30. The DRC 30 reduces the temperature (typically 180 C.) and moisture (typically 15%) of the process gas 32 discharged from the process gas compressor 34. Cooled process gas 32 is mixed with the hot reformed gas 12 to lower the temperature and moisture in bustle gas 16 going to the SF. The moisture reduction of the bustle gas 16 is important to prevent the re-oxidation of the material in the SF, which could cause a significant plant outage and increase the amount of off-spec product.

[0029] The DRC 30 is installed at an elevation high enough to eliminate the need for underground barometric seal leg piping since the DRC 30 can be laid out flexibly or independently from the SF and the reformer 18 by routing the simple carbon steel duct. A U-leg barometric seal leg arrangement is employed instead.

[0030] The cooling water can be stopped during the idling of the DRC 30 or a normal plant operation period since the DRC 30 has no overheat issue with the lower entering gas temperature. This saves the electricity consumed by the pump and eliminates the packing fouling by biological bacteria.

[0031] Replacing the RGC 18 to cool 900+ C. reformed gas 12 with the DRC 30 to cool 180 C. process gas 32 eliminates the refractory-lined duct around the RGC 18 and reduces the size of the packed bed cooler.

[0032] With the reheat line 26, the elimination of the RGC 18 enables the reheat line 26 to be branched from the bustle gas line 16 much closer to the SF. The shorter length of the refractory-lined duct reduces the capital cost. It also reduces the heat loss from the reheat line to increase the discharge temperature of the hot DRI and save electricity consumption at the electric arc furnace. In the case of HBI plants, it can reduce the amount of unbriquetted product due to low discharge temperature.

[0033] Without the reheat line 26, the elimination of the RGC 18 and the brick orifice 22 in the bustle gas line 16 reduces the pressure drop to save electricity consumption for the process gas compressor 34 during the normal operation period. Alternatively, it will eliminate the mechanical adjustable hot valve 22 in case it is installed instead of the brick orifice 22.

[0034] Although the present invention is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following non-limiting claims for all purposes.