Patent Application
20170297113
The present disclosure relates to metal production processes and facilities, and particularly to the use of by-product off-gases for gas atomization of molten materials such as slag and/or metals in such processes and facilities.
In facilities producing molten materials such as metals, gases (off-gases or air) are conveyed from one part of the process to another for one of the following purposes:
(1) To exhaust off-gases from process equipment so as to maintain sanitary working conditions around the process equipment; and/or
(2) To heat or cool process equipment.
In either of the above cases, the off-gas may:
A) Be laden with particulate;
B) Have a wide range of compositions (e.g. similar to air, oxygen free (N2, H2O, CO2 rich), fuel rich (CO, H2) or sulfur rich (SO2));
C) Be cold or hot depending on the process from which it emanated.
In all cases, the gases used or produced in these processes must be conveyed through or from the process using rotary equipment (e.g. an induced draft fan, blower or compressor) which must be purchased for this purpose. Therefore most metallurgical facilities have a plethora of such rotary equipment.
In addition to this, unless the gases are of low temperature and clean, the gases produced from metallurgical applications must be burned and/or cooled and/or cleaned by off-gas treatment systems as there is no use for these by-product gases. These gas treatment systems are expensive, and therefore significantly drive up the cost of metallurgical extraction plants, accounting for about 30 to 50% of operating plant capital expenditures. There is therefore a need to reduce or eliminate where possible off-gas handling equipment while maintaining good working conditions in-plant and maintaining off-gas emission targets.
Furthermore the energy in the gas by-products is seldom recovered because the gases are dispersed throughout the plant and are of too low a temperature to permit economic energy recovery. There is therefore a lost opportunity to recover low grade heat in smelters.
Finally, no use has been identified for the by-product gases from metallurgical applications and for this reason they are wasted to atmosphere via the expensive off-gas treatment systems previously mentioned, without heat recovery because of the lack of centralization and sufficient heat quality.
For example, in FeNi smelter furnaces, cooling air is wasted to atmosphere without energy recovery; and secondary calcine and tapping fume off-gases are likewise wasted to atmosphere via a secondary baghouse cleaning system. Since no use has been found for these by-product gases, they must be treated by expensive off-gas handling equipment before being released to the atmosphere.
Similarly, in FeCr smelters, CO2-rich furnace off-gas is cooled and wasted to atmosphere without recovery of energy or use of the properties of the off-gas. Again, this is because no use has been found for these off-gas products and as a result these gases are wasted to atmosphere via expensive off-gas treatment systems without value recovery.
In addition, CO2 emission from metallurgical plants is an environmental concern, and all metals producers are under pressure to reduce their greenhouse gas emission. For this purpose, carbon dioxide reforming units have been used to convert the CO2-rich off-gas to a mixture of hydrogen and carbon monoxide (synthetic gas), which can then be used as a fuel in different processes (for example upstream dryer, calciner, furnace, or pre-reduction units). However, for this reforming process to be thermodynamically favourable, the CO2-rich gas needs to be preheated to above ˜900° C., which represents an additional operating cost.
Carbon dioxide is only one example of an emission which can cause environmental concerns. Emissions from metallurgical plants may include a wide variety of other undesirable components, including gases and particulate solids, which are of concern when released into the environment. Furthermore, the reduction or removal of these undesirable components from the off-gases of a metallurgical plant typically requires costly equipment and processes. Examples of undesirable gases which may be contained in the off-gases of metallurgical plants include CO2, sulphur-containing species such as SO2, SO3, and H2S nitrogen oxides (NOx) such as NO and NO2, phosphorus-containing gases, fluorides (such as HF and SiF4) and/or organic species such as furans and dioxins. Examples of undesirable particulate solids include dust, which must typically be removed from off-gases.
Slag is another by-product of metal production processes conducted in metallurgical furnaces. Slag typically comprises a mixture of metal oxides with silicon dioxide, and is produced in amounts ranging from roughly 10 percent to several times the amount of metal produced by the process.
Molten slag is periodically tapped from the furnace and is allowed to air cool and solidify, with the heat being lost to the environment. Much of the slag produced by these processes continues to be discarded as waste. However, there has been recent interest in the use of granulated slag in a variety of commercial products, and equipment and processes have been developed for the granulation and processing of slag to produce granulated products such as proppants in oil and gas production, and roofing granules.
Particularly promising processes and equipment for conversion of slag to granular products by gas atomization are disclosed in commonly assigned U.S. Provisional Patent Application No. 62/007,180, and in U.S. Provisional Patent Application No. 62/007,284, both filed on Jun. 3, 2014. According to the processes disclosed therein, molten slag from a furnace is directly and economically converted to a variety of granular products by gas atomization using ambient air which is supplied to an atomization apparatus by a common air blower.
There remains a need for simpler and more economical processes and equipment for handling by-products such as slag and off-gases, in order to alleviate at least some of the problems discussed above.
In an embodiment, there is provided a process for preparing a granular product, comprising: (a) providing a molten material; (b) feeding the molten material to a dispersion apparatus; (c) feeding a gas to the dispersion apparatus, wherein the gas is a by-product off-gas; (d) contacting the gas with the molten material in the dispersion apparatus, whereby the molten material is dispersed and solidified by contact with the gas to form said granular product.
In another embodiment, there is provided a system for preparing a granular product, comprising: (a) a metallurgical furnace containing a molten material selected from one or more of molten metal and molten slag; (b) a gas atomization plant located proximate to the metallurgical furnace; (c) a gas supply system for supplying a by-product off-gas to the gas atomization plant; (d) a molten material supply system for transporting the molten material from the metallurgical furnace to the gas atomization plant.
The invention will now be described, by way of example only, with reference to the attached drawings, in which:
The following is a detailed description of metallurgical processes and facilities which include a process and equipment for gas atomization of molten slag and/or molten metals, and in which there is integration of at least one off-gas handling process with at least one gas atomization process, and the equipment associated with these processes.
The inventors have discovered that by-product off-gases from metallurgical processes can be used for gas atomization of slag and metals from metallurgical furnaces, to produce one or more of the following benefits:
A. Elimination of off-gas handling equipment, and centralization of off-gas treatment facilities to those required solely for atomization of molten slag and/or molten metal.
B. Elimination of furnace, metal tapping, calcine transfer, dust control, and reduction equipment fans. Instead, the atomization fan can evacuate gases from these processes and use them for atomization.
C. Elimination of operating expenditures associated with the use of furnace, metal tapping, calcine transfer, dust control, and reduction equipment fans, in contrast to system that atomize slag and/or metal with air.
D. Centralization of heat from the above mentioned processes, and upgrading of this heat via slag and/or metal atomization to provide more economic slag and molten metal heat (energy) recovery.
E. Production of off-gases with high temperatures (versus air with lower temperature) for process units requiring heat (drying units, water pre-heating, etc.).
F. Elimination of off-gas treatment systems and capital expenditures associated with granulation and atomization since the high temperature off-gases can now be re-used in processes that are already equipped with such equipment. A specific example is drying in FeNi rotary kiln-electric furnace (RKEF) plants.
G. Utilization of inert gases to atomize metals or slags into shot or powders in order to prevent their oxidation.
H. Improved metal recovery efficiencies vs. current slag crushing, sorting and jigging operations and the reduced use or elimination of such by-product post treatment plants.
I. If atomization is carried out using a CO2-rich off-gas from the process: A) a fraction of carbon-containing gaseous species can be dissolved into the molten material (as dispersion increases the specific surface area enhancing dissolution); and B) temperature of the CO2-rich gas will increase as a result of contact with molten material, which facilitates the reforming process with less preheating or without any extra preheating.
It can be appreciated that the above advantages lead to significant cost-downs over the current state of the art that make:
Molten slag is periodically tapped from the furnace 10 through the slag tap hole 18, and is tapped directly into a movable slag vessel or a slag launder or runner, in which the molten slag is transported to another area of the plant. During transport, the slag is maintained in a molten state. The transportation of the molten slag in a slag vessel or launder is represented by arrow 22 in
The furnace 10 in
As will be appreciated, the furnace cooling air becomes heated as it cools the bottom wall and side wall of the furnace. In
The system according to the present embodiment also includes a gas atomization plant 28 to atomize the molten slag and produce slag granules suitable for use in commercial products such as proppants and/or roofing granules. The gas atomization plant 28 is located in close proximity to the metallurgical furnace 10, and receives the molten slag from furnace 10 via a slag vessel or launder, as represented by arrow 22.
The molten slag is atomized inside plant 28 by a gas flow from an induced draft (ID) fan 30, wherein the supply of atomizing gas from the ID fan 30 to gas atomization plant 28 is represented by arrow 32 in
In typical installations, the gas input to gas atomization plant 28 is instead routed through an air blower (not shown but replaces the ID fan) and may comprise air at ambient temperature and pressure. However, in the process and system according to the present embodiment, the gas input to the ID fan 30 comprises exhausted off-gases from the furnace bottom wall and/or the lower side wall, as represented by arrow 24 and/or 26. Such exhausted off-gases could not be fed to the blower utilized in current air atomization plants as they are hot and dirty. In the present embodiment, the gas input to ID fan 30 comprises the combined off-gas from the furnace bottom wall and the lower side wall, and therefore
According to the present embodiment, the ID fan 30 for supplying off-gas to the gas atomization plant 28 also draws air into the furnace cooling system. This permits the elimination of any fans for supplying cooling air to the furnace 10, thereby providing a reduction in capital expenses and operating costs. In addition, the use of the off-gas for atomization permits the elimination of a separate off-gas treatment system for the off-gas, and providing a further reduction in capital expenses and operating costs.
Therefore, in the present embodiment, air circulation through the furnace air cooling system and off-gas circulation to the gas atomization plant is provided by the same ID fan 30. It will be appreciated that the ID fan 30 may not necessarily need to be located between the furnace 10 and the gas atomization plant 28, but may instead be located upstream of the furnace 10 so as to blow cooling air to the furnace walls and to blow the heated air to the gas atomization plant 28.
In
The off-gas used for atomization is exhausted by the gas atomization plant 28 as a slag granulation off-gas which is represented by box 40, and the removal of the off-gas from the gas atomization plant 28 is represented by arrow 42. The off-gas 40 contains heat extracted from the furnace side wall and bottom wall, and heat extracted from the molten slag. Therefore, use of the off-gas exhausted from the furnace cooling system in the gas atomization plant 28 upgrades the heat in the off-gas, thereby permitting its use in downstream process equipment for energy transfer. For example, the hot off-gas 40 from gas atomization plant 28 may be processed to recover heat therefrom, or it may be fed to other process units which require heat, such as drying units, water pre-heating units, etc. These other process units are represented by box 44 in the drawings.
Although the above description relates to an embodiment where the off-gas used for atomization is air from the furnace cooling system, and wherein molten slag is the material being atomized, this is not necessarily the case. For example,
The embodiment of
Instead of being collected in hood 54, at least a portion of the off-gas vented from furnace 10 may be conveyed directly to the gas atomization plant 28 through ID fan 30. For this purpose,
Due to the variability in the processes carried out in the metallurgical furnace, the off-gas may be of varying composition, and this is further discussed below. Regardless of the composition of the off-gas used for atomization, it is important to emphasize that an important aspect of the present invention is the use of an induced draft fan 30 to withdraw off-gases (for example from the interior of the furnace or from the bottom of the furnace) and to supply the off-gases for atomization. This replaces a conventional blower which draws in ambient air and blows the air for atomization. This improvement is applicable to all embodiments disclosed herein.
It is also important to emphasize that the use of off-gases for the purpose of granulating may result in less oxidation of the molten material than would be the case if ambient air were used as the atomizing gas. In this regard, the off-gas may be depleted in oxidative species such as oxygen or may be substantially free of oxidative species. The extent of the oxidation is dependent on the composition of the off-gas, but this reduction in the level of oxidation can be realized from a variety of off-gases from a number of sources within the system, such as the off-gases which are vented from the furnace as in
Another important aspect of the present invention is that the use of the off-gas for atomization results in upgrading of the off-gas heat. This is an important benefit where it is desired to recover heat from the off-gas or use the off-gas in another process step where heat is required, e.g. in drying or preheating, and is realized in all embodiments disclosed herein.
In some embodiments, the off-gas supplied to the gas atomization plant 28 for the purpose of atomizing molten metal or slag may be laden with particulates. Use of the process and system as described herein permit the elimination of a separate off-gas treatment system, and the particulate laden off-gas is supplied to the gas atomization plant 28 by ID fan 30 as described above in the first and second embodiments. The off-gas from the gas atomization plant 28 is treated as discussed above.
Another important aspect of the present invention is that atomization of metal/slag may use CO2-rich off-gases as the atomizing gas. Thus, according to this aspect, not only is the atomization of the metal/slag accomplished by using an off-gas, but the CO2-emission from the plant is simultaneously reduced. The CO2 reduction is brought about by partial CO2-capture by dissolution of the CO2 in the metal/slag. Also, the CO2-rich off-gas is heated in the atomization plant, and therefore the off-gas from the atomization plant is sufficiently pre-heated so that it can be directly (or with minimum preheating) converted to synthetic gas (CO+H2) in a reformer. Accordingly, in this aspect of the invention, the other process units represented by box 44 comprise a reformer for producing synthetic gas.
Atomization of the metal/slag may also be conducted with off-gases containing one or more other undesirable components, defined herein as including gases and particulate solids which are of concern when released into the environment, and which typically must either be partially or completely removed by treatment of the off-gases.
For example, where the undesirable components include one or more gases such as CO2, sulphur-containing species such as SO2, SO3, and H2S nitrogen oxides (NOx) such as NO and NO2, phosphorus-containing gases, fluorides (such as HF and SiF4) and/or organic species such as furans and dioxins. The reduction of the concentration of these gases in the off-gas is accomplished as discussed above with reference to CO2, i.e. the reduction is brought about by dissolution of the undesirable component(s) in the molten metal/slag during the formation of said granular product in the atomization plant, such that a concentration of the undesirable component(s) in the hot off-gas of the gas atomization plant is less than a concentration of the undesirable component(s) in the off-gas supplied to the gas atomization plant. This may reduce the need for expensive equipment and processes to remove these undesirable components from the off-gas.
Where the undesirable components include one or more gaseous organic species such as furans and dioxins. The reduction of the concentration of these organic species in the off-gas may be accomplished by combustion of the organic species by contact of the organic species with the molten metal/slag in the presence of oxygen in the off-gas and/or in the metal/slag. Furthermore, at least a portion of the gases produced by combusting the organic species in the gas atomization plant may become dissolved in the molten metal/slag during the formation of the granular product. Thus, where some or all of the organic species are combusted to form carbon dioxide and water, the gas atomization plant may further function as an afterburner.
Where the undesirable components include particulate solids such as dust, the dust particles may become incorporated into the granular product during atomization of the molten metal/slag in the gas atomization plant. This may reduce the need for expensive equipment and processes to remove dust from the off-gas.
Finally, the present invention permits the integration of one or more off-gas streams into the off-gas from the gas atomization plant. This permits a reduction in the off-gas treatment equipment in the system, resulting in reductions in both capital and operating expenditures, and this benefit is realized by all embodiments disclosed herein.
In a further embodiment, molten metal tapped from furnace 10 through tap hole 20 may be granulated by gas atomization plant 28, rather than slag. In this regard,
The composition of the metal tapped from furnace 10 will of course depend on the specific metallurgical process being conducted therein. For example, where the furnace 10 is a ferronickel smelting furnace, the molten metal tapped through tap hole 20 may comprise ferronickel (FeNi). However, it will be appreciated that the processes and systems disclosed herein are not limited to any specific metallurgical processes. For example, the processes and systems disclosed herein can be applied to the production of pig iron in an ironmaking blast furnace.
The use of hot and/or dirty off-gases for atomization may require the ID fan 30 to comprise a dirty gas fan with radial blades which are capable of handling dirty off-gases rather than fresh air blowers with backwardly curved impeller blades. This applies to all embodiments disclosed herein.
In some embodiments, the off-gas supplied to the gas atomization plant 28 may be substantially oxygen-free. For example, in some embodiments, the off-gas may be rich in gases such as N2, H2O or CO2 which will result in little or no oxidation of metals contained in the molten slag or molten metal during atomization. For example, the furnace off-gases from FeCr smelters are rich in CO2 and their use as atomizing gases may be particularly beneficial in the production of pig iron or other metals in which oxidation during atomization is to be avoided. In other embodiments, the off-gas may be rich in fuel such as CO or H2, or may be rich in sulfur-containing species such as SO2.
Although the invention has been described with reference to certain specific embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/053,170 filed Sep. 21, 2014, the contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2015/050923 | 9/21/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62053170 | Sep 2014 | US |
