WATER-BASED HEAT TRANSFER FLUID COOLING SYSTEMS INTRINSICALLY SAFE FROM BOILING LIQUID EXPANDING VAPOR EXPLOSION (BLEVE)IN VARIOUS PYROMETALLURGICAL FURNACE APPLICATIONS

Abstract

A cooling system for use in support of a pyro-metallurgical furnace includes a liquid heat transfer fluid blend of 10%-50% water with monoethylene glycol (MEG), diethylene glycol (DEG), or triethylene glycol (TEG), and corrosion inhibitors. When using such glycols, a minimum of 10% water prevents the heat transfer fluid from becoming too viscous for economical pumping, and a maximum of 50% water prevents BLEVE incidents inside the furnace. Such intrinsically safe cooling system circulates the liquid heat transfer fluid blend with an optimally sized pump, filtration, pressurization, and at flow velocities sufficient to avoid film boiling.

Claims

1. A water-based heat transfer fluid cooled system that is intrinsically safe from BLEVE when used in a pyro-metallurgical furnace, comprising: at least one water-cooled appliance comprising a vertical lance, a subsonic top submerged lance (TSL), a sonic lance, a torch, a tuyere, and a burner block, as are variously included in both ferrous and nonferrous pyro-metallurgical furnaces; a coolant circulation network disposed in, jacketed around, or embedded within the water-cooled appliance of the furnace and providing for intrinsically safe liquid cooling of the appliance; a coolant comprising a blended mixture of a single phase organic compound of glycol alcohol, water, and a corrosion inhibitor, wherein the water is limited to a range of about 10% to 50% of the total by weight, and wherein all of the water is fully absorbed in the glycol alcohol; and a pump with a particular critically sized minimum capacity dependent on the viscosity and specific heat of the coolant and that circulates the coolant through the coolant circulation network at a predetermined minimum volume and velocity to preclude film boiling; wherein, the coolant continually physically absorbs the water and desiccates the interior passages of the coolant circulation network such that a leak of the coolant into the pyro-metallurgical furnace cannot cause a BLEVE with free water.

2. The water-based heat transfer fluid cooled system of claim 1, wherein the appliance comprises a subsonic top submerged lance (TSL) subject to wear and bending that can be caused by the inadequate or uneven cooling conventionally provided by an oxidizing gas flow down into a nonferrous pyro-metallurgical furnace, and wherein the circulation of the coolant through a jacket surrounding the TSL precludes such wear and bending safe from BLEVE caused by leaks of coolant.

3. The water-based heat transfer fluid cooled system of claim 1, wherein the coolant has a predetermined specific heat greater than 2.3 kJ/kg.Math.K, a predetermined viscosity of less than 20 mPa.Math.s, and the glycol alcohol is one of monoethylene glycol (MEG), diethylene glycol (DEG), and propylene glycol (PEG).

4. An oxidizing gas injection system for a pyro-metallurgical furnace, comprising: an oxidizing gas injector for a pyro-metallurgical furnace; a cooling jacking disposed outside, around and along the full length of the oxidizing gas injector; a heat transfer fluid mixture comprising water, corrosion inhibitors, and glycol, and that combined has a predetermined specific heat greater than 2.3 kJ/kg.Math.K, and a predetermined viscosity of less than 20 mPa.Math.s, and wherein, the heat transfer fluid mixture is intrinsically incapable of a boiling liquid expanding vapor explosion (BLEVE); a liquid pumping system that circulates the heat transfer fluid mixture through the cooling jacking and that maintains a minimum fluid velocity at predetermined points within the cooling jacket to prevent film boiling of the heat transfer fluid mixture; a coolant pressurization system connected to contain the heat transfer fluid mixture and raise its boiling point; a filter connected to remove contaminants from the heat transfer fluid mixture; and a heat exchanger connected to remove and dispose of heat from the heat transfer fluid mixture.

5. A gas injection system for a pyro-metallurgical furnace, comprising: a heat transfer fluid mixture of water, corrosion inhibitors, and monoethylene glycol (MEG), and having in combination simultaneous predetermined limits on viscosity and specific heat; wherein, the heat transfer fluid mixture is intrinsically incapable of a boiling liquid expanding vapor explosion (BLEVE); a cooling system that extracts and disposes of heat from the heat transfer fluid mixture and that provides liquid pumping for minimum circulation velocities that preclude film boiling of the heat transfer fluid mixture; and a gas injection lance with a liquid cooled jacket that extends the full length to a lance tip, and that receives the heat transfer fluid mixture from the cooling system, and that returns heated heat transfer fluid mixture, and that thwarts thermal curving of the gas injection lance by precluding uneven heating of it during operation; wherein, the liquid cooled jacket maintains a minimum velocity of the heat transfer fluid mixture within at any particular point to prevent film boiling; and wherein, the gas injection lance includes a conduit for the injection of a gas flow into a ferrous or nonferrous pyro-metallurgical furnace.

6. The gas injection system of claim 5, wherein the heat transfer fluid mixture has a predetermined viscosity of less than 20 mPa.Math.s.

7. The oxygen injection system of claim 5, wherein the heat transfer fluid mixture has a predetermined specific heat greater than 2.3 kJ/kg.Math.K.

8. The gas injection system of claim 5, wherein the liquid cooled jacket maintains even temperatures that prevent curving of the lance with an inclusion of swirlers, and maintains said minimum velocity flow of 2.0 meters per second of the heat transfer fluid mixture within at least the gas injection lance tip to prevent film boiling.

9. The gas injection system of claim 8 wherein the solid feed to the furnace is fed down inside the gas injection lance and directly into the bath to reduce a loss of feed to a rush of off-gas.

Description

SUMMARY OF THE DRAWINGS

[0032] FIG. 1 is a functional block diagram in a schematic type view of a cooling system embodiment of the present invention that is intrinsically safe from BLEVE should any of its liquid, water-based coolant escape or leak into a pyro-metallurgical furnace;

[0033] FIG. 2 is a schematic view of a particular type of top submerged lance furnace (TSL) with liquid cooling that has been improved for use in a gas injection system embodiment of the present invention;

[0034] FIG. 3 is a cross-sectional diagram of a top submerged lance (TSL) embodiment of the present invention that circulates a heat transfer fluid that is intrinsically safe from BLEVE as part of the cooling system of FIG. 1;

[0035] FIG. 4 is a perspective view of a particular type of top submerged lance furnace (TSL) with liquid cooling that has been improved for use as a gas injection system embodiment of the present invention; and

[0036] FIG. 5 is a functional block diagram of an oxygen gas injection system for a furnace embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Water makes an excellent choice as a coolant because its low viscosity makes it easy to pump and its high specific heat means that coolant pumping volumes and speeds can be kept as low as is possible. A balanced combination of these considerations means the pumps in water-based cooling systems can be economized. But introducing water-based coolants into high heat ferrous and non-ferrous pyro-metallurgical furnaces runs a high risk of boiling liquid expanding vapor explosion (BLEVE).

[0038] FIG. 1 represents a water-based cooling system 100 in an embodiment of the present invention that is intrinsically safe from BLEVE. A heat transfer fluid mixture 102 comprises water, glycol alcohol, and corrosion inhibitors in a homogeneous solution that are circulated around in a closed loop by a liquid pump 104. The percentage of water used in the heat transfer fluid mixture 102 has both high and low limits. In general, water can in this use can range from 10% to 50%.

[0039] Said another way, the coolant comprises a blended mixture of a single phase organic compound of glycol alcohol, and water, and a corrosion inhibitor, wherein the water is limited to a range of about 10% to 50% by weight. So all of the water is fully absorbed in the glycol with no excess water left to support a BLEVE.

[0040] Glycol is any of a class of organic compounds belonging to the alcohol family. The glycol molecule has two hydroxyl (OH) groups attached to different carbon atoms. The term glycol is often applied to the simplest member of the class, ethylene glycol.

[0041] The minimum percentage of water that can be used is limited by the adverse impacts of increasing viscosity and reduced specific heat that bear on the acquisition and operating costs of liquid pump 104. As viscosity increases, it requires a greater pumping effort and a stronger liquid pump 104 to maintain a minimum coolant velocity 106. And as the specific heat of heat transfer fluid mixture 102 is decreased by diluting the water, the greater will be the pumping effort required of a larger capacity liquid pump 104 to maintain a higher, minimum level coolant velocity 106 that will compensate for the inefficiency.

[0042] In practice, the heat transfer fluid mixture must have a room-temperature viscosity of less than 20 mPa.Math.s. And the heat transfer fluid mixture 102 must have a specific heat greater than 2.3 kJ/kg.Math.K. Otherwise, the minimum requirements for a suitable pump 104 become unreasonable and/or unmanageable.

[0043] The maximum percentage of water that can be used safely is limited by the risks of BLEVE. Short of that threshold, the mixed coolant blend 102 will burn, and not BLEVE, if it escapes from a cooler 108 into a high heat ferrous or non-ferrous pyro-metallurgical furnace 110.

[0044] Intermolecular bond types determine whether two chemicals are miscible, that is, whether they can be mixed together to form a homogeneous solution. Here, the water and glycol in the heat transfer fluid mixture 102 form a homogeneous solution. When two chemicals like water and glycol mix, the bonds holding the molecules of each chemical together must break, and new bonds must form between the two different kinds of molecules. For this to happen, the two must have compatible intermolecular bond types. Water and MEG glycol do. The more nearly equal in strength the two intermolecular bond types are, the greater will be the miscibility of the two chemicals. Usually there is a limit to how much of one chemical can be mixed with another, but in some cases, such as with CH.sub.3OH (MEG) and H.sub.2O (water), there is no limit and any amount of one is miscible in any amount of the other.

[0045] As a consequence, the percentage of water in the heat transfer fluid mixture 102 will have a practical range between 10% and 50%. The optimum percentage of water plus corrosion inhibitors in the heat transfer fluid mixture 102 is generally about 25%. No excess water is left unabsorbed to support a BLEVE. And the water that is absorbed is impeded from BLEVE.

[0046] The heat transfer fluid mixture 102 is circulated in a closed system and pressurized by a pressurization system 112. Typical pressures run 2-7 bar. Raising the pressure inside the closed system raises the boiling point of the heat transfer fluid mixture 102. The minimum boiling point of the heat transfer fluid mixture 102 under pressure should be no less than 175 C.

[0047] A filter 114 is used to remove contaminants from the heat transfer fluid mixture 102 as it circulates. Otherwise, the contaminants can interfere with the coolant's efficiency. The coolants here are under very high heat loads.

[0048] A chiller or heat exchanger 120 is used to remove and dispose of the heat gained by the heat transfer fluid mixture 102 in circulation, e.g., a cooler 108 inside furnace 110. Such chillers and heat exchangers are conventional.

[0049] FIG. 1 shows cooler 108 only in general. In particular, such can be a panel cooler, or a cooling jacket for a top submerged lance (TSL), torch, or tuyere. All of these applications will bring water-based liquid coolants into close proximity with a pyro-metallurgical furnace 110 and all must be intrinsically safe from BLEVE.

[0050] FIG. 2 represents an oxygen injection system for a high heat ferrous or non-ferrous pyro-metallurgical furnace, herein referred to by the general reference numeral 200. Such is water cooled and intrinsically safe from BLEVE. Oxygen injection system 200 circulates a heat transfer fluid 202 that is a homogenous mixture of water and one of monoethylene glycol (MEG), diethylene glycol (DEG), or polyethylene glycol (PEG).

[0051] These glycols, like all low-molecular-weight alcohols, are soluble in all proportions in water. The heat transfer fluid 202 further includes corrosion inhibitors. MEG is preferred because it is so completely miscible with water. But its toxicity might not make its use a first choice.

[0052] Despite its being an organic compound, MEG is quite polar because of the differing electro negativities of the oxygen and carbon atoms it contains. Water is also as polar because of the different electro negativities of hydrogen and oxygen. Thus with both being very polar, they are excellent solvents for one another.

[0053] Dow Chemical Company DOWTHERM SR-1 and DOWTHERM 2000 inhibited ethylene glycol-based heat transfer fluids are useful herein, and such already include corrosion inhibitors. These inhibitors prevent corrosion of metals in two ways. First, they passivate the metal surfaces, and react with them to prevent acids from attacking. A passivation process results that does not foul the internal heat transfer surfaces. Conventional inhibitors, in contrast, usually coat heat transfer surfaces with a thick silicate gel that gets in the way of good heat transfer. Second, the inhibitors in DOWTHERM fluids buffer acids that form as a result of glycol oxidation. (All glycols produce organic acids as degradation products.) Such degradation will accelerate in the presence of oxygen and/or heat. If left in solution, such acids lower the pH and will contribute to corrosion. The formulated inhibitors used in DOWTHERM fluids neutralize such acids.

[0054] Ethylene glycol (MEG) disrupts hydrogen bonding when dissolved in water. Thus, the use of ethylene glycol not only depresses the freezing point, but also elevates the boiling point such that the operating range for the heat-transfer fluid mixture is broadened on both ends of the temperature scale. Ethylene glycol alone has a freezing point of 8.6 F. (13 C.) and a boiling point of 388 F. (198 C.). But, ethylene glycol is toxic. DEG is not so toxic.

[0055] Heat transfer fluid mixture 202 has these elements in a blend in a combination that expresses simultaneous predetermined ranges of viscosity, and of specific heat. The heat transfer fluid mixture 202 is intrinsically incapable of a boiling liquid expanding vapor explosion (BLEVE) by including less than 50% by volume as water, or even less as empirically determined as appropriate in specific applications.

[0056] Water inside a pyro-metallurgical furnace can be catastrophic in two ways. First it can be the fuel that gets triggered to produce a BLEVE. And second, the refractory linings can be severely damaged by water absorption. It is therefore an object of the present invention to cool oxygen lances with liquids that cannot BLEVE, and with liquids that will not damage refractory.

[0057] Oxygen injection system 200 further comprises a cooling system 204 that extracts and disposes of heat from the heat transfer fluid mixture and that provides liquid pumping for minimum circulation velocities that preclude film boiling of the heat transfer fluid mixture. A cooling plant 206 can be a part of the general cooling of the pyro-metallurgical furnace that already exists. A heat exchanger 208 provides the isolation needed to maintain the heat transfer fluid mixture 202 in its required composition and purity. A pump 210 circulates the heat transfer fluid mixture 202. But the flow velocity achieved depends on where it's being measured because the cross sectional area and temperatures at various points vary widely along the path of the circuit.

[0058] However, at no point should the capacity of pump 210 be so insufficient as to maintain a velocity of the heat transfer fluid mixture that will prevent film boiling. At the hottest points in the circuit, that will typically be a minimum of 2.0 meters per second.

[0059] An oxygen lance 212 has a protective liquid cooled jacket 214 that extends its full length to a tip. The protective liquid cooled jacket 214 receives the heat transfer fluid mixture 202 from the cooling system 204. It returns a hot heat transfer fluid mixture. The cooling here of oxygen lance 212 will stop any tendency of thermal curving by precluding uneven heating of oxygen lance 212 during operation. To do that, the liquid cooled jacket 214 may include swirlers and restrictors, flows that maintain a minimum velocity flow at critical points to prevent film boiling. Oxygen lance 212 has as its basic purpose to provide for the injection of an oxygen flow 218 into a pyro-metallurgical furnace 220.

[0060] Gas injection system 200 also uses a heat transfer fluid mixture 202 that has a predetermined viscosity less than 20 mPa.Math.s, and a predetermined specific heat greater than 2.3 kJ/kg.Math.K. These two limits allow economical choices to be made for pump 210.

[0061] Mechanisms for swirling heat transfer fluids and for making tip replacements possible for lances are conventional and plentiful, and are therefore not necessary to describe in particular detail here. Both would of course enhance and improve most embodiments of the present invention.

[0062] FIG. 3 represents an oxygen injection lance 300 in an embodiment of the present invention that can be a part of cooling system 100 (FIG. 1). In a top submerged lance (TSL) configuration, oxygen injection lance 300 injects a supply of oxygen 302 down a conduit 304 down to, and out of, a copper lance tip 306. A supplemental fuel is received at a fuel manifold 310 connected to a fuel jacket 312 that encases oxygen conduit 304. The supplemental fuel joins and mixes with the oxygen escaping at the copper TSL tip 306 below.

[0063] A heat transfer fluid inflow manifold 314 forms an annular plumbing connection with a heat transfer fluid supply jacket 316. A heat transfer fluid mixture is directed under pumping pressure down to the copper lance tip 306 where it turns and flows back up outside in a liquid cooling jacket 318 to a heat transfer fluid outflow manifold 320. The velocity of the heat transfer fluid mixture turning back up inside the metal lance tip 306 is critical. The intense heat from submerging the metal TSL tip 306 in the furnace bath will provoke gas bubble formation and film boiling. Both can be combatted with high velocities for the heat transfer fluid. The specific heat and viscosity of the heat transfer fluid will determine the required velocity to prevent film boiling at a specific heat flux. The specific heat of the heat transfer fluid mixture will thus be prevented from degrading due to boil gases mixing in.

[0064] The down flowing and exiting oxygen and supplemental fuel assist in overall cooling of the copper lance tip 306. Pre-chilling them both is therefore helpful.

[0065] Top submerged lance (TSL) types of pyro-metallurgical furnaces smelt non-ferrous metals from ore sulphides that will burn and self generate heat with injected oxygen. Herein, we describe embodiments of the present invention that are applied as improvements to specific commercial products like the Glencore ISASMELT, Outotec AUSMELT, and other commercially marketed TSL furnaces as exemplars. A typical example is that of FIG. 4.

[0066] Top submerged lances present a particular challenge, addressed here, in that uneven cooling and the resulting heat excursions can cause them to both curve and to wear too fast. Typically, a portion of any material fed in above the bath will be lost into the off-gas stream.

[0067] The MEG glycol we prefer here is highly hygroscopic, and most of the water vapor in the gas is absorbed by the glycol. The rich glycol clutches the absorbed water.

[0068] Lean, water-free glycol confiscates free water from the coolant by physical absorption. Absorption is a process that may be chemical (reactive) or physical (non-reactive). Absorption occurs when a substance is chemically integrated into another.

[0069] Therefore, the amount of water in the coolant mixture should not usually exceed the glycol in the same coolant mixture. In conventional applications of glycol as a desiccant, the rich glycol with absorbed water is dehydrated in a rejuvenation system. But in embodiments of the present invention, the water is left in the rich glycol state for the water's beneficial contributions to lowered viscosity and high specific heat. At the same time, there can be no unabsorbed water left in the coolant to BLEVE. Since the glycol used functions as a desiccant, any random water that does get into the coolant system, or even condense there, will be physically absorbed almost immediately.

[0070] FIG. 4 represents an ISASMELT-type furnace 400 as a kind of TSL vessel with an improved liquid cooled lance embodiment of the present invention, herein referred to by the general reference numeral 402.

[0071] Most of the energy needed here to heat and melt feed materials like chalcopyrite (CuFeS.sub.2), and other sulfide of copper and iron minerals, is derived from a reaction of oxygen forced down inside lance 402, with the sulfur fuel in a feed ore concentrate 404. Supplemental energy fuel 406 like coal, coke, petroleum coke, oil, natural gas, and other fuels are also injected down inside lance 402 to make up any fuel deficiencies. Solid, supplemental fuel is also sometimes added through the top of furnace 400, e.g., in with the feed ore concentrate 404.

[0072] TSL vessels that run with an immersed lance 402 universally experience high wear to the tip. Some tips may even simply burn off. So conventional lances are often constructed with replaceable tips to keep maintenance costs down. Other types of oxygen lances, like in basic oxygen furnaces, are run with their tips three hundred millimeters above the surface and provide a supersonic injection of oxygen and fuel that punches through the surface into the matte and slag floating on liquid metal.

[0073] The optimum depth to operate lance 402 is normally maintained with controls based on the tip pressure. Operators must also monitor the matte grade and bath temperature. Too high, and there is a risk of the bath foaming, and downstream processing in the converters will be more difficult. Too low, and refractory wear will increase, in particular downstream in the launders. The TSL is a chemical reactor with a relatively short residence, in the order of about 15 minutes. Measurement and sampling of the reagents (feed, oxygen) is therefore critical. Operators must monitor bath temperature and matte grade. A drop in bath temperature can indicate that the bath may be over oxidized and could foam.

[0074] FIG. 5 represents an improved top submerged lance furnace 500, e.g., in schematic form. A steel containment vessel 502 is internally lined with a refractory. Such refractory may be cooled by liquid cooled copper coolers between the steel containment vessel and the refractory lining. Or, the copper coolers may have a hot face pattern to retain slag or accretions, metal or refractory brick inserts tiled tightly together on the hot faces.

[0075] A TSL 504 includes a cooling jacket 506. These combine to shoot a jet of oxygen/fuel 508 into a bath 510 for reaction. A bath surface 512 is subject to violent sloshing that varies in intensity and frequency with the magnitude of the exothermic reactions ongoing in the bath 510. The measurable pressure of a mixture of process gases 514 will also increase with increasing reactions ongoing in the bath 510. The sloshing and agitation of the heavy materials in the bath 510 will also produce observable vibrations in the vessel 502. And, of course, the matte grade will vary according to the reactions ongoing in the bath 510.

[0076] In one embodiment of the present invention, the tip of TSL 504 is stood off from an average of bath surface 512 by up to three hundred millimeters (300 mm), in others it is submerged into bath 510.

[0077] Although particular embodiments of the present invention have been described and illustrated, such is not intended to limit the invention. Modifications and changes will no doubt become apparent to those skilled in the art, and it is intended that the invention only be limited by the scope of the appended claims.