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WO1992014849A1 - Procede et appareil de degraissage des matieres de rebut consistant en pailles de laminage - Google Patents

Procede et appareil de degraissage des matieres de rebut consistant en pailles de laminage Download PDF

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Publication number
WO1992014849A1
WO1992014849A1 PCT/US1992/001472 US9201472W WO9214849A1 WO 1992014849 A1 WO1992014849 A1 WO 1992014849A1 US 9201472 W US9201472 W US 9201472W WO 9214849 A1 WO9214849 A1 WO 9214849A1
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WO
WIPO (PCT)
Prior art keywords
mill scale
oil
oily
treating solution
oiled
Prior art date
Application number
PCT/US1992/001472
Other languages
English (en)
Inventor
Surendra K. Mishra
John J. Schubert
Original Assignee
Tetra Technologies, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tetra Technologies, Inc. filed Critical Tetra Technologies, Inc.
Publication of WO1992014849A1 publication Critical patent/WO1992014849A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/005—Preliminary treatment of scrap
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B01D17/04—Breaking emulsions
    • B01D17/047—Breaking emulsions with separation aids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/12—Auxiliary equipment particularly adapted for use with liquid-separating apparatus, e.g. control circuits
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates generally to resource recovery. Though this process can have applications to other wastes, it has particular application to 10 the de-oiling of mill scale waste materials.
  • Mill scale wastes are metal oxides formed in hot rolling operations in the aluminum and steel industry. The principal application of this technology
  • mill scale waste includes oxides of iron, FeO, Fe 2 0 3 , and Fe 3 0 4 .
  • layers of mill scale are continually formed on the surface of steel slabs, sheets, and bars when exposed to air at elevated temperatures.
  • the mill scale layers are typically removed by cooling and cleaning the steel with a high pressure water spray, then collected
  • oil dispersed oily and hydrophobic materials
  • oil-contaminated mill scale materials oil-contaminated mill scale materials.
  • the oil may come from a number of sources, such as hydraulic fluid leaking from steel-making equipment, oils from milling operations, and inadvertent dumping of oils and
  • the dispersed oil may to some extent be removed from the wastewater by skimming the surface of the water from a settling tank; however, a significant amount of the oil remains absorbed on the mill scale.
  • the mill scale has value as a recyclable material.
  • the mill scale may be used as resource materials in sintering operations. But the sintering of mill scale having high levels of oil contamination is generally avoided because of unacceptable hydrocarbon emissions and equipment fouling. Thus, a need exists for removing sufficient amounts of the oil from the mill scale to make it useful in sintering and other steel manufacturing operations.
  • Some systems employ organic treating agents such as soaps or surfactants.
  • surfactants must be removed before the treating solution can be recycled; otherwise, continuous monitoring of the system to ensure the appropriate surfactant level would be required.
  • separation of the organic materials from the treating solution requires expensive equipment and constant replenishing of surfactant, often adding tremendous costs to the overall operation.
  • the invention relates to resource recovery and specifically to the recovery of mill scale waste materials. More particularly, the invention relates to a method and apparatus for treating and recovering mill scale materials comprising contacting the mill scale with a recyclable inorganic treating dispersion, then recovering the de-oiled mill scale.
  • the inorganic treating dispersion is an aqueous solution or suspension comprising an inorganic treating agent. Throughout the text, solution will be referred to mean a dispersion.
  • the inorganic treating solution includes a pH modifier selected from the group consisting of potassium hydroxide, sodium hydroxide, calcium oxide, calcium hydroxide, sodium carbonate, and potassium carbonate and a dispersant selected from the group consisting of sodium silicate, potassium silicate, sodium phosphate and potassium phosphate.
  • a pH modifier selected from the group consisting of potassium hydroxide, sodium hydroxide, calcium oxide, calcium hydroxide, sodium carbonate, and potassium carbonate
  • a dispersant selected from the group consisting of sodium silicate, potassium silicate, sodium phosphate and potassium phosphate.
  • the invention comprises a closed loop wastewater treatment system.
  • the treating solution, mixed with an oily wastewater/mill scale mixture, is continually recycled or recirculated through the system without having to add additional water.
  • the method includes a recycled or recirculated inorganic treatment solution capable of removing significant levels of oil from the mill scale particles, to the level such that the mill scale can be reused.
  • a particular advantage of the invention is that while the treating agent concentration in the treating solution may be high, e.g., about 10 percent by weight (for heavy oil contamination), the treating solution may also be effective at low treating agent concentrations, e.g., down to about 0.05 percent by weight (for light oil contamination).
  • a preferred embodiment of the invention comprises separate classification, treatment, recycling and recirculation steps.
  • the mill scale materials are classified according to size into an oversized coarse particle component and an undersized fine particle component.
  • the treating step comprises contacting each component separately with the treating solution, which preferably consists of inorganic treating agents and more preferably comprises effective amounts of an inorganic pH-modifier and inorganic dispersant, ranging from about 0.05 percent by weight (for light oil contamination) to about 10 percent by weight (for heavy oil contamination).
  • the treating solution may be heated from ambient temperature to boiling, with higher temperatures within the range of 160°F to 200°F being preferred.
  • the temperature for the treating solution is dependent upon the level of oil removal required and the type and oxidation level of the oil. Operating at a higher temperature will improve the overall rate of oil removal from the mill scale waste.
  • the coarse particles are treated after classification, or as required, which may need a one stage reactor, depending on the oil content and the type of oil present.
  • the fine oily mill scale particles may be stirred vigorously in a treatment vessel containing the treating solution, followed by separation of the de-oiled fine mill scale particles from the treating solution.
  • the same procedure is followed except the de-oiled fine mill scale particles are rinsed after stirring but before the solid-liquid separation.
  • it is essential to repeat this fine particle treatment and solids-liquid separation several times.
  • Treatment vessels, where the oily mill scale is contacted with the treating solution, and their corresponding solid-liquid separators are connected in a cascading series as shown in Figures 1 and 2.
  • Substantial oil removal in the steel industry depends upon the makeup of the sinter plant feed and the type of air pollution control facility used. Typically, for dry systems, the oil limit is about 0.1 percent by weight and for wet systems, the oil limit is about 1.0 percent by weight. Nevertheless, higher oil-containing mill scale waste can be blended appropriately with cleaner mill scale waste as feed to the sinter plant, so long as the final feed meets the operational specifications of the sinter plant.
  • Separation of both fine and coarse de-oiled mill scale particles from the treating solution may be accomplished with a solids-liquid separation step including filtering or hydrocycloning.
  • the underflow consists of the treated fine mill particles, while the effluent, or specifically, the overflow, consists of the treating solution, containing oil, to be recycled or recirculated.
  • the overflow consists of the mill particles, while the effluent, or specifically, the filtrate consists of the treating solution, containing oil, to be recycled or recirculated.
  • an organic flocculant such as Clearfloc 751 or Jayfloc 911 should be added to the treating solution after the treatment stages to remove trace amounts of oil and solids. But in a preferred and alternate embodiment, substantially no organic ingredients are present during the mill scale treatment stages.
  • the remaining wastewater effluent contains treatment agents as well as microscopic oil droplets and ultra-fine mill scale.
  • An important aspect of the process is the recycle or recirculation step of the treating solution.
  • Recycle of the treating solution comprises removing sufficient oil from the wastewater effluent to provide a treating solution in condition for reuse, then recycling the treating solution back to contact the oily mill scale waste.
  • one embodiment of the invention recirculates a portion of the treating solution to contact the oily mill scale before recycling.
  • Recirculating the treating solution comprises contacting it with "upstream" fine oil mill scale which has a higher content of oil than the fine mill scale just contacted by the treating solution.
  • the recycle step further comprises contacting the effluent with a flocculant in an amount sufficient to remove oil and ultra-fine solids from the effluent.
  • the flocculant is a polymer preferably comprising a cationic quarternized amine having a molecular weight in the range of 50,000 to 40,000,000 and charge density in the range of 5 to 100%, preferably quarternized for high pH (>11.0) applications.
  • the success of the flocculant used is evaluated on the basis of total suspended solids and the oil content of the resultant clarified solution.
  • the aggregated or flocculated material (“floe") is separated from the clarified effluent.
  • the effluent is filtered through a deep bed sand filter to remove residual flocculant from the clarified effluent.
  • the success of the flocculant used is evaluated on the basis of total suspended solids and the oil content of the resultant clarified solution.
  • the concentration of any leftover flocculant in the effluent may then be reduced, preferably using an oxidizing agent, to produce a substantially inorganic treating solution for recycling.
  • the oxidizing agent comprises hydrogen peroxide, ozone, permanganate, hypobromous acid, chlorine dioxide, hypochlorous acid, hypoiodous acid, or a member selected from the group consisting of chlorine, bromine and iodine.
  • Figure 1 is a schematic flowsheet of an alternate embodiment of the present invention.
  • Figure 2 is a schematic flowsheet of a preferred embodiment of the present invention.
  • this invention relates to a method for recovering oil-contaminated mill scale solids comprising treating the oily mill scale with an inorganic treating solution to remove oil from the surfaces of the mill scale.
  • oil is removed from the resulting wastewater effluent to provide a reusable treating solution which may then be recycled back to contact additional oily mill scale.
  • FIG. 1 This embodiment comprises classifying the mill scale into fine and coarse particle components; removing the various types of oil and lubricants from the fine and coarse mill scale materials in the treatment stages; separating the de-oiled mill scale from the liquid; and recovering the de-oiled mill scale for use in sintering operations.
  • an improved recycling stage is provided which includes removing oil from the wastewater effluent (hereinafter "effluent") to provide a substantially de-oiled effluent stream comprising the inorganic treating solution and recycling the treatment solution back for additional mill scale treatment.
  • the recycling stage includes a flocculation step in which any remaining microscopic oil in the effluent may be contacted with a small amount of an organic flocculant to remove the oil. The flocculant in the effluent is degraded from the effluent to obtain a substantially inorganic treating solution which may be recycled back to the treatment stage(s) and contacted with the oily mill scale.
  • the treating solution in an aqueous inorganic solution comprising an alkali treating agent which modifies the pH of the mill scale particle surfaces and a dispersant to modify the mill scale surface and facilitate oil removal.
  • an alkali treating agent which modifies the pH of the mill scale particle surfaces and a dispersant to modify the mill scale surface and facilitate oil removal.
  • the treating solution of a specific embodiment of the present invention may contain a low concentration of treating agents, e.g., below 1 or 2 percent and in some cases as low as 0.1 percent by weight, and still be effective. Thus, only periodic replenishment of the treating agents is necessary.
  • the treating agent comprises a separate pH- modifier such as sodium hydroxide together with a separate dispersant such as a sodium silicate.
  • the treating solution comprises sufficient pH-modifier to alter the pH of the mill scale surface to a desired level.
  • the pH-modifier is an alkali or base which raises the pH of the treating solution or slurry.
  • the pH of the fine mill scale surfaces may be approximated by measuring the pH of the slurry (often referred to as "bulk pH"), while the pH of the coarse mill scale surfaces may be approximated by measuring the pH of the treating solution rinsing stream in the treatment rinser.
  • the pH-modifier preferably comprises potassium hydroxide or sodium hydroxide.
  • Other pH-modifiers which may also be used include sodium chloride, sodium or potassium bicarbonate, and magnesium hydroxide.
  • Monovalent pH-modifiers such as sodium hydroxide are preferred because, although divalent pH-modifiers may be used, they often tend to agglomerate the mill scale fine particles.
  • the pH-modifier should be added in an amount sufficient to obtain a pH from 7 to 9 for light oil contaminants and 9 to 12.5 for heavier oil contaminants. Thus, lower concentrations of pH-modifiers are generally required for light oil contamination than for heavy oil contamination.
  • Light oils are defined as those with relatively low viscosity and high vapor pressure, such as hydrocarbons having carbon chain lengths of 15 or less. Heavier oil contaminants are hydrocarbons with carbon chain lengths greater than 15.
  • the mill scale particles are classified based on the type of oil contamination (e.g., light oil versus heavy oil contamination) prior to size classification. In such an embodiment, mill scale contaminated with light oils are directed to one collection device (not shown) while mill scale contaminated with heavier oils are directed to another collection device (not shown). Each component may then be size-classified and/or treated separately as discussed below.
  • the dispersant of this invention broadly includes any surface active agent which promotes separation of the mill scale particles, and may include polymeric electrolytes or polyphosphates.
  • the function of the dispersant is to modify the surface of the mill scale materials to facilitate removal of oil and lubricants during the treatment stages.
  • the dispersant of the present invention is inorganic and preferably comprises a silicate or phosphate of sodium or potassium. More preferably, the dispersant comprises sodium silicate.
  • the treating solution comprises sodium hydroxide in addition to the sodium silicate dispersant.
  • a treating solution consisting of water and sodium silicate may under certain circumstances constitute a treating solution which both modifies pH and the surfaces of the mill scale to facilitate oil removal.
  • FIGURE 1 A first figure.
  • the mill scale materials are fed to a classifying stage which comprises classifying or segregating the mill scale feed materials into a "coarse” component and a "fines” component.
  • the mill scale feed materials are passed over a size separator, e.g., a classifying screen 11, which mechanically classifies the mill scale particles into overflow "coarse” particles and underflow "fine” particles.
  • a stream of recycled treating solution may be directed downward onto the classifying screen 11 , along line 13.
  • hot water (not shown) may be directed downward onto the classifying screen 11.
  • the overflow coarse particles are then gravity fed through line 15 to the treatment rinser 19.
  • the coarse particles should preferably be 8-mesh or greater with the fine particles being smaller than 8-mesh. More broadly, however, the division between “coarse” and “fine” particles should vary from case to case depending on the particle size distribution of a particular oily mill scale feed, the type and extent of oil contamination, and the desired level of oil removal. It has been discovered that finer mill scale particles have a proportionately higher amount of oil contamination relative to their particle weight than do the coarser mill scale particles. A typical oil and grease distribution is shown in Table 1. Therefore, in accordance with this invention, it is generally desirable to treat the fine particles with greater amounts of treating agents for longer contact periods than the coarse particles.
  • each component is separately contacted with the treating solution in a variety of treating steps.
  • the fines component is stirred vigorously in a vessel containing the treating solution, followed by rinsing and separation of the de-oiled fine mill scale particles from the treating solution.
  • the coarse component is treated by spraying the component with treating solution, then separating the de-oiled coarse mill scale from the treating solution.
  • the de-oiled mill scale should be separated from the treating solution with a solids-liquid separation step including filtering or hydrocycloning.
  • the resulting liquid or effluent comprises water, oil, the inorganic treating agent (e.g., sodium hydroxide and/or sodium silicate), and ultra-fine mill scale particulates.
  • the inorganic treating agent e.g., sodium hydroxide and/or sodium silicate
  • the oily coarse mill scale materials are preferably rinsed with a treating solution at treatment rinser 19.
  • the treatment rinser 19 includes means for contacting the mill scale with a treating solution stream, e.g., a spraying device 23.
  • the treating solution stream is sent from the reclamation vessel 125 along line 27 and then connecting to line 25.
  • treatment rinser 19 contains a solids-liquid separator 21, including a vacuum horizontal belt filter or hydrocyclone, to separate the solids from the liquid after contacting the mill scale with the treating solution.
  • the spraying device, belt filter, and hydrocyclone are themselves conventional devices, are recognized by persons skilled in the art, and will not be described herein in detail.
  • the treating solution and water may be heated from ambient temperature to boiling, with higher temperatures within the range of 160°F to 200°F being preferred.
  • the temperature for the treating solution is dependent upon the level of oil removal required and the type and oxidation level of the oil. Operating at a higher temperature will improve the overall rate of oil removal from the mill scale waste.
  • the temperature can be monitored by placing a sensor above the reclamation vessel 125.
  • the de-oiled coarse mill scale may be recovered as resource material pumped through line 29.
  • the recovered coarse mill scale is then dried and directed to a sintering plant, wherein it may be heated at temperatures sufficiently high to cause sintering.
  • the coarse mill scale may be sintered separately, it may also be desirable to mix the de-oiled coarse mill scale with de-oiled fine mill scale, prior to sintering.
  • the filtrate from the treatment rinser 19, comprising treating agent, water and oil, is directed to settling tank 81 along line 31.
  • the fines mill scale (preferably less than
  • the treatment vessel 33 which includes a slurry of treating solution and preferably the recycled treating solution directed from the classifying screen 11.
  • the fines mill scale feed materials are preferably directed along line 17, as underflow from classifying screen 11 to treatment vessel 33 along with water or recirculating treating solution to form the slurry.
  • the treatment vessel 33 includes a stirrer 35 and heating means, e.g., a heating coil or steam (indicated by arrows), to increase the temperature of the slurry.
  • the .temperatures of the slurry may range from ambient to boiling, with higher temperatures within the range of 160°F to 200°F being preferred.
  • the temperature for the treating solution is dependent upon the level of oil removal required and the type and oxidation level of the oil.
  • the temperature can be controlled by placing appropriate sensors over the treatment vessels 33, 51, and 67. Additionally, the temperature in the reclamation vessel 125 is monitored with a temperature sensor. Recycled treating solution from reclamation vessel 125 may be directed on line 27 to treatment vessel 33. Preferably, a constant stream of treating solution is recycled to treatment vessel 33 from reclamation vessel 125 with treating solution also directed optionally on lines 41, 63, and 71 to other treatment rinsers 45, 57, and 73 respectively.
  • chemicals such as sodium hydroxide and sodium silicate are added to the reclamation vessel 125 either manually or through dispensers 127 and 129, to make the inorganic treating solution comprise a pH-modifier and dispersant in the desired amounts.
  • the pH is monitored by testing the recycled solution within reclamation vessel 125.
  • Dispensers 127 and 129 may include any means for introducing the chemicals separately into the recycled treating solution.
  • the chemicals are preferably dispensed in a controlled fashion, for example, from chemical metering pipes through pipes or tubes. Treatment chemicals may also be added to the solution at virtually any point in the system; to one of the treatment vessels 33, 51 or 67, or the treatment rinsers 45, 57 or 73.
  • the slurry in treatment vessel 33 is stirred vigorously using stirrer 35 for a time sufficient to remove oily material from the surfaces of the mill scale.
  • the stirring time can be varied depending on the type and amount of oil contamination, and should be determined experimentally.
  • the fines are removed from treatment vessel 33 and directed on line 37 to fines treatment rinser 45, which may be designed in a manner similar to that of coarse mill scale treatment rinser 19.
  • treatment rinser 45 comprises a spraying device 43 for dispensing a stream of treating solution from line 41 onto the fine mill scale and a solids-liquid separator 29, e.g., a vacuum belt filter or hydrocyclone, for separating the liquid from the mill scale and preferably for removing as much treating solution and oil from the mill scale as possible.
  • a solids-liquid separator e.g., a vacuum belt filter or hydrocyclone
  • the fines may be rinsed with the treating solution prior to drying under a vacuum.
  • treatment of the mill scale fines is repeated several times using treatment vessels 51 and 67, each followed by rinsing and separation in treatment rinsers 57 and 73, to produce the desired removal of oil contamination, each yielding a de-oiled fine particle stream and an oily filtrate stream.
  • the rinsing stage may be followed by conventional means of solids-liquid separation, including treatment with a dewatering screen, a vacuum or gravity drained belt, or a centrifuge.
  • a preferred solid-liquid separator is a hydrocyclone.
  • the recovered de- oiled mill scale (both coarse and fines component) has less than 0.1 percent by weight oil contamination.
  • it is considered essential for reducing oil contamination to below about 0.1 percent to include several stages as shown in Figure 1. Each stage includes the steps of treating the mill scale by contacting it with treatment solution, then performing solids-liquid separation to remove the treatment solution with oil, leaving a less oily mill scale.
  • the overflow from treatment rinser 45 is sent through line 47 to the treatment vessel 51, while the filtrate from treatment rinser 45 travels through line 49, which connects to line 31 and ends in the settling tank 81.
  • the treating solution from reclamation vessel 125 is sent into treatment vessel 51 through line 53.
  • treatment vessel 51 After stirring, all the contents of treatment vessel 51 are sent, via line 55, to treatment rinser 57. There, the mill scale are sprayed with the treating solution from reclamation vessel 125 which is sent along line 63.
  • the overflow from treatment rinser 57 is pumped along line 61 to treatment vessel 67.
  • the contents of treatment vessel 67 are contacted with the treating solution from reclamation vessel 125 along line 65.
  • the filtrate from treatment rinser 57 is sent through line 59 connecting with line 31 and ending in the settling tank 81.
  • Another aspect of the invention involves the recycling or recirculation stages.
  • the importance of a recycling system stems from both environmental and economic factors.
  • a mill scale treatment system which produces wastewater effluent creates a need for additional treatment or disposal facilities to handle contaminated liquids.
  • disposing of the effluent creates a need to replenish the supply of treatment chemicals.
  • this invention preferably includes a recycling stage for treating the liquids from the treatment stages.
  • the recycling stages comprise directing the filtrate from the coarse particle treatment rinser 19 through line 31 and from one or all of the fine particle treatment rinsers 45, 57 and 73 via lines 49, 59, and 77 respectively, to settling tank 81.
  • the system is a "closed-loop" system, wherein all the filtrate from the treating stages is directed to the settling tank 81 and continuously recycled back to the treatment stages.
  • the effluent composed mainly of treating solution and oil, as well as any other material not separated and recovered with the mill scale, is permitted to settle into layers, e.g., a layer comprising treating solution and a surface layer of oil.
  • oil/grease content is determined on a dry weight basis, and the following ranges are for example only and do not dictate the requirements of the invention.
  • a very high oil/grease content would be greater than 2 percent by weight.
  • a high oil /grease content would be 0.4 - 0.5 percent by weight.
  • a marginal oil/ grease content would be 0.15 percent by weight.
  • a clean oil/grease content would be ⁇ 0.1 percent by weight.
  • valves 79 and 89 will be closed and the particles will travel along line 85, connect with line 87 and get sent to treatment rinser 73 to be recovered as coarse mill scale.
  • valves 79 and 86 and to open valve 89 to direct these solids through line 91 into treatment vessel 93 wherein an oxidizing agent such as ozone or peroxide may be added.
  • the oxidizing agent degrades absorbed oil from the surfaces of the oily ultra fine particles.
  • valves 89 and 86 will be closed. The material will go through valve 79 via line 83 and will be returned to treatment vessel 33 for further treatment. If the oil/grease content is very high, it may be desirable to close valves 79 and 86 and to open valve 89 to direct these solids through line 91 into treatment vessel 93 for storage until it is removed for disposal or outside processing beyond the scope of this invention.
  • the solids in treatment vessel 93 may be separated from any remaining oily phase and treating solution by allowing the solids to settle at bottom.
  • the oily phase may be removed, e.g., by skimming, from treatment vessel 93 through line 95 and collected or disposed of.
  • the remaining materials with a high oil/ grease content may be directed back to treatment vessel 33 through line 97 (which connects to line 137) for further treatment. If the materials have a low oil/ grease content they will be sent to treatment rinser 73 through line 99 to be blended with de-oiled mill scale.
  • the effluent from settling tank 81 which comprises oil and treating solution, is preferably directed over weir 101 to skimming vessel 103, where any oily phase may be skimmed from the surface and directed through line 105 which connects with line 109 for collection or disposal.
  • This oil may be combined with extracted oil from extractor vessel 135 which is also sent through line 109.
  • the floes from settling tank 115 are preferably treated with an oxidizing agent (e.g., peroxide or ozone) or a solvent (e.g. diesel oil or alkyl amine) as shown by arrow 143.
  • the treated floes may be directed to a gravity separator (not shown) to remove the oil.
  • the remaining solids-liquid phase if it has an acceptably low level of oil and grease, may be directed through line 87 to one of the treating rinsers, e.g., treatment rinser 73. If the level of oil and grease is unacceptably high, valve 136 may be opened and the solid-liquid phase may be directed through line 137 back to the slurry in treatment vessel 33.
  • the remaining effluent in sl mming vessel 103 may then be directed through line 107 to a means for removing additional oil which preferably comprises a flocculation vessel 111, which preferably includes a stirrer 35.
  • a flocculation vessel 111 the effluent is preferably contacted with a polymer flocculant as shown by arrow 139.
  • the polymer flocculant preferably comprises a high molecular weight cationic quaternized polymer having a molecular weight in the range of 50,000 to 40,000,000.
  • the flocculant is preferably mixed with the effluent in a sufficient amount and for a sufficient time.
  • An especially preferred flocculant is a quaternized amine cationic polymer having a charge density in the range of 5 to 100%.
  • Clearfloc 751 sold by Clearwater, Inc., Pittsburgh, Pa.
  • Jayfloc 911 Cationic Flocculant sold by Callaway Chemical Company, Columbus, Georgia.
  • Jayfloc 911 Cationic Flocculant is an extremely high molecular weight, high charge density cationic emulsion polymer.
  • Clearfloc 751 is a high molecular weight, very high charge density cationic polyacrylamide.
  • the product is supplied as a low viscosity water-in-oil emulsion and it generally performs in the pH range of 2.5 to 12.5.
  • Polymer addition is monitored using a streaming current detector, preferably a detector by Milton Roy.
  • This on-line streaming current measurement device measures the charge density on the particles. If the charge density is high, more polymer is added. Similarly, if the charge density is low, less polymer is added.
  • the Milton Roy coagulant control center is an on-line electrokinetic charge analyzer with measuring, recording and control functions. It is the only on-line instrument which directly measures the result of coagulation addition by instantaneously measuring the electric current is generated.
  • One monitor would be placed on line 107, before the polymer is added (at arrow 139).
  • a second monitor would be placed on line 123, after the hydrogen peroxide is added, to ensure the polymer has been destroyed. The second monitor would detect the charge, thus if the particles are more negatively charged then the polymer has been destroyed.
  • the effluent is directed through line 113, to a secondary settling tank 115.
  • the flocculated effluent is separated, with the clarified effluent in the upper layer being recovered through line 117, and the aggregated solid and oil fraction being directed through line 133 to extractor vessel 135.
  • the effluent should be filtered through a deep bed sand filter 119.
  • the filtered effluent traveling along line 120, is treated in a final treatment vessel 121 by mixing it with an oxidizing agent, e.g., peroxide or ozone, as shown by arrow 141. If insubstantial amounts of flocculant remain in the clarified effluent, the effluent in stream 117 may be directed immediately to treatment vessel 121, bypassing sand filter 119.
  • the recycle stream 123 preferably comprises aqueous inorganic treating solution in condition for recirculating back to reclamation vessel 125, where either water or a pH modifier and/or dispersant may be added as necessary to the recycled solution (through lines 127, 129,and 131, respectively) to obtain the desired composition of treating solution for use in any one of the previously described treating steps.
  • the pH is monitored by testing the recycled solution from within the reclamation vessel 125.
  • the process begins with a classifying stage where the mill scale feed materials are separated into a "coarse” component and a "fine” component.
  • the mill scale feed materials are passed over a size separator, e.g., a classifying screen 203, desirably of 8-mesh, which mechanically classifies the mill scale particles into overflow "coarse” particles and underflow "fine” particles.
  • a stream of treating solution travelling along line 201 is directed downward onto the screen 203 to push the "fine” particles through the screen into treatment vessel 221, while the "coarse” particles are sent to treatment rinser 207.
  • water (not shown) may be directed downward onto screen 203.1n the illustrated embodiment, coarse particles are 8-mesh or greater, and fine particles are smaller than 8-mesh.
  • the mesh size used to separate "coarse” and “fine” particles may vary. The factors affecting this variation are the particle size distribution of a particular oily mill scale feed, the type and extent of oil contamination, and the desired level of oil removal.
  • the mill scale classified as "coarse” by screen 203 is separately contacted with the treating solution in a variety of treating steps.
  • the coarse component is treated by spraying it with a treating solution from the plant's recycled treating solution, and then separating the de-oiled coarse mill scale from the treating solution, with a solids-liquid separation step.
  • the liquid or "filtrate” resulting from the separation comprises water, oil, the inorganic treating agent (e.g., sodium hydroxide and/or sodium silicate), and ultra-fine mill scale particulates.
  • the inorganic treating agent e.g., sodium hydroxide and/or sodium silicate
  • the oily coarse mill scale materials are gravity fed to the treatment rinser 207 along line 205.
  • the treatment rinser 207 includes means for contacting the mill scale with a stream of treating solution, e.g., a spraying device 209.
  • the treating solution and water may be heated from ambient temperature to boiling, with higher temperatures within the range of 160°F to 200°F being preferred.
  • the temperature for the treating solution is dependent upon the level of oil removal required and the type and oxidation level of the oil. Operating at a higher temperature will improve the overall rate of oil removal from the mill scale waste.
  • the temperature may be controlled by placing sensors above reclamation vessel 309.
  • the treatment rinser 207 includes a solid-liquid separator, comprising a vacuum horizontal belt filter 213. This filter separates the solids from the liquid as the mill scale is contacted with the plant's recycled treating solution from line 211.
  • the de-oiled coarse mill scale is sent through line 215 to be recovered as resource material.
  • the recovered coarse mill scale is then dried and directed to a sintering plant. There it may be heated at temperatures sufficiently high to cause sintering.
  • the coarse mill scale may be sintered separately, it may also be desirable to mix the de-oiled fine mill scale with the de-oiled coarse mill scale, prior to sintering.
  • the liquid or "filtrate" from the treatment rinser 207 is separated from the mill scale by the vacuum horizontal belt filter and directed through line 217 to the second sump 269.
  • the filtrate is comprised of the treating agent, water, oil, and ultra-fine mill scale particulates.
  • the "fine" mill scale feed materials are preferably directed as underflow from classifying screen 203 along with the treating solution, through line 219 to a first treatment vessel 221, in which the fine mill scale particles are stirred vigorously along with the treating solution.
  • the de- oiled "fine” mill scale particles are separated from the treating solution.
  • the underflow is channeled through line 219 to a first treatment vessel 221, which includes a slurry of treating solution.
  • the treating solution in the first treatment vessel 221 is provided by three sources, namely solution recirculated from the treating vessel 235 through line 229, material recirculated from line 275, and material recirculated from the overflow of the second hydrocyclone 227 through line 239.
  • a constant stream of treating solution is recirculated to the first treatment vessel 221 by these means.
  • the treatment vessel 221 includes a stirrer 223 and a heating means, e.g., a heating coil or steam (indicated by arrows), to increase the temperature of the slurry.
  • a heating means e.g., a heating coil or steam (indicated by arrows)
  • the temperature of the slurry may range from ambient to boiling. Again, higher temperatures within the range of 160°F to 200°F are preferred, because operating at higher temperatures will improve the overall rate of oil removal.
  • the temperature can be controlled by placing appropariate sensors above the treatment vessels 221, 235, and 243. Additionally, the temperature in reclamation vessel 309 may be monitored in a similar fashion.
  • the top layer of the slurry in the first treatment vessel 221 contains more oil than in the second and third treatment vessels 235 and 243.
  • the first treatment vessel 221 is stirred vigorously using stirrer 223 for a time sufficient to remove oil and lubricants from the surfaces of the mill scale.
  • the residence time for stirred treatment depends on the type and amount of oil contamination, and is preferably determined empirically.
  • the slurry from the first treatment vessel 221 is directed through line 225 to a solid-liquid separator, such as a first hydrocyclone 227.
  • a solid-liquid separator such as a first hydrocyclone 227.
  • it is considered essential to include several stages of treatment so as to reduce oil contamination of the recovered mill scale to below 0.1 percent by weight. Each stage includes treating the mill scale by contacting it with treatment solution, then perfo ⁇ ning solid-liquid separation to remove the treatment solution with oil and to leave a less oily mill scale. The less oily mill scale is treated further to produce the desired level of reduced oil contamination.
  • the first hydrocyclone 227 separates the liquid from the mill scale and preferably removes as much treating solution and oil from the mill scale as possible.
  • the first hydrocyclone 227 has the highest oil output of the three hydrocyclones.
  • the overflow of liquid from hydrocyclone 227 is sent along line 231 to the second sump 269.
  • the underflow from the first hydrocyclone 227, comprising the partially treated mill scale fines, is directed through line 233 to the second treatment vessel 235.
  • the contents of the second treatment vessel 235 are vigorously stirred by agitator 223, and additionally, the recirculated liquid from the first sump 263 is added via line 236.
  • This addition of recirculated liquid also helps to maintain a liquid balance within treatment vessel 235.
  • the flow of liquid depends on the demand for water in treatment vessel 235. The water is needed to adjust the solid content level.
  • the flow of liquid into treatment vessel 235, from line 236, can be controlled by valve 267 located between lines 265 and 236.
  • the ultra-fine oily mill scale may settle at the bottom of settling tank 273 and be periodically removed. These solids are recovered for recycle through line 275 back to the fines processing first treatment vessel 221. 5
  • the effluent from settling tank 273, which now comprises oil and treating solution, is preferably directed over weir 279 where any oily phase may be skimmed from the surface and directed through line 283 for collection or disposal.
  • the remaining effluent may then be directed through line 285 to a means for removing additional oil and generating a recycled solution.
  • Another aspect of the invention involves the recycling and recirculation stages.
  • the importance of a recycle and recirculation system stems from both environmental and economic factors.
  • a mill scale treatment system which
  • this invention preferably includes a recirculation stage for treating the liquids from the treatment stages.
  • Recycled treating solution from reclamation vessel 309 may be directed to treatment rinser 207 along line 211.
  • a constant stream of treating solution from reclamation vessel 309 is recycled to treatment vessel 243 and treatment rinser 255 along lines 245 and 257.
  • chemicals such as
  • sodium hydroxide and sodium silicate are added to the reclamation vessel 309, either manually or through dispensers 311 and 313 to make the inorganic treating solution comprise a pH-modifier and dispersant in the desired -23- treatment vessel 221 along line 229, while the mill scale are sent on to the second hydrocyclone 227 along line 237.
  • the overflow liquid water and oil
  • the underflow mill scale are sent for further treatment by line 241 into the third treatment vessel 243.
  • the plant's recycled treating solution is introduced, via line 245, into the third treatment vessel 243.
  • the mill scale are sent to the third hydrocyclone 249, by line 247.
  • the overflow liquid from the top of the third hydrocyclone 249 travels along line 251 to the first sump 263.
  • the liquid in sump 263 has the lowest concentration of oil and grease throughout the system.
  • the underflow mill scale from hydrocyclone 249, now devoid of oil and grease, are sent through line 253 to a vacuum horizontal belt filter 255 and are sprayed again with the plant's recycled treating solution sent from line 257.
  • the solids which are de-oiled mill scale are sent along line 259 to be recovered, together with the coarse mill scale, as resource material to be sintered.
  • the liquid drawn from the vacuum horizontal belt filter 255 is sent to the first sump 263.
  • valve 267 When valve 267 is open, the liquid flows through line 236 back to the second treatment vessel 235. This is done to maintain a balance within the second treatment vessel.
  • the liquid going into treatment vessel 235 from line 236 should equal the liquid exiting line 237. If valve 267 is closed, the liquid travels to sump 269 through line 265, where it is combined with the filtrate from the coarse processing (line 217) and the overflow (line 231) of hydrocyclone 227. This combined effluent is then sent to settling tank 273 through line 271.
  • the effluent is composed of the treating solution, oil and any other material not separated and recovered with the mill scale.
  • the effluent settles into layers of oil, treating solution and ultra-fine oily mill scale. amounts.
  • the pH is monitored by testing the system's recycle solution within reclamation vessel 309.
  • Dispensers 311 and 313 may include any means for introducing the chemicals separately into the recycled treating solution.
  • the chemicals are preferably dispensed in a controlled fashion, for example, from chemical metering pipes through pipes or tubes.
  • the recirculation stages comprise directing the effluent from both the fine particle treatment rinser 255 (along line 261) and the overflow of the third hydrocyclone 249 (along line 251), into the first sump 263. If valve 267 is closed, the contents of the first sump 263 are sent through line 265 to the second sump 269. Additionally, the overflow from the first hydrocyclone 227, (travelling along line 231) and the filtrate of the coarse treatment rinser 207 (travelling along line 217) are sent to the second sump 269. From the second sump 269, the effluent is directed to the settling tank 273 through line 271.
  • the effluent composed mainly of treating solution and oil, as well as any other material not separated and recovered with the mill scale, is permitted to settle into layers, e.g., a layer comprising treating solution and a surface layer of oil.
  • a small remnant of solid particles, including ultra fine mill scale not retained with the solids in the solids-liquid separator, e.g., the hydrocyclone overflow, may settle at the bottom of settling tank 273 and be periodically removed. These solids may be recycled through line 275 back to the fines processing treatment vessel 221.
  • the effluent from settling tank 273, which comprises oil and treating solution, is preferably directed over weir 279 to skimming vessel 281, where any oily phase may be skimmed from the surface and directed through line 283 for collecion or disposal.
  • skimming vessel 281 After removing the oil from the effluent by skimming, the remaim ' ng effluent in skimming vessel 281 (which may still contain trace amounts of oil and fine particles) may then be directed through line 285 to means for removing additional oil which preferably comprises a flocculation vessel 289, which preferably includes a stirrer 223.
  • the effluent is preferably contacted with a polymer flocculant 287, preferably comprising a high molecular weight cationic quaternized polymer having a molecular weight in the range of 50,000 to 40,000,000.
  • An especially preferred flocculant is a quaternized amine cationic polymer having a charge density in the range of 5 to 100%.
  • Clearfloc 751 sold by Clearwater, Inc., Pittsburgh, Pennsylvania
  • Jayfloc 911 Cationic Flocculant sold by Callaway Chemical Company, Columbus, Georgia.
  • Jayfloc 911 Cationic Flocculant is an extremely high molecular weight, high charge density cationic emulsion polymer.
  • Clearfloc 751 is a high molecular weight, very high charge density cationic polyacrylamide.
  • the product is supplied as a low viscosity water-in-oil emulsion, and it generally performs in the pH range of 2.5 to 12.5.
  • the Milton Roy coagulant control center is an on-line electrokinetic charge analyzer with measuring, recording and control functions. It is an on-line instrument which directly measures the result of coagulation addition by instantaneously measuring the electric current is generated.
  • one such monitor would be placed on line 285, before the polymer is added (at arrow 287).
  • a second monitor would be placed on line 307, after the hydrogen peroxide is added, to ensure the polymer has been destroyed. The second monitor would detect the charge. Thus if the particles are more negatively charged, the polymer has been destroyed.
  • flocculation vessel 289 the flocculant is preferably mixed with the effluent in a sufficient amount and for a sufficient time using stirrer 223. From flocculation vessel 289, the effluent is directed to the second treatment vessel 293 through line 291. After additional stirring with stirrer 223 to ensure complete mixing, the effluent is sent along line 295 to the clarifier 297. At this stage, the flocculated effluent is separated, with the clarified effluent in the upper layer being directed through line 301, and the aggregated solid and oil fraction being recovered through line 299.
  • the filtered effluent is treated in a final treatment vessel 303 by mixing it with an oxidizing agent, e.g., hydrogen peroxide 305 using stirrer 223.
  • the resulting recycle stream 307 preferably comprises aqueous inorganic treating solution in condition for recirculating back to reclamation vessel 309, where a pH modifier and/or dispersant, such as sodium hydroxide or sodium silicate,may be added as necessary to the recycled solution (through lines 311 and 313 respectively) to obtain the desired composition of treating solution for use in any one of the previously described treating steps.
  • a pH modifier and/or dispersant such as sodium hydroxide or sodium silicate
  • This example relates to size classification of typical mill scale waste materials. Contaminated mill scales from an actual steel mill were screened into various size fractions using a series of classification screens. The particle size distribution obtained is summarized as follows:
  • Example 2 This example relates to treatment of the coarse particle fraction.
  • One hundred grams of the coarse mill scale fraction were transferred to a Buchner funnel fitted with a polyester filter medium.
  • the mill scale particles were spread out on the filter medium.
  • a measured volume of an aqueous solution containing treatment chemicals (A) and (B) was poured into the funnel, mixed with the mill scale using a spatula, and filtered under vacuum.
  • treatment chemical (A) is sodium hydroxide
  • treatment chemical (B) is sodium silicate.
  • the mill scale particles thus treated were removed for a standard oil and grease analysis. The results are summarized in Table 2. It may be desirable to treat the coarse fraction several times to obtain less than 0.1% oil content.
  • Example3 This example relates to treatment of the fines particle fraction from
  • Example 1 Seven tests were conducted, the results of which are summarized in Table 3.
  • Test No. 1 in the first stage of the treatment step, 100 grams of the fine (smaller than 8 mesh) mill scale fraction were transferred to a beaker to which measured amounts of chemicals (A) and (B) were added. The concentration of chemicals (A) and (B) was 5 lbs./ton, each on a dry weight basis.
  • the particles in the beaker were slurried to a predetermined solid concentration of 70 percent by weight using preheated tap water.
  • the temperature of the slurry thus prepared was maintained at about 200 °F by controlling the temperature of the hot plate on which the beaker sat. The temperature was continuously monitored with a thermocouple while the slurry was being mixed with an electric stirrer.
  • the slurry was poured into the Buchner funnel with the same type of filter medium as that used in the treatment of the coarse particles in Example 2. After gravity drainage of liquid was complete, a measured volume of preheated treating solution containing predetermined amounts of chemicals (A) and (B) was added to the Buchner funnel. The liquid was drained under vacuum.
  • This example relates to treatment of the wastewater filtrate.
  • the filtrate collected from the processing and rinsing stages in Example 3 was allowed to settle under gravity for 30 minutes in a first beaker. Supernatant from this beaker was transferred into another beaker and maintained as a slurry using an electric stirrer. To this second beaker a high molecular weight cationic polymer was introduced at a controlled rate.
  • Two polymers found to be most effective were Clearfloc 751, a quarternized copolymer sold by Clearwater, Inc., Pittsburgh, Pennsylvania and Jayfloc 911, a quarternized methacryloxyethyl trimethyl ammonium methyl sulfate sold by Calloway Chemical Co., a division of Exxon Co., Columbus Georgia.
  • This example relates to the recirculation of the clarified effluent as treating solution.
  • concentrations of chemicals (A) and (B) were determined prior to reusing the clarified effluent from Example 4 as a recycled treating solution. Any loss in their concentrations was compensated for with the addition of their desired respective amounts.
  • the treating solution was then brought to the desired temperature level, after which it was used in the process as a processing and rinsing solution.
  • the effectiveness of the recycled effluent by its repeated use was tested by going through the processing sequence as discussed above in Examples 2-4. Table 4 shows the effectiveness of a typical treated and recycled effluent on the oil and grease content of oily mill scale particles.

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Abstract

Procédé de traitement des matières de rebut consistant en pailles de laminage, comprenant le traitement desdites pailles de laminage par une solution inorganique renfermant une matière alcaline modificatrice du pH, telle que l'hydroxyde de sodium, et un dispersant tel que le silicate de sodium. Selon le mode opératroire priviligié, les pailles sont triées entre fractions fines et fractions grossières avant le traitement, les fractions fines étant traitées successivement par contact d'une solution puis soumises à une séparation solide-liquide. Après enlevèment des huiles par écumage, floculation et extraction, la solution de traitement inorganique est recyclée. Le dispositif de récupération des pailles de laminage dégraissé comprend: a) un dispositif de triage par grosseur (203) des pailles de laminage graisseuses; b) un dispositif permettant de soumettre les pailles ainsi triées à la solution de traitement (221 et 227); c) un dispositif permettant de séparer les pailles des effluents véhiculant lesdites graisses dont les pailles ont été essentiellement débarrassées (227); d) un dispositif permettant de séparer les graisses desdits effluents de manière à obtenir une solution de traitement essentiellement dégraissée (273); e) un dispositif permettant de récupérer les pailles de laminage dégraissées (215, 259); f) un dispositif de recyclage de la solution de traitement (309).
PCT/US1992/001472 1991-02-26 1992-02-25 Procede et appareil de degraissage des matieres de rebut consistant en pailles de laminage WO1992014849A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2058040A3 (fr) * 2007-11-09 2011-04-20 Petroleo Brasileiro S.A. - PETROBRAS Procédé de traitement d'effluents de l'industrie pétrolière en vue de leur évacuation ou leur réutilisation
CN102605179A (zh) * 2012-02-24 2012-07-25 武汉理工大学 一种用于含钒页岩的酸浸设备
GB2530663A (en) * 2014-09-05 2016-03-30 Darlow Lloyd & Sons Ltd Reuse of by-products from metallurgical processes

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4792407A (en) * 1986-11-25 1988-12-20 Ultrox International Oxidation of organic compounds in water
US4855061A (en) * 1988-04-26 1989-08-08 Cpc Engineering Corporation Method and apparatus for controlling the coagulant dosage for water treatment
US4988391A (en) * 1983-09-08 1991-01-29 Bormann Georg Von Process, plant and/or apparatus for treating oil-contaminated debris or like materials
US5047083A (en) * 1989-06-15 1991-09-10 Nalco Chemical Company Process for de-oiling mill scale

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4988391A (en) * 1983-09-08 1991-01-29 Bormann Georg Von Process, plant and/or apparatus for treating oil-contaminated debris or like materials
US4792407A (en) * 1986-11-25 1988-12-20 Ultrox International Oxidation of organic compounds in water
US4855061A (en) * 1988-04-26 1989-08-08 Cpc Engineering Corporation Method and apparatus for controlling the coagulant dosage for water treatment
US5047083A (en) * 1989-06-15 1991-09-10 Nalco Chemical Company Process for de-oiling mill scale

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2058040A3 (fr) * 2007-11-09 2011-04-20 Petroleo Brasileiro S.A. - PETROBRAS Procédé de traitement d'effluents de l'industrie pétrolière en vue de leur évacuation ou leur réutilisation
CN102605179A (zh) * 2012-02-24 2012-07-25 武汉理工大学 一种用于含钒页岩的酸浸设备
GB2530663A (en) * 2014-09-05 2016-03-30 Darlow Lloyd & Sons Ltd Reuse of by-products from metallurgical processes
EP3186403A1 (fr) * 2014-09-05 2017-07-05 Darlow Lloyd & Sons Limited Réutilisation de produits dérivés provenant de procédés métallurgiques, traitement des déchets et produits issus de ceux-ci

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