Background of the Invention

The subject invention is directed to a process for producin briquettes from the fines produced by metallurgical processe wherein less than 3% by weight of the briquette formed, is th binder material. Also disclosed is a process descriptio comprising proper sequencing and juxtapositioning of variou apparatus for producing such briquettes.

Solids handling is a major part of a variety of processes especially metallurgical processes. Size degradation inevitabl occurs during handling, resulting in the creation of "fines" ( generic term generally used for particles that are smaller tha 1/4") . Fines are produced in a variety of other ways as well. Du to the small particle size which vitiates recoveries, an associated problems with handling, fines in the unagglomerate state cannot be remuneratively used. Many metallurgical processe today are generating ultrafine baghouse dusts that are listed a hazardous wastes by EPA, and must be disposed of at considerabl cost. These costs are going to be higher as the number of disposa sites shrinks and regulations become even more demanding Consequently, there is great interest in the industry to someho avert these disposal costs and perhaps reduce the waste stream through recycling. The baghouse dusts, because of their ultrafin size, are not amenable to briquetting by the standard method

available to date. This invention will relate a way of briquettin these fines, among other things.

Agglomeration of fines to make them more usable has been common practice for more than 100 years. One method o agglomeration is to use binders. The most commonly used binder include sodium silicate, a lime and molasses combination, Portlan cement and water, and steric acid, among others. These binder typically make up about 10% by weight of the final product; and agglomeration is generally a batch process. Briefly, binder components and the fines are delivered int typical mixing equipment and the mixture is stirred together for certain length of time to produce a homogeneous mix: No particula attention is paid to the particle size of the binder components a they are delivered into the fines. However, it is known that th surface area of the binder should ideally be greater than or equa to the surface area of the fines. Thus, any binding proces involves a basic surface area balance. Since the binder is relatively minor part of the agglomerate by weight, it become clear that to create the same surface area out of the binder a that of a much larger amount by weight, of particulates, is quit a challenge. The typical way of delivering the binder to the mi necessarily requires that a considerable amount of binder be used

But one cannot keep adding the binder indefinitely. Afte all, there is a common sense upper limit on the binder percentag for the mixture to be economically viable. The process, due to th batch nature, is forced to stop at a certain binder percentag

which in most cases is not really enough to produce a high qualit agglomerate. Consequently, typical binder systems produce a agglomerate with poor green strength ( i.e. the strength necessar to hold the agglomerate in a given form or shape after partia curing) which is insufficient for maintaining that form or shap during handling and transportation of the resulting briquettes Typically, such agglomerates are post cured with heat, followed b a curing time of about 24 hours before the agglomerates can b handled or transported. Thus, storage must be made available t accommodate the agglomerates during this long cure period. Whe such agglomerates are eventually used in the process, high binde content results in excessive energy costs to break the binder dow and the inorganic binder residue becomes an impurity.

Some three-part organic binder systems, including one tha claims to use a relatively low binder percentage compared to th standard inorganic binder, have recently been offered. However these systems use lead based catalysts leading to high lead conten and also a high level of free formaldehyde, both of which ar considered to be hazardous to health. These systems are known t contain a solvent package that poses potential health an environmental hazards as well. Further, these systems comprise high viscosity resin (over 250 cps) impeding the resin's ability t produce small enough particles that are necessary to achieve th required surface area balance. For these reasons, these binde systems would be unattractive to the Industry.

The following invention relates to bonding fine particles a agglomerating these particles on a continuous basis by using uncommonly low quantity of binder, i.e. less than about 3%. T binder is organic in nature and can burn off completely, leaving residue. The low quantity of binder substantially maintains t original chemistries, i.e. the percentage breakdown of most or a of the components or elements in the original fines is almo unchanged. Also, the low quantity of binder saves handling a transportation costs, and saves on energy costs as the agglomerat material is economical in various energy consuming processes.

Therefore, it is an object of this invention to provide means by which metallurgical fines can be agglomerated with less amounts of binder while at the same time producing an agglomera with sufficient strength to undergo handling, transportation, a use without untimely degradation of the material.

It is a further object of the invention to provide a bind system, devoid of carcinogens or other potentially hazardo components, for the agglomeration of fines.

In addition, this invention will present a way agglomerating ultrafine dusts such as electric arc furnace dust basic oxygen furnace baghouse dust, among others.

Finally, it is an object of the invention to provide continuous agglomeration process which avoids the need for lengt cure times and thus for holding or storage accommodation.

Summary of the Invention The subject invention relates to method for briquetting fine and ultrafines comprising mixing the fines and ultrafines on continuous basis with a binder system having low viscosity of up t about 200 cps and at least 50% solids, such that the resultin briquette contains less than about 3% binder by weight of th briquette.

The invention further relates to a process for producin briquettes from fines and/or pretreated ultrafines comprisin discharging the fines and/or pretreated ultrafines into a hig speed mixer; discharging the components of a binder system into th high speed mixer through fog nozzles simultaneously with th discharge of the fines and/or pretreated ultrafines; agitating th binder and the material to produce a homogeneous binder-fines ultrafines mixture; discharging the homogeneous binder-fines ultrafines mixture into a delay box for a period of time such tha the mixture is at the point of incipient cure; discharging th mixture at the point of incipient cure into a briquetting press an forming briquettes therefrom; discharging the briquettes onto heated conveyor for a period of not longer than 4 minutes to cur the briquettes, and collecting the cured briquettes.

, Brief Description of the Drawings

FIG. l represents a schematic diagram of the equipmen sequence used to achieve briquetting of fines and ultrafine according to the subject invention.

Detailed Description of the Invention The subject invention relates in general to a method for briquetting industrial fines. More specifically, the invention disclosed herein relates to a binder system to be used in the briquetting process, to the process itself and to the equipment used to carry out the process. For ease of understanding, the following discussion is divided into sections relating to each of the foregoing areas.

Processing

The present invention is a continuous process for producing briquettes from fines by use of a three part thermosetting polymeric binder system of low viscosity, and one that does not contain lead and has a low enough level of free formaldehyde so as to not require it to be considered carcinogenic. This system allows for binding of the particulates and shaping them into a desired form, such as a pillow briquette, without the need for the typical long cure period of 24 hours. The resulting briquette has less than about 3% binder by weight of the briquette. Specifically, the briquettes are produced by charging the binder-particulate mixture into forming equipment, such as a typical briquetting press, in a manner that the fines and the liquid binder components are intimately mixed to create a polymeric matrix in which the particles are "locked". To achieve this "locked" state, two steps must occur sequentially in a very precise

time frame. The importance of the time frame cannot be overstated. If the forming operation takes place too soon, the resultan briquette has poor green strength, if it takes place beyond th time of initial set, the binder actually resists the briquettin operation, resulting in a weak briquette. First, intimate mixin between particulates and the binder components should occur. Then, , the shaping operation, or briquetting, should occur precisely a the moment of incipient cure.

It has already been mentioned that bonding of particulate with a liquid binder must conform to a surface area balance. Thi requires that the binder particles be delivered in the form of relative particle size that is much smaller than the particle siz of the material being bonded. Thus, the goal is to fractionate o atomize the binder into as small a particle size as possible. Th binder components are formulated to have low viscosity which make them amenable to atomization. Clearly, the thinner the liqui binder or lower the viscosity of the liquid binder, the more easil this is accomplished. However, lowering the viscosity should no be accomplished by simply adding solvents. This reduces the solid content and reactivity. In the binder used in present invention, the resin viscosity was not lowered at the expense of reactivity.

Once the binder is atomized, the intimate mixing of binder an fines is achieved through delivering a fine mist of the atomize binder components into the fines or particulates that are in highly agitated or fluidized state. This is accomplished by usin a high speed mixer that fluidizes the particles on one hand, an

injects the binder components, through special fog nozzles directly into the particulates, on the other. This ensures uniform and intimate binder particulate mixture. Once the binde is uniformly mixed with the particulates, the mixture is discharg into a delay box where it is held in continuous motion until t moment of incipient cure, as mentioned earlier.

More specifically, the gel time, or the initial set time, a neat binder system such as that disclosed herein, is typicall under 150 seconds at 75°F. Of course, the initial set achieved i a binder-particulate combination is dependent on the particula material involved. Since mixing time is determined by the mixi equipment, a special mechanism or the delay box is herein disclos to build a "delay" into the process in such a way that t residence time of the binder-particulate mixture in the high spe mixer, together with the residence time in the delay mechanis equals the time of initial set. Consequently, the mixture is at point of incipient cure as it is discharged from the delay box in the forming/shaping equipment, such as a briquetting press.

It is important to recognize that the polymeric curing proces just discussed goes through three stages. In the first stage, al of the binder components are in a liquid state. Upon mixing, th process of cross-linking begins and the material goes through "plastic" or the second stage. The third stage, which is a fina and hardened or cured stage is achieved shortly thereafter. In th case of the binder used in the present invention, the plastic stag is extremely short-lived but a nonetheless critical one since onl

in this stage is the material amenable to shaping or forming. Th forming has to be completed in the "plastic" stage, otherwise th quality of the resulting agglomerate is poor. Hence, th criticality of the time frame. Continuing, the mixture is discharged from the delay box a the opportune moment, into the briquetting press where it is forme and dropped on a heated conveyor belt on which it travels abou three minutes before it drops into a holding container. Th briquettes are strong enough at this point for handling, transportation, and use.

Pretreatment of Ultrafine Materials

The foregoing works well in the case of particulates in the - mesh to +100 mesh range. If, however, the particulates contai more than 10% material of ultrafine size, or smaller than 225 mesh, the total surface area is such that it cannot be covered by usin small quantities of binder. A special pretreatment step i employed prior to the agglomeration process described earlier t make the ultrafine dust more amenable to bonding. Th pretreatment is carried out by passing the ultrafines through a pi mixer where a hydrophobizing organosilane solution is sprayed o the dust.

Three objectives are realized in the pretreatment steps. The are: 1) to increase the particle size and reduce the overal surface area; (2) to make the dust more amenable to bonding sinc organosilane also acts as an adhesion promoter with the organi

resin; and, (3) to make the dust hydrophobic so that it flow through the process without caking.

The general formula of an organosilane shows two classes o functionality:

RπSiX(4-„)

The X group is involved in the reaction with the inorgani substrate, which in this case is the ultrafine dust. The bon between X and the silicon atom in coupling agents is replaced by bond between the inorganic substrate and the silicon atom. X is hydrolyzable group, typically, alkoxy, acyloxy, amine, or chlorine The most common alkoxy groups are methoxy and ethόxy, which giv methanol and ethanol as by-products during coupling reactions Since chlorosilanes generate hydrogen chloride as a by-produc during coupling reactions, they are generally less utilized tha alkoxysilanes.

The most common application for silane coupling agents is t bond an inorganic substrate to a polymer. This may be depicted a follows:

(Dus Polymer

(Binder)

Organic)

The number of hydrolyzable X groups on the silane is anothe important parameter in controlling bond characteristics. Th

traditional silane coupling agents contain three hydrolyzable groups. They have maximum hydrolytic stability, but tend to be hydroscopic. At the opposite end are the silanes with one hydrolyzable group. These yield the most hydrophobic interfaces, but have the least long term hydrolytic stability. Consequently, silanes with one hydrolyzable group are used in the present invention, including but not limited to, aminopropyl trimethoxy silane and other such silanes.

Method of Application Deposition from aqueous alcohol solutions is the most facile method for preparing silated surfaces. A 95% ethanol-5% water solution is adjusted to pH 4.5-5.5 with acetic acid. Silane is added with stirring to yield a 2% final concentration.

For less soluble silanes 0.1% of a non-ionic surfactant is added prior to adding silane. Bulk deposition on dust is usually accomplished by a spray-on method. It assumes that the total amount of silane necessary is known and that sufficient adsorbed moisture is present on the filler to cause hydrolysis of the silane. The silane is prepared as a 25% solution in alcohol. The powder is placed in a high intensity solid mixer, e.g. twin cone mixer with intensifier or a pin mixer. The solution is pumped into the agitated powder as a fine spray. In general, this operation is completed within a few minutes. The pretreated dust is then introduced in the regular process described earlier.

Binder Systems

The binder systems are organic polymers that can cure or crosslink in under 5 minutes at room temperature, i.e. 77° F ± 2° F. These may include but are not limited to epoxies, polyesters, alkyds, and phenolic urethanes, specially formulated to meet the above general criteria. These binder systems can be two or three component systems that are not required to be disclosed as cancer-causing as per the current EPA guidelines. The viscosity of the combined binder components should not exceed 200 cps and should have a minimum solids content of 50%.

The binder system used in the present invention is a 3 component system, although others, as mentioned above, can be acceptable. The preferred 3 component system according to the subject invention is a binder system such as the Delta Set system commercially available from Delta Resins and Refractories or Pep- Set Binder Systems commercially available from Ashland Chemical. Such systems typically include a phenolic resin, a polyisocyanate- based co-reactant and an amine catalyst. Typical two-part systems such as epoxy or bis-phenol A resins do not require the addition of the activator or catalyst mentioned above.

Eguipment

The line diagram of FIG. 1 assumes a two component briquette containing fines received in receiving bin 1 through surge hopper

2a and ultrafines from surge hopper 2b. This situation is often encountered in metallurgical process where there is a growing

12

SUBSTITUTE SHEET (RULE 2«

interest in recycling the baghouse dust (ultrafines) by mixing with metallics from another waste stream, also available on sit A typical case from an integrated steel mill would be that briquetting a mixture of electric arc furnace dust (containi zinc, lead, etc.) from hopper 2b and millscale fines from hopp 2a. In case of stainless steel industry, it would be a mixture stainless electric arc furnace dust (containing valuable nickel a chrome) from hopper 2b and stainless grindings from hopper 2 There is interest not only in recovering metals through recyclin but also in averting the cost of disposing of the electric a furnace dust which is very expensive presently and will only g more so in the future.

Where there is only a single material briquetting, the seco component hardware, including hopper 2b, silane solution tank and pretreatment mixer 5, can be left out.

A given amount of fines are discharged from the surge hopp 2a, by conveyor belt 12 to a dryer 3. From the dryer 3, if use or from the hopper 2a if the dryer is not used, the fines a discharged into the high speed mixer 7. Simultaneously, the prop amount of ultrafines are delivered into pretreatment mixer 5 whe the ultrafines are pretreated with silane from tank 4 in continuous operation and discharged via conveyor 14 into the sa high speed mixer 7. The conveyor belts 13 and 14 can optionally enclosed conveyor belts in case the dusts being handled a "lifted" or hazardous dusts. Such conveyor belts are sold by Omn Lift, Inc., among others. The dust and fines, while in a high

agitated and fluidized state, get evenly coated with the binde components sprayed into high speed mixer 7 through commerciall available fog nozzles connected to lines 6a, 6b and 6c from binde tank 6. The mixed material is then discharged in the delay box to match the proper time for initial set. Then, at the opportun moment, the mixed material is discharged into the standar briquetting press 9 where briquettes are formed and dropped onto heated conveyer belt 15 which is maintained at 180°F on which th briquettes travel for about three minutes. From conveyor belt 1 the cured briquettes drop into the briquette collection bin 10 The briquettes are ready at this point for handling, transportatio and use. Total processing time, from hoppers 2a and/or 2b, is no more than about 5-7 minutes.

Example 1

High carbon ferrochrome fines were supplied by Union Carbide The fines were -8 mesh in size. Time output of the screw conveye was measured at 120 lbs/min. The binder components pumps wer calibrated to maintain the feed rate of approximately 1% tota binder percentage by weight or .6 lb. each of resin and co-reactan per minute. The activator pump was set at a number "five" settin and delivered 0.03 lb/min. directly into the resin stream. Thes flow rates were verified by actual check on weights through th bypass lines. Upon measuring the amounts, all the components wer mixed in a cup to verify complete cure as well as the set time.

The actual set time of the binder and ferrochrome fines wa measured at 130 seconds. The delay box timer was adjusted to 12 seconds since the residence time in the mixer was known to be 1 seconds. The briquetting machine was set at 1,900 psi pressing force Feed screw was set at 2. All systems were turned on and th briquetting performed.

The invention has been described with reference to th preferred embodiment. Obviously, modifications and alteration will occur to others upon a reading and understanding of thi specification. It is intended to include all such modification and alterations in so far as they come within the scope of th appended claims or the equivalents thereof.