CA1109819A - Agglomerates produced from coke oven carryover fines and liberated coal tar - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A coke oven system is provided having a coke oven preferably with pipeline charging for converting coal into coke. Carryover fines are collected from the coke oven and preferably a preheater therefor, and then agitated by agitator means and the collected carryover fines thereby agglomerated. Preferably, the carryover fines are first mixed with water to form an aqueous mixture, and then agglom-erated. The agglomerated carryover fines are then preferably separated from the aqueous mixture by separated means. The agglomerated carryover fines are preferably conditioned in dryer means and recirculated to the coke oven preferably through a preheater.

Description

. 1~09819 This application is a division of copending application No. 294,779 filed January 11, 1978.
The presentinvention relates to a product for charging a coke oven system.
BACKGROUND OF THE INVENTION

A coke oven is used for making coke from coal.
The crushed coa]. is indirectly heated to generally above 1500F in an oxygen deficient, pressurized atmosphere by heating the sidewalls of the oven with oil, gas or coal.
Coal tar volatiles are ~riven-off from the coal, leaving behind coke for use in making iron and steel. The liberated coal tar volatiles are separate]y collected and distilled to provide as a by-product a basic raw mat-erial for the ch~mical industry One of the problems with coke ovens has been loss of coal as carryover ~ines. That is, fine coal particles, in various stages of devolatilization and carbonization, are emitted from the coke overl through the exit mains with the volatiles. In a conventional oven, the amount of carryover fines usually runs between 50 and 100 pounds per charge. These carryover fines are generally collected in a dust collector, wet scrubber and pitch trap along with some coal tar and ash, and disposed of as waste.

Recently, it has been found that the efficiency of coke ovens can be substantially improved by preheating the coal. Preheating also permits utilization of lower ~.

llVg8~9 grades of coal and provides an improved coke product. Pre-heating involves flash heating typically pulverized coal to about 500F before charging to the coke oven. The coking can thus be done faster wi~h added production for a given size coke oven, while producing a stronger more consistent coke composition from coal blends comprising large portions of low grade coal. Preheating is credited with providing greater assurance of complete coking and also reducing air pol]uting emissions that take place when green coke is pushed.

The problem is that preheating also causes even larger losses of coal due to increases in carryover fines.
The grinding of coal to fine particles and the explosive force exerted on flash heating produce this increased carry-over. The high and efficient yield of usable coke from low-grade coal, however, more than offsets the losses in carryover fines. It has been suggested to use clarifiers to retrieve coal fines trapped by spray water and recycle these to the preheater, but this procedure adds to the cost of installation and operation and still results in loss of substantial carryover fines.

A compounding problem with coke ovens is air pollu-tion during charging. It has been estimated that 70 per-cent of all emissions from a coke oven occur during charging.
A prominent solution for this problem, which has been com~er-cially used, is pipeline charging. Pipeline charging involves grinding and screening the coal to form a mass of coal particles.
with a maximum size of 1/4 inch and most under 1/8 inch.
This mass can be pressurized typically by steam and propelled through pipes to charge the coke oven. The big attraction for 1~)9819 this system is that the coal enters the ovens through a closed s~ationary network, with little opportunity Eor dust emissions.

Pipeline charging, however, further increases the tendency of fine coal particles to carryover to the oven exhaust system. With preheating, anywhere between 200 and -; 1000 pounds of carryover fines will typically flow into the exit mains during a pipeline charge, with the equipment designed to handle 2000 pounds of carryover fines. See Iron Age (March 1, 1976) pp. MP-9 to 12. The stringencies : of recent environmental controls on coke ovens require these losses be accepted.

The present invention overcomes these difficulties and disadvantages. It provides a closed coke oven system where substantially all carryover fines are reclaimed and recycled to the coke oven with minimum cost in equipment and operation. The most pertinent art is believed to be the disclosures of United States Patent Nos. 3,268,071, 3,617,228, 3,637,464, and 3,665,066 and Ganadian J. of Chem. Eng., Vol.
54 February/April 1976, pp. 3-12, which have little or no relation to the present coke oven system.

: SIJMMARY OF THE INVENTION
.; . _. . . _ . __ _ ' A coke oven system is provided that is an essentially -~ 20 closed system reclaiming virtually all carryover fines at low cost. Air pollution and effluent emissions are minimized.

The coke oven system comprises a coke oven for con-verting coal into coke, and preferably preheater means for preheating the coal to at least about 500F before charging 11098~9 io t:h(. coke ov~.~n. I~l-ef(~raL~Iy tll~ c~o~] :is ch~r(;ed to the ~okc~ oven pll~umatically by ~ cl.i.ne charying. ~rhe system ha.s collector means on ~hc coke oven and prehe.lt:er means, if In~ed, for collectil~lg carry-over fines from t^he erllissiol-ls ~rom ~ t~ cok/~ oven and preheater.
The collected carryover .fin~s, whicll i.nclude liberated coaJ.
tar volatiles, are preferably bl.eJlC;Cd and mixed to form a mass of carryover fi.nes with liberated coal tar throughout. Coal fines feed, which contains coa] tar, in an unliberated state, may be added to the blend, if desired, to reduce the percentage o~ lib-erated coal tar in th~ blend and increase the hardness of theagglomerated product. The aqueous mixture is then ci.rculated to agitator means for agi.tat.ing and agglomerating the collected carry-over fines.
Theinvention of application No. 294,779 provides a coke oven system comprising:
A. a coke ovel-l for convert:ing coal :into coke;
B. collector mealls for collecting carryover fines and lib-erated coal tar from the coke oven; and C~ agitator means for mixing the carryover fines and lib-erated coal tar collected from the coke oven with water to forman aqueous mixtur.e, said agitator means also agglomerating the carryover fines and liberated coal tar collected from the coke oven to form agglomerates.
The invention of the aforementioned application also con-templates a method of agglomerating coke oven carryover fines comprising the steps of:
A. collecting carryover fines and liberated coal tar fromthe coke oven of a coke oven system; and B. agitating said carryover fines and liberated coal tar of 98~9 the coke oven with water to form an aq~eous mixture and to agglom-erate the car~yove~ flnes and liberated coal tar in the aqueous mixture to form agglomerates and the resulting product.
Preferably, agc31Omerat:ioll is performed by first circulating the blend to mixin~ means for mixing the collected carryover fines with water to form an aqueous m:ixture. The aqueous miY~tUre is then circulated to the agi-tator means ancl there agglomerated. The agglomerated carryover fines are then scparated from the aqueous mixture by separator means.
By this proce~ure, the agglomerated c~rryover fines can be used as a separate by-product of the coke overl system. Preferably, however, the agglornerated carryover fines are circulated to dryer ~eans for conditioning the agglomerate carryover fines for re-charging to the system. The clried and conditioned agglomerated carryover fines are thell charged by recycle means to the coke oven or preheater along with coal feed.
However, this invention is concerned with a product for charging a coke oven system, said product prepared by:
A. collecting carryover fines and liberated coal tar from a coke oven system;
B. forming an aqueous mixture consisting essentially of said - carryover fines, liberated coal tar, and water;
C. agitating said aqueous mixture to agglomerate said carry-: over fines with said liberated coal tar to from agglomerates;
D. separating said agglomerates from said aqueous mixtureto provide said product.

- 5a -8~9 0ther details, objects and advanta~es of the inven~ion will become apparent as the followi.ng description of the presently preferred embodiments and presently preferred methods of practicing the same proceed.

BRIEI D~SCRIPTION OF THE DRAWINGS
_ _ __ _ In the accompanying drawings are shown the presently preferred embodiments of the i.nvention and are illustrated presently preferred methods of practicing the same, in which:

Figure l is a schematic of a coke oven system illustrating the present invention; and Figure 2 is a sche-matic of a coke oven system illustrating the present inven-tion.

DESCRIPTION OF THE PREFERRED EMBODI~ENTS

Referring to Figure l, a coke oven system is illustrated. Coal particles 10 preferably of maximum par-ticle size of l/4 inch and most under l/8 inch are charged to the system. The coal particles are preferably prepared by grinding in a rotating cone crusher or the like and wet screening of coal. Coal particles 10 are typically dried to a moisture content of about 10 to 15 percent.

Coal particles 10 are charged to preheater 11 where the coal particles are flash heated to about 500F in about 5 to 8 seconds, preferably with waste gas from the coke oven.
The preheated coal particles 12 are then charged to the coke oven 13, which is of a standard design. Preferably, the charging to coke oven 13 is done pneumatically by pipeline charging. In the coke oven 13 the coal particles are heated to about 1500 ~o 1850F, driving off the coal tar volatiles 14A and producing furnace or foundry coke 14B, as desired.

In preheater 11, considerable airborne particulate emissions are produced due to the extremely rapid and high temperature heating of the fine coal particles 10. The moisture content in coal particles lO causes some particles to virtually explode and fragment during the rapid heating.
The carryover fines 15 are collected from the preheater 11 and circulated to dust collector 16, where the carryover fines 17 are separated from the gaseous emissions 18. The separated carryover fines are often referred to as preheat filter cake and ash pit residues depending on the particular technique of separation in dust collector 16. Typically, dust collector 1~ is a series of cyclone separators and wet scrubbers in combination, where ~he fines from the cyclones are collected in an ash pit and the fines from the scrubbers are collected as filter cake.

Similarly, airborne particulate emissions 19 from coke oven 13 are emitted through an exhaust main and circulated to dust collector 20, wllere carryover fines 21 are collected as filter cake and ash pit residues and sep-arated from gaseous emissions 22. Again typically, dust collector 20 is a series of cyclone separators and wet scrubbers in combination. These carryover fines include substantial quantities of coal tar ~olatiles liberated from the coal in the coke oven. Also carryover fines 23, which include substantial coal tar, are collected from the pi~ch trap of the coke o~en 13.

Typical compositions of the collected carryover fines are as follows:

. .
-7- .

~11098~9 ~., filter _ake ~ pi ch ash Moisture content* 50.0% 20.0 20.0 Tar (oil content 25.0% 31.2 41.4 of solids)**
% of ash in solidsb** 17.3% 5.6 6.0 * Moi.sture conten~ is weight % of water of carryover fine feed.
0 '~ b Weight % of toluene extractable oil on a water free basis b*~ Weight % on oil free and water free basis The carryover fines 17 collected from preheater 11 and the carryaver fines 21 and 23 collected from coke oven 13 are then pumped and blended in a suitable blender 25. The carryover fines are blended to provide sufficient liberated coal tar, preferably 3 to 30 percent and most desirably 5 to 20 percent by weight on a wet basis of the carryover fine feed, to insure effective agglomerating in a later step of the process. In this connection, it should be noted that "liberated coal tar" means that the coal tar attains a freed state, by heating, separate from or along with the coal par-~icles in various stages of coking.

Sufficient liberated coal tar is present in an indiscriminate blend of the carryover fines from the coke oven and preheater, which in a typical system is ~0 percent from the cyclone separators (i.e. ash pit), 19 percent from the wet scrubbers (i.e. filter coke) and 1 percent from the pitch trap. However, if too much liberated coal tar is present to provide agglomerates of sufficient hardness to withstand l~g819 recirculation Lo ~he coke oven or preheater, con~rolled q~ n~i~ies o~ coal part-icles 10~, containillg lln]iberated coal tar, can be added to reduce the pel-cerltage of liberated coal t.ar in the blend. Preferably, blender 25 is the feed p~lmp to mixer 27 (hereafter described) that functions to transport and homogenize, possibly in controlled proportions, the separately collected components of carryover fines from the coke oven and preheater. Because of the consistency of the collected carryover fines, with liberated coal tar in-cluded, a pump for viscous materials such as Moyno pump, orscrew-type feeder is preferred for blender 25.

The blended carryover fines 26 are then preferably mixed and dispersed in water in mixer 27, which for agglomer-ation of a water dispersion is a high shear mixer. Preferably the dispersion is between 5 and 40 percent and most desirably between lS and 25 percent carryover fines in water. In mixer 27, the dispersion is agitated and agglomerated ~o agglomerates of less than 1/4 inch and mostly less than 1/8 inch in size. The intensi.ty of mixing and the temperature in mixer 27 control the residence time required and the size of the agglomerates. A temperature of about 50C is pre-ferred in the mixer and a resi.dence time in the order of 5 seconds to 1 minute. Process heat may be provided by the heat content of the carryover fines, or steam may be injected to achieve the desired temperature. Experimentation in the individual system is necessary to optimize the agglomerate size and hardness. For example, if the agglomerates prove to be too large at 50C, the temperature could be raised to reduce the viscosity and in turn the agglomerate size. Altern-atively, the amount of carryover fines containing small ~09819 quantities of liberated coal tar can be increased in thefeed blend to reduce the a~glomerate size and hardness.
Coal particles lOA can also be and preferably are proportion-ally added at the blender 25 ~o control agglomerate size and hardness. If the agglomerates are too small or hard, the intensity of mixing can be reduced or t~e amount of carry-over fines containing larger quantities of liberated coal tar is increased in the feed blend.

Respecting high shear mixer 27, in one desirable embodiment, a 60 gallon tank with a 14.7 !TP. agitator operat-ing at 1500 rpm and an impeller diameter of 14 inches (28 meters/sec. peripheral speed) can be used on a 25 per-cent carryover slurry. Three turbine impellers mounted at : different heights on the shaft and 4 or 8 radial baffles (donut baffles or "stage dividers") can also be used. Such a mixer vol~lme will provide about 20 seconds residence time, which for 10 tons per hour processing rate is expected to be ideal.

After mixer 27, the agglomerated mixture 28 can be circulated to holding or surge tank 29, which is provided with agitator 30. An additional residence time of 2 to 5 minutes can thus be imparted to the mixture to finish forming the agglomerates under a gentler agitation. Depending on the performance of the high intensity mixer discussed above, however, the agitated holding tank 29 may not be needed and the agglomerated mixture 28 can go directly to separator 31.

The agglomerated mixture 31 or 28 is pumped to a separator 32 which separates the agglomerated carryover fines from the water by size and/or density. Preferably, a vibratory dewatering screen, with a suggested mesh size of 1~098~L9 65 mesll, is used for separcltor 32. A coarser mesh (e.g.
30 mesh) may also be used if there is no objection to some ~ines being recycled with the wa~:er. Alternatively, a sieve bend of an appropriate mesh size, such as that manufactured by authority from DSM NV Vederna]dse Staatsmijnen, may be used for separator 32. Otiler commercially available size separators such as an elutriator, or cyclone or spiral sep-arator may also be utilized. Alternatively, the agglomerated carryover may also be separated in a float-sink tank where the agglomerates, which tend to float, are skimmed off by a rotating paddle through an overflow, while the water and unagglomerated carryover fines, which tend to sink, are removed through the bottom of separator 32 as an underflow 33 substantially free of carryover fines and agglomerates.
This underflow is recylced to mixer 27 for use in mixing and agglomerating as above described.

The separated agglomerated carryover fines 34 may then be processed through dewatering means (not shown), such as a centrifuge, to remove water absorbed on the agglom-erates. Such separated water is also recirculated back tomixer 27 for reuse. Dewatering apparatus is not, however, necessary or preferred.

Agglomerated carryover fines 34 may be used as a separate commercial product. Preferably, however, the separated agglomerated carryover fines 34 are heated to 500F in dryer 35 and conditioned by oxidation, hydrolysis, polymerization and the like to a hardened mass. A vibrating, shallow fluid bed dryer is preferred, such as that manufac-tured by Jeffrey. Generally, about 25 percent water is the design load on dryer 35. This is a maximum figure based on experimentation with a stationary 8-inch sieve screen. With 1~98~9 a vibrating dewatering screen in separator 32, the typical moisture content in separated agglomerated carryover fines 34 is expected to be on the order oE 10 to 15 percent.

The retention time in dryer 35 is preferably greater than 30 seconds and up to generally one hour is contemplated, with the retention time usually on the order of 5 to 20 minutes. And the heating is not as rapid as in preheater 11 so that the agglomerated carryover fines are "conditioned" preparatory for charging to preheater 11 or alternatively coke oven 13. Such conditioning substantially hardens the agglomerates and reduces the fragmentation and carryover emissions for the agglomerates on charging to the preheater by removing volatiles (primarily water) 37. If appropriate, the volatiles 37 may be collected and separated in the dust collector (not shown) and carryover fines 38 circulated to the blender 25. The dried carryover agglom-erates 36 are then preferably charged to preheater 11 along ~ith coal particles 10, and subsequently processed into coke in coke oven 13 as above described.

Referring to ~igure 2, an alternative coke oven system is illustrated in which the agglomeration is performed under dry conditions. In description of this embodiment, the components are designated with corresponding prime numbers to those described in connection with Figure 1 to show sim-ilarities and differences from the coke oven system and em-bodied method there described.

Coal particles 10' are prepared as described in connection with ~igure 1 of the same controlled particle size. The coal particles are then charged in preheater 11' and preheated as there described. The preheated coal -1.2-- ~1098~

particles 12' are then charged to coke oven 13', where they ~re processed into coal tar volatiles 14A' and furnace or foundry ~oke 14B' as there described. Carryover fines 17' and 21' are collected from dust col.lectors 16' and 20', re-spectively and circulated to a mixer 27' through blender 25', i.f desired, along with the collection 23' from a pitch trap.

In mixer 27', the carryover fines are agitated, preferably under fairly gentle conditions, to form agglom-erates. Mixers particularly suitable for this purpose are double arm kneader-mixers, pug mills, paddle mixers, dough mixers and the like.

Generally, the carryover fines will contain too much liberated coal tar. For this reason, coal particles lOA' are usually added to the mixer 27' preferably by mixing with the carryover fines in mi.xer 25'. To provide good agglomeration, the carryover fi.nes should be preferably 3 to 30 percent and most desirably 5 to 20 percent by weight of the total material passing through the mixer.
The residence time in rnixer 25' is preferably on the order of 2 to 15 minutes.

The agglomerated carryover fines 34' are then circulated to dryer 35', where the agglomerates are pref-erably heated and conditioned as above described in connec-tion with Figure 1. The conditioned agglomerated carryover fines 36' are then preferably recycled to the coke oven system and preferably preheater ll'.

coke oven system is thus provided ~hich is almost entirely closed. The atmospheric emissions are minimized, and no effluent is produced. Conversely, only small amounts 11~98~

`~.....
of makcup water 39 need he added to the system to maintain the operation ~here a~p,lomerati.on is prepared in an aqueous mediuM. In addi.tion, no additional components such as heat need be ac~decl to the system. And most importantly, essentially a].l coal charged to the system is processed into coke witll minimum expense in capital outlay and operation.

~ lile the preferred embodiments of the invention have been specifically described, it i.s distinctly under-stood that the invention may be otherwise variously embodied and used within the scope of the following claims.

1 l~

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A product for charging a coke oven system, said pro-duct prepared by:
A. collecting carryover fines and liberated coal tar from a coke oven system;
B. forming an aqueous mixture consisting essentially of said carryover fines, liberated coal tar, and water;
C. agitating said aqueous mixture to agglomerate said carryover fines with said liberated coal tar to form agglomerates;
D. separating said agglomerates from said aqueous mix-ture to provide said product.

2. A produce prepared as set forth in claim 1 and additionally by:
E. drying the separated agglomerates for charging the coke oven system.

3. A product for charging a coke oven system, said product prepared by:
A. collecting carryover fines and liberated coal tar from a coke oven system; and B. agitating said collected carryover fines with said liberated coal tar to form agglomerates.

4. A product prepared as set forth in claim 1 and additionally by:
C. drying the agglomerates for charging the coke oven system.