CA1271156A - Method and apparatus for the cooling of coke - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A dry cooling method and apparatus for cool-ing coke has an upper zone in which the coke is cooled only by heat exchange indirectly to a fluid in the walls of the upper zone, and a lower zone in which the coke is cooled exclusively by direct contact with a cooling gas containing water vapor and which is then recircu-lated through a coking coal preheating plant.

Description

~l2~115i SPECIFICATION

Field o~ the Invention The present invention relates to a method of an to an apparatus for the d~y cooling of coke and, particularly, to the two-stage cooling of coke in which at laast during the second cooling stage a cooling gas containing water vapor is used and is passed in counterflow to the coke to be cooled.

Background of the Invention -~ .
The dry cooling of coke with a cooling gas is a common practice in coke production and two-stage processes have been ; described in which the coke and a first cooling yas are passed ln counterflow through one part of a two-compartment coke cooler for carrying out the two-stage process. In this first stage, the coke is cooled to about 800 C and then enters a second compartment in which -~ 15 the coke is cooled with a cooling gas containing water vapox.
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In general the dry cooling of coke has been known for many decades and the glowing coke pushed from the coka oven is customarily, in such processes, dumped into a cooling tower in which it is passed in counterflow at least during the first stage to a rising strea~ of inert cooling gas~.

In the cooling tower or cooling shaft, the coke functions as a movable bed~of olids which is brought into direct heat e~change~with the cooling gas.

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The circulation path of the cooling yas con~aining the water vapor is used by directly con~acting the coking coal ~herewi~h in the thermal treatment of the coking coal, i.e. the drying and preheating thereof. The water vapor and other vapors which arise during the heat treatment of the coking coal and are found in the circulat-ing cooling yas after this thermal treatment can be used effectlvely in the second cooling stage for the coke.
While this system has proved to be highly effective in practice, ~here are still some problems. For example, since the firs~ coke-cooling stage utilizes an inert gas and the second stage a reclrculated gas containing water vapor, the gates, locks or o~her means provided bet-ween the two stages to maintain separation of the gases must often be complex. In many instances, it is not possible to provide a suitable separation and the process deteriorates because of the incursion of water vapor into the otherwise inert cooling gas of the first s~age. In this earlier system, it is especially important to ensure that there will be a substantlal freedom from water vapor in the inerts gas of the first stage.
Another drawback of this earlier system is that the inert gas, after leaving the first cooling stage must, in turn, be cooled. This can only be effected realis-tically in an indirec~ heat-exchange process which, for the reasons already noted, provides a comparatively poor yield or recovery of heat.
U.S. patent 2,952,065 describes a dry-cooling process for coke which allows practically complete recovery 30~ of the sensible heat of the glowing coke. Here, in a single-stage vessel, the coke bed is treated with an inert ;~ ~ cooling gas in counterflow and, in addition, the bed ls passed into con~act with water-cooled surfaces of the walls of this vessel and baffles, partitions and other elements ~: :
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Prior to the use of water vapor in the second stage coollng gas, the cooling gas consisted essentially of ~n inert gas. The term "inert gas" as used herein is in-tended to refer to any yas which does not react with coke, e.g. in an oxidizing mannerr ~o result in loss ~hereof.
The hot inert qas leaving the coke cooler is usually employed separately to yenerate steam in a boiler of the tuhe type serving for waste-heat recovery.
In ~he past, moreover, it has heen felt that the dry cooling o~ the coke and the drying and preheating of the coking coal could not be carried out in direct heat ; exchange between the coking coal and the coke with one and the same circulating medium, because the vapors from the apparatus for drying and preheating the coal caused high burn-off losses of the coke, largely as a consequence of the water-gas reaction.
All earlier coke dry-cooling processes, as far as applicants are aware, have the disadvantage o~ high equipment cost and/or poor heat transfer in the heat ex-changers which are used.
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The problem of recovering the sensible heat of the cooling gases resulting from the dry cooling of a i coke without a significant burn-up of the coke by the choice - of the gas which is used has been resolved in part in the process described in German open application DE-OS 32 03 732. In this process the coke cooling is carried out in the manner described originally, i.e. in two stages in which the inert gas is used only in the first stage and in the second ~ stage the cooling gas contains water vapor.
`,~ 30 This system reduces the burn-up of the coke ~ to 1% by weight or less.
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introduced in-to the vessel and which are contacted by the moving bed and ~he cooling yases passing through the inter-stices of the bed.
Because of the use of the inert gas, a burn-off of co~e is laryely prevented and the dust content of the effluent gas can be comparatively low.
However, this process is likewise charac-terized by poor utilization of the heat content oi the inert gas.
The only cooling effected in this process, therefore, i~ a single-stage cooling and, as a practical matter, by inert gas exclusively.
The distribution of the heat transfer between that which is effected directly to the cooling gas and that which is effected indirectly to the cooling water is largely dependent on the construction of the cooling shaft.
One especially critical requirement, since the cooling gas also traverses the hottest part of the bed of coke in the shafk, is that the gas bè totally free from water vapor to prevent burn-o~f by the oxygen content of the cooling gas and/or by the water-gas reaction.
Thi~ ex~remeIy stringent requirement prevents any direct coupling of the cooling-gas path with the coal preheatiny or drying operation and, ior example, it will be 25~ clear that the coke-cooliny gas, if it is recirculated cannot in this case be introduced into any flow path, e.g.
expanded fluidized bed or pneumatic column, throuyh which ~he preheated coal is passed.

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Objec~s o~ the Invention . .
It is the principal object of this invention to provlde a method of and an apparatu.s for the dry cooling of coke which avoicls the drawbacks of the earller systems mentloned.
Another object of this inventlon is to provlde a method of and an apparatus for the dry cooling of coke which afford better utilizatlon of the heat extrac~ed from the coke, enables ~he coke-cooling gas ~o be utilized effectively in thermal pretreatment of the coking coal and, particularly, in a direct treatment thereof which generates the water vapor which can be utilized effectively in a cooling gas for the coke without significant burn-off there of.
Yet another object of the invention is to provide an improved method and apparatus of the class described which does not require separate cooling-ga~ cir-cula~ions or direct separation of an inert cooling gas from ~' a cooling gas containing water vapor.

S~~mary of the In~ention These objects and others which will become apparent hereinafter are attained, in accordance with the invention in a two-stage process for the cooliny of glowing coke in which the glowing coke is caused to descend through 25~ a coollng shaft or tower in an upper portion of this ~ower, corresponding to the first cooling stage, the coke is cooled to a ~emperature of abou~ 800 C in indirect heat exchange with a cooling medium through heat-exchange walls contacted - by the descending coke bed, while in ~he lower portion of ".' ~ : :
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f~71~5~i ~lle col~lmn or tower and in the second stage of ~he cooling process, the coke is cooled in counterflow to a cooling gas containing water vapor. The first-stage cooliny can be effected in indirect heat exchanye with feed water which is transformed ~o steam and which is passed throu~h the heat-exchanger walls in a direction generally opposite the direc-tion of movement of the coke bed.
Advantageously, the cooling gas recovered - from the second-stage cooling is used for the direct contact and thexmal trea~ment of the coking coal so that the cooling ga~ containing water vapor is generated by the evaporation of water and by the generation of vapors from the thermal txeatment of the coking coal.
The two-stage shaft cooler of the invention thus has an inlet for the glowing coke at the upper end thereof, a zone formed with the aforementioned heat-ex-changer walls below this inlet and a zone below this heat-exchanger zone, th& zone being ~raversed in succession by the coke. Means is provided for introducing the cooling gas at the bottom of the second zone and for removing the cool-ing ga~ at a region between the two zones. A coke gate can be provided between the two zones to block gas flow from the second zone up through the first zone.

According to the invention, therefore, the coke cooling is carried vut in the first zone substantially or predominantly by thermal radiation between the coke and the heat-exchanger walls and to a somewhat lesser degree by ~` thermal conduction between the coke and these walls, i.e.
exclusively indirectly. A direct cooling between the coke bed in the first stage and a cooling gas is thereby excluded. This means that only a single cooling-gas cir-cula~ion need be provided and expensive retrocooling or .~ .
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-' ~Zt7~L156 waste-heat recovery can be avoided. Furthermore, steam can be cJenera~ed espe~ially effe~tively in accordance with the lnvention which allows a practically complete recovery of the sensible heat of the glowing coke.
In practice, little difficulty has been found in carrying out ~he process steps or ln providing the shaft construction previously described in that the choice of materialst dimensions and even the overall technical con-cepts do not have a degree of criticality or sensitivity to dimensions whi~h limits the versatility of the process or the use of the apparatus.

Brie~ Description of the Drawings The above and other objects, ~eatures and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing, the sole FIGURE of which is a flow diagram illustrating the principles of this inven-tion.

Specific Description .. .. _ The glowing coke upon being pushed from the ;~ coke oven, is introduced at a temperature of 105 C to 1100 C~
into the inlet 2 to a hopper 10 of a cooling shaft or tower lj also referred to as a cooling vessel herein.
The hopper 10 functions as a storage or `~ 25 antechamber in which any temperature loss is minimal From this hopper the coke passes as a des-cending bed in the direction of arrow A downwardly through a ~irst cooling zone or stage la in which the coke is cooled, ~ exclusively by thermal radiation and conduction, to a tem-`~; 30 perature of 80Q to 850C.

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For this purpose, the first stage or zone is provided as a heat exchanger in which, between the walls of the column and the vertical partitions g, a feed water is introduced at 8a and steam is recovered a~ 8_ so that the general water flow is in ~he direction of arrow B in the heat exchanger which is generally designated at 8.
A constriction or coke gate 7 at the bottom of the first zone admits the coke to the second staye or zone lb.
The coke ga~e 7 is formed as a downwardly convergent funnel which can terminate above a conical ba$fle whose apex is turned upwardly and which has been shown in broken lines at 7a, the baffle serving to deflect the rising cooling gases into an annular compartmant 6 around the construction.
In the second zone 1_ the coke is cooled as much as possible, substantially reaching a temperature of about 200C a~ the outlet end 3 from which the cooled coke is discharged.
The cooling gas introduced at 5 through perforated walls 5a has a temperature of about 150C and contains water vapor such that the water vapor content of this gas ls 50 to 90% by volume and it derives from a pre-heating and drying plant 4 for the coking coal.
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Specific Example The aforementioned cooling gas enters the second zone lb in the region of the coke outlet 3 and passes in counterflow to the descending bed of coke, i.e. in ~he direction o$ arrow C.
It is dischargad at 6 with a temperature of about 600C.

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~f the total available ~emperature differen-tial, about 850 to 900K is used, about 200 to 250K being recovered in the first cooling zone for steam generation, i.e. about 25% available heat recovery, while the remaining 75% is transferred to the cooling gas, and is used in the coal drylng and preheating plant 4.
1 kg of coke carries an enthalpy of 1674 kJ
into the cooling shaft. 1423 kJ is technologically util-ized. 376 kJ is employed to generate abou~ 0.16 kg of steam at about 20 bar while 1074 kJ is employed for coal preheat-ing and drying. The latter requires, however, 544 to 83~
kJ/kg of coal which corresponds to 724 to 837 kJ per kg of coke. This demonstrates, even with losses, an effective coupling of the coke-drylng cooling in the second stage and the coal preparation in the drying and preheating plant.
In practice such a drying and preheating plant can include a pneumatic convayor 4a in which the predried coke is heated by the cooling gas from the second stage of the shaft as it entrains the coal upwardly in an expanded fluidized bed. The gas/coal mixture is separated ~ in a cyclone 4b from which the coal is collected in a - ~ storage hopper 4c as preheated coal ready for introduction into the coke oven. The gas phase is then utilized in a ~urther pneumatic conveyor or expanded fluidized bed 4d to

2~5 dry the coal before this coal is supplied to the preheating unit 4a. Gas/solid separation i5 effected at cyclone 4e and the sollds are delivered at 4f to the preheating unit 4a while the yas-containing vapor is driven from the coal, is : ,:
recycled by the blower 4~ to ~he inlet 5 of the second coke-cooling zone.

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Claims (6)

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

1. A method of dry-cooling coke which com-prises the steps of:
(a) introducing glowing coke at an upper end of a cooling shaft and in succession through an upper cool-ing zone and a lower cooling zone;
(h) Cooling said coke to a temperature of about 800 to 850 C in said upper cooling zone exclusively by radiation and conduction indirect heat exchange to fluid-containing walls forming said upper zone and provided within said upper zone; and (c) cooling said coke in said lower zone exclusively by circulating therethrough in counterflow to the coke in said lower zone, a cooling gas containing water vapor and removing said cooling gas before said cooling gas reaches said upper zone.

2. The method defined in claim 1 wherein said cooling gas, upon removal from said lower zone is passed into direct contact with coking coal to preheat said coking coal whereby vapors from said coking coal are intro-duced into said cooling gas and said cooling gas is recircu-lated to said cooling zone containing said vapor.

3. An apparatus for carrying out the method of claim 1 which comprises a shaft into which glowing coke is introduced and which is internally subdivided in an upper cooling zone formed with walls containing a fluid heated by indirect cooling of coke, and a lower cooling zone provided with a cooling gas inlet at a lower end of said lower cool-ing zone and a cooling-gas outlet substantially at a junc-tion between said zones, fluid-cooled walls of said upper cooling zone terminating at said junction.

4. The apparatus defined in claim 3, further comprising a coke gate disposed at said junction and allow-ing downward movement of said coke from said upper zone to said lower zone while preventing cooling gas from said lower zone from rising into said upper zone.

5. The apparatus defined in claim 4, further comprising means for introducing feed water into said walls at a lower portion thereof and for recovering steam from said walls at an upper portion thereof.

6. The apparatus defined in claim 5 wherein said cooling gas is passed in direct heat exchange with coking coal in a drying and preheating plant including:
a first pneumatic conveyor in which said cooling gas from said outlet entrains dried coking coal upwardly;
a first separator separating said cooling gas from the upwardly entrained coking coal which is collected as preheated coking coal;
a second pneumatic conveyor receiving said cooling gas from said first separator and entraining coking coal upwardly to dry said coking coal;

a second separator for separating said cool-ing gas from the coking coal entrained upwardly in said second pneumatic conveyor, the coking coal separated in said second separator being supplied to said first conveyor; and means for recycling cooling gas from said second separator to said lower zone.