AU746076B2 - Method and apparatus for drying coal - Google Patents

Method and apparatus for drying coal Download PDF

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Publication number
AU746076B2
AU746076B2 AU53506/00A AU5350600A AU746076B2 AU 746076 B2 AU746076 B2 AU 746076B2 AU 53506/00 A AU53506/00 A AU 53506/00A AU 5350600 A AU5350600 A AU 5350600A AU 746076 B2 AU746076 B2 AU 746076B2
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Prior art keywords
gas
fluidized bed
coal
bed dryer
dryer
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AU53506/00A
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AU5350600A (en
Inventor
Masaki Fukunaga
Jun Kobayashi
Yasutaka Shihara
Isao Sugiyama
Masahiko Yokomizo
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Nippon Steel Corp
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Nippon Steel Corp
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Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION reassignment NIPPON STEEL & SUMITOMO METAL CORPORATION Request to Amend Deed and Register Assignors: NIPPON STEEL CORPORATION
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION Request to Amend Deed and Register Assignors: NIPPON STEEL & SUMITOMO METAL CORPORATION
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
    • C10B57/08—Non-mechanical pretreatment of the charge, e.g. desulfurization
    • C10B57/10—Drying
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B45/00—Other details
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B3/00—Drying solid materials or objects by processes involving the application of heat
    • F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
    • F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
    • F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed

Description

S&FRef: 520438
AUSTRALIA
PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT
ORIGINAL
Name and Address of Applicant: Actual SInventor(s): Address for Service: Invention Title: Nippon Steel Corporation 6-3, Otemachi 2-chome, Chiyoda-ku Tokyo 100-8071 Japan Masahiko Yokomizo Yasutaka Shihara Masaki Fukunaga Jun Kobayashi Isao Sugiyama Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Method and Apparatus for Drying Coal The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c 1- METHOD-AND APPARATUS FOR DRYING COAL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for drying coal which are especially effective for drying coal to be charged into coke ovens.
2. Description of the Related Art In the production of coke, the drying of coal before charging into coke ovens is carried out for the purpose of improving the quality of the coke and the productivity of a coke oven'. The moisture content of charging coal before drying is usually about 7 to 10% and the purpose of drying is to dry coal to a moisture content of 0 to 6% in a coal dryer. When the moisture content of coal after drying is retained at a certain value, it is sometimes called "coal humidity control', :A fluidized bed dryer is widely used for drying coal. In a fluidized bed dryer, coal charged into the dryer is dried while being fluidized by a hot gas blown in from beneath a dispersion plate. Thus, the gas is always fed to the dryer at a rate high enough to fluidize the coal.
When drying coal using a fluidized bed dryer, fine coal included in the coal is carried away in the exhaust gas. Therefore, it is possible to not only dry coal but also to classify the coal, in a fluidized bed dryer, if coal finer than a prescribed grain size is carried away from the dryer, together with the gas, by properly controlling the upward flow rate of the gas blown into the dryer. The fine coal is then recovered by solid-gas separation.
As a source of the gas fed into a fluidized bed dryer, a hot gas generated by an exclusive hot blast generator may be used and supplied into the fluidized bed dryer, but flue exhaust gas from coke ovens can also be 2used as a portion or all of the feed gas. Japanese Unexamined Patent Publication No. 57-33774 discloses a drying system wherein an organic heating medium heated by the recovered sensible heat of coke oven gas is circulated in a heating conduction pipe installed in a fluidized bed dryer and, at the same time, combustion exhaust gas from a coke oven is injected into a fluidized bed dryer as hot gas.
in chamber-type coke ovens, coking chambers and combustion chambers are alternately arranged in one line, separated by brick walls about 100 mm in thickness. Heat generated in the combustion chambers is transferred to coal in the coking chambers through the brick walls. An array of combustion chambers is usually partitioned into 26 to 34 small chambers, and a regenerator is arranged beneath each of the combustion chambers. The small .chambers including regenerators are divided into two .groups. The regenerators of the first group are at a high .temperature after completing heat storage, and fuel gas and air are preheated in the regenerators, and then mixed with each other and burnt in the upper chambers (upward flow). Then exhaust gas after combustion is led downward in the chambers of the second group (downward flow) and is exhausted through a flue after extraction of its heat in regenerators located below the chambers.
The temperature of a regenerator of the first group falls by preheating the gas, while the temperature of a regenerator of the second group is raised by heat storage. After the lapse of a predetermined time the function of the first group is switched to the heat storage side and the second group to the combustion side.
By repeating the switching at a predetermined interval, the preheating operation and the heat storage operation, are carried out alternately to enhance regeneration efficiency. The operation of alternately changing the status of a combustion chamber from the combustion side to the down-flow side and vice versa, as describe above, -3 is called combustion changeover.
The operations of the supply and stoppage of air and gas during combustion changeover is explained hereafter based on Figure 4.
First, the amount of gas supplied to combustion chambers which have been the combustion side (provisionally called "side is reduced to reach zero within a prescribed time. Then, the amount of air for combustion is reduced to reach zero within a prescribed time. At this moment, the exhaust system from the combustion chambers and regenerators of the down-flow side (provisionally called "side to the flue is switched from open to close. After that, the exhaust system from the combustion chambers and regenerators of the side A, which have been the combustion side till then, is switched from close to open enabling exhaust to ~:the flue. Then, air is gradually introduced to the combustion chambers of the side B, which have been the :down-flow side till then and, finally, the introduction of fuel gas is commenced.
chamber-type coke ovens, the changeover of the combustion gas is done at a constant interval as described above. During the changeover period, as shown in the bottom row of Figure 4, the flow of the combustion exhaust gas from the coke ovens is interrupted, though only for a short period of time. In, a conventional method where the flue exhaust gas from coke ovens is used as feed gas for a fluidized bed dryer, no countermeasures are given to cope with the interruption of the combustion exhaust gas during the above-mentioned combustion changeover period, and a stable operation of drying coal is not ensured.
Besides, since the exhaust gas from a fluidized bed dryer contains completely or nearly saturated steam at a high temperature, there is a problem that the condensation of steam occures due to the cooling of the exhaust gas in the exhaust gas pipe and then clogging of -4 the filter cloths of the dust catcher located in the downstream of the pipe occures.
Further, a sufficient volume of gas has to be supplied to a fluidized bed dryer for fluiditing the coal regardless of the coal feeding rate. while, the flue exhaust gas from coke ovens used as dryer feed gas always has a temperature above a certain level to dry the coal.
When a fluidized bed dryer is started, the coal feed rate is gradually increased. However, since the amount of feed gas is retained above a certain level as described above, there is a problem that the coal is excessively dried while the coal feed rate is low.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and, in drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens, to provide :a method and an apparatus for drying coal capable of stably drying coal even during the combustion changeover :of coke ovens.
Another object of the present invention is to prevent the condensation of moisture, in the exhaust gas from a fluidized bed dryer, from taking place. A further object of the present invention is to prevent excessive drying of coal during the start of the operation of a fluidized bed dryer from taking place. A, yet further object of the present invention is to suppress the emissions of fine coal from a fluidized bed dryer and to improve the quality of coke.
The present invention is conceived to solve the above-mentioned problems and the gist of the present invention is as follows: A method for drying coal by a-fluidized bed dryer using flue exhaust gas from coke ovens as a portion or all of a feed gas to the fluidized bed dryer, characterized in that; an exhaust gas from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, when supply of the flue exhaust gas from coke ovens is interrupted or reduced.
A method for drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens as a portion or all of a feed gas to the fluidized bed dryer, characterized in that; an amount of coal fed to a f luidized bed is reduced, as well as the exhaust gas from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
A method for drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens as a portion or all of a feed gas to the fluidized bed dryer, characterized in that; both an amount of coal discharged from the fluidized bed and an amount of coal fed to the fluidized bed are reduced, as well as the exhaust gas :from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, when the supply of :the flue exhaust gas from coke ovens is interrupted or reduced to maintain the thickness of a coal layer in the fluidized bed within a predetermined thickness.
A method for drying coal according to item (2) or characterized in that; an amount of coal fed to the fluidized bed is controlled so that temperature of coal at an exit of the dryer is kept nearly constant, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
A method for drying coal according to item (2) or characterized in that; an amount of coal fed to the fluidized bed is controlled so that a difference between temperature of the feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range.
A method for drying coal according to item (2) or characterized in that; the flue exhaust gas of coke ovens is used as a feed gas to the fluidized bed dryer, and an amount of coal fed to the fluidized bed is 6 increased so that the temperature of the coal at an exit of the dryer is kept within a predetermined target range, when the supply of the flue exhaust gas from coke ovens is resumed.
A method for drying coal according to item characterized in that; an amount of coal fed to the fluidized bed is increased so that a difference between temperature of a feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range.
A method for drying coal according to any one of items to characterized in that; a portion or all of the route of gas exhausted from the fluidized bed dryer and circulated to be fed to the fluidized bed dryer 15 is heat-insulated, and a portion of gas is heated.
A method for drying coal according to any one of items to characterized in that; when gas exhausted from fluidized bed dryer is circulated and reused as a feed gas to fluidized bed dryer, a gas is blown for a purpose of cleaning a dust catcher installed in the route of said circulating gas, and an amount of gas corresponding to an amount of gas increased by said gas blowing is added to an amount of gas discharged to the outside.
(10) A method for drying coal according to any one of items to characterized in that; a warning signal is issued before supply of the flue exhaust gas from coke ovens is interrupted or reduced, and following a sequence based on said signal, one or more of the following actions is/are taken: changing an amount of the exhaust gas circulated and used as a feed gas to the fluidized bed dryer, changing an amount of coal fed to the fluidized bed, changing an amount of coal discharged from the fluidized bed, heating a circulating gas, and blowing a gas for the cleaning of the dust catcher.
(11) A method for drying coal according to any one of items to characterized in that; when the supply of the flue exhaust gas from coke ovens is interrupted or reduced, a hot gas supplied from a hot gas generator is used as a portion of a feed gas to the fluidized bed dryer.
(12) A method for drying coal according to any one of items to wherein hot gas supplied from a hot gas generator is used as a feed gas to the fluidized bed dryer together with the flue exhaust gas from coke ovens, characterized in that; the supply volume and temperature of the feed gas to fluidized bed dryer are maintained at respectively predetermined target values by controlling the supply volume and/or the temperature of the hot gas in accordance with a variation of the supply volume of the flue exhaust gas from coke ovens.
S(13) A method for drying coal according to any one of items to and characterized in that; one or o both of a circulating gas and the flue exhaust gas from coke ovens fed to fluidized bed dryer is/are heated.
(14) A method for drying coal according to any one of S.items to and characterized in that; a portion of a feed gas is supplied to a plenum chamber of the oo 25 fluidized bed and, at the same time, the remaining portion of said feed gas is supplied to the exhaust gas from the dryer at a point between a freeboard section of the dryer and dust catcher.
A method for drying coal according to any one of items to wherein flue exhaust gas from coke ovens is used as a portion or all of a feed gas to fluidized bed dryer, characterized in that; flue exhaust gas from two coke ovens having different timing of combustion changeover is mixed and used as a feed gas to fluidized bed dryer.
(16) A method for drying coal according to any one A04659 MI. I HIUA VVr,)+3J -8of items to (12) and characterized in that; the coal feed rate to said dryer is graduially increased while feeding a feed gas to said dryer and adding water to the fluidized bed during a start of an operation of the fluidized bed dryer.
(17) A method for drying coal according to any one of items to (12) and characterized in that; both the flue exhaust gas from coke ovens and the circulating gas discharged from the fluidized bed dryer are used as a feed gas to the fluidized bed dryer, a consumption amount of the circulating gas is controlled based on a coal temperature measured at an exit of the fluidized bed dryer, an extracted gas volume from the coke oven flue is also controlled at the same time, and a **15 coal temperature at the exit of the fluidized bed dryer is stabilized by the above three measures.
(18) A method for drying coal according to any one of items to (12) and characterized in that; both the flue exhaust gas from coke ovens and the circulating gas discharged from the fluidized bed dryer are used as a feed gas to the fluidized bed dryer, a consumption amount of the circulating gas is controlled based on a difference between temperature of the feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer, a volume of the gas extracted from the flue of coke ovens is also controlled at the same time, and a coal temperature at the exit of the fluidized bed dryer is stabilized by the above three measures.
(19) A method for drying coal according to any one of items to (12) and characterized in that; fine coal contained in the gas discharged fromt the fluidized bed is separated by solid-gas separation, said separated fine coal is mixed and kneaded with an additive composed of liquid containing heavy hydrocarbon derived from coal or petroleum, and said mixed and kneaded fine coal is used as feedstock to the coke ovens together with 9coal dried by the fluidized bed dryer.
A method for drying coal according to any one of items to (12) and characterized in -that; fine coal contained in a gas discharged from the fluidized bed is separated by solid-gas separation, said separated fine coal is mixed and kneaded with an additive composed of liquid containing heavy hydrocarbon derived from coal or petroleum, said mixed and kneaded fLine coal is formed by pressure-forming, and said formed fine coal is used as feedstock to the coke ovens together with the coal dried by the fluidized bed dryer.
By the present invention described above, it is ,made possible to always ensure a necessary amount of gas supply for a fluidized bed dryer by circulating and *15 reusing the gas exhausted from fluidized bed dryer as .9..feed gas for the fluidized bed dryer, even when the supply of the flue exhaust gas of coke ovens is interrupted or reduced due to a combustion changeover at :the coke ovens, etc.
When the exhaust gas from fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed 9*99 dryer, coal drying capacity is decreased due to a reduction in temperature and an increase in moisture 9. ~.content ofsaid feed gas. However, the moisture content ofthe coal discharged from the dryer can be kept at a target value by reducing an amount of coal fed to the fluiizedbed whil~e the feed gas is circulated for reuse.
it is also possible to maintain a stable fluidization condition of the coal in the dryer and ensure a stability of coal drying rate and classification characteristics by maintaining the thickness of the coal layer in the fluidized bed by reducing an amount of coal discharged from the fluidized bed, as well as by reducing an amount of coal fed to the fluidized bed.
The present invention also includes apparatus for carrying out the methods for drying coal according to items to (20) as follows: 10 (21) An apparatus for drying coal having fluidized bed dryer for drying coal and a gas pipe for supplying some or all of the flue exhaust gas from coke ovens to the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer back to the fluidized bed dryer, and a gas circulation system controller used for controlling so that a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
(22) An apparatus for drying coal having a fluidized bed dryer for drying coal and a gas pipe for supplyi-ng ~:some or all of the flue exhaust gas from coke ovens to :the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer back to the fluidized bed dryer, a gas circulation system controller used for controlling so that a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, and a coal feed amount controller used for controlling so that an amount of coal fed to the fluidized bed is decreased, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
(23) An apparatus for drying coal having fluidized bed dryer for drying coal and a gas pipe for supplying some or all of the flue exhaust gas from coke ovens to the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer back to the fluidized bed dryer, a gas circulation system controller used for controlling so that a gas exhausted from the 11 fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, a coal feed amount controller used for controlling so that an amount of coal fed to the fluidized bed is decreased, and a coal discharge amount controller used for controlling so that thickness of coal layer of the fluidized bed is maintained by reducing an amount of coal discharged from the fluidized bed, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
(24) An apparatus for drying coal according to item (22) or characterized in that; an amount of coal fed to the fluidized bed is controlled so that temperature of coal at an exit of dryer is kept nearly 'constant, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
An apparatus for drying coal according to item (22) or characterized in that; an amount of coal fed to the fluidized bed is controlled so that a difference between temperature of a feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range.
(26) An apparatus for drying coal according to items (22) or characterized in that; when the supply of the flue exhaust gas from coke ovens is resumed, the gas circulation system controller is used for controlling so that the flue exhaust gas from coke ovens is used as a feed gas to the fluidized bed dryer, and the coal feed amount controller is used for increasing an amount of coal fed to the fluidized bed so that temperature of coal at an exit of the dryer is kept within a predetermined target range.
(27) An apparatus for drying coal according to item characterized in that; an amount of coal fed to the fluidized bed is increased so that a difference between temperature of a feed gas to the fluidized bed and 12 temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range.
(28) An apparatus for drying coal according to any one of items (21) to characterized in that; a portion or all of the route of the gas exhausted from the fluidized bed dryer and circulated to be fed to the fluidized bed dryer is heat-insulated, and a heating means is provided to heat some of the gas.
(29) An apparatus for drying coal according to any one of items (21) to characterized in that; when a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, a gas cleaning controller of a dust catcher installed in 15" the route of a circulating gas is used for blowing a gas for a purpose of cleaning, and a dryer exhaust gas 0. controller is used for controlling so that an amount of a gas corresponding to an amount of gas increased by said gas blowing is added to an amount of gas discharged to the outside.
20 (30) An apparatus for drying coal according to any one of items (21) to comprising; a stack to discharge gas exhausted from the fluidized bed dryer to the outside, an exhaust gas pipe to conduct the gas exhausted from the fluidized bed dryer to the stack, SNo. 1 control valve installed on a gas pipe to supply some or all of the flue exhaust gas from coke ovens to fluidized bed dryer and a controller for said No. 1 control valve, No. 2 control valve installed on the exhaust gas pipe, and a controller for No. 2 control valve, and No. 3 control valve installed on the gas circulation pipe, and a controller for No. 3 control valve; and controlling so that; when the gas exhausted from the fluidized bed dryer is circulated and reused as a feed 13 gas to the fluidized bed dryer, the controller for No. 1 control valve closes No. 1 control valve, the controller for No. 2 control valve closes No. 2 control valve, and the controller for No. 3 control valve opens No. 3 control valve.
(31) An apparatus for drying coal according to any one of items (21) to characterized in that; the coke ovens have means to issue a warning signal before supply of the flue exhaust gas from coke ovens is interrupted or reduced, and following a sequence based on said warning signal, the gas circulation system controller, the coal feed amount controller, the coal discharge amount controller, the heating means, the gas cleaning controller of the dust catcher, and the controllers for Nos. 1 to 3 control valves carry out one or more of the following actions: changing an amount of the exhaust gas circulated and used as a feed gas to the fluidized bed dryer, 20 changing an amount of coal fed to the fluidized bed, changing an amount of coal discharged from the fluidized bed, heating a circulating gas, and blowing gas for cleaning a dust catcher.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general schematic diagram of a system for drying coal according to the present invention.
Figure 2 is partial schematic diagrams of a system for drying coal equipped with a hot gas generator according to the present invention.
Figure 3 is a partial schematic diagram of a system for drying coal with a dust catcher equipped with a heating means according to the present invention.
Figure 4 is a diagram showing a changeover situation of combustion gas systems of coke ovens.
Figure 5 is a diagram showing control situations in 14 Example I of the present invention.
Figure 6 is a diagra-m showing control situations in Example 2 of the Present inlvention.
Figure 7 is a diagram showing control situations in Example 3 of the present invention.
Figure 8 is a diagram showing changeover situations of flue exhaust gas from coke ovens in Example 4 of the present invention.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
Embodiments of the present invention are described hereafter based on Figures 1 to 4.
Combustion exhaust gas generated at coke ovens I is discharged to the atmosphere through stack 4 of coke ovens 1 atrpassi ng through flue 2. The temperature of 15 the combustion exhaust gas passing th' rough flue 2 is 150'C to 250'C and with a coke oven producing approximately 1,000 tdy(a coal (wt hrigrate of t/h) the combustion exhaust gas volume is roughly 60,000 m 3 /h.
Coal is fed to fluidized bed dryer 7 from coal feeder 15, hot air is blown in as feed gas 34 from *beneath a dispersion plate 14, and the coal fdt h dryer forms fluidized bed 13 with an upward gas flow coming through the dispersion plate 14. Moisture *25 contained in the coal is dried in fluidized bed 13 and the colis dicagdfrom fluidized bed dryer 7 after being adjusted to a prescribed temperature and a prescribed moisture content.
According to the present invention, an exhaust gas from coke ovens 1 is supplied to fluidized bed dryer 7 through gas pipe 8 branched out from the coke oven flue 2 and blower 12. Exhaust gas 32 discharged from fluidized bed dryer 7 is discharged to the atmosphere through stack after passing through dust catcher 16 and blower 18 via exhaust gas pipe 17. A bag filter can be used as dust catcher 16. A cyclone type dust catcher is also applicable, but a bag filter is sometimes preferable because a cyclone type dust catcher cannot separate and capture fine coal of a grain size of roughly 20 pm Further, it is possible to circulate exhaust gas 32 of fluidized bed dryer 7 through gas circulation pipe 21 branched out from exhaust gas pipe 17 and reuse it as feed gas 34 for the fluidized bed dryer.
Exhaust gas flow meter 5 and control valve 6 for exhaust gas from coke ovens to control flue pressure of coke ovens 1 are installed on flue 2 of the coke ovens.
Flow meter 9 and No. 1 control valve 10 are installed on gas pipe 8, No. 2 control valve 19 is installed on exhaust gas pipe 17, and No. 3 control valve 22 is installed on gas circulation pipe 21. Since the exhaust gas volume can be estimated by comhbustionl calculation, :15 exhaust gas flow meter 5 is not indispensable. Openings and flow rates of Nos. 1 to 3 control valves can be regulated by respective controllers (26 to 28). Further, the coal feed rate at coal feeder 15 is controlled by coal feed rate controller 24 and the coal discharge rate from the fluidized bed dryer by coal discharge rate controller 25. Gas circulation system controller 23 can .control the circulating gas by giving control instructions to the controllers for Nos. 1 to 3 control valves.
25 Hot gas generated by hot gas generator 11 (Figure 2) can be used as some of the feed gas for fluidized bed dryer 7. The exhaust gas from coke ovens or the circulating gas Used as feed gas for fluidized bed dryer 7 can also be usedas feed gas for hot gas generator 11, besides being directly supplied to fluidized bed dryer 7.
The coke ovens 1 usually have two combustion gas systems. By changing from one system over to the other after the lapse of a predetermined combustion time combustion is always maintained in one of the two systems. The changeover is usually done once every 15 to min. During changeover of the combustion gas systems, combustion gas flow of the system used till then (system 16 A) is gradually reduced as shown in the uppermost row of Figure 4, and when the flow is reduced to zero the combustion gas flow rate of the system to be used from then (system B) is gradually increased. For this reason, the flow rate of the exhaust gas from coke ovens decreases, becomes zero and then increases again during a combustion changeover period. The time required for a combustion changeover is generally 2 to 3 min. In a method-to use flue exhaust gas from coke ovens as feed gas for fluidized bed dryer 7, the supply of the exhaust gas from coke ovens for the feed gas is interrupted during combustion changeover at coke ovens i.
By the present invention, when the supply of the flue exhaust from coke ovens gas is interrupted or 15 reduced, the gas discharged from fluidized bed dryer 7 is circulated through gas circulation pipe 21 to be reused as feed gas for the fluidized bed dryer. The process is specifically described hereafter based on Figures 1 to 4.
No. 3 control valve 22 installed on gas circulation pipe 21 is kept closed during stable operation or slightly open for controlling the coal temperature at the exit of the dryer. If the temperature of the flue gas from coke ovens 1 is too high during stable operation, it is effective to lower the gas temperature by mixing a small amount of the circulating gas, which is cooler, and e .the circulating gas can also be used for controlling the drying capacity when moisture of feed coal fluctuates.
At the beginning of a combustion changeover of coke ovens 1, No. 3 control valve 22 is opened to a certain degree from a closed or slightly open position. By this, a recycling flow of circulating gas 33 is established through gas circulation pipe 21 by means of blowers 12 and 18. When a prescribed flow rate of circulating gas 33 is secured, No. 1 control valve 10 is gradually closed and, as a result, the amount of the flue exhaust gas from coke ovens supplied till then to fluidized bed dryer 7 is decreased gradually and the flow to stack 4 increases.
17 The valve actuation speed of No. 1 control valve which is not necessarily constant, has to be determined in accordance with the operation conditions of the coke ovens, since the combustion exhaust gas amount fluctuates depending on the operation rate of coke ovens 1 or its combustion conditions.
when gas is circulated through gas circulation pipe 21, it is acceptable also to open No. 3 control valve 22 and to close No. 2 control valve 19. By this, the phenomenon of air flowing back from stack 20 into gas circulation pipe 21 during gas circulation can be prevented from occurring.
Nos. 1 to 3 control valves can be controlled by the respective controllers (26 to 28) based on instructions from gas circulation system controller 23. It is of ****course possible to unify gas circulation system controller 23 with some or all of the controllers (26 to 28) for Nos. 1 to 3 control valves into a single controller unit. or, the controllers for the control valves can be integrated into respective control valves.
Control of a change of the feed gas for fluidized 0 0.bed dryer 7 during combustion changeover of coke ovens 1.
can be commenced upon receipt of a signal of commencement of a combustion changeover from the coke ovens, or based on a change of flow rate of the flue exhaust gas measured by the flue exhaust gas flow meter 5, etc. It is further preferable to receive a warning signal from coke ovens 1 in a certain period of time prior to the commencement of a combustion changeover, and commence the control of change of the feed gas for the fluidized bed dryer basing on the warning signal, as shown in the middle and lowermost rows of Figure 4. The warning signal is received, for example, I. min. before the flue exhaust gas flow becomes zero, and the gas recycling through gas circulation pipe 21 is commenced upon its receipt. In this way a problem of a shortage of the feed gas for fluidized bed dryer 7 due to delay in starting the gas 18 recycling can be avoided.
Since circulating gas 33 used during combustion c hangeover of coke ovens 1 has already been used for drying coal at-fluidized bed dryer 7, its temperature is lower than the flue exhaust gas from coke ovens as a matter of course, and its moisture content is high.
Hence, its coal drying capacity tends to be lower than that of the flue exhaust gas from coke ovens. By the present invention, the dryness degree of the coal discharged from fluidized bed dryer 7 can be maintained constant by decreasing the coal feed rate to fluidized bed 13 of fluidized bed dryer 7 while the circulating gas is used. It is preferable in this case to control the coal feed rate so that the coal temperature at the *.15 delivery side of the dryer is kept constant, by which the .*9.moisture content of the coal can be kept roughly constant. This results from the fact that, whereas the coal temperature at the delivery side of the dryer can be measured accurately, stable on-line measurement of the moisture content of coal is difficult. It is preferable that coal thermometer 30 be installed near the exit of the fluidized zone. It is acceptable to'insert it into a coal layer immxediately above coal discharger 37 at the exit of the fluidized bed as indicated by 30a in Figure 1 or in a discharged coal chute immediately below coal discharger 37 as indicated by 30b in Figure 1.
The coal feed rate to fluidized bed 13 during the use of the circulating gas can also be controlled so that the difference between the temperature of feed gas to the fluidized bed and the gas temperature at the exit of the fluidized bed dryer falls within a predetermined range.
Since the gas supply amount to the fluidized bed is generally kept constant to maintain the fluidization condition, the difference between the feed gas temperature and the gas temperature at the exit of the dryer changes in proportion to the amount of heat transferred per unit time from the gas to the coal.
-19 Consequently, by controlling the coal feed rate so that the above amount of heat falls within a predetermined range, it is possible to keep the moisture content of the coal at the delivery side of the dryer within a target range.
When reducing the coal feed rate to fluidized bed dryer 7 as stated above, it is preferable to maintain the coal layer thickness at fluidized bed 13 constant by reducing the coal discharge rate from fluidized bed dryer 7 at the same time. The reason for this is that, if the coal discharge rate from the fluidized bed dryer is left unchanged without reduction, the amount of coal residing in the fluidized bed dryer decreases as a result and thinning of the coal layer in fluidized bed 13 may lead *15 to a fall of differential pressure of the fluidized coal zone in fluidized bed 13 and, subsequently, a failure in :stable fluidization (blow-by).
Since the time required for a combustion changeover of the coke ovens is only about 2 to 3 min., the period of time during which the fluidized bed dryer uses the recycled gas is also short. Accordingly, although the ~.coal drying capacity of the gas is decreased by recycling the feed gas during the while, sufficient coal quality after drying is ensured by reducing the coal feed rate .25 and, additionally, the coal discharge rate as described above, and the decrease in the dried coal production due to the decreased coal feed rate can be minimized.
when a combustion changeover at the coke ovens is completed and the f low rate of the f lue exhaust gas f rom coke ovens returns to normal, it becomes possible to use the flue exhaust gas for feeding fluidized bed dryer 7.
While keeping the gas volume fed to fluidized bed dryer 7 roughly constant, the flue exhaust gas is introduced as feed gas for fluidized bed dryer 7 by opening both No. 1 control valve 10, which was closed during the combustion changeover, and also No. 2 control valve 19. Since the coal drying capacity of the feed gas increases with the change of the gas, the coal feed rate to the fluidized bed is increased so that the temperature of the coal discharged from fluidized bed dryer 7 stays within a predetermined target range. By this, the gas changing operation is completed while controlling the temperature and moisture content of the coal discharged from fluidized bed dryer 7 to respective targets. It is also acceptable to increase the coal feed rate to the fluidized bed so that the difference between the temperature of the feed gas for the fluidized bed and the temperature of the gas at the exit of the fluidized bed dryer falls within a predetermined range.
As for the control of the feed gas for the fluidized bed dryer during combustion changeover of the coke ovens, the changing operation may be done based on a predetermined pattern regarding the changes of the reused circulating gas volume and the coal feed rate to the fluidized bed dryer. This control method can be used effectively especially when the coal fed to the fluidized bed dryer shows a small fluctuation in moisture.
To maintain the coal drying capacity of the feed gas for the fluidized bed dryer as high as possible during gas recycling, it is preferable to keep the temperature of the feed gas as high as possible but not to the extent that it deteriorates the coal quality. By the present invention it is possible to keep a high coal drying capacity of the recycled gas by: making heat loss as small as possible through application of heat-insulation to the portion of the exhaust gas pipe 17 from the exit of fluidized bed dryer 7 to the branching point of gas circulation pipe 21, dust catcher 16 and the surfaces of gas circulation pipe 21 exposed to the atmosphere; and heating parts or all of the above heatinsulated portions either by stea-m by installing steam pipes or installing heating means 29 using an electric heater or high temperature gas, etc. In the case of gas pipes, it is possible to minimize heat loss by insulating 21 them with heat insulating materials. Figure 3 shows a Situation where heating means 29 is installed to dust catcher 16.
When a bag f1ilter is used as dust catcher 16, gas blowing operations are sometimes practiced to dedust the filter cloths of said bag filter, such as reverse blowing of air or pulse blowing of air or nitrogen to the filter cloths. The present invention allows for a method to blow gas as described above for cleaning the dust catcher during the gas recycling by discharging an amount of gas corresponding to said gas blowing to the outside of the system (through stack 27 in the case of Figure The coal drying capacity can be increased by this since the dust catcher cleaning gas is mixed with the recycled gas and the humidity of the recycled gas is lowered.
As described before, it is also possible to use the hot gas generated by hot gas generator 11 together with the flue exhaust gas from coke ovens as feed gas for fluidized bed dryer 7. while the gas is recycled due to a 20 combustion changeover of the coke ovens, the coal drying capacity of the feed gas for fluidized bed dryer 7 can be maintained by increasing the -temperature and flow of the gas generated by hot gas generator 11. Besides the method of mixing the hot gas generated by hot gas generator 11 with the recycled gas as shown in Figure 2 during the gas recycling, it is also possible to raise the temperature of the recycled gas itself by using the recycled circulating gas 33 as feed gas for hot gas generator 14 as shown in Figure 2 In the case where the flue exhaust gas from coke ovens and the hot gas generated by hot gas generator 11 are used as feed gas for fluidized bed dryer 7, when the flow and heat amount of the flue exhaust gas fall during combustion changeover, etc., it is possible to maintain the coal drying capacity of the feed gas for fluidized bed dryer 7 also by increasing the heat amount to be supplied to the gas at hot gas generator 11. In this case 22 it is possible, even if supply of the flue exhaust gas fluctuates, to keep normal operation of fluidized bed dryer 7 by controlling the supply volume and temperature of the hot gas from hot gas generator 11, following the fluctuation of the flue exhaust gas supply, so that the supply volume and temperature of the feed gas for fluidized bed dryer 7 are maintained at predetermined respective target values, It is also possible to rai-se the temperature of the flue exhaust gas by supplying it to hot gas generator 11 for heating.
As a result of drying coal in fluidized bed 13, the moisture of the gas fed to fluidized bed dryer 7 increases. The temperature of the gas falls as its heat is lost to the surroundings during its passage from fluidized bed dryer 7 until it is discharged to the atmosphere through stack 20 via dust catcher 16. when the gas temperature falls to or below the dew point, condensation occures. The condensate wets the filter cloths of the bag filter, which is often used for dust catcher 16, and causes clogging of the filter cloths.
By the present invention, while a portion of the flue exhaust gas from coke ovens is supplied to plenum chamber 35 of fluidized bed dryer 7 as feed gas for 0drying coal at the fluidized bed dryer 7, it is possible to add another portion of the flue exhaust gas from coke ovens to the exhaust gas from fluidized bed dryer 7 at a point between freeboard section 36 of fl~uidized bed dryer 7 and dust catcher 16. Since the flue exhaust gas is hot and its moisture content is low, the temperature of the exhaust gas mixed with said flue exhaust gas is raised and its humidity lowered and, thus, occurrence of condensation in the exhaust gas system can be prevented.
As a result, clogging of the filter cloths of the bag filter can also be prevented.
A coke-making process is generally composed of several coke ovens. within each coke oven, the timing of combustion changeover is simultaneous. However, the 23 timing of combustion changeover can be different between the different ovens.
By the present invention, the timing of combustion changeover of one coke oven is differentiated from another oven and flue exhaust gas from two ovens with different timing of combustion changeover is mixed to form the feed gas for fluidized bed dryer 7. By this, during combustion changeover of one oven, the flue exhaust gas volume from the other oven can be increased and thus interruption of the feed gas for fluidized bed dryer 7 is avoided, making it possible to operate a fluidized bed dryer 7 continuously and stably.
As it is necessary, first, to fluidize the coal in fluidized bed 13 at operation start of fluidized bed 15 dryer 7, a sufficient amount of the feed gas is supplied to fluidized bed 13 and the coal feed rate is gradually increased. when the flue exhaust gas from coke ovens is used as feed gas, the temperature of the feed gas is always high regardless of the operating condition of fluidized bed dryer 7. For this reason, while the coal feed rate is low at the beginning of operation, coal is excessively dried resulting in production of coal having lower moisture content than intended. When coal is excessively dried, there is a risk of dust emission or ignition of the coal after being discharged from the dryer.
By the present invention, it is possible to maintain constant the moisture content of the coal discharged from the dryer and prevent the excessive drying from taking place even at the beginning of operation of fluidized bed dryer 7 by adding water to the coal in fluidized bed 13 and increasing the coal feed rate gradually during the beginning of operation. Specifically, during the period from the initial stage of coal feeding until a stable fluidization status (pressure loss of the coal layer becomes roughly constant or achieves a predetermined range) is established, water is added to fluidized bed 13 24 in an amount corresponding to the heat amount required to dry the moisture and raise the sensible heat of the coal during stable operation,. The water can be sprayed in the form of mist either to the fluidized coal layer or to one or both of the freeboard sections near the exit Of the fluidized bed where upward exhaust flow exists and the coarse grain coal is moving toward the discharge port.
The moisture content of the coal fed to fluidized bed dryer 7 is not always constant and sometimes fluctuates with the passage of time. Therefore, it is necessary to maintain the moisture content of theL discharged coal at the dryer exit constant by changing the coal drying capacity of the dryer while keeping the coal feed rate constant. In the meantime, in order to maintain the fluidization condition of the fluidized bed constant, it is necessary to kepthe fow rate of the .feed gas for fluidized bed dryer 7 constant. For this reason, f.luctuation of moisture content of the feed ca has to be coped with by changing the coal drying capacity through a change of the feed gas temperature.
By the present invention wherein the flue exhaust gas from coke ovens is used as feed gas for the fluidized bed dryer, however, the flue exhaust gas temperature is determined by the operating conditions of the coke ovens 25 and it cannot be changed even if the moisture content of the feed coal fluctuates.
By the present invention, not only when the supply of the flue exhaust gas from coke ovens is interrupted or reduced but also in the stable operation status, a portion of the gas discharged from the fluidized bed dryer is circulated for use as feed gas for the fluidized bed dryer, the amount of the circulated gas is controlled based on the temperature of the coal measured at the exit of the fluidized bed dryer, and the amount of gas extracted from the flue of the coke ovens is also controlled, in parallel. The temperature of the coal at the exit of the fluidized bed dryer can be stabilized by 25 the above actions. When the moisture content of the feed coal for dryer 7 rises, the drying capacity becomes insufficient if the feed gas temperature is left unchanged, and the coal temperature at the exit of the dryer falls as a result. Accordingly, if a temperature decrease of the coal at the exit is detected, the coal drying capacity of the feed gas can be increased by reducing the reused circulating gas volume and increasing the extracted gas volume 3 from the coke oven flue. on the contrary, if the moisture content of the feed coal falls, the drying capacity becomes excessive if the feed gas temperature remains unchanged and, as a result, the coal temperature at the exit of the dryer rises.
Accordingly, the coal drying capacity of the feed gas can be decreased by taking an action which is reverse to the case in which the coal moisture content increases. it -is possible to keep the temperature and moisture content of the coal discharged from the dryer exit always constant by the control actions described above even when moisture content of the coal fed to dryer 7 fluctuates. The abovementioned control of the reused circulating gas volume and the extracted gas volume from the coke oven flue can be done based also on the difference between the temperature of the feed gas for the fluidized bed and the temperature of the gas at the exit of the fluidized bed dryer. Since the gas supply rate to the fluidized bed is generally kept constant to maintain the fluidization condition, the difference between the feed gas temperature and the gas temperature at the exit of the dryer changes in proportion to the amount of heat transferred per unit time from the gas to the coal.
Consequently, by controlling -the reused circulating gas volume and the extracted volume of coke oven flue gas based on the above amount of heat, it is possible to keep constant the temperature and moisture content of coal discharged from the dryer exit.
A fluidized bed dryer 7 can classify coal while 26 drying it. The feed gas blown in from under fluidized bed 13 forms an upward flow, and fine coal of small grain size in the coal in fluidized bed 13 is carried by the upward gas flow to the outside of the dryer together with the exhaust gas. It is possible to control the range of grain size of the fine coal to be carried away by the exhaust gas by specifically setting the flow speed of the upward gas flow. The fine coal included in the exhaust gas is captured by dust catcher 16 as classified fine coal.
By separating the fine coal carried away by the gas discharged from the fluidized bed by solid-gas separation, and mixing and kneading said separated fine coal with an additive composed of liquid containing heavy hydrocarbon derived from coal or petroleum, it is possible, by the present invention, to use said kneaded 'Line coal as coke oven feedstock together with the abovementioned coal dried by the fluidized bed dryer. Said additive has a function to bind the fine coal to form it into pseudo particles by kneading. The addition amount of the above-mentioned additive is preferably, by mass, in a range of 3 to 25 parts against 100 parts of fine coal.
The reason for this is that, if the addition is below 3 in the above ratio, it is difficult to evenly mix dry fine coal but if it exceeds 25, the tar content in the additive may form local liquid pools or coal may stick to components of the transfer system during transport to the coke ovens.
Since fine grains of coal are eliminated from the coal discharged from fluidized bed dryer 7 by the above process, dust emission during transport to the coke ovens is minimal. Besides, since the recovered fine coal is mixed and formed by the binder, it can be used as coke oven feedstock without causing dust emission.
As stated above, fine coal can be pressure-formed after being mixed and kneaded with a binder. in this way, fine coal can be changed into formied coal of any size and 27 shape, and the generation of dust by the breaking up of coal which has been formed into pseudo particles can be avoided. Further, when the formed fine coal is charged into coke ovens, the bulk density of the charged coal is increased and coke quality can be enhanced.
Example Some embodiments of the present invention are described hereafter based on Figure 1.
The present invention was applied to a coal drying operation to decrease the moisture content of coal for coke production from about 10% to 6% using a fluidized bed dryer. The subject coke oven is composed of 100 coking chambers in total, namely two half-ovens each of which has 50 coking chambers. The fluidized bed dryer dries coal to be fed to the coke oven and its coal (wet) processing capacity is 100 t1/h.
Flue exhaust gas from the above-mentioned coke oven was used as feed gas for the fluidized bed dryer. The temperature of the coke oven exhaust gas was 220'C and the flue exhaust gas volume per half oven was 82,000 Nm/h.
0.0. Out of the above-mentioned flue exhaust gas volume of a coke oven, 65,000 Nrn 3 /h was extracted from flue 2 to gas pipe 8 and fed to fluidized bed dryer 7. During the normal operation, No. 2 control valve 19 was set at an opening of 60% maintaining a stable control range and, at the same time, No. 3 control valve 22 was set at an opening of 5% to circulate about 7,000 Nm 3 /h of dryer exhaust gas from pipe 17 through gas circulation pipe 21.
A gas volume of 68,000 NM3/h out of a total of 72,000
I
Nn 3 made up of 65,000 Nin 3 /h of coke oven flue exhaust gas and 7,000 Nm 2 /1h of circulating gas, was used as feed gas 34 for fluidized bed dryer 7. The remaining 4,000 Nm3/h was mixed with exhaust gas 32 fronm the fluidized bed dryer at a point between the freeboard section of dryer 7 and dust catcher 16. Further, a steam pipe of roughly 10-mm in diameter was arranged in serpentine 28 fashion around the hopper portion under the bag filter and covered with a heat insulating material for heat insulation of the exhaust, gas 32 from the fluidized bed dryer.
As a result of drying coal under the above-described condition, the temperature of the coal at the dryer exit was 52'C, controlled within a target temperature range of to 55'C, and the target coal moisture of 6% at the dryer exit was achieved, the moisture being lowered by 4% in the dryer.
The frequency of combustion changeover of the coke ovens in these Examples was set at 30 min. as the coke ovens operated at an output level of 100 t/h, although it can be as short as 15 min. when oven output is high.
(Example 1) Control of the feed gas for the fluidized bed dryer during combustion changeover is described hereafter based on Figures 4 and The coke ovens issue a warning signal 1 min. prior to the commencement of a combustion changeover. Upon commencement of the combustion changeover, a fuel gas closing operation of the combustion side of system A was commenced in the first place, as shown in Figure 4, to attain a complete closure in 15 sec. Then, a closing operation of the air for combustion was commenced to attain a complete closure in 15 sec. After 4 sec. of the complete closure, system B was turned to the combustion side, and air of the combustion side began to be introduced to attain a normal level in 15 sec., then fuel gas began to be introduced to attain a normal gas flow level in 15 sec. The change of the flue exhaust gas flow of the coke ovens with the passage of time was as shown in the lowermost row of Figure 4 and the uppermost row of Figure Controllers 23 to 28 of the fluidized bed dryer begin to control the valves upon receipt of the abovementioned warning signal of a combustion changeover. The 29 control schemes are described hereafter based on Figure First, No. 1 control valve 10 was gradually closed from an opening of 55% to finally reach an opening of In parallel, No. 3 control valve 22 was opened from an opening of 5% to an opening of 40%, then No. 2 control valve 19 was closed from an opening of 60% to an opening of As a result of the above valve operations, 60,000 Nm3/h out of the fluidized bed dryer exhaust gas 32 was recycled through gas circulation pipe 21. In the meantime, the flow of feed gas 34 to the fluidized bed dryer was set at 56,000 Nmn/h, 8,000 Nm 3 /h less than during normal operation, and 56,000 Nm 3 /h out of the above-mentioned recycled gas was used as feed gas 34, and 4,000 NM 3 /h was mixed with the fluidized bed dryer exhaust gas 32 at a point between the freeboard section of dryer 7 and dust'catcher 16. Besides the above, while the circulating gas was used, the coal feed rate to the dryer was reduced by 15% from 100 t/h of normal operation to 85 t/h. The above sequence of valve operations and adjustment of the coal feed rate were carried out following a prescribed pattern based on the warning signal of combustion changeover. when a combustion changeover was completed, the valve operations were reversed from those at the commencement of the combustion changeover, then, after completing these valve operations, the coal feed rate was returned to the normal position.
Air from the atmosphere is used in pulsating jets for dedusting the bag filter, which operation usually requires 7 Nm 3 /min. of air. During the above combustion changeover of the coke ovens, the air flow was increased to 35 Nrn 3 /min.
Even when the supply of the flue exhaust from coke ovens gas was interrupted during combustion changeover of the coke oven, the feed gas for fluidized bed dryer 7 was secured and fluidization of the fluidized bed was 30 sustained by recycling the gas. Further, insufficient drying of coal was minimized by reduction of the coal feed rate to the fluidized bed during combustion changeover.
The temperature of the gas discharged from fluidized bed dryer 7 was lowered to approximately 50'C and the gas contained roughly 5 t/h of fine coal smaller than 0.1 rm in grain size. Although moisture content of the exhaust gas was 25%, neither condensation nor clogging of filter cloths occurred at the bag filter, thus, fine coal several micrometers in size could be captured and the exhaust gas could be discharged to the atmosphere without further treatment, due to a portion of the fluidized bed 0 *1 dryer feed gas being mixed with the dryer exhaust gas at beef~ 15 the freeboard section and also the hopper portion under 0004 the bag filter being heated with steam and covered with heat insulating materials.
***Eighty percent of the fine dust collected by the bag goo f filter was fine coal of less than 0.1 mm in grain size.
Tax- was added to this as an additive. The temperature of *888 the tar was maintained at about 80 0 C to lower its 8888 viscosity and keep it liquefied and, by mass, 10 to 88parts of tar was added to 100 parts of fine coal. Then, 8..8 pseudo particles of fine coal were obtained through kneading the above mixture, which pseudo particles showed *.644 suppressed dust emission when charged to the coke ovens 0:46 together with the coal discharged from fluidized bed dryer 7.
(Example 2) Following the control pattern shown in Figure 6, control operations were carried out to regulate the flow of circulating gas 33 to 72,000 Nm 3 /h during combustion changeover of the coke ovens, maintain the flow of feed gas 34 for the fluidized bed dryer constant and maintain the coal feed rate constant at 100 t/h. The other conditions were kept the same as in Example 1 above.
Since the flow of feed gas 34 for the dryer was kept 31 constant, the fluidization state of the fluidized bed was maintained while keeping the coal feed rate constant.
Since the coal feed rate was kept constant during the use of the circulating gas, the moisture in the coal discharged from the dryer rose by somne extent. However, because the period of use of the circulating gas was as short as less than 2 min., the production amount of the coal having the higher moisture content was controlled to approximately 3 t, and the rise in the coal moisture was as small as from 6% during normal operation to 7%.
(Example 3) Following the control pattern shown in Figure 7, the :::.flow of circulating gas 33 during combustion changeover *of the coke ovens was regulated to 68,000 Nn 3 /h and 15 combustion exhaust gas heated to 280*C separately by a hot gas generator was used at a flow rate of 10,000 Nm 3 /h :as a-portion of the feed gas, only while the circulating gas was used. The total flow of feed gas 34 for the fluidized bed dryer was kept constant, and the coal feed rate was also kept constant at 100 t/h. The other conditions were kept the same as in Example 1 above.
Since the gas from the hot gas generator was additionally used, *a sufficient coal drying capacity of the feed gas was ensured, and thus the moisture of the discharged coal was kept equal to that of normal operation while maintaining the same coal feeding rate as during normal operation.
(Example 4) The feed gas for the dryer was secured by using the flue exhaust gas from coke ovens from two ovens (East Oven and West Oven) having different timing of combustion changeover, using the exhaust gas from both ovens during normal operation, and increasing the supply volume of the exhaust gas from one oven during a combustion changeover of the other oven. The control pattern is shown in Figure 8.
The flue exhaust gas volume of either East Oven or 32 West Oven is 100,000 Nm 3 /h during normal operation. A volume of 40,000 Nm 3 /h out of the exhaust gas from each of the ovens is used as feed gas for the dryer during normal operation. At the time of a combustion changeover at East Oven (12:310), the gas supply rate from West Oven was increased to 80,000 Nrn 2 /h to secure the feed gas for the dryer. Conversely, at the time of a combustion changeover at West Oven (12:45), the gas supply rate from East Oven was increased to 80,000 Nm 3 /h to secure, in -the same way, the feed gas for the dryer.
By this, stable coal drying operation was ensured, since flue exhaust gas from coke ovens having a constantly sustained drying capacity was used as the dryer feed gas.
:15 By the present invention, it is possible to always secure as much feed gas for a fluidized bed dryer as required by reusing exhaust gas from the fluidized bed.
dryer as feed gas for the fluidized bed dryer by circulating it when supply of flue exhaust from coke ovens gas is interrupted or reduced due to causes such as a combustion changeover of coke ovens.
.It iS possible to maintain moisture of the coal discharged from the dryer to a target value by reducing the coal feed rate to the fluidized bed while the feed *.25 gas is circulated for reuse.
The coal drying capacity of the recycled gas can be kept high by insulating the gas recycling route and installing heating means using steam or electric heaters, etc. to some or all of the above-mentioned heat-insulated portion.
The coal drying capacity can be raised by blowing gas for cleaning the dust catcher during the recycling of gas since the gas for cleaning Ithe dust catcher is mixed into the recycled gas.
Condensation of moisture in the exhaust gas route is prevented from occurring by supplying the flue exhaust gas from coke ovens to the exhaust gas from the fluidized 33 bed dryer.
By mixing flue exhaust gas from two coke ovens having different timing of combustion changeover and using the mixed gas for feeding a fluidized bed dryer, interruption of feed gas for the fluidized bed dryer is avoided and thus continuous stable operation of the fluidized bed dryer is made possible.
By adding water to coal in a fluidized bed and gradually increasing the coal feeding rate during operation start of a fluidized bed dryer, moisture content of coal discharged from the dryer is kept constant, preventing over-drying from occurring even during starting.
By adding an additive to fine coal carried by 15 exhaust gas from a fluidized bed, kneading and then pressure-forming the fine coal and additive, the fine coal can be turned into coke oven feedstock to be used together with the coal dried by a fluidized bed dryer.
**o*i *o *oo

Claims (5)

1. A method for drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens as a portion or all of a feed gas to the fluidized bed dryer, characterized in that; an exhaust gas from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, when supply of the flue exhaust gas from coke ovens is interrupted or reduced.
2. A method for drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens as a portion or all of a feed gas to the fluidized bed dryer, characterized in that; an amount of coal fed to a fluidized bed is reduced, as well as the exhaust gas from the fluidized bed dryer is circulated and reused as a .is1 feed gas to the fluidized bed dryer, when the supply of the flue exhaust gas from coke ovens is interrupted or ~.reduced.
3. A method for drying coal by a fluidized bed dryer using flue exhaust gas from coke ovens as a port-ion or all of a feed gas to the fluidized bed dryer, characterized in that; both an amount of coal discharged from the fluidized bed and an amount of coal fed to the fluidized bed are reduced, as well as the exhaust gas from the fluidized bed dryer is circulated and reused as *.25 a feed gas to the fluidized bed dryer, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced to maintain a thickness of a coal layer in the fluidized bed within a predetermined thickness.
4. A method for drying coal according to claim 2 or 3, characterized in that; an amount of coal fed to the fluidized bed is controlled so that temperature of coal at an exit of the dryer is kept nearly constant, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced.
355. A method for drying coal according to claim 2 or 3, characterized in that; an amnount of coal fed to the fluidized bed is controlled so that a difference between 35 temperature of the feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range. 6. A method for drying coal according to claim 2 or 3, characterized in that; the flue exhaust gas of coke ovens is used as a feed gas to the fluidized bed dryer, and an amount of coal fed to the fluidized bed is increased so that temperature of the coal at an exit of the dryer is kept within a predetermined target range, when the supply of the flue exhaust gas from coke ovens is resumed. 7. A method for drying coal accordin g to clai-m 6, characterized in that; an amount of coal fed to the fluidized bed is increased so that a difference between temperature of a feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range. 8. A method f or drying coal according to any one of claims 1 to 3, characterized in that; a portion or all of the route of gas exhausted. from the fluidized bed dryer and circulated to be fed to the fluidized bed dryer is neat-insulated, and a portion of gas isheated. 9. A method for drying coal according to any one of claims I to 3, characterized in that; when gas exhausted from the fluidized bed dryer is circulated and *reused as a feed gas to -the fluidized bed dryer, a gas is blown for a purpose of cleaning a dust catcher installed in the route of said circulating gas, and an amount of gas corresponding to an amount of gas increased by said gas blowing is added to an amount of gas discharged to the outside. A method for drying coal according to any one of claims 1 to 3, characterized in that; a warning signal is issued before supply of the flue exhaust gas from coke ovens is interrupted or reduced, and following a sequence based on said signal, one or more of the following actions is/are taken: changing an amount of the exhaust gas circulated and used as a feed gas to the fluidized bed dryer, changing an amount of coal fed to the fluidized bed, changing an amount of coal discharged from the fluidized bed, heating a circulating gas, and blowing a gas for the cleaning of the dust catcher. 11. A method for drying coal according to any one of claims 1 to 3, characterized in that; when the supply of the flue exhaust gas from coke ovens is interrupted or reduced, a hot gas supplied from a hot gas generator is used as a portion of a feed gas to the fluidized bed dryer. 12. A method for drying coal according to any one of claims 1 to 3, wherein hot gas supplied from a hot gas generator is used as a feed gas to the fluidized bed dryer together with the flue exhaust gas from coke ovens, characterized in that; the supply volume and temperature of o the feed gas to the fluidized bed dryer are maintained at :.*respectively predetermined target values by controlling the 20 supply volume and/or the temperature of the hot gas in accordance with a variation of the supply volume of the flue exhaust gas from coke ovens. o 13. A method for drying coal according to any one of claims 1 to 3 and 12, characterized in that; one or both of e* 25 a circulating gas and the flue exhaust gas from coke ovens fed to the fluidized bed dryer is/are heated. 14. A method for drying coal according to any one of claims 1 to 3 and 12, characterized in that; a portion of a feed gas is supplied to a plenum chamber of the fluidized bed and, at the same time, the remainder of said feed gas is supplied to the exhaust gas from the dryer at a point between the a freeboard section of the dryer and the dust catcher. A method for drying coal according to any one of claims 1 to 3, wherein the flue exhaust gas from coke ovens S3S s used as a portion or all of a feed gas to the fluidized '6 ed dryer, characterized in that; flue exhaust gas from two A04659 coke ovens having different timing of combustion changeover is mixed and used as a feed gas to the fluidized bed dryer. 16. A method for drying coal according to any one of claims 1 to 3, 12 and 15, characterized in that; the coal feed rate to said dryer is gradually increased while feeding a feed gas to said dryer and adding water to the fluidized bed during a start of an operation of the fluidized bed dryer. 17. A method for drying coal according to any one of claims 1 to 3, 12 and 15, characterized in that; both the flue exhaust gas from coke ovens and the circulating gas discharged from the fluidized bed dryer are used as a feed gas to the fluidized bed dryer, a consumption amount of the circulating gas is controlled based on a coal temperature 15 measured at an the exit of the fluidized bed dryer, an 0extracted gas volume from the coke oven flue is also controlled at the same time, and a coal temperature at the 0a exit of the fluidized bed dryer is stabilized by the above .0 40 three measures. 20 18. A method for drying coal according to any one of claims 1 to 3, 12 and 15, characterized in that; both the flue exhaust gas from coke ovens and the circulating gas discharged from the fluidized bed dryer are used as a feed gas to the fluidized bed dryer, a consumption amount of the 25 circulating gas is controlled based on a difference between *temperature of the feed gas to the fluidized bed and 000",s temperature of gas at an exit of the fluidized bed dryer, a volume of the gas extracted from the flue coke ovens is also controlled at the same time, and a coal temperature at the exit of the fluidized bed dryer is stabilized by the above three measures. 19. A method for drying coal according to any one of claims 1 to 3, 12 and 15, characterized in that; fine A04659 -38 coal contained in the gas discharged from the fluidized bed is separated by solid-gas separation, said separated fine coal is mixed and kneaded with an additive composed of liquid containing heavy hydrocarbon derived from coal or petroleum, and said mixed and kneaded fine coal is used as feedstock to the coke ovens together with coal dried by the fluidizedi bed dryer. A method for drying coal according to any one of claims 1 to 3, 12 and 15, characterized in that; fine coal contained in a gas discharged from the fluidizedi bed is separated by solid-gas separation, said separated fine coal is mixed and kneaded with an additive composed of liquid containing heavy hydrocarbon derived from coal or petroleum, said mixed and kneaded fine coal is formed by .15 pressure-forming, and said formed fine coal is used as feedstock to the coke ovens together with the coal dried :by the fluidized bed dryer. 21. An apparatus for drying coal having fluidized bed dryer for drying coal and a gas pipe for supplying some or all. of the flue exhaust gas from coke ovens to the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer back to the fluidized bed dryer, and C *25 a gas circulation system controller used for controlling so that a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer when the supply of the flue exhaust gas from coke ovens is interrupted or reduced. 22. An apparatus for drying coal having a fluidized bed dryer for drying coal and a gas pipe for supplying some or all of the flue exhaust gas from coke ovenis to the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer back to the fluidized bed dryer, 39- a gas circulation system controller used for controlling so that a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, and a coal feed amount controller used for controlling so that an amount of coal fed to the fluidized bed is decreased, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced. 23. An apparatus for drying coal having fluidized bed dryer for drying coal and a gas pipe for supplying some or all of the flue exhaust gas from coke ovens to the fluidized bed dryer, characterized by comprising; a gas circulation pipe for circulating and supplying a gas exhausted from the fluidized bed dryer :15 back to the fluidized bed dryer, a gas circulation system controller used .for controlling so that a gas exhausted from the flu-idized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, a coal feed amount controller used for controlling so that an amount of coal fed to the fluidized bed is decreased, anid a coal discharge amount controller used for controlling so that thickness of coal layer of the *.25 fluidized bed is maintained by reducing an amount of coal discharged from the fluidized bed, when the supply of the flue exhaust gas from coke ovens is interrupted or reduced. 24. An apparatus for drying coal according to claim 22 or 23, characterized in that; an amount of coal fed to the fluidized bed is controlled so that temperature of coal at an exit of the dryer is kept nearly constant, when the supply of the flue exhaust from coke ovens gas is interrupted or reduced. 25. An apparatus for drying coal according to claim 22 or 23, characterized in that; an amount of coal fed to the fluidized bed is controlled so that a difference 40 between temperature of a feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range. 26. An apparatus for drying coal according to claim 22 or 23, characterized in that; when the supply of the flue exhaust gas from coke ovens is resumed, the gas circulation system controller is used for controlling so that the flue exhaust gas from coke ovens is used as a feed gas to the fluidized bed dryer, and the coal feed amount controller is used for increasing an amount of coal fed to the fluidized bed so that temperature of coal at an exit of the dryer is kept within a predetermined *target range. :27. An apparatus for drying coal according to claim 26, characterized in that; an amount of coal fed to the fluidized bed is increased so that a difference between :temperature of a feed gas to the fluidized bed and temperature of gas at an exit of the fluidized bed dryer falls within a predetermined range. 28. An apparatus for drying coal according to any one of claims 21 to 23, characterized in that; a portion or all of the route of the gas exhausted from the fluidized bed dryer and circulated to be fed to the fluidized bed dryer is heat-insulated, and a heating .25 means is provided to heat some of the gas. *29. An apparatus for drying coal according to any one of claims 21 to 23, characterized in that; when a gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, a gas cleaning controller of a dust catcher installed in the route of a circulating gas is used for blowing a gas for a purpose of cleaning, and a dryer exhaust gas controller is used for controlling so that an amount of a gas corresponding to an amount of gas increased by said gas blowing is added to an amount of gas discharged to the outside. An apparatus for drying coal according to any -41 one of claims 21 to 23, comprising; a stack to discharge gas exhausted from the fluidized bed dryer to the outside, an exhaust gas pipe to conduct the gas exhausted from the fluidized bed dryer to the stack, No. 1 control valve installed on a gas pipe to supply some or all of the flue exhaust gas from coke ovens to the fluidized bed dryer and a controller for said No. 1 control valve, 1 0 No. 2 control valve installed on the exhaust gas pipe and a controller for said No. 2 control valve, and No. 3 control valve installed on the gas circulation pipe, and a controller for No. 3 control S valve; and controlling so that; when the gas exhausted from the fluidized bed dryer is circulated and reused as a feed gas to the fluidized bed dryer, the controller for No. 1 control valve closes No. 1 control valve, the controller for No. 2 control valve closes No. 2 control valve, and the controller for No. 3 control valve opens No. 3 control valve. 31. An apparatus for drying coal according to any one of claims 21 to 23, characterized in that; the coke ovens have means to issue a warning signal before supply of the flue exhaust gas from coke ovens is interrupted or reduced, and following a sequence based on said warning signal, the gas circulation system controller, the coal feed amount controller, the coal discharge amount controller, the heating means, the gas cleaning controller of the dust catcher, and the controllers for Nos. 1 to 3 control valves carry out one or more of the following actions: changing an amount of the exhaust gas circulated and used as a feed gas to the fluidized bed dryer, changing an amount of coal fed to the .4 Ilui1dised bed. changing an amount of coal discharged fromn the fluidised bed, heating a circulating gas, and blowing gas for cleaning a dust catcher. 3. A method for drying coal, substantially as hiereinbefore described with reference to any one of the examples. 3. An apparatus for drying coal, substantially as hereinibefore described wvith reference to Figures 1-3. 3)4. Dried coal when produced by the method of any one of 'claimns 1 -20 or ev 0 000 4 asse 6000 0 0.. @0 0 Dated 18 August, 2000 Nippon Steel Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON I R :\IB1Z jO5264.doc:baiv
AU53506/00A 1999-08-18 2000-08-18 Method and apparatus for drying coal Expired AU746076B2 (en)

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RO121939B1 (en) 2008-08-29
KR100360223B1 (en) 2002-11-11
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CN1120872C (en) 2003-09-10
CN1285388A (en) 2001-02-28

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