CA2725276A1 - Method for producing pulverized coal - Google Patents
Method for producing pulverized coal Download PDFInfo
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- CA2725276A1 CA2725276A1 CA2725276A CA2725276A CA2725276A1 CA 2725276 A1 CA2725276 A1 CA 2725276A1 CA 2725276 A CA2725276 A CA 2725276A CA 2725276 A CA2725276 A CA 2725276A CA 2725276 A1 CA2725276 A1 CA 2725276A1
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- Prior art keywords
- drying gas
- pulverizer
- temperature
- volume
- oxygen level
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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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/04—Safety devices
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
- B02C23/18—Adding fluid, other than for crushing or disintegrating by fluid energy
- B02C23/24—Passing gas through crushing or disintegrating zone
- B02C23/34—Passing gas through crushing or disintegrating zone gas being recirculated to crushing or disintegrating zone
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B5/00—Making pig-iron in the blast furnace
- C21B5/001—Injecting additional fuel or reducing agents
- C21B5/003—Injection of pulverulent coal
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B17/00—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement
- F26B17/10—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers
- F26B17/101—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers the drying enclosure having the shape of one or a plurality of shafts or ducts, e.g. with substantially straight and vertical axis
- F26B17/103—Machines or apparatus for drying materials in loose, plastic, or fluidised form, e.g. granules, staple fibres, with progressive movement with movement performed by fluid currents, e.g. issuing from a nozzle, e.g. pneumatic, flash, vortex or entrainment dryers the drying enclosure having the shape of one or a plurality of shafts or ducts, e.g. with substantially straight and vertical axis with specific material feeding arrangements, e.g. combined with disintegrating means
-
- 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
- F26B21/06—Controlling, e.g. regulating, parameters of gas supply
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Food Science & Technology (AREA)
- General Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Manufacturing & Machinery (AREA)
- Metallurgy (AREA)
- Solid Fuels And Fuel-Associated Substances (AREA)
- Drying Of Solid Materials (AREA)
- Disintegrating Or Milling (AREA)
- Coke Industry (AREA)
Abstract
Method for producing pulverized coal, the method comprising the steps of heating a drying gas, preferably an inert gas, in a hot gas generator (26) to a predefined temperature; feeding the heated drying gas into a pulverizer (20); introducing raw coal into the pulverizer (20), the pulverizer (20) grinding the raw coal into pulverized coal; collecting a mixture of drying gas and pulverized coal from the pulverizer (20) and feeding the mixture to a filter (34), the filter (34) separating the dried pulverized coal from the drying gas; collecting the dried pulverized coalfor further use and feeding the drying gas from the filter (34) to a recirculation line (38) for returning at least part of the drying gas to the hot gas generator (26); and determining an oxygen level in the drying gas, preferably in the recirculation line (38), and comparing the determined oxygen level to a predetermined oxygen level threshold. According to a preferred embodiment of the invention, if the determined oxygen level is higher than a predetermined oxygen threshold, water is injected into the heated drying gas before it is fed into the pulverizer (20), the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxygen level threshold.
Description
Method for producing pulverized coal TECHNICAL FIELD
The present invention generally relates to a method for the production of pulverized coal, in particular for use in the metallurgical industry.
BACKGROUND ART
In the metallurgical industry, pulverized coal is generally injected as com-bustible into blast furnaces. It is important, in order to ensure good functioning of the blast furnace, that the pulverized coal is of good quality, i.e. that the pulverized coal has the right consistence, size and humidity level. The pulver-ized coal is generally produced in a grinding and drying installation, wherein raw coal is ground in a pulverizer and dried to the right humidity level before the resulting pulverized coal is fed to a hopper for storage or direct use in a blast furnace. It is known to subject the freshly ground coal to a stream of hot gas so as to dry the pulverized coal. The pulverized coal can e.g. be entrained by the hot gas from the pulverizer to a filter, where the pulverized coal is then separated from the gas and fed to the hopper. Part of the gas is recirculated and heated before it is reintroduced into the pulverizer .
For the correct functioning of the grinding and drying installation, it is im-portant to monitor the oxygen level in the drying gas, generally downstream of the filter. If the oxygen level becomes too high, the combination of drying gas and pulverized coal may become an explosive mixture with potentially danger-ous consequences. Generally, in the recirculation line, i.e. in the line returning the drying gas back to the pulverizer, exhaust gasses are extracted from the drying gas and fresh air is injected.
In known grinding and drying installations, the oxygen level in the drying gas is monitored and, if the measured oxygen level is found to be too high, the amount of fresh air introduced into the drying gas in the recirculation line is
The present invention generally relates to a method for the production of pulverized coal, in particular for use in the metallurgical industry.
BACKGROUND ART
In the metallurgical industry, pulverized coal is generally injected as com-bustible into blast furnaces. It is important, in order to ensure good functioning of the blast furnace, that the pulverized coal is of good quality, i.e. that the pulverized coal has the right consistence, size and humidity level. The pulver-ized coal is generally produced in a grinding and drying installation, wherein raw coal is ground in a pulverizer and dried to the right humidity level before the resulting pulverized coal is fed to a hopper for storage or direct use in a blast furnace. It is known to subject the freshly ground coal to a stream of hot gas so as to dry the pulverized coal. The pulverized coal can e.g. be entrained by the hot gas from the pulverizer to a filter, where the pulverized coal is then separated from the gas and fed to the hopper. Part of the gas is recirculated and heated before it is reintroduced into the pulverizer .
For the correct functioning of the grinding and drying installation, it is im-portant to monitor the oxygen level in the drying gas, generally downstream of the filter. If the oxygen level becomes too high, the combination of drying gas and pulverized coal may become an explosive mixture with potentially danger-ous consequences. Generally, in the recirculation line, i.e. in the line returning the drying gas back to the pulverizer, exhaust gasses are extracted from the drying gas and fresh air is injected.
In known grinding and drying installations, the oxygen level in the drying gas is monitored and, if the measured oxygen level is found to be too high, the amount of fresh air introduced into the drying gas in the recirculation line is
2 reduced. This allows lowering the oxygen level in the drying gas.
However, in some circumstances, e.g. if the raw coal is very dry and/or if the installation is run under reduced load, the reduction of the amount of fresh air introduced into the drying gas may not be enough to sufficiently reduce the oxygen level. Indeed, once the amount of fresh air introduced into the drying gas is reduced to zero, i.e. no more fresh air is introduced, the oxygen level may in such circumstances still be too high. In order to avoid any damage to the installation it may then be necessary to shut down the grinding and drying installation. Such a shut down not only leads to a loss of production, but also to extra costs relating to the replacement or conditioning of the drying gas.
OBJECT OF THE INVENTION
The object of the present invention is to provide an improved method for producing pulverized coal, which does not present the drawbacks of the prior art methods. This object is achieved by a method as claimed in claim 1.
GENERAL DESCRIPTION OF THE INVENTION
To achieve this object, the present invention proposes a method for pro-ducing pulverized coal, the method comprising the steps of:
- heating a drying gas, preferably an inert gas, in a hot gas generator to a predefined temperature;
- feeding the heated drying gas into a pulverizer;
- introducing raw coal into the pulverizer, the pulverizer grinding the raw coal into pulverized coal;
- collecting a mixture of drying gas and pulverized coal from the pulverizer and feeding the mixture to a filter, the filter separating the dried pulverized coal from the drying gas;
- collecting the dried pulverized coal for further use and feeding the drying gas from the filter to a recirculation line for returning at least part of the dry-
However, in some circumstances, e.g. if the raw coal is very dry and/or if the installation is run under reduced load, the reduction of the amount of fresh air introduced into the drying gas may not be enough to sufficiently reduce the oxygen level. Indeed, once the amount of fresh air introduced into the drying gas is reduced to zero, i.e. no more fresh air is introduced, the oxygen level may in such circumstances still be too high. In order to avoid any damage to the installation it may then be necessary to shut down the grinding and drying installation. Such a shut down not only leads to a loss of production, but also to extra costs relating to the replacement or conditioning of the drying gas.
OBJECT OF THE INVENTION
The object of the present invention is to provide an improved method for producing pulverized coal, which does not present the drawbacks of the prior art methods. This object is achieved by a method as claimed in claim 1.
GENERAL DESCRIPTION OF THE INVENTION
To achieve this object, the present invention proposes a method for pro-ducing pulverized coal, the method comprising the steps of:
- heating a drying gas, preferably an inert gas, in a hot gas generator to a predefined temperature;
- feeding the heated drying gas into a pulverizer;
- introducing raw coal into the pulverizer, the pulverizer grinding the raw coal into pulverized coal;
- collecting a mixture of drying gas and pulverized coal from the pulverizer and feeding the mixture to a filter, the filter separating the dried pulverized coal from the drying gas;
- collecting the dried pulverized coal for further use and feeding the drying gas from the filter to a recirculation line for returning at least part of the dry-
3 PCT/EP2009/056763 ing gas to the hot gas generator;
- determining an oxygen level in the drying gas, preferably in the recirculation line, and comparing the determined oxygen level to a predetermined oxygen level threshold.
According to a preferred embodiment of the invention, the oxygen level in the drying gas is determined during a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer and if, during the grinding cycle, the determined oxygen level is higher than a predetermined oxygen threshold, water is injected into the heated drying gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxygen level threshold. The injection of water into the drying gas during the grinding cycle allows increasing the overall volume of the drying gas, thereby reducing the relative oxygen volume. The water injection therefore allows reducing the oxygen level to an acceptable level and thereby avoids any damage to the installation or the need to shut down the grinding and drying installation.
According to a preferred embodiment, the method further comprises in-jecting, in the recirculation line, fresh air into the drying gas wherein, if the determined oxygen level is higher than the predetermined oxygen level thresh-old, the volume of fresh air injected into the drying gas is reduced.
Advantageously, the method comprises first reducing the volume of fresh air injected into the drying gas, and then, if the volume of fresh air injected reaches zero and the oxygen level is still higher than the predetermined oxygen threshold, injecting water into the heated drying gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxygen level threshold.
Preferably, the predetermined oxygen threshold is chosen to be between 0 and 14 volume %, preferably between 5 and 12 volume %.
According to a further aspect of the present invention, the method com-prises the further steps of determining an exit temperature of the mixture of
- determining an oxygen level in the drying gas, preferably in the recirculation line, and comparing the determined oxygen level to a predetermined oxygen level threshold.
According to a preferred embodiment of the invention, the oxygen level in the drying gas is determined during a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer and if, during the grinding cycle, the determined oxygen level is higher than a predetermined oxygen threshold, water is injected into the heated drying gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxygen level threshold. The injection of water into the drying gas during the grinding cycle allows increasing the overall volume of the drying gas, thereby reducing the relative oxygen volume. The water injection therefore allows reducing the oxygen level to an acceptable level and thereby avoids any damage to the installation or the need to shut down the grinding and drying installation.
According to a preferred embodiment, the method further comprises in-jecting, in the recirculation line, fresh air into the drying gas wherein, if the determined oxygen level is higher than the predetermined oxygen level thresh-old, the volume of fresh air injected into the drying gas is reduced.
Advantageously, the method comprises first reducing the volume of fresh air injected into the drying gas, and then, if the volume of fresh air injected reaches zero and the oxygen level is still higher than the predetermined oxygen threshold, injecting water into the heated drying gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxygen level threshold.
Preferably, the predetermined oxygen threshold is chosen to be between 0 and 14 volume %, preferably between 5 and 12 volume %.
According to a further aspect of the present invention, the method com-prises the further steps of determining an exit temperature of the mixture of
4 drying gas and pulverized coal exiting the pulverizer; and controlling the exit temperature by controlling a volume of water injected into the heated drying gas before feeding it into the pulverizer. By controlling the amount of water injected into the drying gas upstream of the pulverizer, the temperature of the drying gas entering the pulverizer can be adjusted rapidly so as to take into account temperature differences occurring due to raw coal with different levels of humidity being introduced into the pulverizer. It is thereby possible to maintain the temperature of the drying gas exiting the pulverizer, hereafter referred to as exit temperature, as constant as possible.
The present aspect is of particular advantage during a startup phase of the installation, wherein the method comprises a startup cycle wherein heated drying gas is fed through the pulverizer without introducing raw coal, the exit temperature being kept below a first temperature threshold, and a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer, the exit temperature being kept at a preferred working temperature. According to an important aspect of the invention, the method comprises:
- during the startup cycle, heating said drying gas to a temperature above the first temperature threshold and injecting a volume of water into the heated drying gas, the volume of water being calculated so as to reduce the tem-perature of the heated drying gas to obtain an exit temperature below the first temperature threshold; and - at the beginning of the grinding cycle, reducing the volume of water injected into the heated drying gas so as to compensate for the drop in exit tempera-ture.
During a startup phase of the installation, drying gas is generally fed through the installation before raw coal is introduced into the pulverizer.
This allows the individual components to be heated to the desired working tempera-ture. By controlling the amount of water injected into the drying gas upstream of the pulverizer during this startup phase, the drying gas, which may be heated to a temperature above the maximum tolerated exit temperature, can be cooled down again so that the temperature downstream of the pulverizer does not exceed the first temperature threshold.
When the raw coal introduction is then started, a sudden drop in exit tem-
The present aspect is of particular advantage during a startup phase of the installation, wherein the method comprises a startup cycle wherein heated drying gas is fed through the pulverizer without introducing raw coal, the exit temperature being kept below a first temperature threshold, and a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer, the exit temperature being kept at a preferred working temperature. According to an important aspect of the invention, the method comprises:
- during the startup cycle, heating said drying gas to a temperature above the first temperature threshold and injecting a volume of water into the heated drying gas, the volume of water being calculated so as to reduce the tem-perature of the heated drying gas to obtain an exit temperature below the first temperature threshold; and - at the beginning of the grinding cycle, reducing the volume of water injected into the heated drying gas so as to compensate for the drop in exit tempera-ture.
During a startup phase of the installation, drying gas is generally fed through the installation before raw coal is introduced into the pulverizer.
This allows the individual components to be heated to the desired working tempera-ture. By controlling the amount of water injected into the drying gas upstream of the pulverizer during this startup phase, the drying gas, which may be heated to a temperature above the maximum tolerated exit temperature, can be cooled down again so that the temperature downstream of the pulverizer does not exceed the first temperature threshold.
When the raw coal introduction is then started, a sudden drop in exit tem-
5 perature occurs due to the addition of cold and wet material. By overheating the drying gas in the hot gas generator and subsequently cooling it through water injection, the temperature of the drying gas entering the pulverizer can be quickly adapted to the new operating conditions. A reduction of the quantity of injected water allows a rapid temperature increase of the drying gas entering the pulverizer so as to compensate for the temperature drop due to the intro-duction of the raw coal. As a consequence, the transition time, wherein pulver-ized coal is produced at lower temperature is considerably reduced or even avoided. The amount of unusable coal slurry is also considerably reduced, thereby increasing the efficiency of the installation.
The volume of water injected into the heated drying gas can be deter-mined based on the exit temperature. Alternatively, the volume of water injected into the heated drying gas can be determined based on a pressure drop measured across the pulverizer. It is not excluded to use other measure-ments, alone or in combination, to determine the volume of water to be injected into the heated drying gas.
Preferably, during the grinding cycle and after compensation for the drop in exit temperature, the method comprises the further steps of reducing the heating of the drying gas; and reducing the volume of water injected into the heated drying gas to maintain the desired exit temperature. This allows reduc-ing consumption of energy once the installation is running. Indeed, the impor-tance of the overheating and subsequent cooling of the drying gas is particu-larly important during the startup phase of the installation, wherein it allows providing a buffer to compensate for the drop in temperature occurring when the introduction of raw coal is started. Once the installation is running, only smaller temperature drops might occur and the buffer can be reduced. During
The volume of water injected into the heated drying gas can be deter-mined based on the exit temperature. Alternatively, the volume of water injected into the heated drying gas can be determined based on a pressure drop measured across the pulverizer. It is not excluded to use other measure-ments, alone or in combination, to determine the volume of water to be injected into the heated drying gas.
Preferably, during the grinding cycle and after compensation for the drop in exit temperature, the method comprises the further steps of reducing the heating of the drying gas; and reducing the volume of water injected into the heated drying gas to maintain the desired exit temperature. This allows reduc-ing consumption of energy once the installation is running. Indeed, the impor-tance of the overheating and subsequent cooling of the drying gas is particu-larly important during the startup phase of the installation, wherein it allows providing a buffer to compensate for the drop in temperature occurring when the introduction of raw coal is started. Once the installation is running, only smaller temperature drops might occur and the buffer can be reduced. During
6 normal operation of the grinding and drying installation, there is hence no need to over heat the drying gas in the hot gas generator and subsequently cooling it to the working temperature.
In the recirculation line, part of the drying gas can be removed as exhaust gas. Apart from fresh air, hot gas can also be injected into the drying gas in the recirculation line.
The method may also comprise continuous monitoring of the exit tempera-ture and comparing the measured exit temperature to a maximum temperature, wherein, if the measured exit temperature exceeds the maximum temperature, the volume of water injected into the heated drying gas is increased. This allows using the water injection means used for general process control, to be used for emergency cooling also.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more apparent from the following description of one not limiting embodiment with reference to the attached drawing, wherein Fig.1 shows a schematic representation of a grinding and drying installation used for carrying out the method according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 shows a grinding and drying installation for producing pulverized coal using the method according to the present invention.
Such a grinding and drying installation 10 comprises a pulverizer 20 into which raw coal is fed via a conveyor 22. In the pulverizer 20, the raw coal is crushed between internal mobile pieces (not shown) or any other conventional grinding means into a fine powder. At the same time, a hot drying gas is fed through the pulverizer 20 to dry the pulverized coal. The drying gas enters the pulverizer 20 through a gas inlet 24. Upstream of the pulverizer 20, the grinding and drying installation 10 comprises a hot gas generator 26 in which a drying gas can be heated to a predefined temperature. Such a hot gas generator 26 is
In the recirculation line, part of the drying gas can be removed as exhaust gas. Apart from fresh air, hot gas can also be injected into the drying gas in the recirculation line.
The method may also comprise continuous monitoring of the exit tempera-ture and comparing the measured exit temperature to a maximum temperature, wherein, if the measured exit temperature exceeds the maximum temperature, the volume of water injected into the heated drying gas is increased. This allows using the water injection means used for general process control, to be used for emergency cooling also.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more apparent from the following description of one not limiting embodiment with reference to the attached drawing, wherein Fig.1 shows a schematic representation of a grinding and drying installation used for carrying out the method according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 shows a grinding and drying installation for producing pulverized coal using the method according to the present invention.
Such a grinding and drying installation 10 comprises a pulverizer 20 into which raw coal is fed via a conveyor 22. In the pulverizer 20, the raw coal is crushed between internal mobile pieces (not shown) or any other conventional grinding means into a fine powder. At the same time, a hot drying gas is fed through the pulverizer 20 to dry the pulverized coal. The drying gas enters the pulverizer 20 through a gas inlet 24. Upstream of the pulverizer 20, the grinding and drying installation 10 comprises a hot gas generator 26 in which a drying gas can be heated to a predefined temperature. Such a hot gas generator 26 is
7 powered by a burner 27, such as e.g. a multiple lance burner. The heated drying gas is carried from the hot gas generator 26 to the pulverizer 20 via a conduit 28. As the heated drying gas passes through the pulverizer 20, from the gas inlet 24 to an outlet 30, pulverized coal is entrained. A mixture of pulverized coal and drying gas is carried from the pulverizer 20, via a conduit 32, to a filter 34, where the pulverized coal is again removed from the drying gas and fed to a pulverized coal collector 36, ready further use. The drying gas exiting the filter 34 is fed to a recirculation line 38 for feeding it back to the hot gas generator 26. The recirculation line 38 comprises fan means 40 for circulat-ing the drying gas through the installation. The fan means 40 may be located upstream or downstream of a line 42, e.g. a stack, which is used to extract part of the drying gas from the recirculation line 38.
The recirculation line 38 further comprises gas injection means 44 for in-jecting fresh air and/or hot gas into the recirculation line 38. The injected fresh air and/or hot gas is mixed with the recycled drying gas. The injected fresh air allows reducing the due point of the drying gas and the injected hot gas is used to improve the thermal balance of the grinding and drying circuit.
According to an important aspect of the present invention, the installation 10 comprises water injection means 46 arranged downstream of the hot gas generator 26 and upstream of the pulverizer 20. The importance of the water injection means 46 will become clear in the description herebelow.
The water injection means 46 helps to regulate the dew point of the drying gas by regulating the oxygen level therein. In the recirculation line 38, part of the drying gas is extracted via the line 42 and fresh air may be injected via the gas injection means 44. In conventional installations, the oxygen level is monitored for safety reasons by means of an oxygen sensor 45 and, if the oxygen level is found to be too high, the gas injection means 44 is instructed to reduce the amount of fresh air introduced into the dying gas. A problem however occurs when the gas injection means 44 reaches its shut-off point, i.e.
when the gas injection means 44 is completely turned off and no fresh air is
The recirculation line 38 further comprises gas injection means 44 for in-jecting fresh air and/or hot gas into the recirculation line 38. The injected fresh air and/or hot gas is mixed with the recycled drying gas. The injected fresh air allows reducing the due point of the drying gas and the injected hot gas is used to improve the thermal balance of the grinding and drying circuit.
According to an important aspect of the present invention, the installation 10 comprises water injection means 46 arranged downstream of the hot gas generator 26 and upstream of the pulverizer 20. The importance of the water injection means 46 will become clear in the description herebelow.
The water injection means 46 helps to regulate the dew point of the drying gas by regulating the oxygen level therein. In the recirculation line 38, part of the drying gas is extracted via the line 42 and fresh air may be injected via the gas injection means 44. In conventional installations, the oxygen level is monitored for safety reasons by means of an oxygen sensor 45 and, if the oxygen level is found to be too high, the gas injection means 44 is instructed to reduce the amount of fresh air introduced into the dying gas. A problem however occurs when the gas injection means 44 reaches its shut-off point, i.e.
when the gas injection means 44 is completely turned off and no fresh air is
8 injected into the dying gas. If the oxygen level is then still found to be too high, the volume of fresh air injected into the dying gas cannot be further reduced and a shutdown of the installation becomes necessary.
According to the present invention, the oxygen level in the drying gas can be reduced by injecting water into the drying gas by means of the water injection means 46. When the oxygen level measured by the oxygen sensor 45 is too high, the water injection means 46 can be instructed to increase the volume of water injected into the drying gas, thereby reducing the oxygen level downstream of the filter 34.
Preferably, the oxygen level is first reduced by the conventional method of reducing the volume of fresh air injected into the dying gas by the gas injection means 44 and if this is not sufficient, the oxygen level is then further reduced by increasing the volume of water injected into the drying gas by the water injection means 46.
Another function of the water injection means 46 may be to help regulate the temperature of the drying gas at the exit of the pulverizer 20. In operation, the drying gas is heated to a predefined temperature in the hot gas generator 26 and fed through the pulverizer 20. The temperature of the drying gas is reduced in the pulverizer 20 as the heat from the drying gas is used to dry the pulverized coal. The level of humidity of the raw coal determines the tempera-ture loss of the drying gas. In order to prevent damage to the filter 34, the temperature of the mixture of pulverized coal and drying gas exiting the pulverizer 20, hereafter referred to as the exit temperature, is monitored, e.g.
by means of a temperature sensor 48.
In order to maintain a correct exit temperature, the temperature of the dry-ing gas entering the pulverizer needs to be controlled, which is generally achieved by controlling the output power of the burner 27 of the hot gas generator 26. Unfortunately this process has a relatively slow response time, meaning that once the installation has determined that the exit temperature is too high or too low and the burner 27 has been made to react in consequence,
According to the present invention, the oxygen level in the drying gas can be reduced by injecting water into the drying gas by means of the water injection means 46. When the oxygen level measured by the oxygen sensor 45 is too high, the water injection means 46 can be instructed to increase the volume of water injected into the drying gas, thereby reducing the oxygen level downstream of the filter 34.
Preferably, the oxygen level is first reduced by the conventional method of reducing the volume of fresh air injected into the dying gas by the gas injection means 44 and if this is not sufficient, the oxygen level is then further reduced by increasing the volume of water injected into the drying gas by the water injection means 46.
Another function of the water injection means 46 may be to help regulate the temperature of the drying gas at the exit of the pulverizer 20. In operation, the drying gas is heated to a predefined temperature in the hot gas generator 26 and fed through the pulverizer 20. The temperature of the drying gas is reduced in the pulverizer 20 as the heat from the drying gas is used to dry the pulverized coal. The level of humidity of the raw coal determines the tempera-ture loss of the drying gas. In order to prevent damage to the filter 34, the temperature of the mixture of pulverized coal and drying gas exiting the pulverizer 20, hereafter referred to as the exit temperature, is monitored, e.g.
by means of a temperature sensor 48.
In order to maintain a correct exit temperature, the temperature of the dry-ing gas entering the pulverizer needs to be controlled, which is generally achieved by controlling the output power of the burner 27 of the hot gas generator 26. Unfortunately this process has a relatively slow response time, meaning that once the installation has determined that the exit temperature is too high or too low and the burner 27 has been made to react in consequence,
9 some time passes before the exit temperature reaches the correct exit tempera-ture again.
The response time is particularly important during a startup phase of the installation. Indeed, initially, heated drying gas is fed through the installation before the raw coal is introduced. This allows the installation to heat up and reach the ideal working conditions. When, after a certain time, raw coal is then introduced into the pulverizer 20, the exit temperature suddenly drops well below the desired exit temperature. Conventionally, the burner 27 then reacts by further heating the drying gas so as to reach the desired exit temperature.
The desired exit temperature is then however only obtained after a long delay and any pulverized coal obtained in the meantime may have to be discarded because it has not been sufficiently dried. Indeed, during a transition period wherein the exit temperature is too low, unusable coal slurry is generally obtained instead of dried pulverized coal.
According to the present invention, during the startup phase, the burner 27 is set to heat the drying gas well above the desired exit temperature. The heated drying gas is then subjected to controlled cooling by injecting water into the heated drying gas through the water injection means 46, whereby the drying gas is cooled so that the desired exit temperature can be achieved.
After a certain heat-up time of the grinding and drying installation, when the raw coal is introduced into the pulverizer 20, the exit temperature suddenly drops well below the desired exit temperature. Instead of compensating for this sudden drop by adapting the heating temperature of the burner 27, the amount of water injected into the drying gas by the water injection means 46 is reduced. The heated drying gas is hence cooled less and the desired exit temperature can be kept stable. The reaction time of this procedure is considerably lower than the conventional one, thereby considerably reducing or avoiding a transition period wherein the exit temperature is too low and the production of unusable coal slurry.
It should be noted that this method shows its most dramatic advantages during the startup phase, i.e. during a transition period shortly after raw coal is initially introduced into the pulverizer. The present method is however also advantageous during normal operation of the installation. When a reduction of the humidity in the raw coal occurs, the exit temperature can be quickly brought 5 back to the desired exit temperature should a sudden drop in temperature occur.
In order to optimize energy consumption, it is advantageous to gradually reduce both the heating and the subsequent cooling of the drying gas once the exit temperature has stabilized. If no such subsequent cooling is required, the
The response time is particularly important during a startup phase of the installation. Indeed, initially, heated drying gas is fed through the installation before the raw coal is introduced. This allows the installation to heat up and reach the ideal working conditions. When, after a certain time, raw coal is then introduced into the pulverizer 20, the exit temperature suddenly drops well below the desired exit temperature. Conventionally, the burner 27 then reacts by further heating the drying gas so as to reach the desired exit temperature.
The desired exit temperature is then however only obtained after a long delay and any pulverized coal obtained in the meantime may have to be discarded because it has not been sufficiently dried. Indeed, during a transition period wherein the exit temperature is too low, unusable coal slurry is generally obtained instead of dried pulverized coal.
According to the present invention, during the startup phase, the burner 27 is set to heat the drying gas well above the desired exit temperature. The heated drying gas is then subjected to controlled cooling by injecting water into the heated drying gas through the water injection means 46, whereby the drying gas is cooled so that the desired exit temperature can be achieved.
After a certain heat-up time of the grinding and drying installation, when the raw coal is introduced into the pulverizer 20, the exit temperature suddenly drops well below the desired exit temperature. Instead of compensating for this sudden drop by adapting the heating temperature of the burner 27, the amount of water injected into the drying gas by the water injection means 46 is reduced. The heated drying gas is hence cooled less and the desired exit temperature can be kept stable. The reaction time of this procedure is considerably lower than the conventional one, thereby considerably reducing or avoiding a transition period wherein the exit temperature is too low and the production of unusable coal slurry.
It should be noted that this method shows its most dramatic advantages during the startup phase, i.e. during a transition period shortly after raw coal is initially introduced into the pulverizer. The present method is however also advantageous during normal operation of the installation. When a reduction of the humidity in the raw coal occurs, the exit temperature can be quickly brought 5 back to the desired exit temperature should a sudden drop in temperature occur.
In order to optimize energy consumption, it is advantageous to gradually reduce both the heating and the subsequent cooling of the drying gas once the exit temperature has stabilized. If no such subsequent cooling is required, the
10 water injection system can be switched off.
Advantageously, the water injection means 46 is also used for an emer-gency cooling. The method may comprise continuous monitoring of the exit temperature and comparing the measured exit temperature to a maximum temperature. When the measured exit temperature exceeds the maximum temperature, the water injection means 46 is instructed to increasing the volume of water injected into the heated drying gas, thereby reducing the temperature of the drying gas entering the pulverizer 20 and consequently also the temperature of the drying gas exiting the pulverizer 20.
REFERENCE SIGNS
10 grinding and drying installation 34 filter pulverizer 36 pulverized coal collector 22 conveyor 38 recirculation line 24 gas inlet 40 fan means 26 hot gas generator 42 line 27 burner 44 gas injection means 28 conduit 45 oxygen sensor outlet 46 water injection means 32 conduit 48 temperature sensor
Advantageously, the water injection means 46 is also used for an emer-gency cooling. The method may comprise continuous monitoring of the exit temperature and comparing the measured exit temperature to a maximum temperature. When the measured exit temperature exceeds the maximum temperature, the water injection means 46 is instructed to increasing the volume of water injected into the heated drying gas, thereby reducing the temperature of the drying gas entering the pulverizer 20 and consequently also the temperature of the drying gas exiting the pulverizer 20.
REFERENCE SIGNS
10 grinding and drying installation 34 filter pulverizer 36 pulverized coal collector 22 conveyor 38 recirculation line 24 gas inlet 40 fan means 26 hot gas generator 42 line 27 burner 44 gas injection means 28 conduit 45 oxygen sensor outlet 46 water injection means 32 conduit 48 temperature sensor
Claims (16)
1. Method for producing pulverized coal, the method comprising the steps of:
- heating a drying gas in a hot gas generator to a predefined temperature;
- feeding the heated drying gas into a pulverizer;
- introducing raw coal into the pulverizer, the pulverizer turning the raw coal into pulverized coal;
- collecting a mixture of drying gas and pulverized coal from the pulverizer and feeding the mixture to a filter, the filter separating the dried pulver-ized coal from the drying gas;
- collecting the dried pulverized coal for further use and feeding the drying gas from the filter to a recirculation line for returning at least part of the drying gas to the hot gas generator - determining an oxygen level in the drying gas and comparing the deter-mined to a oxygen level predetermined oxygen level threshold characterized in that the oxygen level in the drying gas is determined during a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is in-troduced into the pulverizer, and if, during the grinding cycle, the determined oxygen level is higher than the predetermined oxygen level threshold, water is injected into the heated dry-ing gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxy-gen level threshold.
- heating a drying gas in a hot gas generator to a predefined temperature;
- feeding the heated drying gas into a pulverizer;
- introducing raw coal into the pulverizer, the pulverizer turning the raw coal into pulverized coal;
- collecting a mixture of drying gas and pulverized coal from the pulverizer and feeding the mixture to a filter, the filter separating the dried pulver-ized coal from the drying gas;
- collecting the dried pulverized coal for further use and feeding the drying gas from the filter to a recirculation line for returning at least part of the drying gas to the hot gas generator - determining an oxygen level in the drying gas and comparing the deter-mined to a oxygen level predetermined oxygen level threshold characterized in that the oxygen level in the drying gas is determined during a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is in-troduced into the pulverizer, and if, during the grinding cycle, the determined oxygen level is higher than the predetermined oxygen level threshold, water is injected into the heated dry-ing gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the predetermined oxy-gen level threshold.
2. Method according to claim 1, wherein, in the recirculation, line, fresh air is injected into the drying gas, and wherein, if the determined oxygen level is higher than the predetermined oxvgen level threshold, the volume of fresh air injected into the drying gas is reduced.
3. Method according to claim 2, wherein, if the volume of fresh air injected reaches zero and the oxygen level is still higher than the predetermined oxygen threshold, water is injected into the heated drying gas before it is fed into the pulverizer, the volume of water injected being calculated so as to reduce the oxygen level below the prede-termined oxygen level threshold.
4. Method according to any of the previous claims, wherein the predetermined oxygen threshold is chosen to be between 0 and 14 volume %.
5, Method according to claim 4, wherein the predetermined oxygen threshold is chosen to be between 5 and 12 volume %.
6. Method according to any of the previous claims, comprising:
determining an exit temperature of the mixture of drying gas and pulverized coal exiting the pulverizer; and controlling the exit temperature by controlling a volume of water injected into the heated drying gas before feeding it into the pulverizer, the volume of water injected being calculated so as to bring the exit temperature to the preferred working temperature.
determining an exit temperature of the mixture of drying gas and pulverized coal exiting the pulverizer; and controlling the exit temperature by controlling a volume of water injected into the heated drying gas before feeding it into the pulverizer, the volume of water injected being calculated so as to bring the exit temperature to the preferred working temperature.
7. Method according to claim 6, wherein the method comprises:
- a startup cycle wherein heated drying gas is fed through the pulverizer without introducing raw coal, the exit temperature being kept below a first temperature threshold, and - a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer, the exit temperature being kept at a preferred working temperature, wherein - during the startup cycle, said drying gas is heated to a temperature above the first temperature threshold and injecting a volume of water into the heated drying gas, the volume of water being calculated so as to re-duce the temperature of the heated drying gas to obtain an exit tempera-ture below the first temperature threshold; and - at the beginning of the grinding cycle, the volume of water injected into the heated drying gas is reduced so as to compensate for the drop in exit temperature.
- a startup cycle wherein heated drying gas is fed through the pulverizer without introducing raw coal, the exit temperature being kept below a first temperature threshold, and - a grinding cycle wherein heated drying gas is fed through the pulverizer and raw coal is introduced into the pulverizer, the exit temperature being kept at a preferred working temperature, wherein - during the startup cycle, said drying gas is heated to a temperature above the first temperature threshold and injecting a volume of water into the heated drying gas, the volume of water being calculated so as to re-duce the temperature of the heated drying gas to obtain an exit tempera-ture below the first temperature threshold; and - at the beginning of the grinding cycle, the volume of water injected into the heated drying gas is reduced so as to compensate for the drop in exit temperature.
8. Method according to claim 6 or 7, wherein the volume of water injected into the heated drying gas is reduced at a rate determined by the exit tempera-ture.
9. Method according to any of the preceding claims, wherein the volume of water injected into the heated drying gas is reduced at a rate determined by a pressure drop measured across the pulverizer.
10. Method according to any of claims 7 to 9, wherein, during the grinding cycle and after compensation for the drop in exit temperature, the method com-prises the steps of:
- reducing the heating of the drying gas; and reducing the volume of water injected into the heated drying gas to main-tain the desired exit temperature.
- reducing the heating of the drying gas; and reducing the volume of water injected into the heated drying gas to main-tain the desired exit temperature.
11. Method according to any of the previous claims, wherein, in the recirculation line, at least part of the drying gas is extracted as exhaust gas.
12. Method according to any of the previous claims, wherein, in the recirculation line, fresh air and/or hot gas is injected into the drying gas.
13.. Method according to any of the previous claims, comprising:
continuous monitoring of the exit temperature and comparing the measured exit temperature to a maximum temperature; and if the measured exit temperature exceeds the maximum temperature, in-creasing the volume of water injected into the heated drying gas.
continuous monitoring of the exit temperature and comparing the measured exit temperature to a maximum temperature; and if the measured exit temperature exceeds the maximum temperature, in-creasing the volume of water injected into the heated drying gas.
14. Method according to any of the previous claims, wherein the drying gas is heated in a hot gas generator powered by a lance burner.
14
16. Method according to any of the previous claims, wherein water is injected into the heated drying gas by means of a water injection device arranged between the hot gas generator and the pulverizer.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| LU91451 | 2008-06-02 | ||
| LU91451A LU91451B1 (en) | 2008-06-02 | 2008-06-02 | Method for producing pulverized coal |
| PCT/EP2009/056763 WO2009147153A1 (en) | 2008-06-02 | 2009-06-02 | Method for producing pulverized coal |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2725276A1 true CA2725276A1 (en) | 2009-12-10 |
| CA2725276C CA2725276C (en) | 2016-02-09 |
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| CA2725276A Expired - Fee Related CA2725276C (en) | 2008-06-02 | 2009-06-02 | Method for producing pulverized coal |
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| US (1) | US20110192079A1 (en) |
| EP (1) | EP2300562B1 (en) |
| JP (1) | JP5758800B2 (en) |
| KR (1) | KR101590920B1 (en) |
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| AU (1) | AU2009253965B2 (en) |
| BR (1) | BRPI0913362B1 (en) |
| CA (1) | CA2725276C (en) |
| LU (1) | LU91451B1 (en) |
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| TW (1) | TWI475105B (en) |
| UA (1) | UA104863C2 (en) |
| WO (1) | WO2009147153A1 (en) |
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| CA2782436C (en) | 2009-12-04 | 2018-05-22 | Barrick Gold Corporation | Separation of copper minerals from pyrite using air-metabisulfite treatment |
| US8349036B2 (en) | 2010-01-06 | 2013-01-08 | General Electric Company | Systems and method for heating and drying solid feedstock in a gasification system |
| JP5949414B2 (en) * | 2012-10-05 | 2016-07-06 | 新日鐵住金株式会社 | Grinding plant exhaust gas control device, grinding plant exhaust gas control method, and computer program |
| US9494319B2 (en) * | 2013-03-15 | 2016-11-15 | General Electric Technology Gmbh | Pulverizer monitoring |
| KR101522781B1 (en) * | 2013-10-17 | 2015-05-26 | 주식회사 포스코 | Manufacturing method of caking coal using coal dust and manufacturing method of coke |
| CN104841544B (en) * | 2015-06-02 | 2017-08-11 | 天华化工机械及自动化研究设计院有限公司 | A kind of nitrogen sealing and circulating PVA milling methods |
| KR101759329B1 (en) * | 2015-12-23 | 2017-07-18 | 주식회사 포스코 | System for amplifying coke-oven gas and this method |
| CN107051689A (en) * | 2017-01-16 | 2017-08-18 | 中国电力工程顾问集团西南电力设计院有限公司 | A kind of lime stone dry grinding prepares arrangement |
| CN107488770A (en) * | 2017-10-17 | 2017-12-19 | 中冶赛迪工程技术股份有限公司 | A kind of Coal Grinding System of Pci humidification process and device |
| CN113322101A (en) * | 2021-06-30 | 2021-08-31 | 昆明理工大学 | Phosphorus coal gasification reaction device for combined production of yellow phosphorus and synthesis gas |
| CN113336207A (en) * | 2021-06-30 | 2021-09-03 | 昆明理工大学 | Combined production system of yellow phosphorus and synthesis gas |
| RU2771032C1 (en) * | 2021-08-13 | 2022-04-25 | Федеральное автономное учреждение "25 Государственный научно-исследовательский институт химмотологии Министерства обороны Российской Федерации" | Processing line for the production of finely dispersed coal fuel |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US1467744A (en) * | 1922-10-24 | 1923-09-11 | Winkler William | Caster |
| AR207472A1 (en) * | 1974-08-16 | 1976-10-08 | Coaltek Ass | AN APPARATUS FOR HEATING GRANULAR MATERIAL TO HIGH TEMPERATURES |
| DE2656046A1 (en) * | 1976-12-10 | 1978-06-29 | Babcock Bsh Ag | Jet tube wood chip dryer safety system - has water injected by sprays at combustion chamber inlet and outlet points |
| JPS54108062A (en) * | 1978-02-13 | 1979-08-24 | Hosokawa Micron Kk | Explosionnproof pulverizing method and its device |
| SU787448A1 (en) * | 1978-04-14 | 1980-12-15 | Восточный научно-исследовательский углехимический институт | Method of thermal preparation of coal for coking |
| DE2852164C2 (en) * | 1978-12-02 | 1985-06-20 | Klöckner-Humboldt-Deutz AG, 5000 Köln | Method and device for operating a hot gas generator within a mill-drying plant |
| US4244529A (en) * | 1979-05-07 | 1981-01-13 | The Cleveland Cliffs Iron Company | Inerting of pulverizing mills for combustible materials |
| DE2949720C2 (en) * | 1979-12-11 | 1982-08-26 | Alfelder Eisenwerke Carl Heise, KG vorm. Otto Wesselmann & Cie., 3220 Alfeld | Method and device for drying and heating moist coal |
| DE3128865C2 (en) * | 1981-07-22 | 1989-02-02 | Rheinische Braunkohlenwerke AG, 5000 Köln | Process and device for the mill-drying of pre-crushed raw lignite to pulverized lignite |
| KR900002655B1 (en) * | 1983-08-01 | 1990-04-21 | 더 뱁콕 앤드 윌콕스 컴퍼니 | Safety system for coal pulverizers |
| SU1736995A1 (en) * | 1989-05-23 | 1992-05-30 | Восточный научно-исследовательский углехимический институт | Method of preparing coal for coking |
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| DE4223151C2 (en) * | 1992-07-14 | 1994-11-10 | Loesche Gmbh | Process for grinding raw lignite |
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-
2008
- 2008-06-02 LU LU91451A patent/LU91451B1/en active
-
2009
- 2009-06-02 WO PCT/EP2009/056763 patent/WO2009147153A1/en active Application Filing
- 2009-06-02 EP EP09757534.4A patent/EP2300562B1/en active Active
- 2009-06-02 KR KR1020107029782A patent/KR101590920B1/en active IP Right Grant
- 2009-06-02 CN CN2009801198479A patent/CN102046758A/en active Pending
- 2009-06-02 UA UAA201015594A patent/UA104863C2/en unknown
- 2009-06-02 CA CA2725276A patent/CA2725276C/en not_active Expired - Fee Related
- 2009-06-02 US US12/994,927 patent/US20110192079A1/en not_active Abandoned
- 2009-06-02 AU AU2009253965A patent/AU2009253965B2/en active Active
- 2009-06-02 TW TW098118117A patent/TWI475105B/en active
- 2009-06-02 BR BRPI0913362-3A patent/BRPI0913362B1/en active IP Right Grant
- 2009-06-02 JP JP2011511036A patent/JP5758800B2/en active Active
- 2009-06-02 RU RU2010154520/05A patent/RU2502780C2/en active
Also Published As
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| JP2011522916A (en) | 2011-08-04 |
| CN102046758A (en) | 2011-05-04 |
| RU2502780C2 (en) | 2013-12-27 |
| JP5758800B2 (en) | 2015-08-05 |
| AU2009253965B2 (en) | 2014-12-04 |
| EP2300562B1 (en) | 2015-02-25 |
| TW201009064A (en) | 2010-03-01 |
| LU91451B1 (en) | 2009-12-03 |
| EP2300562A1 (en) | 2011-03-30 |
| UA104863C2 (en) | 2014-03-25 |
| US20110192079A1 (en) | 2011-08-11 |
| CA2725276C (en) | 2016-02-09 |
| BRPI0913362A2 (en) | 2015-11-24 |
| KR20110016463A (en) | 2011-02-17 |
| TWI475105B (en) | 2015-03-01 |
| AU2009253965A1 (en) | 2009-12-10 |
| BRPI0913362B1 (en) | 2018-01-23 |
| RU2010154520A (en) | 2012-07-20 |
| KR101590920B1 (en) | 2016-02-02 |
| WO2009147153A1 (en) | 2009-12-10 |
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