JP5758800B2 - Powdered coal production method - Google Patents

Description

  The present invention relates to a method for producing pulverized coal, and particularly to a method for producing pulverized coal used in the metallurgical industry.

  In the metallurgical industry, pulverized coal is usually put into a blast furnace as a combustible material. What is important to ensure good functioning of the blast furnace is the use of good quality pulverized coal, that is, the density, size and humidity level of the pulverized coal are appropriate. Pulverized coal is generally produced in a crushing and drying facility. In this case, the raw coal is pulverized in a pulverizer and dried to an appropriate drying level, and then the produced pulverized coal is conveyed to a storage hopper or directly used in a blast furnace. A method of drying pulverized coal by exposing the pulverized coal to a hot air stream is also known. It is also known that, for example, pulverized coal is carried in a hot gas from a pulverizer to a filter and then separated from the hot gas and fed into a hopper. A portion of the hot gas is recirculated and heated before being sent again into the grinder.

  In order for the crushing and drying equipment to function properly, it is important to monitor the oxygen level in the dry gas, usually downstream of the filter. If this oxygen level becomes too high, the mixture of dry gas and pulverized coal can become an explosive mixture with significant danger. Therefore, in general, in the recirculation line, that is, the line for returning the dry gas to the pulverizer, the gas is extracted from the dry gas and discharged, and fresh air is injected.

  In known mill drying equipment, the oxygen level in the dry gas is monitored and if the measured oxygen level is found to be too high, the amount of fresh air introduced into the dry gas in the recirculation line is reduced. This makes it possible to reduce the oxygen level in the dry gas.

  However, in situations where the coking coal is extremely dry and / or where the equipment is operated with reduced load, the oxygen level can be reduced by reducing the amount of fresh air introduced into the dry gas. May not be sufficiently reduced. In fact, even if the amount of fresh air introduced into the dry gas is zero, that is, even when no fresh air is introduced, there is a possibility that the oxygen level may remain high in the above situation. In such a situation, it is necessary to stop the crushing and drying equipment in order to prevent any damage to the equipment. However, stopping the equipment in this way not only causes a production loss, but also requires extra costs for replacement or adjustment of the dry gas.

  An object of the present invention is to provide an improved method for producing pulverized coal that does not cause the disadvantages of the conventional methods. This object is achieved by the method according to claim 1.

In order to achieve the above object, the present invention provides the following steps:
Heating a dry gas, preferably an inert gas, to a predetermined temperature in a hot gas generator;
A process of feeding heated dry gas into a pulverizer,
A step of charging raw coal into a pulverizer and pulverizing raw coal with the pulverizer to produce pulverized coal;
Collecting a mixture of dry gas and pulverized coal from a pulverizer, feeding the mixture to a filter, and separating the dried pulverized coal from the dry gas by the filter;
Sending dry gas from the filter to the recirculation line to collect the dry pulverized coal for further use and returning at least a portion of the dry gas to the hot gas generator, and preferably recirculate the oxygen level in the dry gas A method for producing pulverized coal comprising the steps of measuring in a line and comparing the measured oxygen level to a predetermined oxygen level threshold is provided.

  In a preferred embodiment of the present invention, the oxygen level in the dry gas is measured during the pulverization cycle during which the heated dry gas is fed through the pulverizer and the raw coal is fed into the pulverizer. If the measured oxygen level is higher than a predetermined oxygen threshold, water is injected into the heated dry gas before the heated dry gas is fed into the pulverizer, and the volume of the injected water has a predetermined oxygen level. Calculated to decrease below the oxygen level threshold. By injecting water into the dry gas during the milling cycle, the overall volume of the dry gas can be increased, thereby reducing the relative oxygen volume. Accordingly, the oxygen level can be lowered to an acceptable level by injecting water, thereby avoiding damage to the equipment or avoiding the need to stop the crushing and drying equipment.

  In yet another preferred embodiment, the method of the invention includes the step of injecting fresh air into the dry gas in the recirculation line, where the oxygen level measured in this step is higher than a predetermined oxygen level threshold. The volume of fresh air injected into the dry gas is reduced.

  Also, as an advantageous aspect, the method of the present invention first reduces the volume of fresh air injected into the dry gas, then the injected fresh air volume reaches zero and the oxygen level is higher than the predetermined oxygen threshold. Includes a step of injecting water into the heated dry gas before feeding the heated dry gas into the grinder. The amount of water injected is calculated so that the oxygen level drops below a predetermined oxygen level threshold.

  Preferably, the predetermined oxygen threshold is selected within a range of 0-14% by volume, preferably within a range of 5-12% by volume.

  According to yet another aspect of the present invention, the method of the present invention measures the outlet temperature from a pulverizer of a mixture of dry gas and pulverized coal and heats the heated dry gas before it is fed into the pulverizer. The method further includes controlling the outlet temperature by controlling the amount of water injected into the dry gas. By controlling the amount of water injected into the dry gas upstream of the pulverizer, the temperature of the dry gas entering the pulverizer is taken into account by taking into account the temperature differences caused by the raw coal at various moisture levels that are input into the pulverizer. Is adjusted quickly. This makes it possible to keep the temperature of the dry gas exiting the grinder, as described below as outlet temperature, as constant as possible.

This aspect includes an operation start cycle in which dry gas heated without introduction of raw coal is fed through the pulverizer and the outlet temperature is kept below the first temperature threshold, and the heated dry gas is pulverized in the pulverizer. In the process of the present invention, which is composed of a pulverization cycle in which the raw coal is fed into the pulverizer and the outlet temperature is maintained at a preferred processing temperature, and is particularly advantageous at the start of operation of the facility for carrying out the process of the present invention. It is. In accordance with an important aspect of the present invention, the method includes
In a start-up cycle, a constant volume of water calculated to heat the dry gas to a temperature above the first temperature threshold and to reduce the temperature of the heated dry gas to a temperature below the first temperature threshold. Injecting into heated dry gas;
At the beginning of the milling cycle, a step is included that reduces the amount of water injected into the heated dry gas to compensate for the decrease in outlet temperature.

  In the start-up phase of the equipment, the dry gas is usually fed through the equipment before the raw coal is introduced into the grinder. This allows individual elements to be heated to the desired processing temperature. By adjusting the amount of water injected into the dry gas upstream of the pulverizer in this operation start stage, the dry gas that can be heated to the maximum allowable outlet temperature or more is cooled again to lower the temperature, and the pulverizer It is possible that the downstream temperature does not exceed the first temperature threshold.

  Next, when the charging of the raw coal is started, the outlet temperature rapidly drops due to the addition of the cold and wet raw coal. It is possible to quickly adapt the temperature of the dry gas entering the pulverizer to new processing conditions by overheating the dry gas in the hot gas generator and performing rapid cooling via water injection of the dry gas. It is. By reducing the amount of injected water, it is possible to rapidly increase the temperature of the dry gas entering the pulverizer and compensate for the temperature drop caused by the introduction of raw coal. As a result, the transition time until pulverized coal is produced at low temperatures is clearly reduced or not required at all. The amount of unusable coal slurry is also greatly reduced, resulting in improved equipment efficiency.

  It is possible to measure the amount of water injected into the heated dry gas with reference to the outlet temperature. Alternatively, the amount of water injected into the heated dry gas can be measured based on the pressure drop measured over the entire pulverizer. It is also possible to measure the amount of water injected into the heated dry gas by combining other measurement methods alone or in combination.

  Preferably, the method of the present invention includes a step of reducing the degree of heating of the dry gas during the pulverization cycle and after compensating for the temperature drop of the outlet temperature, and reducing the amount of water injected into the heated dry gas to obtain a desired outlet. A step of maintaining the temperature is further included. Thereby, it becomes possible to reduce the energy consumption after an installation once operate | moves. Indeed, overheating of the dry gas and subsequent cooling is particularly important during the start-up phase of the facility because they serve as a buffer to compensate for the temperature drop that occurs when the coking coal input is started. Once the equipment is in operation, only a small temperature drop occurs and the buffering action can be reduced. Therefore, it is not necessary to superheat the drying gas in the hot gas generator while the pulverization / drying equipment is operating normally, and it is not necessary to subsequently cool it to the processing temperature.

  In the recirculation line, it is also possible to remove part of the dry gas as exhaust gas. In the recirculation line, it is also possible to inject hot gas into the dry gas separately from fresh air.

  The method further includes continuously monitoring the outlet temperature, comparing the measured outlet temperature to the maximum temperature, and injecting into the heated dry gas if the measured outlet temperature exceeds the maximum temperature. It is also possible to include a step of increasing the amount of water produced. By including such a process, the water injection means used for general process control can be used for emergency cooling.

It is a schematic diagram of the crushing drying equipment used for implementation of the method of the present invention.

Means for carrying out the invention

  In the following, non-limiting embodiments of the present invention will be described, and the present invention will be further clarified with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a pulverization and drying facility for producing pulverized coal using the method of the present invention.

  The pulverizing and drying facility 10 includes the pulverizer 20 to which raw coal is sent via a conveyor 22. In the pulverizer 20, the raw coal is ground into an internal moving piece (not shown) or any other conventional pulverizing means to make a fine powder. At the same time, the pulverized coal is dried by the hot dry gas being fed into the pulverizer 20. The dry gas enters the pulverizer 20 through the gas inlet 24. In the pulverization / drying facility 10, a hot gas generator 26 is disposed upstream of the pulverizer 20, and the dry gas is heated to a predetermined temperature in the apparatus 26. The hot gas generator is provided with a burner 27 such as a multi-lance burner. The heated dry gas is conveyed from the hot gas generator 26 through the conduit 28 to the grinder 20. When the heated dry gas passes through the pulverizer 20 from the gas inlet 24 to the outlet 30, the pulverized coal is floated and carried. The mixture of pulverized coal and dry gas is conveyed from the pulverizer 20 via the conduit 32 to the filter 34, where the pulverized coal is removed again from the dry gas and sent to the pulverized coal collector 36 for use. The dry gas exiting the filter 34 is sent to the recirculation line 38 to be sent back to the hot gas generator 26. The recirculation line 38 is provided with fan means 40 for circulating dry gas throughout the facility. The fan means 40 is arranged on the line 42, for example upstream or downstream of the stack, for removing a part of the dry gas from the recirculation line 38.

  The recirculation line 38 is further provided with gas injection means 44 for injecting fresh air and / or hot gas into the recirculation line 38. The injected fresh air and / or hot gas is mixed with the recycle dry gas. It is possible to lower the dew point of the dry gas by injecting fresh air, and the heat balance of the pulverizing and drying circuit is improved by using this hot air injecting hot gas.

  According to an important aspect of the present invention, the facility 10 is provided with a water injection means 46 at a location downstream of the hot gas generator 26 and upstream of the grinder 20. The importance of this water injection means 46 will be clarified in the following description.

  The water injection means 46 is useful in adjusting the dew point of the dry gas by adjusting the oxygen level in the dry gas. In the recirculation line 38, a portion of the dry gas is withdrawn via line 42 while fresh air can be injected through the gas injection means 44. In conventional installations, for safety reasons, the oxygen level is monitored using the oxygen sensor 45 and if the oxygen level is found to be too high, the amount of fresh air introduced into the dry gas into the gas injection means 44 is reduced. An instruction is given to reduce it. However, a problem arises when the gas injection means 44 reaches the closing point, i.e. when the gas injection means 44 is completely stopped and fresh air is no longer injected into the dry gas. That is, when it is found that the oxygen level is too high, the fresh air injected into the dry gas cannot be further reduced, so the facility needs to be stopped.

  According to the present invention, it is possible to reduce the oxygen level in the dry gas by injecting water into the dry gas using the water injection means 46. When the oxygen level measured by the oxygen sensor 45 is too high, the water injection means 46 is instructed to increase the amount of water injected into the dry gas, thereby reducing the oxygen level downstream of the filter 34. Is possible.

  Preferably, the oxygen level is reduced by a conventional method that first reduces the volume of fresh air injected into the dry gas by the gas injection means 44, and if that is not sufficient, it is injected into the dry gas by the water injection means 46. The amount of water is increased and the oxygen level is further reduced.

  Still further, the water injection means 46 has a function of assisting temperature adjustment of the dry gas at the outlet of the pulverizer 20. During operation, the dry gas is heated to a predetermined temperature in the hot gas generator 26 and fed into the grinder 20. The temperature of the drying gas is reduced in the pulverizer 20 because heat from the drying gas is consumed to dry the pulverized coal. The temperature loss of the dry gas is determined by the moisture level of the raw coal. In order to prevent damage to the filter 34, for example, a temperature sensor 48 is used to monitor the temperature of the mixture of pulverized coal and dry gas coming out of the pulverizer 20 (hereinafter referred to as outlet temperature).

  In order to accurately maintain the outlet temperature, the temperature of the dry gas entering the pulverizer needs to be controlled, and this temperature control is usually achieved by controlling the output of the burner 27 provided in the hot gas generator 26. . Unfortunately, the response time of this control process is relatively slow, so once the facility determines that the outlet temperature is too high or too low, some time earlier than when the outlet temperature reaches the correct outlet temperature again. The burner 27 is configured to react in response to the temperature.

  This response time is particularly important during the start-up phase of the installation. In fact, first, dry gas heated before the raw coal is introduced is fed into the facility. This allows the equipment to be heated to reach the ideal processing temperature. When the raw coal is charged into the pulverizer 20 after a certain period of time, the outlet temperature rapidly decreases to a temperature considerably lower than the desired outlet temperature. In the prior art, by further heating the dry gas, the burner 27 has reacted to reach the desired outlet temperature. However, the time to reach the desired outlet temperature was greatly delayed, and the pulverized coal obtained during that time had to be discarded because of insufficient drying. In fact, during the transition period when the outlet temperature is too low, a generally unusable coal slurry is produced instead of dried pulverized coal.

  According to the present invention, at the start of operation, the burner 27 is set so that the drying gas is heated and the drying gas is sufficiently higher than the desired outlet temperature. The heated dry gas is then cooled under controlled conditions by water injection through the water injection means 46 into the heated dry gas, and may reach the desired outlet temperature by cooling the dry gas. It is possible. After heating the pulverization and drying equipment for a certain period of time, when the raw coal is charged into the pulverizer 20, the outlet temperature rapidly drops to a much lower temperature than the desired outlet temperature. Instead of the operation of adapting the heating temperature of the burner 27 to compensate for this rapid temperature drop, an operation of reducing the amount of water injected into the dry gas by the water injection means 46 is performed. As a result, the degree of cooling of the heated dry gas is reduced, and the desired outlet temperature can be stably maintained. Since the reaction time required for this treatment is considerably shorter than in the prior art, the transition period when the outlet temperature is too low is shortened and the production of unusable coal slurry is also reduced or prevented.

  It should be noted that the method exhibits maximum and dramatic advantages in the start-up phase, i.e. in the transition period immediately after the coking coal is first introduced into the grinder. However, this method also has advantages in standard operation of the equipment. Even if the moisture in the raw coal decreases and a sudden temperature drop occurs, the outlet temperature can be quickly returned to the desired outlet temperature.

  In order to optimize energy consumption, once the outlet temperature has stabilized, it is advantageous to reduce both drying gas heating and subsequent cooling. When such subsequent cooling is unnecessary, the supply of the water injection device can be stopped.

  As an advantage, the water injection means 46 is also used for emergency cooling. The method of the present invention can also include the operation of continuously monitoring the outlet temperature and comparing the measured outlet temperature to the maximum temperature. If the measured outlet temperature exceeds the maximum temperature, the water injection means 46 is instructed to increase the amount of water injected into the heated dry gas, and thereby the amount of dry gas entering the pulverizer 20 is increased. The temperature is lowered, and as a result, the temperature of the dry gas exiting the grinder 20 is also lowered.

10: Crushing and drying equipment 20: Crusher 22: Conveyor 24: Gas intake port 26: Hot gas generator 27: Burner 28: Conduit 30: Gas outlet 32: Conduit 34: Filter 36: Pulverized coal collector 38: Recirculation line 40 : Fan means 42: Line 44: Gas injection means 45: Oxygen sensor 46: Water injection means 48: Temperature sensor

Claims (13)

Heating the dry gas to a predetermined temperature in the hot gas generator;
A process of feeding heated dry gas into a pulverizer,
A step of charging the raw coal into a pulverizer to pulverize the raw coal into pulverized coal
Collecting a mixture of dry gas and pulverized coal from a pulverizer and feeding the mixture to a filter for separating the dried pulverized coal from the dry gas;
Collecting the dried pulverized coal for further use and sending the dried gas from the filter to the recirculation line to return at least a portion of the dried gas to the hot gas generator, and measuring the oxygen level in the dried gas And a method for producing pulverized coal comprising a step of comparing the measured oxygen level with a predetermined oxygen level threshold,
The oxygen level in the dry gas is measured during a grinding cycle in which heated dry gas is fed and raw coal is fed into the grinder,
In the recirculation line, fresh air is injected into the dry gas,
If the measured oxygen level is higher than a predetermined oxygen level threshold, the fresh air volume injected into the dry gas is first reduced,
Even if the volume of fresh air injected is zero , if the oxygen level is higher than the predetermined oxygen threshold, water is injected into the dry gas before the dry gas is fed into the grinder, and the amount of water injected Is a quantity calculated such that the oxygen level is reduced below a predetermined oxygen level threshold.
The method of claim 1 , wherein the predetermined oxygen threshold is selected within a range of 0 to 14% by volume. The method of claim 2, wherein the predetermined oxygen threshold is selected within a range of 5 to 12 volume percent. Measuring the outlet temperature of the mixture of dry gas and pulverized coal coming out of the grinder, and adjusting the amount of water injected into the heated dry gas before the dry gas is fed into the grinder includes the step of adjusting the claim 1-3 thereof injected amount of water, characterized in that the amount calculated as the outlet temperature is preferably the treatment temperature
The method in any one of. An operation start cycle in which dry gas heated in a state where no raw coal is charged is fed into the pulverizer, and the outlet temperature is kept below the first temperature threshold;
A pulverization cycle in which heated dry gas is fed into a pulverizer, raw coal is charged into the pulverizer and the outlet temperature is maintained at a preferred processing temperature,
In the treatment start stage, the dry gas is heated to a temperature equal to or higher than a first temperature threshold, water is injected into the heated dry gas, and the amount of water injected is reduced by lowering the temperature of the heated dry gas. The amount of water calculated to obtain an outlet temperature below one temperature threshold, and at the beginning of the grinding cycle, the amount of water injected into the heated dry gas is reduced to compensate for the drop in outlet temperature The method of claim 4 wherein: 6. A method according to claim 4 or 5 , characterized in that the amount of water injected into the heated dry gas is reduced at a rate determined by the outlet temperature.   7. The amount of water injected into the heated dry gas is reduced at a rate determined based on a pressure drop measured throughout the grinder. the method of. During the grinding cycle processing step and after compensation for outlet temperature drop,
According to any one of claims 5-7, characterized in that steps reduce the degree heating drying gas, and heated volume of water injected into the drying gas in the reduced and maintained at a desired outlet temperature step is included the method of. In the recirculation line, the method according to any one of claims 1 to 8, at least a portion of the drying gas, characterized in that the withdrawn as an exhaust gas. In the recirculation line, the method according to any one of claims 1 to 9, characterized in that fresh air and or hot gas is injected into the drying gas. Continue to monitor the outlet temperature, compare the measured outlet temperature with the maximum temperature, and increase the amount of water injected into the heated dry gas if the measured outlet temperature exceeds the maximum temperature the method according to any one of claims 1 to 10, characterized in that steps are included. The method according to any one of claims 1 to 11, drying gas, characterized in that it is heated in a hot gas generator in which the heat supply by the lance burner. During the heated drying gas, the method according to any one of claims 1 to 12, characterized in that water is injected with a water injection device arranged between the hot gas generator and a pulverizer.

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