JP2006321646A - Method for preventing spontaneous ignition in coal storage silo - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spontaneous ignition preventive method for reliably preventing spontaneous ignition while preventing the heat generation of coal and degradation of the handling property of coal caused by excessive humidification without excessively increasing the equipment cost in a coal storage silo. <P>SOLUTION: Coal is unloaded by an unloader 2 from a plurality of holds 6 of a coal carrier 1, the coal is humidified as necessary by a water sprinkling device 4 on a belt conveyor 3, and immediately charged and stored in a coal storage silo 5. Either or each countermeasures of reduction of the unloading rate and increase of the humidification is performed for the coal in holds 6A, 6C and 6E in which the maximum methane concentration during the navigation (transport) exceeds the predetermined value (for example, 30% LEL). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technology for preventing spontaneous ignition in a coal storage silo installed in a facility that uses a large amount of coal such as a coal-fired power plant, a coal gasification plant, and a pulverized coal injection blast furnace.

  When coal is stored in a coal storage silo (hereinafter also simply referred to as a “silo”), the coal is oxidized by the air entering the silo and generates heat, which may cause spontaneous ignition. If such spontaneous ignition occurs, it may lead to a large fire accident, and even if the damage is minor, the coal is often altered and cannot be used. In order to prevent spontaneous ignition, the following methods have been proposed or implemented as conventional techniques.

(1) Method of measuring humidity with a hygrometer installed in the silo upper space, and performing watering, water spraying, steam blowing, etc. into the silo so as to keep this humidity at a predetermined value (Patent Documents 1 and 2) See).
(2) A method in which a plurality of temperature sensing sensors and watering nozzles are installed in a lattice shape in the silo upper space, respectively, and watering is concentrated on a site where abnormal temperature rise is detected (see Patent Document 3).
(3) The silo is equipped with a moisture detector using electromagnetic waves and a plurality of water spouts, and when the moisture distribution state of coal is constantly measured by the moisture detector and a dry part is detected, A method in which water is intensively sprayed from the upper water spout (see Patent Document 4).
(4) A method in which when an abnormal temperature rise is detected in the silo, the coal is once discharged out of the silo, cooled, and then recharged into the silo.
(5) A method of pre-watering coal before charging into the silo.

  However, in the method (1), even if the coal bed is locally dried, water is uniformly sprayed over the entire coal bed, so that more water than necessary is used, and the calorific value of the coal. There is a problem that it is difficult to cut out or to cut coal.

  In addition, since the methods (2) and (3) perform water spray intensively in the dry part, the problem of the method (1) can be solved, but the method is to cope with the phenomenon after a certain degree of progress. It is unsuitable for equipment with poor response, such as large silos. Furthermore, it is necessary to provide many measuring instruments in the silo, and there is a problem that the equipment cost increases.

  In addition, the method (4) above has the advantage of saving equipment costs because it can be done with existing equipment, but it cannot supply coal to the downstream equipment during payout from the silo and recharging, and the operating rate There is a problem that decreases.

In addition, the method (5) has the advantage of saving equipment costs because it does not require measurement, humidification, etc. after charging coal into the silo. Since humidification is not performed, it is necessary to spray the coal into the silo after spraying a large amount of water for safety so that a dry portion does not occur in the coal bed in the silo. For this reason, like the above (1), more than necessary water is used, and there is a problem that the calorific value of coal is reduced and handling properties such as coal cutting failure are deteriorated.
JP 59-142981 A (Claims etc.) JP-A-58-188237 (Claims etc.) JP 7-61546 A (claims, etc.) Japanese Patent Publication No. 2-58165 (claims, etc.)

  Accordingly, an object of the present invention is to prevent spontaneous ignition in a coal storage silo that can reliably prevent spontaneous ignition while preventing deterioration of coal calorific value and coal handling property due to excessive humidification without increasing equipment costs. It is to provide a method.

  The present inventors have the advantage that the method of cooling the coal outside the silo and humidifying the coal used in the methods of the prior arts (4) and (5) is simple and can save equipment costs. We thought that the above problem could be solved by developing a new method that successfully incorporated these measures, and conducted the following studies.

  Coal carriers usually have a plurality of separate holds, and in order to prevent spontaneous ignition of coal in these holds, water must be sprinkled on the coal before loading at the loading site. Has been done. However, over time, coal undergoes an oxidative exothermic reaction in accordance with local characteristics such as the particle size distribution and air flow path, and a dry portion may be generated, resulting in spontaneous ignition. For this reason, the methane concentration in each hold is monitored as a means of detecting the dry state of coal, and when the methane concentration exceeds the allowable value, an inert gas is introduced into the hold or watering is performed. To prevent spontaneous ignition.

  By the way, in the method of the above prior art (5), regardless of the level of methane in each cargo hold during transportation, the coal unloaded from all cargo holds is uniformly humidified and charged into a coal storage silo. Was.

  In this way, regardless of the methane concentration of each cargo hold during transportation, uniform humidification of coal unloaded from all cargo holds will result in excessive humidification for safety reasons, and the calorific value of coal. Will result in a decrease in handling and deterioration in handling. However, if the amount of humidification is saved in an attempt to maintain the calorific value and handling of the coal, the coal unloaded from the hold where a high methane concentration has been detected will be insufficiently humidified, and the silo will be removed before the required storage days. It is thought that a dry portion is generated in the inside, and in a severe case, spontaneous ignition occurs.

  Therefore, first, the present inventors conducted the following experiment in order to clarify the relationship between the methane concentration in the hold during transportation and the degree of coal drying in the silo. In other words, information on the maximum methane concentration for each cargo hold during transportation is obtained in advance, and coal unloaded from the hold whose maximum methane concentration exceeds 20% LEL (lower explosion limit) at the time of unloading is stored in one silo. The coal unloaded from the hold where the same concentration was 20% LEL or less was divided into separate silos and stored separately, and the temperature change of the coal bed in each silo was investigated. In addition, no humidification was performed on any of the coals before unloading into the silo after unloading. As is clear from the comparison of the measurement results shown in FIG. 4, the coal unloaded from the hold where a high methane concentration was detected was compared to the coal unloaded from the hold where a low methane concentration was detected. The temperature of is already high at the time of charging into the silo, and the rate of temperature increase is significantly high. Therefore, it was found that the coal retained in the hold where a high methane concentration was detected had already dried to a considerable extent at the time of unloading and was likely to spontaneously ignite in a short period in the silo.

  It is theoretically possible to grasp the dry state of the coal in each hold at the time of unloading by collecting a sample and performing a moisture analysis every time it is unloaded from each hold. However, at present, moisture analysis is performed on average for all coal unloaded from all holds, but when moisture analysis is performed for each coal unloaded from each hold, the number of samples increases several times at a time. However, it takes a lot of time to perform the reduction operation and analysis, and it takes a longer time than before to obtain the analysis results, so measures should be taken before loading into the silo based on the analysis results. It is practically impossible to do.

  Therefore, the present inventors grasped the dry state of the coal in each cargo hold at the time of unloading based on the methane concentration information in each cargo hold at the time of voyage (transport) based on the above knowledge and the like. Therefore, it was judged that it was most effective and practical to take necessary measures before charging coal storage silos only to coal whose drying was considerably advanced, and the present invention was completed.

  In the invention according to claim 1, when unloading coal from a plurality of holds of a coal carrier, humidifying the coal as necessary, and immediately storing it in a coal storage silo, This is a method for preventing spontaneous ignition in a coal storage silo, in which either or both of the unloading speed and the humidification amount are adjusted for each coal in each hold according to the maximum methane concentration.

  The invention according to claim 2 is the highest methane concentration during transportation when unloading coal from a plurality of holds of a coal carrier, humidifying the coal as necessary, and immediately storing it in a coal storage silo. Is a method for preventing spontaneous ignition in a coal storage silo, in which either or both of a reduction in the unloading speed and an increase in the humidification amount are taken for coal in a hold where the concentration exceeds a predetermined concentration.

The invention described in claim 3 is an apparatus for preventing spontaneous ignition of coal immediately after being unloaded from a coal carrier and humidified as necessary, and then immediately stored in a coal storage silo. Or it is the spontaneous combustion prevention apparatus in the coal storage silo characterized by including the apparatus of (b).
(A) Unloading speed calculating means for calculating the coal unloading speed based on the maximum methane concentration in each cargo hold of the coal carrier during transportation, and conveying means for conveying the coal to the coal storage silo at the unloading speed. (B) a humidification amount calculating means for calculating the humidification amount of the coal based on the maximum methane concentration in each hold of the coal carrier during transportation; and a moisture supply means for supplying moisture of the humidification amount; Humidifier with coal

  According to the present invention, it is only necessary to adjust either or both of the coal unloading speed and the amount of humidification outside the silo, so that it is possible to cope with only existing equipment and the equipment cost is not increased. In addition, even when it is necessary to humidify the coal, only the necessary coal is humidified according to the information on the maximum methane concentration in each hold, so that excessive humidification can be prevented, and the calorific value of the coal and the handling of the coal While maintaining the above, it is possible to reliably prevent spontaneous ignition.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment
An example of the embodiment is shown in FIG. As shown in FIG. 2A, coal that has been transported by sea from a coal carrier 1 from an overseas loading site is unloaded by an unloader 2 at a landing site, and on a belt conveyor (conveying means) 3 as necessary. After being humidified by the watering device (moisture supply means) 4, it is immediately charged and stored in the coal storage silo 5.

  As shown in FIG. 1B, the coal carrier 1 has a plurality of compartments (also referred to as “holds”) 6 (in this example, 6 holds of 6A to 6F). A gas detector (not shown) for measuring the methane concentration is provided. During voyage (during transportation), the methane concentration in each hold 6 is periodically measured, and the value of the maximum methane concentration in each hold 6 is reported to the landing site.

  In landing sites that have received reports of the maximum methane concentration value in each hold 6 during the voyage, hold 6 (6A in FIG. 1), where the maximum methane concentration exceeds a predetermined concentration (for example, 30% LEL (lower explosion limit)). 6C, 6E) with respect to the coal (hereinafter referred to as “high methane concentration coal”), hold 6 (6B, 6D, FIG. 1) having a maximum methane concentration of a predetermined concentration (30% LEL) or less. 6F) From the coal held in 6F) (hereinafter referred to as “low methane concentration coal”), the unloading speed is lowered and the water is discharged while the watering amount (humidification amount) is increased. In addition, the increase in the humidification amount with respect to the said high methane density | concentration coal also includes humidifying only a high methane density | concentration coal, without humidifying a low methane density | concentration coal. And the high methane density | concentration coal which performed the said countermeasure is inserted into the same silo 5 as a low methane density | concentration coal.

  Here, as the above-mentioned predetermined concentration, 30% LEL (lower explosion limit), which is an upper limit alarm value of methane concentration in the hold, is exemplified, but it is more natural if it is necessary to store in the silo 5 for a longer period than usual. If ignition is likely to occur, the predetermined concentration may be set to a lower value, such as 20% LEL or even 10% LEL.

  Moreover, the degree of decrease in the unloading speed and the degree of increase in the amount of water spray (humidification amount) for high methane concentration coal can be determined as follows, for example.

  That is, regarding the degree of decrease in the unloading speed, the unloading speed is changed variously with respect to the high methane concentration coal, and the silo 5 is charged in advance, and the initial temperature and the heating rate of the coal bed in the silo 5 are measured. Perform an experiment. And this initial temperature and temperature rising rate become comparable to the initial temperature and temperature rising rate of the coal bed formed by unloading low methane concentration coal at a normal unloading speed and charging it into the silo 5. The unloading speed can be obtained, and the degree of decrease in the unloading speed can be determined from this.

  As for the degree of decrease in the amount of water spray (humidification amount), in the same manner as the unloading speed, the water spray amount (humidification amount) was changed in advance for high methane concentration coal and charged into the silo 5 in advance. Experiments are conducted to measure changes in the initial temperature and heating rate of the inner coal bed. And this initial temperature and temperature rising rate become comparable with the temperature rising rate of the coal bed formed by humidifying the low methane concentration coal with the normal watering amount (humidification amount) and then charging it into the silo 5. Such a watering amount (humidification amount) is obtained, and from this, the degree of increase in the watering amount (humidification amount) can be determined.

  The adjustment of the unloading speed may be performed by a coal conveying device provided with an unloading speed calculating means (not shown) and a conveying means (belt conveyor 3). The unloading speed calculating means is configured to calculate the unloading speed based on the relational expression obtained in the above experiment when the maximum methane concentration in each hold is input. The conveying means (belt conveyor 3) may be configured to be adjusted by the transmission so that the conveying speed corresponds to the unloading speed calculated by the unloading speed calculating means.

  Moreover, what is necessary is just to perform adjustment of a watering amount (humidification amount) with the coal humidification apparatus provided with the humidification amount calculating means (not shown) and the water | moisture-content supply means (watering apparatus 4). The humidification amount calculating means is configured to calculate the humidification amount based on the relational expression obtained in the above experiment when the maximum methane concentration in each hold is input. The water supply means (watering device 4) may be configured to adjust and supply the moisture amount corresponding to the humidification amount calculated by the humidification amount calculation means using the flow rate control valve. The unloading speed calculation means and the humidification amount calculation means can be easily configured using an existing process computer or the like.

  As described above, since it is only necessary to adjust the coal unloading speed and the amount of humidification on the belt conveyor 3, it can be handled only by existing equipment such as the unloader 2, the watering device 4, and the process computer. Since it is not necessary, the equipment cost is not increased. Furthermore, even when humidification is required for coal, only the truly necessary coal is humidified according to the information on the maximum methane concentration for each hold (funakura), so drying can be performed with the minimum amount of humidification. Can be prevented. As a result, spontaneous combustion can be reliably prevented without excessively reducing the calorific value of coal or making handling such as cutting difficult.

(Modification)
In the above embodiment, an example is shown in which high methane concentration coal and low methane concentration coal are stored in the same silo without being distinguished, but high methane concentration coal and low methane concentration coal are stored separately in separate silos. You may do it. In this case, if the silo storing the high methane concentration coal is used first, spontaneous ignition can be prevented even if the unloading rate of the high methane concentration coal is reduced or the increase in the humidification amount is reduced. And a further effect of reducing the added mass can be obtained.

  Moreover, in the said embodiment, although the example which implements simultaneously the countermeasure of both the fall of unloading speed and the increase in the humidification quantity with respect to high methane concentration coal was shown, you may implement only any one countermeasure. In particular, as described above, when storing high methane concentration coal and low methane concentration coal separately in separate silos, high methane concentration coal can be used preferentially, so it is not always necessary to take both measures simultaneously. Absent.

  Moreover, in the said embodiment, although the example which uses only one value (this example 30% LEL) was shown as a predetermined density | concentration which is a threshold value of countermeasure implementation with respect to high methane density | concentration coal, you may use several values. . For example, two values of 20% LEL and 30% LEL are used as the predetermined concentration, and different discharges are applied to coal in silos exceeding 20% LEL and below 30% LEL and coal in silos exceeding 30% LEL. Speed and / or different humidification amounts may be applied. Alternatively, for the former coal, only one of the countermeasures for reducing the unloading speed and increasing the humidification amount may be performed, and for the latter coal, both countermeasures may be performed simultaneously.

  In order to grasp the effect of the application of the method of the present invention, 12 coal storage silos (storage capacity 30,000 tons per unit) installed in a coal-fired power plant are connected to a coal carrier (transport capacity 60 to 88,000 tons, In the case of storing coal (KP coal) unloaded from the number of holds 6-7), the following experiment was conducted.

  First, in the present Example, the effect about the case where the countermeasure only of the increase in humidification amount was implemented with respect to high methane concentration coal was confirmed.

  That is, the unloading speed was constant at 3000 t / h, which is a normal unloading speed, regardless of the level of methane concentration in each hold. And it is divided into Funakura coal (low methane concentration coal) whose maximum methane concentration is 30% LEL or less and Funakura coal (high methane concentration coal) exceeding 30% LEL, and humidification is applied to low concentration methane coal. Without being carried out, it was stored in the first silo as it was. The high methane concentration coal is further divided into two, one of the coals is not humidified and stored in the second silo as it is, and the other coal is coal moisture on the belt conveyor. Watering was performed at a rate equivalent to 0.4% by mass, and the mixture was humidified and stored in a third silo. The amount of coal stored in each of the first to third silos was the same. And the temperature change of the coal bed in each 1st-3rd silo was measured.

  FIG. 2 shows a comparison of the temperature change of the coal bed in each silo. As shown in the figure, when high concentration coal is stored in a silo at the same unloading speed as low methane concentration coal and not humidified, the rate of temperature rise of the coal bed is clearly large. It has become. On the other hand, even if the unloading speed is the same as that of the low methane concentration coal, if the high methane concentration coal is humidified and stored in a silo, the temperature rise rate of the coal bed is almost the same as that of the low methane concentration coal without humidification. It turns out that it is suppressed to the same extent.

  Next, unlike the above-described Example 1, in this example, the effect was confirmed for the case where only measures for lowering the unloading speed were performed on high methane concentration coal. In this example, the same KP coal as in Example 1 was used as the coal brand, but coal unloaded from a coal carrier having a different port entry time from Example 1 was used.

  In other words, regardless of the methane concentration in each hold, the coal in any hold was not humidified after unloading and before silo loading. In the same manner as in Example 1 above, it is divided into coal in a hold (low methane concentration coal) having a maximum methane concentration of 30% LEL or less and coal in a hold (high methane concentration coal) exceeding 30% LEL. Concentrated methane coal was unloaded at a normal unloading speed of 3000 t / h and stored in the first silo. The high methane concentration coal is further divided into two, one of which is unloaded at the same normal unloading speed of 3000 t / h as the low concentration methane coal and stored in the second silo, and the other coal is unloaded. Was reduced by half to 1500 t / h and stored in a third silo. Note that the amount of coal stored in each of the first to third silos was the same as in Example 1. And the temperature change of the coal bed in each 1st-3rd silo was measured.

  FIG. 3 shows a comparison of changes in the temperature of the coal bed in each silo. As shown in the figure, when coal with high concentration is not humidified like coal with low methane concentration and is unloaded at the same discharge rate as coal with low methane concentration and stored in a silo, the rate of temperature rise of the coal bed is clear Is getting bigger. On the other hand, even when humidification is not performed as in the case of low methane concentration coal, if the unloading speed of high methane concentration coal is reduced and stored in a silo, the temperature rise rate of the coal bed will be the normal unloading speed. It can be seen that it is suppressed to the same extent as the low methane concentration coal unloaded in

  Since the effect of the method of the present invention was confirmed from the experimental results of Examples 1 and 2, the method of the present invention was applied to the coal storage silo in actual operation.

  That is, 30% LEL is adopted as the above-mentioned predetermined concentration, which is a threshold value for implementing countermeasures against high methane concentration coal, and as a countermeasure against high methane concentration coal, while taking into consideration coal brands and cargo handling schedules comprehensively. One or both of the measures for lowering the unloading speed and increasing the humidification amount were appropriately selected.

  In this way, even when humidification of coal is required, the average amount in this silo is increased by finely dividing the hold of coal carriers and increasing the amount of humidification only to coal that really needs countermeasures. The amount of humidification was reduced by 0.78% by mass compared to before application of the present invention. As a result, the amount of heat loss used to evaporate the water in the coal can be used effectively, and the calorific value of the coal increased by an average of about 4.5 kcal / kg.

  Moreover, the frequency of occurrence of equipment troubles due to deterioration of the handling property of coal such as chute clogging during the transportation to the subsequent crushing equipment and hanging on the shelves in the hopper due to the cutting of excessive humidified moisture is also the same as before application of the present invention. Assuming that 100%, it was greatly reduced to 24%.

  Furthermore, although more than one year has passed since the present invention was applied, it was confirmed that even if the amount of humidification was reduced as described above, a dry state was not generated at all in the silo, and spontaneous ignition could be prevented reliably. .

(A) is a flowchart for demonstrating the spontaneous-fire prevention method in the coal storage silo which concerns on implementation of this invention, (b) is a longitudinal section which shows typically distribution of the highest methane concentration in the several hold of a coal carrier. FIG. It is a graph which shows the relationship between the storage days in a coal storage silo, and the temperature of a coal bed in Example 1. FIG. It is a graph which shows the relationship between the storage days in a coal storage silo, and the temperature of a coal bed in Example 2. FIG. It is a graph which compares the high methane density | concentration coal and the low methane density | concentration coal, and shows the relationship between the storage days in a coal storage silo, and the temperature of a coal bed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Coal carrier 2 ... Unloader 3 ... Conveying means (belt conveyor)
4. Water supply means (watering device)
5 ... Coal storage silo 6 ... Funakura (hold)

Claims (3)

When unloading coal from multiple cargo holds of a coal carrier, humidifying the coal as necessary, and immediately storing it in a coal storage silo,
A method for preventing spontaneous ignition in a coal storage silo, wherein either or both of a discharge speed and a humidification amount are adjusted for each coal in each cargo hold according to a maximum methane concentration in each cargo hold during transportation. When unloading coal from multiple cargo holds of a coal carrier, humidifying the coal as necessary, and immediately storing it in a coal storage silo,
A method for preventing spontaneous ignition in a coal storage silo, characterized in that either or both of a reduction in unloading speed and an increase in humidification amount are taken for coal in a hold where the maximum methane concentration during transportation exceeds a predetermined concentration. A device for preventing spontaneous ignition of coal immediately after being unloaded from a coal carrier and humidified as necessary and then stored in a coal storage silo, comprising the following devices (a) and / or (b) A self-ignition prevention device for a coal storage silo.
(A) Unloading speed calculating means for calculating the coal unloading speed based on the maximum methane concentration in each cargo hold of the coal carrier during transportation, and conveying means for conveying the coal to the coal storage silo at the unloading speed. (B) a humidification amount calculating means for calculating the humidification amount of the coal based on the maximum methane concentration in each hold of the coal carrier during transportation; and a moisture supply means for supplying moisture of the humidification amount; Humidifier with coal