JPH0641324B2 - Coal quality deterioration prevention method - Google Patents

Description

The present invention relates to a method for preventing deterioration of coal quality in a coal pile, and more particularly to a method for preventing deterioration of coal quality by long-term encapsulation of an inert gas in the coal pile.

Storage of coal in factories that consume a large amount of coal as an energy source, such as a steel mill and a thermal power plant, is often performed by outdoor storage by the mountain stack method, that is, open storage. However, if coal is stored in the atmosphere for a long period of time like open piles, the highly active hydrocarbonaceous matter or sulfur content in the coal will combine with oxygen in the atmosphere to deteriorate the quality of coal and further promote oxidation. There is also a risk of spontaneous combustion of stored coal due to heat generation.

Conventionally, as a method for preventing such quality deterioration of coal,
A method of handling coal by a wet method, a silo coal storage method, a method of expelling oxygen in the coal storage, and the like are performed. However, the wet method is not preferable because it increases the amount of heat of carbonization of coke.
In addition, silo coal storage is not suitable for large-scale storage of coal because it is premised on the case of small-scale coal storage. Therefore, what has been attracting attention in recent years is the method of expelling oxygen from coal storage, specifically, the input of dry ice into the coal pile,
Injecting nitrogen gas into the pile of coal (Japanese Patent Publication No. 54-3148)
1) etc. are carried out, but even with this method, the deterioration of coal can be effectively suppressed while the carbon dioxide gas or nitrogen gas remains in the pile, but with the passage of time, carbon dioxide gas or nitrogen gas Escapes into the atmosphere through the voids in the coal pile, and at the same time as this carbon dioxide gas or nitrogen gas escapes into the atmosphere, oxygen enters again and the quality deterioration prevention effect also decreases. . Therefore, a large amount of carbon dioxide gas or nitrogen gas must be consumed in order to suppress deterioration of coal quality over a long period of time, which is not an economically preferable method. Therefore, as a method that can minimize the consumption of inert gas and effectively prevent the deterioration of coal quality over a long period of time, some methods have been proposed to prevent the escape of blown inert gas. Has been done.

Further, one of the major problems in the conventional coal quality deterioration prevention method in the coal pile is that it is not possible to adequately follow the quality deterioration characteristics that differ for each coal brand. That is, for example, when nitrogen gas is blown into a pile of coal, even if the nitrogen gas is blown under the same blowing conditions for coal brands with different particle sizes, moisture, etc., the same level of quality deterioration prevention effect is expected. It was impossible to do this, and sometimes even more nitrogen gas could be blown. Therefore, from the economic and quality control standpoints, it has been demanded to take necessary and minimum quality deterioration prevention measures according to different quality characteristics for each coal brand.

Therefore, the present inventors considered the problem of the prior art, that is, effective prevention of quality deterioration of coal for a long period of time due to minimum inert gas consumption of stored coal, and different quality deterioration characteristics for each coal brand. We have continued our research to establish quality deterioration prevention technology. As a result, among the methods already proposed to date, a method of blowing an inert gas that replaces the oxygen in the voids in the coal pile with an inert gas, and pressure-bonding the surface layer of the pile with a roller, etc. The method of blocking the inflow of outside air and the outflow of inert gas by increasing the bulk density in the mountain or by spreading the resin agent on the surface of the coal mountain and enclosing the inert gas in the mountain for a long time is called so-called ventilation. Optimal conditions are found according to the rate,
In addition, there is a strong correlation between the quality deterioration characteristics and the air permeability that differ for each coal brand, and therefore the air permeability of the incoming coal is evaluated, and by determining each of the above treatment methods according to this evaluation. The inventors have completed the present invention by finding that quality deterioration due to an inert gas can be effectively and economically performed over a long period of time.

(Structure of the invention) That is, the present invention, when the coal is stored outdoors for a long time by the pile method, depending on the air permeability of the coal defined by the following formula, the relationship between the air permeability and the oxidation suppression effective period determined in advance. Based on the above, if the target storage period is not exceeded, the inert gas is blown into the coal pile as it is, and if the target storage period is not reached, the coal is piled under pressure or further coal is applied. Inert gas is sealed by spraying a resin agent on the surface of the mountain and the ventilation rate is reduced.
It is a method for preventing deterioration of coal quality, which is characterized in that adjustment is made so that the above-mentioned effective period for inhibiting oxidation comes within a target storage period.

formula: K: Air permeability [m ² / Hr · m · water column] ΔP: Pressure hardening of packed bed [m · water column] L: Packed layer thickness [m] V: Superficial velocity [m / Hr] The active gas is a non-oxidizing gas typified by nitrogen and carbon dioxide, but is not particularly limited thereto. The air permeability of coal may be determined by sampling incoming coal in advance, and each quality deterioration method is appropriately selected according to the air permeability thus obtained. Originally, the air permeability is a measure of gas permeability of a porous material, and is a content well known in the art. However, according to the findings of the present inventors, the air permeability of coal as in the case of the present invention. , Mainly related to the particle size distribution and water content of coal. Therefore, the present invention is deeply correlated with the form or progress of coal deterioration during storage, and the present invention can be said to be a system utilizing them as a control factor.

Hereinafter, the present invention will be described in more detail.

As described above, as a method for preventing the quality deterioration of coal in Mt.yama for a long time, (i) a method of blowing an inert gas into the mound, and (ii) pressure-bonding the Mt. Method to increase the bulk density of the part to contain the inert gas, and (iii) Spread the resin agent on the surface of the mountain to block the ventilation from the surface to prevent the inflow of outside air and the outflow of the inert gas. There is a method to contain the inert gas. By appropriately adopting each of these means according to the air permeability of the coal, the inert gas is enclosed in the coal for a long period of time, and the deterioration due to the oxidation of the coal is economically and effectively prevented.

In a preferred embodiment of the present invention, the above-mentioned means (i) to (iii) may be sequentially combined in accordance with the measured air permeability, and, for example, generally, first, the coal product is first mixed with an inert gas. It is preferable to completely replace the oxygen in the mountains, then press-fasten the surface layer with a roller or the like, and then spray the resin agent on the surface to completely shut off the air. However, various changes can be made to the order of this step, and the present invention is not limited only to the combination and order of the blowing of the inert gas, the pressure fastening, and the spreading of the resin agent as described above. The air permeability is not particularly limited as long as it has a ventilation rate that can realize the target oxidation suppression effective period within the storage period.

Next, the correlation between the aspect of each of these methods and the air permeability will be described in more detail.

First of all, the “inert gas blowing” method is for improving the inert gas substitution rate of coal, and the blowing amount should be originally changed according to the bulk density (particle size distribution) of coal. is there. Therefore, by using coal with an average particle diameter of 10 mm and 5 mm, the flow rate of the blown gas was changed variously to replace the inert gas (oxygen concentration in the voids seen in coal piles).
The area of 10% or less / the total volume of the voids) was measured. The results are summarized in the graph in Figure 1 (however, blowing gas = nitrogen gas, blowing time = 24 hours, coal pile = 22).
kt / mountain). In the figure,-●-shows an average particle diameter of 10 mm, and-○-shows an average particle diameter of 5 mm. From the results shown in Fig. 1, the replacement rate of the inert gas increases with each particle size as the blowing flow rate increases, but when the rate exceeds 1000 Nm ³ / Hr, the replacement rate becomes saturated in all cases, and the particle size In other words, there is no correlation with the air permeability. This means that the effective blowing flow rate for any particle size is 1000 Nm ³ / Hr or less, so that the optimum blowing amount according to each air permeability can be seen. Therefore, in the present invention, effective quality deterioration can be prevented by evaluating the air permeability as a factor correlating with the bulk density of coal and determining the optimum blowing flow rate in the range of 1000 Nm ³ / Hr or less.

That is, the optimum blowing flow rate according to the ventilation rate can be achieved when the pressure drop ΔP (that is, the nozzle original pressure) in the pile becomes constant.

For example, considering that nitrogen gas is used as the inert gas, ΔP = V · L / K = constant as described above,
Normally, the height L of the coal pile is constant in terms of the size of the yard lifting device, and therefore V / K = constant may be set in order to keep ΔP constant.

Here, since the air permeability K is obtained by measuring as described above, the optimum V is determined accordingly.

In other words, it can be said that K can be determined by measuring the pressure loss ΔP of the coal packed bed at a predetermined inert gas flow rate V.

Note that K is the packing density, that is, the void ratio ε, and the particle size d of coal.
It was confirmed to depend on p. It is arranged by the following formula.

Here, gc: Gravity conversion factor φ: Shape factor (0.5) μ: Viscosity of inert gas (kgf · hr / m ² ) If the above formula is used, the air permeability K will be the particle size and packing density of each pile. Since the required oxidation suppression effective period can be secured by adjusting it appropriately, the optimum inert gas blowing amount V (this is the empty column in the ventilation rate calculation formula can be determined from the relationship of V / K = constant). It is defined as velocity, but generally the area of cumulus is almost constant, so generally it can be treated as an inert gas blowing rate (Nm ³ / Hr)).

Next, in order to investigate the correlation between the "inert gas containment" method and the air permeability, the oxidation suppression effective period without gas containment ("effective" here means the inert gas replacement rate (Meaning 60% or more) was performed on the air permeability. The results are shown graphically in Fig. 2 (however, blowing gas = nitrogen gas, blowing time = 24 hours, coal pile = 22 kt / mountain). It can be seen from FIG. 2 that coal having a relatively large air permeability has a short oxidation suppression effective period, and it is necessary to contain an inert gas. Therefore, depending on the air permeability of the coal, for example, by changing the weight of the roller to perform pressure fastening of the surface layer of the coal pile, or by spraying the resin agent on the surface of the coal pile, necessary and sufficient inertness is achieved. Contain gas. Specifically, it is sufficient if the inert gas can be confined to the extent that the inert gas substitution rate of 60% or more can be maintained during the required storage period. As for the resin agent used for containing the inert gas, any resin agent can be used as long as it can form a resin layer on the surface of the coal pile to substantially block the outside air and the gas in the void inside the coal pile. For example, the resin disclosed in JP-A-58-117270 may be used, but the present invention is not particularly limited to such a specific resin composition and type.

In the present invention as described above, each processing means is selected according to the air permeability of coal, but the air permeability of the pile of coal at that time should be as constant as possible, For example, when the variation in the particle size distribution of coal is large and the particle size segregation inside the pile becomes large by the usual loading method, when the inert gas blown in due to an abnormal increase in the air permeability of one part of the pile is blown out. There is. Therefore, according to the present invention, the aeration rate is evaluated for each coal brand, and if a variation in the particle size distribution is confirmed by this, the loading method for outdoor storage of coal is changed from general one-row loading to so-called bale loading. Therefore, it is effective to make the particle size and air permeability of the entire coal mine as uniform as possible.

Next, the present invention will be described in more detail by way of examples.

(Effects of the invention) Example 1 In order to compare the effects due to the containment of the inert gas, the inert gas was blown into the coal pile under the following conditions, and the presence or absence of the containment of the inert gas The difference in quality deterioration prevention effect was measured by measuring the FI value. However, the FI value mentioned here is an index showing the quality of coal and is generally expressed by the logarithm of the maximum fluidity. Experiment A was one in which the inert gas was sealed in and Experiment B was not performed.

Experimental conditions (Experiments A and B) Target brand: Pitton coal Coal FI value at arrival: 3.7 Coal weight: 22kt / mountain Inert gas injection (nitrogen gas) Average flow rate: 500Nm ³ / Hr Injection time: 24 hours Injection amount: 12000Nm ³ Coal loading method: 1-row loading Storage period: 120 days (Experiment A only) Encapsulation of inert gas ： Roller (ground pressure 0.5kg / cm ² ) pressure molding of pile surface layer and resin (acrylic resin agent) The surface was sprinkled, but after blowing gas. The air permeability of this example is 10 ⁵ m ² / Hr
・ The m · water column became 10 ² m ² / Hr · m · water column after spraying the resin agent. Experiment results (FI value) Experiment A: 3.3 Experiment B: 2.5 As is clear from the experiment results, when the FI values of A and B were compared under the same conditions except that the gas was confined, A was compared to when it arrived. 0.4 and B were -1.2, and it was confirmed that the quality deterioration prevention effect of about 3 times was confirmed by sealing immediately after the gas was blown.

Example 2 A sample of Blue Creek charcoal was evaluated for air permeability, and was stored under the following optimum conditions according to the present invention. Further, an experiment was conducted under the conditions shown in Table 1, the FI value was measured every 10 days, and the results are shown in a graph in FIG. However, the symbols in the figure are-○-: Experiment C,-●-: Experiment D,-△
−: Experiment E, − ▲ −: Experiment F, respectively.

Air permeability = 5000 m ² / Hr · m · water column FI value = 3.5 Processing conditions: Inert gas blowing: Flow rate: 600 Nm ³ / hour Inert gas containment: Roller ground pressure 0.4 kg / cm ² Resin agent spray resin Air permeability after spraying: 10 ² m ² / Hr ・ m ・ water column Coal loading method: 1 row volume From the results in Fig. 3, the FI value decreases with the passage of storage time for each method, but when compared at the time of 120 days, the decrease from the FI value at the time of receipt shows the maximum quality deterioration prevention effect. In Experiment C, the quality deterioration was about -0.3, and in Experiment F in which the quality deterioration was not prevented at all, it was -2.0.
It was confirmed to be / 7. In addition, Experiments C and D of the present invention, in which the inert gas was blown in and contained, were stored for 12 hours.
The FI value declined from the time of arrival at the 0th day was -0.3 to -1.2, which is a very superior quality compared to -1.8 of Experiment E in which only the inert gas blowing, which is a conventional quality deterioration prevention method, was performed. It showed the effect of preventing deterioration. Even when the same inert gas was blown in and confined, the experiment C (FI value decrease -0.3) conducted at the optimum inert gas blowing flow rate of 600 Nm ² / Hr by the evaluation of the air permeability was the non-optimal value. Compared to the experiment C (FI value decrease −1.2) conducted at 300 Nm ³ / Hr, the effect of preventing quality deterioration was about 4 times.

As is clear from the above description, according to the present invention, not only can the quality deterioration of coal be prevented for a long period of time by the minimum inert gas consumption, but considering different quality deterioration prevention characteristics for each coal brand, Further, it is possible to effectively prevent the quality deterioration of coal.

[Brief description of drawings]

FIG. 1 is a graph showing the rate of replacement of gas in coal with an inert gas due to changes in the blowing flow rate; FIG. 2 is a graph showing the relationship between air permeability and oxidation suppression effective period; and FIG. It is a graph which shows the quality deterioration of coal with progress of a storage period.

Claims (1)

[Claims] 1. When the coal is stored outdoors for a long time by the mountain stack method, based on the relationship between the air permeability and the oxidation inhibition effective period, which is determined in advance, according to the air permeability of the coal defined by the following formula:
If the target storage period is not exceeded, the inert gas is blown into the coal pile as it is, and if the target storage period is not reached, by pressure fastening of the coal pile surface layer or further to the coal pile surface. The deterioration of coal quality, which is characterized by containing inert gas by spraying the resin agent in order to reduce the air permeability and adjusting so that the above-mentioned effective period for inhibiting oxidation comes within the intended storage period. Prevention method. formula: K: Permeability [m ² / Hr · m · water column] ΔP: Pressure hardening of packed bed [m · water column] L: Packed layer thickness [m] V: Superficial velocity [m / Hr]