KR101582232B1 - Method of Drying Coal - Google Patents

Abstract

In order to reduce the water content of the coal, the present invention adds coal ash having a similar chemical / physical property to coal in a specific amount to lower the plasticity of the coal and adhere to the wall of the supply pipe or the storage furnace It is possible to increase the recovery rate of the coal, to dry a large amount of coal in a relatively short time, to increase the drying efficiency without paying expensive equipment cost and high energy cost, Not only can it be dried by any dryer, but also the drying temperature can be lowered, so that explosion of volatile matter can be prevented and the coal can be effectively dried.

Description

Method of Drying Coal [

The present invention relates to a method for drying coal, and more particularly, to reduce the water content of coal, a coal ash having similar chemical / physical properties to coal is added in a specific amount to lower the plasticity of the coal, And to a method of drying coal in which a large amount of coal can be dried at a low temperature in a short time.

Compared to petroleum and natural gas, coal has advantages in terms of supply and price, and it is used as a major fuel in various power plants. However, due to the rapid increase in demand for coal and the shortage of supplies, the price of raw coal has been continuously increased. In order to fill the supply shortage, it is inevitable to receive and supply low grade coal. Especially, There is a trend.

Generally, coal is divided into peat, brown coal, lignite, sub-bituminous coal, bituminous coal, and anthracite grades, , Volatile matter, high volatile bituminous coal, and anthracite is divided into semi-anthracite, anthracite, meta-anthracite and anthracite anthracite. Among these, low rank coal (LRC) refers to brown coal and lignite bituminous coal, while bituminous coal and anthracite coal are classified as high rank coal (HRC).

Here, low grade and high grade do not mean coal quality but merely indicate the difference in the degree of carbonization. By using dehydration, drying and stabilization, it is possible to use bituminous coal (high grade, HRC : high rank coal).

Low-grade coal such as lignite has a lot of pores and a large amount of lipid hydrocarbons, which leads to a rise in temperature due to the accumulation of adsorption heat due to absorption / desorption of moisture, and the possibility of spontaneous ignition due to the oxygen- The use thereof has been limited.

The moisture of coal is divided into free water, interstitial water, surface water, and bound water. A large part of the coal water occupies the free water adhering to the surface of the coal. The water present between the molecules of the coal and the molecules is the internal water, and the number of the bonds is chemically bonded to the coal molecules. The free water and the surface water are dried at 100 ± 5 ° C, but the internal water and the coupling water are destroyed and dried at about 400 ° C.

However, in order to remove water from the coal, it has to be dried at a high temperature of 400 ° C or more, so that a great deal of cost and energy are consumed. When the coal is dried at such a high temperature, the pores of the coal are mainly oxidized by oxygen oxidizing reactors, hydroxyl groups (-OH), carboxyl groups (-COOH), carbonyl groups , -C = O). When they are exposed to air, they are oxidized by reacting with moisture and oxygen components, thereby raising the temperature inside the pores and causing spontaneous ignition.

On the other hand, coal with high water content is easily attached to the wall of the storage furnace, coal supply pipe, etc., resulting in low recovery rate of coal, and coal is attached to the surface of coal attached to the wall of coal storage pipe and coal supply pipe, Coal supply pipe, etc. are clogged. In addition, not only the pulverization is not performed well but also the combustion efficiency in the boiler is reduced, leading to a reduction in the efficiency of the power generation system.

In addition, since the pulverized coal is excessively dried, there is a problem that dust is generated and pollution of the working environment occurs and a pollution problem occurs. Therefore, a dust collecting facility and the like are required, and there arises a problem of dust scattering loss of coal Coal is desperately required to be able to effectively dry the coal to a moisture content of less than 10% through a drying process.

In this connection, the method of "Coal drying method" of Korean Patent No. 10-0048711, "Coal drying device in pulverized coal production facility" of Korean Utility Model Application No. 1999-0040978, "Pulverized coal production device" of Korean Patent Publication No. 2004-0013436, , A coal drying apparatus of Korean Patent Publication No. 2006-0055937, and a coal water treatment apparatus of Korean Patent No. 10-0651771, or the like, or a fluidized bed method or a heat exchanger is introduced And an indirect heating drying method in which the heating medium is indirectly contacted with coal to dry the heating medium. However, these drying methods have a problem in that expensive expensive equipment is required and the operation cost is too large to be economical.

Particularly, in Korean Patent No. 10-0960793, low-grade coal having a moisture content of 30% or more is made into high-grade coal for power generation with a calorific value of less than 10% and calorific value of 6,500 kcal / kg or more through high- However, since the heavy oil powder serving as a catalyst in the drying of coal contains a large amount of sulfur, a process such as secondary desulfurization treatment is required, and the carbon component in the heavy oil is hydrophobic, but the sulfur component is contained (H ₂ SO ₄ ) is generated during the reaction with water, so that it becomes a strong acid, which destroys the hydrophilic bond of the lower coal and lowers the drying efficiency of the coal. Heavy metals such as vanadium and nickel are also contained in the heavy oil, which pollutes and corrodes the boiler.

Accordingly, the present inventors have made intensive efforts to solve the problems of the prior art. As a result, the present inventors have found that, in order to control the water content of coal, coal ash having similar chemical / physical characteristics to coal is used, It has been found that when mixed with a specific amount, it is possible to reduce the plasticity of coal and dry it at a low temperature in a short time, and also to prevent the explosion of volatile matter, thereby completing the present invention.

The main object of the present invention is to provide a method of drying coal, which minimizes the drying equipment of coal, and can prevent spontaneous ignition while lowering the drying temperature of coal.

In order to achieve the above object, the present invention provides a method for drying coal, comprising the steps of: (a) mixing 1 to 20 parts by weight of coal fly ash with 100 parts by weight of coal; and (b) And a drying step for drying the coal.

The method of drying coal according to the present invention can prevent the clogging or clogging of the coal ash with chemical composition like coal, And it is possible to dry a large amount of coal in a relatively short period of time because the plasticity of the coal is lowered. At the same time, the drying efficiency can be increased without paying expensive equipment cost and high energy cost. Not only can it be dried but also the drying temperature can be lowered, so that explosion of volatile matter can be prevented and the coal can be effectively dried.

1 is a graph showing shear strength according to general moisture content.
FIG. 2 is a graph showing the frequency of mass depending on the size of coal and coal size.
FIG. 3 is a graph showing the cumulative specific surface area according to the grain size and coal particle size.
4 is a graph showing shear strength versus moisture content of a coal-laden mixture and coal.

In the present invention, in order to control the moisture content of coal, when the coal is pulverized in a specific amount by mixing coal with pulverized coal having a specific chemical / physical property in a specific amount, the calcination of the coal is reduced, At the same time, it has been confirmed that spontaneous ignition of coal can be prevented, and coal can be effectively dried by using a minimizing drying facility.

Accordingly, in one aspect, the present invention provides a method of drying coal comprising the steps of: (a) mixing 1 to 20 parts by weight of fly ash with 100 parts by weight of coal; and (b) drying the coal mixed with fly ash And drying the coal.

Specifically, in order to control the water content of the coal, the coal drying method of the present invention reduces the plasticity of the coal by mixing the fly ash having similar chemical / It is possible to prevent the spontaneous ignition of the coal at the same time as it is lowered, and the coal can be effectively dried using the minimizing drying equipment.

Plasticity refers to the property of a material whose shape is changed by an external force but does not return to its original shape even when the external force is lost. When the force exceeds the elastic limit, the internal pressure of the gap between the particles and the particles It is expressed by the capillary pressure which is the difference from the atmospheric pressure.

This plasticity is expressed by the following equation (1) because the capillary pressure is a driving force.

는 계면 에너지이며, r은 입자간의 간극(이하 관로)의 반경이다.Where DELTA P is the capillary pressure,

Is the interfacial energy, and r is the radius of the gap between the particles (hereinafter referred to as the channel).

Therefore, the plasticity is improved as the channel is narrower and longer, and the presence of a substance having a large surface tension in the channel, such as water, greatly increases the plasticity.

) 이하가 되면 모세관 압력이 극대가 되며, 입자의 유동이 막히게 된다고 제안하며 하기 수학식 2를 제시하였다(R.H.Weltmann, Green, J. Appl . Physics ., 144, 569~576, 1993).However, according to Weltmann et al., The amount of water present in the pipeline is at the threshold value

(RHWeltmann, Green, J. Appl . Physics . , 144, 569-576, 1993), suggesting that the capillary pressure is maximized and the flow of particles is blocked.

는 최종전단강도(일반적으로 가소성 소재의 항복점으로 간주함)이고,

은 입자 유동이 막히게 되는 액체의 임계 농도이며, A와 α는 입자충전 pF와 콜로이드를 포함하는 입자들의 함량과 종횡비에 의존하는 상수이다. here,

Is the final shear strength (generally regarded as the yield point of the plastic material)

Is the critical concentration of the liquid in which the particle flow is clogged, and A and alpha are constants that depend on the content and the aspect ratio of the particles containing the particle filled pF and colloid.

에 대한 가소성 소재의 전단응력의 의존성은 매우 잘 유사하다. 따라서 보다 적은 액체를 포함한 소재는 가소성을 나타내지 않으며, 가압성형이 가능하다.
As shown in Figure 1,

The dependence of the shear stress of the plastic material on the tensile strength is very similar. Therefore, a material containing less liquid does not exhibit plasticity, and pressure molding is possible.

The present inventor therefore intends to disclose a method of drying coal by focusing on the reduction of the number of free surfaces of the coal surface and the increase of the capillary pressure by narrowing the channel between the coal particles in order to effectively dry the surface water and internal water of the coal.

Thus, the coal drying method of the present invention does not directly dry the moisture in the gaps between the coal particles, that is, the surface water and the internal water, but has a large specific surface area in the gaps between the coal particles, When the particles of the added solids are made narrower and longer, the capillary force is increased, and the surface water and the internal water move to the capillary, and the water distribution becomes uniform. Therefore, when moisture is transferred to the capillary generated due to the addition of the remainder, the capillary force becomes stronger as shown in Equation 1, so that the capillary force has a shear strength which hinders the flow of the coal particles, and the plasticity is lost.

Therefore, the coal added with the residual society is not easily attached to the wall of the storage furnace, the coal supply pipe, etc., and the phenomenon of clogging of the coal storage pipe and the coal supply pipe is eliminated and the recovery rate of coal is increased. Internal water can be pushed to the surface of coal by capillary force and dried in a short time with less energy.

In the present invention, the type of coal is not limited, and any coal having a water content of 10% or more can be used without limitation. Such coal is pulverized to an average particle size of 1 mm to 10 mm by using a roller crusher or the like, and is preferably ground to an average particle size of 1 mm to 3 mm. If the average particle size is less than 1 mm, problems such as scattering during transportation of the coal occur, and when the average particle size exceeds 10 mm, the coal is low in flowability and the inert material content is high, There is a problem that the drying efficiency is also lowered during mixing.

Generally, reject ash is generated after refining to use fly ash, which is a by-product of power generation after coal combustion in a thermal power plant, for use in concrete, concrete, etc., and about 20 to 30% And the quality and characteristics of coal are different depending on the type of coal, the coal ash processing capacity of each power plant, the type of boiler, the combustion condition, and the treatment method. Therefore, most of them are currently not recycled and discarded.

Accordingly, in the present invention, the by-product, which is a byproduct generated after coal combustion, has similar chemical / physical characteristics to coal, thereby improving the drying efficiency of coal without changing the refractory point of coal. .

In the present invention, the fly ash has a content of SiO ₂ and Al ₂ O ₃ of 60 to 90 wt%, preferably 66.06 wt% of SiO _2, 21.05 wt% of Al ₂ O _3, 3.28 wt% of Fe ₂ O ₃ , 1.24 wt%, MgO 0.56 wt% and C 7.23 wt%, and has a composition similar to ordinary coal.

The fly ash is smaller as compared with that of coal and has a larger specific surface area. Preferably, the fly ash having an average particle size of 0.1 탆 to 5 탆 and a specific surface area of 0.7 m ² / g to 3.2 mm ² / g is used When the mean particle size of the fly ash is less than 0.1 탆, problems such as scattering may occur in the course of operation. When the average particle size exceeds 5 탆, the capillary force of the coal particle gap can not be increased and the coal can not be effectively dried .

In addition, when the fly ash having a specific surface area of less than 0.7 m ² / g is mixed, the capillary pressure can not be increased and the drying efficiency is insufficient. When the fly ash exceeding 3.2 mm ² / g is mixed, Additional processes are needed.

In the present invention, the mixing amount of coal and coal fly ash is 1 to 20 parts by weight of coal fly ash mixed with 100 parts by weight of coal. The mixing amount of coal and fly ash is preferably 2 to 10 parts by weight, preferably 2 to 8 parts by weight, more preferably 3 to 6 parts by weight, based on 100 parts by weight of coal. In the case of mixing more than 20 parts by weight of the fly ash, the unburned carbon content of the fly ash is usually 7 to 8 wt%, which is about 500 Kcal / kg, so that there is a problem that the amount of heat of the coal having the heat value of about 6,000 Kcal / kg or more can be reduced at the power plant. Therefore, it is possible to increase the amount of fly ash by concentrating the unburned carbon content through electrostatic separation or magnetic separation. Accordingly, in the present invention, the fly ash may contain unburned carbon in an amount of 3 to 50% by weight, preferably 10 to 50% by weight, and more preferably 40 to 50% by weight.

As described above, in the method for drying coal according to the present invention, coal is mixed with fine fly ash having a large specific surface area and then dried. The drying method can be applied to a variety of conventional methods such as an air stream drying method in which a hot air stream is directly contacted with coal, a fluidized bed method, an indirect heat drying method in which a heat medium is indirectly contacted with coal by introducing a heat exchanger, The temperature is lower than 240 ° C., preferably 105 ° C. to 200 ° C., in order to reduce the possibility of spontaneous ignition due to the volatiles contained in the coal.

If it is dried below 105 ° C, it takes a long time to dry and there is a problem that the drying equipment becomes too large. If it is dried above 200 ° C, there is a possibility of spontaneous ignition due to volatile matter contained in coal.

In the coal fueling process using the coal drying method according to the present invention, coal is pulverized to an average particle size of 1 to 10 mm or less by using a roller crusher or the like, and 2 to 10 wt% Are mixed in a kneader, and then the mixed coal mixture is dried in a drier. The coal mixture thus mixed with the dry sludge is pulverized into fine powder in the pulverizer and supplied to the boiler for fuel conversion.

Therefore, the method of drying coal according to the present invention can prevent the clogging or clogging on the wall of the supply pipe or the storage furnace by adding a chemical substance similar to coal to the coal, thereby increasing the recovery rate of coal, It is possible to dry a large amount of coal in a relatively short period of time because the plasticity of the coal is low and at the same time to increase the drying efficiency without paying expensive equipment cost and high energy cost and it is possible to dry And the drying temperature can be lowered, so that the explosion of the volatile matter can be prevented, and the coal can be effectively dried.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these examples are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples.

[Example]

Example  One

(Fig. 2) and a specific surface area of 1.6 m < 2 > / g (Fig. 3) were added to 95 kg of coal having an average particle size of 3 mm and a specific surface area of 0.3 m & 5 kg of the soda ash having the chemical composition shown in Table 2 were mixed.

division SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO K ₂ O Na ₂ O SO ₃ Volatile matter Fixed carbon Coal 7.27
wt% 3.77
wt% 1.21
wt% 0.33
wt% 0.03
wt% 0.14
wt% 0.01
wt% 0.16
wt% 31.39
wt% 55.26
wt%

division SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO K ₂ O Na ₂ O SO ₃ lg-loss C A cup society 66.06
wt% 21.05
wt% 3.28
wt% 1.24
wt% 0.56
wt% 0.57
wt% 0.32
wt% 0.00
wt% 5.31
wt% 7.23
wt%

Example  2

(Fig. 2) and a specific surface area of 1.6 m < 2 > / g (Fig. 3) were added to 90 kg of coal having an average particle size of 3 mm and a chemical composition shown in Table 1 below having a specific surface area of 0.3 m & And 10 kg of the soda ash having the chemical composition shown in Table 2 were mixed.

Comparative Example  One

In the above Example 1, coal which does not mix the residual sludge was used.

[Test Example]

Shear Strength Measurements: To compare the plasticity of the uncoated coal according to Examples 1 and 2 and the uncoated coal according to Comparative Example 1, the coal- The maximum shear strength was measured by adding 5% water each and stirring with a kneader. The maximum shear strength was measured while the moisture content was increased by 5%, and the shear strength was measured until the value decreased rapidly. Shear strength was measured with a Japanese plastometer.

As a result, the measurement result of the shear strength of the coal, which is not mixed with the coal-sand society mixture and the residual sand, is shown in FIG. In the case of Example 1, in comparison of the shear strength, the water reducing effect was shown to be 5 wt% in the same shear strength, and the water reducing effect of about 10 wt% in comparison with the yield point of the uncoated coal was confirmed.

In the case of Example 2, the moisture reduction effect was shown to be 10 wt% in the same shear strength, and the moisture reduction effect was observed to be about 15 wt% in comparison with the yield point of the uncombined coal.

Therefore, the addition of a finer grain size and a larger specific surface area reduces the plasticity of the coal, that is, the moisture content of coal, without paying for expensive equipment and high energy costs. The recovery of coal can be increased and the capillary of coal can be narrowed and increased, so that a large amount of coal can be dried in a relatively short time.

* Measurement of moisture change: To test the drying behavior of coal mixed with the coal of Comparative Example 1 and that of Examples 1 and 2, moisture of 40wt% was added to each raw material and kneaded to prepare a mixture of 1 cm in thickness and 5 cm x 5 cm When the moisture content of the molded body was 30 wt% after being molded into a rectangular parallelepiped body, it was put into a dryer preheated at 200 DEG C, and the change in water content until each weight was measured is shown in Table 3.

Time (minutes)
moisture
Amount (wt%) 1 minute 2 minutes 3 minutes 6 minutes 9 minutes 12 minutes 15 minutes Comparative Example 1 1.5 3 6 18.75 26.25 30 30 Example 1 3.75 8.25 15.75 26.25 30 30 30 Example 2 5.25 15 22.5 30 30 30 30

As shown in Table 3, the drying speed of the coal added with the residual sludge was very fast and the drying rate of the 10 wt% added sample (Example 2) was almost twice as fast as that of the coal (Comparative Example 1).

Although this experiment was carried out in a small dryer, it is difficult to expect the results shown in Table 3 in a large-scale drying facility. However, when a small size and a large specific surface area are added, the capillary of the coal becomes narrower and larger, It was confirmed that the coal could be dried. Therefore, when the results of FIG. 4 and Table 3 are analyzed, it can be said that the moisture reduction effect is more than 20 wt% due to the addition of the solids.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereto will be.

Claims (4)

In the method for drying coal,
(a) mixing a specific surface area of 100 parts by weight of coal 0.7m ² /g~3.2m ² / g of glass society 1 to 20 parts by weight; And
(b) drying the mixed coal;
And drying the coal.
The method for drying coal according to claim 1, wherein 2 to 10 parts by weight of the solids is mixed.
delete The method for drying coal according to claim 1, wherein the residual sludge comprises 3 to 50% by weight of unburned carbon.

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