JP3588128B2 - Coal / water mixture and its production method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a coal / water mixture, in particular, burning a solid fuel such as coal in a pressurized fluidized bed, driving a steam turbine with generated steam, and further driving a gas turbine with high-pressure, high-temperature combustion gas. The present invention relates to a mixture of coal and water supplied to a combustion furnace of a pressurized fluidized-bed boiler combined cycle power plant that obtains electric power with high efficiency and a method for producing the same.
[0002]
[Prior art]
The pressurized fluidized-bed boiler can obtain energy from generated steam and high-pressure combustion gas, so that high-efficiency power generation is possible. However, one of the problems is to continuously and stably supply solid coal particles into a pressurized combustion furnace. BACKGROUND ART Conventionally, as a method of supplying coal to a fluidized bed combustion furnace, coal particles and water are mixed to form a paste-like fluid (hereinafter referred to as Coal-Water Paste; hereinafter abbreviated as CWP), and the CWP is pressurized and pumped by a pump. There is a wet supply method (for example, Japanese Patent Application Laid-Open No. 62-155433) in which the liquid is supplied from a spray nozzle. The CWP supply method requires no pretreatment such as drying and is lower in cost than a dry supply method, for example, a method in which the pressure is increased by a lock hopper and then pneumatically conveyed.
[0003]
However, in the wet feed system, it is necessary to minimize the amount of water added to coal in order to maintain the power generation efficiency at a high level. Moreover, no agent for dispersing the coal particles is added to reduce the production cost. For this reason, CWP has a higher viscosity and extremely poor fluidity than high-concentration coal / water slurry developed as an alternative fuel to heavy oil.
[0004]
In general, it is known that the particle size of coal particles constituting a mixture is important for reducing the water content of the high-concentration coal / water slurry. For example, Japanese Patent Application Laid-Open No. 56-501568 discloses a particle size structure that is optimal for reducing water content. As a method for adjusting the particle size to the optimum one, for example, there is a method described in JP-A-62-30190. However, in the production of high-concentration coal / water slurry, an agent for dispersing coal particles is added, and the coal particles are in a sufficiently dispersed state.
The high-concentration coal / water slurry has a maximum diameter of 0.6 mm and a weight average diameter of 0.02 mm, whereas the CWP used in the pressurized fluidized bed combustion furnace has a maximum diameter of 6 mm and a weight average diameter of 1 mm. The particle size range is roughly 2 mm, and the particle size range of the coal particles is significantly different from that of the high-concentration coal / water slurry.
[0005]
[Problems to be solved by the invention]
As described above, in the prior art, since the chemical changes the surface of the coal into a property that is easily wetted by water, the particle size distribution is adjusted in a dispersed state in which coal particles hardly aggregate. On the other hand, CWP supplied to the pressurized fluidized bed combustion furnace is manufactured in a state of high viscosity without adding a chemical, so that coal particles having a property of being hardly wetted by water (hydrophobicity) inevitably have a significant agglomeration. In state. For this reason, even if the particle size configuration optimized for the conventional high-concentration coal / water slurry is applied to the production of CWP, the coal particles aggregate and behave as apparently coarse particles. Therefore, the water content could not be minimized in the high-concentration coal / water slurry particle size configuration. An object of the present invention is to provide a low-cost coal / water mixed fluidized bed combustion furnace fuel capable of producing low-moisture CWP with low stirring power and stably supplying it to the combustion furnace, and a method for producing the same.
[0006]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a method for producing CWP used as a fuel for a coal / water mixed fluidized bed combustion furnace, and as a result, the above object of the present invention has been achieved by employing the following configuration. That is, coal particles having a particle size of 0.02 mm or less are 10 to 20% by weight of the total coal amount, particle sizes of 1 mm or more are 50 to 70% by weight of the total coal amount, and particle sizes 0.02 to 1 mm are 10 to 20% by weight of the total coal amount. This is a coal / water mixed fluidized bed combustion furnace fuel obtained by mixing and stirring coal and water so as to have a particle size configuration of の 40% by weight. Here, the coal / water mixture obtained by mixing coal and water has a weight average diameter in a range of 0.03 to 0.07 mm in a coarse particle group of coal having a weight average diameter in a range of 1.0 to 2.0 mm. Can be obtained by mixing and stirring the fine particles of coal in water with water.
[0007]
The fuel for a coal-water mixed fluidized-bed combustion furnace of the present invention can be used as a fuel for a pressurized fluidized-bed combustion furnace or the like, but is not limited thereto. Can also be used.
[0008]
In order to use CWP as a fuel for a combustion furnace, it is a necessary requirement that the CWP has a low water content and that coal particles are hardly settled and separated. The size composition of the coal particles is closely related to these two requirements. In other words, the optimum particle size composition for CWP can be determined by the particle size condition that minimizes the amount of water and hardly causes sedimentation and separation.
[0009]
When the weight ratio of the particles having a particle size of 0.02 mm or less of the coal is in the range of 10 to 20% by weight, the water content of CWP is minimized, and separation is difficult. When the amount of the fine particles having a particle size of 0.02 mm or less is less than 10% by weight, CWP tends to cause sedimentation and separation, and cannot be pumped stably. When the amount of the fine particles having a particle size of 0.02 mm or less is more than 20% by weight, it is necessary to increase the water content in order to increase the viscosity and maintain the fluidity.
[0010]
Further, when the weight ratio of the particles having a particle diameter of 1 mm or more is in the range of 50 to 70% by weight, the amount of water in the CWP is minimized, and separation is difficult. When the amount of coarse particles having a particle diameter of 1 mm or more is less than 50% by weight, CWP tends to cause sedimentation and separation, and when the amount of coarse particles having a particle diameter of 1 mm or more is more than 70% by weight, the water content increases.
Furthermore, when the weight average diameter of the coal particles is small, the amount of water increases to keep the viscosity constant. The weight average diameter effective for lowering the water content is 1 to 2 mm. In addition, when finely pulverizing so that the weight average diameter is 0.03 mm or less, the pulverizing power increases sharply, and when coarse particles having a weight average diameter of 0.07 mm or more are used, CWP is easily separated. Become.
[0011]
[Action]
Generally, to increase the concentration of solids in a solid-liquid mixture, ie, reduce the amount of liquid, the particle size configuration is adjusted so that the solid particles are closest packed. As described above, in the production of CWP, there is no addition of an agent for dispersing coal particles, and the aggregation of the particles is remarkable due to high viscosity. Therefore, it is the aggregated particles rather than the single particles that are involved in close packing of the particles. According to the present invention, close packing is realized as an aggregated particle group, so that CWP with low moisture content can be produced.
[0012]
Further, since the particle size of the pulverized product obtained by the ordinary pulverization operation can be suppressed to a substantially constant range, if the coarse particles and the fine particles of coal are mixed as in the present invention, the adjustment of the desired particle size configuration can be performed with high accuracy. Can do well.
On the other hand, since CWP is produced by mixing and stirring in a state of extremely low water content, the fine particles are particularly easily aggregated, a lump of fine particles is generated, and the power required for homogeneous mixing is increased. Therefore, if the fine particle group is mixed with water in advance, a lump of fine particles cannot be formed, and a low power and uniform CWP can be obtained.
[0013]
【Example】
An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a dispersed state (FIG. 1A) and an agglomerated state (FIG. 1B) of coal particles.
In the production of CWP, there is no addition of an agent for dispersing coal particles, and the particles are remarkably aggregated due to high viscosity. As a result, apparently, it behaves as if the granularity configuration has changed, so it is necessary to adjust the granularity configuration to be specific to CWP.
[0014]
FIG. 2 is a so-called particle size distribution curve diagram showing the weight ratio under the sieve to the particle size of coal in CWP.
The particle size distribution of CWP of coal A (constant moisture = 3%, fuel ratio = 1.8) is shown in comparison with the particle size distribution of high concentration coal / water slurry manufactured using coal A. In the case of CWP of coal A, the particle size of 0.02 mm or less is 12% by weight, and the particle size of 1 mm or more is 40% by weight. Weight average diameter _{D 50} of the high-concentration coal-water slurry while a 0.015mm As shown, the particle size at 1.5mm when the CWP is very coarse. Charcoal A CWP was produced by mixing and stirring coarse particles of D ₅₀ = 1.5 mm and fine particles of D ₅₀ = 0.03 mm at a weight ratio of 8: 2.
In order to maintain the power generation efficiency at a high level, the water content in CWP is set to 22% by weight, so that the viscosity is 10 Pa · s, which is very high, 10 times that of the conventional high concentration coal / water slurry.
[0015]
In order to use CWP as a fuel for a pressurized fluidized bed combustion furnace, it is a necessary requirement that the CWP has a low water content and that coal particles hardly settle and separate. The size composition of the coal particles is closely related to these two requirements. In other words, the optimum particle size composition for CWP can be determined by the particle size condition that minimizes the amount of water and hardly causes sedimentation and separation.
[0016]
Fig. 3 shows the particle size of three types of coal A, coal B (constant moisture = 7%, fuel ratio = 1.0) and coal C (constant moisture = 1.5%, fuel ratio = 2.8). FIG. 4 is a diagram showing changes in the amount of water in CWP and the rod penetration depth when the weight ratio of particles of 0.02 mm or less is changed. However, the weight ratio of particles of 1 mm or more was fixed. Curves A, B, and C in the figure show the water content of coals A, B, and C, respectively, and curves D, E, and F show the rod penetration depths of coals A, B, and C, respectively.
A large rod penetration depth indicates that the sedimentation and separation are difficult, and a small rod penetration depth indicates that the coal is separated from the CWP and the amount of hard pack is increased.
[0017]
Considering these three types of coal, when the weight ratio of the particles having a particle size of 0.02 mm or less shown in the horizontal axis of FIG. 3 is in the range of 10 to 20% by weight, as shown by the curves A, B, and C in FIG. It can be seen that the water content is at a minimum and is in a range where separation is difficult as shown by curves D, E and F in FIG. When the amount of the fine particles having a particle diameter of 0.02 mm or less is less than 10% by weight, CWP is liable to cause sedimentation and separation and cannot be pumped stably. If the content of fine particles of 0.02 mm or less is more than 20% by weight, the viscosity increases and the amount of water increases to maintain fluidity.
[0018]
FIG. 4 shows the water content and the rod penetration in the CWP when the weight ratio of the particles having a particle size of 1 mm or more was changed under the condition that the weight ratio of the particles having a particle size of 0.02 mm or less was kept constant for the above three types of coal. It is a figure showing change of depth. Curves G, H, and I in the figure show the water content of coals A, B, and C, respectively, and curves J, K, and L show the rod penetration depths of coals A, B, and C, respectively.
When the weight ratio of the particles having a particle diameter of 1 mm or more shown in the horizontal axis of FIG. 4 is in the range of 50 to 70% by weight, the water content becomes minimum as shown by the curves G, H, and I in FIG. , K, and L, it can be seen that they are in a range where separation is difficult. When the amount of coarse particles having a particle diameter of 1 mm or more is less than 50% by weight, CWP tends to cause sedimentation and separation, and when the amount of coarse particles having a particle diameter of 1 mm or more is more than 70% by weight, the water content increases.
[0019]
Figure 5 is a diagram showing the relationship between the moisture and the weight average diameter D ₅₀ of the A charcoal CWP under the conditions as constant viscosity 10 Pa · s. When the weight average diameter D ₅₀ is small, the water content is increased to a constant viscosity. Conditions of _{D 50} to low moisture as possible is found to be _D 50 = 1 to 2 mm.
It is easily understood that the smaller the particle size, the higher the water content under the same viscosity condition. However, if the particle size is made larger than necessary, the effect of lowering the water content is not obtained, and the number of coarse particles becomes too large, causing problems such as blockage in the piping. If the weight average diameter _{D 50} is in the range of 1.0 to 2.0 mm, the above requirements are met.
[0020]
It is a view showing a change in rod penetration depth and grinding power consumption when changing a weight average diameter D ₅₀ of the particles group mixing the coarse particle group for A charcoal in FIG. The curve M in the figure shows the relationship with the rod penetration depth, and the curve N shows the relationship with the grinding power.
Grinding power indicated by curve N rapidly increases when the D ₅₀ shown in the horizontal axis in FIG. 6 pulverized so that less 0.03 mm. Further, CWP is easily separated when the weight average diameter _{D 50} using the group of fine particles of Me or coarse 0.07 mm.
[0021]
Next, one embodiment of a specific method for adjusting the particle size configuration of the present invention will be described in detail.
FIG. 7 is a view showing the present embodiment, in which a pressurized fluidized bed combustion furnace 101 is housed in a pressure vessel 104, an air dispersion plate 105 is provided at the bottom, and a fluid medium particle 102 is filled thereon. Have been. The pressurized air 106 is supplied into the pressure vessel 104 and then supplied as combustion air 107 through the air dispersion plate 105 into the pressurized fluidized bed combustion furnace 101 to fluidize the fluidized medium particles 102 to form the fluidized bed 109. Form. In the pressurized fluidized bed combustion furnace 101, CWP 14 is pumped from a pump 15 through a CWP supply conduit 16 and supplied from a CWP spray nozzle 17 into a fluidized bed 109 for combustion. After the combustion gas is exhausted from the upper part of the furnace and dust is removed by the cyclone 103, the combustion gas is introduced into a gas turbine (not shown) through a conduit 108.
[0022]
On the other hand, the raw coal in the bunker 1 is supplied to the crusher 2, crushed to a predetermined particle size by the crusher 2, and then coarse particles are removed by the sieve 3. The coarse particles after the removal of the coarse particles are supplied to the distributor 5, a part of the coarse particles is continuously supplied to the CWP adjusting tank 9 via the conduit 6, and the rest is supplied to the crusher 8 from the conduit 7. Are crushed to a predetermined particle size to form fine particles. In the CWP adjusting tank 9, limestone 12 as a desulfurizing agent and water 13 necessary for producing CWP are added in addition to the coarse particles from the conduit 6 and the fine particles from the pulverizer 8, and are rotated by the electric motor 11. The CWP 14 is mixed and stirred by the stirrer blade 10 and has fluidity.
[0023]
The conditions of the pulverizer 2 are set so that raw coal having a maximum diameter of about 50 mm can be pulverized to a particle size of 6 mm or less. The pulverization of raw coal may be of any type as long as it can be pulverized to a predetermined particle size. The size of the sieve 3 was determined so that the maximum diameter of the coal particles of CWP was 6 mm. The distributor 5 has a function of distributing the pulverized coal at a predetermined ratio, and is set according to the properties of the coal.
In the above apparatus, dolomite or limestone particles having a maximum diameter of about 3 mm are used as the desulfurizing agent. The CWP preparation tank 9 and the stirrer blade 10 are schematically shown and do not limit the present invention.
[0024]
When the raw coal is pulverized by a general pulverizer, the particle size composition of the pulverized material varies depending on the properties of the raw coal, the type of pulverization, and various conditions of pulverization. However, in the single-stage pulverization of raw coal, fine particles are insufficient, and the above-mentioned optimum particle size configuration cannot be obtained. Therefore, the particle size can be adjusted by a method in which the fine particles are manufactured in a separate system and mixed with the coarse particles. Coarse particle group to become a cornerstone of particle size configuration, low moisture reduction, weight average diameter _{D 50} of the stable transportation can be achieved in the range of 1.0~2.0mm is desirable.
On the other hand, when the fine particle group is pulverized more than necessary, a great amount of pulverizing power is required. Weight average diameter D ₅₀ of the particles group is kept low grinding power be in the range of 0.03～0.07Mm, and it is possible to obtain an optimum particle size configuration by mixing coarse particles.
[0025]
At the time of mixing the fine particles, if the fine particles are directly mixed with water, the fine particles aggregate, and the stirring power required for homogeneous mixing is increased. FIG. 8 is an example of a flow for CWP production in consideration of this point.
The raw coal in the bunker 1 is supplied to a crusher 2, crushed to a predetermined particle size by the crusher 2, and coarse particles are removed by a sieve 3. The coarse particles after the removal of the coarse particles are supplied to the distributor 5, and a part of the coarse particles is continuously charged into the CWP preparation tank 9 via the conduit 6. Further, the remainder of the coarse particles is supplied from the conduit 7 to the crusher 8 and crushed to a predetermined particle size to form fine particles. The fine particles are continuously charged into the CWP preparation tank 23 and mixed and stirred with water 20 by a stirring blade 19 rotated by an electric motor 18 to form a fine slurry. Since the fine particles to be supplied into the CWP preparation tank 9 are in the form of a slurry, they can be stably supplied at a constant rate by the pump 21.
If the particles are preliminarily adjusted to water, the aggregation of the fine particles is reduced, so that the mixing ratio of the fine particles can be reduced.
[0026]
In the CWP adjustment tank 9, limestone 12 and water 13 are added as a desulfurizing agent in addition to the coarse particles and the fine particles, and are mixed and stirred by the stirrer blades 10 rotated by the electric motor 11 to produce a fluid CWP 14. Then, it is supplied to the pressurized fluidized bed combustion furnace 101 similarly to the flow of FIG.
[0027]
【The invention's effect】
As described above, according to the present invention, CWP can be stably supplied with a smaller amount of water, and CWP can be produced without requiring any production power.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state of dispersion and agglomeration of coal particles according to an example of the present invention.
FIG. 2 is a diagram showing a weight ratio under a sieve with respect to a particle size of coal in CWP of an example of the present invention.
FIG. 3 is a graph showing the amount of water in CWP and the rod penetration depth with respect to the weight ratio of particles of 0.02 mm or less in Examples of the present invention.
FIG. 4 is a diagram showing the amount of water in CWP and the rod penetration depth with respect to the weight ratio of particles of 1 mm or more in Examples of the present invention.
5 is a diagram showing the relationship between the moisture and the weight average diameter D ₅₀ of the CWP embodiment of the present invention.
6 is a view showing a change in rod penetration depth and grinding power consumption when changing a weight average diameter D ₅₀ of the particles group mixing the coarse particles of the embodiments of the present invention.
FIG. 7 is a system diagram showing an embodiment of the present invention.
FIG. 8 is a system diagram showing another embodiment of the present invention.
[Explanation of symbols]
1 ... bunker, 2, 8 ... crusher, 3 ... sieve, 9 ... CWP adjustment tank,
101: pressurized fluidized bed combustion furnace; 104: pressure vessel

Claims (2)

Coal particles having a particle size of 0.02 mm or less are 10 to 20% by weight of the total coal amount, particle sizes of 1 mm or more are 50 to 70% by weight of the total coal amount, and particle sizes 0.02 to 1 mm are 10 to 40% of the total coal amount. Fuel for a coal-water mixed fluidized bed combustion furnace obtained by mixing and stirring coal and water so as to have a particle size composition of weight%. Coal fine particles having a weight average diameter in the range of 0.03 to 0.07 mm and water are mixed and stirred with coarse coal particles having a weight average diameter in the range of 1.0 to 2.0 mm. The fuel for a coal-water mixed fluidized bed combustion furnace according to claim 1, which is used.

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