JPS6354758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the dehydration of low-rank coal such as lignite from which water is released in liquid form when heated in an atmosphere where water cannot evaporate (hereinafter referred to as non-evaporation atmosphere). The present invention relates to a dehydration method and apparatus for preheating the low-rank coal with moving hot water and then heating it with steam.

In this specification, the term "low-grade coal" refers to 1. low-grade coals such as sub-bituminous coal and lignite (coal with a low degree of coalification); 2. coal analogues such as lignite, peat, and grass coal (with a low degree of coalification). 3. Coal source materials such as plants and their decayed materials (organic solids that are assumed to transform into coal when subjected to coalification). More simply, it is defined as ``a porous organic solid that loses water in liquid form when heated in an atmosphere where water cannot evaporate.''

Generally, to dehydrate organic solids such as lignite,
Conventionally, evaporative drying methods such as flash drying method and indirect heating drying method have been used. However, these technologies have drawbacks such as high heat consumption, the need to refine the dehydrated product into fine particles in advance, and the tendency for dehydrated products to generate dust and spontaneously ignite. Therefore, alternative technologies have been developed for some time. development is underway.

By the way, when porous organic solids such as lignite are heated in a non-evaporating atmosphere, physical and chemical changes occur, and the water contained in the pores of these solids is released in liquid form (hereinafter referred to as liquid dehydration). phenomenon) is known. Dehydration methods that utilize this liquid dehydration phenomenon include a method in which lignite is immersed in hot water with a pressure higher than the saturated steam pressure (hereinafter referred to as underwater heating dehydration method), and a method in which lignite is heated in a saturated steam atmosphere ( There is a saturated steam dehydration method (hereinafter referred to as saturated steam dehydration method). The former is introduced in Australian Patent No. 430626 and the latter was proposed in the early part of this century.

The former technique has the drawback that the lignite is still immersed in hot water even after heating is completed, and the dehydration rate decreases due to reabsorption of moisture during the depressurization process. A practical application of the latter technology is Australian Patent No. 190490.
There is a dehydration method for lignite that involves batch processing using multiple pressure vessels of the same shape with a time lag in the treatment process.

For example, as shown in Figure 1, lignite is first charged into a pressure vessel at atmospheric pressure, preheated, saturated steam is supplied from an external steam source to heat and pressurize it, and then the pressure is reduced to atmospheric pressure and dehydrated. Discharge lignite. That is, liquid dehydration is performed in the preheating and heating processes, and evaporative dehydration of residual water is performed in the pressure reduction process. By the way, hot water generated during heating is used for preheating in order to improve thermal efficiency. For this purpose, a hot water reservoir connected via a pipe is installed below each pressure vessel, and the hot water is used to convert the hot water into lignite and brown coal. A feature of this technology is that it is separated and stored. This preheating is performed by utilizing the time lag between the processing steps of each pressure vessel. In other words, when a certain pressure vessel and its associated hot water reservoir are in the depressurization process, the steam or the hot water (hereinafter referred to as preheating medium) that evaporates is transferred between this pressure vessel and its associated hot water reservoir and other pressure vessels that are in the preheating process. It is moved even with a pressure difference of . Of the preheating media mentioned above, steam fills the pressure vessel during the preheating process and preheats the brown coal, but hot water is introduced into the pressure vessel immediately after the brown coal is charged and exchanges heat only by flowing down the brown coal layer. and immediately discharged into a hot water reservoir.

In such a saturated steam dehydration method, a hot water storage device must be provided for each pressure vessel, making the dehydration equipment large-scale.At the beginning and end of the heating process when saturated steam is supplied, the internal pressure of the pressure vessel and lignite Since the steam flow rate fluctuates due to the difference in temperature, it is necessary to increase the amount of steam generated or install a large-capacity accumulator.As mentioned above, the movement of the preheating medium to improve thermal efficiency depends on the pressure between the two containers. Since hot water below atmospheric pressure (approximately 100℃) cannot move into a pressure vessel that is at atmospheric pressure due to coal injection, the sensible heat of hot water at such a temperature cannot be transferred. It has drawbacks such as not being able to be used for preheating, and contact between lignite and hot water during the preheating process being limited to the time when the hot water is flowing down, resulting in short time and insufficient heat recovery.

The present invention is a dehydration technology for porous organic solids such as lignite that effectively utilizes the liquid dehydration phenomenon in order to solve the problems of the evaporative drying method, and is adopted in the underwater heating dehydration method described above. A dehydration method for low-rank coal that solves the drawbacks of the saturated steam dehydration method by organically combining preheating of brown coal by immersion in hot water and dehydration by steam heating employed in the saturated steam dehydration method, and its method. The purpose is to provide equipment.

The present invention connects two or more pressure vessels in an annular shape by interconnecting the lower part of the upstream pressure vessel and the upper part of the downstream pressure vessel which are adjacent to each other through a pipe, and The low-rank coal to be dehydrated is loaded into a continuous group of pressure vessels, and the pressure vessel at one end of this group is designated as the most upstream pressure vessel.
The low-rank coal is dehydrated by injecting high-temperature and high-pressure steam to heat the low-rank coal, and hot water consisting of moisture separated from the low-rank coal and condensed water of steam is sequentially sent to the downstream pressure vessel to dehydrate them. The low-rank coal in the pressure vessel is preheated, and surplus water is discharged from the pressure vessel at the other end of the group, which is the most downstream side, and the heating dehydration of the most upstream pressure vessel is completed, and the pressure vessel When the hot water has been discharged from the inside, or when some steam has been supplied to the pressure vessel immediately downstream of the most upstream pressure vessel, After sealing off the pressure vessel and releasing the internal water vapor to reduce the pressure, the dehydrated low-rank coal is discharged to complete the series of dehydration operations, and then the coal is placed next to the pressure vessel, which was the most downstream, and further downstream. When the low-rank coal to be dehydrated is loaded into the side pressure vessel and the preparation for preheating is completed, the number of coals equal to the number of the group, starting from the pressure vessel adjacent to the downstream side of the pressure vessel which was the most upstream pressure vessel, is This heating dehydration method for low-rank coal is characterized in that the same dehydration operation as described above is performed in a pressure vessel, and the dehydration operation is sequentially transferred downstream.

A preferred embodiment is characterized in that the group of pressure vessels is formed by all pressure vessels connected in an annular manner.

Further, a preferred embodiment is characterized in that the total number of pressure vessels connected in an annular manner is 20 or less.

The present invention also provides a plurality of pressure vessels for heating and dehydrating low-rank coal to be connected to a closed system having upstream and downstream directionality, and lower portions of the pressure vessels adjacent to each other on the upstream side of this closed system. a hot water transfer pipeline connected to the upper part of the pressure vessel on the downstream side via an on-off valve; a high-temperature, high-pressure steam supply pipeline connected to the steam source via the on-off valve of each of the pressure vessels; This heating dehydration apparatus for low-rank coal is characterized by having a pipe line equipped with an on-off valve for releasing the internal steam from each pressure vessel to reduce the pressure.

The present invention will be explained below based on examples. FIG. 2 shows a simplified plan view of an apparatus for carrying out the dewatering method of the invention. The dehydration device includes a plurality of, for example, n pressure vessels A ₁ , A ₂ , ..., A _i , ... having the same shape.
_These are on-off valves B ₁ , B ₂ ,...,
Conduits C ₁ , C ₂ ,…, C _i ,…C _o with B _i ,…B _o interposed
are connected to form a closed circuit. The pipe connects the lower part of the pressure vessel and the upper part of the pressure vessel immediately downstream (following the direction of arrow P in Figure 2) as shown in Figure 3 (-arrow view in Figure 2). are doing.

Referring to FIG. 3, lignite K is sized by a sizing means M and conveyed by a conveying means Q, for example, a belt conveyor. The conveying means Q is equipped with a distributing means R, such as a tripper, and lignite is sequentially introduced from an upstream pressure vessel. The pressure vessel receives lignite at atmospheric pressure, is sealed, is preheated by the procedure described below, is supplied with steam from a steam source S, and is heated.
Thereafter, the pressure is reduced and the dehydrated lignite is discharged at atmospheric pressure.

This dehydration treatment process will be explained in detail below.
We will now explain the state immediately before steam is supplied from the steam source S to a certain pressure vessel _A1 . A pressure vessel A ₁ and a total of i pressure vessels A ₁ that are continuous downstream thereof,
A ₂ , ..., A _i are filled with lignite and sealed.
These pressure vessels are shown shaded in FIG. Of these i group pressure vessels, the (i-1) group pressure vessels excluding the most downstream pressure vessel A _i have valves B ₁ ,
Communication is established by opening B ₂ ,...,B _i-2 ,
It is filled with high-pressure hot water to preheat the lignite.

Next, the valve _D1 is opened to supply steam from the steam source S to the pressure vessel _A1 . At this time, when valve B _i-1 is opened and pressure vessels A _i-1 and A _i communicate with each other, the hot water in pressure vessel A ₁ is pushed out to the downstream pressure vessel, and the lignite at the top is sequentially turned into a steam atmosphere. At the same time, the hot water in each pressure vessel immediately upstream is injected into the other pressure vessels A ₂ , A ₃ , . . . , A _i . When the pressure vessel A _i is filled with hot water in this manner, the pressure in the vessel becomes high enough to be approximately equal to the pressure in the pressure vessel A ₁ . During this time, heating dehydration using steam is performed in the pressure vessel _A1 , and hot water consisting of condensed water of the steam generated thereby and water released from the lignite accumulates at the bottom of the vessel together with the remaining preheated water. Furthermore, if steam is supplied until all the hot water in pressure vessel A ₁ is discharged, the other pressure vessels A ₂ , A ₃ , ..., A _i cannot accommodate all the hot water, so pressure vessel _A After the hot water is filled with hot water, the valve E _i (not shown) of the drain pipe located at the bottom is opened and the excess hot water is discharged.

The supply of steam to the pressure vessel _A1 is terminated (the supply of steam may be stopped by detecting that no hot water is discharged from the pressure vessel _A1 or that steam has entered the pressure vessel _A2) . ) and on-off valve B ₁ with conduit C ₁
is shut off, valve _F1 is opened to reduce the pressure in pressure vessel _A1 , and then the dehydrated lignite is taken out. During this time, the valve D ₂ is opened and the supply of steam from the steam source S to the pressure vessel A ₂ is started. By this time, the charging of lignite and the sealing of the pressure vessel A _i+1 should have been completed. Then, heat dehydration is performed using the above-mentioned procedure, and the pressure vessel is
Hot water is injected into A ₃ , A ₄ , ..., A _i+1 to perform preheating. Note that when the pressure is reduced, steam is released outside the container via the pipe _G1 , but its enthalpy per unit volume is only 1/20 of the enthalpy of hot water at the same temperature, so the heat loss is extremely small. However, as shown in FIG. 3, for example, the bunker U ₁ above the pressure vessel,
It is also possible to reduce the amount of heat released by passing the lignite layer through the lignite layer in U ₂ , ....

By repeating the series of operations described above, lignite is dehydrated in liquid form through a series of temperature-raising processes, including underwater high-pressure preheating with relatively low-temperature hot water and gradually high-temperature hot water, and heating with steam. Thereafter, due to the reduced pressure in the steam, the remaining moisture is evaporated using the sensible heat of the brown coal without the hot water re-absorbing moisture into the brown coal, and the dehydration further progresses.

By the way, in the present invention, there is a mode in which n=i. This embodiment is advantageous because all the pressure vessels can be used with the least wastage, and is particularly convenient when implementing the present invention using a limited number of pressure vessels. However, when the steam supply process for a certain pressure vessel A ₁ is completed, it is not possible to immediately start supplying steam to the pressure vessel A ₂ . Because the pressure vessel of A _i+1 means the pressure vessel of A ₁ , so the pressure vessel A ₃
It is not possible to move hot water from upstream pressure vessel A ₂ to ~A _i+1 , and the depressurization, coal discharge, and coal injection operations of pressure vessel A ₁ must be completed before steam is supplied to pressure vessel A ₂ . It is necessary to keep it.

Since the high temperature side (upstream pressure vessel side) of the hot water inside the pipes C ₁ , C ₂ , ... is located below, convection within the pipes tends to occur when the movement of the hot water stops.
Therefore, in the embodiment where n=i, a certain pressure vessel
In order to prevent convection from occurring during the period when A ₁ is depressurizing or discharging coal, each pipe C ₁ , C ₂ ,
Either check valves are provided in... or the on-off valves B ₁ , B ₂ ,...
You only need to close all of them during this period. Also,
During this period, we will start supplying a small amount of steam to pressure vessel A ₂ , and for this period only we will be supplying one vessel less than usual.
The hot water may be moved to the (i-2) pressure vessels of A ₃ , A ₄ , . . . , A _i and drained at a smaller flow rate than the pressure vessels A _i .

On the other hand, n>i, and at the same time as the steam supply process of a certain pressure vessel A ₁ is completed, the supply of steam to the pressure vessel A ₂ is started, and at the same time, the steam supply to the pressure vessel A ₃ , A ₄ ,
..., there is an embodiment in which hot water is transferred to the (i-1) group of A _i+1 . In this embodiment, the supply of steam can be made continuous, and the hot water can be constantly moved in the pipes C ₁ , C ₂ , . . . , so that convection can also be reduced. Note that a convection prevention method such as the above-mentioned n=i may be used in combination. If flow rate adjustment valves are used for valves B ₁ , B ₂ , ... and valves E ₁ , E ₂ , ... to make the flow rate of hot water in the pipes C ₁ , C ₂ , ... higher than the convection speed, convection will occur. This method is preferable because it prevents this and also makes the rate of drop of the liquid level in the pressure vessel constant during the steam supply process, so that fluctuations in the steam flow rate are extremely small.

Regardless of the above-mentioned embodiments, if the base number n of the pressure vessel is increased, the temperature of the lignite being preheated can be raised more sufficiently, and the heating time can be shortened. However, there is a limit to its reduction, and if n is made too large, the processing time will actually become longer, and as a result, the thermal efficiency will decrease due to heat dissipation, so n is preferably 20 or less. However, as can be seen from the above description, it is necessary that the number is 2 or more.

By the way, the optimal values for the heating, preheating, and coal discharge times vary depending on the physical properties of lignite (specific heat, thermal conductivity, etc.), moisture content, capillary condition, particle size, and capacity of the pressure vessel. By appropriately selecting n and i and bringing them close to the optimum values for each processing time, it is possible to improve thermal efficiency and shorten processing time.

In the above explanation, the steam supplied from the steam source was saturated steam, but in the dehydration method according to the present invention, a considerable portion of the heating of lignite is carried out in water, so even if superheated steam is supplied, Since evaporative dehydration is limited to the final stage, the characteristics of liquid dehydration can be fully utilized. In this case, the superheated steam is saturated and further condensed into hot water in the pressure vessel that receives superheated steam from the steam source. Therefore, this pressure vessel is supplied with superheated steam and simultaneously discharges hot water and supplies it to other pressure vessels.

Furthermore, although the dehydrated product has been described using lignite, it goes without saying that any porous organic solid that dehydrates into a liquid state when heated in an emergency atmosphere can be applied. It should be added that the heating process in this dehydration method can also be applied to meet the industrial demand for heating solid materials to high temperatures that do not cause liquid dehydration.

As described in detail above, according to the present invention, the hot water is transferred to another pressure vessel arranged in an annular manner at the same time as steam heating at this pressure. There is no need for a reservoir, and the entire facility can be simplified.

In addition, since the hot water can be injected into downstream pressure vessels regardless of its temperature, increasing the number of pressure vessels makes it possible to use hot water that cannot be used with saturated steam dehydration.
Heat can be recovered even from hot water below 100°C, and the heat recovery rate can be significantly improved.

In a pressure vessel that is supplied with steam, the low-rank coal that is dehydrated is only in the supplied steam atmosphere, and it can be said that the low-rank coal in the hot water is still in the final process of preheating. Therefore, since the steam supplied sequentially dehydrates the low-rank coal newly exposed on the hot water surface, there is no need to supply a large amount of steam in batches, and moreover, if a constant amount is supplied continuously, Therefore, the steam source can be operated regularly.

The preheating of the dehydrated product is performed with hot water, but unlike the above-mentioned underwater heating dehydration method, the heating process is performed with steam, so it is possible to prevent the hot water from being re-adsorbed during depressurization, and
Residual water can also be evaporated during pressure reduction using the sensible heat of low-rank coal.

Since preheated water is injected from the top of the pressure vessel and discharged from the bottom, heat exchange is performed without causing convection within the vessel. Therefore, the preheated water exhibits a stable temperature drop with extremely little fluctuation, and the temperature decreases as it goes downstream, resulting in high thermal efficiency.
It also has many remarkable effects, such as being able to preheat the dehydrated material without applying a sudden heat load.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the treatment process in the conventional saturated steam dehydration method, FIG. Figure 3 is the arrow view of Figure 2.
FIG. 2 is a simplified elevational view of a portion of the device of the present invention. A ₁ , A ₂ ,…, A _o …pressure vessel, C ₁ , C ₂ ,…, _Co
...Pipe line, K...Lignite, S...Steam source.

Claims (1)

[Claims] 1. Two or more pressure vessels are connected in an annular manner by interconnecting the lower part of the upstream pressure vessel and the upper part of the downstream pressure vessel which are adjacent to each other through a pipe,
Among the pressure vessels, a continuous group of pressure vessels is loaded with low-grade coal to be dehydrated, and the pressure vessel at one end of the group is designated as the most upstream pressure vessel, and high-temperature, high-pressure steam is injected into it to dehydrate the low-grade coal. Coal is dehydrated by heating, and hot water consisting of water and steam condensed water separated from the low-rank coal is sequentially sent to downstream pressure vessels to preheat the low-grade coal in those pressure vessels. Excess water is discharged from the most downstream pressure vessel at the other end of the group, and when the heating dehydration of the most upstream pressure vessel is completed and the hot water is discharged from the pressure vessel,
Or, when some steam is supplied to the pressure vessel immediately downstream of the pressure vessel that is the most upstream,
The most upstream pressure vessel is isolated from the immediately downstream pressure vessel, the steam inside is released and the pressure is reduced, and the dehydrated low-rank coal is discharged to complete the series of dehydration operations. When the low-rank coal to be dehydrated is loaded into the pressure vessel that is adjacent to the pressure vessel that was downstream, and the preparation for preheating is completed, the pressure vessel that is located downstream of the pressure vessel that is the most upstream Carry out the same dehydration operation as described above with the same number of pressure vessels as the number of the group, counting from the number of pressure vessels that have been prepared.
A method for heating and dehydrating low-rank coal, which is characterized by sequentially moving such dehydration operations downstream. 2. The method of heating and dehydrating low-rank coal according to claim 1, characterized in that the group of pressure vessels is formed by all pressure vessels connected in an annular manner. 3. The method for heating and dehydrating low-rank coal according to claim 1 or 2, wherein the total number of pressure vessels connected in a ring is 20 or less. 4. A plurality of pressure vessels for heating and dehydrating low-grade coal to be connected to a closed system with upstream and downstream directionality, and pressure vessels on the lower and downstream sides of the pressure vessels that are adjacent to each other on the upstream side in this closed system. a hot water transfer pipeline connected to the upper part of the pressure vessel via an on-off valve; a high-temperature, high-pressure steam supply pipeline connected to a steam source via the on-off valve of each of the pressure vessels; 1. A heating dehydration device for low-rank coal for thermal dehydration, comprising a pipe line equipped with an on-off valve for opening and reducing the pressure of internal steam.