Patent Application
20150013215
The present invention relates to a method for separating solvent-containing water, which is generated in the process for producing an ashless coal by removing ash from a coal, into a solvent and water.
Examples of methods for producing an ashless coal include a method described in PTL 1. PTL 1 describes a method for producing an ashless coal, wherein a slurry is prepared by mixing a coal and a solvent, a solvent-soluble coal component is extracted by heating the resulting slurry, a solution containing the solvent-soluble coal component is separated from the slurry, from which the coal component has been extracted, and thereafter, an ashless coal is obtained by recovering the solvent from the separated solution. An oil component derived from a coal is used as the solvent.
PTL 1: Japanese Unexamined Patent Application Publication No 2005-120185
Here, in the above-described process for producing an ashless coal, water (H2O) is produced from the coal serving as a raw material. In the extraction of the coal component, the slurry is heated to a temperature of, for example, 300 to 420 DEG C. The coal undergoes a thermal decomposition reaction under such high temperatures, and methane (CH4), carbon dioxide (CO2), water (H2O), and the like are produced. Also, the coal serving as a raw material contains water in the first place, and the water is separated from the coal in extraction of the coal component with the solvent.
The water (H2O) produced from the coal through thermal decomposition and the water (H2O) separated from the coal in extraction of the coal component are discharged as a gas (water vapor) to the outside of the system of an ashless coal producing facility, while much solvent is present in the gas (solvent-containing water). Therefore, if the gas concerned is entirely discarded, a solvent loss increases significantly, and fresh supplementation of much solvent becomes necessary. As a result, the running cost increases.
Meanwhile, in order to discard the gas containing the solvent, for example, a treatment to remove the solvent from the gas by using an adsorbent is necessary, and in the case where the amount of solvent contained in the gas is large, the treatment cost increases significantly. Also the solvent adsorbed by the adsorbent is not readily separated from the solvent. That is, reuse of an adsorbent which has been used for the adsorption treatment is difficult.
The present invention has been made in consideration of the above-described circumstances, and it is an object to provide a method capable of separating solvent-containing water, which is generated in the process for producing an ashless coal, into a solvent and water readily without using any adsorbent or the like.
The present invention is a solvent separation method for separating solvent-containing water, which is generated in the process for producing an ashless coal, into a solvent and water, the method including an extraction step of extracting a solvent-soluble coal component by heating a slurry obtained by mixing a coal and the solvent, a separation step of separating a solution containing the solvent-soluble coal component from the slurry obtained in the above-described extraction step, and an ashless coal acquisition step of obtaining an ashless coal by vaporizing and separating the solvent from the solution separated in the above-described separation step. This solvent separation method is characterized in that a solvent-containing water supply step of supplying the above-described solvent-containing water into a pressure vessel for solvent separation purposes and a temperature retention step of retaining the temperature of the above-described solvent-containing water that has been supplied into the above-described pressure vessel for solvent separation purposes at a predetermined temperature are included and the above-described solvent-containing water is separated into the solvent and water by moving water in the liquid form downward and moving the solvent upward in the above-described pressure vessel for solvent separation purposes due to the difference between the density of water and the density of the solvent at the predetermined temperature.
In this regard, the term “solvent-containing water” refers to water in the state in which a solvent and water are mixed (mixed state) regardless of a liquid state or a gas state. Also, the term “is generated in the process for producing an ashless coal” is in the sense of being generated as a by-product in any portion of the process for producing an ashless coal.
According to the present invention, the solvent-containing water, which is generated in the process for producing an ashless coal, can be separated into the solvent and water readily without using any adsorbent or the like. As a result, the adsorbent can be reused, the solvent loss can he reduced and, in addition, the water disposal cost can be reduced.
The embodiments according to the present invention will be described below with reference to drawings.
As shown in
Also, on the downstream side of the gravity settling vessel 7, a solvent separator 10 to vaporize and separate the solvent from a solvent-insoluble component concentrate (solid content concentrate) separated in the gravity settling vessel 7 (to separate and recover the solvent from the solid content concentrate) is disposed.
Also, the ashless coal producing facility 100 is provided with a pressure vessel for solvent separation purposes 11 to separate the solvent-containing water into the solvent and water. This pressure vessel for solvent separation purposes 11 is connected to the extraction vessel 6 with a pipe 25. That is, in the present embodiment, the solvent-containing water in the gas, which is generated in the extraction step in the process for producing an ashless coal, is supplied from the extraction vessel 6 to the pressure vessel for solvent separation purposes 11, so as to be separated into the solvent in the liquid form and water in the liquid form.
In this regard, the pressure vessel for solvent separation purposes 11 may be connected to the gravity settling vessel 7 rather than the extraction vessel 6 with a pipe or the like. That is, the solvent-containing water (the solvent is a liquid and the solvent is mixed into the water vapor) in the gas, which is generated in the extraction step, may be supplied from the gravity settling vessel 7 to the pressure vessel for solvent separation purposes 11, so as to be separated into the solvent and water. Meanwhile, in the case where a very small amount of water is generated in the gravity settling vessel 7, the solvent-containing water generated here can be separated into the solvent and water in the pressure vessel for solvent separation purposes 11 by connecting the pressure vessel for solvent separation purposes 11 to the gravity settling vessel 7.
Furthermore, one pressure vessel for solvent separation purposes 11 may be connected to both the extraction vessel 6 and the gravity settling vessel 7, or each of the extraction vessel 6 and the gravity settling vessel 7 may be connected to one pressure vessel for solvent separation purposes 11. In the case where water remains in the slurry supplied to the gravity settling vessel 7, the water can be removed by discharging the solvent-containing water in the gas containing the solvent from the gravity settling vessel 7 to the pressure vessel for solvent separation purposes 11.
Also, the pressure vessel for solvent separation purposes 11 may be connected to the slurry preparation vessel 3 with a pipe or the like. This is because in the case where a coal containing much water is handled, the slurry preparation vessel 3 is heated to 100 to 120 DEG C., which is in the vicinity of the boiling point of water, to recover water from the coal through vaporization and, thereby, the water concentration in the slurry transferred to the extraction step can be decreased. The solvent-containing water generated here can be supplied from the slurry preparation vessel 3 to the pressure vessel for solvent separation purposes 11, so as to be separated into the solvent and water.
Also, a tank may be disposed at some midpoint of the pipe 25 connected to the pressure vessel for solvent separation purposes 11. The solvent-containing water is condensed once into a liquid in the tank concerned (the solvent-containing water is condensed by lowering the temperature of the solvent-containing water) and, thereafter, water is vaporized from the solvent-containing water by heating to a temperature higher than or equal to the boiling point of water again. Thus a vapor (including the solvent) resulting from concentration of the water is transferred from the tank concerned to the pressure vessel for solvent separation purposes 11. According to this step, the solvent concentration in the solvent-containing water transferred to the pressure vessel for solvent separation purposes 11 is reduced, and the solvent loss factor can be further reduced. In this regard, the solvent remaining in the tank is drawn from the tank and is reused.
Here, an ashless coal production method (process for producing an ashless coal) includes an extraction step, a separation step, and an ashless coal acquisition step. Each of these steps will be described below and, in addition, a method for separating the solvent-containing water, which is generated in the process for producing an ashless coal, into the solvent and water will be described. In this regard, the coal serving as a raw material in the production of the ashless coal is not specifically limited. A bituminous coal having a high extraction rate (ashless coal recovery percentage) may be used or a cheaper bony coal (sub-bituminous coal, brown coal) may be used. Meanwhile, the ashless coal refers to a coal having an ash content of 5 percent by weight or less, and preferably 3 percent by weight or less.
(Extraction Step)
The extraction step is a step of extracting a solvent-soluble coal component through heating of the slurry obtained by mixing the coal and the solvent, in the present embodiment, this extraction step is divided into the slurry preparation step of preparing the slurry by mixing the coal and water and the solvent-soluble component extraction step of extracting (dissolving into the solvent) a solvent-soluble coal component by heating the slurry prepared in the slurry preparation step.
In extraction of the solvent-soluble coal component through heating of the slurry obtained by mixing the coal and the solvent, a solvent having a large solvent power with respect to a coal, which is an aromatic solvent (hydrogen donor solvent or solvent not having a hydrogen donating property) in many cases, and a coal are mixed and are heated, so that organic components in the coal are extracted.
The solvent not having a hydrogen donating property is a coal derivative which is refined mainly from a coal carbonization product and which is a solvent primarily containing a bicyclic aromatic. This solvent not having a hydrogen donating property is stable even in a heated state, has excellent affinity for a coal, where the proportion of a soluble component (here, a coal component) extracted by a solvent (may be referred to as an extraction rate) is high, and is a solvent readily recoverable by a method of distillation or the like. Examples of primary components of the solvents not having a hydrogen donating property include naphthalene, methylnaphthalene, dimethylnaphthalene, and trimethylnaphthalene, which are bicyclic aromatics. Components of other solvents not having a hydrogen donating property include naphthalenes, anthracenes, fluorenes, which have aliphatic side chains, and in addition, biphenyls and alkylbenzenes having long aliphatic side chains are also included in the solvent not having a hydrogen donating property.
In this regard, in the case explained above, the solvent not having a hydrogen donating property is used as the solvent. However, as a matter of course, hydrogen donating compounds (including coal liquefaction oil) typified by tetralin may be used as the solvent. In the case where the hydrogen donor solvent is used, the yield of ashless coal is improved.
The specific gravities of these solvents (ratio to the weight of water having the same volume) is about 1 at room temperature (ambient temperature).
Meanwhile, the boiling point of the solvent is not specifically limited. Solvents having boiling points of, for example, 180 to 300 DEG C., in particular 240 to 280 DEG C. are used preferably from the view point of, for example, reduction in pressures in the extraction step and the separation step, the extraction rate in the extraction step, the solvent recovery percentages in the ashless coal acquisition step and the like.
The slurry preparation step is executed in the slurry preparation vessel 3 shown in
The mixing ratio of the coal to the solvent is, for example, 10 to 50 percent by weight in terms of dry coal, and more preferably 20 to 35 percent by weight.
The solvent-soluble component extraction step is executed in the preheater 5 and the extraction vessel 6 shown in
The heating temperature in the solvent-soluble component extraction step, is not specifically limited in so far as the solvent-soluble component is dissolved and is, for example, 300 to 420 DEG C., and more preferably 360 to 400 DEG C. from the view points of sufficient dissolution of the solvent-soluble component and an improvement in extraction rate.
Also, the heating time (extraction time) is not specifically limited but is, for example, 10 to 60 minutes from the view points of sufficient dissolution and an improvement in extraction rate. The heating time is a total of the heating times in the preheater 5 and the extraction vessel 6 shown in
In this regard, the solvent-soluble component extraction step is performed in the presence of an inert gas, e.g, nitrogen. The pressure in the extraction vessel 6 is preferably 1.0 to 2.0 MPa, although depending on the temperature in the extraction and the vapor pressure of the solvent used. In the case where the pressure in the extraction vessel 6 is lower than the vapor pressure of the solvent, the solvent is volatilized and is not confined in the liquid phase, so that extraction cannot be performed. In order to confine the solvent in the liquid phase, a pressure higher than the vapor pressure of the solvent is necessary. On the other hand, if the pressure is too high, the apparatus cost and the operation cost increase, so that there is no economy.
(Method for Separating Solvent and Water)
As described above, in extraction of the coal component, the slurry is heated to a temperature of, for example, 300 to 420 DEG C. Here, under such high temperatures, the coal undergoes a thermal decomposition reaction, and methane (CH4), carbon dioxide (CO2), water (H2O), and the like are produced. Also, the coal serving as a raw material contains water in the first place, and water is insoluble in the solvent, so that water is separated from the coal in extraction of the coal component with the solvent.
(Solvent-Containing Water Supply Step)
The solvent-containing water supply step is a step of supplying the solvent-containing water to the pressure vessel for solvent separation purposes. The water (H2O) produced from the coal through thermal decomposition and the water (H2O) separated from the coal in extraction of the coal component are in the state of a gas containing the solvent (the state of solvent-containing water vapor) and is supplied (discharged) to the pressure vessel for solvent separation purposes 11 through the pipe 25. The temperature in the pressure vessel for solvent separation purposes 11 is specified to be lower than the temperature in the extraction vessel 6 and, therefore, the water vapor is condensed into a liquid.
(Temperature Retention Step)
The temperature retention step is a step of retaining the temperature of the solvent-containing water that has been supplied into the pressure vessel for solvent separation purposes 11 at a predetermined temperature and is executed in the pressure vessel for solvent separation purposes 11 shown in
The solvent collected in the upper portion of the pressure vessel for solvent separation purposes 11 is drawn from the upper portion of the pressure vessel for solvent separation purposes 11, and the water collected in the lower portion of the pressure vessel for solvent separation purposes 11 is drawn from the lower portion of the pressure vessel for solvent separation purposes 11. The drawn solvent is returned to the solvent tank 2 and is reused. The drawn water is discarded.
Also, the temperature retention step is performed preferably in the presence of an inert gas, e.g., nitrogen. That is, it is preferable that the inert gas, e.g., nitrogen, be filled in the pressure vessel for solvent separation purposes 11. The pressure in the pressure vessel for solvent separation purposes 11 is specified to be a pressure higher than the saturated vapor pressure of water in such a way that a water vapor is condensed and the resulting water keeps the liquid state and is adjusted to be a pressure of, for example, 0.3 to 2.0 MPa by introduction of a nitrogen gas into the pressure vessel.
Also, the solvent-containing water supplied to the pressure vessel for solvent separation purposes 11 may be agitated with an agitator or the like and, thereafter, the agitation may be stopped at the point in time when the temperature becomes constant at the predetermined temperature, followed by standing.
Meanwhile, the slurry is heated to a temperature of, for example, 300 to 420 DEG C. in the extraction vessel 6. The heater 11a is not necessary insofar as the temperature of the solvent-containing water supplied from the extraction vessel 6 to the pressure vessel for solvent separation purposes 11 can be retained at a temperature of, for example, 120 DEG C. or higher for a predetermined time without heating.
(Case Where Extraction Vessel 6 is not Provided)
In some cases, the extraction vessel 6 is not provided, and a solvent-soluble coal component is extracted in the pipe between the preheater 5 and the gravity settling vessel 7. For example, the length of the pipe between the preheater 5 and the gravity settling vessel 7 is specified to be sufficient for extraction of the coal component and the coal component is extracted in the pipe between the preheater 5 and the gravity settling vessel 7. The coal is directly supplied into the pipe, through which the solvent heated to a high temperature (for example, 380 DEG C.) is passed, between the preheater 5 and tbe gravity settling vessel 7. In this case, the pressure vessel for solvent separation purposes 11 is connected to the gravity settling vessel 7, the solvent-containing water is supplied (discharged) from the gravity settling vessel 7 to the pressure vessel for solvent separation purposes 11, and the solvent-containing water is separated into the solvent and water.
The explanation of the production process of an ashless coal will be continued.
(Separation Step)
The separation step is a step of separating a solution containing the coal component dissolved in the solvent from the slurry obtained in the extraction step. Put another way, the separation step is a step of separating the slurry obtained in the extraction step into the solution containing the coal component dissolved in the solvent and a solvent-insoluble component concentrate (solid content concentrate). This separation step is executed in the gravity settling vessel 7 shown in
The gravity settling method is a method for settling and separating the solvent-insoluble component through the use of the gravity by holding the slurry in the vessel. A continuous separation treatment is possible by supplying the slurry into the vessel continuously while the supernatant liquid is discharged from the upper portion and the solid content concentrate is discharged from the lower portion continuously.
In order to prevent reprecipitation of the solvent-soluble component eluted from the coal, it is preferable that the inside of the gravity settling vessel 7 be heat-insulated or heated and pressurized. The heating temperature is, for example, 300 to 380 DEG C., and the pressure in the vessel is specified to be, for example, 1.0 to 3.0 MPa.
Meanwhile, as for the method for separating the solution containing the coal component dissolved in the solvent from the slurry obtained in the extraction step, a filtration method, a centrifugal separation method, and the like are mentioned besides the gravity settling method.
(Ashless Coal Acquisition Step)
The ashless coal acquisition step is a step of obtaining an ashless coal by vaporizing and separating the solvent from the solution (supernatant liquid) separated in the above-described separation step. This ashless coal acquisition step is executed in the solvent separator 9 shown in
As for the method for separating the solvent from the solution (supernatant liquid), a common distillation method or vaporization method can be used and, for example, a flash distillation method is used. A separated and recovered solvent can be used repeatedly by circulation to the slurry preparation vessel 3. An ashless coal (HPC) containing substantially no ash (for example, ash content is 3 percent by weight or less) can be obtained from the supernatant liquid by separation and recovery of the solvent. The ashless coal hardly contains ash, contains no water, and exhibits a calorific value higher than that of the raw material coal. Furthermore, the plastic property of coal, which is particularly important quality of a raw material for the coke for steelmaking, is improved to a great extent, and even when the raw material coal does not have the plastic property of coal, the resulting ashless coal (HPC) has good plastic property of coal. Therefore, the ashless coal can be used as, for example, a blend coal of the raw material for coke.
(By-Product Coal Acquisition Step)
A by-product coal acquisition step is a step of obtaining a by-product coal by vaporizing and separating the solvent from the solvent-insoluble component concentrate (solid content concentrate) separated in the gravity settling vessel 7. This by-product coal acquisition step is a step of recovering the solvent from the solid content concentrate through vaporization and separation and is executed in the solvent separator 10 shown in
As for the method for separating the solvent from the solid content concentrate, a common distillation method or vaporization method can be used as with the above-described ashless coal acquisition step. A separated and recovered solvent can be used repeatedly by circulation to the slurry preparation vessel 3. A by-product coal (may be referred to as RC, or residual coal), in which the solvent-insoluble component containing ash and the like has been concentrated, can be obtained from the solid content concentrate by separation and recovery of the solvent. The by-product coal contains ash but no water and has a sufficient calorific value. The by-product coal does not exhibit the plastic property of coal. However, an oxygen-containing functional group has been eliminated, so that in the case of use as a blend coal, the plastic property of coal of the other coal contained in this blend coal is not hindered. Therefore, this by-product coal can be used as part of blend coal of the raw material for coke as with a common non- or slightly-caking coal or can be used as various fuels rather than the raw material for coke. In this regard, the by-product coal may be discarded without being recovered.
Experiments to separate a solvent-containing water into a solvent and water were performed.
A vertically long autoclave 50 used in the experiment was a cylindrical pressure vessel having a diameter of 62.3 mm and had a structure in which a liquid was drawn from the bottom of the autoclave 50 and a plurality of places at the predetermined heights from the bottom, as shown in
A solvent: 1,200 g and water: 1,200 g were put into the autoclave 50. At room temperature (ambient temperature), the solvent and the water were in a mixed state and the separability was very poor. That is, at room temperature (ambient temperature), there was almost no difference between the density of the water and the density of the solvent.
The temperature of the mixed solution composed of the solvent and the water was raised to the predetermined temperature while agitation was performed. The temperature conditions were specified to be 50 DEG C., 90 DEG C., 100 DEG C., 120 DEG C., 150 DEG C., and 200 DEG C. The agitation was stopped when the temperature of the mixed solution became constant at a predetermined temperature. After the agitation was stopped, standing was performed for 30 minutes. Subsequently, the liquid was taken out of the autoclave 50 into sampling containers 51a to 51f, and the water concentration of the liquid was measured. The results are shown in Table 1.
As is clear from Table 1 and
On the other hand, in the cases where the retention temperatures were 100 DEG C., 120 DEG C., and 150 DEG C., low values of water concentration were shown in the upper portion of the autoclave 50, high values were shown in the bottom, and large changes were observed within the range of 400 mm to 600 mm from the bottom. Consequently, it is clear that the separation performance of the solvent was high in the cases of 100 DEG C., 120 DEG C., and 150 DEG C. In particular, the highest water concentration at the bottom of 98 percent by weight was shown in the case of 150 DEG C. Therefore, it was found that the temperature range in which the retention temperature was 150 DEG C. was the best temperature range for the solvent separation condition.
On the basis of this separation test, it was made clear that the difference between the density of the water and the density of the solvent changed with the temperature to a great extent (depended on the temperature to a great extent). The present invention has taken advantage of this property found here.
(Operations and Advantages)
The solvent separation method according to the present invention includes the temperature retention step of retaining the temperature of the solvent-containing water that has been supplied into the pressure vessel for solvent separation purposes at the predetermined temperature, and the solvent-containing water is separated into the solvent and water by moving the water in the liquid form downward and moving the solvent upward in the above-described pressure vessel for solvent separation purposes through the use of the difference between the density of the water and the density of the solvent at the predetermined temperature. In this regard, the pressure vessel is used in order to confine the water in the liquid phase in the container. According to the present invention, the solvent-containing water can be separated into the solvent and the water readily by retaining the temperature of the solvent-containing water at the predetermined temperature in the pressure vessel without using an adsorbent or the like. Consequently, the adsorbent can be recovered and reused for extracting the coal component, so that the solvent loss can be reduced and, in addition, the water disposal cost can be reduced. In this regard, the solvent-containing water supply step of supplying the solvent-containing water into the pressure vessel for solvent separation purposes may be performed continuously or be performed discontinuously.
Also, in the above-described temperature retention step, the separation performance between the solvent and the water can be improved by retaining the temperature of the solvent-containing water at the predetermined temperature and, in addition, allowing the solvent-containing water to stand.
Also, in the temperature retention step, the temperature of the solvent-containing water in the pressure vessel for solvent separation purposes is retained at a temperature of 100 to 180 DEG C. inclusive and, thereby, the separation performance between the solvent and the water becomes very good, so that the separation time can be decreased. There is a merit that the capacity of the pressure vessel for solvent separation purposes can be reduced. More preferably, the temperature of the solvent-containing water in the pressure vessel for solvent separation purposes is retained at a temperature of 120 to 150 DEG C. inclusive.
Also, the pressure in the pressure vessel for solvent separation purposes is specified to be a pressure higher than the saturated vapor pressure of water and, thereby, the water can be completely confined in the liquid phase in the pressure vessel, so that the separation performance between the solvent and the water is further improved.
Also, an inert gas is filled in the pressure vessel for solvent separation purposes and, thereby, explosion of the solvent can be prevented.
Also, it is preferable that the solvent-containing water, which is generated in the above-described extraction step in the process for producing an ashless coal, be supplied to the pressure vessel for solvent separation purposes. Water is generated at the maximum in the extraction step in the process for producing an ashless coal, and a loss of solvent mixed into water and discharged to the outside of the system can be reliably reduced by supplying the solvent-containing water generated in at least this extraction step to the pressure vessel for solvent separation purposes and separating the solvent-containing water into the solvent and water.
Up to this point, the embodiments according to the present invention have been explained. However, the present invention is not limited to the above-described embodiments and can be variously modified and be executed within the scope of the claims.
1: coal hopper
2: solvent tank
3: slurry preparation vessel
4: transfer pump
5: preheater
6: extraction vessel
7: gravity settling vessel
8: filter unit
9, 10: solvent separator
11: pressure vessel for solvent separation purposes
100: ashless coal producing facility
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-019488 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/050180 | 1/9/2013 | WO | 00 |
