JPS62235392A - Stabilization of coal-water slurry having high concentration in low-viscosity state - Google Patents

Abstract

PURPOSE:To prevent the variation of properties of a concentrated coal-water slurry even after a long-term storage and to maintain the viscosity of the slurry at a low level in high stability, by adding a mixture of silicate, etc., to an aqueous slurry of powdered coal added with a surfactant. CONSTITUTION:Water and a surfactant are added to finely pulverized coal and preferably the pH of the mixture is adjusted to 6-11 to obtain a coal-water slurry. The slurry is added with one or more polyvalent-metal ion removing agent selected from alkali metal silicate, borate, carbonate, sulfate, sulfite and fluoride. EFFECT:The above removing agent is available at a low cost, resistant to degradation and stable. It has strong bonding force to polyvalent metallic ion and high removing effect of the ion.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a technology for producing highly concentrated coal-water slurry by mixing finely pulverized coal and water to form a slurry with a low viscosity that can be transported through pipes. relates to a method for keeping the viscosity of a slurry low and stable.

[Conventional technology]

Powder slurry transportation technology has been researched for a long time as a method for transporting solid powder in a fluid state that is easy to handle. In recent years, this slurry transportation technology has been applied to the transportation of 1 coal, and it is safe without worrying about spontaneous combustion of 1 coal or dust scattering, etc. Moreover, since it can be transported through pipes, it is easy to handle and improves transportation efficiency. As a method that can do this, the development of technology for producing Takaniwa coal-water slurry is being actively carried out.

The manufacturing technology for high-concentration coal-water slurry is as shown in various technologies that have already been published. By mixing charcoal and water,
This is a method for producing a coal-water slurry containing coal in an amount of 60 to 7% ON.

The high concentration coal-water slurry prepared in this way was 100%
However, it has a viscosity of about 0 to 2000 op, and has sufficient flow characteristics to be transported through pipes as a fluid.

Such a highly concentrated stone return slurry is filled with coal particles very densely, and in its flowing state, individual coal particles constantly repeatedly collide with other coal particles. In a slurry containing such a high concentration of coal, a slight change in the slurry composition or the introduction of a small amount of impurity into the slurry can greatly change the flow characteristics, and this may cause problems when transporting the high concentration coal-water slurry through pipes. If the above-mentioned change in flow characteristics occurs, it will have a large impact on causing problems such as blockage of pipes, and generally, the higher the pH value, the higher the pH value.

It is well known that the viscosity of slurry decreases. This is because the amount of charge on the surface of coal particles changes due to changes in the hydrogen ion concentration in the slurry medium.

This is thought to be because the action of the surfactant adsorbed on the surface of the coal particles changes, and the interaction between particles changes. In this way, in a high-concentration coal-water slurry, the coal particles are packed very densely and the distance between each particle is very small, so even a slight change in the interaction between particles can affect the viscosity of the slurry. Changes greatly.

In addition to hydrogen ions, positively charged metal ions, particularly polyvalent metal ions, are also known to increase the viscosity of slurry.

As is well known, the acidity of the coal surface varies depending on the rank of the coal and the conditions during coal storage, but coal water slurry is generally acidic. Also, 1 coal contains ash,
Its main components are silica and alumina, but it also contains chromium, vanadium, and iron.

Since other heavy metals are contained, these heavy metals are eluted in the acidic slurry and increase the slurry viscosity over time.

To solve this problem, there is a method of increasing the pH of the slurry by adding alkali when preparing the slurry, but even if the slurry is alkaline prepared in this way, if it is stored for a long time, the slurry will become acidic, and as described above. It is not a fundamental solution to the problem.

Furthermore, the finely pulverized coal is combined with a surfactant and a polyvalent metal ion to form an alkali metal salt of an anion or a polyvalent metal ion to form a highly stable salt. The present inventors disclosed a method for producing a highly concentrated coal-water slurry, which is characterized in that the slurry is mixed with water containing an inorganic complex-forming agent that forms chemical compounds, in JP-A-59-2069.
Although proposed in Publication No. 1, this method is similar to the above-mentioned PH adjustment method.

Since the additives react with the polyvalent metal ions eluted over time, the additives decrease, and eventually lose their effectiveness, it is necessary to take measures to add the additives when storing the slurry. The present inventors have conducted intensive studies on methods for removing such polyvalent cations from slurry, and have found that the above additive itself deteriorates over time even if it does not react with polyvalent metal ions. It became clear that the system lost its effectiveness and was economically wasteful. In particular, fine particles are necessary for high-concentration coal-water slurry to increase fluidity as mentioned above.
For this reason, the temperature of the slurry increases during pulverization, and the higher the temperature, the faster the rate of deterioration of the additive becomes, further worsening economic efficiency.

[Problem that the invention seeks to solve]

The dispersion medium of the highly concentrated coal-water slurry is water, and once the slurry is produced, the surface of the coal particles is constantly in contact with water. As is well known, water is a polar solvent and has a strong ability to dissolve dissociative substances.Coal has a carbonaceous content,
Silica, alumina.

It is a mixture with ash composed of other metal salts, and part of the ash becomes exposed on the particle surface when crushed.

Therefore, the ash in the coal present in the highly concentrated coal-water slurry is also constantly in contact with water, and some of the components therein are eluted into water, which is a good solvent, and as mentioned above, the viscosity of the slurry make it higher.

Generally, the lower the pH, the faster the dissolution of ash becomes, but it is impossible to reduce the dissolution amount to zero in any pH range. In the production of high-concentration coal-water slurry, caustic soda or the like is generally added to make it alkaline, but even in this case, the ash in the coal dissolves over time, increasing the viscosity of the slurry. In addition, the elution characteristics of ash vary greatly depending on the nature of the ash in the coal, and with some coals, a large amount of ash elutes at the same time as the Konoba coal-water slurry is produced. Some are difficult to manufacture.

An object of the present invention is to maintain a stable viscosity of a slurry at a low viscosity without changing the properties of the slurry even after long-term storage.

[Means for solving problems]

The above purpose is to add one or a mixture of alkali metal salts of silicic acid, boric acid, carbonic acid, sulfuric acid, sulfurous acid, and hydrofluoric acid to an aqueous slurry made by adding water and a surfactant to pulverized coal. This is achieved by

It is also necessary to adjust the pH of the coal water slurry to 6 to 11 depending on the type of coal.

[Effect]

In order to solve the above-mentioned difficulties, the inventors conducted extensive research,
The reason why the viscosity of high-concentration coal-water slurry increases over time was considered as follows.

In the production of high-concentration coal-water slurry, a surfactant is added to reduce its viscosity, and this surfactant is usually anionic. The added surfactant adsorbs onto the surface of the coal particles with its hydrophobic groups, making the surface of the coal hydrophilic and negatively charging the coal particles. In this way, the anionic surfactant has the effect of changing the coal surface, which is originally hydrophobic, to be hydrophilic, and, so to speak, has the effect of converting the highly concentrated coal-water slurry from a hydrophobic colloid to a hydrophilic colloid. By adding anionic surfactants.

The ability to reduce the viscosity of highly concentrated coal slurry is due to the above-mentioned two effects of the surfactant.

That is, by first making the surface of the coal particles hydrophilic,
A thin film of water is formed around the coal particles to prevent coal particles from agglomerating together due to steric hindrance.Secondly, the coal particles are negatively charged to generate electrostatic repulsion between the coal particles. Reduces the viscosity of the slurry by preventing particles from coagulating with each other. For the first effect, it is not necessary to use an anionic surfactant, and nonionic surfactants can also achieve the purpose, but in high-concentration coal-water slurry, 1 coal grade is 70% As mentioned above, in such a highly concentrated slurry, the coal particles are packed very closely together, so the particles are very close to each other, and in such a state, the electrostatic repulsion of particles r16 Anionic surfactants are especially used in highly concentrated coal-water slurries for several reasons, which play an important role in preventing agglomeration.

From the above considerations, it is thought that in a highly concentrated coal-water slurry, the charge on the particles plays a very important role vp1 in reducing the viscosity, and under conditions where the amount of charge on the particles is reduced, the slurry viscosity increases. As is well known, the amount of charge of negatively charged hydrophilic colloid particles varies greatly depending on the type and concentration of cations in the solvent. This is because cations are selectively adsorbed around negatively charged particles, resulting in the particle's tl! This is because the charge is neutralized, and the stronger the adsorption of cations, the smaller the amount of charge on the particle. Adsorption of cations on negatively charged particles is related to the stability of hydrophilic colloids;
It has been studied for a long time. As is well known, the adsorption of cations to negatively charged particles is strongest for H ÷ ions in the first order, and for polyvalent metal ions it becomes weaker as the valence decreases. This is related to the charge density of cations, and it is said that ions with higher charge density are more strongly adsorbed.

From this, it is possible to well explain the properties of high-concentration coal-water slurry in which the slurry viscosity changes greatly due to changes in PH as described above.

In our research on high-concentration coal-water slurry, the inventors discovered that there is a phenomenon that cannot be explained by the above pH change alone. That is, when a highly concentrated coal-water slurry is prepared and stored for a long time, the slurry particle size increases over time.

In view of the above considerations, analysis of the supernatant liquid of slurry 2 revealed that the concentration of cations such as calcium and magnesium was significantly increased compared to when the slurry was produced.

The present inventors have already proposed a method for removing polyvalent metal ions in a slurry by adding an anion that forms a poorly soluble salt with the polyvalent metal ion or a complexing agent that forms a stable metal complex. Discloses a method for manufacturing slurry with stable properties by masking harmful polyvalent metal ions and preventing adsorption of these metal ions to coal particles, reducing the viscosity of highly concentrated coal-water slurry. However, even with the slurry produced in this way, it was observed that when stored in ff for a long period of time, the concentration of cations in the supernatant increased as described above, and the viscosity of the slurry increased. It was observed that the rate of viscosity increase over time varied depending on the type of additive. From this new fact, as mentioned above, the additive itself is responsible for the rapid increase in viscosity.
It became clear that it was.

Based on the above, the present inventors searched for an additive that is inexpensive, stable without causing deterioration, and has a strong binding force for polyvalent metal ions and has a large removal effect. As a method to prevent thickening, we have found a method of adding sodium silicate or the like as a polyvalent metal ion removing agent to the slurry.

〔Example〕 The present invention will now be explained with reference to the following examples.

<Example 1> Coal, water, and anionic surfactant were put into a ball mill, and 1 coal was 99% less than 60 mesh.

100 meshes or less 93%, 200 meshes or less 80%
, wet-pulverized to a particle size distribution of 65% of 400 mesh or less to prepare a high-concentration coal-water slurry. The coal concentration in the slurry was 69% by weight.

Anionic surfactant: 0.5% by weight based on dry coal
Added. In addition, at 151 m of slurry, 0.3% by weight of sodium hydroxide was added to the dry coal, so that the pH of the prepared slurry was about 8.

The viscosity of the slurry thus prepared was 4200Qp.
Met. This slurry is hereinafter referred to as optical slurry. In this example, the pH of the slurry was adjusted to 8, but it was adjusted to 6-1.
It is sufficient if it is within the range of 1.

When sodium salt of hexametaphosphoric acid was added to the slurry prepared as above as an anion that forms an insoluble salt with a polyvalent metal cation, the viscosity of the slurry decreased to 1200 cp at a coal concentration of 69% by weight4. did. Here, the amount of sodium hexametaphosphoric acid added was 0.1% based on the dry weight of coal in the slurry. This slurry to which sodium hexametaphosphate was added is hereinafter referred to as slurry A.

Add sodium silicate (water glass) to the original slurry prepared as above in place of the above sodium hexametaphosphate.
is also 0.1% based on the dry weight of coal in the slurry.
Added. The viscosity of this slurry was 1200 cp at a coal concentration of 69% by weight (same as Rally A).
It is called.

As described above, sodium hexametaphosphate and sodium silicate are equally effective in reducing the viscosity of slurry. Slurries A and B prepared as above were stored at a temperature of 65° C. and their viscosity was fixed over time. The results are shown in Figure 1. Slurry A had a viscosity of J
ζ started to rise, and after 3 days it reached the same viscosity as the original slurry, but slurry B
Even after a day had passed, the viscosity remained the same as at the time of preparation, and unlike slurry A, no increase in viscosity was observed.

The reason for the increase in the viscosity of slurry A is that ash is eluted from the coal over time, and the generated polyvalent metal cations and hexametaphosphate anions combine to form a water-insoluble phosphate, resulting in the addition of hexametaphosphate. One is that it consumes acid. In addition to this, hexametaphosphoric acid is in an aqueous solution.

pH He is known to change to orthophosphoric acid depending on temperature and other conditions, or to polyphosphoric acid through polycondensation, and the polyvalent metal ions that have been eluted in this way are insoluble in water. The ability to make salt disappears. It is considered that another major cause of the rapid increase in the viscosity of Slurry A in the storage test described above is the deterioration of hexametaphosphoric acid itself as described above.

It is known that silicic acid, like hexametaphosphoric acid, undergoes polycondensation depending on the conditions in an aqueous solution, but as is clear from Figure 1, the viscosity of slurry n does not increase over time. , it can be seen that it exists stably. this is,
The rate of polycondensation reaction of silicic acid is very slow under the conditions of the aqueous solution in the slurry, and during the above period, even if polycondensation occurs, it will not be a problem and can be ignored, or the rate of polycondensation reaction of silicic acid This is thought to be due to the fact that even polycondensates have the ability to bond with polyvalent metal ions and form insoluble salts.

As revealed in this example, sodium silicate is excellent in reducing the initial viscosity of slurry, and at the same time, it is excellent in preventing the viscosity of slurry from increasing and maintaining its properties stably over a long period of time. It was found that it has certain characteristics.

<Example 2> In Example 1, MllL and sodium silicate were added to the slurry at a rate of 0.005,0.01°0.05,0 to dry coal.
．． A slurry containing 1% by weight was prepared. The viscosity of each slurry immediately after adding sodium silicate is coal concentration 69f.
The fi amount% was all 1200ap. Using these slurries, a storage test was conducted in the same manner as in Example 1, and the viscosity of each slurry was measured over time. The results are shown in Figure 2, and it can be seen that as the amount of sodium silicate added decreases, the tendency for viscosity to increase over time becomes stronger. This is not because silicic acid deteriorates over time like hexametaphosphoric acid and loses its ability to capture polyvalent metal ions, but rather because the ash in the coal dissolves into the slurry water over time, and the silicic acid This is because when the amount added is small, it is insufficient for the amount of eluted ash. Calcium ions (Ca”+
) The results of measuring the concentration are shown in Figure 3. Together with the increase in the viscosity of the slurry, the Ca' concentration in the supernatant liquid increased, and when the amount of sodium silicate added was small, ash content was eluted. It can be seen that the absolute amount is insufficient compared to the quantity.

<Example 3> A base slurry was prepared in the same manner as in Example 1 using different coal from that used in Example 1.

The coal used in this example had a relatively low ash content.

It is thought that the elution of ash was also reduced compared to the slurry prepared in Example 1. By the way, C in the supernatant liquid
When the concentration of a”10 was measured, it was 3.2 mmol/’tz
was found to be very low. Calcium chloride (CaCQx) was added to this slurry to simulate ash elution, and sodium silicate was added to the slurry thus prepared and its viscosity was measured to confirm its effect. The results are shown in FIG. 4. The coal concentration of the slurry used in this example was 67% by weight, and the amount of CaCΩ2 added was 0.071% by weight based on the coal. In Figure 4, ■
The dashed line left in the figure shows the viscosity of the slurry before adding CaCQz, and the point marked with ■ shows the viscosity of the slurry when the amount of CaCQz is added.As can be seen from this result, 5iOa is twice as much as Ca'' By adding a molar amount of sodium silicate, the slurry viscosity completely decreases to the value before adding CaCQz. From this example, it is clear that the ability of sodium silicate to capture polyvalent cations and r-ions and the reduction in slurry viscosity shows how much sodium silicate is required.

<Example 4> In order to investigate what kind of polyvalent metal cations are involved in increasing the viscosity of the slurry, ions eluted from coal were analyzed.6 Coal pulverized to a particle size of 0.5a+m or less By mixing 60 g and 120 g of water and adding hydrochloric acid or sodium hydroxide to this, 1
5I! ! ! After leaving the dried material for about 3 weeks, polyvalent metal ions in the supernatant were analyzed. The results are shown in FIG. 5. In FIG. 5, only the samples with relatively high concentrations among those analyzed are shown. When the pH is low, aluminum
It can be seen that a large amount of ions such as iron are eluted, but the amount of these ions eluted rapidly decreases as pII increases. It can be seen that almost no elution occurs. In comparison, alkaline earth metal ions such as calcium and magnesium have a pH of 6 to 8.
From the results of this example, it can be seen that calcium or magnesium ions are the main polyvalent metal ions that affect the thickening of the slurry over time. It is thought that there are.

<Example 5> In Example 4, it is calcium ions or magnesium ions that influence the thickening of the slurry over time, and these are dissolved in a considerable concentration in the slurry supernatant even when the pH increases. Based on this result, the viscosity-lowering effect of sodium silicate was further confirmed in this example. A slurry was prepared in the same manner as in Example 1 using coal different from those used in Examples 1 and 3. The coal used in this example had a relatively high ash content and It is thought that there are many ions. In preparing the slurry, sodium hydroxide was added so that the pH of the slurry was approximately 6. A slurry was prepared in which the pH was adjusted to 8.5 by further adding sodium hydroxide to this slurry, and a slurry in which sodium silicate was further added in an amount of 0.1% by weight based on the dry coal in the slurry. The relationship between the viscosity of these slurries and the coal concentration is
The one shown in the figure is pH 8 immediately after 3W production.
The viscosity of the slurry shown in 2 is the viscosity of the slurry prepared by adding sodium hydroxide to the slurry to adjust the pH to 8.5, and the viscosity shown in 3 is the viscosity of the slurry with the addition of sodium silicate. From the results shown in Figure 5, PH
It is possible to reduce the viscosity of the slurry by setting the viscosity to 8.5, but from the results of Example 4, the viscosity and rate of decrease are low because calcium or magnesium ions remain in the supernatant of this slurry. It is thought that by adding sodium silicate to this, the remaining calcium or magnesium ions were completely removed from the supernatant, making it possible to further reduce the viscosity.

<Example 6> In Example 1, 0.1% by weight of sodium borate was added to the dry coal in the slurry, and the viscosity was measured. there were. In addition, this slurry was used in Example 1.
When subjected to a storage test in the same manner as above, the viscosity increased to 2300 cP after 30 days.

<Example 7> When sodium carbonate was added in place of sodium borate in the same manner as in Example 6, the viscosity of the slurry was 2.
At 100 cp, the viscosity was 2500 ap after 30 days in a similar storage test.

<Example 8> When sodium sulfate was added in the same manner as in Example 6 instead of sodium forate, the viscosity of the slurry was 2.
800 op, and after 30 days in the same storage test, the viscosity was 3600 cp. is 1
At 900 ap, its viscosity was 3000 cp after 30 days in a similar storage test.

<Example 10> When sodium fluoride was added in the same manner as in Example 6 instead of sodium borate, the slurry viscosity was 1.
400 cp and after 30 days in a similar storage test its viscosity was 1500 cp.

<Example 11> A coal-water slurry was produced by pulverizing coal containing about 18% ash using a ball mill in the coexistence of water and an anionic surfactant. At this time, the mixing ratio of coal and water was adjusted so that the coal concentration was 65 wt%, and sodium hydroxide was added so that the pH of the slurry produced was 8. The coal concentration was adjusted by adding water to the slurry prepared in II, and the viscosity thereof was measured. The results are shown in FIG. 61.

Furthermore, a slurry was produced in the same manner as above, but this time, 0.1 wt% of sodium silicate was added to the coal and the slurry was pulverized. All other conditions are the same as above. The viscosity of this slurry was measured in the same manner as above, and the results are shown in Figure 6-2.
Shown below. At the same coal concentration, the viscosity of the slurry to which sodium silicate was added was clearly lower, demonstrating the effectiveness of the present invention.

Furthermore, the slurry to which no sodium silicate was added exhibited l1ffl properties in which the apparent viscosity decreased with the shear rate, and had a pseudo yield value.

This means that the coal particles in this slurry have a high degree of agglomeration, and from the considerations mentioned above, cations are generated by the elution of the ash content of one coal, which neutralizes the electric charge of the particles and causes the particles to intersect. It can be seen that the repulsive force of On the other hand, the slurry to which sodium silicate was added was almost a Newtonian fluid, and no yield value as described above was observed. This shows that the dispersibility of the coal particles in this slurry is high. The prepared slurry containing sodium silicate was heated to 80°C and 70°C.

When the slurry was held at 50°C and 20°C and its viscosity changed over time, it was found that the viscosity of the slurry held at 80°C was approximately 3000 cp after one week, and had no fluidity at all after one month. . Those kept at 70, 50° and 20°C had a temperature of 1700 and 1300.130, respectively, after one week.
It shows a viscosity of 0 c p and 3000.1 after one month.
It was 30G, 1300cp. The coal concentration of the slurry used in one test was 65 wt%, and the viscosity immediately after production was 1250 cp. When the Ca''+ concentration in the filtrate of the slurry kept at each temperature for one month was measured, it was 1900 r) p m t at 80°C, 800 ppm at 70°C, and about 110 at 50 and 20°C.
It was 0pp.

From this result, it is clear that the higher the temperature, the faster the ash elutes, and the temperature when storing the slurry was 70℃.
It can be seen that the effects of the present invention can be sustained over a long period of time by keeping the temperature below 50°C, preferably below 50°C.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the charge neutralization of coal particles caused by polyvalent metal ions eluted into a high-concentration coal-water slurry, so that even when stored for a long period of time, the properties of the slurry do not change and the viscosity becomes low. can be retained.

[Brief explanation of drawings]

Figure 1 is a graph showing the results of Example 1 of the method for stabilizing low viscosity of high concentration coal water slurry of the present invention, Figures 2 and 3 are graphs showing the results of Example 2 of the present invention, and Figure 4 is a graph showing the results of Example 2 of the present invention. Graph showing the results of Example 3 of the present invention.

Claims (1)

[Claims] 1. Silicic acid, boric acid, carbonic acid, sulfuric acid, sulfite,
A method for stabilizing a highly concentrated coal-water slurry with low viscosity, characterized by adding one of alkali metal salts of hydrofluoric acid or a mixture thereof. 2. Alkali metal salts of silicic acid, boric acid, carbonic acid, sulfuric acid, sulfurous acid, and hydrofluoric acid are added to the coal-water slurry, which is prepared by adding water and a surfactant to finely ground coal and adjusting the pH to 6 to 11. A method for stabilizing a highly concentrated coal-water slurry with low viscosity, characterized by adding one or a mixture thereof.