JPS62205193A - Storage of coal water slurry in high concentration - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a technology for producing a highly concentrated coal-water slurry by mixing pulverized coal and water to create a slurry with a low viscosity that can be transported through pipes. The present invention relates to a method of reducing the viscosity of a slurry and preventing thickening of the slurry over time during storage.

(Prior art) Powder slurry transportation technology has been researched for a long time as a method of transporting solid powder in the form of an easy-to-handle fluid.In recent years, coal's natural There is no need to worry about ignition or dust scattering, it is safe, and since it can be transported through pipes, it is easy to handle, and technology for producing highly concentrated coal-water slurry is being actively developed as a method that can improve transport efficiency. As previously disclosed, conventional high-concentration coal-water slurry is made by adjusting the particle size distribution of pulverized coal and water with pulverized coal prepared so that the void ratio is as small as possible. By mixing coal with 6
The content was 0 to 70% by weight or more.

The highly concentrated coal water slurry prepared in this way is too
It has a viscosity of ~2000 cP and has sufficient flow characteristics to be transported through pipes as a fluid. However, such a highly concentrated coal-water slurry is packed with one coal particle very densely, and in its fluid state. Individual coal particles are constantly colliding with other coal particles. In a slurry containing such a high concentration of coal, slight changes in slurry composition,
The mixing of small amounts of impurities into slurry can significantly change its flow characteristics, and if such changes in flow characteristics occur during pipeline transportation of high-concentration coal-water slurry, problems such as pipeline blockage may occur. It turns out.

The viscosity of a high-concentration coal-water slurry is greatly influenced by its p I-1 value, and it is generally well known that the higher the PH value, the lower the viscosity of the slurry.

This is thought to be because changes in the hydrogen ion concentration in the slurry medium change the amount of charge on the surface of the coal particles, change the action of the surfactant adsorbed on the surface of the coal particles, and change the interaction between particles. It will be done. In this way, the highly concentrated coal-water slurry is packed with coal particles very densely, and the distance between the particles is very small, so even a slight change in the interaction between particles can change 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 the water slurry of coal is generally acidic. In addition, coal contains ash, the main components of which are silica and alumina, but also chromium,
Since it contains vanadium, iron, and other heavy metals, these heavy metals are eluted in the acidic slurry and increase the slurry viscosity over time.

In order 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. It is not a fundamental solution.

Additionally, there is a method of adding anionic alkali metal salts or complexing agents that form insoluble salts with metal ions during slurry production (Japanese Patent Application Laid-open No. 59-206491), but the elution of metal ions from coal is extremely difficult. Because the process progresses gradually, if the slurry is stored for a long period of time, the amount added at the time of production alone will not be enough.If a large amount of this additive is added at the time of production, the sedimentation of coal particles will increase, so storage should be stabilized. In order to do this, it is necessary to keep the amount added during production to the minimum necessary, and this is still not a fundamental solution for preventing an economic increase in slurry viscosity.

[Problem that the invention seeks to solve]

The dispersion medium of highly concentrated coal-water slurry is water, and whether the slurry is
Once the coal particles are formed, 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 is a mixture of carbonaceous matter and ash composed of silica, alumina, and other metal salts. A portion of the ash is exposed on the particle surface through crushing.

Therefore, the ash content in the coal that is present in the highly concentrated coal-water slurry is also in constant contact with water, and some components of it 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, it is generally made alkaline by adding loading soda, etc. However, the ash content 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 production of highly concentrated coal-water slurry. Some are difficult to manufacture.

Furthermore, when the slurry is stored for a long period of time, the elution of ash progresses over time, so the slurry viscosity gradually increases.

[Means for solving problems]

As mentioned above, in high-concentration coal-water slurry, dispersion medium (water)
The elution of ash into the water is unavoidable. Therefore, in order to make high-concentration coal-water slurry into a truly high-concentration, low-viscosity slurry, the ash that has eluted as described above must be removed from the water by some method. , it is necessary to eliminate that influence.As described below, the present inventors have developed the following method based on the results of considering the viscosity reduction mechanism of high-concentration coal-water slurry. As a means of removing the cations generated from the dispersion medium, it is possible to add anions that combine with the cations to form water-insoluble salts, or to add anions that combine with the cations to form extremely stable salts. We came up with a method to remove the influence of cations by adding a complexing agent that forms a complex salt.

[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 the viscosity of the slurry, and this surfactant is usually anionic. The added surfactant makes the surface of the coal adsorbed on the surface of the coal particles hydrophilic by its hydrophobic groups, thereby negatively charging each coal particle. 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. The reason why the viscosity of a highly concentrated coal slurry can be reduced by adding an anionic surfactant is due to the above-mentioned two effects of the surfactant. That is, first, by making the surface of the coal particles hydrophilic, it is possible to increase the amount of water around the coal particles.
1. Forming a film to prevent coal particles from aggregating with each other due to steric hindrance.Secondly, by negatively charging the coal particles, electrostatic repulsion is generated between the coal particles to prevent coal particles from agglomerating with each other. This reduces the viscosity of the slurry.

The first action can be achieved with nonionic surfactants instead of anionic surfactants, but in high-concentration coal-water slurry, the coal concentration is 70% by weight or more. In such a highly concentrated slurry, the coal particles are packed very closely together, making them very close to each other. play an important role. For this reason, anionic surfactants are particularly used in highly concentrated coal-water slurries.

Thus, in a highly concentrated coal-water slurry, the charge on the particles is thought to play a very important role in reducing the viscosity, and under conditions that reduce the amount of charge on the particles, the slurry viscosity increases. As is well known, the amount of charge of negatively charged hydrophilic colloid particles varies greatly depending on the N cations and the concentration in the solvent. Is this negative? This is because cations are selectively adsorbed around iF-charged particles and neutralize the charge on the particles, and the stronger the adsorption of cations, the smaller the amount of charge on the particles. The adsorption of cations onto negatively charged particles is related to the safety of hydrophilic colloids and has been studied for a long time. As is well known, adsorption of cations to negatively charged particles is strongest for H+ ions, followed by polyvalent metal ions, which 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 found that P H
We discovered that there are some phenomena that cannot be explained by change alone.

That is, when a high concentration coal water slurry is heated and stored for a long time, the slurry particle size increases with the passage of time. and,
Analysis of the supernatant liquid of the slurry revealed that the concentration of cations such as calcium and magnesium had increased significantly compared to when the slurry was manufactured. The inventors have already

Anions that form poorly soluble salts with polyvalent metal ions as a means of removing polyvalent metal ions in the slurry.

Alternatively, the addition of complexing agents that form stable metal complexes can mask harmful polyvalent metal ions and prevent the adsorption of these metal ions onto coal particles, reducing the Although a method for producing a slurry with stable properties by increasing its viscosity has been disclosed, even when the slurry produced in this way is stored for a long period of time, the cation solubility in the supernatant increases as described above, and the slurry becomes viscous. It was observed that the viscosity of

Based on this new fact, the present inventors hereby provide a method for preventing thickening of stored slurry over time by constantly monitoring the calcium ion concentration in the slurry, and when the measured value becomes larger than a predetermined tolerance value. We found a method in which an anion that forms a poorly soluble salt with the above polyvalent metal ion or a complexing agent that forms a stable metal complex is added in accordance with the above measured calcium ion concentration.

〔Example〕

<Example 1> Coal was ground in a ball mill in the coexistence of water and an anionic surfactant to prepare a highly concentrated coal-water slurry. The particle size distribution of the coal after pulverization is 97% below 60 mesh, 10
89% below 0 metshu.

200 mesh or less 80%, 400 mesh or less 55%
Met. The coal concentration in the slurry was 62% by weight, and the anionic surfactant was added in an amount of 0.5% by weight based on the coal. This slurry was heated to 20℃ and 50℃.

When an egg storage test was conducted for one day at a temperature of 70°C, it was found that the slurry viscosity increased. The viscosity of the slurry immediately after production is 700. It was pa・S, but it was 20.50.
The viscosity of the slurry after Miki storage test at 70℃ is 720
,950. and increased to 1500-Pa·8. Incidentally, the coal concentration in the slurry during viscosity measurement was all adjusted to 62x, which is the value immediately after production.

The concentrations of Ca'' and MgQ+ in the supernatant of each slurry were measured, and it was found that the concentrations of each ion increased in the slurry stored at high temperatures.Table 1 shows the analysis results.

Table 1 The degree of thickening due to storage and the absolute value of the elution amount of the above ions vary depending on the type of coal used for the slurry, but the above trends are common to all types of coal.

In addition, in the above test, the pH was adjusted to 7.9 during slurry production.
However, the slurry pH after the storage test was also approximately 7.9.
In this test, almost no change in pH was observed. Silicic acid was selected as an anion that combines with polyvalent metal ions to form an insoluble salt in the slurry after storing eggs for days at 70°C, and after adding an aqueous solution of sodium silicate to the slurry, the viscosity of the slurry was measured. 700 at 62% concentration
．． pa·3, and it was found that the viscosity returned to that immediately after production.

<Example 2> The slurry produced in Example 1 was subjected to a storage test using the apparatus shown in FIG. 1 to confirm the effects of the present invention. In storage tank 1, the slurry was kept warm and stored. In order to prevent coal particles in the slurry from settling during storage, the slurry in the tank 1 was circulated using a pump 2 and piping 3, and the slurry in the tank was stirred by a stirring blade 4. Calcium ions (Ca2+) in the slurry in the tank were measured once using a calcium ion electrode 5 and a detector 6 inserted into the tank. When the calcium ion concentration reached 1100 pp or more, the aqueous solution of sodium silicate stored in the drug tank 9 was supplied into the storage tank 1 using the metering pump 8. The pump 8 was controlled by a pump control Ja7, and the supply of sodium silicate was stopped when the concentration of Calcilla 11 ions detected by the calcium ion electrode 5 and the detector 6 reached 50 ppm.

In this way, the slurry was stored at 70°C, where the viscosity increase was greatest in Example 1.

When we investigated the tendency of the egg to thicken, we found that even after leaving the egg for a day,
Even after being left for 60 days, the slurry viscosity was exactly the same as that immediately after production.During the 0 bottle storage test, the sodium silicate aqueous solution
It was injected once a day, and the amount of each injection was about 1.6 Q per ton of slurry. However, the concentration of the sodium silicate aqueous solution in the chemical tank was 20% by weight.

This example revealed that the method of the present invention can prevent slurry from increasing in viscosity and maintain stable properties during storage. In this example, sodium silicate was used as an additive. Additives include anionic alkali metal salts that combine with polyvalent metal ions to form grass-soluble or insoluble salts, or organic salts that combine with polyvalent metal ions to form highly stable complex compounds. or.

If an inorganic complex forming agent is used, the same effects as in this example can be obtained, and this example is not intended to limit the scope of the present invention. Examples of additives other than sodium silicate include sodium A phosphate, EDTA, and sodium bromate.

<Example 3> In order to investigate the eluted components of coal ash, two types of coal were immersed in water with various pH values, and the ions eluted were analyzed. Coal was pulverized, and coal with a particle size of 37 to 105 μm was separated. 60g of this coal was mixed with 30g of water adjusted to various pH values.
After being immersed in 0 g for about - months, the composition of the supernatant liquid was analyzed. pH during soaking;! 11a was carried out by sequentially adding hydrochloric acid or an aqueous sodium hydroxide solution to keep the pH constant. The analysis results of the purified liquid are shown in Figures 2 and 3. The elution amount of each component differs depending on the type of coal, but the elution amount of iron, aluminum, etc. ions decreases as the pH increases, and 1. p of concentrated coal water slurry
It can be seen that when the pH reaches the pH range of 7 to 9, the elution amount becomes almost zero. On the other hand, Ca” ten and M
gt+ indicates that a considerable amount of coal is eluted even in the above pH range, and these two ion species are the main cause of the thickening of the slurry over time shown in Example 1. I understand that. In Example 2, the Ca 2+ concentration in the slurry was detected as the criterion for additive injection, but from the results of this example, it was found that the Mg 2+ concentration could be used as the criterion, and that the criterion could be changed depending on the type of coal. It can be seen that it is necessary to select the substance in advance.

〔Effect of the invention〕

According to the present invention, during long-term storage of high-concentration coal-water slurry, increase in slurry viscosity due to polyvalent metal ions eluted into the slurry can be prevented, so that the properties at the time of manufacture can always be maintained.

In Example 2, the additive aqueous solution was put into the tank (
(Fig. 1), the place where the slurry is added is preferably a place where the slurry is being stirred. In this sense, the input position is circulation pipeline 3.
Inside or near the stirring blade is best.

In Example 2, Ca''+ ion concentration was added until it became below a predetermined amount, but since the necessary addition amount can be calculated in advance from the slurry discharge in the storage tank and the measured ion concentration, this necessary amount was added by the pump controller 7. It is also conceivable to control the pump 8 so as to add it.

[Brief explanation of drawings]

Claims (1)

[Claims] 1. The concentration of cations in the highly concentrated coal-water slurry is measured constantly or intermittently, and when the value exceeds a predetermined value, an alkali metal salt of an anion combined with a polyvalent metal ion, or A method for storing a highly concentrated coal-water slurry, characterized by adding a complex forming agent that forms a complex compound combined with polyvalent metal ions.