Method for recovering potassium chloride

Abstract

To provide a method for simply and efficiently recovering potassium chloride from chlorine bypass dust recovered by a chlorine bypass device installed in cement clinker manufacturing equipment.SOLUTION: A method for recovering potassium chloride from chlorine bypass dust recovered from a chlorine bypass device installed in cement clinker manufacturing equipment, involves a mother liquor preparation process (S1) where the chlorine bypass dust is mixed with water to remove insoluble components to yield a mother liquor from which insoluble components have been removed, and a precipitate recovery process (S2) to evaporate moisture so that a portion of the mother liquor remains to recover precipitates that have crystallized in the remaining mother liquor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering potassium chloride (KCl) from chlorine bypass dust recovered in a chlorine bypass device installed in a cement clinker production facility. [Background technology]

[0002] Potassium chloride is widely used for agricultural and industrial purposes, but domestic procurement is difficult, and most of it is imported. However, due to recent changes in the international situation, it is becoming more difficult to import as it is now difficult to obtain a stable supply of potassium chloride.

[0003] On the other hand, the cement industry is a mass production and mass consumption industry, and resource and energy conservation are continuing to be top priorities. The production of cement clinker involves a burning process using a burning kiln, and the effective use of this kiln for waste disposal contributes to resource circulation.

[0004] In such cement clinker production facilities, potassium chloride is generated within the production facilities due to the influence of chlorine contained in the cement clinker raw materials, incineration waste, burner fuel, etc., and this potassium chloride adheres to the inner walls of the facilities and causes duct blockages, impairing stable operation. For this reason, a chlorine bypass device is installed to discharge and treat chlorine-containing gas from the production facilities (see, for example, Patent Documents 1 and 2).

[0005] In a cement clinker manufacturing facility equipped with such a chlorine bypass device, gas is usually extracted from near the entrance (end of the kiln) of the calcination kiln, where the chlorine component is most concentrated, to the chlorine bypass device, and the chlorine concentration in the manufacturing facility is controlled so that the chlorine concentration of the cement clinker raw material before it is supplied to the calcination kiln is 1.0 mass% or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2022-154608 A [Patent Document 2] JP 2022-128169 A Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a method for simply and efficiently recovering potassium chloride from chlorine bypass dust recovered by a chlorine bypass device installed in a cement clinker production facility. [Means for solving the problem]

[0008] As described above, in conventional cement clinker production, in order to prevent the adverse effects of potassium chloride generation and to perform stable operation, chlorine is extracted from the production facility to the chlorine bypass device. In this chlorine bypass device, dust (chlorine bypass dust) is recovered, but the chlorine bypass dust has little value as a resource and is actually disposed of as waste.

[0009] The present inventors have focused on the fact that the chlorine bypass dust contains potassium chloride, and as a result of investigating and examining the components contained in the chlorine bypass dust, have found that potassium chloride can be easily and efficiently recovered by utilizing its solubility, and have completed the present invention. In addition, they have found that the potassium chloride concentration in the chlorine bypass dust can be sufficiently increased by increasing the chlorine concentration in the production facility as much as possible and supplying high-concentration chlorine to the chlorine bypass device.

[0010] That is, the present invention is as follows. [1] A method for recovering potassium chloride from chlorine bypass dust recovered from a chlorine bypass device installed in a cement clinker production facility, comprising: a mother liquor preparation step of mixing the chlorine bypass dust with water and removing insoluble components to obtain a mother liquor from which insoluble components have been removed; a precipitate recovery step of evaporating water so that a portion of the mother liquor remains, and recovering a precipitate precipitated in the remaining mother liquor; A method for recovering potassium chloride, comprising the steps of:

[0011] [2] The method for recovering potassium chloride according to the above [1], wherein in the precipitate recovery step, 8 to 18 vol % of the mother liquor is allowed to remain. [3] The precipitate recovery step a first recovery step of evaporating a portion of the mother liquor and then removing the precipitate; a second recovery step of evaporating the water and recovering the precipitate in the remaining mother liquor; The method for recovering potassium chloride according to the above [1] or [2], characterized by having:

[0012] [4] The method for recovering potassium chloride according to the above [3], wherein in the first recovery step of the precipitate recovery step, 50 to 75 vol % of water in the mother liquor is evaporated. [5] The method for recovering potassium chloride according to the above [3] or [4], wherein in the second recovery step of the precipitate recovery step, 8 to 18 vol % of the mother liquor is allowed to remain. [6] The method for recovering potassium chloride according to any one of the above [1] to [5], wherein the chlorine bypass dust has a chlorine concentration of 8 mass% or more.

[0013] [7] The method for recovering potassium chloride according to the above [6], wherein the chlorine concentration of the chlorine bypass dust is 12 mass% or more. [8] The method for recovering potassium chloride according to the above [7], characterized in that in the cement clinker production facility, the chlorine concentration of the cement clinker raw material before being supplied to a calcination kiln is adjusted to 1.2 mass% or more.

[0014] [9] The method for recovering potassium chloride according to the above [7] or [8], characterized in that a chlorine-containing fuel is supplied as fuel for a burner of a calcination system of the cement clinker production facility, and the chlorine concentration of the chlorine bypass dust is adjusted.

[10] The method for recovering potassium chloride according to [9] above, characterized in that the chlorine-containing fuel is waste plastic.

[11] The method for recovering potassium chloride according to any one of the above [7] to

[10] , characterized in that the chlorine concentration of the chlorine bypass dust is adjusted by adjusting the amount of exhaust to a chlorine bypass device of the cement clinker production facility. Effect of the Invention

[0015] According to the method for recovering potassium chloride of the present invention, potassium chloride can be recovered simply and efficiently. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a process flow diagram of a method for recovering potassium chloride according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a process flow diagram of a potassium chloride recovery method according to another embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic explanatory diagram of a cement clinker production facility for recovering chlorine bypass dust, which is a raw material in the potassium chloride recovery method of the present invention. [Figure 4] FIG. 1 is a schematic diagram for explaining the behavior of chlorine components in a cement clinker production facility for recovering chlorine bypass dust, which is a raw material in the potassium chloride recovery method of the present invention. [Diagram 5] FIG. 1 is a schematic diagram of a chlorine bypass device installed in a cement clinker production facility for recovering chlorine bypass dust, which is a raw material in the potassium chloride recovery method of the present invention. [Figure 6] FIG. 1 is a diagram showing an outline of a preliminary test of an embodiment. [Figure 7] FIG. 1 shows an outline of the test in Example 1. [Figure 8] FIG. 1 shows an outline of the test in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The method for recovering potassium chloride of the present invention is a method for recovering potassium chloride from chlorine bypass dust recovered from a chlorine bypass device installed in a cement clinker production facility, and is characterized by comprising a mother liquor preparation step (Step 1) of mixing the chlorine bypass dust with water and removing insoluble components to obtain a mother liquor from which the insoluble components have been removed, and a precipitate recovery step (Step 2) of evaporating water so that a portion of the mother liquor remains, and recovering precipitates precipitated in the remaining mother liquor (see FIG. 1 ).

[0018] In the potassium chloride recovery method of the present invention, potassium chloride can be recovered simply and efficiently by utilizing the difference in solubility of components contained in the chlorine bypass dust. That is, the chlorine bypass dust in the chlorine bypass unit contains alkali salts and sulfates that precipitate when the extracted gas is cooled, as well as cement raw materials (calcium components) that are drawn in during gas extraction. However, potassium chloride can be recovered efficiently by recovering the precipitate in a state in which calcium chloride, which has a higher solubility than potassium chloride, is dissolved in the mother liquor.

[0019] Here, chlorine bypass dust refers to a deposit (dust) that precipitates when gas extracted from a cement clinker manufacturing facility is cooled. Usually, air is extracted from the cement clinker manufacturing facility through an extraction duct from the vicinity of the inlet (end of the kiln) of the calcination kiln where the chlorine component is most concentrated in the cement clinker manufacturing facility.

[0020] Each step will be described below. [Mother liquor preparation process] The mother liquor preparation process is a process in which the chlorine bypass dust is mixed with water, and insoluble components are removed to obtain a mother liquor from which the insoluble components have been removed. Specifically, the chlorine bypass dust is mixed with water to obtain a chlorine bypass dust slurry, which is then filtered and washed to prepare the mother liquor.

[0021] The mixing ratio (mass ratio) of water to the chlorine bypass dust is not particularly limited as long as the amount is an amount that sufficiently dissolves potassium chloride, and is, for example, preferably 2.0 times or more, more preferably 3.0 times or more, and even more preferably 3.5 times or more, relative to the chlorine bypass dust. As the water, industrial water, tap water, groundwater, etc. can be used.

[0022] [Precipitate recovery process] The precipitate recovery step is a step of evaporating water so that a part of the mother liquor remains, and recovering the precipitate in the remaining mother liquor. For example, it is preferable to leave 8 to 18 vol% of the mother liquor, and more preferably leave 10 to 15 vol% of the mother liquor. This allows highly soluble calcium chloride and the like to remain in a dissolved state in the mother liquor, and a precipitate with a high potassium chloride concentration can be recovered. This precipitate may be used as it is, or potassium chloride may be purified. Note that leaving 8 vol% of the mother liquor means, for example, that the mother liquor, which is made by adding water to the chlorine bypass dust to make the total volume 1000 ml, is evaporated until the total volume becomes 80 ml.

[0023] The method for evaporating water is not particularly limited, and generally, a heat treatment is carried out. The heat treatment may be carried out under normal pressure or under reduced pressure.

[0024] This precipitate recovery step preferably includes a first recovery step and a second recovery step. Specifically, it preferably includes a first recovery step in which a part of the mother liquor is evaporated and then the precipitate is removed, and a second recovery step in which water is further evaporated and the precipitate in the remaining mother liquor is recovered.

[0025] (First recovery process) The first recovery step is a step of removing the precipitate after evaporating a part of the mother liquor. In this step, components with lower solubility than potassium chloride, such as calcium hydroxide and calcium sulfate, are precipitated, and the precipitate is removed by filtration or the like.

[0026] In this step, it is preferable to evaporate 50 to 75 vol % of the water in the mother liquor, and more preferably 60 to 75 vol % of the water. The first recovery step may be a treatment divided into a plurality of steps.

[0027] (Second recovery process) The second recovery step is a step of further evaporating water after the first recovery step and recovering precipitates in the remaining mother liquor. In this step, the precipitates (dust) containing high concentrations of potassium chloride are recovered by filtration or the like while components that are more soluble than potassium chloride contained in the chlorine bypass dust are left dissolved in water.

[0028] In this step, as explained in the above-mentioned precipitate recovery step, it is preferable to leave 8 to 18 vol % of the mother liquor, and more preferably 10 to 15 vol % of the mother liquor remaining.

[0029] [Mother liquor treatment process] The method for recovering potassium chloride of the present invention may include a mother liquor treatment step (Step 1') in which the mother liquor obtained in the mother liquor preparation step is treated with CO2 or an iron component is added to remove precipitates (heavy metals) (see FIG. 2). Examples of the iron component include ferrous chloride, ferrous sulfate, and ferric chloride. By adding an iron component, heavy metals such as Pb can be preliminarily co-precipitated and removed. At this time, a flocculant such as a polymer flocculant can also be used. The amount of the iron component to be added can be appropriately adjusted depending on the composition of the chlorine bypass dust (content of heavy metals), and is preferably about 0.1 to 2 mass % and more preferably about 0.2 to 1 mass % relative to the chlorine bypass dust solution (mother liquor). In addition, heavy metals such as Pb can be precipitated and removed as lead carbonate or the like by CO2 treatment. The pH may be adjusted to 6 or more using hydrochloric acid and / or sodium hydroxide.

[0030] Next, a facility or apparatus for recovering the chlorine bypass dust, which is the raw material in the potassium chloride recovery method of the present invention, will be described.

[0031] [Cement clinker manufacturing facility] The cement clinker production facility used in the method of the present invention is not particularly limited as long as it is a facility capable of producing cement clinker by burning cement clinker raw materials. For example, a general production facility that has been conventionally used for producing cement clinker, as shown in FIG. 3, can be used.

[0032] As shown in FIG. 3, the cement clinker production facility 1 has a rotary kiln (calcination kiln) 3, a preheater 5, a calciner 4, and a cooler 7, which are generally referred to as a calcination system.

[0033] The preheater 5 is equipped with multiple cyclones. The raw materials are supplied to the cyclones at the top of the preheater 5 and are preheated by the high-temperature exhaust gas from the rotary kiln 3. In the rotary kiln 3, the raw materials are burned at high temperatures by a burner 9 arranged on the outlet side (before the kiln) while rotating. In the rotary kiln 3, the side connected to the preheater 5 is called the kiln end, and the side connected to the cooler 7 is called the kiln front. The cooler 7 is used to cool the high-temperature burnt material (clinker) discharged from the kiln front.

[0034] Here, in the rotary kiln 3 of the cement clinker production facility 1, the raw material flow and the gas flow intersect, and chlorine brought into the rotary kiln 3 together with the cement clinker raw materials is vaporized in the rotary kiln 3, and the vaporized chlorine gas is returned to the calciner 4 and the preheater 5, adheres to the cement clinker raw materials again, and circulates through the firing system (see symbol A in FIG. 4).

[0035] Meanwhile, in the cement clinker production facility 1, gas is extracted to a chlorine bypass device 11 through an extraction duct 10 extending from the vicinity of the end of the rotary kiln 3. Reference numeral 12 denotes a raw material chute continuing from the lowest cyclone to the calcination kiln, which is a location where clogging due to potassium chloride is likely to occur (see reference numeral B in FIG. 4).

[0036] As shown in Fig. 5, the chlorine bypass device 11 is connected to an extraction duct 10 extending from near the end of the rotary kiln 3 of the cement clinker manufacturing facility 1, and relatively heavy dust is collected in a cyclone 13 and returned to the cement clinker manufacturing facility 1. Meanwhile, gas containing fine dust particles is sent to a cooler 14 where it is cooled, and the precipitate is collected in a dust tank 15 as dust called chlorine bypass dust.

[0037] In the method of the present invention, the chlorine bypass dust contained in the dust tank is used, and it is preferable to use chlorine bypass dust containing more potassium chloride. The chlorine bypass dust has a chlorine concentration of, for example, 8% by mass or more, preferably 12% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. Since potassium acting as a counter to chlorine is brought in in excess from the cement clinker raw material, etc., a large amount of potassium chloride is recovered according to the chlorine concentration. The chlorine concentration of the chlorine bypass dust is measured using fluorescent X-ray analysis.

[0038] In the method of the present invention, as described above, it is preferable to use chlorine bypass dust having a chlorine concentration of 12 mass% or more. As a method for obtaining chlorine bypass dust having such a high chlorine concentration, for example, there can be mentioned a method for adjusting (increasing) the chlorine concentration of the cement clinker raw material before being supplied to the calcination kiln to 1.2 mass% or more.

[0039] Methods for adjusting (increasing) the chlorine concentration of the cement clinker raw material before it is fed to the calcination kiln include adjusting the composition and / or amount of the fuel fed to the burner of the calcination system, adjusting the composition and / or amount of the waste incinerated in the calcination kiln, and adjusting the composition of the cement clinker raw material. Among these methods, the method for adjusting the composition and / or amount of the fuel fed to the burner of the calcination system and the method for adjusting the composition and / or amount of the waste incinerated in the calcination kiln are preferred because they allow for rapid adjustment of the chlorine concentration in the cement clinker facility, and the method for adjusting the composition and / or amount of the fuel fed to the burner of the calcination system is particularly preferred. Note that the adjustment of the composition refers to changing the input material to one containing more chlorine, and the adjustment of the amount refers to increasing the input amount (input ratio) of the material containing chlorine.

[0040] Specific examples of methods for adjusting the composition and / or amount of fuel supplied to the burner of the calcination system include a method of supplying a fuel with a higher chlorine content as fuel for the burner of the calcination system and increasing the amount (ratio) of the chlorine-containing fuel. Normally, carbon-containing fuels such as heavy oil and coal are used as the fuel (thermal energy source) for the burner, but in the present invention, it is preferable to use a chlorine-containing fuel as part or all of it. An example of the chlorine-containing fuel is waste plastic. Also, examples of the burner of the calcination system that supplies the chlorine-containing fuel include a burner installed in a calcination kiln and a burner installed in a calciner. EXAMPLES

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0042] [Preliminary Examination] A slurry of chlorine bypass dust was prepared by adding 3000 ml of water to 1000 g of chlorine bypass dust having a chlorine concentration of 9.2% by mass. The slurry was filtered and washed with 1000 ml of water to remove insoluble components, and about 4000 ml of filtrate was obtained (this filtrate was used in the following examples). 400 ml of the filtrate was taken out and used as a mother liquor. When all the water in this mother liquor was evaporated and dried, 35 g of precipitate was collected. An outline of the preliminary test is shown in FIG. 6. Table 1 shows the results of the component analysis of the collected precipitate. In the table, % indicates mass % (same below).

[0043] [Table 1]

[0044] [Example 1] A 400 ml portion was taken from the filtrate to be used as the mother liquor. Water was evaporated from the mother liquor until the remaining volume was 50 ml (87.5 vol% of the total volume was evaporated), and 22 g of the target precipitate containing potassium chloride was recovered. An outline of Example 1 is shown in FIG. 7. Table 2 shows the results of the component analysis of the recovered precipitate.

[0045] [Table 2]

[0046] [Example 2] A 400 ml portion was taken from the filtrate to obtain a mother liquor. Water was evaporated from the mother liquor until the volume was 100 ml (75 vol% of the total volume was evaporated), and the precipitate was removed by filtration. The amount of the precipitate was 6 g. Water was then evaporated until the volume was 50 ml (12.5 vol% of the total volume was evaporated), and 16 g of the target precipitate containing potassium chloride was recovered. An outline of Example 2 is shown in FIG. 8. The results of the component analysis of the recovered precipitate are shown in Table 3.

[0047] [Table 3]

[0048] When the remaining mother liquor was evaporated to dryness, 11 g of precipitate was obtained. The components of this precipitate were analyzed and the results are shown in Table 4.

[0049] [Table 4]

[0050] [Example 3] A 1000 ml portion was taken from the filtrate to prepare a mother liquor. 10 g of ferrous sulfate was added to this 1000 ml mother liquor, the pH was adjusted to 7 to 10, and the mixture was further filtered. 400 ml of this filtrate was taken to prepare a treated mother liquor. The same procedure as in Example 2 was carried out to obtain 17 g of the target precipitate containing potassium chloride. The results of the analysis of the components of this precipitate are shown in Table 5.

[0051] [Table 5]

[0052] [Example 4] Except for changing ferrous sulfate to ferrous chloride, the procedure of Example 3 was repeated to obtain 16 g of the target precipitate containing potassium chloride. The components of this precipitate were analyzed, and the results are shown in Table 6.

[0053] [Table 6]

[0054] As shown in Tables 2 to 6, precipitates containing high concentrations of chlorine and calcium were recovered according to the methods of Examples 1 to 4. Moreover, in Examples 3 and 4 in which an iron component was added, heavy metals were reduced. [Industrial Applicability]

[0055] INDUSTRIAL APPLICABILITY The method for recovering potassium chloride of the present invention is industrially useful since it can recover potassium chloride from chlorine bypass dust simply and efficiently. [Explanation of symbols]

[0056] 1. Cement clinker manufacturing facility 3. Rotary Kiln 4. Calcination furnace 5 Preheater 7. Cooler 9. Burner 10 Extraction Duct 11 Chlorine Bypass Unit 12 Raw material chute 13. Cyclone 14 Cooler 15 Dust Tank 16 Bag Filter

Claims

1. A method for recovering potassium chloride from chlorine bypass dust recovered from a chlorine bypass device installed in a cement clinker production facility, comprising: a mother liquor preparation step of mixing the chlorine bypass dust with water and removing insoluble components to obtain a mother liquor from which insoluble components have been removed; a precipitate recovery step of evaporating water so that a portion of the mother liquor remains, and recovering a precipitate precipitated in the remaining mother liquor; A method for recovering potassium chloride, comprising the steps of:

2. 2. The method for recovering potassium chloride according to claim 1, wherein in the precipitate recovery step, 8 to 18 vol % of the mother liquor is allowed to remain.

3. The precipitate recovery step comprises: a first recovery step of evaporating a portion of the mother liquor and then removing the precipitate; a second recovery step of evaporating the water and recovering the precipitate in the remaining mother liquor; 2. The method for recovering potassium chloride according to claim 1, further comprising the steps of:

4. 4. The method for recovering potassium chloride according to claim 3, wherein in the first recovery step of the precipitate recovery step, 50 to 75 vol % of water in the mother liquor is evaporated.

5. 5. The method for recovering potassium chloride according to claim 4, wherein in the second recovery step of the precipitate recovery step, 8 to 18 vol % of the mother liquor is allowed to remain.

6. The method for recovering potassium chloride according to any one of claims 1 to 5, characterized in that the chlorine bypass dust has a chlorine concentration of 8 mass% or more.

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