WO2013057981A1 - Process for dewatering slurry - Google Patents

Abstract

Provided is a process for simply improving the handleability of a thixotropic slurry in transportation and so on. A process for dewatering a slurry which has a thixotropic region, including a step of dewatering the slurry by pressure filtration to a water content lower than that at the lowest flow value.

Description

Slurry dewatering method

The present invention relates to a method of dewatering slurry such as clay, sand, industrial waste containing fine powder such as dust captured in a wet dust collection process, and sludge. The present invention also relates to a method for producing an industrial raw material using the slurry as a raw material.

In general, industrial waste containing fine powders such as clay, sand, and dust collected in the wet dust collection process, and sludge slurry can be reused or recycled as industrial raw materials to reduce waste. Is important from the viewpoint of global environmental conservation. However, some of these slurries exhibit thixotropic properties. In this case, since the viscosity of the slurry increases with time, handling such as transportation is difficult, which has been an obstacle to reuse or recycling as an industrial raw material.

Therefore, in Japanese Patent Application Laid-Open No. 2000-160152 (Patent Document 1), muddy water is kept quiet for a long time in a muddy water tunnel excavation method such as a mud type shield method, a muddy water type propulsion method, and an earth pressure type shield method using a muddy water transport method. However, in order to return the mud water to a low viscosity mud again, a long and powerful stirring device is required. By adding an acid salt alone or adding an oligophosphate and a specific unsaturated carboxylic acid polymer salt in combination at a specific ratio and maintaining the oligophosphate in the muddy water at a specific concentration, It describes how to prevent the increase economically and accurately. Further, it is described that the classification performance of the earth and sand separator, particularly the centrifugal separator, is prevented, the increase in the specific gravity of the muddy water can be prevented efficiently, and the excavation efficiency can be increased.

JP 2000-160152 A

However, in the method described in Japanese Patent Laid-Open No. 2000-160152 (Patent Document 1), the addition of an additive is a method for suppressing the thixotropy of cutting mud water. Therefore, the control is complicated, and an additive is added. In addition, since it is a chemical treatment method in which the effect of the additive differs depending on the target substance such as the pH of mud for cutting, it is not universal.

The present invention has been created in view of the above circumstances, and provides a method for easily improving handling properties such as transportation to a slurry exhibiting thixotropy by a method different from the method of adding an additive. Let it be an issue.

As a result of intensive investigations to solve the above problems, the present inventors have found that even in a slurry exhibiting thixotropy, there are regions where thixotropy develops due to moisture content and regions where thixotropy does not develop. It was. In addition, when focusing on the relationship between the flow value and the water content, which is an index of the fluidity of the slurry, the flow value decreases as the water content of the slurry decreases. Found that the flow value soared. According to the results of the study by the present inventors, it was found that in a region where the water content is smaller than the water content at which the flow value is the lowest point, the slurry no longer has thixotropy and becomes a cake and can be transported stably. It was. This invention is completed based on the said knowledge, and is specified by the following.

In one aspect, the present invention is a method for dehydrating a slurry having a thixotropic region, the method including a step of dehydrating the slurry to a moisture content lower than a moisture content at which the flow value is the lowest point by pressure filtration. It is.

In one embodiment, the method for dewatering a slurry having a thixotropic region according to the present invention is as follows. When the water content at which the flow value is the lowest point is a (%), the water content x (%) of the slurry after dehydration is: The following formula: a-5 ≦ x <a is satisfied.

In another embodiment of the method for dehydrating a slurry having a thixotropic region according to the present invention, pressure filtration is performed by a filter press.

In yet another embodiment of the method for dewatering a slurry having a thixotropic region according to the present invention, the filter cloth washing step is performed between the end of the dehydration step by pressure filtration and the start of the next dehydration step. .

In another embodiment of the method for dehydrating a slurry having a thixotropic region according to the present invention, the slurry contains slaked lime.

In still another embodiment of the method for dehydrating a slurry having a thixotropic region according to the present invention, the slaked lime is slaked lime in dust collected in a wet dust collecting step of a calcium carbide electric furnace.

In another embodiment of the method for dehydrating a slurry having a thixotropic region according to the present invention, the slurry contains hydrotalcite and / or carbon.

In another embodiment of the method for dehydrating a slurry having a thixotropic region according to the present invention, the slurry contains 1 to 10% by mass of hydrotalcite and / or 1 to 15% by mass of carbon.

In another aspect, the present invention is a cake obtained by performing the dehydration method described above.

In yet another aspect, the present invention is a method for producing an industrial raw material, including performing the dehydration method described above.

In one embodiment of the method for producing an industrial raw material according to the present invention, the slurry contains slaked lime, and the industrial raw material is a clinker raw material.

Further another aspect of the present invention is a clinker manufacturing method including a step of supplying a clinker material obtained by the above manufacturing method to a firing furnace after a step of transporting the raw material of the clinker by a screw conveyor.

In one embodiment of the method for producing a clinker according to the present invention, the clinker is calcium sulfoaluminate (CSA) or cement clinker.

According to the present invention, it is possible to easily improve handling properties such as transportation for a slurry exhibiting thixotropy without adding an additive to the slurry. For this reason, clay, sand, industrial waste containing fine particles such as dust collected in the wet dust collection process, and sludge such as sludge have been effectively used so far, which have been difficult to reuse or recycle as industrial raw materials. become able to.

An example of the flowchart of the method of spin-drying | dehydrating the slaked lime containing slurry collected at the wet dust collection process of the calcium carbide electric furnace using this invention is shown. An example of the flowchart of the method of transporting the slaked lime cake obtained through the dehydration method concerning this invention to a clinker baking furnace is shown. It is a figure which shows the relationship between the moisture content of the slaked lime collected by the wet dust collection process of the calcium carbide electric furnace, and a flow value. It is a figure which shows the relationship between the moisture content of the slaked lime byproduced with the acetylene generator, and a flow value.

In the present invention, a slurry having a thixotropic region is to be treated. Even if the slurry contributes to the expression of thixotropic properties such as dust generated from an electric furnace for producing clay or calcium carbide, the thixotropic properties are generally not expressed in a high water content state. As the water content decreases, thixotropy develops. Since it is difficult to strictly determine whether a substance has thixotropy, in the present invention, the flow value decreases as the moisture content decreases, and the region where the flow value is 150 mm or less is referred to as “thixotropic region”. Is defined.

Specific examples of the slurry having a thixotropic region include, but are not limited to, clay, sand, industrial waste containing fine powder such as dust captured in a wet dust collection process, and sludge such as sludge. A typical example is a slurry obtained by capturing dust generated from an electric furnace for producing calcium carbide in a wet dust collecting process (hereinafter referred to as “electric furnace-generated slurry”).

In one embodiment, the electric furnace-generated slurry contains hydrotalcite, and typically contains 1 to 10% by mass, more typically 2 to 8% by mass, which is effective for developing thixotropy. It is thought that it has contributed. In addition, in one embodiment, the slurry contains carbon in the form of graphite, and typically contains 1 to 15% by mass, more typically 5 to 15% by mass, which is a thixotropic property. It is thought that it contributes to the expression of.

A large amount of dust containing slaked lime as a by-product was generated from the electric furnace for producing calcium carbide, but it was not used for use because of its thixotropy and was generally discarded. Therefore, it is important to find out how to use slaked lime contained in dust. If this slaked lime is used as a raw material for cement, it can be used as a lime raw material instead of limestone, and it is possible to reduce the amount of CO ₂ generated from the cement kiln, which has great utility but has thixotropic properties. When transporting with transportation equipment such as bucket elevators and screw conveyors in the manufacturing process, the torque of rotating machinery increases, transportation stops due to adhesion to transportation equipment, and it is difficult to stably transport without trouble with transportation equipment. Was blocked. ADVANTAGE OF THE INVENTION According to this invention, the method of improving easily handleability, such as transport with respect to the slurry which has the above thixotropic regions, can be provided.

The inventor focused on the relationship between the flow value and the moisture content of the slurry having a thixotropic region. As the moisture content of the slurry decreased, the flow value decreased and the flow value was 150 mm or less. Then, the slurry is no longer bulky and highly integrated, which places a heavy load on the transportation equipment. However, it has been found that the flow value increases rapidly when the water content falls to a certain level. And it turned out that thixotropic property lose | disappears by making it into a moisture content smaller than the moisture content from which a flow value becomes the lowest point, it becomes cake shape and can be transported stably. In addition, on the measurement principle of the flow value, the lower limit of the flow value is 100 mm.

Therefore, in one embodiment of the present invention, a step of dehydrating the slurry having a thixotropic region to a moisture content lower than the moisture content at which the flow value becomes the lowest point is performed by pressure filtration. The flow value is an index of plastic fluidity, and is determined by a flow test (physical test method for JIS R 5201 cement). However, excessive dehydration consumes wasteful energy and is uneconomical. Therefore, when the moisture content at which the flow value is the lowest point is a (%), the moisture content x ( %) Is preferably dehydrated so as to satisfy a-5 ≦ x <a, and more preferably dehydrated so as to satisfy a-2 ≦ x <a. The water content is defined as the mass percentage obtained by dividing the water that evaporates when the slurry is dried and dehydrated at 105 ° C. by the solid content that does not reduce the weight (JIS A 1125 Aggregate Moisture Test Method and Surface Water Content Based on Water Content Test method).

The reason why the dehydration is pressure-filtered is that it is difficult to sufficiently reduce the water content by other dehydration methods such as vacuum filtration, vacuum filtration, and heat drying. As a method of pressure filtration, a filter press in which filter plates are arranged in a filter chamber and a filter cloth is sandwiched therebetween, and sludge is pressed into the filter chamber to perform filtration and dehydration is preferable. In addition, since the filter cloth is washed between the end of the dehydration process by pressure filtration and the start of the next dehydration process, clogging of the filter cloth is prevented, and continuous processing becomes possible. . Further, since the slurry components adhering to the filter cloth are deposited and cause clogging, it is preferable to maintain the wet state by immersing the filter cloth in water without drying the filter cloth after washing the filter cloth. . As such a method, for example, a method described in JP-A-2001-25612 can be mentioned.

The slurry dehydrated by the dehydration method according to the present invention no longer has thixotropy, is cake-like and can be easily transported, and can be used as various industrial raw materials depending on the components contained. For example, a slaked lime-containing cake obtained by dehydrating an electric furnace-generated slurry can be used as a clinker production raw material. A clinker is a pulverized product containing one or more minerals that is fired until a part of its components melts (semi-molten state), and is baked into a lump, and the type is particularly limited. Illustrative examples include calcium sulfoaluminate (CSA) and clinker such as cement. Calcium sulfoaluminate typically has CaO, CaSO ₄ , and Al ₂ O ₃ as chemical compositions, and CaO, CaSO ₄ , 3CaO · 3Al ₂ O ₃ · CaSO ₄ (Yelimeite, or It is a reaction product containing a chemical substance called Hauine and defined in CAS No. 12005-25-3.

FIG. 1 schematically shows a series of steps until dust discharged from an electric furnace for producing calcium carbide is dehydrated by a filter press. The exhaust gas containing dust from the electric furnace 101 for producing calcium carbide is separated from the exhaust gas by a wet dust collector 102 such as a spray tower, a cyclone scrubber, a venturi scrubber, and a tiezen washer and recovered as a slurry. This slurry settles in the sedimentation pit 103, and then stays and stirs in the thickener 104, and then is supplied to the filter press 105 to be dehydrated to become a slaked lime cake. The filtrate discharged from the filter press 105 can be reused repeatedly in the sedimentation pit 103.

The cake obtained by the dehydration method according to the present invention can be dry-transported as a powder by crushing, for example, by a screw conveyor or a bucket elevator. In FIG. 2, the process example in the case of carrying out dry transport of the slaked lime cake and throwing into a clinker baking furnace is shown typically. When the slaked lime cake is put into the slaked lime receiving hopper 201, it is temporarily stored in the slaked lime tank 204 through the screw conveyor 202 and the bucket elevator 203. Thereafter, the material is supplied to the raw material crusher / dryer 206 by the screw conveyor 205, pulverized to a predetermined size and dried, and then charged into a firing furnace 207 such as a cement kiln. The conditions of the firing furnace may be appropriately adjusted depending on the type of clinker. For example, when firing CSA, firing is performed at a temperature of about 1100 to 1300 ° C.

Examples of the present invention will be described below, but these are for illustrative purposes and are not intended to limit the present invention.

Below, the origin of the slaked lime slurry used for the Example and the comparative example is shown.
(1) Lime content Slaked lime 1: Dust captured in the wet dust collection process of the calcium carbide electric furnace.
Slaked lime 2: By-product slaked lime generated in the process of producing acetylene gas by the carbide method.
Table 1 shows the composition and average particle size of these slaked lime. In the table, chemical components were measured by JIS R5202 (chemical analysis method for cement). However, fixed carbon was measured according to JIS M8812 (coal and coke-industrial analysis method), and CO ₂ was measured according to JIS R 9011. The moisture content was measured according to JIS A 1125 with an infrared moisture meter (model FD610, manufactured by kett). Igloss is the loss on ignition, and was measured according to the test method for loss on ignition of soil (Geotechnical Society standard) JGS0221: 2009. The carbon morphology was measured by X-ray diffraction. Hydrotalcite was determined from the diffraction intensity by powder X-ray diffraction using an X-ray diffraction Rietveld method “SIROQUANT Version 2.5” (manufactured by Sitronics). The average particle diameter was 50% of the volume-based cumulative fraction measured by JIS R 1629 (a method for measuring particle size distribution by laser diffraction / scattering method of fine ceramic raw material). In the table, FC means fixed carbon.

<Test for slaked lime 1>
When the relationship between the water content and the flow value when the slurry of slaked lime 1 was dehydrated by a filter press, the results shown in FIG. 3 were obtained. As can be seen from FIG. 3, the flow value decreases as the moisture content gradually decreases from 169%, but the flow value rapidly increases when it falls below 67%. When the transportability (current value of the screw conveyor) of the slaked lime 1 slurry at each water content was evaluated, the flow value reached the lowest point from 150 mm or less in the region where the flow value decreased with the decrease in the water content. Up to 20A was shown, but at a moisture content lower than 67%, which is the lowest moisture content, the current value of the screw conveyor suddenly decreased and the transportability was remarkably improved.

Using a slurry of slaked lime 1, the filter press was continuously carried out for 1 week under the conditions shown in Table 2.
* 1: Slaked lime 1 + limestone refers to an input to a filter press in which 10 parts by mass of limestone with a sieve opening of 2 mm is added to 100 parts by mass of the slurry of slaked lime 1 and the apparent solid content concentration is approximately doubled. .
* 2: Regarding the type of filter press, “A” is “ISDNC-R type filter plate outside dimensions (length and width)” × Number of rooms: 1500 × 25 made by Ishigaki Co., Ltd. It is “single filter cloth running”, and has a function of rinsing the filter cloth with water after the dehydration process is completed and immersing the filter cloth in the water by pouring water into the filter chamber until the start of the next dehydration process. B is “MAFS filter plate outer dimensions (length and width) × room number: 100 × 36 automatic filter press” manufactured by Makino Co., Ltd., and water is poured into the filter chamber and the filter cloth is immersed in the water. Has no function.
* 4: In Experiment No. 6, after dehydration, the dehydrated slaked lime cake was pushed out by a twin screw conveyor with a dryer "Satake Biaxial Multipurpose Dryer SRA", and steam was supplied into the screw side plate jacket. It was dried at a surface temperature of 200 [° C.].
* 5: In the transportation process, slaked lime was received with a hopper by a dump truck, and slaked lime was transported with a screw feeder. At this time, in Experiment Nos. 4 to 6, the moisture content of the cake was reduced by mixing slaked lime with a low moisture content.
* 6: In the transportation process, when the screw shaft motor is not overloaded and can be transported without equipment failure, it is marked as ◯. In the transportation process, the current overload fluctuation of the screw shaft motor is large and the torque is large. The case where the equipment failure such as abnormal current or shaft breakage occurred and transportation was impossible during one week was marked as x.

The results after one week of operation are shown in Table 2. In the experimental example where the transportation is impossible, the result is shown.
In Experiment No. 1, dehydration was continuously performed until the water content was lower than the water content at which the flow value was the lowest point until the end of the test. The transportation in the transportation process was also good.
In Experiment No. 2, at the start of operation, the flow value was dehydrated to a moisture content lower than the lowest moisture content and transport was good, but water was poured into the filter chamber and the filter cloth was immersed in water. Since a filter press that does not have the function to perform was used, the performance of the filter press gradually deteriorated, and as the water content increased, it entered the thixotropic region and became impossible to transport during the test.
In Experiment No. 3, the solid content concentration before dehydration was increased compared to Experiment No. 2, but as in Experiment No. 2, the performance of the filter press gradually deteriorated and entered the thixotropic region as the water content increased. During the test, transportation became impossible.
Experiment No. 4 differs from Experiment No. 2 in that the moisture content of the cake was reduced by mixing slaked lime with a low moisture content in the transport process. Although the overall moisture content itself was low, it was expected that there would be no problems in transportation. However, as in Experiment No. 2, the performance of the filter press gradually deteriorated and the moisture content increased and entered the thixotropic region. Transportation became impossible on the way. Although it is not intended that the present invention be limited by theory, as slaked lime 1 enters the thixotropic region and becomes a highly integrated mass as the dewatering power of the filter press decreases, other slaked lime with low moisture content It is thought that the mixing was not successful even if the addition was added, and the effect could not be eliminated sufficiently.
Experiment No. 5 differs from Experiment No. 2 in that the solid content concentration before dehydration is increased and the moisture content of the cake is lowered by mixing slaked lime with a low moisture content in the transport process. Although the overall moisture content itself was low, it was expected that there would be no problems in transportation. However, as in Experiment No. 2, the performance of the filter press gradually deteriorated and the moisture content increased and entered the thixotropic region. Transportation became impossible on the way.
In Experiment No. 6, the operation of drying after dehydration was performed with respect to Experiment No. 5, but the water content of the slaked lime 1 was not sufficiently reduced. It became impossible to transport during the test.

<Test for slaked lime 2>
When the relationship between the water content when the slurry of slaked lime 2 was dehydrated by a filter press and the flow value was examined, the results shown in FIG. 4 were obtained. From FIG. 4, the flow value decreases as the water content gradually decreases from 80%, the flow value reaches the lowest point (about 161 mm) near the water content of 40%, and the flow value gradually increases. I understand. The slurry of slaked lime 2 at each moisture content did not show thixotropic properties at any moisture content. In addition, transportation with a screw feeder was possible regardless of the moisture content.

101 Calcium Carbide Manufacturing Electric Furnace 102 Wet Dust Collector 103 Sedimentation Pit 104 Thickener 105 Filter Press 201 Slaked Lime Accepting Hopper 202 Screw Conveyor 203 Bucket Elevator 204 Slaked Lime Tank 205 Screw Conveyor 206 Raw Material Crushing Dryer 207 Firing Furnace

Claims (13)

1. A method for dehydrating a slurry having a thixotropic region, the method comprising a step of dehydrating the slurry to a moisture content lower than the moisture content at which the flow value is the lowest point by pressure filtration.
2. 2. The method according to claim 1, wherein the water content x (%) of the slurry after dehydration satisfies the following formula: a-5 ≦ x <a, where a (%) is the water content at which the flow value becomes the lowest point. .
3. The method according to claim 1 or 2, wherein the pressure filtration is performed by a filter press.
4. The method according to any one of claims 1 to 3, wherein a filter cloth washing step is performed between the end of the dehydration step by pressure filtration and the start of the next dehydration step.
5. The method according to any one of claims 1 to 4, wherein the slurry contains slaked lime.
6. The method according to claim 5, wherein the slaked lime is slaked lime in dust collected in a wet dust collecting process of a calcium carbide electric furnace.
7. The method according to any one of claims 1 to 6, wherein the slurry contains hydrotalcite and / or carbon.
8. The method according to claim 7, wherein the slurry contains 1 to 10% by mass of hydrotalcite and / or 1 to 15% by mass of carbon.
9. A cake obtained by carrying out the dehydration method according to any one of claims 1 to 8.
10. A method for producing an industrial raw material, comprising performing the dehydration method according to any one of claims 1 to 8.
11. The manufacturing method according to claim 10, wherein the slurry contains slaked lime, and the industrial raw material is a clinker raw material.
12. A method for producing a clinker, comprising a step of supplying a clinker material obtained by the method according to claim 11 to a firing furnace after a step of transporting the raw material of the clinker by a screw conveyor.
13. The method for producing a clinker according to claim 12, wherein the clinker is calcium sulfoaluminate (CSA) or cement clinker.

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