JP2014008495A - Method for reducing amount of sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively reducing an amount of sludge with a simple method and without diffusing any harmful substance.SOLUTION: Sludge is contained in a pressure-resistant container 10, and an amount of sludge is reduced by heating the pressure-resistant container 10 in an oxidative atmosphere so as to bring the inside of the pressure-resistant container 10 into a pressurized state without diffusing any harmful substance in the atmosphere, and consequently the sludge is converted into powder with significantly reduced offensive odor, or into odorless powder. Furthermore, to reduce partial pressure of carbon dioxide which may be produced by heat-treating the sludge, an alkaline aqueous solution is put into the pressure-resistant container 10, and as a result the produced carbon dioxide is absorbed therein. Thus increase in carbon dioxide partial pressure in the pressure-resistant container 10 is prevented, and safe and efficient reduction of the amount of the sludge is achieved.

Description

The present invention relates to a sludge reduction treatment method, and more particularly to a sludge reduction treatment method of heating and pressurizing in an oxidizing atmosphere in a pressure vessel. Also, reducing sludge usually leads to volume reduction.

According to the Environmental Assessment Glossary (Ministry of the Environment), sludge is mud generated from sewage treatment plants, water purification plants, industrial wastewater treatment facilities, civil engineering construction sites, etc. and in the manufacturing process of various manufacturing industries. Inorganic, not only from mud (organic sludge) mixed with organic matter, but also from metal washing and water purification plant sedimentation basins, etc. Including natural ones (inorganic sludge). This also includes sewage from civil engineering and construction sites. All are treated as industrial waste, and the generation amount accounts for 1/3 of the total industrial waste. The sludge referred to in the present invention also refers to these.

Sludge has a strong odor and contains a lot of moisture. Generally, a method of incineration is used for the disposal of sludge. The incineration process evaporates the moisture in the sludge and reduces the volume, and the organic matter in the sludge burns and decomposes to eliminate odor. Moreover, it may be used as a fertilizer when embedding in the soil. In any case, if the sludge to be discarded is accumulated without being treated, the odor generated from the sludge may cause environmental problems. Furthermore, hazardous substances contained in the sludge can cause further environmental problems.

Since sludge contains a lot of organic matter, as described above, incineration is generally used for sludge treatment. When sludge is incinerated, the effect of weight reduction can be fully expected, but harmful metal substances bound to organic matter in the sludge, such as mercury and arsenic, will be scattered around and will adversely affect the surrounding environment. there is a possibility. In addition, in order not to diffuse harmful substances generated during the incineration process, it is necessary to pass through a filter for separating and recovering harmful substances, or to pass through liquids. It is also necessary to consider. Furthermore, when the sludge to be incinerated is contaminated with radioactive substances, the radioactive substances may be released and diffused into the air together with the incineration gas to diffuse the contamination by the radioactive substances. Therefore, it is not preferable to incinerate the sludge contaminated with radioactive substances because it causes secondary environmental pollution.

In addition, when sludge is incinerated, harmful gases such as dioxins are generated in the combustion gas with the incineration of organic substances contained in the sludge and may be discharged into the air. Therefore, in order to ensure that hazardous substances such as dioxins are not discharged, incineration must be performed at a temperature of 1000 ° C or higher, and it is necessary to use an incinerator that can withstand high incineration temperatures. The burden is also a problem.

In light of the fact that reducing the sludge treatment is effective for solving problems such as storage and transportation of the treated sludge, the present inventors reduced the amount of sludge without incineration. As a result of intensive research, we have found that sludge can be reduced without generating harmful substances by heating in a pressure vessel.

The present invention has been made in view of the above problems, and its purpose is to reduce sludge reduction while avoiding secondary environmental pollution such as generation and diffusion of harmful substances in a simple method. An object of the present invention is to provide a sludge reduction treatment method capable of reducing odor and reducing odor.

In the sludge reduction processing method according to the first aspect of the present invention for solving the above-mentioned problem, when processing sludge in a pressure vessel, the inside of the pressure vessel is set to an oxidizing atmosphere, the outside of the pressure vessel is heated and the pressure vessel is heated. The inside is in a pressurized state.

According to the present invention, all volatile harmful substances that may be generated by the treatment can be confined inside the pressure vessel. Moreover, since sludge is reduced in volume inside a sealed pressure vessel, there is no problem of drainage and exhaust. Note that the oxidizing atmosphere referred to in the present invention refers to an atmosphere containing oxygen. This includes not only the oxygen concentration in the atmosphere, but also oxygen as well as the oxygen atmosphere mainly composed of oxygen.

When the reaction temperature according to the constitution of the present invention is 100 ° C. to 250 ° C. or less, since organic substances in the sludge are decomposed, dioxins are never generated and no harmful substances are newly generated. Further, when the inside of the pressure vessel is an oxidizing atmosphere with a high oxygen concentration, it is not necessary to use chemicals in the first place, and since no chemicals are used at all, there is no secondary contamination by chemicals. In the case of an oxidizing atmosphere having a high oxygen concentration, the organic matter in the sludge is oxidized and vaporized at normal pressure.

Even when the inside of the pressure vessel before heating is an oxidizing atmosphere mainly composed of air, if the pressure vessel is exhausted at a temperature of 100 ° C. or higher, the sludge to be treated can be dried at once by the exhaust.

A sludge reduction treatment method according to a second aspect of the invention is characterized in that in the sludge reduction treatment method according to the first aspect, an alkaline aqueous solution is placed inside the pressure vessel.

According to this invention, in the invention according to claim 1, when sludge is heat-treated in an oxidizing atmosphere having a high oxygen concentration, carbon dioxide is generated. Therefore, in order to reduce the partial pressure of carbon dioxide, an alkaline aqueous solution, for example, an aqueous sodium hydroxide solution, is put in the pressure vessel, so that the generated carbon dioxide is absorbed, and the partial pressure of carbon dioxide in the pressure vessel is increased. Can be prevented. As a result, the partial pressure of oxygen inside the pressure vessel is relatively recovered, the oxidation reaction is easier to proceed, the pressure inside the pressure vessel can be lowered, and the efficiency of sludge reduction treatment is prevented while reducing the efficiency. Can be processed.

According to the present invention, it is possible to perform sludge reduction treatment without diffusing harmful substances into the atmosphere and without using chemicals, thereby generating secondary pollution that generates harmful substances. The sludge can be treated without any problems, and the odor problem can be reduced by greatly reducing the odor when treated in an oxidizing atmosphere where the oxygen concentration in the pressure vessel is low. When treated in an oxidizing atmosphere having a high concentration, the amount can be reduced as an odorless powder.

It is the figure which showed typically the outline of the apparatus in the weight reduction processing method of the sludge which concerns on embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings.

First, an outline of a pressure vessel used in the sludge reduction treatment method according to the present embodiment will be described. The pressure vessel 10 includes a container part 11 that houses sludge to be treated therein and a lid part 12 that is attached to the container part. Since the pressure vessel 10 is pressurized in a sealed state and heated from the outside during the sludge reduction process, it is necessary to prevent the vessel portion 11 and the lid portion 12 from being easily separated. For this reason, a flange portion is provided outside the container portion 11 and the lid portion 12, respectively, and the container portion 11 and the lid portion 12 are communicated with each other in a state where the container portion 11 and the lid portion 12 are overlapped. A plurality of holes are formed in the flange portions of the cover 11 and the lid portion 12, and are fixed with fasteners 18. For example, a bolt and a nut can be used as the fastener 18. The bolt is passed through the hole, and the container 11 and the lid 12 are fixed by tightening with a nut from a direction opposite to the bolt insertion direction. In addition, it can also be set as the structure which clamps the flange part of the container part 11 and the cover part 12 with a vise-like instrument from the outside.

As the material of the pressure vessel, a metal material having thermal conductivity is used. Specifically, stainless steel, iron and the like can be preferably used.

Various methods such as heating with an IH heater or a gas burner can be adopted as the method of heating the pressure vessel, but it is preferable to use electric heating from the viewpoint of temperature control, particularly from the viewpoint of temperature management and thermal efficiency. An IH heater can be preferably used. Therefore, a material suitable for electromagnetic induction heating such as SUS430 can be preferably used as the material of the container when the IH heater is used as a heat source. However, in the case of an all-metal compatible IH heater, a metal such as aluminum or copper may be used, and at least the heat-resistant container heating surface may be a conductor.

The lid 12 can be provided with a thermometer 16 and a pressure gauge 17 for measuring the temperature and pressure in the pressure vessel 10. Further, the lid 12 can be provided with an exhaust pipe 13 for exhausting air in the pressure-resistant vessel 10 and gas generated by processing, and a supply pipe 14 for supplying (injecting) oxygen. The supply pipe 14 is connected to the oxygen cylinder 30 when oxygen is supplied into the pressure vessel 10. The exhaust pipe 13 and the supply pipe 14 can be provided separately or can be shared.

A safety valve 15 can be provided in the exhaust pipe 13. The safety valve 15 is activated when the pressure inside the pressure vessel 10 reaches a set value, and reduces the pressure inside the pressure vessel 10. The safety valve 15 is for emergency use in consideration of safety and does not normally operate.

When the sludge is thermally decomposed in the process of reducing the sludge, carbon dioxide is generated, and the partial pressure of carbon dioxide in the pressure vessel 10 is increased.

Therefore, in order to reduce the partial pressure of carbon dioxide, an alkaline aqueous solution, for example, a sodium hydroxide aqueous solution is placed in the pressure resistant vessel 10 to absorb the generated carbon dioxide, and the partial pressure of carbon dioxide in the pressure resistant vessel is reduced. The rise can be prevented.

Next, the sludge reduction processing method according to the present embodiment will be described.

In the present embodiment, the sludge as a starting material is converted into an odorless powdery product through an encapsulation process, an oxidizing atmosphere forming process, a heating and pressurizing process, a heat retaining process, and a decompression / cooling process.

The sludge to be treated is disposed in the container portion 11 of the pressure vessel 10, the lid portion 12 is attached to the container portion 11 of the pressure vessel 10, and the fasteners 18 such as bolts and nuts are provided so that the pressure vessel 10 is sealed. By fully fixing with, the sealing process is completed.

After this sealing step, the process proceeds to an oxidizing atmosphere forming step. The oxidizing atmosphere only needs to be an atmosphere containing oxygen, and the concentration of oxygen in the atmosphere is not limited. Therefore, if the atmosphere is an air atmosphere, the above-described encapsulation process is performed, and the oxidizing atmosphere forming process is completed at the same time. become. This is advantageous in that it does not require extra steps.

On the other hand, the higher the oxygen concentration in the pressure vessel 10, the greater the weight loss effect. For this reason, in order to increase the oxygen concentration, the treatment can be performed in an oxidizing atmosphere mainly composed of oxygen. In this case, an oxygen cylinder 30 is connected to the supply pipe 14 of the lid portion 12 of the pressure vessel 10, and oxygen is supplied into the pressure vessel 10 through the supply pipe 14. Although this increases the procedure of the process, there is an advantage in terms of weight loss effect.

These complete the oxidizing atmosphere forming step.

Here, since the oxygen cylinder 30 is often in a high pressure state, if the high pressure oxygen is supplied into the pressure vessel 10, the inside of the pressure vessel 10 is inevitably pressurized. For example, at a pressure of 0.5 MPa, the oxygen partial pressure in the container is about 25 times the oxygen partial pressure in the atmosphere.

After this oxidizing atmosphere forming step, the process proceeds to a heating and pressurizing step. Since the partial pressure of water vapor increases as a function of temperature due to heating, the inside of the pressure-resistant vessel 10 is in a pressurized state. For example, at 200 ° C., the partial pressure of water vapor is about 2 MPa. If it does so, the water | moisture content contained in sludge will evaporate inside the pressure-resistant container 10 which is the airtight state, and water vapor | steam will generate | occur | produce, or the organic substance contained in sludge will decompose | disassemble and gas will be generated, and the inside of the pressure-resistant container 10 will be pressurized. The Rukoto. That is, the pressurizing process proceeds simultaneously with the heating process. Therefore, in consideration of the pressure increase due to heating, in order to ensure sufficient safety, the operating pressure of the safety valve is set so that the pressure in the pressure resistant container 10 is 2.5 MPa or less, and the temperature of the heat resistant container 10 is 250. It heats so that it may become below 200 degreeC, Preferably it is below 200 degreeC. Thereby, a pressurization process and a heating and pressurization process are completed. In order to form an oxidizing atmosphere having a high oxygen concentration, hydrogen peroxide or ozone may be used instead of the above oxygen. However, keep in mind that hydrogen peroxide can react violently with sludge.

After this heating and pressurizing process, the process proceeds to a heat retaining process. In this heat retention step, the temperature is set to 150 ° C. to 210 ° C., and the temperature is kept around 1 hour. Adjust the heat retention time appropriately with sludge.

After this heat retention step, the process proceeds to a pressure reduction / cooling step. In this step, the safety valve 15 of the exhaust pipe 13 provided on the lid portion 12 of the pressure vessel 10 is opened, and the pressure inside the heat resistant vessel 10 is reduced to 0.1 MPa. When the pressure is reduced by exhausting the pressure vessel 10 at a temperature of 100 ° C. or higher, the object to be treated can be dried. Moreover, it cools to room temperature by stopping heating and leaving it to stand.

The pressure in the pressure vessel can be processed by setting the upper limit of the pressure condition high, but the pressure vessel is required to have a high level of pressure resistance as the pressure is set higher. However, since it is necessary to increase the heating conditions for increasing the pressure, it is necessary to consider the cost. In view of this viewpoint, in the present invention, the weight reduction treatment can be preferably performed in the range of 0.1 MPa to 2.0 MPa in an air atmosphere. The lower limit value of 0.1 MPa is the same as the atmospheric pressure, and is therefore the same as when processing in an open system. Further, the upper limit value is less than 2.0 MPa in an air atmosphere, and a sufficient amount can be reduced.

On the other hand, when the inside of the pressure vessel is processed by increasing the oxygen concentration as compared with that in an air atmosphere, the pressure inside the pressure vessel can be preferably reduced in the range of 0.1 MPa to 2.5 MPa.

The sludge undergoes these weight reduction treatments, and all moisture is evaporated together with the harmless gas generated in the treatment process. When treated in an oxidizing atmosphere with a low oxygen-free concentration, the odor is greatly reduced and reduced. When the treatment is performed in an oxidizing atmosphere having a high oxygen concentration, the amount can be reduced as an odorless powder.

When sludge is heated with high pressure oxygen supplied to the pressure vessel 10, carbon dioxide is generated. In order to reduce the partial pressure of carbon dioxide, an alkaline aqueous solution, for example, a sodium hydroxide aqueous solution is placed in the pressure vessel 10 to absorb the generated carbon dioxide, and the partial pressure of carbon dioxide in the pressure vessel 10 is reduced. The rise can be prevented. As a result, the oxygen partial pressure in the pressure vessel 10 is relatively recovered, the oxidation reaction is facilitated, the pressure inside the pressure vessel 10 can be lowered, and the sludge reduction treatment efficiency is prevented from being lowered. The upper limit value of the pressure in the pressure vessel 10 can be lowered, and processing can be performed safely.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. For example, even if an atmosphere having a constant oxygen concentration is formed by the oxidizing atmosphere forming step, the oxygen concentration may be increased or decreased thereafter. As a result of the reduction, a hypoxic state may be considered.

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
As the pressure vessel, a pressure vessel made of SUS430 having a capacity of 3 L was used. The lid portion of the pressure vessel was opened, a beaker containing 50.88 g of sludge was placed in the vessel portion, the lid portion was attached to the vessel portion, and tightened with bolts and nuts to fix. The atmosphere inside the pressure vessel was air only. Next, the set temperature of the IH heater was adjusted with 170 ° C. as the upper limit, and the pressure vessel was heated with the IH heater.

When the temperature reached 160 ° C., the IH heater was adjusted so that the temperature of the pressure vessel was maintained at 160 ° C., and the heating was continued until 5 hours passed from the start of heating. The relationship between temperature and pressure at this time was 0.75 MPa at 157 ° C. After 5 hours, heating with the IH heater was stopped. After stopping the heating, in order to reduce the pressure in the pressure vessel, the safety valve was opened and the air in the pressure vessel was discharged. All the water evaporated. After confirming that the pressure vessel was cooled by leaving the pressure vessel, the lid was opened and the vessel containing the sludge was taken out. As a result, the sludge was a powder with significantly reduced odor. When the weight of this powder was measured, it was 12.55 g, and the weight loss rate was 75.3% as compared with the starting sludge. That is, it was confirmed that the pressure can be reduced sufficiently with a pressure of less than 2.0 MPa in an atmosphere of air inside the pressure vessel.

(Example 2)
A pressure vessel similar to that of Example 1 was used. The lid portion of the pressure vessel was opened, and a beaker containing 200 g of sludge was placed and arranged in the vessel portion, and the lid portion was attached to the vessel portion and fixed with bolts and nuts. Next, the set temperature of the IH heater was adjusted with 170 ° C. as the upper limit, and the pressure vessel was heated with the IH heater. Here, assuming that the amount of sludge in the pressure vessel is increased, it can be said that this is substantially the same as when the pressure vessel is in a low oxygen state in addition to the state of the first embodiment. Therefore, in order to make the inside of the pressure vessel low in oxygen, the safety valve was heated until the temperature reached 100 ° C., and the air in the pressure vessel was exhausted, and then the safety valve was closed at 100 ° C. By this operation, the atmosphere inside the pressure vessel was made almost free of oxygen.

Heating was continued after the air was evacuated. When the temperature reached 170 ° C., the IH heater was adjusted so that the temperature of the pressure vessel was maintained at 170 ° C., and the heating was continued until 5 hours passed from the start of heating. The relationship between temperature and pressure at this time was 1.02 MPa at 168 ° C. After 5 hours, heating with the IH heater was stopped. After stopping the heating, in order to reduce the pressure in the pressure vessel, the safety valve was opened and water vapor in the pressure vessel was discharged. After confirming that the pressure vessel was cooled by leaving the pressure vessel, the lid was opened and the vessel containing the sludge was taken out. As a result, the sludge was a powder with significantly reduced odor. When the weight of this powder was measured, it was 69.6 g, and the weight loss rate was 65.2% as compared with the starting sludge. As a result, it was confirmed that the amount of sludge in the pressure vessel can be sufficiently reduced even when it is assumed that the amount of sludge is increased.

(Example 3)
A pressure vessel similar to that of Example 1 was used. The lid portion of the pressure vessel was opened, a beaker containing 20 g of sludge was placed in the vessel portion, the lid portion was attached to the vessel portion, and tightened with bolts and nuts to fix. Subsequently, the air in a pressure vessel was sucked with a vacuum pump, and the pressure inside the pressure vessel was lowered. Subsequently, oxygen was injected from the high-pressure oxygen cylinder into the pressure vessel, and the pressure in the pressure vessel was adjusted to 0.70 MPa. When the operating pressure of the safety valve is set so that the upper limit of the pressure in the pressure vessel is 2.5 MPa or less, the set temperature of the IH heater is adjusted to the upper limit of 200 ° C., and the pressure vessel is heated with an IH heater The water contained in the sludge evaporated and the pressure increased due to the water vapor. The relationship between temperature and pressure at this time was 2.01 MPa at 156 ° C., 2.20 MPa at 167 ° C., and 2.40 MPa at the maximum temperature of 172 ° C.

Heating was performed while adjusting the temperature while paying attention not to exceed the safety valve operating pressure value, and heating by the IH heater was stopped after 2 hours. The temperature decreased to about 50 ° C., and the pressure also decreased. Furthermore, the safety valve was opened, and after confirming that the pressure in the pressure vessel had dropped sufficiently, the container and lid were removed, and the beaker with sludge was taken out. The sludge was completely dried. In the state, it was an odorless powder. The odorless powder weighed 3.2 g. Compared to the starting material, sludge, the weight loss rate was 84%.

Example 4
The same pressure resistant container as in Example 1 was used. A beaker containing 50.6 g of sludge is placed in the lower container of the pressure vessel, and a sodium hydroxide aqueous solution in which 10 g of sodium hydroxide is dissolved in 100 ml of water is stored in the beaker containing the sludge. -Put outside. Subsequently, the air in a pressure vessel was sucked with a vacuum pump, and the pressure inside the pressure vessel was lowered. Subsequently, oxygen was injected from the high-pressure oxygen cylinder into the pressure vessel, and the pressure in the vessel was adjusted to 0.92 MPa. When the operating pressure of the safety valve is set so that the upper limit of the pressure in the pressure vessel is 2.5 MPa or less, the set temperature of the IH heater is adjusted up to 200 ° C., and the pressure vessel is heated with an IH heater The water contained in the sludge and the water in the pressure vessel were evaporated and the pressure was increased by water vapor.

Regarding the relationship between temperature and pressure, the pressure was 2.15 MPa at 152 ° C., but thereafter there was a rapid increase in temperature and pressure. Since the rapid temperature rise was confirmed, the IH heater was turned off to prevent overpressurization. The relationship between temperature and pressure after several minutes was 1.75 MPa at 156 ° C. and 1.72 MPa at 150 ° C. The pressure after the rapid temperature increase is lower than that in Example 2, which can be explained as that the generated carbon dioxide was absorbed by the sodium hydroxide aqueous solution. After confirming that the pressure had dropped to 1.70 MPa, heating with the IH heater was resumed. Heating was performed while adjusting the temperature while paying attention not to exceed the safety valve operating pressure value of 200 ° C. and pressure of 2.5 Mpa, and heating by the IH heater was stopped after 2 hours. The temperature decreased to about 50 ° C., and the pressure also decreased. Furthermore, the safety valve was opened, and after confirming that the pressure in the pressure vessel had dropped sufficiently, the container and lid were removed, and the beaker with sludge was taken out. The sludge was completely dried. In the state, it was an odorless powder. The weight of this odorless powder was 8.10 g. Compared to the starting material, sludge, the weight loss rate was 84%.

As described above in detail, the sludge can be reduced without incineration. In the treatment method of the present invention, since no chemical is used, secondary pollution caused by incineration, for example, generation of toxic gas can be eliminated, and diffusion of harmful metals contained in sludge into the air can be prevented. In particular, due to an accident at the Tokyo Electric Power Fukushima Daiichi Nuclear Power Station, radioactive materials are released outside the power plant, and the treatment of sludge containing radioactive materials has become a serious problem. Sludge can be reduced while preventing diffusion of air into the air.

DESCRIPTION OF SYMBOLS 10 ... Pressure-resistant container 11 ... Container part 12 ... Cover part 13 ... Exhaust pipe 14 ... Supply pipe 15 ... Safety valve 16 ... Thermometer 17 ... Pressure gauge 18 ... Fastener 19 ... Valve 20 ... ... IH heater 30 ... Oxygen cylinder

Claims (2)

When treating sludge in a pressure vessel,
A sludge reduction treatment method characterized in that the inside of the pressure vessel is an oxidizing atmosphere, the outside of the pressure vessel is heated and the inside of the pressure vessel is brought into a pressurized state. The sludge reduction treatment method according to claim 1, wherein an alkaline aqueous solution is placed inside the pressure vessel.