JP2002355699A - Supercritical water oxidative decomposition method for organic sludge and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a supercritical water oxidative decomposition method for organic sludge capable of eliminating the defect of the conventional oxidation treatment of organic sludge such as sewage sludge or the like using supercritical water and capable of suppressing ammonia, nitric acid, nitrous acid and total nitrogen in treated water. SOLUTION: In a method for reacting organic sludge and an oxidizing agent in supercritical water to perform the supercritical water oxidative decomposition of organic sludge, the solid concentration of organic sludge is set to 5% or more to perform supercritical water oxidative reaction at 450-550 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for oxidizing organic sludge generated from a biological treatment apparatus for organic wastewater represented by sewage sludge.

[0002]

2. Description of the Related Art Heretofore, as a method of oxidizing organic sludge such as sewage sludge, a method of mainly incineration has been generally used. However, sewage sludge has a water content of 97-98.
Therefore, in order to incinerate the sewage sludge, it was necessary to dehydrate the sewage sludge in advance by a dehydrating means such as a screw press type dehydrator, and to reduce the water content to a range where incineration is possible.

On the other hand, in recent years, a method of directly oxidizing sewage sludge using water in a supercritical state has been proposed. Since sewage sludge obtained by treating sewage with a biological treatment apparatus has a low calorific value, it is general that the sewage sludge is concentrated to 5 to 15% by weight and subjected to a supercritical water oxidation treatment.

Referring to FIG. 3, a conventional supercritical water oxidation apparatus for supercritical water oxidation of concentrated sludge will be described. FIG. 3 is a flow sheet showing the configuration of a conventional supercritical water oxidation apparatus. As shown in FIG. 3, the conventional supercritical water oxidation apparatus 30 includes a tubular long pressure-resistant closed reactor 31 as a reactor for performing a supercritical water oxidation reaction, and upstream of the reactor 31, A concentrated sludge pump 39 for supplying the concentrated sludge, an air compressor 40 for supplying the oxygen, and a double-tube heat exchanger 32 for preheating the reactants, and a heat exchanger for cooling the reaction products downstream of the reactor 31 A device 33 and a cooler 34 are provided. The concentrated sludge supplied to the reactor 31 is obtained by converting sewage sludge treated by a biological treatment device (not shown) into a concentrator 42 such as a centrifugal concentrator.
It is concentrated in. The separated liquid obtained by concentrating the sewage sludge is discharged out of the system.

When the reaction product is cooled by the heat exchanger 33, the temperature of the heat medium becomes high, and the heat medium is used by the double-tube heat exchanger 32 as a heat source for preheating the mixed fluid to be processed. Further, the supercritical water oxidation apparatus 30 includes a pressure control valve 35 for controlling the pressure in the reactor 31 downstream of the cooler 34 and a gas-liquid separator 36 for gas-liquid separation of the reaction product into gas and slurry. A solid-liquid separator 37 is provided downstream of the pressure control valve 35 and separates a solid reaction product from the reaction product by solid-liquid separation of a slurry-like reaction product. The inorganic solids separated by the solid-liquid separator 37 are mainly contained in the reactants and did not contribute to the reaction, and may also contain salts generated by the supercritical water oxidation reaction. is there.

[0006] When the concentration of sludge is low in the conventional supercritical water oxidation cracking apparatus, it is necessary to supply an auxiliary fuel to perform supercritical water oxidation.

[0007] In the supercritical water oxidation treatment of sewage sludge, in order to stably and efficiently treat the sludge, the supply of auxiliary fuel is reduced while ensuring the fluidity of the sludge, and the processing fluid after the supercritical water oxidation decomposition is processed. It is important that no special post-processing is required to process

However, since the calorific value per unit amount of organic matter in the sludge is low, it is necessary to efficiently recover heat and increase the sludge concentration in order to reduce the amount of auxiliary fuel. However, when the concentration of the sludge increases, the fluidity of the sludge extremely decreases, and it becomes difficult to supply the sludge to the supercritical hydroxylation decomposition apparatus.

In recent years, due to the problem of eutrophication in closed water bodies, the regulation of nitrogen and phosphorus emissions has tended to be strengthened. Therefore, nitrogen and phosphorus do not remain as much as possible in treated water after supercritical hydroxylation decomposition. It is required to do so.

[0010] As means for satisfying these requirements, JP-A-11-90494 discloses that the sludge concentration is adjusted to about 5 to 15% in accordance with the amount of heat exchange, and the reaction temperature is set to 600 ° C or higher. A method is described in which auxiliary fluid is eliminated while maintaining the fluidity of sludge, and supercritical water oxidation of sewage sludge is performed without leaving nitrogen in the treated water.

Heretofore, in supercritical water oxidation of sewage sludge, all nitrogen components in sewage sludge are once converted to ammonia by hydrolysis, ammonia is oxidized to nitric acid and nitrous acid, and treated by the reaction of ammonia with nitric acid and nitrous acid. It has been considered that nitrogen components disappear from water (see the following reaction formulas (1) to (3)).

[0012] The nitrogen component _{+ H 2 O → NH 4 ...} (1) NH 4 + O 2 → NO 2 and NO 3 ... (2) NH 4 + NO 2 and NO 3 → N 2 or N 2 O in sewage sludge (3) In this series of reactions, the rate of oxidation of ammonia shown in reaction formula (2) is rate-determining, and the production of ammonia by hydrolysis in reaction formula (1) and the conversion of ammonia in reaction formula (3) Since the reaction with nitric acid or nitrous acid occurs quickly, it was considered that nitric acid or nitrous acid did not remain in the treated water, and that all nitrogen components could be removed from the treated water by completely oxidizing ammonia. For that, 60
It was thought that it was necessary to carry out supercritical hydroxylation at a high temperature of 0 ° C. or higher.

However, when the supercritical hydroxylation of sewage sludge was examined in detail, organic nitrogen other than ammonia in the sludge was converted to ammonia by hydrolysis at a low temperature of about 450 ° C. as shown in reaction formula (4). Formation is the main reaction, and when the temperature rises to 500 ° C. or higher, the reaction formula (5)
As shown in the figure, it was confirmed that the production of nitric acid and nitrous acid by oxidation was the main reaction.

Organic nitrogen + H ₂ O → NH ₄ (4) Organic nitrogen + O ₂ → NO ₂ or NO ₃ (5) When the concentration of sewage sludge was concentrated to about 5 to 15%, the concentration was increased. Because the ratio of organic nitrogen in the sludge increases, if the reaction temperature is supercritically hydroxylated at a high temperature of about 550 ° C,
Nitric acid and nitrous acid remain in the treated water. On the other hand, when the concentrated sludge is subjected to supercritical water oxidation at a low reaction temperature of about 400 ° C., even in the case of organic nitrogen, ammonia production becomes the main reaction, and the ammonia contained in the sludge also remains. A large amount of ammonia remains.

Therefore, when sewage sludge is subjected to supercritical water oxidation, ammonia remains at low temperatures and nitric acid remains at high temperatures, making it difficult to reduce total nitrogen in the treated water.

[0016] By the concentration of the sewage sludge, the concentrated sludge concentrated to a predetermined concentration and the separated liquid separated from the solid matter are discharged. At this time, Table 1 shows typical compositions of the raw sludge, the concentrated sludge, and the separated liquid.

[0017]

[Table 1]

As shown in Table 1, as compared with the ratio of ammonia in the raw sludge, the ratio of ammonia increases in the concentrated sludge, whereas the ratio of ammonia increases in the separated liquid. That is, by the concentration operation, the water-soluble ammonia flows out to the separated liquid side, and the ratio of organic nitrogen in the concentrated sludge increases. As a result, the concentration of the nitrogen-containing organic compound in the concentrated sludge relatively decreases. It seems to increase. As a result, at a reaction temperature of 550 ° C. or higher, the production amounts of nitric acid and nitrous acid are larger than the residual ammonia amount, and it is considered that nitric acid and nitrous acid remain in the treated water.

[0019]

The problem to be solved by the present invention is to solve the drawback of the conventional oxidation treatment of organic sludge such as sewage sludge using supercritical water, and to solve the problem of ammonia and nitric acid in treated water. It is another object of the present invention to provide a method and apparatus for supercritical hydroxylation and decomposition of organic sludge which can suppress nitrous acid and total nitrogen.

[0020]

Means for Solving the Problems A first invention for solving the above-mentioned problems is a method for supercritically hydrolyzing organic sludge by reacting organic sludge and an oxidizing agent in supercritical water. The present invention relates to a method for supercritically hydrolyzing organic sludge, wherein the solid concentration of organic sludge is 5% or more and a supercritical hydroxylation reaction is performed at 450 to 550 ° C.

A second invention for solving the above problems is:
In an apparatus for reacting an organic sludge with a solid concentration of 5 or more and an oxidizing agent in supercritical water and supercritically hydrolyzing the organic sludge, the mixed fluid of the organic sludge and the oxidizing agent is treated with water. A treatment object supply means for supplying a pressure at or above a critical pressure, a reactor for performing a supercritical hydroxylation reaction of the treatment object mixed fluid, and a cooling means for cooling a reaction fluid after reaction flowing out of the reaction vessel; A supercritical hydroxylation decomposition apparatus having a take-out means for taking out a cooled processing fluid flowing out of the cooling means, and a measuring means for measuring properties of the processing fluid;
A supercritical water oxidation decomposition apparatus characterized in that reaction temperature control means for controlling the reaction temperature of the supercritical water oxidation reaction to 450 to 550 ° C. according to the properties of the processing fluid measured by the measurement means is provided. It is.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The organic sludge in the present invention is
It is obtained by biological treatment of organic wastewater such as domestic wastewater and industrial wastewater.

According to a first aspect of the present invention, there is provided a method for reacting an organic sludge and an oxidizing agent in supercritical water to supercritically hydrolyze the organic sludge, wherein the solid matter concentration is increased to 5% (% by weight) or more. The organic sludge obtained is subjected to supercritical water oxidation at 450 to 550 ° C.

The supercritical water is water in a supercritical state. In the present invention, the water is 22 MPa or more, preferably 22 to 2 MPa.
At a pressure of 5 MPa, the temperature is controlled at 450 to 550 ° C., and the concentrated organic sludge is supercritically hydroxylated,
Ammonia, nitric acid, nitrous acid and total nitrogen in the treated water can be suppressed.

In the supercritical water oxidation reaction, the concentrated sludge is oxidatively decomposed in the presence of supercritical water and an oxidizing agent. In the present invention, the supercritical water oxidation treatment is conventionally performed at 600 ° C. or higher. Is controlled at 450-550 ° C. and 5%
The concentrated organic sludge is subjected to a supercritical hydroxylation decomposition treatment.

In the present invention, the reaction temperature is 450-55.
The temperature is 0 ° C., preferably 480 to 520 ° C., but the optimum reaction temperature varies depending on the ratio of ammonia and organic nitrogen in the concentrated organic sludge used as the raw material. For example, when concentrated sludge with a sludge concentration of about 10% is reacted at 500 ° C, the total amount of nitric acid and nitrous acid generated by the oxidation reaction in the reaction temperature range, and the ammonia and the hydrolysis reaction originally contained in the sludge, The total amount of ammonia produced is the theoretical equivalent of the reaction that produces nitrogen or nitrous oxide from ammonia and nitric acid or nitrous acid, and ammonia and nitric acid or nitrous acid react quickly in this reaction temperature range. Ammonia, nitric acid,
No nitrous acid remains.

The sludge concentration of the organic sludge to be treated is as follows:
It is necessary that the solid concentration is 5% (% by weight) or more. If it is less than 5%, the ratio of ammonia in the organic sludge will be high. Therefore, even if all the nitrogen components are converted to nitric acid and nitrous acid by the reaction of organic nitrogen, the remaining amount of ammonia is larger than that in the treated water. Ammonia remains.
The upper limit of the sludge concentration of the organic sludge is not particularly limited. However, if the concentration is too high, the fluidity of the organic sludge decreases and the operability deteriorates. Therefore, the upper limit is preferably about 15%. Examples of the concentration and separation means for concentrating and separating organic sludge include means such as centrifugal concentration, gravity concentration, and pressure flotation concentration.

Examples of the oxidizing agent in the present invention include air, pure oxygen, hydrogen peroxide, and liquid oxygen. These oxidizing agents may be used in a stoichiometric amount or more. The reactor for supercritical hydroxylation decomposition is a pipe (tubular)
Molds are preferred.

Since water is a good solvent for organic substances and gaseous substances in the supercritical state, supercritical water, organic substances and oxidizing agent form a homogeneous phase in the reactor, and the supercritical water oxidation reaction The organic matter is oxidatively decomposed in a very short time depending on the reaction temperature. However, since the reaction temperature in the present invention is relatively low, if the reaction time is short, the organic substance may not be decomposed. Therefore, the reaction time is 1 minute or more, preferably 2 to 3 minutes. This can prevent the organic matter from remaining undecomposed.

The temperature of the supercritical hydroxylation decomposition reaction is 450 to 5
As a method of controlling the temperature to 50 ° C., feedback control may be performed by measuring properties of the treated water.

The properties of the treated water include the concentrations of ammonia, nitric acid, and nitrous acid in the treated water, the pH of the treated water, and the like.

For example, in order to measure and control the concentrations of ammonia, nitric acid and nitrous acid in the treated water, the following may be performed. For example, when the ammonia concentration in the treated water is higher than a certain value, it is considered that the reaction temperature is lowered.Therefore, the reaction temperature may be increased, and when the nitric acid and nitrite concentrations are higher than the certain values, the reaction temperature may be lower. Since the reaction temperature is considered to be rising, the reaction temperature may be lowered.

The reaction temperature can also be controlled by measuring the pH of the treated water. For example, when the reaction temperature is low, the pH of the treated water increases due to the generation of ammonia, and when the reaction temperature is high,
Since the pH of the treated water decreases due to the production of nitric acid and nitrous acid, the reaction temperature can be feedback-controlled by measuring the pH of the treated water.

To lower the reaction temperature, water or a separation liquid having a low calorific value (separation liquid obtained when condensing organic sludge) may be supplied to the reaction system. An auxiliary fuel such as isopropyl alcohol may be supplied to the reaction system. By controlling the supply amount of water or the separated liquid and the supply amount of the auxiliary fuel, the reaction temperature is set to 450 to 5
It can be controlled at 50 ° C.

The second embodiment of the present invention will be described with reference to the drawings.

The second embodiment of the present invention will be described with reference to the flowchart of FIG.

As shown in FIG. 1, the supercritical hydroxylation decomposition apparatus of the present invention comprises a tubular (tubular) long pressure-resistant closed type reactor 10 as a reactor for performing a supercritical hydroxylation reaction. In the upstream of the vessel 10, there are provided a concentration separation means 2 for concentration and separation of sewage sludge supplied from the biological treatment equipment for sewage and a concentration sludge tank 6 for storing the concentration sludge concentrated and separated by the concentration separation means 2. It has a separation liquid tank 3 for storing the separation liquid separated from the separation means 2. In the concentration separation means 2, the raw material sewage sludge is concentrated to a solid concentration of 5% (% by weight) or more.

A pressurizing and supplying pump 26 as a pressurizing and supplying means for supplying a fluid to be treated such as concentrated sludge to a pressure higher than the critical pressure of water, and a pressurizing and supplying means as a pressurizing and supplying means for supplying an oxidizing agent under pressure. A supply pump 28 (a pressurized supply compressor when the oxidizing agent is a gas such as oxygen) and a preheater 12 of a double-pipe heat exchanger as preheating means for preheating the mixed fluid to be processed.

In order to control the reaction temperature, a pressurized supply pump 5 as auxiliary fuel supply means for pressurized supply of auxiliary fuel, and a separation liquid supply means for supplying separation liquid from a separation liquid tank Supply pump 4 is provided.

In the reactor 10, the preheated mixed fluid of the object to be treated is heated to a supercritical pressure of 450 to 550 ° C.
Supercritical hydroxylated decomposition.

Downstream of the reactor 10, a double-tube heat exchanger 14 and a cooler 16 for cooling the processed fluid after the reaction are provided. The flow passages of the supercritical water splitting and cracking apparatus including the preheater, the reactor, the heat exchanger, and the cooler have substantially the same diameter.

Further, the supercritical water splitting / decomposing apparatus comprises a reactor 1
A pressure control valve 18 for controlling the pressure within 0 is provided downstream of the cooler 16. As means for taking out the cooled processing fluid, a gas-liquid separator 20 for gas-liquid separation into gas and slurry is used.
Is provided downstream of the pressure control valve 18 and a solid-liquid separator 22 that separates the inorganic solid from the reaction product by solid-liquid separation of the slurry-like reaction product. The inorganic solid separated by the solid-liquid separator 22 is mainly contained in the reaction product,
It does not contribute to the reaction and may additionally contain a salt formed by the supercritical hydroxylation reaction.

The reaction temperature in the reactor 10 is set to 450 to
In order to control the temperature to 550 ° C., a pH measuring means 21 is provided as a measuring means for measuring properties of the processing fluid flowing out of the gas-liquid separator 20. The pH value of the processing fluid is sent to the reaction temperature control means 23 as an electric signal. As the reaction temperature control means 23, a feedback control device or the like can be used. The supply amount of the auxiliary fuel and the separated liquid is controlled by the pH value. In FIG. 1, a pH meter is illustrated as a means for measuring the properties of the treated water.
In addition to the meter, a means for directly measuring the concentrations of ammonia, nitric acid, and nitrous acid in the treated water may be used.

If ammonia remains in the processing fluid flowing out of the reactor 10, the pH of the processing fluid rises. An increase in the concentration of ammonia in the processing fluid is expected to decrease the reaction temperature (the above-mentioned reaction formula (4)). Sends a signal to the auxiliary fuel supply means 5,
The reaction temperature may be raised by increasing the supply amount of the auxiliary fuel, and the production amounts of nitric acid and nitrous acid may be increased.

When nitric acid and nitrous acid remain in the processing fluid flowing out of the reactor 10, the pH of the processing fluid decreases. An increase in the concentration of nitric acid and nitrous acid in the processing fluid is expected to increase the reaction temperature (the above-mentioned reaction formula (5)). A signal is sent from the temperature control means 23 to the separation liquid supply / supply means 4 to supply the separation liquid having a low calorific value to the supercritical hydroxylation reaction system, thereby lowering the reaction temperature and reducing the production amount of nitric acid and nitrous acid. Suppress. In addition, water may be supplied instead of the separated liquid in order to lower the reaction temperature.

As mentioned above, the reaction temperature is 450 to 550 ° C.
By controlling to. Ammonia, nitric acid and nitrous acid can be eliminated from the treated water.

[0047]

EXAMPLES Example 1 Reaction temperature 510 ° C., reaction pressure 24 MPa, reaction time 2
The solid content concentration is 10.0% under the condition that the oxygen ratio is 1.5.
Was subjected to a supercritical water oxidation reaction so that the pH of the treated water became 4.8. In addition, isopropyl alcohol (IPA) and water were used for temperature adjustment.

The progress of the above reaction is shown in Table 2 and FIG.

[0049]

[Table 2]

[0050]

According to the method of the present invention described in claim 1,
The organic sludge can be subjected to the supercritical hydrolytic decomposition treatment at a relatively low temperature, and nitrogen can be reliably removed from the treated water.

According to the method of the present invention described in claim 2, the organic substances contained in the organic sludge can be sufficiently subjected to the supercritical hydroxylation decomposition treatment.

In the method of the present invention described in claim 3, by controlling the reaction temperature according to the properties of the treated water, it is possible to reliably remove nitrogen from the treated water even if the properties of the organic sludge fluctuate. it can.

According to the method of the present invention, the reaction temperature can be controlled by measuring the pH of the treated water in addition to the above-mentioned effects, so that the cost can be controlled more easily and at low cost.

By controlling the reaction temperature according to the properties of the treated water, the apparatus of the present invention described in claim 5 can reliably remove nitrogen from the treated water even if the properties of the organic sludge fluctuate. it can.

According to the apparatus of the present invention described in claims 6 and 7, in addition to the above effects, the pH of the treated water can be measured to control the reaction temperature, so that the cost can be controlled more easily and at low cost.

[Brief description of the drawings]

FIG. 1 is a flowchart of the apparatus of the present invention.

FIG. 2 is a graph showing the course of a reaction in Examples.

FIG. 3 is a flowchart of a conventional supercritical hydroxylation decomposition apparatus.

[Explanation of symbols]

 2 Concentration and separation means 3 Separation liquid tank 4 Separation liquid supply means 5 Auxiliary fuel supply means 6 Condensed sludge tank 10 Reactor 12 Preheater 14 Heat exchanger 16 Cooler 18 Pressure control valve 20 Gas-liquid separator 21 pH measurement means 22 Solid Liquid separator 23 Reaction temperature control means 24 Heat medium pipe 26 Pressurized supply pump 28 Pressurized supply pump

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Suzugaki 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation (72) Inventor Shinji Ito 1-2-8 Shinsuna, Koto-ku, Tokyo Olga (72) Inventor Akira Suzuki 1-2-8 Shinsuna, Koto-ku, Tokyo Organo Corporation F-term (reference) 3K061 AA12 AB01 AC02 BA01 BA08 CA01 DA03 4D059 AA03 BC01 BC02 BE31 BE37 BE41 CB09 DA44 DA47 DB02 EA05 EB06 EB16

Claims (7)

[Claims] 1. A method of reacting an organic sludge and an oxidizing agent in supercritical water to supercritically hydrolyze the organic sludge, wherein the solid concentration of the organic sludge is 5% or more and 450 to 550. A supercritical water oxidation decomposition method for organic sludge, wherein a supercritical water oxidation reaction is carried out at a temperature of ° C. 2. The method of claim 1, wherein the reaction time of the supercritical hydroxylation reaction is 1 minute or more. 3. The method according to claim 1, wherein the reaction temperature is controlled at 450 to 550 ° C. by measuring properties of the processing fluid.
Or the method for supercritically hydrolyzing organic sludge according to 2 above. 4. The process fluid has a pH property, and when the pH of the process fluid decreases, a separation liquid obtained when condensing water or organic sludge is supplied to a reaction system, and the pH of the process fluid is adjusted to a pH value. The method according to claim 3, wherein the reaction temperature is controlled by supplying an auxiliary fuel when the temperature rises. 5. An apparatus for reacting an organic sludge having a solid content of 5% or more and an oxidizing agent in supercritical water and supercritically hydrolyzing the organic sludge to treat the organic sludge and the oxidizing agent. Supply means for supplying the mixed fluid at a pressure equal to or higher than the critical pressure of water, a reactor for performing a supercritical hydroxylation reaction of the mixed fluid, and a processed fluid flowing out of the reactor after the reaction A supercritical hydroxylation decomposition apparatus comprising a cooling means for cooling the processing fluid, a take-out means for taking out a cooled processing fluid flowing out of the cooling means, a measuring means for measuring properties of the processing fluid, and a measuring means for measuring the properties of the processing fluid. Depending on the properties of the processed fluid, the reaction temperature of the supercritical hydroxylation reaction is 450 to 5
A supercritical water splitting / decomposing apparatus comprising a reaction temperature control means for controlling the temperature to 50 ° C. 6. The supercritical hydroxylation decomposition apparatus according to claim 5, wherein the property of the processing fluid is a pH of the processing fluid, and the measuring means is a pH measuring means. 7. The method according to claim 1, wherein the reaction temperature control means is configured to control the p of the processing fluid.
When H decreases, water or a separated liquid obtained when the organic sludge is concentrated is supplied to the reactor, and when the pH of the processing fluid increases, an auxiliary fuel is supplied to control the reaction temperature. The supercritical water splitting / decomposing apparatus according to claim 6, wherein: