JP3284933B2 - Supercritical water oxidation method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a supercritical water oxidation method in which a raw material containing an organic substance and water is placed in a supercritical state of water in the presence of oxygen, and the organic substance in the raw material is oxidatively decomposed. The present invention relates to a supercritical water oxidation apparatus to be carried out.

[0002]

2. Description of the Related Art A supercritical water oxidation method in which a raw material containing an organic substance and water is placed in a supercritical state of water in the presence of oxygen and the organic substance in the raw material is oxidatively decomposed is disclosed in, for example, Japanese Patent Publication No. 1-3853.
No. 2 and JP-A-7-275870. The critical point of water is a pressure of 22 MPa and a temperature of 374 ° C. In a supercritical state beyond this critical point, the physical properties of water change remarkably, and organic substances and oxygen can be dissolved at a high concentration. In supercritical water, the oxidative decomposition reaction of organic substances remarkably proceeds. Utilizing such properties of supercritical water, for example, treatment of organic waste is being developed.

[0003] In a supercritical water oxidation apparatus, it is important in what procedure a raw material supplied to a reactor is brought to a supercritical state of water. In general, in the state diagram of FIG. 1, the raw material is raised from the state a at normal pressure and room temperature to a state g by using a high-pressure pump to raise the raw material to a state g at a stretch, and the raw material in the state g is heated to the supercritical state h. That is being done. State h
When oxygen is supplied to the raw material in the supercritical state, the oxidative decomposition reaction of the organic substance in the raw material remarkably proceeds in the reactor as described above. According to this method, the operation of pressurizing and heating the raw material can be performed mainly in the liquid phase, so that the apparatus configuration can be made relatively compact. Suppose that the temperature is raised from normal pressure, normal temperature state a to the critical temperature,
If the pressure is then increased to the supercritical state, the operation of increasing the pressure and heating the raw material will be performed almost in the gas phase,
The device configuration is complicated and large, and there is a problem in operational safety.

[0004]

However, according to the study results of the present inventors, it has been found that the above-mentioned general method has some problems. First, when the fluidity of the raw material to be treated is poor, a high-pressure pump for continuously increasing the pressure of the raw material from the state a at normal pressure and normal temperature to a critical pressure or higher is expensive, and the pressure loss is extremely low. There is a problem of being large. Second, the apparatus for heating the raw material in the high-pressure state g is expensive. In other words, the heating device continuously or intermittently retains the raw material in a container (including piping), and indirectly heats the material from outside the container during this time. , The cost of the apparatus increases.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned problems of the prior art, to make it relatively easy to raise the pressure above the critical pressure even for a raw material having poor fluidity, and to reduce the cost of the heating device. It is an object of the present invention to provide a supercritical water oxidation method and an apparatus therefor.

[0006]

According to the supercritical water oxidation method of the present invention, a raw material containing an organic substance and water is placed in a supercritical state of water in the presence of oxygen, and the organic substance in the raw material is oxidized and decomposed. In the supercritical water oxidation method, the raw material is pressurized to 5 to 15 MPa lower than the critical pressure of water, and the pressurized raw material is heated to raise the temperature. The organic material is oxidatively decomposed by supplying oxygen to the pressurized raw material.

In the supercritical water oxidation apparatus according to the present invention, a raw material containing an organic substance and water is mixed at a pressure of 5 to 15 M lower than the critical pressure of water.
A first pump for raising the pressure to Pa , a heat exchanger for raising the temperature of the raw material raised by the first pump, and a second pump for raising the temperature of the raw material raised by the heat exchanger to a critical pressure of water or higher. Oxygen supply means for supplying oxygen to the raw material pressurized by the second pump; and reacting the raw material supplied with oxygen by the oxygen supply means in a supercritical state of water to oxidatively decompose organic substances in the raw material. And a reactor.

Further, the supercritical water oxidation apparatus according to the present invention comprises:
A high-temperature reactant discharged from the reactor is fed to the heat exchanger to indirectly exchange heat with the raw material. Further, in the supercritical water oxidation apparatus according to the present invention, the first pump or the second pump is a hydro pump, and operates using a pressure of a high-pressure reactant discharged from the reactor as a driving force. It is characterized by doing.

According to the present invention, first, the raw material is pressurized to a level sufficiently lower than the critical pressure of water, that is, to 5 to 15 MPa. At such a pressure, the pressure can be increased relatively easily even for a raw material having a somewhat poor fluidity.

Next, the temperature of the pressurized raw material is raised. As a means for raising the temperature, it is preferable to use a heat exchanger from the viewpoint of heat recovery in a process described later. As described above, the raw material introduced into the heat exchanger is merely pressurized to a level sufficiently lower than the critical pressure of water, so that the thickness of the heat exchanger can be made relatively thin, Cost can be reduced.

Next, the temperature of the raw material heated in the heat exchanger is raised to a value higher than the critical pressure of water. According to the inventors' findings, 5-1
Raw materials heated to 200 ° C. or more under a pressure of 5 MPa have remarkably improved fluidity and are being liquefied. For this reason,
At this stage, the raw material having poor fluidity can be handled as a liquid at this stage, and the raw material can be easily pressurized to a pressure higher than the critical pressure of water.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an apparatus system diagram showing an embodiment of the present invention. This embodiment shows a method and apparatus configuration for supercritical water oxidation of sewage sludge generated in a sewage treatment plant.

This sludge is organic with a water content of 80 to 95% and contains a small amount of inorganic substances. The substance is viscous like kneaded mud and has a strong odor. When this sludge is supercritically hydroxylated, the organic matter, which is the main component of the sludge, is oxidized and decomposed to become water and oxidizing gas, thereby rendering it harmless.

In FIG. 2, a sludge storage tank 10 stores sludge 11 as a raw material. A sludge supply pump 13 is connected to the bottom of the sludge storage tank 10 via a pipe 12. The discharge side of the sludge supply pump 13 is connected to a heat exchanger 15 via a pipe 14. The sludge outlet of the heat exchanger 15 is connected to a high-pressure pump 18 via a pipe 16 and a check valve 17. The high-pressure pumps 18 are of a hydro type, and two high-pressure pumps are arranged in parallel and operated for switching.

The discharge port on the sludge side of the high-pressure pump 18 is a check valve 1
9, connected to a mixer 21 via a pipe 20. The mixer 21 has an oxygen supply port, in which the sludge from the high-pressure pump 18 and oxygen are mixed. As for oxygen, the air taken in from the pipe 22 is sent to an oxygen generator 24 by a blower 23, and the oxygen produced by the oxygen generator 24 is compressed by an oxygen compressor 25, and after the pressure is increased to the critical pressure of water or higher, the mixing is performed. Is supplied to the vessel 21.

A reactor 26 is connected to an outlet of the mixer 21. The reactor 26 has a simple structure in which tubes are connected to each other, and oxidative decomposition of organic matter in sludge in a process in which supercritical sludge containing oxygen passes through the tube of the reactor 26. The reaction proceeds and is completed. The outlet side of the reactor 26 is connected to a heat exchange tube 28 provided in the heat exchanger 15 via a pipe 27. The outlet side of the heat exchange tube 28 is connected to a gas-liquid separator 32 via a pipe 29, a cooler 30, and a pipe 31. The gas separated by the gas-liquid separator 32 is released from the pipe 33 to the atmosphere.

On the other hand, the liquid side of the gas-liquid separator 32 is connected to a parallel-switchable solid-liquid separator 35 via a pipe 34, and the ash separated here is discharged out of the system from a pipe 36. The liquid side of the solid-liquid separator 35 is a pipe 37, a switching valve 38, a check valve 39.
The liquid-side inlet of the high-pressure pump 18 is connected to the second gas-liquid separator 43 through a check valve 40, a switching valve 41, and a pipe 42. Have been. The gas separated by the gas-liquid separator 43 is released from the pipe 44 to the atmosphere. The liquid side of the gas-liquid separator 43 is a pipe 45
Is connected to the treated water storage tank 46 through the pipe, and the treated water is discharged from the pipe 47 to the outside of the system. Further, an auxiliary high-pressure pump 48 is connected to the treated water storage tank 46, and the treated water is joined from the auxiliary high-pressure pump 48 to the pipe 37 via a pipe 49 so as to be supplied to the liquid-side inlet of the high-pressure pump 18. .

Next, the flow of the processing operation in this system will be described. The sludge supply pump 13 is operated to continuously supply the sludge stored in the sludge storage tank 10 to the present apparatus.
The sludge is pumped up by the sludge supply pump 13 from the normal temperature and normal pressure state a of FIG. 1 to about 10 MPa, and is changed to the normal temperature and medium pressure state b to be supplied to the heat exchanger 15. The high-temperature (about 600 ° C.) reactant sent from the outlet of the reactor 26 continuously flows through the heat exchange tube 28 in the heat exchanger 15 and is supplied to the heat exchanger 15. The sludge and the high-temperature reactant exchange heat, and the sludge is heated to about 300 ° C.

In order to efficiently promote heat exchange, the heat exchanger 15 is provided with a stirrer 50 for stirring the sludge. The heated sludge is in the high-temperature, medium-pressure state c shown in FIG. 1, and the sludge changes from the initial viscous state to a liquid state with extremely high fluidity. For this reason, the sludge after leaving the heat exchanger 15 can be handled as a liquid, and the pressure loss when passing through the pipe or the reactor can be small.

Since the sludge introduced into the heat exchanger 15 is merely raised to a level sufficiently lower than the critical pressure of water as described above, the thickness of the tank body constituting the heat exchanger 15 is reduced. The thickness can be made relatively thin, and the cost of the heat exchanger can be reduced.

The sludge heated in the heat exchanger 15 is supplied to a pipe 16
Is sent to the high-pressure pump 18 via. This high pressure pump 1
Numeral 8 denotes a hydro-type, which raises the sludge to about 25 MPa above the critical pressure by alternately operating two pumps provided in parallel.

The operation at this time will be described with reference to FIG.
The hydro-type high-pressure pumps 18A and 18B are provided with sludge chambers 52A and 52B at the boundaries of the pistons 51A and 51B in the cylinder.
B and back pressure chambers 53A and 53B. First, of the liquid side switching valves communicating with the back pressure chambers 53A and 53B, 38
A and 41B are closed and 38B and 41A are open.

In the high-pressure pump 18A, the switching valve 38
Since A is closed, the back pressure of the treated water from the pipe 37 does not act on the back pressure chamber 53A, and the back pressure chamber 53A has a low pressure. Therefore, the sludge from the heat exchanger 15 flows into the sludge chamber 52A via the pipe 16A and the check valve 17A. High pressure pump 1
8B, since the switching valve 38B is open, the back pressure chamber 5
The back pressure of the treated water from the pipe 37 acts on 3B, and the back pressure chamber 53B becomes high pressure. Accordingly, the sludge in the sludge chamber 52B is raised to a pressure higher than the critical pressure and is sent from the pipe 20 to the mixer 21 via the pipe 20B and the check valve 19B.

Next, the switching valves 38A and 41B on the liquid side communicating with the back pressure chambers 53A and 53B are opened, and the switching valves 38B and 41A are closed. In the high-pressure pump 18A, since the switching valve 38A is open, the back pressure of the treated water from the pipe 37 acts on the back pressure chamber 53A, and the back pressure chamber 53A becomes high pressure. Therefore,
The sludge flowing into the sludge chamber 52A is pressurized above the critical pressure and sent to the mixer 21 from the pipe 20 through the pipe 20A and the check valve 19A. In the high-pressure pump 18B, since the switching valve 38B is closed, the back pressure of the treated water from the pipe 37 does not act on the back pressure chamber 53B, and the back pressure chamber 53B has a low pressure. Therefore, the sludge from the heat exchanger 15 is
B, flows into the sludge chamber 52B via the check valve 17B.

As described above, the parallel high-pressure pump 18
Switching valves 38A, 38B, 41 on the back pressure chamber side of A, 18B
By alternately switching the opening and closing of A and 41B, the sludge can be pressurized almost continuously and sent to the mixer 21.

The pressurized sludge is supplied to a mixer 21 as described later.
To the reactor 26, and the treated water as a product here is sent to the back pressure chamber side of the high-pressure pump 18 while maintaining the pressure, so that the sludge and the treated water are substantially continuous. .
In other words, it can be considered that the extrusion flow is formed by the high-pressure pump 18. The pressure loss caused in the process of passing this pushing flow through the pipes and devices of each system is compensated by supplying high-pressure water from the auxiliary high-pressure pump 48 to the pipe 37 from the pipe 49. The auxiliary high-pressure pump 48 is a driving force for the extrusion flow, and the high-pressure pump 18 plays a role in maintaining the pressure of the extrusion flow at a critical pressure or higher.

The sludge supplied to the mixer 21 has a temperature (about 300 ° C.) and a pressure (about 25 MPa) in the state d in FIG.
a), and is mixed with the oxygen compressed by the oxygen compressor 25 in the mixer 21. The sludge mixed with oxygen is sent from the mixer 21 to the reactor 26.

In the process of passing through the tube of the reactor 26, the organic matter in the sludge undergoes an oxidative decomposition reaction, the temperature of which rises due to the decomposition heat at this time, and proceeds to the critical state of the state e in FIG.
When the oxidative decomposition reaction proceeds further, it enters the supercritical state region,
The oxidative decomposition reaction proceeds at an accelerated rate.

The organic matter is decomposed into water and an oxidizing gas (mostly carbon dioxide gas) by the oxidative decomposition reaction, and the reaction is completed at the outlet of the reactor 26 to become a stable reactant. The temperature of the reactant at this time rises to about 600 ° C. due to the heat of decomposition,
The state becomes the state f in FIG. Since the degree of temperature rise of the reactant may vary greatly depending on the concentration of organic substances in the sludge as a raw material, the reactor 26 has a double pipe structure, and a temperature control means (not shown) is provided. Preferably, a heat medium is passed through the outer tube of the double tube structure so that the sludge or reactant can be cooled and heated. With this temperature control means, the operation can be stabilized at the time of start-up or steady operation.

The reactant exiting the reactor 26 is sent from a pipe 27 to a heat exchange tube 28 provided in the heat exchanger 15. In the course of passing through the heat exchange tube 28, the reactant exchanges heat with the raw material sludge, and the temperature drops to about 300 ° C. The reactant exiting the heat exchanger 15 enters a cooler 30 via a pipe 29, where it is cooled to approximately normal temperature. The reactant exiting the cooler 30 passes through a pipe 31 to the gas-liquid separator 3.
2 where the gases in the reactants are separated and released from pipe 33 to the atmosphere.

The reactant from which the gas has been separated by the gas-liquid separator 32 is connected via a liquid-side pipe 34 to a parallel-switching solid-liquid separator 35.
Ash in the reactant separated here is supplied to the pipe 3
From 6 is discharged out of the system. The reactant flowing out of the liquid side of the solid-liquid separator 35 is water. The reactant is supplied to the liquid side inlet of the high-pressure pump 18 via the pipe 37, and is used for pressurizing the sludge as described above. Is sent to the second gas-liquid separator 43.

In the second gas-liquid separator 43, the separated gas is discharged from a pipe 44 to the atmosphere. Second gas-liquid separator 43
The treated water from which the gas has been separated is temporarily stored in a treated water storage tank 46 via a liquid-side pipe 45 and then discharged out of the system from a pipe 47. An auxiliary high-pressure pump 48 is connected to the treated water storage tank 46, and the pressure of the treated water is increased by the auxiliary high-pressure pump 48 and supplied to the liquid-side inlet of the high-pressure pump 18 to be used for increasing the pressure of sludge.

As described above, according to this embodiment, sludge having poor fluidity can be relatively easily increased to a pressure higher than the critical pressure of water, and the sludge can be efficiently brought to a temperature close to the critical temperature of water. A supercritical water oxidation method capable of heating and reducing the cost of a heat exchanger and an apparatus therefor can be provided.

In the above embodiment, the case where the raw material is sewage sludge has been described. However, the present invention is not limited to this, and any raw material containing organic matter and water may be used. In addition, the first sludge feed pump
The boosting of the stage is about 10 MPa, and the boosting of the second stage by the high-pressure pump is about 25 MPa. However, the present invention is not limited to this, and may be changed as appropriate according to the composition of the raw materials and the like. However, if the pressure increase in the first stage is low, for example, 1 MPa, when the temperature of the pressurized material is raised to near the critical temperature of water in the next step,
At about 180 ° C., the water in the raw material reaches the saturation temperature, and if it is heated further, it becomes superheated steam, and the handleability deteriorates significantly.
Also, if the boosting of the first stage is high, for example, 20 MPa,
Only the operation and the device become complicated, and the operation and effect of the present invention cannot be sufficiently enjoyed.

Therefore, the degree of boosting in the first stage is 5 to 1
It is preferable to select in the range of 5 MPa. If the first stage pressure is, for example, 5 MPa, the raw material can be heated in the liquid phase up to about 260 ° C., and the first stage pressure is increased to, for example, 15M.
If it is Pa, it can be up to about 340 ° C.

In the above embodiment, the second-stage high-pressure pump for increasing pressure is a hydro pump, and the hydro pump is operated by using the pressure of the high-pressure reactant discharged from the reactor as a driving force. did. However, the invention is not limited thereto, and the first-stage pressure increasing pump may be a hydro-type pump, and the hydro-type pump may be operated using the pressure of the high-pressure reactant discharged from the reactor as a driving force. In this case, another type of pump is used for the second-stage boosting pump.

In the above embodiment, the sludge as the raw material was heated to about 300 ° C. by the heat exchanger 15 and supplied to the reactor 26 at this temperature. However, if the temperature is 200 ° C. or higher, the fluidity of the raw material is improved. Therefore, after the raw material is heated to about 200 ° C. in the heat exchanger, the second-stage pressurization is performed, and then the raw material is heated by another heating means. The temperature may be raised to near the critical temperature of water.

[0038]

According to the present invention, a raw material containing an organic substance and water is pressurized to a level sufficiently lower than the critical pressure of water, the raised raw material is heated, and the heated raw material is cooled to a critical temperature. The organic substance is oxidatively decomposed by increasing the pressure to a pressure higher than the pressure and supplying oxygen to the increased pressure, so that the first-stage pressure increase makes it relatively easy to increase the pressure even on a material having poor fluidity. It is. When raising the temperature of the pressurized raw material, since the raw material is merely raised to a level sufficiently lower than the critical pressure of water, the thickness of the heat transfer surface constituting the heating device should be relatively thin. And the cost of the heating device can be greatly reduced.

Further, the fluidity of the heated material is remarkably improved and liquefaction is progressing. For this reason, even the original raw material having poor fluidity can be handled as a liquid in the second pressurization stage, and the raw material can be easily pressurized above the critical pressure of water.

Further, since the high-temperature reactant discharged from the reactor is fed to the heat exchanger and indirectly exchanges heat with the raw material, the amount of heat held by the reactant is effectively used for heating the raw material. Can be recovered. Further, since the first pump or the second pump is a hydro-type pump and is operated using the pressure of the high-pressure reactant discharged from the reactor as a driving force, the pressure held by the reactant is added to the raw material. It can be effectively collected for pressure.

For this reason, according to the present invention, it is relatively easy to increase the pressure above the critical pressure even for a raw material having poor fluidity, and it is possible to reduce the cost of the heating device and the pressure increasing device. An oxidation method and an apparatus thereof can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a state of water and a raw material according to the present invention.

FIG. 2 is an apparatus system diagram showing an embodiment of the present invention.

FIG. 3 is an apparatus system diagram for explaining an operation of the high-pressure pump according to the embodiment of the present invention.

[Explanation of symbols]

 10 Sludge storage tank 13 Sludge supply pump 15 Heat exchanger 18 High pressure pump 21 Mixer 25 Oxygen compressor 26 Reactor 30 Cooler 32 Gas-liquid separation Vessel 36 solid-liquid separator 43 second gas-liquid separator 45 treated water tank 48 auxiliary high pressure pump

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 1/74 C02F 11/00 B01J 3/00 B01J 19/00

Claims (4)

(57) [Claims] In a supercritical water oxidation method in which a raw material containing an organic substance and water is placed in a supercritical state of water in the coexistence of oxygen, and the organic substance in the raw material is oxidatively decomposed, the raw material is subjected to a critical pressure of water. also boosts the low 5 to 15 MPa, the pressurized raw material heated to warm, and the raw materials this heated is raised to above the critical pressure of water, by supplying oxygen to the boosted starting material, the organic material A supercritical water oxidation method characterized by performing oxidative decomposition of water. 2. A first pump for raising a raw material containing an organic substance and water to 5 to 15 MPa lower than a critical pressure of water,
A heat exchanger for raising the temperature of the raw material pressurized by the first pump, a second pump for raising the temperature of the raw material raised by the heat exchanger to a critical pressure of water or higher, and a pressure increase by the second pump. An oxygen supply unit for supplying oxygen to the raw material, and a reactor for reacting the raw material supplied with oxygen by the oxygen supply unit in a supercritical state of water to oxidatively decompose organic substances in the raw material, Supercritical water oxidation equipment. 3. The super-cooling apparatus according to claim 2, wherein a high-temperature reactant discharged from said reactor is sent to said heat exchanger to indirectly exchange heat with said raw material. Critical water oxidation equipment. 4. The method according to claim 1, wherein the first pump or the second pump is a hydro pump, and operates using a pressure of a high-pressure reactant discharged from the reactor as a driving force. The supercritical water oxidation apparatus according to claim 2 or 3.