JPH1071379A - Method for treating waste without discharging waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the discharge of waste water to the outside of a system in the treatment of waste by concentrating a part of waste water by utilizing the remaining heat of flash gas and subsequently burning highly conc. org. matter in waste water in a combustion furnace and heating the waste water by sensible heat of combustion exhaust gas to take out the same sludge of an inorg. compd. to the outside of the system. SOLUTION: When solid waste is treated, at first, solid waste is crushed by a pretreatment means to prepare an aq. slurry and useful matter such as iron or glass is recovered by specific gravity difference. Next, the aq. slurry containing an org. solid is heated by heat exchangers 16, 18 to be supplied to a reactor. The formed slurry after hydrothermal reaction is flashed through a flash drum 23 and the reaction formed slurry obtained at this time is supplied to a separation means 24 and waste water containing chloride or the like is separated to prepare a product slurry. A part of waste water is conc. by utilizing the remaining heat of flash gas and highly conc. org. matter is burnt in a combustion furnace 70 and waste water containing an inorg. compd. is heated to be taken out of the system as sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of waste containing organic solids such as municipal solid waste and industrial waste, and in particular, makes the wastewater discharged from the waste treatment system into a non-wastewater. The present invention relates to a method for treating waste with non-wastewater as described above.

[0002]

2. Description of the Related Art Solid waste such as general waste such as municipal solid waste and industrial waste discharged from factories and the like is increasing year by year. I have. From such a viewpoint, after crushing solid waste in water and recovering useful materials such as iron, aluminum and glass that can be recycled in the form of a water slurry,
Dehydrate to a state having a suitable moisture value, and then heat (2
(50-350 ° C), high-pressure (100-150 kg / cm2G), a high-temperature, high-pressure reaction product slurry obtained by a hydrothermal reaction for a predetermined residence time is finally depressurized to atmospheric pressure. Product slurry.

[0003]

After separating solid waste such as municipal solid waste and industrial waste into unburnable and combustible materials, only the combustible materials have a combustion temperature of 750 to 950 ° C. After the temperature of the exhaust gas obtained by burning in the incinerator was lowered to 300 to 400 ° C. on the way of discharging, when dust accompanying the exhaust gas was removed by, for example, a bag filter or an electric dust collector, a certain amount of stagnation in the exhaust gas was observed. There was a problem that dioxin would be generated if time was given. Also, after dust removal by the bag filter or the electric dust collector, etc., the pH value of the slurry containing solids dissolved in the liquid is shifted to the acidic side at the time of gas / liquid contact in the washing tower in the next step. Then, for example, after injecting an appropriate amount of NaOH or the like as an alkaline substance into the circulating solution of the slurry and neutralizing, the generated neutralized slurry is separated into cake and filtrate by a separation means, and the cake is buried or newly incinerated. However, due to the strictness of discharge standards, the remaining filtrate cannot be discharged to the sea or river without sufficient neutralization treatment.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to separate solid waste from a reaction slurry formed by a hydrothermal decomposition reaction in a reactor into a product slurry and wastewater. Another object of the present invention is to provide a method for treating waste by using non-waste water in which waste water is reused so that the waste water is not discharged out of the system.

[0005]

In order to achieve the above object, according to a first aspect of the present invention, waste containing organic solids is slurried in a pretreatment step, and the waste slurry is treated with an alkaline substance. The multi-stage flash, the separation of the product slurry and the wastewater by multi-stage flash, separation means, and the like, the wastewater after the centrifugation, After concentrating in a concentration step using the excess heat of the flash gas obtained by flashing a part of the multi-stage flash, high-concentration organic matter contained in the wastewater is burned in a combustion furnace and contains only inorganic compounds. The wastewater containing the inorganic compound is heated using the sensible heat of the flue gas discharged from the combustion furnace and taken out of the system as sludge of the inorganic compound. And In the second aspect of the present invention that a portion of the waste water is concentrated in the concentration step, by reusing the recovered condensed water and the recovered water in the system, and do not emit waste water out of the system. Further, in the third invention mainly based on the second invention, the concentrated wastewater generated when a part of the wastewater is concentrated in the concentration step and the flash gas are used to convert the product slurry obtained by the separation means into a combustion aid. As a combustion treatment in a combustion furnace, the generated combustion gas is separated into clean combustion gas and recovered water and sludge in the crystallization step of the next step, and the recovered water is not discharged to the outside of the system. Then, it is supplied to the pretreatment means and reused.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for treating waste with non-wastewater according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a block diagram showing the configuration of a system for carrying out the method for treating wastes from non-wastewater according to the present invention, FIG. 2 is a flow diagram around a concentration process, and FIG. 3 is a flow diagram around a combustion furnace and a crystallization process. is there.

Hereinafter, the solid waste treatment will be described in detail with reference to FIG. 1. When the solid waste in an unsorted state is treated, the waste contains useful materials such as iron, aluminum and glass which can be recycled. Therefore, it is necessary to collect the waste first and to make the waste solid enough to be conveyed for continuous operation of the solid waste treatment system.
A pretreatment means 10 for this purpose is provided, and this pretreatment means 10 is composed of a crushing device, a separation device for useful materials, a dewatering device, and the like.

[0009] Therefore, in this pretreatment means, solid waste containing organic solid matter in an unsorted state is converted into a water slurry by crushing in water.
By utilizing the difference in specific gravity of incombustibles contained in the crushed material, useful materials such as iron, aluminum, and glass that can be recycled are recovered. Then, the water slurry containing the organic solid matter from which the incombustible substances have been removed is dehydrated to a solid matter content of about 10 to 20% by weight, and the viscosity is adjusted to such an extent that it can be transported to the subsequent processing step.

The waste slurry stored in the storage tank 12 treated by the pretreatment means 10 is a normal temperature slurry. The waste slurry in the storage tank 12 is fed to the subsequent reactor 14 by a pumping means such as a high-pressure pump (not shown) so that a hydrothermal reaction occurs during the circulation in the reactor 14. ing.

The waste slurry to which alkali has been added, which is fed by a high-pressure pump (not shown), is heated from room temperature to a reaction temperature before being supplied to the reactor 14. For this reason, the first and second heat exchangers 16 and 18 are stepwise heated. The waste slurry heated to an appropriate temperature is supplied to the reactor 14. The reaction temperature in the reactor 14 is 250 to 350 ° C, preferably 280 to 300 ° C.
° C, and the reaction pressure may be at least the saturated vapor pressure at the reaction temperature.

The reaction time is usually 5 to 60 minutes, preferably 1 to 60 minutes.
0 to 30 minutes. The reaction temperature is determined in relation to the residence time, and the reaction time can be lowered by increasing the reaction time, and conversely, the reaction time can be shortened by increasing the reaction temperature. It is desirable to determine according to the solid matter whose reaction is rate-determining in the waste slurry.

The operating temperature in the reactor 14 is 250 to 350
The temperature is raised to an appropriate temperature of about ℃, and the slurry is fed while being pressurized to about 170 atm by the high-pressure pump, and in the embodiment, the reaction temperature is increased by the first heat exchanger 16 and the second heat exchanger 18. The temperature is raised stepwise until it is fed to the reactor 14. In the process of passing through the reactor 14, the temperature of the waste slurry is increased while maintaining the reaction temperature and at the same time or higher than the saturated steam at the reaction temperature, and the reaction time is several minutes to tens of minutes. It is thermally decomposed by the hydrothermal reaction.

By the way, raw material waste such as municipal solid waste includes:
Since an organic chlorinated resin such as vinyl chloride which generates hydrogen chloride upon thermal decomposition is contained, an alkaline substance is added to a slurry subjected to a hydrothermal reaction to neutralize the hydrogen chloride. Therefore, an alkaline tank 20 is provided, and the alkaline substance supplied from the tank 20 is continuously injected and supplied. As the alkaline substance, Na ₂ CO ₃ , NaOH or the like is used.

Examples of the alkaline substance include sodium hydroxide (NaOH), sodium carbonate (Na ₂ CO ₃ ), calcium hydroxide (Ca (OH) ₂ ), potassium carbonate (K ₂ CO ₃ ), and sodium hydrogen carbonate. (NaHC
An alkali metal compound or an alkaline earth metal compound such as O ₃ ), potassium hydrogen carbonate (KHCO ₃ ), and sodium formate (NaHCOO) can be used, but sodium carbonate (Na ₂ CO ₃ ) is most preferable from practical considerations. .

The pH of the reaction product slurry at the outlet of the reactor 14 is a weakly acidic pH = 3-5.
What is necessary is just to adjust the addition amount of an alkaline substance so that it may become. Since the solid waste to be treated is various, the addition amount is 1 to 5% by weight based on the unit feed amount of the solid waste slurry, but the alkali addition amount is determined while detecting the outlet pH of the reactor 14. Can be adjusted.

The alkaline substance is added for the purpose of preventing corrosion of liquid-contacting parts such as reactors, heat exchangers, and other piping due to generation of hydrochloric acid and the like by the reaction. The supply amount of the alkaline substance from the alkaline tank 20 is a continuous injection method, and is generally injected at a ratio of less than 10% by weight, preferably 4 to 8% by weight based on the solid content of the waste slurry. Is the amount necessary for neutralizing the generated hydrogen chloride, depending on the type of solid waste.

For injection of such an alkaline substance,
An alkali supply pump 22 is provided in the supply pipe,
It is connected directly downstream of the storage tank 12 to inject it into the solid waste slurry. The pump 22 is a variable pump capable of feeding back the result obtained by measuring the pH value of the reaction product with the pH meter 32 and adjusting the amount of alkali to be injected via the control means 34.

In the present embodiment, the flash gas obtained by flashing the slurry formed after the hydrothermal reaction in the reactor 14 through the flash drum 23 from the reactor 14 is supplied to the first heat exchanger 16. Heat exchange with the slurry before the reaction. In addition, the first heat exchanger 1
6, a second heat exchanger 18 is disposed downstream of the first heat exchanger 18.
A heating medium or high-pressure steam is introduced from the outside to heat the pre-reaction slurry heated by the heat exchanger 16 to a predetermined reaction temperature. Of the liquid (slurry) and gas (flash gas) obtained by flashing with the flash drum 23, the reaction product slurry is supplied to the separation means 24, where it is depressurized to atmospheric pressure and concentrated by centrifugal filtration or the like. In the process, wastewater containing flash gas and chlorides is separated into product slurry.

On the other hand, a flash gas such as CO ₂ , CO, and H ₂ obtained by flashing through a flash drum 23 is supplied to a first heat exchanger 16 as shown in FIG. After the heat exchange, a part of the flash gas is condensed into a gas-liquid mixed phase flow, supplied to the first condensed water separator 40, and separated into the flash gas and the condensed water. The flash gas is supplied to the shell side of the third heat exchanger 44 through the line 43. Then, in the third heat exchanger 44, a part of the circulating water separated by the separation means 24 described later flows through the tube side of the third heat exchanger 44, and flows through the line 43 during circulating heating. The enthalpy of the circulating water is increased by the flash gas.

A part of the flash gas used for heating the circulating water is condensed to form a gas-liquid mixed-phase flow to form a line 45.
Is supplied to the second condensed water separator 46 through the circulating fluid and is separated into flash gas and condensed water. Further, the flash gas is sent to the combustion furnace 70 through the line 53 and is incinerated together with the concentrated wastewater. The condensed water separated by the first condensed water separator 40 and stored at the bottom is sent to the pretreatment means 10 through the line 65 and reused, but flows in through the line 42 on the way. Circulating water and second condensed water separator 46
Is supplied to the pretreatment means 10 through the line 52 together with the condensed water discharged from the bottom of the pretreatment device.

On the other hand, a part of the circulating water separated by the separation means 24 passes between the third heat exchanger 44, the evaporator 48, and the concentration circulating pump 50, which constitute a part of the concentration step 100, by a line 47, 49, it is supplied via a line 41 to a line 51 circulatingly connected by a line 51. In addition, the concentration step 100 is performed in addition to the third heat exchanger 44, the evaporator 48, and the concentration pump 50 described above.
The second condensed water separator 46, the concentrated wastewater pump 55, the first
It comprises a recovered water separator 59, a first recovered water discharge pump 62, and a first vacuum pump 120.

During circulation, the circulating water, which is heated while flowing through the tube side of the third heat exchanger 44 and whose enthalpy has increased, is flushed in an evaporator 48 to be separated into gas and liquid. A mixed gas of water vapor separated and generated by isenthalpy expansion in the evaporator 48 and air leaked from a flange or the like (non-condensable gas) by the first vacuum pump 120 passes through a line 57 and exchanges heat in a heat exchanger 58 and then condenses. I care
A liquid mixed phase flow is supplied to the first recovered water separator 59 to separate gas and liquid. Then, the separated gas is sucked and discharged by the first vacuum pump 120 having a vacuum of about 200 Torr. The gas separated into gas and liquid by the first recovered water separator 59 is sucked and discharged by the first vacuum pump 120, for example, in a line 57.
And a so-called non-condensable gas mainly containing air leaked into the pipe from a flange used for connection of the line 60 or the like.

The separated liquid (recovered water) is fed to the separation means 24 by a first recovered water discharge pump 62 via a line 63, and is re-used as washing water after filtering the reaction product slurry by a centrifugal filter, for example. It is being used. The concentrated wastewater that has been flushed and separated by the evaporator 48 having a vacuum pressure of about 200 Torr at a temperature of about 70 ° C. is temporarily stored at the bottom of the evaporator 48 and sent to the concentration circulation pump 50 via the line 49. Is to be paid.
Then, a part of the concentrated wastewater is withdrawn from the concentrated wastewater pump 55 from the middle of the line 49 via the line 54 and fed to the combustion furnace 70 through the line 56 for processing.

Next, as shown in FIG. 3, the enthalpy of the flash gas is passed through the first condensed water separator 40, the third heat exchanger 44 and the second condensed water separator 46 (operating temperature of about 80 ° C.). The flash gas after recovery and the concentrated wastewater discharged from the separation means 24 via the line 56 via the concentration step 100 are each heated to about 900 to 950 ° C.
In the combustion furnace 70 having a furnace temperature of In the combustion treatment of the flash gas and the concentrated wastewater, the product slurry of 50 to 55% by weight separated by the separation means 24 is used as a combustion aid, and is burned while blowing appropriate excess air. When the product slurry is used as a combustion aid, the product slurry and an auxiliary fuel such as coal may be mixed in advance to increase the calories.

The concentrated wastewater passes through line 56 to combustion furnace 70
And the organic matter contained in the concentrated wastewater is almost completely burned to become a combustion gas accompanied by ash. Like the concentrated wastewater, the flash gas discharged from the second condensed water separator 46 is supplied to the combustion furnace 70 through the line 53 and is incinerated. The combustion gas is blown into a wastewater storage tank 72 via a dip tube 71 below the combustion furnace 70.
The lower area of the dip tube 71 is immersed in the storage liquid in the wastewater storage tank 72, and the ash accompanying the combustion gas is washed while passing through the storage liquid to become clean combustion gas. I have.

The dip tube 71 is supplied to the waste water storage tank 72 from a storage liquid supply pump 88 via a line 89.
A circulation line is formed in which the stored liquid is supplied to the upper portion of the dip tube 71 and flows down while the inner wall surface of the dip tube 71 exhibits a wet wall state. If the stored liquid is circulated in the circulation line for a long time, the stored liquid circulating in the circulation line is used to prevent ash and unburned substances from gradually accumulating in the system. Is partly withdrawn through a line 90 and sent to a crystallization step 200 in the next step. The amount of the storage liquid extracted from the extraction valve 91 via the line 90 is controlled by the level control LC87 so that the liquid depth in the wastewater storage tank 72 is constant.

The ash and the like are washed and removed by the liquid stored in the wastewater storage tank 72, and the cooled combustion gas is supplied to the shell side of the fourth heat exchanger 74 via the line 73. After applying sensible heat to the stored liquid flowing through the tube side of the fourth heat exchanger 74 and heating the stored liquid through the tube side of the fourth heat exchanger 74 with the sensible heat of
The fuel gas is returned to the wastewater storage tank 72 again through the tank 5, and the combustion gas having sensible heat applied to the stored liquid is sent to the venturi scrubber 101 through the line 100. Here, in order to remove ash and the like accompanying the combustion gas, the venturi scrubber 10 is used as circulating water circulating through the seventh separator 106 and the circulating pump 107 through the lines 110 and 111.
It sprays through one.

In particular, a major object of the present invention is that
The combustion gas of 50 ° C. is blown into the wastewater storage tank 72 through the dip tube 71 at the lower part of the combustion furnace 70 to
By rapidly cooling to 90 ° C., the generation of dioxins contained in the combustion gas is eliminated. Also, the seventh
Replenishing water is supplied to the separator 106 from the outside through a line 109, and liquid is extracted through a line 108 so that the stored liquid at the bottom of the seventh separator 106 becomes constant by overflow.

The withdrawn liquid is returned to the wastewater storage tank 72 from the line 108. Further, a part of the stored liquid extracted from the circulation line 90 is used for the crystallization step 2
00, a fourth heat exchanger 74, a crystallization can 76, and a storage liquid circulation pump 79 are connected to lines 75, 7 respectively.
The crystallization is performed during the circulation of the stored liquid in the circulation line, which is connected to a line 77 which forms a circulation line for performing crystallization by being connected at 7, 78. In the present invention, the crystallization step 200 includes the fourth heat exchanger 74, the crystallization can 76, the second recovered water separator 82, the stored liquid circulation pump 79, the second recovered water discharge pump 85, and the concentrated liquid extraction pump 93. , Centrifuge 95, separated liquid return pump 97, second
It comprises a vacuum pump 125.

The withdrawn liquid heated by the combustion gas is heated by the combustion gas while flowing through the fourth heat exchanger 74, passes through a line 75, and is crystallized by a crystallization can 76 (operating temperature is 60 ° C.).
To 65 ° C.) to generate steam from the heated storage liquid by isenthalpy expansion. The water vapor is condensed after exchanging heat with cooling water in a heat exchanger 81 through a line 80,
Subsequently, the soaked air (non-condensable gas) and condensed water are supplied to the second recovered water separator 82 in a state of forming a so-called gas-liquid mixed phase flow, and gas-liquid separation is performed.

A non-condensable gas is sucked and released into the atmosphere from the top of the second recovered water separator 82 by a second vacuum pump 125 having a vacuum pressure of about 100 Torr. It is stored at the bottom of 82 and is fed from the second recovered water discharge pump 85 via line 84 to the separating means 24 through line 83 as recovered water. Then, the water is used as washing water in the separating means 24.

The concentrated liquid of the stored liquid separated by flash in the crystallization can 76 is temporarily stored in the crystallization can 76, and is then withdrawn through a line 92 by a concentrated liquid extraction pump 93. And the centrifuge 9 via line 94
5 and subjected to centrifugation to separate into cake-like sludge and separated water. The separated water passes through the separated liquid return pump 97 via the line 96, and is returned again to the line 77 forming the above-mentioned circulation line via the line 98. The sludge is extracted through a line 99, solidified with a solid agent as appropriate, and then subjected to disposal such as landfill.

[0034]

As is apparent from the above description, in the present invention, the reaction product slurry obtained by the hydrothermal reaction in the reactor is treated in the system through a concentration step, a combustion furnace and a crystallization step. Since the treated water is reused by the pretreatment means, wastewater is not discharged out of the system. In addition, a combustion furnace is provided between the concentration step and the crystallization step, and the concentrated wastewater and flash gas obtained in the concentration step are burned using a product slurry obtained by the separation means as a combustion aid, and the obtained combustion gas is discharged. The dioxin entrained in the combustion gas is completely eliminated due to rapid cooling in the wastewater storage tank at the bottom of the combustion furnace.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a system for implementing a method for treating waste with non-wastewater according to the present invention.

FIG. 2 is a flowchart around a concentration step.

FIG. 3 is a flow chart around a combustion furnace and a crystallization step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pre-processing means 12 Storage tank 14 Reactor 16 1st heat exchanger 18 2nd heat exchanger 20 Alkaline tank 22 Alkali supply pump 23 (23A, 23B, 23C) Flash drum 24 Separation means 32 pH meter 34 Control means 40 No. 1 Condensed water separator 44 Third heat exchanger 46 Second condensed water separator 48 Evaporator 50 Concentration circulating pump 55 Concentrated wastewater pump 59 First recovered water separator 62 First recovered water discharge pump 70 Combustion furnace 72 Wastewater storage tank 74 Fourth Heat exchanger 76 crystallization can 79 stored liquid circulation pump 82 second recovered water separator 85 second recovered water discharge pump 88 stored liquid supply pump 93 concentrated liquid extraction pump 95 centrifugal separator 97 separated liquid return pump 100 concentration step 101 venturi scrubber 102 chimney 106 seventh separator 107 Ring pump 120 first vacuum pump 125 second vacuum pump

Claims (3)

[Claims] 1. A waste containing organic solids is slurried in a pretreatment step, an alkaline substance is added to the waste slurry, and a high pressure obtained by subjecting the alkaline waste slurry to a hydrothermal reaction in a reactor. Multistage flash, separation of product slurry and wastewater by separation means, etc., by using the excess heat of the flash gas obtained by multistage flashing a part of the wastewater after centrifugation. After being concentrated in the wastewater, the high-concentration organic matter contained in the wastewater is burned in a combustion furnace to produce wastewater containing only inorganic compounds, and the inorganic compound is utilized using sensible heat of combustion exhaust gas discharged from the combustion furnace. A method for treating waste with non-wastewater, comprising heating wastewater contained therein and removing the wastewater as sludge of an inorganic compound. 2. A part of the wastewater according to claim 2 is concentrated in a concentration step, and the collected condensed water and recovered water are reused in the system so that the wastewater is not released out of the system. A method for treating waste using non-waste water. 3. The concentrated wastewater and flash gas generated when a part of the wastewater according to claim 2 is concentrated in the concentration step is burned in a combustion furnace using the product slurry obtained by the separation means as a combustion aid. In the crystallization step of the next step, the generated combustion gas is separated into clean combustion gas, recovered water and sludge, and the pre-processing means is performed so that the recovered water is not discharged to the outside of the system. A method for treating waste with non-waste water, wherein the waste is supplied to and reused.