JPH10300053A - Method of treating liquid organic sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the worsening of the character of an exhaust gas as caused by incomplete decomposition by oxidation of an oily substance contained in a diluted liquid by jetting separated water obtained in an oil-water separation process into a combustion furnace to accomplish decomposition by oxidation of organic matters contained in the separated water. SOLUTION: A diluted liquid recovered into a diluted liquid tank 104 is sent to an oil-water separator 106 by a diluted liquid pump 107 to separate an oily substance and the oily substance is mixed into the concentrated liquid through a line 121. On the other hand, the separated water after the separation of the oily substance is introduced into a sprayer 116 through a separated water supply pump 109 and a line 111 and then, sprayed into a furnace. The separated water sprayed into the furnace is instantaneously heated up to the temperature in the furnace (700 deg.C-900 deg.C) and organic matters contained in the separated water are decomposed by oxidation. The number of sprayers 116 may be several, not limited to one. This can solve a problem of worsening the character of an exhaust gas as caused by incomplete decomposition by oxidation of the oily substance contained in the diluted liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Sewage sludge, a typical organic sludge, is:
Approximately 50 million m ³ annually throughout Japan (based on concentrated sludge: water content 9)
8%), which is increasing year by year.
Generally, organic sludge such as sewage sludge contains large amounts of organic substances such as proteins, fats and carbohydrates together with water, so it is easy to rot, and it is necessary to stabilize, detoxify, and reduce its volume from the viewpoint of preventing odors and public health. It has been. Many sewage treatment plants in large cities burn sludge from the viewpoint of difficulty in securing landfills. JP-A-5-337497 proposes a method in which organic sludge is subjected to high-temperature and high-pressure treatment in advance to form a liquefied material, and then the liquefied material is burned. According to this method, since the organic sludge is supplied to the combustion furnace as a liquefied material having good fluidity,
At the time of the combustion treatment, a spray combustion method having good combustion efficiency can be adopted, and there is an advantage that the combustion furnace can be downsized and the operation can be easily determined. In addition, the present applicant has proposed a method in which liquid organic sludge is first sprayed and burned with a burner, and at least a part of the flame is melted while maintaining the temperature of the flame at or above the melting temperature of the inorganic material (JP-A-7-35318).
No.)

[0003] However, when the water content of the liquid organic sludge is high, the lower heating value based on the water content is low, and the fire temperature at the time of combustion becomes low. There is a problem that the melting of the inorganic substances contained in the steel does not occur or is insufficient. When the inorganic substances contained in the organic sludge are not sufficiently melted, the resulting ash becomes bulky and the heavy metals contained therein are easily eluted, and the ash is landfilled. During the treatment, the heavy metal component is eluted, which may cause environmental pollution.

[0004] The inventors of the present invention have previously disclosed a method of concentrating liquid organic sludge and burning this concentrate in order to raise the flame temperature and stably melt the inorganic matter when the liquid organic sludge is burned. (JP-A-7-305822)
issue). In the concentration step of this method, a dilute solution having a low solid content or substantially no solid content is obtained,
This diluted liquid is also sprayed into the combustion furnace in order to oxidatively decompose organic substances contained therein. However, in the oxidative decomposition of organic substances in such a dilute solution, the oily substances contained in the dilute solution are unlikely to undergo oxidative decomposition. There is a problem that the concentration of carbon monoxide therein increases and the exhaust gas properties deteriorate.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for injecting into a combustion furnace a dilute liquid having a low solid content or substantially no solid content, which is obtained when the liquid organic sludge is concentrated. It is an object of the present invention to solve the problem of deterioration of exhaust gas properties due to incomplete oxidative decomposition of oily substances contained in the diluted liquid.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, from a liquid organic sludge, a concentrated liquid having a high solid content and a concentration step of obtaining a dilute liquid having a low solid content or substantially no solid content, An oil-water separation step of separating oil and water contained in the obtained diluted liquid, and combustion in which the concentrated liquid obtained in the concentration step and the oil substance obtained in the oil-water separation step are burned in a combustion furnace And an oxidative decomposition step in which the separated water obtained in the oil-water separation step is jetted into a combustion furnace to oxidize and decompose organic substances contained in the separated water. Provided.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Organic sludge used as a raw material to be treated in the present invention includes sewage sludge discharged from ordinary sewage treatment plants and excess sludge discharged from various organic wastewater biological treatment apparatuses. Included. As the liquid organic sludge in the present invention, organic sludge having a relatively high water content before dehydration is also an object of treatment, but dewatered sludge obtained by once dehydrating the organic sludge having a high water content To
A liquid organic sludge obtained by maintaining a temperature of 150 ° C. or higher and a pressure of a saturated steam pressure or higher at that temperature is a preferable object. As the dehydration of the organic sludge described above, mechanical dehydration (vacuum dehydration, pressure dehydration, belt press dehydration, and centrifugal dehydration) is usually used, but is not particularly limited. However, it is desirable to add a sludge conditioning chemical to the organic sludge before dehydration, and it is particularly advantageous to add a polymer flocculant. Therefore, regarding the dehydration method, belt press dehydration or centrifugal dehydration, which is suitable for adding a polymer flocculant, is desirable.
The dewatering of the organic sludge is preferably performed so that the moisture content of the obtained dewatered sludge is in the range of 60 to 90% by weight, preferably 70 to 80% by weight.

In order to convert the dewatered sludge into a liquefied material, the dewatered sludge is reacted at a temperature of 150 ° C. or higher, preferably 200 to 250 ° C., and a pressure higher than the saturated steam pressure at the reaction temperature, for example, a reaction temperature of 200 ° C. In case of 16kg /
What is necessary is just to hold | maintain under the conditions of reaction pressure more than cm < ² > (absolute pressure). The liquefaction of the dehydrated sludge can be performed, if necessary, in the presence of an alkaline substance as a liquefaction accelerator.
This alkaline substance, with respect to the solid content in the dewatered sludge,
It is advisable to add 0-20% by weight, preferably 0-5% by weight. Examples of the alkaline substance include, for example, alkali metal compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, sodium formate, potassium formate, calcium oxide, calcium hydroxide, and hydroxide. And alkaline earth metal compounds such as magnesium. The time for maintaining the dewatered sludge under the reaction conditions varies depending on the type of the target sludge, but is generally within 120 minutes, usually,
0-60 minutes. The liquefaction device may be any heat exchanger of the indirect heating type, but since it handles sludge presenting a solid state, a screw-type heat exchanger having a scraper inside or a screw-type heat exchanger having a helical blade is used. Use is preferred. As the pressure in the liquefaction reaction, a self-generated pressure due to water vapor from sewage sludge can be used. However, if necessary, the pressure can be increased using, for example, nitrogen gas, carbon dioxide gas, argon gas, or the like. The sludge liquefied matter thus obtained has a very good fluidity and is sufficiently pumpable.

[0009] The present invention provides a method for concentrating a liquid organic sludge obtained as described above to obtain a concentrated solution having a high solid content and a concentrated solution having a low or substantially no solid content. An oil-water separation step of separating oil and water contained in the dilute liquid obtained in the concentration step, and burning the concentrated liquid obtained in the concentration step and the oil substance obtained in the oil-water separation step A combustion step of burning in a furnace; and an oxidative decomposition step of jetting separated water obtained in the oil-water separation step into the combustion furnace and oxidatively decomposing organic substances contained in the separated water. FIG.
Shows an example of the flow sheet of the method of the present invention. In FIG. 1, reference numeral 103 denotes a concentrator, 104 denotes a diluent tank, and 105
Is a concentrate tank, 106 is an oil / water separator, 107 is a diluent supply pump, 108 is a concentrate supply pump, 109 is a separation water supply pump, 113 is a burner for combustion, 114 is a combustion furnace, 115 is a combustion flame, and 116 is a combustion flame. Each of the devices for spraying the separated water is shown. In order to carry out the present invention according to the flow sheet shown in FIG. 1, the liquid organic sludge is supplied to a concentrating device 103 through a line 101, where it is separated into a concentrated liquid and a dilute liquid. The concentrated liquid is collected in the tank 105, and the dilute liquid is collected in the tank 104. As the concentration device 103, a separation device using specific gravity difference separation such as stationary separation or centrifugal separation, or an evaporator, particularly a flash for discharging high-temperature and high-pressure liquid organic sludge to a flash tank at atmospheric pressure to evaporate water. Various conventionally known devices such as an evaporator can be used. The solid concentration in the concentrate is 5 to 50% by weight,
In particular, it is 10 to 30% by weight. On the other hand, the solid content concentration in the dilute solution is less than 10% by weight, particularly 0 to 5% by weight.
It is. The concentrated liquid collected in the concentrated liquid tank 105 passes through the concentrated liquid supply pump 108 and the line 110 and is supplied to the burner 1.
13 is introduced. Further, oxygen or an oxygen-containing gas as a combustion supporting gas is introduced into the burner 113 through a line 120. The concentrate and oxygen or oxygen-containing gas introduced into the burner 113 are supplied to the combustion furnace 114 from the tip of the burner.
And a combustion flame 115 is formed in the furnace.

On the other hand, the dilute liquid collected in the dilute liquid tank 104 is pumped by the dilute liquid pump 107 into the oil-water separator 10.
6 where the oil is separated and the oil is mixed into the concentrate via line 212. On the other hand, the separated water from which the oily substance has been separated is supplied to the separated water supply pump 10
9. It is introduced into the spraying device 116 through the line 111, and sprayed into the furnace from there. The separated water sprayed into the furnace is instantaneously heated to the furnace temperature, and organic substances contained in the separated water are oxidized and decomposed.

The oil-water separator can be any device that can separate a dilute liquid into an oil phase (oil substance) and an aqueous phase (separated water). As such a device, a specific gravity difference separation device, an extraction device, an oil-water separation device using a coreless resin, or the like can be used. Also, oil-water separation is possible because the oily substance floats on the liquid surface by simply performing the separation by standing in the diluted liquid tank. The dilute liquid contains an oily substance having a content of 0.1 to 5% by weight, particularly 0.5 to 2% by weight. In the oil-water separation step, the oily substance is separated. You. In this case, the degree of separation of the oily substance is such that the concentration of the oily substance contained in the separated water is 1%.
The degree of separation is not more than 0.1% by weight, preferably not more than 0.1% by weight.

The number of spraying devices 116 is not limited to one but may be plural. Further, the separated water can be sprayed toward a central portion in the combustion furnace by a spraying device, but preferably can be sprayed toward a furnace wall surface. When spraying toward the furnace wall, the temperature of the furnace wall can be lowered to improve the durability of the furnace wall, and at the same time, the sludge sprayed from the center of the furnace is prevented from adhering to the furnace wall. it can.

In the present invention, as described above, the concentrated liquid obtained by the concentrating device 103 is injected into the combustion furnace 114 via the burner 113 together with the oily substance obtained by the oil / water separating device 106, and the combustion is performed. Is done. In this case, line 1
Air, oxygen-enriched air or oxygen gas is used as the supporting gas after passing through 20. The type of burner is not particularly limited, but it is preferable to use an external or internal mixing two-fluid spray burner or a low-pressure air spray burner. Combustion gas generated by combustion of the concentrate and oily substances in the furnace,
Decomposed gas generated by oxidative decomposition of organic matter in the separated water is discharged out of the furnace through the line 117. The high-temperature exhaust gas discharged outside the furnace is subjected to heat recovery from the exhaust gas through a heat exchanger, and then sent to a subsequent-stage exhaust gas treatment facility.
Here, the harmful gas contained in the exhaust gas is removed and then released to the atmosphere.

The water content of the concentrate is related to the calorific value of the concentrate and to the flame temperature when the concentrate is sprayed and burned. By lowering the water content of the concentrate, the calorific value of the concentrate increases and the flame temperature also increases. For example, when the concentrate is burned by air, the lower heating value of the concentrate is 1260 k
cal / kg, 2150 kcal / kg, and 3050
At kcal / kg, the maximum temperatures of the combustion flames are 1170 ° C., 1520 ° C. and 1740 ° C., respectively.
Becomes The lower heating value of the concentrated solution changes depending on the water content of the concentrated solution. For example, a concentrated solution having a lower heating value of 3970 kcal / kg in an anhydrous state has a water content of 20% by weight and 40% by weight. % And 60% by weight, the lower heating value is 3050 kcal /
kg, 2150 kcal / kg and 1260 kcal / kg
kg. The lower calorific value of the concentrated liquid is represented by the following equation. H (L) = H (U) -600 × W In the above formula, H (L) indicates a lower calorific value (kcal / kg). H (U) indicates a higher calorific value (kcal / kg), which is a calorific value measured by a calorimeter and is a calorific value including latent heat when water vapor condenses. W indicates the amount of water vapor (kg) generated during combustion. When the concentrated liquid is burned in the combustion furnace, the steam generated during the combustion flows out to the outside together with the combustion gas without being condensed. Therefore, the latent heat of the steam is not used for heating the solid content (sludge) in the concentrated liquid. Therefore, as the calorific value used to study the flammability of the concentrate,
The lower heating value is adopted.

In the present invention, as described above, the water content of the concentrated solution is controlled by adjusting the concentration ratio of the organic sludge in the concentration step, that is, by adjusting the operating conditions of the concentration device 103. However, in this case, the water content of the concentrated solution is usually controlled to 90% by weight or less, preferably 70% by weight or less. On the other hand, the concentrated liquid has a higher viscosity as its water content decreases. If the viscosity is too high, the concentrated liquid cannot be sprayed smoothly from the burner. Therefore, from this viewpoint, the viscosity of the concentrated liquid is 20 ° C.
The apparent viscosity at a shear rate of 10 s to ¹ measured in
It is good to control to 000 cp or less, preferably 50 cp or less.

Since the water content and the viscosity of the concentrated liquid have a correlation, by adjusting the water content of the concentrated liquid, both the calorific value and the viscosity of the concentrated liquid can be controlled. From this viewpoint, the water content of the concentrated liquid is set to 50 to
By controlling the content to 90% by weight, preferably 50 to 70% by weight, the spray from the burner can be performed smoothly, and moreover, the amount required for melting the inorganic substances in the sludge is 1%.
A flame of 200 ° C. or higher, preferably 1400 to 1500 ° C., can be formed. Conversely, by controlling the viscosity of the concentrate to 10 to 2,000 cp, preferably 10 to 500 cp, the spray of the concentrate from the burner can be carried out smoothly, and moreover, the melting of inorganic substances in the sludge can be performed. Required 1200 ° C. or higher, preferably 1400
A flame of ~ 1500C can be formed.

In the present invention, the concentrated liquid is burned by a burner, and at least a part of the combustion flame is maintained at a temperature higher than the melting temperature of the inorganic substance contained in the sludge. Therefore, the inorganic substances in the sludge are melted in the flame and become molten powder. This molten powder is very fine, and those having a particle size of 10 μm or less represent 50% or more. Further, the molten powder exhibits a spherical shape due to the effect of surface tension when the inorganic substance is melted. This molten powder flows out of the furnace together with the combustion gas, but is separated and recovered from the combustion gas by a filter or an electric dust collector installed outside the furnace.

In the present invention, the temperature of at least a part of the combustion flame needs to be maintained at a high temperature as described above, but the temperature of the entire furnace does not need to be at such a high temperature.
In the case of the present invention, the temperature of the furnace wall inner surface is 500 to 1000 ° C.
It is not necessary to use a special material as the furnace wall material, and by keeping the furnace wall inner surface temperature at such a low temperature, heat loss escaping from the inside of the furnace to the outside of the furnace is suppressed. You.

In the case of the present invention, at least a part of the flame 115 is maintained at a temperature higher than the melting temperature of the inorganic substance contained in the sludge, and the inorganic substance is melted when the concentrated liquid is burned. Since the inorganic substance is usually melted at a temperature of 1200 ° C. or more, it is 1200 ° C. or more, preferably 1400 to 1
A flame having a temperature of 500 ° C. may be formed. Further, in such combustion of the concentrated liquid, the temperature of the entire furnace is in a temperature range of 700 to 900 ° C.

[0020]

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

Example 1 Sewage sludge was selected as an organic sludge, and a dewatered cake of mixed raw sludge discharged from a treatment plant using a standard activated sludge method was used for the test. This sludge is obtained by adding a polymer flocculant and then dewatering it by a belt press. Its typical properties are
It has a water content of 78% by weight, an organic matter ratio of 78% by weight, and a lower calorific value of 3,940 kcal / kg.

The dewatered sludge was liquefied using a continuous sludge liquefaction apparatus (processing capacity: 250 kg / hr). This device is composed of a press-in device, a reactor (scratch surface heat exchanger), a pressure reducing valve, a flash tank, a concentrated solution tank, a condenser, a dilute solution tank, and a heat medium boiler. It was supplied by a medium boiler. The dewatered sludge was introduced into the reactor at a pressure of 85 kg / cm ² using a press-in device, and heated to about 260 ° C. while performing scraping to prevent clogging and promote heat transfer. The residence time at the reaction temperature was about 10 minutes. The dewatered sludge was sufficiently liquid at the outlet of the reactor, and the liquid sludge in a high temperature and high pressure state was discharged to a flash tank at atmospheric pressure via a pressure reducing valve.
In the flash tank, the water in the sludge was evaporated, and the temperature of the sludge was cooled to 100 ° C. Low-boiling components such as organic acids and oily substances were discharged from the upper part of the flash tank together with water vapor, cooled to room temperature with a condenser, and stored in a dilute liquid tank. On the other hand, the concentrate remaining in the lower part of the flash tank was automatically discharged by operating a valve and stored in the concentrate tank. By the above operation, the water content was 78% by weight.
(Solid content 22% by weight) from dewatered sludge to solid content 2
A concentrated solution of 5% by weight and a dilute solution having a solid concentration of 2% by weight and producing an offensive odor were obtained.

The dilute solution obtained as described above contained 1% by weight of an oily substance. This oil was a heavy oil. The diluted liquid was allowed to stand in a tank for 2 hours to separate the oily substance from the separated water by floating the oily substance on the liquid surface. The floating oil was collected and mixed with the concentrate. Next, a mixture of 100 parts by weight of the concentrated liquid and 0.4 parts by weight of the oily substance is sent to an externally mixed high-pressure two-fluid spray burner at a flow rate of 188 L / h using a snake pump, and sprayed into the combustion furnace. At the same time, kerosene for combustion was used at a rate of 16 liters / h to maintain the flame temperature, and was burned. At this time, oxygen-enriched air containing 30 vol% oxygen was used as the oxygen-containing gas for combustion. Under these conditions, the mixture formed a flame and burned, and continued burning. The flame combustion was continued for one hour or more, and the combustion flame temperature at this time was about 1500 ° C. Next, when the combustion is stabilized, the separated water obtained above is withdrawn from the lower part of the dilute liquid tank, and the flow rate is reduced to 7 by a pump.
It was sprayed into the combustion furnace at 5 liter / h to decompose organic matter in the separated water. In addition, a sampling probe was inserted into the exhaust gas duct outlet, and the molten powder was collected. Examination of the molten powder with a microscope revealed that it had a very small sphere. This means that the inorganic component melted in the combustion flame and became spherical due to surface tension.
Also, when the carbon monoxide concentration in the combustion exhaust gas was examined,
Its concentration was 0.1 ppm.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 except that a dilute solution was used instead of the separated water. Examination of the concentration of carbon monoxide in the combustion exhaust gas in this case revealed that the concentration was as high as 1 ppm.

[0025]

According to the present invention, the dilute liquid obtained when the liquid organic sludge is concentrated is separated into oil and water, and the oily substance obtained during the oil and water separation is sprayed into a combustion furnace as a mixture with the concentrated liquid. The separated water after removing the oily substance causes it to squirt into the combustion furnace,
Organic matter contained in the separated water is oxidatively decomposed. According to such a method, in the separated water jetted into the combustion furnace,
It contains virtually no organic matter that is difficult to oxidatively decompose and contains only organic matter that is easily oxidatively decomposed.Therefore, oxidative decomposition of organic matter in the separated water injected into the combustion furnace occurs smoothly, and monoxide in the combustion exhaust gas The carbon concentration is low and the exhaust gas emitted is of good quality. Also, by mixing the oily substance with the concentrate, the calorific value of the concentrate can be increased, and the amount of auxiliary fuel used can be reduced.

[Brief description of the drawings]

FIG. 1 shows an example of a flow sheet of the method of the present invention.

[Explanation of symbols]

 103 Concentrator 104 Dilute liquid tank 105 Concentrate liquid tank 106 Oil-water separator 107 Dilute supply pump 108 Concentrate supply pump 109 Separation water supply pump 113 Burner 114 Combustion furnace 115 Combustion flame 116 Sprayer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeo Terada 2-81-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside the Tokyo Metropolitan Sewerage Bureau (72) Inventor Toshiro Harada 2-81-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Metropolitan Sewerage Bureau (72) Inventor Shinji Ito 5-5-16-1 Hongo, Bunkyo-ku, Tokyo Organo Corporation (72) Inventor Makoto Inoue 2-4-2, Kyomachibori, Nishi-ku, Osaka-shi, Osaka Chugai Furnace Industrial Co., Ltd. Inside the company (72) Inventor Masao Nonohiro 2-4-7 Kyomachibori, Nishi-ku, Osaka-shi, Osaka Inside Chugai Furnace Industry Co., Ltd. (72) Inventor Toshiaki Teraya 2-4-2, Kyomachibori, Nishi-ku, Osaka-shi, Osaka Chugai Furnace Industry Co., Ltd.

Claims (2)

[Claims] 1. A concentration step of obtaining, from a liquid organic sludge, a concentrated liquid having a high solid content, a dilute liquid having a low solid content or substantially no solid content, and a diluting liquid obtained in the enriching step. An oil-water separation step of separating oil and water contained in the liquid, a combustion step of burning the concentrated liquid obtained in the concentration step and the oil substance obtained in the oil-water separation step in a combustion furnace, A method for treating liquid organic sludge, comprising an oxidative decomposition step in which separated water obtained in the oil-water separation step is jetted into a combustion furnace to oxidatively decompose organic substances contained in the separated water. 2. The method according to claim 1, wherein the liquid organic sludge is obtained by dehydrating an organic sludge and subjecting the dehydrated sludge to a high-temperature and high-pressure treatment.