JP5027697B2 - Sewage sludge treatment method - Google Patents

Description

  The present invention relates to an improvement of a sewage sludge treatment method for dewatering and incinerating sewage sludge generated from a sewage treatment plant.

  As shown in Patent Document 1, a method for treating sewage sludge generated from a sewage treatment plant is to incinerate dehydrated sludge in an incinerator such as a fluidized furnace to take out incineration ash, and the incineration exhaust gas is a dust collector and a scrubber (exhaust gas treatment). A method of treating with an exhaust gas treatment apparatus including a tower is widely known.

  In addition, many developments have been made on sludge dewatering methods. Basically, flocs are formed by adding polymer flocculants and inorganic flocculants to sewage-concentrated sludge generated from sewage treatment plants. A method of dehydration after increasing the viscosity is adopted.

However, there is a limit to the dewatering performance by the dehydrator, and there is a situation in which the water content after dewatering cannot be sufficiently reduced depending on the sludge. For this reason, even if dehydrated sludge was put into the incinerator and incinerated, it could not be self-combusted because of the high water content, and auxiliary fuel such as city gas and heavy oil had to be supplied to the incinerator. In the current situation where global warming prevention is screamed, injecting new fuel to incinerate sewage sludge, which is essentially combustible, simply consumes a lot of energy to evaporate water. This is undesirable.
Japanese Patent No. 3812432

  Therefore, the object of the present invention is to solve the above-mentioned drawbacks of the prior art, and reduce the moisture content of dewatered sludge to a level at which incinerators can self-combust without the need for extra fuel, thereby discharging global warming gas. It is providing the sewage sludge processing method which can suppress the quantity.

In order to solve the above problems, the present invention provides a sewage sludge treatment method in which a flocculant is added to a sewage sludge, dehydrated and incinerated, and the incineration exhaust gas is treated by an exhaust gas treatment apparatus including a dust collector and a scrubber. In addition to raising the temperature of the hot effluent generated in the air by heat exchange with the white smoke prevention air heated by the incineration exhaust gas, the sewage sludge is heated to 40-90 ° C. by supplying it to the heater, and the dehydrating property is improved. It is characterized by improving. In addition, the kind of warmer is not specifically limited.

In addition, it is preferable to heat a sewage sludge to 50-80 degreeC .

  In the present invention, the scrubber wastewater is supplied to a heater installed before the sludge of the dehydrator is added, and the sewage concentrated sludge to which the flocculant is added is heated to 40 to 90 ° C, more preferably 50 to 80 ° C. . As a result, thermal alteration or thermal destruction occurs in the cell membrane of the microorganism that occupies the main part of sewage sludge, and the intracellular moisture can be transferred to the outside. It can be reduced by about 2 to 4% compared to the conventional case. As a result, the thermal burden in the incinerator is reduced, and self-combustion can be achieved without supplying auxiliary fuel. Moreover, although the scrubber wastewater is low temperature water of about 50 to 70 ° C. and has a low utility value as an energy source, the present invention can be effectively used.

  In addition, although there is a prior art in which sewage sludge is heated and dehydrated at a high temperature and a high pressure, the present invention only needs to be heated at normal pressure, so a pressure device is not required, and the apparatus can be simplified. Furthermore, in the prior art, since the cell membrane of microorganisms in the sewage sludge is completely destroyed, there has been a problem that the properties of the dehydrated filtrate are extremely deteriorated. In the present invention, the heating temperature is 40 to 90 ° C. In addition, since the cell membrane is not completely destroyed, deterioration of the properties of the dehydrated filtrate discharged from the dehydrator can be suppressed.

  The scrubber drainage or the fresh water heated by the scrubber drainage may be supplied to the heater as it is. However, if the temperature is raised using the exhaust heat of the incineration exhaust gas and then supplied to the heater, the scrubber drainage Even when the temperature of fresh water raised by drainage or scrubber drainage is low, operation is possible without any problem.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a block diagram showing an embodiment of the present invention. The most basic devices conventionally used in this type of sewage sludge treatment system are a dehydrator 1, an incinerator 2, a dust collector 3, and a scrubber 4. , Chimney 5. First, the dehydrator 1 is a device for dewatering sludge generated from a sewage treatment plant. The type of the dehydrator 1 is not particularly limited, and various dehydrators conventionally used for sludge dehydration can be used. In this embodiment, a rotary pressure dehydrator manufactured by the applicant company is used. It was used. The solid content concentration of the sludge is about 3% (water content 97%). However, according to the rotary pressure dehydrator, the water content can be dehydrated to about 80%.

  The dewatered sludge dehydrated by the dehydrator 1 is put into the incinerator 2 and incinerated. There are various types of dewatered sludge incinerator 2, but recently, fluid incinerators have become widespread from the viewpoint of preventing dioxin generation and downsizing of facilities. However, if the moisture content of the dewatered sludge remains at 80%, it cannot be self-combusted, and auxiliary fuel is required as described above. A heat exchanger 6 is disposed immediately after the incinerator 2, and the air used in the incinerator 2 is preheated by high-temperature incineration exhaust gas. In the case of a fluidized incinerator, the heat exchanger 6 preheats the fluidizing air.

The high-temperature incineration exhaust gas discharged from the incinerator 2 contains a large amount of incineration ash and contains harmful components such as SO _X , so the incineration ash is removed by the dust collector 3 and the scrubber is further removed. After 4 is brought into gas-liquid contact with the washing water to remove SO _{X and the} like, it is discharged from the chimney 5. The incineration exhaust gas that has passed through the scrubber 4 contains water vapor with a saturated concentration, so that when it is directly discharged from the chimney 5 into the atmosphere, white smoke is generated due to condensation of the water vapor. Therefore, a white smoke prevention heat exchanger 7 is conventionally provided, and air is heated and supplied to the chimney 5 to prevent white smoke.

  The above configuration is the same as that of the prior art, but in the present invention, the warmer 8 is installed before the sludge is added to the dehydrator 1, and the warm water discharged from the scrubber 4 is supplied to the warmer 8 by a pump. Warm up. The heating temperature is 40 to 90 ° C, more preferably 50 to 80 ° C. The main component of sewage sludge is a collection of microorganisms, and this heating causes thermal alteration or thermal destruction of the microbial cell membrane, allowing intracellular moisture to move outside during dehydration. Will improve.

  As shown in data to be described later, when the temperature is lower than 40 ° C., the improvement of dewaterability is insufficient, and a favorable effect is obtained particularly at 50 ° C. or higher. Conversely, when heated to a high temperature exceeding 90 ° C, the cell membrane of the microorganism is completely destroyed and the cell fluid flows out, and the turbidity concentration in the dehydrated filtrate of the dehydrator 1 increases or is taken into the cell. This is not preferable because it causes problems such as increased dissolution of phosphorus.

Although there is some variation depending on the equipment, the scrubber drainage is hot water of about 50-70 ° C. Therefore, the scrubber wastewater can be supplied to the heater 8 as it is, but as shown in FIG. 1, the scrubber wastewater heater 9 raises the temperature using the exhaust heat of the incineration exhaust gas and supplies it to the heater. By doing so, even when the temperature of the scrubber drainage is low, operation is possible without any problem. In this embodiment, the scrubber drain heater 9 is heated after being heated to 80 to 90 ° C. by heat exchange with the white smoke prevention air heated by the white smoke prevention heat exchanger 7. Is supplied to the vessel 8. In the reference embodiment shown in FIG. 2, the temperature of the fresh water is raised by heat exchange with the warm waste water generated in the scrubber 4 by the heat exchanger 10 and then heat exchange with the white smoke prevention air heated by the incineration exhaust gas. The temperature is rising .

  If the concentrated sludge heated in this way is dehydrated by the dehydrator 1, the dewaterability is improved, so that a dehydrated sludge having a moisture content of 2 to 4% lower than the conventional one can be obtained. According to the rotary pressure dehydrator as in this embodiment, the moisture content is conventionally 80%, but according to the present invention, a dewatered sludge having a moisture content of about 76 to 78% can be obtained. . If the moisture content reaches such a level, it is possible to cause the incinerator 2 to self-combust, so that no auxiliary fuel is required at all or only a small amount is required when necessary. Therefore, it becomes possible to reduce the water content of the dewatered sludge to a level at which the incinerator can self-combust without reducing the amount of global warming gas without requiring extra fuel.

  In the present invention, the flocculant is added to the concentrated sludge before the heater 8. However, depending on the properties of the sludge, it is also effective to add the flocculant after the heater. The type of the flocculant is a polymer flocculant, an inorganic flocculant, or a combination of both.

The operation and effect of the present invention will be described below with specific numerical values. Here, the scale of the incinerator 2 is set to 100 tons / day. In the past, 43 m ³ _N / h city gas was required as auxiliary fuel to incinerate dehydrated sludge with a moisture content of 80%, and its energy intensity was 464 MJ / tonne-sludge. At this time, scrubber wastewater having a water temperature of 50 ° C. was discharged from the scrubber.

In contrast, in the present invention, the scrubber drainage is heated to 87 ° C. by the scrubber drainage heater 9 shown in FIG. 1, and the concentrated sludge to which the polymer flocculant has been added in advance is heated from 20 ° C. to 60 ° C. After warming, it is sent to the dehydrator 1 to obtain dehydrated sludge having a moisture content of 78%. This dewatered sludge can be burned without using auxiliary fuel, and energy saving of 464 MJ / ton-sludge (1935 MJ / h) becomes possible. In addition, when the incinerator 2 has the same capacity, the amount of concentrated sludge that can be treated increases from 27.7 ton / h to 30.6 ton / h. In addition, when the above-mentioned 100 ton / day incinerator is operated for 330 days a year and converted into the amount of greenhouse gas emissions derived from auxiliary fuel, 708 ton-CO ₂ / year of the conventional system is 0 ton in the system of the present invention. -CO ₂ / year, enabling significant reduction.

  In addition, using concentrated sludge with an addition rate of flocculant of 0.6%, when not heating at room temperature, when heated to 40 ° C, when heated to 60 ° C, when heated to 80 ° C When a dehydration test was performed in the laboratory, the results shown in Table 1 were obtained. When the heating temperature is raised in this way, the moisture content of the dewatered sludge decreases, but the turbidity concentration in the dehydrated filtrate increases, so 90 ° C is the limit, and practically 80 ° C or less. preferable.

It is a block diagram which shows embodiment of this invention. It is a block diagram which shows the reference form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dehydrator 2 Incinerator 3 Dust collector 4 Scrubber 5 Chimney 6 Heat exchanger 7 Heat exchanger for white smoke prevention 8 Heater 9 Heater for scrubber drainage 10 Heat exchanger

Claims (2)

By adding a coagulant to the sewage sludge incinerated after having dehydrated, the sewage sludge processing method for processing the incineration exhaust gas by the exhaust gas treatment apparatus including a dust collector and scrubber was heated hot wastewater generated in the scrubber by incineration exhaust white smoke A sewage sludge treatment method characterized by heating the sewage sludge to 40 to 90 ° C. by raising the temperature by heat exchange with the air for prevention and supplying it to a heater to improve dewaterability .   The sewage sludge treatment method according to claim 1, wherein the sewage sludge is heated to 50 to 80 ° C.

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