JPH0160730B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for burning sludge produced in the treatment of water, sewage, industrial wastewater, etc., and treating it as a sintered product. Generally, sludge generated in water supply, sewage, industrial wastewater treatment, etc. is often treated by landfilling after going through a thickening and dewatering process. It has become difficult to even determine the amount of carbon dioxide, and for this reason, incineration methods such as fluidized beds are being widely adopted. However, the conventional fluidized bed incineration method has extremely superior properties, such as having little unburned content (components reduced by burning) in the residual ash, requiring a small equipment footprint, and producing no odor. Since the ash is processed at a relatively low temperature, it is difficult to handle because it is a fine powder, and it is prone to scattering and muddy runoff during transportation and at landfill sites.Furthermore, the heavy metals contained in the residue are leached, which poses a threat to the environment. There were many points that needed to be improved, such as the fact that the In order to facilitate the handling of the residue and prevent the elution of heavy metals, various solidification techniques have been proposed, including a method of adding a solidifying agent such as cement or asphalt, and a method of heating and melting the residue and then allowing it to cool and solidify. It is being Among these methods, the method of adding a solidifying agent is effective in containing harmful substances and improving the soil quality of the landfill, but the price of the solidifying agent is high and it is not possible to solidify the entire amount of the above-mentioned residue that is discharged daily. Have difficulty. In addition, the conventional melting method is an excellent method because the volume of the molten material is significantly reduced and becomes granular or lumpy, making it easy to handle and containing harmful substances such as heavy metals, but the running cost is high. , has little utility value. As described above, there are still many problems that need to be solved with conventional waste solidification technology, and the current situation is that there is an urgent need to develop new technologies from the viewpoints of resource and energy conservation. Generally, when sludge is calcined, the sludge is dispersed or shaped as appropriate before being fed into a fluidized fluidized furnace to make it easier to handle and reuse. On the contrary, the sludge significantly foams, expands, deforms, and causes cracks, making it impossible to obtain a dense sintered material that is convenient for reuse. In addition, when the sludge exhibits such remarkable foaming and expansion, the sludge gradually fuses together and becomes swollen and lumpy in a so-called snowball style, which impedes the smooth operation of the fluidized bed furnace and makes it difficult to discharge. year,
Furthermore, damage such as damage to the ejection mechanism may occur. Furthermore, in order to make the agglomerated sludge easier to reuse, a crushing mechanism,
Since this creates the disadvantage of requiring a separate sieving mechanism and reprocessing using these mechanisms, baking and drying has no choice but to be abandoned. That is, when the fluidized bed furnace is raised and maintained at the sintering temperature of the sludge in order to obtain a sintered product by fluidized sludge sintering, the sludge foams and expands significantly, and becomes fused and agglomerated. Although it is known that it is effective to turn sludge into a sintered product, there is a temperature range (hereinafter referred to as sintering temperature range) in which a dense and easily recyclable sintered product can be obtained. In practice, this method was inconvenient and uneconomical because there was no or very limited number of methods (named). The present invention solves the current situation by effectively utilizing the energy contained in waste.
The purpose of inorganic materials is to make them easier to handle by firing them, to prevent the elution of harmful substances such as heavy metals, and to pave the way for reuse. In particular, the present invention aims to provide an effective treatment method that eliminates the various drawbacks of conventional sludge treatment, prevents foaming and fusion of sludge, and easily produces dense, strong sintered material that is convenient for reuse. It is something to do. The present invention relates to a method for burning sludge generated in the treatment of water, sewage, industrial wastewater, etc. Excessive CaO component (10% or more) in sludge inorganic matter
If it is contained, the firing temperature will rise, and near the firing temperature, a low-viscosity melt will be rapidly produced, narrowing the firing temperature range. These sludges contain 10 to 80% of ignition loss components (also referred to as ignition loss components.Hereinafter referred to as ignition loss components), and this ignition loss components are produced by CO or As C, it reacts with the iron contained in the sludge inorganic matter, resulting in a low melting point,
This method was developed based on the fact that the firing temperature range becomes narrow due to excessive production of low-viscosity melt (see Table 1 below). The feature of the present invention is that the sludge is dehydrated using chemical-free injection or an organic flocculant, and then granulated and dried to a moisture content of 40% or less, until the sludge loses its content by ignition to 5% or less, preferably 2% or less. After fluidized combustion at a temperature of 600°C to 900°C, the incinerated ash is further heated to 1000 ml in a second fluidized bed process.
℃~1250℃, and the fluidized medium used in the first stage fluidized bed process is treated using the fired product fired in the second stage fluidized bed process to obtain a sintered product. It is in. As described above, according to the present invention, foaming of sludge is suppressed in the firing process, the sludge does not fuse together to form a lump, and a sintered product that is dense and strong and convenient for reuse can be obtained. The firing temperature range is widened, and the temperature control of the firing furnace becomes extremely easy, making it possible to process the sludge into a state convenient for disposal or reuse. In this case, the first stage fluidized bed is used to efficiently burn organic matter at a relatively low and uniform temperature, and the second stage fluidized bed is heated to an appropriate temperature to further heat up the inorganic matter to form a strong sintered material. It is important to control the moisture content of the sludge introduced into the first stage fluidized bed.
By drying the sludge to 40% or less (preferably 20% or less) and granulating it to a diameter of about 2 to 7 mm, the sludge can be efficiently fluidized and incinerated, and the sintering of inorganic substances can proceed smoothly. Therefore, it is best to treat it as dry granulated sludge. By using the sintered material of the second-stage fluidized bed as the fluidized medium of the first-stage fluidized bed used in the present invention, there is no need to replenish silica sand, etc., and the sensible heat of the sintered material is effectively utilized, resulting in energy saving and economical. can be processed. The sludge sent to the first-stage fluidized bed is granulated, and the fluidized medium used is the sludge that has been calcined, so that the sludge is rarely pulverized in this fluidized bed. Moreover, when introduced into the second stage fluidized bed, the sintering is completed rapidly, and the feed material and the sintered product are appropriately mixed, so that no special fluidizing medium is required. As sintering progresses, due to the difference in specific gravity, it is selectively discharged from the bottom,
In addition, the high-temperature exhaust gas from the second-stage fluidized bed furnace is used as a heat source for the first-stage fluidized bed furnace, and the exhaust gas from the first-stage fluidized bed furnace is used for drying, reducing oil consumption to the same level as a general fluidized bed furnace. It is possible to obtain a baked product depending on the amount. Embodiments of the present invention will be described in detail with reference to the drawings.
First, organic flocculant C is added to the concentrated sludge obtained from settling tank A, etc., which has a moisture content of about 95% and contains organic matter, and is dehydrated in dehydrator B, resulting in a dehydrated cake with a moisture content of 70 to 80%. Let it be D. (Dehydrated sludge properties are shown in Table 1)

[Table] Next, this dehydrated cake D is led to a granulation dryer 2 by a belt conveyor 1, and is granulated and dried using steam from a combustion exhaust gas waste heat boiler 12 from a second stage fluidized bed furnace, which will be described later. The sludge, which has been granulated and dried to a particle size of approximately 2 to 7 mm with a moisture content of 10% or less, is temporarily stored in a storage tank.
to be stored. The dust-containing dust discharged from the granulation dryer 2
D' is collected by a cyclone 4, the dust D' is returned to the granulation unit attached to the dryer, and the removed exhaust gas G is collected by a scrubber 5 and a deodorizing device 6 and then released into the atmosphere. The washing water G' is sent to the heat exchanger 14, and is returned to the sedimentation tank A or the like for reprocessing. The dried sludge E granulated and dried in this manner is supplied in fixed amounts to the first stage fluidized bed furnace 9 by a belt conveyor' and a screw feeder 7. in this case,
The amount of sludge to be supplied is controlled to a predetermined amount by a measuring device 8 installed at the lower part of the storage tank 3, and the sludge is transported. This dried sludge E is uniformly distributed and supplied into the first stage fluidized bed furnace 9, instantaneously reaches the ignition temperature, and undergoes thermal decomposition and a partial oxidation reaction. The reaction temperature is controlled by the supply amount and air blowing amount, and a reaction product (ash) with a ignition loss component of 5% or less is produced in about 10 minutes of residence time, and this reaction product is transferred to the second stage fluidized bed furnace 12 Since the second stage fluidized bed furnace 12, which is supplied to If processing is performed without using a fluid medium, the equipment can be made smaller and the amount of air blown can be reduced. The second stage fluidized bed furnace exhaust gas has a high temperature and high O ₂ concentration, so some of it is used for drying sludge.
The other part can be used as oxygen for the combustion air of the first stage fluidized bed furnace 12 and as a heat source. (In this case, the fuel consumption can be reduced to about 1/2 compared to when heat is not recovered.) By setting the temperature of the first stage fluidized bed to 400 to 800°C and varying the residence time, the ignition loss components are volatilized. Burning weight loss ingredients are 60.5% 25% 10% respectively
5% 4% 3% 2% 1% sludge and each of these sludges having different contents of ignition loss components was fluidized in a second stage fluidized bed furnace, and the results shown in Table 2 were obtained.

[Table] From these results, it can be seen that the sintering temperature range can be expanded if the sludge is combusted to volatilize the ignition loss components before raising and holding the sludge to the sintering temperature. In other words, even if it burns, it will be impossible to sinter if the ignition loss component is 6% or more;
% or less, there is a sintering temperature range of 100°C, and by processing within that range, it becomes extremely easy to sinter. The calcined ash from the second stage fluidized bed furnace 12 is discharged out of the system from the discharge lock damper 13, and the combustion exhaust gas F may be discharged into the atmosphere from the chimney 20 by the induction fan 19, but a part of it may be bypassed. The air is circulated to the first stage fluidized bed furnace 9 and used as a heat source or part of the combustion air. In the figure, 15 is a hot air stove, 16 is a fuel pump for fuel such as heavy oil, 17 and 18 are air supply fans for combustion, and 21 is a burner. H indicates water supply. Next, examples of the present invention will be shown. Example Dehydrated sludge is granulated and dried to a particle size of 3 to 5 mm with a moisture content of 10% or less, and an inner diameter of 200 mm at a feed rate of 10 KgDS/h.
Fluidized combustion air is supplied to the first stage fluidized bed furnace with a height of φ3m.
It was operated at a reaction temperature of 700°C at 1.5Nm ³ /min. As the fluidizing medium, calcined sludge (diameter 2 to 4 mm) was added so that the height of the static bed was 400 mm. The fluidized medium (fired product) achieved stable combustion conditions at 500 to 900°C, could be used in place of silica sand, and reduced the pressure loss in the stationary bed to about 2/3 or less. The fluidized incineration material discharged from the first-stage fluidized bed furnace (with a ignition loss of 2% or less) is sent to the second-stage fluidized bed furnace by a bucket conveyor. The second stage fluidized bed furnace has a cross-sectional area of about 1/2 to 1/4 of the first stage, uses a fluidized bed with an inner diameter of 100φ and a height of 3 m, and uses the granular incineration material itself without using a fluidized medium. A fluidized bed was formed. Fluidized bed height is approx.
Stable operation was possible with a fluidized air flow rate of 0.5 Nm ³ /min and a fluidized bed temperature of 1050°C to 1100°C, maintained at 80 to 100 cm. It was found that a hard sintered product with a particle size of 2 to 4 mm was obtained, and the elution of heavy metals from the sintered product was sufficiently suppressed. For comparison, when powder of 1 mm or less was fluidized and combusted, about 1/3 to 1/2 was carried away with the exhaust gas. Furthermore, when this incinerated ash was operated in a fluidized fluidized furnace at 1050°C, the furnace pressure fluctuated drastically and a stable fluidized state could not be obtained. When the first stage was controlled at 1050°C and granulated dry sludge was supplied, lumps were formed and operation became impossible. The exhaust gas (900 to 1000℃) of the fluidized bed furnace for firing is used for combustion, and the exhaust gas (600 to 800℃) of the fluidized bed furnace for combustion is
℃) for sludge drying, sintered material was obtained at the same level of oil consumption as in the case of incineration alone. In the present invention, dried sludge is dried and granulated to a water content of 40% or less, which is incinerated at 600 to 900°C in the first stage fluidized bed process so that the loss on burning is 5% or less.
The incinerated ash is calcined at 1000 to 1250°C in a second-stage fluidized bed process, and the fluidized medium used in the first-stage fluidized bed process is treated using the fired product calcined in the second-stage fluidized bed process. As a result, there is no need to replenish silica sand, etc., and the sensible heat of the sintered product is effectively used, making energy-saving and economical processing possible.The sludge sent to the first stage fluidized bed is granulated. , and the fluidized medium used is the sludge that has been calcined, and the sludge is rarely pulverized in this fluidized bed, and moreover, when it is led to the second stage fluidized bed, it quickly stops burning. , the feed material and the sintered product are appropriately mixed, no special fluidized medium is required, and as sintering progresses, it is selectively discharged from the bottom due to the difference in specific gravity, and it is also discharged from the second stage fluidized bed furnace. The high-temperature exhaust gas is used as the heat source for the first-stage fluidized bed furnace, and the exhaust gas from the first-stage fluidized bed furnace is used for drying, thereby producing a fired product with the same amount of oil consumption as a general fluidized bed furnace and improving the firing process. In this process, foaming of sludge is suppressed, the sludge does not fuse together and become lumps, and a dense, strong sintered product that is convenient for reuse can be obtained. Moreover, the firing temperature range is widened, and the temperature control of the firing furnace is easy. This makes it extremely easy to process sludge, making it possible to process it into a state that is convenient for disposal or reuse, allowing it to be disposed of as a treated product that does not cause secondary pollution, reducing lining costs, and making treatment operations easy. This method can completely eliminate all the problems of conventional methods.

[Brief explanation of drawings]

The drawing is a flow sheet of an embodiment of the method of the invention. A... Sedimentation tank, B... Dehydrator, 1... Belt conveyor, 2... Granulation dryer, 3... Storage tank, 4...
... Cyclone, 5 ... Scrubber, 6 ... Deodorizing device, 7 ... Screw feeder, 8 ... Weighing machine, 9 ... First stage fluidized bed furnace, 10 ... Ash discharge lock damper, 11 ... Belt Conveyor, 12...
Second stage fluidized bed furnace, 13...Calcined ash discharge lock damper, 14...Waste gas heat exchanger, 15...Hot blast furnace, 16...Heavy oil pump, 17, 18...Combustion fan, 19...Induction Juan, 20...Chimney, 2
1...Burner.

Claims (1)

[Scope of Claims] 1. Dried sludge is dried and granulated to a water content of 40% or less, which is incinerated at 600 to 900°C in the first stage fluidized bed process so that the loss on ignition is 5% or less. The incinerated ash is calcined at 1000 to 1250°C in the second stage fluidized bed process, and the fluidized medium used in the first stage fluidized bed process is treated using the fired product calcined in the second stage fluidized bed process. A fluidized sludge firing method characterized by: 2. The first fluidized bed process is performed using the exhaust gas from the second fluidized bed process as a heat source, and the exhaust gas from the first fluidized bed process is used as a heat source for drying sludge. A sludge burning method according to claim 1. 3. Claim 1, wherein the second stage fluidized bed process is performed without using a fluidized medium.
The sludge burning method described in Section 2 or Section 2.