JP3574178B2 - Sludge drying method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for drying sludge.
[0002]
[Prior art]
Conventionally, sewage sludge, food production sludge discharged from food production plants, etc., and animal waste sludge including blood discharged from animal slaughterhouses, etc., are oil temperature dehydration treatments already developed by the present applicant. Has been processed by law.
[0003]
In this method, sludge was immersed in heating oil, dewatered by stirring under reduced pressure, and the solid was powdered so that it could be used as an organic fertilizer or feed.
[0004]
However, when oil-temperature dehydration treatment is performed using sludge of a type that cannot be used for fertilizers or feeds, solid matter after dehydration may be used as landfill for landfill or dumped at sea.
[0005]
[Problems to be solved by the invention]
In this way, when landfilling solid materials that cannot be effectively used as fertilizers and feeds, or when dumping at sea, if there is a large amount of residual oil in the solid materials, oil can penetrate into the soil and adversely affect groundwater. In addition, there is a possibility that the oil component floats on the sea surface to form an oil film, which adversely affects marine animals.
[0006]
[Means for Solving the Problems]
Therefore, in the sludge treatment method of the present invention, the sludge is immersed in oil such as heated animal oil, vegetable oil, mineral oil, or a mixed oil of two or more of these in the cooker, and the cooker is sealed. The sludge is heated using the heated oil as a heat medium while reducing the pressure in three stages, and the three-stage reduction is performed by maintaining the oil temperature at 63 ° C to 66 ° C and reducing the oil temperature by 100 mmHg to 300 mmHg from normal pressure. An initial depressurization to perform depressurization, then a middle-term depressurization to maintain the oil temperature at 54 ° C. to 56 ° C. and a depressurization of 500 mmHg to 700 mmHg from normal pressure, and then to maintain the oil temperature at around 62 ° C. As a three-stage decompression consisting of a late decompression of 700 mmHg to 750 mmHg, the sludge evaporates to the moisture of the core of the solid tissue in the sludge, and the heating with the heat medium under the three-stage decompression is performed for about 1 hour to After 2 hours, the treated solid The product is taken out of the cooker, oil-processed by a centrifuge or a pressing machine, and the oil-processed solid is brought into contact with a solvent such as normal hexane to extract the oil component and deoil the oil to about 1% oil content. I decided to do it.
[0007]
【Example】
An embodiment of the present invention will be described.
[0008]
Sludge as a raw material usually uses sewage sludge having a water content of about 95% to 97%, but also includes sludge discharged from food manufacturing factories, blood discharged from animal slaughterhouses, and the like. Animal waste sludge can also be used.
[0009]
About 800 kg of these sludges are introduced and immersed in heating oil previously stored at a weight ratio of about 5% of the raw sludge in a 6.5 m ³ sealable cooker.
[0010]
As the heating oil in the cooker, vegetable oils such as animal oil, fish oil, rapeseed oil and the like, mineral oils and the like are used as oil types, but one kind or a mixed oil of two or more kinds may be used.
[0011]
These oils are heated by injecting steam into a jacket formed on the peripheral wall of the cooker.
[0012]
The sludge introduced and immersed in such heating oil is heated using the heating oil as a heat medium.
[0013]
In addition, when the sludge is heated by the heating oil in the cooker, the pressure is reduced in three stages.
[0014]
In the three-stage decompression, an initial decompression of 100 mmHg to 300 mmHg is performed from normal pressure for 5 to 10 minutes after sludge is introduced.
[0015]
The most suitable vacuum is 250 mmHg. The temperature of the oil at this stage is between 63C and 66C.
[0016]
Next, for about 20 minutes, middle-term depressurization is performed at 500 mmHg to 700 mmHg from normal pressure.
[0017]
The most suitable vacuum is 650 mmHg. The oil temperature at this stage is between 54C and 56C.
[0018]
Then, for about 30 minutes, a late stage pressure reduction from 700 mmHg to 750 mmHg is performed from normal pressure.
[0019]
The most suitable reduced pressure is 750 mmHg. The temperature of the oil at this stage is around 62 ° C.
[0020]
Such depressurization is achieved by performing a depressurizing operation in the cooker while constantly adjusting the opening degree of a leak valve provided halfway while constantly extracting air in the cooker with a vacuum generator.
[0021]
When the sludge is heat-treated while performing these three stages of pressure reduction, the water (about 97%) in the sludge evaporates, is taken out of the cooker, is condensed by the condenser, and is drained.
[0022]
Moreover, the moisture contained in the solid structure in the sludge is also heated, and the specific gravity becomes smaller than the specific gravity of the oil, and the specific gravity of the tissue-containing water and the oil is reversed, thereby causing a substitution action between the water and the oil. The water in the core also evaporates, and the moisture content of the solid product becomes 5% to 6%.
[0023]
After such heating oil treatment under reduced pressure, the solid matter in the cooker is removed from the cooker and the oil contained therein is squeezed by a centrifugal separator or a squeezing machine.
[0024]
The residual oil ratio of the squeezed solid product is 10 to 30%, and in this state, there is no hindrance to use as a fertilizer.
[0025]
Normal hexane as a solvent is further contacted with the oil-pressed solid having a residual oil ratio of 10 to 30%.
[0026]
Specifically, for example, the solid material is powdered into a powdered state, and thin hexane is sprayed with normal hexane from above while being placed and conveyed thinly on a mesh conveyor, and the oil contained in the solid material is eluted to form a mesh conveyor. A continuous extraction device is used in which the oil is dropped downward to remove the oil, and the deoiled powdered compact is collected.
[0027]
The solid matter thus deoiled has a residual oil ratio of about 1%, and the solid matter in such a state has no adverse effect on the environment even if it is landfilled or dumped at sea. When used, there is no oil oxidation phenomenon and it can withstand long-term storage.
[0028]
【effect】
According to the present invention, in order to perform the dewatering treatment of the sludge by the oil temperature under the three-stage decompression condition, it is possible to dewater to the water content of the core contained in the solid component, and the solid component after dehydration is initially To remove oil with normal hexane and other solvents, so that the residual oil content is extremely low, and the environment is polluted even when landfilling or dumping at sea. It has the effect of less likely to cause a problem.
[0029]
Further, after dehydration of the solid under the three-stage decompression condition, in order to carry out deoiling with a solvent in the final treatment step, the water content of the core in the solid is almost completely evaporated, Because the moisture content of the mold component and the heating oil are replaced by specific gravity, the oil easily penetrates into the solid component, and a large number of gaps for moisture evaporation and oil penetration are formed in the solid component tissue. In addition, the solvent easily comes into contact with the oil-impregnated oil even during deoiling after the oil has been pressed.

Claims (1)

The sludge is immersed in an oil such as a heated animal oil, a vegetable oil, a mineral oil, or a mixed oil of two or more thereof in a cooker. The sludge is heat-treated as a heat medium, and the three-stage decompression is performed by maintaining the oil temperature at 63 ° C to 66 ° C and reducing the pressure to 100 mmHg to 300 mmHg from normal pressure, and then reducing the oil temperature. It consists of a medium-term decompression in which the pressure is kept at 54 ° C to 56 ° C to reduce the pressure to 500 mmHg to 700 mmHg from the normal pressure, and a late pressure reduction in which the temperature of the oil is kept at about 62 ° C and the pressure is reduced to 700 mmHg to 750 mmHg from the normal pressure. 3 as a stage vacuum evaporate to a moisture of the core portion of the solid tissue in the sludge, moreover, after about 1 hour to 2 hours heating at the heat medium in such three stages under reduced pressure, treated solids Remove from cooker and centrifuge or And oil extraction process by expeller, further processing method of sludge characterized in that deoiled by extraction of oil to about 1% or so oil content by causing the solids were oil extraction process is contacted with a solvent such as n-hexane.