JPS62136299A - Method for liquefying treatment of sewage sludge - Google Patents

Abstract

PURPOSE:To reduce running cost, by a method wherein sewage sludge is subjected to reaction treatment under an alkaline condition and under pressure equal to or more than saturation steam pressure at predetermined temp. and the reaction product is cooled. CONSTITUTION:Sewage sludge is supplied to a dehydrator 1 through a line 20 to receive dehydration treatment and the dehydrated sludge is introduced into a heat exchange type reaction apparatus 2 through a line 7 while receives the alkaline substance added from a line 8. The sewage sludge is reacted with the alkaline substance at 300-350 deg.C in the reaction apparatus 2 and liquefied to form an oily substance which is, in turn, withdrawn from a line 11. This reaction treatment product is introduced into a cooling apparatus 3 to be cooled to 100 deg.C or less and subsequently introduced into a first separator 4 through a line 12 and a high density slurry is introduced into a second separator 5 to be separated into a solid and an oily substance. By this method, economical treatment can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for liquefying sewage sludge.

[Prior art]

The amount of sludge discharged from sewage treatment plants (sewage sludge) is approximately 50 million rr annually nationwide. It is a true amount of 7 years (98% moisture content), and it is increasing year by year. Conventionally, about 80% of such sewage sludge is disposed of in a landfill after dewatering, but in this case, there is a need to secure a landfill site, and with the development of urbanization, the landfill site is increasing. Securing it is becoming more difficult every year. In addition, sewage sludge can also be incinerated, and in this method, the treated product is incinerated ash whose volume is significantly reduced compared to the amount of sewage sludge that is the raw material to be treated. This is a very effective method from the point of view of reducing the volume of the raw material to be treated. however.

In the case of this method, since a large amount of thermal energy is required to evaporate water in the sewage sludge, the running cost is high and it is not economical.

〔the purpose〕

The present invention aims to solve the above-mentioned problems found in conventional sewage sludge treatment.

〔composition〕

According to the present invention, after sewage sludge is subjected to a reaction treatment under alkaline conditions and other conditions at a temperature of 250 to 350° C. under pressure equal to or higher than the saturated water vapor pressure of the reaction temperature, the obtained reaction treatment product is Provided is a method for liquefying sewage sludge, which is characterized by performing cooling treatment.

The sewage sludge used as the raw material to be treated in the present invention includes various types of sludge discharged from ordinary sewage treatment plants, such as primary sedimentation tank sludge, surplus sludge, and mixed sludge thereof. etc. are included. The sewage sludge may be one that has been subjected to digestion treatment, but it is advantageous to use raw sludge that has not undergone digestion treatment.

To carry out the method of the present invention, sewage sludge may be maintained at high temperature and high pressure conditions under alkaline conditions.

In this case, an alkaline substance is usually used to create alkaline conditions;
For example, alkaline compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium formate, and potassium formate.

Examples include alkaline earth metal compounds such as calcium oxide, calcium hydroxide, and magnesium hydroxide. The amount of such an alkaline substance used is 0.001 to 0.5 part by weight, preferably 0.01 to 0.2 part by weight, per 1 part by weight of sewage sludge (dry basis). The water content of sewage sludge is 60-85% by weight, preferably 70-80% by weight.

Although the reaction treatment in the present invention is carried out at high temperature and high pressure,
In this case, the reaction temperature is generally 250 to 350°C, preferably 300 to 320°C, and the reaction pressure may be at least the saturated water vapor pressure at the reaction temperature. The reaction time is usually 5 to 180 minutes.

In the present invention, self-generated pressure due to water vapor generation from sewage sludge can be used as the pressure, but if necessary, it can also be pressurized using, for example, nitrogen gas, carbon dioxide gas, argon gas, etc.

In the present invention, the reaction product obtained as described above is subjected to a cooling treatment. Cooling treatment 1 Usually, the high temperature reaction product extracted from the reactor is heated to 100°C.
It is preferable to cool as quickly as possible to a temperature below.

The cooled product obtained above usually consists of an aqueous phase and a slurry phase, with the slurry phase forming an upper phase with respect to the aqueous phase. The oily substances produced by the liquefaction treatment of sewage sludge are included in the slurry phase.

The cooling treatment product has good phase separation properties and can be easily separated into a slurry phase and an aqueous phase by standing still. The good phase separation property of this product is one of the major features of the present invention. Separation of cooling products requires
Ordinary solid-liquid separation means are applied, but in general, separation means that utilize the density difference between the slurry phase and the aqueous phase, such as centrifugal separation, in addition to the above-mentioned gravity separation by e-placement, may be employed. I can do it. In the present invention, in order to obtain a reaction product with good phase separation, the Pll of the separated aqueous phase is 4 to 4.
11. It is preferable to adjust the amount of the alkaline substance added and the reaction conditions so that the amount is preferably 6 to 10.

In the present invention, the oily substance produced by the liquefaction treatment of sewage sludge exists as a dispersion medium for the solid content in the slurry phase. Normal solid-liquid separation means are used to separate and recover liquid oily substances from this slurry phase, but in order to reduce the amount of oily substances remaining in the solid content and increase the recovery rate of oily substances, It is preferable to subject the slurry phase to a solid-liquid separation process that involves pressurization, such as a screw press or pressure filtration, or a solid-liquid separation process that involves a load, such as centrifugation. In this case, heating at a temperature of about 50 to 100'C can be used in combination, if necessary. Recovery of the oily substance from the slurry phase is also possible by extraction or distillation, but this is not a very preferable method since it requires a large amount of thermal energy.

When carrying out the present invention, by adjusting the reaction conditions, a three-phase cooling treatment product consisting of a slurry phase, an aqueous phase and an oil phase is obtained, in which an oil phase is further present on top of the aqueous phase. be able to.

According to research conducted by the present inventors, it has been found that such a three-phase cooling treatment product can be produced by adjusting the reaction treatment temperature and reaction treatment time. For example, such a product can be produced by raising the temperature of sewage sludge to a temperature increase rate of 5 to 350°C, maintaining this temperature for about 30 minutes, and then cooling it. . The separation process for such a three-phase product is 1
This can be carried out by various methods, for example, as described above, first, the liquid phase and the slurry phase are separated by a solid-liquid separation means, and then the aqueous phase and the oily substance phase forming the liquid phase are separated. This can be carried out by separation means that utilize density differences, such as static separation or centrifugation, or conversely, the oily substance phase is first separated from the aqueous phase and the slurry layer, and then the primary It can also be carried out by separately separating the aqueous phase and slurry phase remaining in the solution.

The method of the present invention is preferably carried out (1) As the reaction apparatus, it is advantageous to use an external heating type or heat exchange type reaction apparatus, that is, a flow reactor equipped with an external electric heater or a heating mechanism using a heat medium. It is. In such a reactor, sewage sludge is heated to a predetermined reaction temperature while flowing through the reactor, and is held at that reaction temperature for a predetermined period of time before being extracted from the reactor.

Next, a flow sheet of a preferred embodiment of the present invention is shown in the drawings. In the drawing, 1 is a dehydration device, 2
3 indicates a reaction device, 3 indicates a cooling device, 4 indicates a first separation device, and 5 indicates a second separation device.

Sewage sludge with a water content of 90% by weight or more is supplied to the dewatering device 1 via a line 20, where it is dehydrated, and the resulting separated water is removed via a line 6. It is preferable to use a polymer flocculant in combination with this dehydration treatment.

On the other hand, the dehydrated water content is 85% by weight or less, usually 70~
The 80% by weight sewage sludge is introduced into the reactor 2 through line 7 after addition of alkaline substances via inlet 8 . This reactor is a heat exchange type reactor, in which a heating medium is introduced through line 9 and discharged through line 10, during which time the contents within the reactor are heated.

The sewage sludge and alkaline substances introduced into the reactor 2 flow through the reactor as an extrusion flow at a predetermined speed,
The sewage sludge is extracted through line 11, during which time it undergoes a reaction treatment and is liquefied into an oily substance. The reaction product extracted through line 11 is introduced into cooling device 3, where it is cooled to below 100°C, and then through line 12
is introduced into the first separation device 4 through. As this first separation device 4, one that utilizes a density difference is preferably used, and a static tank, a centrifugal separator, or the like is used. From the first separator 4, a water phase with a lower density is extracted through a line 13, while a slurry phase with a higher density is extracted through a line 14 and introduced into a second separator [5]. .

As the second separator, a solid-liquid separator such as a screw press or a pressure filter is preferably used, and the slurry phase introduced into the second separator 5 is separated here into solids and oily substances. The solids are removed through line 16, while the oil is recovered through line 15.

〔effect〕

According to the present invention, sewage sludge, which was conventionally treated as industrial waste, can be converted into liquid fuel (with a calorific value of approximately 8,000 kcal).
7 kg) can be converted into a useful oil.

Moreover, in this case the yield of oily substances reaches a value as high as approximately 50% based on dry organic matter. It is an unexpected fact discovered for the first time by the present inventors that sewage sludge can be converted into an oily substance useful as a liquid fuel in high yield.

Furthermore, the slurry phase containing an oily substance obtained by the present invention is easily separated from the aqueous phase, and the oily substance can be easily separated and recovered from the slurry phase. It's easy. Therefore, the sewage sludge treatment method of the present invention can be said to be a technically and economically very advantageous method.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Mixed raw sludge discharged from a treatment plant using the standard activated sludge method was selected as sewage sludge, a polymer flocculant was added to it on a 1.0% DS (dry matter) basis, it was dewatered using a belt press, and it was tested. Using. In this case, the properties of the dehydrated sludge are as shown in Table 1. Note that V and S shown in Table 1 indicate the organic matter ratio.

Table-1 Moisture content near 5% V, S,: 8/1% Calorific value: 4130 kca Q / kg, DS To 100 g of the above dehydrated sludge, 5% DS standard Na 2 Co 3
1.3 g was added, filled into an autoclave with an internal capacity of 300 mm, and heated to 300°C. At this time, the pressure was previously increased to 120 kg/cJG with N2 gas, and the pressure increase due to temperature rise was controlled to 120 kg/CIITG using a pressure regulating valve. temperature is 30
After reaching 0°C, the reaction was immediately cooled to below 100°C to complete the reaction.

Thereafter, the reaction product was cooled to room temperature, collected in a glass sample bottle, and allowed to stand overnight.

After standing, one reaction product was separated into two phases: an aqueous phase in the upper part and a slurry phase in the lower part. In order to measure the amount of oily substances present in both phases, both phases were extracted separately with an organic solvent (CH2CD, 2), the oil was separated, and its weight was measured. As a result, the water phase contained 1.1 g of oily substance and the slurry phase contained 9.0 g of oily substance. Based on the dry organic matter standard of sewage sludge, the overall recovery rate of oily substances was 48.1%.

The amount from the slurry phase alone was 42.9%. The oil recovered from this slurry phase was 7800 kca Q
It showed a calorific value of 1.2 kg, was fluid at room temperature, and could be used as a fuel oil.

Example 2 100g of the same dehydrated sludge as in Example 1 was taken, and Na
1.3g of 2Co3 was added, the autoclave was filled, heated to 300°C, and held at that temperature for 30 minutes. The pressure was controlled at 120 kg/cJG as in Example 1. After the reaction, the reaction product was cooled to room temperature, collected in a sample bottle, and allowed to stand overnight.

After standing still, the reaction product was separated into three phases: a floating phase (oil substance) in the upper part, an aqueous phase in the middle, and a slurry phase in the lower part.

As a result of extracting each phase separately with an organic solvent and determining the amount of each extracted oily substance, the floating phase was 4.5g and the aqueous phase was 0.7g.
, the slurry phase contained 5.9 g of oily material. The overall recovery rate of oily substances was 52.9%, 21.4% from the floating phase alone, 28.0% from the slurry phase alone, and 49.4% from the floating phase + slurry sum. It was done. The calorific value of the mixture of oily substances recovered from the floating phase and the slurry phase was as high as 8000 kca Q /kg, and could be sufficiently used as fuel oil.

Example 3 Sewage sludge was subjected to reaction treatment in exactly the same manner as in Example 1. After one reaction, the obtained reaction product was cooled to room temperature and separated into two phases using a laboratory centrifuge. Thereafter, the slurry phase was separated and compressed while heating to obtain 6 g of an oily substance. The recovery rate of this oily substance was 28.6%,
Its calorific value was as high as 7,500 kca Q /kg, which was sufficient for use as fuel.

[Brief explanation of drawings]

The drawing shows an example of a flow sheet for implementing the present invention. DESCRIPTION OF SYMBOLS 1... Dehydration device, 2... Reactor, 3... Cooling device, 4... First separation device, 5... Second separation device. Designated agent Director of the Institute of Pollution Resources Research, Agency of Industrial Science and Technology Shigeyoshi Oba Patent attorney Toshiaki Ikeura Proceedings amendment date March 11, 1985 Commissioner of the Japan Patent Office Kuro 1) Yu Akira 1, Indication of the case 1985 patent Application No. 279679 2. Name of the invention: Sewage sludge liquefaction treatment method 3. Person making the amendment Relationship to the case: Patent applicant (2 others) 4. Sub-agent 151 5. Date of amendment order: Initiator 6. Number of inventions increased by amendment 08. Contents of amendment The following amendments will be made to the specification of the application. (1) Amend the claims as shown in the attached sheet. (2) On page 3, lines 2 to 4, ``After the sewage sludge is subjected to reaction treatment,'' should be corrected as follows: 1. "After adding an alkaline substance to sewage sludge and subjecting it to a heating reaction treatment under pressure equal to or higher than the saturated water vapor pressure at the heating temperature," (3) "The sewage sludge is...
``It is used, but'' is corrected as follows. "Just add an alkaline substance to sewage sludge and hold it under high temperature and high pressure conditions." (4) Add the following sentence after "..." on page 4, line 13. "The reaction temperature is determined in relation to the reaction time, and the reaction temperature can be lowered by increasing the reaction time, and
By increasing the number of reaction sites, the reaction time can be shortened. In the case of the present invention. Depending on the reaction time, it is also possible to employ a reaction temperature of 150°C or 400°C. ” “Claims (1) After adding an alkaline substance to sewage sludge and subjecting it to a heating reaction treatment under pressure equal to or higher than the saturated water vapor pressure at the heating temperature,
A method for liquefying sewage sludge, which comprises cooling the obtained reaction product. (2) After adding an alkaline substance to sewage sludge and subjecting it to a heating reaction treatment under pressure equal to or higher than the saturated water vapor pressure at the heating temperature,
The obtained reaction product is cooled, the obtained cooled product is separated into an aqueous phase and a slurry phase, and the separated slurry phase is further separated into a solid content and an oily substance. A liquefaction treatment method for sewage sludge. ”

Claims (2)

[Claims] (1) Sewage sludge is heated under alkaline conditions at a reaction temperature of 250℃.
A method for liquefying sewage sludge, which comprises carrying out a reaction treatment at a temperature of 350°C to 350°C under a pressure higher than the saturated water vapor pressure of the reaction temperature, and then cooling the obtained reaction product. (2) Sewage sludge is reacted under alkaline conditions at a reaction temperature of 250℃.
After reaction treatment at ~350°C under pressure higher than the saturated water vapor pressure of the reaction temperature, the obtained reaction product is cooled, and the obtained cooled product is separated into an aqueous phase and a slurry phase. A method for liquefying sewage sludge, which comprises: and then further separating the separated slurry phase into a solid content and an oily substance.