JP2002233899A - Centrifugal separator provided with function for improving quality of raw sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that when deterioration of the centrifugal separator performance with respect to solid-liquid separation of raw sludge by a centrifuge, due to change in quality of the raw sludge, or the like, is caused, conventionally, only any of complex and inconvenient countermeasures such as improvement of coagulation properties of the sludge by changing the kinds of chemicals used or upgrading of the centrifuge itself, is taken and there is no simple and convenient countermeasure. SOLUTION: The process using this centrifugal separator involves: a sludge supply stage 2 for supplying raw sludge to a centrifuge 1; and a separated liquid return stage 5 for returning a part of a separated liquid discharged from the centrifuge 1 to the sludge supply stage 2 and mixing the returned separated liquid with the raw sludge to reduce the organic matter content of the raw sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a centrifugal separator for sludge dewatering and sludge concentration in a sewage treatment plant or a sewage treatment plant, and more particularly to a centrifugal separator having a sludge reforming function.

[0002]

2. Description of the Related Art A centrifugal separator such as a centrifugal dehydrator or a centrifugal concentrator is used as a centrifugal separator for sludge treatment. The centrifugal separator separates raw sludge into a separated liquid and a dewatered cake or a separated liquid and a concentrated sludge. It is known to reduce the water content of the dewatered cake or concentrated sludge while maintaining the separated liquid in a good SS (solid matter) recovery rate.

FIG. 3 is a flow sheet showing a conventional centrifugal separator using a centrifugal dehydrator as the centrifugal separator. In FIG. 3, reference numeral 1 denotes a centrifugal dehydrator, and each of the centrifugal dehydrators 1 rotates. It has a general configuration in which a possible outer trunk bowl and an inner trunk screw are provided, and a differential speed, which is a rotation difference between the outer trunk bowl and the inner trunk screw, can be adjusted. Reference numeral 2 denotes a sludge supply step of supplying raw sludge to the centrifugal dehydrator 1 by a sludge supply pump P1, and reference numeral 3 denotes a chemical injection facility for injecting a chemical such as a flocculant into the sludge supply step 2.

Next, the operation will be described. The centrifugal dewatering machine 1 to which the raw sludge is supplied from the sludge supply step 2 by operating the sludge supply pump P1 is operated under a constant treatment amount (water load) and a constant chemical injection rate, so that the specific gravity of water and sludge is increased. Using the difference, the raw sludge is solid-liquid separated into a separated liquid and a dewatered cake. In this case, if the differential speed between the outer shell bowl and the inner screw of the centrifugal dehydrator 1 is reduced, the water content of the dewatered cake is reduced, but on the other hand, the SS recovery rate tends to be deteriorated. When it is increased, the opposite tendency is shown.

As described above, the dewatering performance of the centrifugal dewatering machine 1 varies greatly depending on the above-mentioned operating conditions, the properties of raw sludge, the type of injection chemicals (coagulant), etc., and these elements (factors) are optimally adjusted. This is very important.

If the dewatering performance deteriorates in such a treatment situation, the properties of the raw sludge are modified by changing the type of chemicals injected into the sludge in the sludge supply step 2 from the chemical injection equipment 3 or At present, this is supported by upgrading the centrifugal dewatering machine 1 itself.

Here, one example of the normal operation conditions of the centrifugal dehydrator 1 shown in FIG. 3 will be specifically described. The nominal capacity of the sludge supply pump P1 is 10 m ³ / h, and the chemical injection rate of the chemical injection equipment 3 Is 1.5% / TS, mechanical conditions (difference speed between the outer bowl and the inner screw of the centrifugal dehydrator 1)
Is optimally tuned.

[0008] The TS (total evaporation residue) concentration of the raw sludge under the ordinary operating conditions of such a centrifugal dewatering machine 1 is 10,000 to
25,000 mg / l, VTS (organic matter content)
Is around 80%. That is, 80% of the TS is an organic component having a low specific gravity. The water content of the dehydrated cake in the dehydration treatment by the centrifugal dehydrator 1 is about 80%, the TS of the separated liquid is about 4,000 mg / l, and the VTS of the separated liquid is about 30%.

That is, in the centrifugal dewatering treatment of the sludge by the centrifugal dehydrator 1, when the centrifugal dehydration is performed while maintaining the SS recovery rate of 95% or more (the SS of the separated liquid is low), the properties of the dewatered separated liquid are as follows. However, the TS concentration does not decrease extremely due to the high DS concentration as a dissolved substance, but on the other hand, solids mainly composed of organic substances having a low specific gravity are almost completely removed.
The concentration drops extremely. Therefore, VTS of the dehydrated separation liquid
Is considerably lower than the VTS of raw sludge.

FIG. 4 is a flow sheet showing a centrifugal separator for injecting dilution water into raw sludge as one of the measures to be taken when the dewatering performance is deteriorated. In FIG. 4, reference numeral 4 denotes a dilution water injection facility. When dilution water (5 m ³ / h of fresh water or miscellaneous water) is injected from the dilution water injection equipment 4 into the raw sludge (TS 20,000 mg / l · VTS 80%) of the sludge supply step 2, the VTS of the dilution water is 2%. Very low but TS is also 200
Since it is very low at mg / l, the VTS of the raw sludge diluted in the sludge supply step 2 and supplied to the centrifugal dewatering machine 1 is 79%, and in reality it hardly decreases.

[0011]

The conventional centrifugal separator is constructed as described above, and solid-liquid separation into a dewatered cake or a concentrated sludge and a separated liquid is carried out simply by charging raw sludge as it is into a centrifuge. Therefore, the solid-liquid separation performance is greatly affected by the properties of the raw sludge, the type of chemicals such as flocculant, and the mechanical specifications of the centrifuge.
There is a problem that only the improvement of the sludge cohesion by changing the type of chemicals and the upgrading of the mechanical device itself are required. Therefore, a simple method for improving the solid-liquid separation performance is desired.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to use an existing centrifuge as it is, but to add a few steps without changing operating conditions and mechanical specifications. It is an object of the present invention to provide a centrifugal separator having a sludge reforming function capable of improving the solid-liquid separation performance such as reducing the water content of the dewatered cake or concentrated sludge and improving the SS recovery rate just by doing.

[0013]

According to the present invention, there is provided a centrifugal separator having a sludge reforming function, comprising: a centrifuge for solid-liquid separation of raw sludge into a separated liquid and a concentrated liquid or a dewatered cake; A sludge supply step of supplying raw sludge to the sludge supply step, a chemical injecting facility for injecting a chemical into the sludge supply step, and returning the separated liquid discharged from the centrifugal separator to the sludge supply step. And a separation liquid returning step of reducing the organic matter content of the raw sludge by mixing the two.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a flow sheet showing a centrifugal separator according to Embodiment 1 of the present invention.
The same or corresponding parts as those described above are denoted by the same reference numerals, and redundant description will be omitted. In FIG. 1, reference numeral 5 denotes a separation liquid returning step for returning a part of the separation liquid discharged from the centrifugal separator (centrifugal dehydrator or centrifugal concentrator) 1 to the sludge supply step 2; 5 is a pump P for returning the separated liquid.
2 are provided. Here, the separated liquid returning step 5 is composed of a pipe connecting the separated liquid discharge pipe 1a of the centrifugal separator 1 and the pipe of the sludge supply step 2 via the pump P2.

Next, the operation will be described. The centrifugal separator 1 to which the raw sludge is supplied from the sludge supply step 2 separates the raw sludge into a dewatered cake or a concentrated sludge and a separated liquid by the centrifugal action of the centrifugal separator. A part of the separated liquid is returned to the sludge supply step 2 through the separated liquid return step 5 by the pump P2.

As described above, a part of the separated liquid discharged from the centrifuge 1 is returned to the sludge supply step 2, so that the raw sludge supplied to the centrifuge 1 from the sludge supply step 2 is returned and separated. The mixed liquid becomes sludge diluted with the return separation liquid. For this reason, although the TS of the raw sludge is reduced to some extent, the VTS is also sufficiently lowered. As a result, the difference in specific gravity between the water and the sludge component of the raw sludge is increased, and the solid-liquid separation performance is improved.

As described above, when the separation liquid having a low VTS is mixed into the raw sludge, the composition of the sludge component contained in the raw sludge decreases in the ratio of the organic component having a low specific gravity and the inorganic component having a high specific gravity. The ratio increases, and as a result, the specific gravity of the sludge component of the raw sludge increases, so that the solid-liquid separation performance of the centrifugal separator 1 utilizing the specific gravity difference between water and the sludge component improves.

Next, the centrifugal separator using the centrifugal dehydrator shown in FIG. 1 according to the first embodiment and the conventional centrifugal separator using the centrifugal dehydrator shown in FIGS. The results obtained are described below. In this experiment, each centrifugal separator to be compared had the same normal operating conditions. That is, the nominal capacity of each sludge supply pump P1 is 10 m ³ / h, and the TS concentration of the raw sludge is 20,000.
mg / l, VTS 80%, chemical injection rate 1.5%
/ TS. In the case of FIG. 4, the dilution water is 5 m ³ /
h, TS 200 mg / l, VTS 2%. further,
In the case of FIG. 1, the return separation liquid was 5 m ³ / h.

As a result of the experiment, in the case of the centrifugal separator shown in FIG. 3 in which only the chemical was injected into the raw sludge, the water content of the dehydrated cake obtained by the solid-liquid separation by the centrifugal dehydrator 1 was 80%, and the separated liquid was TS. Is 4000 mg / l and VTS is 30%, and the VTS of the separated liquid is considerably lower than that of the raw sludge. Next, in the case of the centrifugal separator in FIG. 4, the raw sludge into which the dilution water is injected and supplied to the centrifugal dehydrator 1 is TS.
Is 13,000 mg / l and the VTS is 79%, and the VTS of the diluted sludge supplied to the centrifugal dehydrator 1 hardly decreases compared to the VTS of the undiluted sludge. It can be seen that it is insufficient for reforming (increase in specific gravity) and is not effective for improving solid-liquid separation performance.

On the other hand, in the case of the centrifugal separator shown in FIG. 1 according to the first embodiment of the present invention, a part of the separated liquid discharged from the centrifugal dehydrator 1 is returned to the sludge supply step 2 so that the returned separated liquid is separated. The raw sludge that is diluted and supplied to the centrifugal dehydrator 1 has a TS of 14,500 mg / l and a VTS of 76%, and the TS of the raw sludge decreases, but the VTS also decreases. It can be seen that the material is reformed (increased in specific gravity) and is effective in improving the solid-liquid separation performance. The water content of the dehydrated cake after solid-liquid separation was 76%,
000 mg / l and VTS was 25%.

Embodiment 2 FIG. FIG. 2 is a flow sheet of a centrifugal separator according to Embodiment 2 of the present invention. The same or corresponding parts as those in FIGS. 1, 3 and 4 are denoted by the same reference numerals, and redundant description is omitted. In FIG. 2, reference numeral 6 denotes a mixing tank for mixing raw sludge, return separation liquid, and chemicals, and reference numeral 7 denotes a centrifugal separator 1.
Is a separation liquid pit for temporarily storing the separation liquid discharged from. That is, in the second embodiment, the sludge supply pump P1
Raw sludge is temporarily stored in the mixing tank 6,
Is supplied to the centrifugal separator 1 by the pump P3, the separated liquid discharged from the centrifugal separator 1 is temporarily stored in the separated liquid pit 7, and the stored separated liquid is pumped by the pump P3.
The raw sludge diluted with the returned separated liquid is returned from the mixing tank 6 to the centrifugal separator 1 by the pump P3 by returning the sludge to the mixing tank 6 and mixing the raw sludge, the separated liquid, and the chemical in the mixing tank 6.
Is to be supplied to

Therefore, the sludge supply step in the second embodiment comprises a pump P1, a mixing tank 6, and a pump P3, and the separation liquid return step 5 includes the step of mixing the stored separation liquid from the separation pit 7 with the pump P2. 6 and the same operation and effect as in the first embodiment can be obtained.

In the second embodiment, the separated liquid temporarily stored in the separated liquid pit 7 is returned to the mixing tank 6, but in the present invention, the stored separated liquid in the separated liquid pit 7 is pumped by the pump P2. You may make it return directly to the pipeline of the sludge supply process 2 shown in FIG. Further, the addition of a chemical such as a flocculant may be adjusted by a control device using a measuring device such as a sludge concentration meter or a viscometer. In this case, more stable sludge treatment can be performed. Further, in the second embodiment, the chemical injection is performed in the mixing tank 6. However, the chemical injection is performed in the pipe of the sludge supply process that connects the discharge side of the pump P3 and the centrifugal separator 1. You may.

[0024]

As described above, according to the present invention, part of the separated liquid discharged from the centrifuge separated into solid and liquid by the centrifuge is returned to the sludge supply step for the centrifuge.
Because it was configured to reduce the organic matter content of the raw sludge by mixing the raw sludge and the separated liquid, it is a very simple configuration that only uses the existing centrifugal separator and provides a separated liquid return step, Raw sludge, which is diluted with the returned separation liquid and supplied to the centrifuge, has a large specific gravity difference between water and sludge components, so that the solid-liquid separation performance of the centrifuge can be improved with little change in operating conditions and equipment. There is an effect that it can be improved. In addition, since the sludge is diluted with the return separation liquid, the throughput of the centrifugal separator increases. However, since the limiting factor of the centrifugal separator is SS (solid matter) load, the operation is not hindered, and The above-mentioned effect can be obtained without extending the operation time.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing a centrifugal separator having a sludge reforming function according to Embodiment 1 of the present invention.

FIG. 2 is a flow sheet showing a centrifugal separator having a sludge reforming function according to a second embodiment of the present invention.

FIG. 3 is a flow sheet showing a conventional centrifugal separator.

FIG. 4 is a flow sheet showing another conventional centrifugal separator.

[Explanation of symbols]

 1 Centrifugal separator 2 Sludge supply process 3 Chemical injection equipment 5 Separation liquid return process

Continuation of the front page F term (reference) 4D057 AA11 AB01 AC01 AC06 AD01 AE03 AF05 BC07 CA01 4D059 AA03 BE38 BE54 BE70 CA21 CB30 EA01 EA04 EB11

Claims (1)

[Claims] 1. A centrifuge for solid-liquid separation of raw sludge into a separated liquid and a concentrated liquid or a dewatered cake, a sludge supply step for supplying raw sludge to the centrifuge, and a chemical injected into the sludge supply step Raw sludge, comprising: a chemical injecting facility for carrying out, and a separated liquid returning step of returning the separated liquid discharged from the centrifugal separator to the sludge supply step, and mixing the raw sludge and the separated liquid. A centrifugal separator having a reforming function.