JPS6150698A - Seed sludge return control apparatus of digestion tank - Google Patents

Abstract

PURPOSE:To properly hold bacterial concn. by preventing the lowering in the bacterial concn. of a first digestion tank, by providing controller for stopping the return of seed sludge when the concn. of the solid in the first digestion tank is higher than the solid concn. of return sead sludge. CONSTITUTION:The solid concn. D1 in a first digestion tank 2 and the solid concn. Dr of return sludge measured by a densitometer 15 are compared by a comparator 18 and the output thereof is inputted to a second controller 19 which in turn outputs a control signal C2 for stopping a return pump 13 when D1>Dr is formed. The aforementioned control signals C1, C2 are inputted to the control circuit of the return pump 13 to control the operation stoppage of the return pump 13. By this method, the return amount of seed sludge is controlled in proportion to the amount of the org. substance charged in the first digestion tank and the return of seed sludge is stopped when the solid concn. in the first digestion tank becomes higher than that of return seed sludge.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for returning digested sludge from a second digestion tank to a first digestion tank in an anaerobic digestion process for treating organic sludge using an anaerobic digestion method. Digestion tank seed sludge return control device (1) that controls the amount.

[Technical background of the invention and its problems]

Anaerobic digestion has been used for a long time as a method for treating organic sludge. Recently, it has received particular attention due to resource conservation, due to its good nature.

Anaerobic treatment is performed on carbohydrates and fats in chlorinated sludge.

It consists of two processes: a liquefaction reaction by acid-producing bacteria that decomposes Tanbakutora into volatile organic acids as soil, and a gasification reaction by methane bacteria that decomposes volatile organic acids into carbon dioxide and methane.

Figure 2 shows the basic configuration of the anaerobic digestion process.

In Fig. 2, organic sludge passes through pipe 1 and is intermittently fed into the first digestion tank 2, where the organic sludge is retained and finally processed through liquefaction and gasification reactions. Methane, carbon dioxide gas, etc. (decomposes by 1.

Ru.

The first digestion tank 2 has 30 to 4
It is heated to about 0°C.

Further, in order to uniformly mix the introduced organic sludge and bacteria (Z), the generated digestion gas is circulated by a blower 91 to stir the inside of the first digestion tank.

The digested sludge that has been digested in the first digester is transferred to the transfer pipe 3.
The separated supernatant fluorine is sent to the fluorocarbon digestion tank 4 and condensed, and the separated supernatant is discharged into rivers etc. through the pipe 5 or returned to the water treatment process where it is sedimented and concentrated. Digested sludge is sent to the next sludge treatment step through pipe 6.

The digestion gas generated in the $1 digestion tank 2 and the second digestion 414 is finally stored in the gas tank 8 (= through the pipe 7 and used for fuel and other purposes).

In such an anaerobic digestion process, seed sludge is often returned from the second digestion tank to the first digestion tank in order to improve digestion efficiency.

This is because the digested sludge sedimented and concentrated in the J2 digestion tank has a high concentration of acid-producing bacteria and methane boxes, so returning this to the first digestion tank increases the bacteria concentration in the first digestion tank. .

Methods such as constant ratio control and constant solids concentration control are used to control the amount of seed sludge returned.

Constant ratio control is to control the ratio between the amount of organic sludge input and the seed sludge returned to be constant according to a set value, but the filtration rate of the settled wet sludge in the second digestion tank is When the concentration decreases, the concentration resistance of the first digestion tank also decreases, which causes a problem in that the digestion efficiency decreases.

On the other hand, in the solids concentration control, the amount of seed sludge returned is controlled so that the solids concentration in the first digestion tank reaches the set value (one foot in accordance with the set value). If the concentration of sludge is not reduced to the concentration of dissolved substances, the amount of seed sludge returned decreases, making it impossible to maintain a level of sludge commensurate with the amount of input material, resulting in a decrease in digestion efficiency.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a seed sludge return control device for a digestion tank that can maintain an appropriate bacterial concentration in a first digestion tank regardless of the solids concentration of the organic sludge introduced.

[Summary of the invention]

The present invention provides a seed sludge return control device for a digestion tank ( =, measure the flow rate of organic sludge input into the first digestion tank and the flow rate of seed sludge returned from the second digestion tank to the first digestion tank, and calculate the amount of leaked sludge returned in accordance with the amount of organic sludge input. A first controller for controlling the solid matter concentration of the first digestion tank 2 and the solid matter concentration of the returned seed sludge is measured, and when the solid matter concentration in the first digestion tank is higher than the solid matter concentration of the returned seed sludge, the seed sludge is removed. A second controller is installed to stop the return, and can be used to prevent fluctuations in the flow rate and solids concentration of the organic sludge fed into the first digestion tank, or decreases in the solids concentration of the seed sludge that is precipitated and concentrated in the second digestion tank. The amount of seed sludge returned is controlled so that the digestion reaction in the first digestion tank can continue stably regardless of the situation.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

In Figure 1 (=), the flow rate 11-1 of the organic sludge introduced into the first digestion tank 2 is measured by the flow meter 10 provided in the pipe line 1 (-) and is input to the calculator 16, and is calculated by the following calculation ( = Therefore, the seed sludge return amount target value Q is determined.

Qr=ni-Q+ Here, Ql is the amount of input organic sludge, and K is a constant.

On the other hand, the digested sludge sedimented and concentrated in the second digestion tank 4 passes through the return pipe line 11 via the return pump 13 and is returned as seed sludge to the first digestion tank 2 (-), and its return flow rate fPr and solids concentration are Each is measured by flow rate #t12 and concentration meter 14.

The above return flow rate target value Qr and return flow rate measurement value? .

is manually input to the first computing unit 17 and outputs a control signal C1 to stop the return pump 3 so that the seed sludge return amount Q becomes the target value Qr +=.

On the other hand, the solid matter concentration in the first digestion tank 2 measured by the densitometer 15 and the solid matter concentration Dr of the returned sludge are compared by a comparator 18, and the output thereof is manually inputted to the second controller 19, and the DI
> Dr, outputs a control signal C2 to stop the return pump.

The control signals C1 and C3 are inputted to the control circuit of the return pump 13 to control the stoppage of the return pump 13.

As a result, the amount of seed sludge returned is controlled in proportion to the amount of organic sludge input into the first digestion tank, and when the solids concentration in the first digestion tank becomes larger than the solids concentration of the seed sludge to be returned, Returning the seed sludge is stopped, and the concentration in the first digestion tank is maintained at an appropriate value.

〔Effect of the invention〕

As explained above, according to the present invention, an amount of seed sludge commensurate with the amount of organic sludge input is returned, so that the bacteria concentration in the first digestion tank is maintained appropriately, and further, the bacteria concentration in the second digestion tank is In an abnormal state where the digested sludge becomes sedimented and concentrated, the return of the low-concentration seed sludge is stopped, preventing a decrease in the bacterial concentration in the first digestion tank, and thus ensuring a stable digestion process at all times. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a control system diagram showing one embodiment of the present invention, and FIG. 2 is a system diagram showing the general configuration of the digestion process. 2 First digestion tank 4 Second digestion tower 10, 12 Flow meter] 3 Return pump 14, 15 Concentration meter 16 Arithmetic unit 17, 1.9 Controller 18 Comparator

Claims (1)

[Claims] In a seed sludge return control device for a digestion tank that controls the amount of seed sludge returned from a second digestion tank to a first digestion tank in an anaerobic digestion process for treating organic sludge using an anaerobic digestion method,
First control that measures the flow rate of organic sludge introduced into the first digestion tank and the flow rate of seed sludge returned from the second digestion tank to the first digestion tank, and controls the amount of seed sludge returned in accordance with the amount of organic sludge input. A second method that measures the solids concentration in the vessel and the first digestion tank and the solids concentration of the returned seed sludge, and stops the seed sludge return when the solids concentration in the first digestion tank is higher than the solids concentration of the returned seed sludge. A seed sludge return control device for a digestion tank, characterized by being equipped with a controller.