JPS58114799A - Fermentation treatment of waste water of paper mill - Google Patents

Abstract

PURPOSE:To reduce running costs by flashing the digesting liquid which is subjected to methane fermentation under the reduced pressure to generate steam, and utilizing the recompressed steam which is obtained by increasing the pressure of said steam with a recompressor as a heat source for methane fermentation. CONSTITUTION:The waste liquid from paper mills is fed through a pipe 5 into a methane fermenting tank 1, where the liquid is subjected to methane fermentation at 51-53 deg.C. The produced digesting liquid is fed through a pipe 8 into a vacuum flashing drum 2. The steam produced by flashing under the reduced pressure is supplied to a recompressor 3 through a pipe 11, and the remaining liquid is fed through a pipe 9 to a sludge separating tank. After the steam is increased in pressure with the recompressor 3, the steam is fed to a barometric condenser 4. In said condenser, the pressurized steam is condensed by the water fed through a pipe 7 to hot water which is fed into the tank 1 where the hot water heats the fermenting liquid up to 51-53 deg.C.

Description

[Detailed Description of the Invention] Wastewater from a paper mill generally contains organic matter such as fine pulp fibers, so if this wastewater is sent to a methane fermentation tank and fermented, methane gas can be obtained. The methane gas can, for example, be used as part of the fuel consumed in factories.

By the way, methane fermentation of paper mill wastewater is economically 51-5.
Since it is necessary to maintain a fermentation temperature of 3° C., when carrying out methane fermentation, it is necessary to heat the waste liquid to a desired temperature using steam or the like as a heat source. Therefore, regardless of whether waste steam or the like can be used as a heat source, if this is not the case, a separate steam production boiler must be installed to heat the waste liquid.

On the other hand, the digestive fluid flowing out from the methane fermentation tank at 51-53℃ needs to be treated with activated sludge next, but since the optimum temperature for activated sludge treatment is below 40℃, the digestive fluid from the fermentation tank is cooled. The temperature must be lowered using a container, etc. However, cooling with a simple cooler means wasting the thermal energy held by the digestive fluid. However, if the reduced pressure flash evaporation method is used to cool the digestive fluid, the temperature of the digestive fluid will drop and water vapor will be generated.If this water vapor is boosted in pressure with a recompressor, it can be used as a heat source for the methane fermentation tank. The present invention is precisely based on this knowledge.

That is, the present invention provides a wastewater treatment method that involves methane fermentation of paper mill liquor at a temperature of 51 to 53°C, in which the digestive fluid flowing out from the methane fermentation tank is flashed under reduced pressure to generate water vapor. The pressure of the steam is increased using a recompressor, and the resulting pressurized steam is used as a heat source to operate a methane fermentation tank.
The present invention provides a method for fermenting wastewater from a paper mill, which is characterized by maintaining the fermentation temperature at ~53°C.

According to the method of the present invention, there is no need for a boiler for producing steam to heat the waste liquid to the fermentation temperature, and only by adding a small amount of mechanical energy to the steam generated by the vacuum flash, the amount of heat required for methane fermentation can be produced. The economic gain is extremely large.

The present invention will be described in detail below with reference to the accompanying drawings. In FIG. 1, wastewater from a paper mill is sent to a methane fermentation tank 1 through a pipe 5. In methane fermentation tank 1, the liquid temperature is 51~
The temperature is maintained at 53°C to carry out methane fermentation, and the generated methane gas is taken out of the system from the vibro. After fermentation, the digestive juice is supplied from the fermentation tank 1 to the vacuum flash drum 2 through a pipe 8, where a portion of the water in the digestive liquid is evaporated and the temperature of the flash residual liquid is lowered to 45 to 47°C. This residual liquid is sent through pipe 9 to a sludge separation tank (as shown).

The water vapor generated in the vacuum flash drum 2 is transferred to the pipe 10.
The air is then supplied to the recompressor 3, where it is boosted in pressure and then fed to the barometric condenser 4. In the barometric condenser 4, the pressurized steam is condensed by the water sent from the pipe 7, becomes hot water, and is injected into the methane fermentation tank 1, and the effluent in the tank is heated to a fermentation temperature of 51 to 53°C.

Note that the pipe 11 is a pipe that guides gas such as hydrogen sulfide that remains without being condensed in the barometric condenser 4 to the vacuum generator.

Figure 2 is a flowchart showing another embodiment of the present invention, 5
In this example, in order to further reduce operating costs, two vacuum flash drums and two barometric condensers are installed. That is, the digestive fluid flowing out from the methane fermentation tank 1 is sequentially supplied to the vacuum flash drums 2 and 1, and steam is generated in each vacuum flash drum.

The water vapor generated in the flash drum l on the high vacuum side is
The primary barometric capacitor 4' passes through the pipe 1ge.
After being condensed by water sent from pipe 7, the water is introduced into secondary barometric condenser 4 through pipe τ as cooling water for secondary barometric condenser 4. The flash residual liquid in the primary flash drum 1 is 45
The temperature drops to about ~47°C, and this residual liquid is sent to the sludge separation tank (as shown) through pipe 9.

The water vapor generated in the flash drum 2 on the low vacuum side is supplied to the recompressor 3 through the pipe 10, where it is pressurized and then sent to the secondary barometric condenser 4. In this condenser 4, the pressurized steam is condensed by the cooling water supplied from the pipe 1, and becomes hot water, which is then transferred to the methane fermentation tank 1.
The liquid in the tank is heated to a fermentation temperature of 51 to 53°C. In this way, two vacuum flash drums are installed.
By using stages, the throughput and compression ratio of the recompressor can be reduced, thereby reducing operating costs.

Note that the pipe 11 is connected to a vacuum generator as in the case of FIG.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are flow sheets each showing an embodiment of the present invention.

Claims (1)

[Claims] l. In a wastewater treatment method consisting of methane fermentation of paper mill wastewater at a temperature of 51 to 53°C, the digestive fluid flowing out from the methane fermentation tank is flashed under reduced pressure to generate water vapor, and the water vapor is A method for fermenting wastewater from a paper manufacturing factory, characterized in that the pressure is increased in a recompressor, and the resulting pressurized steam is used as a heat source to maintain a methane fermentation tank at a fermentation temperature of 51 to 53°C.