JPH0665795B2 - Odorous gas treatment method in kraft pulp mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for collecting and processing an odorous gas generated from each device in a kraft pulp manufacturing process. More specifically, the present invention relates to a method for treating odorous gas that can reduce the amount of odorous gas to be collected.

[Prior Art] The kraft pulp method is widely used as a method for producing chemical pulp, but since sodium sulfide is used as a chemical liquid for pulp cooking, odorous gases such as hydrogen sulfide, methyl mercaptan, and dimethyl sulfide are produced in pulp. It arises from the process.

Even if the amount of odorous gas containing these components is very small, the odor is strong, and if it is released into the atmosphere, it affects residents around the factory. For this reason, odorous gas has been collected at its source and oxidatively decomposed by combustion, etc., but there are many places where odorous gas should be collected during the manufacturing process. Due to the large amount of gas, etc., it can be collected from sources with relatively high concentration, such as blower gas from digester, evaporator exhaust, deodorizing tower exhaust, or exhaust from unbleached pulp washing equipment that produces a large amount of odorous gas. Stayed

Further, conventionally, it has been carried out to separately transfer the high-concentration odorous gas that has a risk of explosion and the low-concentration odorous gas that does not have a risk to the combustion device. The transfer system is equipped with flashback preventive devices such as flame arresters and water traps to prevent the danger of ignition and explosion, and also with a raptier disc to protect the devices in the event of an explosion. Alternatively, dilution with air has been performed. Dilution with air has caused a large amount of gas to be collected and has made it difficult to collect and process all odorous gases. Further, since the odorous gas generation source is a fluid of relatively high temperature, it has a large amount of moisture and corrodes the water pipe of a combustion apparatus such as a recovery boiler, so that a cooling dehumidifying tower has also been installed.

[Problems to be Solved by the Invention] The present invention collects almost all of the odorous gas generated in the kraft pulp manufacturing process, reduces the amount of gas to be collected, and further has no danger of explosion or the like. Provided is a method for collecting and treating a volatile gas.

[Means for Solving the Problems] In the present invention, odorous gas is divided into two systems, a low-concentration odorous gas generation source and a high-concentration odorous gas generation source, and the odor is passed through a cooling and dehumidifying device provided for each system. A odorous gas treatment method in which a gas is sucked and collected by a suction device, transferred to a combustion device, and burned, wherein the high-concentration odorous gas has a low odor Diluting with gas and dividing the collection system into high-concentration odorous gas collection system and low-concentration odorous gas collection system according to the degree of tightness of the odorous gas source, and pressure control valves for each system To provide a predetermined negative pressure for each system to provide an odorous gas treatment method for a kraft pulp mill.

The present invention, in a method for treating odorous gas by dividing it into a high-concentration odorous gas system and a low-concentration odorous gas system,
High concentration odorous gas should be treated while diluting with low concentration odorous gas below the explosion limit of odorous components at the inlet side of the cooling and dehumidifying tower installed in the odorous gas system to prevent the risk of explosion and the like. The first feature is that the amount of gas is greatly reduced. Conventionally, a method has been implemented in which odorous gas is separated into high-concentration odorous gas and low-concentration odorous gas and then treated, but air is used to prevent the risk of explosion of high-concentration odorous gas. It was necessary to dilute it with or to install auxiliary equipment such as a rupture disk in case of danger of explosion. In order to prevent the danger of ignition and explosion by the suction device installed on the gas outlet side of the cooling dehumidifier, the present invention dilutes the high-concentration odorous gas with the low-concentration odorous gas on the gas inlet side of the cooling dehumidifier. Eliminates the risk of ignition and explosion, reduces the amount of gas to be burned, and eliminates the need to install auxiliary equipment such as rupture disks.

The second feature of the present invention is to install a pressure control valve in each gas collection system near the high-concentration odorous gas generation source and the low-concentration odorous gas generation source according to the size of the hermeticity, and control the pressure from the generation source. This is because the pressure of the portion reaching the valve was adjusted to a predetermined negative pressure. That is, when the source is a device with low airtightness, for example, when collecting the odorous gas generated from the pulp washing device or when the path from the source to the pressure control valve is long, increase the negative pressure, Even in the case of the same low-concentration odorous gas generating source, the negative pressure is lowered in the case of a black liquor tank or the like having a high airtightness.
In this way, by controlling the negative pressure by controlling the tightness of the odorous gas generation source, the amount of collected gas was suppressed to the necessary minimum, and the amount of collected gas to be treated was reduced. .

Negative pressure is usually controlled in the range of about −50 mmAq to −150 mmAq. It is preferable to increase the negative pressure when the gas temperature is high and when the pipe length is long.

The method of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing one embodiment for carrying out the method of the present invention. High concentration odorous gas collection system 1
And a low-concentration odorous gas collection system 2 are installed, and cooling and dehumidifying devices 3, 3'are installed in each system. Those that belong to the high-concentration odorous gas collection system are digester blow gas, evaporator exhaust gas, deodorizing tower exhaust gas, etc., and odorous gas of about several thousands ppm or more as total reduced sulfur. Those that belong to the low-concentration odorous gas are pulp cleaning equipment exhaust gas,
Vent gas from waste liquid storage tank, exhaust gas from black liquor oxidation tower, etc., and odorous gas of less than about 1000 ppm as total reduced sulfur.

When collecting gas from a highly hermetic device such as a digester blow gas storage tank 4, it is preferable to provide a vent 5 with an adapter so that some air can be sucked from the adapter from the viewpoint of preventing the device from being destroyed. Alternatively, it may be sent from the high-concentration odorous gas storage tank 6 to the gas generation source side of the pressure control valve 8 via the blower 7. When collecting low-concentration odorous gas from a low-concentration odorous gas source such as the pulp cleaning device 9 and the black liquor tank 10, a low-sealing odorous gas source such as the pulp cleaning device 9 and black A pressure control valve 8 is installed separately from a highly-sealing odorous gas generation source such as the liquid tank 10, and a system with high sealing has a low negative pressure.
A system with low airtightness raises the negative pressure. This is because the amount of air other than the odorous gas sucked in is reduced and the amount of gas to be collected is minimized.

The sucked odorous gas passes through the pressure control valve 8 and enters the cooling and dehumidifying devices 3, 3 '. On the odorous gas generation source side of the cooling / dehumidifying device, the high-concentration odorous gas is diluted by the low-concentration odorous gas sent through the duct 12 by the suction fan 11 on the outlet side of the cooling / dehumidifying device. Dilution position of high concentration odorous gas,
Any position may be used as long as it is on the cooling device side of the pressure control valve 8, but a position closer to the pressure control valve 8 is preferable for preventing danger such as explosion. The low concentration odorous gas for dilution is
It is preferable that the black liquor oxidizer 15 is used instead of the air used for oxidation and then used for diluting the highly concentrated odorous gas.
This is to reduce the amount of odorous gas that should be collected.

The high-concentration odorous gas and the low-concentration odorous gas that have passed through the cooling / dehumidifying device 3 are fed into the combustion device by the suction fans 13, 13 '. It is preferable to install a plurality of suction fans in parallel and use different power supply systems. This is to prevent the release of untreated odorous gas to the atmosphere by stopping the operation of the suction fan even in the event of a power failure or failure.

It is preferable to install a communication duct 14 on the gas inlet side of each cooling / dehumidifying device between the low concentration odorous gas collection system and the high concentration odorous gas collection system. This is to enable alternate inspection and maintenance of the cooling and dehumidifying device. During normal operation, this communication duct is closed.

[Effect of the Invention] According to the present invention, since the amount of odorous gas to be collected and treated can be significantly reduced, there is provided an odorous gas treatment method capable of completely treating odorous gas generated in the pulp manufacturing process.

ADVANTAGE OF THE INVENTION According to this invention, the catching treatment method which the operation maintenance is easy is provided without the need to install the auxiliary equipment prepared for the danger of explosion, such as a flashback prevention device and a rupture disk.

[Brief description of drawings]

FIG. 1 is a flowchart showing one embodiment of the odorous gas treatment method of the present invention. 1: High concentration odorous gas collection system 2: Low concentration odorous gas collection system 3: Cooling dehumidifier, 8: Pressure control valve

Claims (1)

[Claims] 1. A odorous gas is divided into two systems, a low-concentration odorous gas generation source and a high-concentration odorous gas generation source, and the odorous gas is sucked and collected by a suction device through a cooling and dehumidifying device provided for each system. Then, it is transferred to a combustion device, and is a odorous gas treatment method for combustion treatment, wherein the high-concentration odorous gas is diluted with a low-concentration odorous gas on the odorous gas generation side of the cooling and dehumidifying device,
In each of the high-concentration odorous gas collection system and the low-concentration odorous gas collection system, the collection system is divided according to the tightness of the odorous gas source, and each system is equipped with a pressure control valve. A method for treating odorous gas in a kraft pulp mill, which is characterized in that a predetermined negative pressure is applied separately.