JPS6053250B2 - Recovery boiler black liquor treatment method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to black liquor treatment for a recovery boiler used in the production of kraft pulp, and particularly to a treatment method and apparatus structure suitable for reducing SOx in exhaust gas.

In the production of kraft valves, wood chips are fed into a wooden pot, which is then boiled with white liquor containing caustic soda and soda sulfide. As a result, the cellulose becomes a valve, and a resin-containing liquid called black liquor is produced as a residue. In order to recover the chemicals contained in this black liquor and utilize its combustible components, this black liquor is concentrated in a multi-effect can, and the dust from the recovery boiler is mixed into this concentrated black liquor. It is introduced into an internal burner, injected, dried, and burned on the hearth to generate steam. Conventionally, in such processing, as will be explained in detail later, the amount of dust components in the black liquor injected from the burner varies greatly over time, so SOx, which is a pollutant, is contained in the exhaust gas of the recovery boiler. This resulted in a large amount of . The present invention aims to reduce the generation of SOx, which is a pollutant, in such a recovery boiler. The present inventors focused on the relationship between changes in the properties of black liquor and the generation of SOx, and changed the black liquor processing system to mix the dust-containing black liquor back into the black liquor tank that stores concentrated black liquor. By incorporating this process, it is possible to suppress changes in the black liquor properties, stabilize black liquor combustion in the burner, maintain optimal operating conditions, and reduce SOx in exhaust gas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventional examples and embodiments of the present invention will be described in detail below with reference to the drawings.

Conventional Example An example of the conventional treatment of black liquor in the production of kraft valves is as shown in the system diagram of Fig. 2. The black liquor from which cellulose has been separated and concentrated in the multi-effect can 1 is temporarily stored in the black liquor tank 2. After being stored, the amount equivalent to combustion in the recovery boiler is taken out and injected from the burner 6 into the furnace 7 of the recovery boiler via the route described below, dried, and burned in the hearth.

The combustion gas from combustion in the hearth contains 20 to 30 f/NT.
Contains a large amount of dust.

Since this dust is mainly composed of mirabilite and contains chemicals such as soda carbonate, it is collected in a hopper 11 provided at the bottom of the boiler body and the economizer 10 and sent to the mixing tank 5. A dust collector 3 is provided downstream of the flue of the economizer 10 to further collect dust and send it to a dust tank 4. Note that the dust tank 4 may be omitted and the dust collected here may be sent into the mixing tank 5. The black liquor in the black liquor tank 2 is introduced into the mixing tank 5 via the conduit 21 and the dust tank 4 which mixes the dust collected by the dust collector 3 downstream of the flue 13. Here, the dust collected by the boiler, the economizer 10, and the hopper 11 is mixed with the black liquor, and the mirabilite quantitatively captured from the mirabilite silo 12 is mixed with the black liquor.

The black liquor mixed with dust and the like in the mixing tank 5 passes through a conduit 22 and is injected from a black liquor burner 6 into a furnace 7, where it is dried and then combusted. As is clear in this system,
Changes in the amount of dust collected in the dust collector and hopper result in changes in the properties of the black liquor sprayed from the burner, and as described later,
An increase in the amount of dust during medium blowing results in an increase in PSOx. As mentioned above, in a recovery boiler, the combustion gas contains a large amount of dust, which not only adheres to the heat transfer surface and reduces the heat transfer effect, but also causes blockage of the gas flow path, resulting in an inoperable state, resulting in overheating. Container tube 8, evaporation tube 9, economizer 10
A large number of medium blowers are installed to remove dust at regular intervals, but during this medium blowing a large amount of dust is intensively flaked off and scattered, so it is collected by the hopper 11 and dust collector 3. The amount of dust also increases rapidly immediately after the medium blowing.

For this reason, the composition of the black liquor mixed with dust fluctuates extremely over time, as shown in the graph of FIG. The first point is that this fluctuation causes an increase in SOx in the exhaust gas.
The figure shows actual measured values, but the correlation can be analyzed. In other words, the decrease in calorific value makes combustion in the furnace unstable, making it difficult to maintain a high temperature.At the same time, the increase in Na2sO4 causes a further decrease in temperature because this reduction is an endothermic reaction.
This is contrary to the fact that increasing the calorific value of black liquor, stabilizing combustion in the furnace, and maintaining high temperature are essential conditions for reducing SOx, and it is clear that this results in an increase in SOx. . The conventional ones had drawbacks as described above.

Example 1 FIG. 3 is a system diagram showing one embodiment of the present invention.

This embodiment is different from the above conventional example in that the conduit 22 connecting the mixing tank 5 and the burner 6 is removed, and the mixed black liquor in the mixing tank 5 is mixed into the black liquor tank 2 through the conduit 22, and the burner 6 The black liquor in the black liquor tank is supplied through a branch pipe 24 branched from a conduit 21 extending from the black liquor tank 2 to the dust tank 4. Other points are the same as the above conventional example. Therefore,
The parts that are different from the conventional example will be explained below. The mixed black liquor in the mixing tank 5 is passed through the conduit 22 to the black liquor tank 2.
and mixed with stored black liquor. The black liquor burner 6 is supplied with the dust mixture in the black liquor tank 2 through a branch pipe 24 branched from a conduit 21 connecting the black liquor tank 2 and the dust tank 4, and injects it into the furnace. For this reason, black liquor whose properties change when mixed with dust etc. can be taken out for combustion as black liquor with almost no change in properties by being mixed with stored black liquor, resulting in an extreme reduction in calorific value and N
Since there is no increase in a2sO4 and therefore the combustion is stable, the SOx in the exhaust gas becomes stable and low and does not cause pollution problems. Embodiment 2 This embodiment shown in the partial system diagram of FIG. 4 is a modification of Embodiment 1, and its effects are remarkable compared to the conventional example.

This embodiment differs from Embodiment 1 in that the mixed liquid in the mixing tank 5 is not mixed into the black liquor 2, and the liquid in the dust tank 4 is not introduced into the mixing tank 5. The mixed liquid in the mixing tank 5 is mixed into the tank 2 and is supplied to the burner 6. Therefore, the black liquor conduit between the dust tank 4 and the mixing tank 5 in Embodiment 1 was removed, and the mixing tank 5
The conduit 22 between the black liquor tank 2 and the conduit 24 that supplies the black liquor tank 2 to the burner 6 are removed, and instead the conduit 25 that directly leads the liquid in the black liquor tank 2 to the mixing tank 5 and the conduit 25 that leads the liquid in the mixing tank 5 directly to the burner 6 are removed. A new conduit 22 supplying the burner 6 is provided. As is obvious from the above piping, in this embodiment, the black liquor mixed with the dust-containing black liquor in the dust tank 4 is introduced into the mixing tank 5, where it is mixed with the black liquor from the hopper 11. A mixture of dust and the like is injected into the furnace from the burner 6.

Therefore, the combustion black liquor injected from the burner 6 has dust added to it in the dust tank as in the past, but does not have dust added to it in the mixing tank, so it is significantly more stable than the conventional example. The amount of S in the exhaust gas will be reduced. Embodiment 3 This embodiment shown in the partial system diagram of FIG. 5 is another modification of Embodiment 1, and its effects are remarkable compared to the conventional example.

This embodiment differs from Embodiment 1 in that the liquid in the dust tank 4 is not introduced into the mixing tank 5, but the black liquor from the black liquor tank is directly introduced into the mixing tank 5, and the burner The combustion black liquor supplied to the dust tank 6 is not that in the black liquor tank 2, but is the liquor in the dust tank 4.

Therefore, the conduit between the dust tank 4 and the mixing tank 5 in the first embodiment and the conduit 24 from the black liquor tank 2 to the burner 6 are removed, and instead the conduit 21 from the black liquor tank 2 to the dust tank 4 is removed. A conduit 27 that is branched to reach the mixing tank 5 and a conduit 28 that extends from the dust tank 4 to the burner 6 are newly installed.
As is obvious from the above piping, in this example,
The black liquor from the black liquor tank is directly introduced into the dust tank and the mixing tank, and the mixed liquid such as dust in the mixing tank is returned to the black liquor tank. is supplied as the combustion liquid, and compared to the conventional example, the liquid in the mixing tank is returned to the black liquor tank, so fluctuations in the properties of the combustion black liquor are reduced, and the amount of SOx in the exhaust gas is reduced compared to the conventional example. can be stabilized to a significantly lower amount than that of

As is clear from the above, according to the present invention, there is no change in the amount of combustion black liquor injected from the burner even when the amount of exhaust gas dust changes during the medium blowing process in the black liquor treatment of the recovery boiler in the production of craft valves. It is possible to perform stable combustion by keeping the calorific value almost constant, and the extreme Na2sO4
Stable low SOx in exhaust gas due to no increase in
It is extremely effective in preventing pollution because it can be easily operated.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in properties and the amount of SOx generated during and before and after the black liquor mortarization of a conventional recovery boiler. Figure 2 is a system diagram showing an example of conventional black liquor processing; Figures 3~
FIG. 5 is a system diagram and a partial system diagram of black liquor treatment in an embodiment of the present invention, respectively. 1...Multi-effect can, 2...Glaze black liquor rogoku, 3...Dust collector, 4.
...Dust tank, 5...Mixing tank, 6...Burner, 7...Furnace, 8.
...superheater, 9...evaporation tube, 10...
... Economizer, 11 ... Hopper, 12 ...
- Glauber's Salt Silo, 13... Flue, 21-28...
···conduit.

Claims (1)

[Scope of Claims] 1. In a device in which black liquor is burned in a recovery boiler, dust collected from the combustion gas of the recovery boiler is mixed into the black liquor, and the dust-containing black liquor is returned to the black liquor tank. A method for treating black liquor in a recovery boiler, the method comprising the steps of: 2. A method for treating black liquor in a recovery boiler according to claim 1, wherein supplementary mirabilite or the like is also mixed into the dust-containing black liquor. 3 A device having a black liquor tank, a black liquor mixing tank into which dust collected from the combustion gas of the recovery boiler and supplementary mirabilite, etc. are mixed, and a black liquor burner of the recovery boiler, and the liquid in the mixing tank is A black liquor processing device for a recovery boiler, comprising a pipe for introducing the black liquor into the black liquor tank and a pipe for directly supplying the black liquor in the black liquor tank to the black liquor burner. 4. Black liquor tank, dust tank that collects dust in the black liquor downstream of the combustion gas flue of the recovery boiler, mixing tank that mixes dust in the recovery boiler and supplementary mirabilite, etc. into the black liquor, and black liquor of the recovery boiler. In an apparatus having a liquid burner, a pipe for introducing the liquid in the dust tank into the black liquor tank, a pipe for introducing the liquid in the black liquor tank into the dust tank, a pipe for introducing the liquid in the black liquor tank into the black liquor tank, and a pipe for introducing the liquid in the black liquor tank into the dust tank. 1. A recovery boiler black liquor processing apparatus comprising a pipe for introducing the liquid into a mixing tank and a pipe for supplying the liquid in the mixing tank to the black liquor burner. 5 Black liquor tank, dust tank that collects dust in the black liquor downstream of the combustion gas flue of the recovery boiler, mixing tank that mixes dust in the recovery boiler and supplementary Glauber's salt, etc. into the black liquor, and black liquor of the recovery boiler. In an apparatus having a liquid burner, a pipe for introducing the liquid in the mixing tank into the black liquor tank, a pipe for introducing the liquid in the black liquor tank into the dust tank, a pipe for introducing the liquid in the black liquor tank into the dust tank, and a pipe for introducing the liquid in the black liquor tank into the dust tank. 1. A black liquor processing device for a recovery boiler, comprising a pipe introducing the dust tank into a mixing tank, and a pipe supplying the liquid in the dust tank to the black liquor burner.