JPH07293848A - Black liquor fired boiler - Google Patents

Abstract

PURPOSE:To secure the predetermined density of black liquor without accompanying the faulty operation of a bypass damper or the deterioration of boiler efficiency when the inlet gas temperature of a direct contact type evaporator is reduced. CONSTITUTION:A black liquor fired boiler, in which first stage thickening is effected through a boiler furnace 8, an economizer 10, a direct contact evaporator 5, a dust collector 11 and a multi-layer vacuum evaporating boiler, and, subsequently, black liquor, on which said first stage thickening is applied, is introduced into a direct contact evaporator to effect second stage thickening and obtain the black liquor used as fuel, is constituted. An exhaust gas circulating duct 15, guiding the outlet gas of the dust collector to the inlet port of the economizer, is provided and the flow rate of the outlet gas, passing through the exhaust gas circulating duct, is regulated whereby the inlet gas temperature of the direct contact evaporator is regulated. The regulation of flow rate of the outlet gas is effected by a circulating gas amount regulating damper 16, provided in the exhaust gas circulating duct.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black liquor combustion boiler used for a soda recovery boiler in a pulp mill,
In particular, it relates to the configuration of a device for concentrating black liquor, which is fuel.

[0002]

2. Description of the Related Art Drainage liquid (dark black liquor) produced in pulp manufacturing process
Has a combustible substance concentration of about 7 to 12%. In order to use this as the fuel for the soda recovery boiler, the combustible substance concentration is 6%.
It must be concentrated to 0% or more.

Conventionally, as a device for concentrating a dark black liquor to 60% or more, which is necessary for self-combustion, a sensible heat of a multiple vacuum evaporator and boiler exhaust gas is used even for a dilute black liquor mainly made of general wood. Although the direct contact evaporator was used together, the performance of multiple vacuum evaporators has improved in recent years, so it is possible to concentrate the dark liquid to a high concentration of 70% or more with only multiple vacuum evaporators. The direct contact evaporator is no longer used.

However, it is difficult to concentrate the dark black liquor to 50% or more in the dark black liquor containing bagasse or bamboo as the main raw material, since it contains a large amount of impurities such as silica. A method is adopted in which the black liquor concentrated to about 50% in an evaporator is further introduced into a direct contact evaporator to evaporate the water content in the black liquor to concentrate it to 60 to 75%.

FIG. 3 shows an example of a conventionally known black liquor combustion boiler apparatus of this type. In this figure, 1 is a pipe for supplying a black liquor, 2 is a multiple vacuum evaporator, 3 is a dark liquor tank, 4 is a black liquor transport pump, 5 is a direct contact evaporator, 6 is a black liquor circulation pump, and 7 is Oscillator, 8 is a boiler furnace, 9
Is an evaporation tube group, 10 is a economizer, 11 is a dust collector such as an electric dust collector, 12 is an induced draft fan, 13 is a bypass duct for bypassing the economizer gas to the direct contact evaporator 5, 14
Is a bypass damper provided in the bypass duct 13,
Reference numeral 17 indicates a chimney.

The dark black liquor supplied from the pipe 1 is concentrated to about 50% in the multiple vacuum evaporator 2 and stored in the dark black liquor tank 3. This thick black liquor is introduced into the direct contact evaporator 5 by the black liquor transport pump 4, and is evaporated to moisture by vapor-liquid contact with the boiler exhaust gas, and is concentrated to a concentration of 60 to 75%. The black liquor concentrated to such a predetermined concentration is supplied from the oscillator 7 into the boiler furnace 8 and burned. Boiler exhaust gas generated by combustion is evaporated tube group 9 and economizer 10.
Then, the water in the black liquor is evaporated by being guided to the direct contact evaporator 5. The boiler exhaust gas containing the evaporated water is guided to the dust collector 11 to remove the dust in the exhaust gas, and then is attracted by the attracting fan 12 and discharged from the chimney 17. The inlet gas temperature of the direct contact evaporator 5 is adjusted to a predetermined value by adjusting the opening degree of the bypass damper 14 and increasing or decreasing the bypass flow rate of the economizer gas flowing to the direct contact evaporator 5.

The dark black liquor is supplied to the direct contact evaporator 5 by the method shown in FIG.
The black liquor is pumped at and sprayed into the direct contact evaporator 5 to ensure the contact area of the black liquor with the exhaust gas. In addition to the cyclone evaporator method, the black liquor in the lower reservoir is mechanically scooped up and the upper exhaust gas flow There is also a cascade evaporator system that contacts with. Further, inorganic components such as sodium and sulfur in the black liquor are discharged outside the furnace after the reduction reaction and reused in the cooking process. On the other hand, organic components such as lignin are burned to generate electric power and steam necessary for the factory.

By the way, since the temperature of the boiler exhaust gas introduced into the direct contact evaporator 5 is, in principle, proportional to the combustion amount of the black liquor, the temperature of the inlet gas of the direct contact evaporator 5 decreases when the black liquor combustion is under low load. . Even when the boiler heat transfer surface is relatively clean, the inlet gas temperature of the direct contact evaporator 5 decreases. When the inlet gas temperature of the direct contact evaporator 5 decreases, the heat quantity of the boiler exhaust gas, which is a heating source, decreases, so that the black liquor concentration in the direct contact evaporator 5 is insufficient and the concentration of black liquor supplied to the oscillator 7 decreases. And the stable combustion becomes difficult. Therefore, in order to obtain a predetermined black liquor concentration, it is necessary to lower the outlet gas temperature of the direct contact evaporator 5 by an amount corresponding to the lowering of the inlet gas temperature of the direct contact evaporator 5. However, if the outlet gas temperature of the direct contact evaporator 5 is lowered, another serious inconvenience occurs such that low temperature corrosion of the dust collector 11 and the induced draft fan 12 installed in the subsequent stage is promoted.

In order to eliminate such inconvenience, conventionally, when the inlet gas temperature of the direct contact evaporator 5 is lowered for some reason, a part of the economizer gas is bypassed to absorb heat in the economizer 10. Many measures are taken to reduce the amount and increase the temperature of the gas at the inlet of the direct contact evaporator 5.

[0010]

In order to adjust the inlet gas temperature of the direct contact evaporator 5, the opening degree of the bypass damper 14 is adjusted and the bypass flow rate of the economizer gas flowing to the direct contact evaporator 5 is adjusted. You have to increase or decrease. However, since a large amount of dust in the submicron order is contained in the economizer gas, the movement of the bypass damper 14 becomes poor due to clogging of dust, or the bypass damper 14 becomes stuck and becomes inoperable. It is easy to cause inconvenience,
Not only does it require an excessive amount of labor for maintenance and inspection, but it often causes problems in adjusting the gas temperature. For this reason, generally, an operating method has been adopted in which the heat quantity of the inlet gas of the direct contact evaporator 5 is increased by increasing the combustion air excess rate and increasing the combustion gas quantity. An increase causes a decrease in boiler efficiency, which is not preferable.

The present invention has been made in order to eliminate the inconvenience of a black liquor combustion boiler having a direct contact evaporator, and its object is also to reduce the inlet gas temperature of the direct contact evaporator. The purpose is to ensure a predetermined black liquor concentration without causing a malfunction of the bypass damper and a decrease in boiler efficiency.

[0012]

In order to solve the above-mentioned problems, the present invention comprises a boiler furnace, a economizer, a direct contact evaporator, a dust collector, and a multiple vacuum evaporator. The first-stage concentration is carried out through a vacuum evaporator, and then the concentrated black liquor subjected to the first-stage concentration is introduced into a direct contact evaporator to remove the second-stage concentrated black liquor. In a black liquor combustion boiler that uses fuel, an exhaust gas circulation duct that guides the outlet gas of the dust collector to the inlet of the economizer is provided, and by adjusting the flow rate of the outlet gas that flows through the exhaust gas circulation duct, The inlet gas temperature of the direct contact evaporator was adjusted. To adjust the flow rate of the outlet gas flowing through the exhaust gas circulation duct, a circulation gas amount adjustment damper is provided in the exhaust gas circulation duct, and the opening degree of this circulation gas amount adjustment damper is adjusted according to the inlet gas temperature of the direct contact evaporator. Can be done by

[0013]

[Operation] When the outlet gas of the dust collector is circulated to the inlet of the economizer, although the outlet gas temperature of the economizer (direct contact evaporator gas temperature) decreases, direct contact occurs due to an increase in the gas amount. Since the amount of heat retained in the gas at the inlet of the evaporator increases, the ability to evaporate the water content in the black liquor does not decrease, and the black liquor can be concentrated highly efficiently. In addition, since the outlet gas of the dust collector has a small amount of dust content, the circulating gas adjusting damper is not fixed, the boiler device can be operated with high efficiency, and maintenance and inspection are facilitated. In addition, since the outlet gas temperature of the direct contact evaporator does not decrease, low temperature corrosion of the dust collector and the induced draft installed in the subsequent stage of the direct contact evaporator is also prevented. Furthermore, since the boiler device of this method circulates the outlet gas of the dust collector, which is attracted by the induced draft fan, to the inlet of the economizer that has a lower pressure than this, it is necessary to install a circulating draft fan. There is no need, and the configuration can be simplified.

[0014]

EXAMPLE FIG. 1 shows a black liquor combustion boiler according to an example. In this figure, reference numeral 15 indicates an exhaust gas circulation duct that guides the outlet gas of the dust collector to the inlet of the economizer, and reference numeral 16 indicates a circulating gas amount adjustment damper provided in the exhaust gas circulation duct. The same reference numerals are displayed in the portions corresponding to FIG.

As is clear from this figure, in the black liquor combustion boiler of this example, instead of the structure in which a part of the economizer gas is bypassed and introduced into the direct contact evaporator 5, the outlet of the dust collector 11 is replaced. It is characterized in that the gas is introduced into the direct contact evaporator 5 through the exhaust gas circulation duct 15 by the induced draft fan 12. The circulating gas amount adjusting damper 16 is used for the direct contact evaporator 5.
It is opened when the inlet gas temperature of is decreased and closed when the inlet gas temperature of the direct contact evaporator 5 is increased. The opening degree is controlled according to the inlet gas temperature of the direct contact evaporator 5. In addition, regarding the black liquor flow and concentration method,
The description is omitted to avoid duplication because it is the same as that described in the section of the prior art.

When the outlet gas of the dust collector 11 is circulated to the inlet of the economizer 10, the temperature of the gas in the economizer 10 is lowered, and the outlet gas temperature of the economizer 10 is also lowered accordingly. However, since the gas temperature inside the economizer is lowered as a whole, the temperature difference from the feed water is reduced and the heat absorption in the economizer 10 is reduced. As a result, the heat quantity of the boiler exhaust gas at the inlet of the direct contact evaporator 5 increases. Therefore, the ability to evaporate the water content in the black liquor does not decrease, and the concentration rate of the black liquor also decreases.
In this case, since the outlet gas temperature of the direct contact evaporator 5 does not decrease, the dust collector 1 installed at the subsequent stage of the direct contact evaporator 5
The low temperature corrosion of 1 and induced draft fan 12 is also prevented. Moreover, since the outlet gas of the dust collector 11 has a small amount of dust, the dust does not clog and the operation of the circulation gas adjustment damper 16 does not become sick, and the boiler device can be operated with high efficiency. Maintenance and inspection becomes easy. Furthermore, since the boiler device of this method circulates the outlet gas of the dust collector, which is attracted by the induced draft fan, to the inlet of the economizer that has a lower pressure than this, it is necessary to install a circulating draft fan. Without
The configuration can be simplified.

FIG. 2 shows the operating conditions and the effects of the boiler device according to this example in comparison with the comparative example.

In case A of FIG. 2, the boiler load is 100%.
At this time, the operating conditions are necessary for concentrating the black liquor concentration to 62% without circulating the boiler exhaust gas. The heat transfer area of the economizer 10 is installed so that this balance can be maintained. Case B has a black liquor concentration of 62% without circulating the boiler exhaust gas when the boiler load is reduced to 70%.
It is an operating condition necessary for concentrating to%. Case C is
When the boiler load is reduced to 70%, the operating conditions are necessary to keep the outlet gas temperature of the direct contact evaporator 5 at the same temperature as the case A without circulating the boiler exhaust gas. Case D is an example using the present invention, and is an operating condition necessary to obtain the outlet gas temperature and the black liquor concentration of the direct contact evaporator 5 similar to Case A when the boiler load is reduced to 70%.

As is clear from this figure, Case B is
When the boiler load is reduced to 70%, the outlet gas temperature of the economizer 10 is reduced. Therefore, in order to obtain a black liquor concentration of 62%, the outlet gas temperature of the direct contact evaporator 5 must be 120 ° C. Therefore, low temperature corrosion of the dust collector 11 and the flue and the induced draft fan 12 in the subsequent stage becomes a problem. Also, case C
Can maintain the outlet gas temperature of the direct contact evaporator 5 at 150 ° C., but since the difference in gas temperature in the direct contact evaporator 5 is small, the outlet black liquor concentration of the direct contact evaporator 5 is 58.
It drops to 5%, self-combustion becomes unstable, and combustion of auxiliary fuel becomes necessary. On the other hand, in case D, 19220
By bypassing the dust collector outlet gas of kg / h to the inlet of the economizer 10, a black liquor concentration of 62% can be obtained, and the outlet gas temperature of the direct contact evaporator 5 is set to 15%.
It can also be kept at 0 ° C. Therefore, the self-combustion of the black liquor by the boiler furnace 8 does not become unstable, and the low temperature corrosion of the dust collector 11, the flue, and the induced draft fan 12 does not become a problem.

[0020]

As described above, according to the present invention,
When the temperature of the inlet gas of the direct contact evaporator was lowered, the outlet gas of the dust collector was circulated to the inlet of the economizer to increase the heat quantity of the boiler exhaust gas at the inlet of the direct contact evaporator. It is possible to prevent a decrease in the concentration rate of black liquor. Further, in this case, since it is not necessary to lower the outlet gas temperature of the direct contact evaporator, it is possible to prevent low-temperature corrosion of the dust collector, the induced draft fan, etc. installed in the subsequent stage of the direct contact evaporator. Also, since the outlet gas of the dust collector with a small dust content is bypassed,
Malfunctions due to clogging of the circulating gas adjustment damper 16 are prevented, the boiler device can be operated with high efficiency, and maintenance and inspection is facilitated. Furthermore, the boiler device of this method is
Since the outlet gas of the dust collector, which is attracted by the induced draft fan, is circulated to the inlet of the economizer that has a lower pressure than this, there is no need to install a circulating draft fan, and the configuration is simplified. be able to.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a black liquor combustion boiler according to an embodiment.

FIG. 2 is a table showing the effects of the present invention.

FIG. 3 is a configuration diagram of a black liquor combustion boiler according to a conventional example.

[Explanation of symbols]

 1 Dark Black Liquor Supply Pipe 2 Multiple Vacuum Evaporation Can 3 Thick Black Liquor Tank 4 Black Liquor Transport Pump 5 Direct Contact Evaporator 6 Black Liquor Circulation Pump 7 Oscillator 8 Recovery Boiler Furnace 9 Evaporative Water Pipe Group 10 Coal Saver 11 Dust Collector 12 Induction fan 15 Exhaust gas circulation duct 16 Exhaust gas adjustment damper 17 Chimney

Claims (2)

[Claims] 1. A boiler furnace, a economizer, a direct contact evaporator, a dust collector, and a multi-vacuum evaporator, the first-stage concentration is performed through the multi-vacuum evaporator, and then, In the black liquor combustion boiler in which the concentrated black liquor subjected to the first stage concentration is introduced into a direct contact evaporator to use the black liquor subjected to the second stage concentration as a fuel, the outlet gas of the dust collector Is provided to the inlet of the economizer, and the inlet gas temperature of the direct contact evaporator is adjusted by adjusting the flow rate of the outlet gas flowing through the exhaust gas circulation duct. Black liquor combustion boiler. 2. The black liquor combustion boiler according to claim 1, wherein a circulating gas amount adjusting damper is provided in the exhaust gas circulating duct, and an opening of the circulating gas amount adjusting damper is set to an inlet gas of the direct contact evaporator. A black liquor combustion boiler that is adjusted according to the temperature.