JP2989916B2 - Additive for suppressing dust trouble in soda recovery boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an additive for suppressing dust adhesion trouble in a combustion apparatus (boiler, furnace, etc.) using by-product fuel obtained from pulp waste liquid.

[0002]

2. Description of the Related Art A soda recovery boiler uses, as a by-product fuel, a concentrated waste liquid called black liquor that is produced when wood chips are digested to separate fibers, and the combustion heat of organic substances in the black liquor is reduced. This is a very important boiler in a paper mill that generates steam while recovering the chemical (soda) contained in black liquor.

FIG. 1 is a diagram for explaining a method of adding the additive of the present invention using a simple flow sheet of a paper making process including a schematic diagram of a soda recovery boiler. The conventional technique will be described below with reference to this drawing. The remaining waste liquid that is washed after digesting wood chips is concentrated via an evaporator to become a dark black liquid. The dark liquor is burned in the furnace 10 of the recovery boiler 9 together with the fuel oil for combustion from another heavy oil line 8, and this combustion gas gives heat to the tube of the super heater 11 and the bank tube 13, and further passes through the economizer 15. After leaving the recovery boiler, the dust is removed by the dust collector 16 and then discharged from the chimney 17. The Na ₂ SO ₄ in the black liquor is reduced in the furnace to NaS, and is converted to green liquor from the furnace bottom and carried to the causticizing step. On the other hand, the separated fiber component is subjected to a paper machine after the bleaching step to be a product.

To remove the sticky dust adhering to the heat transfer surface of the tube, a mechanical method such as a soot blower 12 for periodically injecting steam or a hand lance is used. 14 is a hopper for collecting fallen dust, and 18 is a char bed.

[0005]

In a combustion apparatus using a by-product fuel obtained from a pulp waste liquid, there is a problem that the exhaust gas temperature and the draft pressure are increased due to the adhesion of dust generated together with the exhaust gas to various parts of the boiler. Conventionally, a mechanical operation such as a soot blower was used to remove the dust, but only about 70 days of continuous operation was possible. Regarding the adhesion of dust, those containing chlorine in the dust have a lower melting point than those not containing chlorine, and the initial melting point is around 570 ° C. Since this temperature is lower than the gas temperature, the dust is partially melted and solidified, and adheres to the vicinity of the super heater and the bank. Stuck dust can lead to blockage of superheaters and banks, raise draft resistance and exhaust gas temperature, and can even shut down in tens of days. As described above, the adhering dust is removed by injecting steam with a soot blower, but the amount of steam reaches about 3 to 5% of the generated steam, so that the loss is extremely large. Increase.

In recent years, by adding a compound of magnesium or calcium into a boiler, the continuous operation period can be extended to about 90 days, but it is still short.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress the adhesion of dust in a soda recovery boiler to a greater extent than conventional additives without relying on mechanical operation, and to significantly extend the continuous operation period of the boiler. It is another object of the present invention to provide a novel additive that contributes to reducing the amount of steam required for a soot blower.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors first studied the sticking phenomenon of dust, and the sticking of dust occurs due to the presence of a low melting point substance such as a eutectic substance due to chlorine. Therefore, if these low-melting substances are reduced and the content of sodium sulfate as the main component is increased, the appearance of the initial melting point near 570 ° C. of the dust disappears or decreases, and the melting point of the dust is the melting point of sodium sulfate. From the viewpoint that the temperature rises to a certain temperature of 850 ° C or higher and dust troubles are solved, we continue to search for substances that do not form low-melting substances together with chlorine in dust or substances that inhibit the absorption of chlorine in gas. As a result, it was found that iron or iron compounds, as well as non-metal sulfates, contained substances that increase the melting point of dust, and could be used as an additive suitable for the above purpose. It has reached the light.

Accordingly, the present invention relates to an additive for suppressing dust adhesion trouble in a soda recovery boiler that uses black liquor as a by-product fuel obtained from pulp waste liquor. , Iron carbonate, iron acetate, iron citrate, iron oxalate and iron hydroxide
At least one selected from iron compounds having a valency of II and / or
Alternatively, the present invention provides an additive for suppressing dust trouble of a soda recovery boiler comprising at least one sulfate selected from ammonium sulfate, methyl sulfate, ethyl sulfate and amyl sulfate, wherein the additive is in a slurry or an aqueous solution. Is what you do. Further, the present invention provides the above additive in an amount of 5 to 50,000 ppm based on black liquor,
The slurry is added to the fuel supplied to the soda recovery boiler or to the combustion gas of the boiler in any state of the slurry and the aqueous solution, provided that the amount of the iron compound and / or sulfate added is Fe ₂ O ₃ and And / or a method for suppressing dust trouble in a soda recovery boiler, which is converted into ammonium sulfate.

[0010]

The mechanism of the effect of suppressing the adhesion of dust by the additive of the present invention is as follows. (1) The addition of iron or an iron compound reduces the amount of reducing substances in dust and suppresses the production of sodium carbonate and sodium thiosulfate. Since sodium carbonate easily absorbs chlorine and sodium thiosulfate is a low-melting substance, reduction of reducing substances is effective for increasing the melting point. Sulfur dioxide in the gas becomes sulfur trioxide due to the catalytic action of iron oxidation, and converts sodium carbonate in dust to sodium sulfate, contributing to a higher melting point.

(2) Nonmetal sulfate decomposes at about 350 ° C. to generate sulfuric acid (sulfuric anhydride). The sulfuric anhydride is taken into the dust, converts sodium carbonate into sodium sulfate, and inhibits absorption of chlorine in the gas. Further, chlorine existing in the dust is liberated and discharged as hydrogen chloride by the action of sulfuric anhydride. By this action, the content of sodium sulfate as the main component is increased, and the melting point is increased.

By causing the reactions (1) and (2) on the surface of the dust particles, the dust is prevented from enlarging and sticking due to the collision of the particles, heat absorption is improved, and the gas temperature rises.
An increase in draft pressure can be suppressed. Further, since the surface of the dust particles only needs to have a high melting point, the addition amount of iron or an iron compound and a nonmetal sulfate may be relatively small, which is economical.

The flow sheet of FIG. 1 shows a black liquor portion, a heavy oil portion, a furnace portion, and a portion in front of a bank as addition portions of the additive according to the present invention. In the case of the property, it is possible to add the additive from the storage tank 5 to the fuel (black liquor or heavy oil) via the strainer 6 and the injection pump 7 in addition to the combustion gas. (Eg or). On the other hand, in the case of non-metal sulfate, there is a problem in adding it to fuel. This is because the nonmetal sulfate is decomposed by the alkali component in the fuel, and the sulfate is reduced in the high-temperature reduction region, thereby impairing the effect of addition. Therefore, when adding the nonmetal sulfate, it is desirable and effective to add it to the combustion gas.

[0014]

EXAMPLES The present invention will be further described below with reference to examples. The combustion conditions and specifications of the used soda recovery boiler are as follows. (1) Combustion conditions: automatic operation with an excess air ratio of 3.7% (2) Fuel used: co-firing of heavy oil + black liquor (ash content of black liquor 35)
(3) Specifications of boiler: evaporation amount 258 T / H, steam temperature 5
00 ° C, steam pressure 100 kg / cm ² The type and condition of the additives used in the test were as follows:
Three types: (1) aqueous solution of FeSO ₄ , (2) F
eSO ₄ powder, (3) FeSO ₄ water slurry,
(4) mixed powder of FeSO ₄ and ammonium sulfate, (5) FeSO
₄ and ammonium sulfate slurry, (6) aqueous solution (including complex) of FeSO ₄ and ammonium sulfate, (7) powder of ammonium sulfate, (8) slurry of ammonium sulfate, (9) aqueous solution of ammonium sulfate, (10) Fe ₂ O ₃ Powder, (11) Fe ₂ O ₃ oil slurry, (12) Fe
(13) a water slurry of (OH) ₂ , and (13) a powder of Fe (OH) ₂ . Further, instead of iron sulfate, iron nitrate, iron carbonate, iron acetate, iron citrate, iron oxalate, Fe ₃ O ₄ , FeO
Oxides such as OH and hydroxides such as Fe (OH) ₃ can also provide the same effect. 5 to 5
The reason for setting the content to 0000 ppm is that there is almost no effect when the content is less than 5 ppm, and when the content is more than 50,000 ppm, the effect of suppressing dust adhesion is small instead of the added amount, and conversely, the attached amount tends to increase.

Example 1 The relationship between the amount of ferrous sulfate (FeSO ₄ ) added to the fuel black liquor in the form of an aqueous solution and the amount of dust attached is as follows.

[Table 1] The relationship between the amount of addition and the amount of dust adhering when the aqueous solution of FeSO ₄ is sprayed into the gas of the super heater section is as follows.

[Table 2] Example 2 The relationship between the addition amount and the adhesion amount when FeSO ₄ powder having an average particle size of 100 μm or less was sprayed with pressurized air into the inlet of the super heater at the upper part of the furnace is as follows.

[Table 3] Example 3 The relationship between the added amount and the attached amount when FeSO ₄ was converted into a water slurry having an average particle diameter of 50 μm or less and injected into black liquor is as follows.

[Table 4] Example 4 The relationship between the addition amount and the adhesion amount when FeSO ₄ was made into a water slurry having an average particle size of 50 μm or less and sprayed with pressurized air into the upper part of the furnace and the inlet of the super heater was as follows.

[Table 5] Example 5 FeSO ₄ and ammonia sulfate ((NH ₄ ) ₂ SO ₄ ) were mixed to form an aqueous solution (one part slurry), and the relationship between the amount added and the amount of adhesion when added to the fuel black liquor was as follows. It is as follows.

[Table 6] Relationships such as Example 6] FeSO ₄ and (NH ₄₎ amount when injected into the furnace top and superheater inlet ₂ were mixed SO ₄ powder with pressurized air and coating weight is as follows .

[Table 7] Example 7 The results when an aqueous solution of (NH ₄ ) ₂ SO ₄ was injected into the combustion gas are as follows. Note that the concentration of ammonium sulfate is 4
0% (saturated liquid 41%) was used.

[Table 8] Example 8 The result when (NH ₄ ) ₂ SO ₄ powder was injected into the combustion gas is as follows. The used (NH ₄ ) ₂ S
The concentration of O ₄ was around 99%.

[Table 9] Example 9 The result when (NH ₄ ) ₂ SO ₄ was slurried and injected into combustion gas is as follows. In addition, since the ammonium sulfate concentration of the slurry is 50 to 70%, when the concentration becomes high, an anionic or nonionic activator is added to give wettability.

[Table 10] Reference Example 1 The results when Fe ₂ O ₃ powder was injected into a combustion gas (upper furnace, super heater) are as follows.

[Table 11] Reference Example 2 The result of adding an oil slurry of Fe ₂ O ₃ to heavy oil is as follows.

[Table 12] Reference Example 3 The result of adding a water slurry of Fe (OH) ₂ to black liquor is as follows.

[Table 13] [Reference Example 4] The result of adding the powder of Fe (OH) ₂ to the combustion gas is as follows.

[Table 14] Reference Example 5 The result of adding Fe powder (average particle diameter: 100 μm) together with air into a combustion gas in a furnace from a burner section is as follows.

[Table 15] Above 50,000 ppm of iron powder, the temperature of the exhaust gas increased, and the amount of adhesion tended to increase.

[0016]

As described above, all of the additives of the present invention react with chlorine in combustion gas and dust and hinder the absorption of chlorine from combustion gas into the duct. Since the melting point is raised and dust troubles in the soda recovery boiler are largely suppressed, the continuous operation period of the boiler can be significantly extended, and at the same time, the amount of steam required for the soot blower can be reduced. Therefore, there are significant industrial benefits.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method of adding an additive of the present invention using a simple flow sheet of a papermaking process including a schematic diagram of a soda recovery boiler.

[Explanation of symbols]

1: Additive additive (black liquor) 2: Additive (heavy oil) 3: Additive (furnace) 4: Additive
Additive additive location (before bank entrance), 5: additive storage tank, 6: strainer, 7: infusion pump, 8:
Heavy oil line, 9: recovery boiler, 10: furnace, 11: super heater, 12: soot blower, 13: bank tube, 14: hopper, 15: economizer, 16: dust collector, 17: chimney, 18: charbed.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) D21C 11/12 F23J 1/00 F23G 7/04

Claims (4)

(57) [Claims] 1. An additive added to suppress dust adhesion trouble in a soda recovery boiler using black liquor as a by-product fuel obtained from pulp waste liquor, wherein the additive is iron sulfate, nitric acid A soda recovery boiler, which is a slurry or an aqueous solution containing at least one of iron, iron carbonate, iron acetate, iron citrate and iron oxalate, each of which is selected from the group consisting of iron compounds having a valence of II or III. Additive for suppressing dust trouble. 2. The additive for suppressing dust trouble of a soda recovery boiler according to claim 1, wherein the additive further contains at least one sulfate selected from ammonium sulfate, methyl sulfate, ethyl sulfate and amyl sulfate. Agent. 3. An additive added to suppress dust adhesion trouble in a soda recovery boiler using black liquor as a by-product fuel obtained from pulp waste liquor, wherein the additive is iron hydroxide ( II) and iron hydroxide (II
Dust trouble in a soda recovery boiler, characterized by being a slurry or an aqueous solution containing an iron compound selected from I) and at least one sulfate selected from methyl sulfate, ethyl sulfate and amyl sulfate. Control additive. 4. The additive according to claim 1, 2 or 3,
The iron compound is 5 to 50,000p based on black liquor.
pm so as to be added to the fuel supplied to the soda recovery boiler or to the combustion gas of the boiler in any state of a slurry and an aqueous solution, provided that the amount of the iron compound added is Fe ₂ O ₃ A method for suppressing dust trouble in a soda recovery boiler, which is a converted one.