JPH0323801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a recovery boiler, and more particularly to a method of operating a recovery boiler that can increase the recovery rate of chemicals and reduce the amount of air pollutants such as sulfur oxides emitted.

When producing pulp, it is necessary to separate the wood components cellulose (fiber) and lignin (resin) and extract only the cellulose.
Chemicals such as Na ₂ S and NaOH are used to perform chemical separation. The solution containing dissolved lignin and the above chemicals after pulping processes such as cooking and washing is discharged as a waste liquid called black liquor, but the recovery boiler burns this black liquor to reduce the inorganic chemicals in the black liquor and convert it into sodium. ₂ Sya
It recovers Na ₂ CO ₃ and supplies the steam needed for the pulp process and other equipment.

Recovery boilers are roughly divided into two types: the Swedish type and the Tomlinson type (American type). Of these, the Swedish type sprays black liquor in fine particles into the furnace and dries it using radiant heat inside the furnace. This is to burn the solid matter that falls to the bottom of the furnace in the form of fine powder. On the other hand, in the Tomlinson method, black liquor is injected in the form of coarse particles toward the furnace wall. As a result, the black liquor is partially dehydrated while passing through the combustion gas, and after adhering to the wall, it dries due to the radiant heat of the furnace. It falls to the bottom of the furnace, accumulates, and burns. Of these two types, the Swedish type suspends black liquor particles and dries them, so a considerable amount of unburned matter (solid matter) is included in the combustion gas, resulting in so-called carry over of unburned matter. Unburnt particles cause secondary combustion in the slag screen and superheater, creating localized high temperature areas. As a result, partially melted smelt adheres firmly to the tube group, interfering with continuous operation of the boiler. Additionally, this type of boiler has a relatively low combustion temperature, resulting in a high concentration of air pollutants, particularly sulfur oxides (SOx), in the exhaust gas, and a low rate of reduction of chemicals.

On the other hand, in the Tomlinson type boiler, the black liquor is dried on the furnace wall surface, so there is almost no carryover of unburned particles as mentioned above, and there is sufficient time for the black liquor to dry, so the black liquor concentration It burns well regardless of the type of fuel. Furthermore, since there is less moisture in the combustion section, the combustion temperature is higher than that of the Swedish type, and as a result, the amount of SOx generated can be kept low and the reduction rate of chemicals is also high.

The purpose of this generation is to provide a recovery boiler operating method that can obtain a higher reduction rate and further reduce SOx emissions without impairing the advantages of the Tomlinson type recovery boiler described above. In short, this invention is a method of operating a recovery boiler in which black liquor is sprayed in the form of coarse particles onto the furnace wall, dried, and dropped to the bottom of the furnace as a char to form a charvet, which is then combusted to recover chemicals. The amount of air supplied is approximately 50% of the total air supply amount, the secondary air amount is approximately 30% of the total air amount, and the temperature of the chartreuse is approximately 50% of the total air supply amount.
The temperature is 1000℃ to 1100℃, and tertiary air is supplied in an amount of about 20% of the total air supply to burn unburned components in the exhaust gas, and the combustion gas temperature due to secondary air is set to about 1200℃ to 1300℃. The method is characterized in that it is a method of operating a recovery boiler.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Figure 1 shows a Tomlinson type black liquor combustion boiler. The boiler main body 1 is provided with an oscillator 2. The oscillator 2 sprays black liquid L in coarse particles,
The sprayed black liquor crosses the furnace and adheres to the opposing wall surface, where it is dried by the radiant heat inside the furnace. During drying on the wall surface, a large number of air bubbles are generated inside the black liquor, and the dried porous solids (char) are successively peeled off from the wall surface and fall to the bottom of the furnace to form a charbet 3. The solids forming the chartreuse 3 are burned at the bottom of the furnace. The code A ₁ indicates primary air,
Air is supplied from air nozzles formed on the front and rear walls and both side walls near the bottom of the furnace. A molten substance called smelt is produced by combustion of the chartreuse, which is discharged from the furnace through a smelt spout 4 to recover useful substances (chemicals) such as Na. Primary air A ₁ is supplied to secure the amount of heat necessary for the reduction reaction of these useful substances, and for this purpose it is necessary to form an appropriate reducing atmosphere with a small amount of air and at the same time maintain the temperature of the chamber 3 at a high level. It is necessary to. As will be described later, the temperature of the chamber needs to be approximately 1000℃ or higher, preferably approximately 1050℃, and in order to maintain the temperature of the chamber as above and create a reducing atmosphere, the primary air _A1 must be equal to the total air supply amount. Approximately 50% of
shall be. By maintaining the reduction zone formed at the bottom of the furnace at the above temperature, an appropriate amount of sodium salt sublimates, and this reacts with SOx contained in the furnace gas to produce a desulfurization effect to form sodium compounds. The following formula (1) shows an example of desulfurization,
SOx For example, SO ₂ reacts with Na ₂ O to form Na ₂ SO ₄ (dead nitrogen)
will occur.

Na ₂ O + SO ₂ + 1/2O ₂ →Na ₂ SO ₄ ...(1) The generated Na ₂ SO ₄ is collected as dust by a dust collector placed at the boiler outlet.

FIG. 2 shows the relationship between the chartreuse temperature and the amount of SO ₂ generated, as confirmed by the inventors. Conventionally, the temperature of a chartreuse is between about 700°C and about 900°C. For example, when the temperature of the chartreuse is between 700°C and 800°C, the SO ₂ concentration is between 400 and 600 ppm, whereas when the temperature of the chartrette is about 1000°C, the SO 2 concentration is It was confirmed that the concentration of ₂ was 100 to 300 ppm, with a maximum of about 1/6 and an average decrease of about 1/3. However, if the temperature is higher than 1100°C, the amount of nitrogen oxides (NOx) produced will increase, so the chamber temperature should be 1000 to 1100°C, preferably 1050°C, as mentioned above.
Good condition.

In addition to performing the above-mentioned functions, the primary air A ₁ also performs a part of the function of shaping the chartreuse 3 into a trapezoidal shape together with the secondary air _A2 described later, and it collects the solids that have fallen to the bottom of the furnace. The mixture is blown up to the top, shaping the entire chamber, and supplying new solids to the upper portion of the chamber, which is the combustion section, to ensure good continuation of combustion.

Next, in order to effectively carry out the reducing action inside the chamber 3, it is preferable that the surface temperature of the chamber 3 is high and that the temperature distribution is uniform.
For this purpose, the shape of the chamber 3 is formed into a substantially trapezoidal shape with a flat top, as shown in FIG. 1, so that the entire top burns evenly. i.e. secondary air A ₂
By supplying the char, the char burns mainly at the top of the charvet 3, and the heat of this combustion forms a high-temperature reducing atmosphere of about 1000° C. or higher inside the charvet 3 as described above.

FIG. 3 shows the temperature distribution of each part of the boiler according to the operating method according to the present invention. (denoted as B) is about 1300°C to 1400°C.

Secondary air _A2 flows into the furnace from the secondary air port 5 and completely dries and burns the black liquor, but since it is injected into the furnace at a relatively high wind pressure of 150 to 200 mmAq, it is difficult to dry the black liquor. It also serves to flatten the top of 3. By forming the chamber 3 in the above shape, the temperature of the chamber can be maintained at a high temperature of 1000°C or more, and since the inside of the chamber is isolated from the combustion air, a highly reducing atmosphere can be formed, increasing the efficiency of reducing chemicals. Become. Therefore, it is preferable that the secondary air A ₂ is at the above-mentioned wind pressure and the supply amount is about 30% of the total air supply amount.

A ₃ is tertiary air, and is supplied from above the oscillator 2 at a wind pressure of about 150 to 200 mmAq, similar to that of the secondary air A ₂ , and completely removes unburned matter rising from the bottom of the furnace while strongly stirring the inside of the furnace. burn it. The supply amount of tertiary air _A3 is approximately 20% of the total air supply amount,
In addition, the temperature of the tertiary air port (indicated by symbol c) is about 1000 to 1200°C because unburned matter is reburned.

The completely combusted gas passes through the slag screen 6, the primary superheater 7a, the secondary superheater 7b, the evaporative water pipe 8, the economizer 9, and the air preheater 10, and is discharged to the outside of the system. In addition, the temperature at each part above is approximately
800℃~1000℃, inlet of secondary superheater 7b (code E
) at approximately 650℃ to 700℃, secondary superheater 7
Approximately 550℃~ at the outlet of b (indicated by symbol F)
The temperature will be 650℃.

By carrying out this invention, the temperature of the chartreuse can be maintained high, thereby increasing the reduction rate of chemicals in the smetol and reducing the amount of SOx discharged.

Furthermore, since the chartreuse can be formed and maintained in an ideal trapezoidal shape, the reduction rate can also be increased from this point of view.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a recovery boiler for carrying out the method according to the present invention, Figure 2 is a diagram showing the relationship between chartreuse temperature and SO ₂ emissions, and Figure 3 is a diagram showing the temperature distribution of the recovery boiler. It is a line diagram. 1... recovery boiler body, 3... charbet.

Claims (1)

[Claims] 1. In a method of operating a recovery boiler in which black liquor is made into coarse particles, sprayed onto the furnace wall, dried, and dropped to the bottom of the furnace as a char to form a chervet and burn it to recover chemicals, the amount of primary air supplied to the vicinity of the bottom of the furnace is The amount of secondary air should be approximately 50% of the total air supply, the secondary air amount should be approximately 30% of the total air supply, and the temperature of the Charvet should be approximately 50% of the total air supply.
The temperature is 1000℃ to 1100℃, and tertiary air is supplied in an amount of about 20% of the total air supply to burn unburned components in the exhaust gas, and the combustion gas temperature by secondary air is set to about 1200℃ to 1300℃. A method of operating a recovery boiler, which is characterized by operating a recovery boiler.