JPH0159489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an in-furnace desulfurization method in a solid combustion furnace.

Sulfur oxides (hereinafter referred to as SOx) generated when sulfur-containing fuel is burned are a substance that causes pollution, so there is a need for a method to effectively remove them. A technology has been proposed or put into practical use. However, all of these methods target liquid or gaseous fuels, so when applied to the desulfurization of exhaust gas that contains a large amount of dust, such as exhaust gas from a solid combustion furnace, the desulfurization equipment may be clogged with dust or desulfurization may occur. This led to problems such as a decline in the rate. As a solution to this problem, a dry in-furnace desulfurization method was proposed in which a solid SOx absorbent such as limestone, slaked lime, or dolomite is directly injected into the furnace. However, this method has the disadvantage that SOx absorption is poor because the absorbent is directly supplied into the high-temperature oxidizing atmosphere, and as a result, a large amount of absorbent is required.

The present inventors investigated the cause of the poor efficiency of conventional in-furnace desulfurization and obtained the following knowledge. In other words, it is an oxidizing atmosphere like the atmosphere inside a normal furnace, but the oxygen concentration is 1 to 5%.
If the temperature is very low, below 900°C, sulfate producing reactions such as Na ₂ O + SO ₂ + 1/2O ₂ →Na ₂ SO ₄ …(1) CaO+SO ₂ +1/2O ₂ →CaSO ₄ …(2) occur. Hard to happen. On the other hand, in a reducing atmosphere, Na ₂ O + H ₂ S → Na ₂ S + H ₂ O ... (3) CaO + H ₂ S → CaS + H ₂ O ... (4) CaO + COS → CaS + CO ₂ ... (5) CaSO ₄ +4CO→CaS+4CO ₂ …(6) Na ₂ O+SO ₂ +3C→Na ₂ S+3CO …(7) The main sulfide-producing reactions are Na ₂ SO ₄ ,
It was found that sulfides such as Na ₂ S and CaS are more stable than sulfates such as CaSO ₄ . Therefore
To increase the amount of sulfides produced such as Na ₂ S and CaS,
It is only necessary to shift the equilibrium of reaction equations (3)(4)(5)(6)(7) to the right, and to do so, the reducing gases H ₂ S, COS, CO It can be seen that it is better to increase the concentration of such gases and to supply the desulfurization agent to the reduction region.

The present invention has been made based on the above findings, and an object of the present invention is to provide a desulfurization method that can efficiently desulfurize even when applied to solid fuel combustion exhaust gas containing a high concentration of dust. With the goal.

In the following explanation, the air ratio refers to the ratio of the actual amount of air to the theoretical amount of air required for combustion, and with respect to the front-rear direction, the left side is the front, and the right side is the front, with reference to Figure 1. is referred to as the rear.

The desulfurization method according to the present invention is a two-stage combustion method in which combustion air is divided into two parts and supplied into the furnace. Alternatively, by supplying an inorganic desulfurization agent made of an alkaline earth compound,
The temperature range of the next combustion zone is 900 to 1300°C, and the generated reducing sulfur compounds are absorbed and removed in the form of sulfides.

In the air two-stage combustion method, powdered fuel and air for transporting the fuel are supplied into the furnace from a burner installed on the front wall, and the combustion air is divided into two parts and supplied into the furnace to start combustion. This is a combustion method in which a primary combustion zone with a reducing atmosphere is formed upstream of a secondary air supply port, and a secondary combustion zone is formed downstream of the same supply port.

The desulfurization agent is supplied to the primary combustion zone through a desulfurization agent supply port provided in the furnace wall between the primary combustion air supply port and the secondary air supply port.

Pulverized coal, which is made by pulverizing coal, is often used as a fuel. In addition, as a desulfurizing agent, Na ₂ CO ₃ ,
Alkali such as CaCO ₃ , Ca(OH) ₂ and dolomite are often used.

First, the structure of the combustion furnace used in this invention will be explained.

In FIG. 1, 1 is a furnace body consisting of a cylindrical peripheral wall 2 having a heat absorbing jacket, a front wall 3 and a rear wall 4 provided at both ends thereof, 5 is an opening made in the center of the front wall 3, It has a combustion primary air supply port 6 projecting forward. Reference numeral 7 denotes a burner arranged in the center of the primary combustion air supply port 6 toward the inside of the furnace, from which a mixture of pulverized coal and air for fuel transportation is supplied.
8 is a wind box installed in front of the front wall 3, which is used for combustion.
It communicates with the inside of the furnace via the secondary air supply port 6. 9 is a plurality of combustion secondary air nozzles provided slightly closer to the rear wall from the center of the length of the peripheral wall 2; 10 is a combustion secondary air nozzle;
A plurality of desulfurizing agent nozzles are provided on the peripheral wall 2 on the upstream side of the secondary air nozzle 9, and 11 is a flue provided at the rear end of the peripheral wall 2.

In the combustion furnace having the above structure, a mixture of pulverized coal and air for fuel transportation is supplied from the burner 7 into the furnace.
Furthermore, primary air for combustion is supplied from the wind box 8 into the furnace to reduce the air ratio to 1.0 or less.

Further, a substantially stoichiometric amount of secondary air for combustion is supplied into the furnace from the nozzle 9. As a result, a primary combustion area a is formed upstream of the nozzle 9, and a secondary combustion area b is formed downstream of the nozzle 9. 1
Since the secondary combustion zone a is a reducing atmosphere with a temperature of 900 to 1300°C, it has optimal conditions for in-furnace desulfurization. Therefore, a desulfurizing agent is supplied into the furnace from the nozzle 10 to effectively perform desulfurization in the furnace.

FIG. 2 shows a modification of the combustion furnace. This furnace 21 is a box-shaped large vertical furnace, and the lower end of the front wall 22 is provided with a primary combustion air supply port 23, a burner 24, and a wind box 25, which have the same structure as the combustion furnace shown in FIG. A mixture of pulverized coal and air for fuel transportation is supplied from the burner 24, and primary air for combustion is supplied from the wind box 25. Further, a combustion secondary air nozzle 26 is provided on the front wall 22 above the burner 24, and a desulfurizing agent nozzle 27 is provided on the front wall 22 between the nozzle 26 and the burner 24. Also in this case, a primary combustion zone c of a reducing atmosphere is formed upstream of the secondary combustion air nozzle 26, and a secondary combustion zone d is formed downstream of the nozzle 26. Therefore, the desulfurizing agent is supplied from the nozzle 27 to the primary combustion zone c.

Figure 3 shows the desulfurization method in the two-stage air combustion method and the desulfurization method in the single-stage combustion method according to the present invention at an oxygen concentration of 3%, CaO/SO ₂ and
This figure shows the relationship between the furnace temperature and the desulfurization rate at a NaO/SO ₂ equivalent ratio of 4. As is clear from the figure, according to the desulfurization method of the present invention, the desulfurization rate can be significantly improved.

According to the in-furnace desulfurization method of this invention, by setting the temperature range of the primary combustion zone to 900 to 1300°C, sulfur compounds in the exhaust gas are converted to H ₂ S, which is a reducing gas,
By supplying an inorganic desulfurization agent made of an alkali compound or an alkaline earth compound to the primary combustion zone of this reducing atmosphere, the reducing sulfur compound can be converted to sulfurization such as Na ₂ S, CaS, etc. It can be absorbed and removed in the form of objects. Thus, according to the desulfurization method of the present invention, sulfur compounds, particularly SOx, generated in the furnace can be absorbed and removed as sulfides, which are more stable than sulfates.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a combustion furnace showing an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of the front part of the furnace showing a modified example, and FIG. 3 is a graph showing the relationship between furnace temperature and desulfurization rate. It is.

Claims (1)

[Claims] 1 In the air two-stage combustion method in which combustion air is divided into two and supplied into the furnace, alkaline compounds or alkaline earth compounds are added to the primary combustion zone of the reducing atmosphere formed upstream of the secondary combustion air supply port. By supplying an inorganic desulfurization agent consisting of
An in-furnace desulfurization method in a solid combustion furnace, characterized in that the temperature is 900 to 1300°C, and the generated reducing sulfur compounds are absorbed and removed in the form of sulfides.