JPS6319762B2 - - 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 liquefied or gaseous fuels, so if they are applied to desulfurizing exhaust gas that contains a large amount of dust, such as exhaust gas from a solid combustion furnace, they may cause furnace clogging due to dust or reduce the desulfurization rate. This led to problems such as deterioration. 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 the absorption rate of SOx is low 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 findings. 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℃, the reaction Na ₂ O + SO ₂ + 1/2O ₂ →Na ₂ SO ₄ …(1) CaO + SO ₂ +1/2O ₂ →CaSO ₄ …(2) is unlikely to occur. 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) The main reaction is to generate sulfides such as CaSO ₄ +4CO→CaS+4CO ₂ …(6) Na ₂ O+SO ₂ +3C→Na ₂ S+3CO …(7)
Na ₂ S, CaS than sulfates such as Na ₂ SO ₄ , CaSO ₄
It was found that sulfides such as
Therefore, in order to increase the amount of sulfides such as Na ₂ S and CaS produced, it is sufficient to shift the equilibrium of reaction equations (3), (4), (5), (6), and (7) to the right; Increase the concentration of reducing gases such as _H2S , COS, and CO in the temperature range of 900 to 1300℃, and
It turns out that it is better to supply a desulfurizing agent such as Na ₂ CO ₃ , CaO, Ca(OH) ₂ .

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 this invention carries out a three-stage combustion method by separately supplying fuel and combustion air into the furnace, and supplies the desulfurization agent to the secondary combustion zone in a reducing atmosphere at a temperature of 900 to 1300 degrees Celsius. Features.

The reason why the temperature of the reducing atmosphere is limited to 900 to 1300°C is to allow the above reaction formulas (2), (3), and (4) to proceed rapidly from the left side to the right side.

The three-stage combustion method supplies primary fuel and primary air to the furnace from a burner installed on the front wall, and also supplies secondary air from around or downstream of the burner. A primary combustion zone with an oxidizing atmosphere is formed in the front or upstream side of the furnace, and a secondary fuel is supplied around or downstream of the primary combustion zone to form a secondary combustion zone with a reducing atmosphere. This is a combustion method in which tertiary air is supplied around or downstream of the secondary combustion zone to form a tertiary combustion zone.

The desulfurizing agent may be supplied to the secondary combustion zone together with the secondary fuel, or may be supplied separately from the fuel or air from between the secondary fuel supply position and the tertiary air supply position.

Pulverized coal, which is made by pulverizing coal, is used as fuel. In addition, as desulfurizing agents, CaCO ₃ , Ca(OH) ₂ ,
Alkali such as NaCO ₃ and dolomite are 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, Front-protruding secondary air supply port 6
has. 7 is a burner placed in the center of the secondary air supply port 6 facing inside the furnace, from which the primary fuel and
Next air is supplied. Reference numeral 8 denotes a wind box provided on the front surface of the front wall 3, which communicates with the inside of the furnace via a secondary air supply port 6. Reference numeral 9 indicates a plurality of secondary fuel nozzles provided slightly forward from the center of the length of the peripheral wall 2;
A plurality of tertiary air nozzles are also provided on the peripheral wall 2 behind the secondary fuel 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, the burner 7 supplies primary fuel and primary air for feeding the fuel into the furnace.
Furthermore, secondary air is supplied from the wind box 8 into the furnace to make the air ratio 1.0 or more. Combustion is carried out in this state, and a high-temperature primary combustion zone a with an oxidizing atmosphere is created at the front of the furnace.
form.

Also, secondary fuel is supplied from the secondary fuel nozzle 9 into the furnace to make the air ratio 1.0 or less. In this state, slow reductive combustion is performed to form a secondary combustion zone b on the downstream side of the primary combustion zone a. The combustion zone b is the temperature
Since it is a reducing atmosphere of 900 to 1300°C, it has optimal conditions for in-furnace desulfurization. Therefore, a desulfurizing agent is supplied into the furnace together with the secondary fuel to effectively perform desulfurization inside the furnace.

Furthermore, a substantially stoichiometric amount of tertiary air is supplied from the tertiary air nozzle 10 into the furnace with respect to the residual fuel of the secondary combustion, so that the tertiary combustion area c is supplied to the downstream side of the secondary combustion area b.
form.

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 secondary air supply port 23, a burner 24, and a wind box 25 having the same structure as that of the combustion furnace shown in FIG. Primary fuel and primary air are supplied from the burner 24, and secondary air is supplied from the wind box 25. Further, a secondary fuel nozzle 26 is provided above the burner 24, that is, on the downstream side, and a tertiary air nozzle 27 is provided further above the burner 26, that is, on the downstream side. Tertiary air is supplied. Thus, in this case as well, primary, secondary and tertiary combustion zones d, e, f are formed. A desulfurizing agent nozzle 28 is provided at an intermediate position between the secondary fuel nozzle 26 and the tertiary air nozzle 27, from which the desulfurizing agent is supplied to the secondary combustion zone e.

Figure 3 shows the furnace temperature and desulfurization rate at an oxygen concentration of 30% and a CaO/SO ₂ equivalence ratio of 4 for the desulfurization method in the three-stage combustion method and the desulfurization method in the two-stage air combustion method according to the present invention. It shows the relationship. As is clear from the figure, according to the desulfurization method of the present invention, the desulfurization rate can be significantly improved.

As described above, according to the in-furnace desulfurization method of the present invention, a three-stage combustion method is carried out by separately supplying fuel and combustion air into the furnace, and secondary combustion in a reducing atmosphere at a temperature of 900 to 1300°C is performed. Since fine powder desulfurization agent is supplied to the area, H ₂ S, COS, which is highly reactive with desulfurization agent,
Can increase the concentration of reducing gases such as CO,
As a result, desulfurization can be achieved at a high desulfurization rate even for exhaust gas containing a large amount of dust, such as combustion exhaust gas of solid fuel.

[Brief explanation of the drawing]

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)

[Scope of Claims] 1 A three-stage combustion method is carried out by separately supplying fuel and combustion air into the furnace, and fine powder desulfurization agent is supplied to the secondary combustion zone in a reducing atmosphere at a temperature of 900 to 1300°C. An in-furnace desulfurization method characterized by: 2. The method according to claim 1, wherein the desulfurization agent is supplied together with the secondary fuel. 3. The method according to claim 1, wherein the desulfurizing agent is supplied from between the secondary fuel supply position and the tertiary air supply position.