JPS61208412A - Three-stage combustion method to suppress nox with simultaneous desulphurization - Google Patents

Abstract

PURPOSE:To save the amount of supplied desulphurization agent and the transportation cost for its use in recycling the recovered desulphurization agent by supplying the desulphurization agent to the tertiary combustion zone in a three-stage combustion method. CONSTITUTION:A primary fuel is burned at a high temperature and in an oxidizing atmosphere to form a primary combustion zone 3. The ash produced in this process is melted and taken out of a discharge outlet 4. The primary combustion gas contains substantially no ash. Secondary fuel is supplied to the primary combustion gas, and the latter is burned by the surplus air of the primary air in a reducing atmosphere to form a secondary combustion zone 7, and the NOx previously produced is reduced to N2. The fuel not burned in the secondary combustion gas is burned slowly at a low temperature in an oxidizing atmosphere to form a tertiary combustion zone 16. A powdered desulphurization agent in calcium family is directly jetted into the tertiary combustion zone 15 to form CaSO4 from SO2 in it. The tertiary combustion gas is passed through a bag filter 9 to catch the power containing the desulphurization agent, and part of the caught powder is again jetted into the tertiary combustion zone 16, and other part is discharged out of the system to be replaced by fresh desulphurization agent.

Description

[Detailed description of the invention] Industrial applications This invention deals with nitrogen oxides (N) in combustion gas.

This relates to a three-stage combustion method that suppresses the generation of X) and at the same time removes sulfur from the same gas.

Conventional technology and its problems Conventionally, this type of combustion method is as shown in Fig. 2.
The supplied fuel is burned in a high temperature reducing atmosphere to create a primary combustion zone (
Desulfurization The agent is supplied to the primary combustion zone (21) and
In step 1), the supplied fuel is burned in a high-temperature reducing atmosphere with primary air, and the resulting ash and desulfurization reaction products are molten and removed from the outlet (24) provided at the bottom of the primary combustion chamber (23).
There are known methods to extract it from

However, in this method, since the ash generally contains silicic acid as a main component, the desulfurizing agent supplied to the primary combustion zone (21) mostly reacts with this silicic acid to form a complex silicate compound. Therefore, in order to ensure high desulfurization efficiency, it is necessary to use a large amount of desulfurization agent, and the desulfurization efficiency per unit use of desulfurization agent is low. In addition, since the recovered desulfurization agent taken out from the outlet (24) contains a large amount of ash, the total amount of ash is too large to be recycled, and the circulating transportation cost per unit amount of desulfurization agent is It was very expensive.

This invention was made in view of the above-mentioned circumstances, and provides a three-stage combustion method that can reduce the amount of A5A agent supplied and reduce the transportation cost for recycling and reusing the recovered desulfurization agent. The purpose is to provide.

Means for Solving the Problems The combustion method according to the present invention achieves the above objectives by:
The secondary fuel is burned in a high temperature oxidizing atmosphere with excess primary air.
A secondary combustion zone is formed, and secondary fuel is supplied to the downstream side of the zone, and the surplus of the primary air is burned in a reducing atmosphere to form a secondary combustion zone. In the three-stage combustion method, in which a tertiary combustion zone is formed by supplying secondary air and slowly burning the unburned content of the secondary fuel in a low-temperature oxidizing atmosphere, a desulfurizing agent is supplied to the tertiary combustion zone. do.

In the combustion method according to the present invention, the combustion temperature in the primary combustion zone is set to a temperature higher than the pour point of the ash, and the molten ash produced in the zone is taken out from the bottom of the furnace.

Further, the remainder of the desulfurizing agent discharged from the tertiary combustion zone together with the tertiary combustion gas is recovered, and at least a portion of it is recycled and supplied to the zone.

Examples of desulfurization agents include CaC(L+, Ca(OH)
2,'caos Calcium-based compounds such as dolomite are usually used in powder form.

In addition to the effects of the invention, according to the three-stage combustion method of the present invention, the desulfurization agent is supplied to the tertiary combustion zone, and the ash produced in the primary combustion zone is taken out in a molten state from the same zone. The ash melt and the desulfurization agent are completely separated, and the desulfurization agent contains almost no ash in the tertiary combustion zone. Therefore, it is possible to solve the problem of increasing the amount of desulfurization agent supplied due to the formation of silicate compounds as explained at the beginning of this specification, and to significantly improve the desulfurization efficiency per unit amount of desulfurization agent supplied. can.

In addition, by supplying the desulfurization agent to the tertiary combustion zone as described above, the residual desulfurization agent recovered from the zone contains almost no ash as described above, so the desulfurization agent is circulated to the tertiary combustion zone. The total amount of circulation during supply is reduced,
Circular transportation, costs can be significantly reduced.

In addition, by making it possible to recycle the recovered desulfurization agent at low transportation costs, the amount of fresh desulfurization agent used can be reduced, and in this respect, the desulfurization efficiency per unit amount of desulfurization agent used can be improved. can be improved.

Furthermore, the ash melt removed from the primary combustion zone does not contain any desulfurization agent, making ash disposal easy.

EXAMPLES Next, examples of the present invention will be given to demonstrate the above effects.

In FIG. 1, primary fuel and primary air are supplied to a burner (2) provided on the side of a primary combustion chamber (1), and the primary fuel is combusted at high temperature in an oxidizing atmosphere. The primary fuel used is one that generates a large amount of ash through combustion, the combustion temperature is set to be higher than the pour point of the ash, and the primary air has an air ratio (
Actual amount of air supplied/amount of air theoretically required for combustion)
The feed is applied to create an air excess of 1 or more, preferably about 1.4. In this way, a primary combustion zone (3) is formed within the primary combustion chamber (1) by combustion of the primary fuel.

The ash generated in the zone' (3) is melted by the high-temperature atmosphere, and the molten material adheres and accumulates on the inner surface of the furnace, and further flows down along the same surface to the bottom of the furnace in the primary combustion chamber (1). It is continuously taken out from the takeout port (4) provided in the. Therefore 1
The secondary combustion gas contains almost no ash. In the primary combustion zone (3), combustion takes place in a high temperature oxidizing atmosphere;
A considerable amount of NOx is generated.

The primary combustion gas containing surplus primary air flows from the primary combustion chamber (1) through the communication hole (5) of the partition wall (14) to the same chamber (1).
) Secondary combustion chamber (6) connected to the upper side, that is, the wake side
guided by. Secondary fuel is supplied to the same chamber (6) and burned in a reducing atmosphere using the surplus of primary air. The amount of secondary fuel supplied is less than 30% of the total amount of fuel supplied. A secondary combustion zone (7) is thus formed within the secondary combustion chamber (6). In the zone (7), combustion is performed in a reducing atmosphere as described above, so the NOx generated earlier is reduced to N2.

Since the secondary combustion gas contains a large amount of unburned components such as hydrocarbon radicals and carbon monoxide, the secondary combustion gas is then
Leading the secondary air to a tertiary combustion chamber (15) connected above the secondary combustion chamber (7), that is, on the downstream side and equipped with a heat absorption tube group (8), and supplying the secondary air to the same chamber (15), The unburned components are slowly burned in a low-temperature oxidizing atmosphere. In this way, the tertiary combustion chamber (15
) to form a tertiary combustion zone (16). Same zone (1
In 6), as mentioned above, slow combustion takes place in a low-temperature oxidizing atmosphere, so there is little thermal NOX generation, and total NOx is reduced.
xQ degree is extremely low. In addition, the amount of ash accompanying the secondary combustion gas is determined by the fact that the amount of secondary fuel supplied is 30% of the total amount of fuel supplied.
% or less, it is also 30% or less of the total ash content.

Note that the partition wall (14) separates the primary combustion chamber (1) and the secondary combustion chamber (
6), and the role of increasing the NOx reduction effect;
The function is to prevent the ash generated in the primary combustion zone (3) from moving to the secondary combustion zone (7) along with the primary combustion gas, but this may be provided in some cases. Sometimes there isn't.

In the tertiary combustion zone (16), sulfur content exists as S02. Therefore, from slightly above the secondary air supply position of the tertiary combustion chamber (15), powdered calcium-sium desulfurization agent was introduced into the tertiary combustion zone (15) using pneumatic air at an equivalent ratio of Ca/S = 4.
When directly injected into 5), 802 reacts with the desulfurization agent and changes to Ca 2 SO 4 (70% desulfurization rate).

The tertiary combustion gas discharged from the top of the tertiary combustion chamber (15) is passed through the bag filter (9), and the desulfurizing agent-containing powder that has accompanied the gas is captured. is the conveyor (
10). A part of the collected powder is transferred to the ejector (
11) to the tertiary combustion zone (16) and is also injected into the same zone (16). While the recovered desulfurization agent is recycled and reused in this way, the amount of desulfurization reaction products, unreacted materials, fly ash, etc. contained in the desulfurization agent-containing powder gradually increases and accumulates. ,
A part of the desulfurizing agent-containing powder is discharged outside the system, and fresh desulfurizing agent is instead transferred from the hopper (12) to the ejector (
13), it is pneumatically fed to the tertiary combustion zone (16) and supplementary supplied into the zone (16) in a mixed state with the recovered desulfurization agent. Since the powder discharged outside the system contains almost no ash, it can also be used for other raw materials.

If the desulfurization agent is circulated at a circulation ratio (fresh desulfurization agent/circulated desulfurization agent) of approximately 1, the apparent equivalence ratio Ca
In order to make /S about 4, it is sufficient to use fresh desulfurization agent in an amount such that the equivalence ratio Ca/S is about 2, and the desulfurization efficiency per unit amount of desulfurization agent used improves (in this specification). In the conventional method mentioned at the beginning, the desulfurization agent is used in an amount such that the equivalent ratio Ca/S is about 4).

In addition, since the fly ash contained in the powder is also circulated to the secondary combustion zone (8) together with the recovered desulfurization agent, the unburned content contained in the fly ash is also subjected to combustion again, improving combustion efficiency. The combustion furnace can be made more compact.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet for a two-stage combustion method showing an embodiment of the present invention, and FIG. 2 is a flow sheet for a conventional two-stage combustion method. (1)...Primary combustion chamber, (2)...Burner, (3
)...Primary combustion zone, (4)...Outlet, (5)
...Communication hole, (6)...Secondary combustion chamber, (7)...
Secondary combustion zone, (8)... Endothermic tube group, (9)...
Bag filter-1 (10)...conveyor, (11)...
...Ejector, (12) ...Hopper, (13)
...Niji1ctor, (14)...Bulkhead, (15)・
...Third combustion chamber, (16)...Third combustion zone. Figure 2 above

Claims (3)

[Claims] (1) Burn primary fuel in a high-temperature oxidizing atmosphere with excess primary air to form a primary combustion zone, and create a secondary combustion zone on the downstream side of the zone.
Secondary fuel is supplied and the surplus of the primary air is combusted in a reducing atmosphere to form a secondary combustion zone, and secondary air is supplied to the downstream side of the zone to reduce the unburned content of the secondary fuel to a low temperature. A NOx suppression three-stage combustion method that simultaneously performs desulfurization, characterized in that a desulfurizing agent is supplied to the tertiary combustion zone in a three-stage combustion method in which a tertiary combustion zone is formed by slow combustion in an oxidizing atmosphere. (2) The combustion method according to claim 1, wherein the combustion temperature in the primary combustion zone is set to a high temperature higher than the pour point of ash, and the molten ash produced in the zone is taken out from the bottom of the furnace. (3) Combustion according to claim 1 or 2, in which the remainder of the desulfurizing agent discharged from the tertiary combustion zone along with the tertiary combustion gas is recovered and at least a part of it is circulated and supplied to the zone. Law.