JPS6176814A - Low nox combustion - Google Patents

Abstract

PURPOSE:To reduce NOx by a method wherein a radiating member is provided in the lower part of a furnace, the first air ratio for combustion air supplied to a burner forming incomplete combustion area is set less than 1, the second air ratio for combustion air supplied to the burner forming a gas phase reduction area is set less than the first air ratio. CONSTITUTION:Main burner 1, sub burner 2, oxidizing burner 3 and NOx port 3' are arranged sequentially from the lower part to the upper part of the front wall and the rear wall 8 of the furnace 9 in the combustion device while an air box 5 surrounding them is provided. A radiating member 6 having the section of chevron shape is positioned between the lower part of the flame of main burner 1 and the bottom of the furnace. According to this positioning, a somewhat incomplete combustion area M, having the air ratio less than 1 (first air ratio), the gas phase reduction area P of the second air ratio smaller than the first air ratio and the complete combustion area O are formed. The exhaust gas, taken out of an exhaust duct through a tube path re-throwing the exhaust gas, is supplied into the furnace from the bottom of the furnace as recirculating gas 4.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a combustion method for reducing harmful substances such as NOx in exhaust gas from a combustion device such as a boiler.

<Conventional technology and its problems> Conventional methods for reducing NOx, a harmful component in exhaust gas, include exhaust gas recirculation, two-stage combustion, split flame, water injection, or injection of reducing agents such as NH3. .

These are because the generation of NOx is due to N2 and 02 in high temperature gas.
The main cause of NO generation is the reaction with N2 in the fuel and the reaction with N2 (Zuer nitrogen) in the fuel. Countermeasures include lowering the gas temperature, exhaust gas recirculation to lower the 0□ partial pressure, or direct reduction. This is done by decomposing NO through reaction with an agent.

However, in recent years, based on experimental considerations regarding the chronic nature of NOx generation, a method has been developed to reduce NOx by changing the amount of air supplied to the combustion device, that is, the air ratio, and changing the burner arrangement without using any particular reducing agent.

That is, the main burner is located below the furnace, and the air ratio is set to 1 or less, preferably 0.85 to 0.95, to achieve slightly incomplete combustion. In this case, thermal NOx (Then
nal NOx), H, ], N2 becomes CN, NH due to thermal decomposition of heavy oil in the fuel excess region.

Produces radicals such as 02 reacts to prompt N
Generate O. Next, an auxiliary burner is placed above this raw burner, the air ratio is set to about 0.4, a 2C phase reduction zone is formed, and the above-mentioned No is reduced by NHz, ON, CO, etc., and N, Co, CO2, N20 It's something that can turn into something. However, it is not always possible to convert NO into N2 sufficiently in this gas phase reduction region, and some residual 110N remains, and since it also contains CO, an oxidation burner is installed downstream of the sub-burner, and an air supply port ( An oxidation burner is also called an afterburner. This area is also called a complete combustion area. The air ratio in this area is 1 or more, preferably 1. 3 to prevent NOx and Co from being contained in the exhaust gas after this area.

In this case, the fuel distribution is approximately 65% in the main burner and 65% in the auxiliary burner (
The reduction in NOx was large when the burner was set at about 30% for the planet burner (also called a planet burner) and about 5% for the oxidation burner (afterburner).

<Objective of the Invention> The object of the present invention is to propose a method of arranging and combusting the burner to reduce NOx, and further to provide a combustion method that improves the effect of reducing NOx.

<Summary of the Means> In short, the present invention provides a method for combustion in which a small complete combustion zone is formed in the lower part of the furnace, and a gas phase reduction zone is formed above it, in which a radiant member is provided in the lower part of the furnace, and the above-mentioned small part is further provided. A first air ratio for the combustion air supplied to the burner forming the small complete combustion zone is less than 1, and a second air ratio for the combustion air supplied to the burner forming the gas phase reduction zone is set to the second air ratio for the combustion air supplied to the burner forming the gas phase reduction zone. This method is characterized by a low NOx combustion method in which the air ratio is lower than 1.

<Example> An example of the present invention will be described below using the drawings. FIG. 1 is a longitudinal cross-sectional view of a device showing an embodiment of the present invention, and FIG. FIG. Main burners 1. Secondary burner 2. Oxidation burner 3. The NO port 3' is located, and a wind box 5 is provided surrounding it. In the illustrated example, each burner is arranged so that four pipes are lined up in the horizontal direction.

This arrangement forms a gas phase reduction region P5 complete combustion region 0 with an air ratio less than 1 (first air ratio) and a slightly smaller complete combustion region M1 with a second air ratio smaller than the first air ratio. An exhaust gas duct (not shown) is connected to a pipe (not shown) for reintroducing exhaust gas.
The exhaust gas taken out is supplied into the furnace from the bottom of the furnace as recirculation gas 4. In FIG. 1, which is the first embodiment of the present invention, there is a cross section between the lower part of the flame of the main burner 1 and the bottom of the furnace.
A radiant member 6 having a chevron-like shape is positioned therein.

This radiant member is made of a refractory material such as plastic chrome ore, receives the heat of the main burner 1, is heated to a high temperature, and radiates heat rays. On the other hand, the recirculating gas 4 forms a vortex flow in the MX section shown in the figure, entraining a portion of the flame, and incinerates the unburned carbon particles in the mixed gas by reacting with the 02 by the radiant heat of the radiant member. It also has the effect of radiating strong heat rays to the unburned materials in the slightly complete combustion region and promoting the reaction process with O2.

The main burners 1a to 1d are spaced apart from each other, and heat rays pass through this space to give radiant heat to the gas body.

FIG. 3 shows another embodiment of the arrangement of the radiant members, in which the radiant member 6a is located on the bottom water wall of the reactor.

FIG. 4 corresponds to FIG. 1, and the upper surface of the radiant member 6b is a partially cylindrical curved surface, and the center C4°C2 of the cross section (which forms part of the cylindrical surface and has an arcuate cross section) is located at the center of the green burner 1. and the sub-burner 2.

In FIG. 5, a partially cylindrical curved surface is similarly formed on the radiant member 6c corresponding to FIG. be.

:If all Iqa radiation members are made of f17, the flame that is the light source will flicker and sway, so the relationship that the partial cylindrical mirror surface and parallel rays will be focused will not be established, but 1
1G! J is a set of radiation rays from a member11
You can expect it. This has the same effect as when radiant heat from the radiant refractory brick wall that is formed during stoker firing generates the volatile content of the coal on the stoker surface on the coal feeder side, making ignition easier.

By carrying out this invention, the incineration reaction treatment of unburned components in the slightly incomplete combustion zone M and the gas phase reduction zone P is promoted,
The effect of maintaining the combustion conditions due to the arrangement of the radiant member can be achieved. In addition, especially when short-flame gas is used as fuel, the effectiveness of the radiant member in ensuring a reaction is significant.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of the apparatus showing the first embodiment, Fig. 2 is its front view, Fig. 3 is a longitudinal sectional view of the bottom of the furnace showing one embodiment of the radiant member arrangement, and Fig. 4 is the other FIG. 5 is a longitudinal sectional view showing an example of radiant member arrangement. FIG. 5 is a longitudinal sectional view showing another example of radiant member arrangement. 1... Raw burner 2... Sub-burner 3
...Oxidation burner 3'...No boat 4...Recirculation gas 5...Wind box Figure 1 Figure 2 Figure 4 5 1■'

Claims (1)

[Claims] 1. In a method of combustion in which a slightly incomplete combustion zone is formed in the lower part of the furnace and a gas phase reduction zone is formed above it, a radiant member is provided in the lower part of the furnace, and the slightly incomplete combustion zone is further formed. A first air ratio of combustion air supplied to the burner is less than 1, and a second air ratio of combustion air supplied to the burner forming the gas phase reduction zone is smaller than the first air ratio. A low NOx combustion method characterized by the following.