JPS6029510A - Method of decreasing nox in incinerator by blowing steam into it - Google Patents

Abstract

PURPOSE:To alleviate damages on the wall and on the floor of a furnace, by decreasing generation of NOx by blowing steam into the primary air so that the concentration of O2 right above the fuel in a combustion chamber and at an outlet port of fuel exhaust gas in an incinerator is determined within a predetermined range. CONSTITUTION:To control ignition and combustion of waste on a drying grate 3 by blowing the minimum quantity of the primary air which is needed to dry waste on the drying grate 3. On a combustion grate 4, the rate of the secondary air after being mixed with steam is controlled by the primary damper 9 so that the concentration of O2 right above a waste layer is within the range of 0.5- 8%. In order to control the primary air, the feeding rate of steam is automatically controlled by the primary feed rate controlling valve 12 provided to the primary steam feed pipe 11, so that the concentration of O2 in the primary air is within the predetermined range of 10-21% by the steam being mixed with the air. With such an arrangement, dameges on the wall and on the floor of a furnace can be alleviated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing NOx in an incinerator by steam injection.

In order to reduce the NOx generated in an incinerator, it is necessary to reduce the 02 concentration directly above the fuel on the grate, and to suppress the generation of NOx due to the secondary air supply, it is necessary to reduce the 02 concentration directly above the fuel on the grate. A method is used to reduce the amount of secondary air and the amount of secondary air, but in this case, as the temperature inside the furnace increases, the life of the incinerator decreases due to talin force adhesion to the furnace wall, damage to the refractories, etc. Problems such as increased burnout of the grate occur as the temperature rises.

(1) In order to solve the above problem, it is necessary to reduce the temperature inside the furnace, and possible methods for this include an inside-furnace water spraying method and an exhaust gas recirculation method.

However, the former has the following drawbacks.

(1) Sprayed water evaporates in the incinerator and absorbs the latent heat of vaporization, thereby lowering the temperature inside the incinerator. However, if there is a waste heat boiler, this vaporized water vapor absorbs some of the gas sensible heat. Although it is possible to recover latent heat of vaporization, it is very difficult to recover latent heat of vaporization. For this reason, when the incinerator is attached to a waste heat boiler or the like, the amount of recovered heat is reduced by injecting water into the incinerator.

(2) When water spraying is carried out in an incinerator, the sprayed water may come into direct contact with the furnace walls, hearth, etc., and the lifespan of the furnace walls, hearth, etc. may be reduced.

(3) Since the combustion gas is rapidly cooled by the spray water, there is a possibility that CO and lower hydrocarbons that have not been completely combusted will be emitted as they are.

(4) The combustion of fuel on the hearth is rapidly cooled by the in-furnace water spray, creating a cold space inside the furnace; (2) combustion becomes unstable;

Furthermore, the latter has the following drawbacks.

(1) In order to reduce the temperature inside the furnace, it is necessary to circulate combustion exhaust gas equivalent to 10 to 40% of the secondary air volume, which increases the construction cost of this equipment and the running cost of the circulation blower. arrive.

(2) When exhaust gas is used as secondary air, since this exhaust gas contains 6 to 10% of 02, there is a possibility that NOx will be generated by blowing in this exhaust gas.

(3) If circulating exhaust gas can be supplied together with the primary air supplied under the grate, the 02 concentration directly above the garbage layer can be lowered, so it is possible to reduce NOx, but there is S in the exhaust gas.
Since it contains corrosive gases such as Ox and IC, there is a possibility of corrosion of the grate, hopper under the grate, etc.

(4) In the case of exhaust gas recirculation, compared to the case of in-furnace water spraying, there is no self-denitrification effect due to CO1H2 etc. due to water gasification reaction, so even if the 02 concentration at the incinerator outlet is the same, Compared to the case of internal water spraying (3), the NOx concentration (calculated as 0212%) is 10 to 20 F higher.

Therefore, an object of the present invention is to provide a method for reducing NOx in an incinerator by blowing steam, which can eliminate the above-mentioned drawbacks.

That is, the present invention provides an incinerator using steam injection, which is characterized by injecting water vapor into the combustion air so that the 02 concentration directly above the fuel in the combustion chamber of the incinerator is within a predetermined range.
According to this method, -
Next, water vapor is injected into the air to reduce NOx generation, so compared to the conventional method of spraying water directly into the combustion chamber, there is less damage to the furnace walls, hearth, etc., and the combustion gas Since the exhaust gas is not cooled rapidly, incomplete combustion can be prevented and combustion can be stabilized.Compared to the conventional method of circulating exhaust gas, there is no need for circulation equipment, and various types of exhaust gas contained in the exhaust gas can be It is also possible to eliminate the problems of NOx generation due to gas and corrosion of fire grates, etc.

(4) Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 and 2. (1) is a combustion chamber of a waste incinerator (2), and a drying grate (3), a combustion grate (4), and a post-combustion grate (5) are sequentially provided in the lower part of the combustion chamber. (6) (n (
Reference numeral 8) denotes a combustion air supply pipe connected below each of the above-mentioned fire grates (3), (4), and (5), and a first damper (9) is interposed in the middle of each pipe. The opening degree of each first damper (9) is controlled via a first detector OQ that detects the 02 concentration directly above the garbage in the combustion chamber (1), that is, directly above the combustion grate (4). Ru. αυ is the first steam supply pipe connected to the upstream side of the first damper (9) of the primary air supply pipes (6), (7), and (8), and the first flow control valve a'4 is installed in the middle of the pipe. It is mediated. This first
The flow rate control valve (a) is controlled via a first moisture detector (2) that detects the moisture value of the primary air downstream of the first damper (9). α4 is a combustion secondary air supply pipe connected to multiple locations in the upper part of the combustion chamber (1), and a second damper 00 is interposed in the middle of each branch pipe. The opening degree of this second damper aO is controlled (5) via a second concentration detector Q0 that detects the 02 concentration at the combustion exhaust gas outlet. θη is a second water vapor supply pipe connected midway through the secondary air supply pipe Q4, and its control is performed via a second moisture detector θ value that detects a second flow rate control value.

@■η is a blower that supplies primary and secondary air. By the way, the steam that is blown into each combustion air is the low-pressure steam that comes out of the heat recovery boiler installed in this incinerator together with the incinerator (2) and rotates the turbine. . Incidentally, FIG. 2 shows a flowchart of the entire equipment.

Next, the effect will be explained.

First, the amount of primary air supplied to the drying grate (3) is set to the minimum amount necessary for drying the waste, and ignition and combustion of the waste in the drying grate (3) is controlled. Next, the combustion grate (4
), the amount of secondary air after water vapor mixing is controlled via the first damper (9) so that the 02 concentration (dry base) just above the garbage layer is within the range of 0.5 to 8%. .

That is, this secondary air is normal air (02 concentration 21%) (
6) Instead, by mixing water vapor, the 02 concentration becomes 1.
In order to be able to adjust to a constant value X% within the range of 0 to 21%, the first The first flow rate control valve θ″4 at the water vapor supply pipe 0η route is automatically adjusted.

Y = Buttocks
The primary air is adjusted to below the 02 concentration (21%) in the air, and the 02# degree (dry base) above the garbage layer surface is 05 to 8%.
The first air vibration is adjusted to a constant concentration of 2% within
Adjust with tamper (9).

As a result, even though the total amount of oxygen in the air is the same, the oxygen partial pressure on a wet basis is low, which suppresses combustion and reduces the amount of NOx generated. Due to the self-denitration effect caused by the gasification reaction, NO
x is reduced. Then, the combustion chamber (on top of υ, -
Secondary air is supplied from the secondary air supply pipe Q41 to combust the unburned gas that could not be completely combusted with the secondary air, and the amount of secondary air is 02 concentration in the exhaust gas (
The second damper aυ is controlled so that the dry haze is completely detected and this value becomes a constant value within 4 to 10%.

That is, as in the case of secondary air, water vapor is mixed into secondary air, and the 02 concentration is set to a constant value B% within the range of 10 to 21%.
In order to be able to adjust the moisture concentration C (%) in the secondary air after steam mixing to the concentration shown by the following equation (2),
Automatically adjust the second flow rate control valve (g) in the middle of the second steam supply pipe Q7).

C = Chronic B -100... (2) As a result, even if the total amount of oxygen in the secondary air is the same, because the partial pressure of oxygen on a moisture basis is lower, the amount of unburned gas by the secondary air is lower. Combustion is suppressed and the amount of NOx generated is reduced, and at the same time, NOx is further reduced due to the self-denitration effect caused by the water gasification reaction between water vapor and carbon in the flame.

If the furnace outlet temperature cannot be lowered below the specified temperature (for example, 950°C) by only supplying the secondary air, set the temperature at a position that does not cause NOx generation (8) to keep the furnace outlet temperature constant. The air, water vapor, or air after the above-mentioned water vapor mixture is supplied for cooling.

According to the above method, water vapor is blown into the secondary air to reduce NOx generation so that the 02°C directly above the fuel and at the fuel exhaust gas outlet in the combustion chamber of the incinerator is within a predetermined range. Compared to the conventional method of spraying water directly into the combustion chamber, there is less damage to the furnace walls, hearth, etc.
In addition, since the combustion gas is not cooled rapidly, incomplete combustion can be prevented and combustion can be stabilized.Compared to the conventional method of circulating exhaust gas, there is no need for circulation equipment, and the amount of It is also possible to eliminate the problems of NOx generation due to various gases and corrosion of the fire grate. Furthermore, as the steam injected into the primary and secondary air, low-pressure steam generated by a boiler with an incinerator and energy recovered by rotating a turbine is used, so the heat contained in the garbage is used. Energy can be recovered effectively.

[Brief explanation of drawings]

(9) The drawings show one embodiment of the present invention, and FIG. 1 is a schematic overall configuration diagram, and FIG. 2 is a flowchart diagram. (1)... Combustion chamber, (2)... Incinerator, (4)...
・Combustion grate, (6) (7 bar 8)...-secondary air supply pipe, (9)...first damper, 01...first concentration detector, Qυ...first steam supply Pipe, α...first flow control valve, 03...first moisture detector, aΦ...secondary air supply pipe, 0υ...second damper, CI...second concentration detector , αη...Second steam supply pipe, (to)...
Second flow control valve, (l10...Second moisture detector agent Yoshihiro Morimoto (10)

Claims (1)

[Claims] 1. A method for reducing NOx in an incinerator by blowing steam into the combustion air so that the 02 concentration directly above the fuel in the combustion chamber of the incinerator is within a predetermined range.