JPS58120004A - Two-staged combustion - Google Patents

Abstract

PURPOSE:To further lower the concentration of NOx in exhaust gas, by feeding a specified rate of ammonia into the air to be fed into the combustion furnace on the secondary stage, or a subsequent part, in two-staged combustion. CONSTITUTION:A specified rate of ammonia is injected into the secondary air feeding line 7 from its middle part, passing through a line 8, in two-staged combustion. The more the injection rate of NH3 gas is increased, the larger the effect can be expected. But the injection rate is to be determined, considering the concentration of NOx being fed into an oxidation part 4B, which is different according to the ratio of fuel to the primary air, together with the target rate of NOx to be lowered, economy, and other. With such an arrangement, residual NOx which is not reduced in the reduction part 4A is reduced in the oxidation part 4B, so that the concentration of NOx in exhaust gas is further decreased, and the exhaust gas is discharged, passing through a line 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stage combustion method, and more specifically, a two-stage combustion method aiming at reducing nitrogen oxides (NO,) in which combustion air is divided into two or more stages and supplied. Regarding.

Many methods have been proposed and implemented to reduce NO,@[ in the combustion exhaust gas, among which the main methods for reducing NO in the furnace are as follows.

(1) Two-stage combustion method in which combustion air is divided, (2) Exhaust gas circulation method in which combustion air is mixed with combustion exhaust gas, (3) Non-catalytic reduction method in which high-temperature combustion gas KNE(s) is injected, (4) ) A fuel injection method in which a portion of the fuel is injected into the ultra-high temperature combustion gas.

These methods are employed singly or in combination in waste incinerators, heating furnaces, lira, etc. However, in general, in fluidized bed incinerators and other fluidized bed incinerators, the ultra-high temperature section (
1100℃ or higher], so the fuel injection method cannot be applied.Also, since it is not burner combustion, the effect of the exhaust gas circulation method is very small.The non-catalytic reduction method is SOO ~ 95
This method involves injecting a small amount of NHs gas into the combustion gas at 0°C, but since the combustion gas and NEIs gas are mixed in a superimposed manner, it is necessary to use a special injection nozzle or the like. Therefore, the simple two-stage combustion method is currently the mainstream for fluidized bed combustion furnaces.

The present inventor previously discovered that in such a two-stage combustion method, the gas residence time in the primary combustion section should be sufficient so that NOx is sufficiently reduced in the primary combustion section where the oxygen temperature is low at 11 degrees Celsius or oxygen is completely absent. Low NO that supplies secondary air after a long period of time and completely burns the remaining unburned matter.

I proposed a two-stage combustion method (Request No. 1852-141918)
(No.), NO, the reduction effect was not necessarily sufficient.

The purpose of the present invention is to improve the two-stage combustion method and further improve the KNO
, K provides a method that can suppress .

The present invention provides ammonia in the air supplied to the second stage or later in a two-stage combustion method in which air for the combustion furnace Km is dividedly supplied to two or more stages to reduce NO in the combustion gas. It is characterized by supplying.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a fluidized bed furnace for explaining a typical embodiment of the present invention. In the figure, combustion air is divided into two stages and supplied into the fluidized bed furnace 1 from a primary air supply line 5 and a secondary air supply line 7, respectively. In other words, the amount of supplied fuel is close to the theoretical air amount (primary air ratio = 0.
8 to 14) Air for cooling is supplied from the primary air supply line 5 to the ped ss via the air box 2, and fuel supplied from the fuel supply line 6 is supplied to the ped s3 under oxygen-deficient conditions on the north wall. After being given a predetermined residence time in the reducing part 4, the combustion gas rising from the zero-order ped part 3, which is primarily combusted in Multiply the supply by 5. Then, in oxidation step 54B, the combustion gas is neutralized and the remaining unburnt components are completely combusted. In this case, the predetermined gas residence time given by the reducing section 4 is such that NOx in the combustion gas rising from the ped section 3 is sufficiently reduced by the unburned components contained together with N! This is the time required for the LO to 3.0 seconds.

In the present invention, a predetermined amount of ammonia (N
Hs) Inject gas. The amount of NHs gas injected is large, but the concentration of NO in the combustion gas flowing into the oxidizing section 48 varies depending on the fuel and primary air ratio.
[Determined] taking into account NOx suppression goals and economic efficiency.

Usually, an injection amount of less than so optt based on the total amount of combustion gas, that is, less than 1/2000 of the total amount of combustion gas, is sufficient. Even if 1/2000 or more is injected, the effect of increasing the amount will not be significant. By injecting this ammonia gas, residual NO, which has not been reduced in the reducing part 4m, is reduced in the oxidizing part 4B, and the black concentration in the exhaust gas discharged from the line 9 is further reduced.

In addition, break I11 in Figure 1? In the square indicated by in 7m and 8m,
The present inventor previously proposed a method of supplying secondary air by dividing it into two parts (or three parts) (Japanese Patent Application No. 141915/1982), but in this method, when NH and gas are injected into the secondary air, The NO8 concentration in the exhaust gas discharged from the line 9 is further reduced compared to the method described above in which the secondary air is not divided. In this case, it has been experimentally determined that the effect is the same even if the NHs gas is injected into either the upper or lower stage of the divided secondary air.

As mentioned above, injecting 1 m of KN) gas in the secondary air is difficult to mix with the combustion gas, so the residual No. 8 and the injected N
The reaction with H, is fast, and NO shown in the following formula.

The effect is great because sufficient oxygen is provided for the reaction between and NHs.

In addition to gas, waste gas containing NH and gas components may be used, and KHCN gas may be used instead of NHm gas.

Next, Fig. 2 shows the primary air supply amount (i.e., the primary air ratio ) shows the results of gas injection when two-stage combustion of fuel (sekigen) is performed. The primary air ratio on the horizontal axis is 2
It shows the degree of staged combustion, and the NO concentration on the vertical axis is the value in the combustion gas.

In the figure, -M is the case of two-stage combustion alone, -B is the case of two-stage combustion and S is injected into the secondary air at 110 WIp, S
Similarly, aC shows the case where 460 NHs were injected. If two-stage combustion is not performed (primary and overall air ratios are both K 1.2 B), 270-NO! It can be seen that the NO concentration decreases to nearly 110jP by performing two-stage combustion and lowering the primary air ratio (curve m).On the other hand, in the case of -1i1B%C, For example, No.ls 1 degree, which was 130p under two-stage combustion alone with the primary air ratio of 0.9, is 110-6Gwes@Todoroki's NEL for the amount of gold combustion gas, and the gas is transferred to the secondary air. It can be seen that the temperature decreases to about 80 to 6 o- by injecting it to .

In addition to secondary air, the injection position of NHs gas is
I tried injecting loss gas into the reducing section 4m and bed section 3 shown in Figure 1, but it did not have much effect.

%, it has no effect at all when injected into the bed portion 3.

The present invention can be applied to a combustion furnace for gas fuel, oil, pulverized coal, or waste using a burner 13 as shown in FIG. 3, in addition to the combustion furnace shown in FIG. This combustion furnace 11
are the primary combustion chamber 11A and the secondary combustion 1! Primary air is supplied from the twin 16 to the air box 14, which is divided into IIB and IIB and is penetrated by the burner 13 to which fuel 15 is supplied. Further, secondary air is supplied to the secondary combustion chamber 11BK from a line 17, and NHs gas is injected into the line 17 from a line 18. In this case, for example, the 1
The amount of secondary air is set to be close to the theoretical amount of air of the amount of fuel supplied from the line 15, primary combustion is performed in a relatively oxygen-deficient state within the primary combustion chamber 1111, and the amount of fuel is supplied into the secondary combustion chamber 11B.
By injecting a predetermined amount of air into the secondary air, the NOx concentration in the exhaust gas 19 can be reduced more than the effect of two-stage combustion alone.

Furthermore, FIG. 4 shows an example in which the present invention is applied to a normal two-stage combustion method in which combustion air supplied from around the burner is divided. A primary air box 14A and a secondary air box 14B are provided around the burner 130 inserted into the furnace wall, and primary air and secondary air are supplied from lines 16 and 17, respectively, and the secondary air is supplied from line 18. A predetermined amount of N1(s gas is supplied from

In addition, in the figure, 20 is a flame, and 21 is 2 containing 'NHs gas.
Even in the above-mentioned furnace configuration in which the secondary air is injected into the secondary air from the line 18, NO in the exhaust gas can be reduced more than just two-stage combustion.

concentration can be reduced.

If the effects of the present invention are enumerated, they are similar to manure.

(1) The degree of second-stage combustion can be reduced. In other words, the two-stage combustion I) increases the degree (lowers the primary air ratio), so the cNo, a degree decreases, but only by a small amount,
By injecting the gas into the secondary air under slow two-stage combustion conditions (e.g. primary air ratio = 1.15) K,
Even if the NO8 concentration is the same as under strong two-stage combustion conditions (for example, primary air ratio = 0.*)! can be achieved.

(2) Higher combustion efficiency than α)K above can be obtained.

Generally, as the primary air ratio decreases, the amount of unburned matter discharged outside the furnace increases, so being able to increase the primary air ratio leads to high combustion efficiency.

(3) When the primary air ratio increases due to (1) above, the proportion of combustion in the bed section increases and the proportion of post-combustion burning in the freeboard section decreases, so the furnace volume can be reduced. This is advantageous in large-scale furnaces such as fluidized bed incinerators and fluidized bed boilers. Furthermore, in the case of a fluidized bed boiler, when the primary air ratio increases, the combustion rate in the bed portion where the heat transfer coefficient is large increases, so the heat transfer area can be reduced. In addition, in the case of fluidized bed incineration, the combustion rate in the bed increases, so the amount of auxiliary fuel can be reduced.

(4) From (1) K above, in the case of fluidized bed boiler 2, a high degree of NO suppression and desulfurization using limestone can be simultaneously achieved in the furnace. If the primary air ratio is lowered, the in-furnace desulfurization rate will deteriorate, so operate under conditions with a high primary air ratio (slow two-stage combustion conditions) where the in-furnace desulfurization rate is high, and as the primary air ratio increases, Since the decrease in the NO□ suppression effect can be compensated for by injecting gas into the secondary air, it is possible to achieve a high degree of NoX suppression and a high degree of in-furnace desulfurization at the same time. You can save money.

(5) It is a very simple method. In other words, the NHs gas is simply injected into the furnace before the secondary air enters the furnace, and since it is injected into the furnace together with the secondary air, it mixes very well with the combustion gas, making it ideal for non-catalytic reduction. There is no need to provide a special injection nozzle or the like.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing a combustion furnace to which the present invention is applied, FIG. 2 is a diagram illustrating the effect (1G) of the combustion method of the present invention, and FIGS. 31a and 4 are It is a figure which shows the ammonia injection method of another combustion furnace to which this invention is applied. 1...furnace, 3-bed section, 4--creeboard section,
4A... Reduction section, 4B... Oxidation section, 7... Secondary air supply line, 8... Zero loss gas injection line. Attorney Takeshi Kawakita Nagatsutsu 1 Figure 2 Figure 3 Procedural amendments April 7, 1937 Commissioner of the Japan Patent Office Haruki Shimada 1, Indication of the case 1939, Request for Permission No. 17, No. 2, First name of the invention Two-step passion method 3 Relationship with the case of the person making the amendment 4 Proxy attorney 〒lHI 3″' (Ma5 is) Patent attorney Yokita Takecho 5 Date of amendment order Voluntary 6 , The number of inventions will increase by the amendment to 7, and the subject of the amendment will be changed.
(3) Figures 2 and 4 of the drawings are respectively revised to Attachment 5.

Claims (1)

[Claims] (1) In a two-stage combustion method in which combustion air is dividedly supplied to a combustion furnace in two or more stages to reduce NO in the combustion gas, ammonia is supplied to the air supplied in the second stage or later. A two-stage combustion method characterized by: