JPS6020648B2 - Method for reducing NOx in combustion exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-stage combustion method, and in particular reduces nitrogen oxides N○× and other air pollutants such as carbon monoxide CO and hydrocarbons in combustion gas, and produces clean combustion gas. The present invention relates to a method for treating combustion gases that can be released into the atmosphere.

Most of the N○x in the combustion gas is nitric oxide NO.
The remainder is often nitrogen dioxide N02.

From the standpoint of air quality conservation, the development of methods for removing these N○× is currently being actively pursued. Conventionally, the following methods are listed as N○× reduction methods mainly used.

'1} Various methods are being considered, including the low NOM combustion method, the low excess air combustion method, the multi-stage combustion method, and the exhaust gas recirculation method.

The basic principles of these methods are to lower the oxygen Q concentration in the combustion chamber and to lower the flame temperature. As the amount of melon is reduced, the amount of unburned materials such as CO and decomposed hydrocarbons increases. Therefore, there is a limit to the reduction of N○× in practice. '2} Selective or non-selective catalytic reduction method Injecting and mixing a gaseous reducing substance such as ammonia and hydrogen into the combustion gas and then passing it through a catalyst layer. This method reduces the
There are many technical and economic problems such as secondary pollution caused by dust of heavy metals used as catalysts, equipment blinds, and running costs.

'31 Selective or non-selective non-catalytic reduction method Directly injecting reducing substances into the combustion gas, such as N ratio or other easily oxidizable substances such as carbon, hydrocarbons, etc., alone or in combination ~ N○ k
(e.g. Hakama Kaisho 49-47244 50
−? However, there are problems such as damage to the low-temperature heat recovery unit due to reducing substances and substances generated by the action of these substances, and new pollution caused by release into the atmosphere.

In addition, depending on the operating conditions, the decomposition of reducing substances may actually result in an increase in the production of N melon.
The ○x combustion method and the non-catalytic reduction method described in {3' above are relatively inexpensive and simple low-N○x methods, but as mentioned above, they tend to generate harmful substances such as unburned substances. , N○× reduction effect has a limit, and it is difficult to reduce it by 30% or more in practice.
The present inventors stated, ``During research on the multi-stage combustion method (hereinafter referred to as the OFA method), we moved the secondary air blowing position of the OFA method to a completely different location than before, and found that confirmed that secondary air itself has a considerable reducing effect as well as an oxidizing effect.

In order to effectively put this action of reducing N○× into N2 into practical use, it is necessary to ensure the combustion gas conditions at the secondary air blowing position. It was found that blowing is effective and that the hydrocarbons in parentheses themselves also have the effect of reducing N○×. Of course, the above conditions can also be achieved by a method other than the hydrocarbon injection method, for example, by improving the combustion itself of the main burner. Based on the above findings, we have completed a method for cleaning combustion gas, that is, the method of the present invention. The present invention is based on "'11 When air is divided into multiple stages and mixed into combustion gas containing NOx at a temperature of 850 to 1300°C and an oxygen concentration of zero or approximately zero,"
The amount of NO in the combustion gas is reduced by mixing and burning at regular intervals so that the next divided air is mixed into the region where the combustion reaction of the oxygen in the previously mixed air has almost finished. A method for processing combustion gas characterized by the following.

'21 Assuming that a combustion gas containing N○× at a temperature of 950 to 1400°C and an oxygen concentration of about 5% or less is combusted with oxygen in the combustion gas, the oxygen concentration in the combustion gas is The decomposed hydrocarbons present in the combustion gas obtained by dividing a plunderable amount of hydrocarbons in one or multiple stages and sequentially mixing and combusting the combustion gas in a temperature range of 850 to 1300°C. And, assuming that unburned materials such as carbon monoxide are completely oxidized, the remaining oxygen concentration is i.
When dividing and mixing air in an amount of 5% or more in multiple stages, the air is divided at regular intervals so that the next divided air is mixed into the region where the combustion reaction of oxygen in the previously mixed air has almost completed. By sequentially mixing and burning the fuel at the same time, the above-mentioned fuel is substantially completely oxidized, and at the same time, N
The gist of the present invention is a combustion gas processing method characterized by reducing ○k.

That is, ``In the present invention, the combustion gas under certain conditions in which the secondary air itself has a considerable reducing effect at the same time as the oxidizing effect is defined as a combustion gas having a temperature of 850 to 1300°C and an 02 concentration of zero or approximately zero, preferably -2% to i%, and in order to secure the combustion gas under this condition, the hydrocarbon injection method, the combustion improvement method of the main burner, and other appropriate methods are explored as described above.

Furthermore, ``The above 02 concentration is -2%'' means ``The 02 concentration is 2% after a simple calculation that does not take into account the chemical reaction in the combustion gas where combustible substances are present due to lack of oxygen.'' When air is mixed with air, theoretically, the above-mentioned unburned substances are completely combusted and 02 disappears.In the present invention, the air is divided into two stages or multiple stages into the combustion gas under the above-mentioned conditions. The gas is injected from outside the system and mixed rapidly with the combustion gas.

In this case, the air injection amount is such that the 02 concentration after mixing is 1.5.
It is preferable to set it to % or more. In addition, in the present invention, the 02 concentration generated in ordinary boilers, heating furnaces, etc. is approximately 5% or less, preferably 0.5 to 2%, and even if some unburned materials such as C○ and decomposed hydrocarbons are contained. Hydrocarbons are often divided into one or more stages and injected from outside the system into a region where the temperature of the combustion gas stream is 950 to 1400 degrees Celsius, where a CO concentration of 100 to 10,000 is permissible. The above 02 concentration condition, i.e. zero or almost zero, preferably -2 to 1%, is ensured by sequentially and rapidly mixing with the combustion gas, and the downstream temperature of this combustion gas is 850 to 1300o.
Air is divided into two or multiple stages and injected from outside the system into the region o, and is rapidly mixed with the combustion gas one after another.

In this case, the injection amount of the hydrocarbon is set so that the 02 concentration after mixing becomes the cloud or approximately zero, preferably -2 to 1%, and when the injection is divided into multiple stages, 1 It is effective to set the injection amount in each stage so that the 02 concentration after mixing is 2% or less.

Further, the amount of air injected on the downstream side is set so that the 02 concentration after mixing becomes 1.5% or more as described above. Furthermore, according to this hydrocarbon injection method, at the time of hydrocarbon injection,
While the above 02 concentration conditions are ensured, it is also possible to achieve the effect that NO skin in the combustion gas is considerably reduced to N2.

As a result, the final concentration of N○× in the combustion exhaust gas was 30
The characteristics and effects of the method of the present invention, which not only can reduce the amount of CO by more than %, but also substantially eliminate the presence of unburned substances (CO<5 melon skin), are summarized below.

'1} It is a non-catalytic method.

{2) The materials to be supplied outside the system necessary for reduction and oxidation of N○× are hydrocarbons and air that are normally used in boilers, heating furnaces, etc., so no special handling is required and a new There is no concern about further pollution occurring.

Leg: By using it in conjunction with the low-N○x combustion method, it is possible to achieve an extremely effective reduction in N○x, and virtually no unburned matter is generated.

■ Hydrocarbons for blowing include gaseous ones such as methane, methane, and propane, as well as 950-14
Any liquid material that can be easily gasified at a temperature of 00°C may be used, such as gasoline (including naphtha) and kerosene.

The method of the present invention is an apparatus that generates N○k-containing combustion gas and is equipped with a device that can realize the desired conditions (temperature and oxygen concentration) of the combustion gas for application of the present invention, including modification.
It can be applied to boilers, various industrial heating furnaces, etc.
Hereinafter, the method of the present invention will be explained in further detail by giving experimental examples that are the basis of the present invention.

Experimental example 1 Figure 1 shows the experimental equipment used in this experiment.

In Figure 1, combustion gas 1 is supplied to burner 2 installed at the bottom of the furnace.
made by.

Combustion air 3 is pressurized by a forced draft fan 4 and sent into the furnace using a so-called forced draft method. The fuel 20 can be either liquid or gas. In this experiment, A to C
Heavy oil and propane gas were used. The inner surface of this cylindrical experimental furnace 5 is mainly lined with refractory bricks 6 except for the heat transfer tube group 13 for controlling combustion gas temperature. The furnace length is approximately 18 mm, and in order to reproduce the actual combustion gas flow velocity in a practical furnace, the furnace seats are arranged in several stages in the flow direction, and the inner diameters are 80 mm, 70 mm, and 50 mm, respectively. There were 30 mosquitoes. For convenience, these four sections with different diameters are connected from the upstream side of the combustion gases to the first chamber 7.
, a second chamber 8, a third chamber 9, and a fourth chamber 10.
The first chamber 7 corresponds to a so-called hot air generating furnace, and the combustion gas generated here is sequentially passed through the second, third and fourth chambers and is released into the atmosphere from the chimney 11. Immediately in front of the second chamber 8, an air intake 12 for adjusting the temperature and composition of the combustion gas is installed. The third chamber 9 is partially provided with a group of heat transfer tubes 13 assuming a convective heat recovery section of a practical reactor, and is configured to be cooled with seawater 14. Hydrocarbons (hereinafter referred to as after-fuel)
15 and air (hereinafter referred to as afterair) 16 are injected at a combustion gas composition provided at a pitch of about 50 ribs in the furnace length direction.
The measurement was carried out at various locations using the temperature measurement hole 17. When injecting the afterfuel into the furnace, air 18 or steam 19 is allowed to be entrained in order to promote diffusion and mixing. Commercially available propane gas, methane gas, naphtha, etc. were used as after fuel. FIG. 2 also shows a schematic diagram of typical injection pipes 15 and 16 used to disperse afterfuel and afterair into the combustion gases.

Figure 2 A? B is the afterfuel injection pipe, Fig. 2 C, D
indicates the aftercare injection tube. First, to explain the afterfuel injection pipe AF-M type shown in Fig. 2A, line 1
A predetermined amount of fatafuel flowing in from 3/6 holes in the circular pipe wall of the bait tube 2 in 6 axial directions to 2 in the circumferential direction for each step (8.4 ribs) 3 It ejects into flaming gas.

Note that 4 is an in-furnace flue, and 5 is a refractory brick, which corresponds to 6 in FIG. Next, to explain the afterfuel injection pipe AF-S type shown in Fig. 2B, it has a simple structure in which the 11'28 pipe 2 is inserted to the center of the furnace flue 4 and afterfuel is spouted from its tip 2'. It should be noted that t second
Both types of injection tubes shown in Figures A and 8 can also be used with entrained gases (air, steam, etc.) to increase the diffusion effect.
This entrained gas is introduced through line 6. The afterair injection pipe type AA-M shown in Fig. 2C is of almost the same type as the afterfuel injection pipe AF-M shown in Fig. 2A.
In the B pipe 2, there are 6 ejection holes (diameter 2 x 2) provided in the circumferential direction in 6 stages on the circular pipe wall. .

The afterfuel injection pipe AA-S type shown in Fig. 2D is of almost the same type as the afterfuel injection pipe AF-S type shown in Fig. 2B, but in this AA-S type, the 2B pipe 2 is The tip 2' is provided so as to open □ not in the inner center but in the furnace wall, so that afterair is blown into the furnace wall. This is a case where the air blown out into the combustion gas is sufficiently dispersed due to the momentum of the jet flow, and the blowing position can be changed arbitrarily in consideration of the dispersion ability. Note that the diameter of the after-air injection pipe is larger than that of the after-fuel injection pipe simply because the blowing flow rate is larger.

The two typical injection pipes, M type and S type, have been explained above, but the function of the injection pipe is that it can quickly disperse and mix the combustion gas and the injected material. The number of pipes 2 and the number of jet holes 3 need to be changed. In addition, in practice, both the afterfuel and afterair injection pipes are exposed to high-temperature combustion gases of 850°C or higher, so in order to protect the injection pipes, a double pipe system is used and a cooling medium such as air, water, or steam is used. It is necessary to cool it down.

First, by using the apparatus shown in FIG.
Combustion gas was generated under the conditions of 00,000 Kca'/day and a combustion air ratio of 0.8 to 2.0, and the basic characteristics when afterair was blown into this combustion gas were investigated.

That is, using 110 kg/day of propane gas and an air ratio of 0. Combustion gas was generated under the conditions of 1.15 and 1.15, and the characteristics were investigated when afterair was injected by moving an AA-M type injection pipe shown in Figure 2C to the ridges of the bonito path.

The results are shown in FIG. In addition, the 02 concentration of the combustion gas before and after the after injection is ~, respectively, where ^ is 0. -0.5%, 2% when in group, 3%, 5.5% when ^ is 1.15
Met. In addition, the NO concentration before after-injection was 0. About 15 when working & about 20 when wind, ^ is 1.15
With 0 leg skin, about 95% of the N○× is NO, and the rest is N02.
Met. In Figure 3, the axis is the combustion gas temperature just before the afterair injection position.The vertical axis is the NO concentration and N○x concentration after afterair injection, and the NO concentration before injection is the concentration (N○x), divided by the percentage. In the figure, curve 1 is the NO concentration after after-injection of combustion gas when combustion is performed at the above air ratio input of 0.98, and curve 2 is the NO concentration after the combustion gas is blown at the air ratio ratio of 0.98. Curve 3 shows the NO concentration after after-injection of the combustion gas during combustion, and curve 4 shows the NO concentration after after-injection of the combustion gas during combustion at an air ratio of 1.15. N○ after injecting combustion gas into aftertaea when combusting with
This is the observation result of x concentration. Note that "N mentioned in this specification
0x, NO and CO values are all converted to 0%02 concentration level using the following formula.

Rib: 2, ≧; 2'rib' N.

=2. Half 2'N. 'C.

=2. $'C. '(Here, N○×, NO and CO are 0
The %02 conversion values, NOx', NO', and CO' are actually measured values at the actual blood deposit 2 concentration 02'.

) As shown in curves 3 and 4 in Figure 3, even if afterair is injected into the combustion gas whose Q concentration is 3% and combustion has been completed, it has no effect on reducing N○×, but curves 1 and 2 As shown, when the Q concentration is -0.5%, when afterair is introduced into a temperature range below 1200°C, a clear denitration effect is seen, and the effect is maximum near 950°C.

Also, considering that the band-shaped part shown with diagonal lines in Fig. 3 corresponds to the N02 base that has been present in the combustion gas from the beginning,
When the 02 concentration is -0.5%, as shown in curves 1 and 2, conversion from NO to N02 occurs at temperatures below 80,000, and the amount of NQ generated increases as the temperature decreases. saw it and was served.

In other words, in a high temperature castle, only the denitrification reaction of N○k occurs,
It was confirmed that as the temperature decreases, the oxidation reaction of NO to N02 coexists, and eventually the oxidation reaction becomes dominant. Furthermore, when the value was 120,000 or more, N0x did not decrease, but rather tended to increase. In addition, in FIG. 3, area Q is N02 generated by after-air injection.
The region 8 corresponds to the NO that has been reduced to N2 by the afterair injection, and the region y corresponds to the NO that is present after the afterair injection.

From the above, in the conventional OFA method, the secondary air is 13
In this case, the use of secondary air tends to increase NO x, but the NO x reduction effect in the combustion area of primary air becomes dominant, and the overall effect is It is presumed that an attempt is made to reduce N○k.

Next, similar to the case of after-air described above, the peculiarities when propane gas was blown into the combustion gas as after-fuel were investigated, and the results are shown in FIG.

In this case, combustion gas is generated using propane gas of 130k9/day under conditions of air ratio of 1.1 and 1.6, and injection pipes of the AF-M type shown in Figure 2A are installed at various points along the bonito path. I moved it and filled it with propane gas as an after-fuel. In addition, the 0 of combustion gas before and after propane gas injection
The two concentrations were 2% and 0% when ^ was 1.1, and 9% and 8% when input = 1.6, respectively. The N○x concentration before propane gas injection is approximately 200 skin when the injection is 1.1,
When the input was 1.6, there were about 250 legs, and about 95% of the nuclear NOx was NO, and the rest was NQ. In FIG. 4, the combustion gas temperature immediately before the propane gas blowing position on the machine shaft, the vertical axis shows the NO concentration and N○× concentration after propane gas blowing, and the NOk concentration (N○x) before blowing.

The value divided by is expressed as a percentage (%). In the figure, curve 1 is the NQ ratio of the combustion gas after propane gas injection when combustion is performed at the above air ratio ^1.1, and curve 2 is the combustion scale gas when combustion is performed at the air ratio ^1.1. N○× concentration after propane gas injection, curve 3 is air ratio 1.6
Curve 4 is the observation result of the N○k concentration after propane gas injection into the combustion gas when combustion is performed at an air ratio of ^1.6. The band-shaped portion shown is the amount equivalent to NQ present in the combustion gas from the beginning. As shown in curves 1 and 2 in Figure 4, the characteristics when propane gas is blown into combustion gas with a Q concentration of 2% are that in the region of 1400 qo or more, the blown propane gas is completely combusted and the N○x is Although it tends to increase, the reduction reaction of NOk to N2 starts around 1400℃, and the reaction rate reaches its maximum around 700℃, and below 700qo, the oxidation reaction of NO to NQ also coexists, and the temperature becomes lower. It was confirmed that the oxidation reaction becomes more dominant.

In addition, as shown in curve 3.4, the characteristics when propane gas is blown into the combustion gas with an 02 concentration of 9% are also
%, but in this case, it is noteworthy that the reduction reaction does not occur so markedly, but the efficiency of oxidizing NO to N02 in the low temperature castle is extremely high. As explained above with reference to FIGS. 3 and 4, the temperature of the combustion gas immediately before the afterair or afterfuel injection position and the temperature of this gas. It has been found that depending on the 02 concentration conditions in the combustion gas, considerable reduction and denitrification of N○× can be expected by blowing afterair or afterfuel into the combustion gas.

In addition, as a result of the above experiment, although not mentioned in Figures 5 and 4, decomposed hydrocarbons and CO
The oxidation reaction characteristics of unburnt substances such as carbon dioxide, etc., and the generation characteristics of unburnt substances such as decomposed hydrocarbons and CO due to afterfuel injection are controlled by the conditions of the combustion gas at these injection positions. It has also become clear that it is difficult to substantially eliminate the oxidation, and that the amount of oxidation generated is often impractical.

Therefore, in the present invention, as a method that combines not only the reduction of N○× by afterair and afterfuel but also the cleaning of the fuel in afterair, as described above, the temperature is 850 to 1300℃, , preferably -2 to 1%, and the concentration of unburned substances such as decomposed hydrocarbons and CO is about 100 to 10,000 in the combustion gas,
By blowing after air to make the Q concentration in the combustion gas 1.5% or more, N○× is reduced and the combustion gas becomes clean and substantially free of unburned matter.

At this time, the reason why the Q concentration is set to 1.5% or more is because if the Q concentration is lower than this, the unburnt substances will not be completely burned and removed. Also,
02 concentration of combustion gas before afterair injection -2
~1%, and concentration of unburned substances such as decomposed hydrocarbons and CO 100~
10,00■ Since the critical conditions cannot be met with ordinary boilers, industrial heating furnaces, etc., we inject afterfuel before injecting afterair to ensure the above conditions, and further reduce N○ x by the reducing action of afterfuel itself. This is what we are trying to do. Next, an experimental example will be given to confirm the effectiveness of the above method.

Experimental Example 2 Using the apparatus shown in FIG. 1, either propane gas as afterfuel or afterair was blown into combustion gas generated using propane gas of 130 k9/day in multiple stages.

As injection pipes for blowing, a plurality of AF-M type shown in FIG. 2A and AA-M type shown in FIG. 2C were used. The results are shown in FIGS. 5 and 6. Figure 5 shows one stage of propane gas in combustion gas with a 02 concentration of 1% (point of arrow a in Figure 5) and three stages of propane gas (points of arrows b, c, and d in Figure 6). This is what it looks like when it is divided into 2 parts and blown into it.

The temperature of the combustion gas just before blowing is 1350℃.
(arrow a in Figure 5), 1120qo (arrow b in Figure 5), 1030qo (arrow c in Figure 5), and 900
qo (arrow d in Figure 5). The propane gas blowing amount is 13 kg/day, and the after air blowing amount is 60 k9/day, 60 k9/day, 240 k9/day from the upstream side.
It was day. Note that arrow G in FIG. 5 indicates the flow direction of the combustion gas. Changes in the concentrations of 02 and N○k in the combustion gas at this time were as shown in FIG.

NO Hiro, which had 180 units, was reduced to 12 units by blowing in propane gas, and by sequentially injecting afterair gas, it became a rocky site, 4 morning units, and finally 3 pieces of blood, and the existence of unburned materials was practically recognized. I couldn't.

In addition, the 02 concentration in the combustion gas, which was initially 1%, was reduced to -i. 2%t −0
．． It changed sequentially to 6%, 0%, and 2%. For comparison, the total amount of 360k9/day is 11 with one stage of aftercare.
When it was blown into a location with a combustion gas atmosphere at 20°C (arrow b in Figure 5), NOx, which was 120 degrees, was reduced by only 1 point in the 9Q style, and by blowing afterair in multiple stages, it was extremely effective to reduce NOx. It was confirmed that it was possible to decrease k.

Figure 6 shows three stages of propane gas in combustion gas with a 1% concentration of 02 (points indicated by arrows b, c, and d in Figure 6) and one stage of Afterair (points indicated by arrow a in Figure 6). This is what it looks like when it is divided into 2 parts and blown into it.

The temperature of the combustion gas just before blowing is 1350o.
o (arrow b in Figure 6), 1130q0 (arrow c in Figure 6), 1050 0 (arrow d in Figure 6), and 95
0qo (arrow a in Figure 6). The amount of propane gas blown from the upstream side is 6.5k9/day, 3.25k
9/day, 3.25 [9/day, after-air blowing amount was 360k9/day. Note that "arrow G in Figure 6 indicates the flow direction of the combustion gas.
The concentration changes of 2 and N○k were as shown in FIG.

The initial concentration of N○x was 180 pm, which gradually decreased to 145 feet, 10 blood, and 7 ruts by blowing propane gas.
After-air blowing resulted in 5 mottled plates, and the presence of unburnt material was virtually not confirmed. For comparison, propane gas is used in one stage and the total amount is 13k9/day.
The result of blowing into a location with a combustion gas atmosphere of 350oo (arrow b in Figure 6) was 12 liters of blood as shown in Figure 5 above, and by blowing propane gas in multiple stages, it was extremely effective to remove nitrogen. It was confirmed that ○k was decreased.

In addition, in the method of the present invention, steam, combustion exhaust gas, air, etc. can be entrained in the afterfuel in order to promote the diffusion and mixing effect of the afterfuel into the combustion gas. The following experimental example is given to confirm this entrainment effect. Experimental Example 3 Using the apparatus shown in Figure 1, propane gas as after-oil is entrained in the combustion gas generated by burning 80k9 days of propane gas with an air amount of 1285k9/day using steam or air as an entrainment medium. The denitrification rate was measured by blowing in various amounts and then blowing afterair.

In addition, steam or air-entrained propane gas blowing is carried out at ``02 concentration 0.2-0.5%, temperature 1020-1060.
The injection was carried out into the combustion gas at .degree. C. using an AF-M type shown in FIG. 2A as an injection tube. The amount of propane gas injected was 4k9/day, and the NO power level in the combustion gas just before propane gas injection was 11 times. In addition, after-air blowing after propane gas blowing is performed at a blowing amount of 312
It was done at k9/day. The results are shown in FIG. In Figure 7, when steam is used as the entraining medium, curve 1' is curve 2'.
is the case when air is used as the entraining medium. From FIG. 7, it was confirmed that the denitrification rate gradually improved as the amount of steam entrained increased.

In addition, when air is used, the effect of changing the 02 concentration, which is the governing factor of the denitrification reaction, is greater than the promotion of diffusion and mixing effects, and it has been confirmed that it is not possible to say with certainty whether air entrainment is good or bad. Ta. Therefore, it can be said that it is preferable that the entrainment medium is inert. Next, the changes in the furnace, which are the main factors when purifying combustion gas by blowing afterfuel and afterair, will be explained using an experimental example.

Experimental Example 4 Using the apparatus shown in Fig. 1, 3.25 k9/day of afterfuel is added to the combustion gas generated when propane gas is combusted with an air flow of 655 x 9/day at a temperature of approximately 1150 oo. Propane gas with air 2
Inject k9 days using the AF-M type injection pipe shown in Figure 2A, and further inject 115 k9 days in a temperature range of about 9000 C on the downstream side.
/day after-hours were injected using the AA-M type injection tube shown in Figure 2C.

The results are shown in FIG. In FIG. 8, the axis of the machine indicates the distance [desk] from the outlet of the first chamber (hot air generating furnace) in both the upper figure and the lower figure.

The upper diagram shows the flow rate of combustion gas in the furnace (curve 1) and temperature distribution (curve 2), and the residence time to any position in the furnace (curve 3).
).

The lower figure shows the concentration distribution of C○ (curve 4), N0 (curve 5), N○× (:NO+N02) (curve 6) and Q (curve 7) in the combustion gas. , arrow b indicates a fault in air-entrained propane gas blowing, and arrow a indicates a fault in after-air blowing.

The following was clarified from the upper and lower diagrams in Figure 8. ○
} The N○× concentration decreased from 14 anchor-like to 7-string blood in less than 1 second by propane gas and afterair blowing, and "there was hardly any change after that.

{2) The CO concentration increased from bow-legged to approximately 4,000 ft in less than 1 second by propane gas blowing, and decreased to 2 takuda in less than 1 second by after-air blowing.

{3' The 02 concentration was approximately 1% in the main combustion gas, but Q disappeared due to the injection of propane gas, and it became approximately 2% due to the injection of afterair gas.

In addition, gas analysis in the combustion gas after treatment revealed that ``
Propane gas, formaldehyde, hydrogen cyanide and N
The presence of each component in the ratio was virtually not observed. As can be seen from the above experimental results, the denitrification reaction of N○× and the oxidation reaction of unburned substances such as CO are extremely fast, and the pure reaction time is less than 0.9 stages, excluding the diffusion and mixing time of reactants. it is conceivable that.

Experimental Example 5 A practical experiment similar to Experimental Example 4 was conducted and an example of the data is shown in Table 1.

Note to Table 1) Both Faftafuel and Faftaair were blown in one stage.

Experiments Nos. 5 and 9 were cases in which the effects of the present invention were fully utilized; the denitrification rates were 60% and 80%, respectively, and there was virtually no unburned material.In experiment No. 8, the denitrification rate was high, but This generates smoke and poses a practical problem.It was confirmed that under the conditions of experiment numbers 3 and 7, the NOx concentration became considerably high by blowing propane gas and afterair. Examples of implementations when applied to are listed below.

Embodiment Example 1 A case in which the present invention is implemented in a boiler will be described using FIG. 9.

A flame 6 is formed in the furnace by the burner 9 using the fuel 1 and the combustion air IQ, and the combustion gas sequentially flows through the specular heat recovery section and the convection heat recovery section 3, 5, and 5.

Normally, complete combustion of the fuel 1 is required by the burner 9, but in the present invention, the afterair 8 is inserted into the wake side ○2 of the combustion gas, so the combustion air blade D' or For example, if fuel 1 is C
In the case of heavy oil, the amount of air can be kept up to about the theoretical amount of air, and in the case of hydrocarbon fuel, the amount of air can be kept up to about 5% of unburned matter in the combustion gas flow. By creating such a combustion state, the main combustion part of burner 9 will first burn approximately 2
It is possible to reduce N○× by 0%. Next, the temperature of the combustion gas is 95
Afterair 7 is injected into G from 0 to 1400q○ using the afterfuel injection injection tube tortoise. The amount of afterfuel blown is set so that the amount of combustible matter in the blown combustion gas is approximately 5 to 10%. This afterfuel injection reduces N○x by about 40%. Furthermore, the temperature of the combustion gas on the downstream side is 850 to 1300qC.
Now, air 8 is blown into G2 using the injection pipe 12 for afterair blowing.
Set the blowing amount so that the concentration is 1.5% or more. This afterair injection makes the amount of unburned matter virtually zero, further reducing N○x by about 40%.
Approximately 70% NO reduction can be achieved. Embodiment Example The second turtle Q diagram shows an industrial furnace heating furnace (scaling furnace for olefin production,
This is a case where the basic operation of the present invention is repeated in two stages and applied to a reforming furnace for producing NH3, methanol, etc., a heating furnace for petroleum refining and petrochemicals, etc.).

Using fuel 1 and combustion air 2, flame 6 is formed in the furnace by burner 9, and combustion gases G, , G2, G3, and G4 pass through radiation heat recovery section and convection heat recovery section 3, 4, and 5. It flows sequentially.

The fuel 1 is completely combusted by the burner 9, the 02 concentration in the combustion gas G is 3%, and the amount of unburned matter is zero. First, afterfuel is blown into G, where the combustion gas is about 1200° C., using the afterfuel injection injection pipe 12. The amount of afterfuel blown is calculated as combustion gas G,
It is assumed that all of the 02 in the combustion gas contributes to the combustion of the blown afterfuel, and the combustion gas is set so that 1 to 10% of filtrate is present. On this wake side, the temperature of the combustion gas is 11
Afterair 8 is injected into G2 at approximately 00:00 using the afterair injection injection pipe 13. The amount of afterair injection is calculated from 1 to 10 unburned substances in the combustion gas G2.
% is completely burned, and 02 is 0 in the combustion gas.
．． Set it so that it exists at 5 to 2%. Further, on the downstream side, afterfuel 7 and afterair 8 are injected into G3 at a temperature of about 1000q0 and ○4 at a temperature of about 90000q0 using injection pipes 14 and 15.
The amounts of afterfuel and afterair are set based on calculations similar to those described above so that the amount of unburned matter and 02 in the combustion gas is approximately 1 to 5% and 1.5 to 2.5%, respectively. By these operations, the amount of unburned substances in the treated combustion gas G3 becomes substantially zero, and a reduction of about 70% can be achieved compared to the initial content in the NOx combustion gas G.

Embodiment Example 3 This embodiment is a case in which the boiler described in Embodiment Example 1 is divided into three stages and blown in sequentially, and an outline thereof is shown in FIG. 11.

New after fuel injection tubes 13 and 14 in addition to 11
These injection pipes 11, 13, and 14 are installed at locations where the combustion gas temperature ranges from 1,300°C to 100,000°C.

Further, after-fuel injection is performed so that the 02 concentration in the combustion gas after injection is 1% to 2%, and the 02 concentration reduced per stage is 0.5% or more. Other operating conditions are as shown in Embodiment Example 1. By dividing and injecting the Fatafuel into multiple stages in this way, it is possible to achieve an even wider reduction in NO than in the case of the first embodiment.

Embodiment Example 4 This embodiment is a case where the Afterfuel injection pipes 13 and 14 in Embodiment Example 3 are replaced with Afterair injection pipes, and Afterair is injected in three stages.

After air blowing in each stage is performed so that the 02 concentration in the combustion gas after blowing is -1 to 1.5%, and the increased 02 concentration per stage is 0.5% or more. Furthermore, ``The final or third stage afterair injection is performed when the Q concentration in the combustion gas is 1% or less just before blowing.This means that if the 02 concentration in the combustion gas is 1.5% or more, the This is because denitrification in the final stage cannot be substantially achieved.
Other operating conditions and the like are the same as in the first embodiment. By dividing and blowing the afterair into multiple stages in this manner, it is possible to achieve a further reduction in N○× than in the case of the first embodiment.

Of course, it is also an extremely effective method to reduce NO by dividing both afterfuel and afterair into the combustion gas in multiple stages.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the combustion device used in the experimental example of the present invention, Fig. 2 is a schematic diagram of the afterfuel and afterair injection pipe used in the combustion device of Fig. 1, and Figs. A chart showing the basic characteristics when injecting Afterfuel or Afterair, Figures 5 and 6 are charts showing the effect when using both Afterfuel and Afterair, and Figure 7 shows when an entrained medium is used when injecting Afterfuel. Figure 8 is a diagram showing changes in the main factors in the furnace when afterfuel and afterair are injected. Figures 9 to 11 are schematic diagrams of actual furnaces used in embodiments of the present invention. It is a diagram. 1 figure O 2 figure 3 spear 4 figure 5 figure 6 figure spear 7 figure 8 figure o 9 figure o 10 figure on n figure

Claims (1)

[Claims] 1. When air is divided into multiple stages and mixed into combustion gas containing NOx at a temperature of 850 to 1300°C and an oxygen concentration of zero or approximately zero, the oxygen in the previously mixed air is A method for treating combustion gas, characterized in that NOx in the combustion gas is reduced by sequentially mixing and burning at regular intervals so that the next divided air is mixed into the region where the combustion reaction has substantially completed. 2. Assuming that a combustion gas containing NOx at a temperature of 950 to 1400°C and an oxygen concentration of about 5% or less is combusted with oxygen in the combustion gas, the oxygen concentration in the combustion gas is zero or approximately zero. In the temperature range of 850 to 1,300°C of the combustion gas obtained by dividing and sequentially mixing and burning the amount of hydrocarbons in one or multiple stages, the cracked hydrocarbons and carbon atoms present in the combustion gas are Assuming that unburnt materials such as carbon oxide are completely oxidized, the remaining oxygen concentration is 1.5%.
When dividing and mixing the above amount of air into multiple stages, the air is divided at regular intervals so that the next divided air is mixed into the region where the combustion reaction of oxygen in the previously mixed air has almost completed. By sequentially mixing and burning, the unburned materials are substantially completely oxidized and at the same time NOx in the combustion gas is removed.
A method for processing combustion gas, characterized by reducing.