JP3835966B2 - Waste fluidized bed incinerator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waste fluidized bed incinerator, and more particularly to a fluidized bed incinerator used for sewage sludge incineration.
[0002]
[Prior art]
Conventionally, stoker type incinerators and fluidized bed type incinerators have been mainly used as waste incinerators, but in sewage sludge incinerators, fluidized bed type incinerators with a large heat load capacity are advantageous.
On the other hand, sewage sludge has a high nitrogen content in the waste, and even if a fluidized bed incinerator is used, the water content in the waste is high and the combustion temperature is low. As a result, nitrous oxide (N ₂ O) tends to increase.
However, nitrous oxide has a greenhouse effect coefficient that is 310 times that of carbon dioxide (CO ₂ ), and is extremely affected by global warming.
[0003]
Thus it is to change the sub conversion rate as the technique of reducing nitrogen oxide (N _{2 O)} from the HCN and NH ₃ as the N _{2 O} of the deadline to N _{2 O} and NO in the fluidized bed (selectivity), Methods such as raising the combustion temperature, lowering the oxygen concentration (air ratio), and promoting mixing with contact particles are effective.
[0004]
[Problems to be solved by the invention]
However, even if such a method is adopted, the total concentration (2N ₂ O + NO) of the exhaust concentration as a whole of the nitrogen oxide is almost constant just by changing the conversion ratio to N ₂ O and NO.
That is, NO increases when trying to reduce N ₂ O, while N ₂ O increases when trying to reduce NO. NO is a substance that is extremely problematic in terms of air pollution.
For this reason, the two-stage combustion method is effective as a substance that can reduce both at the same time, but the two-stage combustion method causes a reduction in combustion efficiency and desulfurization efficiency.
In view of such problems, the present invention has an object to provide a waste fluidized bed incineration capable of simultaneously reducing both N ₂ O and NO without causing a decrease in combustion efficiency and desulfurization efficiency.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a waste product in which a free board area in which a combustion gas product or the like is recombusted is provided above a fluidized bed into which the waste product is charged . In the fluidized bed incinerator, a temperature rising burner is disposed above the fluidized bed, and a second temperature rising burner is disposed above the fluidized bed in a furnace wall position facing the secondary air introducing nozzle. And the second temperature raising burner are combined to form a combustion promoting body, areas having different air ratios are formed across the combustion promoting body, and the air ratio on the combustion promoting body inlet side from the temperature raising burner is changed to the combustion promoting body. It is characterized by being set lower than the air ratio on the outlet side.
A combination of the secondary air introduction nozzle and the second temperature raising burner constitutes a combustion accelerator, and the air ratio on the combustion accelerator inlet side is set lower than the air ratio on the combustion accelerator outlet side, thereby reducing NO. And the amount of N ₂ O generated can be reduced.
[0006]
The invention of claim 2, wherein the above the fluidized bed waste is turned on, the waste fluidized bed type incinerator combustion gas product or the like is provided with a freeboard zone being re-combustion, the flow A temperature rising burner is disposed above the bed, and a second temperature rising burner is further disposed above the layer at the furnace wall facing the secondary air introduction nozzle. The secondary air introduction nozzle and the second temperature increase burner configure the combustion promotion body in combination, an oxygen concentration in the combustion promotion body inlet side of the heated burner, characterized by being set lower than the oxygen concentration of the combustion promotion body outlet.
A combination of the secondary air introduction nozzle and the second temperature raising burner constitutes a combustion accelerator, and the oxygen concentration on the combustion accelerator inlet side is set lower than the oxygen concentration on the combustion accelerator outlet side, thereby reducing NO. And the amount of N ₂ O generated can be reduced.
[0007]
[0008]
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention.
FIG. 1 shows a fluidized bed combustion apparatus according to a first embodiment of the present invention, in which 1 is a fluidized bed combustion furnace, 2 is a pushing fan, 3 is an air heater, and the air heated by the air heater 3 flows as primary air. It is introduced into the fluidized bed 11 from the bottom of the layer 11. A part of the heated air is introduced as secondary air from the secondary air introduction nozzle 12.
[0010]
Reference numeral 4 denotes a sewage sludge charging pump, which is charged with sludge into the heated fluidized bed 11.
Reference numeral 5 denotes a temperature rising burner. A combustion flame generated by a combustible gas such as LPG or LNG heats the space on the inlet side of the combustion promoting body 6 from the temperature rising burner 5 positioned above the fluidized bed 11 and air in the space A The ratio is reduced, in other words, the oxygen concentration is reduced.
Above the combustion promoting body 6, a free board region B is formed in which combustion gas products (pyrolysis gas) are reburned by secondary air.
[0011]
The exhaust gas discharged from the fluidized bed combustion furnace 1 is discharged to the atmosphere through the induction fan 9 and the chimney 10 after removing fly ash and air pollutants through the gas cooler 7, the cyclone 8 and the like. This point is well known.
[0012]
FIG. 2 shows a radiation converter 20 composed of an assembly of a large number of ceramic tubes 21 such as Al2O3, which comprises the ceramic tube 21 and a frame plate 22 for fixing the ceramic tube 21, and the adjacent space 23 between the ceramic tubes 21 is heated. When the combustion gas product or the like (pyrolysis gas) passes, the ceramic tube 21 can be heated to form a radiation converter having a radiation rate of about 80%.
Such a radiation converter 20 is used as the combustion accelerator 6.
[0013]
Next, the operation based on the embodiment will be described.
In the generation of N ₂ O and NO, intermediate products such as HCN and NH ₃ produced from waste nitrogen content play a major role. N ₂ O is produced mainly by HCN, and is produced by the reaction (1) of NCO formed by oxidizing HCN with NO.
Looking at the relationship with temperature, the N ₂ O emission temperature strongly depends on the combustion temperature, and shows a maximum value at 730 to 830 ° C. In this higher temperatures field (2), (3) for the conversion reaction to NO in the NCO is faster than the conversion reaction to _{N 2} O of (1) a, _{N 2} O decreases with increasing temperature. In addition, in a high temperature field of 1230 ° C. or higher, the N ₂ O generation suppression reaction of (4) and the decomposition reactions of (5) and (6) by H and OH radicals exceed the generation reaction, and N ₂ O generation is further suppressed. However, on the other hand, thermal NOx significantly increases.
[0014]
NCO + NO → N ₂ O + CO (1)
NCO + O → NO + CO (2)
NCO + OH → NO + CO + H (3)
NCO + H → NH + CO (4)
N ₂ O + H → N ₂ + OH (5)
N ₂ O + OH → N ₂ + HO ₂ (6)
[0015]
Further, when the relationship between the combustion temperature and NO and N ₂ O is summarized, as shown in FIG. 4, both tend to decrease as the combustion temperature rises.
In the prior art, it is said that the NO generation amount increases and the N ₂ O generation amount decreases as the combustion temperature increases, but in this test result, the NO generation amount increases as the combustion temperature increases. The trend was the opposite of the previous finding that it was reduced.
[0016]
That is, RUN1 in FIG. 4 burns in a state where neither the temperature raising burner nor the combustion promoting body 6 (radiation converter 20) is provided, and RUN2 burns in the state in which only the combustion promoting body 6 (radiation converter 20) is provided. RUN3 is an embodiment of the present invention, and shows a combustion in a state where a temperature raising burner and a combustion accelerator (radiation converter) are provided, and FIG. 4 shows an average value of the upper surface of the fluidized bed and the inlet temperature of the combustor. it is a graph showing the relationship between the concentration of NO and N _{2 O} and.
As is apparent from this figure, RUN3 has a combustion average temperature of 880 ° C. to 970 ° C. that is 100 ° C. or more higher than RUN1, and both NO and N ₂ O are reduced in proportion to this.
[0017]
On the other hand, the air ratio from the upper surface of the fluidized bed to the inlet of the combustion promoting body and the test results on the relationship between NO and N2O are summarized in FIG.
As is apparent from this figure, RUN3 is RUN1 or air ratio is reduced from 1.3-1.4 to 1.0-1.1 from RUN2, proportional both of NO and _{N 2} O by reduction to is doing.
In addition, the free board area B on the outlet side of the combustion promoting body 5 has a high air ratio due to the introduction of secondary air, whereby the air ratio of the space A on the inlet side of the combustion promoting body 6 from the temperature raising burner 5 is changed to the combustion promoting body 6. It is set lower than the air ratio of the free board area B on the outlet side, in other words, the temperature rising burner 5 is disposed above the fluidized bed 11 and the combustion promoting body 6 is further disposed above the fluidized bed 11. By setting the oxygen concentration in the body A inlet side space A to be lower than the oxygen concentration on the outlet side of the combustion promoting body 6, both NO and N ₂ O generation amounts are reduced.
[0018]
FIG. 6 shows a state in which NO and N ₂ O are reduced in RUN 3 (promoter + burner) based on FIGS. 4 and 5.
Therefore, according to the present embodiment, N ₂ O is reduced by the increase in the combustion temperature by the temperature raising burner 5, and the air ratio of the fluidized bed portion to the combustion promoting body inlet side space A is set from the free board area B on the outlet side. by setting a low, FuelNOx is reduced, because the NO be _{N 2} O is reduced as a result. Although the combustion temperature is increased by the temperature raising burner 5, the thermal NOx does not increase, and the carbon dioxide concentration, the dioxin concentration, and the ammonia concentration are all significantly lower than the RUN1 of the prior art in the RUN3 of this embodiment. It was confirmed that
[0019]
3 shows another embodiment in which a combustion burner (second temperature raising burner 25) is used instead of the radiation converter 20 shown in FIG. 1, and the furnace wall position facing the secondary air introduction nozzle 12 is shown. A second temperature raising burner 25 is arranged, and a combination of the secondary air introduction nozzle 12 and the combustion burner 25 constitutes a combustion accelerator.
This embodiment can also obtain the same effect as the above embodiment.
[0020]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a waste fluidized bed incinerator capable of simultaneously reducing both N ₂ O and NO without causing a decrease in combustion efficiency and desulfurization efficiency.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a fluidized bed combustion apparatus according to a first embodiment of the present invention.
FIGS. 2A and 2B are a front view and a plan view showing a radiation converter made of an assembly of a large number of ceramic tubes such as Al 2 O 3.
FIG. 3 is a schematic view showing a fluidized bed combustion apparatus according to a second embodiment of the present invention.
FIG. 4 is a graph showing the relationship between the average value of the upper surface of the fluidized bed, the combustion body inlet temperature, and the concentrations of NO and N ₂ O.
FIG. 5 is a graph summarizing test results on the relationship between the air ratio and NO and N ₂ O from the upper surface of the fluidized bed to the combustion promoting body inlet.
FIG. 6 is a graph showing a state in which NO and N ₂ O are reduced in this example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fluidized bed type combustion furnace 2 Push-in fan 3 Air heater 4 Sewage sludge injection pump 5 Temperature rising burner 6 Combustion promoting body 11 Fluidized bed 12 Secondary air introduction nozzle 25 Second temperature rising burner (combustion burner)
A Space from the temperature rising burner to the combustion accelerator inlet side b Free board area

Claims (2)

In a waste fluidized bed type incinerator having a freeboard area where combustion gas products etc. are reburned above a fluidized bed into which waste is charged,
A temperature raising burner is disposed above the fluidized bed, and a second temperature raising burner is disposed above the fluidized bed at a furnace wall position facing the secondary air introduction nozzle. The secondary air introduction nozzle and the second temperature rise Combustion accelerators are composed of a combination of burners, areas with different air ratios are formed across the combustion accelerators, and the air ratio on the combustion accelerator inlet side of the temperature rising burner is lower than the air ratio on the combustion accelerator outlet side A waste fluidized bed incinerator characterized by having been set up. In a waste fluidized bed type incinerator having a freeboard area where combustion gas products etc. are reburned above a fluidized bed into which waste is charged,
A temperature raising burner is disposed above the fluidized bed, and a second temperature raising burner is disposed above the fluidized bed at a furnace wall position facing the secondary air introduction nozzle. The secondary air introduction nozzle and the second temperature rise configure the combustion promotion body in combination burner, waste fluidized bed incinerator, characterized in that the oxygen concentration in the combustion promotion body inlet side of the heated burner, is set lower than the oxygen concentration of the combustion promotion body outlet.

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