Fluidized bed incinerator and combustion method in which...

Details Fluidized bed incinerator and combustion method in which... Fluidized bed incinerator and combustion method in which...

2001-12-05

2004-09-14

Rinehart, Kenneth (Department: 3749)

Furnaces

Process

Treating fuel constituent or combustion product

C110S208000, C110S210000, C110S243000

Reexamination Certificate

active

06789487

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluidized bed incinerator, and more particularly, to a fluidized bed incinerator and a combustion method in which generation of NO
x
, CO and dioxine can be suppressed at the same time.
2. Description of the Related Art
Exhaust gas such as NO
x
, CO, and dioxine are generally prescribed as regulation object materials about environmental quality. These materials can be decreased by providing a post processing apparatus to an incinerator. However, it is desirable from the viewpoint of the cost reduction in the manufacture, operation and maintenance of the incinerator to suppress the generation of these materials in the incinerator.
As one of the suppressing techniques of the NO
x
generation in combustion, a conventional technique is known in which air for the combustion is supplied to 2 steps. In the first step, an air surplus rate of supplied air is set to in a range of 0.8 to 0.9. In the second step, air is supplied to supplement a lack of air, resulting in complete combustion in the whole system. In this technique, the increase of flame temperature and the appearance of a local high temperature region are prevented by restraining rapid combustion reaction, and the generation of NO
x
is suppressed through the decrease of an oxygen quantity. In this technique, however, it is easy for incomplete combustion and unstable combustion to be caused, and they must be careful of the generation of non-combusted components such as CO. Therefore, this technique needs to be used together with another exhaust gas processing technique.
FIG. 1
is a diagram showing the structure of another conventional fluidized bed incinerator disclosed in Japanese Patent No. 2,637,449. The conventional fluidized bed incinerator will be described with reference to FIG.
1
. The fluidized bed incinerator is composed of a combustion furnace
113
, a cyclone
117
, and a hopper
118
. The combustion furnace
113
is composed of a first air supply port
101
, a second air supply port
102
, a furnace output port
105
, a fuel input port
110
, a heat transferring section
111
, and a convectional heat transferring section
112
.
In the bottom of the combustion furnace
113
, fluidized material such as sand and fuel such as coal and sludge supplied from the fuel input port
110
are mixed and fluidized by air supplied from the first air supply port provided at the bottom to form a bed section
106
as a fluidized bed. Thus, combustion is carried out in the bed section
106
. The temperature of the bed section
106
is controlled by flowing water or steam to the heat transfer pipe
111
provided in the bed section
106
. Also, the convectional heat transferring section
112
is provided in the free board B
108
as a combustion region above the bed section
106
to collect thermal energy of the exhaust gas by flowing water or steam in the convectional heat transferring section
112
. For purposes of suppression of the generation of NO
x
and CO, the second air is supplied from the second air supply port
102
. Generally, the bed section
106
is operated in the condition that an air rate of the first air quantity to a theoretical air quantity is 1.0 for the suppression of the generation of CO. The reason is as follows. That is, the temperature of a free board section A
107
is as low as 500 to 700° C. because the combustion in the fluidized bed is carried out at the temperature of 800 to 900° C. and the second air supply port
102
is provided above the bed section
106
. When the fuel is combusted in the air rate of 1.0 or below in the bed section
106
, a lot of CO is generated. The complete combustion cannot be carried out even if the second air is supplied. As a result, a part of CO is exhausted from the furnace output port
105
. Therefore, in the actual operation, the air rate of the first air quantity to theoretical air quantity in the bed section
106
can be reduced only to about 1.0. For this reason, the bed section
106
is not set to deoxidation atmosphere, so that the generation quantity of NO
x
increases (150-250 ppm (O
2
6% conversion)).
It should be noted that the cyclone
117
collects non-combusted ash in the exhaust gas. The hopper
118
stores the non-combusted ash. The stored the non-combusted ash is supplied to the bottom of the combustion furnace
113
as the fuel.
As described above, with the generation of the exhaust gas at the time of the combustion, it is not easy to achieve both of the suppression of generation of NO
x
and the suppression of generation of CO and dioxine kind at the same time. For the suppression of generation of NO
x
, it is necessary to realize a deoxidation atmosphere by decreasing an air surplus rate of a quantity of air supplied actually in the combustion to a quantity of air to be supplied for the complete combustion of fuel (theoretical air quantity). On the other hand, for the suppression of generation of CO and dioxine, it is necessary to realize an oxidation atmosphere by increasing the air surplus rate. That is, it is difficult to simultaneously suppress the generation of NO
x
, and the generation of CO and dioxine kind because of difference air surplus rates.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a fluidized bed incinerator and a combustion method in which the generation of NO
x
, CO, and dioxine can be suppressed at the same time.
In an aspect of the present invention, a fluidized bed incinerator having a combustion furnace includes first to fourth combustion sections. Fuel is supplied to the first combustion section and a combustion exhaust gas is exhausted after the fourth combustion section. First to fourth airs are supplied to the first to fourth combustion sections in first to fourth air surplus rates, respectively. The second air surplus rate is equal to or more than the first air surplus rate, the third air surplus rate is equal to or more than the second air surplus rate, and the fourth air surplus rate is equal to or more than the third air surplus rate.
Here, it is desirable that the first combustion section combusts the fuel in a first temperature range in deoxidation atmosphere by the first air, to suppress generation of NO
x
and dioxine. It is desirable that the second combustion section combusts a non-combusted component of the fuel in a second temperature range in the deoxidation atmosphere by the second air, to suppress the generation of NO
x
and dioxine and to dissolve NO
x
and dioxine generated in the first combustion section. It is desirable that the third combustion section combusts a non-combusted component of the fuel in a third temperature range by the third air, to suppress the generation of NO
x
and dioxine and to dissolve NO
x
and dioxine generated in the second combustion section, and a fourth combustion section carries out complete combustion of a non-combusted component of the fuel in a fourth temperature range in oxidization atmosphere by the fourth air, to suppress the generation of NO
x
and dioxine and to dissolve NO
x
and dioxine generated in the third combustion section. In this case, the first to third temperature ranges may be substantially the same, and may be a range of 800° C. to 900° C.
Also, the fourth temperature range may be equal to or lower than each of the first to third temperature range, and may be a range of 750° C. to 850° C.
Also, the first temperature range of the first combustion section may be controlled by a first temperature control section, and the fourth temperature range of the fourth combustion section may be controlled by a second temperature control section. On the other hand, the second and third temperature ranges of the second and third combustion sections may be controlled by changing the second and third air surplus rates, respectively.
Also, it is desirable that the first air surplus rate is in a range of 0.5 to 0.7, the second air surplus rate is in a range of 0.7 to 0.9, the third air surplus rate is in a range of 0.9 to 1.15, and the fourth ai

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