Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of removing sul~ur
and nitrogen oxides by dry process and more particularly,
it is concerned with a method for the separation of sulfur
and nitrogen oxides from a waste gas using a carbonaceous
adsorbent to which ammonia is added.
The accompanying drawings are to illustrate the
principle and merits of the present invention in more detail:
Fig. 1 and Fig. 2 are schematic views of the prior
art systems of adding ammonia.
Fig. 3 and Fig. 4 are schematic views of the systems
of addin~ ~mmon;a according to the present invention.
Fig. 5 and Fig. 6 are gxaphs showing the change of
pressuxe loss of a waste gas passing through a moving bed
with the passage of time respectivel~ in the case of the
prior art and the present invention.
2. Description of the Prior Art
A method of removing sulfur and nitrogen oxides by
2D dry process has been known wherein a waste gas is passed
through a moving bed formed of a carbonaceous adsorbent to
remove sulfur oxides in the waste gas, while ammonia is addea
to remove nitrogen oxides. In this case, ammonia gas alone
or diluted with another suitable gas is added to a duct of
the waste gas before the moving bed as shown in Fig. 1.
Referring to Fig. 1, waste gas 1 and ammonia gas or an
ammonia-cont~in;ng gas 3 fed by means of ammonia mixing
device 6 are brought into contact with moving bed 4 consisting
of carbonaceous adsorbent 2 in a transverse direction.
However, this prior art method has the disadvantage that
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1 ammonia sul~ate or ammonium hydrogensulfate is formed,
cleposited and grown in a waste gas flue and inlet por-tion formed
of a louver or perforated plate to the moving bed and the
passage area of waste gas is thus reduced to increase the
pressure loss o~ waste gas, to cause a deflection of waste
gas and to lower the removal efficiency of sulfur and
nitrogen oxides.
The temperature of a waste gas to be processed in an
apparatus for removing sulfur and nitrogen oxides by dry
process is generally within a range of room temperature to
180C. In this temperature range, the reaction'of ammonia
and sulfur oxides precedes that of ammonia and nitrogen
oxides, so in the prior art method wherein a single moving '
bed is used and ammonia is added to a waste gas before flowing
in the moving bed, disadvantages are unavoidable that a
large removal efficiency of nitrogen oxides cannot be given
; and the consumption of ammonia is markedly increased. In
order to overcome this disadvantage, there has been proposed
a method wherein in a system comprising two moving beds 'l
and 5 of carbonaceous adsorbent 2'as shown in Fig. 2, waste
gas l is passed through first moving bed 4 with adding a
small amount of ammonia 3' or without adding ammonia before
first moving bed 4, in which desulfurization is mainly carried
out by the adsorption action of the carbonaceous adsorbent,
the waste gas passing through first moving bed 4 is then
mixed with ammonia 3 and passed through second moving bed 5
in which denitrification is mainly carried out. This method
needs two moving beds resulting in increase of the,
installation cost.
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SU~M~RY OF THE INVENTION
It is an object of the presen-t invention to provide a
method of removing sulfur and nitrogen oxides by dry process
whereby the above described disadvantages are overcome.
It is another object of the present invention to
provide an improved method oE adding ammonia to a system wherein
removal of sulfur and nitrogen oxides is carried out using a
carbonaceous adsorbent.
These objects can be attained by a method of removing
sulfur oxides and nitrogen oxides by dry process wherein a
waste gas containing sulfur and nitrogen oxides is passed
through a moving bed formed of a carbonaceous adsorbent and
nitrogen oxides are removed by the reducing action of ammonia
simultaneously with sulfur oxides, characterized in that
ammonia is directly added to the moving bed of the carbon-
aceous adsorbe~t.
DETAILED DESCRIPTION OF THE INVENTION
The inventors have made ef~orts to overcome the above
described disadvantages of the prior art and consequently,
have found that this object can be accomplished by adding
ammonia directly to a moving bed of carbonaceous adsorbent.
That is to say, in accordance with the present inven-
tion, there is provided a method of removing sulur oxides and
nitrogen oxides by dry process wherein a waste gas containing
sulfur and nitrogen oxides is passed through a moving bed
formed of a carbonaceous adsorbent and nitrogen oxides are
removed by the reducing action of ammonia simultaneously with
sulfur oxides, characterized in that ammonia is directly added
to the moving bed of the carbonaceous adsorbent.
Useful examples of the carbonaceous adsorbent are
!
,
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l activatecl carborls ac-tivated cokes, semi-cokes and the like
wllich are co~monl used, and -the ar~monia is used in tne fol~m
of am~onia gas alone or diluted wi-t~ another sllitable gas~
~lle moving bed is ordinaril-~ held at a tempera-ture of from
oom temperature to 180 ~.
hig. ~ shows one embodiment of the present invention,
in which ammonia gas or diluted ammonia ~as 3 is directly
fed to mOVillg bed 4 formed of carbonaceous adsorbent 2 via
ammonia dispersing device 7 provided in the interior of
moving bed 4, while a waste gas 1 is passed through moving
bed 4 in such a ma~ner as to be -transversely contacted with
carbonaceous adsorbent 2.
According to the method of t-he p:esent invention 7
ammonia is directlr added to a moving bed of carbonaceous
adsorbent, so ammonium sulfate or ammonium h-rdrogensulfate
is formed on only the moving carbonaceous adsorben-t and
continuously discharged therefrom. ~hereforej clogging of
a flue and a perforated plate or louver at the inlet part
of a moving bed due to formation, dopsition and growth of
~0 ammonium sulfate or ammonium hydrogensulfate can effective
ly be avoided, thus decreasing remarkably the pressure loss
of a waste gas, preventing a waste gas flow from deflection
and holdin~ uniform for a long time.
Fig. 4 shows another embodiment OI the presen-t inven-
tion, in which a plurality of ammonia dispersing devices 7
and 7' are provided in a single moving bed to feed ammonia
dividedl~J. In this embodiment, substantially the same effects
can be obtained as in the case o~ providing a plurality of
moving beds and the removal efficienc7 of nitrogen oxides
can be increased with a decreased consumption of ammonia by
the use of a simple apparatus. ~hat is, the installa-tion
cost and operation cost of this appara-tus can rnarkedly be
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decreased.
Of course, the direct addition or Leed of ammonia
accordinG to the present invention is no-t limited to the
case of using a single moving bedO
The present invention ~Jill be explained in detail
with re~erence to the following examples. It will be obvi-
ous to -those skill in the art that various changes and
modi~ications can be made in the components~ ratios, opera-
tional order and the like wi-thout departing from the spirit
of the present invention. Therefore, the present invention
should not be construed as being limited to the following
examples.
~xample 1
A waste gas from combustion of fuel oil cont~inin~
860 ppm of S02 and 170 ppm of N0x was transversel~ passed at
a temperature of 155 C and a flow rate of 1000 Nm3/H through
a moving bed of granular activated carbon downwardly moved
at a rate of 40 1/H. Ammonia was diluted with the waste
gas after passed through the moving bed and directly intro-
duced into -the moving bed through a gas dispersing device
provided just behind a louver at the waste gas inlet side.
The quantitv of ammonia added was 0O43 i~m3/H. The pressure
loss of the waste gas in the moving bed was hardly changed
with the passage o~ time as shown in ~ig. 6~ The concentra-
tion of S02 in tne waste gas at the outlet of the moving bed
after 100 hours was 80 ppm and that of M0x was 90 ppm.
~omparative Exam~le 1
The procedure o~ ~xample 1 was repeated except ~ing
ammonia to a waste gas duct be~ore the moving bed. The
pressure loss of the waste gas in the moving bed ~ras changed
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1 with -the passa~e of time as shown in ~igJ 5. The pressure
loss was g,aduall~- increased and amounted to 235 mmAq al~ter
16~ hollrs. ~he concentration of S02 in the ~las-te gas at
the outlet of the moving bed alter 100 hours was 91 ppm and
that o~ M0x was 100 ppM.
Example 2
A ~aste gas from combustion OI fuel oil containing
9 ppm of S02 and 300 ppm of N0~ was transversely passed at
a temperature ol 155 C and a ~lo~r rate of 1000 Nm3/E through
a moving bed o~ activated ~ormed coke do~mwardly moved at a
ra-te o~ 80 1/H. Ammonia was diluted with the waste gas af-ter
passed through the moving bed and dividedly introduced into
the moving bed at a rate of 0.18 Nm3/E to the inlet portion
of -the moving bed and at a rate of 0~27 Nm3/H to the middle
portion ol the moving bed~ ~he concentration of S02 in the
waste gas after passed through the moving bed was 0-2 ppm
and that o~ N0x was 63 ppm.
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