Environmental Engineering Reference
In-Depth Information
remove simultaneously NO
x
, SO
x
, and particulate matters by ejecting a mixture of
CaO, NaHCO
3
, and NH
3
into the upstream flue gas. This multi-pollutants removal
technology is rather complicated and less economical, thereby being applied
seldom in real furnaces.
CuO/Al
2
O
3
oxidization and adsorption combined with SCR/SNCR
[69]
.
Both the desulfurization and denitration reactions of this technique occur in a
same unit. The highlight lies in the feature that a -Al
2
O
3
sorbent impregnated
with CuO is used in the desulfurization process. At temperatures ranging from
300 - 500 °C, the sorbent reacts with SO
2
to produce CuSO
4
. Assisted by the
CuSO
4
catalysis, NO
x
can be reduced by NH
3
ejection. To maintain a recycled
process, CuO is finally regenerated by deoxidizing CuSO
4
with some reductive
gas such as H
2
and CH
4
and the enriched SO
2
product is collected. Apparently, the
key point of this technique lies on the high-performance adsorbent preparation.
Since 1960s, only a related study from Pittsburg Energy Technology Center has
reported a series of test results constructed a small-scale industrial demonstration
unit. However, no industrial application has been reported because of its
quickly-decreasing sulfur absorption capability after regeneration, poor
anti-poison performance, and absorbent abrasion with fly ash.
Precious metal catalytic combined with SCR/SNCR
. A so-called SNO
x
technology
[70-75]
belongs to this category. Firstly, fuel gas is heated up to 405 °C
and then sent into the SCR unit for reducing NO
x
into N
2
through NH
3
-based
reactions. Thereafter, the flue gas passes through the second reactor where the
contained SO
2
transforms into SO
3
through catalytic oxidation, SO
2
will be
converted into SO
3
. Finally, the flue gas is cooled down by a heat exchanger
before passing through a wet scrubber to remove SO
3
. Another example is the
SNO
x
TM
technology of ABB Company, in which dual-bed catalytic reactors are
used to oxidize SO
2
and reduce NO
x
so as to accomplish deSO
x
and deNO
x
simultaneously. Moreover, the DESONO
x
technology developed in a German
company, can simultaneously remove SO
2
, NO
x
, CO, and unburned hydrocarbons
at temperatures ranging from 400 - 460 °C. All pollutants in flue gas except NO
x
are all disposed through oxidization reactions with precious metals catalysts. That
is, CO and unburned hydrocarbons are converted into CO
2
and water, and SO
2
is
oxidized into SO
3
before changing to sulfate. It should be noted that precious
metal catalysts cannot be absent in both the SNO
x
TM
and DESONO
x
technologies
when converting SO
2
and NO
x
into SO
3
and NO
2
, respectively
.
These
circumstances necessitate high investment and operation cost. Again, in
Search WWH ::
Custom Search