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Dr. Hubert Baier General Manager - Europe
Building Capacities for the
Improvement of the Air Quality
NOx – Abatement Lima, 22.06.2016
For clarification
It is mandatory to know the sources and options of
prevention of man made and ground based emissions
which effect human health and environment directly.
2
Process Emission of NOx
NO
x-E
mis
sio
n
Temperature
molten glass
Melting boiler
CFB with De-NOx
Dry bottom furnace
Cement Kiln with De-NOx
Formation of NOx
Nitrogen source Reaction partner Mechanism of
formation
N2 from air Exhaust gas thermal NOx
|N≡N|
N2 + O ↔ NO + N
N + O2 ↔ NO + O
„Zeldovich-Mechanism“
strongly related to
temperatures >1.250°C
prompt NOx
Flame front Fast formation reaction;
little relation to
temperature
Nx from fuel fuel NOx
i.e. pyridin from oil C5H5N N2 + CH ↔ N + HCN
HCN → NHx + Ox ↔ NOx
Fast reaction >800°C;
without correlation to the
temperature
4
Burning carbon based fuels
(coal, lignite, oil or solid
alternative fuel) results in
radiant heat for the
clinkerization process
C(s) + O2 (g) → CO2(g)
ΔHo= -393 kJ/mol
T=25°C
Flames in a combustion process
Source: PROCESS // Optimization - ZKG 02 2012
Simplified Kinetics of the Combustion
Measures to reduce NOx emissions
Primary measures are usually correspond with reduction for the
NOx formation influencing factors:
- Combustion temperature
- Oxygen supply (i.e. fuel-air ratio)
- Dwell time
- Temperature profile
(as higher T in on
the first level, as better
the reduction)
- Quantity of volatiles (only
highly volatile lignite
achieves an emission
level <200 mg/Nm3)
7
Measures to reduce NOx emissions
Primary measures - in the combustion chamber
8
1 Combustion Chamber
2 Main burner zone
3 NOx-reduction
4 after burner
5 flue gas
6 air-coal mix injection
7 coal-air mix injection
8 air injection
9 coal-flue gas mix
10 flue gas recyculation
11 flue gas outlet to cleaning
Measures to reduce NOx emissions
Secondary measures
9
Scrubber
Process
Deposition designation reactant Reaction
conditions
product Advantage/
dis-
advantage
Dry
NOx SNCR NH3 900-1000°C H2O, N2 Well
established,
waste free
NOx SCR NH3 300-450°C H2O, N2 Well
established,
waste free
SO2, NOx Electron
beam
NH3 50-100°C Fertilizer Not proven
under real
conditions
wet
SO2, NOx Walther O3, NH3 40-50°C Fertilizer No sales of
final product
SO2, NOx Saarberg-
Hölter-Lurgi
FeII-EDTA 40-50°C N2, gypsum Not proven
under real
conditions
Measures to reduce NOx emissions
Secondary measures are always applied in reduction of already
formed NOx to elemental nitrogen. Until only two principles are
established under daily conditions
SNCR ("selective non catalytic reduction")
reacting with urea or Ammonia:
4NO + 4NH3 + O2 → 4N2 + 6H2O + heat
2NO + (NH2)2CO + ½ O2 → 2N2 + 2H2O + CO2 + heat
Disadvantage:
- NOx-reduction potential 50%
- Ammonia slip
- Requires the exact
reaction temperature/
best reaction temperature
at ~950°C
10
Credit: SandeNOx
Measures to reduce NOx emissions
Secondary measures are always applied in reduction of already
formed NOx to elemental nitrogen. Until only two principles are
established under daily conditions
SCR ("selective catalytic reduction")
reacting with Ammonia and a catalyst:
4NO + 4NH3 + O2 → cat. → 4N2 + 6 H2O + heat
2NO + 4NH3 + O2 → cat. → 3N2 + 6 H2O + heat
- High reduction efficiency (90%)
- No Ammonia slip
Disadvantage:
- SOx + O2 → 2SO3
- NH3 + SO3 + H2O → NH4HSO4 (sticky salt)
- 2NH3 + 2SO3 + H2O + ½ O2 → 2NH4SO4 (sticky salt)
- Catalysts sensitive against temperature fluctuation > 370°C
11
Measures to reduce NOx emissions
12
Hybrid SNCR/ SCR system from REDECAM© for power plants
Measures to reduce NOx emissions
13
Staged Combustion
In this NOx reducing method, only a portion of the fuel is burned in
the main chamber. All of the fuel is eventually burned, producing
the same amount of energy, but this method greatly reduces the
temperature in the main chamber. As temperatures decreased, the
amount of thermal NOx is reduced.
Catalytic Converters
These devices are utilized to lower the toxicity of the emissions of
many combustion processes such as stationary engines, boilers,
heaters and internal combustion engines. Catalytic converters
break down nitrogen oxides into separate nitrogen and oxygen
particles. Some catalytic converters are also used to reduce the
high CO levels produced when reducing NOx, as low CO levels
are important to ensuring complete combustion.
Measures to reduce NOx emissions
14
Flue Gas Recirculation
Flue Gas Recirculation, FGR, is a method of NOx reduction that
lowers the temperature of the flame, and therefore reduces
thermal NOx. A portion of the exhaust gas is re-circulated into the
combustion process, cooling the area. This process may be either
external or induced, depending on the method used to move the
exhaust gas. Flue Gas Recirculation may also minimize CO levels
while reducing NOx levels.
Reducing O2 levels
By reducing the amount of O2 that is available to react with the
nitrogen, NOx is reduced. This is achieved through the use of
oxygen trim controls. To minimize the O2levels, a combustion
analyzer is used to adjust the fuel and air mixture. This method
can reduce the level of NOx produced by up to 10%, but it may
increase the emissions of Carbon Monoxide (CO) very
significantly. This method is widely used in many processes such
as in rich burn engines.
Measures to reduce NOx emissions
15
Flue Gas Recirculation
Flue Gas Recirculation, FGR, is a method of NOx reduction that
lowers the temperature of the flame, and therefore reduces
thermal NOx. A portion of the exhaust gas is re-circulated into the
combustion process, cooling the area. This process may be either
external or induced, depending on the method used to move the
exhaust gas. Flue Gas Recirculation may also minimize CO levels
while reducing NOx levels.
Reducing O2 levels
By reducing the amount of O2 that is available to react with the
nitrogen, NOx is reduced. This is achieved through the use of
oxygen trim controls. To minimize the O2levels, a combustion
analyzer is used to adjust the fuel and air mixture. This method
can reduce the level of NOx produced by up to 10%, but it may
increase the emissions of Carbon Monoxide (CO) very
significantly. This method is widely used in many processes such
as in rich burn engines.
Measures to reduce NOx emissions
16
Low NOx Burners
By changing the shape and formation of the flame by using plates
to control airflow, a more elongated flame is created in the burner.
The temperature is decreased due to the extended flame and
surface area, and the lower temperature reduces the amount of
thermal NOx. CO levels may be elevated when using low
NOx burners. It is important to monitor CO and True NOx levels to
better control Low NOx burners.
Low Nitrogen Fuel Oil
The use of low nitrogen oils, which can contain up to 15-20 times
less fuel bound nitrogen than standard No. 2 oil, can greatly
reduce NOx emissions as fuel bound nitrogen can contribute
anywhere between 20-50% of total NOx levels.
Measures to reduce NOx emissions
17
Water/Steam Injection
Water or steam injection reduces the amount of NOx produced by
lowering the temperature of the flame during combustion. The
lower temperature allows for the decrease of thermal NOx.This
method can result in an increase of 3-10% boiler efficiency losses
and excess amounts of condensation may form.Some advanced
designs of steam injection technology do not have significant
impact on boiler efficiency.
Measures to reduce NOx emissions
18
SCR (Selective Catalytic Reduction)
SCR is a process where a reductant, most often ammonia, is
added to the flue. The reductant then reacts with the NOx in the
emissions and forms H2O and N2 (ambient nitrogen). This
process may take place at anywhere between 500°F and 1200°F
depending on the catalyst used. SCR may reduce NOx emissions
by up to 90%. SCRs are mainly used in large industrial and utility
boilers.
SNCR (Selective non-catalytic Reduction)
SNCR is a process that involves a reductant, usually urea, being
added to the top of the furnace and going through a very long
reaction at approximately 1400-1600 °F. This method is more
difficult to apply to boilers due to the specific temperature needs,
but it can reduce NOx emissions by 70%.
Costs of NOx reduction in German power plants
19
Primary
measures
NOx
Reduction %
CAPEX
€/kWel
€ct./kWh
Low NOx-Burner 30-50 10-15 0.035-0.045
Air staging
combustion 50 5-20 0.03-0.05
SNCR 50 5-30 0.05-0.13
SCR 70-90 50-80 0.15-0.25
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