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Ammonia measurement
challenges in SCR units
CEM-2014, 16.5.2014
Olli Antson, Kati Lehtoranta
VTT Technical Research Centre of Finland
Engines and Emissions team
221/05/2014 2
Ammonia measurement challenges in SCR units
Contents
Focus of the team´s research
Emission regulation in marine engines
SCR unit in emission reduction
Case examples on NH3 measurements
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Focus of the team´s research
High speed
enginesMedium speed
engines
Emission
measurement
421/05/2014 4
Emission Regulation in marine engines by IMO
It is well known that ship emissions contribute significantly to global emissions and to
local emissions at ports.
The regulation by International Maritime Organization (IMO) includes rules to decrease
emissions of sulphur compounds and nitrogen oxides. There is regulation also on
energy efficiency of ships which includes greenhouse gas emissions, and regulation on
VOC emissions.
These rules gradually set the maximum allowed sulphur percentage in fuel to 0.5%
globally by the year 2020, and to 0.1 % in specific emission control areas by the year
2015. Ships can also comply with these rules by installing an after-treatment system for
SOx removal.
Also NOx emissions are restricted gradually in marine diesel engines and the limits
referred as Tier I, II and III are given as specific emissions (g/kWh) based on the
maximum operating speed of the engine.
The current Tier II standard can be met by optimization of combustion process, but Tier
III standards which are planned to come into force in 2016 (postponed to 2021) are
expected to require an after-treatment unit for emission control.
The tight requirements set by IMO Tier III can be met by utilizing SCR technology
(Selective Catalytic Reduction).
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SCR – Selective Catalytic Reduction
Urea decomposition:
(NH2)2CO -->NH3 + HNCO
HNCO + H2O --> NH3 + CO2
Main NOx reduction reaction in SCR:
4NO + 4NH3 + O2 → 4N2 + 6H2O
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Case examples on NH3 measurements
Case 1: FTIR and impinger sampling (at VTT’s medium speed engine
laboratory)
Case 2: FTIR and in-situ laser method (at a customer´s medium speed
engine)
Case 3: FTIR and diode laser method (a gas engine equipped with a side-
flow SCR unit, at a customer´s SCR installation)
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Case 1: FTIR and impinger sampling at VTT’s medium
speed engine laboratory
Engine: Wärtsilä Vasa 4R32,1640 kW.
Fuel: HFO with 2.4% S
SCR: Extruded honeycomb with 35 cpsi, volume 40,5 dm3, V2O5 catalyst
Exhaust gas: 500 kg/h, temperature 260-340 °C
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Case 1: FTIR and impinger sampling at VTT’s medium
speed engine laboratory
Test SCR operation:
Measured NOx efficiency at exhaust T 260-340 °C
When temperature decreases
NOx efficiency decreases –
and ammonia slip formation
enhances (while keeping urea
dosing constant)
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FTIR sampling
FTIR
N2
Heated probe and sampling line,
Zero gas
Exhaust
gas
~ 3
00°C
Heated filter and pump
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Impinger sampling
Sample from hot exhaust gas
through a steel tube, sample flow
1,5-2 l/min, bubbled through 50 or
20 ml of water (in ice bath) with a
sampling time of 30-40 min.
Exhaust
gas
~ 3
00°C
Steel tube 200°C
P
0°CH2O
Exhaust
gas
~ 3
00°C
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FTIR and impinger sampling - Results
Results from 4 different cases,
FTIR as an average of the impinger
sampling time (error bars show the
measurement uncertainty)
→ Results at same level, or
FTIR gave lower values for these
extractive methods
Note. The impinger sampling in water
– all ammonia probably not measured
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Case 2: FTIR and in-situ laser method
Engine: Medium speed diesel engine
Fuel: HFO and LFO (Sulphur contents: HFO ~ 2.4%, LFO <0.05%)
SCR: V2O5 based catalyst
Ammonia slip measurement with FTIR and in-situ laser
FTIR 1
N2
Heated probe and sampling line,
Zero gas
Exhaust
gas
~ 3
00°C
Heated filter and pump
In-situ laser
FTIR 2
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FTIR and in-situ laser method – Results (LFO)
→ Similar ammonia
results with both
methods
(2 FTIR units were
utilized)
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FTIR and in-situ laser method – Results (HFO)
→ With FTIR clearly
lower ammonia values
are recorded
→ Sulphur related
reactions cause
interference to ammonia
measurement with FTIR
(extractive sampling)
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Case 3: FTIR vs. diode laser measurement
A gas engine equipped with a side-flow SCR unit.
The actual target of this field campaign was to compare different catalyst setups by
varying exhaust flow and urea feed, but it was also possible to compare the NH3 results
with different measurement methods.
This SCR unit contains several sampling points for extractive sampling.
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Case 3: FTIR vs. diode laser measurement
There is a systematic difference between the NH3 results. During a two week campaign
the laser device gave 15-30% larger values than FTIR instrument. A reason for these
differences could not be found.
The laser device was operated by using factory settings for NH3 analysis.
The calibration of FTIR instrument was carried out at laboratory before the measurement
period with reference gases (NH3 in N2). During the field measurements only zero gas
was tested daily.
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Ammonia measurement challenges in SCR units
Results
• Sampling line problems: gas phase reactions, sulphur related reactions
cause interference to ammonia measurement when sampling is
required (like for FTIR measurement)
→ Significant especially when using fuels with high sulphur
contents: measured NH3 slip levels are lower than actual levels
• Unresolved deviations between FTIR and laser instrument
Further developments
- Total sample collection and in-situ laser measurement
- Extractive sampling
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