Ammonia measurement challenges in SCR units

Transcription

1 Ammonia measurement challenges in SCR units CEM-2014, Olli Antson, Kati Lehtoranta VTT Technical Research Centre of Finland Engines and Emissions team

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 NH 3 measurements 21/05/2014 2

3 Focus of the team s research High speed engines Medium speed engines Emission measurement 21/05/2014 3

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 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). 21/05/2014 4

5 SCR Selective Catalytic Reduction Urea decomposition: (NH 2 ) 2 CO -->NH 3 + HNCO HNCO + H 2 O --> NH 3 + CO 2 Main NOx reduction reaction in SCR: 4NO + 4NH 3 + O 2 4N 2 + 6H 2 O 21/05/2014 5

6 Case examples on NH 3 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 sideflow SCR unit, at a customer s SCR installation) 21/05/2014 6

7 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 dm 3, V 2 O 5 catalyst Exhaust gas: 500 kg/h, temperature C 21/05/2014 7

8 Case 1: FTIR and impinger sampling at VTT s medium speed engine laboratory Test SCR operation: Measured NOx efficiency at exhaust T C When temperature decreases NOx efficiency decreases and ammonia slip formation enhances (while keeping urea dosing constant) 21/05/2014 8

9 Exhaust gas ~ 300 C FTIR sampling Heated probe and sampling line, FTIR N 2 Heated filter and pump Zero gas 21/05/2014 9

10 Exhaust gas ~ 300 C Impinger sampling Steel tube 200 C 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 min. H 2 O 0 C P 21/05/

11 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 21/05/

12 Exhaust gas ~ 300 C 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: V 2 O 5 based catalyst Ammonia slip measurement with FTIR and in-situ laser In-situ laser Heated probe and sampling line, FTIR 1 FTIR 2 N 2 Heated filter and pump Zero gas 21/05/

13 FTIR and in-situ laser method Results (LFO) Similar ammonia results with both methods (2 FTIR units were utilized) 21/05/

14 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) 21/05/

15 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 NH 3 results with different measurement methods. This SCR unit contains several sampling points for extractive sampling. 21/05/

16 Case 3: FTIR vs. diode laser measurement There is a systematic difference between the NH 3 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 NH 3 analysis. The calibration of FTIR instrument was carried out at laboratory before the measurement period with reference gases (NH 3 in N 2 ). During the field measurements only zero gas was tested daily. 21/05/

17 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 NH 3 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 21/05/

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