High pressure conversion of NOx and Hg and their capture as aqueous condensates in a laboratory oxy-fuel compression system

Transcription

1 High pressure conversion of NOx and Hg and their capture as aqueous condensates in a laboratory oxy-fuel compression system Rohan Stanger*, Timothy Ting, Terry Wall University of Newcastle 3rd Oxyfuel Combustion Conference SPAIN 3/7/213

2 Introduction Research needed to reduce risk of corrosion in CO2 liquefaction Explore passive cleaning option during compression (ie low cost) Determine the extent of Hg/NOx conversion & capture under high pressure Undertaken in support of the Callide Oxyfuel Project

3 CPU from Callide Oxyfuel Project Hg carried over into compression Most Hg removed in fly ash Hg2+ removed Cryo-HEX susceptible to Hg attack Air Liquid design for CPU (Tranier, J. P. et al 29; Spero, C 211; Court, P et al 211)

4 Possible mechanisms of H2SO4, HNO3 and Hg(NO3)2 formation in CO2 compression Upstream Processing NO+ ½O 2 NO 2 Hg+NO2 product? Hg+N2O4 product? de-sox de-nox Fly Ash capture SO 2 + NO 2 NO+ SO 3 +H 2 O H 2 SO 4 NO 2? +H 2 O HNO 3 Hg? +NO - 3 Hg(NO 3 ) 2 From AP/IC paper; H2SO4 PROBABLE HNO3 EXPECTED Hg(NO3)2 UNCERTAIN Any elemental mercury or mercury compounds present in the gaseous CO2 will (also) be converted to mercuric nitrate since mercury compounds react readily with nitric acid. Vince White, Laura Torrente-Murciano, David Sturgen, David Chadwick, Purification of oxyfuel-derived CO2, International Journal of Greenhouse Gas Control, 4, , 21

5 Three Stage Compression Gas Sample Point Variable Speed Motor dry gas meter exhaust O2 5% NO/N2 N2/CO2 MFC MFC MFC bypass vent Pressure Control Pressure Control AC Scrubber Gas Sampling Dilution Air To gas analysers Hg permeation tube + water bath H2O Saturator Liquid Sampling Gases compressed from atmospheric conditions Real simulation of gas-liquid contact (ie high surface area) Variable pressure in stages 2 and 3

6 Gas Sampling & Analysis Dilution air IN 9L/min Furnace at 7 C for Hg total Sample gas (with venturi) 1L/min Vacuum gauge Hg only Ohio Lumex RA-915+ Hg gas analyser Diluted sample gas to analysers (1:1 dilution) Thermoscientific 42i NO-NO2-NOx Analyser Bosch Wide Band O2 sensor

7 Liquid Sampling of Condensates From 2nd or 3rd stage Gas / Liquid Separator Pressure Control Gas to 3rd stage or exit Condenser Air needle valve To gas analysers Air + "volatiles" H2O + "stable species" Allows measurement of volatile species during depressurising ph, Hg, NO3-, NO2-, liquid volume

8 Retrofitting SCUBA tank Air Compressor Gas sampling + dilution system 3 piston heads + Variable Speed Motor Moisture separators + pressure control Diagrams: Piston drive + moisture separators

9 NO2 formation in dry compression easy mass balance NO + ½ O2 NO2 6 NOx Conccentration, ppm rd Stage 2 bar 2nd Stage 9 bar 1st Stage 7 bar Total NOx ± 7.5ppm NO NO2 NOx Time, minutes Sampled from back to front (3 rd stage, 2 nd stage, 1 st stage) so conversion not affected by sampling

10 Hg Removal during dry compression Hg + O2 + N2 no reaction Hg +NO2 product Hg, ng/m st Stage 3 bar 2nd Stage 11 bar NOx on (5ppm) NOx off No water required to remove Hg from gas Time, minutes Feed: 5% O2 12ng/m3 Hg N2 balance, 1LPM

11 NOx behaviour in wet compression 2NO 2 N 2 O 4 + H 2 O (L) HNO 2 + HNO 3 (aq) NO, ppm Feed st Stage 3 bar 2 nd Stage 1-18 bar 3 rd Stage 3 bar 15ppm NOx 1ppm NOx 5ppm NOx NO2, ppm Captured in condensate 15ppm NOx 1ppm NOx 5ppm NOx Pressure, bar Pressure, bar Feed: 5% O2, 5-15ppm NO, N2 balance, 1 SLPM

12 NOx removed by H2O in compression 2NO 2 N 2 O 4 + H 2 O (L) HNO 2 + HNO 3 (aq) ppm NOx 1ppm NOx 5ppm NOx 86.7% removed NOx Captured, ppm % removed 86.5% removed Pressure, bar

13 Hg removed by NO2 in wet compression Hg +NO 2 (G) product Hg +HNO 3 (aq) Hg(NO 3 ) st Stage 2nd Stage 3rd Stage HgNO 3 14 Hg concentration, ng/m Pressure, bar g O2 shut-off No Hg capture 97-99% Hg removal 5ppm NOx 3% O2 1ppm NOx 3% O2 15ppm NOx 3% O2 15ppm NOx no O2

14 Volatile NOx and Hg measured from liquid condensates on depressurisation NO 2 / NO / HNO 2 (aq) NO x (G) 14 Hg (aq) Hg (G) 25 Volatile NOx from liquid, ppm NO NO2 Hg Slow process occurs over hours 3-1% of NOx in liquid volatile < 1% of Hg in liquid volatile Volatile Hg from liquid, ng/m Time, minutes

15 Liquid Hg determination Hg 2+ + Sn 2+ (aq) Hg + Sn 4+ (aq) Hg (G) 1 9 SnCl / HCl injection Stable Hg from liquid, ng/m SnCl / HCl injection SnCl / HCl injection 1 SnCl / HCl injection Time, minutes

16 Concentration, g/l Concentration, µg/l Liquid Analysis Summary nd Stage NO3-3rd Stage NO3-2nd Stage Hg 2nd Stage NO2-5ppm NOx 1ppm NOx 15ppm NOx ph 1 to -.2 3rd Stage NO2-5ppm NOx 1ppm NOx 15ppm NOx 3rd Stage Hg For standard conditions of 3 / 1 / 3 bar g for stages 1 / 2 / 3 1 SLPM, 5% O2, 1ng/m3 Hg, N2 bal Mass Balance Closure Feed NOx ppm NOx % Hg % Poor mass closure due to build-up in compressor in nonwetted areas

17 Small Pressure Reactor used for dry Hg -NO2 kinetics tests* O2 MFC 5% NO/N2 N2 MFC MFC bypass Hg permeation tube + water bath bypass used without water Pressure Gauge Pressure Relief Back Pressure Regulator Dilution + Gas Analysers + dry gas meter Gases injected at pressure Feed Hg adjusted for each pressure Flow constant at 1 SLPM 5% O2, target 2µg/m3 Hg, N2 bal high pressure low pressure * Used in previous NOx kinetic study (Ting, Stanger, Wall IJGHGC 213)

18 Hg-NO2 reaction in dry gas confirmed! 25 2 Hg total, ng/m Wet results Feed Hg 5ppm NOx 1ppm NOx 15ppm NOx Model 5 1% removal! Pressure, bar g No Hg 2+ in gas detected Atmospheric kinetic model* applied at high pressure d[ Hg dt ] = 452 exp [ Hg RT ][ NO 2 ] 2 Product unknown * From Hall, Schager, and Ljungstrom, An experimental study on the rate of reaction between mercury vapour and gaseous nitrogen dioxide. Water, Air, and Soil Pollution, (1-2): p

19 Conclusion Significant Hg & NOx captured during compression process (1% Hg, ~9% NOx) Significant deposition (ie poor recovery in liquid) Hg removed from gas by NO2/N2O4 Product unknown, but predicted by kinetics Water in compression retards Hg capture by early NOx removal Highly acidic condensates stable Hg 3-1% volatile NOx

20 Acknowledgements The authors also wish to acknowledge financial assistance provided through Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is supported by Australian Coal Association Low Emissions Technology Limited and the Australian Government through the Clean Energy Initiative.

21 Thanks for listening..questions?

22 Experimental & predicted NO2 formation NO2, ppm ppm NOx 1ppm NOx 15ppm NOx Model Pressure, bar g d[ NO dt 2 ] = exp [ NO] T 2 [ O 2 ]

23 Kinetic Modelling d[ NO dt 2 ] = exp [ NO] T 2 [ O 2 ] 5 Hg (NO2 rxn) NO2 2 NO2 concentration, ppm NO2 (eq) Hg concentration, ug/m3 G exp RT = K P = [ N O [ NO ] ] 1 NO N2O4 (eq) Hg (N2O4 rxn) Time, seconds.5 d[ Hg dt d [ Hg dt ] = 5.15x1 ] = 452 exp [ Hg RT exp [ Hg RT ][ N ][ NO 2 O 4 2 ] ] 2

24 Initial Results from Small Reactor Hg Concentration, ng/m bar N2 3% O2/N2 1ppm NOx, 3% O2/N2 2 bar N2 3% O2/N2 1ppm NOx, 3% O2/N Time, minutes NOx injection has significant impact on Hg at high pressure

25 Hg Absorption in HNO3 in small reactor 12 Hg Concentration, ng/m bar 5 bar 1 bar 15 bar 2 bar 25 bar feed Hg ~ 1,ng/m 3 Final steady state equivalent to stable oxidation Hg + N2 in.1m HNO3 (ie ph 1) Time, minutes

26 But Hg desorbs from the liquid when depressurised 7 Gaseous Hg in reactor during depressurisation 6 Hg desorbed from liquid after depressurising 5 bar Hg Concentration, ng/m bar 15 bar 1 bar 5 bar 25 bar 1 bar 15 bar 2 bar 25 bar Time, minutes HNO3 not sufficient to oxidise gaseous Hg need gaseous oxidiser such as NO2

27 Modelling Compression Stages Stage 1 Stage 2 Stage 3 3 bar 11 bar 3 bar NO2 concentration, ppm Hg concentration, ug/m3 NO2, ppm NO, ppm NO measured NO2 measured Hg model Hg measured Time, minutes

28 High pressure conversion of NOx and Hg and their capture as aqueous condensates in a laboratory oxy-fuel compression system Rohan Stanger*, Timothy Ting, Terry Wall University of Newcastle 3 rd Oxyfuel Combustion Conference SPAIN 3/7/213