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 WallUniversity of Newcastle3rd Oxyfuel Combustion ConferenceSPAIN30/07/2013

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

CPU from Callide Oxyfuel Project

Air Liquid design for CPU (Tranier, J. P. et al 2009; Spero, C 2011; Court, P et al 2011)

Cryo-HEX susceptible to Hg attack

Hg2+ removed

Most Hg removed in fly ash

Hg0 carried over into compression

Possible mechanisms of H2SO4, HNO3 and Hg(NO3)2 formation in CO2 compression

Upstream Processing

de-SOxde-NOx

Fly Ash capture

NO+ ½O2 →NO2

SO2+ NO2 → NO+ SO3+H2O→ H2SO4

↓ NO2 ↑?

↓ +H2O→ HNO3

Hg ↓ +NO3

-→ Hg(NO3)2

H2SO4 PROBABLE HNO3 EXPECTED Hg(NO3)2

UNCERTAIN

From AP/IC paper;

“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, 137-142, 2010

Hg+NO2 → product?

Hg+N2O4 → product?

↓?

Three Stage Compression

• Gases compressed from atmospheric conditions

• Real simulation of gas-liquid contact (ie high surface area)

• Variable pressure in stages 2 and 3

Pressure Control

Pressure Control

Gas Sample Point

MFC

MFC

MFC

O2

5% NO/N2

N2/CO2bypass

Hg0 permeation tube+

water bath

Liquid Sampling

exhaust

dry gas meter

ACScrubber

Gas Sampling

Dilution Air

To gas analysers

H2O Saturator

Variable Speed Motor

vent

Gas Sampling & Analysis

Thermoscientific

42i NO-NO2-NOx Analyser

Ohio Lumex

RA-915+ Hg0 gas analyser

Bosch

Wide Band O2 sensor

Dilution air IN

9L/min

Sample gas

(with venturi)

1L/min

Diluted sample gas to analysers

(1:10 dilution)

Vacuum gauge

Furnace at 700°C for Hg total

Hg0 only

Liquid Sampling of Condensates

• Allows measurement of “volatile” species during depressurising

• pH, Hg, NO3-, NO2-, liquid volume

AirTo gas analysersAir + "volatiles"

H2O + "stable species"

Pressure Control

Condenser

Gas / Liquid Separator

Gas to 3rd stage or exit

From 2nd or 3rd stage

needle valve

Retrofitting SCUBA tank Air Compressor

3 piston heads + Variable Speed Motor

Gas sampling + dilution system

Moisture separators +

pressure controlDiagrams: Piston drive + moisture separators

NO2 formation in dry compression– easy mass balance

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35 40 45

Time, minutes

NOx

Conc

cent

ratio

n, p

pm

NONO2NOx

3rd Stage20 bar

2nd Stage9 bar

1st Stage7 bar

Total NOx± 7.5ppm

Sampled from back to front (3rd stage, 2nd stage, 1st stage) so conversion not affected by sampling

NO + ½ O2 → NO2

Hg Removal during dry compression

Feed: 5% O2 1200ng/m3 Hg0 N2 balance, 10LPM

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60 70 80 90

Time, minutes

Hg0

, ng

/m3

1st Stage3 bar

2nd Stage11 bar

NOx on (500ppm)

NOx off

No water required

to remove

Hg0 from gas

Hg0 + O2 + N2 → no reaction Hg0+NO2 → product

NOx behaviour in wet compression

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25 30

Pressure, bar

NO

, p

pm

1500ppm NOx1000ppm NOx500ppm NOx

0

50

100

150

200

250

300

350

400

450

500

0 5 10 15 20 25 30

Pressure, bar

NO

2, p

pm

1500ppm NOx1000ppm NOx500ppm NOx

Feed: 5% O2, 500-1500ppm NO, N2 balance, 10 SLPM

Feed 1st Stage

3 bar

2nd Stage

10-18 bar

3rd Stage

30 bar

2NO2 → N2O4 + H2O (L) → HNO2 + HNO3 (aq)

Captured in condensate

NOx removed by H2O in compression

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25 30 35Pressure, bar

NO

x C

aptu

red,

ppm

1500ppm NOx1000ppm NOx500ppm NOx

86.7% removed

90.2% removed

86.5% removed

2NO2 → N2O4 + H2O (L) → HNO2 + HNO3 (aq)

Hg0 removed by NO2 in wet compression

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30 35

Pressure, bar g

Hg0 c

once

ntra

tion,

ng

/m3

500ppm NOx 3% O21000ppm NOx 3% O21500ppm NOx 3% O21500ppm NOx no O2

1st Stage 2nd Stage 3rd Stage

O2 shut-offNo Hg capture

97-99%Hg removal

Hg0+NO2 (G) → product Hg0+HNO3 (aq) → Hg(NO3)2

HgNO3

“Volatile” NOx and Hg measured from liquid condensates on depressurisation

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

Time, minutes

Vola

tile

NOx

from

liqu

id,

ppm

0

5

10

15

20

25

Vola

tile

Hg fr

om li

quid

,ng

/m3

NO

NO2

Hg0

Slow process occurs over hours

3-10% of NOx in liquid volatile

< 1% of Hg in liquid volatile

NO2 / NO / HNO2 (aq) → NOx (G) Hg0 (aq) → Hg0 (G)

Liquid Hg determination

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200

Time, minutes

Stab

le H

g0 fr

om li

quid

, ng

/m3

SnCl / HCl injection

SnCl / HCl injection

SnCl / HCl injection

SnCl / HCl injection

Hg2+ + Sn2+ (aq) → Hg0 + Sn4+ (aq) → Hg0 (G)

0

50

100

150

200

250

2nd StageNO3-

3rd StageNO3-

2nd StageNO2-

3rd StageNO2-

Con

cent

ratio

n,

g/L

500ppm NOx1000ppm NOx1500ppm NOx

Liquid Analysis Summary

Mass Balance Closure

Feed NOxppm

NOx %

Hg%

500 14.0 22.41000 51.1 56.71500 57.2 6.4

Poor mass closure due to build-up in compressor in non-wetted areas

For standard conditions of

3 / 10 / 30 bar g for stages 1 / 2 / 3

10 SLPM, 5% O2, 1000ng/m3 Hg0 , N2 bal

pH 1 to -0.2

05

10152025303540

2nd Stage Hg 3rd Stage Hg

Con

cent

ratio

n,

µg/

L

500ppm NOx1000ppm NOx1500ppm NOx

Small Pressure Reactor used for dry Hg0-NO2 kinetics tests*

• Gases injected at pressure

• Feed Hg adjusted for each pressure

• Flow constant at 10 SLPM

• 5% O2, target 2µg/m3 Hg0, N2 bal

* Used in previous NOx kinetic study (Ting, Stanger, Wall IJGHGC 2013)

bypassBack Pressure

Regulator

Pressure Gauge

Pressure Relief

used without water

bypass

Hg0 permeation tube

+water bath

high pressure

low pressure

MFC

MFC

MFC

O2

5% NO/N2

N2Dilution

+Gas Analysers

+dry gas meter

0

500

1000

1500

2000

2500

0 5 10 15

Pressure, bar g

Hg

tota

l, n

g/m

3

Feed Hg500ppm NOx1000ppm NOx1500ppm NOxModel

Atmospheric kinetic model* applied at high pressure

100% removal !

No Hg 2+ in gas detected

Product unknown

Hg-NO2 reaction in dry gas confirmed!

22

00

]][[13219exp45200][ NOHgRTdt

Hgd

=

* 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, 1995. 81(1-2): p. 121-134

0

500

1000

1500

2000

2500

0 5 10 15

Pressure, bar g

Hg

tota

l, n

g/m

3

Feed Hg500ppm NOx1000ppm NOx1500ppm NOxModel

Wet results

Conclusion• Significant Hg0 & NOx captured during compression

process (100% Hg, ~90% NOx)

• Significant deposition (ie poor recovery in liquid)

• Hg0 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→ 3-10% volatile NOx

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.

Thanks for listening

…..Questions?

Experimental & predicted NO2 formation

][][530exp2400][2

22 ONOTdt

NOd

=

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15

Pressure, bar g

NO

2, p

pm

500ppm NOx1000ppm NOx1500ppm NOxModel

Kinetic Modelling

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140 160

Time, seconds

NO

2 co

ncen

trat

ion,

pp

m

0

0.5

1

1.5

2

2.5

Hg0

con

cent

ratio

n,ug

/m3

22

00

]][[13219exp45200][ NOHgRTdt

Hgd

=

]][[40958exp1015.5][42

0320

ONHgRT

xdtHgd

−

=

][][530exp2400][2

22 ONOTdt

NOd

=

22

42

][][exp

NOONK

RTG

P ==

∆−

NO2

NO2 (eq)

NON2O4 (eq)

Hg0 (NO2 rxn)

Hg0 (N2O4 rxn)

22

00

]][[13219exp45200][ NOHgRTdt

Hgd

=

Initial Results from Small Reactor

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25 30

Time, minutes

Hg C

once

ntra

tion,

ng

/m3

0 bar N2 3% O2/N2 1000ppm NOx, 3% O2/N2

20 bar N2 3% O2/N2 1000ppm NOx, 3% O2/N2

NOx injection has significant impact on Hg at high pressure

Hg Absorption in HNO3in small reactor

0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25 30

Time, minutes

Hg C

once

ntra

tion,

ng/

m3

0 bar 5 bar 10 bar 15 bar 20 bar 25 bar

feed Hg0 ~ 10,000ng/m3

Hg0 + N2 in 0.1M HNO3 (ie pH 1)

Final steady state equivalent to stable oxidation

But Hg desorbs from the liquid when depressurised

0

1000

2000

3000

4000

5000

6000

7000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Time, minutes

Hg C

once

ntra

tion,

ng

/m3

5 bar

10 bar

15 bar

20 bar

25 bar

20 bar

25 bar15 bar

10 bar

5 bar

Gaseous Hg in reactor during depressurisation

Hg desorbed from liquid after depressurising

HNO3 not sufficient to oxidise gaseous Hg0

– need gaseous oxidiser such as NO2

Modelling Compression Stages

0

100

200

300

400

500

600

0 1 2 3 4 5

Time, minutes

NO

2 co

ncen

trat

ion,

pp

m

0

0.2

0.4

0.6

0.8

1

1.2

Hg0

con

cent

ratio

n, u

g/m

3

NO2, ppm

NO, ppm

NO measured

NO2 measured

Hg0 model

Hg0 measured

Stage 1

3 bar

Stage 2

11 bar

Stage 3

30 bar

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

30/07/2013