HBr-Enhanced Sorbents, reactions with SO2

Mohamad J. Al-Jebooria, John Blameya, Belen Gonzaleza,Thomas Hillsa,

Edward J. Anthonyb, Vasilije Manovicb, Nick Florina, Paul S. Fennella*

m.al-jeboori@imperial.ac.uk; p.fennell@imperial.ac.uk

a Dept. of Chemical Engineering and Chemical Technology

Imperial College London

b School of Applied Sciences, Cranfield University

Cambridge, 2nd September 2013

One active research area in our group is focussed on testing different

ways to improve long-term sorbent reactivity in the calcium looping

cycle, using a small fluidised bed reactor. These include:

• Sorbent modification using different dopants (HBr, sea water dopants)

• Studying the influence of dopants on the reactivation of Ca-based

sorbents in the presence of sulphur

• Synthesis of novel CaO-based sorbents

• Introduction of steam to improve the reactivity of sorbent

Improving the long-term sorbent reactivity in the

calcium looping cycle

Reactor Design

Schematic diagram of experimental apparatus

Reactivity test procedure

• Study the reactivity of Ca-based sorbent usingatmospheric pressure fluidised bed reactor.

• Off-Gas sampled by FTIR–looking at CO2 todetermine start/end of calcination/carbonation.

• The flow-rate of gas into the fluidised bed fordry experiments was 47.5 cm3/s, with 15 % v/vCO2, balance N2 or air.

• The flow-rate of gas for 10 % v/v steamexperiments was 52.8 cm3/s, with 13.5 % v/vCO2, 10 % v/v steam, balance N2.

• 10, 13 or 20 cycles; calcination at 900 °C for600 seconds; carbonation at 700 °C for 600seconds.

Experimental Measurements

Results from a typical experiment. Temperature as function of time: bed temperature(—), wall temperature (—), setpoint (—). CO2 concentration as a function of time (—)

Calcination

Carbonation

Ca

libra

tio

n

Synergistic effect between most effective HBr dopant

concentrations and 10% steam

Carrying capacity g/g over 10 cycles: calcination

at 900 °C for 600 seconds; carbonation at 700 °C

for 600 seconds

Carrying capacities are in g/g of the

calcined material.

The combined presence of steam

and dopant significantly increased

the carrying capacity of the sorbent.

Effect of seawater, and synergic effect between most

effective SW dopant concentrations and 10% steam

on the reactivation of Longcliffe limestone

Carrying capacity in g/g over 13 cycles: calcination at 900

°C for 600 seconds; carbonation at 700 °C for 600 seconds

Using sea water

increases the carrying

capacity of sorbent.

However, it has less

effect on CC in

comparison of using

pure HBr.

Effect of sulphur concentrations on the reactivity of Longcliffe

limestone

Carrying capacity in g/g over 13 cycles: calcination at 900 °C for

600 seconds; carbonation at 700 °C for 600 seconds

The presence of SO2

reduces the cyclical

carrying capacity of

the limestone.

Performance of Longcliffe upon sulphation in : undoped and doped

limestone with 0.167 mol% HBr

Carrying capacity in g/g over 13 cycles: calcination at 900 °C for 600

seconds; carbonation at 700 °C for 600 seconds

Doping with HBr very slightly

improved the carrying

capacity of limestone in

presence of SO2.

Performance of Longcliffe upon sulphation in presence of steam :

undoped and doped limestone with 0.167 mole-% HBr

Carrying capacity in g/g over 13 cycles: calcination at 900 °C for 600

seconds; carbonation at 700 °C for 600 seconds

The combined presence

of steam and dopant

marginally increased the

carrying capacity of the

sorbent in presence of

SO2.

XRF selected data for HBr doped Longcliffe limestone,

upon sulphation with 555 ppm SO2, after 13 cycles

0.167 mole-%HBr 0.189 mole-%HBr

Composition Mole-% Mole-%

CaO 84.85 86.18

SO3 13.72 12.88

SiO2 0.902 0.401

MgO 0.45 0.51

HBr 0.00 0.00

XRF - observation

No bromine moiety was left in the HBr-doped sorbent after 13 cycles.

This is because, at high temperature and in the presence of oxygen:

• SO3(g) reacts with doped limestone to form CaSO4(s) and Br2(g)

• HBr(g) may be formed which could be oxidised to form HOBrO3(g)

Sulphation; reaction pathway

• Upon doping, HBr solution reacts with the calcium carbonate to form a

salt and CO2:

• With the increase of temperature upon cycling the formation of

CaOHBr species is feasible;*

*Al-Jeboori, M.J., et al., “Effects of Different Dopants and Doping Procedures on the Reactivity of CaO-based Sorbents for CO2

Capture”, Energy & Fuels, 2012. 26 (11): p. 6584–659,

Sulphation; reaction pathway

• Upon sulphation under oxidising conditions, the sulphur displaces the

bromine in a sulphation reaction, producing calcium sulphate and

releasing bromine. The bromine may evolve from the system upon

cycling as Br2, HBr and HOBrO3 :*

*Duong, D.N.B., & Tillman, D.A. (2009) “The 34th International Technical Conference on Coal Utilization & Fuel Systems”,

Clearwater, Florida

This is a preliminary mechanism to be considered. We are currently conducting

thermodynamic analysis to confirm the mechanism.

• The pellets were provided by CanmetENERGY, and prepared using a

published method*

• 90 % w/w calcined Cadomin limestone, 10 % w/w commercial calcium

aluminate cement (Ca-14)

• Size fraction 500-710 μm

• During the pelletisation process, the calcined limestone and calcium aluminate

cement powders were subjected to a spray of water. As a result, all of the

pellets were partially hydrated and carbonated from the pelletisation process

• Samples of pellets were subjected to TGA analysis prior to the fluidised bed

experiments to establish carbonation and hydration extents

• XRF analysis was performed to determine the composition of the pellets and

the original Cadomin limestone

Pelletisation

* Wu, Y.H., et al., “Modified lime-based pellet sorbents for high-temperature CO2 capture: Reactivity and attrition behaviour”. Fuel,

2012. 96(1): p. 454-461.

XRF data for chemical composition of the

pellets and the original Cadomin in wt-%

Species Original Cadomin Pellets

CaO 95.46 86.50Al2O3 0.77 6.92

MgO 1.03 2.94

SiO2 1.61 1.71

Fe2O3 0.61 1.29

K2O 0.08 0.194

SO3 0.07 0.17

CuO n/a 0.122

Cr2O3 n/a 0.069

SrO 0.05 0.059

NiO 0.00 0.022

MnO 0.31 N/A

Rh 0.01 N/A

Synergistic effect between pelletisation and steam on the

reactivation of limestones

Carrying capacity in g/g over 20 cycles: calcination at 900 °C for 600

seconds; carbonation at 650 °C for 600 seconds

The effects of pelletisation

and the presence of steam

on the carrying capacity of

the sorbent are additive, as

in the case of doping and

steam.

Pelletisation - observations

General observations were as follows:

• When cycling between 650 °C and 900 °C at 15% CO2 for 600 or 1200

seconds, the pellets showed a reduced initial capacity for CO2 and a

marginal improvement in capacity after 13 cycles.

• Introducing steam upon cycling significantly improved the long-term

carrying capacity of the pellets in comparison with the original limestone.

• The pellets showed a reduced mass loss in comparison to the original

limestone.

Conclusions

General observations were as follows;

• Doping with optimal concentration of HBr showed a significantimprovement in long-term carrying capacity.

• Additive effects have been observed between doping with HBr and theeffects of steam on the long-term reactivity.

• Doping with seawater showed improvement in the long-term carryingcapacity. In addition, additive effects were observed upon using 10%steam.

• SO2 caused a significant decrease in the carrying capacity of limestone,the amount of sulphur (conditions ranged from 555 to 1080 ppm).

• Doping with HBr 0.167 – 0.205 mole-% showed a very marginalimprovement in long-term carrying capacity when sulphur was present.

Conclusions-continued

• The addition of 1-2% steam upon sulphation of Longcliffe limestone

showed a marginal improvement in long-term carrying capacity.

• Marginally additive effects have been noted between doping and the

effects of steam in long-term carrying capacity of CaCO3 upon sulphation.

• XRF results for doped Longcliffe with HBr (0.167 % and 0.189 % mole of

HBr per mole of Longcliffe) after 13 cycles in presence of SO2 showed no

bromine moiety left in the sorbent.

• Pelletisation proved to be excellent approach to improve the reactivation of

limestones.

• Introducing steam upon cycling of pellets showed additive effects on the

long term reactivity.

Acknowledgment

This work was financially supported by :

• The European Community’s Seventh Framework Programme

(FP7/2007-2013) under the GA 241302 − CaOling project.

• CanmetENERGY, Natural Resources Canada.

Thank you

Q & A

Dr Paul Fennell

Email: p.fennell@imperial.ac.uk

Dr Mohamad Al-Jeboori

Email: m.al-jeboori@imperial.ac.uk

Dept. of Chemical Engineering and Chemical Technology

Imperial College London