Alkali sulphation in flames

Thomas Ekvall(thomas.ekvall@chalmers.se)

Project funded by The Swedish Research Council

Department of Energy and Environment, Division of Energy Technology, Chalmers University of Technology, Sweden

5th Meeting of the IEAGHG International Oxyfuel Combustion Research Network – 27th -30th October 2015, Wuhan, China

mailto:thomas.ekvall@chalmers.se

Outline

Aim

Background

• What has been done and why

Project description

• Experimental setup

Results

Summary

Aim

• Investigating K-S-Cl chemistry in combustion

• Is there a difference between air-fuel and oxy-fuel combustion?

Aim - Background – Project description – Results - Summary

Alkali salts

• 𝐾 + 𝐶𝑙 → 𝐾𝐶𝑙

• Deposits

• High temperature corrosion

• Lower operating temperatures -> Lower efficiency

Coal vs Biomass

Coal

• Fossil

• Large resources

• High sulphur content

Biomass

• Renewable

• High alkali content (mainly potassium, K)

• High chlorine (Cl) content

Biomass fired boiler

Aim – Background – Project description – Results - Summary

Alkali salts

• 𝐾 + 𝐶𝑙 → 𝐾𝐶𝑙

• Depositions and High temperature corrosion

• 𝐾𝐶𝑙 + 𝑆𝑂𝑋 → 𝐾2𝑆𝑂4

• Higher melting point (less sticky)

Degree of sulphation: How much KCl will be converted to 𝐾2𝑆𝑂4?

• More sulphur → higher degree of sulphation

Co-Combustion

Coal + Biomass

• Partly renewable

• High alkali content

• High chlorine content

• High sulphur content

Co-fired boiler

Aim – Background – Project description – Results - Summary

Oxy-Fuel combustion

Combustion

O2

Fuel

CO2SO2H2OKClHClK2SO4

Ash removal Condenser

CO2SO2H2OHCl

CO2SO2

KClK2SO4

H2OHCl

Aim – Background – Project description – Results - Summary

Project description

Aim

• Investigating K-S-Cl chemistry in combustion

• Compare air and oxy-fuel combustion

• Will the higher sulphur content in a oxy-fuel system result in a higher degree of sulphation?

Experimental methodology

• Isolating the chemistry of interest

• Neglecting release of inorganic species and ash retention

• Get a better control of the amount of K, S and Cl in the system

Aim – Background – Project description – Results - Summary

Experimental setup

Fuel

• Propane

• 1.73 g/s (80kW)

Oxidizer

• Air

• Oxy-Fuel

• 25% O2• 75% dry flue gases

Injections

• SO2 (g)

• KCl (aq)

Aim – Background – Project description – Results - Summary

Experimental setup

Sulphur injection

• Gaseous SO2

• 0.15 - 2.2 Nl/min

• 100 - 3000 ppm

KCl injection

• Aqueous solution, 3.34 wt%

• 0.9 l/h

• 100 ppm

Aim – Background – Project description – Results - Summary

Experimental setup

Measurement systems

• Gas composition • FTIR

• HCl concentration (KCl+SOx->K2SO4+HCl)

• Solid particles• IACM™ *

• KCl aerosols

*IACM™ (In-situ Alkali-Chloride Monitor)

Aim – Background – Project description – Results - Summary

Results

Air (port 2)

OF25 (port 3)

No KCl KCl

Aim – Background – Project description – Results - Summary

Sulphation of Potassium Chloride

• Good agreement between experiments and simulations*

• Higher degree of sulphation oxy-fuel combustion

• Complete sulphation already at S/K=3 for OF25

• Suggests oxy-fuel to be a preferred from a corrosion point of view

Aim – Background – Project description – Results - Summary

*For simualtion deatails: Ekvall, T.; Normann, F.; Andersson, K.; Johnsson, F., Modeling the alkali sulfation chemistry of biomass and coal co-firing in oxy-fuelatmospheres. Energy and Fuels 2014, 28 (5), 3486-3494.

Sulphation of Potassium Chloride

• Only an effect of higher SO2 concentration?• No

• Additional reason still to be found

Aim – Background – Project description – Results - Summary

For simualtion deatails: Ekvall, T.; Normann, F.; Andersson, K.; Johnsson, F., Modeling the alkali sulfation chemistry of biomass and coal co-firing in oxy-fuelatmospheres. Energy and Fuels 2014, 28 (5), 3486-3494.

Reaction Routes during Sulphation

Sulphation via:

SO2SO3SO2 or SO3

Other:

SO3 formation

Pre-sulphation

Aim – Background – Project description – Results - Summary

Air OF25

Summary

• The alkali chemistry is of importance due to the corrosivity of the salts that they might form. Between chlorides and sulphates the latter is to prefer from a HTC point of view.

• A higher degree of sulphation is reached during oxy-fuel combustion compared to air combustion. Almost complete combustion is reached for S/K=3.

• It seems to be possible to use a higher biomass to coal ratio if the two fuel categories are co-combusted in a oxy-fuel unit without having alkali related problems to the same extent as is expected for air combustion.

Aim – Background – Project description – Results - Summary

Acknowledgement

• Tomas Leffler, the division of Combustion Physics at Lund University.Gratefully acknowledged for his contribution to this work providing both instrumentation and knowledge regarding alkali measurements.

• The Swedish research councilAcknowledged for their financial support

Thank you!

P.S. Reduced maintenance is always appreciated!

Alkali sulphation in flames

Thomas Ekvall(thomas.ekvall@chalmers.se)

Project funded by The Swedish Research Council

Department of Energy and Environment, Division of Energy Technology, Chalmers University of Technology, Sweden

5th Meeting of the IEAGHG International Oxyfuel Combustion Research Network – 27th -30th October 2015, Wuhan, China

mailto:thomas.ekvall@chalmers.se