Alkali sulphation in flames - PDF Free Download

5 th Meeting of the IEAGHG International Oxyfuel Combustion Research Network 27 th -30 th October 2015, Wuhan, China Alkali sulphation in flames Thomas Ekvall (thomas.ekvall@chalmers.se) Department of Energy and Environment, Division of Energy Technology, Chalmers University of Technology, Sweden Project funded by The Swedish Research Council

Outline Aim Background What has been done and why Project description Experimental setup Results Summary

Aim - Background Project description Results - Summary Aim Investigating K-S-Cl chemistry in combustion Is there a difference between air-fuel and oxy-fuel combustion?

Coal vs Biomass Biomass fired boiler Coal Fossil Large resources High sulphur content Biomass Renewable High alkali content (mainly potassium, K) High chlorine (Cl) content Alkali salts K + Cl KCl Deposits High temperature corrosion Lower operating temperatures -> Lower efficiency

Co-Combustion Co-fired boiler Coal + Biomass Partly renewable High alkali content High chlorine content High sulphur content Alkali salts K + Cl KCl Depositions and High temperature corrosion KCl + SO X K 2 SO 4 Higher melting point (less sticky) Degree of sulphation: How much KCl will be converted to K 2 SO 4? More sulphur higher degree of sulphation

Oxy-Fuel combustion O 2 Combustion Ash removal Condenser Fuel CO 2 SO 2 H 2 O KCl HCl K 2 SO 4 KCl K 2 SO 4 CO 2 SO 2 H 2 O HCl H 2 O HCl CO 2 SO 2

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

Experimental setup Fuel Propane 1.73 g/s (80kW) Oxidizer Air Oxy-Fuel 25% O 2 75% dry flue gases Injections SO 2 (g) KCl (aq)

Experimental setup Sulphur injection Gaseous SO 2 0.15-2.2 Nl/min 100-3000 ppm KCl injection Aqueous solution, 3.34 wt% 0.9 l/h 100 ppm

Experimental setup Measurement systems Gas composition FTIR HCl concentration (KCl+SO x ->K 2 SO 4 +HCl) Solid particles IACM * KCl aerosols *IACM (In-situ Alkali-Chloride Monitor)

Results No KCl KCl Air (port 2) OF25 (port 3)

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

Reaction Routes during Sulphation Air OF25 Sulphation via: SO 2 SO 3 SO 2 or SO 3 Other: SO 3 formation Pre-sulphation

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.

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 council Acknowledged for their financial support

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