Alkali metals, mainly sodium and potassium, together with other ash forming inorganic components in biomass increases fouling, slagging, and high temperature corrosion during biomass combustion or gasification. To reduce the amount of alkali vapor to an acceptable level, which may be affected by Si, Al, Ca, S, Mg, and P, the information on the speciation of alkali metals is essential. In this study, thermodynamic equilibrium calculations were performed to determine the distribution and mode of occurrence of gaseous chlorine and alkali metals of three types of biomass (corn stover, switch grass, and wheat straw) in combustion and gasification processes. The influence of temperature, pressure, and air-fuel ratio was also evaluated. Results show that the excess air has limited influence on the speciation of chlorine and potassium during combustion. However, the influence of the excess air is significant during gasification. Increasing excess air enhances the formation of vapor HCl and KOH as well as reduction in vapor KCl and K2Cl2. In biomass combustion and gasification, increasing pressure increases vapor HCl and K2Cl2 and reduces the amount of vapor KCl and KOH. At higher temperatures (>1100K), the gaseous alkali species increased greatly. The results will be useful in the better development of hot gas clean-up technologies.

1.
Jensen
P. A.
,
Stenholm
M.
and
Hald
P.
, “
Deposition Investigation in Straw–Fired Boilers
”,
Energy & Fuels
,
11
,
1048
1055
,
1997
.
2.
Wei
X.
,
Lopaz
C.
,
Puttkamer
T. V.
,
Schnell
U.
,
Unterberger
S.
and
Hein
K. R. G.
, “
Assessment of Chlorine-Alkali-Mineral Interactions during Co-Combustion of Coal and Straw
”,
Energy & Fuels
,
16
,
1095
1108
,
2002
.
3.
Dayton
D. C.
,
French
R. J.
and
Milne
T. A.
, “
Direct observation of Alkali Vapor Release during Biomass Combustion and Gasification. 1. Application of Molecular Beam/Mass Spectrometry to Switch grass Combustion
”,
Energy & Fuels
,
9
,
855
865
,
1995
.
4.
Wei
X.
,
Schnell
U.
and
Hein
K. R. G.
, “
Behaviour of gaseous chlorine and alkali metals during biomass thermal utilization
”,
Fuel
,
84
,
841
848
,
2005
.
5.
Jensen
A.
and
Dam-Johansen
K.
, “
TG-FTIR Study of the Influence of Potassium Chloride on Wheat Straw Pyrolysis
”,
Energy & Fuels
,
12
,
929
938
,
1998
.
6.
Dayton
D. C.
and
Belle-Oudry
D.
, “
Effect of Coal Minerals on Chlorine and Alkali Metals Released during Biomass/Coal Co-firing
”,
Energy & Fuels
,
13
,
1203
1211
,
1999
.
7.
Jensen
P. A.
,
Frandsen
F. J.
,
Dam-Johansen
K.
and
Sander
, “
Experimental Investigation of the Transformation and Release of Gas Phase of Potassium and Chlorine during Straw Pyrolysis
”,
Energy & Fuels
,
14
,
1280
1285
,
2000
.
8.
Kurkela, E., “Formation and removal of biomass-derived contaminants in fluidized-bed gasification processes”, VIT publications No. 287, 1996.
This content is only available via PDF.
You do not currently have access to this content.