Chalmers University of Technology
Oxy-fuel combustion research
at Chalmers
Daniel Kühnemuth and Daniel Fleig
Division of Energy Technology
Department of Energy and Environment
Contact:
[email protected]
[email protected]
Chalmers Energy Conference, 26-27.02.2011, Gothenburg, Sweden
Chalmers University of Technology
Experimental research
in oxy-fuel combustion
•
Nitrogen Chemistry
» NO emissions
» NOx - reburning
•
Sulphur Chemistry:
» Fate of Sulphur
» SO2 emissions
•
Radiative Heat Transfer
» Radiation intensity
Chalmers University of Technology
Combustion
experiments
•
Cylindrical combustion chamber
(D = 800 mm, H = 2400 mm)
•
Top-fired burner, swirling, non-premixed
•
Dry or wet flue gas recycle
•
100 kWth propane or
pulverized lignite
•
Controlled feed gas concentration of
oxygen (O2) and nitric oxide (NO)
•
Possibility for staged combustion
•
In-furnace measurements
Chalmers University of Technology
NOx and SOx
emissions in oxy-fuel
Importance of research:
– Emissions from the combustion process can lead to
hardly controllable acid formation in the CO2
compression and cleaning part (corrosion)
– NOx and SOx concentrations might be elevated in the
vent stream from the CO2 cleaning (stack)
– The level of permitted NOx and SOx concentrations in
the liquid CO2 is not regulated yet
Chalmers University of Technology
NOx and SO2 emissions
The main difference between air and oxy-fuel firing is an increased
concentration of combustion products (due to flue gas recycle / absence
of air-borne nitrogen)
O2
+
Fuel
Wet or dry flue gas recycle
Combustion
Flue gas
Several oxy-fuel cases are investigated and compared to air-firing
• Studies on NOx formation:
– Propane as fuel with NO injection
– Lignite as fuel
• Studies on SOx formation:
– Lignite as fuel
Chalmers University of Technology
NOx reduction by reburning
• Depending on the recycle ratio of flue gas 60 to 80% of NOx produced
are recycled back to the furnace.
• The reaction of NO with hydrocarbon radicals in the flame zone is called
reburning:
N2
NO
Recycle of NO containing flue gas is the most important reason for
increased reduction efficiency in oxy-fuel combustion
Additional information: Kühnemuth, D.; Normann, F.; Andersson, K.; Johnsson F.; Leckner, B.; Reburning
of Nitric Oxide in Oxy-Fuel Firing—The Influence of Combustion Conditions, Energy and Fuels, 2011
(http://pubs.acs.org/doi/abs/10.1021/ef101054t)
Chalmers University of Technology
SO2 reduction through increased
sulphur self-retention by ash
• Around three times higher SO2 concentration in oxy-fuel
compared to air-fired conditions (for the fuel investigated)
• However, lower SO2 emissions [mg/MJ]
• Higher amount of S in ash during oxy-coal combustion
• Higher SO2 concentration in oxy-fuel might favour sulphate formation
and formation of SO3 (as modeling shows)
Additional information: Fleig, D.; Andersson, K.; Johnsson, F.; Leckner, B. Conversion of Sulfur during
Pulverized Oxy-coal Combustion, Energy and Fuels, 2011 (http://pubs.acs.org/doi/abs/10.1021/ef1013242)