Performance of a wet Flue Gas Desulphurisation Pilot Plant under Oxy-fuel Conditions

Transcription

1 Performance of a wet Flue Gas Desulphurisation Pilot Plant under Oxy-fuel Conditions IEAGHG workshop, Oxy-fuel combustion, January 25/26, 2011 Brian B. Hansen and Søren Kiil Department of Chemical and Biochemical Engineering Kgs Lyngby, Denmark

2 Outline Introduction Objective Wet FGD and Oxy-fuel combustion Experimental investigation Pilot plant outline and methodology Results Absorber ph Desulphurisation degree Content of residual limestone Conclusions and future work 1

3 (DTU) Founded in Hans Christian Ørsted (Danish Physicist) Engineering education and research About DTU 19 departements (Lyngby) 4500 employes (1050 Ph.D. Students) 6500 bachelor and master students 2

4 Project objective Objective To investigate the effect of oxy-fuel combustion on wet FGD operation Parameters studied: - CO 2 atmosphere - Higher flue gas temperature (H 2 O content) - Higher SO 2 concentration - Reduced flue gas flow rate 3

5 Oxy-fuel and wet FGD Flue gas desulphurisation Vattenfall A/S Ensuring a clean CO 2 stream or recycle stream Wet FGD widespread, traditional and highly efficient CaCO 3 (s) + SO 2 (g) + 2H 2 O + ½O 2 CaSO 4 2H 2 O(s) + CO 2 Potential process conditions dependent on recycle location 4

6 Potential wet FGD process changes CO 2 atmosphere - CO 2 absorption (absorber) and a decreased limestone dissolution rate CaCO H + Ca 2+ + CO 2 + H 2 O Higher saturation temperature - Wet recycle yields higher gas phase water content - Decreased SO 2 solubility SO 2 concentration/flue gas flow rate - Recycle location or changing modes of operation (air-firing/oxy-fuel) - Prolonged gas phase residence time - Increased importance of liquid phase transport resistance External oxidation 5

7 Pilot plant outline Overview Packed tower absorber - Downscaled (single vertical channel) - Co-current flow - Multiple sampling sites - Well controlled gas and liquid streams 6

8 Experimental overview Air-firing - ph 5.4 Base-case Oxy-fuel - ph 5.4 Oxy-fuel (~ 90 % CO 2 ) Oxy-fuel and 10 mm adipic acid Oxy-fuel - ph 5.0 Oxy-fuel Oxy-fuel and low gas flow rate Oxy-fuel, low flow and T (~ 53 o C) 7

9 Experimental methodology Experimental procedure Steady state - 5 days desulphurisation ppm SO 2 flue gas (natural gas burner) Oxy-fuel experiments ppm SO 2 flue gas (gas cylinders) - Until a steady limestone consumption rate 8

10 Sampling procedure Sampling Gas phase composition - Absorber profile - Overall degree of desulphurisation Absorber ph - Multiple sampling points Residual limestone - Thermal analysis in STA Netzsch-Gerätebau GmbH 9

11 Absorber ph Slurry ph Base case ph Oxy-fuel ph Oxy-fuel ph Distance from absorber inlet [m] ph decrease as SO 2 is absorbed SO 2 + H 2 O H 2 SO 3 HSO H + HSO ½ O 2 H + + SO 4 2- Oxy-fuel ph increased absorber ph 2 10

12 Absorber ph Slurry ph Base case ph 5.4 Oxy-fuel ph 5.4 Oxy-fuel ph 5.4 (10 mm adipic acid) Distance from absorber inlet [m] Oxy-fuel ph 5.4 (10 mm adipic acid) High and stable absorber ph 11

13 Absorber desulphurisation Degree of desulphurisation Base case ph Oxy-fuel ph Oxy-fuel ph 5.4 (10 mm adipic acid) 0.7 Oxy-fuel ph Distance from absorber inlet [m] Increased degree of desulphurisation - Oxy-fuel ph 5.4 (10 MM adipic acid) - Oxy-fuel ph

14 Absorber desulphurisation Degree of desulphurisation Oxy-fuel ph 5.0, low flow and high temperature 0.9 Oxy-fuel ph 5.0, low flow 0.8 Base case ph Oxy-fuel ph Distance from absorber inlet [m] Increased degree of desulphurisation - Oxy-fuel experiments with low flow rates 0 Base-case 5.4 and Oxy-fuel ph 5.0 very similar 13

15 Total degree of desulphurisation Experiment C SO2 [ppm] C CO2 [%] ph T [ o C] η (±1) [%] Air-firing CO 2 atmosphere (ph 5.4) ph 5.4 (10 mm adipic acid) ph Reduced flow rate Elevated Temperature CO 2 atmosphere - Increased desulphurisation degree - Lower ph counters the effect - High degree of desulphurisation with 10 mm adipic acid or low Q flue 14

16 Residual limestone Experiment C SO2 [ppm] C CO2 [%] ph CaCO 3 (±0.6) [g/l] η (±1) [%] Air-firing CO 2 atmosphere (ph 5.4) ph 5.4 (10 mm adipic acid) ph Reduced flow rate Elevated Temperature CO 2 atmosphere - Increased residual limestone content - Also with 10 mm adipic acid - Lower ph counters this effect 15

17 Discussion Dissolution of limestone CaCO 3 (s) Ca 2+ + CO 2-3 (1) H + + CO 2-3 HCO - 3 (2) HCO H + CO 2 + H 2 O (3) CO 2 (aq) CO 2 (g) (4) Critical ph changes with CO 2 Above critical ph ( ) - Increased HCO - 3 concentration - Increased CO 2-3 at the particle surface - Lower Ca 2+ concentration at the particle surface - Drastic reduction in limestone dissolution rate (ΔCa 2+ ) Allers et. Al 2003 Verified experimentally by Allers et al and Chan et al

18 Conclusions Desulphurisation of an oxy-fuel flue gas stream A higher absorber ph An increased content of residual limestone An increased degree of desulphurisation A minor correction of ph (5.0 vs. 5.4) compensate for the changes High degrees of desulphurisation obtained for low flow rates - No temperature effect could be distinguished Publication Manuscript Performance of a wet flue gas desulphurisation pilot plant under oxy-fuel conditions accepted by Industrial and Engineering Chemistry Research Expected publication in spring

19 Thank you for the Attention Further information: