Calcination rate of limestone under regenerator conditions of Ca-L process

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1 Calcination rate of limestone under regenerator conditions of Ca-L process T. Shimizu, S. Furukawa, H.-J. Kim, L.Y. Li Niigata University, Japan

2 Background Global warming caused by the increase in CO 2 concentration in the atmosphere CO 2 capture and storage(ccs) Removal of CO 2 from the flue gas followed by geostorage

3 CO 2 capture processes Flue gas wet scrubbing Heat demand for regeneration of amine solution is large. Oxyfuel combustion Power consumption to separate oxygen from nitrogen is large. Chemical Looping Combustion (CLC) Existing power plant cannot be used. Calcium Looping CO 2 capture (CaL) Existing power plant is used by adding ASU and CaL.

4 Calcium-Looping (CaL) process CaL process consists of a carbonator (CO 2 absorber) and a CaO regenerator. In the regenerator, CaCO 3 is decomposed by heat. CO2-free gas CO2, H2O CaO+CO2 CaCO3 CaO CaCO3 CaCO3 CaO+CO2 Flue gas (CO %) Carbonator Fuel O2 CO2 Regenerator

5 Design of regenerator For the design of regenerator (calciner), i.e., determination of solid residence time, CaCO 3 decomposition rate is necessary. Measurement of CaCO 3 decomposition rate Requirements Temperature: about 950 CO 2 concentration: nearly 100% High heat transfer rate Small particles: < 1 mm

6 Objective of this work Measurement of CaCO 3 decomposition rate Principles of the rate measurement Change in reactant (e.g. mass change) TGA Accurate measurement of mass change Slow heat transfer from heater to CaCO 3 Difficult to attain 950, CO 2 100% condition

7 Principle of rate measurement Change in product (e.g. CO 2 formation rate) Dilution of produced gas by diluent followed by measurement of CO 2 concentration Direct measurement of CO 2 flow rate Diluent feed CO 2 feed CO 2 formation Time

8 Principles of CO 2 formation rate measurement CO 2 concentration measurement by NDIR IR Det. In Out It takes relatively long time to replace gas in the absorption cell. Slow response

9 Principles of CO 2 formation rate measurement Thermal mass-flow sensor Heater Flow Temp. Difference For the case of constant gas composition, good linearity and relatively fast response

10 Comparison of response Concentration NDIR analyzer Flow rate Mass-flow sensor The response of mass flow sensor was fast (90% response in 5 s). mass flow sensor CO 2 analyzer

11 Experimental

12 Experimental apparatus Mass flow sensor Mass flow sensor Filter P Limestone TC Quartz fluidized bed I.D.:26 mm Bed height:80 mm BM: Quartz sand QS Heater CO 2 A batch of CaCO 3 (1 g) was injected to the bed fluidized by CO 2. The flow rate of CO 2 was measured at the exit.

13 Experimental conditions Bed temp (initial):1223±5k 1243±5K 1263±5K Gas:CO 2 100% BM: Quartz sand, 96 μm and 148 μm CO 2 flow rate :0.24 NL/min 0.54 NL/min (about 5U mf at 1223 K) Limestone size:350~420 μm Analysis of Chichibu limestone (wt.%) CaCO 3 MgCO 3 SiO 2 Al 2 O 3 Fe 2 O

14 Results and discussion

15 Bed temperature after limestone feed Constant temperature was attained except for initial 10 s after injection. Temperature [K] Initial temperature 1223K Initial temperature 1243K Initial temperature 1263K Time after charging limestone [s]

16 Increment of CO 2 flow rate Time scale of CO 2 formation was sufficiently longer than the time scale of sensor s response. Produced CO2 flow [L/s] Average temperature 1216K Average temperature 1233K Average temperature 1251K Time after charging limestone [s]

17 Final conversion of CaCO 3 to CO 2 Average temperature [K] Final conversion QS average size 96μm 148μm Final conversion [-] [-] Total Final amount conversion of produced of CaCOCO 3 was 2 was higher calculated than 93%. by integrating formation profile.

18 Change in conversion (X) with time Conversion ratio X [-] T=1216K QS:average particle diameter of 96μm QS:average particle diameter of 148μm Time [s] Only minor influence of bed material size on rate of conversion change was observed Conversion ratio X [-] T=1233K QS:average particle diameter of 96μm QS:average particle diameter of 148μm Conversion ratio X [-] T=1251K QS:average particle diameter of 96μm QS:average particle diameter of 148μm Time [s] Time [s]

19 Apparent reaction order ln(1-x) [-] Average temperature 1216K Average temperature 1233K Average temperature 1251K Slope: k Time after charging limestone [s] A straight line relationship between ln(1-x) and time: dx/dt=k(1-x) k:rate const. [s -1 ]

20 Assumed reaction rate expression Driving force of CaCO 3 decomposition: Difference between equilibrium pressure (P eq ) and CO 2 partial pressure around the particle (P). = P eq exp T The decomposition rate is assumed to be given by the driving force (P eq - P), unreacted fraction of the solid (1 X), and rate constant (k ), as: dx/dt=k (P eq -P)(1-X).

21 Determination of activation energy -2.5 ln(k/(peq-p)) [-] Run 1 Run 2 Run T -1 [K -1 ] For whole temperature range: Ea=193kJ/mol (within the range of literature value)

22 Conclusion A method to measure CaCO 3 decomposition rate under Ca-L process conditions (in fluidized bed) was proposed. The reaction order with respect to solid conversion and activation energy were determined. Bedmaterial size had only minor influence of decomposition rate.

N 2 O Decomposition by CaO under Conditions of Carbonator of Calcium Looping Cycle

1 71 st IEA-FBC, Seoul, Korea, Nov.4-6, 2015 N 2 O Decomposition by CaO under Conditions of Carbonator of Calcium Looping Cycle T. Shimizu,, S. Sizuno, K. Ito, R. Houshito, H.j. Kim, L.y. Li Niigata University,