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Research Papers: Gas Turbines: Cycle Innovations

# Analysis and Comparison of Reactivity and $CO2$ Capture Capacity of Fresh Calcium-Based Sorbents and Samples From a Lab-Scale Dual Fluidized Bed Calcium Looping Facility

[+] Author and Article Information
Senthoorselvan Sivalingam1

Lehrstuhl Energiesysteme, Technische Universität München (TUM), Boltzsmannstrasse 15, 85748 Garching, Germanysivalingam@es.mw.tum.de

Stephan Gleis, Hartmut Spliethoff

Lehrstuhl Energiesysteme, Technische Universität München (TUM), Boltzsmannstrasse 15, 85748 Garching, Germany

Craig Hawthorne, Alexander Charitos, Guenter Scheffknecht

Institute of Combustion and Power Plant Technology (IFK), University of Stuttgart, Pfaffenwaldring 23, D-70569 Stuttgart, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 133(7), 071705 (Mar 21, 2011) (6 pages) doi:10.1115/1.4002683 History: Received May 16, 2010; Revised May 25, 2010; Published March 21, 2011; Online March 21, 2011

## Abstract

Naturally occurring limestone and samples from a lab-scale dual fluidized bed (DFB) calcium looping test facility were analyzed in a thermogravimetric analyzer. The reactivity of the samples evaluated at typical carbonation conditions prevailed in the carbonator was compared with raw samples. The rate of carbonation and carbonation capacity of the samples were compared with respect to the following three categories: number of calcination-carbonation cycles, carbonation temperature, and $CO2$ concentration. It is suspected that the much lower activity of the DFB sample is attributed to the differences in experimental conditions, i.e., partial carbonation of the DFB particles, fast heating rate in the calciner and thus a rapid calcination reaction, and particle attrition in the circulating fluidized bed calciner riser. These harsh conditions lead to sintering and thus a loss of surface area and reactivity. Sintered DFB samples showed low (nearly one-third of the raw samples) but stable conversions with increasing number of cycles. Hydration was used as an attempt to regenerate the lost capture capacity of partially carbonated and sintered DFB sample. Hydration of the DFB sample was successful in increasing the maximum capture capacity in the fast reaction regime to values almost as high as that of a fresh sample in its first carbonation cycle. Although more investigation is required to investigate the effect of hydration on the CaO particle morphology, a process modification to enhance the $CO2$ capture efficiency of the carbonator via particle hydration was proposed.

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## Figures

Figure 1

CaL process flow diagram for CO2 separation from hot gas mixtures

Figure 2

Llinseis® STA PT1600 TGA. Custom made sample holder is on the top right.

Figure 3

A typical TGA curve showing several calcination-carbonation cycles

Figure 4

Comparison of the CaO conversion for fresh limestone and for a sample taken from the DFB facility. N is the calcination-carbonation cycle number in the thermobalance. Tcarbonation=700°C, YCO2=15 vol %, Tcalcination=850°C, and YCO2=0 vol %.

Figure 5

Comparison of CaO to CaCO3(XCaO)mol % conversion for raw and DFB samples. The CO2 concentration varied as 5 vol %, 10 vol %, and 15 vol %; Tcarbonation=650°C; and Tcalcination=850°C.

Figure 6

Comparison of the change of XCaO rate (first derivatives) for raw and DFB samples. The CO2 concentration varied as 5 vol %, 10 vol %, and 15 vol %; Tcarbonation=650°C; and Tcalcination=850°C.

Figure 7

Comparison of CaO to CaCO3(XCaO)mol % conversion for raw and DFB samples in 15 vol %CO2. Carbonation temperatures varied as 600°C, 650°C, and 700°C; Tcalcination=850°C.

Figure 8

CaO to CaCO3(XCaO)mol % conversion of raw, DFB, and hydrated DFB samples in 15 vol %CO2 at 700°C. The rate of change of XCaO is plotted on the secondary y axis; Tcalcination=850°C.

Figure 9

Comparison of the maximum conversion of CaO to CaCO3 in the fast reaction regime for the limestone, the sample taken from the DFB, and the hydrated DFB sample. N is the calcination-carbonation cycle number in the thermobalance. Tcarbonation=700°C, YCO2=15 vol %, and Tcalcination=850°C.

Figure 10

Schematic of a water spraying system proposed for the calcium looping based CO2 separation process

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