Incorporation of High Pressure Clc into IGCC Systems for Carbon Capture

Incorporation of High Pressure CLC into IGCC Systems for Carbon Capture

 

Oscar Nordness^*, Zhiquan Zhou, George M. Bollas

^* Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, 191 Auditorium Road, Unit 3222, Storrs, CT, 06269-3222, USA. Email:oscar.nordness@uconn.edu

Coal is nowadays considered to be the world's “fastest growing” fossil fuel [1] and currently provides 29.7% of the global energy supply, primarily in the form of electricity [1]. Coupled with this energy however, is the production of considerable greenhouse gas emissions, mainly in the form of CO₂. Currently coal combustion produces over 44% of global CO₂ emissions [1]. Integrated gasification combined cycle (IGCC) plants offer an attractive option for electricity production from coal gasification, while allowing for mercury removal and CO₂ capture at much lower additional costs. At the same time, chemical-looping combustion (CLC) offers the highest estimated efficiency for CO₂ capture [2]. Raising the operating pressure of an IGCC increases the thermal efficiency of the process, while decreasing the energy required for CO₂ compression [3]. However, when IGCC is combined with CLC, the effect of the high-pressure on the synthesis gas-CLC is not well understood, as it depends on the selection of oxygen carrier and other process conditions [4]. In this presentation the effect of elevated pressure on CLC of CH₄ and syngas was studied using copper and nickel oxygen carriers in an alternating-flow fixed bed reactor (Figure 1). Experiments were conducted at the conditions shown in Table 1 at pressures of 1, 5, and 10 bar. These conditions were selected based on standard operations conditions, but at an extended time scale in order to achieve reduction and oxidation at elevated pressure. Figures 2 and 3 show experimental results of the reduction of NiO and CuO with CH₄ at different system pressures (1, 5 and 10 bar) and a bed temperature of 800 °C. Figures 4 and 5 present the experimental results of the NiO-syngas and CuO-syngas systems at 1 and 5 bar. It was found that the reduction of CuO with both CH₄ and syngas occurred with slower reaction kinetics than that of NiO across all pressures, however CuO achieved higher CO₂ selectivity. The elevation of pressure with consistent gas flowrates resulted in increased residence time of the reduction and oxidation gases within the reactor. This allowed for a longer period of reaction for CH₄, which significantly increases the CO₂ selectivity. Elevated pressure contributed to increased solid carbon formation for reduction of CuO with CH₄ and syngas as well as for NiO with syngas. The formation of solid carbon was found to decrease at elevated pressures in the case of NiO reduction with CH₄. Although increased CO₂ selectivity with elevated pressure shows promise for IGCC integration and carbon sequestration, the added carbon formation presents new challenges within the IGCC + CLC system.

Table 1: Experimental Conditions

Oxygen Carrier	20 wt.% NiO/Al2O3, 36 wt.% CuO/SiO2
Load	2.2 grams
Reactor Dimensions	I.D. 9.6 mm, height 482 mm
Total Flow	100 sccm
Temperature	800 °C
Pressure	1, 5, 10 bar
Oxidation	8 min, 20 vol.% O2/Ar
Reduction (CH4)	3 min, 10 vol.% CH4/Ar
Reduction (syngas)	60 min, 5 vol.% CO, 5 vol.% H2 /Ar

 

 

Figure 1: Fixed-bed chemical-looping setup used in this work.

Figure 2: Chemical-looping reduction selectivity and carbon formation using NiO/Al₂O₃ and 10% CH₄/Ar in fixed-bed reactor at (a) 1 bar and 800 °C; (b) 5 bar and 800 °C and (c) 10 bar and 800 °C.

Figure 3: Chemical-looping reduction selectivity and carbon formation using CuO/SiO₂ and 10%CH₄/Ar in fixed-bed reactor at (a) 1 bar and 800 °C; (b) 5 bar and 800 °C and (c) 10 bar and 800 °C.

Figure 4: Chemical-looping reduction selectivity and carbon formation using NiO/Al₂O₃ and 5%CO/5%H₂/Ar in fixed-bed reactor at (a) 1 bar and 800 °C and (b) 5 bar and 800 °C.

Figure 5: Chemical-looping reduction selectivity and carbon formation using CuO/SiO₂ and 5%CO/5%H₂/Ar in fixed-bed reactor at (a) 1 bar and 800 °C and (b) 5 bar and 800 °C.

 

 

Acknowledgement

This material is based upon work supported by the National Science Foundation
under Grant No. 1054718. Support by W.R. Grace & Co. by providing the Al₂O₃/SiO₂ matrices is gratefully acknowledged.

References

[1]       “Coal,” Center for Climate and Energy Solutions, 2014. [Online]. Available: http://www.easybib.com/cite/view.

[2]       L.-S. Fan, Chemical Looping Systems for Fossil Energy Conversions. American Institute of Chemical Engineers, Wiley & Sons, 2010.

[3]       IPCC Special Report on Carbon Dioxide Capture and Storage. New York: Cambridge University Press, 2005.

[4]       J. Adanez, A. Abad, F. Garcia-Labiano, P. Gayan, and L. F. de Diego, “Progress in Chemical-Looping Combustion and Reforming technologies,” Prog. Energy Combust. Sci., vol. 38, no. 2, pp. 215–282, Apr. 2012.