Chemical looping

Figure 7. A simplified scheme of a chemical looping for oxy-combustion.

HyPr-RING method was proposed in 1998 in 2000, a project started in Japan to develop this method to a commercial process. Figure 3.14 shows the concept of FlyPr-RING process. Two chemical loops are included in this process. The first chemical loop is the water cycle. 

Coal-Direct Chemical Looping Reforming Process... 

Moreover, from chemical looping processes, the sequestration-ready C02 stream can also be produced at higher pressures. 

The heat integration of this configuration includes the utilization of the heat generated from the combustion of calcium sulfide in the first chemical loop in the regeneration of the calcium-based sorbent in the second chemical loop (Andrus et al., 2005). The output gas... 

Another integrated carbon capture technology is called the fuel-flexible process developed by General Electric (GE). This process takes different feedstocks such as coal and biomass and produces hydrogen and electricity in adjustable ratios (Rizeq et al., 2002). The reaction scheme for this process involves two chemical loops operated using three fluidized-bed reactors as shown in Figure 17.5. 

Heat from all the hot exhaust gas streams is used for steam generation to drive the steam turbine. Thus, the final products from the GE fuel-flexible process are pure hydrogen from the first reactor, C02 from the second reactor, and heat for electricity production from the third reactor. A portion of the solids in the chemical loops needs to be purged to avoid ash accumulation and maintain solid reactivity (Rizeq et al., 2002). The overall energy conversion efficiency for the GE fuel-flexible process is estimated to be 60% (Rizeq et al., 2003). 

Simplified schematic of the syngas chemical looping process for hydrogen production from coal. 

With the unique reactor and smart particle designs, the oxygen carrying capacity and recyclability of the iron-based chemical looping particles have been radically improved, and OSU s SGR process has shown a great potential for commercialization. Its pilot-scale demonstration is currently under way. In addition, the sulfur present in coal is expected to react with Fe and form FeS. Flence, the SGR process has the capability of removing... 

Andrus, H.A.E. Jr. et al., ALSTOM s Hybrid Combustion-Gasification Chemical Looping Technology Development, Proceedings of the 22nd Annual International Pittsburgh Coal Conference, Pittsburgh, PA, September 2005. 

Andrus, H.E. et al., Hybrid Combustion-Gasification Chemical Looping Coal Power Technology Development, ALSTOM Technical Report for Project DE-FC26-03NT41866,2006. 

Cho, P., Mattisson, T., and Lyngfelt, A., Comparison of iron-, nickel-, copper- and manganese-based oxygen carriers for chemical-looping combustion, Fuel, 83(9), 1215,2004. 

Corbella, B.M. et al., Performance in a fixed-bed reactor of titania-supported nickel oxide as oxygen carriers for the chemical-looping combustion of methane in multicycle tests, I EC Res., 45(1), 157, 2006. 

Ishida, M. et al., Application of Fe203-Al203 composite particles as solid looping material of the chemical-loop combustor, Energy Fuels, 19(6), 2514,2005. 

Lyngfelt, A., Leckner, B., and Mattisson, T., A fluidized-bed combustion process with inherent C02 separation, application of chemical-looping combustion, Chem. Eng. Sci., 56(10), 3101, 2001. 

Mattisson, T., Johansson, M., and Lyngfelt, A., Multicycle reduction and oxidation of different types of iron oxide particles-application to chemical-looping combustion, Energy Fuels, 18(3), 628, 2004. 

In a coupled nuclear hydrogen generation system, the reactor loop will be coupled to the chemical loop via an intermediate heat exchanger (IHX). This coupling is illustrated in Figure 1. 

Figure 11.14. Schematic representation of chemical looping combustion (CLC).

Chemical Looping Combustion (CLC). CLC is an oxyfuel concept where combustion is achieved using a metal oxide as the oxygen carrier without mixing fuel and air. A schematic of CLC concept is shown in Figure 11.14. 

Brandvoll, 0. and Bolland, O. Inherent C02 capture using chemical looping combustion in a natural gas fired power cycle. Journal of Engineering for Gas Turbines and Power, 2002, 126, 316. 

CLC. See chemical looping combustion Clean Coal Technology Program, 515 Clean Energy Systems (CES), 459 cleanup... 

Another approach to bringing oxygen together with fuel is through a chemical looping process. 

A modified gas turbine cycle, a H2-fueled chemical-looping combustion, has been proposed in Japan. The oxidizer air or oxygen is replaced by a solid metal oxide, e.g., NiO. An increase in the efficiency up to 66.8 % is predicted compared with 61.6 % as the best figure for H2/O2 cycles [23]. 

ISHIDA, M., JIN, H., OKAMOTO, T., Hydrogen Fueled Gas Turbine Cycle with Chemical-Looping Combustion, Proc. New Energy Systems Conversion, (3rd Int. Conf., Kazan, 1997) 69-73. 

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