A network to promote further development and scale-up of processes for CO₂ capture which involve solid looping cycles operating at elevated temperatures.

Figure 1. Pilot-scale calcium looping rig
(30 kW) at INCAR_CSIC, Oviedo, Spain
(Courtesy of Dr Carlos Abanades)

Introduction

The International High Temperature Solid Looping Cycles Network was adopted as an IEAGHG network in December 2008 and builds upon four preceding international workshops on in-situ CO₂ removal organised largely by academia and government laboratories. The aim of the network is to promote further development and scale-up of processes for CO₂ capture which involve solid looping cycles operating at elevated temperatures. At the industrial scale such processes are likely to use dual circulating fluid-bed technology, although fixed bed and pressurised bed variants are also possible. The most notable applications are high temperature carbonation/ calcination (the forward and reverse steps of the reaction between CaO and CO₂) to remove CO₂ from flue gases or reformed gas streams as well as solid bed oxidation/ reduction loops which allow a variant of oxy-combustion of fossil fuels.

One aim of the network is to expand current participation beyond the research community to include potential operators, plant designers and equipment suppliers as the technology is starting to move from the bench scale to pilot and industrial demonstration scale.

Background

High temperature solid looping cycles involve the use of a solid reactant to transfer either CO₂ or O2 from one reactor to another. For example, CO₂ at relatively low concentration can be scrubbed from flue gases, with the sorbent then being regenerated to yield a pure stream of CO₂. Metal oxides can transport oxygen from the air to react with fuel, effectively 'burning' the fuel to yield a pure stream of CO₂ and H2O, which can then be easily separated and the CO₂ stored. Alternatively, there exist a number of methods of producing H2 or syngas from hydrocarbon-based fuels, while simultaneously producing pure CO₂.

Figure 2. CANMET Energy Technology Center mini pilot-scale sorbent looping test facility. Courtesy of Professor E.J. Anthony, CanMet, Canada.

Calcium Looping Cycles

The carbonation/ calcination reactions occur at temperatures higher than those used in the steam cycle of conventional coal-fired power plants, so that it is theoretically possible to recover the heat used to regenerate the sorbent at temperatures suitable for highly efficient modern power generation. There are energy losses due to the need to produce pure oxygen for firing the calciner and for compression of the captured CO₂ but the process has intrinsic efficiency advantages as additional power can be generated from the capture system.

Although the favoured feedstock, limestone, is abundant and cheap, the processes based on calcination/ carbonation have suffered from loss of reactive capacity after a number of cycles and from attrition of the sorbent material.

Recent studies on sorbent reactivation, the role of the sorbent residual activity and the development of more durable synthetic sorbents have shown that the process is feasible. Integration of the looping cycle with the production of cement is a subject of considerable interest and ongoing research.

Figure 3. 120 kW Chemical Looping test
rig (Courtesy of Tobias Proell and
Christoph Pfeiffer, TU Vienna, Austria).

Chemical Looping Combustion

The other high temperature application often referred to as 'chemical looping' combusts fuel by reducing solid metal oxides which are then re-oxidised in the other half of the cycle. This is effectively a form of oxy-combustion and theoretically has the potential to be a very efficient form of CO₂ capture.

Chemical Looping Combustion (CLC) is a method of indirect combustion where fuel and air are never mixed. The concept has therefore been classified as 'unmixed combustion'. Metal oxides are used to transport oxygen from air to fuel in the solid phase. If a suitable metal oxide is used as the oxygen carrier, the CLC system can be operated in such a way that the exhaust gas consists of CO₂ and H2O only and allows for subsequent water condensation, compression, and storage of CO₂. The costly gas–gas separation steps are inherently avoided. Therefore, CLC is one of the most energy-efficient approaches to carbon capture from power production or fuel upgrading.

Meeting and Summary Reports

This network builds upon four preceding international workshops on in-situ CO₂ removal, ISCR. The fourth and last meeting of the ISCR series was held at Imperial College, London, in July 2008. Click here for presentations from the meeting.

For details of the network meetings and past presentations, please login to the members area.

Membership

Membership of this network is open to countries and industries actively engaged in practical research on CO₂ capture, or seeking ways to promote such activities.

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Network contacts

For information on Network activities contact:

Mike Haines, Project Manager, IEAGHG: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

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