CLEANKER – Integrated calcium looping process for CO₂ capture

In detail, the concept involves the use of a so-called carbonator, which is intended to capture CO₂ from the kiln exhaust gas through the carbonation of CaO, and an Oxyfuel-driven calciner to generate the purest possible flow of CO₂. The CaO/CaCO₃ is then exchanged between these units and/or partly circulated. Once it has been cooled for heat recovery, the CO₂-enriched exhaust gas flow is transferred to a processing installation. Thus it's possible to capture the CO₂ emissions arising from both the fuel and the material.

The aim of the CLEANKER (CLEAN clinKER) project is to perform large-scale testing of this technology as an integrated method (Technology Readiness Level 7). It is planned to treat 4 000 m³/h exhaust gas in a demonstration plant to be connected to an existing kiln line at the Buzzi Unicem works in Vernasca in Italy. In the course of the test campaign, various raw materials are also to be studied with regard to their suitability for use as CO₂ sorbents. The intention is thus to check the feasibility of the integrated calcium looping concept and the maintenance of constant product quality. VDZ is providing measurement technology, analytical services and cement expertise to support the project. Following demonstration of the technology, a technical and economic study will be performed for existing cement works based on scaling-up of the results and modelling of this process.

Use will also be made for this purpose of the process technology model developed by VDZ, which will be expanded for the specific application by incorporating the experimental results obtained. The following ambitious targets have been set for integration of the method into the clinker burning process:

• CO₂ capture > 90 %
• Increase in electrical energy demand < 20 %
• Specific primary fuel requirement for CO₂ capture (SPECCA) < 2 MJ_LHV/kg_CO2
• Costs of CO₂ capture < 30 €/t_CO2
• Increase in cement production costs < 25 €/t_cement     

Above and beyond the demonstration of CO₂ capture, the project is also intended to test CO₂ storage by means of the mineralisation of waste materials. The project is currently in the design and development phase.

A promising method of CO₂ capture from cement works exhaust gases is process integration of a calcium looping process, which up until now has only been viewed as a system for the downstream capture of CO₂ from the exhaust gas. This technology is considered to offer potential for the cement industry in particular, as CaO is used as sorbent for CO₂. The resultant CaCO₃ can be directly utilised as a raw material component.