A major challenge in limiting the greenhouse gas emissions is the decarbonisation of energy intensive industries, where CO2 emissions are inevitable due to the production process, such as the production of lime. Depending on the type of kiln, one ton of burnt lime accounts for more than one ton of CO2. A variety of technologies to capture these emissions is available or currently being developed. The carbonate looping process (CaL) is one of the most promising capture technology in this sector, since it i) can be retrofitted to existing plants, ii) has a considerably low energy penalty, and iii) uses the same materials as the production process. It is a post-combustion CO2 capture technology using natural limestone as sorbent. In the carbonator, the CO2 in the flue gas stream is absorbed by calcium oxide (CaO), according the reversible carbonation reaction at a temperature of approximately 650°C. The formed calcium carbonate (CaCO3) is transferred to the calciner to be regenerated at a temperature of approximately 900°C. The required heat can be supplied either straight-forward via oxy-combustion in the calciner or indirectly, e.g. with heat pipes from an external combustor. The latter has advantage that no technically pure oxygen, which requires an energy intensive air separation unit (ASU), is necessary. This further improves the efficiency and economics of the process. The general feasibility of the indirectly heated carbonate looping process (IHCaL) has previously been demonstrated at pilot scale.

Recently, the existing 300 kWth IHCaL pilot plant at Technical University Darmstadt has been modified and operated for over 400 hours, with the objective to investigate the feasibility of this technology to be integrated into lime plants. During the test period, three different fuels, i.e i) propane, ii) lignite, and iii) waste derived fuels, were fired in the combustor, and the CO2 contained in the associated flue gases was captured in the carbonator. A natural limestone from Germany with two different particle sizes was used as sorbent. Aiming at specific conditions comparable to an integration into a lime plant, CO2 was added to the flue gas stream and a high make-up rate replacing deactivated material was applied. A special focus was given on the generation of highly calcined material, which was purged from the system. The collected purge was analyzed in order to assess its chemical composition and usability as educt for lime production.

During the 9th High Temperature Solid Looping Cycles Network Meeting comprehensive findings obtained during the pilot testing will be presented, such as i) the effect of variation in CO2 inlet concentration of the carbonator and make-up ratio on the process performance ii) performance of the heat pipe heat exchanger while firing different fuels, and iii) physico-chemical properties of the purged material.