Pressurised regenerative calcium cycle for utility scale energy storage: pilot-scale demonstration of carbonation cycle

A. Maddocks
The University of Newcastle,
Australia

Keywords: energy storage, calcium looping, carbon dioxide

Summary:

The Pressurised Regenerative Calcium Cycle (PRC2), developed at The University of Newcastle, Australia, is a novel technology for grid-scale and micro-grid scale energy storage. The process relies on the cyclic calcination and carbonation of calcium carbonate rich materials where low cost electrical energy drives the calcination reaction and electricity is generated as required through the carbonation reaction. A proof-of-concept study was undertaken to demonstrate that the temperature of a fluid bed reactor could be kept constant during the carbonation cycle without any additional heating. Experiments were undertaken in a 1 Nm3/s fluid bed using 2300 kg of calcium carbonate which was calcined to produce calcium oxide. The carbonation process was studied between 540 to 740 oC with carbon dioxide concentrations up to 15 vol.%. The temperature of the fluid bed was kept constant by utilising the heat released during the carbonation reaction only until the bed material approached saturation. Carbon dioxide capture efficiencies of up to 90% were achieved (i.e. 90% of the inlet carbon dioxide was captured in the fluid bed), which were close to the theoretical maximum capture efficiencies. A ramping experiment was conducted to demonstrate the response of the process to increasing carbon dioxide concentrations. The temperature of the fluid bed was increased from 540 to 710 oC at a heating rate of 3 oC/min by increasing the carbon dioxide concentration in a step-wise manner. The proof-of-concept experiments successfully demonstrated that the temperature of a fluid bed reactor can be maintained using the heat released during the carbonation of calcium oxide. This process allows for the flue gas to be utilised for electricity production via either a Brayton or Rankine cycle.