UCLA

This thesis investigates the energy usage in the production processes of a low carbon-footprint building material called CO2NCRETE. It consists of capturing carbon dioxide (CO2) gas into limestone through the carbonation of three-dimensional printed portlandlite pre-formed structures. Carbonation can be enhanced by compressing and/or concentrating the CO2 in the flue gas. Compression of the flue gas from atmospheric pressure to high pressure (3 MPa) results in high energy requirements for the building material production process. Consequently, the high energy requirements present an opportunity to investigate improvements into the reduction of net energy use. Hot flue gas (~150C) emitted from coal-fired power plants can be used as an input into the CO2NCRETE production process. An average coal-fired power plant producing 500 MW of electricity and emitting 700 kg/s of flue gas was used as a case study. In order to make the process energy efficient, two waste heat recovery systems were analyzed to provide power for the pressurized carbonation process. The first waste heat recovery system consists of an organic Rankine cycle using R245fa as a working fluid and operating between the flue gas at 150C and a cold source at 20C. It was found to generate 13.7 kW per MW generated by the coal-fired power plant power under maximum net power conditions. The second system consists of a transcritical Rankine cycle using CO2 as a working fluid operating also between a hot source at 150C and a cold source at 20C. Under the same conditions, the transcritical Rankine cycle was found to generate 15.7 kW per MW generated by the coal-fired power plant. Finally, the compressed carbonation in CO2NCRETE production was modeled at the lab scale. The compressed carbonation was found to require 2,181 kg of flue gas, and produce 638 kg of CO2NCRETE per day. The energy requirement was 1,589 kJ/kg of CO2NCRETE. At this production rate, the waste heat recovery systems could provide 2.3% of the total energy required. However, the waste heat recovery systems will provide an increasing fraction of the energy necessary for compression as production rate and pressure are reduced.