CO 2 liquefaction is an essential process for long-distance ship transportation. The conventional CO 2 liquefaction process employs either an external coolant or liquid expansion followed by multistage compression to obtain liquefied CO 2 at low pressure. However, these processes consume considerable amounts of energy, which presents an obstacle to commercialization. Thus, the CO 2 liquefaction process needs to be carefully researched and designed to reduce the operating energy. In this study, two alternative CO 2 liquefaction processes are proposed and evaluated. These alternative processes use multistage expansion and multistream heat exchangers to lower the input stream temperature for the compressor. In addition, the system is operated in a more efficient manner by operating the process with an optimized compression ratio. Evaluation of the economic feasibility was performed in this study for a complete assessment of the alternative processes. As a result, about 98.1 kWh/t of CO 2 was consumed for alternative process 2, which is only 91.8% of the total operating energy of existing CO 2 liquefaction processes, and the CO 2 liquefaction costs for alternative process 2 were reduced by 5.5%.

Carbon dioxide (CO 2 ) conversion technology has been estimated as a potentially practical solution for global warming problems although it still has some weaknesses such as cost and energy consumption. In this study, a combined steam reforming process with dry methane reforming process for the CO 2 treatment was investigated. Because the dry methane reforming process could generate synthesis gas from carbon dioxide, it could decrease the CO 2 emissions from the existing steam reforming process. Models for the steam reforming process and the combined process were developed and extended mitigation cost was suggested to evaluate CO 2 reduction of the overall process. The combined process could reduce net CO 2 emission by 67% compared with the reference steam reforming process, and the extended mitigation cost of the combined process ranged from 21 to 26.5 (US$/CO 2 ton) according to the change of the cost for CO 2 transportation.

Postcombustion CO2 capture with aqueous monoethanolamine (MEA) scrubbing is one of the most promising and well-proven techniques for reducing CO2 emissions into the atmosphere. However, this process has a critical problem: the high reboiler heat energy requirement for solvent regeneration at the stripper reboiler. To reduce the reboiler heat requirement, this paper suggests a new stripper configuration for CO2 capture with MEA, namely a combined rich vapor recompression (RVR) and cold solvent split (CSS). The RVR is a newly developed configuration, involving vaporizing a cold solvent in the heat exchanger, thereby maximizing the heat exchanger preheating duty under low pressure. The CSS is a well-known configuration, feeding the split cold solvent to the stripper top and eliminating the reflux rate in the stripper by cooling the stripper top. The RVR process is dramatically improved when it is combined with the CSS configuration. To show the effect of this combined process, this study includes simulation of the Base process and of five alternative processes and also comparisons with reported data. A base model was established based on the operating data from a 0.1 MW pilot plant in South Korea. Consequently, the reboiler heat requirement in the combined the RVR and CSS process was reduced from 3.44 MJth/kg CO2 to 2.75 MJth/kg CO2. The total equivalent energy requirement for CO2 capture and the compression process was reduced from 1.224 MJe/kg CO2 to 1.150 MJe/kg CO2. This combined configuration reduced the total equivalent work by up to 6.0% compared with the conventional MEA process and was 1.7–3.4% lower than that of the lean vapor recompression (LVR) process, which is a well-known advanced MEA process.

In this study, a combined Rankine cycle was modeled and optimized. This process consists of a coal combustion unit, a steam cycle, a CO 2 capture process, a gas conditioning process, and a CO 2 organic Rankine cycle (ORC). This process is able to extract additional power without consuming additional fossil fuel by integrating the CO 2 -ORC with the steam cycle and a liquefied natural gas (LNG) evaporation process. Unlike conventional ORC, the CO 2 -ORC utilizes the low grade waste heat only for super heating of working fluid, while the main evaporation process is achieved by seawater. The CO 2 condensation process in the ORC takes place at a temperature lower than the ambient temperature by coupling with the LNG evaporation system as a cold sink. Furthermore, a fraction of liquefied CO 2 is purged for the sequestration. Therefore, CO 2 liquefaction can be achieved without an additional refrigeration cycle. This process not only produces more power with the same fuel consumption but also reduces CO 2 removal energy. The gross power is increased from 42.21 to 90.54 MW e compared with the conventional power plant, and total CO 2 removal energy is decreased about 9%. The optimum design and operating conditions were also obtained through parameter sensitivity analysis. The power reduction of the proposed process resulting due to the CO 2 capture process installation was identified as 19.3%. However, the net power generation is about 73% higher than that of the conventional power cycle even without CO 2 capture.

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