Reducing energy penalties in carbon capture with Organic Rankine Cycles

Carbon capture and storage are considered one of the most promising technologies to reduce emissions in a midterm. Its main drawback is the energy penalty caused by the CO2 separation and compression processes. It increases the CO2 avoided cost and it is an important driving force to propose new and improved capture methods with lower energy requirements. In the case of oxyfuel systems, power plant efficiency penalty is 10-13 percentage points. It is mainly caused by the Air Separation Unit and CO2 compression. The possibilities for the integration of these two necessary processes are limited due to the low temperature of their waste energy. One possibility to take advantage of this low-temperature heat is by using Organic Rankine Cycles, which generate power by means of an organic compound as working fluid. This paper proposes the integration of an ORC with the low-temperature processes associated with oxyfuel combustion in order to reduce its energetic penalty. Results show that a reduction in power requirements around 25% could be achieved. It decreases the efficiency penalty from 11 to 8.2 percentage points and contributes to make more attractive this technology. A comparison between different organic compounds is also conducted to select the suitable substances which minimize penalties in the integration process. (C) 2011 Elsevier Ltd. All rights reserved.