(27b) Design of Energy Saving CO2 Separation Process Using Circulating Fluidized Bed

Authors: 
Kansha, Y., The University of Tokyo
Ishizuka, M., The University of Tokyo
Mizuno, H., The University of Tokyo
Tsutsumi, A., The University of Tokyo
By fossil fuel combustion, large amounts of greenhouse gases (GHGs) are generated and emitted into the atmosphere. The reduction of carbon dioxide (CO2) emission has become a major target in efforts to suppress global warming. Carbon capture and storage (CCS) has attracted attention in the past decades to reduce greenhouse gas (GHG) emissions. CO2 separation from gas mixtures requires huge amounts of energy. In fact, CO2 separation from gas mixtures is one of the most energy intensive process in CCS. Therefore it is necessary to reduce the energy consumption of CO2 separation for propagation of CCS.

The most widely used method among CO2 separation is a chemical absorption using amine based solution such as monoethanolamine (MEA). In the conventional CO2 separation by absorption using amine based solution, the thermal energy is supplied from the bottom of regenerator which utilizes reaction heat for regeneration of the solutions and heat of vaporization for stripping. To reduce the supply of the thermal energy, authors have developed CO2 gas separation processes based on self-heat recuperation. Applying the self-heat recuperation to thermal processes, not only the latent heat but also the sensible heat of the process stream can be circulated into the processes without any heat addition, leading to minimizing exergy destruction of heat transfer and reduction of the process energy consumption. However, the absorption using solution physically and chemically requires additional energy for separation of liquid/gas, vaporization for stripping.

In this paper, an innovative energy saving CO2 separation process using chemical absorption was proposed for energy saving point of view. In this process, metal oxide particles were selected as absorbents not for requiring separation energy of liquid/gas. These particles were fluidized by feed gas mixture for increasing segregation effect in the bed and heat transfer rate from chemical reaction to a heat pump system. Heat of absorption was recuperated and supplied to the heat of thermal decomposition through the heat pump by following exergy recuperation. In addition, some of the heat was circulating with absorbents. The energy saving performance of the proposed process was evaluated by simulations.