Energy Intensity Reduction of Ca-Looping CO2 Capture by Applying Mixing Loop Seals and Cyclonic Systems

This work faces the challenge of cutting the specific energy demand in the CO2 capture process based on Ca-looping technology. The use of high-temperature sorbents allows an efficient integration of the excess heat flows. Up to now, several investigations studied the Ca-looping integration with external systems such as a steam cycle. In this research, a further step is done by comparing technological solutions for the internal heat integration with the aim of reducing the energy needs. Particles preheating before entering the regeneration reactor appears as an opportunity for energy saving since solids have to be heated up around 250–300°C from one reactor to another. Two different internal heat integration possibilities making use of a particle separation device and a mixing valve are presented and compared. The former consists of the inclusion of a cyclonic preheater. This configuration presents the a priori advantage of a more developed technology since it is widely used in the cement industry but the drawback of a worse gas–solid heat exchange. Although there is a lack of practical experience regarding the use of a single seal valve to feed two reactors, this configuration presents a promising prospective related to the excellent heat exchange features of the solid flows. The aim is to obtain comparative results by means of implementing advanced thermochemical models, in order to make progress on the development of less energy-intensive configurations of the calcium looping.

Superimposition of Elementary Thermodynamic Cycles and Separation of the Heat Transfer Section in Energy Systems Analysis

In a wide variety of thermal energy systems, the high integration among components derives from the need to correctly exploit all the internal heat sources by a proper matching with the internal heat sinks. According to what has been suggested in previous works to address this problem in a general way, a “basic configuration” can be extracted from the system flowsheet including all components but the heat exchangers, in order to exploit the internal heat integration between hot and cold thermal streams through process integration techniques. It was also shown how the comprehension of the advanced thermodynamic cycles can be strongly facilitated by decomposing the system into elementary thermodynamic cycles which can be analyzed separately. The advantages of the combination of these approaches are summarized in this paper using the steam injected gas turbine (STIG) cycle and its evolution towards more complex system configurations as an example of application. The new concept of “baseline thermal efficiency” is introduced to combine the efficiencies of the elementary cycles making up the overall system, which demonstrates to be a useful reference to quantify the performance improvement deriving from heat integration between elementary cycles within the system.