Tool for optimization of energy consumption of membrane-based carbon capture.

The reduction of CO2 emissions is a very challenging issue. The capture of CO2 from combustion processes is associated with high energy consumption and decreases the efficiency of power-producing facilities. This can affect the economy and in specific cases, such as waste-to-energy plants, also their classification according to legislation. To allow the minimization of energy consumption, an optimization tool for membrane-based post-combustion capture was developed. The approach allows finding optimal membrane properties, membrane areas, and pressures for individual separation stages from the point of view of energy consumption. The core of the approach is represented by a mathematical model of the separation system that is based on a network flow problem. The model utilizes external simulation modules for non-linear problems to enable finding globally optimal results. These external modules approximate non-linear dependencies with any desired precision and allow using different mathematical descriptions of individual membrane stages without making changes to the model. Moreover, it allows easy substitution of the external module by experimental data and the model can be easily modified for specific purposes such as decision making, designing the separation process, as well as for regulation of process parameters in the case of dynamic operation. The ability of the model to optimize the process was verified on a case study and the results show that the optimization can significantly reduce the energy consumption of the process. For separation of 90% of CO2 at the purity of 95% from initial flue gas with 13% CO2 with state-of-the-art membranes based on the Robeson upper bound and three-stage process, the minimum power consumption was 1.74 GJ/tCO2 including final CO2 compression.

Material analysis of Bottom ash from waste-to-energy plants.

Bottom ash (BA) from waste-to-energy (WtE) plants contains valuable components, particularly ferrous (Fe) and non-ferrous (NFe) metals, which can be recovered. To assess the resource recovery potential of BA in the Czech Republic, it was necessary to obtain its detailed material composition. This paper presents the material composition of BA samples from all three Czech WtE plants. It was found that the BA contained 9.2-22.7% glass, 1.8-5.1% ceramics and porcelain, 0.2-1.0% unburnt organic matter, 10.2-16.3% magnetic fraction, 6.1-11.0% Fe scrap, and 1.3-2.8% NFe metals (in dry matter). The contents of individual components were also studied with respect to the BA granulometry and character of the WtE waste collection area.