• Energy Research
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Abstract This study deals with behaviour and washing efficiency of a venturi scrubber in self-priming operation. Usually the washing liquid is injected into the throat by means of a pump, in such a way that the amount of liquid added per cubic metre of gas is adjustable independent from the gas flow rate. In contrast to this kind of design, the venturi scrubber used works via a self-priming operation, i.e. the washing liquid is injected by means of a pressure difference between the inside and outside of the venturi throat as a result of the hydrostatic pressure of the liquid and the static pressure of the flowing gas. As is well known from the literature, the cleaning efficiency of a venturi scrubber improves with the amount of liquid added per volume of gas and with increasing gas velocity in the throat. However, high gas velocities and high charges of washing liquid cause a large pressure drop. Hence, the separation efficiency and energy consumption of the scrubber have to be optimized. It is shown that the separation efficiency could be improved by a multistage injection of the washing liquid. Due to the self-priming operation, the separation efficiency remains at a high level even if the gas velocity decreases, and thus requires no regulation from the outside. Liquid separation after the venturi scrubber is realized by an immersion tube in combination with swirl promotors in the diffuser section of the scrubber which increase the rotation of the gas—liquid flow. Thereby, droplets are pushed aside to the diffuser walls and are deposited.

Biomass (especially algae) is a renewable energy source that can be a great alternative to fossil fuels. Wet algal biomass converts into products such as solid, aqueous, and gaseous phases as well as biocrude in hydrothermal liquefaction (HTL). The aim of this work was to provide detailed exergy analyses of the production of biocrude from Nannochloropsis sp. by HTL. Physical and chemical exergy of the HTL products, exergy losses, exergy efficiency, and exergy distribution of the HTL process were determined in this research. The highest exergy loss and the lowest efficiency values obtained for the heat exchanger were 65,856.83 MJ/hr and 66.64%, respectively, which was mainly caused by the irreversibility of the heat transfer process. Moreover, the HTL reactor had high efficiency (99.9%) due to the complex reactions that occurred at high temperature and pressure. Also, the optimum operating conditions of the reactor were obtained at 350 °C and 20 MPa by using sensitivity analysis. The high overall exergy efficiency of the process (94.93%) indicated that HTL was the most effective process for the conversion of algae. In addition, the exergy recovery values of the overall exergy input values in the HTL process for biocrude, as well as the aqueous, solid, and gas phases, were nearly 74.88%, 18.42%, 0.86%, and 0.76%, respectively. Exergy assessment provides beneficial information for improving the thermodynamic performance of the HTL system.

The purpose of this study was to test the feasibility of a specific mineral carbonation reaction route applied to different types of alkaline industrial residues, i.e. biomass, paper sludge and municipal solid waste incineration bottom ashes and stainless steel slags and dust. This new approach includes the dissolution of industrial residues in hydrochloric acid (HCl), followed by precipitation of iron compounds from the resulting aqueous solutions and the precipitation of calcium carbonates to employ in industrial applications (Carbon Capture, Utilisation and Storage, CCUS). The aim of this work is to apply this stepwise treatment to different types of poorly valorised industrial residues to assess which may be the most promising ones to employ for the process, in terms of total content of specific elements in the obtained products. Our results clearly indicate that the investigated ashes and slags consist of 20-30 wt% CaO which is bound in a broad variety of mineral phases. Reaction of slags and ashes with HCl leads to the formation of Si-rich solid residues and Ca-rich aqueous solutions. Dissolution residues from ash treatment might be used as lightweight concrete aggregate in case of appropriate mechanical properties, whereas dissolution residues from slag treatment might serve as metallurgical Cr concentrates. Resulting aqueous solutions show high concentrations of Ca (>10 g/L), up to 27 g/L of Fe and significant amounts of heavy metals like Pb, Ba, Zn, Cu, Ni. The concentration of dissolved Fe decreases to 2 mg/L by adding NH3 which leads to the precipitation of amorphous iron phases. Finally, calcium carbonates with a purity of 79-97% are precipitated by injecting CO2 at pH 9. These carbonates present lower heavy metal contents than the input materials (e.g. 0.3 wt% ZnO compared to 0.9 wt% for EAF-FD).