Superstructure investigation for P-recovery technologies integration with macroalgae based hydrothermal liquefaction

Book chapter, 2018

The aim of this work is to identify profitable and environmentally benign technological paths connecting phosphorus (P) recovery with macroalgae based hydrothermal liquefaction (HTL). For this purpose, a thorough literature review of relevant technologies in different fields of application was carried out. Together with a citation network analysis (CNA) a framework comprising qualitative and quantitative information about process significance, conditions, material and energy flows for a comprehensive list of potentially involved technologies was developed. On the basis of this information framework, processes were combined into a superstructure of options for P-recovery from macroalgae based HTL. Based on criteria such as technology maturity and severity of process conditions, two different but not mutually exclusive approaches for utilizing HTL waste streams were identified: exploiting the carbon and/or the nutrients potential of the streams. The process layout selected consists of hydrothermal liquefaction, catalytic hydrothermal gasification (CHG), incineration of solid residues, acidic leaching of incineration ashes, crystallization and precipitation of P in form of magnesium ammonium phosphate (struvite), methane steam reforming and biocrude upgrading through hydrotreatment. The selected layout's model was based on HTL reaction kinetics (kinetic constants extrapolated from experiment data and verified with laboratory results from HTL of macroalgae Ulva Lactuca collected from several sites of the Swedish coast) and on performances averaging (according to literature sources) for the other subprocesses sections. Net revenues as high as 21 $/tdry macroalgaewere predicted, coming mainly from upgraded oil and a small part from struvite, while including material and energy costs for operating the system. This revenue is highly affected by the cost of the macroalgae feedstock. Finally, environmental aspects and constraints related to the process, were addressed and evaluated with the cumulative energy demand (CED) indicator, which resulted stable around 34 MJeq/kgproducts.