Simulation of polyolefins waste gasification for chemical recycling applications in Aspen Plus

Abstract

The Dutch government program “ A circular economy in the Netherlands by 2050“ prioritizes the 100% recycling of plastics used in the country by 2050 to reduce the consumption of fossil resources and increase the value of the plastic waste, which is currently incinerated or exported in its majority [1]. This objective can be facilitated by including chemical recycling techniques to recover valuable chemicals such as syngas (H2/CO) and monomers (ethylene/propylene) from plastic waste [2]. Among the chemical recycling techniques, gasification is a mature technology with the highest flexibility on the feedstock composition, allowing to treat complex mixtures as plastic waste [3]. In this framework, the project “Towards improved the circularity of polyolefin-based packaging” evaluates the technology readiness level of gasification for recycling a plastic waste mixture representative of the packaging sector (39.6% of the European plastics demand in 2019 [4]), to increase the knowledge of polyolefins waste (PW) gasification to contribute in closing the plastics loop [5]. The Process and Energy Department of TU Delft is part of this project and is responsible for gasifying a polyolefins waste mixture representative of the packaging sector (PW-DKR350) in a novel Indirectly Heated Bubbling Fluidized Bed Steam Reformer (IHBFBSR) [6]. This thesis focuses on developing a kinetic model of the IHBFBSR, which describes the bed hydrodynamics according to the two-phase theory (TPM) in Aspen plus as a complementary tool for the validation of the experimental work and narrow down the number of laboratory tests by identifying the gasification parameters (temperature, ER and SF ratios) that optimizes the following key performance indicators: carbon conversion efficiency (CCE), cold gas efficiency (CGE), product gas yield (GY) and tar yield (TY). This document describes the development of the TPM-IHBFBSR model. It starts with a literature review of the most-used modelling approaches for carbonaceous materials. Next, it describes the upgrading strategies applied, according to the equilibrium and kinetic approaches, emphasizing in the hydrodynamic models and simulation settings. Through this part were identified the optimal gasification parameters: 680°C<T<800°C, ER=0.15 and SF=2. Finally, the comparison of the TPM-IHBFBSR model and its previous versions against two validation cases found in the literature, highlights the advantage of having developed an adaptable model to a particular PW mixture, making possible to continue improving it