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A detailed kinetic model describing the consumption of key components and product distribution in the Fischer-Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al 2 O 3 commercial catalyst is developed. The developed model incorporates the H 2 Oassisted CO dissociation mechanism developed by Rytter and Holmen and a novel approach to product distribution modeling. The model parameters are optimized against an experimental dataset comprising a range of process conditions: total pressure 2.0-2.2 MPa, temperature 210-230 C, CO conversion range of 10%-75% and feed with and without added water. The quality of the model fit measured in terms of mean absolute relative residuals (MARR) value is 23.1%, which is comparable to literature reported values. The developed model can accurately describe both positive and negative effects of water on the rate kinetics, the positive effect of water on the growth factor, temperature and syngas composition on the kinetics and product distribution over a wide range of process conditions, which is critical for the design and optimization of the Fisher-Tropsch reactors.

By adding energy as hydrogen to the biomass-to-liquid (BtL) process, several published studies have shown that carbon efficiency can be increased substantially. Hydrogen can be produced from renewable electrical energy through the electrolysis of water or steam. Adding high-temperature thermal energy to the gasifier will also increase the overall carbon efficiency. Here, an economic criterion is applied to find the optimal distribution of adding electrical energy directly to the gasifier as opposed to the electrolysis unit. Three different technologies for electrolysis are applied: solid oxide steam electrolysis (SOEC), alkaline water electrolysis (AEL), and proton exchange membrane (PEM). It is shown that the addition of part of the renewable energy to the gasifier using electric heaters is always beneficial and that the electrolysis unit operating costs are a significant portion of the costs. With renewable electricity supplied at a cost of 50 USD/MWh and a capital cost of 1,500 USD/kW installed SOEC, the operating costs of electric heaters and SOEC account for more than 70% of the total costs. The energy efficiency of the electrolyzer is found to be more important than the capital cost. The optimal amount of energy added to the gasifier is about 37–39% of the energy in the biomass feed. A BtL process using renewable hydrogen imports at 2.5 USD/kg H2 or SOEC for hydrogen production at reduced electricity prices gives the best values for the economic objective.

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Pyrolysis of plastics is one of the efficient ways to recover plastic waste. Pyrolysis refers to a thermal degradation of long-chain organic molecules into smaller hydrocarbons. Many ongoing research studies are trying to gain a better understanding of the pyrolysis technology with the aim of establishing new industrial processes for plastic recycling. The pyrolysis process can thermally degrade plastics or a mixture of biomass and plastics (co-pyrolysis) in the absence of oxygen. Temperature has the most impact on pyrolysis. Other processes to use in the conversion of plastic wastes into valuable products, are steam cracking and gasification. The objective of this study is to find the best operation conditions for conversion of plastic wastes in a fluidized bed reactor. A comprehensive literature study, experimental tests and computational particle fluid dynamics (CPFD) simulations are performed. A fluidized bed reactor is one of the most promising reactors for conversion of plastics in a continuous process. Experimental tests were performed to investigate the optimal operational conditions for conversion of plastics in a bubbling fluidized bed reactor. Steam was used as the fluidizing agent and sand as the bed material. From literature, it was found that the best temperature to avoid liquefaction in the reactor is 600℃ or higher. The minimum fluidization velocities for steam at 600℃ was found to be 0.18 m/s. CPFD simulations were performed and the computational result agreed well with the experimental data regarding minimum fluidization velocity. The CFPD model was further used to study the conversion of biomass to a product gas. The product gas contained 22% CO, 7.5% H2 and 7% CH4. Based on the literature review, the experimental results and the simulations, this study recommends investigation of conversion of plastics and biomass in a bubbling fluidized bed reactor. The study concludes that thermal co-pyrolysis or co-gasification of biomass and plastics at temperatures above 600°C using sand as the bed material and steam as the fluidizing gas give reliable operating conditions for the future studies. A proper biomass to plastics ratio should be used to avoid melting of plastics in the feeding system and in the reactor. It is crucial to operate the reactor well above the minimum fluidization velocity, to avoid defluidization.