Power to Fuel: Optimisation and characterisation of a small scale methanol synthesis reactor

Power to Fuel: Optimisation and characterisation of a small scale methanol synthesis reactor

de Jong, Alex (TU Delft Mechanical, Maritime and Materials Engineering)

de Jong, W. (mentor)
Vroegindeweij, P.S.M. (mentor)
van Kranendonk, J. (mentor)
de Jong, W. (graduation committee)
Vroegindeweij, P.S.M. (graduation committee)
Eral, H.B. (graduation committee)
Goetheer, E.L.V. (graduation committee)

Delft University of Technology

2022-12-07

In the effort against climate change the company ZEF has as its target to make methanol (CH3OH) out of atmospheric CO2; a process which can be seen as power-to-fuel and/or power-to-x. In light of the developmental cycle within ZEF a new reactor with an increased size and enhanced mass manufacturability is required. The reactor contains three main components: reactor bed, condenser and heat exchanger. The heat exchanger design has been shown to be highly efficient as well as the underlying design philosophy [1]. However, an exact in depth evaluation of the condenser performance has not been performed yet. Furthermore, in light of reactor optimisation, an investigation on the reactor bed design for the use case of ZEF is seen as necessary. The condenser plays a dual role in the reactor: it acts as the separation mechanism of products from the recycle stream and as vital factor in generating mass flow. Due to the current modelling architecture/philosophy of ZEF computationally simple descriptions of condensation phenomena are desired. A method based on linear relations for the latent heat release is developed. In combination with a PT-flash plug-in for MatLab this allows for modelling of heat effects and liquid-gas separation due to condensation. According to literature local heat transfer of condensation is significantly hampered com- pared to ideal Nusselt Film Condensation theory. The reason for this degradation is the presence of Non-Condensable Gasses which will limit the heat flux of the condensing species to the condenser surface. A sub model is used to evaluate whether this effect is significant. A combined model and experimental approach is used for evaluation of these models. The reactor bed is the generation site of the methanol and in previous work it has been found there might be limiting effects in this bed [1]. Evaluation of literature on the causes indicates that mass transfer and temperature limitations are likely the cause. Furthermore literature suggests that the reactor bed might be able to attain a higher Space Time Yield. A set of models are made to describe the mass and heat transport of the reactor bed. These are based on 1-D heat transfer correlations, a linearized Thiele modulus, and the Bussche & Froment kinetic model. Furthermore, the reactor bed and condensation models are integrated into an existing overall model. This enables the simulation of synergy between these processes. A new reactor bed design is made based on these models which should increase the Space Time Yield, and is subject to experimental validation. For the experimental validation a new reactor was designed and build based upon the new models developed. Characterisation experiments indicate satisfactory qualitative behaviour of the condensation modelling. Quantitatively deviations are observed which are expected to be due the over prediction of methanol formation by the reactor bed models. The reactor bed model deviations are mainly attributed to a lower than predicted mass flow rate, and adverse flow fields in the reactor bed. A new reactor bed design is proposed which should significantly reduce the adverse flow field effects while increasing thermal performance. The reactor bed design used allows for a decrease in catalyst size without causing a significant decrease in mass flow rate. An increase of a factor 1.25 for the Space Time Yield compared to the previous design has been observed during experiments. Insulation performance is satisfactory with the insulation performing within 20 W as modelled. Thermal efficiency has decreased by a factor 1.8 and is attributed to the under performance of the reactor bed. Furthermore, the control of the reactor has been evaluated in terms of mass flow rate measurements, the prevention of the stalling of flow, and control. A new mass flow rate measurements device based on differential pressure, a new feed injection design, and further development of control have been experimentally validated. Designs for each of these subjects have been found to be satisfactory. Furthermore, it was found that reactor bed geometry also has an effect on the control of the reactor.   

Methanol
Reactor design
Reactor Modelling

http://resolver.tudelft.nl/uuid:c70dd2a9-a8b0-4e77-bfbb-732f9af15325

2024-12-07

Student theses

master thesis

© 2022 Alex de Jong