Tobias Lülf

29 Aug 2012

Dipl.-Ing. Tobias Lülf

Since May 2012: Ph.D. Student at Aachener Verfahrenstechnik, Chemical Process Engineering, RWTH Aachen University

5/2011 – 10/2011: Internship: EnviroChemie GmbH: Component selection and construction of a pilot set-up for washwater recycling by membrane filtration

4/2010 – 8/2010: Student research project in Beersheba, Israel on monopolar and bipolar ion exchange membrane characterization

2006 – 2012: Diploma of Mechanical Engineering at RWTH Aachen University. Major: Chemical Process Engineering

Abstract


Recovery of an argon rich reaction atmosphere by membrane hybrid processes

Silicon carbide is widely used as an abrasive and in high temperature applications. Applications as reinforcements are also present, as silicon carbide is thermal and mechanically stable.

In a silicon carbide production process an argon and hydrogen containing gas stream is used as reaction atmosphere. During the reaction, carbon monoxide is formed.

The net reaction equation is given by:

SiO2(s) + 3C(s) ↔ SiC(s) + 2CO(g).

To maintain an economically sustainable process, the reaction atmosphere must be recycled. Different suitable process chains have been identified. Carbon monoxide can be transferred to carbon dioxide and hydrogen by means of water gas shift reaction (WGS). The carbon dioxide level is reduced by means of absorptive processes of monoethanolamine or pressurized water scrubbing (MEA or PWS), whereas the desired hydrogen concentration can be realized by the application of a membrane process (MEM).

The derived process chains were modeled in Aspen Plus®. Models for membrane separation were implemented in Aspen Custom Modeler® and imported to Aspen Plus®.

To investigate the performance, each process was modeled in stand-alone mode. Thus, optimum operation points in terms of material and energy demands were identified. In a second step the stand-alone blocks were interconnected to give coupled process chains. Optimum operation points for the connected process chains were investigated by sensitivity analyses of relevant process parameter. If coupling was observed to shift the point of optimal operation, operation conditions of each process in the process chain were adapted.

Recycling impurities were considered by setting the inlet boundary conditions of the separation process chains to the maximum content for each component, whereas the product stream of the separation route had to fulfill the boundary conditions for the reaction atmosphere. The absorption fluid recycling was modeled by the same procedure.

The water gas shift reactor is modeled by equilibrium conversion, depending on temperature and stream composition. Operational costs were estimated by applying cost factors for material streams and energy demands to evaluate the process efficiencies.

Stand-alone modeling showed a minimum in energy consumption in the amine scrubbing process for a carbon dioxide loading of about 0.28 moles CO2 per mole of monoethanolamine. For the membrane process the trade-off between the application of large membrane areas and high pressures affects the membrane costs, energy consumptions and material costs due to argon losses. Thus optimum operation depends on the applied economical boundary conditions.

In comparison to other process chains, namely water gas shift - pressurized water scrubbing - membrane separation and water gas shift - membrane separation the presented process chain operates at lowest costs. Here a hydrogen rich byproduct stream is found in the membrane permeate. This stream can be used in heat generation or energy conversion.