Design of extraction and storage of product gas from Chalmers`gasifier

Abstract

In 2010 a joint project between Volvo Technology Corporation (VTEC), Göteborg Energi AB and Chalmers University of Technology (Chalmers) was started. The project aims to investigate whether substitute natural gas or a less refined gas is usable in heavy vehicle engines. The main criteria will be the overall efficiency, from well to wheel, while fulfilling the regulations regarding emissions in both EU (Euro 6 emission regulations) and the US. The project is a result of the political will to exchange fossil fuel in the transport sector to renewable alternatives. One part of the project is that Chalmers shall provide VTEC with gas from Chalmers’ biomass gasifier that is tar, water and particle free. To be able to provide this gas there is a need for an installation that extract and clean around 3 [mN3/h] (50 [dmN3/min]). Furthermore, the gas needs to be compressed and stored in tanks before it can be delivered. This work focuses on the design of this cleaning and storage installation and includes a preliminary hazard analysis (PreHA). The system that results from this work include a particle filter, a venturi scrubber and a packed column for tar and water removal followed by two diaphragm compressors to pressurise the clean product gas. The solvent proposed for the scrubbers is diesel which may be exchanged when the concentration of accumulated tar gets too high. The dimensioning of tar and water removal is based on HYSYS simulation. The simulation shows that a large fraction of the heavier tars is removed already in the venturi scrubber, while the lighter tars like benzene are removed in the packed column. The simulation shows no indications on tar condensing in the compressors, up to 200 [bar], predicting a sufficient level of tar removal for the proposed system. For the packed column the calculated height is between 10 and 20 [m] depending on which level to remove the tar. This is very high and probably is due to that only gas absorption is considered, which can be seen as a worst case scenario as in the real case also condensation of the tars takes place. An estimate is that the height in reality will be lower than 10 [m]. Regarding the PreHA, the analysis has illustrated the need for gas detection systems both within the systems and for the surrounding, this to minimise the risk of explosive mixtures and toxic environments. Furthermore the need of training and knowledge of the operator will be essential to run the installation in a safe way.