A Pinch Targeting Study of the Borealis Cracker Plant in Stenungsund
Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2008
Författare
Hedström, Hanna
Johansson, Daniella
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
In this master’s thesis a pinch targeting study of the Borealis AB cracker plant in Stenungsund has been carried out. The cracker plant uses large amounts of electricity (~400 GWh/year) and fuel (~4 300 GWh/year) and is therefore a large contributor to CO2 emissions, 1.2 % of the total emissions in Sweden. The plant was built in the 1960’s and as a result of the low fuel and electricity prices at the time energy efficiency was not a high priority. The energy market looks different today, and with the present focus on environmental issues the view on energy use has changed. The Swedish national gas grid has been extended to Stenungsund, which creates a possibility for Borealis to deliver fuel gas to the network. Therefore the aim of this study has been to identify process locations with potential for energy savings. To perform the study, data was collected from process design studies, historical process data and the experience of process engineers. The data was processed in ProPi where the pinch temperature, pinch violations and theoretical minimum hot and cold utility usage were calculated. The potential for hot and cold utility savings was investigated with a GCC (Grand Composite Curve) analysis. Some limitations were made to make the study feasible within the allocated time frame. The furnaces were left outside of the scope of the study as well as the already integrated coldboxes and intermittent heat exchangers. The study was limited to the onsite/offsite area and the by-product area. All other facilities were excluded. The results of the study show that there is a large potential for energy savings, with pinch violations of 94 MW in the onsite/offsite part of the cracker plant and 1.5 MW in the by-product area. Several possible matches for additional internal heat exchange were identified. The by-product area was already rather well integrated, however a few possibilities for energy efficiency were found. In particular a single process integration measure was identified that could potentially reduce the pinch violations by 60 %. Another important result of the study is that there is no theoretical demand for external heating of the process in the onsite/offsite. Today 63 MW of steam is used for heating. The on-site utility boilers have a production that is equivalent to this number which means that theoretically there is no need for them. Decreasing of steam use will lead to a lower use of residual fuel gas, which could be upgraded to natural gas specifications and sold to the natural gas grid. Performing the internal heat exchanges with the largest potential could decrease the CO2 emissions of Borealis by 15%. In future work more thorough investigations of the suggested retrofits should be carried out with economical and mechanical evaluations. New regulations from the EU are likely to increase the prices of CO2 emission allowances at the same time as fuel prices are rising, which will lead to increased profitability for energy savings. Therefore some of the energy efficiency measures that are not of economical interest today may be so in the near future.
Beskrivning
Ämne/nyckelord
Kemiteknik , Chemical Engineering